PISMO BEACH CITY COUNCIL STAFF REPORT
Agenda Item #12.B
Meeting Date: July 1, 2025
TITLE:
2024 Northern Cities Management Area (NCMA) Annual Report RECOMMENDATION:
No action recommended, for information only.
DISCUSSION:
A California Superior Court Ruling in 2008 adjudicated the rights to the Santa Maria Groundwater Basin (SMGB) 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 that 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, 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.
The 2024 NCMA Annual Report1 (Attachment 1), prepared by GSI Water Solutions, Inc. (GSI), was filed with the Court as required on April 30, 2025. The following is a summary of the report’s highlights and important information
Groundwater Conditions
During 2024, 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 and 2023/24 winter season. The rise in water level is not only a direct result of above average precipitation, but is also attributed to groundwater recharge associated with the prolonged spill event of Lopez Lake from February 2024 through June 2024 as well as ongoing efforts by all NCMA agencies to minimize groundwater extraction and maximize surface water supply sources while maintaining the water conservation practices and requirements implemented during the recent drought.
Groundwater 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 1 Full URL:
https://accesspismo.pismobeach.org/WebLink/DocView.aspx?id=687316&dbid=0&repo=Laserfiche Council Agenda 7-1-2025 12.B-1
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) 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 poses a risk of seawater intrusion. The following are evaluations of groundwater levels through the seasons in calendar year 2024.
Spring 2024
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 2024 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 collaborative water management and conservation efforts. The proactive basin management 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 2024 groundwater elevations in the deep aquifer system main production zone along the coast ranged from 11.3 to 18.1 feet above 0.0 NAVD 88, compared to 7.5 to 13.5 feet the previous year. In the southernmost portion of the area, the groundwater elevations, flow, and gradient are less well known because there are 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 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 10 feet to more than 50 feet above 0.0 NAVD 88 in spring 2024. These data show an overall increase in alluvial groundwater elevations from April 2023 to April 2024.
Fall 2024
Groundwater elevations in the alluvial aquifer within the Cienega Valley in October 2024 were 2 to 12 feet lower than elevations at the start of the irrigation season in April 2024, Council Agenda 7-1-2025 12.B-2
which is a typical cyclical response to the irrigation season. No discernable pumping depression was observed in the Cienega Valley in 2024. October 2024 groundwater elevations in the deep aquifer system main production zone along the coast ranged from
10.7 to 15.9 feet above 0.0 NAVD 88.
Deep Well Index
In 2024, the Deep Well Index started the year above the trigger value with an index value
12.3 feet in January. The index value high occurred in April at 13.8 feet, and then generally declined, reaching a low point of 11.5 feet in October 2024.
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. The groundwater elevation in 2024 continued to trend upward, consistent with reported groundwater levels in 2023. In 2024, well 32C03 ranged from 12.8 feet (October 2024) to 23.0 feet (April 2024) above mean sea level (NAV 88). The 2024 seasonal high-water level in Well 32C03 is the highest seen since 2012.
Change in Groundwater Storage
The change in groundwater in storage in the NCMA portion of the SMGB between April 2023 and April 2024 is estimated by comparing water level grids created for these periods and calculating the volume change from April 2023 to April 2024. The same selection of wells is 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.
An increase in groundwater in storage reflects a net increase in water levels across the aquifer. From April 2023 to April 2024, the NCMA portion of the SMGB experienced a net increase of groundwater in storage. The net increase in groundwater storage from April 2023 to April 2024 is calculated to be approximately 530 acre-feet (AF); that is, there was approximately 530 AF more groundwater in storage in the NCMA portion of the SMGB in April 2024 than in April 2023. This increase in groundwater in storage may be attributable to groundwater recharge from above-average precipitation during the winter of 2023/24 and from prolonged infiltration from Arroyo Grande Creek during the Lopez Lake spill event, which extended from February through June of 2024.
Groundwater Quality
Analytical results of key water quality data (chloride, total dissolved solids (TDS), and sodium) in 2024 were generally consistent with historical concentrations and observed ranges of constituent concentrations. In general, no water quality results from monitoring events throughout 2024 indicate an immediate threat of seawater intrusion.
