Laserfiche WebLink
14 <br /> Discussion of Results <br /> The elevated metal concentrations and total lead concentrations at and slightly above the <br /> TTLC in soil are indicative of impacts of historical ship-building activities such as sand- <br /> blasting or metal plating. The volatile organics detected in the soil and ground water <br /> appear to have been derived from a variety of aged petroleum products that were likely <br /> used on-site during past ship-building activities. The petroleum hydrocarbons identified in <br /> the soil samples have tentatively been identified by the laboratory as aged gasoline (C4 - <br /> C12) and hydraulic or cutting oils (greater than C18). Additionally, the naphthalenes detected <br /> in the ground-water sample from boring B4 were reported to be typical of aged gasoline. <br /> It appears that contamination is not as extensive (vertically) on the eastern portion of the <br /> parcel as on the western portion. On the eastern portion near borings Bl and B2, <br /> petroleum hydrocarbon concentrations in soil decrease from designated levels at the 3-foot <br /> depth to levels just above detection limits at the 5-foot depth; the total metal concentrations <br /> decrease from levels at or slightly above the TTLC (lead only) and/or elevated levels at the <br /> 3-foot depth to typical soil metal concentrations at the 5-foot depth. On the western portion <br /> of the parcel at boring B4, petroleum hydrocarbon concentrations in soil are at designated <br /> levels at both the 3-foot and 5-foot depths, and soil metal concentrations generally increase <br /> with depth to the 5-foot sample, which contained a total lead concentration equaling the <br /> TTLC. Additionally, VOCs have not been detected in ground water beneath the eastern <br /> portion during this or any previous investigations (RESNA, May 1992), but petroleum <br /> hydrocarbons were detected in the ground-water sample collected from boring B4 during <br /> this investigation. The presence of low metal concentrations (some exceeding the primary <br /> MCLS) in several site wells, which were sampled during previous investigations, is addressed <br /> further below. However, there is a preliminary indication that soluble metal concentrations <br /> are quite low under the slightly alkaline soil conditions on-site, and that metals are <br /> affectively attenuated by the soil well above the water table. <br /> N <br />