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SOIL VAPOR EXTRACTION PILOT STUDY REPORT San Joaquin County Montgomery Ward Auto Service Center Public Health Services Department 5400 Pacific Avenue, Stockton CA Site Code 2163 i ' samples were not tested by EPA Method 8260 for confirmation All testingcompleted b was P Y a State of California certified hazardous waste testing laboratory Table 10 provides a summary of analytical results and Appendix J contains the laboratory reports Figure 10 shows these new data, along with past data, plotted on a site map These ' data suggest there are two separate plumes at the site (see Figure 11 ) The first plume is centered around soil borings B-6 and B-11, in the former UST area This plume extends in a northeast to southwest direction, covering a surface area of approximately ' 2,700 square feet The second plume is centered around monitoring well MW-2, near the former fuel islands, and covers a surface area of approximately 2,800 square feet In cross-section (see Figure 11 for location), the plume below the former gasoline UST ' excavation extends from approxnnately 15 feet bgs to approximately 60 feet bgs (see Figure 12 ) The plume appears to be fairly uniform in its lateral extent at all depths from the surface ' to the ground water table However, the plume shows higher concentrations in soil at deeper zones The cross section of the plume near the former fuel islands (see Figure 11 for location), ' extends from approximately 15 feet bgs to approximately 50 feet bgs (see Figure 13 ) In this plume, the maximum soil contaminant concentrations are found at shallow depths 7.0 VES AND AIR SPARGING PILOT TESTING This section presents the field measurements made before, during and after the SVE and Air ' Sparging pilot tests and also presents the results of the laboratory analyses performed during the tests All field measurements are provided in tables included in Appendix K 7.1 Measurements Prior to Startm Pilot Tests Prior to conducting the VES pilot test, the following measurements were recorded ' ■ Vapor concentrations using a field instrument in all VEW wells and soil vapor probes, ■ Pressure (vacuum) readings in VES wells and soil vapor probes, ■ Laboratory analyses of vapor concentrations in soil vapor probes, ■ Vacuum pressure and vapor concentrations at inlet to VES unit, and ■ Concentration of oxygen in wells The field measurement are included in Appendix K and the laboratory analyses of vapor concentrations are included in Appendix L 7.2 VES Pilot Tests Scenarios Three mayor soil vapor extraction pilot test scenarios were implemented as follows ■ The first test scenario involved extraction well VEW-lA Well VEW-1A was connected to the vapor extraction unit Air flow, vacuum pressure and vapor concentrations was measured at the VES manifold immediately after the VES unit was started At that time (at 1440 hrs), one soil vapor sample (VEW-1AO1440) was Project No 1232 - 8 - ENVIRONMENTAL AUDIT; INC �