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].� ATC Associates Inc. <br /> 1117 Lone Palm Avenue, Suite 201 <br /> Modesto, California 95351 <br /> 209-579-2221 <br /> fax: 209-579-2225 <br /> ASS O C I ATE S INC. <br /> technology. Drilling will be conducted by a State-licensed C57 drilling company. A field geologist <br /> will be present to log soil samples. Descriptions of soil types encountered and sample collection <br /> intervals will be recorded on boring logs. Soil samples will be collected at the base of each boring <br /> location, field screened with a Photoionization Detection (PID) meter, and submitted for laboratory <br /> analyses. <br /> Following soil gas sample collection, the direct push drive rods will be removed and the borings will <br /> be backfilled with neat cement grout to the ground surface. Drill cuttings, if any, will be stored on <br /> site in a 55-gallon drum pending laboratory results. <br /> Sampling Methodology <br /> In an effort to appropriately conduct soil gas sampling on site, ATC will follow the guidelines <br /> established by the RWQCB Los Angeles Region and the Department of Toxic Substances Control <br /> (DTSC) in documents entitled Advisory—Active Soil Gas Investigations dated January 28, 2003 and <br /> Interim Final — Guidance For the Evaluation and Mitigation of Subsurface Vapor Intrusion to <br /> Indoor Air dated December 15, 2004, revised February 7, 2005. <br /> Temporary Soil Gas Point Design/Connections <br /> The temporary soil gas sampling points will be advanced to an approximate depth of six feet bgs. <br /> Once the drive rods have been advanced to the predetermined depth, they will be pulled back to <br /> expose the soil gas sampling probe. Approximately 10 feet of /8-inch outside diameter Nylaflow® <br /> tubing will be attached down hole as post run tubing to the soil gas sampling point tip creating a <br /> continuous seal associated with the soil gas pathway. The tubing will extend from the base of the <br /> boring above the ground surface. The tubing will be sealed at the surface using a pinch clamp. <br /> Bentonite chips will be applied around the drive rods and hydrated prior to collecting any samples. <br /> The soil gas sampling points will require a minimum of 20 minutes for equilibration prior to <br /> collecting soil gas samples. <br /> Purge Volume Test <br /> To ensure the removal of ambient air from the sampling system and to determine the appropriate <br /> number of purge volumes prior to collecting a representative soil gas sample, an initial purge volume <br /> test will be conducted utilizing one of the temporary soil gas sampling points. One purge volume is <br /> estimated to be approximately six cubic centimeters per linear foot of tubing. The tubing will be <br /> premeasured prior to the installation of the temporary soil gas point. A stepped purge test of one, <br /> three, and seven tubing volumes will be conducted. The well will be purged at a rate of <br /> approximately 100 milliliters per minute (mL/min) to 200 mL/min. The appropriate number of purge <br /> volumes will be selected based on the analytical data provided by the mobile laboratory associated <br /> with each stepped purge volume. If none of the analytes of interest are detected during the stepped <br /> purge test from the selected temporary soil gas sampling point, ATC will default to purging three t <br /> volumes prior to sampling each soil gas sampling point. In the event that the mobile laboratory is not <br /> available, ATC will default to three purge volumes. <br /> S:\Environmental\25847\38\Workplans\2010 May SGS.doc 4 <br />