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'. 29 September 2005 AGE-NC Project No 95-0167 ' Page 5 of 8 a distinct hydrologic unit with respect to the flow of groundwater(Maxey, 1964) A`flow unit' may ' be defined as a hydrogeologic unit and is characterized by significantly greater hydraulic conductivity values than overlying and underlying units, a flow unit is capable of serving as a preferred migration route, and could potentially allow migration of large contaminant masses over ' great distances ' Based on a previous AGE-conducted CPT investigation (Cone Penetrometer Testing Report - November 2001, 2003), AGE had presented a preliminary subsurface hydrogeologic model of the site consisting of fifteen informal zones, a vadose(unsaturated)zone and fourteen hydrologic units, ' developed primarily from one CPT lithologic log (CPT-3) Incorporating the CPT-generated lithologic data from the six additional CPT borings of December,2004 - January 2005, AGE has refined the site hydrogeologic model, which now consists of seven informal zones, a vadose ' (unsaturated) zone and six hydrogeologic units (Figures 3 through 6), the fifteen previous hydrogeologic units are incorporated as subunits within the present hydrogeologic units (Table 1) ' The seven hydrogeologic units identified are as follows (depths are approximate and can vary by several feet across the site) ' . Vadose Zone - Extending from surface grade to approximately 38 feet bsg, the vadose zone is composed primarily of clay, silt, silty clay, clayey silt, sandy silt, and silty sand This zone is characterized by low to moderate pore pressures ' HUL HU3 and HU5 - These_zones are composed primarilyof clay, silt sit hcla and clayey silt with generally minor, discontinuous lenses of silty sand, sandy silt, and sand These units are ' characterized by moderate or fluctuating (between low to moderate with depth) pore pressures ' HU2,HU4 and HU6-These zones consist primarily of sand, silty sand,sandy silt,gravelly sand and cemented sands, with lesser occurrences of clay, silty clay or clayey silt intervals Pore pressures within these units are generally low These units may be considered flow units ' The model presented is interpretational and will be modified as additional data is collected 3 3 ANALYTICAL RESULTS OF GRAB GROUND WATER SAMPLES ' A total of twenty-nine grab ground water samples were collected and analyzed for the petroleum hydrocarbon constituents listed in Section 2 2 , the analytical results are listed according to the hydrogeologic unit in which the samples were collected (Table 2) •' t ' Advanced CcoEnvironmental,Inc 1