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• 18 July 2002 <br /> AGE-NC Project No 96-0254 <br /> Page 11 of 17 <br /> Oxygen depletion in the subsurface is another characteristic of passive biodegradation The core of <br /> a contaminant plume typically exists under anaerobic conditions and only the margins are aerobic <br /> Therefore, even though anaerobic biodegradation is much slower than aerobic biodegradation, <br /> anaerobic processes may dominate the degradation of contaminants <br /> Natural attenuation is normally used where low concentrations of hydrocarbons are present, after <br /> completion of another method of remediation or in an area where no domestic or irrigation wells are <br /> threatened <br /> I The natural attenuation process is usually time consuming, it can take many years for the <br /> hydrocarbon plume to reach levels comparable to those of active remediation methods Costs for <br /> natural attenuation are definitely lower than the active remediation options, however, the periodic <br /> costs could accumulate overtime andpotentiallybeconsiderable depending onthe duration and type <br /> of monitoring requirements <br /> I Fate and Transport modeling may be used to demonstrate that hydrocarbons in soil do not pose a <br /> threat to ground water Where groundwater has been impacted modeling may be used to evaluate <br /> the possibility of hydrocarbons to impact nearby ground water receptors <br /> 6.0. GROUND WATER REMEDIATION ALTERNATIVES <br /> AGE believes that ground water extraction, In-situ $ioremediation/bioenhancement, and natural <br /> attenuation are appropriate remedial technologies or strategy to consider to address <br /> hydrocarbon-impacted ground water on the subject site <br /> 6 1 GROUND WATER EXTRACTION <br /> ' There are several different methods for treatment of extracted ground water,which are collectively <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 /> facility The extraction is performed using an automatic pump system to maintain capture <br /> characteristics in the aquifer and to assure that process volume requirements are maintained After <br /> treatment,the wateris usually discharged into a sanitary sewer,however,a sanitary sewer connection <br /> is not readily available at the site <br /> I� <br /> Advanced GeaEavimnmentnl,Inc <br /> I � <br />