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1 ' 25 February 2005 • AGE-NC Prod ect No 01-0827 ' Page 5 of 10 ' Identified at depths between 60 and 65 feet bsg In former UST area ' Based on the subsurface soil distribution, AGE developed a preliminary subsurface model limited to the area near the former UST excavation, with the hydrostratigraphy consisting of four Informal hydrogeologic zones (Figures 3 and 4) Hydrogeologic units may be defined as significant vertical ' intervals of soil having significant lateral extent and having similar hydrologic characteristics (I e hydraulic conductivity, transmissivity, etc ) over its vertical and horizontal extent AGE has Informally identified the four informal hydrogeologic zones in geologic cross sections A-A'and B-B' ' (Figures 3 and 4, respectively) as having significant intervals of apparently porous to semi-porous grained soil separated by significant intervals of finer-grained, less permeable soil , the four hydrogeologic zones identified are as follows(depths are approximate and can vary by several feet across the site) • Hydrogeologic Unit 1 -generally between surface grade and 20 feet bsg locally less, consists primarily of laterally continuous, less permeable, fine grained, silty clay and clayey silt • Hydrogeologic Unit 2-Located between 20 and 30 feet bsg,consists primarily of permeable I• to semi-permeable, fine to medium sand and silty sand with limited minor gravels cut and fills, representing the first ground water currently observed at a depth of 25 feet bsg ' • Hydrogeologic Unit 3 - Located between 30 and 60 feet bsg, consists primarily of less permeable, fine grained, silty clay and clayey silt zone, some limited sand zones of limited lateral continuity (only at well MW-2) I0 Hydrogeologic Unit 4 - Located between 60 feet and 65 feet bsg, consists primarily of permeable to semi-permeable,fine to medium sand with hmrted minor fine grained material, the depth interval of well MW-6 The hydrostratigraphic model presented is Interpretational and will be modified as more data is collected Based upon ground water monitoring well Information obtained from the site, the depth to ground I water at the site has ranged from 45 feet bsg, during the late 1992, up to the most shallow depth to water of 20 feet bsg in the mid 1998 The low ground water table coincides with the operation of the former UST system The water table currently occurs at a depth of approximately 25 feet bsg 4.0. PETROLEUM HYDROCARBON DISTRIBUTION IN SOIL Between the first UST removal ofA April 1987 and February 2005 eighteen soil borings B1 • p �' g g ( through Advanced GeoEnvironmental,Inc I