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PROPOSAL FOR REMEDIATION SERVICES <br /> MOBIL SERVICE STATION #10-NP4 <br /> TRACY, CALIFORNIA <br /> levels in site monitoring wells vary seasonally over a <br /> range of 1 to 2 feet; <br /> o Groundwater flows to the north or northeast across the <br /> site; and <br /> o The hydraV is conguctivity of saturated soils was assumed <br /> to be 10 to 10 cm/s. <br /> Site Contamination <br /> a Soil contamination is primarily limited to two areas on <br /> the property. Adjacent to the underground gasoline <br /> storage tank area located in the northeast corner of the <br /> property and in the vicinity of a waste oil tank formerly <br /> located on the west side of the property. Contaminants <br /> adjacent to the underground gasoline storage tank are <br /> primarily volatile organic compounds associated with <br /> gasoline. Contaminants in soil near the waste oil tank <br /> includes volatile organic compounds and may include <br /> semivolatile organic compounds. The total petroleum <br /> hydrocarbon (TPH) level in a soil sample collected in <br /> 1986 above the water table in the underground gasoline <br /> tank excavation was 2 parts per million (ppm) . A TPH <br /> concentration of 61 ppm was reported in a soil sample <br /> collected in 1986 above the water table near the waste <br /> oil tank excavation; <br /> o Gasoline constituents potentially present in soils <br /> off-site in the vicinity of two service stations located <br /> on the other side of Tracy Boulevard and Grant Line Road <br /> do not currently need remediation. TPH concentrations in <br /> soil samples collected during drilling of wells MW-6 and <br /> MW-8 were 2 ppm and 25 ppm, respectively. Benzene <br /> concentrations in the same samples were 0. 48 ppm and 0. 62 <br /> ppm, respectively; <br /> o Site groundwater contamination is restricted to areas <br /> east and northeast of the pump islands and underground <br /> gasoline storage tank area. Traces (less than 0. 01 feet) <br /> of free product have only been noted in well MW-3 . No <br /> petroleum hydrocarbons have been detected in wells <br /> southwest (MW-1) or north (MW-2) of this area. , TPH <br /> concentrations in this area range from 1 ppm to 30 ppm, <br /> in wells MW-4 and MW-5 to 3 , 000 ppm in well MW-3 . <br /> Benzene concentrations range from 0. 034 ppm to 7 ppm in <br /> these wells; and <br /> o Off-site groundwater contamination may need to be <br /> remediated. TPH concentrations in wells MW-6 and MW-8, <br /> -2- <br />