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PROPOSAL FOR REMEDIATION SERVICES <br /> MOBIL SERVICE STATION #10-NP4 <br /> Ai TRACY, CALIFORNIA <br /> o Evaluation of potential off-site sources of <br /> contamination. Based upon current information, there <br /> appears to be a possibility of an off-site source of <br /> contamination. This possible off-site source may <br /> potentially contribute to concentrations of petroleum <br /> hydrocarbons reported in site monitoring wells thus <br /> unnecessarily increasing Mobil's cleanup costs. <br /> We will contact DHS, RWQCB, and LHD to determine whether <br /> fuel releases have been reported at other facilities in <br /> the site vicinity. If a fuel release is confirmed at a <br /> nearby service station, we will contact RWQCB with regard <br /> to obtaining their assistance in collecting samples of <br /> the fuel stored at those sites for fuel fingerprinting <br /> analyses. This procedure compares spectrographic <br /> analyses of the petroleum hydrocarbon compounds present <br /> in contaminated site monitoring wells to fuel stored on <br /> adjacent facilities. Although approximate, a positive <br /> match may indicate that an adjacent facility is an <br /> additional source of the petroleum hydrocarbons detected <br /> in groundwater at the site; <br /> o Assessment of groundwater flow direction and gradient. <br /> Groundwater flow direction has not been accurately <br /> determined. Groundwater flow direction and gradient <br /> affect contaminant recovery. <br /> We will survey reference point elevations and locations <br /> of each of the site monitoring wells. We will use these <br /> data to calculate groundwater elevations from existing <br /> and new water level data to estimate water table <br /> gradients and groundwater flow direction; <br /> o Evaluation of physical and chemical properties of soil <br /> on-site. Data on physical and chemical properties of <br /> site soils, particularly data on the distribution of <br /> hydrocarbons in site soils is not available. These data <br /> are necessary to select appropriate remediation <br /> technologies and to assess the need for excavating and <br /> treating soils on-site. <br /> We will drill six soil borings at the locations shown on <br /> Figure 1 to characterize site soils. Each boring will be <br /> drilled to a total depth of ten feet using hollow-stem <br /> auger drilling equipment. One soil sample from each <br /> boring will be analyzed for TPH (modified EPA Method <br /> 8015) ; and benzene, toluene, ethylbenzene, and xylenes <br /> (BTEX) (EPA Method 8020) . <br /> -4- <br />