SR0085141_SSNL - Laserfiche WebLink

Home Browse Search

A36 REGIONAL AQUIFER-SYSTEM ANALYSIS—CENTRAL VALLFY, CALIFORNIA Valley was delineated by Berkstresser (1973). With the vertical variations in water quality. It is therefore a exception of several localized pods of shallow saline generalization of the dissolved-solids concentrations that water, ground water in the continental and Volcanic are likely to be found in a particular area, and it is most deposits of the Sacramento Valley is fresh. Several representative of the ground-water cones commonly localized shallow saline zones were described by Berk- used. About 11 percent of the wells in the Sacramento stresser. Of these,four are now known to be underlain by Valley data set yielded water with dissolved-solids con- freshwater. These shallow saline zones, underlain by centrations that were higher or lower than the mapped freshwater, are located around the northern part of the interval, This proportion of concentrations not conform- Delta, along the Sacramento River, adjacent to the ing to mapped intervals is probably similar for the San Sutter and Yolo bypasses, and around the base of Sutter Joaquin Valley (Fogelman, 1982b). Buttes. The zone around Sutter Buttes reflects the The U.S. Environmental Protection Agency (1979) configuration of the underlying marine deposits (Berk- secondary drinking-water standards recommend a limit stresser, 1973). of 544 mglL for dissolved solids.The California Domestic The base of freshwater as delineated by Page (1973b) Water Quality Regulations allow a maximum of 1,000 for the San Joaquin Valley is more complex. In the San mglL if water of better quality is not available.However, Joaquin Valley, the base of freshwater lies within the because dissolved-solids concentrations only indicate the unconsolidated continents] deposits of Pliocene to Holo- total amount of dissolved constituents in water, the cene age, the more consolidated marine and sedimentary usability of water that exceeds 504 mglL needs to be deposits of Tertiary age, and the igneous and metamor- evaluated according to the concentration of each chemical phic racks of pre-Tertiary age. Unlike the Sacramento constituent. Valley, the base of freshwater it)the San Joaquin Valley Dissolved-solids concentrations are lower in the north- is underlain by a saline water body. The depths to the ern part and along the east side of the Central Valley. base of freshwater in the San Joaquin Valley range from Dissolved solids are higher in the south-central part of less than 100 to more than 3,540 ft below land surface. the Sacramento Valley and in the western part of the San Joaquin Valley. This distribution reflects the low concen- DISSOLVED SOLIDS trations of dissolved solids in recharge water that origi- nates in the Cascade Range and the Sierra Nevada, and The area] distribution of dissolved-solids concentra- the predominant regional ground-water flow pattern. tions in ground water of the Central Valley is shown in In the Sacramento Valley, dissolved-solids concentra.- figure 24. The map for the Sacramento Valley was tions generally do not exceed 500 mglL. Two large areas prepared using a combination of data for dissolved solids of shallow ground water in which concentrations of measured by the residue-on-evaporation method (72 dissolved solids range from 500-1,504 mg/L are present percent of the analyses)(Brown and others, 1970, p. 145) in the southern part of the Sacramento Valley (fig. 24). and data derived from specific conductance measure- One area is south of the Sutter Buttes in the Sutter basin, ments (Fogelman, 1982a). and the other is west of the Sacramento River extending The map for the San Joaquin Valley was produced from West Sacramento on the north to the confluence of primarily from dissolved-solids measurements made us- the Sacramento and San Joaquin Rivers on the south(fig. ing the residue-on-evaporation method. Where data were 1 24). sparse, the map was modified by examining additional 1 In the San Joaquin Valley, dissolved-solids concentra dissolved-solids data calculated as the sum of the dis- tions are lower on the east side and higher on the west solved constituents. Because 2,000 mglL of dissolved side of the valley. In the center and on the east Side of the solids is considered to be the maximum concentration in valley, dissolved-solids concentrations generally do not freshwater(Olmsted and Davis, 1961, p. 134), only those exceed 500 mg/L; on the west side, most of the ground wells that yielded water with a dissolved-solids concen- water contains concentrations of dissolved solids in tration of less than 2,000 mglL were used to prepare the excess of 500 mg/L. Concentrations of dissolved solids map.An exception to this was made along the southwest generally increase to the west, and concentrations in margin of the San Joaquin Valley, where shallow ground excess of 2,000 mglL are not uncommon along the west water has high dissolved-solids concentrations. The wa- margin of the valley. ter samples were collected between 1974 and 1982 in the Sacramento Valley and between 1934 and 1485 in the San HYDAOCHEMICAL FACIES Joaquin Valley- Because figure 24 is a two-dimensional representation Where a few ions dominate the dissolved-solids content of data compiled from existing wells with a wide variety of ground water, the term"hydrochemical facies"(Back, of depths and screen lengths, the map cannot show ` 1:361)is used to describe the dominant ion patterns. The