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' 15 June 1999 AGE-NC Protect No 98-0450 Page 26 of 27 Following agency concurrence, a Remedial Action Work Plan detailing proposed soil vapor extraction activities should be prepared Development of a Remedial Action Work Plan will be based on the final agency-approved corrective action alternative 6 2 RECOMMENDED GROUND WATER CORRECTION ACTION As with impacted soil, previous site investigation results indicate that on-site petroleum hydrocarbon-impacted ground water appears to extend south of the former UST area The specific ' petroleum hydrocarbons detected include BTEX, TPH-g, TPH-d and MTBE Hydrocarbons were previously detected in ground water samples collected from the saturated sand unit at approximately 50 feet bgs Several corrective action alternatives, including ex-situ and in-situ remedial methods, were identified and evaluated that may be applicable to address existing on-site ground water impacts Treatment options included in-situ air sparging, ground water extraction, in-situ ' bioremediation/bioenhancement, and natural attenuation (Table 7) Natural attenuation of impacted ground water can not be considered an acceptable remedial alternative until hydrocarbon-impacted soil is remediated and the tendency of detected fuel additives does not allow for passive remediation Ground water extraction and air stripping appears technically feasible for hydrocarbon mass reduction in the source area However, ground water extraction does not appear to be cost effective beyond the application of on-site source area control Additionally, assessment of ground water ' extraction would require additional costs associated with pumping tests and capture zone analysis In-situ bioremediation/bioenhancement is not a cost effective remedial option and is not likely to ' rapidly remediate the fuel additives identified at the site ' Based on subsurface conditions, in-situ air sparging technology appears to be a logistically feasible alternative at the site, due to the presence of a high porosity saturated zone This layer would allow for the transfer of infected air to the vadose zone potentially resulting in the vertical collection of ' contaminants AGE recommends air-sparging with soil vapor extraction Following agency concurrence, a Remedial Action Work Plan detailing proposed air-spaiging activities should be prepared Development of a Remedial Action Work Plan will be based on the final agency-approved corrective action alternative _ Y 7.0. LIMITATIONS Our professional services were performed using that degree of care and skill ordinarily exercised by Adianced GeoEn-sironmentai,Inc