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2021 AHR Review: New Elk Mine <br /> Surface Water: A prediction was made that increases in TDS would be observed at various stream <br /> sites during the irrigation season (June-September). Deterioration of the alluvial and surface water <br /> quality are concerns associated with coal refuse piles, specifically modifications of the potentiometric <br /> surface and water quality impacts in the flooded workings These concerns are discussed in the The <br /> Probable Hydrologic Consequences (PHC), Section 2.05 of New Elks mining and reclamation <br /> permit. <br /> Ground Water: The Probable Hydrologic Consequences (PHC), Section 2.05 of New Elks mining <br /> and reclamation permit discusses the possibility increasing TDS. <br /> The frequency of monitoring was changed with TR73 to reduce sampling during an inactive mining <br /> period. As previously noted by the Division in the adequacy review of TR73, historic data from NE- <br /> 1-10 should be included in the AHR together with data from the current monitoring period. NE-1-10 <br /> is completed in the Allen seam, approximately 1000' from existing mine workings, down the <br /> projected potentiometric gradient. <br /> TDS/Sulfate levels in the alluvial wells have fluctuated significantly between the years 2019 and <br /> 2020 and appear to be within natural levels according to the 2021 report. The TDS and Sulfate levels <br /> are consistent with expectation in the PHC. Frequency and location of monitoring should be reevaluated <br /> as mining reinitiates. <br /> Predicted impacts to ground water quality include increasing TDS in the form of sodium and <br /> bicarbonate. Elevated TDS levels in backfill aquifers are likely according to the PHC section of the New <br /> Elk permit. Well PAW 2 is completed in backfilled spoil. <br /> 25. Agreement of observed hydrologic Impacts with PHC <br /> CDRMS regulation 2.05.6(3) <br /> Overall, PHC predictions appear to be accurate, as illustrated by the following examples. New Elk does <br /> not anticipate recharge to shallow aquifer systems to be adversely affected by mining operations. Water <br /> levels in wells have remained stable during recent monitoring. Per the PHC, constituent concentrations in <br /> backfill aquifers namely TDS and sulfate, are expected to be higher than premising concentrations for an <br /> extended period of time after mining. <br /> The data for TDS concentrations in wells in backfill aquifers have shown apparent impacts from mining. <br /> Sulfate concentrations exhibit similar trends as TDS. TDS/ Sulfate levels in these wells should continue <br /> to be monitored in future years. Backfill aquifers will continue to have an impact on surface base flow <br /> water quality (TDS), conditions. <br /> Adequacy Questions <br /> DRMS February 2023 <br /> 1. The inclusion in the AHR submittal of monitoring data comprising more than the past year along <br /> with an analysis of increasing and decreasing trends seems appropriate given the backfill in <br /> placed in the Purgatoire River. Going forward please include additional years of data. A <br /> discussion with DRMS as to whatwould be reasonable given the status of mining would be <br /> welcome. <br /> 2. As previously noted by the Division in the adequacy review of TR73, historic data from NE-1-10 <br /> should be included in the AHR together with data from the current monitoring period. <br /> Page 5 of 6 <br />