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Cross Gold Mine <br />December 2024 G-6 <br /> <br /> <br />gallons/day) to keep the mine dry in peak snowmelt (Zulch, 1919). In 1919 the Caribou mine had over <br />5,000 linear feet of workings below the water table. It extended to a depth of over 1,000 feet below the <br />ground surface. Assuming an 8x8 (foot) opening dimension over this length results in 320,000 square <br />feet of discharge area. Using 600 feet of head loss to dewatering (400 level to 1000 level dewatering), a <br />transmissivity of 1.88x10-4 gallon/day/ft2 is calculated. This is a comparatively low transmissivity for <br />highly fractured rock. The low value may reflect the lower transmissivity of fractured aquifers with depth, <br />particularly over 400-500 feet deep (Freeze and Cherry, 1979). <br /> <br />Groundwater discharges to surface water at the mine as Coon Track Creek baseflow, from scattered <br />springs and seeps, and as drainage from the Cross Adit and the Idaho Tunnel of the Caribou mine. <br />Groundwater from theses mine tunnels is treated before discharge to Coon Track Creek. In late <br />summer and fall months the only flow in Coon Track Creek is from treated groundwater discharge from <br />drains (tunnels). This was the condition in late July 2021 when the data for the water table map in <br />Appendix G-4, Map 3 was collected. <br />The Middle Boulder Creek basin (containing the Coon Track Creek sub-basin or catchment) has been <br />the location of precious and base metal mining, milling, and smelting for over 150 years. The Cross <br />Gold Mine is the only currently operating mine in the historic district. Much of the district’s ore deposits <br />have metals hosted in sulfide minerals. Long-term watershed studies note some increases in dissolved <br />constituents attributed to reaction with rocks in the basin (Murphy et al., 2003). However, decades of <br />unregulated mining on Middle Boulder Creek have not affected in-stream water quality for pH, dissolved <br />solids, or toxic metals (Murphy, 2006). <br /> <br />Baseline groundwater data is collected and summarized in Appendix G-5. Included in this data are <br />histograms of the sampling results for parameters of concern such as iron, cadmium, zinc, and other <br />metals. These histograms show how frequently the groundwater sampled has tested above or below <br />the strictest applicable CDPHE standard for that parameter. <br /> <br />The waste rock is primarily composed of gneiss and quartz monzonite. These materials are benign and <br />have been analyzed for leachability and acid production by DRMS-approved methods. The results of <br />the analyses demonstrated the materials are non-acid producing and non-metals leaching. Due to the <br />nature of the waste rock generated by mining operations, significant impact to groundwater quality is <br />not expected. Analyses were conducted by Core Laboratories in 1994 on two composite samples from <br />the Cross Mine. Exhibit U contains the results of these tests and discussion. <br />The mining district is located near the northeastern exposed limit of the Colorado Mineral Belt. The <br />deposits of the Caribou district have been described by the U.S. Geological Survey (USGS) as <br />"polymetallic veins with abundant carbonates or the associated wall rock has been altered to contain <br />carbonates." The vein structures occur as steeply dipping northeast-striking veins that cut the east/west <br />striking veins. The vein mineralization was emplaced during multiple phases (up to seven) and includes