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Ground Water - San Jacinto Basin Subunit

The aquifer system of the San Jacinto Basin consists of a series of interconnected alluvium-filled valleys bounded by steep-sided bedrock mountains and hills. The thickness of deposits in these valleys typically ranges from 200 to 1,000 ft (Wildermuth Environmental, Inc., 2000). Collectively, alluvium covers about one-half of the total area in the subunit. Prior to development, recharge to the flow system was from infiltration of mountain streams, primarily the San Jacinto River. Presently, recharge is largely from irrigation return flows and from percolation ponds filled with reclaimed water. Ground-water discharge occurs primarily by ground-water pumpage. Water levels in the alluvium-filled subbasins are greatly affected by local management practices, including augmentation of ground-water pumpage by use of imported water and recharge with reclaimed water.

Two studies were conducted in the San Jacinto Subunit.

(View the Hamlin et. al. Report)



The SANSUS study provides an integrated, regional assessment of ground-water quality in the San Jacinto sub basin of the Santa Ana watershed. Wells were selected using a grid-based program to produce equal-area, random cells (Scott, 1990).  The program was used to generate 30 cells in the San Jacinto Basin.  An attempt was made to select one well per cell. Wells from adjacent cells were used to populate cells that either had no active wells or contained wells that did not meet NAWQA selection criteria, such as those lacking well-construction data.


In response to concern about potential degradation of ground-water quality, the California State Water Resources Control Board (SWRCB) implemented the California Aquifer Susceptibility (CAS) program with the objectives of assessing water quality and determining the susceptibility of ground water used for public supply to contamination resulting from anthropogenic activities.  The SANCAS study utilized production wells located in the San Jacinto Basin.


Scott, J.C., 1990, Computerized stratified random site-selection approaches for design of a ground-water-quality sampling network, U.S. Geological Survey, Water Resources Investigations Report 90-4101 

Wildermuth Environmental, Inc. (Wildermuth), 2000, TIN/TDS Study-Phase 2A of the Santa Ana Watershed: Final Technical Memorandum, San Clemente, California, July 2000.

(Photos by Scott Hamlin, USGS)

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