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1 <br /> Corrective Action Plan <br /> Because the most severely impacted soil lies beneath the present water table, excavation and ex- <br /> situ treatment of hydrocarbon soil is considered technically infeasible and is, therefore, not <br /> subjected to economic evaluation. <br /> 4.1.2 Soil Vapor Extraction <br /> The soil vapor extraction process involves drawing air through the soil under vacuum whereby <br /> ' volatile hydrocarbons, such as the gasoline constituents impacting the soil at this site, are <br /> removed by the combined process of evaporation and enhanced biodegradation. In this process, <br /> air is introduced into the impacted soil horizon through static air injection wells and then drawn <br /> ' through the impacted zones. The soil vapor is removed to the surface by means of extraction <br /> wells, connecting piping, and a high volume/high vacuum positive displacement air pump. <br /> Gasoline, due to its high volatility, is particularly amenable to soil vapor extraction. <br /> To minimize the impact to the atmosphere,the petroleum hydrocarbons in the extracted soil vapor <br /> must be removed prior to its emission. The process options for treating extracted soil vapor <br /> ' include combustion through either thermal or catalytic oxidizers (TOX or COX) and adsorption <br /> through granular activated carbon(GAC)_ Because the estimated volume of impacted soil at this <br /> ' site and the total amount of hydrocarbons in the soil are relatively small compared to other fuel <br /> leak sites, GAC is clearly the most cost-effective method for eliminating hydrocarbons from the <br /> extracted soil vapor. A cost comparison summary for GAC and TOX/COX are included in the <br /> Appendix E. <br /> 4.1.3 Passive Bio-Remediation for Soil (No Further Action) <br /> ' Because the groundwater at the site is impacted with constituents exceeding the drinking water <br /> maximum contaminant levels by up to several thousand times and because the most severely <br /> ' impacted soil is beneath the groundwater table, passive bio-remediation is not considered an <br /> acceptable alternative and is therefore given no further consideration. <br /> 4.2 Feasible Remediation Alternatives for Groundwater <br /> The primary objectives of the proposed groundwater remediation system is to control migration <br /> of the impacted groundwater away from its source and to recover groundwater which has already <br /> been impacted by petroleum hydrocarbons. At this site, an equally important objective is to lower <br /> the groundwater elevation levels thereby exposing petroleum-hydrocarbon-impacted soil. The <br /> ' only feasible alternative which will accomplish these objectives is the extraction of groundwater <br /> by pumping. The only other alternative is no further action, relying on intrinsic bio-degradation <br /> ' processes to reduce hydrocarbon concentrations to acceptable levels over time. Air sparging <br /> might be beneficial in accelerating the reduction of hydrocarbon concentrations by enhancing <br /> both volatization and bio-degradation processes; however, used alone, this method does nothing <br /> ' to control migration from the source and, in fact, accelerates migration. Air sparging, therefore, <br /> will be discussed only as a supplementary method with groundwater extraction. <br /> .1 <br /> ' OST <br /> 701-1-2.cap Page 8 <br /> 1 <br />