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19 October 2012 AGE-NC Project No. 97-0312 Page 11 of 22 and MW-6. Moderate concentrations have been detected sporadically in these wells. The intermittent detections in the perimeter wells may be the result of seasonal shifts of the contamination plume. e,'I The fuel additive 1,2-DCA was the only chemical detected, at a concentration of 190 pg/I, in groundwater samples collected from CPT borings (CPT-1-66 feet). In addition to the on-site monitoring wells, two on-site domestic wells, referred to as the "large" and "small" wells, have been intermittently sampled since December 1997. Low concentrations of petroleum hydrocarbons (or other chemicals) have been sporadically detected in the small well but were below the method detection limits in confirmation samples collected shortly after detectable concentrations were reported by the laboratory. The historical extent of TPH-g and BTEX compound-impacted groundwater appears to be limited to the immediate area surrounding UST-1 and UST-5. Relative to the inferred source area near the former UST cluster and UST-1 and UST-5, the TPH-d plume appears to extend just north of UST-6; the western extent of the TPH-d plume appears to be located between the former UST location and UST-2; the eastern extent of the TPH-d plume appears to be east of UST-3 and the southern extent of the TPH-d plume appears to be located between UST-5 and UST-4. The distribution of dissolved petroleum hydrocarbons can be approximated by utilizing an equation for an ellipsoid; the dimensions of the ellipsoid were estimated to have a short radius of 48 feet, a long radius of 84 feet and an average thickness of 19.5 feet. Assuming an average saturated porosity of 20%, the calculated volume of hydrocarbon-impacted groundwater is approximately 241,300 gallons. Based on the average concentration of TPH-d and TPH-g in samples collected d�'•t,j from on site groundwater monitoring wells, the impacted groundwater plume contains approximately 47 gallons of TPH-d and 0.2 gallons of TPH-g. Volume/mass calculations � `•;' input data was presented in the AGE prepared, Quarterly Report-September 1999, dated 29 December 1999. In addition to the petroleum hydrocarbon and BTEX impact detected in samples collected from the six on-site monitoring wells, MTBE was detected in grab groundwater samples collected from three soil borings advanced in June 1999(B-14, B-15 and B-17). MTBE was detected in the grab samples from borings B-14, B-15 and B-17 at concentrations of 6.4 pg/I, 8.4 pg/I and 9,700 pg/I, respectively. However, the MTBE plume does not appear to be extensive and has not migrated to any of the groundwater monitoring wells. Tables which illustrate impacted groundwater and analytical results at the site are provided in Appendix C and Tables 2 and 3. r Advanced GeoEnvironmental,Inc. v •