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F�- <br /> January 28,2003 <br /> Job Number:LG02496 <br /> Page 4. 4 <br /> The' resence of nitrates and DBCP are not uncommon in shallow ound-water aquifers in San <br /> P gr <br /> Joaquin County.and other parts of the Central Valley. Nitrate in ground water occurs as a result <br /> k of the application of fertilizers; livestock waste, and untreated septic tank waste.' Nitrate is <br /> mobile and often accumulates,in the shallow,ground-water zones:. <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.'. If was thought that ground water at that time <br /> was close to a"natural" condition, Based on the work by Bryan,itis estimated that under natural <br /> conditions, ground-water concentration of nitrate is no more'then-about"13.5 NO, (3 mg/L-N). j <br /> Areas having 24.75 mg/L NO (5.5 mg/L-N)or more are those in which nitrate concentrations.,' ' <br /> may be increasing.3 I <br /> DBCP was not detected in the water sample. DBCP"is a nematocide and soil fumigant for <br /> vegetables, and grapes.' It is ihought.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.4 <br /> 5.0 GEOLOGY, SOIL, AND-PERCOLATION TEST_ <br /> The surficial geologic deposits near the site are reported to be composed of Pleistocene age <br /> (10,000 year to 2 million years ago) ModestoFormation. According to Atwater', the site is made <br /> up of compact silt and very fine sand. <br /> Bryan,K:, 1923,Geology'and groun - a er resources of Sacramento Valley of alifortiia:U.S - <br /> Geological Suirvey.Water-Supply Paper 495,285p.. <br /> F".. " 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:DIBROMOCHLOROPROPANE. Internet:http,//www.epa'gov./OGWDW/dwh/c-soc/dibromoc.html <br />,�I 'Atwater;B.F., 1982,Geologic Maps of.the Sacramento-San'Joaquin Delta:U.S. Geologic Survey i <br /> Miscellaneous Field Studies Map MF-140I,scale 1:24,000. <br /> x <br /> o � <br /> r <br />