Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-44 TODD/W&C
4.4.6 Total Dissolved Solids
Groundwater in the Indio Subbasin shows a wide range of salinity, measured in terms of TDS concentrations. No fixed Consumer Acceptance Contaminant Level has been established for TDS. Instead, TDS is regulated by Secondary Maximum Contaminant Levels (SMCLs), or Consumer Acceptance Contaminant Level Ranges, set by the SWRCB: a recommended 500 milligrams per liter (mg/L) level, an upper 1,000 mg/L level, and a short-term 1,500 mg/L limit. While primary maximum contaminant levels (MCLs) are health-based standards, SMCLs, such as those for TDS, are based on aesthetic concerns such as taste, color, and odor.
4.4.6.1 Sources
TDS in the Subbasin is derived from natural sources, return flows from agricultural and landscape irrigation, recharge of imported Colorado River water, wastewater discharge (municipal and septic tanks), and subsurface inflows from adjacent Subbasins, such as the Desert Hot Springs Subbasin, which is characterized by poor water quality (DWR, 1964). Natural elevated TDS concentrations occur in the upper aquifer, typically along the Coachella Valley margins. Potential saltwater intrusion from the Salton Sea is addressed in Section 4.5.
Completion of the Coachella Canal in 1949 allowed use of Colorado River water for agricultural irrigation, with subsequent use for golf course and large landscape irrigation. As shown in the land use map (Figure 2-6 in Chapter 2, Plan Area) agriculture is most extensive in the East Valley. Irrigation results in evaporative concentration of TDS in shallow groundwater; the agricultural drain system helps alleviate such salt loading locally (see Figure 2-5 in Chapter 2, Plan Area).
Colorado River water has been used to replenish the Indio Subbasin and reverse overdraft. Deliveries have occurred from the Coachella Canal to Dike 4 (1994-2008), TEL-GRF (since 2009) and PD-GRF (since 2019), as well as from the Colorado River Aqueduct (CRA) to the WWR-GRF since 1973. The CRA supply has lower TDS concentration than the Coachella Canal supply, because it is diverted higher along the Colorado River.
Water use for domestic purposes results in salt loading to wastewater. Locations of water reclamation plants (WRPs) and other wastewater treatment facilities are shown in Figure 2-5 in Chapter 2, Plan Area.
As described in Chapter 2, Plan Area, three WRPs currently provide recycled water for irrigation. For the other WRPs, treated effluent is discharged either to onsite percolation/evaporation ponds or to the Coachella Valley Storm Channel (CVSC) that conveys water to the Salton Sea. Some portions of the Subbasin (mostly rural) use septic tank/leachfield systems to treat and dispose wastewater.
4.4.6.2 Distribution and Trends
TDS concentrations in the Indio Subbasin reflect multiple factors affecting geographic and vertical distribution as well as trends. These factors have changed over time as a result of changing land uses and water and wastewater management activities.
Figure 4-11 shows the spatial distribution of the most recent TDS concentrations results from wells included in this analysis. As noted in Section 4.4.3, the map shows the most recent value for each well with water quality data between 1990 and 2019, and shallow monitoring wells were excluded.
Figure 4-11 shows that groundwater over large portions of the Indio Subbasin has TDS concentrations less than 500 mg/L. While TDS concentrations are depth-dependent in many portions of the Indio Subbasin, a few spatial patterns are observed on the map. Groundwater in the center of the Subbasin has low TDS
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-45 TODD/W&C concentrations, often less than 250 mg/L. The highest TDS concentrations (>1,500 mg/L) are observed near the Salton Sea. TDS concentrations along the perimeter of the Subbasin are frequently greater than 500 mg/L. The median TDS concentration in all wells included in the analysis is 308 mg/L. Of total wells sampled, 10 percent indicate most-recent TDS values greater than 1,000 mg/L, 32 percent indicate most- recent concentrations greater than 500 mg/L, and most wells show concentrations below 500 mg/L.
The top left portions of Figures 4-20 through 4-33 illustrate the vertical distribution of TDS concentrations for the 14 cross sections (A-A’ through N-N’; see Figure 4-19 for locations). As shown, TDS concentrations generally are less than 500 mg/L and lowest concentrations occur in deep wells in the central Indio Subbasin. Several of the cross sections show shallow wells with screens at or just below the water table.
These are few in number and not distributed evenly across the Subbasin but provide information on local shallow groundwater quality including in the vicinity of WRPs and groundwater replenishment facilities.
TDS trends are shown as selected time-concentration plots in Figure 4-34; note that the vertical scales mostly are 100 to 1,100 mg/L with three exceptions having scales up to 2,100 mg/L to accommodate higher concentrations. The time-concentration plots include some groupings of wells that are near one another but with screens in different vertical zones. The plots indicate that TDS concentrations in shallow zones typically are higher and more variable than in deeper zones.
As summarized in the 2002 CVWMP, TDS concentrations in groundwater averaged less than 250 mg/L in the 1930s; and in the 1970s, groundwater typically contained 300 mg/L TDS in the shallow aquifer and 150 to 200 mg/L TDS in the deep aquifer. The 2002 CVWMP reported then-current TDS concentrations in the shallow aquifer averaging 544 mg/L, and in the deep aquifer averaging 204 mg/L (CVWD, 2002). The 2015 Salt and Nutrient Management Plan (SNMP, 2015) reported that the median TDS concentration was 520 mg/L in the shallow aquifer of the West Valley and 195 mg/L in the deep aquifer of the West Valley.
In the East Valley, the median TDS concentration was reported as 698 mg/L in the shallow aquifer and 160 mg/L in the deep aquifer. Increases in TDS concentrations since 1990 are indicated on Figure 4-34, with lower rates of increase generally in deeper zones as well as in the central and eastern Thermal Subarea.
The various factors contributing to salt loading are being evaluated and managed to protect groundwater quality in the context of other sustainability criteria such as potential storage depletion, seawater intrusion, and chronic groundwater level declines. Chapter 8, Regulatory and Policy Issues, provides updates on salinity management, the 2015 Salt and Nutrient Management Plan, and other salinity-related issues.
4.4.7 Nitrate
Groundwater in the Indio Subbasin shows a range of nitrate concentrations from very low background levels (less than 1 mg/L) to concentrations exceeding the drinking water standard. The drinking water standard or primary MCL for nitrate is 45 mg/L when measured as nitrate.2 Nitrate concentrations were reported from 932 wells between 1990 and 2019. The most recent measurements from each well show a median nitrate concentration of 3.6 mg/L. For 104 wells, or 11 percent of all wells sampled, the most recent nitrate concentrations were greater than 45 mg/L. Shallow monitoring wells (associated with local monitoring around facilities such as WRPs) are not included in this
2 The MCL is 10 mg/L for nitrate when measured as nitrogen. All nitrate as nitrogen concentrations were converted to nitrate as nitrate for this groundwater quality assessment.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-46 TODD/W&C accounting because the mapping is intended to depict water quality in vertical zones that generally provide groundwater supply to production wells. In general, wells with high nitrate concentrations are relatively shallow wells. However, one well with a recent detection greater than 45 mg/L is a relatively deep well (400 feet deep well MW-4D) providing monitoring downgradient from CVWD’s Water Reclamation Plant 7 (WRP-7) in an area that was historically used for agriculture.
Elevated nitrate was identified as an emerging issue in the 2010 CVWMP Update. In Chapter 8, Regulatory and Policy Issues, an updated focus is on small water systems. Since 2010, nitrate as nitrogen was measured from 85 wells serving small water systems. Of these, nitrate concentrations exceeded the primary MCL in 5 wells.
Quantification of nitrate loading to the groundwater system is being addressed through the SNMP process.
4.4.7.1 Sources
Historical land uses have contributed to nitrate currently detected in groundwater. Such legacy nitrate loading has occurred from historical agriculture and agricultural development of mesquite lands as well as rural septic systems (prior to development of centralized wastewater collection, treatment, and disposal systems). Historically, portions of the now-urban Indian Wells were characterized by extensive mesquite forests (Huberty, et al., 1948). Under natural conditions, moisture was insufficient to decompose leaves and twigs and consequently, large amounts of nitrogen-containing litter accumulated under the trees. When the lands were cleared, leveled, and irrigated for agriculture, the organic matter was decomposed and nitrate was leached by irrigation return flow and migrated to the underlying water table. In addition, irrigated agriculture historically extended farther northwestward into now-urban areas (DWR, 1964, see Plate 13); assuming fertilizer use, such agriculture represents legacy loading of nitrate.
Ongoing activities that currently contribute nitrate loading include use of nitrogen-based fertilizers for agriculture, golf courses, and landscaping; septic tank percolation; and wastewater disposal through percolation.
4.4.7.2 Distribution and Trends
Nitrate concentrations in Indio Subbasin groundwater vary spatially, with depth, and temporally, as summarized in the following paragraphs.
Figure 4-12 shows the spatial distribution of most recent nitrate concentrations in groundwater. As discussed in Section 4.4.3, the map shows the most recent value for each well with water quality data between 1990 and 2019, and shallow monitoring wells were excluded.
As shown, the highest nitrate concentrations occur mostly along the western margins of the Indio Subbasin. Some of these areas, such as northwestern portions of the Thermal Subarea, have a long history of agricultural and urban development, as well as nitrate loading from multiple sources associated with native vegetation, agricultural processes, and wastewater percolation. A study was conducted in 2019 (Todd, 2019) of shallow groundwater near the WRP-10 in Palm Desert. Analysis of the groundwater using nitrate and oxygen isotopes indicated that the primary source of nitrate in groundwater near WRP-10 is soil nitrate; in other words, the nitrate derived from mesquite tree debris stored in soils. The study also revealed the isotopic signatures of nitrate from fertilizer, manure, and wastewater.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-47 TODD/W&C The cross sections (Figures 4-20 to 4-34) indicate that nitrate concentrations generally are higher in shallow groundwater compared with deeper groundwater. Cross Sections D-D’, G-G’, and I-I’ particularly illustrate the contrast of high nitrate concentrations in shallow wells and lower concentrations in deeper wells. While deeper groundwater tends to be higher quality, the occurrence of nitrate loading, pumping, and the vertical transport of water through screened well intervals can cause nitrate-rich water to migrate downward.
Nitrate trends are documented in the time-concentration plots on Figure 4-35.3 Review of the plots shows significant variability in shallow nitrate concentrations and local increases in nitrate concentrations, mostly in the western areas where concentrations are already elevated in shallow wells. The occurrence of high nitrate concentrations in shallow zones and increasing nitrate concentrations in nearby deeper wells is also revealed in Figure 4-35 (for example, see lower left plots), which suggests local downward migration.
4.4.8 Arsenic
Arsenic was identified in the 2010 CVWMP Update as an emerging issue. An update is provided in Chapter 8, Regulatory and Policy Issues. Arsenic is found to have carcinogenic and non-carcinogenic effects on health if ingested at high levels over a long period of time. Both the federal and California state governments have established a primary drinking water MCL for arsenic of 10 μg/L.
Both the areal and vertical distributions of arsenic were examined. Arsenic naturally occurs in groundwater, generally derived from basin sediments, and often dissolved in groundwater with anoxic or high-pH conditions. As shown on Figure 4-13, arsenic concentrations are highest in the southern portion of the Indio Subbasin, directly northwest of the Salton Sea. Review of the cross sections indicates low arsenic concentrations except in the southernmost sections (see Figures 4-32 and 4-33). Figure 4-32 (Cross Section M-M’) indicates that arsenic concentrations are higher in deeper groundwater. Arsenic could be more prevalent in deeper groundwater because the deeper groundwater has anoxic conditions, a longer residence time, or geothermal activity.
Of the most recently measured arsenic concentrations in all wells, arsenic levels were below the detection limit (ranging from 0.06 to 3.95 μg/L) in 55 percent of wells. While most arsenic concentrations are low, 153 wells, or 16.9 percent of all wells, had the most recent arsenic measurements greater than the 10 μg/L MCL. As shown in Figure 4-13, elevated arsenic concentrations occur in the eastern portion of the Indio Subbasin, near the Salton Sea. The maximum arsenic measurement observed was 136 μg/L.
Arsenic is primarily a concern for small water systems and private domestic wells. As described in Chapter 8, Regulatory and Policy Issues, arsenic in small water systems is being addressed by Riverside County and by CVWD's Disadvantaged Communities Infrastructure Task Force. Large public water systems are able to selectively drill wells in areas or to depths with low arsenic concentrations, decommission affected wells, or provide water treatment to remove arsenic prior to delivery. These activities are less accessible to small water systems or private domestic well owners. Only 10 out of 234 CVWD, DWA, CWA, or IWA public supply wells show arsenic concentrations greater than 10 μg/L in their most recent measurement; 4 of these 10 wells have not been sampled in the past 15 years. All four wells are CVWD wells, inactive, and no longer permitted under the SWRCB’s Division of Drinking Water (DDW) program for municipal use.
3 Note that vertical scales on Figure 4-35 are mostly 0 to 25 mg/L except five plots with scales of 0 to 60 mg/L to accommodate high nitrate concentrations along the western Subbasin margin.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-48 TODD/W&C CVWD has installed three treatment plants between 2004 and 2006 to reduce arsenic levels in wells serving groundwater to communities located along the eastern and northern shores of the Salton Sea including Mecca, North Shore, Bombay Beach, Hot Mineral Spa, Thermal, Oasis, and Valerie Jean.
4.4.9 Chromium-6
Chromium-6 is the oxidized form of the metal chromium and occurs in oxygen-rich groundwater near chromium-bearing rocks. It was identified in the 2010 CVWMP Update as an emerging issue (see update in Chapter 8, Regulatory and Policy Issues) because of the State assessment occurring at the time to establish a lower public health goal and MCL. The total chromium (hexavalent and trivalent) MCL is 50 μg/L. In 2014, California adopted a 10 μg/L MCL for chromium-6, but this MCL was rescinded in 2017 due to a court ruling that the California Department of Public Health “had failed to consider the economic feasibility of complying with the MCL.” While the MCL for total chromium currently remains at 50 μg/L, the SWRCB is evaluating relevant water treatment options and costs as a basis for establishing a MCL for chromium-6 in accordance with the court order (see discussion in Chapter 8, Regulatory and Policy Issues).
Both the geographic and vertical distributions of chromium-6 were examined. Figure 4-14 shows the geographic extent of elevated chromium-6 concentrations in the Indio Subbasin. While chromium-6 can be due to anthropogenic (human-caused) pollution, its extent in Indio Subbasin and its geologic occurrence in surrounding formations clearly signals that chromium is naturally occurring. Groundwater in the mid-to-southeastern portion of the Indio Subbasin often contains chromium-6 concentrations greater than 10 μg/L. Several cross-sections (see Figures 4-20 to 4-33) show higher chromium concentrations in deeper groundwater (I-I’, E-E’), but others show that chromium-6 occurrence varies more horizontally (J-J’, F-F', G-G’).
Chromium-6 is stable in aquifers with oxidizing groundwater conditions. In some portions of California, elevated chromium-6 conditions have been linked to nitrate-rich irrigation return flow from agriculture (Hausladen et al., 2018; McClain et al., 2019). Agriculture does not appear to increase chromium concentrations in Indio Subbasin because chromium does not co-occur with high nitrate concentrations and chromium-6 concentrations are lower in shallow groundwater.
Chromium-6 concentrations are stable in most wells and have decreased in areas where Colorado River water is used to replenish natural groundwater. Chromium-6 concentrations in Colorado River water are far below the total chromium and withdrawn chromium-6 MCLs, ranging from not-detected to 0.09 μg/L in 2016 and 2018 (CAP, 2017 and 2019) at Lake Havasu (above the Colorado River Aqueduct and All- American Canal intakes). For example, the chromium-6 map (Figure 4-14) indicates an area of relatively low concentrations in the vicinity of the TEL-GRF where groundwater quality changes have been observed.
Cross section J-J’ (Figure 4-29) extends north-south from a high-concentration area toward TEL-GRF and shows the location and depth of CVWD Well 06S07E34A01S. While Figure 4-29 indicates a most recent chromium-6 concentration of 8.7 ug/L (from 2016) review of available total chromium data from 2017 to 2019 indicates that total chromium concentrations (and hence chromium-6 concentrations) have decreased to below detection limits as recharge water from the TEL-GRF has reached this well, and total chromium concentrations have decreased from 16 μg/L to below detection limits.
Of the most recent measurements in wells, the maximum chromium-6 concentration is 22 μg/L, and the median concentration is 6.2 μg/L. In total, 76 wells (31.5 percent of all wells with chromium-6 measurements) have their most-recent samples showing chromium-6 concentrations of at least 10 μg/L.
A higher density of wells has been tested for chromium-6 in regions known to have elevated chromium-6
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-49 TODD/W&C concentrations, which may contribute to the high observed frequency. Total chromium concentrations appear to be fully represented by chromium-6 occurrence and show a similar distribution of concentrations. A comprehensive comparison of CVWD well data showed that 102 percent of the chromium was chromium-6. The chromium-6 analytical test is more sensitive than the total chromium analytical test and is one explanation for the small difference. For most-recent measurements of total chromium, 98 wells (29.5 percent of total wells) have concentrations greater than 10 μg/L, and the median concentration is 5.45 μg/L.
Out of 180 CVWD, DWA, CWA, or IWA public supply wells, 6 wells had chromium-6 concentrations over 20 μg/L, 67 had concentrations greater than 10 μg/L, and the remainder indicate concentrations less than 10 μg/L. As discussed in Chapter 8, Regulatory and Policy Issues, the GSAs have anticipated a chromium- 6 MCL that is lower than the total chromium MCL and have investigated possible water treatment options.
4.4.10 Uranium
Uranium has a MCL of 20 picocuries per liter (pCi/L), or about 30 μg/L. At this concentration, the effect of radiation is negligible, but the chemical properties of uranium can cause kidney damage over time.
As shown in Figure 4-15, uranium concentrations are higher in the northwestern portion of the Indio Subbasin. The 2010 CVWMP Update discussed Colorado River water as a potential source of uranium.
Recent uranium sampling at Lake Havasu, the diversion point for the CRA, has indicated the presence of uranium at levels less than 5 μg/L (Central Arizona Project, 2015, 2017, 2019). Available data indicate that the likely source of uranium in the Subbasin is from local geologic sources. Uranium is often derived from eroded granite (Jurgens et al., 2010), such as the granites to the west of the northern Indio Subbasin or the bedrock northeast of the Subbasin. Uranium often occurs in shallow, oxygen-rich groundwater and in iron oxides on the surfaces of aquifer sediment. Soluble uranium often occurs in association with calcium and bicarbonate (Jurgens et al., 2010), and groundwater in the Palm Springs Subarea has been characterized as a calcium-bicarbonate water type (DWR, 1964).
In the Indio Subbasin, uranium concentrations greater than 20 pCi/L MCL were only detected in four shallow monitoring wells, which are not considered in the basin-wide analyses because they do not represent regional conditions or production well depths. The median uranium concentration in the Subbasin is 3.34 pCi/L.
4.4.11 Fluoride
Fluoride is a naturally occurring element found in concentrations exceeding the California primary MCL (2 mg/L) in portions of the Indio Subbasin. While fluoride is a necessary component of a healthy diet to prevent dental cavities, fluoride at concentrations greater than 4 mg/L (the federal EPA MCL) can cause mottled teeth and bone disease.
As shown on Figure 4-16, elevated fluoride concentrations are observed along the eastern side of the Indio Subbasin and northern boundary of the Salton Sea. Of the most-recent fluoride measurements from wells, the median concentration is 0.6 mg/L, and the maximum concentration is 12.0 mg/L. In total, 93 wells, or 10.1 percent of all wells sampled, have their most-recent fluoride measurement greater than the 2 mg/L MCL. These higher concentrations are likely due to proximity to the San Andreas Fault and geothermally active areas near the Salton Sea. Other parts of the United States also see higher concentrations occurring near faults and geothermically active areas (McMahon et al., 2020).
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-50 TODD/W&C Fluoride is primarily a concern for small water systems and private domestic wells. Review of available data indicate that 54 small water systems have reported fluoride data since 2010. Thirteen small water systems reported fluoride concentrations greater than 2 mg/L and six detected fluoride at concentrations greater than 4 mg/L. As summarized in Chapter 8, Regulatory and Policy Issues, CVWD has an active program to assist small water systems in disadvantaged areas that have water supply problems including water quality issues. Large water systems are able to selectively drill wells in areas with low fluoride concentrations or provide treatment to meet the MCL, while these activities are less accessible to small water systems or private domestic well owners. Only 3 out of 233 CVWD, DWA, CWA, or IWA public supply wells had the most recent measurement show fluoride concentrations greater than 2 mg/L in their most recent measurement. None of the three wells have been sampled in the past 15 years and they are known to be inactive.
4.4.12 Perchlorate
Perchlorate was identified in the 2010 CVWMP Update as an emerging issue (see Chapter 8, Regulatory and Policy Issues), because of historical contamination in the Colorado River that originated from two manufacturing facilities. Perchlorate may also occur naturally in arid basin settings. Cleanup activities have since mitigated perchlorate levels in Colorado River water. Perchlorate loading into Las Vegas Wash has decreased more than 90 percent since 1998 and levels have consistently remained below 2 μg/L since 2009 at MWD’s Lake Havasu intake (MWD, 2020). CVWD monitors the Coachella Canal at Avenue 52.
Perchlorate results at this location have been below detection limits from 2017 to 2020. By way of comparison, the California MCL is set at 6 μg/L. As documented in Figure 4-17, detections of perchlorate in the Indio Subbasin have been highly localized with concentrations less than 2 μg/L.
4.4.13 Dibromochloropropane
DBCP is a pesticide banned in the United States since 1979 because it is hazardous to gastrointestinal and pulmonary health. California has an MCL of 0.2 μg/L for DBCP. While it is broken down in sunlight, it can remain in groundwater for decades; because it is denser than groundwater, it tends to sink to the bottom of aquifers. DBCP has been detected in public supply and private irrigation wells but has not been detected in public supply wells above the MCL. Three private irrigation wells have most-recent DBCP concentrations greater than 0.2 μg/L. The maximum concentration observed was 0.4 μg/L. As shown in Figure 4-18, the wells with high DBCP measurements are relatively localized in the central Thermal Subarea. The DBCP occurrence is limited to unconfined portions of the Subbasin where specific historical irrigated agricultural practices occurred.
4.5 Seawater Intrusion
The Indio Subbasin is located over 60 miles from the Pacific Ocean and is not vulnerable to seawater intrusion in the traditional sense. However, it is potentially vulnerable to saltwater intrusion from the Salton Sea. Percolation of high TDS groundwater from the shallow aquifer may also be a source of degradation to the deep aquifer. High rates of production in the lower aquifer near the Salton Sea could pull in dense, saline water, and thus degrade groundwater quality in deep portions of the aquifer.
Potential saltwater intrusion along the Salton Sea northwestern boundary is monitored through two sets of nested monitoring wells, installed and managed by CVWD. Results from these monitoring wells do not suggest current groundwater degradation due to saltwater intrusion.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-51 TODD/W&C The Salton Sea is about 30 feet deep, 35 miles long, and 15 miles wide. Its primary source of water is agricultural drainage, transported through the Alamo River, New River, Coachella Valley Stormwater Channel, and agricultural drains. The Salton Sea has no outflowing streams, but the rate of evaporation is higher than the rate of inflows, causing a decline in the surface elevation, decrease in surface area and volume, and salinization. Salton Sea levels measured by the USGS have dropped 9.6 feet from January 2000 to January 2020, and the shoreline has retreated. Salinity levels have increased over the past two decades, and TDS levels in the Salton Sea during 2019 were greater than 69,000 mg/L (Salton Sea Authority, 2020).
While increasing salinization of the Salton Sea suggests an increased potential for saltwater intrusion, the dropping Salton Sea levels and retreating shoreline suggest a groundwater gradient from the Subbasin toward the sea and therefore less potential for intrusion from the sea. However, local groundwater gradients can change based on changes in groundwater pumping, recharge, and density differences between groundwater and Salton Sea water.
To detect and track potential saltwater intrusion, two sets of dedicated nested monitoring wells have been installed. The northernmost set of nested monitoring wells, about 2.1 miles north of the Salton Sea, was installed in 1996 with perforation depths at 300-390, 730-770, 1220-1260, and 1,430-1,470 feet below ground surface (bgs) (see Figure 4-33). All wells but the deepest well have shown stable or decreasing TDS concentrations, indicating that saltwater intrusion from the Salton Sea is not currently occurring in this region. The shallowest well (labelled 07S09E30R04S on Figure 4-34), shows a decreasing TDS trend during 1996-2019, from about 500 mg/L to under 200 mg/L. Well 07S09E30R03S, with the 730- 770 feet bgs screen, has maintained TDS concentrations under 300 mg/L, excepting occasional data spikes (Figure 4-34).
High TDS concentrations are observed in the two deepest nested wells in this set (see Figure 4-33). TDS concentrations in 07S09E30R02S, with the screened interval 1,220-1,260 feet bgs, have ranged from 3,500 to 4,000 mg/L from 2016 through 2019. TDS concentrations in the deepest well, 07S09E30R01S, decreased from over 17,000 mg/L to 5,000 mg/L from 1997 through 2013. Concentrations began to increase after 2015. In recent years concentrations have increased to 12,000 mg/L. While the recent TDS concentrations have remained lower than concentrations during 1996 through 2000, the recent increase in TDS concentrations as indicative of saltwater or deep poor-quality groundwater. The deepest well is likely not representative of conditions found in the portion of the Subbasin historically containing freshwater.
The second set of nested wells is located north of Oasis and about one mile west of the Salton Sea’s shore with screened intervals at 420-480, 720-780, 1035-1095, and 1315-1375 feet bgs (Figure 4-33). All four wells have maintained stable TDS concentrations of less than 500 mg/L since measurements began in 2003. The two deepest wells show TDS concentrations of less than 250 mg/L. These results indicate that saltwater intrusion is not occurring in this area.
4.6 Groundwater Dependent Ecosystems
A GDE is defined in the GSP Regulations as “ecological communities or species that depend on groundwater emerging from aquifers or on groundwater occurring near the ground surface.” In its Alternative Assessment Staff Report, DWR recommended that the Alternative Plan Update identify GDEs in the Indio Subbasin. This has been accomplished using best available information (including data available from DWR) and by applying the expertise of a professional wetland scientist.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-52 TODD/W&C DWR provides the Natural Communities Commonly Associated with Groundwater (NCCAG) dataset through the online SGMA data portal. This NCCAG dataset was used for initial identification of potential GDEs in the Subbasin. Once downloaded, the data were compiled using a set of six pre-existing dataset sources; this process is explained in detail on DWR’s Natural Communities Dataset Viewer (see:
https://gis.water.ca.gov/app/ncdatasetviewer/sitedocs/) . Because DWR’s NCCAG dataset was not verified prior to public distribution, DWR recommends evaluation of NCCAG-identified locations by a licensed biologist.
For this Alternative Plan Update, the NCCAG dataset locations were assessed by a licensed wetlands biologist, as documented in the Technical Memorandum, Indio Subbasin Groundwater Dependent Ecosystems Study (Woodard & Curran, 2021), which is provided in Appendix 4-B. The study includes a review of the U.S. Environmental Protection Agency ecoregions and a preliminary review of special-status (threatened and endangered) species within the Indio Subbasin. The desktop assessment used publicly available statewide and regional data layers and involved visual review of 1,045 individual locations to determine potential GDE status. The biologist then selected 15 locations for GDE field assessment. The field study was conducted from January 11-14, 2021, at 13 sites. Two sites were not accessible at the time of field deployment and were therefore eliminated from the field assessment. Upon completion of the in- person field verification, the preliminary desktop GDE assessment was refined.
As shown on Figure 4-36, 50 (5%) of the 1,045 sites were determined to be Probable GDEs, 932 sites (89%) were determined to be Probable non-GDEs, and 63 sites (6%) were determined to be Playa Wetland Communities.
Probable GDEs consist of areas with apparent
dense riparian and wetland vegetative
communities along mapped drainage systems
with potential for deep-rooted phreatophytes
and/or visible, natural surface water flow.
These Probable GDE clusters comprise hot or
cold springs, seeps, and stream channels that
convey snowmelt from the surrounding San
Jacinto mountain front. Due to their location in
upper canyons where groundwater extraction
is generally not occurring, the specific areas in
the Indio Subbasin where Probable GDEs were
identified do not have existing groundwater
data available for review (see Figure 4-5).
Probable GDEs identified along the mountain-
front may be associated with surface runoff,
snowmelt, or springs and seeps from up-gradient sources.
Representative photo of a Probable GDE, a spring in
Chino Canyon.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-53 TODD/W&C Probable Non-GDEs are areas that appeared
incorrectly mapped based on current land
development and land-use or that otherwise
appeared to be dry upland areas, cultivated
and/or flooded agricultural land, obvious
humanmade ponds, lakes, and other features,
channelized drains, and areas with no other
indicators of groundwater presence near the
surface. It should be noted that dry washes,
arroyos, bajadas, and other ephemeral
conveyances where water only flows in
response to heavy precipitation events were
classified as Probable Non-GDEs for this
study.
Playa Wetland Community includes areas of
wetland habitat along the Salton Sea exposed seabed (playa) generally downstream of stream, agricultural drain, or stormwater channel outlets. The receding of the Salton Sea is exposing thousands of acres of playa each year and water from irrigation ditches and other drainages that previously flowed directly into waters of the Sea now spreads out on the exposed playa of the Sea where new vegetation and wetlands currently exist as a result. As discussed in the Indio Subbasin Groundwater Dependent Ecosystems Study, the Coachella Valley Multiple Species Habitat
Conservation Plan (CVMSHCP) (Coachella
Valley Association of Governments, 2007)
identifies some of these playa wetlands as
part of the CVSC/Delta Conservation Area,
which includes the CVSC, agricultural drains
emptying into the Salton Sea that may
contain desert pupfish habitat, and areas
along the seashore that contain sensitive
natural communities. The CVMSHCP
acknowledges that this habitat is sustained
largely by agricultural runoff and outflow in
the CVSC, but that maintenance of the drains
and the flood control channel periodically
modifies the habitat.
The Indio Subbasin Groundwater Dependent Ecosystems Study in Appendix 4-B provides additional documentation, including a table of the state and federal threatened and endangered species listed for the Indio Subbasin, field assessment notes, maps, and photographs of the GDE field assessment sites.
Representative photo of a Probable Non-GDE, a
bajada in the southeast portion of the Subbasin.
Representative photo of a Playa Wetland Community
along the Salton Sea exposed seabed.
Chapter 4: Current and Historical Groundwater Conditions FINAL Indio Subbasin Water Management Plan Update 4-54 TODD/W&C Figure 4-36. GDE Assessment
FINAL
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-1 TODD/W&C CHAPTER 5: DEMAND PROJECTIONS
5.1 Introduction
Water resources planning requires reliable estimates of future water demands. Many factors can affect the amount of water used in the future, including local climate, existing water use patterns, population growth, seasonality, employment, economic trends, environmental needs, and water conservation efforts. As demographic changes occur within a region over time, future demand projections may also change. For example, population projections were much higher in the 2010 Coachella Valley Water Management Plan Update (2010 CVWMP Update) (Coachella Valley Water District [CVWD], 2012) and have been reduced to reflect more tempered growth over the last decade (refer to Chapter 1, Introduction). Revising the demand forecast with updated demographic projections is important for anticipating future water use more accurately when compared to projected supplies identified in Chapter 6, Water Supply.
To provide an adequate long-range forecast of future water demands, this 2022 Indio Subbasin Alternative Plan Update (Alternative Plan Update) uses a 25-year planning period from 2020 through 2045. Projected water demands are broken into four major categories: municipal, agricultural, golf, and other. Projections for each of these four categories were developed separately and then summed in the final section of this chapter.
5.2 Factors Affecting Future Water Demands
There are a number of uncertainties and changes in the region and state that could affect future water demands in the Plan Area. These uncertainties include the following:
• Revised Growth Forecast—The Southern California Association of Governments (SCAG) released new socioeconomic growth forecasts in early 2020 (Connect SoCal)1 that significantly reduced previously projected increases in population, housing, and employment. The SCAG forecast was developed in coordination with City and County municipalities and was based on the land use designations in their respective adopted General Plans. Connect SoCal reduced projected growth in the Plan Area to levels more similar to those published in the 2002 Coachella Valley Water Management Plan (2002 CVWMP) (CVWD, 2002).
• Agricultural Land Conversions—Connect SoCal identified specific parcels that were currently vacant or used for agriculture but are planned for conversion to urban uses. Connect SoCal relied on those developable parcels, coupled with the housing and employment growth projections, to estimate increases in municipal demand and associated decreases in agricultural demand. Given changes in agricultural pumping statewide as a result of the Sustainable Groundwater Management Act (SGMA), cropped lands in the Plan Area may increase faster than expected. • Development on Tribal/Reservation Lands—There are over 28,000 acres of Tribal/Reservation lands in the Plan Area. While much of the Tribal/Reservation lands in the West Valley has been developed to varying degrees, a substantial amount of Tribal/Reservation land in the East Valley is largely undeveloped. All five Tribal governments in the Plan Area were contacted by the Groundwater Sustainability Agencies (GSAs) with requests for land use and water demand
1 https://scag.ca.gov/connect-socal
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Indio Subbasin Water Management Plan Update 5-2 TODD/W&C projections for their Tribal/Reservation lands. Several of the Tribes indicated that projected Tribal/Reservation land uses were already included in municipal General Plans; therefore, Connect SoCal adequately captures Tribal/Reservation growth. Others did not respond; for the purposes of analysis, all Tribal/Reservation lands were assumed to grow in accordance with Connect SoCal. • Long-Term Conservation Regulations—Following the 2012–2016 drought, California passed two major pieces of conservation legislation: Assembly Bill (AB) 1668 (Friedman) and Senate Bill (SB) 606 (Hertzberg). As outlined in Making Conservation A California Way of Life (California Department of Water Resources [DWR] and California State Water Resources Control Board [SWRCB], 2018), the legislation requires establishing, implementing, reporting, and enforcing urban water use objectives, along with agricultural water use efficiency. These objectives and standards are currently under development and future impacts are uncertain.
5.3 Municipal Demands
This section summarizes the process used to develop the municipal water demand projections for the Plan Area, which includes the cities of Cathedral City, Coachella, Indian Wells, Indio, La Quinta, Palm Desert, Palm Springs, and Rancho Mirage, and unincorporated areas in Riverside and Imperial Counties. Water agencies serving as GSAs for this Alternative Plan Update include CVWD, Coachella Water Authority (CWA), Desert Water Agency (DWA), and Indio Water Authority (IWA). A small portion of the Plan Area extends into San Diego County. However, this area is not included in this analysis, which uses SCAG’s population, housing, and employment forecasts that do not address San Diego County. This small area is mostly rugged uplands, contains minimal development, and is not likely to be developed further. This section documents the datasets, methodologies, and assumptions used to develop water demand projections for all municipal uses within the Plan Area boundary.
5.3.1 Municipal Demand Methodology
The municipal demand forecast used unit demands and adjustment factors based on a variety of information, including customer billing data and a geographic information system (GIS) database with parcel-level land use information. The base projection year was established as 2016 based on the availability of detailed demographic data from SCAG via Connect SoCal. Future water demand projections were based on SCAG growth projections for 2020,2 2035, and 2045. Future water demands were projected in 5-year increments with linear projections used for the other 5-year increments. The methodology used to develop municipal water demand projections was as follows:
1. SCAG Regional Growth Forecast—SCAG provided socioeconomic forecasts for population, households, and employment. These SCAG data served as the starting point for analysis. Additional information was required to estimate total housing units for the region.
2. SCAG Land Use Inventories—SCAG GIS data about local land use planning was used to ensure future growth projections did not exceed allowable land uses in the region. GIS mapping was used to identify vacant and agricultural lands identified by local jurisdictions for future development.
3. Housing Unit Analysis—Additional information about vacancy rates was used to estimate baseline and projected housing units for the Plan Area, including housing units used by seasonal residents
2 2020 forecast is a projection based on SCAG demographic data and does not reflect actual 2020 water use.
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Indio Subbasin Water Management Plan Update 5-3 TODD/W&C and other part-time uses. Recent development data and land use information were used to allocate future housing units into the single-family and multiple-family sectors.
4. Employment Analysis—SCAG employment forecasts were used to allocate future commercial, industrial, and institutional (CII) demands.
5. Unit Demand Factors—Customer billing data provided by the GSAs from July 2014 to June 2019 was averaged by GSA to determine baseline water demands for each GSA. The multiple-year average was used to capture annual weather variations. Water demand projections were calculated using gallons per housing unit for residential and landscape uses, and gallons per employee for CII uses.
6. Water Loss—Water loss estimates were based on validated Water Loss Audit reports provided by the GSAs. An average 3 years of available water loss audits (for 2016, 2017, and 2018) were used to develop a water loss estimate.
7. Adjustment Factors—Future demands were adjusted for indoor passive conservation based on savings from the natural replacement of indoor devices and from implementation of DWR’s 2015 Model Water Efficiency Landscape Ordinance (MWELO) (DWR, 2015) for future developments. No additional adjustments were made to reflect required AB 1668 and SB 606 implementation in the baseline demand projection.
The basic unit of municipal demand projections are jurisdictions (i.e., cities and unincorporated county areas) in the Plan Area, as shown in Figure 5-1. Within each jurisdiction, demographic factors were considered homogeneous. For example, the average vacancy rate for a city was considered the same in instances where a city was split between multiple water agencies or when a city was both inside and outside the Plan Area boundary. Unincorporated areas were separated into distinct estimates for the West Valley and the East Valley. The East Unincorporated geographic area (see Section 5.3.2 below) includes both Riverside and Imperial Counties.
For each of the GSAs, socioeconomic data and demand projections were totaled by each GSA Area, which is defined as being limited to the portion of the GSA’s jurisdictional area in the Plan Area. For example, the CVWD Area includes all of CVWD’s jurisdictional area in the Plan Area, whether or not those demands are currently served by their domestic water system. For customers that are not connected to the CVWD domestic water system but are in the CVWD Area, demands met by private wells or small water systems are allocated to CVWD as the overlying GSA.
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Indio Subbasin Water Management Plan Update 5-4 TODD/W&C Figure 5-1. Jurisdictions within Plan Area
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Indio Subbasin Water Management Plan Update 5-5 TODD/W&C
5.3.2 SCAG Regional Growth Forecast
Socioeconomic projections of population, households, and employment were provided by SCAG, which is a joint powers authority that encompasses six counties (i.e., Imperial, Los Angeles, Orange, Riverside, San Bernardino, and Ventura Counties). These data were originally prepared for the 2020-2045 Regional Transportation Plan and Sustainable Communities Strategy, also known as Connect SoCal.3 Initial work on the growth forecast was based on draft materials released in November 2017 as part of SCAG’s local input and envisioning process.4 These data include base year estimates for 2016 and projections for 2020, 2035, and 2045. Forecasts for 2025, 2030, and 2040 were based on linear interpolation. The draft datasets were released in November 2018. The final socioeconomic growth projections were released with the final version of Connect SoCal, which was adopted by SCAG on May 7, 2020.5 SCAG made some adjustments to the draft projections based on feedback received from local jurisdictions (for example, projections were reduced for the Cities of Indian Wells and La Quinta), and these adjustments were reflected in the final Connect SoCal totals.6
Connect SoCal’s regional growth forecast is comprised of the most recent and detailed data available for the Plan Area. This regional growth forecast is based on jurisdictional General Plans and is intended to represent the most likely growth scenario considering a combination of recent and past trends and regional growth policies. In the Coachella Valley, this forecast anticipates less growth than in previous forecasts. SCAG has reduced projections downward for Coachella Valley, particularly in the unincorporated areas of Riverside County in the East Valley. Traditionally, developing previously undeveloped land on the urban fringe (i.e., greenfield development) has been the method for accommodating growth in the Coachella Valley. SCAG’s recent forecasts have increasingly looked toward infill development on vacant land in urbanized areas and redeveloping land use types to accommodate future growth.
The growth forecast in the 2010 CVWMP Update was based on Riverside County Projections 2006 (RCP-06) (Riverside County Center for Demographic Research, 2006) and was adopted by the Coachella Valley Association of Governments and SCAG. SCAG then used this forecast to develop its 2008 Regional Transportation Plan (SCAG, 2008). The RCP-06 forecast was prepared in late 2006 and early 2007; it was developed during a period of significant economic growth and development in the Coachella Valley before the housing market collapse and economic recession. Between 2000 and 2008, Riverside County’s population increased by over 500,000, making it one of the fastest-growing metropolitan areas in the United States over that period. This rate of growth slowed following the economic recession, which impacted housing development and population growth in the Coachella Valley. Although Connect SoCal substantially reduced its regional growth forecast from its RCP-06 projection, the current rate of growth in Connect SoCal is higher on average than recent development data suggest. Despite fluctuations in projections, current Plan Area growth is consistent with long-term growth trends (i.e., the growth rate effectively averages boom and bust periods) in the Coachella Valley over the last 30 years.
3 https://scag.ca.gov/sites/main/files/file-attachments/0903fconnectsocal-plan_0.pdf?1606001176 4 http ://scagrtpscs.net/Pages/DataMapBooks.aspx
5 https://www.connectsocal.org/Pages/default.aspx
6 2045 population projections for the cities of Indian Wells and La Quinta were reduced by 2,900 and 1,300 persons, respectively.
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Indio Subbasin Water Management Plan Update 5-6 TODD/W&C SCAG growth estimates are benchmarked to the U.S. Census Bureau’s (Census Bureau’s) 2010 Census, which is currently more than 10 years out of date. The more current 2020 Census data are not expected to be released until mid-2021, and there have been additional delays as a result of the coronavirus disease 2019 (COVID-19) pandemic. Once 2020 Census data are released, the GSAs will be able to confirm the accuracy of SCAG’s baseline estimates. In addition, the current COVID-19 pandemic has resulted in increased work-from-home patterns that may result in additional short- and long-term socioeconomic changes for the region. In the short term, water demands are likely to decrease as a result of the COVID--19 related economic downturn and decreases in recreational/tourism activity. In the long term, the Plan Area may experience an increase in population due to relocation from larger metropolitan areas where working from home is more expensive. Given the uncertainty of these potential changes, Connect SoCal growth projections have not been adjusted.
5.3.2.1 Seasonal Population
The Coachella Valley is unique in that it includes a high number of homes identified as vacant for “seasonal, recreational, or occasional uses” as defined by the Census Bureau. These homes are not the primary residence of owners or renters based on where they spend most of their time. Past reports indicate that a significant percentage of these properties are used as part-time retirement homes, with fewer units used as weekend homes or as short-term rentals. In the Coachella Valley, these include homes for people who live in one primary location, but also have a second home in a warmer location to spend winters and/or weekends. Tourism is also an important part of the region’s economy, and many homes are used as short-term rentals. The emergence of the sharing economy and internet-based platforms such as Airbnb for short-term rentals has more recently resulted in changes to the short-term rental market.
The region’s seasonal population is not counted under the Census Bureau’s definitions of households and population used by SCAG.
For the purposes of this Alternative Plan Update, growth in residential water demand is a function of current and projected housing units, which includes all vacant and seasonal units. Housing unit counts provide a strong correlation to water demand. Vacant housing units and other amenities such as municipal parks and common areas that serve the seasonal population have year-round water uses, particularly for outdoor irrigation. Due to the seasonality of the tourist industry and outdoor irrigation requirements in the summer, these homes often use the most water when they are vacant. SCAG’s population forecast was expanded for this Alternative Plan Update to reflect seasonal population in the Plan Area.
5.3.2.2 Growth Forecast for the Plan Area
SCAG provided socioeconomic forecasts at various levels of geographic units, including 11,267 transportation analysis zones (TAZs), which were developed independently by SCAG and resemble the Census Bureau’s block groups. These TAZs were used to split forecasts of population, households, and employment by water agency and by Plan Area. To split individual TAZs, data were clipped along jurisdictional boundaries for further analysis using parcel-level land use data. Using land use data provided greater precision when locating population centers. Figure 5-2 is a map of the Plan Area showing the largest growth in population by TAZ.
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Indio Subbasin Water Management Plan Update 5-7 TODD/W&C Figure 5-2. TAZ Based Population Projections for Plan Area
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Indio Subbasin Water Management Plan Update 5-8 TODD/W&C Socioeconomic Forecast for the Plan Area
Table 5-1 lists the socioeconomic population, household, and employment forecasts for the GSAs in the Plan Area as developed by SCAG. SCAG population estimates do not include seasonal population.
Appendix 5-A contains tables of the complete projections for each GSA by jurisdiction. In the Plan Area, the cities with the largest projected net increases in population are Coachella, with an increase of 84,000 persons (i.e., a 185-percent increase), and Indio, with an increase of 41,200 persons (i.e., a 47 -percent increase). As a result, CWA and IWA have the fastest-growing populations among the GSAs.
Table 5-1. Socioeconomic Growth Forecast for GSAs Within Plan Area Water Provider Permanent Population Households Employment 2016 2045 2016 2045 2016 2045
Coachella Valley Water District 221,065 311,500 84,390 129,132 105,736 138,001 Coachella Water Authority 44,417 115,504 9,460 32,539 8,599 23,582 Desert Water Agency 53,763 71,693 25,516 35,331 35,529 45,989 Indio Water Authority 83,147 117,351 23,662 38,553 27,530 37,971 Plan Area Total 402,392 616,048 143,028 235,555 177,394 245,543 Note: SCAG population estimates do not include seasonal population.
Source: SCAG Connect SoCal
Figure 5-3 shows that overall Plan Area population is projected to grow by 213,656 (53 percent) by 2045.
The higher growth rate of 92,527 households (65 percent) indicates a general long-term decline in the number of persons per household, which is the result of an overall aging population and increases in seasonal/part-time occupancy. Employment is also anticipated to grow slower than population or households, with 68,149 new employees (38 percent) by 2045. This is a result of net travel out of the region for work, as well as a large number of retirees in the Plan Area.
The Coachella Canal runs adjacent to agriculture fields in the East Valley.
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Indio Subbasin Water Management Plan Update 5-9 TODD/W&C Figure 5-3. Socioeconomic Growth Forecast for Plan Area
Forecast Population with Seasonal Residents
For the purposes of analysis, SCAG’s socioeconomic forecast was used to project the region’s total population, including seasonal residents. The projection used vacancy rates and persons per household estimates from State of California Department of Finance (DOF) for cities and Census Bureau American Community Survey (ACS) (Table B25004) for unincorporated areas (see Section 5.3.4), along with an assumed 50-percent occupancy rate for seasonal residents. By definition, these seasonal residents would spend less than half the year in these housing units. However, vacant housing units and other amenities that serve seasonal residents would have year-round water uses, such as outdoor irrigation. Table 5-2 provides a forecast of Plan Area population with seasonal residents.
Table 5-2. Total Plan Area Population with Seasonal Residents Water Provider 2016 2020 2025 2030 2035 2040 2045
Coachella Valley Water District 267,136 287,987 308,015 328,042 348,069 364,297 380,523 Coachella Water Authority 45,828 54,736 66,488 78,241 89,993 105,175 120,357 Desert Water Agency 66,755 70,451 74,164 77,878 81,591 85,576 89,561 Indio Water Authority 91,366 96,107 103,429 110,751 118,072 124,408 130,743 Plan Area Total 471,085 509,281 552,096 594,912 637,725 679,456 721,184
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Indio Subbasin Water Management Plan Update 5-10 TODD/W&C
5.3.3 SCAG Land Use Inventories
Land use information was used during analysis to ensure that municipal water demand projections were consistent with local General Plans and did not exceed allowable land uses in the Plan Area. This land use information was also used to quantify future development of agricultural land. Land use data were retrieved from SCAG’s 2016 Combined Land Use Datasets for Riverside County.7 SCAG then encoded this data layer into GIS. These data are available in various formats, including SCAG’s GIS Open Data Portal.8 SCAG’s land use data include existing land uses, adopted General Plan land use, Specific Plan land use, and adopted zoning codes for each jurisdiction as of 2016. Since each jurisdiction in the region has their own approach to categorizing land uses, SCAG aggregated these categories into their own land use definitions.
These land use data were then reviewed by local jurisdictions beginning in summer 2017, and SCAG’s final dataset reflects each jurisdiction’s local input.
5.3.3.1 Parcels Identified for Development
Future land use projections were based on future development of parcels identified as vacant, agricultural, or under construction as of 2016 in SCAG’s existing land use database. SCAG identified existing land uses by using the most recent County Assessor’s property information. These data represent the best available estimate of current land uses at a regional level.
Parcels identified as remaining vacant, agricultural, or identified as undevelopable or protected in local General Plans, or as part of a conservation area, were excluded from analysis and not considered developable. While some redevelopment of existing parcels is anticipated in the region, SCAG land use data do not provide estimates about the extent to which existing land uses would be available for redevelopment. This information would need to be developed through additional participation from City planning departments.
Table 5-3 and Figure 5-4 show the availability of land identified for development by jurisdiction. Vacant land accounts for 71 percent of land identified for development in the Plan Area, with future development in the West Valley being primarily on vacant land. Agricultural land accounts for 25 percent of the land identified for development, with most of that land in the East Valley. The cities of Coachella and Indio have the largest acreage in agriculture identified for development. These cities are also projected to be the fastest growing in the region. Portions of Imperial County in the Plan Area were excluded from the calculated agricultural to urban conversion, as projected development in Imperial County was assumed to occur on vacant land.
7 http://gisdata.scag.ca.gov/Pages/GIShome.aspx
8 http://gisdata-scag.opendata.arcgis.com/
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Indio Subbasin Water Management Plan Update 5-11 TODD/W&C Table 5-3. Land Available for Future Development (Acres) Jurisdiction Vacant Agriculture Under
Construction
Total
West Valley
Cathedral City 3,282 2 173 3,457
Indian Wells 164 116 117 397
Palm Desert 1,862 0 105 1,967
Palm Springs 4,130 99 311 4,540
Rancho Mirage 2,147 1 1 2,149
Unincorporated 5,093 93 398 5,584
East Valley
Coachella 8,041 3,977 139 12,157
Indio 3,117 3,057 1,061 7,235
La Quinta 1,719 337 180 2,236
Unincorporated 11,490 6,537 24 18,051
Total 41,045 14,219 2,509 57,773
Note: Totals may not sum due to rounding
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Indio Subbasin Water Management Plan Update 5-12 TODD/W&C Figure 5-4. Parcels Planned for Development by Current Land Use
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Indio Subbasin Water Management Plan Update 5-13 TODD/W&C
5.3.3.2 Future Residential Land Uses
For each of the parcels identified for future development, a General Plan or Specific Plan land use was specified based on local land use planning. Under SCAG’s land use definitions, single-family dwelling units are defined as detached dwellings, and multi-family dwelling units are defined as attached residences, apartments, condominiums, or townhouses. Appendix 5-A provides information about allowable densities by General Plan land use and allowable densities by Specific Plan land use. Specific Plan land uses were only applied in the analysis if the Specific Plan was adopted after the most recent General Plan update in each jurisdiction. Densities are measured as dwelling units per acre.
Table 5-4 provides the projected buildout of residential land uses by acre for cities in the Plan Area. SCAG’s growth projections are controlled to not exceed the maximum density specified in local General Plans.
Therefore, the maximum allowable density was assumed to estimate buildout conditions in a manner consistent with SCAG’s methodology.
Table 5-4. Projected Buildout of Residential Land Uses (Housing Units) Jurisdiction Single-Family Multiple-Family
West Valley
Cathedral City 6,069 11,821
Indian Wells 819 0
Palm Desert 6,246 3,396
Palm Springs 3,318 5,554
Rancho Mirage 2,127 2,798
Unincorporated 9,849 3,372
East Valley
Coachella 24,733 38,183
Indio 11,592 9,722
La Quinta 4,510 4,464
Unincorporated 19,655 8,368
Total 88,918 87,678
Residential mixed-use categories in General Plans include mixed residential, which are a combination of single-family detached and multi-family dwellings of any type occurring together, and mixed residential and commercial, which are a mixture of residential and commercial uses occurring in a specified area.
These categories can be a mix of adjacent uses or a mix of uses in a single structure or parcel, such as commercial uses on the ground floor of a building with residential use above. In April and May 2020, the GSAs conducted outreach to City planning departments to determine analysis assumptions for these categories. Responses varied, but based on the feedback, analysis assumed that 75 percent of the units in the “mixed residential” category would be single-family residential, and 25 percent of the acres in the mixed residential and commercial category would include residential multiple-family units.
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Indio Subbasin Water Management Plan Update 5-14 TODD/W&C
5.3.4 Housing Unit Projections
The growth forecast for residential and landscape used in this Alternative Plan Update is based on a forecast of total housing units. SCAG’s Connect SoCal provides socioeconomic projections of households, or occupied housing units, which exclude all vacant units. Additional information about vacancy rates and housing type was used to transform SCAG projections into estimates of total housing units and to separate housing units into the categories of single-family, multiple-family, and mobile home. Additional housing data for the Plan Area are based on the following data sources:
• DOF E-5 Population and Housing Estimates for Cities, Counties and the State—January 1, 2011– 2020. Sacramento, California, May 2020.
• ACS, 2018 American Community Survey 5-Year Estimates (2014–2018) For the Plan Area cities of Cathedral City, Coachella, Indian Wells, Indio, La Quinta, Palm Desert, Palm Springs, and Rancho Mirage, DOF provides the most current and most accurate annual estimates of vacancy rates and total housing units by type. For unincorporated areas in Riverside and Imperial Counties, the most current estimates are from ACS, which derived from an annual survey conducted by the Census Bureau. Unlike the 2010 Census, the ACS is based on a sample and has a margin of error. Multi- year estimates are also provided as part of the ACS to increase statistical reliability. The most current ACS estimates are the 5-year estimates from 2014 to 2018.
ACS data are based on census place, which includes cities and census-designated places (CDPs) in the region. CDPs are concentrations of population defined by the Census Bureau for statistical purposes.
Unincorporated areas in Riverside County include the Bermuda Dunes, Desert Palms, Thermal, Thousand Palms, and Vista Santa Rosa CDPs in the West Valley, and the Mecca, North Shore, and Oasis CDPs in the East Valley. Unincorporated areas of Imperial County include Bombay Beach, Desert Shores, Salton City, and Salton Sea Beach.
5.3.4.1 Vacancy Rates
SCAG’s Connect SoCal counts are limited to occupied households and had to be increased to account for vacant housing units. Vacancy rates were applied to SCAG household projections for each jurisdiction to develop estimates of total housing units for the 2016 base year. Vacancy rates were then used to calculate total housing units based on the formula shown in Equation 5-1.
Equation 5-1. Calculation of Total Housing Units
Housing Units = Households
(1-Vacancy Rate)
Vacancy rates were used instead of a vacant unit count to account for jurisdictions that were split between water agencies or that were both inside and outside of the Plan Area. It was also assumed these vacancy rates would remain constant for each jurisdiction across future projections. A review of historical data from DOF indicate that vacancy rates have been stable over time. According to Connect SoCal, the fastest growing areas have lower average vacancy rates, and as a result, the vacancy rate for new units is lower than the average for the Plan Area.
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Indio Subbasin Water Management Plan Update 5-15 TODD/W&C For cities in the Plan Area, Table 5-5 provides the most recent estimates of households, housing units, and vacancy rates from DOF. The cities of Coachella and Indio have the largest share of growth and have lower seasonal vacancy rates. The cities of Indian Wells, Rancho Mirage, and La Quinta have higher seasonal vacancy rates, but lower rates of overall growth. The overall vacancy rate for Plan Area cities is
29.5 percent. This total is also consistent with the ACS dataset. According to the ACS, seasonally vacant units account for 77 percent of the vacant units among Plan Area cities.
Table 5-5. DOF Vacancy Rates for Plan Area Cities (2016) City Households Housing Units Vacancy Rate
West Valley
Cathedral City 17,048 21,080 19.1%
Indian Wells 2,827 5,262 46.3%
Palm Desert 24,107 38,167 36.8%
Palm Springs 23,191 35,490 34.7%
Rancho Mirage 9,167 14,403 36.4%
East Valley
Coachella 9,769 10,397 6.0%
Indio 25,978 31,449 17.4%
La Quinta 15,318 24,432 37.3%
Total 127,405 180,680 29.5%
Source: DOF, 2020; Table E-5
Table 5-6 provides the most recent ACS 5-year (i.e., 2014 to 2018) estimate of seasonally vacant units for unincorporated areas in the Plan Area. The subtotals for all CDPs were used to determine vacancy rates for these jurisdictions. For the West Valley’s unincorporated CDPs, the overall vacancy rate is 25 percent.
For the East Valley’s unincorporated CDPs, the overall vacancy rate is 12 percent in Riverside County and 37 percent in Imperial County.
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Indio Subbasin Water Management Plan Update 5-16 TODD/W&C Table 5-6. ACS Vacancy Rates for Unincorporated Areas (2014–2018) Census Designated Place Households Housing Units Vacancy Rate West Valley
Bermuda Dunes 2,818 3,746 25%
Desert Palms 4,010 5,191 23%
Thermal 472 693 32%
Thousand Palms 2,728 3,813 28%
Vista Santa Rosa 855 1,022 16%
Subtotal 10,883 14,465 25%
East Valley (Riverside County)
Mecca 1,955 2,191 11%
North Shore 915 915 0%
Oasis 1,028 1,340 23%
Subtotal 3,898 4,446 12%
East Valley (Imperial County)
Bombay Beach 161 467 66%
Desert Shores 323 475 32%
Salton City 1,876 2,833 34%
Salton Sea Beach 141 212 33%
Subtotal 2,501 3,987 37%
Source: ACS, 2018; Table B25004
5.3.4.2 Baseline Housing Units by Type
For the baseline housing unit estimate, additional housing data were used to split housing units into categories of single- and multiple-family units to align with customer billing data. For cities in the Plan Area, this information was derived from DOF estimates, as shown in Table 5-7. For unincorporated areas, this information was derived from the ACS 5-year estimate (2014–2018), as provided in Table 5-8. DOF provides estimates for housing units, and the ACS provides estimates for households. The ACS does not identify a share of vacant units by housing unit type, so vacant units were assigned based on their existing proportion in the subject unincorporated area.
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Indio Subbasin Water Management Plan Update 5-17 TODD/W&C Table 5-7. Housing Unit Type for Plan Area Cities (2016) City Single-Family Multiple-Family Mobile Home
West Valley
Cathedral City 69% 19% 12%
Indian Wells 88% 12% 0%
Palm Desert 69% 22% 10%
Palm Springs 61% 33% 6%
Rancho Mirage 83% 11% 6%
East Valley
Coachella 74% 20% 6%
Indio 72% 18% 10%
La Quinta 88% 11% 1%
Source: DOF, 2020; Table E-5
Table 5-8. Housing Unit Type for Unincorporated Areas (2014–2018) Census Designated Places Single-Family Multiple-Family Mobile Home West Valley
Bermuda Dunes 55% 45% 0%
Desert Palms 100% 0% 0%
Thermal 51% 12% 37%
Thousand Palms 58% 8% 34%
Vista Santa Rosa 79% 4% 17%
East Valley (Riverside County)
Mecca 48% 32% 20%
North Shore 65% 0% 35%
Oasis 27% 0% 73%
East Valley (Imperial County)
Bombay Beach 18% 17% 65%
Desert Shores 45% 11% 44%
Salton City 89% 0% 11%
Salton Sea Beach 33% 0% 67%
Source: ACS 2018; Table B25124
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Indio Subbasin Water Management Plan Update 5-18 TODD/W&C
5.3.4.3 Future Housing Units by Type
Historical development patterns in the Plan Area were used as the basis for projecting future development. DOF provides annual housing information for cities in California.9 Figure 5-5 shows the number of new housing units by type from 2000 to 2020 for cities in the Coachella Valley. A review of ACS data indicate that unincorporated areas represented a small portion of total development. Over that period, single-family homes accounted for 85 percent of new housing units. This trend was generally consistent across the Plan Area. There were fewer multiple-family developments, and there was a net loss of mobile homes in the region over this period. This is in contrast to the City General Plans, many of which anticipate a significant number of future multiple-family developments. DOF estimates are not available for unincorporated areas in Riverside and Imperial Counties. A review of ACS data indicate that unincorporated areas represented a small portion of total development over this period.
Figure 5-5. New Housing Units by Type (2000–2020)
9 State of California, Department of Finance, Tables E-4 and E-5 FINAL
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-19 TODD/W&C For analysis, all new housing units in the Plan Area were allocated into housing unit types using a stock and flow model that used the land use inventory of housing units and the historical rate of growth by housing type to match customer billing data. Equation 5-2 is an example formula for allocating single- family housing units. The formula allows recent housing trends to continue in the short term and allows a shift toward other planned land uses over time based on buildout conditions and local land use planning.
Equation 5-2. Calculation of Single-Family Housing Units HUSF =HUT ÷ �INVSF + �INVMF × ρMF
ρSF �� × INVSF
Where:
HU = total new housing units by type for a projection year INV = current land use inventory in total housing units by housing type ρ = ratio of historical development by type divided by the ratio of historical inventory by type SF = single-family sector
MF = multiple-family sector
T = total
Table 5-9 lists the final projected allocation of new housing units into housing types. In the short term, 85 percent of new housing units are single-family developments. In the long term, there is a shift toward planned multiple-family developments based on the inventory of available land uses. No new mobile home developments were assumed in the region. There are small number of planned mobile home developments in the Plan Area, and for this municipal demand projection, they are captured under the multiple-family category.
Table 5-9. New Units in Plan Area by Housing Type
Housing Type 2020 2025 2030 2035 2040 2045
Single-Family 85% 82% 78% 72% 63% 47%
Multiple-Family 15% 18% 22% 28% 37% 53%
Total 100% 100% 100% 100% 100% 100%
According to SCAG’s Connect SoCal, much of the planned growth in the region is projected to occur within existing cities. As a result, several of the cities in the projection such as Cathedral City, Indio, Palm Springs, and Rancho Mirage were constrained on the continued trend of building primarily single-family homes.
