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Site Background Information: Bob's Muffler Page 4 of 5 On 05 January2004 two eo robe soil borings B-5 and B-6 were advanced off-site to a depth of g p g ( ) p ' 47 feet bsg. A total of nine soil samples and four grab ground water samples were submitted for analysis. ' No analytes were detected at or above laboratory reporting limits in the soil samples analyzed. tFour 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 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. ' Advanced GeoEnvironmental,Inc. 1