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candy Gulch data assessment 19 <br />• 4.2 Water quality characteristics <br />The general trend of water quality as a function of location in the water shed drainage is very <br />useful in understanding the water quality characteristics along Windy Gulch. Average, minimum <br />and maximum concentrations of zinc, cadmium, and overall TDS have been compiled and <br />presented in Figures 4.1, 4.2, and 4.3 for each monitoring installation along Windy Gulch. By <br />identifying variations in water quality along Windy Gulch, measures can be developed and <br />implemented to avoid prolonged exposure to potential water quality impact areas and to provide <br />long term mitigation measures relating to water quality in Windy Gulch. <br />4.2.1 WGU Weir and DP-1 <br />Chemical analysis results from the two upper installations in Windy Gulch (WGU Weir and DP-1), <br />indicate very low or undetectable concentrations of cadmium, zinc, and other metals along with <br />observed average TDS concentrations that are 3 to 4 times lower than downstream monitoring <br />points. The two installations also produce very similar water quality despite the fact that one is <br />surface water while the other is subsurface water. This similarity is probably due to the fact that <br />water sampled from DP-1 is in essence surface water that is flowing under extremely porous talus <br />material in the middle reach of Vyndy Gulch. Also, both sites are above any recent mining activity <br />conducted by Homestake Mining, so the Windy Gulch surface water does not came in contact with <br />any recent waste rock material. Lastly, flow reaching these two locations has little or no contact <br />• with natural talus/alluvium potentially bearing mineralized rock. <br />4.2.2 9700 Weir and DP-3 <br />While water samples collected from DP-3 show an increase in concentrations of zinc and overall <br />TDS relative to the upstream sampling points, there is only a slight increase in cadmium <br />concentrations. Located only a few feet away, water samples collected from the 9700 Weir show <br />similar, but slightly smaller, increases in Cd and TDS. However, there is nearly no increase in the <br />Zn concentration from 9700 Weir samples relative to DP-1 and WGU Weir. <br />Given the losing nature of Windy Gulch between DP-1 and DP-3, it is expected that there is some <br />disparity between the surface samples collected at the 9700 Weir and those bailed from DP-3. <br />Once water infiltrates down into the alluvium, its velocity decreases dramatically, conversely <br />increasing the amount of time the water may be in contact with sources of mineralization within the <br />natural alluvium. Water reaching the weir that has not had prolonged exposure to the local <br />alluvium would be expected to be less concentrated. The more pronounced difference in average <br />zinc concentrations suggests that a subsurface source of zinc, either the natural occurrence of <br />mineralized rock in the Creede Formation or rhyolite, the 9700 rock dump, or both, exists in the <br />gulch between DP-1 and DP-3. <br />• <br />