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I I 4.0 MASS VOLUME ESTIMATION Our review of the results of groundwater sampling event conducted on June 9, 1994 indicate that no detectable petroleum hydrocarbon compounds are present in Site groundwater with the exception that ' toluene was detected at 0 61 ug/L in groundwater from well MW-6 This value is slightly above the detection hmit of 0 5 ug/L and represents the first detection of toluene in groundwater sampled from ' this well In fact, toluene has only been detected previously at the Site in samples from well MW-2 during 1992 at a maximum concentration of 11 ug/L Based on our review of the Site's historical monitoring data and the very low concentration of toluene detected, this apparently isolated detection , of toluene in the absence of confirmation data is not considered significant V ' The June 9, 1994 data validate the data from the previous two sampling events (December 1993, March 1994) indicating non-detectable petroleum hydrocarbons in Site groundwater Based on these ' three quarters of no detections, the volume of groundwater impacted with petroleum hydrocarbons at the Site appears to be insignificant As requested by PHS/EHD, samples collected during the June 1994 event were also analyzed for volatile organic compounds by EPA Method 601 The chlorinated hydrocarbon 1,2-dichloro ethane (1,2-DCA)was detected at 1 1 ug/L in the sample collected from well MW-2 No other detections ' of this compound were reported Although 1,2-DCA has reportedly been used as a lead scavenger in the production of some gasolmes, the presence of 1,2-DCA is not usually associated with gasoline ' hydrocarbon spills The compound 1,2-DCA can be associated with the use of solvents and may be a component of the contents of waste oil tanks used at retail gasoline facilities However, to date, there has been no evidence that a release from the Site waste oil tank has impacted groundwater Based on this low detection in one well at the Site, an estimate of the volume of groundwater ' impacted would be insignificant IThe chlorinated hydrocarbon tetrachloroethylene (PCE) was detected in samples from wells MW-4 and MW-6 at concentrations of 0 75 and 0 63 ug/L These two wells are separated by a distance of rSFUCOR° N0026-001 01 ROF 9 August 1 1994