PISMO BEACH CITY COUNCIL STAFF REPORT
Agenda Item #12.B
Meeting Date: June 18, 2024
TITLE:
2023 Northern Cities Management Area (NCMA) Annual Report RECOMMENDATION:
No action recommended; for information only.
BACKGROUND:
Due to a California Superior Court Ruling in 2008, the rights to the Santa Maria Groundwater Basin (SMGB) have been adjudicated to various agencies. Part of that ruling established three management areas, including the Northern Cities Management Area (NCMA), Nipomo Mesa Management Area (NMMA) and the Santa Maria Valley Management Area (SMVMA). Further, the ruling mandated that “a monitoring program be established in each of the three Management Areas to collect and analyze data regarding water supply and demand conditions,” and an annual report be filed with the Court within 120 days after the end of each calendar year.
The NCMA is comprised of four agencies: the Cities of Arroyo Grande, Grover Beach, and Pismo Beach, and the Oceano Community Services District. Through the NCMA Technical Group (TG), comprised of representatives from each agency, the member agencies work together to manage the SMGB and meet the annual reporting requirements of the Court Order.
The 2023 NCMA Annual Report, prepared by GSI Water Solutions, Inc. (GSI), was filed with the Court on April 30, 2024.
Discussion
The NCMA TG is facilitated by Water Systems Consulting, Inc. (WSC).
Together, the TG and WSC hired GSI to compile the data gathered during quarterly groundwater monitoring and to create the 2023 NCMA Annual Report. A copy of the full report is available for download from the Access Pismo1 public records portal or by scanning the QR Code to the right. A copy is also available upon request from the City Clerk’s Office.
The following list is a summary of the report’s highlights and important information:
1.Groundwater Conditions – During 2023, water elevations generally increased in the NCMA portion of the Santa Maria Groundwater Basin (SMGB) in response to above-average rainfall received during the 2022/23 winter season. The rise in water level is not only a direct result of above average precipitation, but is also attributed to ongoing efforts by all NCMA agencies to minimize groundwater 1 Full URL:
https://accesspismo.pismobeach.org/WebLink/DocView.aspx?id=534817&dbid=0&repo=Laserfiche Council Agenda 6-18-2024 12.B-1
extraction and maximize surface water supply sources while maintaining the water conservation practices and requirements implemented during the recent drought.
2. Ground Water Levels – The greatest threat to the groundwater supply in the area is seawater intrusion. An indicator of whether the NCMA agencies and other stakeholders are successfully averting the threat of seawater intrusion is the groundwater elevation in the NCMA sentry wells near the coastline. The average water elevations of three sentry wells—24B03, 30F03, and 30N02—make up a Deep Well Index. This index was developed by the NCMA in 2007 to gauge the ability of the aquifer to withhold potential landward migration of seawater. A Deep Well Index value above 7.5 feet North American Vertical Datum 1988 (NAVD 88)2 generally indicates that sufficient freshwater flow occurs from the east to the coastline to prevent seawater intrusion. History has shown that a prolonged period in which the Deep Well Index level is below 7.5 feet develops groundwater conditions that pose a risk of seawater intrusion. The following are evaluations of groundwater levels through the seasons in calendar year 2023.
Spring 2023 – In the mostly urbanized areas north of Arroyo Grande Creek, groundwater is extracted from the deep groundwater aquifers of the Paso Robles Formation and the Careaga Sand. The water elevation contours in the deep aquifer system in spring of 2023 generally showed a westerly to southwesterly groundwater flow, as has been seen in past years. These groundwater flow gradients and positive (above 0.0 NAVD 88) groundwater elevations are developed and maintained primarily because the NCMA agencies have managed this portion of the basin through cooperative water management and conservation efforts. The proactive management of the basin and collaborative efforts by the agencies was necessary to respond to lower water levels in the Deep Well Index more than a decade ago. The combined NCMA efforts are to ensure that fresh groundwater flow to the ocean continues to create a barrier to seawater intrusion.
April 2023 groundwater elevations in the deep aquifer system main production zone along the coast ranged from 7.5 to 13.5 feet above 0.0 NAVD 88, compared to 6.7 to 8.6 feet the previous year. In the southernmost portion of the area, the groundwater elevations, flow, and gradient are less well known because there are only a limited number of wells and point sources of water level data. The groundwater gradient and flow in this area are generally inferred on the basis of historical records and trends as well as water level data from the Nipomo Mesa Management Area (NMMA) farther east.
