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MAR 31 2016 <br /> Technical Proposed Location of the LCP Mid-Plume Extraction Well <br /> �,g'p�pryIp',��yE gam-�I Lodi,California <br /> 2338 <br /> Memorandu HFAITaan;:rJART0V-" - Page <br /> Pa e4oage4of4 <br /> 4 <br /> Results of this simulation are shown on Figures 4 and 5 for 3 separate time periods — <br /> current(2014), 2020, and 2025. The results indicate the following— <br /> • Extraction well EW-7 would adequately contain the width of the PCE plume, and <br /> further decrease the high concentration area (>500 Rg/) of the PCE plume; <br /> • As observed in 2025, EW-7 would mitigate the migration of the high <br /> concentration areas of the PCE plume (>100 µg/U, such that by 2025 PCE <br /> concentrations >500 µg/I would no longer migrate downgradient beyond <br /> W. Tokay Street. <br /> 3. Simulation 3 — EW-7 was simulated on a property located on School Street between <br /> Vine Street and Spruce Street. This location was selected as it represented the leading <br /> edge of 100 gg/l PCE plume in the intermediate zone. <br /> Results of this simulation are shown on Figures 6 and 7 for 3 separate time periods — <br /> current(2014), 2020, and 2025. The results indicate the following— <br /> • Extraction well EW-7 would adequately contain the width of the PCE plume for <br /> concentrations >100µg/I; <br /> • As observed in 2025, EW-7 would mitigate the migration of the high <br /> concentration areas of the PCE plume (>100 µg/1), such that by 2025 PCE <br /> concentrations >100µg/I would no longer migrate down-gradient beyond EW-7; <br /> • Remnants of the higher concentration areas (>500 µg/) of the PCE plume would <br /> continue to migrate towards well EW-7 and would slowly dissipate to lower <br /> concentrations over time or be remediated by well EW-7. <br /> The modeling results indicate that a single extraction well located at any of the proposed three <br /> locations adequately captures and mitigates the migration of that portion of the LCP PCE plume <br /> that is prevalent upgradient of its location. However, the remnants of the PCE plume that are <br /> currently down-gradient of the proposed EW-7 locations will continue to migrate down-gradient <br /> and possibly downward into deeper zones in a south-south easterly direction towards City well <br /> 6R and the southern City well field. The optimal location of the proposed extraction well EW-7 <br /> is discussed below. <br /> Recommended Extraction Well Location <br /> Based on the analysis of the currently-available data and the groundwater flow-and-transport <br /> model, we are recommending Simulation 2 with a single extraction well (EW-7) location near <br /> the intersection of Church Street and West Tokay Street. The well location can be either on the <br /> Needham Elementary School property, as shown in Figures 4 and 5 that depict the results of <br /> Simulation 2, or at a location south east of the simulated location (on Church Street or between <br /> Church or School Streets). The recommended extraction rate is 50 gpm and the recommended <br /> screened interval is between 75 and 125 ft-bgs. Final depths and screen intervals would be <br /> based on location-specific data from the soil log collected during the installation of the well. <br /> LAAI&AN THIEADWELL:.ldO1:L8 <br />