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MAR 31 201�roposed Location of the LCP Mid-Plume Extraction Well Technical ENVlRONN�:z� ) Lodi,California ,,1 ` �'�' Memorandum HEALTHPg730392338�py-= � `� Page 3of4 obtained from the quarterly monitoring reports for the LCP were used to develop the current extent of the PCE plume. The extraction rates of the City supply wells were based on the optimized rates developed for the City supply wells following the startup of the surface water treatment plant (SWTP). City wells 2, 8, and 12 were presumed to be off-line for these simulations. The PCE plume extents were input to the model as the initial concentrations and the model was simulated for the years 2014 to 2025. Initially, only a single extraction well designated EW-7 was simulated to determine if it would adequately contain the migration of the LCP PCE plume. Three separate locations for the proposed extraction well, as shown on Figure 1, were selected based on the PCE concentrations and land availability for the construction of the well. Each of these locations was simulated to determine the optimal location. The extraction well was assumed to be screened between 75 to 125 ft-bgs and pumping at a rate of 50 gallons per minute (gpm). The screened interval was designed to cover both the upper and lower intermediate zone. MODPATH, a particle tracking algorithm, was used to simulate the particle-tracking and capture zone of the extraction well. MT3DMS® a 3D contaminant mass transport model, was used to simulate the migration of the LCP PCE plume. Results of each simulation are discussed below— 1. Simulation 1 —This location of EW-7 was simulated on Lodi Avenue between Church Street and S. Pleasant Avenue. This location approximately represented the mid-point between wells G-13 (screened in the Shallow Zone) and well MW-25B (screened in the Upper Intermediate Zone). As stated earlier, the PCE plume appears to migrate from the shallow to the intermediate zone somewhere between G-13 and MW-2513. Both of these wells have similar PCE concentrations (>2000 µm/D. Hence, any extraction well installed at this location would capture the PCE plume as it migrates from the shallow zone (where the source area is located) to the intermediate zone. Results of this simulation are shown on Figures 2 and 3 for 3 separate time periods — current (2014), 2020, and 2025. The results indicate the following— • Extraction well EW-7 would adequately contain the width of the PCE plume in both the upper and lower intermediate zones, and mitigate the migration of the high concentration area (>500 µg/1) of the PCE plume from the shallow to the intermediate zone; • Remnants of the higher concentration areas of the PCE plume would continue to migrate towards well MW-22B (in the Upper Intermediate Zone) and towards City of Lodi Well-06R (Lower Intermediate Zone). However, the higher PCE concentrations would decrease over time. 2. Simulation 2 — EW-7 was simulated near the intersection of Church Street and West Tokay Street on the Needham Elementary School property and in the proximity of well G-25A, which had a PCE concentration at 1,800 µg/I in August 2014. This location was selected as it is close to the leading edge of the higher concentrations (>500 Rg/1) of the PCE plume in the intermediate zone. LAN6AAf WEAD1OWLL -BUL:LO