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To: Mi% Peter Hays <br /> Date: February 21. 2022 <br /> Page 2 <br /> Response 1 <br /> After establishing a pre-mining pattern of groundwater elevations, monthly monitoring <br /> provides no additional benefit. Because there is no dewatering,the effects on groundwater <br /> from pit excavation will occur at a rate such that quarterly monitoring will indicate any <br /> effects in the appropriate amount of time. <br /> Comment 2 <br /> How will the proposed open groundwater pond effect the surrounding ditches, Brush Ditch <br /> and the Big T and Platte Ditch in both the near term and long term? <br /> Response 2 <br /> Sediments in the aforementioned ditches and the change in heads control seepage. Because <br /> the drawdown is minimal, the change in seepage is likewise minimal. The groundwater <br /> model estimates the following pre- and post-estimated ditch seepage: <br /> • Estimated ditch seepage pre-mining: <br /> — Hill and Brush Ditch: 9.8 gpm <br /> — Big T and Platte Ditch: 36.5 gpm <br /> • Estimated ditch seepage post-mining: <br /> — Hill and Brush Ditch: 13.4 gpm <br /> — Big T and Platte Ditch: 42.9 gpm <br /> This change is well within the model's uncertainty and thus, is insignificant. <br /> Comment 3 <br /> What is the supposed source of toluene that was detected in MW-5? <br /> Response 3 <br /> Toluene in MW-05 is non-detect. We have updated the table. When the database queried <br /> the laboratory report, it inadvertently grabbed the method detection quality assurance <br /> sample (surrogate parameter) rather than the analyte result. Attachment 15 presents the <br /> updated water quality tables. <br /> Comment 4 <br /> In Section 5.3.1, it is stated the drawdown in the Dunn well is not expected to be greater <br /> than 2 feet. However, in Figure 16 the graphed drawdown approaches 4 feet. Please <br /> reconcile this discrepancy. <br /> 20220209_10a5_DRMS_Adequacy_Review Response_MASTE <br /> Rdocx TELEST© <br />