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rr 4LTC <br /> A S S O C I A T E S I N C <br /> any of the groundwater samples collected from wells MW2 and MW3. The June 1999 monitoring <br /> results are detailed in ATC's Monitoring Report Second Quarter 1999, dated July 26, 1999; the <br /> September 1999 monitoring results are detailed in ATC's Monitoring Report Third Quarter 1999, <br /> dated October 5, 1999; and the December 1999 monitoring results are detailed in ATC's <br /> Monitoring Report Fourth Quarter 1999, dated December 22, 1999. <br /> Soil cuttings generated during subsurface investigation activities were transported by ATC <br /> personnel to Forward Inc. Landfill in Stockton, California for disposal on November 12, 1999. <br /> Purged groundwater generated during monitoring activities was discharged directly to the City of <br /> Stockton sanitary sewer under permit. <br /> A summary of analytical results for soil is presented in Table 1, historical groundwater monitoring data <br /> are presented in Table 2, and historical analytical results for groundwater are presented in Table 3. <br /> 4.0 EXISTING CONDITIONS <br /> V <br /> 4.1 Soil Conditions <br /> V <br /> 4.1.1 Site Geology <br /> Brown silt and silty sand were encountered in soils boring MWI, advanced by AGE, from surface <br /> grade to depths of approximately 25 feet bgs. Fine to medium sand was encountered at depths <br /> between 25 and 30 feet bgs. Silt was encountered from 30 feet to 65 feet bgs, the maximum depth <br /> explored(AGE, July 1998) <br /> Lean clay and lean clay with sand was encountered in soil borings MW2 and MW3 in the upper 6.5 to <br /> 10 feet of the soil column. Soil from depths between 6.5 to 10 feet bgs and 16.5 to 20 feet bgs <br /> consisted of silt, silty sand, sandy silt, and well graded sand. Soil from depths between 16.5 to 20 feet <br /> bgs and approximately 25.5 feet bgs consisted of lean clay with a layer of poorly graded sand <br /> encountered in boring MW3. Soil from depths between 25.5 feet bgs 26.5 to 31 feet bgs consisted of <br /> poor to well graded sand. Soil from depths between 26.5 to 31 feet bgs and 46.5 to 50 feet bgs <br /> consisted of lean clay and fat clay intermixed with elastic silt and silty sand. Soil from depths between <br /> ` 46.5 to 50 feet bgs and 51.5 feet bgs, the maximum depth explored, consisted of lean clay with sand <br /> and silty sand. Soil boring/well construction logs are contained in Appendix C. A cross section <br /> depicting the site stratigraphy was created and the location of the cross section is shown on Figure 3. <br /> V <br /> The cross section is shown on Figure 4. <br /> 4.1.2 Petroleum Hydrocarbons in Soil <br /> A review of historical soil analytical data and field measurements indicate petroleum hydrocarbon- <br /> affected soils are generally present at the highest concentrations in interior soil borings SP-1 and <br /> MW-I. Petroleum hydrocarbon constituents were generally detected in these borings at depths <br /> ranging from approximately 16 to 28 feet bgs. Petroleum hydrocarbon constituents were not <br /> w:W2574.05Ntpotu\closurc-FS3.doc 3 <br /> V <br />