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11 February 2003 AGE-NC Project No. 98-0520 ' Page 4 of 21 detected in any of the soil samples analyzed from boring MW-10. The BTEX compounds toluene, ethylbenzene and xylenes were detected in soil samples MW-6-35., MW-8-30 and MW-9-20 at maximum concentrations of 0.093 mg/kg, 0.83 mg/kg- and 0.7 mg/kg, • respectively, in the sample from MW-9-20. In addition, MTBE was detected at a concentration of 0.0075 mg/kg in soil sample MW-9-25. On 25 February 2002, one additional ground water monitoring well (MW-7) was installed on-site to a depth of 35 feet bsg. A total of 3 soil samples were submitted for analysis. • No analytes were detected at or above Iaboratory reporting limits in the soil samples analyzed. Analytical results of soil and grab ground water samples,and monitoring well ground water samples. , to date, are summarized in Tables 2 and 3. Cross-sections depicting the general lithology and the approximate distribution of contaminants in the soil beneath the site are illustrated on Figures 3A, ' 313,4A and 4B.'Maps depicting the approximate distribution ofTPH-g in soil and dissolved TPH-g are illustrated on Figures 5 and 6. The vertical extent of impacted soil and ground water has been defined. The lateral extent has been . mostly defined, except towards the north/northwest; however, based on soil analytical results at MW-3, MW-8 and MW-9 (e.g., apparent deeper.contamination at MW-8 versus MW-3 and the ' presence of MTBE in MW-9), AGE believes that there may be adjacent sites providing or contributing to the contamination detected in northernmost wells MW-8 and MW-9. 4.0. 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) of between 15.and 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 tense of green to olive gray fine sand was identified nearthe top of Layer 2. The third layer(Layer 3),at below 35 feet bsg,appears to bean olive green,to brown,unconsolidated coarse to pebbly sand;.this layer was defined on the basis of the two deepest soil borings(MW-6 and B-1)located at the former USTs''No. l and 2, respectively (Figure 2). Geologic cross sections are provided in Figures 3A ' and 4A. Advanced GeoEnviron mental,Inc.