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November 18, 1999 <br /> Job Number. S99307 <br /> Page 5 <br /> Environmental Protection Agency of 45 mg/1-NO, for nitrate (or 10 mg/l as Nitrate N). <br /> The presence of nitrates and DBCP are not uncommon in shallow ground-water aquifers <br /> in San Joaquin County and other parts of the Central Valley. Nitrate sources in ground water <br /> occur from agricultural fertilizers, livestock waste, and untreated septic tank waste. Nitrate is <br /> mobile and often accumulates in the shallow ground-water zones. In the early 1900's, natural <br /> levels of nitrate in ground water were measured in 43 wells throughout the Sacramento Valley by <br /> Bryan.' It was thought that ground water at that time was close to "natural"conditions. Based on <br /> the work by Bryan it is estimated that under"natural" conditions, groundwater concentration of <br /> nitrate is no more then about 3 mg/1-N. Areas having 5.5 mg/1-N or more are those in which <br /> nitrate concentrations may be increasing. ' <br /> DBCP is a nematocide and soil fumigant for vegetables, and grapes. It is thought to cause <br /> _ health problems consisting of kidney damage, liver damage, and cancer. The use of DBCP was <br /> discontinued in 1979. <br /> VI. GEOLOGY, SOILS, AND PERCOLATION TEST <br /> The geology of the site and surrounding area is reported to be the lower member of the <br /> Pleistocene age Riverbank Formation consisting of red semi-consolidated gravel, sand and silt_' <br /> These deposits were mapped by Marchland and Atwater' for the northern Lodi area(Plate 6). <br /> These types of deposits are commonly unconsolidated to semi-consolidated arkosic sediment, <br /> often heterogeneous in nature. This formation were deposited during the Pleistocene glacial <br /> outwash episodes in the western Sierra Nevada Mountains. <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 /> 2 Hull,L.C., 1984, Geochemistry of Ground Water in the Sacramento Valley,California:U.S. Geological <br /> Survey Professional Paper 1401-B. <br /> ' Helley, E.J., and Harwood,D.S., 1985, Geologic Map of the Late Cenozoic Deposits of the Sacramento <br /> ._ Valley and Northern Sierran Foothills, California. USGS miscellaneous field studies map Mf-1790. <br /> 4 Marchand,D.E.,and Atwater,B_F_, 1979,Preliminary Geologic Map showing Quaternary Deposits of <br /> the Lodi Quadrangle,California. USGS Open File Report 79-933,scale 1:62,500. <br /> oatsoti <br /> s <br /> o � <br />