Rather than produce individual estimates by jurisdiction, buildout conditions were aggregated for the entire Plan Area. Several cities in the region have a sphere of influence that could let them expand their service areas into currently unincorporated areas. In addition, cities facing growth constraints could use redevelopment of existing land uses or additional updates to their General Plans as a mechanism to accommodate future growth. For these reasons, jurisdictional-level land use analysis would likely underestimate the potential number of single-family homes.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-20 TODD/W&C
5.3.4.4 Final Housing Unit Projection
Table 5-10 and Figure 5-6 provide the total number of projected housing units by type for the Plan Area.
These were used as the basis for developing demand factors and other projections. Overall, the Plan Area is projected to grow by 120,698 housing units (i.e., 60 percent) by 2045. The mix of new housing units in the projection is similar to the mix of existing housing stock over the long term, with more single-family homes being built in the short term shifting to multiple-family developments over time.
Table 5-10. Housing Units by Type for the Plan Area
Housing Type 2016 2020 2025 2030 2035 2040 2045
Coachella Valley Water District
Single-Family 91,513 103,616 112,313 120,617 128,328 133,810 137,925 Multiple-Family 31,696 33,874 35,825 38,166 41,101 44,311 48,889 Subtotal 123,209 137,490 148,138 158,783 169,429 178,121 186,814 Coachella Water Authority
Single-Family 7,413 11,062 14,135 17,070 19,795 22,623 24,746 Multiple-Family 2,655 3,312 4,001 4,829 5,866 7,522 9,884 Subtotal 10,068 14,374 18,136 21,899 25,661 30,145 34,630 Desert Water Agency
Single-Family 23,709 26,269 28,115 29,878 31,516 32,998 34,111 Multiple-Family 14,543 15,004 15,418 15,915 16,538 17,406 18,644 Subtotal 38,252 41,273 43,533 45,793 48,054 50,404 52,755 Indio Water Authority
Single-Family 20,486 22,824 25,511 28,078 30,461 32,163 33,441 Multiple-Family 8,159 8,580 9,183 9,907 10,814 11,810 13,232 Subtotal 28,645 31,404 34,694 37,985 41,275 43,973 46,673 Plan Area
Single-Family 143,121 163,771 180,074 195,643 210,100 221,594 230,223 Multiple-Family 57,053 60,770 64,427 68,817 74,319 81,049 90,649 Plan Area Total 200,174 224,541 244,501 264,460 284,419 302,643 320,872
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-21 TODD/W&C Figure 5-6. Housing Units by Type for Plan Area
5.3.5 Employment Projection
Connect SoCal employment estimates were used to project future CII water use. SCAG projects regional employment across 20 broad industry sectors as established by the North American Industry Classification System (NAICS). These sectors are based on a set of national employment forecasts and a region’s share of the nation’s employment. For the Coachella Valley, employment is projected to grow at a slower rate than the overall population. This is a result of net travel out of the region for work, as well as the large number of retirees in the Plan Area. Table 5-11 provides employment projections for the GSA Areas in the Plan Area. These employment projections are anticipated to be impacted by the COVID-19 pandemic and resulting economic downturn and the decrease in recreational/tourism activities. Once long-term impact and recovery from the COVID-19 pandemic is better understood, the GSAs will be able to confirm the accuracy of SCAG’s employment forecast.
FINAL
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-22 TODD/W&C Table 5-11. Baseline and Forecast Employees by GSAs
Water Provider Baseline
2016
2020 2025 2030 2035 2040 2045
Coachella Valley Water District 105,736 112,240 116,761 121,284 125,806 131,903 138,001 Coachella Water Authority 8,599 12,209 14,884 17,560 20,235 21,909 23,582 Desert Water Agency 35,529 38,435 40,418 42,402 44,387 45,188 45,989 Indio Water Authority 27,530 30,177 32,108 34,039 35,970 36,970 37,971 Plan Area Total 177,394 193,061 204,171 215,285 226,398 235,970 245,543
5.3.6 Unit Demand Factors
Municipal water demand in the growth projection was calculated using a per-housing unit demand factor (gallons per housing unit per day) for residential and landscape uses and a per-employee demand factor (gallons per employee per day) for non-residential uses. A benefit of this approach over typical per-capita unit water use approaches was the ability to better estimate water uses associated with land use features, such as lot sizes and building footprints not directly associated with population. Housing unit counts also account for the significant number of seasonal residents not captured in federal and state population data. In addition, given that the 2010 Census is now 10 years out of date, there is more potential uncertainty in population estimates, while housing unit counts are recorded by County Assessor property information. Residential uses were divided into single- and multiple-family housing unit types to align with customer billing categories. Demand factors were calculated using a 5-year average of water demand from customer billing data provided by Plan Area water providers. Indoor and outdoor landscape use was estimated to adjust for landscape water use in new developments.
5.3.6.1 Historical Billing Data
Table 5-12 lists the total annual domestic water use for each Plan Area GSA. Baseline water use was based on a 5-year average measured from July 2014 to June 2019. The 5-year average was selected to account for annual variations in water use from weather, as well as other irregularities that can occur over shorter time periods.
Table 5-12. Baseline Domestic Water Use for Plan Area GSAs (Acre-Feet per Year) GSA FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 5-Year
Average
Coachella Valley Water District 93,077 74,078 81,144 86,191 82,782 83,454 Coachella Water Authority 6,590 5,650 6,067 6,140 6,063 6,102 Desert Water Agency 30,599 25,499 28,024 30,357 28,729 28,642 Indio Water Authority 19,399 17,299 15,943 17,546 17,855 17,608 Plan Area Total 149,665 122,526 131,178 140,234 135,429 135,806
Figure 5-7 shows a graph of the monthly baseline water use for each GSA. The baseline period includes California’s drought state of emergency, which ran from January 2014 to April 2017. As indicated in Table 5-12, the highest water use was in fiscal year (FY) 2015 (e.g., FY 2015 is July 2014 through June 2015) and the lowest water use was in FY 2016. Since the end of the drought emergency, water use has continued at a rate that is lower than pre-drought levels. Through June 2019, there has been no indication of a rebound in water use, and given the effects of climate change, drought periods, and new conservation legislation that will be implemented during the planning horizon, further downward pressure on water
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-23 TODD/W&C demand is expected. For the GSAs, 5-year average water use is consistent with the most recent water use data.
Figure 5-7. Baseline Water Use by GSA (Acre-Feet per Month)
Other Water Suppliers in the Plan Area
CVWD and DWA have populations that are both within their service area boundaries and outside their domestic water service areas; these are served by private wells or other water systems, such as mutual water companies and small water systems. For CVWD, this includes Myoma Dunes Water Company (MDWC) and several small water systems. For DWA, this population includes a portion of the DWA jurisdictional area overlapping with Mission Springs Water District (MSWD) and several small water systems. MSWD provides municipal water service to these customers, which includes a small number of customers in the northwest of the Indio Subbasin (i.e., the Garnet Hill Subarea). IWA and CWA serve all customers in their service areas.
For customers in CVWD’s jurisdictional area that are served via domestic water service from other water systems, water demand factors were based on CVWD billing data for unincorporated areas in Riverside County. For customers in DWA’s jurisdictional area served by MSWD, water demand factors were based on the 5-year average water use per MSWD billing data as provided by DWA staff (dated September 30, 2020).
FINAL
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-24 TODD/W&C Non-Domestic Water Supplies in the Municipal Demand Projection Baseline water use includes urban water demands met by a water source other than GSA domestic production, including private wells, recycled water, surface water diversions, and Coachella Canal water.
Although these demands are not currently met by the GSAs’ domestic water supplies, they are still considered municipal demands and are accounted for in the municipal demand forecast. This water is used primarily for turf and landscape irrigation. The demands shown in Table 5-13 are based on 2019 water use for CVWD and IWA and are based on the 5-year average for DWA. For IWA, this water was supplied by CVWD for use in IWA’s service area.
Table 5-13. Non-Domestic Water for Landscape Use (Acre-Feet) Water Provider Acre-Feet
Coachella Valley Water District 6,496
Desert Water Agency 740
Indio Water Authority 2,758
5.3.6.2 Baseline Demand Factors
For analysis, billing data from each GSA were aggregated into five generic customer sectors, as shown in Table 5-14. Each of these customer sectors was associated with an output from the regional growth forecast to develop a unit factor. For the single- and multiple-family sectors, future water demand was based on single- and multiple-family housing units, respectively. For the landscape sector, future water demand was based on total housing units using the assumption that future landscape uses, such as common areas and parks, are driven by future residential development. For the CII sector, future water demand was based on the total number of employees, using the assumption that CII use primarily occurs indoors. The other sector, which includes water uses such as temporary construction meters, was driven by total housing units.
Table 5-14. Variables Used in Unit Factors Calculation
Customer Sector Output from Growth Forecast
Single-Family Residential Single-Family Housing Units
Multiple-Family Residential Multiple-Family Housing Units Landscape Total Housing Units
Commercial, Industrial, and Institutional Employees
Other Total Housing Units
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-25 TODD/W&C Table 5-15 lists the baseline unit factor calculations for each GSA, and the values used to calculate them (i.e., water use and growth forecast). These unit factors were applied to growth forecasts to develop a baseline municipal demand projection before conservation or unaccounted-for water. CWA and IWA have a higher number of persons per housing unit and fewer seasonally vacant units compared to CVWD and DWA. This results in higher water use as measured in gallons per housing unit per day (gphud) when compared to traditional measurement of gallons per capita per day (gpcd).
Table 5-15. Baseline Unit Factor Calculations
Sector Calculation Unit CVWD CWA DWAa IWA
Single-
Familyb
Water Use million gallons per day 42.78 3.62 13.44 9.68 Growth Forecast single-family housing
units
86,678 7,413 23,469 20,486
Unit Factor gphud 494c 489 572 473
Multiple-
Familyb
Water Use million gallons per day 5.02 0.63 1.49 1.56
Growth Forecast single-family housing
units
29,477 2,655 14,441 8,159
Unit Factor gphud 170 239 103 192
Landscape Water Use million gallons per day 25.50 0.53 3.02 4.44 Growth Forecast total housing units 116,155 10,068 37,910 28,645 Unit Factor gphud 220 52 80 155
CII Water Use million gallons per day 5.46 0.65 8.23 2.47 Growth Forecast employees 100,495 8,599 35,328 27,530
Unit Factor gallons per employee
per day
54 76 233 90
Other Water Use million gallons per day 0.96 0.01 0 0.004 Growth Forecast total housing units 116,155 10,068 37,910 28,645 Unit Factor gphud 8.3 1.1 0 0.1
a DWA’s historical billing data are not segregated into the five generic customer sectors. Recent billing data (2019) was used to determine the estimated split for prior years.
b Baseline housing units used to calculate unit factors were based on 2016 estimates of housing. c CVWD’s single-family demand factor was calculated separately on a jurisdictional basis in Table 5-16. 494 gphud is an average across all of CVWD’s jurisdictional area.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-26 TODD/W&C CVWD Single-Family Demand Factors
The CVWD single-family residential demand factor was projected by jurisdiction, as demands and growth rates in CVWD’s service area differ regionally. Table 5-16 lists the demand factors by housing unit for cities in CVWD’s service area. These totals were calculated by matching CVWD’s customer-level database information with SCAG housing information.
Table 5-16. CVWD Single-Family Demand Factors by City
Jurisdiction Single-Family
Water Use
(millions of gallons)
Single-Family
Housing Units
Single-Family
Unit Factor (gphud)
Cathedral City 6.3 12,49 501
Coachella 0.003 5 514
Indian Wells 3.5 4,405 798
Indio 1.1 2,121 521
La Quinta 10.7 20,357 523
Palm Desert 9.5 24,666 387
Palm Springs 0.01 15 482
Rancho Mirage 7.5 11,538 651
Unincorporated 4.2 11,080 379
Demand Factors for Private Wells and Other Water Systems Table 5-17 lists the baseline unit factor calculations for customers served by private wells and other water systems. For customers in CVWD’s GSA area, unit factors were based on CVWD billing data in unincorporated areas of Riverside County. For customers in DWA’s GSA Area, unit factor calculations were based on billing data provided by MSWD. For the small number of residential homes in the MSWD service area served by private wells or other water systems, there were few multiple-family homes, so the single- and multiple-family factors were combined.
Table 5-17. Baseline Unit Factor Calculations for Private Wells and Other Water Systems Sector Unit Factor CVWD DWA
Single-Family gallons per housing unit per day 370 283
Multiple-Family gallons per housing unit per day 129 ..283 Landscape gallons per housing unit per day 47 ..28
CII gallons per employee per day 54 ..445
Other gallons per housing unit per day 11 ..4
501
283
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-27 TODD/W&C
5.3.6.3 Indoor and Outdoor Water Use Estimates
Outdoor water use was estimated to distinguish landscape water savings in new developments. For some customers, water used for landscaping is not directly metered. An industry standard approach to measuring outdoor use, referred to as the minimum month method, is to assume all winter use is categorized as indoor consumption. This method underestimates outdoor use because of winter irrigation in dry climates such as the Coachella Valley.
The method used for this forecast documented the pattern of seasonal variation from dedicated irrigation meters and applied it to other sectors with mixed meters. With dedicated irrigation meters, winter irrigation is directly measured, and seasonal irrigation patterns could be applied to other sectors.
Figure 5-8 is an example plot comparing baseline landscape irrigation and single-family residential water use for CVWD. As shown, the seasonal variation of dedicated landscape meters correlates to single-family water use.
Figure 5-8. Indoor Water Use Estimation
Table 5-18 lists the resulting outdoor water factors developed through analysis of each GSA’s data. These values are an average based on the 5-year billing data used. It is likely indoor/outdoor water use percentages vary across each agency’s jurisdictional area. DWA’s combined billing category of single- family, multiple-family, and landscape water use is disaggregated using the same method used for developing DWA’s demand factors (described above). The other category is not assumed to have outdoor use.
FINAL
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-28 TODD/W&C Table 5-18. Outdoor Water Use Percentages for GSAs
Water Provider Single-
Family
Multiple-
Family
CII Landscape Other
Coachella Valley Water District 67 34 38 100 0
Coachella Water Authority 50 17 35 100 0
Desert Water Agency 69 69 69 100 0
Indio Water Authority 58 33 54 100 0
5.3.7 Baseline Forecast
Table 5-19 shows the baseline municipal demand forecast for the Indio Subbasin. This is projected municipal water use before considering passive conservation and system water loss.
Table 5-19. Municipal Demand Forecast for the Plan Area (acre-feet) Category 2016
Baseline 2020 2025 2030 2035 2040 2045
Baseline Forecast 148,438 167,102 181,873 196,397 210,550 222,393 233,241
5.3.8 Water Loss
Water loss includes real loss, which is physical water lost from a utility’s storage tanks and pressurized distribution system up to the point of customer consumption (e.g., at the water meter) and apparent loss, which include customer metering inaccuracies and data handling errors. As of 2015, SB 555 requires California urban water suppliers to submit an annual water loss audit to DWR. This audit attempts to quantify all inputs and outputs of a supplier’s potable distribution system along with many other factors related to quantifying water losses. SB 555 also directed the SWRCB to develop performance standards for volumetric water loss by July 2020. As of September 2021, the SWRCB has not completed final rulemaking about performance standards but has proposed using a Microsoft Excel-based economic model to calculate a unique volumetric standard for each water supplier. The performance standard is proposed to be quantified in units of real losses per service connection per day (i.e., gallons per connection per day). This value is a performance indicator that is automatically calculated as an output of the American Water Works Association Water Loss Audit prepared annually by urban water suppliers, which is also submitted to DWR.
Three years of available validated Water Loss Audit reports were retrieved from DWR’s Water Use Efficiency (WUE) Data Portal.10 Water Loss Audits calculate water loss based on the difference between production and consumption, which averaged approximately 10 percent across the Plan Area. For this analysis, real water loss was projected on a per-connection basis. The number of service connections included both active and inactive service lines are connected to water mains and fire hydrant laterals.
Table 5-20 lists real losses, apparent losses, and service connections from the most recent water loss audits available at the WUE Data Portal. The only validated Water Loss Audit reports for other small water systems in the service area are from MDWC. These values were used for all other small water systems.
10 https://wuedata.water.ca.gov/
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-29 TODD/W&C Table 5-20. Water Loss Reporting by Water Provider (3-Year Average) Water Provider Real Losses
(gal/conn/day)
Apparent Losses
(gal/conn/day)
Baseline Service
Connections
Coachella Valley Water District 43.3 46.0 104,048
Coachella Water Authority 31.7 8.0 8,319
Desert Water Agency 86.5 16.3 24,469
Indio Water Authority 30.5 10.4 23,130
Other Small Water Systems 49.1 40.2 2,543
Table 5-21 shows the water loss projection for the Plan Area. The number of service connections were escalated from the baseline period using the growth in total housing units, resulting in an average
9.4 percent water loss in 2045. Additionally, it was assumed real losses would be reduced by 10 percent over the planning period based on a minimum potential estimate of water savings based on activities required by SB 555.
Table 5-21. Water Loss Projection for Plan Area (AFY)
-- 2016 Baseline 2020 2025 2030 2035 2040 2045
Water Loss 15,567 17,366 18,459 19,494 20,470 21,183 21,847 Percent of Municipal Demands 10.5 10.4 10.1 9.9 9.7 9.5 9.4
5.3.9 Adjustment Factors
The municipal water demand projection used an inventory growth and replacement model and historical and projected housing units for cities in the Plan Area to estimate water savings rates for single-family residential, multi-family residential, and non-residential plumbing fixtures and appliance inventories. The models were implemented in Microsoft Excel with separate models for outdoor water use, toilets, clothes washers, and urinals. Future outdoor water uses were reduced based on an adjusted outdoor use estimate for new developments. Additional active (conservation program) savings are anticipated but were not included as part of municipal demand projections.
5.3.9.1 Indoor Passive Conservation Savings
The municipal water demand forecast estimates conservation that occurs as a result of changes in state and federal water efficiency requirements for plumbing fixtures, sometimes referred to as passive conservation. These standards have resulted in a significant reduction of indoor water use over time.
Going forward, codes and standards for fixtures and appliances will continue to reduce indoor water demand through the replacement of existing fixtures, and more efficient technologies used in new developments.
Passive conservation savings are based on a demographically driven growth and replacement model that accounts for fixtures from new construction and natural replacement using the same demographic data used in Connect SoCal. Savings estimates are provided for the single-family residential, multi-family residential, and non-residential sectors. The passive conservation model estimates water savings for toilets, showerheads, clothes washers, dishwashers, and urinals. The model estimates the stock of different types of water fixtures annually from 1990 to 2045.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-30 TODD/W&C Table 5-22 shows the historical and current water efficiency standards used to estimate indoor passive conservation savings. Water fixtures installed in new construction were assumed to comply with plumbing codes in effect when the new construction occurred. Natural replacement rates vary by device and are linked to the expected life of the device. When devices fail and are replaced, when spaces are remodeled, or for other reasons, new devices were assumed to comply with plumbing codes in effect when the replacement occurred.
Table 5-22. State and Federal Plumbing Codes
Fixture/Appliance Maximum
Flow Rate Law/Regulation Effective
Year
Residential Toilets
All Models ≤ 3.5 gpf California Statute 1978
All Models ≤ 1.6 gpf California Statute 1992
All Models ≤ 1.28 gpf California (AB715) 2007 2014
Residential Showerheads
All Models 2.5 gpm California (CEC) 1992 1994
All Models 2.0 gpm Federal (CEC Title 20) 2015 2016
All Models 1.8 gpm Federal (CEC Title 20) 2015 2018
Residential Clothes Washers
Standard ≤ 9.5 IWF Federal Energy Independence and Security Act of 2007 2011 Top Loading, Standard ≤ 8.4 IWF Federal Standard (DOE) 2012 2015 Top Loading, Standard ≤ 6.5 IWF Federal Standard (DOE) 2014 2018 Top Loading, Compact
(less than 1.6 ft3 capacity)
≤ 14.4 IWF Federal Standard (DOE) 2012 2015
Top Loading, Compact
(less than 1.6 ft3 capacity)
≤ 12 IWF Federal Standard (DOE) 2014 2018
Front Loading, Standard ≤ 4.7 IWF Federal Standard (DOE) 2012 2015 Residential Dishwashers
Regular 6.5 gal/cycle Federal Energy Independence and Security Act of 2007 2010 Regular 5 gal/cycle Federal Standard (DOE) 2012 2013
Compact 4.5 gal/cycle Federal Energy Independence and Security Act of 2007 2010 Compact 3.4 gal/cycle Federal Standard (DOE) 2012 2013
Non-Residential Toilets
All Models ≤ 3.5 gpf California Statute 1978
All Models ≤ 1.6 gpf California Statute 1992
All Models ≤ 1.28 gpf California (AB715) 2007 2014
Non-Residential Urinals
Standard 1.0 gpf Energy Policy Act of 1992 1994
Standard 0.5 gpf California (AB 715) 2007 2014
Wall-Mounted Urinals 0.125 gpf California (CEC) 2015 Executive Order (EO B-29-15) 2018 gpf = gallons per flush
gpm = gallons per minute at a pressure of 80 psi.
IWF = integrated water factor expressed in gallons per cycle per cubic foot
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-31 TODD/W&C Table 5-23 lists the natural replacement rate for indoor plumbing fixtures. Useful life and associated annual replacement rates were based on standard industry estimates, estimates from plumbing fixture saturation studies, and the best management practice reports from the California Water Efficiency Partnership (see: https://calwep.org/) .
Table 5-23. Parameters Used in Indoor Water Savings Fixtures Sector Fixture Useful Life
(Years)
Replacement Rate
(% per Year)
Residential Toilets 25 4
Residential Showerheads 8 12
Residential Clothes Washers 14 8.3
Residential Dishwashers 13 8
Non-Residential Toilets 40 2.5
Non-Residential Urinals 40 2.5
Table 5-24 lists the frequency of water use per fixture and sector. This information was obtained from focused end-use studies. Residential fixture water use was based on 2016 Residential End Uses of Water, Version 2 (Water Research Foundation [WRF], 2016). Non-residential fixture water use was based on Commercial and Institutional End Uses of Water (WRF, 2000). These studies are the current industry benchmarks for residential and non-residential water uses. These factors were applied on a per-housing unit basis as described below.
Table 5-24. Parameters Used in Indoor Water Savings Fixtures Sector Fixture Frequency of Use
Residential Toilets 4.9 flushes per person per day
Residential Showerheads 7.8 minutes per use
0.7 uses per person per day
Residential Clothes Washers 3.5 cubic feet per load
0.3 cycles per person per day
Residential Dishwashers 0.1 cycles per person per day
Non-Residential Toilets 2.6 flushes per employee per day 4 flushes per occupied hotel room per day
Non-Residential Urinals 1.25 flushes per employee per day
Table 5-25 lists the projected residential indoor passive conservation savings (in AF) for new and existing developments in the Plan Area by GSA. Indoor passive conservation savings were estimated at 8.1 gpcd by 2045 when compared to 2016 savings rates for single-family homes, and 6.4 gpcd savings rates for multiple-family homes. CII savings are 2 gallons per employee per day. Water savings are measured relative to baseline water use. Water use savings by device are converted into gallons per housing unit per day using historical and projected values for vacancy rates and estimates of persons per household.
CII savings include estimates of hotel savings based on occupancy information from the Greater Palm Springs Convention and Visitors Bureau. Chapter 11, Projects and Management Actions describes the Plan Area’s active conservation programs that incentivize indoor water conservation.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-32 TODD/W&C Table 5-25. Indoor Passive Savings in the Plan Area (Acre-Feet) Water Provider 2020 2025 2030 2035 2040 2045
Coachella Valley Water District 547 1,414 1,965 2,393 2,718 2,986 Coachella Water Authority 118 345 528 695 873 1,040
Desert Water Agency 131 335 464 563 642 707
Indio Water Authority 198 512 714 872 993 1,094
Plan Area Total 994 2,606 3,671 4,523 5,226 5,827
5.3.9.2 Outdoor Water Use Adjustment
Unit factors for future uses were adjusted to account for implementation of the MWELO (DWR, 2015).
MWELO sets a minimum standard for outdoor water conservation in California and applies to new construction projects with landscape areas of 500 square feet or more. The size threshold for existing landscapes that are being rehabilitated has not changed from the original 2010 MWELO, remaining at 2,500 square feet. The 2015 MWELO also allows for special landscape areas (SLAs) that allow for extra water in non-residential areas for specific landscape functions such as recreation or for areas irrigated with recycled water.
Table 5-26 lists the Plan Area’s outdoor
passive water savings adjustment factor.
Passive water savings resulting from
implementation of the 2015 MWELO were
based on an evapotranspiration
adjustment factor (ETAF), which when
applied to reference evapotranspiration,
adjusts for plant water requirements and
irrigation efficiency. The current ETAF for
new residential landscapes is 0.55 and the
ETAF for non-residential landscapes is 0.45.
Existing landscapes were assumed to have
an ETAF of 0.7, meaning that new
residential landscapes were assumed to
use 21 percent less water, and new non-
residential landscapes were assumed to
use 36 percent less water. It was also
assumed that 25 percent of dedicated landscape meters were categorized as SLAs such as sports fields, and therefore no savings were assumed to come via MWELO requirements. No savings were assumed from existing landscapes, as these projections typically receive incentives under conservation programs, and are not considered a passive savings. Chapter 11, Projects and Management Actions describes active conservation programs that incentivize outdoor water use efficiency.
The demand forecast assumes desert landscaping in new
residential developments, in accordance with GSA
policies.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-33 TODD/W&C Table 5-26. Outdoor Passive Water Savings Within the Plan Area (Acre-Feet) Water Provider 2020 2025 2030 2035 2040 2045
Coachella Valley Water District 1,981 3,439 4,873 6,275 7,399 8,439 Coachella Water Authority 326 600 867 1,125 1,395 1,630 Desert Water Agency 509 872 1,228 1,575 1,838 2,072
Indio Water Authority 340 717 1,088 1,449 1,721 1,972
Plan Area Total 3,156 5,628 8,056 10,424 12,353 14,113
5.3.10 Water Demands on Tribal/Reservation Lands
In the Plan Area, much of the Tribal/Reservation lands in the West Valley has been developed to varying degrees while a substantial amount of Tribal/Reservation lands in the East Valley is largely undeveloped.
To accurately project water demand on Tribal/Reservation lands, Tribal/Reservation outreach was conducted by the GSAs throughout the planning process consistent with DWR’s Draft Guidance Document for the Sustainable Management of Groundwater: Engagement with Tribal Governments (DWR, 2017).
The GSAs have established communications with Tribes in the Plan Area via the SGMA Tribal Workgroup, which meets quarterly, and Tribal/Reservation email lists. Tribal/Reservation data request letters and follow-up letters were sent to the Tribal/Reservation chairs and Tribal/Reservation administrators on May 1, 2020, and May 14, 2020, respectively. Outreach included follow-up emails and phone calls.
Tribal/Reservation data requested included information about land use, population and housing, water demand, and water conservation. During preparation of this Alternative Plan Update, the Tribes indicated that projected Tribal/Reservation land uses are generally included in municipal General Plans; therefore, Connect SoCal adequately captures Tribal/Reservation growth. As such, Tribal/Reservation2012 water demands were not included here in a separate category for analysis; rather, they are included in this municipal demand forecast.
5.3.11 Final Municipal Demand Forecast
Table 5-27 and Figure 5-9 show the municipal demand forecast with future passive conservation for the Plan Area. Indoor water conservation adjustment factors for new and existing developments included toilets, clothes washers, and urinals. The outdoor water conservation adjustment included implementation of 2015 MWELO for new developments. The total conservation adjustment came to 5,827 acre-feet by 2045 for indoor uses and 14,113 acre-feet by 2045 for outdoor uses. The total consumption estimate for the Plan Area is 235,148 acre-feet in 2045, which is an increase of 71,143 acre- feet (i.e., 43 percent). This 43 percent increase in municipal water demand compares to a projected 53 percent increase in Plan Area population.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-34 TODD/W&C Table 5-27. Municipal Demand Forecast for the Plan Area (Acre-Feet) Category 2016
Baseline 2020 2025 2030 2035 2040 2045
Baseline Forecast 148,438 167,102 181,873 196,397 210,550 222,393 233,241 Passive Conservation - -994 -2,606 -3,671 -4,523 -5,226 -5,827 Outdoor Adjustment - -3,156 -5,628 -8,056 -10,424 -12,353 -14,113 Consumption in Plan Area 148,438 162,952 173,639 184,670 195,603 204,814 213,301 Water Loss 15,567 17,366 18,459 19,494 20,470 21,183 21,847 Municipal Demand Totals 164,005 180,318 192,098 204,164 216,073 225,997 235,148 Note: Passive conservation savings and outdoor adjustment are compared against baseline period.
Figure 5-9. Municipal Demand Forecast for Plan Area
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Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-35 TODD/W&C Table 5-28 and Figure 5-10 show a forecast of total water supplied by GSA area in the Plan Area.
Appendix 5-A contains the final, more detailed municipal water demand forecast by GSA area.
Table 5-28. Total Municipal Demand Forecast for GSA Areas (Acre-Feet) Category 2016
Baseline
2020 2025 2030 2035 2040 2045
Coachella Valley Water District
Consumption 92,411 100,994 106,835 112,888 118,908 123,731 128,225 Water Loss 11,292 12,606 13,375 14,102 14,788 15,218 15,615 Total Demand 103,703 113,600 120,210 126,990 133,696 138,949 143,840 Coachella Water Authority
Consumption 6,102 8,396 10,215 12,045 13,843 15,798 17,600 Water Loss 371 529 654 774 888 1,021 1,147
Total Demand 6,473 8,925 10,869 12,819 14,731 16,819 18,747 Desert Water Agency
Consumption 29,558 31,657 33,055 34,492 35,903 37,043 38,033 Water Loss 2,845 3,070 3,173 3,270 3,360 3,449 3,532
Total Demand 32,403 34,727 36,228 37,762 39,263 40,492 41,565 Indio Water Authority
Consumption 20,366 21,905 23,534 25,244 26,950 28,242 29,444 Water Loss 1,059 1,161 1,257 1,348 1,434 1,495 1,553
Total Deman 21,425 23,066 24,791 26,592 28,384 29,737 30,997 Plan Area Total
Consumption 148,438 162,952 173,639 184,670 195,603 204,814 213,301 Water Loss 15,567 17,366 18,459 19,494 20,470 21,183 21,847 Total Demand 164,005 180,318 192,098 204,164 216,073 225,997 235,148 Notes:
Consumption is calculated as the baseline forecast minus passive indoor and outdoor conservation.
GSA area totals may not sum to Plan Area totals due to rounding error.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-36 TODD/W&C Figure 5-10. Municipal Demand Forecast for GSA Areas
5.4 Agricultural Demands
Agriculture is an essential part of the
Coachella Valley economy, generating an
average of $625 million per year from
2014 to 2018 (County of Riverside, 2018).
Agricultural water demand is met via
Colorado River (Coachella Canal) water,
groundwater, and surface water.
Agricultural demand varies by farmed
parcel, depending on crop type and
sequencing (e.g., many farmers use
trimester cropping). Per the 2019 Crop
Report (CVWD, 2019a), the average
agricultural water demand was 5.2 AFY
per cropped acre and accounted for half
of Plan Area water use. Figure 5-11 shows
agricultural water use from 2010 to 2019.
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Agriculture is an essential part of the Coachella Valley economy.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-37 TODD/W&C Average agricultural demand during this timeframe was 292,150 AFY, which was approximately 51 of total demand in the Plan Area during that period.
The 2010 CVWMP Update assumed agricultural demand decreased in proportion to the increase in urban demand. SCAG’s Connect SoCal identifies conversion of specific parcels from agriculture to urban land uses through 2045. This Alternative Plan Update accounts for reduced agricultural water use associated with the conversion of those parcels, while the municipal demand forecast accounts for new urban demands associated with parcel buildout.
Figure 5-11. Agricultural Water Use, 2010–2019 (AFY)
5.5 Agricultural Land Conversion
SCAG land use data were used to determine the reduction in agricultural parcels over time as they are developed for urban uses. To evaluate projected land conversion, potentially developable agricultural lands from the SCAG Connect SoCal dataset were overlaid with data from the 2019 Crop Census showing farmed and idle lands. Table 5-29 lists available agricultural lands in the Plan Area and the proportion that were cropped in 2019.
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percent
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-38 TODD/W&C Table 5-29. Agricultural Acres by Geographic Unit (Acres) Geographic Units Agricultural
Parcels
2019 Cropped
Parcels
Agricultural Lands that
are Cropped
Cathedral City 2 2 100%
Coachella 4,088 2,819 69%
Indian Wells 116 116 100%
Indio 3,129 1,007 32%
La Quinta 341 87 26%
Palm Desert 0 0 0%
Palm Springs 11 0 0%
Rancho Mirage 1 1 100%
Unincorporated West 1,333 713 53%
Unincorporated East 5,268 2,265 43%
Plan Area Total 14,289 7,010 49%
Figure 5-12 shows that 51 percent of projected agricultural conversions would be on currently farmed parcels (i.e., 7,010 acres currently farmed out of 14,289 acres of available agricultural lands). This anticipated change in agricultural acreage was used to calculate changes in agricultural water use by geographic unit. In contrast to the projected urbanization of 5,973 acres of existing farmed lands, there may also be interest in expanding agricultural production within the planning horizon. To refine the agricultural demand forecast, the GSAs conducted outreach to Growing Coachella Valley, a local farming organization. Constraints on water availability and farming practices in California’s Central Valley may increase commercial interest in local farmlands. This demand forecast assumed an increase of 950 acres of new farming production in the East Valley in 2025. Table 5-30 shows projected net acres of agricultural parcels assumed to be converted to urban uses in 5-year increments through 2045. A GIS analysis was performed of CVWD’s crop data in conjunction with these assumed conversions to determine total acres of cropped land.
Table 5-30. Conversion of Agricultural to Urban by Geographic Unit (Acres) Geographic Units 2020 2025 2030 2035 2040 2045
Cathedral City 0 0 0 0 1 1
Coachella 163 326 489 651 852 1,053
Indian Wells 3 5 8 10 24 38
Indio 365 730 1,095 1,460 1,880 2,300
La Quinta 19 38 57 75 101 127
Palm Desert 0 0 0 0 0 0
Palm Springs 5 11 16 21 29 36
Rancho Mirage 0 0 1 1 1 1
Unincorporated West 65 131 196 261 298 334
Unincorporated East 371 741 1,112 1,482 1,783 2,083
Plan Area Total 991 1,982 2,974 3,961 4,969 5,973
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-40 TODD/W&C Figure 5-12. Developable Agricultural Lands
5-39
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-40 TODD/W&C
5.5.1 Agricultural Demand Factors
The agricultural demand factors used for projecting agricultural demands, in acre-feet per acre of cropped land, is based on the 5-year average (i.e., 2015–2019) agricultural water use in each geographic unit. The crop demand factor considered trimester cropping practices in the Plan Area, as defined in the 2019 Crop Report (CVWD, 2019a). Demand factors were modeled section by section and were rolled up into the 10 geographic units described in Section 5.3, Municipal Demands. Agricultural water supply was calculated based on the 5-year average for groundwater pumping and Canal deliveries and is approximately 30 percent higher than crop consumptive use. Table 5-31 lists the agricultural demand factor for each geographic unit. For Palm Springs and Rancho Mirage, which contain negligible agricultural lands, this analysis assumed other vacant lands would be urbanized and no agricultural lands would be affected.
Table 5-31. Agricultural Demand Factors (Based on 2015–2019 Average) Geographic
Units
Agricultural
Lands
(Acres)a
Crop Demand
(AFY)
Agricultural
Water
Supply (AFY)
Demand Factor
(AF/Acre)
Cathedral City - - 0 0.0
Coachella 4,064 12,813 18,150 4.5
Indian Wells 43 220 312 7.3
Indio 904 2,747 3,894 4.3
La Quinta 328 1,675 2,368 7.2
Palm Desert 76 394 559 7.3
Palm Springs - - - 0.0
Rancho Mirage - - - 0.0
Unincorporated West 10,660 44,295 62,817 5.9
Unincorporated East 38,357 145,968 207,050 5.4
Plan Area Totals 54,432 208,112 295,150 --
a Acreage includes the physical size of agricultural parcels but does not include multiple harvests for non-permanent crops.
5.5.2 Agricultural Conservation
In 2014, U.S. Department of the Interior Bureau of Reclamation (USBR) initiated a Pilot System Conservation Program to fund voluntary water conservation projects to benefit the Colorado River system. As part of that program, CVWD continued to offer rebates to agricultural customers to convert farmed land from a flood/furrow system to drip irrigation through 2019. However, efforts to convert from flood irrigation to drip irrigation have flattened, as users with the financial ability to undertake the conversion have already done so. The remaining users still using a flood/furrow system are mostly small farmers who do not have the necessary infrastructure to implement a conversion. As such, most passive water conservation savings associated with increased irrigation efficiency have already been realized, and the region has experienced demand hardening in agricultural water conservation. For example, Figure 5-11 (above) shows that agricultural water demands from 2010 to 2019 have been relatively flat, indicating demand hardening. Additional passive conservation is anticipated to be negligible moving forward and none was assumed for the agricultural demand forecast. Instead, participation in active agricultural conservation, such as CVWD’s Agricultural Irrigation Efficiency Program, was considered (refer to Chapter 11, Projects and Management Actions).
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-41 TODD/W&C
5.5.3 Final Agricultural Demand Projections
The agricultural demand factors presented above were applied to agricultural acreage anticipated to remain in production over time. Total agricultural demands were calculated based on 2019 cropped acreage, and then water demands associated with lands anticipated for agriculture to urban conversion (totaling 5,973 acres) were subtracted out in 5-year increments. For the 950 acres that are anticipated to convert from idle to cropped, approximately 4,900 AFY were added to the forecast in 2025.
Total agricultural demand in the Plan Area is projected to decline from 295,150 AFY in the baseline (i.e., a 5-year average) to 280,243 AFY in 2045, which is a 5 percent decrease. Table 5-32 lists projected agricultural demand through 2045.
Table 5-32. Projected Agricultural Water Demand (AFY)
Jurisdiction
5-Year
Average
(2015–2019)
2020 2025 2030 2035 2040 2045
Cathedral City 0 0 0 0 0 0 0
Coachella 18,150 17,423 16,696 15,968 15,241 14,345 13,449 Indian Wells 312 293 275 256 238 134 31
Indioa 3,894 2,323 751 0 0 0 0
La Quinta 2,368 2,232 2,095 1,959 1,822 1,638 1,453
Palm Desert 559 559 559 559 559 559 559
Palm Springs 0 0 0 0 0 0 0
Rancho Mirage 0 0 0 0 0 0 0
Unincorporated West 62,817 62,432 62,047 61,662 61,277 61,063 60,848 Unincorporated East 207,050 205,050 208,189 206,188 204,188 202,566 200,944 Plan Area Total 295,150 290,312 287,092 284,693 283,045 281,644 280,243 a City of Indio forecast assumes all actively used agricultural parcels will be converted.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-42 TODD/W&C
5.6 Golf Demand
The golf industry represents a significant water demand sector in the Plan Area, comprising over 18 percent or an average 105,300 AFY of Plan Area water use between 2015 and 2019. Demand for golf course irrigation is met with groundwater, Coachella Canal water, and recycled water. Figure 5-13 shows golf water use over the 2010–2019 timeframe. The 2010 CVWMP Update assumed a proportional increase in golf courses to population growth. Anticipated golf water demand projected in this Alternative Plan Update is based on an assumed continuation of existing golf courses, and minimal growth based on trends in golf course construction over the last 10 years per conversations with the Golf Task Force and Southern California Golf Association, and a review of planned golf courses in approved Water Supply Assessments.
A 5-year average from 2015 to 2019 was used to calculate a golf industry demand baseline of 105,300 AFY.
Three future golf courses were assumed when developing golf industry demand projections, based on a list of approved Water Supply Assessments provided by CVWD staff (dated July 23, 2020) for upcoming development approvals. These three new 18-hole golf courses were assumed to comply with CVWD’s Ordinance No. 1302.4: An Ordinance of the Coachella Valley Water District Establishing Landscape and Irrigation System Design Criteria (Landscape Ordinance) (CVWD, 2019b), which mandates golf course water use efficiency (see discussion below). Assuming three new golf courses would be approximately 150 acres in size, analysis projected water use for each golf course under the Landscape Ordinance at 775 AFY per course or 2,324 AFY total.
CVWD WRP-10 serves golf demands in the mid-Valley area. CVWD WRP-10 recycled water serves golf demands in the mid- Valley area.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-43 TODD/W&C Figure 5-13. Golf Course Water Use, 2010–2019 (AFY)
5.6.1 Golf Conservation
New golf course development and retrofitted landscape water efficiency standards are governed by DWR’s MWELO. All water supply agencies must adopt, implement, and enforce MWELO or a more stringent ordinance. As guidance, MWELO includes a water budget calculation called the Maximum Applied Water Allowance that depends on estimates of evapotranspiration and establishes the upper limit of annual applied water for landscaped areas. Any areas of activity with intense foot or vehicular traffic in the CVWD service area, including golf courses, must comply with CVWD’s Landscape Ordinance. The Landscape Ordinance was developed in conjunction with CVAG, Riverside County, Coachella Valley cities, and major water purveyors. Similar to and based on MWELO, a golf course’s area of irrigated turf used for tees, fairways, greens, and practice areas is limited for all new courses, and in additions or renovations to existing golf courses. Under the Landscape Ordinance, the total turf area of golf courses is limited to a maximum of 4 irrigated acres average per golf hole, and practice areas such as driving ranges and short game areas must not exceed 10 acres of turf. The Landscape Ordinance defines a recreational turf grass ETAF of 0.82. This ETAF adjusts for the additional stress of high traffic on recreational turfgrass and the higher irrigation efficiencies of long-range rotary sprinklers. This ETAF for golf courses in the CVWD service area was estimated by dividing 0.7, which is the seasonal average factor for a mixed cooI/warm season turfgrass, by 0.85, which is the irrigation efficiency of long-range sprinklers.
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Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-44 TODD/W&C During analysis, Landscape Ordinance requirements were considered when estimating future golf course demand. The MWELO Maximum Applied Water Allowance for a 150-acre golf course site (assuming 82 acres turf and 68 acres of other landscaped areas) is 775 AFY.
The golf course demand projection (Table 5-33) assumed no passive conservation on existing golf courses, as CVWD and DWA do not anticipate future golf course renovations unless they associated with their Golf Rebate Program. Chapter 11, Projects and Management Actions discusses the Golf Rebate Program, which is considered active conservation. The Golf Rebate Program provides financial support for turf removal on golf courses.
5.6.2 Final Golf Industry Demand Projections
The total golf industry demand estimate for the Plan Area is 105,300 acre-feet in 2020, increasing to 107,625 acre-feet by 2035, which is an increase of 2,325 acre-feet (2 percent). Table 5-33 lists the golf industry demand projection through 2045.
Table 5-33. Golf Course Demand Projection (AFY)
-- 2020 2025 2030 2035 2040 2045
Plan Area Total 105,300 106,075 106,850 107,625 107,625 107,625
5.7 Other Demands
The Plan Area’s other water demands have been historically composed of those from fish farms and duck clubs, along with polo/turf irrigation and environmental water (i.e., Coachella Canal lining mitigation, which occurred from 2013 to 2015). These demands are relatively small, comprising 3 percent (19,500 AFY) of Plan Area water use over the 5-year period from 2015 to 2019. Figure 5-14 shows other water use over the 2010 to 2019 timeframe. These demands were met with groundwater and Coachella Canal water supplies.
Water demand projections in the 2010 CVWMP Update assumed that fish farm and duck club water use would decrease as some of large fish farm owners ceased operation, and replacement use at these farms was expected to have significantly lower water demand. However, some of these fish farms came back into operation with the economic upturn.
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-45 TODD/W&C Figure 5-14. Other Water Use, 2010–2019 (AFY)
A 5-year average (i.e., 2015 to 2019) of 18,900 AFY, which excludes temporary environmental water used to mitigate for the Coachella Canal lining, was used as the baseline for projecting other demands for existing users through 2045. For this Alternative Plan Update, water demand projections for existing other uses were assumed to be flat. These estimates include no future passive conservation savings for these existing other uses. Future demand also assumes several new recreational lakes and surf parks, along with water use by the Salton Sea Restoration North Shore pilot project.
Four projects in the CVWD Area with approved Water Supply Assessments include large water features categorized as lakes, beaches, or surf parks. These four water features have a total projected demand of 500 AFY. The Salton Sea Restoration North Shore pilot project assumes 2,200 AFY of Coachella Canal water would be diverted to support wetland habitats. These demands are assumed to come online between 2020 and 2025.
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Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-46 TODD/W&C
5.7.1 Final Other Demand Projections
Total other demand is estimated for the Plan Area at 18,893 AFY in 2020 and 21,593 AFY by 2045, which is an increase of 2,700 AF (14 percent). Table 5-34 lists the other demand projection through 2045. This Alternative Plan Update assumes that all additional Other demands (2,700 AFY) are served by Canal water.
Table 5-34. Other Demand Projection (AFY)
-- 2020 2025 2030 2035 2040 2045
Plan Area Total 18,893 21,593 21,593 21,593 21,593 21,593
5.8 Total Water Demands
Table 5-35 and Figure 5-15 present the updated water demand projections for the Plan Area. Total water demand projected for 2045 using the assumptions described above is approximately 644,610 AFY.
Projected water demand for 2045 is about 240,800 AFY lower than the 885,400 AFY originally projected for 2045 in the 2010 CVWMP Update. This reduction is a direct result of significantly reduced sociodemographic growth projections, along with conservation savings that have been achieved by Indio Subbasin water users over the last decade and are assumed for the future through passive conservation.
Table 5-35. Total Projected Water Demands in Plan Area (AFY) Water Demand Type 2020 2025 2030 2035 2040 2045
Municipal 180,318 192,098 204,163 216,074 225,997 235,148 Agricultural 290,312 287,092 284,693 283,045 281,644 280,243 Golf 105,300 106,075 106,850 107,625 107,625 107,625
Other 18,893 21,593 21,593 21,593 21,593 21,593
Plan Area Total 594,823 606,858 617,299 628,337 636,859 644,610
Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-47 TODD/W&C Figure 5-15. Total Projected Water Demands in Plan Area (AFY)
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Chapter 5: Demand Projections FINAL
Indio Subbasin Water Management Plan Update 5-48 TODD/W&C
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Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-1 TODD/W&C CHAPTER 6: WATER SUPPLY
6.1 Overview of Water Supply
The Plan Area relies on a combination of local groundwater, Colorado River water, State Water Project (SWP) exchange water, local surface water, and recycled water to meet water demands. This chapter describes the existing water supplies available to the Plan Area and discusses the key assumptions associated with each water supply source. For the purposes of discussion in this chapter, separate accounting is provided in the following subsections for local groundwater (Section 6.2), local surface water (Section 6.3), Colorado River water (Section 6.4), SWP exchange water (Section 6.5), and recycled water (Section 6.6). Plan scenarios, which assume variable supply assumptions to meet future demands, are described in Chapter 7, Numerical Model and Plan Scenarios.
6.2 Local Groundwater
Groundwater from the Indio Subbasin
represents a source of supply for domestic,
agricultural, and municipal water demands.
In this arid region, natural recharge to
groundwater is limited and groundwater
supply historically has been insufficient to
satisfy local water demands without leading
to overdraft. However, groundwater
remains a key part of the supply portfolio
for the Plan Area. Moreover, the Indio
Subbasin serves an important role in
providing storage capacity that is
replenished when surface water is available
and then utilized when needed, such as
during drought or shortage. The Indio
Subbasin also serves to convey water through groundwater flow from areas of recharge to areas of discharge, including production wells. For example, the Indio Subbasin receives substantial replenishment with imported water at three Groundwater Replenishment Facilities (GRFs) and distributes this water through the aquifer to production wells.
The overall purpose of the Sustainable Groundwater Management Act (SGMA) is to establish a plan for basin management that achieves long-term groundwater sustainability. A sustainable groundwater basin is one in which the groundwater use is balanced with the replenishment from natural sources, return flows, and artificial recharge. The Indio Subbasin is described in detail in Chapter 3, Hydrogeologic Conceptual Model and Chapter 4, Current and Historical Groundwater Conditions.
6.2.1 Uses of Groundwater
Local groundwater was the principal source of not only municipal and rural domestic supply, but also of agricultural water supply, until construction of the Coachella Canal in 1949. Groundwater continues to supply municipal, agriculture, golf courses, and other demands such as fish farms and duck clubs (see Chapter 5, Demand Projections). Managed aquifer recharge with imported water at the GRFs ensures an
Mountain-front runoff and Whitewater River flows
replenish the Indio Subbasin.
Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-2 TODD/W&C adequate supply for users extracting groundwater through numerous production wells. Chapter 2, Plan Area, briefly describes the uses of groundwater, and Figure 2-13 illustrates the distribution of groundwater production wells across the Indio Subbasin.
6.2.2 Groundwater Supply
Groundwater has been a principal source of water supply in the Coachella Valley since the early part of the 20th century. Management of groundwater resources requires knowledge of the groundwater balance which is an estimate of the inflows (gains) and outflows (losses) from the groundwater system.
Historically, the demand for groundwater annually exceeded the limited natural inflows of the arid Indio Subbasin. Sources of natural inflow to the Indio Subbasin average approximately 60,000 acre-feet per year (AFY) from watershed runoff and subsurface inflows from adjacent Subbasins. Limited natural recharge has been supplemented with imported water supplies beginning with the delivery of Colorado River water through the Coachella Canal in 1949. Imported water is now a major component of the inflows to the groundwater balance of the Indio Subbasin through return flows of applied Colorado River water and managed aquifer recharge. This section discusses the sources of inflows and outflows of the Indio Subbasin and compares the average groundwater balance for the 10-year periods of 2000 to 2009 and 2010 to 2019.
6.2.2.1 Groundwater Inflows
The groundwater inflows to the Indio Subbasin consist of a combination of sources, as listed below. • Watershed runoff including subsurface inflow from mountain front areas and surface runoff from the Whitewater River, Snow and Falls Creek channels, minor tributaries along the San Jacinto, Santa Rosa, and Little San Bernardino mountain front, and several smaller streams that flow during wet years (excluding outflow to Salton Sea and surface water diversions); • Subsurface inflows from the San Gorgonio Pass and Mission Creek Subbasins (note that the Desert Hot Springs Subbasin is a no-flow boundary);
• Return flow of applied water, treated wastewater, and septic including deep percolation of water applied to agricultural fields, golf courses, and urban landscapes; septic tanks/leachfield systems, which are distributed across rural portions of the Indio Subbasin and some urban areas; and treated wastewater from municipal wastewater treatment plants; and • Imported water recharge using Colorado River and SWP Exchange supplies, as described in Sections 6.4 and 6.5 below.
Of the above, irrigation return flows and imported water recharge are now the major source of inflows to the Indio Subbasin. Table 6-1 below provides an overview of estimated groundwater inflows comparing the 10-year periods of 2000 to 2009 and 2010 to 2019. Chapter 7, Numerical Model and Plan Scenarios, provides estimates of future groundwater inflows for various management scenarios.
6.2.2.2 Groundwater Outflows
Groundwater outflows are part of the Subbasin’s water balance, as listed below. • Net drain flow and subsurface outflows including subsurface flow from the agricultural tile drain system to the Coachella Valley Stormwater Channel (CVSC) or directly to the Salton Sea and subsurface outflows to the Salton Sea at the Subbasin boundary; and
Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-3 TODD/W&C • Groundwater production for municipal, agricultural, golf and other users who are not served by direct delivery of other sources (non-potable, Canal, or surface water).
Of the above, drain flows are a significant source of outflow from the Indio Subbasin, as tabulated in Table 6-1. The 2010 CVWMP Update discussed the historical correlation between higher groundwater levels in the East Valley and increased drain flows. The upward gradient resulting from increased groundwater levels serves to flush the more saline water in the shallow and semi-perched aquifers into the drain system. Conversely, groundwater level declines in the deep aquifer could result in a downward gradient that could allow more irrigation return flow to recharge the groundwater basin rather than flow to the drains. Chapter 9, Sustainable Management, describes this relationship between groundwater levels, drain flows, and groundwater quality. Chapter 11, Projects and Management Actions, includes a proposed study of the correlation between groundwater levels, vertical gradients, drain flow volume, and salinity export.
Table 6-1 provides an overview of estimated average groundwater inflows and outflows over the 10-year periods from 2000-2009 and 2010-2019. The groundwater balance for the 2010-2019 period shows average gains of 49,100 AFY compared to the 2000-2009 period when the basin was losing 110,000 AFY on average. As described in Chapter 4, Current and Historical Groundwater Conditions, implementation of the 2010 CVWMP Update has reversed decades of declining groundwater levels. The groundwater balance over the last decade has been positive, contributing to increasing storage in the Subbasin. Chapter 7, Numerical Model and Plan Scenarios, provides estimates of future groundwater inflows and outflows across the various management scenarios.
Table 6-1. Indio Subbasin Groundwater Balance (2000-2009 and 2010-2019) -- 2000-2009 Average
(AFY)a
2010-2019 Average
(AFY)b
Groundwater Inflow
Natural Infiltrationc 29,000 28,800
Subsurface inflowsd 11,000 11,800
Return flow of applied water, treated wastewater, and septice 240,000 162,000 Imported water rechargef 51,000 178,400
Total Groundwater Inflow 331,000 381,500
Groundwater Outflow
Net drain flow and subsurface outflowsg 52,000 46,800
Groundwater production 389,000 285,600
Total Groundwater Outflow 441,000 332,400
Change in Storage (10-Year Average) -110,000 +49,100
a 2000-2009 averages from 2010 CVWMP Update.
b 2010-2019 averages are based on historical conditions as measured or simulated in the numerical model. c Natural infiltration of watershed runoff excludes surface diversions and net stormwater outflow through the CVSC to the Salton Sea.
d Subsurface inflows are simulated using the numerical model described in Chapter 7, Numerical Model and Plan Scenarios. e Return flows from applied water, septic system, and treated wastewater percolation minus evapotranspiration. f Imported water recharge minus evaporation.
g Net drain flow includes subsurface outflow from the agricultural complex and excludes discharges from wastewater treatment plants and regulatory water.
Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-4 TODD/W&C
6.2.3 Groundwater Storage
The geologic framework of the Indio Subbasin is described in Chapter 3, Hydrogeologic Conceptual Model.
This framework defines the Subbasin’s storage capacity, namely its lateral basin boundaries (bedrock boundaries and faults), depth of the basin bottom (insofar as data are available), and water-storing characteristics of the aquifer materials in the Subbasin. In 1964, DWR estimated that the Subbasins in the Coachella Valley Groundwater Basin contained approximately 39,200,000 acre-feet (AF) of water in the first 1,000 feet below the ground surface, of which 29,800,000 AF is in the Indio Subbasin. The capacities of the individual Subareas of the Indio Subbasin are shown in Table 6-2.
Table 6-2. Indio Subbasin Groundwater Storage Capacity
Subarea Groundwater Storage (AF)a
Garnet Hill Subarea 1,000,000
Oasis Subarea 3,000,000
Palm Springs Subarea 4,600,000
Thermal Subarea 19,400,000
Thousand Palms Subarea 1,800,000
Indio Subbasin Total 29,800,000
a Storage volume in first 1,000 feet below the ground surface (DWR, 1964).
While use of this groundwater in storage has practical limitations (for example, by the depth of production wells), the significant water storage capacity in the Indio Subbasin provides flexibility for the management of groundwater resources. In brief, storage capacity in the Indio Subbasin allows for local storage of water supplies when available and use of stored water supplies when needed. Sustainable management requires that inflows and outflows to the Subbasin are balanced over the long term such that net storage remains stable.
The Indio Subbasin was at its minimum storage in 2009, with a calculated storage loss of 1,890,000 AF from 1970 to 2009 (see Chapter 4, Current and Historical Groundwater Conditions, and Figure 4-9). This represents use of stored groundwater until the management actions identified in the 2002 CVWMP and 2010 CVWMP Update resulted in cessation of overdraft, a positive Subbasin groundwater budget, and groundwater storage increases. Since 2009, groundwater pumping has decreased and replenishment activities have increased, leading to the observed recovery of groundwater in storage. The GSAs’ management activities have resulted in replacement of approximately 840,000 AF of groundwater in storage, or about 45 percent of the cumulative depletion observed from 1970 to 2009.
This Alternative Plan Update builds on recent management activities for a long-term sustainable groundwater supply. The remainder of this Chapter 6, Water Supply, documents the local and imported water supplies that provide water for direct use and for replenishment to help sustain the Indio Subbasin groundwater supply. Chapter 7, Numerical Model and Plan Scenarios, describes the Subbasin’s water budget.
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Indio Subbasin Water Management Plan Update 6-5 TODD/W&C
6.3 Surface Water
Natural surface water flow in the Coachella Valley occurs as a result of precipitation, precipitation runoff, and stream flow originating from the San Bernardino and San Jacinto Mountains, with lesser amounts from the Santa Rosa Mountains. This watershed runoff is diverted for use, percolates into streambeds, or is captured in mountain-front percolation basins where it recharges the groundwater basin. As shown in Figure 6-1, the 50-year hydrologic period from 1970 to 2019 had an annual average watershed runoff of 52,506 AFY (calculated from U.S. Geological Survey (USGS) stream gages, precipitation, and ungaged tributary estimates), with approximately 43,300 AFY in natural infiltration when accounting for surface water diversions, ET loss, and outflows to Salton Sea. Runoff during the 25-year period from 1995 to 2019 was below average, with 38,196 AFY in watershed runoff and 29,200 AFY in natural infiltration. This 25- year hydrologic period contained multiple drought cycles with below average rainfall.
Figure 6-1. Total Watershed Runoff for Indio Subbasin, 1970–2019 (AFY)
DWA and CVWD both hold State of California surface water rights. CVWD’s rights 1 total up to 328,591 AFY for Whitewater River and multiple tributaries, which exceeds the long-term average watershed runoff of 52,506 AFY. These rights allow CVWD to capture available watershed runoff for replenishment of the groundwater basin.
1 Whitewater River: A001122 (400 cfs up to 289,591 AFY); Creeks: A002922 (up to 39,000 AFY) FINAL
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Indio Subbasin Water Management Plan Update 6-6 TODD/W&C DWA’s rights 2 total up to approximately
13,309 AFY for Chino, Snow, Falls Creek, and
Whitewater River flow. DWA acquired the
water rights of the Whitewater River Mutual
Water Company for 10 cubic feet per second
(cfs) from Whitewater River in 2008. Local
surface water is diverted by DWA for use in its
domestic water supply system. Because
surface water supplies are affected by
variations in annual precipitation, however,
the annual supply is highly variable. Since
1960, the historical surface water diversions
have ranged from approximately 1,400 to
8,500 AFY. For the period of 2010 to 2019, DWA’s average annual surface water diversions from all sources totaled 1,960 AFY. The remaining undiverted surface water has historically been recharged into the Indio Subbasin through natural streambeds.
DWA’s existing surface water diversions include the following:
• Chino West—This diversion serves the domestic water needs of the Palm Springs Aerial Tramway from a small reservoir, which overflows back into the stream. The diversion only provides water supply needs to the Tramway.
• Chino North—This diversion operates by discharging and then recharging the water further downstream nearer to the Whitewater River. This diversion was destroyed in a February 2019 storm, so diversions have not occurred since then.
• Snow Creek/Falls Creek—This diversion involves two separate diversion dams, but the flow is combined before it is diverted for delivery. The diversion is delivered to urban users in the Palm Springs area. A February 2019 storm damaged the Falls Creek diversion, so this dam had zero diversions in 2019 and 2020. Additionally, water is diverted to WWR-GRF for use in DWA’s domestic water supply system.
• Whitewater Canyon—This diversion is an old water distribution system, purchased from the no longer operating Whitewater River Mutual Water Company, which diverts subsurface stream water using wells that are less than 50 feet deep. This diversion is delivered within Palm Springs to a ranch owned and operated by Agua Caliente Band of Cahuilla Indians for agricultural purposes, to Caltrans for landscape irrigation of freeway right of ways, to a rock supply company for dust suppression, and periodically to other entities for non-potable water use. Additionally, water is diverted to WWR-GRF for use in DWA’s domestic water supply system.
6.3.1 Use of Surface Water Supply
Please use: DWA plans to divert as much surface water within its water rights as may be available and deliver that diverted surface water for direct use, and for replenishment into the Indio Subbasin and subsequent extraction for use in DWA’s domestic water supply system. This Alternative Plan Update
2 Snow Creek: A004752 (1.5 cfs); Snow Creek: A013067 (4 cfs); Falls Creek: A008957 (1.5 cfs with 640 AFY cap); Chino West: G331035 (2 cfs); Whitewater Canyon (10 cfs): G330840, G330841, G330842, G330843, G330846, and G331466
DWA diverts surface water from Snow Creek.
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Indio Subbasin Water Management Plan Update 6-7 TODD/W&C assumes DWA will increase annual surface water diversions to 6,000 AFY in 2023. Although only a small portion of the current watershed runoff is diverted for municipal and agricultural use, the Indio Subbasin still benefits from the natural infiltration of watershed runoff that is not diverted. This Alternative Plan Update assumes approximately 96 percent of undiverted flows recharge the groundwater aquifer, while four percent outflows to the Salton Sea, based on calculation of outflow at the Indio gage on the Whitewater River (USGS 10259300).
