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' from the lower sand layer were collected from soil boring B-5 and analyzed for geotechnical • properties. The samples B-5-10 and B-5-40 were described as brown sand and brown sand with silt ' and trace gravel, with porosities at between 34.5% and 30.6%, low organic content (0.4 to 0.6%), and specific gravity values at between 2.67 and 2.72.The samples B-5-20 and B-5-30 were described as brown sandy clay and a gray silty clay, with porosities between 46% and 47.7%, low organic ' content (1.2 to 1.4%), and a specific gravity of 2.72. ' SITE CONCEPTUAL MODEL Based on the data collected to date from soil borings and monitoring well installations, AGE has ' developed a site conceptual model for the release, migration, and distribution of the contaminants in the subsurface as described below: The shallow stratigraphy is composed of an upper layer (Layer 1) consisting of 15 to 20 feet of yellowish to brownish green, generally unconsolidated, fine to medium sand underlain by an 1 approximately 15-foot thick clayey silt layer(Layer 2);northwards,Layer 2 appears to transition into a sandy silt or silty sand with clay, and beneath former USTs No. 1 and 2, a discontinuous lense of green to olive gray fine sand was identified near the top of Layer 2. The third layer (Layer 3), at ' below 35 feet bsg,appears to be an olive green to brown, unconsolidated coarse to pebbly sand;this layer was defined on the basis of the four deepest soil borings (MW-6, B-1, B-5, and B-6) located at the former USTs No. 1 and 2,and down gradient off-site to the north-west.Additional figures and tables can be found in the AGE-prepared Corrective Action Plan (CAP), dated 1 l February 2003. Since the initiation of ground water monitoring in December 1999, ground water elevations have ' ranged from approximately 13 to 19 feet above mean sea level (MSL). The ground water table underlying the site is generally in the form of a trough-like depression, with the base of the trough plunging northwest a low gradient of less than 0.01 foot/foot. ' Releases of petroleum hydrocarbons occurred from the on-site USTs. Once released to the subsurface,the contaminants migrated through the sandy Layer 1 to a vertical depth of approximately ' 20 feet bsg, at which point the contaminants encountered the less permeable clayey silt of Layer 2. The contaminates began to migrate laterally as well as vertically in Layer 2; the direction of lateral migration was dominantly towards the northwest,in the preferred ground water flow direction. The ' lateral and vertical extent of soil and ground water contamination has been defined. Significant petroleum-hydrocarbon impact to soil in the vadose zone is present in borings B-2-20.25, B-4-20, MW-2-25, and MW-4-20, in the area of the former USTs, and in off-site well MW-9-20. TPH-g, TPH-d, and TPH-mo are present at maximum concentrations of 670 mg/kg (B2-20.25), ' 150 mg/kg(MW-9-20),and 120 mg/kg(B-2-20.25),respectively.Most ofthe contamination appears to reside at the top of the clay layer, at approximately 20 feet bsg. ' Advanced GeoEnvironmental,Inc. 1