PISMO BEACH CITY COUNCIL STAFF REPORT
Agenda Item #12.B
June 16, 2026
TITLE:
2025 Northern Cities Management Area (NCMA) Annual Monitoring Report
RECOMMENDATION:
No action recommended, for information only.
BACKGROUND:
The 2025 Annual Monitoring Report for the Northern Cities Management Area (NCMA) (Annual Report) has been prepared pursuant to the requirements of the 2005 Stipulation for the Santa Maria River Valley Groundwater Basin Adjudication (2005 Stipulation) and the January 2008 Judgment After Trial (2008 Judgement). Part of that ruling established three management areas, including the 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 that an annual report be filed with the Court within 120 days after the end of each calendar year. The 2025 NCMA Annual Report, prepared by GSI Water Solutions, Inc. (GSI), has been filed with the Court.
The NCMA is comprised of four agencies: the Cities of Arroyo Grande, Grover Beach, 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.
DISCUSSION:
The TG contracted with GSI to compile the data gathered during quarterly groundwater monitoring and to create the 2025 NCMA Annual Report (Attachment 1). The following is a summary of the report’s highlights and important information.
Groundwater Conditions
During 2025, groundwater elevations generally decreased in the NCMA portion of the Santa Maria River Valley Groundwater Basin (SMRVGB) in response to slightly below- average rainfall received during the 2024/25 winter season, and increased groundwater pumping compared to 2024. The NCMA agencies continued ongoing efforts to minimize groundwater extraction and maximize surface water supply sources while maintaining the water conservation practices and requirements implemented during the recent drought.
Ground Water Levels
The most significant potential impact 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
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—24B03, 30F03, and 30N02—make up a Deep Well Index (DWI). This index was developed by the NCMA in 2007 to gauge the ability of the aquifer to stave off potential landward migration of seawater. A DWI value above 7.5 feet North American Vertical Datum 1988 (NAVD 88) generally indicates that sufficient groundwater flow occurs from the east to the coastline to prevent seawater intrusion. History has shown that a prolonged period in which the DWI 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 2025.
Spring 2025
In the 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 2025 generally showed a westerly to southwesterly groundwater flow, as has been seen in past years. These groundwater flow gradients and positive groundwater elevations are 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 DWI 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.
In Spring 2025 groundwater elevations in the deep aquifer system main production zone along the coast ranged from 10.8 to 16.6 feet (NAVD 88). As compared with 11.3 to 18.1 feet (NAVD 88) in April 2024.
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 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 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 or reversing due to declining water levels on the Nipomo Mesa during drought conditions. 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 8 to 37 feet (NAVD 88) in Spring of 2025. These data show an overall decrease in alluvial groundwater elevations from April 2024 to April 2025.
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Fall 2025
In the alluvial aquifer within the Cienega Valley in October 2025 in the deep aquifer system main production zone along the coast, groundwater elevations ranged from 10.4 to 13.4 feet (NAVD 88). Groundwater elevations in the alluvial aquifer were 1.0 to 13.0 feet lower than the elevations at the start of the irrigation season in April 2025, which is a typical seasonal response.
Deep Well Index
The DWI began the year above the threshold index value of 7.5 feet (NAVD 88) at 12.2 feet in January. The DWI value generally declined throughout the irrigation season, with the lowest reading of 9.5 feet occurring in July. The last calculation of the DWI in 2025 occurred in October with an increased value of approximately 10.5 feet (NAVD 88).
NCMA/NMMA Boundary
The groundwater elevation in the San Luis Obispo County monitoring Well 32C03, which was installed to monitor aquifer conditions along the NCMA/NMMA boundary, typically exhibits regular seasonal fluctuations. The groundwater elevation in 2025 declined slightly following an upward trend of groundwater levels seen in 2024 when Well 32C03 ranged from 12.8 feet (October 2024) to 23.0 feet (April 2024) (NAVD 88). In 2025 the groundwater elevation in Well 32C03 ranged from 9.9 feet (July 2025) to 17.0 feet (January 2025) (NAVD 88). The 2025 seasonal low was 11.0 feet above the seasonal low seen in July 2022, which was below 0.0 feet (NAVD 88).
