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I ISite Background Information/SCM Former MBP - Mossdale AGE NC Project No 99-0570 ' Page 4 of 5 ' water table The vadose zone is predominantly fine-grained material from surface grade to 15 feet bsg The zone is characterized by low pore pressures ' Hydrogeologic Unit 1 (HU1) -At the top of the current saturated zone, HU1 extends from 15 feet to approximately 60 feet bsg and is comprised of laterally continuous, alternating layers of poorly graded sand with silt and silty sand A coarse-grained sand unit occurs between 20 feet and 25 feet , ' bsg at CPT-2 This urut has flow unit characteristics Hydrogeologic Unit 2 (HU2) - HU2 extends from 60 feet to approximately 90 feet bsg and is ' comprised predominantly of stiff, fine-grained soil,with silty clay and a thin bed of poorly graded r sand at 80 feet bsg ' Hydrogeologic Unit 3 (HU3)-HU3 extends from 90 feet bsg to total depth, this zone is composed of interbedded stiff,fine-grained soil,silty poorly graded sand,silty clay,and silty sands from 90 feet ' bsg to approximately 110 feet bsg This unit has flow unit characteristics — Hydrogeologic units were depicted in cross-sectional view B-B' in the AGE-prepared Cone ' Penetrometer Testing Report, dated 28 April 2004 Analytical data from a total of eight grab ground water samples from HU1, HU2, and HU3 are as ' follows TPH-g and TPH-d were detected in grab water samples collected from CPT2-89 at concentrations of 120µg/1 and 95µg/1,respectively These detections are likely due to silt within the water sample causing a false detection of TPH-d, TPH-g and TPH-d were detected in grab water samples collected from CPT2-110 at concentrations of 380 µg/1 and 380µg/1, respectively These detections are likely due to a detection of general biological impact to the site,such as natural ethene from a septic system or silt within the water sample causing a false detection of TPH-d The BTEX compounds toluene and ethylbenzene were detected in ground water samples collected from CPT2-110 at concentrations of 1 3 µg11 and 10 µg/l, respectively However, gas ' chromatography mass spectrophotometer analysis did not identify either of these compounds ' SITE CONCEPTUAL MODEL The general release of hydrocarbons and fuel additives emanated from the eastern edge of the ' northern dispenser island,and the product pipmg J oining the two island northernmost islands Once released into the subsurface,the shallow soil near the dispensers and a coarse grained,poorly to well sorted sand was impacted The soil impacted near the dispenser islands was excavated and backfilled with clean soil Once dissolved in the ground water,the hydrocarbons only appear to have migrated to well MW-2,while MTBE has migrated laterally to wells MW-2 and MW-1, near the UST area _Jftvos7- ' Advanced GeoEnvlronmental,Inc