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Corrective Action Plan 42 1 Groundwater Extraction Although aquifer pump testing has not been conducted at this site, the rate of water level recovery in monitoring wells, observed during monitoring well purging and sampling, has provided considerable understanding as to the water permeability of the shallow aquifer soil at the site Based on extensive experience at saes with similar soil characteristics and well recovery data, sustained recovery rates of 1 to 3 gallons of groundwater from each of the four groundwater extraction wells will effectively lower the groundwater table covering the entire impacted groundwater plume within the radius of influence of at least one extraction well OST is confident that an effective groundwater extraction system is feasible and that the system can be designed and implemented without further aquifer testing 4 2.2 Groundwater Extraction With Air Sparging Air sparging involves injecting air into the groundwater several feet below the water table to ienhance volatization of hydrocarbons and to maintain a fairly high level of dissolved oxygen This enhances the processes of naturally occurring bio-degradation Although conditions at this ' site are not ideal for effective air sparging,the process would probably be beneficial It is DST's opinion,however, that given the substantial uncertainties involving the air sparging process, the cost-effectiveness of its implementation is questionable OST believes that this process is not necessary or economically justifiable for effective groundwater(and soil) remediation 4 2 3 Passive Bio-Remediation for Groundwater (No Further Action) Because the groundwater at the site contains petroleum 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 - � 0 PROPOSED REMEDIATION TECHNOLOGY Based upon the facts and observations cited above, the co-extraction of groundwater and soil vapor is clearly the most cost-effective remediation solution at this site The relative volatile and bio-degradable constituents of gasoline are particularly amenable to the processes of SVE Although a soil vapor treatablily test has not been performed at the site, the soli logs indicate the size characteristics of the soil are well within the range for effective SVE OST has extensive experience implementing SVE at more than a dozen sites with soils having size characteristics similar or finer than the soil encountered at this site For SVE to be effective at this site however, the water table needs to be depressed to expose the 4� � P P most severely impacted soil horizon which presently lies, to a large extent, beneath the water OST 1 701-1 2 cap Page 9