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October 12,2000 <br /> Job Number:LG00-312 <br /> Page 5 <br /> Sacramento Valley by Bryan.Z It was thought that ground water at that time was close to <br /> "natural"conditions. Based on the work by Bryan,it is estimated that under"naturae'.conditions, <br /> ground water concentration containing nitrate is no more then about 3m N Areas having 5.5 <br /> mg/L-N or more are those in which nitrate concentrations may be increasing. <br /> DBCP.was not detected in the water sample..DBCP is a nematocide and soil furnigant 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 /> water.' <br /> VI. GEOLOGY, SOIL AND PERCOLATION TEST <br /> The geologic literature indicates that the surficial deposit&near the site are reported to be <br /> composed of the Pleistocene age(about 10,000 to 2-million years old)Modesto Formation <br /> unconformably overlying portions of the older Pliocene age(about 2-million to 5-million years <br /> old)Laguna Formation(Plate 6).s The Modesto Formation is widespread in the lower elevations <br /> �{ of the Central/Sacramento Valleys and the lower western Sierran foothills. The Modesto <br /> Formation is generally composed of river alluvium, alluvial.terraces, alluvial fans and abandoned <br /> The Modesto Formation often consists of tan and light-gray gravely sand, silt, <br /> channel ridges.' <br /> a Bryan,K., 1923,Geology and ground-water resources of Sacramento Valley of California:U.S. <br /> Geological Survey Water-Supply Paper 495,285p. <br /> .7 <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,DrinlQng water and health,National Primary Drinking Water Regulations,consumer fact <br /> sheet on:DIBROMOCHLOROPRPOANE. Internet:http:l/www.epa-gov./OGWDW/dwhlc-soc(dibromoc.html <br /> s Wagner,D.L.,Bortugno,E.J.,and McJunkin,R.D., 1990, Geologic Map of the San Francisco-San Jose <br /> Quadrangle, California Department of Conservation,Division of Mines and Geology Map No..5A(Geology). <br /> Scale 1:250,000_ <br /> 6 Helley,E.J.,and Harwood,D.S., 1985,Geologic Map of the Cenozoic deposits of the Sacramento <br /> Valley and Northern Sierran Foothills, California. U.S.G.S.Misc.Field Studies Map MF-1790, Scale 1:62:500. <br /> E <br />