This Alternative Plan Update considers two local hydrology scenarios:
1) Historical hydrology conditions – Natural infiltration based on the 50-year historical average (1970 to 2019) of 52,500 AFY for watershed runoff, minus outflows to the Salton Sea and surface water diversions. With projected surface water diversions at 6,000 AFY after 2023, natural infiltration is estimated to average 43,300 AFY through the planning horizon. These assumptions are used only in the baseline scenario in Chapter 7, Numerical Model and Plan Scenarios. 2) Climate change conditions – Natural infiltration based on the drier 25-year hydrologic period (1995 to 2019) that includes reoccurring droughts and aligns with climate change forecasts that predict increasingly drier conditions. Watershed runoff for the 25-year hydrologic period averaged 38,200 AFY. With projected surface water diversions at 6,000 AFY after 2023, natural infiltration is estimated to average 29,200 AFY through the planning horizon. These assumptions are used in all future project scenarios in Chapter 7, Numerical Model and Plan Scenarios.
6.4 Colorado River Water
Colorado River water has been a significant water supply source for the Indio Subbasin since the Coachella Canal was completed in 1949. CVWD is the only agency in the Indio Subbasin that receives Colorado River water allocations.
The Colorado River is managed and operated in accordance with the Law of the River, a collection of interstate compacts, federal and state legislation, various agreements and contracts, an international treaty, a U.S. Supreme Court decree, and federal administrative actions that govern the rights to use Colorado River water within the seven Colorado River Basin states. The 1922 Colorado River Compact apportioned the waters of the Colorado River Basin between the Upper Colorado River Basin (i.e., Colorado, Wyoming, Utah, and New Mexico) and the Lower Basin (i.e., Nevada, Arizona, and California) (USBR, 1922). The 1922 Colorado River Compact allocates 15 million AFY of Colorado River water as follows: 7.5 million AFY to the Upper Basin and 7.5 million AFY to the Lower Basin, plus up to 1 million AFY of surplus supplies. The Lower Basin’s water was further apportioned among the three Lower Basin states by the 1928 Boulder Canyon Project Act (USBR, 1928) and the 1931 Boulder Canyon Project Agreement (USBR, 1931), typically called the 1931 Seven Party Agreement, which allocates California’s apportionment of Colorado River water among Palo Verde Irrigation District (PVID), Imperial Irrigation District (IID), Coachella Valley Water District (CVWD), Metropolitan Water District of Southern California (MWD), City of Los Angeles, City of San Diego, and County of San Diego. The 1964 U.S. Supreme Court decree in Arizona v. California established Arizona’s basic annual apportionment at 2.8 million AFY, California’s at 4.4 million AFY, and Nevada’s at 0.3 million AFY. Mexico is entitled to 1.5 million AFY of the Colorado River under the 1944 United States-Mexico Treaty for Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande (U.S. Government Printing Office, 1946). However, this treaty did not specify a required quality for water entering Mexico. In 1973, the United States and Mexico signed Minute No. 242 of the International Boundary and Water Commission (IBWC) requiring certain water quality standards for water entering Mexico (IBWC, 1973).
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Indio Subbasin Water Management Plan Update 6-8 TODD/W&C California’s Colorado River supply is protected by the 1968 Colorado River Basin Project Act (USBR, 1968), which provides that in years of insufficient supply on the main stem of the Colorado River, supplies to the Central Arizona Project shall be reduced to zero before California will be reduced below 4.4 million AF in any year. This assures full supplies to the Coachella Valley, except in periods of extreme drought.
The Coachella Canal is a branch of the All-
American Canal that brings Colorado River
water into the Imperial and Coachella
Valleys. Under the 1931 Seven Party
Agreement (USBR, 1931), CVWD receives
330,000 AFY of Priority 3A Colorado River
water diverted from the All-American Canal
at the Imperial Dam. The Coachella Canal
originates at Drop 1 on the All-American
Canal and extends approximately 123 miles,
terminating in CVWD’s Lake Cahuilla. The
service area for Colorado River water
delivery under CVWD’s contract with the
U.S. Department of the Interior Bureau of
Reclamation (USBR) is defined as
Improvement District No. 1 (ID-1), which encompasses 136,400 acres covering most of the East Valley and a portion of the West Valley north of Interstate 10. Under the 1931 Seven Party Agreement, CVWD has water rights to Colorado River water as part of the first 3.85 million AFY allocated to California. CVWD is in the third priority position along with IID.
6.4.1 2003 Quantification Settlement Agreement (QSA)
In 2003, CVWD, IID, and MWD successfully negotiated the 2003 Quantification Settlement Agreement (2003 QSA) (CVWD, 2003), which quantifies Colorado River allocations through 2077 and supports the transfer of water between agencies. Under the 2003 QSA, CVWD has a base entitlement of 330,000 AFY.
CVWD negotiated water transfer agreements with MWD and IID that increased CVWD supplies by an additional 123,000 AFY. CVWD’s net QSA supply will increase to 424,000 AFY by 2026 and remain at that level until 2047, decreasing to 421,000 AFY until 2077, when the agreement terminates (Secretary of the Interior, 2003). CVWD’s available Colorado River diversions through 2045, this Alternative Plan Update horizon, are shown on Table 6-3.
As of 2020, CVWD’s available Colorado River water diversions at Imperial Dam under the QSA were 394,000 AFY. This includes the base entitlement of 330,000 AFY, the MWD/IID Transfer of 20,000 AFY, IID/CVWD First Transfer of 50,000 AFY, and IID/CVWD Second Transfer of 23,000 AFY. CVWD’s QSA diversions also deducts the -26,000 AFY transferred to San Diego County Water Authority (SDCWA) as part of the Coachella Canal Lining Project and the -3,000 AFY transfer to Indian Present Perfected Rights.
The Coachella Canal extends approximately 123 miles to
terminate in Lake Cahuilla.
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Indio Subbasin Water Management Plan Update 6-9 TODD/W&C Additionally, under the 2003 QSA, MWD transferred 35,000 AFY of its State Water Project (SWP) Table A Amount to CVWD. This SWP water is exchanged for Colorado River water and can be delivered at Imperial Dam for delivery via the Coachella Canal to the eastern portion of the Indio Subbasin or at Lake Havasu for delivery via the Colorado River Aqueduct to the western portion of the Indio Subbasin at the WWR- GRF. The 2019 Second Amendment (CVWD, 2019b) guaranteed delivery of the 35,000 AFY from 2019 to 2026, for a total of 280,000 AFY of water to the WWR-GRF during that timeframe. MWD can deliver the water through CVWD’s Whitewater Service Connections (for recharge at WWR-GRF) or via the Advance Delivery account.
The MWD/IID Transfer originated in a 1989
agreement with MWD to receive 20,000 AF
of its Colorado River supply. The 2019
Amended and Restated Agreement for
Exchange and Advance Delivery of Water
(CVWD, 2019a) defined the exchange and
delivery terms between MWD, CVWD, and
DWA. The 2019 Second Amendment to
Delivery and Exchange Agreement (CVWD,
2019b) reduced CVWD’s annual delivery of
the MWD/IID Transfer to 15,000 AFY, for a
total of 105,000 AF, if taken at the
Whitewater Service Connections (for
recharge at WWR-GRF) between 2020 and
2026. For those seven years, MWD keeps
the remaining 5,000 AFY, after which CVWD’s allocation increases back up to 20,000 AFY. In this Alternative Plan Update, both the 15,000 AFY MWD/IID Transfer and the 35,000 AF QSA MWD SWP Transfer are assumed to be delivered to WWR-GRF through 2026. CVWD’s total allocations under the QSA, including MWD’s transfer of 35,000 AFY and the MWD/IID Transfer, will increase from 424,000 AFY in 2020 to 459,000 AFY by 2026 and remain at that level for the remainder of the 75-year term of the QSA.
6.4.2 Colorado River Water Consumptive Use
Each year, CVWD submits its water order to USBR for its total QSA entitlement. USBR provides an annual Colorado River Accounting and Water Use Report that provides diversions, return flows, and consumptive use of water diverted from the mainstream of the Colorado River below Lee’s Ferry (USBR, 2020). For the eight years between 2013 and 2020, CVWD consumed less than its QSA allotment by an average of 25,574 AFY. CVWD can transfer up to 20,000 AF of the 1989 Approval Agreement water to MWD, to help mitigate the lower consumption. Despite minor annual variability, CVWD anticipates full consumptive use of its QSA entitlement by 2030. Payback for the over consumption that occurred in years 2001 and 2002 has been completed; no additional payback is assumed during the planning horizon.
Assumptions regarding Colorado River (Canal water) supplies available for use are based on CVWD’s delivery schedule from the QSA, minus estimated Canal conveyance losses (see discussion below). Table 6-3 and Figure 6-2 provides CVWD’s contracted Colorado River water entitlement through 2045. Note that due to the IID/CVWD Second Transfer, CVWD’s Colorado River supplies continue to increase by 5,000 AFY per year through 2027 before reaching a total volume of 424,000 AFY. Table 6-3 lists total Colorado River entitlements under existing agreements. However, this Alternative Plan Update does not assume full QSA ramp up volumes will be available due to ongoing drought and forecasted climate change on the Colorado River system. Section 6.4.4 describes the Colorado River volumes assumed in baseline and climate change.
The Colorado River Aqueduct conveys water to the
western portion of the Indio Subbasin at the WWR-GRF.
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Indio Subbasin Water Management Plan Update 6-10 TODD/W&C Table 6-3. Colorado River Water Entitlements (AFY)
Diversion 2020 2025 2030 2035 2040 2045
Base Entitlement 330,000 330,000 330,000 330,000 330,000 330,000 1988 MWD/IID Approval Agreement 20,000 20,000 20,000 20,000 20,000 20,000 IID/CVWD First Transfer 50,000 50,000 50,000 50,000 50,000 50,000 IID/CVWD Second Transfer 23,000 48,000 53,000 53,000 53,000 53,000 Coachella Canal Lining -26,000 -26,000 -26,000 -26,000 -26,000 -26,000 Indian Present Perfected Rights Transfer -3,000 -3,000 -3,000 -3,000 -3,000 -3,000 QSA Diversions 394,000 419,000 424,000 424,000 424,000 424,000 MWD SWP Transfer 35,000 35,000 35,000 35,000 35,000 35,000 Total Diversions 429,000 454,000 459,000 459,000 459,000 464,000 Assumed Conveyance Losses (5%) -21,200 -22,700 -22,950 -22,950 -22,950 -22,950 MWD/IID Approval Agreement Transfer1 -5,000 -5,000 0 0 0 0 Total Available Deliveries 402,800 426,300 436,050 436,050 436,050 436,050 1 Accounts for -5,000 AFY reduction in MWD/IID Approval Agreement deliveries from 2020–2026 per the 2019 Amendments with MWD.
Source: Colorado River Water Delivery Agreement ( https://www.usbr.gov/lc/region/g4000/crwda/crwda.pdf , Exhibit B)
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Indio Subbasin Water Management Plan Update 6-11 TODD/W&C
Figure 6-2. Colorado River Water Supply Projections
Note: This graphic reflects total Colorado River water diversions and does not reflect conveyance and transfer losses.
6.4.2.1 Conveyance Losses
Conveyance losses, which are defined as the loss of water to evaporation, seepage, or other similar cause resulting from any transportation or delivery of water, are also factored into the water available for delivery. Conveyance losses in the Coachella Canal are estimated to be approximately five percent annually based on the percentage annual average conveyance losses from 2014 to 2019. Regulatory water is defined as metered releases of excess water from the Canal water delivery system needed to meet scheduled deliveries in the gravity flow irrigation water delivery system. Regulatory water is released into the open drain system and flows to the Salton Sea. Although regulatory water is metered, it is considered a loss and not accounted for in the direct deliveries.
6.4.3 Supply Reliability
Colorado River supplies face a number of challenges to long-term reliability including the extended Colorado River Basin drought and shortage sharing agreements, endangered species and habitat protection, and climate change. Due to both California’s and CVWD’s high-priority position regarding Colorado River allocations, CVWD’s Colorado River supply is expected to be reliable.
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Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-12 TODD/W&C
6.4.3.1 QSA Litigation
The 2010 CVWMP Update cautioned against the reliability of CVWD’s Colorado River supplies because of ongoing QSA litigation at the time. However, the QSA has held up to scrutiny under several unsuccessful legal challenges in state and federal court. Immediately following passage of the QSA, in November 2003, IID filed a complaint in Imperial County Superior Court to confirm the validity of the QSA and 12 of the 34 QSA-related agreements. The case was coordinated for trial with other lawsuits challenging QSA environmental and regulatory approvals in the Sacramento County Superior Court. CVWD, IID, MWD, SDCWA, and the State defended these suits, which sought validation of the contracts. In February 2010, a California Superior Court judge ruled that the QSA and 11 related agreements were invalid because the QSA-JPA Agreement created an unconditional obligation for the State to pay for excess environmental mitigation costs, in violation of California’s constitution. The court declined, for jurisdictional reasons, to validate the thirteenth agreement, the IID-CVWD Salton Sea Flooding Settlement Agreement.
The QSA parties appealed this decision. In March 2011, the California Court of Appeal, Third Appellate District issued a temporary stay of the trial court judgment. In December 2011, the California Court of Appeal reversed the lower court ruling and remanded the case back to trial court for decision on the environmental challenges to the QSA Program EIR. In July 2013, a Sacramento Superior Court entered a final judgment validating the QSA and rejecting all of the remaining legal challenges. In May 2015, the California Court of Appeal issued a ruling that dismissed all remaining appeals.
6.4.3.2 Colorado River Interim Guidelines
Since 2000, drought conditions in the Colorado River basin have led to significant fluctuations and decreases in water elevations at key Colorado River reservoirs. Each year, the Secretary of the Interior is required to declare the Colorado River water supply availability conditions for the Lower Basin States in terms of normal, surplus, or shortage. In 2007, USBR adopted Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead (2007 Interim Guidelines).
These 2007 Interim Guidelines will remain in effect for determinations to be made through December 2025 regarding water supply and reservoir operating decisions through 2026 and provide guidance for development of the Annual Operating Plan (AOP) for Colorado River reservoirs (USBR, 2007).
The purposes of the 2007 Interim Guidelines are to:
• Improve USBR’s management of the Colorado River by considering trade-offs between the frequency and magnitude of reductions of water deliveries and considering the effects on water storage in Lake Powell and Lake Mead. USBR will also consider the effects on water supply, power production, recreation, and other environmental resources; • Provide mainstream U.S. users of Colorado River water, particularly those in the Lower Basin states, a greater degree of predictability with respect to the amount of annual water deliveries in future years, particularly under drought and low reservoir conditions; and • Provide additional mechanisms for the storage and delivery of water supplies in Lake Mead to increase the flexibility of meeting water use needs from Lake Mead, particularly under drought and low reservoir conditions (USBR 2007).
In October 2020, USBR released a Review of the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead (7D Review; USBR 2020a). The 7D Review acknowledged the operational stability provided by the 2007 Interim Guidelines and the
Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-13 TODD/W&C cooperation of participating agencies in providing information to inform the post-2026 operations of Lake Powell and Lake Mead. Negotiations began in 2021 for the 2027 Interim Guidelines that may affect available supplies of Colorado River water.
6.4.3.3 Lower Basin Drought Contingency Plan
In May 2019, CVWD entered into the Lower Basin Drought Contingency Plan Agreement (USBR, 2019) to provide an additional mechanism to prevent Lake Mead from reaching critically low elevations by establishing that certain Colorado River users in the Lower Basin make Drought Contingency Plan (DCP) contributions if Lake Mead reaches certain elevations. The Implementation Agreement (CVWD 2019c) explains that the Lower Basin Drought Contingency Plan (Lower Basin DCP) provides that USBR's annual 24-month study's projection of Lake Mead's January 1 elevation will determine the amount of California DCP contributions for the subsequent year, if any. CVWD's portion of California DCP contributions under the Lower Basin DCP is seven percent (which is approximately 14,000 to 24,500 AFY). CVWD will implement its portion of the Lower Basin DCP contributions by storing water in MWD’s Lake Mead DCP Intentionally Created Surplus (ICS) account and/or by CVWD reducing its call for the 35,000 AFY MWD SWP Transfer (refer to description above). MWD will then reduce its USBR water order by an equivalent amount in that year to cover CVWD’s contribution. The Lower Basin DCP is a short-term plan that will end when the 2027 Interim Guidelines are implemented.
6.4.4 Use of Colorado River Water
This Alternative Plan Update considers the QSA ramp up to ensure that all available supply is used. This requires balancing direct uses and replenishment deliveries against the available Colorado River supply (less conveyance and regulatory water losses). This Alternative Plan Update considers two Colorado River delivery scenarios:
1) Historical hydrology conditions – Full ramp up of the 2003 QSA entitlement, along with transfers where there are agreements in place. These assumptions are used only in the baseline scenario in Chapter 7, Numerical Model and Plan Scenarios.
2) Climate change conditions – Full ramp up of the 2003 QSA entitlement and transfers, minus CVWD’s portion of California’s Lower Basin DCP contribution increasing from 14,500 AFY to 24,500 AFY. These assumptions are used in all future project scenarios in Chapter 7, Numerical Model and Plan Scenarios.
To fully utilize the Colorado River water entitlement, the GSAs propose several source substitution (replacing existing groundwater pumping with Canal water deliveries) and replenishment projects that can be found in Chapter 11, Projects and Management Actions.
6.5 SWP Exchange Water
The SWP is managed by the California Department of Water Resources (DWR) and includes 705 miles of aqueduct and conveyance facilities extending from Lake Oroville in Northern California to Lake Perris in Southern California. The SWP has contracts to deliver 4.172 million AFY to the State Water Contractors.
The State Water Contractors consist of 29 public entities with long-term contracts with DWR for all, or a portion of, their water supply needs. In 1962 and 1963, DWA and CVWD, respectively, entered contracts with the State of California for a total of 61,200 AFY of SWP water.
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Indio Subbasin Water Management Plan Update 6-14 TODD/W&C SWP water has been an important component of the region’s water supply mix since CVWD and DWA began receiving and recharging SWP exchange water at the WWR-GRF. Starting in 1973, CVWD and DWA began exchanging their SWP water with MWD for Colorado River water delivered via MWD’s Colorado River Aqueduct. Because CVWD and DWA do not have a physical connection to SWP conveyance facilities, MWD takes delivery of CVWD’s and DWA’s SWP water, and in exchange, delivers an equal amount of Colorado River water to the Whitewater Service Connections (for recharge at WWR-GRF and MC-GRF).
The exchange agreement was most recently re-established in the 2019 Amended and Restated Agreement for Exchange and Advance Delivery of Water (CVWD, 2019a).
6.5.1 SWP Table A Amounts
Each SWP contract contains a “Table A” exhibit
that defines the maximum annual amount of
water each contractor can receive excluding
certain interruptible deliveries. DWR uses Table A
amounts to allocate available SWP supplies and
some SWP project costs among the contractors.
Each year, DWR determines the amount of water
available for delivery to SWP contractors based
on hydrology, reservoir storage, the
requirements of water rights licenses and
permits, water quality, and environmental
requirements for protected species in the
Sacramento-San Joaquin River Delta (Delta). The
available supply is then allocated according to
each SWP contractor’s Table A amount.
CVWD’s and DWA’s collective increments of Table A water are listed in Table 6-4. Original Table A SWP water allocations for CVWD and DWA were 23,100 AFY and 38,100 AFY, respectively, for a combined amount of 61,200 AFY. CVWD and DWA obtained a combined 100,000 AFY transfer from MWD under the 2003 Exchange Agreement. In 2004, CVWD purchased an additional 9,900 AFY of SWP Table A water from the Tulare Lake Basin Water Storage District (Tulare Lake Basin) in Kings County (DWR, 2004). In 2007, CVWD and DWA made a second purchase of Table A SWP water from Tulare Lake Basin totaling 7,000 AFY (DWR, 2007a and 2007b). In 2007, CVWD and DWA also completed the transfer of 16,000 AFY of Table A Amounts from the Berrenda Mesa Water District in Kern County (DWR, 2007c and 2007d). These latter two transfers became effective in January 2010. With these additional transfers, the total SWP Table A Amount for CVWD and DWA is 194,100 AFY.
Previously, the 100,000 AFY MWD Transfer obtained under the 2003 Exchange Agreement included a “Call Back” component that allowed MWD to call-back the 100,000 AFY and assume the entire cost of delivery if it needed the water. In 2019, the Amended and Restated Agreement for Exchange and Advance Delivery of Water (CVWD, 2019a) ended MWD’s right to call back that 100,000 AFY of Table A water.
SWP exchange water is recharged at the WWR-GRF.
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Indio Subbasin Water Management Plan Update 6-15 TODD/W&C Table 6-4. SWP Table A Amounts (AFY)
Agency Original SWP
Table A
MWD
Transfer
Tulare Lake
Basin
Transfer 1
Tulare Lake
Basin
Transfer 2
Berrenda
Transfer
Total
CVWD 23,100 88,100 9,900 5,250 12,000 138,350
DWA 38,100 11,900 - 1,750 4,000 55,750
Total 61,200 100,000 9,900 7,000 16,000 194,100
In some years, DWA and CVWD carry over SWP water to the following year by storing it in San Luis Reservoir. This carryover water is SWP water that is allocated to a State Water Contractor and approved for delivery in a given year but was not able to be delivered to the Contractor by the end of that year. This water is exported from the Delta, but instead of being delivered to the Contractor, it is stored in the SWP’s share of San Luis Reservoir south of the Delta, when space is available, for the Contractor to use in the following year. This variability is reflected in the historical delivery values but does not affect supply projections.
6.5.2 Other SWP Water Types
There are other types of SWP water that can be purchased, such as individual water purchase opportunities and transfers/exchanges. These may be conveyed to CVWD and DWA as available, but no commitments exist.
6.5.2.1 Yuba Accord
In 2008, CVWD and DWA entered into separate agreements with DWR for the purchase and conveyance of supplemental SWP water under the Yuba River Accord Dry Year Water Purchase Program (Yuba Accord). This program provides dry year supplies through a water purchase agreement between DWR and Yuba County Water Agency, which settled long-standing operational and environmental issues over instream flow requirements for the lower Yuba River. The amount of water available for purchase varies annually and is allocated among participating SWP contractors based on their Table A amounts. CVWD and DWA may purchase up to 1.72 percent and 0.69 percent, respectively, of available Yuba Accord water, in years it is made available.
Yuba Accord deliveries have varied from zero in multiple years to a total of 2,664 AFY to CVWD and DWA in 2013. Over the 10-year period from 2010-2019, the average annual amount of Yuba Accord water purchased by the GSAs was 651 AFY. This Alternative Plan Update assumes the same 10-year average of Yuba Accord deliveries annually through 2045.
6.5.2.2 Article 21
Article 21 water (described in Article 21 of the SWP water contracts), “Interruptible Water”, is water that State Water Contractors may receive on a short-term basis in addition to their Table A water if they request it in years when it is available. Article 21 water is used by many Contractors to help meet demands in low allocation years. Article 21 water is not available every year, amounts vary when it is available, and is proportionately allocated among participating Contractors. The availability and delivery of Article 21 water cannot interfere with normal SWP operations and cannot be carried over for delivery in a subsequent year.
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Indio Subbasin Water Management Plan Update 6-16 TODD/W&C The State Water Contractors believe that as reliability increases over time with operation of the Delta Conveyance Facility (see description below), that Article 21 water will become more available to Contractors for purchase. This Alternative Plan Update assumes that once the Delta Conveyance Facility is constructed, approximately 10,600 AFY in Article 21 will be made available to DWA and CVWD annually.
6.5.3 Advance Deliveries
The 1984 Advance Delivery Agreement (amended in 2019 by the Amended and Restated Agreement for Exchange and Advance Delivery of Water [CVWD 2019a]) allows MWD to deliver up to 800,000 AFY of Colorado River water to be credited against its future SWP exchange water obligations. Advance deliveries of exchange water are highly variable and concentrated in wet years, with the Indio Subbasin providing the majority of storage. Figure 6-3 shows the year-end Advance Delivery Account balance for 2003 to 2020, with increases representing MWD’s advance deliveries (water in excess of SWP exchange obligations) and decreases representing deductions taken from the account when MWD delivers previously stored water in lieu of SWP exchange water. As of January 2020, there was 353,946 AF stored in MWD’s Advance Delivery account in the Indio Subbasin.
Figure 6-3. Advance Delivery Account Year-End Balance
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Chapter 6: Water Supply FINAL
Indio Subbasin Water Management Plan Update 6-17 TODD/W&C
6.5.4 Supply Reliability
SWP supplies vary annually due to weather and runoff variations in Northern California and regulatory limitations on exports from the Delta.
6.5.4.1 Delta Exports
The SWP’s and Central Valley Project’s (CVP; managed by USBR) exports from the Delta have decreased since 2005 due to several key environmental decisions. While the SWP primarily serves the State’s population and economic growth, the CVP serves the State’s agricultural industry. In 2005, the U.S. Fish and Wildlife Service (USFWS) released a Biological Opinion that Delta export (combined SWP and CVP) pumping operations would not jeopardize the continued existence of the Delta smelt, a small, endangered fish endemic to the Delta. Environmental groups challenged the action and in May 2007, federal Judge Oliver Wanger ruled that the Biological Opinion was faulty in its assumptions and needed to be performed again. In 2008, the USFWS and National Marine Fisheries Service (NMFS) released a new Biological Opinion that addressed Delta fisheries, restricting operations of the SWP and CVP diversion pumps. In 2009, Wanger struck down the USBR acceptance of the new Biological Opinion, saying USBR failed to comply with the National Environmental Policy Act (NEPA) related to cutbacks in water exports for Central Valley farmers.
In 2009, the Sacramento-San Joaquin Delta Reform Act of 2009 (Delta Reform Act) established the Delta Stewardship Council to create a comprehensive, long-term, legally enforceable plan to guide management of the Delta’s water and environmental resources. The Delta Plan (Delta Stewardship Council, 2013) includes policies and recommendations to achieve the “coequal goals,” which means the two goals of providing more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem. In 2016, USBR and DWR developed the California WaterFix, a twin-tunnels alternative for conveying flows across the natural channels of the Delta, focused on conveyance and ecosystem improvements to significantly reduce reverse flows and fish species impacts associated with the existing south Delta intakes. In 2019, USFWS and NMFS issued revised Biological Opinions (USFWS, 2019) to address California WaterFix. Concurrently, USBR issued the 2018 Addendum (USBR, 2018) to the 1986 Coordinated Operations Agreement (USBR, 1986) with accompanying SWP and CVP operations changes which reduced SWP exports and increased CVP exports, along with more conservative operation of Lake Oroville. Most recently, in 2019, Governor Newsom directed state agencies to proceed with modernizing Delta conveyance with a single tunnel project (see DCF description below).
6.5.4.2 SWP Reliability
State Water Contractors are required to submit annual delivery schedules to the DWR for a suite of potential water allocations; for example, 15 percent, 30 percent, 50 percent, 60 percent, and 100 percent were provided for calendar year 2021. DWR makes an initial SWP Table A allocation for planning purposes, typically in December, prior to the start of each calendar year. Throughout the year, as additional information regarding water availability becomes available and DWR performs hydrologic analyses, the SWP allocation and delivery estimates are updated. Typically, the final SWP allocation for the year is derived by June, and although not typical, can still be updated into the Fall. Table 6-5 presents the historical draft and final Table A allocations over the past 20 years (i.e., 2002 to 2021). Note that CVWD’s and DWA’s contracted Table A amounts increased substantially in 2005 and again in 2010.
Final SWP allocations between 2002 and 2021 have ranged from a high of 100 percent in 2006 to a low of five percent in 2014 and again in 2021. Figure 6-4 shows the variability of Table A allocations for the period
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Indio Subbasin Water Management Plan Update 6-18 TODD/W&C 2002 through 2021. The reliability of SWP deliveries has declined since 2007 when Judge Wanger overturned the Biological Opinion regarding Delta export pumping operations. This decision significantly impacted DWR’s ability to convey SWP supplies across the Delta for export. Since the 2007 Wanger decision, SWP final allocations have averaged 45 percent annually. This period has also been marked by six critically dry years.
Table 6-5. Historical SWP Table A Allocations, CVWD and DWA (2002-2021) Year 100% Table A
Volume Max
Contract (AFY)a
Water Year Type SWP Initial
Allocation (%)
SWP Final
Allocation (%)
2002 61,200 Dry 20% 70%
2003 61,200 Above Normal 20% 90%
2004 71,100 Below Normal 35% 65%
2005 171,100 Above Normal 40% 90%
2006 171,100 Wet 55% 100%
2007 171,100 Dry 60% 60%
2008 171,100 Critically Dry 25% 35%
2009 171,100 Dry 15% 40%
2010 194,100 Below Normal 5% 50%
2011 194,100 Wet 25% 80%
2012 194,100 Above Normal 60% 65%
2013 194,100 Critically Dry 30% 35%
2014 194,100 Critically Dry 5% 5%
2015 194,100 Critically Dry 10% 20%
2016 194,100 Above Normal 10% 60%
2017 194,100 Above Normal 20% 85%
2018 194,100 Critically Dry 15% 35%
2019 194,100 Above Normal 10% 75%
2020 194,100 Below Normal 10% 20%
2021 194,100 Critically Dry 5% 5%
20-year Average -- -- 24% 54%
14-Year Average
Since Wanger
-- -- 20% 45%
a Source: DWR 2018, Bulletin 132-18, Appendix B Table B-4 b Source: DWR 2018, Bulletin 132-18, Appendix B Table B-5B
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Indio Subbasin Water Management Plan Update 6-19 TODD/W&C Figure 6-4. 20-Year Table A Allocation History, CVWD and DWA
DWR’s Final SWP Delivery Capability Report 2019 (DWR, 2020a) was released in August 2020. The delivery reliability of water from the SWP system is an important component for the SWP Contractors’ water supply planning. SWP delivery amounts were modeled for the 2019 SWP Delivery Capability Report using the CalSim II simulation model that incorporates the historical range of hydrologic conditions from Water Years 1922 through 2003. DWR’s analysis determined that long-term average SWP deliveries across all water years through 2015 was 2,414,000 AF, or 58 percent of the maximum of the 4,133,000 AFY available for export from the Delta. 3 Table 6-6 provides a summary of the SWP delivery amounts for existing conditions using the CalSim II modeling for the 2019 SWP Delivery Capability Report. By using this 82-year historical flow record, the delivery estimates modeled for existing conditions reflect a reasonable range of potential hydrologic conditions from wet years to critically dry years.
3 While 4,173,000 AFY is the current combined maximum Table A mount, 4,133,000 AFY is the SWP’s maximum Table A water available for export from the Delta excluding Butte County and Yuba City (DWR, 2020a).
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Indio Subbasin Water Management Plan Update 6-20 TODD/W&C Table 6-6. Estimated Average, Wet-, and Dry-Period Deliveries of SWP Table A Water Estimated SWP Table A
Deliveries (AFY)
Percent of Maximum SWP Table A
for Export (4,133,000 AFY)
Long-term Average 2,414,000 58%
Wet Periods
Single Wet Year (1983) 4,008,000 97%
2-Year (1982-1983) 3,750,000 91%
4-Year (1980-1983) 3,330,000 81%
6-Year (1978-1983) 3,210,000 78%
10-Year (1978-1987) 2,967,000 72%
Dry Periods
Single Dry Year (1977) 288,000 7%
2-Year Drought (1976-1977) 1,311,000 32%
4-Year Drought (1931-1934) 1,228,000 30%
6-Year Drought (1987-1992) 1,058,000 26%
8-Year Drought (1929-1936) 1,158,000 28%
Source: 2019 SWP Delivery Capability Report (DWR, 2020a)
DWR’s analysis further showed a decreasing trend seen in the future long-term average. The Technical Addendum to the 2019 SWP Delivery Capability Report (DWR, 2020b) provides a “Future Conditions with Climate Change and 45 cm Sea Level Rise Scenario” which projects a further decrease in SWP delivery over time. Although the 2019 SWP Delivery Capability Report estimates delivery reliability of 58 percent based on the long-term average, this Alternative Plan Update recognizes the significant reduction in reliability associated with climate change and Delta export litigation and instead assumes 45 percent reliability through the planning horizon.
6.5.5 Delta Conveyance Facility
The Delta Conveyance Facility (DCF) is a DWR project that would improve SWP reliability and result in increased deliveries in the future. The existing SWP water conveyance facilities in the Delta, which include Clifton Court Forebay and the Banks Pumping Plant, enable DWR to divert water to the California Aqueduct. The DCF project includes the construction and operation of new conveyance facilities in the Delta, primarily a new tunnel to bypass existing natural channels used for conveyance. New intake facilities would be located in the north Delta along the Sacramento River between Freeport, California, and the confluence with Sutter Slough. A new tunnel would convey water from the new intakes to the existing Banks Pumping Plant and potentially the federal Jones Pumping Plant, both in Byron, California, in the south Delta. The new facilities would provide an alternate location for diversion of water from the Delta and would be operated in coordination with the existing south Delta pumping facilities (see Figure 6-5).
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Indio Subbasin Water Management Plan Update 6-21 TODD/W&C Figure 6-5. Delta Conveyance Facility – Proposed Corridor Options Source: DCA Board of Directors Special Meeting, February 2021
Construction of the DCF will improve water supply reliability for State Water Contractors by addressing in-Delta conveyance, with its myriad of constraints. Because the SWP currently relies on the Delta’s natural channels to convey water, it is vulnerable to earthquakes, climate change, and pumping restrictions established to protect in-stream species and habitats. Certain pumping restrictions in the south Delta can prevent the SWP from reliably capturing water when it is available, especially in wet weather. The DCF would add new diversions in the north Delta to promote a more resilient and flexible SWP in the face of unstable future conditions. Combined with the current through-Delta method, the addition of DCF is referred to as the “dual conveyance” system.
CVWD and DWA have approved a 2-year agreement to advance their share of funding for DCF planning and design costs. The Agreement in Principle for the Delta Conveyance Facility was approved in November 2020, as outlined in Table 6-7 below. A very preliminary estimate of the DCF benefits is 500,000 AFY. DWA and CVWD approved their participation levels of 1.52 percent and 3.78 percent, respectively. This restores
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Indio Subbasin Water Management Plan Update 6-22 TODD/W&C 26,500 AFY in SWP deliveries to CVWD and DWA over and above current conditions, allocated between 60 percent to Table A and 40 percent to Article 21. With DCF construction, SWP reliability is anticipated to increase to 59 percent as an annual average. DCF deliveries are assumed to begin in year 2040.
Table 6-7. DCF Supply Amounts
Description CVWD DWA Total
DCF Additional Supply (%) 3.78% 1.52% 5.30%
Annual Estimate (AFY) 18,900 7,600 26,500
Table A Supply (AFY) 11,340 4,560 15,900
Article 21 Supply (AFY) 7,560 3,040 10,600
6.5.6 Lake Perris Dam Seepage Recovery Project
In 2017, MWD and DWR began preliminary planning for recovery of seepage below the Lake Perris Dam and delivery of the recovered water to MWD in addition to its current allocated Table A water. The project is composed of installing a series of five pumps placed down-gradient from the face of the Lake Perris Dam that will pump water that has seeped from the lake into the groundwater. The recovered water will be pumped into a collection pipeline that discharges directly into MWD’s Colorado River Aqueduct south of Lake Perris.
CVWD and DWA were invited to partner in the project with MWD, and the parties signed an agreement with DWR in 2021 for funding of environmental analysis, planning, and preliminary design. An additional agreement (or amendment to the existing Exchange Agreement) will be needed to exchange a proportional share of the recovered seepage water, as outlined in Table 6-8 below, for Colorado River water delivered by MWD to WWR-GRF and MC-GRF (MWD, 2020) through MWD’s Colorado River Aqueduct. The project is estimated to recover approximately 7,500 AFY, with 2,752 AFY for delivery to CVWD and DWA, and is anticipated to begin delivery in 2023.
Table 6-8. Lake Perris Seepage Recovery Amounts
Description MWD CVWD DWA Total
Percent of Lake Perris Dam Seepage Recovery (%) 63.30% 32.3% 4.4% 100% Annual Estimate (AFY) 4,747 2,425 328 7,500
6.5.7 Sites Reservoir Project
The Sites Reservoir Project would capture and store stormwater flows from the Sacramento River for release in dry years. Sites Reservoir would be situated on the west side of the Sacramento Valley, approximately 10 miles west of Maxwell, CA. When operated in coordination with other Northern California reservoirs such as Shasta, Oroville, and Folsom, which function as the backbone to both the SWP and the Central Valley Project, Sites Reservoir would increase flexibility and reliability of statewide water supplies in drier periods.
In 2019, CVWD and DWA both entered into an agreement with the Sites Project Authority for the next phase of planning for the Sites Reservoir (Sites Project Authority, 2019; 2020). The Sites Project Authority’s goals are to make water supply and storage capacity available to water purveyors within the Sacramento River watershed, and in other areas of California, who are willing to purchase water supply from the Sites
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Indio Subbasin Water Management Plan Update 6-23 TODD/W&C Reservoir Project. CVWD and DWA are participating members at 10,000 AFY and 6,500 AFY levels, respectively, as shown in Table 6-9. This Alternative Plan Update assumes approximately 30 percent conveyance losses, for total delivery of 11,550 AFY to CVWD and DWA beginning in 2035.
Table 6-9. Sites Reservoir Supply Amounts
Description CVWD DWA Total
Percent of Sites Reservoir Supply (%) 5.2% 3.4% 8.6%
Annual Estimate (AFY) 10,000 6,500 16,500
6.5.8 SWP Delivery to Subbasins
All SWP Exchange water delivered to DWA and CVWD is recharged at WWR-GRF in the Indio Subbasin and at MC-GRF in the Mission Creek Subbasin. According to the 2014 Mission Creek Water Management Agreement (CVWD and DWA, 2014), this includes any water that is paid for or planned to be paid for by the SWP tax or split between the RAC paid by groundwater producers in the West Whitewater River Subbasin Management Area (which includes CVWD’s West Whitewater River Subbasin Area of Benefit [AOB] and DWA’s West Whitewater River Subbasin AOB) and the Mission Creek Subbasin Management Area (which includes CVWD’s Mission Creek Subbasin AOB and DWA’s Mission Creek Subbasin AOB). As such, this includes Table A, Article 21, and Yuba Accord water, in addition to any future increase in Table A reliability (i.e., DCF), Lake Perris Seepage, and Sites Reservoir. Available SWP Exchange water allocated to MC-GRF and WWR-GRF is based on proportional assessable production between the Mission Creek Subbasin Management Area and the West Whitewater River Subbasin Management Area, to be balanced over a 20-year period beginning December 2004. In 2020, total assessable production in the Mission Creek Subbasin Management Area (inclusive of CVWD’s Mission Creek AOB and DWA’s Mission Creek AOB) was 14,244 AF, while total assessable production in the West Whitewater River Subbasin Management Area (again inclusive of CVWD’s West AOB and DWA’s West AOB) was 153,979 AF (CVWD 2020). Based on a cumulative total of 168,223 AF in assessable production between the two management areas, this resulted in an 8 percent/92 percent split between the Mission Creek and West Whitewater River management areas in 2020. As shown in Table 6-10, the projected allotment of SWP exchange water to the two management areas was calculated as 8 to 10 percent to MC-GRF and 90 to 92 percent to WWR- GRF. Urban growth and associated water demand in the Mission Creek Subbasin will result in slightly more SWP Exchange water being delivered to that Subbasin over time. This Alternative Plan Update is coordinated with the Mission Creek Subbasin Alternative Plan Update to establish production estimates and associated SWP delivery estimates for the two management areas through 2045 planning horizon.
Table 6-10. Forecast Split of SWP Delivery to WWR-GRF and MC-GRF Based on Production Assessable Production 2020 2025 2030 2035 2040 2045
West WWR Management Area (AFY) 150,336 155,338 160,640 165,955 170,754 175,202 % West WWR Management Area 92% 92% 91% 91% 91% 90%
Mission Creek Management Area (AFY) 13,281 14,369 15,455 16,543 17,717 18,892 % Mission Creek Management Area 8% 8% 9% 9% 9% 10%
Total West WWR + Mission Creek (AFY) 163,617 169,707 176,095 182,498 188,471 194,093
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Indio Subbasin Water Management Plan Update 6-24 TODD/W&C
6.5.9 Use of SWP Exchange Water
This Alternative Plan Update accounts for all anticipated SWP Exchange water to be recharged at WWR- GRF and MC-GRF (as described above) to ensure that all available supply is used. In order to fully use available SWP exchange supplies, the GSAs will continue to replenish groundwater at maximum delivery levels and pursue additional SWP supplies as they become available. This Alternative Plan Update considers two SWP Exchange delivery scenarios:
1) Historical hydrology conditions – Table A deliveries at 45 percent through 2045 based on average SWP reliability since the 2007 Wanger decision and uncertainty about the future of Delta exports.
These assumptions are used only in the baseline scenario in Chapter 7, Numerical Model and Plan Scenarios.
2) Climate change conditions – Table A deliveries at 45 percent in 2020 based on the 2007 Wanger decision, then reduced by -1.5 percent through straight line projection from 2020 to 2045 due to forecast climate changes. These assumptions are used in all future project scenarios in Chapter 7, Numerical Model and Plan Scenarios.
Scenario modeling described in Chapter 7, Numerical Model and Plan Scenarios, assumes annual variability of Table A deliveries associated with different projected climate years. However, Yuba Accord, Lake Perris Seepage, Sites Reservoir, and DCF supplies are assumed at their full anticipated amounts each year. The projected estimates for all potential SWP Exchange supplies are shown in Table 6-11.
Table 6-11. Forecast of SWP Table A Supplies to WWR-GRF and MC-GRF Existing SWP Supplies 2020 2025 2030 2035 2040 2045
Table A Amount 194,100 194,100 194,100 194,100 194,100 194,100 Assumed SWP Reliability 45% 45% 45% 45% 45% 45%
Average Table A Deliveries w/Assumed
SWP Reliability
87,345 87,345 87,345 87,345 87,345 87,345
Yuba Accord 651 651 651 651 651 651
Sum of Existing SWP Supplies 87,996 87,996 87,996 87,996 87,996 87,996 Estimated Replenishment (AFY)a
WWR-GRF Replenishment 80,853 80,546 80,273 80,019 79,724 79,431 MC-GRF Replenishment 7,143 7,450 7,723 7,977 8,272 8,565 Future SWP Supplies
Lake Perris Seepage 0 2,752 2,752 2,752 2,752 2,752
Sites Reservoir 0 0 0 11,550 11,550 11,550
Delta Conveyance Facility (Additional
SWP Table A/Article 21)
0 0 0 0 0 26,500
Sum of Existing + Future SWP Supplies 88,647 91,399 91,399 102,949 102,949 129,449 Estimated Replenishment (AFY)a
WWR-GRF Replenishment 81,451 83,660 83,377 93,617 93,272 116,849 MC-GRF Replenishment 7,196 7,739 8,022 9,332 9,677 12,600 a Additional 35,000 AFY MWD/SWP Transfer under the QSA is accounted for under Colorado River water above (see Table 6-3) and though replenished at WWR-GRF, that supply is not accounted for in replenishment volumes in this table.
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Indio Subbasin Water Management Plan Update 6-25 TODD/W&C
6.6 Recycled Water
Recycled water is a reliable local resource that can be used to help offset groundwater pumping. Recycled water has been used for golf course irrigation in the Indio Subbasin since the late 1960s. There are currently eight wastewater treatment plants (WWTPs) or water reclamation plants (WRPs) within the Plan Area, with a ninth in construction by Mission Springs Water District (MSWD). Table 6-12 lists the projected wastewater flow at each of the nine facilities within the planning horizon. Within each treatment plant’s tributary area, projected wastewater flows are generally equal to an average 31 percent return-to-sewer ratio for projected municipal water demands, which are described in Chapter 5, Demand Projections. This return-to-sewer ratio is based on the most recent 5-year average (2015-2019) of each WRP’s municipal demands and wastewater flows. CVWD and DWA currently deliver recycled water from three of the WRPs for municipal and golf course irrigation use in the East and West Valley.
Table 6-12. Projected Wastewater Flow in Plan Area (AFY) WWTP/WRPa 2020 2025 2030 2035 2040 2045
MSWD Regional WRF 0 1,000 1,600 2,200 2,800 3,360
Palm Springs WWTP/DWA WRP 6,100 6,600 7,200 7,800 8,400 9,000 CVWD WRP-10 9,800 10,800 11,600 12,300 13,100 14,000
CVWD WRP-7 3,800 4,200 4,500 4,800 5,100 5,400
CVWD WRP-4 6,200 6,700 7,400 8,200 8,800 9,500
CVWD WRP-2 14 14 14 14 14 14
Coachella WRPb 3,700 4,600 5,500 6,500 7,500 8,500
VSD WWTP 7,100 7,700 8,300 8,900 9,300 9,700
Kent SeaTech 6,640 6,640 6,640 6,640 6,640 6,640
Total 43,354 48,254 52,754 57,354 61,654 66,114
a Wastewater from areas outside of current WRP tributary areas are accounted for in return flows from septic systems. b Coachella WRP includes decommissioning of agricultural ponds in 2025 (380 AFY).
CVWD operates WRP-7 and WRP-10, which currently generate recycled water for irrigation of golf courses and large landscaped areas. DWA’s WRP treats secondary supply from the City of Palm Springs WWTP for delivery to irrigation customers. Table 6-13 provides a summary of recycled water currently in use based on the 2-Year average from 2018 to 2019.
Table 6-13. Recycled Water Supply Based on 2018-2019 Wastewater Flows (AFY) -- Palm Springs
WWTP/
DWA WRPa
CVWD
WRP-10
CVWD
WRP-7
Total
AFY of Tertiary Capacity 11,200 16,800 2,800 30,800
Wastewater Treated 6,613 9,884 3,261 19,757
Recycled Water Use (Delivery + Onsite) 4,599 7,783 2,201 14,584 a DWA WRP recycled water use does not reflect conversion of two golf courses in 2020 from recycled water to groundwater.
Recycled water use after those conversions is estimated at 3,413 AFY.
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Indio Subbasin Water Management Plan Update 6-26 TODD/W&C
6.6.1 MSWD Regional WRF
MSWD has completed design of the Regional WRF to treat wastewater flows to secondary levels including nitrification and denitrification. The Regional WRF will be located in the Garnet Hill Subarea and will divert some wastewater flows from existing WWTPs located in the Mission Creek Subbasin that are at capacity.
The Regional WRF will have an initial capacity of 1.5 million gallons per day (mgd) (1,680 AFY) with construction beginning in 2021. The Regional WRF will start receiving flow in 2022 and is projected to reach 1.5 mgd treatment capacity by approximately 2030. Wastewater flows will be from existing sewered customers and from the septic to sewer conversions in the Desert Hot Springs Subbasin, Mission Creek Subbasin, and Garnet Hill Subarea of the Indio Subbasin.
Treated wastewater will be discharged to evaporation/percolation ponds in the Garnet Hill Subarea.
Growth projected by 2045 is expected to provide wastewater flows to a buildout capacity of 3 mgd (3,360 AFY) available for recycling. However, future use of recycled water from the Regional WRF is expected to occur in the Mission Creek Subbasin.
6.6.2 Palm Springs WWTP/DWA WRP
DWA WRP, located in the City of Palm Springs,
has a tertiary treatment capacity of 10 mgd
(11,200 AFY). DWA provides tertiary
treatment of secondary treated supply from
the City of Palm Springs’s WWTP for irrigation
of parks and greenscapes in the Palm Springs
area. The average annual wastewater flow
from 2018 to 2019 was approximately
6,613 AFY, while recycled water demand
totaled 4,599 AFY. With existing wastewater
flows and available tertiary treatment
capacity, this facility could produce
approximately 2,014 AFY of additional
recycled water supply. In 2020, two existing
18-hole golf courses converted from using
recycled water to groundwater, which reduced DWA’s recycled water demands to approximately 3,200 AFY and increased DWA’s availability of wastewater flows for recycling to 3,413 AFY. Growth projected by 2045 is expected to provide an increase of 1,566 AFY of additional wastewater flow available for recycling, based on projected indoor water use.
6.6.3 CVWD WRP-10
CVWD WRP-10 is located in the City of Palm Desert. The plant is a 18.0 mgd secondary treatment facility with a current tertiary treatment capacity of 15 mgd (16,800 AFY). The plant consists of an activated sludge treatment plant, a tertiary wastewater treatment plant, a lined holding basin, 6 storage basins and 21 infiltration basins. WRP-10 delivers recycled water for irrigation of golf courses and homeowner’s associations (HOAs) landscaping. The average annual wastewater flow from 2018 to 2019 was approximately 9,884 AFY, while recycled water demand averaged 7,783 AFY. With existing wastewater flows and available tertiary treatment capacity, this facility could produce approximately 2,100 AFY of additional recycled water supply. Growth projected by 2045 is expected to provide an increase of DWA WRP has a tertiary treatment capacity of
10 mgd (11,200 AFY).
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Indio Subbasin Water Management Plan Update 6-27 TODD/W&C 5,828 AFY of additional wastewater flow available for recycling, based on projected indoor water use, but would require expansion of the non-potable water distribution system with new connections.
6.6.4 CVWD WRP-7
CVWD’s WRP-7 is located in north Indio. The plant is a 5.0 mgd secondary treatment facility with current tertiary treatment capacity of 2.5 mgd (2,800 AFY). The tertiary treated wastewater is used for irrigation of golf courses at Sun City in north Palm Desert and Shadow Hills in north Indio. The plant consists of aeration basins, circular clarifiers, and polishing ponds. Recycled water not used for irrigation is percolated at on-site and off-site percolation ponds. The average annual wastewater flow from 2018 to 2019 was approximately 3,261 AFY, while recycled water demand averaged approximately 2,200 AFY. With existing wastewater flows and available tertiary treatment capacity, this facility could produce approximately 600 AFY of additional recycled water supply (tertiary capacity is the limiting factor). Growth projected by 2045 is expected to provide an increase of 3,016 AFY of additional wastewater flow available for recycling, based on projected indoor water use, but would require expansion of the tertiary capacity of the WRP-7 plant and expansion of the non-potable water distribution system with new connections.
CVWD is planning to expand its WRP-7 tertiary treatment capacity by 3 mgd (5.5 mgd or 6,150 AFY total) with the addition of flocculation tanks, chemical feed, gravity multi-media filters, and associated pumps.
Design is underway for the WRP-7 expansion, with construction anticipated in 2025. The WRP-7 expansion is described in Chapter 11, Projects and Management Actions. However, given that new connections have not yet been identified for this supply, delivery of the recycled water has not been assumed in this supply forecast.
6.6.5 CVWD WRP-4
CVWD WRP-4 is a 9.9 mgd (11,090 AFY)
secondary treatment facility located in the
unincorporated community of Thermal. The
average annual wastewater flow from 2018
to 2019 was approximately 5,482 AFY. WRP-
4 provides secondary treatment consisting
of pre-aeration ponds, aeration lagoons,
polishing ponds, and disinfection. The
treated effluent is currently discharged to
the CVSC pursuant to a National Pollution
Discharge Elimination System (NPDES)
permit. However, CVWD has submitted a
Change Petition (WW0093) and plans to
construct tertiary treatment and begin
delivery of recycled water. Growth
projected by 2045 is expected to provide a
total of 11,082 AFY of wastewater flow that could be tertiary treated and reused within the Planning Area, but would require construction of both tertiary treatment and new non-potable system connections.
CVWD is planning to construct WRP-4 tertiary treatment capacity in phases starting at 2.5 mgd (2,800 AFY) in 2025, then increasing to 5.0 mgd (5,600 AFY) in 2028 and 10.0 mgd (11,200 AFY) by 2031. Design is underway for the WRP-4 tertiary expansion, with construction anticipated in 2025. The WRP-4
CVWD’s WRP-4 has a secondary treatment capacity of
9.9 mgd (11,090 AFY) and has a planned tertiary
expansion.
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Indio Subbasin Water Management Plan Update 6-28 TODD/W&C expansion is described in Chapter 11, Projects and Management Actions. CVWD has filed a wastewater change petition with the State Water Resources Control Board (WW0093) pursuant to Water Code section 1211. The petition seeks authorization to cease the discharge of treated wastewater from WRP-4 to the CVSC. CVWD plans to initiate project-specific environmental review in 2022 to support this change petition.
6.6.5.1 CVWD WRP-2
CVWD WRP-2 is a small treatment plant serving the nearby community of North Shore. WRP-2 has a secondary treatment capacity of 0.18 MGD (202 AFY). Because this WRP serves an existing built-out community, wastewater flows are expected to remain the same as the 2018 to 2019 average of 14 AFY through 2045.
6.6.6 Valley Sanitary District WWTP
Valley Sanitary District (VSD) owns and operates an 11 mgd (12,320 AFY) capacity wastewater treatment facility that serves most of the City of Indio. The average annual wastewater flow from 2018 to 2019 was approximately 6,644 AFY. Secondary treatment is provided by three process trains – activated sludge, oxidation ponds, and wetlands treatment. Effluent from the oxidation ponds and the wetlands is either routed to pasture irrigation or blended with activated sludge effluent, disinfected, dechlorinated, and discharged to the CVSC. Growth projected by 2045 is expected to provide a total of 8,052 AFY of wastewater flow that could be tertiary treated and reused within the Planning Area but would require construction of both tertiary treatment and new non-potable system connections.
VSD and IWA have established a joint powers authority, East Valley Reclamation Authority (EVRA), to implement water reuse in the Indio area. EVRA is currently evaluating the feasibility of developing a potable reuse project that would replenish the Indio Subbasin with 5,000 AFY of advance treated recycled water beginning in 2030. The EVRA potable reuse project is described in Chapter 11, Projects and Management Actions.
6.6.7 Coachella Sanitary District WWTP
The City of Coachella through its Coachella Sanitary District owns and operates a 4.5 mgd (5,040 AFY) secondary treatment wastewater facility utilizing activated sludge and oxidation ditch processes. Treated wastewater is discharged to the CVSC. The average annual wastewater flow from 2018 to 2019 was approximately 3,007 AFY. Growth projected by 2045 is expected to provide a total of 9,667 AFY of wastewater flow that could be tertiary treated and reused within the Planning Area but would require construction of both tertiary treatment and new non-potable system connections. The City of Coachella currently has no plans to pursue water recycling.
6.6.7.1 Kent SeaTech
Kent SeaTech is a fish farm with total design flow of 10.5 mgd. The current wastewater treatment system consists of a channel stocked with tilapia to remove solids, and an earthen “constructed wetland” system that provides further nitrification, denitrification, fine solids polishing, alkalinity restoration, and temperature buffering. The wetland is bypassed from the treatment process during the colder winter months to maintain system-wide warm temperatures for fish production. Water that is not recirculated, reused, or land applied is discharged to the CVSC. The average annual wastewater flow discharged to CVSC from 2018 to 2019 was approximately 6,639 AFY.
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Indio Subbasin Water Management Plan Update 6-29 TODD/W&C
6.7 Planned Water Reuse
Table 6-14 below provides forecasted recycled water deliveries at the three WRPs that currently reuse water. These estimates are based on existing tertiary capacity and planned recycled water connections listed in the GSAs 5-year capital programs and include current water reuse plus increases in wastewater flows anticipated with municipal growth (described in Chapter 5, Demand Projections). These potential supplies would require construction of new non-potable distribution pipelines and facilities (see Chapter 11, Projects and Management Actions).
Table 6-14. Planned Water Reuse at WRPs with Tertiary Capacity (AFY) WWTP/WRP 2020 2025 2030 2035 2040 2045
Palm Springs WTP/DWA WRP 3,413 3,413 3,413 3,413 3,413 3,413 CVWD WRP-10 7,783 10,800 11,600 12,300 13,100 14,000
CVWD WRP-7 2,201 2,800 2,800 2,800 2,800 2,800
Total 13,398 17,013 17,813 18,513 19,313 20,213
CVWD’s goal is to recycle all wastewater that is currently percolated at its WRPs, except for WRP-2 serving an isolated community. CVWD’s planned non-potable connections will expand deliveries from WRP-10 and WRP-7 within existing tertiary capacity and are reflected in Table 6-14 above. CVWD also has tertiary expansions planned for WRP-7 and WRP-4. In collaboration with VSD, IWA plans to advance treat and recycle 5,000 AFY of wastewater from the VSD WWTP for groundwater replenishment and reuse. MSWD plans to develop recycled water connections and groundwater recharge facilities in the Mission Creek Subbasin and convey treated recycled water from the Regional WRF to that Subbasin. Chapter 7, Numerical Model and Plan Scenarios describes these modeled future projects. Table 6-15 provides forecasted wastewater at the region’s WWTPs and WRPs that may be available for recycling with addition of future treatment or distribution system expansions.
Table 6-15. Projected Wastewater Remaining for Future Reuse (AFY) WWTP/WRP 2020 2025 2030 2035 2040 2045
MSWD Regional WRF 0 1,000 1,600 2,200 2,800 3,360
Palm Springs WTP/DWA WRP 2,687 3,187 3,787 4,387 4,987 5,587 CVWD WRP-10 2,017 0 0 0 0 0
CVWD WRP-7 1,599 1,400 1,700 2,000 2,300 2,600
CVWD WRP-4 6,200 6,700 7,400 8,200 8,800 9,500
CVWD WRP-2 14 14 14 14 14 14
Coachella WRP 3,700 4,600 5,500 6,500 7,500 8,500
VSD WWTP 7,100 7,700 8,300 8,900 9,300 9,700
Kent SeaTech 6,639 6,639 6,639 6,639 6,639 6,639
Total 29,956 31,241 34,941 38,841 42,341 45,901
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Indio Subbasin Water Management Plan Update 6-30 TODD/W&C
6.7.1 Use of Recycled Water
The Alternative Plan Update recognizes the potential local water supply available in recycling wastewater.
By 2045, a total of 62,753 AFY of wastewater flow could be available for recycling if the GSAs and other regional partners were to construct the necessary treatment and conveyance facilities. Full use of this potential recycled water supply would require construction of plant expansions or upgrades, along with distribution pipelines and facilities (see Chapter 11, Projects and Management Actions). Recycled water is considered a drought-proof supply that is not limited under climate change conditions. Recycled water deliveries are assumed to be the same in historical hydrology conditions and climate change conditions.
Water reuse can develop a new source of
supply for non-potable irrigation demands
and when highly treated for groundwater
recharge, and offset pumping of
groundwater that is the source of municipal
supply. Where wastewater was disposed to
land and percolated to groundwater,
recycled water development offsets
groundwater pumping, but reduces net
return flows to the groundwater basin.
Besides water supply availability benefits,
reuse projects can also contribute to
improving water quality in receiving
groundwater and surface water bodies. For
example, application of recycled water for
agricultural and landscape irrigation can provide a source of nutrients that lessens the need to apply synthetic fertilizers. CVWD continues to pursue the goal of fully reusing urban wastewater for non-potable applications.
6.8 Other Supplies
CVWD and DWA, along with other local agencies, have investigated and will continue to pursue other water transfer opportunities.
6.8.1 Rosedale-Rio Bravo
In 2008, CVWD entered into an agreement with Rosedale-Rio Bravo Water Storage District (Rosedale Rio- Bravo) for a one-time transfer of 10,000 AF of Glorious Lands Company (GLC) water intended for a property development located in Riverside County within CVWD’s boundary. In 2012, CVWD entered into an Assignment Agreement with GLC to take over GLC’s water rights for the term of the 2005 Water Supply Agreement between GLC and Rosedale Rio-Bravo. The Assignment Agreement provides a total of 252,500 AF to CVWD from Rosedale Rio-Bravo through 2035. CVWD also entered into a letter agreement with MWD in 2012 for the delivery and exchange of up to 16,500 AFY of non-Table A SWP water that Rosedale Rio-Bravo provides to CVWD (CVWD, 2019a). The water from Rosedale Rio-Bravo is delivered to CVWD as exchange water from MWD at the WWR-GRF. In 2020, CVWD finalized a supplemental letter agreement with Rosedale Rio-Bravo and a Point of Delivery Agreement with DWR that increased the limit on the amount Rosedale Rio-Bravo can deliver to CVWD in any one year (from 16,500 to 20,000 AFY) but does not change the total volume delivered during the life of the agreement through 2035.
Recycled water (or blended non-potable water) is used
on parks and open space in the Plan Area.
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Indio Subbasin Water Management Plan Update 6-31 TODD/W&C The balance of Rosedale Rio-Bravo water due to CVWD from 2020 to 2035 is 169,000 AFY or an annual average of 10,563 AFY. This is greater than the 10-year average of Rosedale Rio-Bravo deliveries, which is 7,750 AFY based on the 2010 to 2019 period. Rosedale Rio-Bravo deliveries are assumed to be the same in historical hydrology conditions and climate change conditions. No Rosedale Rio-Bravo supplies are assumed after year 2035.
6.9 Supply Risks and Uncertainties
The existing water supplies used in the Planning Area face risks and uncertainties that could affect long- term supply reliability. These risks and uncertainties include the extended drought in the southwestern United States and legal/regulatory decisions affecting vital contracts and water deliveries. In addition, climate change could impact both supplies and demands. Climate change is discussed in Chapter 8, Regulatory and Policy Issues.
6.9.1 Colorado River
Although CVWD’s Colorado River supply has historically been fully reliable, the extended Colorado River drought prompted the seven Colorado River Basin states and entitlement holders to develop Drought Contingency Plans (DCPs) to reduce the risk of Colorado River reservoirs declining to critically low levels.
The period of 2000 – 2019 was the lowest 20-year period in the historical natural flow record, which dates back to 1906 (USBR 2020a). As of 2019, the combined storage in key Colorado River Basin reservoirs, Lakes Powell and Mead, were at their lowest levels (around 30th percentile) since Lake Powell initially began filling in the 1960s. The Lower Basin DCP was designed to: a) require Arizona, California, and Nevada to contribute additional water to Lake Mead storage at specified reservoir elevations, and b) incentivize voluntary conservation of water to be stored in Lake Mead (USBR 2020a).
