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116 and TPH (EPA Method 8015) None of these constituents were detected in the groundwater samples (Appendix D) The same wells were sampled again in January 1989, two of the three wells were dry and ' groundwater samples from the third well did not detect any of the constituents tested above(Appendix E) A risk assessment was conducted as part of the FS/RAP to evaluate the potential environmental and health risks to local receptors and to estimate acceptable cleanup levels which would be required to mitigate those risks The leachability of the most toxic (carcinogenic) and mobile constituent found in ' the diesel-impacted soil, naphthalene, was estimated using procedures similar to those described in the Designated Waste Methodology (RWQCB, 1989) Using the assumptions and methods described in ' "Rapid Assessment of Potential Groundwater Contamination Under Emergency Response Conditions" (EPA, 1983) the fate and transport of naphthalene was calculated, based on site conditions The method used to predict transport of naphthalene assumed no adsorption to soils and no biological degradation, which is quite conservative since naphthalene partitions strongly to soil organic ' carbon and has a half-life of 12 to 48 days in soil (Howard et al , 1991) Given several conservative assumptions including ' + the regional rainfall recharge rate for the area is 14 inches/year, despite the majority of the site is paved, + The TPH/D concentration in soil, is 28,000 mg/kg, the highest reported concentration of TPH/D, ' • The ratio of naphthalene to TPH/D is 0 002, the highest ratio reported, ' • The nearest domestic water supply which is screened at 200 to 500 feet bgs, approximately 3,000 feet north of the site • No adsorption of naphthalene, and + No biological degradation of naphthalene Given these assumptions the model concluded that dilution and dispersion would reduce the concentration of naphthalene in soil leachate by a factor of 0 0061 prior to reaching the nearest domestic rgroundwater well In other words, a concentration of 1 mg/L naphthalene in soil pore-water at the site would be diluted to 0 0061 mg/L naphthalene in the nearest domestic well after moving to 200 feet bgs, and 3000 feet to the north The rate of transport of naphthalene in soil pore water to the domestic water supply would require approximately 250 years to reach this domestic well, assuming no degradation When adsorption of naphthalene to soil is considered, a concentration of 21,000 mg/kg TPH/D in soil on site would result in a naphthalene concentration at the applied action level, 0 018 mg/L with a TPHID-to-naphthalene ratio of 0 002, again assuming no degradation The applied action level set by SAC36 00 6