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1 ' 16 December 2002 AGE-NC Project No 97-0300 ' Page 7 of 8 ' 8.0• DISCUSSION AND CONCLUSIONS Based on data collected during site assessment activities, AGE concludes ' A mass-volume calculation was made ofthe remaining petroleum hydrocarbon impacted soil at the site, a short diameter of 36 feet, a long diameter of 63 feet and a height of 35 feet were ' used to estimate a coned elliptical volume of approximate 770 cubic yards of impacted soil (Figures 13, 14 and 15) An average concentration of 21 50 mg/kg was used to calculate the total volume of remaining gasoline and 21 90 mg/kg used to calculate the volume of ' remaining diesel in impacted-soil, the mass-volume calculations indicate that an estimated 6 69 gallons of adsorbed gasoline and 6 08 gallons of adsorbed diesel remain in soil • The ground water flow direction and gradient at the site has been relatively constant dunng ' the duration of this investigation In June and September 2000, ground water flowed southeast under gradients of 0 01 ft/ft and 0 002 ft/ft, in December 2000, ground water flowed south under a gradient of 0 001 ft/ft, and in March 2001, ground water flowed ' southwest under a gradient of 0 003 ft/f1 4�8103 • The concentration of TPH-d in ground water samples from well MW-1 decreased from ' 68 µg/1 to non detectable levels between the June 44Wand December 2000 ground water monitoring events MTBE was detected on one occasion at a concentration of 2 µg11, during the initial ground water momtoring event at MW-1 No other petroleum or gasoline ' constituents were detected from wells MW-1,MW-2 or MW-3 The dissolved hydrocarbon plume appears to be well-defined and stable Tables 4 and 5 summarize analytical results for all ground water samples collected at the site ' - Based on depth to ground water measurements observed at the site from June 2000 to March 2001, any remaining residual TPH-impacted soil at the site is at least 15 feet above the ` ' saturated zone • A sensitive receptor survey identified one municipal water well (Station No 77) located 1 approximately 300 feet south of the site on the east side of West Lane and a second municipal water well identified approximately 1,000-feet southeast of the site on the west side of El Pinal Drive I • AGE concludes that petroleum hydrocarbons remaining beneath the site appear to pose minimal risk to human health and beneficial use of ground water down-gradient from the subject site I • Advanced GeoEnvironmental,Inc I