Implementation of the Lower Basin Drought Contingency Plan Agreement (Lower Basin DCP; USBR, 2019) may affect Colorado River water supply through the year 2026. In addition to criteria set in the 2007 Interim Guidelines, the Lower Basin DCP establishes that certain Colorado River users in the Lower Basin, including CVWD, make DCP contributions if specific triggers are met between 2020 and 2026. CVWD agrees to contribute between 14,000 AF and 24,500 AF if the elevation of Lake Mead drops to between 1,045 feet and 1,030 feet before 2026. Negotiations of the 2027 Interim Guidelines that will revisit and may extend these voluntary contributions began in 2021.
CVWD contributes approximately 60 percent of the overall Indio Subbasin water supply from the Colorado River. In the 5-year period from 2015-2019, Colorado River deliveries averaged 343,200 AFY, while water demands totaled 574,500 AFY. Participation in the Lower Basin DCP could reduce the amount of water available for groundwater recharge in the Plan Area. During the term of the Lower Basin DCP, if CVWD is asked to cutback, the cutback will be satisfied by reducing deliveries to the TEL-GRF.
CVWD will continue to monitor the supply conditions on the Colorado River, make appropriate adjustments to its operations, and actively participate in efforts to augment the water supplies of Colorado River.
6.9.2 SWP Exchange
DWR estimates the long-term average reliability of the SWP to be 58 percent declining to 52 percent by 2040 (DWR, 2020a). This decline will likely continue in the absence of programs to balance Delta environmental concerns and water supply needs. A majority of California’s water originates in the Sierra Nevada Mountains as snowpack, eventually flowing through the Delta, where it is delivered to municipal
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Indio Subbasin Water Management Plan Update 6-32 TODD/W&C and agricultural users. At the same time, the hundreds of miles of river channels that crisscross the Delta’s farmed islands provide a migratory pathway for Chinook salmon and other native fish species. The Delta Plan (Delta Stewardship Council, 2013) has the “coequal goals” of providing more reliable water supply for California and protecting, restoring, and enhancing the Delta ecosystem. The shift by the State of California from the twin-tunnels project (California WaterFix) to the single tunnel alternative (DCF) in early 2020 marks a compromise between environmental and water supply interests.
Implementation of the DCF is likely to increase SWP supply reliability by addressing climate resiliency, environmental and habitat protection, and seismic risk. The GSAs receive nearly 20 percent of overall Indio Subbasin water supply from the SWP. In the 5-year period from 2015-2019, SWP deliveries (minus Advance Deliveries) averaged 109,400 AFY while water demands totaled 574,500 AFY. DWR filed a Notice to Proceed for the DCF project in January 2020, is currently in the environmental review process, and expects a Final Environmental Impact Report (FEIR) in 2023. CVWD and DWA approved advancing their share of funding for the planning phase (2021 to 2024) of the project.
At this time, CVWD and DWA will continue participating in the DCF through the Agreement in Principle for the Delta Conveyance Facility, approved in November 2020, which will be used to create a Delta Conveyance Contract Amendment. The dual conveyance approach to SWP delivery supports the goals of Delta health and water supply reliability.
6.9.3 Surface Water
Surface water, including natural infiltration of watershed runoff, represents about 7 percent of the Indio Subbasin water supply. Although CVWD and DWA retain water rights to most of this surface water, there is uncertainty about potential changes in precipitation in the Whitewater River watershed due to climate change. DWR’s modeled climate scenarios have indicated that the Whitewater River watershed will receive less watershed runoff under climate change conditions, reducing total runoff from 99 percent in 2030 to 92 percent in 2070. In this Alternative Plan Update’s climate change scenarios (see Chapter 7, Numerical Model and Plan Scenarios), additional reductions to surface water availability were based on recent local hydrologic conditions to assess impacts of climate change.
6.9.4 Recycled Water
Recycled wastewater has historically been used for irrigation of golf courses and urban landscaping in the Indio Subbasin. The existing WRPs that have tertiary wastewater treatment for recycled water supply currently deliver approximately two percent of the Subbasin’s water supply (13,260 AFY of recycled water delivered over 2015-2019 period). The amount of wastewater available for reuse in the future primarily depends on growth in the Valley, along with the agencies’ plans for construction of tertiary treatment and conveyance. However, the level of water conservation implemented in the future – particularly under the long-term conservation regulations anticipated from Assembly Bill 1668 (Friedman) and Senate Bill 606 (Hertzberg) – could reduce the amount of wastewater generated and available for reuse. Future waste discharge requirements will also dictate the level of treatment, and potentially volume of ongoing discharge, that would be required at the treatment plants. Thus, future growth, conservation, and water quality regulations will all dictate the amount of recycled water supply produced in the Indio Subbasin.
This Alternative Plan Update also acknowledges the financial challenges associated with expansion of the non-potable water treatment and distribution systems. Expansion of the recycled water systems throughout the Indio Subbasin is primarily dependent on availability of grant and loan funding for capital
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Indio Subbasin Water Management Plan Update 6-33 TODD/W&C improvements. Despite this challenge, the GSAs will continue to pursue water reuse projects that reduce groundwater pumping and maximize use of local water.
6.10 Summary
The Indio Subbasin has both imported water and local water sources in its current water supply portfolio.
This available water supply portfolio will be used to meet growing demands – municipal, agriculture, golf, and other demands as described in Chapter 5, Demand Projections – and to achieve groundwater sustainability. The water budgets described in Chapter 7, Numerical Model and Plan Scenarios, provide a deeper understanding of some of the demand and supply uncertainties and associated management actions that will help to meet growing demand and achieve groundwater sustainability. Chapter 11, Projects and Management Actions, summarizes the management actions and capital projects that may need to be implemented to achieve basin sustainability and meet future demands. After Plan adoption, the GSAs will prepare Annual Reports to evaluate their demands, supplies, and groundwater conditions to understand when those projects must be implemented.
A summary of the projected currently available and future water supplies is presented in Table 6-16. The Indio GSAs are committed to achieving sustainability under changing climate conditions and is planning for supply limitations anticipated for both local and imported supplies. Figure 6-6 shows the supply projection with available supplies under climate change conditions. Figure 6-7 shows the supply projection with potential future supplies under climate change conditions. This summary documents available imported and local surface water supplies and does not include the groundwater supply; the available groundwater supply will vary under different management conditions and is quantified in Chapter 7, Numerical Model and Plan Scenarios. The uncertainties surrounding both imported and local water supplies make it important that this Alternative Plan Update continue to implement a management strategy that sustainably manages the groundwater basin through new supplies and source substitution.
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Indio Subbasin Water Management Plan Update 6-34 TODD/W&C Table 6-16. Summary of Projected Non-Groundwater Supplies (AFY) Available Supplies 2020a 2025 2030 2035 2040 2045
Historical Hydrology Conditions
Surface Water Infiltrationb 46,670 43,300 43,300 43,300 43,300 43,300 Surface Water Diversionsc 2,630 6,000 6,000 6,000 6,000 6,000 Colorado River Waterd 402,800 426,300 436,050 436,050 436,050 436,050 SWP Exchange Watere 80,853 80,546 80,273 80,019 79,724 79,431 Recycled Waterf 13,398 13,398 13,398 13,398 13,398 13,398 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Historical Hydrology Subtotal 556,914 580,107 589,584 589,330 578,472 578,179 Climate Change Conditions
Surface Water Infiltrationg 32,570 29,200 29,200 29,200 29,200 29,200 Surface Water Diversionsh 2,630 6,000 6,000 6,000 6,000 6,000 Colorado River Wateri 388,050 411,800 411,550 411,550 411,550 411,550 SWP Exchange Waterj 80,853 80,306 79,795 79,305 78,775 78,248 Recycled Waterk 13,398 13,398 13,398 13,398 13,398 13,398 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Climate Change Subtotal 528,064 551,267 550,506 550,016 538,923 538,396 Projected Future Supplies
Delta Conveyance Facilityl 0 0 0 0 0 23,562
Lake Perris Seepagem 0 2,519 2,510 2,503 2,493 2,484
Sites Reservoirn 0 0 0 10,503 10,464 10,426
Planned Recycled Watero 0 3,615 4,415 5,115 5,915 6,815 Projected Future Supplies Subtotal 0 6,134 6,925 18,121 18,872 43,287 Total Available + Projected Supplies under
Historical Hydrology 556,914 586,241 596,509 607,451 597,344 621,466 Total Available + Projected Supplies under
Climate Change 528,064 557,401 557,431 568,137 557,795 581,683 a 2020 values are projected; they are not actuals.
b Natural infiltration of watershed runoff is based on 50-year (1970 to 2019) historical average and excludes anticipated future diversions. See Chapter 7, Numerical Model and Plan Scenarios for detail on groundwater inflows and outflows. c Surface water diversions in year 2020 are projected; actual 2020 diversions totaled 1,960 AFY. d Colorado River water accounts for base entitlement and transfers listed in Table 6-3 and excludes 5 percent conveyance losses.
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Indio Subbasin Water Management Plan Update 6-35 TODD/W&C e SWP exchange water includes Yuba Accord and excludes transfers to the MC-GRF. SWP values are average annual deliveries based on 45 percent reliability assumption. f Recycled water includes existing annual average deliveries as of 2020 (13,398 AFY). g Natural infiltration of watershed runoff is based on 25-year (1995 to 2019) historical average run backward-forward and excludes anticipated future diversions and outflow to Salton Sea. See Chapter 7, Numerical Model and Plan Scenarios, for detail on groundwater inflows and outflows. h Surface water diversions in year 2020 are projected; actual 2020 diversions totaled 1,960 AFY. i Colorado River water excludes 5 percent conveyance losses and Lower Basin DCP contributions (-14,500 AFY 2020-2026 and -24,500 AFY 2027-2045). j SWP exchange water includes Yuba Accord and excludes transfers to the MC-GRF. SWP values are average annual deliveries based on 45 percent reliability assumption, with -
1.5 percent reduced deliveries by 2045 due to climate change. k Recycled water includes existing annual average deliveries as of 2020 (13,398 AFY). l DCF values are average annual deliveries based on reliability assumptions and excludes transfers to the MC-GRF. DCF is anticipated to begin operation in 2042. m Lake Perris supplies exclude transfers to the MC-GRF. Values are declining because Mission Creek Subbasin Management Area assessable production and associated diversions to MC-GRF are forecast to increase over time.
n Sites Reservoir excludes 30 percent conveyance losses and transfers to the MC-GRF. Values are declining because Mission Creek Subbasin Management Area assessable production and associated diversions to MC-GRF are forecast to increase over time. o Projected future recycled water includes planned non-potable connections at WRP-7 and WRP-10 up to current tertiary capacities. Additional future non-potable expansions at WRP-7, WRP-10, and WRP-4, and East Valley Reclamation Authority’s potable reuse project at VSD WRP, are described in Chapter 11, Projects and Management Actions, but are still in planning phases and not included in the supply projection at this time. Total additional wastewater flow potentially available for water reuse by 2045 equals 42,540 AFY, as shown in Table 6-14.
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Indio Subbasin Water Management Plan Update 6-36 TODD/W&C Figure 6-6. Projected Future Supplies with Historical Hydrology
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Indio Subbasin Water Management Plan Update 6-37 TODD/W&C Figure 6-7. Projected Future Supplies with Climate Change Hydrology FINAL
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Indio Subbasin Water Management Plan Update 7-1 TODD/W&C CHAPTER 7: NUMERICAL MODEL AND PLAN SCENARIOS
This chapter describes the MODFLOW groundwater flow model, the Indio Subbasin water budget, and the Plan Scenarios developed to assess future groundwater conditions and sustainability under different planning assumptions. The Indio Subbasin water budget (or balance) and groundwater flow model are closely linked in that some Indio Subbasin inflows and outflows (including various sources of recharge and well pumping) have been developed using measurements and estimates and then used as input to the groundwater flow model. Other water budget components (including amounts of evapotranspiration, drain flow, Salton Sea inflow and outflow, and changes in groundwater storage) are outputs of the groundwater model and are used as a part of the Indio Subbasin water budget. Water budgets are provided for each of the Plan scenarios, as described in Section 7.5. Model characteristics are summarized including model area and boundaries, layers, aquifer properties, sources and amounts of basin recharge and discharge, and methodologies to develop the inflow and outflow amounts used as model inputs.
Previous and updated model performance results are presented, along with Subbasin water budgets for the period 1997 to 2019. The model is well calibrated and capable of accurately simulating groundwater conditions throughout the Subbasin and over the simulation period.
7.1 MODFLOW Model Description
The numerical groundwater flow model was constructed using the U.S. Geological Survey (USGS) MODFLOW code. It simulates transient three-dimensional groundwater flow within and between the shallow and deep aquifer zones, includes various sources of subbasin recharge, discharge to production wells, evapotranspiration, flow to drains, and flow to and from the Salton Sea.
7.1.1 Previous Versions of the Indio Subbasin MODFLOW Model Several versions of the Indio Subbasin model were developed prior to this version for the Alternative Plan Update:
1. The original MODFLOW model was developed by Graham Fogg (Fogg) in the mid-1990s and calibrated for a 61-year historical period from 1936 to 1996.
2. The original model was subsequently extended by Fogg as a part of the 2002 Coachella Valley Final Water Management Plan (2002 CVWMP) for the Indio Subbasin (Coachella Valley Water District [CVWD], 2002) and the Coachella Valley Water Management Plan 2010 Update (2010 CVWMP Update) (CVWD, 2012) and used to simulate future Subbasin management scenarios beginning in 1997 through a future planning period. The 2010 CVWMP Update version of the model used the best available estimates of groundwater inflows and outflows through 2008; inflow amounts for 2009 and future years were synthesized using assumed future water supply and demand projections.
Other intermediate versions of the model were developed by CVWD for specific purposes, but the 2010 CVWMP Update version was used as the basis for the Alternative Plan Update.
Historical calibration quality of the original 1936 to 1996 model and 2010 CVWMP Update version (through 2008) was good, as documented in a Fogg (2000) Technical Memorandum and in Technical Memorandum No. 2 prepared for the Indio Subbasin GSAs in 2020 (see Appendix 1-A). The original and
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Indio Subbasin Water Management Plan Update 7-2 TODD/W&C 2010 CVWMP Update models accurately simulated regional and local groundwater flow conditions and changes over time (as indicated by low observed-versus-simulated head error residuals).
For this Alternative Plan Update, the 2010 CVWMP Update model input data were updated through 2019 using available data. After updating the model recharge and discharge inputs, a calibration check was performed for the period 1997 to 2019.
For future management alternative scenarios evaluation, new estimates of future recharge, pumping, and other boundary conditions are synthesized for predictive simulations of future conditions, as described in Section 7.5.
7.1.2 Changes Made to Model for Alternative Plan Update Using newly available data, the 2010 CVWMP Update model was updated and revised for the Alternative Plan Update. The major changes were updates to recharge and discharge boundary conditions for the simulation period of 2009 to 2019. Other model input parameters also modified include:
• Replaced top of Model Layer 1 elevation surface with updated digital elevation model (DEM) • Added bathymetry of Salton Sea to top of Model Layer 1 elevation surface • Corrected 1997 initial conditions in the Garnet Hill Subarea • Adjusted Hydraulic Flow Barrier conductance values along the southern portion of the Garnet Hill Fault
• Updated 1997 to 2019 subsurface flux boundary inflow rates from Mission Creek Subbasin • Adjusted 1997 to 2019 pumping in the Garnet Hill Subarea • Updated Salton Sea general head boundary elevations for 2009 to 2019 • Updated streamflow and mountain front recharge rates for 2009 to 2019 • Updated municipal golf and agriculture irrigation return and septic rates for 2009 to 2019 • Updated wastewater percolation rates for 2009 to 2019 • Updated groundwater replenishment rates for 2009 to 2019 • Updated Whitewater River Groundwater Replenishment Facility (WWR-GRF) and Thomas E. Levy GRF (TEL-GRF) recharge basin areas
• Added Palm Desert Groundwater Replenishment Facility (PD-GRF) • Updated production well pumping data sets for 2009 to 2019 • Adjusted model timesteps from 10 to 12 per annual stress period • Created new shallow and deep aquifer observation well groups for calibration assessment In general, the original model grid, layering, horizontal and vertical hydraulic conductivity, and aquifer storage parameters were unchanged from the 2010 CVWMP Update model version. The MODFLOW computer program uses subroutines called packages that read specific individual input data files for site features such as wells or drains, depending on the types being simulated. The same MODFLOW Packages were used in the historical and updated model versions.
For the 1997 to 2019 update, most of the inflow and outflow input data used in the 2010 CVWMP Update version for the period 1997 to 2008 were retained, but actual measurements and better estimates of recharge and discharge were used for the simulation period of 2009 to 2019. Exceptions to this included the annual subsurface boundary inflow rates from the Mission Creek Subbasin, where the entire 1997 to 2019 simulation period was updated using inflow rates simulated by the Mission Creek MODFLOW model, which overlaps the Indio Subbasin model (Wood, 2021). Adjustments were also made to the 1997 model
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Indio Subbasin Water Management Plan Update 7-3 TODD/W&C initial conditions and 1997 to 2008 production well pumping in the Garnet Hill Subarea to improve model calibration.
Changes were also made to how the model input data are pre- and post-processed, and how the model is managed and run. The original and 2010 CVWMP Update versions of the model used a series of spreadsheets and FORTRAN programs to format the input data into standard MODFLOW package input files and to post-process the results. Model input was generated as MODFLOW Package ASCII files that were read by an executable table version of the MODFLOW FORTRAN program.
For the Alternative Plan Update, the 2010 CVWMP Update MODFLOW input files were imported to the Aquaveo Groundwater Modeling System (GMS), a MODFLOW pre- and post-processing computer program that was used to update, run and post-process the model. Some inflow and outflow model input data were pre-processed using the project GIS database and spreadsheets, and the input data were imported and stored within GMS, allowing for efficient processing of model runs. Updated model input files are organized in a GMS data management system that includes GIS layers, ‘map-based’ inputs including points, arcs, and polygons of input data, and model grid-based datasets. Model output including simulated water level maps, hydrographs, and water budget output are also stored and post-processed using the GMS software.
7.2 Model Input and Construction
The groundwater model area is shown on Figure 7-1. The upstream and downstream ends of the model are near the San Gorgonio Pass area in the northwest and the northern portion of the Salton Sea in the southeast, respectively. The southwest edge of the model represents the interface between the unconsolidated sedimentary aquifers of the Indio Subbasin and the consolidated to semi-consolidated rocks of the San Jacinto and Santa Rosa Mountains. The northeast flank of the model represents the interface between the unconsolidated aquifers of the Subbasin and consolidated to semi-consolidated rocks of the Little San Bernardino Mountains, Indio Hills, and Mecca Hills, and the Mission Creek and Desert Hot Springs Subbasins. The adjacent San Gorgonio Pass, Mission Creek and Desert Hot Springs Subbasins are not included in the active model area, but subsurface outflow from these Subbasins into the Indio Subbasin is included in the boundary conditions.
7.2.1 MODFLOW Code and Input Packages
The original Indio Subbasin model was constructed using the USGS ‘MODFLOW 88’ code. For the 2010 CVWMP Update and Alternative Plan Update versions of the model, the code was updated to ‘MODFLOW 2005’.
The model utilizes the following standard MODFLOW Packages:
• BASIC (BAS)
• BLOCK CENTERED FLOW (BCF)
• HORIZONTAL FLOW BARRIER (HFB)
• WELL (WEL)
• RECHARGE (RCH)
• DRAIN (DRN)
• EVAPOTRANSPIRATION (EVT)
• GENERAL HEAD BOUNDARY (GHB)
• PRECONDITIONED CONJUGATE-GRADIENT (PCG) Solver
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Indio Subbasin Water Management Plan Update 7-4 TODD/W&C Figure 7-1. Model Area and Boundaries
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Indio Subbasin Water Management Plan Update 7-5 TODD/W&C
7.2.2 Model Grid and Layers
The model consists of a three-dimensional, finite-difference grid of blocks called cells, the locations of which are described in terms of the 270 rows, 86 columns, and 4 layers. At the center of each cell there is a point called a node at which groundwater elevation (head) is calculated. Inflows and outflows through each model cell, through Subareas, and within the entire model grid are also calculated. The Indio Subbasin model has a node spacing of 1,000 ft in the x-y plane, and variable vertical node spacing representing variable thicknesses of the corresponding aquifer or aquitard intervals. The grid is oriented from northwest to southeast along the length of the valley, coinciding with the principal direction of regional groundwater flow (Figure 7-1).
The MODFLOW model comprises four layers, representing the following hydrostratigraphic units:
• Layer 1 – semi-perched aquifer in East Valley and upper shallow aquifer in West Valley • Layer 2 – shallow aquifer zone
• Layer 3 – regional aquitard in East Valley and shallow-deep transition zone in West Valley • Layer 4 – deep aquifer
The elevation of the tops and bottoms of the model layers are referenced to land surface elevations and reflect aquifer and hydrostratigraphic unit thickness as inferred from borehole data across the basin.
Figure 7-2 shows the elevations of the base of each of the four model layers. The model layer elevations in the Alternative Plan Update model are unchanged from the original and 2010 CVWMP Update versions of the model. The top of Layer 1 is represented by the ground surface elevation and elevation of the bottom of the Salton Sea. The bottoms of each layer generally dip to the southeast, subparallel to the ground surface. In the East Valley, model layer thickness follows geologic characterizations by the California Department of Water Resources (DWR) (1979) that were corroborated by analysis of subsurface data. For example, Model Layer 1 approximately corresponds with the semi-perched zone (100 ft thick), Layer 2 with the upper aquifer unit (80 to more than 260 ft thick), Layer 3 with the regional aquitard (80 to more than 270 ft thick), and Layer 4 with a lower aquifer unit (1,000 ft thick). In the West Valley, aquifer thickness estimated by USGS (Reichard and Meadows, 1992) was initially used and later revised during model calibration.
7.2.3 Aquifer Properties and Horizontal Flow Barrier
Distributions of aquifer hydraulic properties including aquifer transmissivity, horizontal and vertical hydraulic conductivity, and unconfined and confined storage coefficients were developed as a part of the original 1936 to 1996 model to simulate the aquifer and aquitard units in the shallow and deep aquifer zones. The aquifer hydraulic properties in the Alternative Plan Update model are unchanged from the original Layer 2 of the 2010 CVWMP Update versions of the model.
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Indio Subbasin Water Management Plan Update 7-6 TODD/W&C Figure 7-2. Base of Model Layer Elevations
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Indio Subbasin Water Management Plan Update 7-7 TODD/W&C Aquifer hydraulic properties control the rates of groundwater flow, amounts of water in storage, and aquifer responses to recharge and pumping. Initial estimates of transmissivity (T) were obtained in part from previously calibrated values used in an early groundwater model constructed by Reichard and Meadows (1992) for the West Valley, some pumping test results for the East Valley, and abundant specific capacity data for the entire valley. Hydraulic conductivity (K) of the confining bed was estimated based on the sediment texture and heterogeneity and was treated as a calibration parameter.
Heterogeneity was treated as a calibration parameter in the original 1936 to 1996 model. Similarly, vertical K (Kv) of the aquifer zones was based on the degree of fine-grained bedding present in electric and drillers logs. This parameter was also adjusted in the original model calibration.
7.2.3.1 Hydraulic Conductivity and Storage Coefficients Figure 7-3 shows the distribution of horizontal hydraulic conductivity in each model layer. Most model cells were assigned moderate to high hydraulic conductivities, based on the pumping test and specific capacity data, and reflect the properties of the coarse sand and gravel deposits that predominate in the subsurface. Hydraulic conductivities are higher on the southwest margins of the West Valley grading to lower values in the East Valley. Permeabilities also generally decrease southeastward toward the Salton Sea. Southeast of the City of Indio, tight silts and clays up to 100 feet thick are present in the upper aquifer and create a semi-perched zone. Lower permeabilities were assigned to these model cells within Model Layer 3.
The specified ratio of horizontal to vertical hydraulic conductivity varies between 10 and 100 throughout the model, based on the degree of fine-grained bedding present in electric and drillers logs.
Figure 7-4 shows the distribution of aquifer storage coefficients in each model layer (specific yield for Model Layer 1 and specific storage for Layers 2-4). Distribution of specific yield (Sy) from Reichard and Meadows (1992) was initially used in the upper valley for Model Layer 1; these values were subsequently modified slightly during the original model calibration. Similar specific yield values were initially estimated for the unconfined areas and semi-perched zone in the lower valley; these values were later adjusted during calibration. Layers 2, 3, and 4 are convertible (unconfined/confined), and use two storage coefficients: specific yield for unconfined conditions when the simulated water level drops below the top of the layer, and specific storage when the layer is confined. The specific yield values for Layers 2-4 are the same as those used for Layer 1. Specific storage (Ss) values were estimated for each of the Model Layers 2, 3 and 4, and were multiplied by layer thickness to obtain storage coefficient (S) for each model layer. Ss varied in confined versus unconfined areas. Storage coefficients of the aquifer system are much greater in the upper unconfined alluvium than in the deeper confined units.
7.2.3.2 Horizontal Flow Barrier
The Garnet Hill Fault forms a partial barrier to flow between the Garnet Hill and Palm Springs Subareas.
The MODFLOW Horizontal Flow Barrier (HFB) Package was used to simulate the barrier effects of this fault. The fault is simulated as an HFB in each of Model Layers 1-4. Different conductance values were assigned along different segments of the HFB and adjusted during 1936-1996 original model calibration.
For the Alternative Plan Update model and 1997-2019 calibration update, additional adjustments were made to the southern portion of the Garnet Hill Fault HFB to improve calibration in the Garnet Hill Subarea. Several model calibration runs were made using different distributions of conductance along the HFB segments until simulated 1997 to 2019 water levels in both the Garnet Hill and Palm Springs Subareas were calibrated.
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Indio Subbasin Water Management Plan Update 7-8 TODD/W&C Figure 7-3. Model Layer Hydraulic Conductivities
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Indio Subbasin Water Management Plan Update 7-9 TODD/W&C Figure 7-4. Model Layer Storage Properties
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Indio Subbasin Water Management Plan Update 7-10 TODD/W&C
7.2.4 Initial Conditions
Initial head conditions in the 2010 CVWMP Update model are based on the final computed heads for each cell at the end of the 1936 to 1996 calibration simulation, corresponding to the beginning of calendar year 1997. This approach maintains consistency between the model-computed heads and flows from the original calibrated model, as well as continuity between the calibration and predictive models.
Figure 7-5 shows the 1997 initial conditions used in Model Layers 2 and 4, representing the shallow and deep aquifers, respectively. For the 1997 to 2019 model update, the initial conditions used for most of the model area are the same as in the 2010 CVWMP Update model. However, local adjustments were made to the initial conditions in the Garnet Hill Subarea, to correct observed-simulated head offsets at the beginning of the 1997 to 2019 simulation. These adjustments, along with changes in HFB conductance and inflow rates from the Mission Creek Subbasin, improved calibration quality in the Garnet Hill Subarea for the updated 1997 to 2019 simulation.
7.2.5 Inflows
The Indio Subbasin is recharged through a combination of natural inflows of surface water and groundwater, recharge of imported water, wastewater percolation, and irrigation return flows. Sources of recharge to the Subbasin include:
• Subsurface inflow from the San Gorgonio Pass, Mission Creek, and Desert Hot Springs Subbasins • Mountain front and stream channel recharge
• Artificial recharge of imported water
• Wastewater percolation
• Return flows from irrigation (municipal/domestic, agricultural, and golf course) and septic systems
Inflows from the Salton Sea have also been assessed in order to provide a comprehensive accounting of the water budget. As discussed in Section 7.4, inflows from the Salton Sea have been small and groundwater outflows to the Salton Sea also occur. Net groundwater flow has been toward the Salton Sea since 2015.
Figure 7-6 shows the locations of the point sources of recharge including subsurface inflow, mountain front, stream channel, groundwater replenishment, and wastewater percolation. Additional recharge of irrigation return flows is distributed across large areas of the model. For the 1997 to 2019 update, most of the recharge amounts simulated in the 2010 CVWMP Update for the period 1997 to 2008 were unchanged, but new recharge rates for the period 2009 to 2019 were calculated and used as model recharge input.
Subsurface inflow from the Mission Creek Subbasin was updated for the entire 1997 to 2019 period, based on values recently generated from the Mission Creek Subbasin MODFLOW model (Wood, 2021).
Subsurface inflow from the San Gorgonio Pass Subbasin was not changed from the 2010 CVWMP Update model, as updated values were not available from the San Gorgonio model for this Alternative Plan Update. Subsurface inflows from the Mission Creek and San Gorgonio Subbasins used in the 1997 to 2019 model update are shown on Figure 7-7. Subsurface inflows are simulated using the MODFLOW WEL Package.
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Indio Subbasin Water Management Plan Update 7-11 TODD/W&C Figure 7-5. Model Initial Conditions 1997
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Indio Subbasin Water Management Plan Update 7-12 TODD/W&C Figure 7-6. Model Recharge Sources
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Indio Subbasin Water Management Plan Update 7-13 TODD/W&C Figure 7-7. Subsurface Inflow from Mission Creek/Desert Hot Springs and San Gorgonio, 1997-2019 FINAL
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Indio Subbasin Water Management Plan Update 7-14 TODD/W&C Each of the other sources of recharge was estimated individually, then accumulated into a combined MODFLOW RCH Package. Recharge rates over time were accumulated on a model grid cell basis, accounting for cell areas to preserve total recharge amounts, and applied as recharge to the uppermost active model layer (primarily Model Layer 1, except where this layer is dry). The MODFLOW RCH Package also was used to simulate mountain front and stream channel recharge rather than one of the MODFLOW Streamflow Routing Packages, which are sometimes used to simulate groundwater-stream interactions.
Figure 7-8 shows the annual contribution of each source of recharge from 1997 to 2019. For the period 1997 to 2008, the total recharge is the same as was used in the 2010 CVWMP Update model. For this period, the model inputs are only available as mountain front and stream channel recharge, artificial recharge, and total recharge rates. Mountain front and stream channel recharge are combined on Figure 7-8 as natural infiltration, and artificial recharge is shown as managed aquifer recharge (MAR). While the data for various recharge sources are available, the 2010 CVWMP Update model input for 1997 to 2008 is not separated by recharge source. Because the model area does not cover the entire Indio Subbasin area, the allocation by source to the total model recharge input (as shown on the figure) was estimated. The allocation of other recharge inputs in the model (including return flows specified on the graph) was estimated based on water balance information from Indio Subbasin annual reports (see Todd Groundwater and Woodard & Curran, 2021).
The following sections describe each of the sources of recharge to the Subbasin.
7.2.5.1 Subsurface Inflows
Figure 7-6 shows the locations of subsurface inflows specified in the northwestern and eastern boundaries of the model. These boundaries simulate inflow from San Gorgonio Pass (SGP) and Mission Creek (MC) Groundwater Subbasins. Flux estimates for each boundary were applied to Model Layers 1 through 4.
In the original historical model, the amounts of flow from the SGP Subbasin were computed by the model with a time-dependent specified head boundary using the MODFLOW CHD Package. In the 2010 CVWMP Update model, the boundary condition was changed from a CHD boundary to a specified flux boundary, which is used to represent the long-term average inflow for each cell. The amount of inflow was based on a running average of the historical fluxes estimated using the CHD boundary and was set to a value of approximately 8,200 AFY in the 2010 CVWMP Update model, decreasing slightly between 1997 and 2019 (Figure 7-7).
Uncertainty exists in the actual amounts of inflow from the SGP Subbasin. A Groundwater Sustainability Plan and calibrated MODFLOW model are currently in preparation for the SGP Subbasin (that Plan also will be submitted to DWR in January 2022). The SGP GSAs also acknowledge that the quantity of subsurface outflow at the SGP Subbasin eastern boundary with the Indio Subbasin represents one of the largest unknowns in the SGP water budget and groundwater modeling. Based on the preliminary SGP model, historical subsurface outflow from the SGP Subbasin ranged from approximately 18,000 to 29,000 AFY between 1997 and 2019, with an average outflow of around 25,000 AFY. These values are higher than the amounts used as boundary inflow in the historical Indio model.
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Indio Subbasin Water Management Plan Update 7-15 TODD/W&C
Figure 7-8. Inflow by Source 1997-2019
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Indio Subbasin Water Management Plan Update 7-16 TODD/W&C The Indio and SGP Subbasin GSAs have discussed this discrepancy, and plan to reconcile the differences as a part of the next 5-Year Plan update. The outflow/inflow amounts will be refined based on the following planned tasks:
• Sensitivity and Uncertainty Analysis using the San Gorgonio Pass Subbasin MODFLOW model • Review of upcoming data from three nested monitoring well clusters installed in 2019 by the USGS near the Subbasin boundary, followed by evaluation and model calibration to recent (and future) water level trends
• Sensitivity simulations for the Indio Subbasin model using a range of subsurface inflows.
The SGP Subbasin GSAs also are reportedly considering a potential groundwater tracer study near the boundary between the SGP and Indio Subbasins to further estimate the flow amounts.
It is anticipated that these refined evaluations and continued collaboration will allow reconciliation of historical and predicted future subsurface out/inflows between the Subbasins. Subsurface inflow also occurs from the Mission Creek and Desert Hot Springs Subbasins into the Indio Subbasin, across the Banning and San Andreas faults.1 These faults consist of several parallel faults and form the northeasterly boundary of the Indio Subbasin. Groundwater level differences across the Banning Fault in this area were historically on the order of 200-250 feet. The estimated flow across the Banning Fault into the Garnet Hill Subarea and Indio Subbasin in the 2010 CVWMP Update model was set to a constant value of approximately 2,000 acre-feet per year (AFY). For the 1997 to 2019 update, these flows were defined through a collaborative effort between Mission Creek and Indio Subbasin modelers. The rates of inflow to Indio Subbasin over time were updated using annual values obtained from the Mission Creek Subbasin model (Wood, 2021). The inflow rates vary slightly over time (Figure 7-7), and were allocated by Mission Creek modelers over four boundary segments: from Mission Creek Subbasin to Garnet Hill Subarea across the Banning Fault, from Mission Creek Subbasin to Indio Hills West (the portion of Indio Hills within Indio Subbasin), from Indio Hills East (the portion of Indio Hills outside Indio Subbasin) to Indio Hills West, and from Indio Hills East to the Indio Subbasin across the Banning Fault. Total inflow from the Mission Creek and Desert Hot Springs Subbasins into the Garnet Hill Subarea and Indio Subbasin is relatively constant at approximately 4,000 AFY.
The Garnet Hill Fault also forms a partial barrier to flow and demarcates the Garnet Hill and Palm Springs Subareas internal to the model. This barrier was simulated using the MODFLOW HFB Package as previously described and allows variable flow between the Subareas.
7.2.5.2 Surface Water Inflows
Recharge from mountain front inflow and from percolation of stream flows into the Indio Subbasin was estimated for 24 watersheds and stream channels along the southwest edge of the model, along the interface between the Indio Subbasin and the consolidated rocks of the San Jacinto and Santa Rosa Mountains. Many of these watersheds are gaged; gage locations are shown on Figure 2-9 in Chapter 2, Plan Area.
Figure 7-6 shows the locations of the model cells used to represent mountain front and stream channel recharge. No explicit mountain front and stream channel recharge is assumed along the eastern boundary
1 Refer to Figures 3-1 and 3-2 in Chapter 3, Hydrogeologic Conceptual Model, for Subbasins and Subareas. The Indio Hills West area is within the Indio Subbasin and Indio Hills East is in the Mission Creek Subbasin.
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Indio Subbasin Water Management Plan Update 7-17 TODD/W&C of the model. However, subsurface inflow in this area from the Mission Creek and Desert Hot Springs Subbasins is accounted for as described in the previous section.
The same methodologies used in the original and 2010 CVWMP Update models (Fogg, 2000) were applied to estimate annual mountain front and stream channel recharge for the 1997 to 2019 model update.
Previously estimated values for 1997 to 2008 used in the 2010 CVWMP Update model were retained, and new estimates of mountain front and stream channel recharge were developed for 2009 to 2019. Total available water from each neighboring watershed was calculated based on annual precipitation, and gaged streamflow (where available). If streamflow was not gaged at a watershed, a rating factor was developed to compare the gaged precipitation and watershed area of a nearby watershed with gaged data. Total watershed runoff was calculated for each watershed on an annual basis. Surface water diversions from the Snow, Falls, Whitewater, and Chino watersheds were accounted before available streamflow was routed through the Subbasin. Figure 7-8 shows the annual amounts of mountain front and stream channel recharge between 1997 and 2019 (labeled as natural infiltration).
Stream Flow
For stream percolation, it is assumed that 95 percent of the total watershed runoff is available for stream percolation with a portion of that available stream percolation leaving the basin in wet years through surface water flow to the Salton Sea. Watershed runoff is estimated using all available precipitation and stream gauge measurements from the tributary watersheds located along the western edge of the model.
The expected runoff and routing, as well as the recharge locations, use the same methodology as the original and 2010 CVWMP Update models.
The model cells receiving streamflow percolation are shown in blue on Figure 7-6. The resulting available stream flow (95 percent of total watershed runoff) less diversions and subsurface flow for the upper valley (Snow, Falls, and Whitewater streams) is expected to completely percolate to the basin. In a change from the original model, water is routed down the upper portion of the Whitewater River in all years.
Previously, all available stream recharge in dry years was assumed to recharge the model at the edge of the basin, causing increased simulated water levels over observed water levels in some years.
Further down the valley, only selected watersheds are assumed to recharge the basin in wet years along streams tributary to the Whitewater River (Andreas, Chino, Dead, Deep, Murray, Palm, Tahquitz, and Unnamed Watershed #2). In wet years, the available streamflow is routed through stream cells such that the resulting simulated flow at the Whitewater River gauge at Indio matches the observed volume. This means that in extremely wet years, up to 12,800 acre-feet (AF) flows from the lower valley watersheds through the Whitewater River into the Coachella Valley Stormwater Channel and enters the Salton Sea.
The flow of each surface waterway was distributed over the model cells using a stream channel routing factor, one for the upper valley streams and one for streams further down the valley. The respective routing factors were calculated for each wet year, such that flow recharges the model over the course of the surface waterway in the upper valley. The stream routing results in a calculation of the volume of water that percolates and the volume that remains as surface water for each cell of the surface waterway.
The remaining surface water flow at the location of the USGS Indio gage is equal to the monitored flow at that gage. In short, the available streamflow less flow out of the basin percolates along the surface waterways.
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Indio Subbasin Water Management Plan Update 7-18 TODD/W&C Mountain Front Recharge
In addition to the streamflow percolation, the available watershed runoff also recharges the Indio Subbasin as subsurface inflow via fractured bedrock along the perimeter of the alluvial aquifer. The locations in the model for such mountain front recharge is shown as the green model cells on Figure 7-6.
Mountain front recharge has been estimated using total watershed runoff and assuming that an additional 10 percent of the 4-year moving average of total watershed runoff is available for subsurface flow. This is an estimate based on the expected runoff and relative difference of hydraulic properties between the facture bedrock and permeable basin (Fogg, 2000). The longer timeframe acknowledges that subsurface flow is slower than surface water flow and affected by hydrologic conditions of previous years. The annual volume of recharge from stream flow and mountain front recharge is shown on Figure 7-8 as natural infiltration.
7.2.5.3 Artificial Recharge
The annual volumes of artificial recharge were compiled and applied to the locations of the GRFs shown on Figure 7-6. These include the WWR-GRF, TEL-GRF (formerly called Dike 4), the Martinez Canyon Pilot Project location, and the recently-completed Palm Desert GRF (PD-GRF). While Mission Creek GRF is also used for artificial recharge, it is not in the model domain. Evaporative losses were assumed to be four percent of recharged volume for the WWR-GRF and two percent for all other locations, reflecting the larger surface area and windier conditions at the WWR-GRF. These estimates are consistent with evaporative losses estimated in previous planning reports. Total annual recharge volumes at the replenishment facilities are shown on Figure 7-8, indicated as MAR.
7.2.5.4 Wastewater Discharges
There are eight wastewater treatment plants/water reclamation plants (WWTPs and WRPs) currently operating in the Indio Subbasin, with another under construction (see Figure 2-5 for locations). Eight of these are within the active area of the model. Four of these (WRP-2, WRP-4, WRP-7, and WRP-10) are operated by CVWD, and a fifth, WRP-9, was decommissioned in 2015. WWTPs also are operated by City of Palm Springs (Palm Springs WWTP/Desert Water Agency [DWA] WRP), Valley Sanitation District (VSD), and Coachella Sanitation District (CSD). A new Regional WRF is currently under construction by Mission Springs Water District (MSWD) in the Garnet Hill Subarea. Four wastewater plants currently discharge to disposal ponds (Palm Springs WWTP and CVWD WRP-2, WRP-7, and WRP-10), and the MSWD Regional WRF plans to do so at start-up in 2022. The ponds have evaporative losses, calculated by the area of ponds and expected annual evaporation. The remaining volume percolates into the Subbasin, as shown on Figure 7-8. It should be noted that, as percolated wastewater is recycled for use, groundwater pumping deceases, but net return flows to groundwater are reduced.
The other wastewater plants (CVWD WRP-4, VSD, and CSD) discharge to the Coachella Valley Stormwater Channel (CVSC), and no percolation to the Subbasin is assumed from the stormwater channel.
7.2.5.5 Applied Water Return Flows
In areas with irrigated crops, golf courses, and municipal landscaping, irrigation is assumed to be applied when soil moisture falls below a certain threshold. When soil moisture exceeds the root zone storage capacity, the excess irrigation becomes deep percolation to the aquifer. Rainfall and irrigation water comingle in the root zone and in deep percolation. For the purposes of displaying an itemized water
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Indio Subbasin Water Management Plan Update 7-19 TODD/W&C balance, the amount of deep percolation derived from each type of irrigation is estimated as a percentage of the simulated irrigation quantity.
Agricultural Return Flow
This inflow component accounts for the portion of irrigation water that is applied in excess of the evapotranspiration (ET) of the crop, as well as excess precipitation that either percolates directly or runs off and percolates in nearby areas (defined herein as irrigation return flows). For agricultural areas, individual crops are associated with different amounts of irrigation and therefore different return flows based on crop ET and irrigation efficiencies.
Because irrigation is not 100 percent efficient, water is applied in excess of the ET demand. Irrigation efficiency, the percentage of applied water needed beyond the ET demand of the crop, can vary significantly depending on factors including geographic setting, irrigation method, and crop types.
Agricultural deliveries of imported water and groundwater pumping are accounted for and compared with the total crop consumptive use on an annual basis to estimate the irrigation return flows.
The basic methodology used to develop agricultural demand was to calculate crop consumptive use and compare that with total agricultural water use. Land use maps from DWR, annual conservation reports, as well as the trimester CVWD Crop Censuses and interviews with larger growers in the area were used to develop monthly crop acreages. Crop consumptive use was calculated from the ET needs of the specific crops, accounting for irrigation efficiency and effective precipitation in order to estimate applied water per acre. The ET needs of a crop can be estimated as ETc = Kc * ETo, where ETc is the ET demand of the crop, Kc is the crop coefficient, and ETo is the reference ET of the geographic area. The daily reference ET and precipitation were downloaded from the California Irrigation Management Information System (CIMIS) for the local Thermal Springs station.
Monthly crop coefficients (Kc) and growing season information for over 63 crops have been derived from the DWR irrigation estimation tool CPU M+ version 6.9 (DWR 2021). The ET needs of bare soil are accounted in the DWR crop coefficient estimate; if the ET demands of bare soil are higher than those for the crop during a growing season, then the applied water would need to meet the bare soil demand.
According to interviews with local growers, the growing season for each crop type was applied to the CPU crop coefficients (DWR, 2021). In addition, many growers apply irrigation for certain crops in non-growing seasons for climate modification (e.g., frost protection) and/or leaching. The crop coefficient was used to account for some ET, but the remainder is assumed in the surplus of supply to crop demand, thus increasing the return flow volumes. The ETc values were similar to previous values used in CVWD planning (Stantec, 2019), but the DWR method allows for more flexibility in the specific growing seasons and irrigation practices of the Subbasin.
The monthly ET needs of a crop can be satisfied by either applied irrigation or through natural precipitation. Total irrigation was estimated to be the ET demand of the crop less precipitation. Although the amounts in the Indio Subbasin are small, precipitation that exceeds the daily ET demand of a crop is assumed to percolate and is also included in the agricultural return flow estimate.
The comparison of crop consumptive use and delivered agricultural supply was used to calculate an annual return flow percentage. Agricultural supply totals are available for groundwater and surface water deliveries and aggregated on a Township Range Section basis to compare with crop consumptive use.
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Indio Subbasin Water Management Plan Update 7-20 TODD/W&C The Conservation Reports estimated an irrigation efficiency of 72 percent each year (Stantec, 2019), while the annual supply and demand analysis indicates that annual irrigation efficiency varies from 67 to 74 percent, with an average irrigation efficiency of 71 percent of water supply for the period 2009-2019. The remaining agricultural irrigation use (29 percent) becomes return flow. The return flows were distributed throughout the model area based on the crop demand and applied by Township Range. Total annual return flows for agricultural irrigation are shown on Figure 7-8.
Golf Course Return Flow
Like agricultural return flows, irrigation water applied in excess of golf course water demand will result in return flow. Golf courses in the Indio Subbasin are supplied through a variety of sources including imported water, recycled water, potable water from water systems, and onsite groundwater wells.
Irrigation demand for a golf course is dependent on the number of holes, the type and area of turf, and other landscaping. CVWD estimates irrigated area for some golf courses in their service area (for example, in reports on non-potable water). The approximate irrigated area for each golf course was digitized from aerial photos and compared to CVWD estimates (if available) to help calculate the estimated irrigation demand.
The irrigation supply for each golf course was totaled on an annual basis and compared to annual demand.
The results were averaged by municipal area by year, yielding an average golf course return flow range of 21 to 44 percent. The percentage of golf course demand that results in return flow varies over the basin.
The volume of return flow for golf was totaled for each planning Subarea (Subareas are defined in the Water Demand section) and then applied to the digitized irrigated areas of golf within that Subarea.
Previous planning documents have estimated golf course irrigation efficiency, assuming a constant 38 percent average over Irrigation District 1 (Stantec, 2019). The supply and demand methodology varies by time and Subarea, but the basin wide average amounted to 34 percent from 2009 to 2019, similar to previous estimates. Figure 7-8 shows the estimated annual golf course return flow over the model period.
Municipal and Domestic Return Flow
Municipal and domestic return flows to the groundwater basin can result from indoor use (septic tank effluent), outdoor use (landscaping irrigation returns in excess of evapotranspiration), and system losses (pipe leaks). Accordingly, a key indicator for return flows is the relative amount of water used indoors versus outdoors. This varies geographically. For example, landscape irrigation is a significant water use in the West Valley and less so in the East Valley. In addition, the extent of sewer systems and conversely, reliance on septic systems are variable across the Subbasin. For these reasons, this analysis included assessment for each planning Subarea of 1) the percent of outdoor demand that is expected to result in irrigation return flow and 2) the volume that is expected to flow to the septic system. Annual outdoor demand estimates by Subarea were developed as documented in Chapter 5, Demand Projections. The volume of septic system flow was assessed in Chapter 6, Water Supply, for future use based on the sewersheds. Available information on estimated septic return flow was available for 2020 and was projected for 2025 to 2045. Expansion of sewered areas over the past ten years and estimated projection over the next ten years were assumed to be similar.
Municipal return flows were averaged over the entire Subarea. However, no municipal return flow was applied to areas of the basin with little to no development. Municipal return flow averaged 27 percent of total demand basin-wide but ranged on geographic areas from 15 to 40 percent. Figure 7-8 shows the estimated municipal and domestic return flow.
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Indio Subbasin Water Management Plan Update 7-21 TODD/W&C
7.2.6 Outflows
Outflows include groundwater production from agricultural, municipal, golf course, and other pumping wells, drain flows, ET, and groundwater outflows to the Salton Sea.
7.2.6.1 Groundwater Production
For the original and 2010 CVWMP Update models, annual estimates were made of agricultural, municipal, golf course, and other pumping for each Township Range section using the consumptive use method.
Pumping for municipal and domestic use was compiled from available State Water Resources Control Board (SWRCB), USGS, CVWD, and DWA records and estimated for areas with insufficient records. For the updated model, CVWD and DWA metered pumping for municipal and domestic use, and all available metered municipal, agricultural, golf course, and fish farm pumping, were included for years 2009 to 2019.
For the model update, pumping estimates for 1997 to 2009 were not changed except for pumping in the Garnet Hill Subarea, where pumping records from DWA indicated that the 2010 CVWMP Update model overestimated historical pumping.
For homesteads/small water systems in the East Valley that pump less than 25 acre-feet per year and are exempt from well metering required for replenishment assessments, an additional 1,000 AFY was distributed to hypothetical Layer 2 wells at each water system and estimated location of private wells.
Wells were added to Layer 2 to reflect the relatively shallow depths of domestic wells. For West Valley unincorporated areas, an additional 500 AFY of pumping was distributed to hypothetical wells across the area.
Figure 7-9 shows the location of all
simulated pumping wells. Wells were
simulated using the standard MODFLOW
WEL Package and assigned a code for row,
column, and layer in the model. Pumping
wells are simulated as being located at the
respective center of each model cell. For
the 1997 to 2008 period, the same model
cells used in the 2010 CVWMP Update
model WEL Package were retained. For
2009 to 2019, new annual well datasets
were developed using available records of
metered pumping for known municipal,
agricultural, golf, and other known
production wells in the Subbasin. If more
than one production well is located within the same model cell, the annual pumping rates are accumulated. Wells are assigned to model layers based on known or inferred depths. For wells completed (screened) in multiple model layers, total annual pumping from each layer was allocated based on layer transmissivity-based weighting. Most pumping occurs from the deep aquifer (Model Layer 4).
Total annual pumping amounts simulated between 1997 and 2019 are shown on Figure 7-10. As shown, groundwater production has decreased significantly since the mid-2000s, reflecting reduced demands from water conservation and source substitution including increased direct delivery of Colorado River water and recycled water for irrigation uses.
Groundwater production is the largest outflow from the
Indio Subbasin.
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Indio Subbasin Water Management Plan Update 7-22 TODD/W&C Figure 7-9. Location of Production Wells Known to be Active, 1997-2019
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Indio Subbasin Water Management Plan Update 7-23 TODD/W&C Figure 7-10. Groundwater Production, 1997-2019
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Indio Subbasin Water Management Plan Update 7-24 TODD/W&C
7.2.6.2 Drain Flows
Shallow groundwater drainage systems have been installed over a large portion of the East Valley (see Figure 2-5 for locations) where they serve to maintain the water table below crop rooting depths. The model simulates drains in Layer 1 using the MODFLOW EVT Package, with drain locations and elevations based on their construction records. On-farm drains are constructed at approximately 6-foot depths and are connected to CVWD drains that are typically installed at depths of 8 to 10 feet. The model calculates the amounts of drain flow based on the drain elevations, adjacent groundwater elevations, and aquifer/drain conductance (a permeability parameter). Flow from the drains goes either into the CVSC or into a network of open drains that flow directly into the Salton Sea. The drain boundary conditions in the model are maintained at the 1997 configuration.
7.2.6.3 Evapotranspiration
Evapotranspiration from shallow groundwater is simulated in the eastern portion of the model using the MODFLOW EVT Package. Note that the package only estimates ET losses from shallow groundwater levels; other ET and surface water evaporation losses are calculated separately as part the methodology for other components, including applied water return flows, groundwater replenishment, wastewater percolation, and watershed runoff. An ET boundary condition was initially assigned to all cells within the semi-perched zone (see Figure 3-5) in the original historical simulation. As land within the semi-perched zone was developed for agriculture, in locations where drains were installed, the ET boundary was replaced with a drain boundary. Because no additional drain systems were installed after 1997, the ET boundaries were maintained at their 1997 conditions in the model. Inclusion of such ET in the model ensures a complete water budget and acknowledges the hydrologic possibility of phreatophyte ET, including potential GDEs but also non-GDE vegetation around agricultural fields and along drainage channels. ET amounts are calculated based on specified plant rooting depths, reference ET values, and simulated shallow groundwater elevations.
7.2.6.4 Salton Sea
The Salton Sea is simulated as a general head boundary (GHB) with time-varying elevations. For the historical and 2010 CVWMP Update models, actual Salton Sea elevations were used for the periods 1936 to 1999, then held constant at 1999 levels. For the updated 1997-2019 model, actual Salton Sea elevations were simulated through 2019, with sea elevations dropping around 10 feet over the period (Figure 7-11).
Both groundwater outflow to the Sea and inflow from the Sea are simulated, depending on location, time period, and hydraulic gradients between the shallow aquifer and the Sea. Simulated net flow between the Sea and groundwater system is relatively small and inflow from the Sea has been decreasing, as discussed in Section 7.4.
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Indio Subbasin Water Management Plan Update 7-25 TODD/W&C
Figure 7-11. Salton Sea Elevations, 1997-2019
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Indio Subbasin Water Management Plan Update 7-26 TODD/W&C
7.3 Model Update Process and Results
This section documents the model calibration results of the original and 2010 CVWMP Update models, and the performance of the updated 2022 Alternative Plan Update model, along with the updated model water budget. The original and updated models were calibrated to historical groundwater elevation trends in shallow and deep wells. Estimated drain flow rates were also evaluated as a calibration target.
The primary objective of the calibration update was accurate replication of the dynamic water level conditions in shallow and deep wells across the Indio Subbasin, including recent trends since 2009. For the 1997 to 2019 update, only minor “recalibration” via adjustment of input parameters was performed.
Rather, the original 1936 to 1996 and 2010 CVWMP Update models were extended using measurements and better estimates of inflows and outflows primarily for the period after 2008. Minor recalibration was performed in the Garnet Hill Subarea, where selected input parameters were adjusted. These included initial conditions, boundary conditions, historical pumping, and HFB conductance.
The simulated groundwater flow and water budget conditions for the Alternative Plan Update model were compared with measurements and evaluated. This included preparation of maps of simulated shallow and deep aquifer groundwater elevations over time and hydrographs of observed and simulated changes in water levels in the shallow and deep aquifer across the Subbasin. Water budget conditions were also evaluated to assess groundwater inflow and outflow and storage changes.
In general, the Alternative Plan Update model of the Indio Subbasin is well calibrated with observed groundwater elevation and drain flow trends for both the historical and updated periods. In some areas, calibration is better for the recent 2009 to 2019 period than in earlier periods, confirming that the updated input data and water budget are accurate representations of the Indio Subbasin.
7.3.1 Historical Model Calibration Results
The original 1936 to 1996 and 2010 CVWMP Update models were well calibrated to measured groundwater elevation and water budget trends across the basin. Errors between observed and simulated groundwater elevations were generally low, and simulated drain flow amounts over time corresponded to measured and estimated drain flows after the drains were installed.
Figure 7-12 shows 1936 to 2008 model calibration hydrographs for five wells representative of groundwater level conditions across the Subbasin, which have also been monitored for many years. Note the original 1936 to 1996 simulated levels are shown with the black lines on the hydrograph, while the 1997 to 2008 simulated levels from the 2010 CVWMP Update model are shown with orange lines.
The hydrographs shown on Figure 7-12 indicate good overall calibration across the Indio Subbasin. Model- computed drain flows were also compared with measured agricultural drain flows. The very good agreement from the 1950s through the early 2000s showed that the model can simulate real trends in both water levels and flow rates. Moreover, the high calibration quality justifies the use of 1997 simulated groundwater elevations from the historical model as initial conditions for the 1997 to 2019 model update.
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Indio Subbasin Water Management Plan Update 7-27 TODD/W&C Figure 7-12. Model Calibration Hydrographs, 1936-2008
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Indio Subbasin Water Management Plan Update 7-28 TODD/W&C
7.3.2 1997-2019 Model Update Process
The 2010 CVWMP Update dataset was developed during 2008 to 2010 and included measured pumping and recharge data that were readily available at that time, generally through 2008. However, for the simulation period from 2009 to 2019, for which data were not yet available, various modeling assumptions (pertaining to natural and artificial recharge, municipal, resort and irrigation pumping demands, as well as included CVWMP projects) were used to estimate future pumping and recharge amounts and their distributions in the model. Accordingly, for this Alternative Plan Update, model inflows and outflows for the period 2009 to 2019 were updated and the model re-run to confirm calibration quality for this period.
The initial model update runs indicated that the model continues to exhibit good calibration quality for most of the Subbasin. However, simulated water levels in the updated Garnet Hill Subarea were not well calibrated with observed levels in some wells. This appeared to be due to a combination of factors, including offsets in simulated initial conditions (as compared with observed levels in 1997), inaccuracies in the simulated amounts of pumping in the Garnet Hill Subarea, uncertainty in inflow rates from the Mission Creek Subbasin, and characterization of the HFB representing the Garnet Hill Fault. Adjustments of each of these parameters were made to the Alternative Plan Update model to improve calibration in this Subarea. Calibration quality in the Garnet Hill Subarea was improved significantly after these adjustments.
After the initial model update runs, minor adjustments in urban irrigation return flow recharge distributions were also made in the Palm Springs and Indio geographic areas used in the demand forecast.
The total estimated urban return flow volumes developed in Chapter 6, Water Supply, were maintained, but the spatial distributions were adjusted to better align with undeveloped and urban areas. These adjustments also improved local calibration quality.
7.3.3 Water Level Calibration Results
The updated Indio Subbasin model meets both qualitative and quantitative calibration goals. The simulated shallow aquifer (Model Layer 1 and 2) and deep aquifer (Model Layer 4) water level trends throughout the Subbasin are consistent with observed groundwater flow directions and hydraulic gradients characterized in the Subbasin conceptual model and groundwater conditions. An aquitard (Model Layer 3) is locally present between the shallow and deep aquifers. The model reacts well to the large fluxes of recharge and, particularly the dynamic and very large water level mounding response to WWR-GRF and TEL-GRF artificial recharge operations. Long-term trends in shallow and deep aquifer water levels and vertical hydraulic gradients are accurately simulated, as further described below.
Model calibration is also demonstrated by quantitative calibration statistics, which are summarized in Table 7-1. For the quantitative assessment, water level data from 30 shallow and deep monitoring and production wells were used to calculate water level residuals (differences between observed and simulated levels). These wells were selected to be representative of the Subbasin. The summary statistics below are for all model layer water level measurements between 1997 and 2019.
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Indio Subbasin Water Management Plan Update 7-29 TODD/W&C Table 7-1. Model Calibration Summary Statistics 1997 – 2019 Calibration Measure Calibration Results
Mean Residual (Head) -12.15 feet
Mean Absolute Residual (Head) 17.97 feet
Root Mean Squared Residual (RMS-Head) 24.47 feet
Groundwater Elevation Range 1,583 feet
Mean Residual/Range 0.77 %
RMS/Range 1.55 %
The American Society for Testing and Materials (ASTM) recommendations for Mean Residual/Range and RMS/Range are less than 5 percent and 10 percent, respectively (ASTM, 1994, 1998). The Indio Subbasin model calibration quality exceeds these ASTM recommendations.
In the Indio Subbasin model, there are several sources of apparent head residuals that are unrelated to potential inaccuracies in conceptualization of the hydrogeologic system or simulated amounts of inflow and outflow. These include the following.
• The model uses annual stress periods, meaning that the amounts of recharge, pumping, and other inflows and outflows are averaged over each year. In actuality, operations of some of the water supply facilities (such as GRF operations and groundwater production well pumping) and natural inflow sources are not constant at the same rates throughout the year, resulting in some averaging errors in simulated levels.
• Simulated groundwater levels are calculated at the node or center of each model cell containing an observation well. The actual observation wells may be located anywhere within the 1,000 x 1,000-foot model cell, resulting in offsets of as much as 700 feet between the simulated and observed calibration well location.
• The simulated head within the 1,000 x 1,000-foot cell represents the model-calculated average level in the cell. Hydraulic gradients near recharge sources or pumping wells can cause steep local gradients and variable actual elevations within areas simulated by the model cells. • Some observation wells are completed (screened) in multiple aquifers and model layers, resulting in composite observed level or levels that are reflective of a particular aquifer zone, depending on the local vertical flow conditions.
Regardless of these approximations, the model accurately simulates groundwater conditions through the Subbasin and simulation period, as further documented below.
7.3.3.1 Simulated Groundwater Elevation Contour Maps
Figure 7-13 and Figure 7-14 show simulated shallow and deep groundwater elevations in January 2010, near the middle of the updated simulation period, and in January 2020, at the end of the updated simulation period. Visual comparison of the simulated 2020 levels with the most recent measured levels (shown on Figure 4-1) reveals that simulated levels are generally well matched with measured levels.
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Indio Subbasin Water Management Plan Update 7-30 TODD/W&C Figure 7-13. Simulated Shallow and Deep Groundwater Elevations, 2010
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Indio Subbasin Water Management Plan Update 7-31 TODD/W&C Figure 7-14. Simulated Shallow and Deep Groundwater Elevations, 2020
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Indio Subbasin Water Management Plan Update 7-32 TODD/W&C As shown on Figure 7-13, groundwater flow directions in 2010 in the shallow and deep aquifers are northwest-to-southeast across the Subbasin. The hydraulic gradients in both zones are non-uniform with higher gradients in the upper West Valley than in the East Valley. A recharge mound is apparent in the shallow aquifer in the area of TEL-GRF, in response to initiation of recharge in 2009. Comparison of the simulated 2010 levels with the 1997 initial conditions reveals that water levels in both aquifer zones dropped during this period. This decline occurred in several areas of the Indio Subbasin and is also apparent in the observed and simulated hydrographs and water budget change in storage, described below.
