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5.0 RECOMMENDATION FOR SITE CLOSURE SECOR on behalf of CRC recommends the Mayor Mart Site for closure consideration based on the following justification summary ' • Petroleum hydrocarbon source removal remedial actions conducted at the Site have been successful based on sample analysis results from SECOR confirmatory boring SB-1 Conservative estimates of residual petroleum hydrocarbon mass in the subsurface vadose zone indicate an insignificant mass remains • Vadose zone transport modeling indicates that residual petroleum hydrocarbons in the vadose zone will not pose a threat to area groundwater quality Testing data indicate that a ' substantial colony of hydrocarbon utilizing bacteria exists in the area of residual impacts promoting further decay of the insignificant mass remaining ' • Petroleum hydrocarbon impacts to Site groundwater are currently non-existent as verified by five quarters of sampling data indicating no-detectable TPH-as-gasoline or benzene • Vadose zone transport modeling of the chlorinated hydrocarbon 1,2 DCA present in Site soil indicates the potential for impacts to Site groundwater quality Groundwater monitoring data from MW-2 confirms this condition with a detectable concentration of 1 6 ppb 1,2 DCA To date, detection of 1,2 DCA has been irregular and is not expected to increase in concentration over time as a result of continued source degradation • Due to low hydraulic gradients, and a seasonally varying groundwater flow direction, ' simple-conservative groundwater transport estimates for 1,2 DCA indicate a maximum migration rate of 16 feet per year To date, offsite wells (especially Well No 77) have not contained 1,2 DCA The closest active municipal supply well, Well No 77, is ' approximately 2000 feet from the Site At this rate, chemical migration to the municipal well is over 100 years This travel time estimate, combined with the fact of continued source degradation, indicates that long term impacts to local groundwater quality from residual ' 1,2 DCA is not feasible • Affected soil remaining in the former septic leach area consist of insoluble naphthalenes and heavy end hydrocarbons existing at depths above the documented high water level at the Site Vadose zone transport modeling indicates that these conditions do not pose a future ' threat to groundwater quality CRC Environmental Risk Management,Inc SECOR International Inc (SECOR®) 17 November 30 1994 N0026 001 01 add 1