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r , t r , ' 16 August 2001 ry AGE-NC Project No 97-0312 ' Page 14 of 20 ' 8 1 1 Treatment Methods The documented concentrations of' dissolved,hydrocarbons on the site are,not likely to trigger a requirement for treatment of the extracted water The Maximum Containment Levels (MCLS) for benzene(1 0 µg/l) and taste and odor threshold for TPH-g(5 µg11) and TPH-d (100µg/1) are locally exceeded in the areaofUST-1 and UST-5, but do not appear to have a significant vertical or areal ' extent Two ofthe most common methods ofwater treatment are air stripping and carbon adsorption Air stripping involves removal of volatile organic compounds from ground water by promoting the transfer o�contaminants from the dissolved phase to the vapor phase Carbon adsorption utilizes i granular activated carbon to simply"filter" organic compounds out of ground water ' t , A third, but less common method of above-ground treatment of water is bioremediation t iContaminated ground water is "treated" by adding hydrocarbon-degrading microbes or by augmenting natural hydrocarbon degradation activities with the introduction of nutrients i 812 Feasibility iAquifer testing has not been performed at the site However, based on analysis of soil samples collected during previous investigations,certain site-specific assumptions can be made regarding the i feasibility of ground water extraction at the site The subsurface profile of the site is relatively homogenous, consisting predominantly of fine-grained soil types such as silt, clayey silt, sandy silt and uldy T'y-lIedlly, boils of this IIaLiIIC rite not U 1n,,A t,-re i to bu higlhly_«.dlu i,vc� to Srounu VV aci I extraction Based on pumping tests at sites with similar soil types, pumping rates of approximately I- to 2-gallons per minute would be expected However, heavier chain hydrocarbons, like those found at the site,tend to be somewhat immpbile in water, adsorbing to fine-grain soil particles, and Imay require an extended pumping period to approach regulatory clean-up goals The poor cost/benefit potential for a"pump and treat" system at the site should also be considered The relatively expensive start-up costs associated with the system do not appear to be fiscally appropriate for a short period of effective remediation, especially if clean-up goals may not be met Based on the soil type,contaminant characteristics and low cost/benefit potential,a"pump and treat' remediation system is believed to have a limited feasibility 813 Duration , IBased on an extraction rate of approximately 1 to 2 gallons per minute, the majority of extractable hydrocarbon-impacted ground would be extracted within a I- to 2-year period Advanced GeoEnvlronmental,Inc i