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1 Site Background Information: Bob's Muffler Page 4 of 5 1 • No analytes were detected at or above laboratory reporting limits in the soil samples ' analyzed. Four soil samples, one from the upper sand layer, two from the middle silt and clay layer, and one ' from the lower sand layer were collected from soil boring B-5 and analyzed for geotechnical properties. The samples B5-10 and B5-40 were described as brown sand and brown sand with silt and trace gravel,with porosities between 34.5%and 30.6%, low organic content(0.4 to 0.6%),and ' specific gravity values between 2.67 and 2.72.The samples B5-20 and B5-30 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 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), occurring 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 former USTs No. I and 2,and down gradient off-site to the northwest. Additional figures and tables can be found in the AGE-prepared Corrective Action Plan (CAP), dated 11 February ' 2003. Since the initiation of ground water monitoring in December 1999, ground water elevations have ' ranged from approximately 13 feet 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 under a low gradient of less than 0.01 foot/foot. ' Releases ofY etroleum hydrocarbons occurred from the on-site USTs. Once released to the P 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 contaminants began to migrate laterally as well as vertically in Layer 2; the direction of lateral migration was primarily toward the northwest, in the preferred ground water flow direction. The lateral and vertical extent of soil and ground water contamination has been defined. Advanced GeoF_nvironmental,Inc. I