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INTERIM PROBLEM ASSESSMENT' REPORT/INTE RMEDIAL ACTION PLAN -15- Former Beacon Station No. 494, 2185 East Fremont Street Stockton, CA--AMV Project No. 19005.07 ' 7 2.1 round Wa er Pu m in ' This remediation alternative involves recovery of ground water by pumping from one or more extraction wells. Possibilities for disposal of the ground water include discharge to the storm ' sewer or sanitary sewer. Implementation of ground water pumping constitutes a method for both controlling the migration of and removing petroleum hydrocarbons from ground water beneath the site. The testing on monitoring well MW-3 described in Section 6.1 indicates that this; well will yield approximately 0.5 gpm on a long-term, continuous basis. The short-term theoretical extent of the capture zone ' resulting from this pumping was about 20 feet in the downgradient direction. Sustained, continuous pumping could be expected to result in a larger capture zone. After implementation of the recommendations in Section 8.0 of this report (which include ground water pumping from ' monitoring well MW-3), the actual capture zone developed by pumping should be compared with the known distribution of petroleum constituents in ground water. The evaluation may indicate that utilization of an additional existing well or wells (or installation of an additional well or wells) is necessary to achieve a ground water capture zone encompassing the area of ground water known to contain dissolved petroleum constituents. ' One potential drawback of ground water pumping is the possibility for migration of ground water impacted by off-site sources onto the Ultramar site. Operation of a pumping system would require a ground water monitoring program that would detect migration of an off-site plume ' beneath the Ultramar property. In anticipation that ground water pumping might be an appropriate ground water remediation ' method at this site, Ultramar installed underground piping to monitoring well MW-3 at the same time as installation of vapor extraction piping. In addition, Ultramar purchased equipment for the pumping test that can be used for long-term pumping at the site. ' 7.2.2 In Situ Bioremediation ' In situ bioremediation involves stimulating the indigenous microflora or bacteria to enhance the degradation of petroleum hydrocarbons present in ground water. Introduction of oxygen and nutrients into the water table through infiltration wells provides the stimulus. Recirculation of ' the ground water by pumping, along with reinjection, is necessary to control the migration of the dissolved petroleum hydrocarbon plume and to distribute the nutrients and oxygen. ' rptoos.w