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WEISS ASSOCIATES % <br /> G. Boggs / 29 June 1988 page 2 <br /> 4) Discuss the rationale for the placement of MW-4: . ,w.. <br /> Our responses to each of these concerns are presented individually below. <br /> 1. PLACEMENT OF MONITORING WELT: MW-4 <br /> We will install a ground water monitoring immediately adjacent to the southwestern <br /> corner of the concrete sNb, dirrrtl y• cinwn <br /> gradient of talc high-cst hydrmarbQlZ i <br /> concentrations identified (Figure 1). As we discussed on,the telephone on 20 June 1988. <br /> rhls nrnnnsed TAW-4 well lvcativu Avvlwi u6 the picviousIy prepdsed MW 4 well looation <br /> near the northwestern corner of the excavation, since existing monitoring well MW-2 <br /> monitors ground water downgradient. A'IW-4 will be installed after all soil removal has <br /> been completed and the excavation has been backfilled. <br /> Ground water samples will be collected from the three existing wells and from <br /> MW-4, for analysis by EPA Method 8015, gas chromatography with flame ionizatlon <br /> detection (GC/FID), for total fuel hydrocarbons ('I'FHC) and by EPA Method 602, gas <br /> chromatography with photoionization detection (GC/PID) for aromatic hydrocarbons <br /> including benzene, toluene and xylenes (BTX). <br /> I <br /> 2. TANK PIT EXCAVATION <br /> We will excavate, to a depth of 23 to 24 ft., all soil containing discernible <br /> hydrocarbons from the southwestern corner of the tank pit excavation, including the <br /> saturated soil in the vicinity of the high-concentration B-2 sample. We will then collect <br /> one soil sample -per 15 ft-by-15 ft section of exposed wall and floor of the final <br /> excavation to confirm that all soil containing detectable hydrocarbons has been removed. <br /> Both saturated and unsaturated soil will he sampled. The samples will be analyzed by EPA <br /> I <br /> Method 8015, for TFHC. Twenty percent of the samples will also be analyzed by EPA <br /> Method 8020, GC/PID, for aromatic hydrocarbons including BTX, Once this confirmatory <br /> sampling indicates that all detectable hydrocarbons have been removed, we will backfill <br /> the excavation with clean sand or gravel and aerate the removed soil at,the rear of the <br /> Safeway facility. <br /> 3. HYDROCARBONS IN BORING B-2 SATURATED SOIL <br /> The hydrocarbon concentration found in the sample from 20.7 ft depth in boring <br /> B-2 occurs about three ft below the water table. Water levels in the region fluctuate due <br />