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September 20,2002 <br /> Job Number: LG02-261 <br /> Page 5 <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 a"natural" condition. Based on the work by Bryan, it is estimated that under <br /> natural conditions, the ground-water concentration of nitrate is no more then about 13.5 NO3 (3 <br /> 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.3 <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 the CDMG 5 map and is composed of levee <br /> and channel deposits and the lower member of the Pleistocene Modesto Formation (Plate 5). <br /> These deposits are composed of a heterogeneous mix of generally clay, silty, sand, and gravel. <br /> Some beds are composed of claystone, siltstone, sandstone, and conglomerate. <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 sheet <br /> on: DIBROMOCHLOROPRPOANE. Internet:http://www.epa.gov./OGWDW/dwh/c-soc/dibromoc.html <br /> 5 Wagner,D.L.,Bortugno, E.J.,and McJunkin, R.D., 1991,Geologic map of the San Francisco-San Jose <br /> Quadrangle,California: California Division of Mines and Geology Regional Map Series Map No. 5A, Scale <br /> 1:250,000. <br /> ?pE RSO <br /> 1 <br /> $ W <br /> r <br />