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1 ' 20 January 2005 AGE-NC Project No 97-0343 ' Page 17 of 21 ' are maintained After treatment,the water can be discharged into a storm drain or sanitary sewer A waste discharge permit would be required for discharge ' 10 2 1 Treatment Methods ' The Maximum Containment Levels(MCLS) for benzene(1 0 µg/1)and taste and odor threshold for TPH-g(5 µg/l) and TPH-d(100ug/1) are locally exceeded in the area of MW-1 through MW-3,but do not appear to have a significant vertical or areal extent Two of the most common methods of ' water treatment are air stripping and carbon adsorption Air stripping involves removal of volatile organic compounds from ground waterby promoting the transferof contaminants from the dissolved phase to the vapor phase Carbon adsorption utilizes granular activated carbon to simply "filter" ' organic compounds out of ground water A third, but less common method of above-ground treatment of water is bioremediation ' Contaminated ground water is "treated" by adding hydrocarbon-degrading microbes or by augmenting natural hydrocarbon degradation activities with the introduction of nutrients 10 2 2 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 ' feasibility of ground water extraction at the site The subsurface profile of the site is relatively homogenous, consisting predominantly of alternating layers of fine grained(silts clays) and coarse grained(sand) layers Currently, first ground water resides within a coarse grained layer, this would allow extraction be most effective Based on pumping tests at sites with similar soil types,pumping rates of approximately 3- to 5-gallons per minute would be expected However, heavier chain hydrocarbons, like some found at the site, tend to be somewhat immobile in water, adsorbing to I fine-grain soil particles, and may require an extended pumping period to approach regulatory clean- up goals I 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 costibenefit potential,a"pump and treat" remediation system is believed to have a limited feasibility Advanced GeoEmronmental,Inc I