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• • <br /> s <br /> In Soil Gas Boring Al-SGI, tetrachloroethene (PCE) was detected a concentrations greater than <br /> the California Human Health Screening Level of 603 ug/mi. This detection requires further <br /> lateral delineation. <br /> 4.3 Delineation—Groundwater <br /> As previously discussed, groundwater impacts identified at the Site were limited to Monitoring <br /> Well TW-5. Although groundwater results showed detections only in well TW-5, soil below the <br /> groundwater table in Boring E3-1 exhibited TPH impacts. As such, additional delineation of <br /> impacts in groundwater near Boring E3-1 is recommended. As requested by DTSC, an <br /> additional groundwater sample will be collected at TW-5 to determine if benzene is present in <br /> shallow groundwater. <br /> 4.4 Recommended Sampling <br /> Based on the delineation information provided above, Parsons recommends that two additional <br /> soil borings (B1-2 and E3-2) and seven additional soil gas borings (Al-SG2, Al-SG3, and A3- <br /> SG2 through A3-SG6) be drilled to achieve lateral delineation of impacts in soil and soil gas, <br /> respectively. In addition, to delineate potential benzene impacts in Monitoring Well TW-5, an <br /> additional groundwater sample will be collected from the upper 3 feet of the screened interval. <br /> Finally, a grab groundwater sample will be collected from boring E3-2 to determine if impacted <br /> soil below the water table has entered the dissolved phase and contributed to potential impacts in <br /> groundwater at the southwest comer of the Site. This information will also provide additional <br /> Site characterization data. <br /> The attached Figure 6 displays the proposed soil and soil gas boring locations. The attached <br /> Table 1 shows the rationale for the proposed soil/soil gas boring locations, and attached Table 2 <br /> displays the sample intervals and analyses for the proposed soil/soil gas/groundwater sampling. <br /> 4.4.1 Soil Sampling <br /> In an attempt to achieve horizontal delineation of impacts in soil, it is recommended that two <br /> additional borings (131-2 and E3-2) be placed between B1-l/E3-1 and the property boundary, <br /> respectively. Boring E3-2 will be drilled to a maximum depth of 15 feet bgs; the depth where <br /> vertical delineation in Boring E3-1 was achieved. Samples will be collected at depths of 1, 3, 5, <br /> 8 (just above groundwater), 10 and 15 feet bgs. Samples will be analyzed for PAHs using EPA <br /> Method 8310; TPH as gasoline, diesel and motor oil using EPA Method 8015; and for Title 22 <br /> Metals using the EPA Method 6010/7000 Series. Analytical results for E3-2 will be compared to <br /> the results for E3-1 and TB-24 to assess if the concentrations are increasing to the south. In <br /> addition, a grab groundwater sample will be collected from this location by bailing from a <br /> temporary casing with a pre-filter packed screen interval to minimize sediment intrusion into the <br /> grab groundwater sample. The groundwater sample will be analyzed for TPH and PAHs using <br /> EPA Methods 8015 and 8310, respectively, to determine whether or not soil impacts have <br /> contributed to potential groundwater impacts. <br /> At the Bl-2 location, soil samples will be collected at depths of 1, 3 and 5 feet bgs using a hand <br /> auger. The Bl-2 location will be placed between the B1-1 location and the property fenceline to <br /> determine if on-site impacts are observed at the property line. Samples will be analyzed for <br />