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TABLE 3 ANALYTICAL RESULTS of WATER SAMPLES JU1;1 February 9, 1994 TPH as TPH as Ethyl- Sample ID Gasoline Diesel Benzene Toluene benzene Xylene MW-112-9-94 140 ND 7.0 ND ND ND ' MW-412-9-94 ND ND 1.7 ND ND ND MW-512-9-94 ND ND ND ND ND ND :7]1 µg/L = parts per billion (ppb) ND = None Detected 5.0 CONCLUSIONS & RECOMMENDATIONS 5.1 Groundwater Contamination ' Very low concentrations of petroleum hydrocarbons continue to be detected in the two monitoring wells located directly down gradient of the excavation. Both the extent and the magnitude of the dissolved gasoline plume appear to be relatively minor and easily mitigated. At least two options for interim groundwater remediation are available: an extended purge (perhaps 500 gallons) of MW-1 and MW-4, and an air-sparging pilot test ' to flood the aquifer with oxygen and enhance hydrocarbon oxidation. GeoAudit recommends a meeting with the PHS/EHD to discuss these and other alternatives for groundwater treatment. 5.2 Soil Contamination As noted in previous reports, minor concentrations of toluene, ethylbenzene, and xylene were detected in three soil samples from MW-1 when the well was drilled in 1992. Before granting site closure, the PHS/EHD will probably request that this contamination be ' addressed in some way. Although this contamination is probably not extensive, neither the volume of residual contaminated soil nor the average concentrations of hydrocarbons can be estimated with the available data. GeoAudit recommends that a soil boring be drilled ' near MW-1 to determine whether contamination is still present or has remediated naturally. If contamination is detected, one or two additional borings should be adequate to fully delineate its extent. Depending on the volume of soil and the average concentration of contaminants, a plan to either remediate the contamination or justify leaving it in place can be developed. Worc+e lih QR,S/1-py-1.10