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04/27/95 THU 16:20 FAX 510 246 8082 S.V. WASTE SCI. 1@004 Extraction and injection well locations were determined for the site with the aid of WHPA, a modular, semi-analytical groundwater flow model developed by the United States Environmental Protection Agency. WHPA delineates time-related capture zones around pumping wells, or injection fronts around injection wells in homogeneous aquifers of infinite areal extent with steady and uniform ambient groundwater flow, Well interference effects are accounted for in the determination of capture zones and injection fronts. The model assumes two dimensional groundwater flow at steady state and equilibrium conditions. The placement of extraction and injection wells was designed to capture the contaminated groundwater plume, and hydraulically control the flow of the injected stream. After a variety of well placement strategies were evaluated, the design presented on Figure 2 was developed. The existing 4-inch monitoring well MVV-9 will be utilized as an extraction well, and two new 4-inch injection wells (MW-10 and MVV-11) will be drilled approximately 20 feet northeast of MW-8. AM-9 was selected as an extraction well because of its optimal location at the downgradient edge of the plume, which tabes advantage of the natural flow of the plume towards MW-9. As'shown on Figure 2, pumping at a rate of 2.5 gallons per minute (gpm) will result in capturing the plume in approximately 10 weeks. The capture zone was designed to completely capture the plume and provide an additional margin of safety beyond the estimated extent of the plume. The injection wells are placed at the upstream edge of the plume (Figure 3). This positioning allows the water injected at MW-10 and MW-11 to push the plume toward MW-9. Two injection wells were selected to minimize the possibility of ponding and spreading the injected water beyond the influence of the pumping well. The injection rates at MW-10 and AM-11 will be 1 gpm and 1.5 gpm, respectively. Using these extraction/injection rates and the locations of the extraction/injection wells, the entire plume will be impacted by the extraction/injection system, and hydraulic control will be achieved. The groundwater will be extracted from MVV-9 and injected at MW-10 axad MW-11 in a closed loop systems. This closed loop design will ensure that the plume is not spread by the injection front, and that the reinjected water will remain bydraulieally controlled by the influence of the extraction well. As the flow lines of 95R2 East Bay Municipal Utfity District 40429,G4ltpe:mitwp5 3 SoorktM SeiVise Conecr-Remedietkm