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6.0 SUMMARY AND DISCUSSION 6.1 Summary • The USTs and product piping were replaced in the first and fourth quarters of 1998 Impact was reported in soil samples collected from the UST pits • Subsurface soils generally consist of fifteen feet of alternating layers of silty sand and coarse-grained sand overlying a hard clay layer The upper sandy strata appear to be laterally continuous beneath the site The lateral continuity of the hard clay unit was not completely assessed in the vicinity of the former northern UST complex Silty sand and clay strata underlie the hard clay stratum The sandy units above and below the hard clay layer may be hydraulically connected The vertical and lateral extents of strata underlying the hard clay have not been fully assessed • The vertical extent of soil impact remains uncharacterized The vertical extent of soil impact is at least 15 to 20 feet bgs • The lateral extent of petroleum hydrocarbon impact to soil appears to be adequately characterized in all directions except to the east of the site • Groundwater is encountered at approximately 6 to 10 feet bgs, and does not appear to exhibit seasonal fluctuation Groundwater flow direction is generally northeast to east at flow magnitudes ranging from 0 00083 to 0 0015 ft/ft • The lateral extent of dissolved hydrocarbons remains uncharacterized to the east and west The vertical extent of the dissolved hydrocarbons has not been completely assessed • No water supply wells have been identified within a 2,000-foot radius of the site • There are no complete pathways for exposure to humans at this site Potential exposure pathways identified at this time appear to be vapor inhalation, dermal contact, or ingestion by workers excavating in areas immediately adjacent to the northern boundary of the site Risk of exposure via these routes appears low C.5 16) �� 1h . • Approximately 0 22 Kg of MTBE remains in the soil, and approximately 0 483 Kg of- MTBE remains dissolved in the groundwater • P Voe's Truck Plaza\Reports\SCM_09-2003Voes truck plaza SCM doe Page 14 5TKAW5