Change in Groundwater Storage
The change in groundwater in storage in the NCMA portion of the SMGB between April 2024 and April 2025 is estimated by comparing water level grids created for these periods and calculating the volume change from April 2024 to April 2025. The same selection of wells were used from the previous year to the current year. 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. A comparison of April water levels was chosen to comply with the California Department of Water Resources (DWR) recommended reporting requirements.
A decrease in groundwater in storage reflects a net decrease in water levels across the aquifer. From April 2024 to April 2025, the NCMA portion of the SMGB experienced a net decrease of groundwater in storage which is calculated to be approximately 1,149 acre- feet (AF). This decrease in groundwater in storage may be attributable to slightly below- average precipitation received during the winter of 2024/25 and a resulting increase (relative to 2024) in groundwater pumping during 2025.
Groundwater Quality
Analytical results of key water quality data (chloride, total dissolved solids (TDS), and sodium) in 2025 were generally consistent with historical concentrations and observed ranges of constituent concentrations. In general, no water quality results from monitoring
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events throughout 2025 indicate an incipient episode or immediate threat of seawater intrusion.
Water Supply and Production/Deliveries
Total urban water use among the NCMA agencies in 2025 was 5,477 AF. Urban water use over the last 21 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 2016. The decline in pumping since 2013 was, at least in part, the result of the California Water Conservation Act of 2009, which required a 20% reduction in urban water use by 2020. That goal was achieved locally by conservation activities implemented by the NCMA agencies, and relatively low urban water use has been maintained since then.
Agricultural acreage in the NCMA portion of the SMGB has remained relatively constant for more than 20 years. 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 in 2025 (including urban use by the NCMA agencies plus agricultural irrigation and private pumping by rural users) was 8,053 AF as compared to 7,783 in 2024. Of this amount, Lopez Lake deliveries accounted for 4,095 AF (4,173 AF in 2024), California State Water Project deliveries totaled 581 AF (661 AF in 2024), and groundwater pumping from the NCMA portion of the SMRVGB accounted for approximately 3,377 AF (2,949 AF in 2024). The breakdown is shown in Table 1.
Table 1. Water Production by Source (AF)
Agency Lopez
Lake
State
Water SMGB
Groundwater
Other
Supplies
Total
Arroyo Grande 1,891 0 179 0 2,070
Grover Beach 708 0 519 0 1,226
Pismo Beach 1,022 486 36 0 1,545
Oceano CSD 473 95 67 0 636
Urban Water Use 4,095 581 801 0 5,477
Agricultural Irrigation 0 0 2,447 0 2,447
Irrigation by Arroyo
0 0
49 0
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Non-Urban Water 0 0 2,576 0 2,576
Threats to Water Supply
Groundwater
Total groundwater pumping (urban, agriculture, and rural domestic) from the SMRVGB in the NCMA in 2025 was 3,377 AF in 2025 which is 36% of the court-accepted 9,500 AF per year long term safe yield of the NCMA portion of the SMRVGB. In 2024, total groundwater pumping was 2,697 AF, or 28% of the 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, resulting in rising groundwater levels. Groundwater elevations throughout the NCMA portion of the SMGB should rise if several consecutive years of groundwater pumping occur at 30% to 40% 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. These recharge areas to the east include inland reaches of Arroyo Grande Valley and portions of the Nipomo Mesa (DWR 1970). Any increase in the regional pumping, or any other changes that reduce recharge from the east could result in a groundwater deficit in the NCMA and vulnerability to seawater intrusion.
Historically, groundwater flowed from higher elevations in inland areas westward towards the ocean, thereby mitigating seawater intrusion. DWR (2002) documented a pumping depression in Spring 1975 in the deep aquifer system near Black Lake Canyon within the NMMA. By Spring 1995, DWR had documented that the pumping depression had expanded and reversed the coastward groundwater gradient. That same report stated that 1,300 AFY had historically flowed from the NMMA into the NCMA. The groundwater pumping depression was documented in the first NMMA Annual Reports in 2008-2009.
The development of a landward gradient in the southern portion of the NCMA, caused by the pumping depression in the NMMA, reduces the historical recharge volume of subsurface inflow from the Nipomo Mesa to the NCMA. 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 2025, the groundwater flow direction in the northern portion of the NCMA was predominantly toward the ocean. However, along the southeast corner of the NCMA at
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the boundary with the NMMA, there is evidence of landward flow from the NCMA into NMMA.
