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San Jacinto

Statistics

At-A-Glance

Located in California’s South Coast hydrologic region, the San Jacinto subbasin is 158,534.44 acres in size. This High priority basin is home to an estimated 467,751 people (2010 value). It has approximately 1950 wells, of which approximately 61 are water supply wells. Groundwater accounts for approximately 42 percent of the basin’s water supply.

Source: CA DWR
Source: CA DWR

Basin Notes

2003: Bulletin 118

2014: CASGEM basin prioritization – high. Comment:  Basin is in overdraft (MWD). Groundwater quality issues documented in DWR B‐118. Pumping has increased some contaminant distribution in the basin.

2016: basin boundary modification

Revised basin boundary description

2018: Draft basin priority – high. Comments:

  • Groundwater level – 1) CASGEM/WDL/GWIDS: Longterm hydrographs show groundwater level decline. Source: DWR 2) The Hemet/San Jacinto Groundwater Management Area monitors around 200 wells twice a year, but report has no hydrographs and does not summarize long-term history. There is a Basin Storage graph that shows delining storage. Source: Hemet/San Jacinto Groundwater Management Area 2015 Annual Report 3) Historically, extraction in excess of recharge has resulted in lowered groundwater levels and altered directions of groundwater flow. Source: Hemet/San Jacinto Groundwater Management Plan. 
  • Subsidence – 1) Subsidence related to tectonic deformation and aquifer compaction; reported subsidence of 2.3 feet between 1939 and 1959 Lofgren (1976) measured compaction of aquifer materials with a 377-m deep extensometer from 1970 to 1974 and concluded that inelastic compaction of aquifer materials in the depth range of the extensometer amounted to about 1 cm /yr (0.04 ft/yr) and that tectonic subsidence amounted to 0.3-0.6 cm/yr (0.1-0. 2 in/yr). That is, most permanent subsidence (70-80 percent) resulted from groundwater withdrawal, with the remainder from tectonic downwarping of the valley. Source: Land subsidence and aquifer-system compaction in the San Jacinto Valley, Riverside County, California – A progress report
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Reference note: 33.13% of basin is adjudicated

2019: Basin boundary modification approval and denial. Per DWR: “The basin boundary modification request includes the revision of both internal and external boundaries. The request contains six components that utilize qualified geologic maps, alluvial thickness, borehole analysis, and topographic gradients to better define the boundaries of the of the basin. One letter of support is associated with the request. One public comment (neutral) was submitted on the drat decision to approve the modification. Five of the six components of the request meet all regulatory requirements. The removal of the Lake Perris area is denied and not supported by sufficient geologic evidence. The agency did not sufficiently demonstrate that the Lake Perris area is hydrologically disconnected from San Jacinto Basin.” Phase 2 draft priority status: high.

2021: November 17 – GSP submitted to DWR

2023: April 27 – DWR approved GSP

GSA Information

Models