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Corrective Action Plan <br /> 4.2.1 Groundwater Extraction <br /> ' Although aquifer pump testing has not been conducted at this site,the rate of water level recovery <br /> in monitoring wells, observed during monitoring well purging and sampling, has provided <br /> considerable understanding as to the water permeability of the shallow aquifer soil at the site. <br /> ' Based on extensive experience at sites with similar soil characteristics and well recovery data, 2 <br /> sustained recovery rates of I to 3 gallons of groundwater from each of the four groundwater a <br /> ' extraction wells will effectively lower the groundwater table, covering the entire impacted <br /> groundwater plume within the radius of influence of at least one extraction well. OST is <br /> confident that an effective groundwater extraction system is feasible and that the system can be <br /> designed and implemented without further aquifer testing. <br /> 4.2.2 Groundwater Extraction With Air Sparging <br /> Air sparging involves injecting air into the groundwater several feet below the water table to <br /> enhance volatization of hydrocarbons and to maintain a fairly high level of dissolved oxygen. <br /> This enhances the processes of naturally occurring bio-degradation. Although conditions at this <br /> site are not ideal for effective air sparging,the process would probably be beneficial. It is OST's <br /> opinion,however, that given the substantial uncertainties involving the air sparging process, the <br /> ' cost-effectiveness of its implementation is questionable. OST believes that this process is not <br /> necessary or economically justifiable for effective groundwater (and soil) remediation. <br /> 4.2.3 Passive Bio-Remediation for Groundwater (No Further Action) <br /> ' Because the groundwater at the site contains petroleum 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 /> ' 5.0 PROPOSED REMEDIATION TECHNOLOGY <br /> Based upon the facts and observations cited above, the co-extraction of groundwater and soil <br /> ' vapor is clearly the most cost-effective remediation solution at this site. <br /> The relative volatile and bio-degradable constituents of gasoline are particularly amenable to the <br /> ' processes of SVE. Although a soil vapor treatablily test has not been performed at the site,the <br /> soil logs indicate the size characteristics of the soil are well within the range for effective SVE. <br /> ' OST has extensive experience implementing SVE at more than a dozen sites with soils having <br /> size characteristics similar or finer than the soil encountered at this site. <br /> ' For SVE to be effective at this site, however, the water table needs to be depressed to expose the <br /> most severely impacted soil horizon which presently Iies, to a large extent, beneath the water <br /> i <br /> ' OST <br /> 701-1-2.cap <br /> Page 9 <br />