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s - _ - r F Y 1 r 16 August 2001 AGE-NC Project No 97-0312 ' Page 13 of 20 ' 7 4 NO FURTHER ACTION A final potential alternative,,"no further action", may be appropriate for the site A "no further ' action" recommendation would be made based on the following • The majority of contamination found at the site is composed of longer chain hydrocarbons ' which generally migrate at a very slow rate • The predominant soil types found at the site Include silt and clay which tend to prevent, or ' at least greatly retard,vertical and horizontal migration of contaminants thereby limiting the threat of a significant impact to ground water •, The most intensely impacted soil is confined to the upper twenty-five feet of soil ' Historically, ground water has not been higher than 45 feet bsg and has been as great as 94 5 feet bsg, creating a 20-foot or more buffer zone between high concentrations of the ' relatively immobile contaminants and ground water ` Minor costs would be associated with the "no further action" alternative, for instance the monitoring wells on site may need to be abandoned I• ' 8.0. GROUND WATER REMEDIATION ALTERNATIVES Three methods believed to be most arneudbie Lo rernediation of hydrocarbon-impacteu ground eater '= on the site have been evaluated The methods include ground water extraction (pump and treat), bioremediation and natural attenuation In addition, a "no further action" scenario has been evaluated , 8 1 GROUND WATER EXTRACTION ' There are several different methods for treatment of extracted8T ound water,which are collectively called "pump and treat" All methods of pump and treat involve extraction and transfer of ' contaminated ground water from the aquifer to an above-ground treatment or disposal/recycling facility The extraction is performed using an automatic pump system to establish and maintain ' contaminant capture characteristics in the aquifer and to assure that process volume requirements 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 1 , 1 Advanced GeoEnvironmental,Inc