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PRE-TANK REPLACEMENT Site Assessment Results <br />4315 WATERLOO RD, STOCKTON, CA <br />Aegis Project No. 89-047 <br />Page 8 <br />4.0 DISCUSSION OF RESULTS <br />The following subsections discuss the results of sampling in the <br />existing tank basin, the proposed new tank location and existing fuel <br />island. <br />4.1 PETROLEUM HYDROCARBONS IN SOIL: EXISTING TANK BASIN <br />The soil borings drilled near the existing tank basin and associated <br />plumbing system (SB-9 through SB-12, figure 2), were advance several <br />feet away from the tank basin. The samples that were obtained are <br />therefore representative of native soil conditions. Odor observations, <br />PID readings and soil sample analytical laboratory results indicate <br />impact to native soils with low level concentrations of gasoline <br />constituents adjacent to the existing tank basin (Tables 1, Appendix <br />B). Therefore backfill soils in the tank basin probably contain <br />petroleum hydrocarbons. <br />4.2 PETROLEUM HYDROCARBONS IN SOIL: PROPOSED NEW TANK LOCATION <br />Odor observations, PID readings and soil sample analytical laboratory <br />results indicate the presence of petroleum hydrocarbons at low <br />concentrations in the western portion of the proposed new tank <br />location. The contaminants appear localized near the surface, except <br />in the location of boring SB-4, where low level xylenes were detected <br />at 15 ft. below the ground surface (bgs). Because of the proximity of <br />the proposed new tank location to the existing fuel island, the source <br />of contamination may be past leakage/spillage in the existing product <br />lines, or fuel dispensers. <br />4.3 PETROLEUM HYDROCARBONS IN SOIL: FUEL ISLAND <br />Odor observations, PID readings and soil sample analytical lab data <br />indicate impact to native soils with low level gasoline constituents, <br />near the fuel island adjacent to Waterloo road, at boring location SB- <br />6 (figure 2, Appendix B, Table 1). As discussed in section 4.2, the <br />source of contamination may have been past leakage/spillage in the <br />existing product line, or fuel dispensers.