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i Corrects e Action Plan Because the most severely impacted soil lies beneath the present Aater table, escavatlon and ex- situ treatment of hydrocarbon soil is considered technically infeasible and is, therefore, not subjected to economic evaluation 1 4 1.2 Soil Vapor Extraction The soil vapor extraction process involves drawing air through the soil under vacuum whereby volatile hydrocarbons, such as the gasoline constituents impacting the soil at this site, are removed by the combined process of evaporation and enhanced biodegradation In this process, air is introduced into the impacted soil horizon through static air injection wells and then drawn through the impacted zones The soil vapor is removed to the surface by means of extraction wells, connecting piping, and a high volume/high vacuum positive displacement air pump Gasoline, due to its high volatility, is particularly amenable to soil vapor extraction To minimize the impact to the atmosphere,the petroleum hydrocarbons in the extracted soil vapor must be removed prior to its emission The process options for treating extracted soil vapor include combustion through either thermal or catalytic oxidizers (TOX or COX) and adsorption through granular activated carbon(GAC) Because the estimated volume of impacted soil at this site and the total amount of hydrocarbons in the soil are relatively small compared to other fuel leak sites, GAC is clearly the most cost-effective method for eliminating hydrocarbons from the extracted soil vapor A cost comparison summary for GAC and TOX/COX are included in the Appendix E 4 13 Passive Bio-Remediation for Soil (No Further Action) Because the groundwater at the site is impacted with constituents exceeding the drinking water maximum contaminant levels by up to several thousand times and because the most severely impacted soil is beneath the groundwater table, passive bio-remediation is not considered an acceptable alternative and is therefore given no further consideration 4.2 Feasible Remediation Alternatives for Groundwater jThe primary objectives of the proposed groundwater remediation system is to control migration of the impacted groundwater away from its source and to recover groundwater which has already been impacted by petroleum hydrocarbons At this site, an equally important objective is to lower the groundwater elevation levels thereby exposing petroleum-hydrocarbon-impacted soil The only feasible alternative which will accomplish these objectives is the extraction of groundwater by pumping The only other alternative is no further action, relying on intrinsic bio-degradation processes to reduce hydrocarbon concentrations to acceptable levels over time Air sparging might be beneficial in accelerating the reduction of hydrocarbon concentrations by enhancing both volatization and bio-degradation processes however, used alone, this method does nothing to control migration from the source and in fact accelerates migration Air sparging therefore, will be discussed only as a supplementary method with groundwater extraction OST 701-1-2 cap Page 8