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31 October 2011 AGE-NC Project No. 99-0682 Page 6 of 9 3.3.1 Ground Water Extraction There are several different methods for treatment of extracted ground water, which are collectively called `pump and treat'. As the name indicates, all methods involve extraction and transfer of contaminated ground water from the aquifer to an above-ground treatment or disposal/recycling facility. The extraction is performed utilizing an automatic pump system to maintain capture characteristics in the aquifer and to assure that process volume requirements are maintained. After treatment, the water is usually discharged into a sanitary sewer or separate storm sewers. Ground water extraction does not appear to be the most feasible or cost-effective option of treatment for the site based on the following: • Based on the estimated lateral limits of the plume, additional dedicated ground water extraction wells would be needed in order to effectively capture the ground water plume. • Ground water extraction alone does not effectively treat adsorbed hydrocarbons, which are known to be present at the site. • Ground water extraction would require several years of remedial operation to achieve water quality objectives. 3.3.2. Dual Phase Extraction Dual phase extraction (DPE) is a technology that simultaneously recovers adsorbed hydrocarbons from the vadose zone and the saturated zone subsurface by lowering the ground water level to expose soil strata to high vacuum extraction. Dual phase extraction is not considered to be favorable option for remediation of the dissolved and adsorbed phase plumes at the site based on the following: • Well installation, infrastructure installation and system purchase would be costly for a remedial operation. Further, it is highly unlikely that ground water levels could be depressed to expose the adsorbed soil impact in the intermediate zone (depths between 50 to 70 feet bsg). • Several years of costly remedial operation would be required to achieve water quality objectives. • Treatment cost for extracted vapors, accompanied with additional costs for disposal Advanced CeoEnvironmental,Inc.