Cienega Valley – the Cienega Valley is in the central area of the NCMA, generally south of Arroyo Grande Creek. All known groundwater pumping in this area is from the relatively shallow (less than 100 feet deep) alluvial aquifer. Agricultural groundwater production typically results in seasonal drawdown of the alluvial aquifer in the valley. Historically, a portion of the recharge to the alluvial aquifer of 2 Note that 0.0 NAVD 88 is 2.72 feet lower than mean sea level (MSL) and is 0.08 feet above the mean lower low water (MLLW) (which can be thought of as the average height of the lowest tides), as recorded at the Port San Luis tide station datum ( https://tidesandcurrents.noaa.gov/datums.html?id=9412110) .
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the Cienega Valley came from the Paso Robles Formation aquifer on the Nipomo Mesa. However, this recharge mechanism appears to be slowing due to declining water levels on the Nipomo Mesa. This reduction of subsurface inflow exacerbates the seasonal drawdown of the alluvial aquifer in the Cienega Valley. Groundwater elevations in the alluvial aquifer in the Cienega Valley were in the range of 5 feet to more than 50 feet above 0.0 NAVD 88 in spring 2023. These data show an overall increase in alluvial groundwater elevations from April 2022 to April 2023.
Fall 2022 – Groundwater elevations in the alluvial aquifer within the Cienega Valley in October 2023 were 2 to 12 feet lower than elevations at the start of the irrigation season in April 2023, which is a typical seasonal response to the irrigation season.
No discernable pumping depression was observed in the Cienega Valley in 2023.
October 2023 groundwater elevations in the deep aquifer system main production zone along the coast ranged from 8.2 to 12.5 feet above 0.0 NAVD 88.
Deep Wells – In 2023, the Deep Well Index started the year above the trigger value with an index value of more than 9 feet in January. The index value continued to climb through early April, peaking at over 12 feet, and then generally declined through early September, reaching a low point just over 10 feet. Since early September, the index value has increased steadily, finishing the year at about 12 feet NAVD 88.
NCMA/NMMA Boundary – The water elevation in the San Luis Obispo County monitoring well (Well 32C03), which was installed to monitor aquifer conditions along the NCMA/NMMA boundary, typically exhibits regular seasonal fluctuations.
In 2023, well 32C03 recovered to levels well above 0.0 NAVD 88, with a seasonal low value of more than 6 feet NAVD 88 in September. This is a turnaround from the below 0.0 NAVD 88 seasonal low levels experienced in 2021 and 2022. The 2023 seasonal high-water level in well 32C03 is the highest seen since early 2017.
3. Change in Groundwater Storage – The change in groundwater in storage in the NCMA portion of the SMGB between April 2022 and April 2023 is estimated by comparing water level contour maps created for these periods and calculating the volume change from April 2022 to April 2023. Separate estimates of change in groundwater in storage were computed for both the deep aquifer system and for the alluvial aquifer and then summed to represent the total NCMA estimated change in groundwater in storage. Comparison of April water levels was chosen to comply with the California Department of Water Resources (DWR) reporting requirements under the Sustainable Groundwater Management Act (SGMA).3
An increase of groundwater in storage reflects a net increase in water levels across the aquifer. During the period of April 2022 to April 2023, the NCMA portion of the SMGB experienced a net increase of groundwater in storage. The net increase in
3 On September 16, 2014, Governor Jerry Brown signed into law a three-bill legislative package, composed of Assembly Bill 1739 (Dickinson), Senate Bill (SB) 1168 (Pavley), and SB 1319 (Pavley), collectively known as the Sustainable Groundwater Management Act (SGMA).
Council Agenda 6-18-2024 12.B-3
groundwater levels represented an increase of groundwater in storage from April 2022 to April 2023 of approximately 3,610 acre-feet (AF); that is, there was approximately 3,610 AF more groundwater stored in the NCMA portion of the SMGB in April 2023 than in April 2022. The previous years increase was only 270 AF.
4. Groundwater Quality – Analytical results of key water quality data (chloride, total dissolved solids [TDS], and sodium) in 2023 were generally consistent with historical concentrations and observed ranges of constituent concentrations. In general, no water quality results were observed that are a cause of concern.
5. Water Supply and Production/Deliveries
Urban Water Use – Urban water use in 2023 among the NCMA agencies was 5,240 AF, compared to 5,471 AF in 2022. 2023 was the lowest usage in at least the last 25 years. Urban water use in the past 18 years has ranged from 5,240 AF (2023) to 8,982 AF (2007). There has been an overall decline in urban use since 2007, although there have been slight increases since the low point in 2016. The decline in pumpage since 2013 was in direct response to a statewide order by the governor to reduce the amount of water used in urban areas by 20 percent. That goal was achieved locally by conservation activities implemented by the NCMA agencies, and the relatively low urban water use has been maintained since then.
