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Mr. Philip S. Isorena January 12, 2001 Page 3 groundwater table was approximately 39 to 41 feet at locations outside the zone of depression of the groundwater extraction wells. VMP sampling experience has shown that at depths greater than 30 feet, water from the capillary fringe blocks soil pores seasonally, thus preventing collection of soil vapor samples. The borings will be advanced using Geoprobe®direct push drilling equipement. Soil gas will be collected using the Geoprobe® PRT (post run tubing system). The PRT system consists of a stainless steel probe tip that is pushed to the desired sampling depth attached to 2-inch diameter drill rods; then the drill stem is retracted several inches exposing the soil formation. The soil vapor probe is connected to the surface by polypropylene tubing inside the drill rods. Clean new tubing will be used for each sample. After each sample is collected the drill rods will be withdrawn to the ground surface, the probe will be decontaminated, and the used tubing will be replaced. Vendor descriptions of the equipment and sampling process are included in Attachment A. Sample collection and analysis will be performed in the same manner as in previous mobilizations for SVE startup sampling. Soil vapor sampling will consist of operating a 1-cfin vacuum pump appropriate length of time at each location dependent upon depth to purge soil gas in the sampling apparatus and collect a representative sample. The samples will be collected in 1L Tedlaro bags. On the first day of sampling, the Tedlar bag samples will be held overnight in a cooler under chain-of-custody for analysis next day. On the second day of sampling, all samples will be submitted to the mobile laboratory for on-site analysis. All analyses will be completed by the end of the field day. Analyses for VOCs will be performed on-site by a mobile laboratory, Field Portable Analytical, Inc., Cameron Park, California. Two field blind duplicate samples will be collected and analyzed to demonstrate repeatability. Replicate samples will be collected in Summa canisters from at least 4 points and shipped to a fixed base laboratory, Environmental Analytical Services, Inc., San Luis Obispo, California. All analyses will be performed by Method TO-14 with requisite QC including method blanks and surrogate recovery analyses. Vadose Zone Modeling The soil vapor concentration vs. depth results will be used to construct a detailed model of residual VOC contamination in the Source Area. The basic cell geometry and input parameters of the model will be discussed with the RWQCB representative prior to commencing analysis. VLEACH, Version 2.2 (Ravi and Johnson, 1997) will be used to evaluate whether any detectable vadose zone contamination that still remains after soil remediation could result in an impact to groundwater. It is planned to perform leaching analysis for the three primary chemicals of concern: 1,1-dichloroethene, trichloroethene, and 1,1,1-trichloroethane. The output will be in terms of chemical concentrations at 1-foot depth intervals over time (i.e. 5 or 10 years). Proposed Schedule The field work consisting of direct-push soil borings and vapor sampling is scheduled for three days: January 17 through 19, 2001. On-site analytical work will be performed on SVE_CLOS.DOC 1/12/01