Simulated shallow and deep groundwater levels in January 2020 show the same general flow directions and hydraulic gradients as 2010, but local increases in groundwater levels are simulated over this 10-year period. The largest increases are simulated in the upper West Valley and the East Valley, with more stable levels simulated in the mid-valley between 2010 and 2020. The groundwater elevation patterns in the East Valley change dramatically following 10 years of TEL-GRF operation. Groundwater mounding is simulated beneath and downgradient of the TEL-GRF as evidenced by concentric contours.
7.3.3.2 Observed vs. Simulated Hydrographs
Water level data from the 30 monitoring and production wells used for model calibration assessment were plotted on hydrographs and compared with simulated levels. Figure 7-15 shows the locations and aquifer designations of the calibration target wells, and full-size hydrographs are in Appendix 7-A. Water level measurements between 1997 and 2019 are available for the majority of the wells, although a few monitoring wells were not installed until the 2000s and only have water level data after their installation dates.
Figure 7-16 and Figure 7-17 show the observed and simulated groundwater elevation hydrographs in the West Valley and East Valley, respectively. Observed levels are shown as black points on the graphs, while simulated levels are shown as the orange lines. All hydrographs use a 200-foot elevation range, except two wells near the WWR-GRF that use a 400-foot range on the hydrographs. The simulated water levels are generally very well matched with the observed groundwater trends for all shallow and deep wells across the Indio Subbasin, as described below.
West Valley/Palm Springs Subarea
The five calibration wells in the upper West Valley/Palm Springs Subarea (hydrographs along left side of Figure 7-16) show dynamic fluctuations associated with recharge events at the WWR-GRF, with water level mounding and recovery cycles decreasing in magnitude down the valley. The northwesternmost wells nearest the WWR-GRF exhibit fluctuations of over 300 feet in response to very large recharge years.
Model-simulated levels in these wells are very closely matched with observed levels, both with respect to peak and valley magnitudes and timing. The mounding and recovery responses are progressively muted further down valley, but observed and simulated levels remain well-calibrated.
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Indio Subbasin Water Management Plan Update 7-33 TODD/W&C Figure 7-15. Shallow and Deep Model Calibration Wells
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Indio Subbasin Water Management Plan Update 7-34 TODD/W&C Figure 7-16. Model Calibration Hydrographs, West Valley 1997-2019
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Indio Subbasin Water Management Plan Update 7-35 TODD/W&C Figure 7-17. Model Calibration Hydrographs, East Valley 1997-2019
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Indio Subbasin Water Management Plan Update 7-36 TODD/W&C West Valley/Garnet Hill Subarea
Three calibration wells are in the Garnet Hill Subarea (hydrographs along the upper side of Figure 7-16).
The northernmost of these wells is near the WWR-GRF and shows mounding and recovery in response to WWR-GRF recharge, even though it is on the eastern side of the Garnet Hill fault and HFB. The model reproduces the rising and declining water levels observed in this well between 1997 and 2019. The two other calibration wells in Garnet Hill show more stable levels, and the model is well matched with these trends.
Mid-Valley/Thousand Palms to Indian Wells Area
Six calibration wells are in the Thousand Palms to Indian Wells area (hydrographs along the right and bottom sides of Figure 7-16). Observed levels in these wells exhibited declines from 1997 through around 2010, then were characterized by relatively stabilized levels through 2019. The model simulates these trends generally well, although simulated levels are lower than observed in two of the wells near the City of Indio at the end of the simulation. This could be due to the previously mentioned sources of error in the numerical simulation, underestimation of return flow recharge in local areas, or inaccuracies in other model parameters. However, the model generally captures the measured levels in this area showing declines through 2010 followed by stable trends.
East Valley/La Quinta, Coachella, and Thermal Areas
Four calibration wells are around the La Quinta, Coachella, and Thermal areas (hydrographs along the top of Figure 7-17). Observed levels in these wells exhibited declines from 1997 through around 2010, then stabilized or increased through 2019. The model simulates these trends well, although simulated levels in one well near Coachella are lower than observed near the end of the simulation, similar to the previously mentioned simulation trend in the two wells near the City of Indio.
East Valley/TEL-GRF Area
Four calibration wells are in the East Valley near the TEL-GRF (hydrographs along the left side of Figure 7-17). Observed levels in these wells exhibited declines from 1997 through around 2009, then rapidly increased through 2019 in response to initiation of TEL-GRF operations. The model simulates these trends well, with simulated levels in the three wells nearest the GRF rising rapidly and exhibiting the same curve shapes as observed levels. Two of the wells have slightly higher simulated levels than observed while one has slightly lower simulated levels than observed. The model responds to the TEL-GRF recharge operations and simulated levels are well-matched with observed. This is notable because the original Indio Subbasin model was developed prior to TEL-GRF operations and was not calibrated to the strong recharge source, yet still simulates the addition of this source accurately.
East Valley/Mecca, Oasis, and Salton Sea Areas
Six calibration wells are in the East Valley in the Mecca, Oasis, and Salton Sea areas (hydrographs along the bottom and right sides of Figure 7-17). Observed levels in these wells were relatively stable between 1997 through around 2010, then increased through 2019, likely in response to source substitution and in response to initiation of TEL-GRF operations. The model simulates these trends well, with simulated levels in all six wells increasing after 2010 and exhibiting the same trend as observed levels.
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Indio Subbasin Water Management Plan Update 7-37 TODD/W&C
7.3.4 Drain Flow Calibration Results
As an independent calibration target, estimated agricultural drain flow rates were compared with model- simulated drain flows, as shown on Figure 7-18. Model-computed drain flow provides a calibration check for the model, because CVWD has measured flows in the agricultural drains for many years. The measured versus simulated drain flows show good agreement between 1997 and 2002, then diverge slightly between 2003 and 2011, with lower model-predicted drain flows than measured. The differences then decrease between 2012 and 2019, with almost identical estimated and predicted amounts in 2018. Both the estimated and simulated drain flow trends are consistent with observed water level trends, with declining East Valley water levels and drain flows in the 1990s and 2000s, followed by stabilized or slightly increasing levels and drain flows in the 2010s. The generally well-matched drain flows show that the model is capable of simulating real trends in both water levels and flow rates.
7.4 Water Budget
7.4.1 1997-2019 Water Budget
Figure 7-19 shows the transient simulated water budget for all components in the model from 1997 to 2019. Similar results were provided for the historical model period from 1936 to 1996 in documentation provided by Graham Fogg and Associates (Fogg, 2000).
The water budget components include specified recharge, pumping, and subsurface inflows from the San Gorgonio Pass and the Mission Creek Subbasins, along with model-computed flows to ET, drains, and subsurface flow to and from the Salton Sea. The water budget reveals that discharges exceeded recharges for most years between 1997 and 2009, after which time total inflows exceeded outflows for most years between 2010 and 2019. These trends decreased, then increased groundwater storage in the Indio Subbasin, and as previously described, corresponding decreases and increases in water levels were simulated with the model.
7.4.1.1 Evapotranspiration
Transient ET is simulated in the model from 1997 to 2019. The ET rates are relatively uniform over this period, ranging from 4,100 to 5,300 AFY. As discussed in Section 7.2.6.3, this only includes ET losses from shallow groundwater and other ET losses are calculated separately. ET loss from shallow groundwater is mainly in the perched aquifer area in the East Valley.
7.4.1.2 Salton Sea
Figure 7-20 shows the transient simulated flow between the shallow aquifer and Salton Sea from 1997 to 2019. Both groundwater outflow to the Sea and inflow from the Sea are simulated, depending on location, time period, and hydraulic gradients between the shallow aquifer and sea, as illustrated on Figure 720.
Note the simulated flows are for the northern portion of the Sea included in the model domain, and do not include any inflows or outflows in the southern portion of the Sea beyond the Indio Subbasin.
Simulated net flow between the Sea and groundwater system is relatively small, always remaining below 3,000 AFY.
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Indio Subbasin Water Management Plan Update 7-38 TODD/W&C Figure 7-18. Simulated vs. Measured Drain Flows, 1997-2019
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Indio Subbasin Water Management Plan Update 7-39 TODD/W&C Figure 7-19. Annual Model Water Budget, 1997-2019
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Indio Subbasin Water Management Plan Update 7-40 TODD/W&C Figure 7-20. Simulated Salton Sea Inflows and Outflows, 1997-2019
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Indio Subbasin Water Management Plan Update 7-41 TODD/W&C During 1997 to 2014, the model had simulated net inflow from the Sea to the Indio Subbasin, but in 2015 and in subsequent years groundwater outflow to the Sea exceeded inflow from the Sea. This is due to the combination of declining sea levels and increasing shallow groundwater levels over time, resulting in reversals of the hydraulic gradients between the water bodies. As shown on Figure 7-17, the very good calibration of wells 08S08E24A01S, 08S08E03L01S, 07S09E30R02S, 07S09E18H01S, and 07S08E29P01S near the Salton Sea indicates the model is an accurate tool to estimate inflow and outflow rates and directions between the sea and groundwater. Net outflow of groundwater to the Salton Sea is desirable in that it minimizes the potential for saline water intrusion into the aquifer.
7.4.1.3 Change in Groundwater Storage
Accumulation of the inflows and outflows
results in changes in groundwater storage.
Figure 7-21 shows the annual model-
predicted changes in storage between 1997
and 2019. The model-predicted changes in
storage can be compared with the empirical
water budget described in Chapter 4,
Current and Historical Groundwater
Conditions, and shown on Figure 4-9. Note
that the numerical model results are for
calendar years, whereas the empirical
method values are for water years. In
addition, slightly different methods are
used between the two methods to develop
the change in storage values. The model uses changes in simulated heads between years at each of the model cells, multiplied by a specific yield value, while the empirical method uses a water balance approach accounting for all inflows and outflows. Regardless, both methods to estimate annual changes in storage yield similar results, and in particular show the losses in storage experienced during the 2000s followed by the gains in storage during the 2010s.
As documented in Section 7.3, Model Update Process and Results, the model accurately simulates groundwater conditions throughout the Subbasin and simulation period.
Production wells are located throughout the Subbasin.
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Indio Subbasin Water Management Plan Update 7-42 TODD/W&C Figure 7-21. Simulated Change in Storage, 1997-2019
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Indio Subbasin Water Management Plan Update 7-43 TODD/W&C
7.5 Plan Scenarios
Scenarios for the Alternative Plan Update were developed, including baseline scenarios and future scenarios addressing potential future water supply conditions, changes in land use, and implementation of water management projects including source substitution and new water supply projects. Except for the Baseline scenario, climate change conditions were assumed for all Plan scenarios, described in Section
7.5.1 below, reflecting that the Indio GSAs are committed to achieving sustainability under changing climate conditions. Additional discussion of climate change is presented in Section 8.5 and scenarios without climate change are described in Appendix 7-B.
Each scenario was simulated over a 50-year period consistent with SGMA requirements. However, the planning assumptions were only projected for the first 25 years to the 2045 planning horizon. Thereafter, growth and supply assumptions were assumed to continue at the same rate for the second 25 years of the simulation. While extending beyond foreseeable land use and water resource planning projections, the second 25-year projections allow long-term evaluation of water supply and demand conditions, effectively testing Indio Subbasin sustainability under long-term hydrologic variability over 50 years.
The following scenarios are described in this chapter:
1. Baseline (No New Projects): No new supply or management projects or changes to historical hydrology. This scenario is described for comparison purposes only and will never happen, because new projects are in the process of being implemented. However, a baseline is useful to assess the other scenarios.
2. Baseline with Climate Change: Baseline conditions, along with assumptions of the impact of climate change on local hydrology and imported water supplies (climate change hydrology). As with the Baseline, this scenario is described for comparison purposes only and will never happen but is useful to assess the other scenarios.
3. 5-Year Plan with Climate Change: Baseline conditions plus supply and management projects included in the GSA agencies’ 5-year capital improvement plans (CIPs), along with potential climate change hydrology.
4. Future Projects with Climate Change: 5-Year Plan conditions plus implementation of additional supply and management projects that are projected to be completed in the 25-year planning horizon, along with potential climate change hydrology.
5. Expanded Agriculture with Climate Change: Future Projects conditions plus expansion of agriculture resulting in increased water demands, along with potential climate change hydrology.
Additional scenarios developed through the Alternative Plan Update process (including 5-Year Plan, Future Projects, and Expanded Agriculture scenarios under historical hydrology) are described in Appendix 7-B.
7.5.1 Climate Change
To simulate the range of possible future conditions, two different hydrological cycles were used and applied to the Plan scenarios. For the Baseline scenario, the observed hydrology for the Whitewater River watershed from 1970 to 2019 was repeated. In other words, the next 50 years are simulated exactly like the past 50 years. To simulate climate change conditions, a different cycle was selected: the last 25 years
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Indio Subbasin Water Management Plan Update 7-44 TODD/W&C was repeated twice – first in reverse and then forward. The result of the climate change cycle is that the most recent observed drought (2013 to 2017) is included twice early in the simulation. In addition, the long-term average is significantly different for the last 50 years (43,319 AFY) compared with the last 25 years (29,204 AFY). Future climate change is simulated similar to the observed conditions over the last 25 years, a period marked with reoccurring drought and below average rainfall.
The availability of imported water is also expected to be impacted by climate change. As discussed in Chapter 6, Water Supply, SWP reliability is assumed to be 45 percent annually, which is 13 percent lower than DWR's 2019 SWP Delivery Capability Report estimate of 58 percent, but which captures the more recent drier hydrology and Delta export limitations within the SWP system. Under climate change, SWP deliveries are further reduced by an additional 1.5 percent as compared to Baseline conditions by 2045.
For CVWD’s Colorado River entitlement, the climate change scenarios assume the CVWD will contribute from 14,500 to 24,500 AFY of California’s contribution under the Lower Basin Drought Contingency Plan.
Both are conservative assumptions and result in reduced imported water delivered to the Subbasin. In some scenarios with climate change, the decreased volume of imported water results in decreased groundwater replenishment.
This representation of climate change simulates drier future conditions than the climate change recommendations from DWR. Changes to Indio Subbasin streamflow were calculated using change factors for 2030 and 2070 provided by DWR for unimpaired flow within the Salton Sea watershed (HUC 18100200). Change factors are values multiplied by historical monthly or annual streamflow values to calculate probable discharge rates and variability under climate change. In brief, climate change impacts were assessed using DWR data and methodologies and were found to be small, within 10 percent of the 1995 historical value (DWR 2018). Over the 1970 to 2019 hydrological cycle, observed watershed runoff was estimated to be 52,506 AFY, under the DWR recommended climate change projection would be 50,540 AFY, whereas repeating the 1995 to 2019 cycle (our climate change projection) results in the total watershed runoff of 38,196 AFY.
Planning for climate change is important to maintain groundwater sustainability. Future scenarios with projects are presented here with the climate change hydrology to ensure the GSAs can manage the groundwater under changing future conditions. While the Baseline scenario without climate change is discussed in Section 7.6 to illustrate the effects of climate change, all other future scenarios without climate change are presented in Appendices 7-B and 7-C.
7.5.2 Baseline (No New Projects)
The Baseline scenario includes only those supplies and facilities currently in place to support Indio Subbasin management and assumes that no new projects or water supplies will be implemented. The Baseline propagates current conditions into the future to use as a basis for comparing ‘with and without’ future project conditions. Figure 7-22 provides a flow chart that shows the water balance (inflows and outflows) of the Subbasin under Baseline in year 2045, as well as the supplies used to meet demands. The demand forecast for the Plan Area totals 644,610 AFY in year 2045 (see Chapter 5, Demand Projections).
Table 7-2 provides a summary of Baseline supplies used to directly meet demand and Table 7-3 provides a summary of supplies used for replenishment. Other model inflows and outflows (septic system flows, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, and watershed runoff) including groundwater pumping are discussed in Section 7.6. A summary of the assumptions for each supply source is provided below.
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Indio Subbasin Water Management Plan Update 7-45 TODD/W&C The Baseline scenario assumes that passive conservation savings, surface water diversions, and GRF operations will continue to be implemented, along with potable water and sewer consolidations.
Table 7-2. Baseline (No New Projects) Scenario - Modeled Deliveries for Direct Use (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Groundwatera 296,089 308,643 321,483 334,169 344,092 353,244 Colorado Riverb 285,337 284,818 282,419 280,771 279,370 277,969 Recycled Water 13,397 13,397 13,397 13,397 13,397 13,397 Total Direct Use Supplies 594,823 606,858 617,299 628,337 636,859 644,610 a Simulated groundwater pumping in the model scenarios is within 0.03 percent; the slight difference is due to the differences in model area vs. Subbasin extent and numerical precision. b Colorado River deliveries decrease over time due to conversion of agriculture that receives Canal deliveries to urban uses.
Table 7-3. Baseline (No New Projects) Scenario – Modeled Deliveries for Replenishment (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Colorado Rivera 97,000 97,000 82,000 82,000 82,000 82,000 SWP Exchangeb 60,527 60,297 60,092 59,903 79,724 79,431 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Surface Water Diversionsc 2,630 6,000 6,000 6,000 6,000 6,000 Total Replenishment 170,720 173,860 158,655 158,466 167,724 167,431 Note: Groundwater inflows and outflows (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, watershed runoff) are described in Section 7.6. a Colorado River volumes assume that 15,000 AFY MWD-SWP transfer ends in 2027. b SWP Exchange volumes assume Advanced Delivery credit from 2002 to 2035. This assumption is used so as not to double count advanced deliveries in future SWP deliveries.
c Surface water diversions include a small fraction of direct deliveries; for simplicity, all diversion volumes are assumed herein to be directed to WWR-GRF for recovery.
Local Inflows, Outflows, and Supplies: As illustrated in Figure 7-22, inflows to groundwater include subsurface inflow, mountain front recharge, surface water runoff that is diverted for replenishment or percolates along the mountain front or in local channels (minus losses to the Salton Sea), wastewater percolation, and return flows from use (which include septic system percolation). Total surface water runoff from local watersheds is estimated based on the 50-year hydrologic period from 1970 to 2019 and simulated into the future. Runoff inflows are assumed to vary annually, with estimated natural infiltration of watershed runoff (minus diversions and outflows to the Salton Sea) amounting to an annual average of 43,300 AF for the 50-year hydrologic period. Septic system inflow is 8,800 AFY in 2020 and decreases to 4,600 AFY by 2045 due to the connection of septic systems to sewers. Wastewater percolation serves as an inflow to the Subbasin and occurs at five wastewater treatment facility sites (Palm Springs WWTP, CVWD WRP-2, CVWD WRP-7, CVWD WRP-10, and MSWD Regional WRF). Wastewater percolation is assumed to provide an average Subbasin inflow of 6,316 AFY in 2020 and to ramp up to 18,377 AFY by 2045. Return flows from municipal, agricultural, and golf course demands are based on estimates of outdoor water use, as described in Section 7.2.5.5.
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Indio Subbasin Water Management Plan Update 7-46 TODD/W&C Figure 7-22. Baseline (No New Projects) Supply and Demand Flow Chart, 2045 Note: Values in this graphic are rounded to the nearest hundred and may not sum to totals. Colorado River volumes do not sum to total due to underrun under Baseline scenario with no new projects assumption.
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Indio Subbasin Water Management Plan Update 7-47 TODD/W&C Outflows from the Indio Subbasin include drain flow, evapotranspiration, and subsurface outflow.
Subsurface inflow, drain flow, evapotranspiration, and subsurface outflow are derived from the MODFLOW model as described in Section 7.2.5.1 above.
As shown in Table 7-3, local supplies used for replenishment include surface water diversions. Under Baseline, local surface water diversions increase from 2,630 AFY in 2020 to 6,000 AFY by 2023, all of which is diverted to WWR-GRF subsurface storage and then recovered for delivery.
Colorado River: Colorado River water supplies available under Baseline include CVWD’s base entitlement under the 2003 Quantification Settlement Agreement (see Chapter 6, Water Supply), along with transfers where there are agreements in place. Baseline assumes that diversions under the QSA ramp up from 394,000 AFY in 2020 to 424,000 AFY between 2027 and 2045 in 5,000 AFY increments. This ramp-up will allow the CVWD to fully utilize available Colorado River water at its maximum entitlement. The Colorado River supplies used in Baseline include a 15,000 AFY transfer from Metropolitan Water District of Southern California (MWD) delivered to WWR-GRF (MWD retains the remaining 5,000 AFY) and 35,000 AFY of SWP transfer with MWD per the 2003 QSA (described in Chapter 6, Water Supply). Baseline also assumes annual Canal conveyance losses of 5 percent. Under the Baseline scenario, a portion of available Colorado River supply is not able to be beneficially used without the construction of new projects.
Colorado River supplies are assumed to be used for replenishment and direct use, as follows:
• Colorado River Water replenishment:
o TEL-GRF: Recharge limited to current recharge of 37,000 AFY o PD-GRF: Recharge limited to Phase I capacity of 10,000 AFY o WWR-GRF: Recharge of 15,000 AFY of MWD transfer from 2020 to 2026 (totaling 105,000 AF) and recharge of 35,000 AFY of QSA MWD transfer through the planning horizon. • Colorado River Water direct deliveries: Delivery to current agricultural, East Valley golf courses, other recreation, WRP-7, WRP-10, and MVP direct users at current levels equaling 278,000 AFY, less reduced agricultural demands due to urban conversion.
SWP Exchange: Average annual SWP Exchange supplies under Baseline are based on the reliability of SWP deliveries received by CVWD and DWA since 2007 when Federal Judge Wanger overturned the Biological Opinion authored by USFWS and USBR concerning Delta export pumping operations. As described in Chapter 6, Water Supply, this decision significantly impacted DWR’s ability to convey SWP supplies across the Delta for export. Baseline applies an average 45 percent reliability to SWP deliveries.
Additionally, MWD’s Advance Delivery account had 353,946 AF in storage as of January 2020. Baseline assumes that MWD will credit SWP deliveries against the Advance Delivery account at 22,122 AF annually from 2020-2035 so as not to double count these deliveries. Additional SWP Exchange water is available through Yuba Accord deliveries (see Chapter 6, Water Supply) and is assumed to have a 10-year average of 651 AFY.
SWP Exchange supplies modeled under Baseline are varied annually based on the historical variability of SWP Table A deliveries received by the CVWD and DWA, as described in Chapter 6, Water Supply. Final SWP allocations between 2007 and 2021 have ranged from a high of 85 percent in 2017 to a low of 5 percent in 2014 and again in 2021. Baseline applies an annual variability factor that mimics the variability
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-48 TODD/W&C of deliveries associated with different climate years. The variability factors were developed based on the same water years (1970 to 2019) as local hydrology.
SWP Exchange water is assumed to be used for replenishment at WWR-GRF and MC-GRF, and the split of water between these replenishment facilities is to be consistent with the 2004 Settlement Agreement between DWA, CVWD, and MSWD.
Other Supplies: One additional supply is included under Baseline: Rosedale-Rio Bravo deliveries of 10,563 AFY from 2020 to 2035.
Recycled Water: Recycled water supplies are currently produced at three locations: Palm Springs WWTP/DWA WRP, CVWD WRP-7, and CVWD WRP-10. Recycled water supply availability is expected to increase due to development driving an increase in indoor water use and associated wastewater flows within the Plan Area. Total recycled water use is expected to remain at 13,397 AFY as no new projects or non-potable connections are assumed to be implemented under Baseline.
7.5.3 Baseline with Climate Change
The Baseline with Climate Change scenario includes only those supplies and facilities currently in place to support Subbasin management and assumes that no new projects or water supplies will be implemented.
Baseline with Climate Change propagates current management practices into the future under assumptions of future climate conditions and associated supply impacts. Table 7-4 provides a summary of Baseline with Climate Change supplies used to directly meet demand and Table 7-5 provides a summary of supplies used for replenishment. Other model inflows and outflows (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, and watershed runoff) including groundwater pumping are discussed in Section 7.6. Figure 7-23 provides a flow chart that shows the water balance of the Subbasin under Baseline with Climate Change for year 2045, as well as the supplies used to meet demands. The demand forecast for the Plan Area totals 644,610 AFY in year 2045 (see Chapter 5, Demand Projections). A summary of the assumptions applied to each supply source is provided below.
The Baseline with Climate Change scenario assumes that passive conservation savings, surface water diversions, and GRF operations will continue to be implemented, along with potable water and sewer consolidations.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-49 TODD/W&C Table 7-4. Baseline with Climate Change Scenario – Modeled Deliveries for Direct Use (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Groundwatera 296,089 308,643 321,483 334,169 344,092 353,244 Colorado Riverb 285,337 284,818 282,419 280,771 279,370 277,969 Recycled Water 13,397 13,397 13,397 13,397 13,397 13,397 Total Direct Use Supplies 594,823 606,858 617,299 628,337 636,859 644,610 a Simulated groundwater pumping in the model scenarios is within 0.03 percent; the slight difference is due to the differences in model area vs. Subbasin extent and numerical precision. b Colorado River deliveries decrease over time due to conversion of agriculture that receives Canal deliveries to urban uses.
Table 7-5. Baseline with Climate Change Scenario – Modeled Deliveries for Replenishment (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Colorado Rivera 97,000 97,000 82,000 82,000 82,000 82,000 SWP Exchangeb 60,527 60,057 59,614 59,188 78,775 78,248 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Surface Water Diversionsc 2,630 6,000 6,000 6,000 6,000 6,000 Total Replenishment 170,720 173,620 158,177 157,751 166,775 166,248 Note: Groundwater inflows and outflows (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, watershed runoff) are described in Section 7.6. a Colorado River volumes assume that 15,000 AFY MWD-SWP transfer ends in 2027. b SWP Exchange volumes assume Advanced Delivery credit from 2002 to 2035. This assumption is used so as not to double count advanced deliveries in future SWP deliveries.
c Surface water diversions include a small fraction of direct deliveries; for simplicity, all diversion volumes are assumed herein to be directed to WWR-GRF for recovery.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-50 TODD/W&C Figure 7-23. Baseline (No New Projects) with Climate Change Supply and Demand Flow Chart, 2045 Note: Values in this graphic are rounded to the nearest hundred and may not sum to totals. Colorado River volumes do not sum to total due to underrun under Baseline with Climate Change scenario with no new projects assumption.
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Indio Subbasin Water Management Plan Update 7-51 TODD/W&C Local Inflows, Outflows, and Supplies: As illustrated in Figure 7-23, inflows to groundwater include subsurface inflow, surface water runoff (diverted for replenishment or percolating along local channels minus losses to the Salton Sea), wastewater percolation, and return flows from use (which include septic system percolation). However, total watershed runoff is estimated based on the drier 25-year hydrologic period from 1995 to 2019. As shown in Figure 7-23, estimated average natural infiltration of watershed runoff (minus diversions and outflows to the Salton Sea) amounts to 29,204 AFY, approximately 14,000 AFY less than in the Baseline scenario due to the drier climate change assumptions.
In the Baseline with Climate Change scenario, return flows, wastewater percolation, and septic system inflow are the same as in Baseline because the demands, which contribute to these flows, are assumed to remain unchanged. Subsurface inflow, drain flow, evapotranspiration, and subsurface outflow are derived from the MODFLOW model described in Section 7.2.5 above. As with Baseline, available local water inflows also include surface water diverted for replenishment. As with Baseline, local surface water diversions increase from 2,630 AFY in 2020 to 6,000 AFY by 2023, all of which is diverted to WWR-GRF subsurface storage and then recovered for delivery.
Colorado River: Colorado River water supplies available under Baseline with Climate Change use the same planning assumptions as Baseline, except with an assumed reduction in Canal deliveries based on the Lower Basin Drought Contingency Plan (Lower Basin DCP). According to the Lower Basin DCP, CVWD is responsible for a portion of California’s contribution to demand reduction on the Colorado River (see Chapter 6, Water Supply). Under Baseline with Climate Change, Canal deliveries are assumed to be reduced by 14,500 AFY from 2020 to 2026, and by 24,500 AFY after 2026. Colorado River water demand for direct deliveries and recharge capacities are expected to remain the same as in Baseline. Under the Baseline with Climate Change scenario, a portion of available Colorado River supply is not able to be beneficially used.
SWP Exchange: SWP Exchange supplies available under Baseline with Climate Change are the same as under Baseline in terms of 45 percent average annual reliability, variability factors applied based on water years, and Advance Delivery credits applied for 2020 to 2035. Under anticipated climate conditions, reliability is assumed to be reduced by an additional -1.5 percent as compared to Baseline by 2045, as modeled by DWR in its 2019 SWP Delivery Capability Report (DWR, 2020).
SWP Exchange water is assumed to be used for replenishment at the WWR-GRF and MC-GRF, and the allocation of water between these replenishment facilities is consistent with the 2004 Settlement Agreement.
Recycled Water: Recycled water supplies under the Baseline with Climate Change are identical to the Baseline planning assumptions, remaining at 13,397 AFY.
Other Supplies: Rosedale-Rio Bravo deliveries of 10,583 AFY from 2020 to 2035 assume no loss due to climate change.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-52 TODD/W&C
7.5.4 5-Year Plan with Climate Change
The 5-Year Plan with Climate Change scenario includes supplies and facilities currently in place to support Subbasin management, along with new projects planned to be completed as part of the GSAs’ 2020 5-year capital improvement programs (5-year CIPs) and supplies under the control of GSAs. This scenario assumes that climate change will impact imported water and local water supplies. Table 7-6 provides a summary of 5-Year Plan with Climate Change supplies used to directly meet demand and Table 7-7 provides a summary of supplies used for replenishment. Supply inputs used for the model (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, and watershed runoff) and groundwater pumping are discussed in Section 7.6. Figure 7-24 provides a flow chart that shows the water balance of the basin under 5-Year Plan with Climate Change in year 2045, as well as the supplies used to meet demands. The demand forecast for the Plan Area totals 644,610 AFY in year 2045 (see Chapter 5, Demand Projections). A summary of the assumptions applied to each supply source is provided below.
The 5-Year Plan with Climate Change scenario assumes that passive conservation savings, surface water diversions, and GRF operations will continue to be implemented, along with potable water and sewer consolidations. New supply from Lake Perris Seepage project becomes available in 2023. Planned non- potable expansions from WRP-7 and WRP-10 will deliver Canal and recycled water, along with Canal deliveries to East Valley golf courses and the Oasis Distribution System. Additionally, PD-GRF expansion will allow for greater Subbasin replenishment.
Table 7-6. 5-Year Plan with Climate Change Supply Scenario – Modeled Deliveries for Direct Use (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Groundwatera 296,089 271,914 284,754 297,440 307,362 316,514 Colorado Riverb 285,337 317,932 314,733 312,385 310,184 307,883 Recycled Water 13,397 17,013 17,813 18,513 19,313 20,213 Total Direct Use Supplies 594,823 606,858 617,299 628,337 636,859 644,610 a Simulated groundwater pumping in the model scenarios is within 0.03 percent; the slight difference is due to the differences in model area vs. Subbasin extent and numerical precision. b Colorado River deliveries increase over time due to new non-potable connections.
Table 7-7. 5-Year Plan with Climate Change Scenario – Modeled Deliveries for Replenishment (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Colorado Rivera 97,000 93,868 96,817 97,000 97,000 97,000 SWP Exchangeb 60,527 62,576 62,125 61,690 81,268 80,733 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Surface Water Diversionsc 2,630 6,000 6,000 6,000 6,000 6,000 Total Replenishment 170,720 173,007 175,505 175,253 184,268 183,733 Note: Groundwater inflows and outflows (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, watershed runoff) are described in Section 7.6. a Colorado River volumes assume that 15,000 AFY MWD-SWP transfer ends in 2027. b SWP Exchange volumes assume Advanced Delivery credit from 2002 to 2035. This assumption is used so as not to double count advanced deliveries in future SWP deliveries.
c Surface water diversion include a small fraction of direct deliveries; for simplicity, all diversion volumes are assumed herein to be directed to WWR-GRF for recovery.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-53 TODD/W&C Figure 7-24. 5-Year Plan with Climate Change Supply and Demand Flow Chart, 2045 Note: Values in this graphic are rounded to the nearest hundred and may not sum to totals. Colorado River volumes do not sum to total due to underrun under Baseline with Climate Change scenario with no new projects assumption.
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Indio Subbasin Water Management Plan Update 7-54 TODD/W&C Local Inflows, Outflows, and Supplies: Surface water hydrology under 5-Year Plan with Climate Change is the same as Baseline with Climate Change, as are return flows and septic system inflows. Wastewater percolation is expected to be reduced due to an increase in recycled water use (described below). In this scenario, wastewater from the MSWD Regional WRF is transferred north for use in the Mission Creek Subbasin starting in 2027. Subsurface inflow, drain flow, evapotranspiration, and subsurface outflow are derived from the MODFLOW model described in Section 7.2.5.
Colorado River: Colorado River water supplies available under the 5-Year Plan with Climate Change are assumed to remain the same as under Baseline with Climate Change (assuming reductions due to Lower Basin DCP); however, available supply use increases due to planned expansions to replenishment facilities and direct deliveries. Under 5-Year Plan with Climate Change, the PD-GRF is planned to expand to allow for recharge to increase from 10,000 AFY in 2020 to 25,000 AFY in 2023. By expanding recharge at the PD- GRF and reducing the supply available under climate change conditions, the Colorado River supplies used for recharge at the WWR-GRF are reduced from 2023 to 2045 as the supply is utilized for recharge at PD- GRF, additional non-potable connections in the East Valley and mid-Valley, and by the Oasis In-lieu Project.
Increases in Colorado River direct deliveries begin in 2022 at 1,122 AFY and total 36,729 AFY by 2025. As available Colorado River supply is fully utilized in the Mid- and East Valley areas, CVWD will reduce replenishment at the GRFs. The increase in direct deliveries results in a reduction in replenishment of CVWD’s 2003 QSA entitlement at WWR-GRF to 22,645 AFY beginning in 2027.
SWP Exchange: SWP Exchange supplies available under 5-Year Plan with Climate Change are the same as under Baseline with Climate Change, with 45 percent reliability varied annually and -1.5 percent reduction due to climate change. SWP Exchange water is assumed to be used for replenishment at the WWR-GRF and MC-GRF, consistent with the 2004 Settlement Agreement. New supplies (2,500 AFY) from the Lake Perris Seepage Recovery project come online in 2023.
Recycled Water: Recycled water availability is expected to increase due to increased recycled water production and deliveries to new non-potable connections. WRP-7 deliveries increase from 2,201 AFY in 2020 to 2,800 AFY in 2025. WRP-10 deliveries increase from 7,783 AFY in 2020 to 14,000 AFY in 2045. Any recycling of wastewater from WRP-10 and WRP-7 disposed to percolation ponds would offset groundwater pumping, but reduce net return flows to groundwater.
Other Supplies: Rosedale-Rio Bravo deliveries remain the same as in Baseline.
7.5.5 Future Projects with Climate Change
The Future Projects with Climate Change Scenario (Future Projects with Climate Change) includes supplies and facilities currently in place to support Subbasin management, along with projects for new supplies and facilities that are planned by the GSA agencies within the 25-year planning horizon. Supply constraints associated with climate changes are assumed for local and imported supplies. Table 7-8 provides a summary of Future Projects with Climate Change supplies used to directly meet demand and Table 7-9 provides supplies used for replenishment. Other inflows and outflows to the model (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, and watershed runoff) including groundwater pumping are discussed in Section 7.6. Figure 7-25 provides a flow chart that shows the water balance of the Subbasin under Future Projects with Climate Change in year 2045, as well as the supplies used to meet demands. The demand forecast for the Plan Area totals 644,610 AFY in year 2045 (see Chapter 5, Demand Projections). A summary of the assumptions applied to each supply source is provided below.
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Indio Subbasin Water Management Plan Update 7-55 TODD/W&C The Future Projects with Climate Change Scenario assumes that passive conservation savings, surface water diversions, and GRF operations will continue to be implemented, along with potable water and sewer consolidations. Participation in the DCF will restore SWP supply reliability to 59 percent, and Sites Reservoir and Lake Perris Seepage will come online in 2023 and 2035, respectively, and continue through the planning horizon. Planned non-potable expansions from WRP-7 and WRP-10 will deliver increased Canal and recycled water, along with increased Canal deliveries to Mid-Valley Pipeline connections, East Valley golf courses, and the Oasis Distribution System (as compared to the 5-Year Plan scenario). The EVRA potable reuse project will be implemented.
Table 7-8. Future Projects with Climate Change Scenario – Modeled Deliveries for Direct Use (AFY) Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Groundwatera 296,088 271,914 266,364 261,423 267,252 276,404 Colorado Riverb 285,337 317,932 333,122 348,401 350,294 347,993 Recycled Water 13,397 17,013 17,813 18,513 19,313 20,213 Total Direct Use Supplies 594,823 606,858 617,299 628,337 636,859 644,610 a Simulated groundwater pumping in the model scenarios is within 0.03 percent; the slight difference is due to the differences in model area vs. Subbasin extent and numerical precision. b Colorado River deliveries increase over time due to new non-potable connections.
Table 7-9. Future Projects with Climate Change Scenario – Modeled Deliveries for Replenishment (AFY)
Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Colorado Rivera 97,000 93,868 78,428 63,149 61,256 63,557 SWP Exchangeb 60,527 62,576 62,125 72,193 91,732 114,720 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Indirect Potable Reuse 0 0 5,000 5,000 5,000 5,000
Surface Water Diversionsc 2,630 6,000 6,000 6,000 6,000 6,000 Total Replenishment 170,720 173,007 162,116 156,905 163,988 189,277 Note: Groundwater inflows and outflows (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, watershed runoff) are described in Section 7.6. a Colorado River volumes assume that 15,000 AFY MWD-SWP transfer ends in 2027. b SWP Exchange volumes assume Advanced Delivery credit from 2002 to 2035. This assumption is used so as not to double count advanced deliveries in future SWP deliveries. SWP Exchange includes future supplies from DCF, Sites Reservoir, and Lake Perris Seepage as described below.
c Surface water diversions include a small fraction of direct deliveries; for simplicity, all diversion volumes are assumed herein to be directed to WWR-GRF for recovery.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-56 TODD/W&C Figure 7-25. Future Projects with Climate Change Supply and Demand Flow Chart, 2045 Note: Values in this graphic are rounded to the nearest hundred and may not sum to totals.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-57 TODD/W&C Local Inflows, Outflows, and Supplies: Surface water hydrology under Future Projects with Climate Change is the same as Baseline with Climate Change, as are return flows and septic system inflows.
Wastewater percolation is expected to be reduced due to an increase in recycled water use (described below), along with the transfer of MSWD Regional WRF flows to the Mission Creek Subbasin starting in 2027. Subsurface inflow, drain flow, evapotranspiration, and subsurface outflow are derived from the MODFLOW model described in Section 7.2.5.
Colorado River: Colorado River water supplies available under Future Projects with Climate Change are assumed to remain the same as under the 5-Year Plan with Climate Change, but with additional direct deliveries. Under Future Projects with Climate Change, in addition to the replenishment facility expansions discussed under the 5-Year Plan, the TEL-GRF will expand from a capacity of 37,000 AFY in 2020 to 40,000 AFY in 2025. Increases in Colorado River direct deliveries begin in 2022 at 1,122 AFY and amount to 76,839 AFY by 2045. As available Colorado River supply is fully utilized in the Mid- and East Valley, CVWD will reduce replenishment at WWR-GRF and PD-GRF. The increase in direct deliveries results in a reduction in replenishment of CVWD’s 2003 QSA entitlement at PD-GRF beginning in 2031 to a low of 4,535 AFY in 2045. Under this scenario, QSA water is not available for recharge at WWR-GRF starting in 2031.
SWP Exchange: SWP Exchange supplies available under Future Projects with Climate Change include the Table A deliveries (45 percent reliability varied annually based on water year and -1.5 percent reduction due to climate change) assumed under Baseline with Climate Change, with the addition of the following projects:
• Delta Conveyance Facility (DCF) to increase the reliability of SWP deliveries by 26,500 AFY (to 59% of Table A) in 2040 due to improvements in Delta conveyance, reduced by the volume diverted to MC-GRF under the 2014 Mission Creek Water Management Agreement (see Chapter 6, Water Supply).
• Lake Perris Dam Seepage Recovery Project to provide 2,754 AFY, reduced by the volume diverted to MC-GRF. Lake Perris Seepage will come online in 2023 and continue through the planning/modeling horizon.
• Sites Reservoir Project to provide 11,550 AFY, reduced by the volume diverted to MC-GRF. Sites Reservoir will come online in 2035 and continue through the planning/modeling horizon. 30 percent conveyance loss is applied to this supply.
Recycled Water: Recycled water supplies under Future Projects with Climate Change are further expanded from those shown under the 5-Year Plan with Climate Change, including an increase in recycled water deliveries by 6,815 AFY in 2045 and with 5,000 AFY of potable reuse from Valley Sanitary District’s WRP (referred to as the EVRA Potable Reuse Project).
Other Supplies: Rosedale-Rio Bravo deliveries remain the same as in Baseline.
7.5.6 Expanded Agriculture with Climate Change
The Expanded Agriculture with Climate Change Scenario (Expanded Agriculture with Climate Change) includes increased agricultural demands, along with the same suite of planned future projects described under the Future Projects with Climate Change Scenario. This scenario assumes 8,000 acres of additional farmland (inclusive of 1,500 AFY in baseline demand forecast). This scenario assumes that new agricultural growth occurs due in part to expanded availability of Canal water to currently idle lands. The
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-58 TODD/W&C scenario allocates 85 percent of new agricultural demands to Canal water and 15 percent to groundwater.
Table 7-10 provides a summary of Expanded Agriculture with Climate Change supplies used to directly meet demand and Table 7-11 provides a summary of supplies used for replenishment. Other inflow and outflows to the model (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, and watershed runoff) including groundwater pumping are discussed in Section 7.6.
Figure 7-26 provides a flow chart that shows the water balance of the Indio Subbasin under Expanded Agriculture with Climate Change in year 2045, as well as the supplies used to meet demands. The demand forecast for the Expanded Agriculture with Climate Change scenario includes an additional 8,000 acres of agricultural production and totals 679,696 AFY in year 2045 (assuming 15 percent of additional crop demand served by groundwater and 85 percent by Canal water). All water supplies and projects described under Future Projects with Climate Change are applied to this scenario.
The Expanded Agriculture with Climate Change scenario assumes the same projects and supplies as the Future Projects scenario. Planned non-potable expansions from WRP-7 and WRP-10 will deliver increased Canal and recycled water, along with increased Canal deliveries to Mid-Valley Pipeline connections, East Valley golf courses, and the Oasis Distribution System (as compared to the 5-Year Plan scenario). The EVRA potable reuse project will be implemented.
Table 7-10. Expanded Agriculture with Climate Change Scenario – Modeled Deliveries for Direct Use (AFY)
Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Groundwatera 296,088 272,967 268,470 264,581 271,463 281,667 Colorado Riverb 285,337 323,896 345,051 366,295 374,152 377,816 Recycled Water 13,397 17,013 17,813 18,513 19,313 20,213 Total Direct Use Supplies 594,823 613,876 631,334 649,389 664,928 679,696 a Simulated groundwater pumping in the model scenarios is within 0.03 percent; the slight difference is due to the differences in model area vs. Subbasin extent and numerical precision. b Colorado River deliveries increase over time due to new non-potable connections.
Table 7-11. Expanded Agriculture with Climate Change Scenario – Modeled Deliveries for Replenishment (AFY)
Supply (Acre-Feet) 2020 2025 2030 2035 2040 2045
Colorado Rivera 97,000 87,904 66,499 45,255 37,398 33,734 SWP Exchangeb 60,527 62,576 62,125 72,193 91,732 114,720 Other: Rosedale Rio-Bravo 10,563 10,563 10,563 10,563 0 0 Indirect Potable Reuse 0 0 5,000 5,000 5,000 5,000
Surface Water Diversionsc 2,630 6,000 6,000 6,000 6,000 6,000 Total Replenishment 170,720 167,043 150,187 139,011 140,130 159,454 Note: Groundwater inflows and outflows (septic systems, return flows, subsurface inflow and outflow, drain flows, evapotranspiration, watershed runoff) are described in Section 7.6. a Colorado River volumes assume that 15,000 AFY MWD-SWP transfer ends in 2027. b SWP Exchange volumes assume Advanced Delivery credit from 2002 to 2035. This assumption is used so as not to double count advanced deliveries in future SWP deliveries. SWP Exchange includes future supplies from DCF, Sites Reservoir, and Lake Perris Seepage as described below.
c Surface water diversions include a small fraction of direct deliveries; for simplicity, all diversion volumes are assumed herein to be directed to WWR-GRF for recovery.
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Indio Subbasin Water Management Plan Update 7-59 TODD/W&C Figure 7-26. Expanded Agriculture with Climate Change Supply and Demand Flow Chart, 2045 Note: Values in this graphic are rounded to the nearest hundred and may not sum to totals.
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2022 Indio Subbasin Alternative Plan Update 7-60 TODD/W&C Local Inflows, Outflows, and Supplies: Surface water hydrology under Expanded Agriculture with Future Projects and Climate Change is the same as Baseline with Climate Change, as are return flows and septic system inflows. Wastewater percolation is expected to be reduced due to an increase in recycled water use (described below), along with the transfer of MSWD Regional WRF flows to the Mission Creek Subbasin starting in 2027. Subsurface inflow, drain flow, evapotranspiration, and subsurface outflow are derived from the MODFLOW model described in Section 7.2.5.
Colorado River: Colorado River water supplies available under Expanded Agriculture with Future Projects and Climate Change are assumed to remain the same as under the Future Projects with Climate Change, but with additional expansions of direct deliveries. Increases in Colorado River direct deliveries begin in 2022 at 1,122 AFY and amount to 106,663 AFY by 2045. As available Colorado River supply is fully utilized in the Mid- and East Valley, CVWD will reduce replenishment at the GRFs. This results in a reduction in replenishment of CVWD’s 2003 QSA entitlement at TEL-GRF beginning in 2031 to a low of 14,712 AFY in 2045, along with ending QSA deliveries at WWR-GRF in 2028 and PD-GRF in 2031.
SWP Exchange: SWP Exchange supplies are the same as under Future Projects with Climate Change and include Table A deliveries (45 percent reliability varied annually based on water year and -1.5 percent reduction due to climate change) along with DCF, Lake Perris Dam Seepage Recovery Project, and Sites Reservoir Project.
Recycled Water: Recycled water supplies are the same as under Future Projects with Climate Change.
Other Supplies: Rosedale-Rio Bravo deliveries remain the same as in Baseline.
7.6 Scenario Implementation
The calibrated Indio Subbasin MODFLOW model was used to simulate water budgets and groundwater level changes over a future 50-year period, from January 2020 to December 2069. The same model area, boundaries, layering, aquifer characteristics, drains, and evapotranspiration areas used in the historical model were maintained in the future predictive model. Only model inflow and outflow amounts, and selected model boundary conditions, were changed for the scenario simulations. Model inflow and outflow sources and rates were estimated for five scenarios, as described in Section 7.5. Annual model stress periods and 12 timesteps per stress period were used, as with the updated historical model.
Predicted groundwater level changes over time (along with future changes in Subbasin storage, drain flows, and flows to the Salton Sea) were evaluated to assess overall groundwater Subbasin response, local changes, and effectiveness of the potential management actions for each modeled scenario. The methods used to extend the estimates of each element of the water budget and model input are described in detail below.
7.6.1 Inflows
The Indio Subbasin is recharged through a combination of natural inflows of surface water and groundwater, replenishment of imported water, wastewater percolation, and irrigation return flows. Each of these sources was updated to reflect the specific future conditions in each scenario, as described in Section 7.5 above.
Figure 7-27 shows the average water balance by element for each scenario. Figure 7-27 and Table 7-12 shows the average water balance by element for each scenario. The bar chart summarizes each scenario by the average annual contribution by water balance element over the future planning period (2020 to 2045). The following sections describe each of the sources of inflow to the Indio Subbasin.
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2022 Indio Subbasin Alternative Plan Update 7-61 TODD/W&C Table 7-12. Simulated Inflows and Outflows, 25-Year Average (2020-2045) (AFY) Baseline with
Climate Change
(AFY)
5-Year Plan with
Climate Change
(AFY)
Future Projects
with Climate
Change
(AFY)
Expanded
Agriculture with
Climate Change
(AFY)
Inflow
Whitewater River-GRFa 114,775 114,843 100,019 97,637
Thomas E Levy-GRF 36,260 36,260 38,612 37,784
Palm Desert-GRF 9,800 22,736 21,352 10,723
Indirect Potable Reuse - - 2,940 2,940
Wastewater Percolation 12,077 6,244 6,244 6,244
Agricultural Return Flow 83,727 83,727 83,727 88,789
Golf Course Return Flow 34,348 34,348 34,348 34,348
Municipal Return Flow 47,626 47,626 47,626 47,626
Natural Infiltration 29,204 29,204 29,204 29,204
Subsurface Inflow 10,990 11,283 11,297 11,298
Total Inflows 378,806 386,269 375,368 366,592
Outflow
Groundwater Pumping (325,477) (294,397) (271,165) (273,695) Drain Flows (40,903) (50,980) (57,781) (59,416)
Evapotranspiration (from
Shallow Groundwater) (4,480) (5,273) (5,643) (5,730)
Outflow to Salton Sea (4,823) (5,313) (5,497) (5,522)
Total Outflows (375,683) (355,963) (340,086) (344,363)
Average Annual Change in
Storage (AFY) +3,122 +30,306 +35,282 +22,229
Note: Totals may not sum due to rounding.
a Replenishment estimates for Whitewater River-GRF include imported water and surface water diversions.
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Indio Subbasin Water Management Plan Update 7-62 TODD/W&C Figure 7-27. Model Inflows and Outflows by Scenario
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Indio Subbasin Water Management Plan Update 7-63 TODD/W&C
7.6.1.1 Subsurface Inflows
Subsurface inflow from the Mission Creek Subbasin was updated for the entire future period, based on values recently generated from the Mission Creek Subbasin MODFLOW model (Wood, 2021). Predicted subsurface outflows from the Mission Creek Subbasin for future scenarios (corresponding to the Indio Subbasin scenarios) were used as subsurface inflow to the Indio Subbasin. For the Expanded Agriculture with Climate Change scenarios, the Future Projects with Climate Change inflows were used. Flows were allocated to five model boundary segments along the Banning/San Andreas Fault at the eastern edges of the Garnet Hill, Indio Hills, and Thousand Palms Subareas (Figure 7-6). Average annual inflows for the future scenarios range from approximately 2,000 AFY for the Baseline with Climate Change scenario to 2,300 AFY for the Future Projects with Climate Change scenario. Subsurface inflow from the San Gorgonio Pass Subbasin was not changed from the 2010 CVWMP Update model and was kept at the long-term average of approximately 9,000 AFY used in the calibrated historical model, shown on Figure 7-27. As described in Section 7.2.5, uncertainty exists in the historical and potential future amounts of inflow from the San Gorgonio Pass Subbasin. The Indio and San Gorgonio Pass Subbasin GSAs have discussed the discrepancy in simulated amounts of subsurface flow between the Subbasins, and plan to reconcile the differences as a part of the next 5-Year Plan update.
7.6.1.2 Surface Water Inflows
As discussed in Section 7.1, recharge from mountain front inflow and from percolation of stream flows into the Indio Subbasin was estimated for 24 watersheds and stream channels along the southwest edge of the model. Streamflow percolation and mountain front recharge are inflows to the model and vary widely from wet to dry years. As discussed in Section 7.5.1, two hydrological cycles were used for future scenarios, one with Climate Change and one without. Climate change would result in decreased rainfall and therefore decreased mountain front recharge and percolation of stream flows. The long-term average for surface water inflow ranges from 43,319 AFY without climate change and 29,204 AFY with climate change over the entire 50-year simulation. Natural infiltration is shown as dark grey on Figure 7-27.
7.6.1.3 Replenishment
The annual volumes of replenishment were compiled and applied to the locations of the GRFs based on the suite of projects included in each scenario as described in Section 7.5. These include the WWR-GRF, TEL-GRF, and the recently completed PD-GRF. The total volume at each location is a result of the available imported water for replenishment and the capacity of the facility. The available imported water in turn is controlled by the contracts, projects, agreements, and hydrological conditions. The assumptions used to develop the future replenishment amounts were described in Section 7.5. Evaporative losses were assumed to be four percent of recharged volume for the WWR-GRF and two percent for all other locations, reflecting the larger surface area and windier conditions at the WWR-GRF. Total annual recharge volumes at the replenishment facilities are shown as yellow, light orange, and dark orange on Figure 7-27.
7.6.1.4 Wastewater Discharges
Four wastewater plants discharge to disposal ponds (Palm Springs WWTP and CVWD WRP-2, WRP-7, and WRP-10). In addition, a new MSWD Regional WRF will soon be completed in Garnet Hill. Under the Baseline conditions, wastewater will be percolated at this location, but under 5-Year Plan and Future scenarios, wastewater percolation does not continue past 2025 and recycled water from the plant is delivered to Mission Creek Subbasin. The future percolation volumes for all plants were calculated based on expected inflow and recycled water deliveries. For future conditions, evaporative losses were assumed
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Indio Subbasin Water Management Plan Update 7-64 TODD/W&C at two percent of the recharged volume. The ponds have evaporative losses, calculated by the area of ponds and expected annual evaporation. The remaining volumes percolated into the Subbasin are shown as cobalt blue on Figure 7-27.
7.6.1.5 Applied Water Return Flows
Irrigation needs are expected to follow the increases (or decreases) in demands for each of the major categories – agricultural, golf, and municipal. The demands are documented in Chapter 5, Demand Projections, and expected return flows are calculated with the same methodology as the historical model.
Agricultural change, both the conversion of agricultural parcels to urban in some areas and the increase in acreage in others, is detailed in Chapter 5, Demand Projections. Expected return flows were increased or decreased based on the percentage of expected change in agricultural acreage (either conversion to municipal uses or conversion from idle land to active agriculture) by geographic area. Future agricultural demand projections are the same in all scenarios, with the exception of the expanded agricultural scenario. The areal distribution was the same as the historical model which used the CVWD crop censuses to identify specific crop areas, only the volumes adjusted based on land use changes.
Municipal return flow is estimated using the percent of outdoor irrigation expected to result in return flow and the volume of septic system return flow by geographic area. The expected future outdoor municipal demand and septic system flow is documented in Chapter 5, Demand Projections, and the percent resulting in return flow is the same by geographic area as used in the historical model calculations, which relied on the most recent crop census, Section 7.2.5.5.
Return flow from golf courses was based on the calculated return flow in the historical model using the demand and supply at the locations of the existing courses (Section 7.2.5.5). Additional return flow (34 percent of expected demand of each golf course) was added for the three expected new golf courses based on the timing and location of those projects (refer to Chapter 5, Demand Projections).
Municipal return flows also include expected septic system return flow. For all but the Expanded Agriculture with Climate Change scenario, return flows remain the same for each scenario. Agricultural, golf, and municipal return flows are shown green, magenta, and light grey, respectively on Figure 7-27.
As described in Section 7.5 above, the Expanded Agriculture with Climate Change scenario includes an additional 8,000 acres of irrigated agricultural land in the East Valley. Additional agricultural demand was estimated by applying the average applied water rate in the East Valley (5.4 AFY/acre). The irrigation source was assumed to be 15 percent additional groundwater pumping and 85 percent new direct delivery connections. Return flows associated with the additional agricultural were increased relative to the expected demand increase and applied over areas with existing agriculture in the East Valley.
7.6.2 Outflows
For each scenario, the only prescribed outflow was groundwater pumping. The remaining outflows (drain flows, ET, and groundwater outflows to the Salton Sea) are dependent on the simulated water levels of the model.
7.6.2.1 Groundwater Production
For the future scenarios, pumping was assumed to continue from the same distribution of wells in the Subbasin as the historical model. Increased water demands were identified on a geographic area and the volume of pumping for that area was increased to meet the total expected volume (current plus increased demand). The increase in demand is detailed in Chapter 5, Demand Projections. For all but the Expanded
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Indio Subbasin Water Management Plan Update 7-65 TODD/W&C Agriculture with Climate Change scenario, forecasted water demands remain the same, but depending on what projects are implemented, the source of supply differs by individual scenario (e.g., groundwater pumping may shift to Canal direct deliveries). The Expanded Agriculture with Climate Change scenario includes an increase in agricultural water demand, 15 percent of which is assumed to be met by groundwater pumping.
The Baseline and Baseline with Climate Change scenarios reflect the current level of pumping, plus the expected change in demand from municipal, golf, and agricultural uses (it was assumed the increase in demands for the “Other” category is satisfied by other water sources). For the scenarios with planned source substitution projects, pumping volumes are reduced by the expected direct delivery volumes. Most notably, the planned Oasis project will supply up to 32,000 AFY of imported water to growers in the East Unincorporated area, about 25,000 to 27,000 AFY which previously relied on groundwater and therefore pumping in the area is reduced by an equal amount. Groundwater pumping amounts are shown dark blue on Figure 7-27.
7.6.3 Other Predictive Model Inputs
In addition to the inflow and outflow model input datasets, several other model input parameters and future boundary conditions were defined for the future scenario simulations. • The model grid initial groundwater elevation conditions for all predictive scenarios, beginning on January 1, 2020, were set to the values from the final historical simulation ending December 31, 2019.
• The Salton Sea, simulated as a MODFLOW General Head Boundary, was assigned future sea elevations for 2020 to 2069, based on the modified Salton Sea Accounting Model (Tetra Tech and Salton Sea Authority, 2016). Sea level elevations are predicted to decline from -238 ft msl in 2020 to -250 ft msl in 2069, and this decline was applied to the GHB representing the Sea. • Drains and evapotranspiration zones were unchanged relative to the historical model for all scenarios simulated.
In addition, a subset of 12 monitoring wells (see Chapter 10, Monitoring Program) were used as future observation wells for the predictive model simulations. The wells are distributed in the West Valley, Mid Valley, and East Valley areas, and future simulated water levels for each scenario are plotted in a series of hydrographs for each well) (see Section 7.7.1.2).
7.7 Results
Modeling results are presented first in Section 7.7.1 for the Baseline and Baseline with Climate Change scenarios, allowing direct evaluation of the effect of simulated climate change on groundwater levels and storage. Results are shown in terms of the respective water balances, cumulative change in storage, selected hydrographs, and groundwater level change maps.
Section 7.7.2 presents modeling results for all four scenarios with climate change: Baseline with Climate Change, 5-Year Plan with Climate Change, Future Projects with Climate Change, and Extended Agriculture with Climate Change. Results of these scenarios are shown together to allow comparison in terms of model inflows, simulated pumping, simulated drain flow, simulated net outflow to Salton Sea, hydrographs, and maps showing change in groundwater levels.
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Indio Subbasin Water Management Plan Update 7-66 TODD/W&C
7.7.1 Baseline Scenarios - Impact of Climate Change
As discussed in 7.5.1, two separate future hydrological periods were developed so that the GSAs could assess the impacts of climate change. The Baseline scenario was run assuming no change in hydrologic conditions (repeated local hydrology of 1970 to 2019). A second simulation was run for Baseline with Climate Change (repeated local hydrology 1995 to 2019 two times - first backward and then forward). The availability of imported water is also impacted by expected climate change. As discussed in Section 7.5.2 and 7.6.1, SWP reliability is assumed to be reduced by an additional -1.5 percent and Colorado River water deliveries are assumed to be reduced by 24,500 AFY under the climate change scenario as compared to Baseline by 2045.
7.7.1.1 Water Budget – Baseline Scenarios
Figure 7-28 shows the water balances for the scenarios of Baseline and Baseline with Climate Change for the 50-year period 2020 to 2069.
The Baseline scenario (upper Figure 7-28) reflects the expected inflows from natural infiltration and imported water based on the repeated hydrologic conditions of the past 50 years. Mountain front and stream recharge observed over the past 50 years was repeated as model input, and imported water was reduced by an additional -1.5 percent to account for decreased availability of SWP supplies, and Colorado River supplies were reduced by -24,500 AFY, as discussed in Section 7.5.1 and 7.5.2. The chart shows the simulated total annual inflows and outflows between 2020 and 2069 by source, along with simulated annual (black line on the chart) and cumulative (orange line on chart) change in storage. A key difference between the Baseline scenario and Baseline Scenario with Climate Change is the hydrological variability.
The Baseline scenario is characterized by a high average inflow due in part to several wet years that occurred in the 50-year period. These wet years, which occur early in the simulation, provide an increase in storage that serves as a buffer for the end of the model simulation when drought conditions reduce change in storage. Over the planning period, the model simulation shows a 486,000 AF increase in storage by the end of 2045.
In contrast, Baseline with Climate Change (lower Figure 7-28) simulates a drier period of record, with the last 25 years repeated twice and with reductions in imported water (Section 7.5.2). The climate change scenario begins the simulation with drier conditions and does not include the very wet years previously observed in the basin. Without the wet years, the annual change in storage remains close to zero and inflows and outflows generally balance, but cumulative storage does not increase in the early years as in the Baseline. In fact, by the end of the 25-year planning period after drought conditions are repeated, the model shows a cumulative decline in storage amounting to 96,000 AF. Climate change is also assumed to impact imported water availability. While all scenarios assume 45 percent reliability of SWP supplies, the climate change scenarios assume an additional reduction in reliability of -1.5 percent by year 2045.
Further, given the tendency to recurring drought in climate change conditions, those scenarios assume CVWD will contribute to California’s Lower Basin DCP allotment for Colorado River water.
Figure 7-29 shows the cumulative change in groundwater storage for Baseline and for Baseline with Climate Change. The impact of additional inflow in the early part of the simulation in the baseline scenario is evident. By 2033, the Baseline scenario has an additional 553,000 AFY more groundwater in storage over Baseline with Climate Change and by 2044, the Baseline scenario has a cumulative change in storage of 631,000 AFY more than the Baseline with Climate Change. For the rest of the model simulation, 2045
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Indio Subbasin Water Management Plan Update 7-67 TODD/W&C to 2069 when hydrology is the same for both scenarios, this difference in cumulative storage is maintained because both simulations use the observed data from most recent 25 years for this period.
