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January 23,2001 Job Number: LG00-336 Page 5 '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. ' ! VI. GEOLOGY,SOILS,-AND PERCOLATION•TEST The surficial geology of the.site is reported to be the PIeistocene age(.11,000 years to about.2 million-years old) Riverbank Formation: This formation is described as.weathered reddish gravel,sand and.silt often forming alluvial terraces and fans.' "The•Riverbank in the San Joaquin Valley is predominately arkosic'alluviurn while the Sacramento Valley contains more 1- mafic igneous rock fragments'.(Plate 6). Essentially, these formations are consolidated older alluvium: ' The surface and 7near surface soils located on the site are reported to be the San Joaquin loam and San Joaquin complex(Plate 7). The Soil Survey of San Joaquin County describes the San Joaquin Soils as "a moderately well drained soil with a moderately.deep hardpan: Typically, the surface layer and the upper part of the subsoil is brown loam about 16 inches thick- The next part of the subsoil is'a claypan of brown clay,about 10 inches:thick. The lower " part'to a depth of 60 inches is a brown and light brown, indurated hardpan. The San Joaquin loam/complex is thought to form from'granitic rock sources. "' Table 3 presents an excerpt of F some selected engineering properties for'soils located on the subject property.. 3 Hull,L.C., 1984,-Geochemistry of Ground Water in the Sacramento valley,California:U.S.Geological Survey Professional Paper 1401-B. . 'Wagner,D.L,and others, 1987. Geologic M*of the Sacramento Quadrangle. California Division of Mines and Geology Regional Geologic'Map Series,Map No. IA. Scale 1:250,000. 'Heliey,E.J.,and Harwood,D.S.; 1985_ Geologic map of the Cenozoic Deposits of the Sacramento Valley and Sierran Foothills,California. U.S.Geologic Survey Miscellaneous Field Studies Map,MF-1790. 6,USDA Soil Conservation Service, 1992,Soil Suivey of San Joaquin County,-California, Sheet 7. .