Fact Sheets

Groundwater Quality in the Southeast San Joaquin Valley, California

Burton, C.A., and Belitz, K., 2012, U.S. Geological Survey Fact Sheet 2011-3151, 4 p.

Related Study Unit(s): Southeast San Joaquin Valley Groundwater Resources Used for Public Supply

The Southeast San Joaquin Valley (SESJ) study unit is located in California’s San Joaquin Valley and includes parts of Fresno, Kings, and Tulare Counties. The approximately 3,780-square-mile study unit was divided into four study areas: Kings, Kaweah, Tulare Lake, and Tule. The boundaries of these study areas correspond to the groundwater subbasins with the same names (California Department of Water Resources, 2003; Burton and Belitz, 2008). The SESJ study unit has hot, dry summers and cool, moist winters. Average annual rainfall ranges from 7 to 13 inches. The San Joaquin, Kings, and Tule Rivers are the primary streams flowing through the study unit. These rivers originate in the Sierra Nevada to the east.

The primary aquifers consist of alluvial sediments (mixtures of sand, silt, clay, cobbles, and boulders), and continental deposits (poorly consolidated sand, gravel, and clay). Downward flow of groundwater is impeded by a subsurface clay layer known as the Corcoran clay in the western part of the SESJ study unit. The primary aquifers are defined as those parts of the aquifers corresponding to the perforated intervals of wells listed in the California Department of Public Health database. Public-supply wells are typically drilled to depths between 350 and 700 feet below land surface, consist of solid casing from the land surface to a depth of about 150–400 feet, and are perforated or screened below the solid casing. Water quality in the shallower and deeper parts of the aquifer system may differ from that in the primary aquifers.

Land use in the study unit is approximately 85 percent (%) agricultural, 6% urban, and 9% natural. The primary agricultural uses are for orchards, vineyards, cotton, and dairies. The largest urban areas are the cities of Fresno, Visalia, and Tulare.

The primary source of recharge to the groundwater flow system is runoff from the nearby Sierra Nevada (Faunt, 2009). Other sources of recharge include percolation of irrigation return water, precipitation, urban runoff, and irrigation canals (California Department of Water Resources, 2003; Wright and others, 2004). The primary sources of groundwater discharge are water pumped for irrigation and municipal supply. About 40% of the water used in the SESJ study unit comes from groundwater (California Department of Water Resources, 2003).