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Site Background Information: Cherokee Truck Stop AGE NC Project No. 97-0312 Page 8 of 11 generally ranged between moderate(approximately 300 psi)for stiff,fine-grained soils and low for sands and gravelly sand. Hydrogeologic units were depicted in cross sectional views G-G', B-B',D-D' and E-E'. LABORATORY RESULTS OF GRAB GROUND WATER SAMPLES A total of four grab ground water samples were collected and submitted for laboratory analysis for the constituents listed. The fuel additive 1,2-DCA was the only contaminant of concern (COC) detected, at a concentration of 190 micrograms per liter(µg/1), in sample CPT-1-66'. 1,2-DCA-IMPACTED GROUND WATER MASS-VOLUME CALCULATION Based on analytical results for ground water samples collected at the site to date,the vertical extent and lateral extent of 1,2-DCA-impacted ground water are defined. From cross-section and plan views, the 1,2-DCA-impacted ground water plume can be modeled as a half oblate. Using this model,AGE calculated that an estimated 0.141 pounds(lbs),or 0.013 gallons,of 1,2-DCA remains in the groundwater. The assumptions for the calculation of the 1,2-DCA mass is were presented. CONCEPTUAL SITE MODEL Based on the data collected to date from CPT and soil borings and monitoring well installations, AGE has developed a conceptual site model (CSM) for the release, migration, and distribution of the contaminants in the subsurface. Generally, the stratigraphy from surface grade to approximately 60 feet bsg is composed of fine- grained material consisting primarily of silt and clayey silt,with laterally discontinuous intervals of clay and sandy silt. A layer of coarser-grained material (sandy silt, silty sand, and poorly graded sand)is encountered throughout most of the site at depths between 20 feet and 30 feet bsg.At depths ranging from 50 feet to 60 feet bsg, a layer of clay was identified in most soil borings. Below, coarser-grained material(sandy silt,silty sand,and sand)with lesser intervals of silt and clayey silt is encountered throughout most of the site to the total depths of the borings(up to 109 feet bsg);this deep,coarser-grained zone is not encountered in soil borings MW-8 and B 17,located on the eastern edge of the site, below approximately 65 feet bsg. Based on the sediment stratigraphy, the preliminary subsurface hydrogeologic model consists ofthree informal zones,a vadose(unsaturated) zone and two hydrogeologic units; the vadose zone and Hydrogeologic Unit 1 are composed dominantly of fine-grained, generally clays and silts, whereas Hydrogeologic Unit 2 consisted of sands and gravel along with stiff, fine-grained soil. Soil boring locations are shown on Figure 2 and Advanced GeoEnvironmental,Inc.