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GROUND WATER IN THE CENTRAL VALLEY, CALIFORNIA A41
<br /> that ground-water quality is degrading as a result of ground water on the west side of the San Joaquin Valley
<br /> increasing application of agricultural chemicals and (Deverel and others, 1984). Ecological and health effects
<br /> growth of urban population. of selenium and other trace elements in agricultural
<br /> The concentrations of dissolved solids increased signif- drainage water on the west side of the San Joaquin Valley
<br /> icantly since the 1950's throughout the Sacramento have become subjects of extensive study since high
<br /> Valley except for an area south of Sutter Buttes between incidences of mortality and birth defects were observed
<br /> the Sacramento and Feather Rivers (Hull, 1984). How- in waterfowl nesting in the area where drainage water is
<br /> ever, increases in nitrate concentrations were found only discharged (U.S. Bureau of Reclamation, 1984). In a
<br /> on the west side and in the southeastern part of the valley preliminary study (Deverel and others, 1984), the areal
<br /> (Hull, 1984). Hull (U.S. Geological Survey, oral com- distribution of selenium and other inorganic constituents
<br /> mun., 1984)indicated that the rate of nitrate build-up has was examined along the west side of the valley west of
<br /> been increasing since 1912. He found that in 1912 to 1913, Fresno. Selenium concentrations (median concentrations
<br /> 2.2 percent of the wells had nitrate concentrations of 10-11 mg/L) were highest in the central and southern
<br /> greater than 5.5 mg/L; between 1960 and 1969, 4.9 parts (south of Los Banos and south of Mendota) of the
<br /> percent had concentrations exceeding 5.5 mg/L,and from area studied. Extensive studies by U.S. Department of
<br /> 1974 to 1978, 10.5 percent had concentrations exceeding Interior agencies (Bureau of Reclamation, Fish and
<br /> 5.5 mg/L. Wildlife Service, and the Geological Survey) and also
<br /> Studies to determine human impact on ground-water many studies by universities, State water resources
<br /> quality in the San Joaquin Valley were not done, largely agencies, and concerned local agencies are still in
<br /> because different time periods of sample collection and progress (1989).
<br /> the use of different analytical techniques make the
<br /> comparability of the existing data questionable. Because SELECTED REFERENCES
<br /> agricultural practices in the San Joaquin Valley are
<br /> similar to those in the Sacramento Valley,it is likely that
<br /> ground-water quality in the San Joaquin Valley is also Ayers, R.S., 1977, Quality of water for irrigation:Proceedings of the
<br /> degrading as a result of human activities. However, American Society of Civil Engineers,Journal of the Irrigation and
<br /> Drainage Division,v. 103, no. IR2, p. 135-154.
<br /> differences in geology, soils, and irrigation techniques Back,William, 1961,Techniques for mapping of hydrochemical facies,
<br /> could all affect the impact of human activities. Areas of in Geological Survey research, 1961: U.S. Geological Survey
<br /> possible contamination of ground water due to human Professional Paper 424-D, p. D380-D382.
<br /> activities in the San Joaquin Valley were mapped by Bailey, E.H., Blake, M.C., Jr., and Jones, D.L., 1970, On-land
<br /> Templin (1984, pl. 8). Sources listed were industrial, Mesozoic crust in California Coast Ranges:U.S.Geological Survey
<br /> Professional Paper 700-C, p. C70-C81.
<br /> municipal and domestic solid-waste disposal sites, and Bennett, G.D., 1979, Regional ground-water systems analysis:Water
<br /> agricultural chemical build-up. This map suggests that Spectrum, fall 1979, p.36-42.
<br /> human-induced contamination exists throughout much of Berkstresser,C.F.,Jr.1973,Map showing base of fresh ground-water,
<br /> the valley. approximately 3,000 micromhos, in the Sacramento Valley and
<br /> The use of pesticides is another possible impact on Sacramento-San Joaquin Delta,California:U.S.Geological Survey
<br /> Water-Resources Investigations Report 40-73, 1 sheet.
<br /> ground water that has not been studied in detail. Berkstresser,C.F.,Jr.,French,J.J.,and Schaal,M.E.,1985,Data for
<br /> Pesticides have been used intensively in the Central four geologic test holes in the Sacramento Valley,California:U.S.
<br /> Valley for many years and because dissolved-solids and Geological Survey Open-File Report 85488, 110 p.
<br /> nitrate concentrations are increasing, it is likely that Bertoldi, G.L., 1971, Chemical quality of ground water in the Dos
<br /> pesticide concentrations in ground water also are increas- Palos-Kettleman City area, San Joaquin Valley, California: U.S.
<br /> Geological Survey open-file report,45 p.
<br /> ing. 1976, Chemical quality of ground water in the Tehama-Colusa
<br /> The presence of dibromochloropropane (DBCP) in Canal service area,Sacramento Valley,California:U.S.Geological
<br /> ground water in the San Joaquin Valley was mapped by Survey Water-Resources Investigations Report 76-92, 44 p.
<br /> Templin (1984, pl. 7D). The presence of this pesticide at 1979, A plan to study the aquifer system of the Central Valley
<br /> levels above 0.0005 mg/L near Bakersfield, Fresno, of California:U.S. Geological Survey Open-File Report 79-1480,
<br /> Modesto and north of Merced and Stockton coincides 48 p.
<br /> Blair,T.A.,and Fite,R.C.,1957,Weather elements:Englewood Cliffs,
<br /> with land-use patterns. More specifically,these areas are New Jersey, Prentice-Hall, 414 p.
<br /> occupied by orchards and vineyards, where DBCP is Bloyd, R.M., Jr., 1978, Ground-water conditions in the Sacramento
<br /> commonly used. The presence of DBCP in the San Valley,California, 1912, 1961,and 1971,in Evaluation of ground-
<br /> Joaquin Valley suggests that other pesticides have prob- Fater resources—Sacramento Valley: California Department of
<br /> Water Resources Bulletin 118-6, p. 97-136.
<br /> ably built up in ground water of the Central Valley. Brown,Eugene,Skougstad,M.W.,and Fishman,M.J., 1970,Methods
<br /> Selenium,which is toxic to humans and animals at very for collection and analysis of water samples for dissolved minerals
<br /> low concentrations, occurs naturally in the soils and and gases: U.S. Geological Survey Techniques of Water-Resour-
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