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QMMIM PROBLEM ASSESSMENT REPORTMgTERIM RMCMIAL ACTION PLAN -17- Former Beacon Station No. 494, 2185 East Fremont Street Stockton, CA—AMV Project No. 19005.07 Subsurface conditions (such as low permeability) which may limit the potential effectiveness of vapor extraction do not necessarily limit the effectiveness of air sparging. Air can possibly be ' delivered into the subsurface at sufficient pressure to force flow through the low permeability soil units. At present, sparging would not be an advisable alternative because of the uncertainty with regard to gradient direction and the considerable thickness of the vadose zone at this site. 8.0 RECOMMENDATIONS FOR INTERIM ' REMFDUTTON AND ADDITIONAL ASSESSMENT ' Based on data compiled for this site and the analysis of remedial alternatives discussed in Section 7.0, AMV proposes the use of vapor extraction to accomplish remediation of soil at the ' site. For interim remediation of ground water, AMV proposes pumping of monitoring well MW-3 and evaluation of the extent of the resultant capture zone after the system has operated for 60 to 90 days. To delineate the distribution of petroleum constituents in ground water, AMV proposes the installation of at least two additional monitoring wells at off-site locations, once the direction of ground water flow has been verified. ' 8.1 Vapor Extraction System The proposed vapor extraction system will consist of a vacuum blower connected to each ' monitoring well, each vapor extraction well, and each probe. A valved manifold will allow the control of flow from each extraction point. This arrangement allows the system to simultaneously pull soil vapors from virtually all areas of the site, or alternatively, from specific ' extraction points in the vicinity of soil containing the highest TPHg concentrations. The recovered vapors will be treated using an aboveground emissions control system to remove hydrocarbons from the extracted vapor stream before discharge to atmosphere. The vapor flow capacity of the combination thermal and catalytic oxidation unit recently moved to the site by Ultramar is 500 scfm, which is sufficient capacity for extraction from all points simultaneously. ' AMV expects that long-term operation of the vapor extraction system will result in effective remediation of petroleum impacted soils underlying the site. 8.2 Ground Water Pumping As an interim ground water remediation measure, AMV proposes the pumping of monitoring well MW-3 to recover and inhibit the migration of ground water containing petroleum constituents. Although pumping of monitoring well MW-3 should begin to mitigate the most impacted ground water underlying the site, a short-term aquifer test indicated that'pumping of