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ATC Associates Inc. Tlc 7VA doom 1 117 Lone Palm Avenue,Suite B Modesto,.California 95351 . 209-579-2221 A s s o c t A 7 r: s t N c Fax: 209-579-2225 completion of the Geoprobe@ subsurface investigation described in the previous sections of this Work Plan. Soil vapor samples will be collected from the terminal depth of each boring. A 1 to 2-inch diameter steel vapor probe equipped with an expendable steel drive point will be driven into the ground using a direct push drilling rig. When the probe has been advanced to the.desired depth, it will be extracted slightly (approximately six inches), which will open the sampling tip and expose the vapor sampling port. The sampling probe is fitted with a '/8-inch diameter nylon tube through the annulus and is attached to the sampling port with a stainless steel fitting. Hydrated bentonite will be placed around the probe at the ground surface.to inhibit surface air infiltration. A leak detection compound such as isopropyl alcohol (IPA), .1,1 difluoroethane (1,1-1317A), or shaving cream containing isobutene will be applied to the bentonite seal and sample line fittings of the aboveground portion of the sampling apparatus. The system will be allowed,to equilibrate, for 20 to 30. minutes. Following the equilibration period, three tubing volumes of air will be purged with a Summa canister or calibrated syringe connected to the tubing using a valve connection to flush the tubing and allow it to fill with in- situ soil vapor. The purge volume will be calculated based on the internal volume of tubing and annular space around the probe tip. A soil vapor sample will then be. collected for subsequent volatile organic compound (VOC) analyses by attaching a one to six liter Summa canister equipped with a vacuum gauge, flow regulator, and a 2 micron filter to the tubing. The Summa canister will be filled at a flow rate not to exceed 200 milliliters per minute. These sample procedures will.be repeated at each boring location..Following sample.collection, the borings will be backfilled with neat cement grout to the ground surface..All drill cuttings, if any,will be stored on-site in a 5-gallon container pending laboratory results. Sample Analyses The soil vapor samples will be delivered under chain-of-custody documentation to a State- certified analytical laboratory and .analyzed for VOCs, including the leak detection compound, by EPA TO-15. The soil vapor survey will be performed subsequent to. completion of the Geoprobe® assessment. The location of the proposed soil vapor points noted on Figure 2 may be modified based on results of the subsurface investigation described herein: However, no more than two (sets of) soil vapor points;should be necessary at this time unless otherwise directed by the EHD. Page 9 w:\17861\WP for Additional Subsurface Investigation Soil Vapor Study,and Modeling l