Figure 7-28. Annual Model Water Budget for Baseline with Climate Change
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Indio Subbasin Water Management Plan Update 7-68 TODD/W&C Figure 7-29. Cumulative Change in Storage for Baseline and Baseline with Climate Change
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Indio Subbasin Water Management Plan Update 7-69 TODD/W&C These scenarios reflect the same management actions and existing projects. The only difference is the projected hydrology with and without climate change, which is beyond the control of the GSAs. Because the actual future hydrology is unknown and will likely be affected by climate change, it is critical that GSAs assess their existing and planned projects assuming constraints to local and imported surface water supplies. Simulating the management actions and projects under a range of hydrologic conditions helps to evaluate the effectiveness of these actions.
7.7.1.2 Simulated Hydrographs – Baseline Scenarios
Simulated water levels from the 12 model observation wells were used to illustrate the predicted groundwater level changes for Baseline and Baseline with Climate Change. Simulated 1997 to 2019 water levels for the wells are included to provide context for the future scenarios.
Figure 7-30 and Figure 7-31 show the simulated groundwater elevation hydrographs for Baseline and Baseline with Climate Change scenarios in the West Valley and East Valley, respectively. Historical groundwater levels are shown in black. Baseline conditions are shown with solid blue lines on the graphs, while Baseline with Climate Change levels are shown as the dashed lines. All hydrographs use a 300-foot elevation range on the hydrographs.
West Valley/Palm Springs Subarea
The three observation wells in the Upper West Valley/Palm Springs Subarea (hydrographs along the left side of Figure 7-30) show dynamic fluctuations associated with recharge events at the WWR-GRF, with water level mounding and recovery cycles muted in wells located down the valley. For both scenarios, the larger fluctuations are observed in Well 03S04E20F01S near the WW-GRF, as was observed in historical level trends. Predicted fluctuations in well 03S04E34R01S in Palm Springs are lower but still reflect water level fluctuations associated with the wet/dry replenishment cycles at the WW-GRF and show a net rise of around 50 feet by 2045, followed by a decrease from 2045 to 2070. Well 04S05E17Q02S farther southeast shows increases of around 40 feet by 2045 with minor dampened fluctuations possibly associated with the WWR-GRF, but also potentially influenced by simulated replenishment at PD-GRF to the south. Predicted groundwater elevations for Baseline for well 03S04E34R01S in Palm Springs are around 60 feet higher than for Baseline with Climate Change at 2045, while predicted levels in Well 04S05E17Q02S are around 30 feet higher in 2045. Levels in both wells show a slight increasing trend between 2020 and 2045, then a stable or slight declining trend for 2045-2070, reflecting the later lower inflow amounts. Overall groundwater levels in this Subarea are proportional to the groundwater recharge.
Future conditions mirror future recharge– in wet years water levels rise and in dry years water levels decline.
West Valley/Garnet Hill Subarea
The two observation wells in the Garnet Hill Subarea (hydrographs along the top of Figure 7-30) show increasing water level trends for both scenarios. Water levels in Well 03S04E17K01S in the northern portion of Garnet Hill and Well 03S05E30G01S in the southern portion of Garnet Hill are predicted to rise 60 to 80 feet by 2045. Part of the water level rise is due to the MSWD Regional WRF that is expected to percolate treated water in the Baseline scenario.
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Indio Subbasin Water Management Plan Update 7-70 TODD/W&C Figure 7-30. Model Baseline Scenario Hydrographs, West Valley 2020-2069
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Indio Subbasin Water Management Plan Update 7-71 TODD/W&C Figure 7-31. Model Baseline Scenario Hydrographs, East Valley 2020-2069
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Indio Subbasin Water Management Plan Update 7-72 TODD/W&C West-Valley/Cathedral City to Indio Area
Predicted water levels in the three observation wells in the mid- and lower-West Valley/ Cathedral City to Indio area (hydrographs along the bottom of Figure 7-30) show slightly increasing to stable trends for the Baseline scenario. Water levels in Wells 04S05E35G03S and 05S06E16A02S in the Rancho Mirage and Palm Desert areas show increasing levels of around 40 feet, in part due to replenishment at WWR-GRF and PD-GRF. Baseline levels in Indio Well 05S075E08Q01S are predicted to be relatively stable from 2020 to 2070. For Baseline with Climate Change, predicted levels in all four wells are around 20 feet lower than for Baseline, the result being only modest increases in levels in the Rancho Mirage and Palm Desert wells, and slightly declining levels in Indio between 2045 and 2070.
East Valley/La Quinta, Thermal, Mecca, and Oasis Areas
Predicted water levels in the four observation wells in the East Valley areas (Figure 7-31) show stable to slightly decreasing trends for the Baseline scenario. Only minor differences are observed in the simulations for the Baseline with Climate Change scenario.
7.7.1.3 Simulated Change in Water Level Maps – Baseline Scenarios Simulated changes in water levels for the Baseline and Baseline with Climate Change scenarios between 2009 and 2045 are shown (Figure 7-32 and Figure 7-33). 2009 was selected as the period for comparison because it generally reflects historically low groundwater elevations in most of the Subbasin, and these values are used as sustainability criteria for groundwater levels. As detailed in Section 7.5, the Baseline scenarios reflect no new additional projects and the two model simulations simulate different future hydrologic conditions to assess the range of possible outcomes of this no project scenario.
These color-fill contour maps illustrate predicted spatial trends in water level declines or increases across the Subbasin for the scenarios. Simulated changes in water levels are shown for Model Layer 4, representing the deep aquifer. Figure 7-32 shows the predicted change in groundwater levels between the recent historical low, 2009, and the end of the planning period, 2045, for the Baseline scenario and reveals that minor declines (less than 25 feet) would occur in a small area north of the Mid-Valley around Indio. Groundwater level increases would occur in the uppermost West Valley, Garnet Hill, and most of the lower East-Valley areas.
Figure 7-33 shows the predicted changes in levels for Baseline with Climate Change and shows that larger declines (up to 50 feet) would occur under this scenario in the Mid-Valley area north of Palm Springs.
Smaller groundwater level increases are predicted in the uppermost West Valley, Garnet Hill, and most of the lower East-Valley areas, as compared with the Baseline scenario.
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Indio Subbasin Water Management Plan Update 7-73 TODD/W&C Figure 7-32. Change in Groundwater Levels, 2009-2045 Baseline Scenario
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Indio Subbasin Water Management Plan Update 7-74 TODD/W&C Figure 7-33. Change in Groundwater Levels, 2009-2045, Baseline Scenario with Climate Change
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Indio Subbasin Water Management Plan Update 7-75 TODD/W&C
7.7.1.4 Baseline Scenarios Summary
Collectively, the simulated hydrographs and changes in water levels maps for the Baseline and Baseline with Climate Change scenarios indicate that both local increases in future groundwater levels and decreases in levels are predicted. The local differences may be due in part to assumptions regarding the future distributions of replenishment at the GRFs, return flows, and pumping. Regardless, a net increase in Subbasin-wide storage is predicted for the Baseline scenario, while a decrease in total Subbasin storage is predicted for Baseline with Climate Change. In the climate change scenario, simulated groundwater levels are up to 25 feet lower in portions of the Mid-Valley with smaller increases in levels in the West and East Valley than in the baseline scenario without climate change.
The baseline scenarios with and without climate change simulate the same management scenarios under different future hydrology. The differences in water levels and the water budget scenarios highlight the potential range of response under different hydrology, a variable that is not controlled by the GSAs. The baseline scenario with climate change indicates a negative change in storage and does not meet the sustainability goals defined by the GSA. To prepare for an uncertain future, the GSAs are planning for impacts from climate change by assessing future management scenarios under the climate change hydrology and also through adaptive management that will assess the changing groundwater basin.
7.7.2 Climate Change Scenarios – Baseline and with Projects In addition to the Baseline with Climate Change scenario, three other scenarios were simulated to assess planned projects and supply conditions in the near-term (5 years) and planning horizon (25 years) on the Subbasin. These four scenarios were simulated with both the 50-year hydrology and the climate change hydrology. Only the climate change versions of those scenarios are presented here, as the Indio GSAs are committed to achieving sustainability under changing climate conditions.
7.7.2.1 Water Budget – Scenarios with Climate Change
As described in Section 7.5, additional future scenarios were developed to simulate projects included in the GSAs’ 5-year capital improvement plans, future projects, and potential expanded agricultural areas.
Natural inflow, municipal return flows, and golf return flow amounts remain the same for each scenario.
As shown on Figure 7-27, average inflow for groundwater replenishment and wastewater percolation differs between scenarios, reflecting the addition of projects that utilize imported and recycled water for direct use rather than indirect use through replenishment and percolation. Of the scenarios simulated with climate change, the Baseline with Climate Change scenario simulated the greatest average annual inflow to the Subbasin (more than 408,000 AFY) because of increased direct use under other scenarios, while Expanded Agriculture with Climate Change simulates the least inflow (367,000 AFY). However, the difference between these scenarios for the planning period (2020 to 2045) is only ten percent of the total inflow.
Figure 7-34 shows total inflow for all scenarios with climate change assumptions. Note the peaks and valleys are a product of simulating annual variability for wet and dry years. Hydrology plays a critical role for basin inflows because natural infiltration varies based on year type and the volume of available SWP exchange water also varies greatly based on year type. As shown on Figure 7-27, the Future Projects with Climate Change scenario has less average inflow in the first 25 years than Baseline, Baseline with Climate Change, and 5-Year Plan with Climate Change scenarios; this reflects the assumed new source substitution projects coming online to deliver Canal water directly to users. The Expanded Agriculture shows the least
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Indio Subbasin Water Management Plan Update 7-76 TODD/W&C total inflow because additional imported water is delivered to users to meet the increased demand, rather than recharged at GRFs.
Figure 7-35 shows the differences in pumping between the scenarios. As described above, planned source substitution projects will increase the volume of direct deliveries of imported and recycled water and offset a comparable volume of pumping. As described in Section 7.5, these volumes differ among scenarios based on simulated projects. The Baseline scenario assumes expected increases in demand will be satisfied by increased pumping. For the 5-Year Plan with Climate Change and Future Projects with Climate Change scenarios, the new direct delivery connections decrease pumping. The Expanded Agriculture with Climate Change scenario shows a slight increase in pumping over the Future Projects with Climate Change scenario, reflecting an expected increase in agricultural pumping due to the increase in demand. Fifteen percent of the new irrigated agricultural area is assumed to be served by groundwater, with the rest served through direct delivery of Canal water.
Figure 7-36 shows the cumulative change in groundwater storage for the four climate change scenarios.
In the Future Projects with Climate Change scenario, decreased pumping and similar levels of inflow to the other climate change scenarios result in an increase in groundwater storage of 1,394,000 AF at the end of the 50-year simulation. The Expanded Agriculture with Climate Change scenario shows less cumulative storage change due to increased agriculture pumping and reduced groundwater replenishment as increased demands are met by direct delivery of Canal water. The change in storage for Expanded Agriculture with Climate Change is 588,000 AF at the end of the 50-year simulation, while the cumulative storage change for the 5-Year Plan with Climate Change scenario is 691,000 AF. Baseline with Climate Change is the only scenario that results in a negative cumulative change in storage after the 50- year simulation, approximately 542,000 AF is expected to be removed from storage. All scenarios show a net increase in storage at the end of the 25-year planning horizon, followed by declining storage through 2069 for Baseline with Climate Change only, net stable storage for 5-Year Plan with Climate Change projects, and increasing storage for Future Projects with Climate Change and Expanded Agriculture with Climate Change.
Simulated drain flow for the four climate change scenarios is shown Figure 7-37, along with the historical simulated and observed volumes for comparison context. The volume of drain flows is calculated by the model based on defined drain locations, depths, and hydraulic conductance parameter, and predicted groundwater levels at the drains. When groundwater is simulated as rising to or above the drain elevation, groundwater is removed via the drains, with larger amounts of drain flow predicted for higher groundwater elevations. For the Baseline with Climate Change scenario, drain flows are predicted to decline from around 45,000 to 30,000 AFY. The Future Projects with Climate Change scenario involve a decrease in pumping in the East Valley that results in an increase in drain flow, up to 70,000 AFY. For the Expanded Agriculture with Climate Change scenario, groundwater replenishment is reduced in the scenario at Whitewater and Palm Desert GRF facilities in the East Valley to meet the increased direct delivery demands. This reduction of replenishment, especially at TEL-GRF, results in a decrease of drain flows after 2040 relative to the Future Projects with Climate Change scenario. This can be seen on Figure 7-37 when the volume percolated at TEL-GRF is first reduced, and hydrographs of wells near TEL-GRF (e.g., Well 07S07E02G02S) and drain flows both exhibit declines.
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Indio Subbasin Water Management Plan Update 7-77 TODD/W&C Figure 7-34. Total Model Inflow for Future Scenarios
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Indio Subbasin Water Management Plan Update 7-78 TODD/W&C Figure 7-35. Simulated Pumping for Future Scenarios
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Indio Subbasin Water Management Plan Update 7-79 TODD/W&C Figure 7-36. Cumulative Change in Storage for Future Scenarios
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Indio Subbasin Water Management Plan Update 7-80 TODD/W&C Figure 7-37. Simulated Drain Flow for Future Scenarios FINAL
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Indio Subbasin Water Management Plan Update 7-81 TODD/W&C Figure 7-38 shows the net groundwater discharge to the Salton Sea for the four climate change scenarios.
Predicted groundwater discharge amounts increase between 2020 and 2045, then stabilize or slightly decline. Discharge at 2045 ranges from approximately 4,800 AFY for Baseline with Climate Change to 5,500 AFY for Future Projects with Climate Change and Expanded Agriculture with Climate Change. The amounts do not vary much between the scenarios, because flow is limited by the relatively low conductance value assigned to the Sea boundary condition and because groundwater levels in the area north of the Sea are partially controlled by the drain system.
7.7.2.2 Simulated Hydrographs – Future Scenarios with Climate Change Figure 7-39 and Figure 7-40 show the simulated groundwater elevation hydrographs for the four climate change scenarios in the West Valley and East Valley, respectively. Baseline with Climate Change conditions are shown with blue lines on the graphs, 5-Year Plan with Climate Change as the magenta lines, Future Projects with Climate Change as orange lines, and Expanded Agriculture with Climate Change as the green lines.
West Valley/Palm Springs Subarea
The three observation wells in the Upper West Valley/Palm Springs Subarea (hydrographs along the left side of Figure 7-39) show dynamic fluctuations associated with recharge events at the WWR-GRF for all scenarios, with water level mounding and recovery cycles decreasing in magnitude down the valley. The highest groundwater levels in Well 03S04E20F01S near the WW-GRF and in Well 03S04E34R01S in Palm Springs are predicted for the Future Projects with Climate Change scenario, with the lowest levels simulated for the Expanded Agriculture with Climate Change scenario. By the end of the future simulation, Well 04S05E17Q02S farther southeast shows the lowest levels for the Expanded Agriculture with Climate Change scenario.
West Valley/Garnet Hill Subarea
The two observation wells in the Garnet Hill Subarea (hydrographs along the top of Figure 7-39) show increasing water level trends for all scenarios. Water levels in Well 03S04E17K01S in the northern portion of Garnet Hill and Well 03S05E30G01S in the southern portion of Garnet Hill are predicted to rise 30 to 60 feet by 2070, with the largest rises simulated for the Five-Year Plan with Climate Change scenario.
Mid-Valley/Cathedral City to Indio Area
Predicted water levels in the three observation wells in the Mid-Valley/ Cathedral City to Indio area (hydrographs along the bottom of Figure 7-39) show slightly to moderately increasing to stable trends for all scenarios, except the Baseline with Climate Change scenario. Groundwater levels in Well 04S05E35G03S near Rancho Mirage increase 80 feet for the Future Projects Scenario, with Wells 05S06E16A02S in Palm Desert and Well 05S075E08Q01S in Indio also showing the greatest increases for Future Projects with Climate Change. Simulated levels for the 5-Year Plan with Climate Change and Extended Agriculture with Climate Change scenarios also rise in all wells, while levels decline slightly in all wells for the Baseline with Climate Change scenario.
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Indio Subbasin Water Management Plan Update 7-82 TODD/W&C Figure 7-38. Simulated Salton Sea Net Outflow for Future Scenarios FINAL
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Indio Subbasin Water Management Plan Update 7-83 TODD/W&C Figure 7-39. Model Future Scenario Hydrographs, West Valley 2020-2069
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Indio Subbasin Water Management Plan Update 7-84 TODD/W&C Figure 7-40. Model Future Scenario Hydrographs, East Valley 2020-2069
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Indio Subbasin Water Management Plan Update 7-85 TODD/W&C East Valley/La Quinta, Thermal, Mecca, and Oasis Areas
Predicted water levels in the four observation wells in the East Valley areas (Figure 7-40) show slightly decreasing trends for the Baseline with Climate Change and Extended Agriculture with Climate Change scenarios, while levels rise in all wells for Future Projects with Climate Change and 5-Year Plan with Climate Change scenarios.
7.7.2.3 Simulated Change in Water Level Maps – Future Scenarios Simulated changes in water levels for the Future Projects with Climate Change, 5-Year Plan with Climate Change, and Extended Agriculture with Climate Change scenarios between 2009 and 2045 are shown on Figure 7-41 through Figure 7-43. Figure 7-41 shows the predicted change in groundwater levels between 2009 and 2045 for the 5-Year Plan with Climate Change scenario and reveals that minor declines (less than 25 feet) are occur in this scenario in a small area near the City of Coachella in the East Valley area. Level increases are predicted in the uppermost West Valley, the southern portion of Garnet Hill, and most of the Mid-Valley and East Valley areas. Level rises in the Mid-Valley may be associated with simulated operation of the PD-GRF.
Figure 7-42 shows the predicted changes in levels for the Future Projects with Climate Change scenario and similar changes occur for this scenario in the West- and Mid-Valley areas. No declines are predicted except in a very small area where the Whitewater River enters the subbasin.
Figure 7-43 shows the predicted change in groundwater levels between 2020 and 2045 for the Expanded Agriculture with Climate Change scenario. Minor declines (less than 25 feet) occur in this scenario in small areas near the Cities of Indio and Coachella. This decline is likely due to the reduction in groundwater replenishment as expanded agriculture increases the direct delivery of imported water. Level increases are predicted in the Upper West Valley and southern portion of the East Valley. These increases in the Upper West Valley are similar to the groundwater elevation rises observed in all scenarios, a result of continued groundwater replenishment at WWR-GRF.
Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-86 TODD/W&C Figure 7-41. Change in Groundwater Levels, 2009-2045, 5-Year Plan Projects Scenario with Climate Change
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Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-87 TODD/W&C Figure 7-42. Change in Groundwater Levels, 2009-2045, Future Projects Scenario with Climate Change
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Chapter 7: Numerical Model and Plan Scenarios FINAL
Indio Subbasin Water Management Plan Update 7-88 TODD/W&C Figure 7-43. Change in Groundwater Levels, 2009-2045, Expanded Agriculture Scenario with Climate Change
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Indio Subbasin Water Management Plan Update 7-89 TODD/W&C
7.8 Conclusions
Simulation of the Baseline (No New Projects) and Baseline with Climate Change scenarios allows direct evaluation of the effect of simulated climate change on groundwater conditions. As indicated in this chapter, a net increase in Subbasin-wide storage is predicted for the Baseline scenario, but a net decrease in Subbasin storage is predicted for Baseline with Climate Change. With climate change, not implementing new projects is not sustainable.
The major conclusion from simulation of the other three Plan scenarios—5-Year Plan with Climate Change, Future Projects with Climate Change, and Expanded Agriculture with Climate Change—is that the Indio GSAs can maintain a sustainable Subbasin water balance with planned projects for the near-term and future. The three Plan scenarios involve varying project implementation and/or agricultural demands. For all three of these scenarios, simulation results show a net increase in storage at the end of the 25-year planning horizon and continuing stability through the end of the modeling timeframe. The three scenarios show storage increases in the Mid-Valley and most of the East Valley and varying levels of water level declines in the West Valley, which are an artifact of wet and dry year cycles and the subsequent rapid response of groundwater levels near WWR-GRF. These results demonstrate the importance to the Indio Subbasin balance of a portfolio of projects and management actions that allow adjustments through time and across the Subbasin.
Simulation of the 5-Year Plan with Climate Change scenario shows that already-planned projects and management actions can maintain the water balance, even with climate change, while the Future Projects with Climate Change scenario demonstrates that future projects can address uncertainty in water supply, water demand, and other circumstances and maintain the Subbasin water balance.
While the GSAs have a suite of potential projects that can maintain the Indio Subbasin water balance, adaptive management will be critical when planning for future conditions to ensure the most effective projects are implemented in areas where additional resources are needed.
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Indio Subbasin Water Management Plan Update 7-90 TODD/W&C
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Chapter 8: Regulatory and Policy Issues FINAL
Indio Subbasin Water Management Plan Update 8-1 TODD/W&C CHAPTER 8: REGULATORY AND POLICY ISSUES
This chapter describes regulatory and policy issues that could affect implementation of this 2022 Indio Subbasin Alternative Plan Update (Alternative Plan Update). While these issues may represent challenges, the intent of this chapter is to define the issue, identify potential solutions, and consider opportunities.
The 2010 Coachella Valley Water Management Plan Update (2010 CVWMP Update) (Coachella Valley Water District [CVWD], 2012) identified emerging issues and these are updated below; some are updated briefly only in this chapter, and some are discussed in detail in other chapters of this Alternative Plan Update.
This Alternative Plan Update has included recognition of additional issues including:
• Availability of suitable water supply for small community water systems, some of which may lack access to safe and adequate water supplies (see Section 8.4) • Potential occurrence and adverse effects on water supply of per- and polyfluoroalkyl substances (PFAs), a group of man-made chemicals that are persistent in the environment and in the human body, where they can lead to adverse human health effects (see Section 8.2.7)
8.1 Water Quality Policies and Planning
The 2010 CVWMP Update described emerging issues regarding the Colorado River Basin Plan, anti- degradation policy, recycled water policy, Salt and Nutrient Management Plan (SNMP), salinity management, brine management, and agricultural discharge requirements. While no longer emerging issues, the policies and regulations of the State Water Resources Control Board (SWRCB) and Regional Water Quality Control Board (RWQCB) are the subject of continuing review and update by state agencies, and accordingly, warrant regular review by the Groundwater Sustainability Agency (GSAs).
8.1.1 Basin Plan
California’s 1969 Porter-Cologne Water Quality Act established the SWRCB and the nine RWQCBs to preserve and enhance all beneficial uses of the state's water. The RWQCBs develop basin plans that identify beneficial uses for groundwater and surface water within their hydrologic units, establish water quality objectives (WQOs) to protect beneficial uses, and define implementation programs to achieve WQOs. The Basin Plan for the Colorado River Basin Region (Colorado River RWQCB 1993; 2006; as amended) was first prepared and adopted by the Colorado River Basin RWQCB in 1993 and with subsequent amendments. Prepared in accordance with the Porter-Cologne Water Quality Control Act, the Federal Clean Water Act, and other state and federal rules and regulations, the Basin Plan provides guidelines for optimizing use of state waters within the region by preserving and protecting water quality.
The 2010 CVWMP Update reviewed the Basin Plan adopted in 2006 (Colorado River Basin RWQCB, 2006).
This review addressed updates on the Clean Water Act 303(d) list of impaired water bodies, Total Maximum Daily Loads (TMDLs) for surface water bodies, and high priority issues identified as part of the 2007 Triennial Review. These issues mostly were surface water related, including for example, surface water bacteriological objectives, stormwater channel flow, and agricultural wastewater. The current 303(d) list, TMDLs, and selected topics of the most recent Triennial Review are summarized in this section.
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Indio Subbasin Water Management Plan Update 8-2 TODD/W&C
8.1.1.1 303(d) List and TMDLs
Section 303(d) of the federal Clean Water Act requires states, territories, and authorized tribes to prepare a list of water bodies that do not or are not expected to attain water quality standards after application of required technology-based controls. The 303(d) list includes the size of the water body, the sampled pollutants affecting designated beneficial uses, the source of the pollutant, and the water body’s priority status relative to TMDLs. TMDLs are established to limit discharged pollutants and help overcome water quality impairment. TMDLs are implemented through amendments to the Basin Plan or an alternative TMDL plan may be put in place. The 303(d) lists are prepared as part of the Water Quality Assessment of the State’s major waterbodies and meet a requirement of Section 303(d) of the Clean Water Act.
Table 8-1 summarizes approved TMDLs for the Coachella Valley Stormwater Channel (CVSC), while Table 8-2 lists TMDLs under development for the CVSC. Table 8-3 summarizes TMDLs under development for the Salton Sea Watershed.
Table 8-1. Approved TMDLs for the CVSC
Indicator Parameter 30-Day Geometrica Mean Maximum Instantaneous E. coli 126 MPNb/100ml 400 MPN/100ml
Fecal coliform 200 MPN/100ml --- c
Enterococci 33 MPN/100ml 100 MPN/100ml
a Based on a minimum of no less than 5 samples equally spaced over a 30-day period. b Most probable number.
c No more than 10 % of total samples during any 30-day period exceed 400 MPN per 100 ml.
Source: Amendment to Water Quality Control Plan for the Colorado River Basin Region
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Indio Subbasin Water Management Plan Update 8-3 TODD/W&C Table 8-2. TMDLs Under Development for CVSC
TMDL Project Title Impairments Completion Date Comments Coachella Valley Stormwater
Channel - Organochlorine
Compounds TMDL Alternatives
Dichlorodiphenyl-trichloroethane (DDT) June 2022 -
November 2022
The CVSC is 303(d) listed for multiple impairments.
The SWRCB is working on a TMDL Alternative that
will be a part of the Coachella Valley Agricultural
General Order.
Dieldrin
Polychlorinated biphenyl (PCB)
Toxaphene
Coachella Valley Stormwater
Channel - Ammonia, Dissolved
Oxygen, and Toxicity TMDLs
Ammonia September 2024 -
February 2025
The CVSC is 303(d) listed for multiple impairments.
The SWRCB is working on a TMDL Plan to address
these issues. Dissolved Oxygen
Toxicity
Source: Water Quality Control Plan for Colorado River Basin Triennial Review 2020 Appendix B Table 8-3. TMDLs Under Development for the Salton Sea Watershed TMDL Project Title Impairments Completion Datea Comments Salton Sea - Dissolved Oxygen
and Nutrients TMDLs
Dissolved Oxygen December 2023 -
May 2025
The Salton Sea is 303(d) listed for multiple impairments. The SWRCB is working on a TMDL Plan for the entire watershed. Nutrients Salton Sea - Watershed
Ammonia TMDL
Ammonia 48 - 54 monthsb The Salton Sea is 303(d) listed for ammonia. The SWRCB is proposing a TMDL for the entire watershed.
Salton Sea - Toxicity TMDL Toxicity 30 - 36 monthsb The Salton Sea is 303(d) listed for toxicity. The SWRCB is proposing a TMDL at the Salton Sea.
Salton Sea - DDT and DDE
TMDLs
Dichlorodiphenyl-
trichloroethane (DDT)
24 - 30 monthsb The Salton Sea is 303(d) listed for DDT and DDE. The SWRCB is proposing a TMDL for the Salton Sea.
Dichlorodiphenyl-
dichloroethylene (DDE)
Salton Sea Watershed -Bacteria
TMDL
Enterococcus 36 - 42 monthsb The Salton Sea is 303 (d) listed for indicator bacteria. The SWRCB is proposing a TMDL for the entire watershed.
a For ongoing projects, the completion date is the expected implementation date of the TMDLs. b For these new projects, no completion date is available until the project commences. The duration is the expected amount of time it will take for the TMDL to go into effect once the project commences.
Source: Water Quality Control Plan for Colorado River Basin Triennial Review 2020 Appendix B
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Indio Subbasin Water Management Plan Update 8-4 TODD/W&C
8.1.1.2 Triennial Review
The Federal Clean Water Act requires states to conduct public review of water quality standards at least once every three years. Accordingly, the RWQCB conducts a public review process and updates the Basin Plan at least once every 3 years – a process known as “triennial review.” The triennial review may result in amendments to the Basin Plan over the course of the 3-year review cycle.
The most recent Triennial Review for the Colorado River Basin Region was conducted in 2020 (RWQCB, 2020b). Recent triennial reviews are presented on the RWQCB website 1 including the Staff Report and Appendices B and C that list and rank proposed projects (Colorado River Basin RWQCB, 2020). During this Triennial Review, 29 projects have been listed and ranked. Three projects (as numbered by RWQCB) with particular bearing on local water management are summarized below.
Project 9 – OWTS Prohibitions in Areas Where OWTS Pose a Threat to Water Quality This project was included in the 2017 Triennial Review as Item 1, "Evaluate Potential Sources of Nitrates in Prioritized Basins." RWQCB staff has been collecting data and information to identify areas where nitrate pollution from Onsite Wastewater Treatment Systems (OWTS), also referred to as septic systems, may be posing a threat to groundwater quality. In areas where the density of existing OWTS may be contributing to nitrate and other pollution, and the OWTS density cannot be mitigated by existing regulations, staff plans to propose a prohibition of discharge from OWTS. This project is slated for completion in 2025. This RWQCB project represents a potential means of limiting nitrate loading to areas in the Indio Subbasin with relatively dense OWTS. These areas also may include Small Water Systems that are affected by high nitrate concentrations in groundwater (see Section 8.4).
Project 10 – Salton Sea Beneficial Use Review
The Coachella Valley is part of the Salton Sea watershed. As described in the RWQCB Staff Report Appendix B, the Salton Sea is an endorheic (terminal) lake without an outlet, which means that certain pollutants have been concentrating in it since its formation in 1905. Such pollutants include salinity and one of its components, chloride, which are both 303(d) listed impairments to the Salton Sea's Warm Freshwater Habitat (WARM) beneficial use. The Salton Sea is not freshwater and because of its endorheic nature may never meet the current water quality objectives for these pollutants associated with the WARM beneficial use. Under this amendment, staff will determine whether WARM is attainable for these pollutants and establish whether the Salton Sea should be considered a saltwater body for the purposes of applicable water quality objectives. Other pollutants and/or beneficial uses may be included as data are gathered and analyzed. Based on the results of this analysis, changes to the Salton Sea's beneficial uses may be proposed. This project is scheduled for completion between December 2024-May 2025.
Project 12 – Groundwater Numeric Water Quality Objectives in Indio Subbasin This project was included in the 2017 Triennial Review as Item 2, "Establish Water Quality Objectives for Ground Water Throughout the Coachella Valley." RWQCB staff is developing site-specific numeric water quality objectives for total dissolved Solids (TDS) and other constituents in the Indio Subbasin. To help establish appropriate water quality objectives, in 2021 RWQCB initiated a 3-year contract with United States Geological Survey (USGS) to determine existing water quality. Establishment of numeric water
1 https://www.waterboards.ca.gov/coloradoriver/
Chapter 8: Regulatory and Policy Issues FINAL
Indio Subbasin Water Management Plan Update 8-5 TODD/W&C quality objectives by RWQCB for TDS and other constituents could have a significant impact on definition of minimum thresholds for the constituents in the Indio Subbasin.
8.1.2 Antidegradation Policy
The Antidegradation Policy (SWRCB Resolution No. 68-16) is a state water policy that requires regulation of discharges to waters of the state to achieve the “highest water quality consistent with maximum benefit to the people of the State.” Incorporated into all Basin Plans, the policy applies to high quality waters (surface water as well as groundwater) and requires that the high quality be maintained unless the State finds that any change will be consistent with maximum benefit to the people of the State, will not unreasonably affect beneficial uses, and will not result in water quality lower than applicable standards.
The Antidegradation Policy also requires the waste discharge requirements for any proposed discharge to covered waters include the best practicable treatment or control (BPTC) of the discharge to assure that no condition of pollution or nuisance will occur, and that the highest water quality will be maintained consistent with maximum benefit to the people of the State.
In November 2012, the California Third District Court of Appeal issued an opinion in the case “Asociacion de Gente Unida Por El Agua v. Central Valley Regional Water Quality Control Board” (2012) 210 Cal.App.4th 1255 that interpreted the Antidegradation Policy. The Court held that the Antidegradation Policy applies whenever there is “an existing high quality water” and “an activity which produces or may produce waste …that will discharge into such high quality water.” The Court of Appeal determined that a high quality water exists where the baseline water quality (defined to be the best water quality that has existed since 1968) is better than the WQO. If the baseline water quality is equal to or is not meeting the objectives, the water is not “high quality” and all discharges must be managed to meet the current objectives. In that case, the Antidegradation Policy is not triggered. However, if the baseline water quality is better than the WQOs, the baseline water quality must be maintained unless the maximum benefit to the people of the State and related findings required by the Antidegradation Policy are made to permit the discharge.
As described in Section 8.1.4, a Salt and Nutrient Management Plan (SNMP) meeting the requirements of the Recycled Water Policy is required for certain designated basins in California. SNMPs must include an antidegradation analysis demonstrating that the existing projects, reasonably foreseeable future projects, and other sources of loading to the basin included within the plan will, cumulatively, satisfy the requirements of the Antidegradation Policy. In 2015, a Coachella Valley SNMP was prepared and submitted to the Regional Board. The Regional Board provided comments and recommendations on the 2015 SNMP, and as of 2020 a group of local stakeholders are developing a new SNMP, which will include a full antidegradation analysis consistent with the Antidegradation Policy.
8.1.3 Recycled Water Policy
In the Plan Area, recycled water is a significant and reliable local resource used to help offset groundwater pumping. Recycled water has been used for golf course irrigation in portions of the Plan Area since the late 1960s. CVWD and Desert Water Agency (DWA) currently deliver recycled water from three water reclamation plants (WRPs) for municipal and golf course irrigation use in the East and West Valley.
The SWRCB, recognizing the importance of recycled water as a water supply, administers the Recycled Water Policy (adopted in 2009) to encourage the increased use of recycled water and to support water supply diversity and sustainability. The Recycled Water Policy defines the roles of the SWRCB, RWQCBs, and California Department of Water Resources (DWR) among other agencies. DWR responsibilities
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Indio Subbasin Water Management Plan Update 8-6 TODD/W&C relevant to Indio Subbasin management include reviewing urban water management plans, cooperating with SWRCB to track recycled water use, implementing the Sustainable Groundwater Management Act (SGMA), and cooperating with SWRCB to allocate and distribute bond funding.
By way of update, on December 11, 2018, the SWRCB adopted an amendment to the Recycled Water Policy that includes the following goals (SWRCB, 2018) and supports water recycling in the Plan Area:
• Increase the use of recycled water State-wide from 714,000 acre-feet per year (AFY) in 2015 to
1.5 million AFY by 2020 and to 2.5 million AFY by 2030. • Reuse all-dry weather direct discharges of treated wastewater to enclosed bays, estuaries and coastal lagoons, and ocean waters that can be viably put to a beneficial use. • Maximize the use of recycled water in areas with groundwater overdraft, to the extent that downstream water rights, instream flow requirements, and public trust resources are protected.
Annual reporting is required so that SWRCB can evaluate progress toward these goals and revise them as needed. Specific requirements address monthly volumes of influent and wastewater production, specifying level of treatment. Discharge data must specify where the discharge occurs, for example to surface waters (specifying volume required to maintain minimum instream flow), natural systems (wetlands, wildlife habitats, and duck clubs), injection wells and land disposal (e.g., evaporation or percolation ponds). Water reuse must be reported in terms of monthly volume with annual reporting of the distribution to beneficial uses including the following categories: agricultural irrigation, landscape irrigation, golf course irrigation, commercial applications, industrial applications, geothermal energy production, and other non-potable uses (e.g., dust control, flushing sewers, fire protection). Such reporting also must address direct and indirect potable uses such as groundwater recharge, seawater intrusion barriers, reservoir water augmentation, raw water augmentation, and other potable uses.
8.1.4 Coachella Valley Salt and Nutrient Management Plan While encouraging the use of recycled water, the Recycled Water Policy states that salts and nutrients from all sources must be managed on a basin-wide or watershed-wide basis to attain water quality objectives and protect beneficial uses. This is typically through development of a SNMP. As described in this section, the CV-SNMP currently is being planned by local agencies in collaboration with the Colorado River RWQCB.
The original 2009 Recycled Water Policy required development of a SNMP by 2014 for each groundwater basin or subbasin in California (later clarified as applicable to priority basins for the GAMA Priority Basin Project). The 2018 Recycled Water Policy amendment includes a requirement that each RWQCB evaluate each basin or subbasin in its region before April 8, 2021. The RWQCB is required to identify basins where salts and/or nutrients are a threat to water quality and therefore need salt and nutrient management planning to achieve water quality objectives in the long term. These RWQCB evaluations are to be updated every 5 years.
The amended Recycled Water Policy continues to encourage collaborative development of a SNMP among SNMP groups, regional boards, the agricultural community, IRWM groups, water and wastewater agencies, stakeholders, and now, GSAs. It notes that some GSPs may sufficiently address salt and nutrient management to be a functionally equivalent SNMP. The current policy presents the required components of a SNMP, including a monitoring network and plan, water recycling use goals and objectives, salt and
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Indio Subbasin Water Management Plan Update 8-7 TODD/W&C nutrient source identification, implementation measures, and an antidegradation analysis to ensure adherence to the Antidegradation Policy.
Recycled water is used in the Plan Area for non-potable applications including municipal and golf course irrigation. The Recycled Water Policy specifies the levels of treatment for such use of recycled water, while a subsequent general order (SWRCB Order WQ 2016-0068-DDW) provides for permitting, administration, monitoring and reporting. In the Plan Area, three WRPs produce tertiary-treated recycled water consistent with State policy.
The Recycled Water Policy also regulates indirect potable reuse (IPR) for groundwater recharge, which is not currently practiced in the Indio Subbasin. IPR for groundwater recharge involves planned use of recycled water for replenishment of a groundwater basin that is a source of water supply for a public water system; the groundwater basin provides public health benefits, for example through dilution and travel time. As described in Chapter 11, Projects and Management Actions, Indio Water Authority (IWA) is a partner in East Valley Reclamation Authority (EVRA) and is currently evaluating the feasibility of an IPR project to recharge up to 5,000 AFY of recycled water into the Indio Subbasin. While IPR is not currently practiced in Indio Subbasin, it has been used for more than 40 years in other California basins as a reliable, high quality, locally controlled supply and may represent a future option. Accordingly, it is warranted for the GSAs to stay informed of regulatory requirements (including constituents of emerging concern [CECs]) and the experience of other recycling projects.
In 2015, CVWD, DWA, and IWA created an SNMP for the Coachella Valley Groundwater Basin (CVWD, et al., 2015). Subsequently, the 2015 SNMP was evaluated by the Colorado River RWQCB. The RWQCB provided comments and recommendations on the 2015 SNMP’s compliance with the updated Recycled Water Policy (Colorado River Basin RWQCB, 2020). In response, the CV-SNMP was restarted in 2020 by an expanded SNMP agency group that includes all major water and wastewater agencies in Coachella Valley.
These include CVWD, CWA and Coachella Sanitary District, DWA, IWA, Myoma Dunes Mutual Water Company, Valley Sanitary District, Mission Springs Water District, and City of Palm Springs, collectively the SNMP Agencies. As of 2021, SNMP Agencies have submitted a Development Workplan that describes a detailed scope of work for updating the CV-SNMP, including a new groundwater monitoring program to support implementation of the SNMP. The Groundwater Monitoring Workplan was approved by the RWQCB in February 2021. The SNMP Agencies have begun implementing the Groundwater Monitoring Workplan and will report data and program implementation progress for the first year by April 1, 2022.
For the Indio Subbasin, a key issue is the importation of salts with Colorado River water. Importation of Colorado River water for agricultural irrigation (substituting for groundwater pumping) and for groundwater replenishment has been fundamental to reversing chronic groundwater level declines, depletion of storage, subsidence, and seawater intrusion (see Chapter 9, Sustainable Management Criteria). However, Colorado River water has higher average TDS concentrations that must be considered and appropriately managed. As summarized in Section 8.1.5, the 2002 CVWMP and 2010 CVWMP Update have identified and assessed various alternatives for managing salinity. Chapter 9, Sustainable Management, addresses salinity in terms of sustainable management and the role of the CV-SNMP, coordinated with this Alternative Plan Update, in analyzing the salt balance, identifying implementation measures to manage salt loading, and developing an implementation plan to address salinity as well as nutrients.
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Indio Subbasin Water Management Plan Update 8-8 TODD/W&C
8.1.5 Salinity Management
Identified in the 2002 CVWMP and 2010 CVWMP Update as an important issue, salinity management remains a key issue with ramifications for recharge, water recycling, brine management, and agricultural drainage.
8.1.5.1 Impacts of Colorado River Water Recharge
State Water Project (SWP) Exchange supply is provided through the Colorado River Aqueduct (CRA), which delivers water from Lake Havasu (Parker Dam) for recharge at the Whitewater River Groundwater Replenishment Facility (WWR-GRF). Colorado River supply also is provided through the Coachella Canal, a branch of the All-American Canal that brings Colorado River water from Imperial Dam. Water imported via the Coachella Canal is used at the Thomas E. Levy Groundwater Replenishment Facility (TEL-GRF) and Palm Desert Groundwater Replenishment Facility (PD-GRF) groundwater replenishment facilities. TDS concentrations generally are lower for CRA supply (averaging about 590 milligrams per liter (mg/L) from 2010 through 2019), while Coachella Canal supply has averaged about 730 mg/L over the same period. At this time, TDS levels in Colorado River water are meeting or exceeding applicable water quality objectives.
As noted in the 2010 CVWMP Update,
Colorado River water used for direct
delivery and recharge in the Indio Subbasin
generally has higher TDS concentrations
that must be considered and appropriately
managed. Use of Colorado River water
involves salt loading to the Indio Subbasin
and local increases in TDS concentrations
(see Chapter 4, Current and Historical
Groundwater Conditions). CVWD and DWA
have investigated alternatives including
direct importation and recharge of lower
TDS SWP water at the WWR-GRF and MC-
GRF. However, direct importation would
require extensive pipeline construction for
conveyance from western Riverside County and would involve technical and environmental constraints, significant costs, and limited benefits. Another alternative summarized in the 2010 CVWMP Update involved pre-treatment of Colorado River supplies using reverse osmosis. While a proven technology, drawbacks include permitting, environmental issues, and technical and financial feasibility in light of available power and intermittent deliveries of Colorado River water.
Salinity management includes an ongoing, watershed management approach through the Colorado River Basin Salinity Control Program (Program). This is a cooperative watershed effort among several federal agencies and seven states to meet national, international, and state water quality objectives. Federal, state, and local agencies and private organizations participate to implement on-the-ground activities. To guide activities and track performance, the Program has established numeric criteria for salinity, adopted by the seven Basin states and approved by USEPA. These criteria are illustrated by the horizontal lines on Figure 8-1, which is reproduced from the 2020 Review of Water Quality Standards for Salinity, Colorado
Coachella Canal supplies agriculture irrigation demands in the East Valley.
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Indio Subbasin Water Management Plan Update 8-9 TODD/W&C River System (Colorado River Basin Salinity Control Forum, 2020). The graph also shows flow-weighted average annual salt concentrations at three numeric criteria stations, from upstream to downstream:
Below Hoover, Below Parker, and at Imperial. The last two correspond to the diversion points for the CRA and All-American Canal. As shown on Figure 8-1, salinity concentrations have decreased since 1970 at all three numeric criteria stations and waters are currently meeting standards.
These decreasing TDS concentrations reflect work accomplished by the Program which has included construction of salinity control measures (for example, preventing inflow to the river from saline springs and plugging of abandoned, flowing oil, and gas wells), advancement of policies for effluent limitation (for example, policies addressing discharges from fish hatcheries), and implementation of non-point source management plans (for example, improved irrigation practices). While the Program has successfully controlled over 1.22 million tons of salt annually, additional measures have been identified to achieve the identified maximum potential salt reduction of 2.35 million tons per year, equivalent to 106 mg/L at Imperial Dam (Colorado River Basin Salinity Control Forum, 2020). The current plan is to pursue a program designed to remove at least 1.7 million tons annually by 2040, which would result in a 47 mg/L reduction in salinity at Imperial Dam. As of early 2021, the Paradox Valley Unit, which had been removing 95,000 tons of salt annually, was shut down after causing a moderate earthquake and has not been restored by USBR. As of 2021, USBR has taken no action and will work with the Colorado River Basin Salinity Control Forum to explore other options (Montrose Press, 2021).
Figure 8-1. Flow Weighted Average Annual Salt Concentrations at Numeric Criteria Stations
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Indio Subbasin Water Management Plan Update 8-10 TODD/W&C
8.1.5.2 Brine Discharge/ Management
The 2010 CVWMP Update identified brine discharge as a major issue that would be associated with desalination of Colorado River water for municipal or agricultural uses, or replenishment. Desalination of significant flows would result in production of large volumes of brine that would need to be disposed in a cost-effective manner and in compliance with Basin Plan requirements. In discussing Salton Sea restoration, the 2010 CVWMP Update acknowledged that diversion and desalination of drain flows also would reduce inflow to the Salton Sea, with potential environmental impacts. CVWD subsequently piloted desalination of shallow groundwater and not drain flows.
Desalination and brine discharge were also addressed in the 2012 Final Subsequent Program EIR (Final SPEIR) for the 2010 CVWMP Update, which provided comparison of SWP importation and desalination options. The Final SPEIR noted that permitting of discharge of brine to the Salton Sea via wetlands was uncertain. It also generally considered desalination of recharge water as financially infeasible. Similarly, the 2018 IRWM Plan addressed considerations including high costs for handling and disposing brine, large land areas for evaporation ponds, and regulatory issues associated with brine disposal.
As summarized in existing documents, various alternatives have been explored for desalination. These alternatives involve different sources of water for desalination (e.g., CRA, Coachella Canal, drain flows), volumes of supply, methods of storage and conveyance, options for water treatment, and alternatives for brine management and discharge. Continuing issues exist regarding technical feasibility of complex projects, financial feasibility, permitting, and potential environmental impacts. Referring to Section
8.1.1.2, Triennial Review, RWQCB projects could result in water quality objectives that could disallow brine discharge to the Salton Sea. Planning for Salton Sea restoration is ongoing (see Section 8.3), with likely ramifications for brine discharge.
8.1.6 Agricultural Drainage Discharge Regulations
Water discharges from agricultural operations include irrigation runoff, flows from tile drains, and storm water runoff. These discharges can affect water quality by transporting pollutants (for example, pesticides, nutrients, salts, pathogens, and heavy metals) from cultivated fields into surface waters. The quality of receiving surface water bodies and groundwater can be impaired. Groundwater quality is monitored for numerous constituents (see Chapter 4, Current and Historical Groundwater Conditions) and is addressed as an element of sustainable management (see Chapter 9, Sustainable Management).
To control the effects of discharges from irrigated agricultural lands, the SWRCB’s 2004 Nonpoint Source Implementation and Enforcement Policy (NPS Policy) requires all RWQCBs to regulate agricultural discharges by issuing waste discharge requirements (WDRs) or conditional waivers of WDRs (Orders) to growers. These Orders require water quality monitoring of receiving waters and corrective actions when impairments are found. The Conditional Waiver of WDRs for agricultural discharges in the Coachella Valley was adopted in 2014 (RWQCB, 2014).
Agricultural dischargers include entities who operate and maintain agricultural drains (e.g., CVWD) and property owners, renters/lessees, and operators/growers who discharge water, have potential to discharge water, propose to discharge water, or could directly or indirectly affect water quality. The Conditional Waiver does not provide coverage for discharges from crops for personal use, golf courses, polo fields, discharges originating on tribal/reservation lands, or parcels less than five acres.
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Indio Subbasin Water Management Plan Update 8-11 TODD/W&C To comply, the NPS Policy provides for agricultural
dischargers to act individually or collectively in coalition groups. The Coachella Valley Irrigated Lands Coalition
(CVILC) was established in 2013 by CVWD and local
growers/operators to help irrigated agriculture meet the requirements of the Colorado River Basin RWQCB’s
Irrigated Lands Regulatory Program (ILRP) in the Coachella Valley. The CVILC is a membership-based coalition that
implements programs to help farmers and ranchers
reduce their impacts. Programs include best management
practices (BMPs), outreach and education (e.g.,
workshops, information fliers in CVWD billings), and
monitoring of water quality as required by the RWQCB.
To comply with the terms of the 2014 Conditional Waiver and ensure attainment of water quality objectives, the
CVILC developed a Compliance Program in which
members complete an individual Water Quality
Management Plan (Farm Plan) and Drain Water Quality
Management Plan (Drain Plan) and implement
management practices, among other activities. The CVILC also developed a Monitoring and Reporting Program and
a Quality Assurance Project Plan. On November 12, 2020, the Colorado River Basin RWQCB adopted Order R7-2020-0026, which supersedes the 2014 Conditional Waiver. The 2020 Order (RWQCB, 2020a) includes new provisions for the Farm Plan, Drinking Water Supply Well Monitoring, and Education Outreach requirements, among others.
8.2 Groundwater Quality
The 2010 CVWMP Update identified issues including salinity, arsenic, perchlorate, hexavalent chromium(chromium-6), uranium, and nitrate, which also are discussed in Chapter 4, Current and Historical Groundwater Conditions. Carcinogens and Endocrine Disrupting Compounds (EDCs) were also identified as issues in the 2010 CVWMP Update. However, these include a wide variety of chemicals and in many cases, water quality standards have not been established by federal or state regulatory agencies.
Specific issues can be tracked by the GSAs as they emerge.
The GSAs continue to track evolving regulations of emerging contaminants; updates on regulations are provided below for salinity, arsenic, perchlorate, (chromium-6), uranium, and nitrate. For each, the current drinking water standard or Maximum Contaminant Level (MCL) is stated. PFAS are a new emerging issue which is also described below.
8.2.1 Salinity
Salinity is typically expressed in terms of TDS. There is no primary, health-based MCL for TDS; secondary water quality standards are based on consumer acceptance of taste and odor. As indicated in the 2015 SNMP, the California Code of Regulations Title 22 states that there is no fixed consumer acceptance level established for TDS, but there are three Consumer Acceptance Contaminant Level Ranges. Concentrations lower than the Recommended contaminant level (500 mg/L) are desirable for a higher degree of
CVWD samples the drain flows to the
Salton Sea.
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Indio Subbasin Water Management Plan Update 8-12 TODD/W&C consumer acceptance; constituent concentrations ranging to the Upper contaminant level (1,000 mg/L) are acceptable if it is neither reasonable nor feasible to provide more suitable waters; and constituent concentrations ranging to the Short-Term contaminant level (1,500 mg/L) are acceptable only for existing community water systems on a temporary basis pending construction of treatment facilities or development of acceptable new water sources.
The sources and factors affecting the occurrence of salinity are documented in Chapter 4, Current and Historical Groundwater Conditions. Salinity management, the SNMP, and related issues are described in Section 8.1.
8.2.2 Arsenic
Arsenic was identified in the 2010 CVWMP Update as an emerging issue. As discussed in the 2010 CVWMP Update, the primary MCL for arsenic before 2001 was 50 micrograms per liter (μg/L). Under the 1996 Amendments to the Safe Drinking Water Act, the U.S. Environmental Protection Agency (USEPA) was required to publish a revised standard for arsenic by January 2001. USEPA published a final MCL for arsenic of 10 μg/L in 2001, which became enforceable in 2006. California adopted the federal MCL effective November 28, 2008.
As discussed in Chapter 4, Current and Historical Groundwater Conditions, arsenic occurs naturally in groundwater and most of the Indio Subbasin is characterized by arsenic concentrations below the MCL.
However, arsenic is commonly found in groundwater in the southern Subbasin at levels higher than current state and federal drinking water standards. As reported in the 2010 CVWMP Update, Riverside County environmental health officials identified private wells at 19 small community water systems with high levels of arsenic. In response, treatment filters had been installed at about half the systems. All four GSAs provide drinking water supplies that meet all state and federal health standards as documented in their annual water quality consumer confidence reports (available on their respective websites).
CVWD currently operates three water quality treatment facilities in the East Valley to remove naturally occurring arsenic from drinking water before it is delivered to customers. In addition, CVWD is addressing safe drinking water needs through the DAC Infrastructure Task Force. CVWD, in collaboration with the Task Force, completed the East Coachella Valley Water Supply Project (ECVWSP), which identified and mapped small, private water systems; developed a prioritization process that considered criteria such as proximity to existing pipelines, cost, number of people affected and water quality; and conducted preliminary engineering for the top two highest ranked projects. CVWD also has responded to short-term water quality needs. For example, in 2019, CVWD collaborated with Riverside County to provide temporary supplemental water as a safe drinking water supply for Oasis Mobile Home Park in Torres Martinez tribal/reservation lands, which had been found to be out of compliance a few months earlier.
CVWD and the Task Force are seeking grant funds to permanently connect the water system to CVWD (CVWD, May 29, 2020). Lastly, CVWD has responded by providing private well owners with a free water quality test for arsenic and with access to information on point-of-use treatment systems.
8.2.3 Perchlorate
Perchlorate was identified in the 2010 CVWMP Update as an emerging issue because of historical detections in Colorado River supply that originated from two manufacturing facilities and have since been cleaned up to below detection limits (see Chapter 4, Current and Historical Groundwater Conditions).
Perchlorate is hazardous to human health, difficult to remove from water, and resistant to degradation in groundwater. The MCL has been set at 6 μg/L by the State of California, and all four GSAs provide drinking
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Indio Subbasin Water Management Plan Update 8-13 TODD/W&C water supplies that meet or exceed the state and federal standards. In 2015, the State’s Office of Environmental Health Hazard Assessment (OEHHA) published an updated public health goal (PHG) of 1 part per billion (ppb; equivalent to μg/L) for perchlorate in drinking water (OEHHA, 2015). A public health goal is not an enforceable regulatory standard; however, it is intended to provide scientific guidance to the SWRCB Division of Drinking Water (DDW) in reviewing the existing state drinking water standard. State law requires that each regulatory drinking water standard must be set as close to the corresponding PHG as is economically and technologically feasible. Accordingly, the SWRCB will use the PHG to inform its review of the current enforceable regulatory standard for the chemical. In addition, SWRCB has recommended revision of the detection limit for purposes of reporting (DLR) for perchlorate (SWRCB, October 2020). Even though perchlorate detections in Subbasin groundwater are less than 2 mg/L and highly localized (see Chapter 4, Current and Historical Groundwater Conditions), the GSAs continue to monitor perchlorate and to track the review of the perchlorate PHG.
8.2.4 Chromium-6
Hexavalent chromium (chromium-6) was identified in the 2010 CVWMP Update as an emerging issue.
Chromium occurs as trivalent chromium and as chromium-6; while trivalent chromium is non-toxic, chromium-6 has been linked to health effects. Chromium-6 has a complex regulatory history. In 2011, the OEHHA published a PHG of 0.02 ppb (or μg/L) for chromium-6 in drinking water. Subsequently in 2014, the State adopted the country’s first chromium-6 drinking water standard or MCL. That MCL of 10 ppb was then rescinded in 2017 due to a ruling that the state “had failed to consider the economic feasibility of complying with the MCL.” Chromium-6 levels are controlled in California drinking water by existing regulations that include an MCL of 50 ppb for total chromium, which is twice as stringent as the national MCL for total chromium of 100 ppb established by the federal Environmental Protection Agency (EPA).
However, the PHG has not been changed and the SWRCB is working on establishing a new chromium-6 MCL for drinking water. This process could take several years.
Anticipating a potential MCL revision that could affect their groundwater supply, CWA and IWA sponsored a joint study that identified a recommended treatment technology (City of Coachella, 2016). IWA installed chromium-6 removal systems at three wells. CVWD also investigated methods of treating chromium-6 to meet potentially stringent drinking water standards and conducted a successful pilot project to treat water. In addition, local GSAs are tracking and engaging in the regulatory public process. CVWD has provided input to SWRCB, for example, during the SWRCB workshop on the chromium-6 MCL Estimate of Costs (CVWD, 2020).
8.2.5 Uranium
Uranium has a MCL of 20 picocuries per liter (pCi/L), or about 30 μg/L. It was identified in the 2010 CVWMP Update as an emerging issue, reflecting insufficient information at the time regarding potential sources to the Indio Subbasin. However, data now available indicate local geologic sources including bedrock formations to the west and east of the northern Subbasin (see Chapter 4, Current and Historical Groundwater Conditions). DWA has identified high concentrations of uranium as a potential constraint on groundwater supply (DWA, 2016). DWA has sustained the good quality of its delivered water by intermittently ceasing the operation of wells affected by high uranium concentrations. The GSAs monitor for uranium in both groundwater and Colorado River sources used for recharge; all four GSAs provide drinking water supplies that meet the state and federal standards.
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Indio Subbasin Water Management Plan Update 8-14 TODD/W&C
8.2.6 Nitrate
Nitrate has a MCL of 45 mg/L, measured as nitrate. This is equivalent to 10 mg/L measured as nitrogen. It was identified in the 2010 CVWMP Update as a nitrogen compound that is both a nutrient for plants and a human health issue. The sources and occurrence of nitrate are documented in Chapter 4, Current and Historical Groundwater Conditions, while nitrate occurrences in small water systems are summarized in Section 8.4, Small Water Systems, along with CVWD’s ECVWSP, which addresses the issue. Drinking water supplied by the GSAs meets drinking water standards, as documented in their annual water quality consumer confidence reports (available on their respective websites). As a nutrient, nitrate will be addressed in the SNMP update now underway (see Chapter 8, Regulatory and Policy Issues).
8.2.7 PFAS
Emerging contaminants are chemicals that have not been previously monitored or detected but pose a risk to human health (USEPA 2019). PFAS are a group of emerging contaminants that may pose a danger to reproductive, developmental, immunological, and renal health in humans. Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are the two most common forms of PFAS. Currently, California has a drinking water response level of 10 parts per trillion (ppt) for PFOA and 40 ppt for PFOS, based on a running four-quarter average. The EPA Lifetime Health Advisory recommendation is that combined PFOS and PFOA should not be greater than 70 ppt. PFAS have been used in products including firefighting foams, nonstick cookware, and stain- and water-repellent fabrics for many decades. PFAS contamination of groundwater often occurs near firefighting training facilities, wastewater discharge facilities, or landfills.
The SWRCB has undertaken PFAS monitoring throughout the state, measuring PFAS concentrations in groundwater and identifying point sources of PFAS contamination (SWRCB, 2020). An order by the SWRCB in April 2019 required all water systems near landfills or airports to monitor and report PFAS concentrations for four consecutive quarters. In the Indio Subbasin, selected wells are monitored quarterly for PFAS, including wells near Palm Springs and Cathedral City, and west of Desert Shores. One monitoring well at a landfill site in Cathedral City measured 14 ppt PFOA, but a nearby monitoring well did not detect any PFOA (GAMA GeoTracker). No other concentrations have exceeded the California Response Levels or EPA Lifetime Health Advisory.
Due to the emerging nature of PFAS, federal and state guidelines are subject to change. The US EPA may set PFAS standards for drinking water and wastewater discharge. As additional data about the health effects of PFAS become available, the SWRCB DDW may establish notification levels for additional PFAS chemicals. Water systems in Indio Subbasin will continue to comply with monitoring and reporting requirements.
8.3 Salton Sea Restoration
The Salton Sea, a saline lake at the eastern end of Coachella Valley, is located along the Pacific Flyway migratory bird route and serves as important habitat for over 400 bird species including endangered and threatened species (U.S. Fish and Wildlife Service, 2020). Once known for its sport fishery and recreational uses, the Salton Sea has shrunk in size and deteriorated in water quality, leading to loss of the fishery and in recent years, mass die-offs of birds and fish, raising concerns about these beneficial uses.
The primary source of inflow for the Salton Sea is agricultural drainage from the Imperial and Coachella valleys plus inflow from the New River, Alamo River, and Coachella Valley Stormwater Channel. The Salton Sea does not have a natural outlet, so evaporation is the sole outflow, and any influent salts are
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Indio Subbasin Water Management Plan Update 8-15 TODD/W&C concentrated. Moreover, the sea has reduced in volume, leading to more concentration. Consequently, salinity levels have increased over the past several decades. Salinity levels reported in 2020 were greater than 69,000 mg/L, two times greater than the salinity of ocean water (California Natural Resources Agency, 2020). High concentrations of phosphorus and nitrogen compounds in the Salton Sea can also lead to eutrophication. With its current trajectory, the Salton Sea could become hypersaline with elimination of fish that serve as an important food source for migratory birds (Salton Sea Authority, 2016).
Decreased inflows over the past several decades have caused the Salton Sea’s surface elevation and area to decline, which has exposed more of the playa lakebed. The increasingly exposed playa generates dust that degrades air quality.
Indio Subbasin groundwater is connected to the Salton Sea, with potential for groundwater outflow to the sea and seawater inflow from the sea. The latter represents seawater intrusion, a significant source of potential groundwater quality degradation. The occurrence of outflows/inflows depends on respective groundwater and Salton Sea elevations, which can change through time and vary with location. Salton Sea levels and quality are tracked by USGS, while local groundwater levels and salinity also are monitored regularly (see Chapter 4, Current and Historical Groundwater Conditions). The potential for seawater intrusion into Subbasin aquifers has diminished as Subbasin groundwater levels have increased and as the Salton Sea levels have declined and the sea has retreated. As discussed in Chapter 7, Numerical Model and Plan Scenarios, on simulated Salton Sea flows, numerical modeling indicates that groundwater outflow to the sea has exceeded inflow from the sea since 2015. Seawater intrusion is also discussed in Chapter 9, Sustainable Management, in terms of sustainable management as part of this Alternative Plan Update.
