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l - CONCEPTUAL SITE MODEL Based on the data developed to date, including all soil borings,monitoring wells installed and CPT soundings,AGE has developed a site subsurface model for the release,migration and distribution of the varying contaminants in the subsurface as described below The subsurface from site grade to approximately 150 feet bsg is composed primarily of fine- grained soil with a coarse-grained interval of variable thickness and lateral distribution The mayor coarse-grained sand and gravel intervals occurring between 20 and 35 feet below surface grade(bsg) and a laterally continuous coarse-grained sand interval at approximately 75 to 85 feet bsg, dipping in orientation to the southeast A laterally discontinuous yet, significantly thick sand unit extends from 100 feet to 110 feet bsg in the area of CPT30 to CPT3 and CPT5 Overall high pore-pressure was documented in the CPT sounding of the coarse-grained sand below the water table The remaining stratigraphy of the site is comprised ' of silt with clay inter-channel fill areas A laterally continuous clay is present at 110 feet bsg across most of the western distribution of the contaminate plumes ' These characteristics allowed construction of a site geologic/hydrogeologic model of the vadose zone extending from surface grade to approximately 50 feet bsg or the current water table level which fluctuates with seasonal recharge in the area The hydrologic unit defined ' are informal units and vary considerable based on the direction and content The unit are designated to aide in the clarification of flow path ways and to designate migration pathways The first hydrologic unit from 50 feet or the water table to 75 feet bsg, a second hydrologic ' unit from 75 feet bsg to 85 feet bsg,and a third hydrologic unit from 85 feet to approximately 100 feet bsg, a fourth hydrologic unit from 100 feet to 110 feet bsg, a fifth hydrologic unit ' from 110 feet to 145 feet bsg, the sixth and lowest hydrologic unit at 145 to 150 feet bsg The second,fourth locally and sixth are presumed to have a greater ground water velocity and therefore may conduct more ground water DISTRIBUTION OF STODDARD SOLVENT • A release of stoddard solvents occurred from an unidentified source on the western portion ' of the site The most possible source is a set of dry well storm drains Available data is suggestive of a spill or discharge at the western edge of the building in the area of borings P26, P27, CPT32, various wells including the extraction well EW-1 The highest impact to ' soil in the upper vadose zone is present at borings P26, P27, P14, P25 and EW-1 Once released to the subsurface,the contaminants migrated to a vertical depth of approximately 40 feet bsg, at which point the contaminants migrating locally down to a depth of 70 or 80 feet bsg Minor concentrations of 1,2-DCA and tetrachloroethene were detected at the depths of 45 feet to 65 feet bsg,within the stoddard plume area west of the building The highest impact to soil near the water table and below the water table to a depth of 70 feet bsg occurs in the ' area of boring EW-1, P27 to 55 feet and borings P26 and P 3 2 to a depth of 70 feet bsg ' Advanced GeoEnvnronmentai,Inc