2022-09-06_REPORT - C1982056 (3)

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Foidel Creek Mine C-82-056 2021 Annual Hydrology Report reporting has primarily been conducted by TC personnel. In May of 1995, a private firm (Miller Water Monitoring Service) was contracted to assist with hydrologic monitoring at the TC sites and continues to assist in monitoring to date. Prior to June 1986, water quality analyses were performed by the on-site CYCC laboratory. From 1987 to 2000, water quality analyses were primarily performed by ACZ Laboratories (formerly Bookcliffs) of Steamboat Springs, Colorado. From 2001 through 2005, water quality analysis has primarily been performed by SGS North America laboratory of Denver, Colorado. Since mid-2005, analyses are again primarily performed by ACZ Laboratory of Steamboat Springs, Colorado. Whole Effluent Toxicity (WET) testing was historically conducted by SGS, and then Aqua-Tox of Wheat Ridge, Colorado through May 2018 where TC switched to Environ Chem Analytical of Grand Junction, Colorado. Note that in 2003, DRMS approved TR03-42 (See Permit Exhibits 14-5, 14-6, and 14-10), and PR 03-06 (See Permit Exhibits 14-7 through 14-9), which eliminated several surface, alluvial, and bedrock well monitoring sites, and reduced the monitoring frequency of other sites, while adding additional monitoring requirements to existing surface site 305 (located downstream at the time of Twentymile Park subsidence). Data from terminated sites can be found in previous AHRs. Three former US Geologic Survey (USGS) surface water sites (USGS 09243700, USGS 09243800 and USGS 09243900) were monitored for flow by the USGS through the 2001 water year. Prior to the 1989 Water Year, the USGS had collected and analyzed water quality samples from these sites. From the 1989 water year to date, TC has collected water quality samples from these sites for laboratory analysis. Beginning with the 2002 water year, TC took over monitoring of these three sites (referred to as sites 700, 800, and 900, respectively) from the USGS. In 2003, TR03-42 eliminated site 700 on Middle Creek. 3.0 2021 HYDROLOGIC MONITORING PROGRAM The Foidel Creek Hydrologic Monitoring program includes bedrock and alluvial wells, stream points, spoil springs, natural springs, mine discharge, and mine inflow monitoring. Specific monitoring site locations and their elevations are shown on Figure 2. Required monitoring frequencies are listed in Permit No. C-82-056 for reference. Data tables and figures for each site are referenced in the following discussions. Statistical summaries of the historical data and graphs of total dissolved solids (TDS) and field conductivity are also provided after presentation of the 2021 data. Twentymile uses the EQUIS database for data storage and reporting. Because of 3