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Groundwater Well Installation Work Plan Sharpe Army Depot Lathrop, California Ahtna Environmental, Inc. 8 The preliminary design for the proposed wells is as follows: • EWNC7 (Table 1, Figure 13) o Blank casing from the ground surface to 130 ft bgs o Screened casing from 130 to 140 ft bgs o Blank casing sump from 140 to 145 ft bgs • MW543B, MW544B, and MW545B (Table 1, Figure 14) o Blank casing from the ground to 60 ft bgs o Screened casing from 60 to 70 ft bgs • MW546C and MW547C (Table 1, Figure 14) o Blank casing from ground surface to 75 ft bgs o Screened casing from 75 to 85 ft bgs • EWA1R (Table 1, Figure 15) o Blank casing from the ground surface to 30 ft bgs o Screened casing from 30 to 40 ft bgs o Blank casing sump from 40 to 45 ft bgs Each well will be capped with a threaded stainless steel end cap. Well Screen and Centralizers Well screens for extraction wells will be 10 ft of 8-inch diameter, continuous slot, wire-wrap, threaded, Type 304 stainless steel. Well screens for monitoring wells will be 10 ft of 4-inch diameter Schedule 40 PVC. Nominal screen apertures will be 0.020 inches for extraction wells and 0.010 inches for monitoring wells. The supplier will provide clean, wrapped screened casing as described above. Stainless steel centralizers will be placed at the top and bottom of the screen, and every 40 ft upward (as applicable), from the top of the screen. Centralizers will not be placed within the bentonite seal. Plumbness will be aided by the centralizers and by keeping tension on the well casing during construction. The plumbness is checked by lowering a minimum 10-foot swab to the bottom of the well during the filter pack setting phase of construction. Sounding Pipe The preliminary design for the extraction well includes a sounding pipe extending from the ground surface to 128 ft bgs in the C Zone (EWNC7; Figure 13), and surface to 28 ft bgs in the A Zone (EWA1R; Figure 15). The sounding pipe will be constructed of a 2-inch diameter, Schedule 80 PVC. The pipe surface will be free of solvents, oils, grease, paint, and dirt, and will be certified clean from the factory or steam-cleaned on the site before installation. Sections of pipe will be received from the supplier in polyethylene protective wrappers with sealed ends to limit exposure to potential contaminants. The pipe will not be removed from the wrapping before installation.