Agricultural Water Use – Agricultural acreage in the NCMA portion of the SMGB has remained relatively constant for more than 20 years. Thus, the annual applied water requirement for agricultural irrigation has been relatively stable, although it varies with weather conditions. Acknowledging the variability resulting from weather conditions, agricultural applied water is not expected to change significantly given the relative stability of applied irrigation acreage and cropping patterns in the NCMA. Changes in rural domestic pumping have not been significant.
Total Water Use – Total water use in the NCMA in 2023 (including urban use by the NCMA agencies plus agricultural irrigation and private pumping by rural water users) was 7,403 AF, compared to 8,165 AF in 2022. Of this amount, Lopez Lake deliveries were 3,493 AF (2,936 AF in 2022), California State Water Project deliveries totaled 1,213 AF (1,704 AF in 2022), and groundwater pumping from the NCMA portion of the SMGB accounted for approximately 2,697 AF (3,523 AF in 2022). The City of Arroyo Grande produced 0 AF from its Pismo Formation wells, outside the SMGB, in 2023. The breakdown is shown Table 1.
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Table 1. Water Production by Source (AF)
Agency Lopez
Lake
State
Water
Project
SMGB
Groundwater
Other
Supplies Total
Urban Area
Arroyo Grande 1,867 0 69 0 1,936
Grover Beach 793 0 373 0 1,166
Pismo Beach 433 1,037 39 0 1,509
Oceano CSD 400 176 53 0 629
Urban Water Use
Total 3,493 1,213 534 0 5,240
Non-Urban Area
Agricultural Irrigation
Applied Water 0 0 2,045 0 2,045
Rural Water Users 0 0 80 0 80
Non-potable
Irrigation by Arroyo
Grande
0 0 38 0 38
Non-Urban Water
Use Total 0 0 2,163 2,163
Total 3,493 1,213 2,697 0 7,403
6. Threats to Water Supply – Total groundwater pumping (urban, agriculture, and rural domestic) from the SMBG in the NCMA was 2,697 AF in 2023, which is 28 percent of the court accepted4 9,500 acre-feet per year (AFY) long-term safe yield of the NCMA portion of the SMBG.
When pumping is less than the safe yield of an aquifer, groundwater in storage should generally increase and result in rising groundwater levels. As such, groundwater elevations throughout the NCMA portion of the SMGB should rise significantly if several consecutive years of groundwater pumping occurs at 30 to 40 percent of the safe yield, which has been the case in the NCMA for the past decade. However, the data show that the aquifer is still in a tenuous position with respect to the threat of seawater intrusion. According to the DWR Bulletin 63-3 report, both the Paso Robles Formation aquifer and the lower confined portion of the Cienega Valley alluvial aquifer are recharged primarily from subsurface groundwater inflow from the east, where the overlying confining layers are thin to non-existent (DWR, 1970). Any increase in the regional pumping, or any other changes that reduce recharge from the east will leave the NCMA with a serious groundwater deficit that threatens seawater intrusion.
4 The calculated, consensus safe yield value of 9,500 AFY for the NCMA portion of the SMGB was formalized in the 2002 Settlement Agreement through affirmation of the 2002 Groundwater management Agreement among the NCMA agencies, which is described in more detail in the annual report.
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Historically, groundwater flowed from higher elevations inland westward towards the ocean, thereby acting to prevent seawater intrusion. As first recognized in 2008–2009, a well-documented pumping depression5 in the deep aquifer system near Black Lake Canyon within the NMMA appears to have reversed the groundwater gradient. The development of a landward gradient in the southern portion of the NCMA, caused by the pumping depression in the NMMA, likely reduces the historical recharge volume of subsurface inflow into the NCMA from Nipomo Mesa. This reduction of subsurface inflow to the NCMA creates conditions more likely to result in seawater intrusion in the NCMA and NMMA and it exacerbates the seasonal drawdown of the alluvial aquifer in the Cienega Valley.
During 2023, there were no indications of seawater intrusion. This is due in large part to water conservation measures enacted by the NCMA agencies. Urban water use in 2023 was the lowest it has been in at least the last 25 years.
Conclusion and Recommendation
This report is for information only. Staff recommends the City Council receive the NCMA Annual Report, discuss the report and ask any questions it may have.
FISCAL IMPACT:
There is no direct fiscal impact associated with this report.
ATTACHMENTS:
1. 2023 NCMA Annual Report (online attachment only6)
Submitted by: Benjamin A. Fine, P.E., Director of Public Works/City Engineer City Manager Approval:
5 As documented in NMMA annual reports, available at https://ncsd.ca.gov/resources/reports-by-subject . (Accessed March 9, 2021.)
6 Full URL:
https://accesspismo.pismobeach.org/WebLink/DocView.aspx?id=534817&dbid=0&repo=Laserfiche Council Agenda 6-18-2024 12.B-6