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i <br /> L . <br /> ATC Associates Inc. <br /> V 1117 Lone Palm Avenue,Suite 201 <br /> Modesto,California 95351 <br /> 209-579-2221 <br /> %T 4: fax:209-579-2225 <br /> A`SS0C,1ATES iNC:: <br /> La <br /> plastic syringe was used to purge three volumes of air/vapor (117 to 235-milliliters) from each <br /> sampling point. Once purgingwas complete, a 400-ml Summa canister provided by the <br /> L analytical laboratory and equipped with a 200-ml/minute flow restrictor was connected to a <br /> sampling manifold. The Summa canister was then opened, creating a vacuum within the sample <br /> manifold, tubing, and insitu soil void interval. A pressure gauge on the Summa canister was <br /> used to monitor the pressure during the soil vapor sample intake. During sample collection, a <br /> leak check compound (1,1-Difluoroethane [1,1-DFA]) derived from commercial computer "dust- <br /> off' spray was used to identify potential leaks within the above grourid vapor probe assembly by <br /> L <br /> subsequent laboratory analyses. The "dust-off' spray was sprayed into a plastic bag containing <br /> several paper towels. The paper towels were then placed adjacent to, but not touching, each <br /> portion of the sample apparatus, including the area where the Teflon tubing exits the ground. <br /> The 1,1-DFA vapors were allowed to volatilize creating an environment that could introduce the <br /> L 1,1-DFA into the probe assembly and thus into the Summa canister in the event that leaks or <br /> lose fittings were present in the above-ground sample assembly. When sample collection was <br /> almost complete, the paper towels were removed and returned to the plastic bag. <br /> LOnce the sampling activities were completed at each vapor point, the valve attached to the <br /> tubing was closed and a temporary metal lid was put in place. Soil cuttings resulting from the <br /> t drilling were placed in a 55-gallon drum and stored at the site. Field documentation associated <br /> Lwith the drilling and soil vapor sampling activities is provided in Appendix A. <br /> Sample Analyses <br /> The soil vapor samples were transported under chain-of-custody documentation to California <br /> State-certified H&P Mobile Geochemistry Inc. for chemical analyses. The samples were <br /> analyzed for volatile organic compounds including 1,1-DFA by EPA Method.TO-15. Samples <br /> L were screened utilizing EPA Method 82606 to prevent burning out analytical equipment and <br /> attain lower detection limits in the case of high concentrations. <br /> L <br /> L <br /> L <br /> L <br /> i <br /> 4 S:\Environmental\62577\Reports\2011 Soil Gas.doc 4 ATC Associates Inc. <br /> 4 <br /> 1 <br />