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Groundwater Well Installation Work Plan Sharpe Army Depot <br /> Lathrop, California <br /> Project Sharpe Army Depot <br /> Document Groundwater Well Installation Work Plan Date April 2023 <br /> Contractor Ahtna Environmental, Inc. <br /> Contract USACE Contract No.W91238-19-C-0018 <br /> Reviewer Nadia Hollan Burke Organization Environmental Protection Agency Date April 4, 2023 <br /> Item I Reference Review Comment Response <br /> Specific Comment <br /> 1. Section 1.0, The text states that installation of extraction wells EWC4, Revised. Section 1.0 was revised to remove text discussing <br /> Introduction, EWC5, EWC6, and EWC7 will capture 75%of the zone C the percentage of plume capture.The approximate <br /> Page 1 tetrachloroethylene (PCE) plume; however,the basis for capture of plumes by new extraction wells will be <br /> this statement is not discussed and it is not clear how this evaluated after pump tests, and after target flow rates are <br /> was determined since the areas of influence for these decided. <br /> extraction wells have not been determined. Please revise <br /> the text to discuss the basis for the conclusion that <br /> extraction wells EWC4, EWC5, EWC6 and EWC7 will <br /> capture 75% of the zone C PCE plume. <br /> 2. Section 3.2, The text states drilling will either be conducted by mud Clarification. Mud rotary and rotosonic drilling methods <br /> Well rotary or rotosonic methods; however,the text does not have been used successfully for well installation at Sharpe <br /> Installation discuss how each method will be evaluated and ultimately in the past.The selected drilling method will be decided <br /> Activities, Page selected. Please revise the text to describe how the based on cost and driller availability and documented in <br /> 8 proposed drilling methods will be evaluated and selected. the field records and report. No edits to the text were <br /> made. <br /> 3. Section 3.2.1.2, Extraction wells will be installed with screens that have an Clarification.Although no prior seive analysis data could be <br /> Well Screen aperture of 0.020 inches and #3 Monterey sand will be found in the Sharpe Administrative Record, Appendix C of <br /> and used as a sand pack; however, it is not clear if a sieve the 2021-2022 FFA Annual Progress Report(Ahtna, 2022) <br /> Centralizers, analysis has been conducted previously at the site to indicates 0.020-inch screens have been used in all of the <br /> Page 11 ensure the screen aperture is appropriate. Please provide extraction wells at Sharpe (the oldest of these wells having <br /> sieve analysis results for similar sand units that will be been installed in 1989)without adverse outcomes. <br /> targeted for extraction well installation. <br /> Ahtna Environmental Inc. Page 1 of 6 <br />