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r May 30,2000 <br /> Job Number:LG00-135 <br /> Page 4 <br /> mg/1 as N). The DBCP detected in the ground water was non-detectable and below the <br /> maximum contaminate level of 0.02 ug/1. The nitrate detected in the ground water was reported <br /> as NO3 by FGL and is below the maximum drinking water standard of 45 mg/l. <br /> The presents of nitrates and DBCP are not uncommon in shallow ground-water aquifers <br /> '` in San Joaquin County and other parts of the Central Valley. Nitrate in groundwater originates <br /> from agricultural fertilizers, livestock waste, and untreated septic tank waste. Nitrate is mobile <br /> and often accumulates in the shallow ground-water zones. In the early 1900's, natural levels of <br /> nitrate in ground water were measured in 43 wells throughout the Sacramento Valley by Bryan.' <br /> It was thought that ground water at that time was close to "natural"conditions. Based on the <br /> work by Bryan it is estimated that under"natural"conditions,groundwater concentration of <br /> nitrate is no more then about 3 mg/1-NO3 (about 0.67 mg/L-N). Areas having 5.5 mg/1-NO3 <br /> (about 1.2 mg/L-N) or more are those in which nitrate concentrations may be increasing? <br /> DBCP is a nematocide and soil fumigant for vegetables, and grapes. It is thought to <br /> cause health problems consisting of kidney damage, liver damage, and cancer. The use of DBCP <br /> was discontinued in 1979. <br /> VI. GEOLOGY,SOILS, AND PERCOLATION TEST <br /> The geology mapped near the Escalon area consists of Qtc(Modesto Formation): <br /> Continental rocks and deposits of Miocene to Holocene age(24 million to 0 years old)(Plate 6)3. <br /> ` The sediment generally consists of poorly sorted clay, silt, sand, and gravel. <br /> The soil classification on the site consists of the Madera sandy loam and the Honcut <br /> 6. sandy loam. Selected soil properties of both these soils are summarized in the following table <br /> and can be located on Plate 7.4 <br /> ' Bryan,K., 1923,Geology and ground-water resources of Sacramento Valley of California:U.S. <br /> Geological Survey Water-Supply Paper 495,285p. <br /> 2 Hull,L.C., 1984,Geochemistry of Ground Water in the Sacramento Valley,California: U.S.Geological <br /> Survey Professional Paper 1401-B. <br /> 6. <br /> 3 Page,RW., 1984,Geology of the fresh ground-water basin of the Central Valley,California with texture <br /> maps and sections:U.S.Geological Survey Professional Paper 1401-C. <br /> ° USDA Soil Conservation Service,Soil Survey of San Joaquin County,California, Sheet 31. <br /> R, <br /> =0!430 <br /> 1 <br /> � O A <br /> �Jsp Cl <br />