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27 September 2007 AGE-NC Project No. 99-0682 -� Page 6 of 6 TPH-g was detected in the influent vapor samples at concentrations ranging from 4,600 µg/l to 11 ,000 µg/1. Toluene, ethylbenzene and total xylenes were detected in the vapor samples at concentrations as high as 170 µg/l, 190 µg/1 and 720 µg/1, respectively. MTBE and benzene were not detected at or above the laboratory detection limits in all the samples analyzed. • TPH-g and BTEX were detected in the effluent vapor sample collected at 1615 hr on 18 July 2007 at concentrations of 120 µg/1 TPH-g, 3 .5 µg/1 toluene, 6. 1 µg/1 ethylbenzene and n 11 µg/l xylenes. !-J j 4.0. RECOMMENDATIONS < J Based on overall high hydrocarbon concentrations in soil-vapor samples and the projected radius of influence (25 feet), SVE should effectively reduce adsorbed hydrocarbon concentrations in vadose zone soils through the use of a vacuum that creates a negative pressure gradient to cause movement I 1 of vapors toward the extraction wells. AGE concludes that soil vapor extraction could be used as a feasible 4terremediation option for treatment of hydrocarbon-impacted soil at the site as -I compared to soil excavation. At the direction of the EHD, ground water remediation feasibility requires additional evaluation. AGE recommends an ozone bench scale pilot study (laboratory) to determine the potential generation of water quality degrading by-products, prior to a field pilot study, Additionally, due to the fine grained sediments which comprised the upper 40 to 50 feet of the sediment section at the site, AGE Ll recommends performance of a duel-phase extraction (ground water/soil vapor) pilot study from the monitoring well MW4A and VW- I at the site. lAs required by the EHD letter, AGE will prepare a Feasbbility Study evaluating cost-effectiveness of at least two remediation alternatives for ground water at the site. =l 5.0. LIMITATIONS '---I Our professional services were performed using that degree of care and skill ordinarily exercised by environmental consultants practicing in this or similar localities. The findings were based upon analytical results provided by an independent laboratory. Evaluation of the geologic/hydrogeologic -I conditions at the site for the purpose of this investigation was made from a limited number of available data points (i.e. , soil vapor samples) and subsurface conditions may vary away from these data points. No other warranty, expressed or implied, is made as to the professional interpretations, opinions and recommendations contained in this report. L Advanced GeoEnvironmental, Inc.