Due to its ecological importance and changing condition, legislation has been passed on the State and Federal level to support Salton Sea restoration and in-depth studies have been conducted about the Sea.
A recent State initiative is the Salton Sea Task Force, created in 2015, which directs state agencies to create a management plan for ecological restoration (California Natural Resources Agency, 2020). In 2016, a Memorandum of Understanding (MOU) was signed between the U.S. Department of the Interior and the California Natural Resources Agency to affirm that the State will take the lead role in Salton Sea management and facilitate coordination for the Salton Sea Management Plan (SSMP). The State’s SSMP team (including the California Natural Resources Agency, Department of Fish and Wildlife, and DWR) developed a 10-Year Plan identifying a sequence of dust control and fish and wildlife habitat projects around the Salton Sea.
The Salton Sea Authority (founded in 1993 as a Joint Powers Authority) has been working with the State of California to oversee ecological restoration. CVWD is a stakeholder, along with Riverside and Imperial counties, IID, and Torres Martinez Desert Cahuilla Indians. In 2016, the Authority released a Funding and Financial Feasibility Action Plan which sets the foundation for the SSMP. This plan included evaluation of previously proposed restoration alternatives for the Sea, water import alternatives, and alternatives that account for water supply limitations (including the Perimeter Lake concept of establishing a lake around a saline central lake within the current Salton Sea footprint). A North Lake Demonstration Project, involving a 160-acre lake near the community of North Shore, was initiated with DWR grant funding in April 2021 with construction to start in 2022.
As of spring 2021, the SSMP has released an updated draft 10-Year Plan, initiated environmental planning for National Environmental Policy Act (NEPA) compliance, and launched long-term planning with public engagement and an independent review of options for long-term restoration, including water
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Indio Subbasin Water Management Plan Update 8-16 TODD/W&C importation. This long-range plan will also include a Watershed Management Plan component. A watershed management plan will have ramifications for Indio Subbasin water management, including plans for increased water recycling, desalination, and water conservation that could decrease flows into the Salton Sea from drains or the groundwater basin.
8.4 Small Water Systems
On February 16, 2016, the SWRCB recognized the human right to water as a core value under Resolution No. 2016-0010, stating that “every human being has the right to safe, clean, affordable, and accessible water adequate for human consumption, cooking, and sanitary purposes.” Small water systems (SWSs), often serving disadvantaged communities (DACs), may face challenges in providing safe, accessible, and affordable water because they may not have adequate resources to support maintenance, operation, and treatment costs.
SWSs serving DACs are primarily located in rural portions of the East Valley. These SWSs are independent from GSA water systems and depend on local private wells for drinking water supply. In 2017, CVWD estimated that about 10,000 Coachella Valley residents relied on private wells for drinking water (Rumer, Desert Sun, 2017). A recent assessment conducted for this Update used the GAMA data viewer and DDW system information to identify 101 small water systems with 2,772 connections (see also Chapter 2, Plan Area). Most of these SWSs are located within the CVWD service area. Systems marked as inactive were excluded. These water systems include both transient (e.g., campgrounds) and non-transient (e.g., schools, office buildings) non-community systems as well as community water systems, many of which in the Plan Area are mobile home parks. Most of the small systems have only one active well. To ensure safe groundwater quality and a reliable supply to these SWSs in its jurisdiction, CVWD initiated a program to connect them to CVWD’s system on a priority basis.
8.4.1 Groundwater Supply Issues
Groundwater supply to small water systems in Indio Subbasin may face supply challenges related to system reliability, aging infrastructure, lack of funding and expertise for maintenance and operation, and population growth. Water systems with only one or two wells are more vulnerable to a water outage than a larger system. However, groundwater conditions in the Indio Subbasin show recovery of historical groundwater lows, so it is unlikely that wells will be vulnerable to going dry from lowering water levels.
Additionally, most small water system wells with known depths are 400 feet or deeper.
8.4.2 Groundwater Quality Issues
SWSs often do not have the infrastructure to remove contaminants from groundwater. Elevated concentrations of several contaminants have been identified in SWSs. While some SWSs have not reported groundwater quality test results for trace contaminants to DDW in the past 10 years, a total of 76 out of the 101 identified systems reported at least one water quality measurement since 2010.
Many SWSs are vulnerable to naturally-occurring contaminants like arsenic, fluoride, and chromium-6 (see Chapter 4, Current and Historical Groundwater Conditions, for information on groundwater quality in Indio Subbasin). For arsenic and chromium-6, chronic exposure to trace concentrations is harmful to human health, and water treatment to remove trace contaminant concentrations is not possible for most small water systems. In brief, 59 wells from 48 SWSs have reported arsenic concentrations since 2010. Of these, 12 systems reported at least one well with a maximum arsenic concentration greater than the 10 μg/L MCL, and at least 50 percent of arsenic measurements from 2010-2020 had concentrations higher
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Indio Subbasin Water Management Plan Update 8-17 TODD/W&C than the MCL for wells in 11 water systems. For fluoride, a total of 65 wells from 54 SWSs reported fluoride data since 2010, and wells from 13 SWSs have reported fluoride concentrations greater than the 2 mg/L MCL. At least 50 percent of measurements had fluoride levels exceeding 2 mg/L in wells from 9 water systems. Chromium-6 was measured in 30 wells from 25 water systems. Chromium-6 concentrations were >10 μg/L in 10 wells from 9 water systems, but the maximum result recorded in SWSs was 21 μg/L.
High nitrate and TDS concentrations are more prevalent in raw water from SWSs than in untreated groundwater from larger water systems because the wells are more likely to be shallow. Two SWSs measured TDS concentrations between 500 and 1,000 mg/L. No SWSs recorded TDS concentrations greater than 1,000 mg/L.
Nitrate (as N 2) was measured in 85 wells from 72 SWSs. Nitrate concentrations were higher than the 45 mg/L MCL in 5 wells from 5 SWSs. The maximum nitrate concentration measured since 2010 was 97.46 mg/L nitrate as nitrate (reported as 22 mg/L nitrate as N).
8.4.3 Small Water System Consolidations
In response to these water supply issues, the GSAs with multiple small water systems within their respective jurisdictions have completed and continue to work on consolidating communities that currently are not connected to a municipal water system and do not have a reliable water supply source.
CVWD initiated the East Coachella Valley Water Supply Project (ECVWSP) (CVWD, 2018) that assessed the cost and feasibility of connecting 83 small water systems in DACs. The connections were grouped into 43 projects. The timing of connection largely depends on funding availability, with priority given to projects based on cost, permit status, critical need, and the number of systems that can be consolidated through a single project.
CVWD’s small water system consolidation and infrastructure is overseen by CVWD’s DAC Infrastructure Task Force.
Other consolidations include CWA’s Shady Lane Water
Connection Project to connect the severely disadvantaged mobile home community to the CWA municipal water system.
In addition, IWA is consolidating two small mutual water systems in the City of Indio that serve DACs (Boe Bel Heights Mutual Water Association and the Waller Tract Mutual Water Association)
2 The MCL is 10 mg/L for nitrate when measured as nitrogen. All nitrate as nitrogen concentrations were converted to nitrate as nitrate for this groundwater quality assessment.
The East Coachella Valley Water
Supply Project prioritized small
water system consolidations in the
East Valley.
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Indio Subbasin Water Management Plan Update 8-18 TODD/W&C
8.5 Climate Change
Climate change has the potential to affect the availability of imported water supply from the Colorado River and SWP and to affect local water supply and water demand in the Plan Area. Since the 2010 CVWMP Update, substantial climate modeling has yielded quantitative projections of climate change (including temperature increases and changes in precipitation on a regional scale) that are useful to water managers.
The State of California has directed considerable effort toward assessing climate change and incorporating it into planning processes such as the Urban Water Management Plan (UWMP), Integrated Regional Water Management IRWM Plan, and SGMA planning processes.
Since 2010, Indio Subbasin water agencies have included climate change in their respective UWMPs. In addition, the 2018 Coachella Valley IRWM & Stormwater Resource Plan Update (CVRWMG, 2018) includes extensive discussion of the climate change legislative and policy context, effect of climate change on water supply and demand, and climate change mitigation and adaptation. While the focus of this section is climate change impacts on water supply and demand, it is also recognized that climate change will affect related issues such as stormwater and flood risk, surface water quality, and water-related environments.
As part of this Alternative Plan Update, water supply reliability of Colorado River and SWP Exchange water (including climate change effects) is discussed in Chapter 6, Water Supply, and a numerical modeling scenario addressing climate change is described in Chapter 7, Numerical Model and Plan Scenarios.
The following sections provide brief updates on climate change effects relative to the Colorado River, SWP, and local water supply and demand. Recycled water supply is highly reliable and less affected by climate change.
8.5.1 Colorado River Basin
The 2010 CVWMP Update summarized DWR and USBR studies available at the time, which provided mostly qualitative discussions of climate change impacts, including: a decrease in annual flow and increased variability (e.g., more frequent and more severe droughts), an increase in evaporative losses and reduced runoff, and earlier snowmelt and a greater proportion of runoff due to rainfall. Given the substantial reservoir storage in the Colorado River Basin relative to annual runoff, a change in the timing of annual runoff was not considered a significant effect. The 2010 CVWMP Update noted that the Plan Area is protected by California’s first priority to Colorado River supply in the lower basin and CVWD’s high priority among California users of Colorado River supply. Consequently, no reduction in CVWD’s Colorado River supplies was projected at the time.
In 2012, USBR released the 2012 Colorado River Basin Water Supply and Demand Study (Basin Study; USBR 2012). The Basin Study evaluated Colorado River Basin water supply and demand projections (with specific attention to projected climate change through 2060) and evaluated strategies to meet the supply and demand gap. The Basin Study indicated that climate change will reduce system runoff from the Colorado River primarily because of warming and loss of snowpack. Over the next 50 years, Upper Colorado River streamflow is projected to decrease by approximately 9 percent, along with a projected increase in both drought frequency and duration as compared to the observed historical record. Droughts lasting 5 or more years are projected to occur 50 percent of the time over the next 50 years.
In 2019, in response to historical drought and low storage levels in Lakes Powell and Mead, federal legislators passed the Colorado River Drought Contingency Plan Authorization Act, which implements two Drought Contingency Plans, one each for the upper and lower basins (also see Chapter 6, Water Supply).
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Indio Subbasin Water Management Plan Update 8-19 TODD/W&C The Upper Basin DCP involves management of upper basin reservoirs, water demand management, and weather modification to augment precipitation. The Lower Basin DCP sets rules for scaling back water use based on Lake Mead storage conditions. Each of the lower basin states (and California contractors including CVWD) made storage commitments to keep Lake Mead above critically low levels.
Since the Basin Study, USBR has not updated their long-term projections for future conditions of the Colorado River system under climate change. This is due in part to the fact that the Interim Guidelines and Lower Basin DCP only extend through 2026. However, USBR has released interim guidelines for lower basin shortages, which have been conservatively used in this Alternative Plan Update’s scenario of anticipated reductions in Colorado River supplies due to climate change.
8.5.2 State Water Project
The 2010 CVWMP Update summarized DWR analyses based on various global climate models that predicted a warming trend for California, a reduction in exports from the Sacramento-San Joaquin Delta, a decrease in reservoir carryover storage, and a change in the timing of Sierra Nevada runoff due to snowpack changes. All of these were considered to reduce SWP reliability.
The 2018 IRWM & Storm Water Resources Plan Update (IRWM Plan) presents extensive discussion of the effect of climate change on SWP water supplies, noting the water delivered to State water contractors will depend on the amount of rainfall, snowpack, runoff, water storage, pumping capacity from the Delta, and water demand. Temperature increases are expected to modify rainfall and runoff, which may in turn affect SWP operations. As indicated in the IRWM Plan, changes in the regional and seasonal distribution of precipitation and effects on Sierran snowpack are most problematic; increased temperatures may reduce the snowpack at a faster rate, thereby releasing snowmelt water earlier and faster than anticipated and thereby reducing capabilities to capture and store runoff. Water demands in and near the water source could increase, diminishing water availability and reliability to SWP contractors downstream. The reliability of SWP water supply is expected to be reduced for the range of future climate projections studied.
Notably for SGMA planning, in July 2018 DWR published its Guidance Document, Guidance for Climate Change Data Use During Groundwater Sustainability Plan Development (DWR, 2018). This document provides GSAs with information regarding DWR climate change datasets and related tools as technical assistance to develop projected water budgets. DWR provides four projected climate conditions and desktop tools that can be used by GSAs to process the climate change datasets for their water budget studies or to incorporate into a groundwater/surface water model.
As described in Chapter 7, Numerical Model and Plan Scenarios, climate change effects on SWP supply have been evaluated accounting for the recent history of SWP allocations (including drought periods).
Climate change (including effects not only on SWP but also Colorado River supplies) is addressed in four projected scenarios for numerical modeling with comparison to a baseline scenario.
8.5.3 Plan Area Supplies and Demands
Projected water demands are described in detail in Chapter 5, Demand Projections, while Chapter 6, Water Supply, describes available and future water supplies including climate change. DWR’s 2018 Guidance Document (DWR, 2018) provides some summary information on projected climate changes for the Colorado River hydrologic region in California (including Indio Subbasin). Average temperature increases are 2.6 and 5.7 degrees Fahrenheit for 2030 and 2070, respectively, and average precipitation
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Indio Subbasin Water Management Plan Update 8-20 TODD/W&C changes are decreases of 1.3 percent and 2.9 percent, respectively, for 2030 and 2070 (DWR, 2018, Figures A-13 and A-14).
Increased temperatures in the Plan Area would increase water demands for crop and landscape irrigation, municipal water use, and evaporative losses from canals and open reservoirs. Increasing temperatures could also change the distribution and form of precipitation from snow at higher elevations to rain, shifting the timing of runoff earlier in the year. Decreased precipitation would result in decreased runoff and availability of local surface water for diversion. In addition, climate change may result in greater seasonal and annual variability of local precipitation, including higher peak stormwater events that strain the capacity of diversion and recharge facilities. As described in Chapter 7, Numerical Model and Plan Scenarios, potential climate change effects on local surface water hydrology have been assessed using local, recent hydrologic and drought data the numerical groundwater flow model.
Climate change could also lead to shifts in population, industry, and agriculture, which would in turn affect water demands.
8.6 State Water Conservation
In 2009, the State Legislature enacted Senate Bill X7-7 (SBX7-7), the Water Conservation Act of 2009, which requires water suppliers to increase their water use efficiency. The legislation amended the water code and laid out actions to be conducted by DWR to implement the law, including collaboration with urban and agricultural stakeholders, development of methodologies for measuring and reporting water uses, development of urban water conservation targets, preparation of guidebooks, and development of grant and loan funding criteria as incentives for water conservation. The purpose of the law has been to encourage both urban and agricultural water providers to implement conservation strategies, monitor water usage, and report data to DWR. Implementation of water conservation by urban water suppliers has been reported primarily through UWMPs and by agricultural water suppliers through Agricultural Water Management Plans (AWMPs).
In passing this law—which was identified in the 2010 CVWMP Update for close tracking—California was the first state to adopt urban water use efficiency targets, namely a 20 percent reduction in urban per capita water use by 2020. All four GSAs submitted UWMPs in 2010 and 2015 in compliance with the Urban Water Management Planning Act. For the 2020 UWMP, six water suppliers (CVWD, Coachella Water Authority, DWA, IWA, Mission Springs Water District, and Myoma Dunes Mutual Water Company) collaborated to prepare a Regional UWMP (Water Systems Consulting, 2021). As documented in the Regional UWMP, all six suppliers achieved and in fact exceeded the per capita water use reduction of 20 percent by 2020.
With regard to AWMPs, CVWD has an agricultural conservation program in the 2010 CVWMP Update.
CVWD has a long history of agricultural water conservation programs. As a signatory to the QSA, CVWD is currently exempt from the portion of SBx7-7 that requires agricultural water suppliers to develop an agricultural water management plan and implement efficient water management practices. Under the QSA, CVWD implemented an Extra-ordinary Conservation Program including scientific irrigation scheduling, salinity management, salinity field mapping, conversion of irrigation systems to micro- irrigation, distribution uniformity evaluations, grower training and meetings and engineering evaluations.
Subsequently in 2018, the California Legislature enacted Assembly Bill 1668 and Senate Bill 606, which together lay out a new long-term water conservation framework that affects both urban and agricultural water providers. Four primary goals for the framework are to:
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Indio Subbasin Water Management Plan Update 8-21 TODD/W&C • Use water more wisely,
• Eliminate water waste,
• Strengthen local drought resilience, and
• Improve agricultural water use efficiency and drought planning.
DWR and SWRCB developed a “Primer” or handbook that summarizes the 2018 Water Conservation Legislation. Entitled Making Water Conservation a California Way of Life – Primer of 2018 Legislation on Water Conservation and Drought Planning, Senate Bill 606 (Hertzberg) and Assembly Bill 1668 (Friedman), the Primer outlines the key authorities, requirements, timeline, roles, and responsibilities of State agencies, water suppliers, and other entities during implementation of actions described in the 2018 legislation. To plan, develop and implement the new framework, DWR and the SWRCB are working in collaboration with stakeholders to develop new standards for:
• Indoor residential water use,
• Outdoor residential water use,
• Commercial, industrial, and institutional (CII) water uses for landscape irrigation with dedicated meters, and
• Water loss.
CVWD and DWA have been actively engaged in the stakeholder workgroups helping to develop the methodologies and procedures for the regulations. Specifically, CVWD has been a participant in two variance studies addressing indoor use and seasonal residential population and DWA has been a pilot agency for Landscape Aerial Measurements.
With the new law, urban water suppliers will be required to stay within annual water budgets for their service areas, based on these standards. In addition, water suppliers will need to report on implementation of new performance measures for CII water use. The legislation also made important changes to existing urban and agricultural water management planning, with enhanced drought preparedness and water shortage contingency planning for urban water suppliers, small water systems and rural communities.
Urban water conservation is being enhanced by local agencies to provide water supplies efficiently and to prepare for water shortages, including drought. While providing these important benefits, it also is recognized that water conservation has broader water management implications including reduction of wastewater flows, decreased availability of recycled water, and potential increases in wastewater salinity.
8.7 Subsidence
Land subsidence is documented in Chapter 4, Current and Historical Groundwater Conditions. Subsidence was discussed in the 2010 CVWMP Update as an emerging issue, having been recognized in the 1990s as occurring with increased pumping in the East Valley since the 1970s. In 1996, the USGS in cooperation with CVWD established a geodetic network of ground surface monuments to monitor elevation changes.
Results of the monitoring program published in 2007 (Sneed and Brandt, 2007) documented the occurrence of subsidence—and some uplift—and indicated causes as including tectonic activity and groundwater pumping and associated groundwater level declines.
CVWD and USGS have continued the monitoring and analysis program. As documented in a 2020 USGS Scientific Investigations Report (Sneed, et al., 2020) and summarized in Chapter 4, Current and Historical Groundwater Conditions, as much as 2 feet of subsidence occurred in the Indio Subbasin from 1995 to
Chapter 8: Regulatory and Policy Issues FINAL
Indio Subbasin Water Management Plan Update 8-22 TODD/W&C 2010. Since 2010, groundwater levels have stabilized or partially recovered in response to the implementation of source substitution, conservation, and groundwater replenishment programs included in the 2010 CVWMP Update. Elsewhere, up to 1 inch of uplift has been measured since 2011 in the Palm Springs area, corresponding to higher groundwater levels in response to upgradient WWR-GRF recharge.
In the Thermal area, the ground surface has also rebounded about 2 inches over the past 10 years, returning to elevations observed in 2001. Land subsidence stopped in many areas and even rebounded.
Sustainable management criteria for subsidence are discussed in Chapter 9, Sustainable Management, continued monitoring of groundwater levels and subsidence is discussed in Chapter 10, Monitoring Program, and relevant projects and management actions are presented in Chapter 11, Projects and Management Actions.
8.8 Other Issues
8.8.1 Invasive Species
The 2010 CVWMP Update identified an invasive species,
Quagga Mussels, which have been found in the Colorado
River System and pose a threat of infestation to canal and channel facilities. CVWD has successfully prevented
infestation through chlorination and maintenance of
turbulence in its conveyance system. Monitoring
continues to detect and address any problems.
8.8.2 Seismic Response
Seismic response was included in the 2010 CVWMP
Update, which summarized the probability of a magnitude
6.7 or greater earthquake in California as greater than 99 percent, as presented in a 2008 USGS study (USGS Fact
Sheet 2008-3027). With the occurrence of earthquakes
since 2008, USGS has continued refinement of its
earthquake forecast model for California. As summarized in its USGS Fact Sheet 2015-3009, the near-certainty of a large event has not changed. However, the likelihood of moderate-sized earthquakes (magnitude 6.5 to 7.5) is
lower, whereas that of larger events is higher because of the inclusion of multi-fault ruptures.
The 2010 CVWMP Update summarized the CVWD Emergency Response Plan and the disaster/emergency preparedness plans of DWA, City of Coachella, and City of Indio. The federal America’s Water Infrastructure Act of 2018 requires that community (drinking) water systems serving more than 3,300 people develop or update risk assessments and Emergency Response Plans (ERPs) with regular 5-year updates and recertifications.
Recognizing the consequences for water systems, DWR is conducting seismic upgrade projects on its own facilities and has strengthened requirements for local water agencies. For example, upcoming 2020 UWMPs are required to identify potential catastrophic water shortages and appropriate response actions.
New 2020 requirements include a seismic risk assessment and mitigation plan for water system facilities.
CVWD monitors for Quagga Mussels in
the Coachella Canal and Lake Cahuilla.
Chapter 9: Sustainable Management FINAL
Indio Subbasin Water Management Plan Update 9-1 TODD/W&C CHAPTER 9: SUSTAINABLE MANAGEMENT
As described in Chapter 1, Introduction, in 2016 the Indio Subbasin Groundwater Sustainability Agencies (GSAs) submitted an Alternative Plan to DWR (approved in July 2019) that presented the ongoing management of the Indio Subbasin. The Alternative Plan included discussion of goals and objectives, groundwater conditions, emerging issues, water supply and demand, and projects and management actions, among other topics. The Alternative Plan has continued to guide water management in the Indio Subbasin as demonstrated in the annual reports and in this Alternative Plan Update.
The California Department of Water Resources (DWR) approved the Alternative Plan as functionally equivalent to a Groundwater Sustainability Plan (GSP) and provided recommendations to the GSAs in its Alternative Assessment Staff Report (DWR, 2019). This chapter discusses sustainability consistent with the groundwater management objectives of the GSAs and—recognizing the benefits of the Sustainable Groundwater Management Act (SGMA) approach in defining terms, establishing procedures, and setting objective metrics for sustainability—is responsive to the specific DWR recommendations that address sustainability and DWR’s ongoing evaluation.
9.1 Sustainability Indicators and Criteria
SGMA provides a consistent, state-wide definition of sustainable management as the use and management of groundwater in a manner that can be maintained without causing undesirable results, which are defined as significant and unreasonable effects caused by groundwater conditions occurring throughout a basin:
• Chronic lowering of groundwater levels indicating a significant and unreasonable depletion of supply
• Significant and unreasonable reduction of groundwater storage • Significant and unreasonable seawater intrusion
• Significant and unreasonable land subsidence that substantially interferes with surface land uses • Significant and unreasonable degraded water quality, including the migration of contaminant plumes that impair water supplies
• Depletions of interconnected surface water that have significant and unreasonable adverse impacts on beneficial uses of the surface water
The above indicators provide a framework for addressing the multi-faceted and complex nature of sustainability. SGMA also provides the following criteria for quantitative measures that support demonstration of sustainability:
• Minimum Threshold (MT 1) – numeric value used to define undesirable results for each sustainability indicator
• Measurable Objective (MO) – specific, quantifiable goal to track the performance of sustainable management
1 The abbreviations for Minimum Threshold (MT) and Measurable Objective (MO) are provided because these terms are used often; however, the full unabbreviated term is used when helpful for clarity or when included in a quotation.
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Indio Subbasin Water Management Plan Update 9-2 TODD/W&C • Interim Milestone – target value representing measurable groundwater conditions, in increments of 5 years
While providing consistent definitions and criteria, SGMA allows multiple pathways to meet the local needs of each basin. These include not only development of each of these sustainable management criteria, but also use of the groundwater level sustainability indicator as a proxy, identification of additional indicators as decided by local GSAs for a basin, and identification of indicators that are not applicable to the basin. Moreover, it is understood that continued data collection and an improved understanding of basin conditions in the future may lead to changes in the sustainable management criteria through adaptive management.
Sustainability is discussed here with reference to the sustainability goal and objectives that have been defined for water resources management of the Coachella Valley overall and for the Indio Subbasin specifically. Sustainability indicators are presented in the context of management through the Alternative Plan—which is the approved functional equivalent of a GSP—and the Recommended Actions provided by DWR in its Alternative Assessment Staff Report (Staff Report) (DWR, 2019) (see Chapter 1, Introduction).
9.2 Sustainability Goal and Approach
The 2002 Coachella Valley Water Management Plan (2002 CVWMP) (Coachella Valley Water District [CVWD], 2002) and the Coachella Valley Water Management Plan 2010 Update (2010 CVWMP Update) (CVWD, 2012) developed an overarching goal for the Valley “to reliably meet current and future water demands in a cost-effective and sustainable manner.” This Alternative Plan Update continues to be guided by this overall goal, which extends beyond groundwater sustainability to include all available water supplies for Indio Subbasin and water demand management as integral to an overall balance of water supply and demand.
The 2010 CVWMP Update also identified six objectives, which continue to guide this Alternative Plan. In addition, a seventh objective has been developed to address climate change and drought. The updated objectives are as follows:
• Meet current and future municipal water demands with a 10 percent supply buffer • Avoid chronic groundwater overdraft
• Manage and protect water quality
• Collaborate with tribes, state and federal agencies on shared objectives • Manage future costs
• Minimize adverse environmental impacts
• Reduce vulnerability to climate change and drought impacts These goals and objectives extend beyond groundwater resources and thus, for this Alternative Plan Update, a sustainability goal was developed specifically for groundwater sustainability. It is nested under the broader plan goals. The sustainability goal included here supports, rather than supersedes, the plan goals, and provides a qualitative description of the objectives and desired conditions of the Indio Subbasin:
To maintain a locally managed, economically viable, sustainable groundwater resource for existing and future beneficial uses in the Indio Subbasin by managing groundwater to avoid the occurrence of undesirable results.
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Indio Subbasin Water Management Plan Update 9-3 TODD/W&C The sustainability goal has been defined in light of information developed in this Alternative Plan Update.
This information includes the basin setting (Plan Area, Hydrogeologic Conceptual Model, Groundwater Conditions, and Water Budget), discussion of sustainability indicators in this chapter, and the description of planned projects and management actions to ensure that the sustainability goal is achieved and maintained (see Chapter 10, Monitoring Program; Chapter 11, Projects and Management Actions; and Chapter 12, Plan Evaluation and Implementation).
This Alternative Plan Update incorporates a comprehensive approach to local groundwater management.
While acknowledged as functionally equivalent to a GSP, it also utilizes sustainability indicators and criteria as needed. This Alternative Plan is also responsive to the DWR Staff Report Recommended Actions, which are recognized as supporting DWR in its evaluation of Alternative Plan implementation. As indicated in Chapter 1, Introduction, the DWR Alternative Assessment Staff Report provided Recommended Actions 1 through 7, which are reproduced below and addressed in this chapter (and elsewhere in the Update as appropriate). The DWR Staff Recommended Actions included:
• Recommended Action 1. Staff recommend that the Agencies [GSAs] incorporate the information and management activities in the Garnet Hill area from the Mission Creek/Garnet Hill Water Management Plan (Garnet Hill WMP, 2013) into the Alternative for the Indio Subbasin. • Recommended Action 2. Staff recommend that the Agencies describe whether the 2005 groundwater levels can be used as a threshold for land subsidence in the East Valley and the Indio Subbasin generally; determine whether those groundwater levels could also be used as a threshold for other sustainability indicators, such as declining groundwater levels and groundwater storage. If it is determined that the 2005 groundwater levels are not appropriate thresholds or a proxy for thresholds, then the Agencies should provide other quantitative thresholds for groundwater levels, groundwater in storage, and subsidence, and for other sustainability indicators, such as declining groundwater levels and groundwater storage. If not appropriate, provide other quantitative thresholds for groundwater levels, groundwater in storage, and subsidence.
• Recommended Action 3. Staff recommend that the Agencies provide maps showing the areas affected by the primary water quality constituents of concern, which include, at a minimum, fluoride, arsenic, hexavalent chromium (chromium-6), and dibromochloropropane (DBCP). DWR indicated that the wells known to be affected by these constituents should be shown on a map. • Recommended Action 4. Staff recommend that the Agencies incorporate an approved Salt and Nutrient Management Plan (SNMP) into future iterations of the Alternative. • Recommended Action 4a. Staff recommend that the Agencies continue efforts to study the rate and level of increased salt contents in groundwater due to the importation of Colorado River water.
• Recommended Action 5. Staff recommend that the Agencies provide the modeled groundwater elevation that minimizes the risk of saltwater intrusion and discuss how the recent groundwater levels near the Salton Sea referenced in the Alternative compare to the modeled elevation. The Alternative should discuss why the water balance includes inflow from the Salton Sea to the Indio Subbasin and should correlate that inflow with recent groundwater levels and the groundwater model.
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Indio Subbasin Water Management Plan Update 9-4 TODD/W&C • Recommended Action 6. Staff recommend that the Agencies clarify whether there is a minimum threshold associated with the amount of flow in the subsurface drains, below which significant and unreasonable undesirable results would occur, and what that quantified minimum threshold is, if applicable, and the implementation horizon for when the goal for the amount of subsurface flow will be achieved, so as to avoid undesirable results. • Recommended Action 7. Staff recommend that the Agencies provide an identification of groundwater-dependent ecosystems in the Subbasin.
Recommended Action 1, to incorporate information and management activities for the Garnet Hill Subarea, is addressed throughout this Alternative Plan Update. As summarized in Chapter 2, Plan Area, and described in Chapter 3, Hydrogeologic Conceptual Model, and Chapter 4, Current and Historical Groundwater Conditions, the Garnet Hill Subarea is included in the Indio Subbasin. Management of the Garnet Hill Subarea has been coordinated through the Mission Creek/Garnet Hill Water Management Plan (MC/GH WMP, 2013) developed by CVWD, Desert Water Agency (DWA), and Mission Springs Water District (MSWD) in coordination with the 2010 CVWMP Update. The Subarea is included in this Alternative Plan Update and is also included in the Mission Creek Subbasin Alternative Plan Update. Management activities for the Garnet Hill Subarea are incorporated into this Alternative Plan Update, for example through numerical modeling and project implementation (see Chapter 7, Numerical Model and Plan Scenarios and Chapter 12, Plan Evaluation and Implementation).
9.3 Quantitative Criteria for Groundwater Levels
Recommended Action 2 in the DWR Alternative Assessment Staff Report discusses minimum thresholds for groundwater levels. The Staff Report recommends that the GSAs provide quantitative thresholds and consider groundwater levels as a proxy for other sustainability indicators including storage and subsidence.
Quantitative minimum thresholds for groundwater levels are provided in this section, recognizing that chronic lowering of groundwater levels can indicate significant and unreasonable depletion of supply, causing undesirable results to domestic, agricultural, municipal, and other beneficial uses of groundwater if continued over the planning and implementation horizon. As a clarification, drought-related groundwater level declines are not considered chronic if groundwater recharge and discharge are managed such that groundwater levels recover during non-drought periods.
Declining groundwater levels directly relate to other potential undesirable effects (for example, groundwater storage, land subsidence, interconnected surface water, and seawater intrusion); these are described in subsequent sections. Effects on groundwater users are described here.
Groundwater elevation trends in Indio Subbasin are documented in Chapter 4, Current and Historical Groundwater Conditions; hydrographs are presented for 68 wells across the Subbasin. The Indio Subbasin is no longer characterized by overdraft with widespread chronic groundwater level declines. However, the hydrographs (e.g., Figure 4-3 through 4-5) show declines that persisted until the late 2000s, and as shown in Figure 4-9, groundwater in storage in the Indio Subbasin was at its minimum in 2009. The groundwater level declines were halted with the combined effects of groundwater replenishment, source substitution for groundwater (e.g., imported surface water and recycled water), and conservation. Since that time, groundwater levels have risen or at least stabilized throughout the Subbasin.
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Indio Subbasin Water Management Plan Update 9-5 TODD/W&C As noted in the DWR Staff Report, the 2010 CVWMP Update suggested that groundwater levels be maintained above 2005 levels in order to prevent subsidence. However, as discussed in Section 9.5, a 2020 USGS study has provided documentation that subsidence stopped after about 2010. This occurred with stabilizing and rising groundwater levels that followed the historical low groundwater levels and storage in about 2009. As discussed below, historical low groundwater levels were selected as the conceptual basis for meaningful and protective minimum thresholds.
9.3.1 Description of Undesirable Results
Chronic groundwater level declines are widely recognized to cause undesirable effects in production wells.
Relatively shallow wells are more susceptible than deep wells. Private domestic wells may be relatively shallow and thus susceptible to declining groundwater levels. In addition, a private well may be more susceptible to undesirable results because of well construction or maintenance problems. A private well may also represent the sole source of drinking water supply for one or more households.
The following is a generalized description of the undesirable results associated with chronic groundwater level decline; in other words, what can happen in a production well with declining groundwater levels. As groundwater levels decline in a well, a sequence of increasingly severe undesirable results occurs. These include an increase in pumping costs and a decrease in pump output (e.g., flow in gallons per minute).
With further declines, the pump may break suction, which means that the water level in the well has dropped to the level of the pump intake. Well operators can lower the pump inside the well, but this can cost thousands of dollars. Chronically declining water levels will eventually drop below the top of the well screen. This exposes the screen to air, which can produce two adverse effects. In the first, water entering the well at the top of the screen will cascade down the inside of the well, entraining air; this air entrainment can result in cavitation damage to the pump. The other potential adverse effect is accelerated corrosion of the well screen. Corrosion eventually creates a risk of well screen collapse, which would likely render the well unusable. If water levels decline by more than about half of the total thickness of the aquifer (or total length of well screen), water might not be able to flow into the well at the desired rate regardless of the capacity or depth setting of the pump. This might occur where the thickness of basin fill materials is relatively thin. While describing a progression of potential adverse effects, at some point the well no longer fulfills its water supply purpose and is considered to have “gone dry.” For the purposes of this discussion, a well going dry means that the entire screen length (to the bottom of the deepest screen) is unsaturated.
9.3.2 Potential Causes and Effects of Undesirable Results The Indio Subbasin currently is characterized by stable or increasing groundwater levels, but chronic groundwater declines have occurred, most recently until about 2009. No reports are known of wells adversely affected by groundwater levels at that time although other impacts of groundwater level decline (e.g., subsidence or water quality changes) were recognized and addressed. Similarly, groundwater levels typically are affected by drought. Effects on groundwater levels of the most recent drought were variable across the Subbasin and resulted in some decreased groundwater storage from 2012 to 2016, but the GSAs and DWR have received no reports of well problems with groundwater level declines.
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Indio Subbasin Water Management Plan Update 9-6 TODD/W&C Nonetheless, undesirable results of chronic
groundwater level declines could potentially
occur. Causes of declines could include severe
and prolonged drought, climate change (locally
and/or in imported water source areas), or long-
term imbalance of demand over supply. Water
demands may exceed supply if a reduction of
imported water supply occurs. Accordingly, the
GSAs have defined sustainability criteria as
summarized here.
Some of the potential causes of groundwater
level changes, including declines, are within GSA
responsibility; most notably, a GSA is responsible
for groundwater basin management without
causing undesirable results such as chronic
groundwater level declines. SGMA also requires
that a GSA address significant and unreasonable effects caused by groundwater conditions throughout the basin. This indicate s that a GSA is not solely responsible for local or well-specific problems and furthermore that responsibility is shared with a well owner. A reasonable expectation exists that a well owner would construct, maintain, and operate the well to provide its expected yield over the well’s life span, given historical groundwater levels (including droughts) and with some anticipation that neighbors also might construct wells (consistent with land use and well permitting policies).
Groundwater level declines across broad areas of the Indio Subbasin could have deleterious impacts on individual wells and well yields, including the ability of private well owners and small communities to reach groundwater for domestic and drinking water supply. Declining groundwater levels also could have negative effects on other beneficial uses with ramifications for the regional economy: for example, agricultural irrigation and cropping, municipal and golf course cost of supplying water, and property values.
9.3.3 Sustainability Criteria for Groundwater Levels
The general approach to defining sustainability criteria is based on recognition of the following: 1) that historical low groundwater levels have occurred relatively recently in the Indio Subbasin and 2) there has been a lack of reported problems. Accordingly, it can be assumed that maintaining groundwater elevations at or above minimum historical values should not cause undesirable results. This has been substantiated by a review of available information on the location and depths of wells serving small water systems, which indicated that historical groundwater low levels were above the shallowest well depths.
This approach is protective of existing production wells and conservative. In fact, it is quite possible that groundwater levels could be locally lower than the historical minimum without resulting in undesirable effects. However, the lack of undesirable results at historical lows is known and relatively certain. A lower level that remains protective is not known unless local wells in the area are fully documented in terms of well construction (e.g., elevation of screen and bottom of well) with assessment of groundwater levels that might cause undesirable results. As described in Section 12.2.7, Monitoring Network Improvements, Plan Implementation includes an expanded well inventory to document the location and construction of existing wells, which will provide a comprehensive basis for such assessment. Ongoing cooperation with The GSAs have been working to reverse
groundwater overdraft through imported water
replenishment.
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Indio Subbasin Water Management Plan Update 9-7 TODD/W&C well permitting agencies, including the County of Riverside, will ensure that future wells are constructed with sufficient depth.
Determining the level below which undesirable results can occur is the first step in defining the MT. As described below, additional steps involve selection of representative monitoring wells (Key Wells) to track groundwater levels, review of groundwater levels in each Key Well to identify the MT, consideration of how often and how long groundwater levels can be below the MT without causing undesirable results, and decision of how many wells with levels crossing the MT constitute an undesirable result.
9.3.3.1 Selection of Key Wells
Selected Key Wells are shown in Table 9-1 and Figure 9-1. These wells are representative of local groundwater elevation conditions and are appropriate for inclusion in the Key Well groundwater elevation monitoring network (a subset of the overall monitoring program). These wells will be used for well-by- well definition of sustainability criteria (such as undesirable results and minimum thresholds). Future 5- year updates of this Alternative Plan will include review and any needed refinement of this Key Well network.
Table 9-1. Key Well Network for Groundwater Levels
Key Well
Number
SWN Well Name/Owner First Year of
Record
MT (ft msl)
KW_001 03S04E17K01S Private 1954 617.0
KW_002 03S04E22A01S Private 1953 586.4
KW_003 03S04E34R01S DWA Well 21 1973 242.58
KW_004 03S05E30G01S Private 1965 379.9
KW_005 04S04E13C01S DWA Well 23 1975 184.11
KW_006 04S04E24D01S DWA Well 24 1978 164.27
KW_007 04S05E09B01S CVWD Well 4562-1 1962 151.4
KW_008 04S05E15R02S Private 1960 99.0
KW_009 04S05E17Q02S DWA Well 31 1987 134.49
KW_010 04S05E28F02S CVWD Well 4519-1 1974 105.4
KW_011 04S05E29F01S Private 1958 129.3
KW_012 04S05E35G03S CVWD Well 4503-1 1953 55.1
KW_013 04S06E18R01S CVWD Well 4623-1 1953 33.7
KW_014 04S06E20M02S CVWD Well 4628-2 2003 15.4
KW_015 04S06E32N02S CVWD Well 4611-1 2000 -102.6
KW_016 04S06E35P01S Private 1985 -45.4
KW_017 05S05E12H02S CVWD Well 5507-1 1956 4.6
KW_018 05S06E12N01S CVWD Well 5626-1 1980 -65.1
KW_019 05S06E16A02S CVWD Well 5620-1 1976 -42.0
KW_020 05S06E24G01S CVWD Well 5636-1 1965 -86.7
KW_021 05S06E29C01S CVWD Well 5643-1 1956 -37.0
KW_022 05S07E04A01S CVWD Well WRP-7 MW-1 Dave Price 1955 -62.6 KW_023 05S07E06B04S CVWD Well 5720-1 1993 -77.0
KW_024 05S07E08Q01S Private 1967 -79.4
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Indio Subbasin Water Management Plan Update 9-8 TODD/W&C Key Well
Number
SWN Well Name/Owner First Year of
Record
MT (ft msl)
KW_025 05S07E24M04S IWA Well 1C 1985 -92.1
KW_026 05S07E27L01S Private 1965 -142
KW_027 05S07E28E01S CVWD Well 5701-1 1948 -95.5
KW_028 05S07E31P01S CVWD Well 5706-1 1978 -107.6
KW_029 05S07E32B01S CVWD Well 5725-1 2005 -155.2
KW_030 05S08E33D01S CWA 10 1979 -160.7
KW_031 06S07E02D02S Private 1985 -157.2
KW_032 06S07E06B01S CVWD Well 6701-1 1981 -145.4
KW_033 06S07E13M02S CVWD Well 6781-1 1963 -91.4
KW_034 06S07E16A02S CVWD Well 6723-1 1987 -172.7
KW_035 06S07E23F01S Private 1965 -163.2
KW_036 06S07E29B01S Private 1995 -170.9
KW_037 06S07E35L02S Private 1988 -176.6
KW_038 06S08E05R02S CVWD Well 6858-1 1957 -103.4
KW_039 06S08E12Q01S Private 1991 -132.7
KW_040 06S08E22D02S CVWD Well 6803-1 1966 -177.1
KW_041 06S08E25Q01S Private 1979 -188.4
KW_042 06S08E31P01S Private 1989 -184.8
KW_043 06S09E32Q01S Private 1966 -176.0
KW_044 07S07E02G02S Private 1996 -178.2
KW_045 07S08E10P01S Private 1988 -204.2
KW_046 07S08E17G01S CVWD Well 7801-1 1972 -197.3
KW_047 07S08E33B01S Private 1965 -211.4
KW_048 07S09E07J01S CVWD Well 7993-1 1970 -245.9
KW_049 07S09E14C01S Private 1992 -180.6
KW_050 07S09E16M03S Private 1989 -261.5
KW_051 07S09E18H01S Private 1994 -263.1
KW_052 07S09E30R01S CVWD Bernadine 1996 -209.1
KW_053 08S08E03L01S Private 1965 -220.2
KW_054 08S08E24L01S Private 1939 -257.1
KW_055 08S09E07N03S CVWD Gracie 2003 -249.6
KW_056 08S09E30A01S Private 1965 -266.5
KW_057 08S09E33N01S Private 1952 -262.9
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Indio Subbasin Water Management Plan Update 9-9 TODD/W&C Figure 9-1. Selected Key Wells for Groundwater Level Monitoring FINAL
Chapter 9: Sustainable Management FINAL
Indio Subbasin Water Management Plan Update 9-10 TODD/W&C The selection process began with a database of 757 wells that have water level measurements compiled by the GSAs. The selection of Key Wells from this set was based on a quantitative approach that considered wells with long records characteristic of an area and distribution of wells across Indio Subbasin.
In brief, all available groundwater elevation data were plotted as hydrographs and well locations were plotted on a basin-scale map. The five criteria include the following:
1. Available Construction Information – Wells should have construction information including at least total depth.
2. Current Monitoring – Wells need to have been monitored recently to ensure continued access (all selected wells were measured in 2020).
3. Long Record – Wells should have a long period of record to reflect changing conditions in the Subbasin. Wells were evaluated with consideration of length of monitoring record and the number of years since 1990 (the beginning year of the 2010 CVWMP Update model) with consistent monitoring. This period includes overdraft and recovery. Wells were scored based on the number of years with more than two water level monitoring events.
4. Spatial Distribution – Wells were prioritized to provide distribution across the Subbasin (evaluated for no more than one well per township range section) and to select at least one well in each GSA jurisdictions. Wells were given a higher ranking if no other monitoring wells were located in the same township range section (TRS) and a lower ranking if there were several wells in the section. Only the highest scoring well in a TRS was selected. If multiple wells had the same score, the well with the longest record was selected. In addition, areas with clusters of wells were identified and only the highest scoring well was selected.
5. Location near Production Wells – Wells were rated higher in sections that had more production wells. Conversely, wells were rated lower if few or no pumping wells existed in the TRS. Because the purpose of the MTs is to protect current and future beneficial uses including pumping, the key wells need to reflect pumping locations. However, if a large area of the Subbasin did not have an adequately rated well, the best well in that area is proposed.
Each well was rated (low-0, medium-5, and high-10) for the five criteria as summarized in Table 9-2 below.
Table 9-2. Criteria for Selection of Key Wells for Groundwater Level Monitoring Criteria Low Med High
Points 0 5 10 Field Name
Construction N
Y Well Depth
Current Monitoring 15 Years with at Least 2 Measurements since 1990 Areal Distribution >10 5-10 5 Number of Production Wells in Section
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Indio Subbasin Water Management Plan Update 9-11 TODD/W&C After all wells with water level monitoring were scored and ranked, the wells were plotted and vetted against additional considerations. These considerations are more qualitative but help refine the selection of higher ranked wells. These considerations include:
• Small Water Systems – Wells in and around small community water systems are considered in order to be protective of pumping.
• GSA represented – All four of the GSA jurisdiction areas should be represented. • All Subareas represented – insofar as possible at least one well was included per Subarea. • Depth of well – The depth of Key Wells should be representative of the static regional levels.
Wells less than 300 feet were not selected unless they were needed for areal distribution or providing a very long and complete record.
• Location relative to active recharge – Selection of key wells should not be unduly influenced by Groundwater Replenishment Facilities (GRF). Accordingly, monitoring wells for a GRF or on GRF property were not included. The key wells were selected to monitor regional trends and not local operational effects of these facilities.
• SNMP – Wells in the SNMP workplan were considered to provide some overlap of the two programs while recognizing that these are for SNMP objectives. • Representative but not redundant – Hydrographs were visually identified for similar trends in nearby wells to avoid redundancy.
9.3.3.2 Identification of Minimum Threshold
The historical low level represents the conceptual definition of the MT. The MT for each Key Well was based on reviewing its respective hydrograph (from 1990 to 2020) and identifying the historical low groundwater elevation (see hydrographs in Appendix 9-A). These groundwater elevations were designated as MTs. In some cases, the historical low appeared to be a significant outlier and the MT was adjusted. All adjustments were upward, in other words, more protective.
Under current conditions, groundwater levels in all Key Wells are above the MTs and no undesirable results are known to occur. To substantiate this, available information was reviewed on the location and depth of wells serving small water systems, including non-community systems (e.g., schools, businesses) as well as community water systems (e.g., mobile home parks). Section 8.4, Small Water Systems, provides information on small water systems and GSA programs to help provide them with reliable and safe water supplies. While many wells for small water systems do not have known construction or depths, review of available information from 48 wells evaluated in the East Coachella Valley Water Supply Consolidation Study (CVWD, 2018) indicates a range of well depths from 225 to 1,060 feet. Comparison of known depths for small water system wells with the MTs indicated that the respective MTs are above known depths for all small water systems with available information and are protective.
For the future, the GSAs will continue to cooperate with agencies responsible for well permitting to ensure that new wells are constructed with sufficient depth to accommodate groundwater level changes relative to the MTs. This will include provision of information on the Key Wells and the MTs and applicable Subbasin areas, which may be accomplished by contouring MTs or by designating applicable areas around each Key Well to define minimum well depths.
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Indio Subbasin Water Management Plan Update 9-12 TODD/W&C
9.3.3.3 Minimum Thresholds and Criteria for Undesirable Results Undesirable results are based on exceedances of MT levels and must be defined not only in terms of how they occur (see Section 9.3.2 Potential Causes of Undesirable Results), but also when and where. By definition, undesirable results are not just drought-related but chronic and are not just local but basin- wide.
Regular groundwater level monitoring (at least three times per year) and annual reporting provides regular updates that allow response by the GSAs and local groundwater users. Management action response times vary. For example, it may take some time for increased replenishment at GRFs to benefit water levels in the Subbasin. Due to some inevitable delays in results from actions, an undesirable result is when water levels fall below MTs for five consecutive same-season events (e.g., five October monitoring events).
Local areas of groundwater level declines can occur due to conditions such as locally increased pumping.
However, local declines do not necessarily indicate Subbasin-wide issues such as overdraft. Undesirable groundwater level declines of Subbasin-wide significance could occur due to influences such as severe and prolonged drought, climate change, reduction of imported water supply and increased groundwater pumping. While not likely to occur uniformly across the Indio Subbasin, groundwater level declines could be fairly widespread under these conditions. Significant and undesirable results are defined as occurring when groundwater levels are below the MT for five consecutive same-season monitoring events in 25 percent of Key Wells.
To summarize for the Indio Subbasin:
The Minimum Threshold for undesirable results relative to chronic lowering of groundwater levels is defined at each Key Well by historical groundwater low levels. Undesirable results are indicated when groundwater levels are below the MT for five consecutive same-season monitoring events, in 25 percent or more of the Key Wells in the Indio Subbasin.
9.3.3.4 Measurable Objectives and Interim Milestones
For groundwater levels, the MOs are defined here as an operating range of groundwater levels above the MT, allowing reasonable fluctuations with changing hydrologic and surface water supply conditions and with conjunctive management of surface water and groundwater. The groundwater level MTs represent the bottom of the operating range and are protective of groundwater users and beneficial uses. The top of the operating range is not specified because there is no particular high groundwater level to be a sustainability objective and groundwater levels in many areas are increasing. While unconfined groundwater levels across much of the Subbasin are below historical highs, other areas are characterized by artesian conditions or by use of drainage systems to control high groundwater levels.
The Measurable Objective is to maintain groundwater levels above the groundwater level MTs (as quantified above), and to maintain groundwater levels within the operating range as defined in this section.
Groundwater conditions with respect to chronic groundwater level declines are already sustainable and there is no need to define interim milestones.
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Indio Subbasin Water Management Plan Update 9-13 TODD/W&C
9.4 Quantitative Criteria for Groundwater Storage
Groundwater storage is the volume of water in the Subbasin. It provides a reserve for drought or water shortage. The minimum threshold for reduction of groundwater storage is the volume of groundwater that can be withdrawn from a basin or management area without leading to undesirable results.
Undesirable results would involve insufficient stored groundwater to sustain beneficial uses through drought or shortage. The storage criteria are closely linked to groundwater levels. Unlike the other sustainability criteria, the reduction of groundwater storage criteria is not defined at individual monitoring sites but is evaluated as a volume on a basin-wide basis. The sustainability indicator for groundwater storage addresses the ability of the groundwater basin to support existing and planned beneficial uses of groundwater even during drought and water supply shortage.
9.4.1 Description, Causes, and Effects of Undesirable Results As with declines in groundwater level, reduction of groundwater storage could be due to influences such as severe and prolonged drought (locally and/or in imported water source areas), climate change, or a longer-term imbalance of demand over supply. Storage is related to groundwater levels, thus, undesirable results associated with storage would likely be accompanied by one or more undesirable results associated with groundwater levels, including reduced well yields, subsidence, seawater intrusion, and potential depletion of interconnected surface water. Reduction of groundwater storage could affect the ability of groundwater users to support beneficial uses through drought and shortage and have negative effects on the regional economy.
9.4.2 Sustainability Criteria for Groundwater Storage
The potential for reduction of groundwater storage exists for the Indio Subbasin and thus the GSAs have considered minimum thresholds to be defined as the maximum groundwater volume that can be withdrawn without leading to undesirable results. However, use of the groundwater level sustainability criteria (e.g., MTs and MOs) as a proxy for groundwater storage is acceptable provided that GSAs demonstrate a correlation between groundwater levels and storage. Groundwater levels and storage are directly related. This is demonstrated by comparison of groundwater level and storage trends, which reveal similar patterns of historical overdraft, recovery, and response to different water year types including drought (see Chapter 4, Current and Historical Groundwater Conditions). The relationship of levels and storage is reflected in the calibrated groundwater flow model (see Chapter 7, Numerical Model and Plan Scenarios) that has been used to simulate groundwater levels and storage under projected conditions.
Use of groundwater levels as proxy for storage is responsive to DWR’s Recommended Action 2. The rationale for using groundwater levels as a proxy metric for groundwater storage is that the groundwater level MTs and MOs are sufficiently protective to ensure prevention of significant and unreasonable results relating to storage depletion. In brief, groundwater level MTs have been defined to protect beneficial uses and are based on the following:
• A broad geographic distribution of Key Wells that are representative of basin production wells. • MTs based on historical low groundwater levels that are generally consistent with the historical low storage in about 2009, which occurred without reported well problems. • Groundwater level MTs involve groundwater levels below the MT for five consecutive same- season monitoring events, in 25 percent or more of the Key Wells in the Indio Subbasin. Thus,
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Indio Subbasin Water Management Plan Update 9-14 TODD/W&C GSAs are alerted to groundwater level change as it may occur across a broad area, and this perspective will be revealing about storage change as it occurs across the Subbasin.
Accordingly, the MT for storage for the Indio Subbasin is fulfilled by the MT for groundwater levels, modified as follows:
The Minimum Threshold for undesirable results relative to chronic lowering of groundwater levels and depletion of storage is defined at each Key Well by historical groundwater low levels.
Undesirable results are indicated when groundwater levels are below the MT for five consecutive same-season monitoring events, in 25 percent or more of the Key Wells in the Indio Subbasin.
For groundwater storage, the MOs is fulfilled by the minimum threshold for groundwater levels, modified as follows:
The Measurable Objective for groundwater storage is to maintain groundwater levels above the groundwater level MTs (as quantified above) and within the operating range as defined in this section.
Groundwater conditions with respect to groundwater levels and storage are sustainable and there is no need to define interim milestones.
9.5 Quantitative Criteria for Land Subsidence
Land subsidence, the differential lowering of the ground surface, can damage structures and hinder surface water drainage. Portions of the Indio Subbasin are susceptible to and have experienced historical subsidence due to groundwater withdrawals (see Chapter 4, Current and Historical Groundwater Conditions). In response to subsidence, CVWD and United States Geological Survey (USGS) have collaborated on a series of investigations that documented the location and rate of subsidence and provided a correlation of subsidence to groundwater level declines. The most recent USGS study (Sneed and Brandt, 2020) documented stabilized or rising groundwater levels since 2010 that reflect the combined effect of various projects to increase recharge and reduce groundwater pumping. This study also documented that, although a few areas subsided (albeit at a slower rate), most areas stopped subsiding from 2010 to 2017 and some even uplifted.
9.5.1 Description, Causes, and Effects of Undesirable Results The land subsidence experienced historically in Indio Subbasin has been caused by declines in groundwater elevations due to pumping exceeding recharge. Potential undesirable results of land subsidence include disruption of surface drainage, water supply conveyance, and flood control facilities; damage to infrastructure such as pipelines, airport runways, railroads, roads, and highways; damage to structures such as housing, septic systems, distribution lines, and piping; and potential subsidence around a production well, disrupting wellhead facilities.
9.5.2 Sustainability Criteria for Land Subsidence
According to the GSP regulations Section 354.28(c)(5), the minimum threshold for land subsidence is defined as the rate and extent of subsidence that substantially interferes with surface land uses and may lead to undesirable results. However, land subsidence in Indio Subbasin was clearly caused by groundwater level declines, and accordingly, the groundwater level sustainability criteria (MTs and MOs) can be used as a proxy for land subsidence. Use of groundwater levels as proxy for subsidence also is responsive to DWR’s Recommended Action 2.
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Indio Subbasin Water Management Plan Update 9-15 TODD/W&C The historical low groundwater levels and storage occurred in about 2009. Since that time groundwater levels have generally increased and subsidence has stopped or slowed, with some variability reflecting different groundwater level trends in specific areas and residual compaction. The 2010 CVWMP Update indicated that groundwater levels should not be allowed to drop below 2005 levels. However, groundwater levels did generally decline until about 2009 and subsequent USGS study has shown that subsidence rates slowed since about 2010 (Sneed, M. and Brandt, J. T., 2020). Accordingly, the historical low groundwater levels represent a demonstrable turning-point.
While subsidence-induced sagging affected the Coachella Canal (a portion was realigned subsequently in 2014; Sneed, M. and Brandt, J. T., 2020), maintaining groundwater levels above historical lows levels generally is protective against subsidence. Given the mechanics of subsidence, it is unlikely that significant and unreasonable inelastic subsidence would occur with groundwater levels maintained above their MTs.
Accordingly, the MT for land subsidence for the Indio Subbasin is fulfilled by the minimum threshold for groundwater levels, modified as follows:
The Minimum Threshold for defining undesirable results relative to chronic lowering of groundwater levels and subsidence is defined at each Key Well by historical groundwater low levels. Undesirable results are indicated when groundwater levels are below the MT for five consecutive same-season monitoring events, in twenty-five percent or more of the Key Wells in the Indio Subbasin.
For subsidence, the MO is fulfilled by the minimum threshold for groundwater levels, modified as follows:
The Measurable Objective for subsidence is to maintain groundwater levels above the groundwater level MTs (as quantified above), and to maintain groundwater levels within the operating range as defined in this section.
Groundwater conditions with respect to groundwater levels and subsidence are sustainable and there is no need to define interim milestones.
9.6 Interconnected Surface Water and Groundwater-Dependent Ecosystems As stated in Section 9.1, one of the SGMA undesirable results is depletion of interconnected surface water that has significant and unreasonable adverse impacts on beneficial uses of the surface water. Beneficial uses of surface water are various (recreation, water rights, etc.) but an often-important beneficial use is the existence of Groundwater Dependent Ecosystems (GDEs). GDEs are ecological communities (e.g., riparian vegetation or wetlands) or species that depend on groundwater emerging from aquifers or on groundwater occurring near the ground surface.
9.6.1 Background on Indio Subbasin GDEs
As summarized in the DWR Alternative Assessment Staff Report, interconnected surface water is described in the Alternative Plan as not being present in the West Valley because groundwater levels are generally much lower than the ground surface. This is substantiated by depth to groundwater mapping (Figure 4-6) that shows depth to groundwater exceeding 100 feet where groundwater level data are available. However, Figures 4-1 and 4-6 also indicate areas where groundwater level data generally are lacking, and these include western canyon areas where Probable GDEs have been identified (see Chapter 4, Current and Historical Groundwater Conditions). These Probable GDEs may be associated with surface runoff, snowmelt, or springs and seeps from up-gradient sources.
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Indio Subbasin Water Management Plan Update 9-16 TODD/W&C In the East Valley, depths to regional groundwater generally exceed 20 feet but a shallow semi-perched aquifer zone also is present (see delineated area on Figure 4-6). In areas with shallow, semi-perched groundwater, an agricultural tile drain system was installed in the 1950s through the mid-1970s that allows continued agriculture by providing drainage and salt management.
The DWR Staff Report notes that the groundwater model includes evapotranspiration (ET) by phreatophytic vegetation on undeveloped lands that overlie the semi-perched aquifer area and are not served by the subsurface agricultural drain system in the East Valley. As described in Chapter 7, Numerical Model and Plan Scenarios, the current groundwater flow model retained the ET boundary condition, by which ET is calculated by the model based on the extent of the drain system (see Figure 2-5), simulated shallow groundwater elevations, assumed plant rooting depths, and reference ET values. The computed ET rates range from 4,100 to 5,300 AFY and as illustrated in Figure 7-19, are relatively small and uniform over the period 1997-2019. Inclusion of such ET in the model ensures a complete water budget and acknowledges the hydrologic possibility of phreatophyte ET, including potential GDEs but also non-GDE vegetation around agricultural fields and along drainage channels. In brief, the groundwater model indicates the potential for GDEs and accounts for simulated water use (ET) in the water budget.
9.6.2 Identification of GDEs
Vegetation mapping is required to identify the presence of GDEs. In its Staff Report (Recommended Action 7), DWR recommends that the GSAs provide such an identification of groundwater-dependent ecosystems in the Subbasin.
This Alternative Plan Update has included a focused study of GDEs in Indio Subbasin. This study, Indio Subbasin Groundwater Dependent Ecosystems Study, prepared by a Professional Wetland Scientist, is presented in Appendix 4-B. It included a systematic desktop assessment of the California Natural Communities Commonly Associated with Groundwater (NCCAG) database for the Indio Subbasin, a field assessment of 13 selected sites by the wetland scientist and CVWD environmental staff, and identification of probable GDEs, probable non-GDEs, and playa wetland communities. Described in more detail in Chapter 4, Current and Historical Groundwater Conditions, and mapped in Figure 4-34, these are defined as follows:
• Probable GDEs consist of areas with apparent dense riparian and wetland vegetative communities along mapped drainage systems with potential for deep-rooted phreatophytes, and/or visible, natural surface water flow. These are located along stream channels in upper canyon locations that convey snowmelt, water from cold and hot springs, and mountain front inflow from the surrounding bedrock.
• Probable Non-GDEs are areas not correctly mapped in NCCAG including dry upland areas, cultivated and/or flooded agricultural land, obvious human-made ponds, lakes, and other features, channelized drains, and areas with no other indicators of groundwater near the surface, such as dry washes, arroyos, bajadas, and other ephemeral channels where water only flows in response to heavy precipitation events.
• Playa Wetland Community included areas of wetland habitat along the Salton Sea exposed seabed (playa) generally downstream of agricultural drains or the Coachella Valley Stormwater Channel (CVSC). The recession of the Salton Sea is exposing thousands of acres of playa each year and water from irrigation ditches and other drainages that previously flowed directly into the Sea now spreads out on the exposed Salton Sea playa where new vegetation and wetlands currently exist.
