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December 16,2002 Job Number:LG02-213 ` Page s time was.close to "natural"_conditions. Based on the work by Bryan, it is estimated that under natural"'conditions, ground water concentration containing nitrate is no-more than about 13.5 NO3 (3 mg/L-N). Aquifers.having 24.75 mg7L NO3 (5.5 mg/L-N) or more are those in which nitrate concentrations may be increasing.'. DBCP was-not detected in the water sample. DBCP is a nematocide and soil fumigant' .• for vegetables, and-grapes. It is thought to cause health problems consisting of kidney damage, liven damage, and-canger. The use of DBCP.was discontinued in 1979.The Environmental- Protection Agency (EPA) set the maximum contaminate limit (MCL)at 0.2 parts per billion . (ppb) because the EPA believes that given present technology and resources, this is the lowest level to which water systems can reasonably be-required to remove this contaminate should it occur in drinking water.' . RT Theground-water depth and flow directiori for the site was estimated by using the-Sari Joaquin.County Flood Controtand Water Conservation District ground-water depth and elevation maps. The Fall 1998 and Spring.1999 are the most recent ground water.maps available' . for the county.. The depth'to ground water below the site-for this period is about 23 feet. The flow direction is northwest to north rariging about.5 to 5.3 feet per mile for the gradient. See _Plates 2 and.3 for the ground water depth and Plates 4 and 5 for the ground-water graident. VI. GEOLOGY, SOILS,AND PERCOLATION TEST - The surface geology at,the site is shown on Atwater's'map and is composed of " Pleistocene Modesto Formation consisting of oose fluvial sands and silts (Plate 6).1 According to the San Joaquin Soil Survey surface soils located on the parcel are composed of three(3) different soil types (Plate 7)6. The soils are:the Honcut sandy loam (No. 175), Tinnin loamy 3 Hull,L.C., 1984,Geochemistry of Ground-Water in the Sacramento Valley,California_:U.S. Geological, Survey Professional Paper 1401-B. 4 EPA, 1999,Drinking water and health,National Primary Drinking Water Regulations,consumer fact ' 'sheet on:DIBROMOCHLOROPRPOANE:" Internet:http-//w'env.epa.gov./OGWDW/dwh/c-sm/dibromoc-html 5 Atwater,,B.F., 1982,Geologic-Maps of the Sacramento-San Joaquin Delta,California:U.S.Geologic Survey Miscellaneous Field Survey Map MF-1401,21,Sheets,Scale 1:24,000., 6 USDA Soil Conservation Service, Soil Survey of San Joaquin County,California. • w " O