PISMO BEACH COUNCIL AGENDA REPORT
Agenda Item #12.A
SUBJECT/TITLE:
2022 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 2022 NCMA Annual Report, prepared by GSI Water Solutions, Inc. (GSI), was filed with the Court on April 28, 2023.
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 2022 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 2022, water elevations generally decreased in the NCMA portion of the Santa Maria Groundwater Basin (SMGB) in response to below-average rainfall in the last 3 years. The relatively minor decrease in water levels throughout most of the area, despite the below-average rainfall conditions, is less than would be expected given the recent rainfall patterns. That the impacts
1 Full URL:
https://accesspismo.pismobeach.org/WebLink/DocView.aspx?id=473425&dbid=0&repo=Laserfiche
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are not greater is attributed to ongoing efforts by all NCMA agencies to minimize groundwater extraction and maximize surface water supply sources while maintaining the water conservation practices and requirements brought on by the current 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 2022.
Spring 2021 – 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 2022 generally showed a westerly to southwesterly groundwater flow. 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 2022 groundwater elevations in the deep aquifer system main production zone along the coast ranged from 6.7 to 8.6 feet above 0.0 NAVD 88. 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.
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
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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valley. Historically, a portion of the recharge to the alluvial aquifer of 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 30 feet above 0.0 NAVD 88 in spring 2022. These data show an overall increase in alluvial groundwater elevations from April 2021 to April 2022.
Fall 2022 – Groundwater elevations in the alluvial aquifer within the Cienega Valley in October 2022 were 0 to 15 feet lower than elevations at the start of the irrigation season in April 2022, which is a typical seasonal response to the irrigation season.
These conditions are consistent with the pumping depressions observed historically during the fall in the Cienega Valley. The alluvial groundwater elevation in the pumping depression in October 2022, at 4.3 feet below 0.0 NAVD 88, was
7.3 feet higher than in October 2021. October 2022 groundwater elevations in the deep aquifer system main production zone along the coast ranged from 3.4 to 7.0 feet above 0.0 NAVD 88.
Deep Wells – In 2022, the Deep Well Index started the year above the trigger value with an index value of 9.36 feet in January. The index value dropped below the
7.5-foot trigger value briefly in March and then again in April. The index value continued to fall to a low point of 4.4 feet in early September. Recovery occurred through the end of the year, reaching an index value above the 7.5-foot threshold by early December. The index value continued to rise through the end of the year and finished 2022 at about 9.5 feet above 0.0 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 2022, the water elevation in the well dipped below 0.0 NAVD 88 during the second and third quarters. This is similar to conditions in 2014 through 2016 when the water levels in the NCMA/NMMA boundary area typically dropped below 0.0 NAVD 88 in August and remained at a low elevation until early October.
3. Change in Groundwater Storage – The change in groundwater in storage in the NCMA portion of the SMRVGB between April 2021 and April 2022 is estimated by comparing water level contour maps created for these periods and calculating the volume change from April 2021 to April 2022. 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
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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 is a reflection of a net increase in water levels across the aquifer. During the period of April 2021 to April 2022, the NCMA portion of the SMRVGB experienced a net increase of groundwater in storage. The net increase in groundwater levels represented an increase of groundwater in storage from April 2021 to April 2022 of approximately 270 acre-feet (AF); that is, there was approximately 270 AF more groundwater stored in the NCMA portion of the SMRVGB in April 2022 than in April 2021.
4. Groundwater Quality – Analytical results of key water quality data (chloride, total dissolved solids [TDS], and sodium) in 2022 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 2022 among the NCMA agencies was 5,471 AF, a significant decrease from 2021 and the lowest usage in at least the last 25 years. Urban water use in the past 18 years has ranged from 5,471 AF (2022) to 8,982 AF (2007). There has been an overall decline in urban production 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 SMRVGB 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 2022 (including urban use by the NCMA agencies plus agricultural irrigation and private pumping by rural water users) was 8,165 AF. Of this amount, Lopez Lake deliveries were 2,936 AF, California State Water Project deliveries totaled 1,704 AF, and groundwater pumping from the NCMA portion of the SMRVGB accounted for approximately
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).
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3,523 AF. The City of Arroyo Grande produced 2 AF from its Pismo Formation wells, outside the SMRVGB, in 2022. The breakdown is shown Table 1.
Table 1. Water Production by Source (AF)
Agency Lopez
Lake
State Water
Project
SMGB
Groundwater
Other
Supplies1 Total
Urban Area
Arroyo Grande 1,822 0 166 2 1,990
Grover Beach 780 0 425 0 1,205
Pismo Beach 334 1,239 59 0 1,632
Oceano CSD 0 465 179 0 644
Urban Water Use
Total 2,936 1,704 829 2 5,471
Non-Urban Area
Agricultural Irrigation
Applied Water 0 0 2,563 0 2,563
Rural Water Users 0 0 80 0 80
Non-potable Irrigation
by Arroyo Grande 0 0 51 0 51
Total 2,936 1,704 3,523 2 8,165
6. Threats to Water Supply – Total groundwater pumping (urban, agriculture, and rural domestic) from the SMRVGB in the NCMA was 3,523 AF in 2022, which is 37 percent of the court-accepted4 9,500 acre-feet per year (AFY) long-term safe yield of the NCMA portion of the SMRVGB.
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 SMRVGB 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). These recharge areas to the east include inland
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 Section Error! Reference source not found., below, of this report.
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reaches of Arroyo Grande Valley and portions of Nipomo Mesa (DWR, 1970). Any increase in 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.
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.
Dwindling surface water supplies in Lopez Lake toward the end of 2022 were cause for significant concern. The Deep Well Index remained below the 7.5-foot trigger value for a majority of 2022. Had surface water supplies not been replenished by above average rainfall that began in December 2022, the NCMA agencies would have been forced to rely more heavily on groundwater production.
Even a moderate increase in groundwater production during a prolonged period of depressed groundwater levels (as indicated by the Deep Well Index) would greatly increase the risk of seawater intrusion.
During 2022, 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 2022 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 receives the NCMA Annual Report, discuss the report and ask any questions it may have.
FISCAL IMPACT:
There is no direct fiscal impact from this report.
ALTERNATIVES:
Provide staff with direction on how to proceed.
ATTACHMENTS:
None
Submitted by: Meeting Date: May 16, 2023
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.)
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