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March 29,2001 <br /> Job Number: LGO1-031 <br /> Page 5 <br /> (that's about 24.8 mg/L as NO3) or more are those in which nitrate concentrations may be <br /> increasing.3 <br /> DBCP was used as a nematocide and soil fumigant for vegetables, and grapes. It is <br /> thought to cause health problems consisting of kidney damage, liver damage, and cancer. The <br /> use of DBCP was discontinued in 1979. <br /> VI. GEOLOGY, SOILS,AND PERCOLATION TEST <br /> The surficial geology of the site is reported to be the Pleistocene age(10,000 years to <br /> about 1.8 million years old) Modesto Formation. The Modesto Formation is divided into two <br /> members, the lower member is present on the site. The Lower Member consists of <br /> unconsolidated, slightly weathered gravel, sand, silt, and clay.' The Modesto Formation is <br /> generally comprised of old alluvium that forms distinct alluvial terraces, some alluvial fans, and <br /> channel ridges.' (Plate 6). <br /> The soil located on the site is reported to be the San Joaquin Sandy Loam (Plate 7). The <br /> Soil Survey of San Joaquin County describes the San Joaquin Sandy Loam as "a moderately <br /> well drained soil. Typically, the surface layer is brown sandy loam about 13 inches thick. The <br /> upper part of the subsoil is claypan of brown clay about 7 inches thick. The part to a depth of 60 <br /> inches is brown and light brown indurated hardpan. In some areas the surface layer is f ne <br /> sandy loam, loam, or gravelly sandy loam. Permeability is very slow in the San Joaquin soil and <br /> the shrink swell potential is high. On sites for septic tank absorption fields, the very slow <br /> permeability can be overcome by increasing the size of the absorption field. "6 Table 3 presents <br /> an excerpt of some selected engineering properties for soils located on the subject property. <br /> 3 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 Cenozoic Deposits of the Sacramento <br /> Valley and Sierran Foothills,California. U.S. Geologic Survey Miscellaneous Field Studies Map,MF-1790. <br /> 5 Wagner,D.L. and others, 1987. Geologic Map of the Sacramento Quadrangle. California Division of <br /> Mines and Geology Regional Geologic Map Series,Map No. IA. Scale 1:250,000. <br /> 6 USDA Soil Conservation Service, 1992,Soil Survey of San Joaquin County,California, Sheet 7. <br /> � 'pERSOy <br /> Z r <br /> O � <br /> 7'tSOG♦ <br /> r <br />