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I I12 December 2006 . AGE-NC Project No 01-0827 Page 5 of 14 to a depth of 30 or 35 feet bsg in the former UST area While fine to medium sand and silty sand was identified generally at depths between 35 and 55 feet bsg in monitoring well MW-2, east of the former UST area An additional fine-grained sandy silt and clayey silt, were identified generally between 30 feet and 60 feet bsg at the former UST area While a fine sand and silty sand was identified at depths between 60 and 65 feet bsg in former UST area Based on the subsurface soil distribution, AGE developed a subsurface model limited to the area near the former UST excavation, with the hydrostratigraphy consisting of four informal hydrogeologic zones (Figures 3 and 4) The hydrostratigraphic model presented is interpretational Hydrogeologic units may be defined as significant vertical intervals of soil having significant lateral extent and having similar hydrologic characteristics(i a 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 10 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 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 ' a 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) ' 0 Hydrogeologic Unit 4 - Located between 60 feet and 65 feet bsg, consists primarily of permeable to semi-permeable,fine to medium sand with limited minor fine grained material, the depth interval of well MW-6 I Based upon ground water monitoring well information obtained from the site, the depth to ground 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 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 I IAdvanced GeoEnvironmental,inc