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and MW-7) are virtually the same as in the excavation samples, which causes some doubt about the source. This is especially true because the high TPH-g concentrations in the excavation samples may be partly due to differences in the methods used to collect well samples vs. excavation samples, and because the samples were collected at different times by different consultants and analyzed by different laboratories. In addition, Geoprobe boring GP-1 is located within the excavation and GP-3 is located between KF-3 and both off-site monitoring wells, but no TPH-g and very little benzene were detected in the seven soil samples from. GP-1 and GP-3. Had MW-6 and MW-7 been contaminated by a leak from the USTs at the Kwikee Foods site, both GP-1 and GP-3 should be significantly more contaminated. It is therefore difficult to explain the contamination in MW-6 and MW-7 by westward migration of gasoline from the Kwikee Foods property. In any event, it is apparent that the extent of groundwater contamination has not been delineated. 6.0 CONCLUSIONS AND RECOMMENDATIONS The principal conclusion that can be drawn from this investigation is that soil contamination is relatively minor at this site. This was suggested by the results from the drilling investigation done in 1994, when no significant soil contamination was detected in either KF-1 or KF-2. Certainly the hydrocarbon concentrations in the soil are far below what might be expected in view of the existence of four holes in the two USTs that were removed from the site in March 1998. We suggest that the holes were rather tightly plugged by the dense, low-permeability silty clay that is present in the upper 20 feet of the site and which surrounded the USTs when they were removed. This interpretation is supported by the fact that the holes were not apparent when the tanks were removed, and were only located after considerable scraping to remove the clay that coated them. This interpretation is also supported by the operator's inventory records, which did not reveal any obvious inventory losses through leakage. In previous reports, we have suggested that much of the groundwater contamination that has been documented beneath the site may have had an off-site source. Despite the presence of holes in the USTs, an off-site source remains a strong possibility, as suggested by at least two lines of evidence. First, the hydrocarbon concentrations that were detected in the Geoprobe borings in the lower part of the silty clay layer and in the underlying sand bed are remarkably low in comparison to the concentrations (up to 2,700 mg/kg TPH-g) that were detected in the samples that were collected from the silty clay layer at the the base of the excavation at a depth of 14-15 feet. This can be explained by the low hydraulic conductivity of the clay layer, and implies that groundwater contamination in the sand bed is not due to downward percolation of the contaminants through the clay layer. Rather, groundwater contamination is due either to the rise of the groundwater table from the sand bed into the middle part of the clay layer (base of the UST excavation) or to lateral migration from an off-site source. If the middle part of the clay layer were the source of groundwater contamination, then contaminant concentrations should be greater at the present time than they were when the water table was lower, but this is not the case. In fact, concentrations declined significantly this quarter. 8 i