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Groundwater Well Installation Work Plan Sharpe Army Depot Lathrop, California Reviewer Carla Landrum Organization Central Valley Water Board Date April 6, 2023 Item Reference Review Comment Response the proposed extraction wells have not been added for the reason stated in the reponse to General Comment 3. 6. Please discuss how the vertical placement of proposed Clarification.As noted in the response to General extraction wells will not increase the extent of plume Comment 5, since the proposed well locations do not migration, which appears to be the case by intersect the cross-section lines directly(Figure 2), it can be consequence of EWCC7 placement in Figure 3. difficult to interpret a well location in relation to the plume. Figures 3-5 should be used in conjunction with Figures 6 and 8, as well as Table 2 to gain a better understanding of well locations in relation to the plume. As illustrated by Figures Al-A6,the proposed location of EWCC7 is expected to improve plume capture and limit migration by partially filling an existing gap in the extraction well network. 7. In instances where there is insufficient data to estimate Revised. Figures 6, 7, and Al-A6 have been revised to the location of a plume boundary, such as the include a dashed line to indicate estimated plume southernmost TCE plume extent shown in Figure 7,the boundaries. plume boundary should by symbolized by a dashed line. Please update Figure 7, and elsewhere as necessary, to accurately depict plume extent(s) in the Work Plan. 8. Please make sure well construction specifications are Revised. Figure 9 has been revised to indicate the grout clear and accurate. For example, in Figure 9, grout from 0-106 feet. placement is shown from 0 feet— 109 feet yet the bentonite seal is shown from 106 feet— 109 feet. 9. Appendix C Please include all relevant SOPS. For example, the Revised. Updates of all applicable SOPs have been added contents of SOP No. 003 and SOP No. 008 are not to Appendix C, and the text has been revised to specify readily identified within the Work Plan. low-flow sampling in Section 3.2.7. Ahtna Environmental Inc. Page 6 of 6