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March 13,2000 Job Number: LG00-067 Page 5 Based on the work by Bryan it is estimated that under"natural"conditions, ground water concentration of nitrate is no more then about 3 mg/1-N. Areas having 5.5 mg/1-N or more are �. those in which nitrate concentrations may be increasing. 3 DBCP is a nematocide and soil fumigant for vegetables, and grapes. It is thought to cause health problems consisting of kidney damage,liver damage, and cancer. The use of DBCP was discontinued in 1979. VL GEOLOGY, SOILS,AND PERCOLATION TEST The surficial sediment of the site and surrounding area is reported to be the lower member of the Pleistocene age (about 11,000 to 2 million years ago) Modesto Formation that consists of tan and light gray gravely sand, silt, and clay." The Modesto Formation was mapped in the Lodi area by Atwater 5(Plate 6). Shown on the Atwater's geologic map is a dense stipple pattern that represents a deposit of loose sand that is probably wind blown(eolian). The light stipple pattern on the map represents probable river deposits(fluvial). Atwater noted in a shallow boring located along Kingdon Road the wind blown sand was 3.5 feet thick and was overlying compact silty sand and sandy silt(Plate 6). The surface sand thickness was found to be about 1 foot within the soil boring at the proposed project location. The surface and near surface soils located at the proposed project location are reported to be the Devries sandy loam(Plate 7). The Devries sandy loam is described by the Soil Survey report as "moderately deep to a hard pan and somewhat poorly drained. Typically, the surface layer is a grayish brown sandy loam about 13 inches thick. The upper part of the subsoil is light gray, mottled sandy loam about 15 inches thick. The lower part to a depth of 80 inches is a light gray,indurated hardpan. In some areas the surface layer is a fine sandy loam or loam. Permeability is moderately rapid in the Devries soil. Runoff is slow and the hazard of water s Hull,L.C., 1984,Geochemistry of Ground Water in the Sacramento Valley,California: U.S. Geological Survey Professional Paper 1401-B. Helley,E.J.,and Harwood,D.S., 1985, Geologic Map of the Late Cenozoic Deposits of the Sacramento Valley and Northern Sierran Foothills, California.U.S. Geological Survey miscellaneous field studies map MF- 1790, scale 1:62,500, 5 sheets. 5 Atwater,B.F., 1982,Geologic Maps of the Sacramento-San Joaquin Delta,California. U.S. Geological Survey miscellaneous field studies map MF-1401, scale 1:24,000,20 sheets. ra � � e V