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i.* <br /> 14 November 1995 + <br /> AGE-NC Project No, 95-0121 <br />' Page 15 of 20 , <br /> I <br /> I <br /> 714 FEASIBILITY <br /> 1 t <br />' Remediation of large ground water plumes require the installation of many injection and extraction ' <br /> `wells Air injection and extraction rates must be balanced to prevent the forced migration of, <br /> contaminants Extensive piping must be installed to injection and extraction wells As in vapor <br />' extraction, air sparging is not effective in the remediation of longer-chain hydrocarbons, which are <br /> less soluble in water' <br /> 715 DURATION <br />' Air sparging in highly Y Permeable aquifers generally results in rapid reduction of hydrocarbon <br /> , <br /> concentrations in the saturated zone Pilot tests have not been conducted at this site, but remediation <br />' times are generally comparable with sod vapor extraction times At the subject site, we estimate a <br /> remediation period of 12 to 24 months for shorter-chain hydrocarbons It is likely that IAS will have <br /> little effect upon longer-chain (diesel) hydrocarbons present in ground water at the site <br /> 7 2 GROUND WATER EXTRACTION <br />' 7 2 1 BASIC PRINCIPLES <br />' There are several different methods for treatment of extracted ground water, which are collectively t <br /> called "pump and treat" As the name indicates, all methods involve extraction and transfer of <br /> contaminated ground water from the aquifer to an-above-ground treatment or disposal/recycling <br />' method The extraction is performed using an automatic pump system to maintain capture <br /> characteristics in the aquifer and assure process requirements are maintained After treatment, the <br /> water is usually discharged into a storm dram or sanitary sewer A waste discharge permit is usually <br /> required for discharge <br /> 722 , TREATMENT METHODS <br /> The documented presence of hydrocarbons will require treatment for the recovered water Two of <br /> the most common methods of water treatment are air,stripping and carbon adsorption Air stripping <br /> involves removal of volatile organic compounds from ground water by promoting the transfer of <br /> I contaminants from the dissolved phase to the vapor phase -Carbon adsorption utilizes granular <br /> activated carbon to simply"filter" organic compounds out of ground water <br /> , <br /> i <br /> — , a <br />