2024-05-03_PERMIT FILE - C1980007 (2)

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2.05-71 Rev. 11/96- PR07; 04/06-PR10; 12/14- TR136, 04/24 – TR153 Surface and Groundwater Monitoring The surface and groundwater monitoring program has been changed since monitoring began in the 1970’s to add hydrologic resources as the permit area was expanded, and to remove hydrologic resources that were no longer providing reliable or relevant data. These changes were included in Technical Revision Nos. TR-54 (1987), TR-85 (1998), TR-88 (1999), and TR-139 (2016), as well as Permit Revision Nos. PR-10 (2006), PR-11 (2005), and PR-12 (2008). Specifics about each revision can be found in the CDRMS revision files, as well as in Exhibit 18 – “Characterization of Groundwater Systems in the Vicinity of West Elk Mine”, and Exhibit 71 – “Hydrologic Characterization of the South of the Divide/Dry Fork Lease Areas and Hydrologic Monitoring Plan for Mountain Coal Company, LLC, West Elk Mine”. The comprehensive hydrologic monitoring plan for the West Elk Mine facilities and permit area is presented in Exhibit 71. This monitoring program was designed to collect the hydrologic data needed to assess mining-related impacts on hydrologic resources. The monitoring schedule, including a baseline monitoring schedule and “sampling windows” established to capture the rising limb, the peak, and low flow of the hydrograph, is described. The chemical analyte suite for the first five years of monitoring (including the baseline period) of both surface and groundwater resources and subsequent reduced analytical parameters are provided in Exhibit 71 as well. Surface Water Monitoring In 1977 Mountain Coal Company installed, and has since maintained and operated, a network of six continuous recording stream gaging stations to establish the baseline surface water hydrology for the permit and adjacent areas of the West Elk Mine and provide a method of assessing the impacts of mining during the life of the West Elk Mine. Five of these gaging stations are located in the Minnesota Creek drainage basin on Horse Creek, Lick Creek, South Prong, Upper Dry Fork, and Lower Dry Fork. The sixth gaging station is located on Sylvester Gulch a tributary of the North Fork adjacent to the surface facilities. Data records for all of these gaging stations, in both tabular and graphic form have been provided to CDMG in previous permit submittals for the West Elk Mine. These data are also found in the Annual Hydrologic Reports. This comprehensive data base has served to more than adequately characterize the baseline surface water hydrology across the mine plan area for the West Elk Mine. In addition to the original five gaging stations, Mountain Coal Company has installed and operates a gaging station on the main stem of Minnesota Creek, the Lower Minnesota Creek (USGS) gaging station and on the East Fork of Minnesota Creek just upstream of the confluence of East Fork and Dry Fork, Upper Minnesota Creek (USFS) gaging station. MCC also collects flow data from the North Fork of the Gunnison at the Upper North Fork gaging station, which is a USGS gaging station. MCC has since installed additional gaging stations at Middle Dry Fork and Upper and Lower Deep Creek. The locations of all surface water gaging stations can be found on Map 34. The currently monitored stations are listed in Table 5 in Section 2.04.7. In addition to providing baseline data, a portion of the Minnesota Creek gaging station network will be relied upon to determine the existence of stream depletions to Minnesota Creek arising from Mountain Coal Company's mining operations. The extent of depletion, if any, will be quantified by