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Indio Subbasin Water Management Plan Update 9-17 TODD/W&C As described in the next sections, three upper canyon sites have been identified as including Probable GDEs that rely on various up-gradient sources. While recognized as wetland habitat, the Playa Wetland Community habitats are sustained largely by agricultural drain flows and CVSC outflows.
9.6.2.1 Probable GDEs
Probable GDEs are located in the northwestern Indio Subbasin in three canyons along streams (Chino Canyon, Tahquitz, and Palm Canyon creeks). These streams convey mountain front runoff from snowmelt and mountain front recharge, namely subsurface inflow from fractured bedrock along the perimeter of the Indio Subbasin. This mountain front inflow is derived from recharge to mountain areas beyond the Indio Subbasin jurisdiction of the GSAs and sustains the upper canyon flows with runoff, snowmelt, springs (both cold and hot springs), and seeps.
Although flowing into the upper canyon reaches of the Subbasin (see Figure 4-34), the canyon flows are unlikely to be influenced by GSA management and groundwater pumping of the downstream regional groundwater table. This reflects several factors including topographic differences (the canyons are fifty to hundreds of feet higher than the main portion of the Subbasin), and distance upstream and away from active groundwater production areas (see Figure 2-13). While noting that the upper canyon areas with Probable GDEs do not have existing groundwater data, this is because of the lack of local wells and groundwater extraction.
9.6.2.2 Playa Wetland Communities
The Playa Wetland Communities are recognized in the Coachella Valley Multiple Species Habitat Conservation Plan as containing sensitive natural communities and potentially containing desert pupfish habitat. These communities are located at the outlets of agricultural drains and the CVSC and are sustained largely by agricultural drain flows and stormwater channel outflows. As such, these are not associated with depletion of groundwater contributing to interconnected surface water. The agricultural drain system is artificial: designed, built, and maintained for the purpose of conveying agricultural return flows and controlling shallow groundwater levels and quality to allow continued agriculture. The CVSC also is an artificial channel designed and maintained to convey stormwater, drain flows, and other flows to the Salton Sea.
The Salton Sea elevation, however, has declined (for example, by ten feet since 1997 as shown in Figure 7-11) and its shoreline has retreated from the drain outlets and has exposed intervening playa with widths ranging from one quarter mile to more than one mile depending on location. This is illustrated in Figure 9-2 by a series of aerial images for selected years from 1997 to 2019.
As illustrated in Figure 9-2, the Playa Wetland Communities have occurred and expanded as a relatively recent consequence of the shoreline retreat. While the drivers for the location and extent of the wetlands include the drainage outflows coupled with the Salton Sea recession, the relationship between areal extent of the playa wetlands, drain flows, Salton Sea recession, and other factors remain uncertain. The Playa Wetland Communities may continue to change over time affected by continuing Salton Sea recession and by future Salton Sea restoration activities. The interconnection between these factors is uncertain, changing as the Salton Sea recedes, and dependent on other state and federal entities’ management of the Salton Sea.
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Indio Subbasin Water Management Plan Update 9-18 TODD/W&C Figure 9-2. Aerial Imagery showing Salton Sea Recession
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Indio Subbasin Water Management Plan Update 9-19 TODD/W&C
9.7 Water Quality Constituents of Concern
The 2010 CVWMP Update identified specific water quality issues including salinity, arsenic, perchlorate, hexavalent chromium (chromium-6), uranium, nitrate, carcinogens, and Endocrine Disrupting Compounds (EDCs). Some of these were regarded as emerging issues, not having violated water quality standards. As noted in the Alternative Plan Bridge document, the 2010 CVWMP Update did not establish specific water quality thresholds and goals. However, through the Alternative Plan process, the GSAs have continued to identify and track the occurrence of constituents of concern (COCs) with reference to established drinking water standards, have maintained an extensive water quality monitoring program, and have implemented applicable management responses. This is reflected in Chapter 8, Regulatory and Policy Issues, and in Chapter 4, Current and Historical Groundwater Conditions. Chapter 4, Current and Historical Groundwater Conditions, identifies current COCs to include salinity (total dissolved solids or TDS), nitrate, arsenic, chromium-6, uranium, fluoride, perchlorate, and DBCP. These are briefly described in Section 4.4 (along with any drinking water standards) and discussed in terms of occurrence in Indio Subbasin.
In Recommended Action 3, DWR staff recommend that the GSAs provide maps showing the areas affected by the primary water quality constituents of concern, which include, at a minimum, fluoride, arsenic, chromium-6, and DBCP. DWR staff recommend that the maps show the particular wells known to be affected by these constituents.
As documented in Chapter 4, Current and Historical Groundwater Conditions, this Alternative Plan Update has included substantial collection of water quality data into a database. This was followed by evaluation not only of the mapped extent of the four recommended COCs, but also TDS, nitrate, uranium, and perchlorate (see Figures 4-11 through 4-18). In addition, Chapter 4, Current and Historical Groundwater Conditions, provides water quality cross sections for constituents with vertical differentiation (TDS, nitrate, arsenic, and chromium-6) and time concentration plots that represent temporal trends in TDS and nitrate.
9.7.1 Description, Causes, and Effects of Undesirable Results In addition to salinity, the DWR Staff Report identifies fluoride, arsenic, chromium-6, and DBCP as a minimum list of primary water quality COCs. Given that, the following brief summaries are provided along with summaries of the GSA-identified COCs of uranium and perchlorate. These summaries include the drinking water standard (Maximum Contaminant Level [MCL]), general cause of the COC occurrence, distribution in the Subbasin, and management response. The following COCs are linked to potential health effects and all are being monitored. GSAs are addressing COC problems through efforts (such as the CVWD Disadvantaged Communities Infrastructure Task Force) to identify and consolidate small water systems with water quality and reliability issues. Chapter 4, Current and Historical Groundwater Conditions, and Chapter 8, Regulatory and Policy Issues, provide additional documentation and discussion. • Nitrate has a primary drinking water MCL of 45 mg/L, measured as nitrate. Nitrate concentrations in Indio Subbasin groundwater are variable, reflecting multiple sources such as historical extent of mesquite forests; use of nitrogen-based fertilizers for agriculture, golf courses, and landscaping; septic tank percolation; and wastewater disposal through percolation. Large water systems selectively drill wells in areas with low nitrate concentrations and have deactivated historically affected wells. The GSAs are assisting small water systems as noted above.
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Indio Subbasin Water Management Plan Update 9-20 TODD/W&C • Arsenic has a primary drinking water MCL of 10 micrograms per liter (μg/L). It is naturally occurring with high concentrations locally in the Indio Subbasin and at depth. Arsenic has been addressed in large public water systems by selectively drilling wells in areas or to depths with low arsenic concentrations, by decommissioning affected wells, or by providing water treatment to remove arsenic prior to delivery. Riverside County and the GSAs are assisting small water systems is being addressed by affected by arsenic as noted above. • Chromium-6 in Indio Subbasin is naturally occurring with relatively higher concentrations in the Thousand Palms and central Thermal Subareas. The total chromium (hexavalent and trivalent) primary MCL is 50 μg/L, but an MCL of 10 μg/L for chromium-6 was set in 2014 and later rescinded.
As discussed in Chapter 8, Regulatory and Policy Issues, the GSAs have anticipated a chromium-6 MCL that is lower than the total chromium MCL and have investigated possible water treatment options. Replenishment activities may reduce chromium-6 concentrations. • Uranium has a primary MCL of 20 picocuries per liter (pCi/L), or about 30 μg/L. Uranium in Indio Subbasin is naturally occurring with high concentrations in the northwestern portion. However, concentrations greater than the MCL have been detected in only four shallow monitoring wells. • Fluoride has a primary drinking water MCL of 2 mg/L. It is naturally occurring and found in high concentrations along the eastern side of the Indio Subbasin and northern boundary of the Salton Sea. Large water systems selectively drill wells in areas with low fluoride concentrations or provide treatment, and small water systems are assisted by the GSAs as noted above. • Perchlorate has a primary MCL of 6 μg/L and has been detected locally in Indio Subbasin. It may be natural but also is associated with historical manufacturing contamination that affected the Colorado River and has since been mitigated to below detection levels. • DBCP is a pesticide with a primary MCL of 0.2 μg/L. While banned since 1979 it is persistent in groundwater. It has been detected in private irrigation wells in a localized area of central Thermal Subarea. CVWD has managed replenishment to avoid mobilizing DBCP.
Salinity (TDS) is addressed in a subsequent section. Unlike the COCs above, TDS is regulated by Secondary MCLs (or Consumer Acceptance Contaminant Level Ranges) that are set by the SWRCB based on aesthetic concerns such as taste, color, and odor.
9.7.2 Evaluation of Sustainability
The DWR Staff Report finds that the Indio Subbasin GSAs have reasonable quantifications and standards related to groundwater quality, with a recommendation to provide maps to facilitate its ongoing evaluation of the Alternative Plan relative to achieving sustainability. These are provided in Chapter 4, Current and Historical Groundwater Conditions, along with other water quality information. As summarized in the Bridge Document, the Alternative Plan has included identification of COCs, monitoring of groundwater quality, tracking relative to drinking water standards (as relevant), reporting, and management actions. This Alternative Plan Update has improved the data compilation and management relative to water quality COCs and the documentation of groundwater quality conditions.
Groundwater quality monitoring, data compilation, and data review will continue on an established regular basis (see Chapter 10, Monitoring Program) and will detect emerging issues or water quality problems. The 5-Year Alternative Plan Updates will be sufficient for comprehensive examination of water
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Indio Subbasin Water Management Plan Update 9-21 TODD/W&C quality conditions relative to COCs such as listed above, given that groundwater quality conditions generally do not change rapidly. Groundwater quality conditions can be documented with maps and other graphics as warranted.
Additional efforts to define sustainability indicators or to set specific quantitative thresholds are not needed at this time for COCs such as those listed above. However, if a COC water quality condition develops or is recognized with significant and unreasonable results throughout the Subbasin and associated with Subbasin management activities, the ongoing monitoring allows detection, analysis, and reporting of the issue.
9.8 Water Quality Management
The Alternative Plan has recognized salt addition from imported Colorado River water as a significant impact related to managing groundwater overdraft. Elimination of overdraft was identified in the 2002 CVWMP and retained in the 2010 CVWMP Update as a primary goal. This goal recognized the multiple adverse effects of overdraft including chronic groundwater level declines, storage depletion, irreversible subsidence, and seawater intrusion potentially resulting in permanent loss of freshwater storage.
Importation of Colorado River water for irrigation and for replenishment was recognized as critical for halting overdraft although it added salts. The Alternative Plan (including the 2002 CVWMP and 2010 CVWMP Update) has included ongoing studies to assess the addition of salts and to identify reasonable projects and management action.
As summarized in the DWR Staff Report, the GSAs have demonstrated understanding of the water quality impacts associated with using Colorado River to replenish groundwater and have investigated various means to address such impacts, including preparation of a SNMP. As a near-term path toward sustainability with regard to salt management, the DWR Staff Report strongly encouraged the GSAs to further quantify the nature and scope of water quality issues associated with water importation, to establish reasonable and achievable standards, and to begin to adopt and implement projects and management actions to achieve sustainability with regard to groundwater quality.
Specifically, in Recommended Actions 4 and 4a, DWR staff recommend that the GSAs incorporate an approved SNMP into future iterations of the Alternative Plan and continue efforts to study the rate and level of increased salt contents in groundwater due to importation of Colorado River water.
9.8.1 Description, Causes, and Effects of Undesirable Results Salinity was described in the 2002 CVWMP and 2010 CVWMP Update in terms of the salt balance (salt inputs, salt outputs, and net addition). Those descriptions have been supplemented in Chapter 4, Current and Historical Groundwater Conditions, of this Update. Section 4.4, Groundwater Quality, presents a TDS map representing recent conditions, water quality cross sections, and time concentration plots that show temporal trends in TDS.
As discussed in Chapter 4, Current and Historical Groundwater Conditions, groundwater in the Indio Subbasin shows a wide range of salinity, measured in terms of TDS concentrations. TDS is regulated by Secondary MCLs (or Consumer Acceptance Contaminant Level Ranges) that are set by the SWRCB based on aesthetic concerns such as taste, color, and odor. Undesirable results of elevated TDS to drinking water systems can include damage to plumbing and appliances, increased treatment costs, use of bottled water, and increased sampling and monitoring. A recommended level is 500 mg/L, an upper level is 1,000 mg/L, and a short-term level is 1,500 mg/L.
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Indio Subbasin Water Management Plan Update 9-22 TODD/W&C The spatial distribution of TDS (see Figure 4-11) shows a general range of concentrations from less than 250 mg/L in the center of the Subbasin to more than 1,500 mg/L near the Salton Sea. Similarly, the water quality cross sections in Chapter 4, Current and Historical Groundwater Conditions, indicate that TDS concentrations generally are less than 500 mg/L with lowest concentrations in deep wells in the central Indio Subbasin. TDS concentrations in shallow zones typically are higher and more variable than in deeper zones.
The spatial and vertical distribution of TDS
in groundwater reflects multiple sources
including deep infiltration of precipitation,
percolation of precipitation runoff, recharge
of imported Colorado River water,
percolation of treated wastewater, seepage
from septic systems, return flows from
agricultural and landscape irrigation, and
subsurface inflows from adjacent bedrock,
other Subbasins (e.g., Desert Hot Springs
Subbasin) and deep thermal sources (West
Yost, 2021). Historical intrusion from the
Salton Sea also has been indicated (see
Section 9.10). In addition, the occurrence
and distribution of TDS in the Indio Subbasin
has been influenced by historical land uses and water/wastewater management practices.
Percolation through the soil and unsaturated zone involves complex processes that affect the volume, concentration, and specific constituents of TDS; these processes include evapotranspiration that concentrates salts in the root zone and geochemical transformations. Once in the groundwater system, the groundwater flow generally is from northwest to southeast (toward the Salton Sea). However, salt migration through the groundwater system (both vertical and horizontal) is driven by dynamics of groundwater recharge and discharge and thus influenced not only by recharge/percolation, but also by groundwater pumping and the presence of agricultural drain systems that intercept and discharge shallow groundwater. Such relationships are particularly important in the East Valley, where higher salinity occurs in perched and shallow zones. Under conditions of overdraft, lowered groundwater levels in the deep Principal aquifer can result in a downward groundwater flow gradient that could allow higher salinity water to migrate downward to affect deeper zones. Reversal of overdraft and restoration of upward gradients flushes the saline perched water into the agricultural drains and out of the system, thereby protecting deep groundwater quality.
Outflows of TDS from the groundwater systems are primarily through groundwater pumping, agricultural drain flows to the CVSC and Salton Sea, and subsurface outflow toward the Salton Sea.
9.8.2 Salt and Nutrient Management Plan
A SNMP was developed by the CVWD, DWA, and IWA and submitted to the Colorado River RWQCB in 2015. The 2015 Coachella Valley SNMP describes hydrogeology, ambient groundwater quality, projected water quality, objectives, management strategies, and a monitoring plan. However, in a letter (RWQCB, February 19, 2020), the RWQCB provided comments and recommendations on the 2015 SNMP’s compliance with the updated Recycled Water Policy (Colorado River Basin RWQCB, 2020).
CVWD monitors water quality in groundwater, surface
water, and recycled water.
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Indio Subbasin Water Management Plan Update 9-23 TODD/W&C The Salt and Nutrient Management Plan for the Coachella Valley Groundwater Basin (CV-SNMP) was restarted in 2020 by the CV-SNMP agencies (water and wastewater agencies including CVWD, CWA and Coachella Sanitary District, DWA, IWA, Myoma Dunes Mutual Water Company, VSD, MSWD, and City of Palm Springs) working in cooperation with RWQCB staff. This has involved preparing a SNMP Development Workplan to define the approach to be used to update the CV-SNMP in a manner that addresses management of salts and nutrients from all sources in order to protect beneficial uses, comply with the Recycled Water Policy (as revised in 2018, see Chapter 8, Regulatory and Policy Issues), and to address the specific findings and recommendations previously provided by RWQCB staff. The SNMP Development Workplan includes a Groundwater Monitoring Program Workplan (West Yost, 2020) to define the updated SNMP monitoring network, including wells needed to address network gaps, which will be used to monitor the spatial and vertical distribution of salts and nutrients in the Basin.
As of August 2021, workplan development has included preparation of a Groundwater Monitoring Workplan, which was approved by the RWQCB on February 21, 2021. The agencies have begun implementing the Groundwater Monitoring Program Workplan and will submit annual reports to the RWQCB by March 31 of each year beginning in 2022. A draft SNMP Development Workplan was submitted to the RWQCB on May 3, 2021 (West Yost, 2021). The agencies are working on integrating comments received from the RWQCB and will submit the final SNMP Development Workplan in September 2021.
Implementation of the SNMP Development Workplan is scheduled to begin during the first quarter of 2022.
The SNMP update and Alternative Plan Update are coordinated efforts. Elements of this Plan Update specifically supporting the SNMP include:
• Collection and organization of water quality data into a database • Evaluation of the sources, areal extent, vertical distribution, and time trends for TDS and nitrate • Analysis of the water budget (which supports analysis of TDS and nutrient loading, assimilative capacity, etc.)
• Update and refinement of the numerical model (a potential basis for fate and transport modeling) • Improvement of the monitoring program relative to TDS, nitrate, and shallow/deep zones • Identification of projects and actions relevant to water quality management.
The CV-SNMP addresses the Coachella Valley Groundwater Basin (DWR Basin No. 7-021 excluding the San Gorgonio Pass Subbasin) and therefore includes the Indio Subbasin. The Alternative Plan Update can incorporate elements of an approved SNMP relevant to the Indio Subbasin and within the context of the basin-wide SNMP. Progress on the implementation of the SNMP Development Workplan will be provided in the Indio Subbasin Annual Reports and the next 5-year Alternative Plan Update.
9.8.3 Continuing Studies of Salinity in Groundwater
Staff of both DWR and the Colorado River Basin RWQCB have recommended additional study of salinity in groundwater. The DWR Staff Report (Recommendation 4a) calls for continuation of efforts to study the rate and level of increased salt contents in groundwater due to Colorado River importation.
Additional study of salinity in groundwater—including analysis of the rate and level of increased salt contents in groundwater due to Colorado River importation—will be achieved in large part by the CV- SNMP update. Such analysis will be based on data collection to characterize TDS and nitrate loading, including not only quality data but also volumes of multiple sources such as subsurface inflow, replenishment (including the Colorado River sources), wastewater and recycled water, septic systems,
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Indio Subbasin Water Management Plan Update 9-24 TODD/W&C and applied water. The analysis also will include characterization of current groundwater quality in all Subbasin areas/Subareas (with delineation of Management Zones), identification of areas of historical changes, and documentation of historical trends in TDS and nitrate loading. Overall, the analysis will satisfy the recommendation for more information on the rate and level of increased salt due to Colorado River importation.
More broadly, these analyses provide the necessary baseline for SNMP forecasting of TDS and nitrate concentrations in groundwater. The forecasting (using enhanced modeling tools to be developed as part of the SNMP update) will involve simulation of a baseline scenario and management scenarios.
Subsequent selection of a preferred CV-SNMP scenario can be the basis for establishment of management zones (including consideration of vulnerable areas), description of groundwater beneficial uses for each management zone, recommendation of numeric TDS objectives for each management zone, identification of projects and management actions, and development of implementation measures and schedules to achieve sustainability with regard to groundwater quality.
In addition to the CV-SNMP, this Alternative Plan Update has included the systematic efforts of building the data management system, analyzing available water quality data, reviewing the results for data gaps, and planning for new monitoring sites. While not implemented solely to understand salinity, the update and refinement of the numerical groundwater flow model, assessment of the groundwater basin water budget, and quantification of water supplies and demands all contribute to understanding of the groundwater system, which is fundamental to studying salinity.
The assessment of the monitoring network for this Update has been coordinated with the development of the CV-SNMP Development Workplan, which includes a Groundwater Monitoring Program Workplan (West Yost, 2020). The CV-SNMP Groundwater Monitoring Program Workplan describes the physical setting of the groundwater basin as context for the monitoring network, presents an initial sampling network, identifies existing spatial and vertical gaps in the monitoring network, and describes how the gaps will be filled and how the monitoring program will be implemented. Specific wells are identified for groundwater sampling, including 83 wells representing the shallow aquifer system, 98 wells for the deep aquifer system, and 6 wells for the perched aquifer system. The SNMP Groundwater Monitoring Program Workplan also identified 23 gaps in the monitoring network and provides justification for filling these gaps. Reasons for inclusion in the SNMP monitoring program include spatial gaps and the need for tracking potential sources such as subsurface inflows, WWTP discharges, septic tank areas, agricultural and landscaping/golf course areas.
As part of ongoing groundwater basin management in 2021, the GSAs have prepared two applications to DWR for Technical Support Services to install new monitoring wells in the Indio Subbasin and Mission Creek Subbasin. The proposed monitoring wells would provide both groundwater levels and quality data, and thereby support improved basin management for the Indio Subbasin Alternative Plan Update, Mission Creek Alternative Plan Update, and the CV-SNMP.
Chapter 9: Sustainable Management FINAL
Indio Subbasin Water Management Plan Update 9-25 TODD/W&C
9.9 Drain Flow Evaluation
As presented in Chapter 2, Plan Area, and Chapter 3, Hydrogeologic Conceptual Model, an extensive agricultural drainage system (both subsurface tile drainage systems and surface drains) was installed in the East Valley to control high water table conditions, to intercept poor quality shallow groundwater, and to convey the water to the CVSC and Salton Sea. Drain flows are measured at 27 drains and the CVSC, and also have been simulated using the numerical model.
In its Staff Report (Recommended Action 6), DWR recommends clarification of whether there is a minimum threshold associated with the amount of subsurface drain flow below which significant and unreasonable undesirable results would occur, and what that quantified minimum threshold is, if applicable, and the implementation horizon for when the goal for the amount of subsurface flow will be achieved.
As a matter of clarification, the 2010 CVWMP Update presented simulated drain flows based on modeling of future water supply and management scenarios at the time. This Alternative Plan Update revises some of the planning assumptions used in the 2010 CVWMP Update (see Chapter 7, Numerical Model and Plan Scenarios, for updated scenarios) based on current conditions. The 2010 model simulations provided a range of potential 2045 drain flows and predicted that drain flows generally would increase. Higher drain flows are beneficial because they are a response to higher groundwater levels in the East Valley which are protective of the deep aquifer and because they promote export of salt from the Subbasin.
As discussed above, drain flows presented in
the 2010 CVWMP Update were an output of
the model representing projected cumulative
drain flows from open drains and the CVSC.
While providing useful simulations, analysis,
and guidance for water management planning,
the 2010 CVWMP Update did not present a
minimum threshold for drain flows as now
understood under SGMA and GSP Regulations.
Instead, a more direct metric for evaluating
sustainability with regard to protection of the
deep aquifer and salt export is being
considered by the GSAs.
CVWD will be undertaking a drain flow study
(see Chapter 12, Plan Evaluation and
Implementation) to improve understanding of the relationships among groundwater levels, drain flows, salt export, and protection of the deep aquifer throughout the confined aquifer areas in the East Valley.
The Drain Flow Study will study the relationship between groundwater levels in the various aquifers, current and historical crop water application, and flows and salt export through the drain system.
Geochemical and isotope studies may be implemented to assess potential water sources (return flows vs rising groundwater) of drain flows. This study will utilize available groundwater and drain flow information; drain flows have been measured monthly at 27 drain sites since 1985 and water quality sampling has occurred at least annually at 25 sites since 1992. The drain flow study will include review of the amount, location, timing, and water quality of flows at all drain locations and the CVSC. In addition, The Grant Street Drain is part of CVWD’s agricultural
drain system.
Chapter 9: Sustainable Management FINAL
Indio Subbasin Water Management Plan Update 9-26 TODD/W&C planned monitoring well network improvements will yield additional data on perched, shallow, and deep groundwater levels and quality. All data will be compiled into a GIS database as part of the Data Management System (DMS). In addition, the drain flow study can support calibration of the numerical model (which simulate drain flows as an output) and provide important input to any salt balance studies.
By way of background, downward migration of groundwater is a function not only of geology (i.e., the fine-grained aquitard in the East Valley; see Chapter 3, Hydrogeologic Conceptual Model), but largely of vertical hydraulic head differences. Available data indicate that high groundwater levels in the deep zones are generally protective of those deep zones. This is substantiated by the evaluation of TDS and nitrate concentrations with depth in East Valley cross sections (Figures 4-30 through 4-33) that show low concentrations of TDS and nitrate at depth, despite decades of active irrigated agriculture, and higher concentrations in shallow zones. It is also supported by the TDS and nitrate time-concentration plots (e.g., Figure 4-34) that indicate relatively low concentrations in deep wells and less variability, indicating reduced exposure to shallow influences.
Building on the 2010 CVWMP Update, and applying the concepts of SGMA, the GSAs have defined a specific, potential undesirable result, which is degradation of water quality in the deep Principal Aquifer due to downward migration of water with elevated TDS levels found in shallow groundwater zones. High groundwater levels in the deep zone have a direct relationship with good water quality at depth, and accordingly, the GSAs are considering groundwater levels as an appropriate proxy.
According to SGMA, groundwater levels can serve as a useful proxy for a minimum threshold. However, documentation of a strong correlation is needed between the metric (groundwater levels) and the specific undesirable result being assessed (degradation of the deep Principal Aquifer). This documentation is provided in part by this Alternative Plan Update. Additional information will be provided by the new monitoring wells being installed in 2021, specifically with regard to differentiation of shallow and deep groundwater levels and quality. Assuming that groundwater levels can be serve as proxy, a subsequent step will involve identification of representative monitoring sites and establishment of minimum thresholds with respect to protecting deep water quality.
9.10 Seawater Intrusion
SGMA generally has perceived seawater intrusion relative to the Pacific Ocean and not an inland body such as the Salton Sea. The Salton Sea is distinguished by several aspects: salinity in excess of 69 parts per thousand (about twice the amount in the ocean), salinity that gradually is rising, surface water levels that are decreasing, and a shoreline that is retreating.
9.10.1 Background on Monitoring and Management for Seawater Intrusion Seawater intrusion from the Salton Sea has been emphasized in the Alternative Plan as a potentially substantial and irreversible consequence of overdraft, whereby reduced groundwater pressure in Subbasin aquifers would cause relatively dense saline water to intrude and displace freshwater. The 2002 CVWMP Update noted the difficulties in reversing seawater intrusion and removing salts with the potential for permanent loss of freshwater storage. Thus, seawater intrusion is a consequence of overdraft with undesirable results including adverse effects on groundwater quality and associated loss of groundwater supply and loss of groundwater storage.
Recognizing these potential undesirable results in the context of overdraft in the East Valley, the 2002 CVWMP and 2010 CVWMP Update identified and implemented projects and management actions to halt
Chapter 9: Sustainable Management FINAL
Indio Subbasin Water Management Plan Update 9-27 TODD/W&C overdraft. These projects and actions including groundwater replenishment, source substitution, and conservation have been successful in halting and reversing groundwater level declines, increasing groundwater storage, and restoring groundwater outflows to stop seawater intrusion.
CVWD installed nested monitoring wells in 1995 and 2002 near the Salton Sea to provide site-specific data to assess the risk of seawater intrusion (see list in Table 10-2). Monitoring of these wells for levels and quality (as part of the overall monitoring program) allows documentation of areal and vertical extent of seawater intrusion (if any in the vicinity of the wells) and tracking of trends that could provide early warning of seawater intrusion. Groundwater quality constituents including TDS and chloride are tracked in the nested monitoring wells. While TDS concentrations in one of the deepest zones (deeper than 1,430 feet below ground surface) are elevated and fluctuating (see Chapter 4, Current and Historical Groundwater Conditions), the nested monitoring wells have shown no evidence that seawater intrusion is occurring.
In addition, local groundwater management (see Chapter 4, Current and Historical Groundwater Conditions) has focused on minimizing potential seawater intrusion by increasing groundwater levels and restoring groundwater outflow to the Salton Sea. While protective groundwater elevations were not determined, the groundwater flow model was applied to evaluate seawater intrusion as a potential inflow to the Indio Subbasin groundwater. This approach has provided a broad indicator of the risk of seawater intrusion.
The DWR Staff Report acknowledges the Alternative Plan approach and in Recommended Action 5 indicates the following recommended actions for the Update as rephrased below:
• Discuss why the water balance includes inflow from the Salton Sea to the Indio Subbasin. • Discuss how recent groundwater levels near the Salton Sea compare to the modeled elevation. • Correlate Salton Sea inflow with recent groundwater levels and the groundwater model. • Provide the modeled groundwater elevation that minimizes the risk of saltwater intrusion.
Each of these is addressed in the following sections.
9.10.2 Water Balance and Inflow from Salton Sea
DWR recommended discussion of why the water balance includes inflow from the Salton Sea to the Indio Subbasin. This question is relevant to the water balance (see Chapter 7, Numerical Model and Plan Scenarios) and to a description of the undesirable results of seawater intrusion. The undesirable results of Salton Sea intrusion have been long recognized in the Indio Subbasin as degradation of water quality and loss of freshwater storage.
The water balance includes inflow from the Salton Sea because it includes all inflows and outflows to the Subbasin and then uses the groundwater flow model to compute water levels and change in storage.
Accounting for all elements of the water balance is fundamental to understanding the local groundwater system. In other words, seawater intrusion is considered an inflow to the water balance but is not considered a groundwater supply.
9.10.3 Groundwater Elevations and Salton Sea Inflow
DWR recommended discussion of how recent groundwater levels near the Salton Sea compare to the modeled elevation. The correlation of measured and modeled groundwater levels near the Salton Sea is illustrated in Figure 7-17 showing model calibration hydrographs. As discussed in Chapter 7, Numerical Model and Plan Scenarios, the model is very well calibrated.
Chapter 9: Sustainable Management FINAL
Indio Subbasin Water Management Plan Update 9-28 TODD/W&C With regard to Salton Sea inflow, the groundwater flow model has been used to simulate flow between the Indio Subbasin and the Salton Sea. For this Plan Update, the 2010 CVWMP Update model input data were updated for 1997-2019, and some were modified including addition of Salton Sea bathymetry and use of Salton Sea elevations for 2009-2019 to account for Salton Sea level declines. As illustrated in Figure 7-20, inflows from Salton Sea have decreased since about 2005 and outflows to the sea have increased.
Net groundwater outflow to the Sea first occurred in 2015. This is consistent with generally increasing groundwater levels after about 2010.
Groundwater elevation contour maps are provided in the Indio Subbasin Annual Reports for water years 2016-2017, 2017-2018, 2018-2019, and 2019-2020, roughly the period when groundwater outflows to the Salton Sea have exceeded inflows. For reference, the elevation of the Salton Sea has declined from about -235 to -238 feet msl over this period. Review of these maps (with a focus on the groundwater elevation contours closest to the Salton Sea) show the -200-foot contour crossing the shoreline in 2016- 2017 and 2017-2018. In the successive two maps, the -200-foot contour is completely inland (as is the - 220-foot contour) indicating that groundwater levels have risen. At the shoreline, current groundwater levels are mapped as about 18 feet above the current Salton Sea level. This differential would increase with Salton Sea level decline and with groundwater level rise.
In Chapter 7, Numerical Model and Plan Scenarios, Figure 7-14 shows the simulated groundwater elevations in 2020 for the shallow and deep aquifers. Consistent with the 2019-2020 measured data, the -200 foot and -220 foot contours in the shallow aquifer are inland of the shoreline and higher than the sea while the –200 foot contour for the deep aquifer crosses the shoreline, indicating upward groundwater flow. These modeled groundwater elevations indicate a minimal risk of saltwater intrusion.
Regular review of simulated groundwater elevations in the vicinity of the Salton Sea is warranted in addition to the data review and water budget modeling as part of the Annual Reports and 5-Year Updates.
The nested wells provide real data on local groundwater quality from discrete depth zones, any of which could potentially be affected by seawater intrusion. Complementary to the local, zone-specific data is the modeling assessment of outflows and inflows, which provides a broad indicator of net potential for seawater intrusion for the Subbasin.
Similarly, the simulated groundwater elevations can be used as a general indicator of the relative risk of seawater intrusion along the shoreline. Such use of simulated groundwater levels is not a substitute for analysis of measured groundwater levels. However, it can be a reasonable, cost-effective indicator given the low potential for seawater intrusion, as evidenced by the net outflow of groundwater from the Subbasin to the Salton Sea and the lack of data indicating seawater intrusion.
In addition, Salton Sea water levels are currently decreasing, and the shoreline is retreating. Accordingly, the risk of seawater intrusion is declining. Review of any groundwater levels relative to the Salton Sea water levels will need to be monitored and evaluated regularly until the Salton Sea is stabilized.
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-1 TODD/W&C CHAPTER 10: MONITORING PROGRAM
The Indio Subbasin has been extensively monitored by the Groundwater Sustainability Agency (GSAs) for decades, guided by the primary objective to evaluate the effectiveness of water management programs and projects and to modify actions and plans based on factual data. This Alternative Plan Update continues and builds on the existing monitoring programs as presented in previous CVWMP documents and summarized in the Bridge Document (Indio Subbasin GSAs, 2016; see also summary in Chapter 2, Plan Area).
This chapter includes description of the monitoring network, methods and protocols for data collection, and development and maintenance of the data management system (DMS). The monitoring program has been assessed with reference to the sustainability goal and objectives, data gaps have been reviewed, and improvements have been identified for implementation.
10.1 Description of Monitoring Network
As summarized in the following sections, the Monitoring Network addresses groundwater levels, climate and hydrology, groundwater production, subsidence, water quality, and seawater intrusion.
Table 10-1 and the following text provide a summary of
the monitoring network, which documents
groundwater and related surface water and subsidence
conditions, in terms of the type of measurement,
monitoring site locations and spatial coverage,
monitoring frequency, and involved agencies. In most
cases, monitored data are compiled and summarized in
Annual Reports; these data will also be used to update
the Alternative Plan Update in 5 years.
Table 10-1 also documents other sources of data that
are important input to the water budget analysis and to update of the numerical model. These include managed
water supplies and deliveries, such as imported water
deliveries, groundwater replenishment volumes,
wastewater percolation and water recycling, and
municipal water use. As shown, these are mostly
metered, and the data are compiled monthly and
documented in the Annual Report as part of the water
budget analysis.
The GSAs monitor groundwater levels and
quality.
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-2 TODD/W&C Table 10-1. Summary of the Monitoring Network
Monitored Variable Type of
Measurement
Locations Data Interval Data Collection
Agency
Database Storage
Agency
Notes
Groundwater
Levels
Groundwater levels Depth to water,
feet
345 wells in Indio
Subbasin
Quarterly to
Semiannual
All GSAs Indio GSAs Protocols detailed
in Section 10.2.2
Climate and
Hydrology
Rainfall Rain gauge, daily
total, inches
12 Riverside County
stations
Daily Riverside County
Flood Control and
Water Conservation
District
Riverside County
Flood Control and
Water Conservation
District
Download from
web annually for
annual water
budget and model
update
Reference ET (ET0) Daily ETo, inches 4 CIMIS Stations Daily CA DWR, CIMIS program
CIMIS Download from
web
Stream flow Daily average flow,
cfs
19 active USGS
gages
Daily/15 min
interval
USGS USGS Download from
web
Drain flows cubic feet per
second, cfs or total
flow AF
27 sites Monthly CVWD Indio GSAs
Groundwater
Production
Agricultural Metered monthly
total pumping by
well, if above
threshold (above 25
AFY in CVWD and
above 10 AFY in
DWA)
Agricultural
irrigation well
locations
Monthly CVWD, DWA
Indio GSAs Pumping threshold
is above 25 AFY in
CVWD and above
10 AFY in DWA
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-3 TODD/W&C Monitored Variable Type of
Measurement
Locations Data Interval Data Collection
Agency
Database Storage
Agency
Notes
Golf Course Metered monthly
total pumping by
well if above
threshold (above 25
AFY in CVWD and
above 10 AFY in
DWA)
Golf well locations Monthly CVWD, DWA Indio GSAs
Municipal Metered monthly
total pumping by
well if above
threshold (above 25
AFY in CVWD and
above 10 AFY in
DWA)
Municipal well
locations
Monthly Indio GSA Indio GSAs
Community Water
Systems
Systems with
pumping above
threshold are
metered (above 25
AFY in CVWD and
above 10 AFY in
DWA).
Community Water
System wells with
meters
Monthly CVWD, DWA Indio GSAs
Other (e.g., private
individual wells)
Metered
groundwater use
(above 25 AFY in
CVWD and above
10 AFY in DWA)
Well locations Monthly CVWD, DWA Indio GSAs
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-4 TODD/W&C Monitored Variable Type of
Measurement
Locations Data Interval Data Collection
Agency
Database Storage
Agency
Notes
Subsidence
Subsidence InSAR satellite
mapping of ground
displacement, and
GSP Stations
California
groundwater basins
including Indio
Subbasin
Displacement,
2015-2020,
2019-2020, Annual
updated from DWR
DWR (InSAR) DWR SGMA Data
Portal
Download annually,
smooth InSAR
raster data sets
(see Section
6.4.4.6), compare
cumulative
elevation change
since 2015 against
Minimum
Threshold criterion.
Subsidence USGS Coachella Valley 2015-2023 USGS USGS Published report to be provided by
USGS before June
30, 2025.
Groundwater
Quality
Indio Groundwater
Quality Monitoring
Program including
monitoring for CV-
SNMP
Specific
conductance, TDS,
N, and general
minerals
Existing wells in
Indio Subbasin (98
deep, 83 shallow, 6
perched) and 23
proposed well
locations
Quarterly/
Triannual
All GSAs and CV-
SNMP Agencies
Indio GSAs/GAMA Additional
constituents; COCs
Compliance
Monitoring -
RWQCB
Varies depending
on discharge order
WWTP, WRP, other
regulated facilities
Various All GSAs SWRCB Geotracker
database
Download data
annually from
Geotracker
Municipal systems Specific
conductance, TDS,
N, and general
minerals; Title 22
Municipal supply
wells
Monthly All GSAs Indio GSAs Water quality
collected by GSAs
and submitted to
DDW
Triannual
to
ual
Monthly to
ual
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-5 TODD/W&C Monitored Variable Type of
Measurement
Locations Data Interval Data Collection
Agency
Database Storage
Agency
Notes
Rural ag/domestic
wells; community
water systems;
Specific
conductance, N,
and other
constituents
(depending on
monitoring agency)
About 90 wells in
Indio
Various DDW, RWQCB,
USGS, DWR, DPR
SWRCB GAMA
database
Download data
every three years
from GAMA
Other Water
Budget Elements
Canal deliveries- All
Uses
Metered water
deliveries, AF
All points of
delivery
Monthly CVWD Indio GSAs
Surface Water
Diversion
Volume diverted
from tributary
watersheds, AF
Whitewater River,
Snow Creek, Falls
Creek , and Chino
Creek
Monthly DWA Indio GSAs
Groundwater
Replenishment
Reported as acre-
feet per month
Whitewater,
Thomas E Levy,
Palm Desert GRFs
Monthly CVWD, DWA Indio GSAs
Wastewater
percolation ponds
losses
WWTP effluent
discharge,
evaporation,
percolation, AF
WWTPs Monthly CVWD, DWA Indio GSAs
Wastewater
discharge to CVSC
AF CVSC Monthly CVWD Indio GSAs
Recycled water use Recycled water
delivery, AF
CVWD
DWA
Monthly CVWD, DWA Indio GSAs
Municipal Water
Use
Metered water use
by use type
(residential,
commercial,
industrial, etc.)
All water retailers Monthly All GSAs Indio GSAs
Crop Census Land Use by crop
type, acreage
CVWD Trimester CVWD Indio GSAs
Salton Sea
Elevation
Salton Sea USGS USGS
Continuous/15 min
reporting
CVWD, VSD, CWA,
and Kent Seatech
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-6 TODD/W&C
10.1.1 Groundwater Levels
As described in Chapter 2, Plan Area, the Indio
Subbasin GSAs monitor groundwater levels in
345 wells as part of their respective
groundwater level monitoring programs
(Figure 2-11 shows the wells in the current
monitoring network). As shown, 52 of these
wells have been monitored by the Indio
Subbasin GSAs and Mission Springs Water
District (MSWD) as part of the California
Statewide Groundwater Elevation Monitoring
(CASGEM) program. As part of
implementation, the GSAs will upload water
levels for the Key Wells (see Chapter 9,
Sustainable Management) to the Department
of Water Resources (DWR) Monitoring Well
Module and data will be publicly accessible.
10.1.1.1 Spatial and Vertical Coverage
Locations of all wells monitored for groundwater levels are shown in Figure 2-11, while Figure 9-1 shows the Key Wells used to monitor groundwater levels with respect to the Minimum Thresholds established by the GSAs (see Chapter 9, Sustainable Management). The 57 Key Wells for groundwater levels are also listed in Table 9-1 with the respective Minimum Thresholds. The methodology used to select the Key Wells is described in Chapter 9, Sustainable Management.
The scientific rationale for inclusion of key wells in the overall GSAs groundwater level monitoring program has considered the following factors:
• Spatial distribution and density of wells, accounting for variable geographic conditions including topography, hydrology, geologic structures, aquifer characteristics, confined and unconfined conditions, pumping patterns, management activities (including replenishment), and potential impacts to beneficial uses/users
• Length, completeness, and reliability of historical groundwater level record • Well depth and information on well construction
• Regular access to the well for measurements.
Wells in the Indio Subbasin groundwater level monitoring program have unique well information including a well identification number, an identified vertical reference point for measurements, and well completion report if available.
Well density has been a consideration in identifying new dedicated monitoring well sites and adding wells to the monitoring program. By way of comparison, DWR guidance (DWR, Dec 2016 BMP, Table 1) generally recommends between one to ten monitoring wells per 100 square miles. The Indio Subbasin program exceeds this guidance with an area of about 525 square miles and 2020 monitoring of more than 385 wells. More importantly, the Indio Subbasin monitoring program has been developed to account for the variable spatial factors listed above.
Monitoring well located at PD-GRF.
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-7 TODD/W&C In the future, some wells may become unavailable for various reasons (e.g., loss of access). Consistent with ongoing practice, the GSAs will continue to assess the monitoring well network and find suitable replacements. Monitoring program improvements as part of the Alternative Plan Update (coordinated with the Salt and Nutrient Management Plan [SNMP]) include identification of additional existing wells for monitoring across the Subbasin and will include installing new dedicated monitoring wells. Most wells with known construction have long screened intervals and many are screened at depths greater than 300 feet below ground surface. Information on vertical groundwater gradients is available from nested wells, from comparison of deep wells with nearby relatively shallow monitoring wells, and from observation of artesian conditions. Available data have allowed identification of perched, shallow, and deep aquifer zones in the East Valley (see Chapter 3, Hydrogeologic Conceptual Model). Planning is underway to install additional monitoring wells representing the perched and shallow zones; this is a collaborative effort of the Alternative Plan and CV-SNMP (see Section 10.1.5).
10.1.1.2 Monitoring Frequency
Sustainable Groundwater Management Act (SGMA) and the California Statewide Groundwater Elevation Monitoring Program (CASGEM program) require collection of static groundwater elevation measurements at least two times per year to represent seasonal low and seasonal high groundwater conditions. The GSAs in the Indio Subbasin generally provide groundwater level data at least three times a year (with more frequent monitoring at some locations), which is more frequent than recommended and has allowed tracking of seasonal and long-term trends.
10.1.1.3 Climate, Streamflow, and Drain Flow
As summarized in Chapter 2, Plan Area, and Table 10-1, the Indio Subbasin Monitoring Program provides information on climate (rainfall and evapotranspiration), streamflow, and drain flows.
10.1.1.4 Climate
Climate data (including temperature, evapotranspiration, and precipitation) are available from DWR’s California Irrigation Management Information System (CIMIS) for four active CIMIS stations (see Figure 2- 9 for spatial distribution). Precipitation data are collected by the 12 Riverside County Flood Control and Water Conservation District precipitation monitoring stations, also shown in Figure 2-9. In addition, temperature and precipitation data are available from the National Oceanic and Atmospheric Administration (NOAA) station in Indio. As noted in Table 10-1, daily climate data are downloaded and compiled for the Annual Report. Data are used to support groundwater conditions characterization and evaluation of irrigation water demands (agricultural and golf course).
10.1.1.5 Streamflow
Streamflow is measured by the United States Geological Survey (USGS) at 19 locations within the Indio Subbasin, also shown in Figure 2-9. Surface water diversions by Desert Water Agency (DWA) from Snow, Falls, White Water, and Chino watersheds are measured by DWA. Daily streamflow data are downloaded and compiled annually as part of the Indio Subbasin Annual Reports.
10.1.1.6 Drain Flow
The Coachella Valley Stormwater Channel and associated drains (see Figure 2-5) receive intercepted shallow groundwater from agricultural fields and convey the flow to the Salton Sea. CVWD measures drain flows (volumetric meters or flow in cubic feet per second) on a monthly basis at as many as 27 drain
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-8 TODD/W&C sites (depending on occurrence of flow) plus monitoring of the CVSC. A USGS gage station measures flow in the lower CVSC near the Salton Sea (see Figure 2-9). The CVSC and portions of the drain system receive not only shallow groundwater but also flows of Coachella Canal water in excess of requested deliveries (regulatory water), treated wastewater, and fish farm effluent. The drain flow data are used in tracking groundwater outflow and in calibrating the numerical groundwater flow model.
10.1.2 Groundwater Production
CVWD and DWA have been monitoring
(assessing) groundwater production in the
Areas of Benefit (AOBs) making up the West
Whitewater River Subbasin Management
Area since 1982 and the East Whitewater
River Subbasin AOB since 2005. As defined
in the Water Code, Assessable Production
excludes groundwater production from
Minimal pumpers who extract 25 acre-feet
per year (AFY) or less within CVWD’s AOBs
and 10 AFY or less within DWA’s AOB. While
Water Code Section 31635.5 exempts
Minimal pumpers and production reporting
requirements for CVWD, the GSAs may
consider lowering the threshold for
reporting groundwater production as provided by SGMA authorities (Water Code Section 10725.8) excepting de minimis extractors (extracting two AFY or less per year for domestic purposes).
Groundwater extractors with production above the thresholds of 25 AFY within CVWD’s replenishment program areas and 10 AFY within DWA’s replenishment program area are required to install a water use measuring device (i.e., a meter). CVWD encourages well owners to allow CVWD to read their meters directly through metering agreements. However, the groundwater producer can choose to self-report groundwater use totals, if needed. The CVWD groundwater production data set is audited two times a year and summarized as part of the SGMA Annual Report and the annual Engineer’s Report. DWA also audits its groundwater production data as part of the Annual Report and their Engineer's Report.
Figure 2-13 illustrates the groundwater production across the Subbasin for Water Year (WY) 2018-2019.
CVWD and DWA will continue to collect data for all groundwater wells with pumping above the applicable thresholds. As indicated in Chapter 12, Plan Evaluation and Implementation, the planned Subbasin Well Inventory project will identify and compile information about all production wells in the Subbasin.
Resulting knowledge of existing wells will allow refinement of pumping estimates for wells that are not metered.
10.1.3 Subsidence
Land subsidence, resulting from groundwater level declines and aquifer system compaction, has been a concern in the Coachella Valley since the mid-1990s and has been investigated since 1996 through an on- going cooperative program between CVWD and the USGS (Sneed and Brandt, 2020). The USGS has applied satellite-based Global Positioning System (GPS) surveying techniques to determine the location, extent, and magnitude of the vertical land-surface changes in the Coachella Valley. These surveying techniques CVWD and DWA have been monitoring (assessing)
groundwater production since 1982.
Chapter 10: Monitoring Program FINAL
Indio Subbasin Water Management Plan Update 10-9 TODD/W&C include GNSS-Inferred Positioning System and Orbit Analysis Simulation Software (GIPSY-OASIS) and interferometric synthetic aperture radar (InSAR) methods. In addition to areal mapping of vertical changes in land surface elevation, GPS measurements have also been taken at 24 geodetic monuments that have been paired with nearby water level monitoring wells to assess relationships between subsidence and groundwater level change. Results of USGS studies are summarized in Chapter 4, Current and Historical Groundwater Conditions.
The USGS has provided data and analyses through a series of published reports that have addressed conditions from 1993 to 2017 (e.g., Sneed and Brandt, 2013; Sneed and Brandt, 2020). The partnership with USGS is continuing. For the Indio Subbasin, the objectives of the study (October 1, 2021, through June 30, 2025) are to (1) detect and quantify land subsidence using GPS methods (2015–22) and InSAR methods (2017–23) and (2) evaluate the relation between changes in land-surface elevation and groundwater levels at selected sites during 2015–23. USGS also will analyze DWR-provided InSAR results to compute changes in land-surface elevation in the Indio Subbasin during 2017–23. Findings will be published in a report in 2025.
In addition, DWR provides InSAR satellite-based data and GPS data to identify and assess land subsidence across many California groundwater basins, including the Indio Subbasin. The data are available through DWR’s SGMA Data Portal (see Table 10-1). As available, these data will be downloaded and reviewed annually to detect significant changes in land surface elevation. The utility of annual review will be re- evaluated at the next 5-Year Update, at which time the next USGS Report will be available.
10.1.3.1 Spatial Coverage
The satellite-based mapping provided by USGS (for example, see Figure 4-10) provides Subbasin-wide information on subsidence. In addition, Figure 2-10 shows the current network of GPS stations in the valley used by USGS. InSAR mapping for the entire Indio Subbasin is also available for download from the DWR Sustainable Groundwater Management Act (SGMA) portal.
10.1.3.2 Monitoring Frequency
The Monitoring Program will involve annual download and review of InSAR data from the DWR SGMA portal with analysis for any signs (rate and extent) of significant cumulative subsidence. The USGS report will be available for the next 5-Year Update.
10.1.4 Water Quality
Existing water quality monitoring programs for Indio Subbasin GSAs are summarized in Chapter 2, Plan Area, while Chapter 8, Regulatory and Policy Issues, includes discussion of various water quality topics and regulatory-driven water quality monitoring programs. As indicated in Chapter 8, Regulatory and Policy Issues, surface water and groundwater quality monitoring programs are conducted by various agencies for multiple purposes. These address local surface water, imported water sources, groundwater, recycled water, wastewater discharges, and agricultural drain water with sampling and analysis for different physical parameters, inorganic and organic chemical constituents, and/or microbiological organisms.
While being conducted beyond the scope of the Alternative Plan Update, these programs represent sources of information to better understand groundwater quality conditions and trends in Indio Subbasin.
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Indio Subbasin Water Management Plan Update 10-10 TODD/W&C
10.1.4.1 Water Quality Monitoring and Data Compilation
Multiple sources of water quality information are being compiled into the centralized DMS (See Chapter 12, Plan Evaluation and Implementation). As described in Chapter 4, Current and Historical Groundwater Conditions, this Alternative Plan Update has included compilation into a single database of groundwater quality data from various sources including the USGS National Water Information System and the SWRCB website and from each GSA. The GSAs conduct groundwater quality monitoring, as summarized below:
• CVWD—CVWD monitors domestic wells to monitor recharge areas, conducts special studies to address a specific parameter (such as hexavalent chromium) or a specific area, and conducts Coachella Valley Salt and Nutrient Management Plan (CV-SNMP) monitoring • CWA—CWA monitors its domestic wells and conducts CV-SNMP monitoring • DWA—DWA monitors its domestic wells, monitors for State emerging contaminants (e.g., per- and polyfluoroalkyl substances [PFASs]), and conducts CV-SNMP monitoring • IWA—IWA monitors its domestic wells and conducts CV-SNMP monitoring Figure 2-12 shows the spatial distribution of the wells with available water quality data used in this Alternative Plan Update. Chapter 4, Current and Historical Groundwater Conditions, provides the documentation and analysis of the groundwater quality data for multiple constituents of concern including salinity (total dissolved solids [TDS]), nitrate, arsenic, hexavalent chromium, uranium, fluoride, perchlorate, and dibromochloropropane (DBCP). This water quality data compilation included collection of water quality data not only for groundwater but also imported water sources, recycled water, and wastewater discharges for the period 1990 through 2019.
An additional source of relevant water quality data is from the agricultural drain system (see Figure 2-5) that intercepts shallow subsurface flow from agricultural fields in the East Valley. Drain flows are monitored for water quality at 27 drain outlets for general minerals and metals annually and for field pH, temperature, EC, and TDS semi-annually.
As discussed in Chapter 2, Plan Area and Chapter 8, Regulatory and Policy Issues, the SNMP for the Coachella Valley Groundwater Basin (CV-SNMP) was restarted in 2020. The CV-SNMP Groundwater Monitoring Workplan, included in Appendix 2-A, recommended a CV-SNMP monitoring network to include 187 existing wells with the suggested addition of 23 new wells. This Alternative Plan Update includes a focused effort to install additional monitoring wells, including application to DWR’s Technical Support Services (TSS) program for assistance in installing the monitoring wells.
The CV-SNMP agencies plan to monitor network wells at a minimum of once per 3 years, although many are monitored more frequently as part of other programs. The CV-SNMP Development Workplan, also included in Appendix 2-A, suggests a focused analyte list including TDS, nitrate, major cations, major anions, and total Alkalinity. CVWD and other GSAs also plan to add the identified constituents of concern (COCs) to this monitoring network to help meet the objectives of the Alternative Plan.
10.1.4.2 Spatial and Vertical Coverage
Figure 2-12 shows the spatial distribution of wells used in this Alternative Plan Update for groundwater quality characterization and mapping. The existing water quality monitoring programs provide adequate spatial coverage. The planned CV-SNMP monitoring network will provide very good coverage for TDS and nitrate monitoring, with potential extension to other constituents of interest.
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Indio Subbasin Water Management Plan Update 10-11 TODD/W&C Water quality concentrations vary with depth depending on constituent. As shown in Chapter 4, Current and Historical Groundwater Conditions, general variations can be documented but depth-specific data generally are limited due to current lack of shallow wells. The construction details for some wells are unknown, and most wells with known construction data are screened at depths greater than 300 feet.
Exceptions include the monitoring wells that have been sited and designed to monitor GRFs and WRPs, and the two sets of nested wells near the Salton Sea. Planned monitoring network improvements as part of the CV-SNMP include installation of 6 new monitoring wells in the perched aquifer and 17 new wells in the shallow aquifer.
The scientific rationale for selection of wells used in this Alternative Plan Update has included:
• Areal distribution across Indio Subbasin
• Length, completeness, and reliability of historical record • Regular access to the well for sampling
• Well depth, with specific information on well construction preferred.
The water quality program relies heavily on existing municipal wells and existing monitoring programs.
Dedicated monitoring wells could be designed to meet requirements and address gaps not only in the water level monitoring program, but also the water quality monitoring program.
10.1.4.3 Temporal Coverage and Monitoring Frequency
Groundwater quality data in the database complied for the Alternative Plan Update extend back to 1971.
Wells are sampled with a range of frequencies; community water systems and municipal wells are generally sampled triennially for general constituents, but as often as annually for nitrate and quarterly for total coliform bacteria. Agricultural drains are sampled annually or at a higher frequency. The GSAs audit their groundwater quality monitoring programs to ensure that monitoring frequency is adequate.
10.1.5 Seawater Intrusion
The general monitoring of groundwater levels and quality is relevant to monitoring the potential for saline water intrusion from the Salton Sea. As described in Chapter 4, Current and Historical Groundwater Conditions, saline water intrusion is monitored specifically through two sets of dedicated nested monitoring wells, as summarized below in Table 10-2.
Locations of these CVWD monitoring wells are shown on Figure 2-12. One set of four wells is located about 2.1 miles north of the Salton Sea and the other set of four wells is about one mile west of the Salton Sea and north of Oasis. These are monitored for changes in groundwater levels and quality, both of which can be used as potential indicators of saline intrusion.
In addition, the groundwater flow model has been used to simulate flow between the Indio Subbasin and the Salton Sea. The relationship of simulated and observed groundwater elevations to the changing level of the Salton Sea is discussed in Chapter 7, Numerical Model and Plan Scenarios, and Chapter 9, Sustainable Management.
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Indio Subbasin Water Management Plan Update 10-12 TODD/W&C Table 10-2. Summary of Salton Sea Nested Monitoring Wells Depth of Well Perforations,
feet bgs
SWN Nickname Latitude Longitude Top Bottom
07S09E30R04S CVWD Ruth 33.52633 -116.08 350 390
07S09E30R03S CVWD Peggy 33.52633 -116.08 730 770
07S09E30R02S CVWD Sherrie 33.52633 -116.08 1,220 1,260
07S09E30R01S CVWD Bernadine 33.52633 -116.08 1,430 1,470 08S09E07N01S CVWD Dave 33.48447 -116.095 420 480
08S09E07N02S CVWD Rosie 33.48447 -116.095 720 780
08S09E07N03S CVWD Gracie 33.48447 -116.095 1,034 1,094
08S09E07N04S CVWD Richard 33.48447 -116.095 1,315 1,375
10.2 Field Methods for Monitoring Well Data
10.2.1 Protocols for Data Collection and Monitoring
This section focuses on groundwater level monitoring and groundwater quality sampling by Indio Subbasin GSAs. Other data (e.g., climate, streamflow, subsidence) are measured mostly by other agencies (e.g., USGS). Groundwater production is metered, as described in Section 10.1.3.
This section describes general procedures for documenting wells in the monitoring program and for collecting consistent high quality groundwater elevation and groundwater quality data. In general, the methods for establishing location coordinates (and reference point elevations for elevation monitoring) follow the data and reporting standards described in the SGMA Regulations (Section 352.4), CVWD Monitoring Plans, and the guidelines presented by USGS Groundwater Technical Procedures. These procedures are summarized below.
Background data for each monitoring well is required for its inclusion in the monitoring program. These data are generally available for wells in the network described on Table 10-1. As part of Annual Report preparation, location and elevation data are acquired where missing, revised if conditions at a monitored well change, and added when new wells are brought into the program. The methods for acquiring these data follow:
• Location coordinates will be surveyed with a survey grade GPS. The coordinates will be in Latitude/Longitude decimal degrees and reference datum noted. • Reference point elevations will also be surveyed with a survey grade GPS with elevation accuracy of approximately 0.5 feet. During surveying, the elevations of the reference point and ground surface near the well will be measured to the nearest 0.5 foot. All elevation measurements will reference NAVD88 vertical datum. This will involve some re-surveying of well reference points that are based on an earlier datum.
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Indio Subbasin Water Management Plan Update 10-13 TODD/W&C
10.2.2 Field Methods for Groundwater Elevation Monitoring Reference points and ground surface elevations are documented as described above prior to groundwater elevation monitoring in the field. Field methods for collection of depth-to-water measurements are described below:
1. Measurements in all wells will be collected within a consistent period.
2. Active production wells should be turned off prior to collecting a depth to water measurement.
3. Each agency should follow their standard operating procedure and ensure the well has been off for an adequate period before a static measurement is taken (24 hours, when possible).
4. To verify that the wells are ready for measurement, GSA staff will coordinate with well operators and/or owners as necessary.
5. Coordination with well operators/owners should occur approximately three days prior to the expected measurement date. For municipal wells less lead time may be needed.
6. Depth-to-groundwater measurements are collected by either electric sounding tape (Solinst or Powers type sounders) or by steel tape methods. These depth-to-water measurement methods are described in DWR’s Groundwater Elevation Monitoring Guidelines (DWR, 2010). Depth to groundwater will be measured and reported in feet to at least 0.1 foot.
10.2.3 Field Methods for Groundwater Quality Monitoring Groundwater sampling is conducted by trained professionals from the GSAs. Sampling follows standard monitoring well sampling guidelines such as those presented in the National Field Manual for the Collection of Water-Quality Data (USGS, 2012) and/or EPA Groundwater Sampling Operating procedure (SESDROPC-301-R4, 2017).
Generally, the wells have been pumped
prior to sample collection, or are purged.
Purging is conducted until field instruments
indicate that water quality parameters (pH,
specific conductance, and temperature)
have stabilized, and turbidity
measurements are below five
Nephelometric Turbidity Unit (NTUs). Wells
are typically purged a minimum volume
equal to three times the well casing and
parameters are monitored until stable
conditions are reached. The pumping or
purging demonstrates that the sample
collected is representative of formation
water and not stagnant water in the well
casing or well filter pack. For groundwater,
field temperature and conductivity are recorded while the well is being purged to ensure that physical parameters have stabilized before collecting a sample. All groundwater samples are collected in laboratory-supplied, pre-labeled containers and include prescribed preservatives.
CVWD collects water quality data at wells and
distribution system sites.
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Indio Subbasin Water Management Plan Update 10-14 TODD/W&C All field measurements, if collected, are recorded in a field logbook or worksheets and the sample containers are labeled correctly and recorded on the chain-of-custody form. The applicable chain-of- custody sections are completed and forwarded with the samples to the laboratory. Upon receipt of the samples at the laboratory, laboratory personnel complete the chain-of-custody and a copy of the chain of custody is given back to the sampler.
QA/QC assessment of field sampling includes
use of field blanks when required for specific
parameters. Field blanks identify sample
contamination that is associated with the field
environment and sample handling. These
samples are prepared in the field by filling the
appropriate sample containers with the
distilled water used for cleaning and
decontamination of all field equipment. One
field blank per sampling event is collected.
Samples are analyzed in a certified laboratory
that has a documented analytical QA/QC
program including procedures to reduce
variability and errors, identify and correct
measurement problems, and provide a
statistical measure of data quality. The laboratory conducts all QA/QC procedures in accordance with its QA/QC program. All QA/QC data are reported in the laboratory analytical report, including: the method, equipment, and analytical detection limits, the recovery rates, an explanation for any recovery rates that are outside of method specific limits, the results of equipment and method blanks, the results of spiked and surrogate samples, the frequency of quality control analysis, and the name of the person(s) performing the analyses. Sample results are reported unadjusted for blank results or spike recovery.