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California Water Science Center - Santa Ana Basin, National Water Quality Assessment Program

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Ground Water - Inland Santa Ana Basin Subunit

The Inland Basin is filled with alluvial deposits eroded from the surrounding mountains. The thickness of these deposits ranges from less than 200 to more than 1,000 ft (Wildermuth Environmental, Inc., 2000). Recharge to the basin varies seasonally and is largely from infiltration of runoff from the San Gabriel and San Bernardino Mountains. Much of the runoff is diverted into storm-detention basins, which also operate as ground-water recharge facilities. Surface water imported from northern California and the Colorado River is also used to recharge the ground-water basin. Depth to water ranges from hundreds of feet near the flanks of mountains to near land surface along rivers and in wetland areas. Ground-water discharge occurs primarily by ground-water withdrawal for public supply.

Two studies were conducted in the Inland Santa Ana Basin.

(View the Hamlin et. al. Report)
INSUS:The INSUS study provides an integrated, regional assessment of ground-water quality in the Inland 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 Inland 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.INFPS:The INFPS is located in the Inland Basin along a losing reach of the Santa Ana River, ending near the San Jacinto Fault, which forms a partial barrier to ground-water flow. Recharge originates in the San Gabriel and San Bernardino Mountains and is relatively free of contamination. Potential contaminant loading in this unconfined system is from overlying land use, which is primarily urban. The study is based on two convergent flow paths defined by 20 monitoring wells and 7 production wells. Data from six of the seven production wells were collected as part of the INSUS assessment. References: 
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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