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Selected Interim Remedial Action . <br /> The primary goal of the recommended remedial action is to <br /> remediate the TCE and PCE plume . To accomplish this , DDTC has <br /> selected a phased approach . Phase one consists of an Interim <br /> Remedial <br /> Measure ( IRM) . The technology selected for the IRM is : <br /> -- Extraction- of site groundwater from the shallow aquifer <br /> (the upper Tulare Formation) using extraction wells . <br /> -- Treatment of extracted waters using Ambient Temperature Air <br /> Stripping . <br /> -- Discharge/recharge of treated waters by injection wells to <br /> the upper Tulare Formation Aquifer . <br /> Successive phases of the interim remedial action will be based <br /> on data developed through the operation of the previous phases . <br /> Upon compilation and review of this data the depot <br /> will decide how to accomplish the final cleanup of the plume and <br /> the technology to be used ( from those selected) to accomplish <br /> it . <br /> The primary objective of the groundwater extraction action at <br /> DDTC is to effect optimum capture of plume contaminants leading <br /> to a reduction of groundwater contaminant concentrato below the <br /> designed cleanup levels (5 ug/L for TCE and PCE) . The selected <br /> option , extraction wells, has found universal use for <br /> groundwater remediation , and when properly designed and <br /> operated , prove to be long- lived systems . <br /> Air stripping is a mass transfer process in which voltile <br /> contaminants are transferred to the gas phase by passing air <br /> through the mixture . In general , volatile organic <br /> concentrations less than I percent in groundwater are treatable <br /> by air stripping . This process is less hazardous , more <br /> reliable , and -more cost effective than either carbon adsorption <br /> or high temperature steam stripping . <br /> Treated groundwater will be discharged back into uncontami - <br /> nated portions of the upper Tulare Formation Aquifer through <br /> injection wells or spreading basins . Injection wells are the <br /> inverse of extraction wells . Spreading basins are ponds that <br /> allow retained waters to infiltrate vertically through the pond <br /> bottom into the groundwater below. The existing stormwater <br /> retention basin at the depot manage retained craters in part by <br /> shallow recharge of this type . This option is considered to be <br /> both technically and economically feasible and i ` is the best <br /> choice from both the regulatory and environmental viewpoint . <br />