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` March 26,2003 <br /> Job Number:LG02-031 <br /> Page 4 <br /> In the early 1900's, natural levels of nitrate in ground water were measured in forty-three(43) <br /> wells throughout the Sacramento Valley by Bryan? It was thought that ground water at that time <br /> was close to "natural'conditions. Based on the work by Bryan, it is estimated that under <br /> "natural"conditions, ground water concentration containing nitrate is no more then about 13.5 <br /> NO3 (3 mg/L-N). Areas having 24.75 mg/L NO3 (5.5 mg/L-N) or more are those in which nitrate <br /> concentrations may be increasing.' <br /> DBCP was not detected in the water sample. DBCP is a nematocide and soil fumigant for <br /> ` vegetables, and grapes. It is thought to cause health problems consisting of kidney damage, liver <br /> damage, and cancer. The use of DBCP was discontinued in 1979. The Environmental Protection <br /> Agency(EPA) set the maximum contaminate limit(MCL) at 0.2 parts per billion(ppb)because <br /> the EPA believes that given present technology and resources,this is the lowest level to which <br /> water systems can reasonably be required to remove this contaminate should it occur in drinking <br /> r, water.° <br /> 4.0 GEOLOGY, SOILS,AND PERCOLATION TEST <br /> The surface geology at the site is shown on a geologic map prepared by Wagner and others (Plate <br /> 6). The area of the project is mapped as the Pleistocene age Modesto Formation composed of <br /> compact silt and very fine sand.' <br /> The surface and near surface soils located at the site are reported to be the Veritas fine sandy <br /> loam (no. 266) and the Jacktone clay(no. 180)(Plate 7)6. The San Joaquin Soil Survey lists <br /> various engineering properties for the Veritas fine sandy loam (no. 266) and the Jacktone clay <br /> (See Table 1). <br /> 2 Bryan,K., 1923,Geology and ground-water resources of Sacramento Valley of California:U.S. <br /> ` Geological Survey Water-Supply Paper 495, 285p. <br /> 3 Hull,L.C., 1984,Geochemistry of Ground Water in the Sacramento Valley,California:U.S.Geological <br /> ` Survey Professional Paper 1401-B. <br /> J EPA, 1999,Drinking water and health,National Primary Drinking Water Regulations,consumer fact <br /> sheet on: D113ROMOCHLOROPRPOANE. Internet:http://www.epa.gov./OGWDW/dwh/c-soc/dibromoc.htnrl <br /> 'D.L.Wagner and others,Geologic Map of the San Francisco-San Jose Quadrangle, 1990,Map No. 5A: <br /> Division of Mines and Geology,scale 1:250,000. <br /> 6 USDA Soil Conservation Service,Soil Survey of San Joaquin County,Californig Sheet 25. <br /> ?pERiO <br /> ♦ i <br /> � � r <br /> O <br /> iii p c�♦ <br />