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i Site Background Information Waterloo Food& Fuel AGE-NC Project No 99-0559 Page 11 of 11 most severe at the northern edge of the UST excavation and the release was most severe at the southern most dispenser islands (PL-2, PL-4), at the center-north dispenser (PL-5) and even less between the dispenser islands • Once released fuel washed over the USTs and out of the product lines Into the subsurface, the contaminants migrated under the former UST area (CPT2) vertical depth of approximately 80 feet bsg, possible to the former water table level, where the variation concentration in soil samples suggest a smear zone between 90 feet and 150 feet bsg The highest TPH-g and BTEX impact to soil in the upper vadose zone is present at monitoring well borings through the former UST area (MW2) At this point the TPH contaminants migrating down to the water table and west and south to monitoring well MW-3 and MW-4, where non-detect soil samples were collected above 50 feet bsg and Impacted soil below 50 feet bsg The aenal extent of the soil contamination in vadose zone is defined only to the west of the former UST area • The petroleum hydrocarbons then dissolved into the ground water at the former UST area and likely under the former dispenser island The presents of free phase petroleum product at the former UST excavation indicated adsorbed concentrations ofpetroleum hydrocarbons beyond the sorbtive capacity of the soil at the water table,a submerged soil plume below the current water table level, representing a smear zone of contamination and/or the continual vertical migration of petroleum hydrocarbons at a rate faster than the water table can dissolved petroleum hydrocarbons • TPH-g and BTEX compounds were also detected in deeper ground water samples collected from wells near the former UST area, inexplicable Increasing or remaining at stable concentrations with depth,nearly 180 feet bsg at the former UST area The vertical and the lateral extent of TPH and BTEX has not been defined by sample collected in the former UST area,yet low concentration of TPH and BTEX are present south of the former UST area at well MW-6 • The dissolved MTBE has migrated west of the former UST area in the shallow water table and migrated northwest under Waterloo Road The vertical migration of dissolved MTBE has been reduced by the advective forces of sigmficant ground water hydro stratigraphic flow units,particularly at a depth of 100 feet bsg,yet the dissolved plume of MTBE extends well beyond the site and nearly one-half of a mile west of the site • The general combination of free phase petroleum product and a long duration of contamination in the environment likely has generated a vertical diffusion,which likely equal or exceeds the lateral migration distance of the dissolved MTBE west of the site Therefore additional deep ground water extraction from the three main deeper ground water hydrostratigraphic units is justified Advanced GeoEnvironmentai,Inc