During 2025, there were no indications of seawater intrusion.
State Water Project
Extended drought and long-term reduction in snowpack from climate change affect State Water Project (SWP) deliveries. The storage capacity of the state’s two largest reservoirs —Lake Shasta and Lake Oroville—were at 76% and 70% capacity respectively, at the start of 2025. Both lakes filled to capacity by spring 2025, which allowed for 50% Table A deliveries. The immediate threat of allocation reductions to Pismo and Oceano CSD (the only SWP subcontractors in the NCMA) has not significantly materialized in the past several years because the San Luis Obispo County Flood Control and Water Conservation District (District) maintains a buffer, in addition to each agency’s drought buffer, so that full deliveries may still be provided in full, for one or two years.
Over pumping of groundwater in the San Joaquin Valley has resulted in subsidence, which is a lowering of the ground surface. The ground surface has dropped 20–30 feet over the last century; it has dropped several feet in the last decade alone. The reduction in groundwater contributes to a compaction of clay layers, which results in additional subsidence. Compaction of the clay layers is not considered to be reversible.
As the ground surface that the concrete canal is constructed upon drops in elevation, the canal has dropped in places, reducing the conveyance capacity. DWR has made some adaptations to operating procedures, but even so, DWR has reduced the long-term average expected deliveries by 3 percent (not including reductions due to climate change). Without additional infrastructure improvements, DWR expects that the delivery capability of the SWP could be reduced by 18%–87% by 2043.
Lopez Lake
Despite the filling and subsequent spilling of the reservoir in 2023 and 2024, pre-2023 extended drought conditions contributed to recent record low water levels in Lopez Lake.
In 2024, the District Zone 3 adopted the Low Reservoir Response Plan (LRRP), which established actions to take when reservoir storage drops below 20,000 AF. The purpose of the LRRP is to limit downstream releases and municipal diversions to preserve water within the reservoir, above the minimum pool, for a minimum three to four years of drought conditions. Those conditions would force Zone 3 agencies to rely more heavily on groundwater, which would already be impacted by drought.
Preliminary Injunction
In August 2024, a coalition of four environmental groups filed a lawsuit alleging that the County, which operates the Lopez Project on behalf of the Zone 3 agencies, was in violation of the Endangered Species Act (ESA), and requested an increase in water releases from the reservoir to support steelhead. In December of 2024, the court issued a Preliminary Injunction (PI) that required the County to release an additional 1,500 AF
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each year into the creek. Prior to this, the County was operating under the Interim Downstream Release Schedule (IDRS).
The County appealed the ruling stating that the additional releases would harm other species living in the creek. In December 2025 the U.S. Court of Appeals for the Ninth Circuit ruled in favor of the County and release rates returned to those under the IDRS for 2025. The case continues to work its way through the courts.
Because Pismo Beach is entitled to 19.69% of the water in the reservoir, an overall reduction of 1,500 AFY would equate to a reduction of 295 AFY for Pismo Beach.
Wildfire Impacts
In August of 2025, the Gifford Fire burned 131,600 acres in the mountains of Santa Barbara and San Luis Obispo Counties. It burned watersheds immediately east of Upper Arroyo Grande Creek watershed, which drains into Lopez Lake. If there were a significant wildfire in the Arroyo Grande Creek watershed, there would be the potential risks associated with ash, tree falls or denuded sediments flowing into the reservoir. These would have the potential to affect water quality in the reservoir, and potentially to affect operations at the treatment plant if the water released though the dam were impacted.
Conclusion and Recommendation
This report is for information only. Staff recommends that the City Council receive the NCMA 2025 Annual Monitoring Report.
FISCAL IMPACT:
There is no direct fiscal impact associated with this report.
ATTACHMENTS:
1.2025 NCMA Annual Report (online attachment only 1)
Submitted by: Rosemarie Gaglione, P.E., Director of Public Works City Manager Approval:
1 Full URL: https://portal.laserfiche.com/Portal/DocView.aspx?id=788294&repo=r-f36a9aa0
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