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i IHistorical Background AGE-NC Project No 99-0559 IPage 3 of 4 collected from HU5 at 150 feet The highest concentration of MTBE detected at the site was from bonng CPT3, in HU1 TPH-g,benzene and MTBE were detected in the three soil samples collected from CPT-2 at depths of 80 feet(HU3), 110 feet(upper HU5) and 135 feet bsg(middle HU5) The I vertical extent of impacted soil has not been defined in the source area, however, adsorbed concentrations decreased significantly with depth (135 feet bsg) and the 135-foot sample may be inferred to be near the lower margin of impacted soil On 27 September and 01 through 03 October 2001, four Continuous Multichannel Tubing (CMT) ground water monitoring wells (MW-5 through MW-8) were installed Based on analytical results I of grab ground water samples and interpreted soil profiles from CPT data,the CMT monitoring wells were designed and constructed utilizing five separate filter pack intervals, from. 45-65 feet bsg, 87-100 feet bsg, 125-135 feet bsg, 148-160 feet bsg and 174-185 feet bsg, to characterize ground I watergradient,potential contaminant migration pathways and to assess the lateral and vertical extent of impacted ground water west and east of the former UST release IOFF-SITE ASSESSMENT ' • In September and October 2002, five additional, paired soil borings (CPT-4 to CPT-8) were advanced off-site(Figure 2) TPH-g was detected in groundwater samples collected from HU2,HU4 I and Upper HUS of the off-site soil borings, the maximum concentration was 2,000 µg/1 in HU4 In addition, BTEX compounds were detected 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 µg/1, ETBE and TAME were detected at 25 µg/l and 5 6 pg/l,respectively,and TBA and DIPE were detected at 630 µg11 and I18µg/l,respectively However,only TBA was present in Lower HU5,at a concentration of 180 9g/1 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, where the highest concentration of off-site MTBE was detected 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 µg/1 The TCE appears to onginate from an off-site source, since TCE was not detected in CPT borings (e g , CPT-4 and CPT-6) closer to the site IThe vertical extent of dissolved TPH-g,benzene and MTBE does not extend to below 130 feet bsg I Advanced GeoEnvironmental,Inc