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4.2 COMPREHENSIVE SUMMARY OF CHEMICALS IN SITE GROUNDWATER Monitoring data from the Final Quarterly Monitoring Event has been incorporated into a comprehensive table of groundwater monitoring results since the initial installation of the monitoring well network in 1991 Table 6 is an enhancement of the tabulated summary of results provided in the SECOR September 1994 Closure Report since it also includes the following • identification of the investigator/consultant responsible for sample collection, • a Iist of the quality assurance/quality control (QA/QC) duplicate samples collected by each ' consultant, • a summary of the QA/QC travel, replicate and method blanks results Whenever possible, limits of detection were included for each investigator although WESTON analysis results reports appear to have non-standard formats which make interpretation difficult ' 4.3 REVIEW OF PRESENCE OF PCE AND 1,2 DCA The VOCs PCE and 1,2 DCA have been identified in groundwater samples collected from onsite i monitoring wells at the Site Site investigations have revealed that TPH-g, the gasoline constituents BTEX, and total lead (which could have been present from a "regular" leaded gasoline), were non- detectable in the groundwater, in recent sampling events PCE is not associated with and is not a degradation product of gasoline, and there were no known uses of this material at this Site PCE impacts to area groundwater are interpreted to be the result of offsite sources The following sections present a discussion of possible sources in the area 4,3.1 VOC Sources ' Although 1,2 DCA is a potential degradation product of PCE and trichloroethylene (TCE), 1,2 DCA ' is a much more likely a degradation product of 1,1,1 trichloroethane(TCA) Neither PCE, TCE nor TCA were detected in either onsite soils or groundwater at this site The presence of 1,2 DCA without a corresponding presence of any TCA or TCE is unusual, unless another source is present Based on this unusual detection, SECOR conducted a literature search to evaluate possible additional sources for 1,2 DCA Literature searches have revealed that 1,2 DCA, in addition to commonly being encountered in heating oil, may also have been contained in a lead tetraethyl "anti-knock" compound gasoline additive if gasoline containing this additive material had been stored in the onsite tanks, it follows that this may have been the source of 1,2 DCA detected in Site soil and groundwater The material was discovered in soils at depths of 46 and 55 bgs in the former tank pit area Additionally, detections in groundwater have been found in samples collected from MW-2, SECOR IntemaRQnat Inc (5ECORO) CRC E❑WonmMW Risk Management,Inc N0026 001 01 add 14 Novembrr 30 t994