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IIntegral Consulting Inc. <br /> `e ia 601 Montgomery Street <br /> (onsullimy Ill( Suite 888 <br /> San Francisco,CA 94111 <br /> telephone:415.787.6304 <br /> www.integral-corp.com <br /> February 23,2023 Project No. C2074 <br /> Rachel Kerr <br /> Ahtna Environmental, Inc. <br /> 29612th Street <br /> Marina, California 93933 <br /> Subject: 2022 New Extraction Well Evaluation <br /> Dear Ms. Kerr: <br /> Integral has performed an evaluation of five potential new C Zone extraction wells for the <br /> Sharpe Army Depot("the Site"). Groundwater at the Site is currently impacted by a <br /> number of contaminants, particularly tetrachloroethylene (PCE), trichloroethylene (TCE), <br /> and carbon tetrachloride (CT)within the A, B, and C flow Zones. <br /> This analysis used a version of the Site groundwater model that has been updated to <br /> simulate flow conditions through the end of September 2022. This model incorporates all <br /> updates and calibration efforts from the 2022 annual model update as documented in <br /> Appendix D2 to the October 2021-September 2022 Federal Facility Agreement(FFA) <br /> Annual Progress Report. The model used for this extraction well analysis also incorporates <br /> the more extensive updates performed as part of an optimization effort and documented in <br /> Appendix D2 to the FFA. The predictive period of the updated 2022 model extends for 100 <br /> years from the end of the calibration period in October 2022 to October 2122. <br /> Potential new extraction wells were simulated as fully penetrating the C Zone (Layer 4) of <br /> the groundwater model. A representative extraction flowrate of 50 gallons per minute <br /> (gpm)was assigned to the potential new well locations,which were estimated to begin <br /> operation at the beginning of the predictive period. The rest of the existing extraction well <br /> network was operated as a combination of both average 2022 conditions with some <br /> adjustments per a suggested refined operation configuration. This extraction configuration <br /> is documented in detail in Appendix D2 of the FFA. <br /> A particle tracking analysis was performed for each potential new C Zone well location, <br /> where particles starting at the perimeter of the combined C Zone TCE/PCE/CT plume (as <br /> defined by Ahtna as of Fourth Quarter 2022) area where concentrations of those <br /> constituents exceed Site cleanup levels. The forward tracking pathways of these particles <br /> show their respective termination points where they are taken up by a simulated extraction <br /> well (or not). The particle tracking analysis assumes transient groundwater conditions from <br />