SITE INFORMATION AND CORRESPONDENCE_FILE 1

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hydrocarbon impact beneath the site, three soil borings are proposed in the area of the former piping to investigate areas previously not investigated and one soil boring is proposed between the UST's and Well MW-2 to investigate any residual hydrocarbon impact associated with the product delivery activities (Figure 4). Further, an additional groundwater i,:onitoring well is proposed downgradient of Well MW-2. Based on the results of the above investigation, minimal soil impact has been identified within the former tank complex and low dissolved concentrations have been identified in groundwater beneath the site. Vadose zone impact and detectable concentrations of hydrocarbons in capillary fringe soils have not been identified. In regards to soil impact within the former UST's, the lateral and vertical extent of hydrocarbon affected soil is defined. Soil samples 2A, 2B, and 3A collected from beneath the tanks and soil samples collected from the borings for Wells MW-3 and MW-6 define the lateral extent of hydrocarbons. Soil samples collected from the borings for Wells MW-1, MW-3 and MW-6 define the vertical extent of hydrocarbons. The absence of detectable concentrations of hydrocarbons within the capillary-fringe soils appears to be due to the minimal impact of dissolved hydrocarbons within groundwater. In regard to the former piping at the site where soil samples were not collected during station product facility replacements in 1986, several subsurface wells, soil samples, and soil vapor probes have been located in proximity to the former piping (Wells MW-1, MW-6, and MW-7 and Probe VP-6). Data collected from these subsurface investigation do not suggest that the former piping is a significant primary source (Figure 4). To confirm this interpretation, additional soil borings are proposed, as previously discussed. Dissolved hydrocarbon impact on site (with the exception of Well MW-2) is of low concen- tration. In many cases the dissolved total petroleum hydrocarbons calculated as gasoline (TPH-g) and chlorinated compounds are mixed. Where mixtures of the two compounds are present, an increase in the reportable concentrations is common. In respect to Well MW-2, located along the downgradient property boundary and downgradient of the existing USTs, groundwater samples collected from this well contain slightly elevated TPH-g and benzene concentrations (TPH-g 630 and 150 parts per billion [ppb]). Data infer that dissolved TPH-g found in Well MW-2 may be a result of a limited source of hydrocarbons at the existing UST complex. Further investigation is proposed in this area, as previously discussed. The chlorinated compounds that have been identified beneath the site, which are attributed to a documented upgradient source, include: 1,2-Dichloroethane, 1,1-Dichloroethane, trichloroethene, and tetrachloroethene. Tetrachloroethene has been identified at an elevated concentration of 10,000 ppb. 3201357B/CAPREVI 4 June 29, 1995