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.. <br /> May 25, 2004 <br /> ` NOA Project Number: E04061 <br /> Page 7 <br /> The presence of nitrates is not uncommon in shallow ground water aquifers in San Joaquin <br /> County and other parts of the Central Valley. Nitrate in ground water occurs as a result of the <br /> application of fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile and <br /> often accumulates in the shallow ground water zones. <br /> ` hi the early 1900s, natural levels of nitrate in ground water were measured in forty-three (43) <br /> wells throughout the Sacramento Valley by Bryan(1923). It was thought that ground water at <br /> that time was close to"natural'conditions. Based on the work by Bryan, it is estimated that <br /> 6, under"natural'conditions, ground water concentration containing nitrate is no more then about <br /> 13.5 NO3 (3 mg/L-N). Areas having 24.75 mg/L NO3 (5.5 mg/L-N) or more are those in which <br /> nitrate concentrations may be increasing(Hull, 1984). <br /> DBCP is a nematocide and soil finnigant for vegetables, and grapes. It is thought to cause health <br /> problems consisting of kidney damage, liver damage, and cancer. The use of DBCP was <br /> discontinued in 1979. The Environmental Protection Agency(EPA) set the maximum <br /> contaminant limit (MCL) at 0.2 parts per billion (ppb) because the EPA believes that given <br /> present technology and resources, this is the lowest level to which water systems can reasonably <br /> be required to remove this contaminant should it occur in drinking water. <br /> 5.0 SOIL PROFILE AND GEOLOGIC INFORMATION <br /> 5.1 Geology <br /> The geology at the subject Site consists of the Turlock Lake, Laguna, and Mehrten Formations <br /> (Plate 6). These map units represent arkosic alluvium forming Mokelumne River terraces and <br /> ` alluvial fans. The alluvium consists of mixtures of gravel, sand, silt, and clay, of alluvial fan <br /> deposits. The Mehrten Formation contains volcanic tuff breccia. <br /> ` 5.2 Soil Properties in the Vicinity <br /> According to the Soil Survey of San Joaquin County, the majority of the Site is located on San <br /> L Joaquin sandy loam and Jahant loam soils, which formed in alluvium derived from mixed rock <br /> and granitic rock sources, respectively. Alamo clay and Redding gravelly loam are also present <br /> in places (Plate 7). Selected soil properties for these map units are summarized in the following <br /> �. table. <br /> 1. <br /> V <br /> 60 ",44 <br /> 6. <br />