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Groundwater Well Installation Work Plan Sharpe Army Depot <br /> Lathrop, California <br /> Reviewer Nadia Hollan Burke organization Environmental Protection Agency Date April 4, 2023 <br /> Item Reference Review Comment Response <br /> Extraction estimated screened interval for extraction well EWC6 is 92 <br /> Wells and to 102 feet below ground surface (bgs); however, <br /> Monitoring according to Section 3.2.1.1 (Well Casing),the proposed <br /> Wells, Page 1 screen depth of extraction well EWC6 is 112 to 122 feet <br /> bgs. Please revise Table 1 or the text in Section 3.2.1.1 for <br /> consistency. <br /> Reviewer Carla Landrum Organization I Central Valley Water Board Date April 6, 2023 <br /> Item I Reference Review Comment Response <br /> General Comment <br /> 1. Section 1.0, Figures in the Work Plan cite trichloroethene (TCE), Revised.The figures have been revised to include 2021— <br /> Introduction, tetra ch loroethene (PCE), and carbon tetrachloride (CC14) 2022 data. <br /> Page 1 concentrations from 2021 and prior. Please explain why <br /> these Figures do not incorporate 2022 groundwater <br /> sample data for TCE, PCE and CC14. <br /> 2. The South Balloon Groundwater Treatment Plant has Clarification. Proposed well locations were based on a <br /> been offline for approximately one year, primarily during particle tracking simulation using the updated 2022 <br /> 2022. Central Valley Water Board staff do have concerns groundwater model,which included data collected during <br /> with TCE and PCE plume migration to south, southwest the 3Q22 groundwater monitoring event when the South <br /> and west of Sharpe during this time. With this said, please Balloon GWTP was offline. <br /> indicate if the shutdown status of the South Balloon <br /> Groundwater Treatment Plant was taken into <br /> consideration when selecting locations for well <br /> installation and performing groundwater simulations (i.e., <br /> Appendix A). <br /> 3. Extraction well capture zones are generally unclear in the 1. Revised. Particle flow lines on Figures Al-A5 have been <br /> Work Plan,yet they are a primary consideration is revised to include arrows and an updated color. <br /> selecting a location for extraction well installation.The 2. Clarification/Revision. All extraction wells included on <br /> capture zones are shown in Figure 7 of the Work Plan and Figures Al-A6 are active ("on").A note has been added <br /> discussed in Appendix A. to the figures for clarification. <br /> Ahtna Environmental Inc. Page 3 of 6 <br />