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north and northeast of the study site The fourth well (MWO-1X) was installed in the vicinity of monitoring well MW-2, but screened in a deeper horizon Avalon concluded that the lateral extent of petroleum hydrocarbon impact to groundwater was adequately characterized to the north and northeast, but the vertical extent of dissolved petroleum hydrocarbons remains uncharactenzed 3.2 Geologic Conditions Stratus developed geologic cross-sections (Figure 5) based on observations in soil bonngs advanced during previous site investigation activities Copies of these boring logs are included in Appendix A The study area is underlain by a predominantly silty sand stratum between 13 to 18 feet thick A coarse-grained sand layer is encountered at a depth of 6 to 10 feet bgs, and is 2 to 5 feet thick This coarse-grained sand is laterally extensive beneath the site but exhibits some discontinuity in the vicinity of the former northern UST's Underlying the silty sand stratum is a layer of hard clay, encountered at 13 to 18 feet deep under the northern portion of the study area and extending to at least 22 feet bgs Laterally, the clay layer appears be continuous beneath the site except in the vicinity of GP-4 where it was not encountered to the depth of 20 feet bgs The hard clay layer was reported to be grading into a coarse grained sand at samples taken from approximately 20 feet bgs in soil borings MWO-1 through MWO-3 However, the sand stratum underlying the hard clay unit reported at the depth of approximately 22 feet bgs in MWO-1X was not identified in soil bonngs for MWO-1 through MWO-3 The lateral and vertical extent of the hard clay layer has not been adequately evaluated Further subsurface exploration is warranted to determine the vertical and horizontal extent of the hard clay in this vicinity Beneath the hard clay layer in the deepest boring advanced at the site (MWO-1X), strata of silty sand and more dense clay were encountered at depths ranging from 22 to 28 and 28 to 30 feet bgs, respectively The extent of these lower strata, both laterally and vertically, has not been adequately evaluated beneath the site 3.3 Hydrogeology Quarterly groundwater monitoring and sampling began in February 2000 Groundwater flow, through the second quarter 2003 in the shallow-screened monitoring wells, was generally northeast to east North and northwest flow has sporadically been observed Groundwater gradients have been relatively flat, between 0 00083 and 0 0015 ft/ft During the most recent monitoring event (second quarter 2003) groundwater flow was northeast at the gradient of 0 00088 ft/ft Groundwater beneath the site has been measured at depths between 6 and 10 feet bgs Groundwater elevations have fluctuated from 1 to 2 feet between monitoring events, but do P Voe's Truck Plaza\Reports\SCM_09-2003Uoes truck plaza SCM doe Page 7 O-MATu5