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GROUND WATER IN THE CENTRAL VALLEY, CALIFORNIA A39
<br /> Two depth zones are recognizable in the axial trough. salinity usually impairs growth before chloride alone
<br /> In the lower zone, water types are generally sodium reaches toxic levels. Water with chloride concentrations
<br /> bicarbonate, sodium chloride, and calcium sodium bicar- up to 700 mg/L can be used on most crops, depending on
<br /> bonate. Ground water in the upper zone is more variable soils and irrigation practices, without impairing growth
<br /> than in the lower zone. (National Academy of Sciences and National Academy of
<br /> Generally, sodium and calcium are the dominant cat- Engineering, 1973).
<br /> ions of the axial trough ground water. In the northern Chloride concentrations of Central Valley ground wa-
<br /> part of the valley, chloride and bicarbonate are the ter generally are less than 250 mg/L; however, several
<br /> dominant anions, and in the southern part of the valley, areas are notable for having higher chloride concentra-
<br /> sulfate and bicarbonate are the dominant anions. tions.
<br /> There is also a large amount of areal and vertical Two bands of high chloride concentrations are located
<br /> variability of water types on the west side of the San in the Sacramento Valley. One band is adjacent to Salt
<br /> Joaquin Valley; here, in places, the Corcoran Clay Creek near Williams; the other is adjacent to Petroleum
<br /> Member of the Tulare Formation separates different and Salt Creeks near Arbuckle. In these areas, high
<br /> types of ground water.Water types in the zone above the chloride concentrations are attributed to the recharge
<br /> Corcoran Clay Member are less variable than those of the from local streams (Bertoldi, 1976). A third area of high
<br /> axial trough. Sodium is the predominant cation in this chloride concentrations is south of Sutter Buttes, in the
<br /> area with few exceptions. Sodium and sodium calcium southwestern part of the Sutter basin. This area coin-
<br /> predominate in the south,and sodium and calcium sodium cides with a shallow saline water body previously de-
<br /> predominate in the north. Sulfate is the predominant scribed by Berkstresser (1973), which is probably the
<br /> anion in the zone above the Corcoran Clay Member in the source of the high chloride concentrations.
<br /> south (Davis and Poland, 1957; Wood and Davis, 1959; The most notable locations of high chloride concentra-
<br /> Hotchkiss and Balding, 1971), whereas chloride and tions in the San Joaquin Valley are in the northwestern
<br /> bicarbonate predominate in the north. The presence of and north-central part of the valley along the course of
<br /> bicarbonate in the north is attributed to recharge from the San Joaquin River and adjacent lowlands. Within this
<br /> intermittent streams (Hotchkiss and Balding, 1971). area, depth to the base of freshwater is shallower(500 ft
<br /> Chemical analyses for wells perforated below the or less)than elsewhere in the valley. Ground-water flow
<br /> Corcoran Clay Member north of the Fresno-Merced was upward prior to development and, currently, flow
<br /> County line are limited, but the water type is probably remains upward locally in this area (Williamson and
<br /> similar to that above the clay. South of this area to the others, 1989). Therefore, the most probable source of
<br /> Tulare Lake bed, the water type below the Corcoran high chloride in the shallow ground water is upward flow
<br /> Clay Member is generally sodium sulfate (Bertoldi, of saline ground water. Sorenson (1981) mapped high
<br /> 1971). The few wells that are perforated below the chloride concentrations adjacent to and west of the San
<br /> Corcoran Clay Member south of the Tulare Lake bed tap Joaquin River in San Joaquin and Contra Costa Counties.
<br /> ground water that is generally sodium chloride(Dale and Others mapped high chloride concentrations all along the
<br /> others, 1966). San Joaquin River (Page and LeBlanc, 1969; Mitten and
<br /> others, 1970; Hotchkiss and Balding, 1971; Page and
<br /> PROBLEM COMPOUNDS Balding, 1973).
<br /> Local concentrations of boron, chloride, and nitrate in BORON
<br /> the Central Valley are high enough to be a problem either
<br /> to crops or to humans. Other constituents, such as Boron is a critical element in irrigation water supplies.
<br /> pesticides and trace metals, have been investigated only In small quantities, boron is an essential micronutrient;
<br /> on a random basis and, with the exception of selenium in however, boron becomes toxic to sensitive plants at
<br /> the western San Joaquin Valley, are not known to be a concentrations as low as 0.75 mg/L and is toxic to most
<br /> problem. crops at concentrations exceeding 4.0 mg/L. Within this
<br /> range, crops have been classified into three categories of
<br /> CHLORIDE boron tolerance: sensitive (less than 1 mg/L), semitoler-
<br /> ant (1-2 mg/L), and tolerant (more than 2-4 mg/L)
<br /> High chloride concentrations are generally not consid- (National Academy of Sciences and National Academy of
<br /> ered a health hazard. On the basis of taste preference,the Engineering, 1973).
<br /> U.S. Environmental Protection Agency (1979) recom- Boron is found in concentrations greater than 0.75
<br /> mends a limit of 250 mg/L for chloride in drinking water. mg/L in several areas of the Central Valley. Small areas
<br /> High chloride concentrations can be toxic to plants, but of high boron concentrations have been observed in the
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