ARCHIVED REPORTS_REMEDIAL INVESTIGATION REPORT 2000

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Discussion of Results 14 The elevated metal concentrations and total lead concentrations at and slightly above the TTLC in soil are indicative of impacts of historical ship-building activities such as sand- blasting or metal plating. The volatile organics detected in the soil and ground water appear to have been derived from a variety of aged petroleum products that were likely used on-site during past ship-building activities. The petroleum hydrocarbons identified in the soil samples have tentatively been identified by the laboratory as aged gasoline (C4 - C12) and hydraulic or cutting oils (greater than C,O. Additionally, the naphthalenes detected in the ground-water sample from boring B4 were reported to be typical of aged gasoline. It appears that contamination is not as extensive (vertically) on the eastern portion of the parcel as on the western portion. On the eastern portion near borings 131 and B2, petroleum hydrocarbon concentrations in soil decrease from designated levels at the 3-foot depth to levels just above detection limits at the 5-foot depth; the total metal concentrations decrease from levels at or slightly about the TTLC (lead only) and/or elevated levels at the 3-foot depth to typical soil metal concentrations at the 5-foot depth. On the western portion of the parcel at boring B4, petroleum hydrocarbon concentrations in soil are at designated levels at both the 3-foot and 5-foot depths, and soil metal concentrations generally increase with depth to the 5-foot sample, which contained a total lead concentration equaling the TTLC. Additionally, VOCs have not been detected in ground water beneath the eastern portion during this or any previous investigations (RFSNA, May 1992), but petroleum hydrocarbons were detected in the ground-water sample collected from boring B4 during this investigation. The presence of low metal concentrations (some exceeding the primary MCLS) in several site wells, which were sampled during previous investigations, is addressed further below. However, there is a preliminary indication that soluble metal concentrations are quite low under the slightly alkaline soil conditions onsite, and that metals are affectively attenuated by the soil well above the water table.