2012-12-06_REVISION - C1981008 (4)

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5.4 Impact of Spoil Water Quality on Surface Water Quality. The chemistry of the water interacting with the spoil is described in the previous section. The principal impact from a quality perspective is that irrigation water will seep rapidly through the spoil, increase in TDS and possibly discharge through a spoil spring at the lower part of the mine area. Water quality analysis of ground water from GW -N18 has shown that the spoil water quality is nearly the same in pH but slightly higher in TDS. However, as previously mentioned, pre -mine ground water in the overburden is generally high in TDS as well. 5.4.1 Impacts To Receiving Waters The downstream receiving water for the Phase III release areas is Calamity Draw. No spoil water springs have developed during the 10 years since these areas were backfilled. Therefore, water quality has been analyzed using the well GW -N18 since it is immediately downstream from the release areas. See Map R -2. The cross section on this map also shows the relationship of the overburden strata with Calamity Draw, Well GW -N38 and the spoil backfilled pit. As water builds up in the backfilled spoil, it is possible that a spoil spring could develop at the low point of the spoil area and there is also a potential that some spoil water could work its way through some strata that has above average permeability and show up as a spring entering Calamity Draw. No spring has yet shown up but this will be monitored for future impacts. The second possible impact on receiving waters is surface run -off from the reclamation areas. The Revised Universal Soil Loss Equation calculations for Phase II bond release of these areas (submittal SL -11) shows that erosion from these areas is less than pre -mine, and thus will not increase the presence of sediment in surface water run -off. Pond 007 handles all of the surface water runoff from the release areas. All records of discharge from Pond 007 show that the pH has been maintained to be primarily neutral and all discharges have been in compliance with the NPDES discharge permit. Surface water sampling from SW -N108 (showing the surface water quality upstream) and SW- N109 & SW -N103 (showing the surface water quality downstream) demonstrates that the mine area has not affected the receiving waters of Calamity Draw negatively. Appendix 4 shows the surface water sample results for these sites from 1996 to 2012. Figures 5 -7 show the TDS and pH at these three sample points for both pre- mine /mine periods and post mine periods. A cursory analysis of these figures shows that the pH has remained close to 8, and the TDS has stayed within the 500 to 3000 range in both time frames. TDS fluctuation over the course of the years is expected due to fluctuation in flows within Calamity Draw. Flows fluctuate for two primary reasons: seasonal runoff (spring snow melt plus spring /summer storms) and irrigation tail water (mid April to mid October). These combine to produce significantly more flow in the summer than in the winter. In surface runoff, generally, higher flows equate to lower TDS and vice - versa. The overall impacts to the receiving waters is no change. The area will continue to be monitored for evidence of any springs leading to Calamity Draw and any spoil springs that may develop around the perimeter of the mine backfilled spoil area. Any spring that is identified will be immediately reported to the DRMS and the location will be added to the water monitoring list of the permit. SL -14 03DEC12.wpd 74