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AGE-NC Project No. 99-0559 Page 9 of 14 The fuel additive TBA was the only analyte detected in the Lower HU5 samples, at a concentration of 180 pg/I. TPH-g was detected is groundwater samples collected in HU2, HU4 and Upper HU5; the maximum concentration was 2,000 pg/I in HU4. BTEX compounds were detected only in HU2. Fuel additives were detected in all hydrologic units. The highest concentrations were detected in HU4; MTBE was detected in HU4 at a maximum concentration of 2,600 pg/I, ETBE and TAME were detected at 25 pg/I and 5.6 pg/I, respectively, and TBA and DIPE were detected at 630 pg/I and 18 pg/I, respectively. However, only TBA was present in Lower HU5, at a concentration of 180 pg/I. HU4 is a thick poorly graded sand layer encountered at approximately 90 to 110 feet bsg. MTBE is apparently migrated laterally within this unit, especially off-site towards the west. Dissolved MTBE extends off-site past all current sampled locations. The concentrations of dissolved MTBE decreased away from the site, except to the west at CPT4, the highest concentration of MTBE detected off-site. The vertical extent of dissolved TPH-g, benzene and MTBE does not extend to below 130 feet bsg. The solvent TCE was detected in HU2 and HU4 in the off-site borings CPT-5 and CPT-8 (Figure 2), at a maximum concentration of 1,700 pg/I. The TCE appears to originate from an off-site source, since TCE was not detected in CPT borings (e.g., CPT-4 and CPT-6) closer to the site. Computer generated CPT soil descriptions augmented with previously obtained soil sample and CPT soil descriptions were utilized to construct the vertical and lateral geologic model; laboratory analysis of groundwater samples was utilized to assess the hydrocarbon-impact on the dissolved media. SITE STRATIGRAPHY Based on the soil descriptions from CPT and previous soil boring logs, interpretive cross sections were constructed to depict the general hydrogeologic framework beneath the site. The site vadose zone currently extends from the ground surface to 65 feet bsg (water table), and is composed of silt, clayey silt, clay, and 'stiff fine grained' soil, and a gravelly, fine to coarse sand layer between 35 feet and 50 feet. Below the vadose zone, the lithology is composed dominantly of silty fine sand, sandy silt, clayey silt to silty clay and clay. Significant sand intervals were identified at between 90 and 110 feet bsg over the site, a thin discontinuous sand layer was encountered at 150 feet bsg and between 165 and 170 feet bsg. Fine grained, silty clay and clayey silt layers were observed at depths between the surface and 30 to 35 feet bsg, 80 and 90 feet bsg, 105 to 150 feet bsg. Advanced GeoEnvironmental, Inc.