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• not appear to fluctuate seasonally Historically, groundwater levels in nearby wells MW-2 (screened from 5 to 20 feet bgs) and MWO-1X (screened from 20 to 30 feet bgs, in an attempt to determine the vertical extent of impact to groundwater) have been within 0 26 ft of each other It is possible that the sandy strata above and below the hard clay layer are hydraulically connected, and the close tracking of groundwater elevations between wells MW-2 and MWO-1X strongly suggests that this may be the case Historical groundwater elevation data and groundwater elevation contour maps are included in Appendix B 3.4 Extent of Petroleum Hydrocarbon Impact Soil and groundwater beneath the site have been impacted with petroleum hydrocarbons Analytical data indicate the presence of TPHG, TPHD, benzene, MTBE, tertiary-amyl-methyl- ether (TAME), tertiary-butyl-alcohol (TBA), ethanol, and methanol Historical groundwater analytical data are presented in Appendix B, and historical soil analytical data are presented in Appendix C Dissolved and Adsorbed Contamination Mass Estimates are shown in Appendix D Figure 6 presents groundwater analytical data collected during the second quarter monitoring activities Extent of Petroleum Hydrocarbon Impact in Soil Compliance soil samples collected beneath the former southern and northern USTs, in February and October 1998, were impacted with petroleum hydrocarbons In the southern UST compliance samples, TPHD was reported in one sample at the concentration of 300 mg/Kg This is consistent with only diesel having been stored is this UST In the northern UST compliance samples, TPHD (660 mg/Kg and 75 mg/Kg) and MTBE (0 46 mg/Kg and 0 043 mg/Kg, by EPA Method 8260) were reported in two of the samples at depths of approximately 10 5 feet bgs The highest concentration of TPHD was reported in the sample collected the east side of the former 6,000-gallon diesel tank The highest concentration of MTBE was reported in the sample collected from the east side of the former 8,000-gallon gasoline tank Benzene (0 88 mg/Kg) was only reported in the sample collected from the depth of 10 5 feet bgs from the east side of the former 6,000-gallon diesel tank In investigation phases subsequent to compliance sampling TPHG or benzene have not been reported in any samples collected from the zone of groundwater fluctuation (5 to 10 feet bgs) TPHD was reported in one sample (GP-4, advanced in November, 1998) at the concentration of 200 mg/Kg The primary chemical compound that was reported in soil samples in the zone of groundwater fluctuation was MTBE Soil iso-concentration contours for the MTBE reported in soil samples collected from each boring in the zone of groundwater fluctuation are shown in Figure 7 The lateral extent of petroleum hydrocarbon impact beneath the site appears to be adequately characterized, except to the east MTBE concentrations in the 29 samples taken from the zone of groundwater fluctuation are uniformly low and sporadic These concentrations are centered in the vicinities of the former USTs, as well as an area hydrologically downgradient of P Voe's Truck Plaza\Reports\SCM_09-20031Joes truck plaza SCM doc Page 8 5rRA7U5