Council Agenda 7-1-2025 12.B-3
Water Supply and Production/Deliveries
Urban water use in 2024 among the NCMA agencies was 5,356 AF. Urban water use over the past 18 years has ranged from 5,240 AF in 2023 (the lowest in 20 years) to 8,982 AF in 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, a result of the 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 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 in 2024 (including urban use by the NCMA agencies plus agricultural irrigation and private pumping by rural users) was 7,783 AF compared to 7,403 AF in 2023. Of this amount, Lopez Lake deliveries accounted for 4,173 AF (3,493 AF in 2023), State Water Project deliveries totaled 661 AF (1,213 AF in 2023), and groundwater pumping from the NCMA potion of the SMRVGB accounted for approximately 2,949 AF (2,697 in 2023). The City of Arroyo Grande produced 0 AF from its Pismo Formation wells, outside the SMGB, in 2024. The breakdown is shown in Table 1 below:
Council Agenda 7-1-2025 12.B-4
Table 1. Water Production by Source (AF)
Agency Lopez
Lake
State
Water
Project
SMGB
Groundwater
Other
Supplies Total
Urban Area
Arroyo Grande 1,965 0 59 0 2,024
Grover Beach 791 0 436 0 1,227
Pismo Beach 1,099 380 15 0 1,494
Oceano CSD 318 281 12 0 611
Urban Water Use
Total 4,173 661 522 0 5,356
Non-Urban Area
Agricultural Irrigation
Applied Water 0 0 2,307 0 2,307
Rural Water Users 0 0 80 0 80
Non-potable
Irrigation by Arroyo
Grande
0 0 40 0 40
Non-Urban Water
Use Total 0 0 2,163 2,163
Total 4,173 661 2,949 0 7,783
Threats to Water Supply
Total groundwater pumping (urban, agriculture, and rural domestic) from the SMRVGB in the NCMA was 2,949 AF in 2024 which is 31 percent of the court-accepted 9,500 AF per year long term safe yield of the NCMA portion of the SMRVGB. In 2023, total groundwater pumping was 2,697 AF, or 28 percent 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 and result in rising groundwater levels. As such, groundwater elevations throughout the NCMA portion of the SMGB should rise if several consecutive years of groundwater pumping occur 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 reaches of Arroyo Grande Valley and portions of the Nipomo Mesa (DWR 1907). 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.
Council Agenda 7-1-2025 12.B-5
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 NCMA. By Spring 1995, DWR (220) documented that the pumping depression had expanded and reversed the coastward groundwater gradient. 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 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 2024, 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 the boundary with the NMMA, there is evidence of landward flow from the NCMA into NMMA. During 2024 there were no indications of seawater intrusion.
New Threat to Water Supply
In August 2024, a coalition of four environmental groups filed a lawsuit alleging that the County, which operates the Lopez Dam as San Luis Obispo County Flood Control and Water Conservation District Zone 3, is in violation of the Endangered Species Act, and requested an increase of releases from the Lopez Dam to support steelhead populations, and to provide fish passage past the dam. In December 2024, the US District Court ruled in favor of the plaintiffs and ordered a preliminary injunction that requires the County to increase downstream releases into Arroyo Grande Creek. The County is appealing the ruling and oral argument is set before the Ninth Circuit Court of Appeals on August 12, 2025. The additional downstream releases required by the preliminary injunction are detrimental to the resiliency of the water supply portfolios of Zone 3 contractors and to the goal of sustainable management of groundwater through periods of drought in the NCMA. The County has support from NCMA and other Zone 3 agencies, the California Farm Bureau, the San Luis Obispo Farm Bureau, the California State Association of Counties, the Pacific Legal Foundation. And numerous other entities.
Had the preliminary injunction been in place during 2020–2023, the dam would have reached “minimum pool” (poor water quality) in late 2020 to early 2021, and “dead pool” (no water deliveries) in the later half of 2021 into the beginning of 2023. This would have equated to 27 months of poor water quality, and 15 months without drinking water or other downstream deliveries from Lopez Lake. Minimum pool would also have been reached in the 2016/17 drought, with 15 months of poor water quality.
Legal proceedings are anticipated to continue in 2025.
FISCAL IMPACT:
There is no direct fiscal impact associated with this report.
Council Agenda 7-1-2025 12.B-6
ATTACHMENTS:
1.2024 NCMA Annual Report (online attachment only2)
Submitted by: Rosemarie Gaglione, P.E., Director of Public Works City Manager Approval:
2 Full URL:
https://accesspismo.pismobeach.org/WebLink/DocView.aspx?id=687316&dbid=0&repo=Laserfiche This attachment is available online only due to file size. A hard copy may be requested from the City Clerk’s Office.
Council Agenda 7-1-2025 12.B-7