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Groundwater Well Installation Work Plan Sharpe Army Depot <br /> Lathrop, California <br /> 1.0 Introduction <br /> On behalf of the U.S. Army Environmental Command and the U.S. Army Corps of Engineers (USACE) <br /> Sacramento District, per Contract W91238-19-C-0018, Ahtna Environmental, Inc. (Ahtna) has prepared <br /> this Groundwater Well Installation Work Plan (Work Plan) for Sharpe Army Depot (Sharpe). <br /> The Work Plan describes the installation of five new extraction wells and five new monitoring wells to <br /> evaluate and remediate contaminants of concern (COC) at Sharpe, specifically trichloroethene (TCE), <br /> tetrachloroethene (PCE), and carbon tetrachloride (CCI4). These wells were recommended in the 2021 <br /> Federal Facilities Agreement (FFA) Annual Progress Report (2021 FFA Annual Report; Ahtna, 2022a) for <br /> the continued monitoring of Operable Unit 1 (OU 1) remedial action activities. <br /> Table 1-1. Proposed New Wells <br /> Name Well Type Onsite? Location Zone Figure <br /> EWC6 Extraction Yes South Balloon C 6 <br /> EWC7 Extraction Yes South Balloon C 6 <br /> EWC8 Extraction No west of South Balloon C 6 <br /> EWC9 Extraction No west of South Balloon C 6 <br /> EWCC7 Extraction No Central Area C 6 <br /> MW549C Monitoring Yes South Balloon-Central Area C 6 <br /> MW550C Monitoring Yes South Balloon-Central Area C 6 <br /> MW551B Monitoring No west of Central Area B 8 <br /> MW551C Monitoring No west of Central Area C 6 <br /> MW552C Monitoring No west of Central Area C 6 <br /> The proposed wells are listed in Table 1-1 and described below: <br /> • Two extraction wells (EWC6 and EWC7) screened in the C Zone will be located on the western <br /> edge of the facility in the South Balloon. EWC6 will be located near MW415A, and EWC7 will be <br /> between MW540C and MW332C.These wells will inhibit offsite plume migration by shifting the <br /> local hydraulic gradient on the western edge of South Balloon to the east and expanding the <br /> existing capture zone created by EWC4 and EWCS. <br /> • Two extraction wells (EWC8 and EWC9) screened in the C Zone will be located west of South <br /> Balloon on Union Pacific Railroad's (UPRR) property. EWC8 will be located on the west side of <br /> the railroad tracks,just northeast of MW543. EWC9 will be located on the east side of the <br /> railroad tracks, between MW497 and MW407.These wells will inhibit plume migration by <br /> shifting the local hydraulic gradient on the western edge of the South Balloon to the east and <br /> expanding the existing capture zone northwest of EWC4. EWC8, EWC9, and EWC4. <br /> • One extraction well (EWCC7) screened in the C Zone will be located west of the Central Area on <br /> UPRR property.The well will be located on the west side of the railroad tracks, southeast of <br /> EWCC6 and northwest of EWCC4. EWCC7 will inhibit further northward migration of the plume <br /> Ahtna Environmental,Inc. 1 <br />