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Y iso'Rvy aaei�sr:uaa'a GEOMATPiX Mr. Robert D. Mihalovich Chevron Environmental Management Company December 21, 2000 Page 4 center of estimated petroleum hydrocarbon-affected soil will be advanced to a depth of approximately 25 feet bgs to evaluate the vertical extent of affected soil (Figure 3). The remaining borings will be advanced to a depth of approximately 15 feet bgs to assess the lateral extent of affected soil. A continuous core of the soil will be collected, examined, and logged at each location. Geomatrix will collect one soil sample from each soil boring to be submitted for analyses for TPH quantified as crude (TPHc; Cg to C36 carbon range) using U.S. Environmental Protection Agency(EPA) Method 8015; for PAHs using EPA Method 8270 SIM; and for BTEX using EPA 8020. The soil samples submitted for chemical analyses will be collected from the interval of the soil core that visually appears to be most affected by petroleum hydrocarbons or from just above the water table if there are no visual indications of petroleum hydrocarbons. Data from these samples will be used to assess the lateral extent of petroleum- affected soil and to assess potential health risks associated with volatilization of petroleum constituents. In five soil borings near the center of the property where petroleum-affected soil has previously been encountered, additional soil samples will be collected at a depth of 1 foot bgs for health risk assessment purposes (Figure 3). Data from these samples will be used to assess direct exposure to shallow soil. Soil samples will be collected in brass sleeves sealed with Teflon sheets, end caps, and tape. Samples will be labeled and stored in ice filled coolers and delivered to a state-certified analytical laboratory under Geomatrix chain-of-custody procedures. Following sample collection, the borings will be backfilled with grout. To evaluate whether groundwater at the site is affected at or above WQOs, grab groundwater samples will be collected from two borings on the downgradient side of the property and one boring advanced within petroleum hydrocarbon-;affected soil. Grab groundwater samples will be collected following installation of a temporary well consisting of 1-inch-diameter polyvinyl chloride (PVC) blank casing and 10 feet of 0.01-inch slot well screen. Each groundwater sample will be collected using a disposable bailer and will be decanted into 1-liter amber bottles and 40 milliliter(ml) acidified volatile organic analysis (VOA) vials provided by the laboratory. Samples will be labeled and stored in ice filled coolers and delivered to a state-certified analytical laboratory under Geomatrix chain-of-custody procedures. Groundwater samples will be submitted for analysis for TPHg using EPA Method 8015 Modified; BTEX using EPA Method 8021; PAHs using EPA Method 8270 SIM; and TPHd using EPA Method 8015 Modified. The laboratory will perform the TPHd analyses both with and without a silica gel preparation procedure prior to analysis (EPA Method 3630 Modified).