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September 20,2001 <br /> y Job Number: LGO1-098 <br /> Page 6 <br /> In the early 1900's,natural levels of nitrate in ground water were measured in forty-three <br /> (43) wells throughout the Sacramento Valley by Bryan.' It was thought that ground water at that <br /> time 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 than about 13.5 <br /> NO3 (3 mg/L-N). Aquifers having 24.75 mg/L NO3 (5.5 mg/L-N) or more are those in which <br /> nitrate concentrations may be increasing.' <br /> DBCP was not detected in the water sample. DBCP is a nematocide and soil fumigant <br /> for vegetables, and grapes. It is thought to cause health problems consisting of kidney damage, <br /> liver damage, and cancer. The use of DBCP was discontinued in 1979. The Environmental <br /> Protection Agency (EPA) set the maximum contaminate limit(MCL) at 0.2 parts per billion <br /> (ppb) because the EPA believes that given present technology and resources, this is the lowest <br /> level to which water systems can reasonably be required to remove this contaminate should it <br /> occur in drinking water.' <br /> VI. GEOLOGY, SOILS, AND PERCOLATION TEST <br /> The surface geology at the site is shown on Atwater's map and is composed of <br /> Pleistocene Modesto Formation consisting of loose sand and silt, chiefly fluvial'(Plate 6). <br /> The surface and near surface soils located at site are reported to be the Veritas fine sandy <br /> loam (no. 266) (Plate 7)6. The San Joaquin Soil Survey describes the soil as the following: "This <br /> moderately well drained, nearly level soil is on low fan terraces. It is deep to a hardpan. It <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 /> 3 Hull,L.C., 1984,Geochemistry of Ground Water in the Sacramento Valley,California: U.S. Geological <br /> Survey Professional Paper 1401-B. <br /> 4 EPA, 1999,Drinking water and health,National Primary Drinking Water Regulations,consumer fact <br /> sheet on: DIBROMOCHLOROPRPOANE. Internet:http://www.epa.gov./OGWDW/dwh/c-soc/dibromoc.html <br /> 5 Atwater, B.F., 1982,Geologic Maps of the Sacramento-San Joaquin Delta,California: U.S.Geologic <br /> Survey Miscellaneous Field Survey Map MF-1401,21 Sheets,Scale 1:24,000. <br /> 6 USDA Soil Conservation Service, Soil Survey of San Joaquin County,California, Sheet 18. <br /> r. . OE�JOh <br /> Z <br /> C A <br /> 7'tSOG\ <br />