2025-05-02_REVISION - C1981010 (2)

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Gulch. Generally, Johnson,No Name East Pyeatt and Middle Flume gulches exhibit flow over the course of the year. The most noticeable change in surface water quality resulting from mining activities constitutes increased levels of total dissolved solids (TDS). TMI expects higher TDS in some surface water runoff for a few years after reclamation in an area. Increased TDS levels occur periodically when the contribution from precipitation and snowmelt is at a minimum (base flow conditions). Conductivity, TDS and major constituents tend to increase as the ground water contribution comprises a larger portion of flow. For a detailed analysis of surface water impacts,the 2021 Annual Hydrology Report, Section 2.5 of the permit presents the most current information. Leachate that may discharge from the toe of the Horse Gulch Fill probably will cause an increase in the dissolved solids content of natural stream flows in Horse Gulch. Rain or snowmelt provides most natural surface water flows in Horse Gulch. Although loading of Horse Gulch surface flows with dissolved solids from the fill would be a local impact, it does not rise to the level of material damage because use or potential use is not likely to be impaired. An exceedance of an instream standard in Horse Gulch is unlikely because leachate from the fill will probably be alkaline (like all other Trapper leachates)and is not likely to contain high concentrations of the inorganic or metals constituents for which there are numeric standards in Horse Gulch. Ground Water Impacts The 2023 Annual Hydrology Report (AHR), Section 2.5 of the permit presents the most current information regarding springs and seps at TMI. Appendix B presents ground water quality data from 2012 through 2022. Flow from the springs and seeps is shown on Table B-2. A CD submitted with the AHR provides all historical data. The NPDES permit#CO-0032115 issued by the Colorado Department of Public Health and Environment describes water quality monitoring requirements. Pit dewatering occurs in L,N Pits, and well dewatering in the G Pit wells. All pit water is routed to NPDES drainage systems with discharges monitored at the approved outfall. Dust suppression for the main haul road consumes most of the water yielded from dewatering activities. Currently a number of the listed outfalls encompass Phase III bond released areas and therefore are no longer subject to DRMS monitoring requirements. IV. Topsoil Soil information can be found in Section 2.6,Volume II and Section 4.9,Vol. IV. The Division previously granted a variance from topsoil removal in accordance with Rule 4. 06.2(2)(a). Specific areas which the operator will not strip topsoil are limited to rocky areas which occur over limited areas throughout the mine area. Each area approved is handled separately as a minor revision to the permit and no general variance is currently approved. V. Sealing of Drilled Holes and Underground Openings Sealing of wells,holes, and other openings is discussed in permit Section 3. 3,Vol. III. 15