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RN07 Page 23 5/30/18 Response: - Please refer to the discussion of “Ground Water Quality Protection” on page 2.05-130 and the extensive discussion of “Potential Mining-Related Impacts on Ground Water Quality and Quantity” on pages 2.05-133 through 2.05-149. The Foidel Creek Mine mining and related operations will all occur within the Twentymile Park groundwater basin, which is an enclosed basin with little or no potential for groundwater movement out of the basin. The CDRMS has recognized this, as documented in the Permit Renewal RN -05 Decision and Findings of Compliance; “The Wadge overburden and the Twentymile Sandstone are the two major aquifers most likely to be affected by the Foidel Creek Mine….The mine’s annual hydrology reports contain long-term data from these wells. These data show Foidel Creek Mine is in compliance with the Basic Standards for Ground water at the groundwater points of compliance.” All of the groundwater rights identified in Table 9 are owned by either TC or Sage Creek Land & Minerals, an affiliated Peabody subsidiary company. There are currently no domestic or agricultural uses of groundwater within the Twentymile Park basin, so the applicable groundwater quality classification under Regulation 41, Basic Standards for Groundwater, would be “Potentially Usable Quality”. Based on this cl assification, and the lack of current existing uses, the only applicable water quality standard is TDS, which is 1.25 x background levels. Both the water monitoring discussion in the PAP and Water Monitoring Plan (Exhibit 14) have been revised to clarify points of compliance and this compliance threshold and copies of the revised permit materials are included with these responses for replacement in the PAP. Resolved 60. Have the proposed wells WC008A and WC013A been installed (monitoring program Exhibit 14A)? They are shown on Map 13A, but have not been acknowledged as current monitoring wells in the monitoring plan. Response: - The referenced wells have been constructed and are being actively monitored (refer to MR’s 14 -279 and 14-281), and the Hydrologic Monitoring Plan (Exhibit 14) has been reviewed and updated to include these wells. Copies of the revised permit materials are included with these responses for replacement in the PAP. Resolved 61. The Annual Hydrology Reports (AHRs) reference potentiometric surfaces within the written interpretation of the data and they are referenced within the permit related impacts to the hydrologic balance; however, these potentiometric surfaces are not currently being provided within the AHR. Due to the potential impacts from dewatering to the hydrologic balance, as well as the potential for increased aquifer communication due to subsidence, it is appropriate to include potentiometric surface maps with the annual hydrology report going forward. Please provide the Division with potentiometric surface maps for the Wadge Overburden, Twentymile Sandstone, Trout Creek Sandstone, and Fish Creek Sandstone bedrock units. Response: - The references to potentiometric surface in the AHR groundwater discussion are generally being used to characterize direction of groundwater movement or as a general reference relative to observed changes for specific monitoring locations. Generally observed variations in water level for groundwater monitoring wells are relatively small and would not be accurately depicted by a potentiometric surface map. In addition, development and updating of potentiometric surface maps for each aquifer being monitored would be unnecessarily time -