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portion of the plume, and at the larger Rol would almost reach VM-3,which is slightly impacted. The two remedial wells would overlap in the central part of the site near VT-1. It must also be remembered that if any of the existing monitor wells are used for groundwater extraction,radius of influence circles could also be drawn around them and the affected treatment area would be larger. A pumping test in either well would test the estimated Rol and would also establish the _ maximum sustainable pumping rate. Both of these parameters are needed in order to correctly evaluate the cost effectiveness of the pump and treat method. In addition, pumping from both wells concurrently and collecting samples from the influent stream would provide an accurate measure of the combined hydrocarbon concentrations that would be produced,making it possible to better estimate the laboratory costs,treatment requirements,and disposal costs. Because it takes time for concentrations and pumping rates to stabilize,we estimate pumping approximately 5,000 gallons during the test. A large storage tank would be used to hold the extracted water,which would be hauled to an approved disposal facility when the tank reaches capacity. Testing the in-well air stripping method would require the temporary installation of the downhole stripper equipment and connection to a vapor-phase canister of GAC,but would not require groundwater sampling,extraction, storage,or disposal. Determining the Rol in this method would be more difficult,because the only measurable affect of the method in surrounding wells would be a reduction in hydrocarbon concentrations, and that might take several weeks or months to occur. Hence,only VM-9 would be tested, because it would be located closer to the impacted wells and its influence would be felt sooner. However, it is impossible to estimate how long this test would last,and this uncertainty is a significant drawback. COST COMPARISON , Generalized cost estimates for the two methods were developed in consultation with numerous vendors, including well drillers, equipment suppliers,the City of Stockton,In- Strat,Inc. (water disposal facility), and Accelerated Remediation Technologies,Inc. (the vendor of in-well air stripping equipment). Those estimates include both capital expenditures and operation&maintenance costs(O&M). The summary cost comparison in Table 2 is based on those estimates. The initial cost of the in-well stripping method is greater than the groundwater extraction method because the equipment is more high-tech and the pilot test would likely take more time. This higher initialcost is offset by the lower operating costs resulting from less frequent sampling and no water disposal fees,but if cleanup is achieved within one year, the total cost of the pump and treat method would probably be about the same as the cost of the in-well stripping method. Operation and maintenance costs in the second year of pump and treat operation would overtake the costs of in-well stripping,and result in a somewhat higher total remediation cost. 5