2016-11-29_GENERAL DOCUMENTS - C1981010

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Ground Water Impacts TMI has monitored the quality and levels of ground water in mine backfill aquifers using wells GD -3, GF -5, GF -7 and GF -11. These four wells were all included within the SL -4 Phase III bond release area. However, because they are used as ash monitoring wells, they are still sampled and are representative of backfilled aquifer conditions occurring in reclaimed blocks proposed for the SL -17 bond release application. GD -3 and GF -11 show moderate increasing trends in TDS and sulfate concentrations, GF -7 located in the backfill shows a larger impact, and GF -5, also located in the backfill, shows little degradation. These differences in response may be due to the amount of underburden flow occurring in each area, with GF -5 have great amounts of underburden flow and GF -7 having less influence resulting in higher concentrations of monitored constituents. Historical data from the backfill wells indicate leachate forms in the spoil/ash backfill. This leachate is alkaline, and high in dissolved solids (TDS), mainly sulfates. This concentration may continue for several hundred years, as predicted for the Seneca II Mine in Routt County, Colorado (USGS Water -Resources Investigations Report 92-4187). The alkalinity (pH near 7) appears to have prevented significant mobilization of metals in the spoil/ash backfill. Upper Williams Fork Units that discharge to the shallow aquifer systems do not extend south into the mine areas within the area request for release. No impacts to adjudicated wells are anticipated in areas down -gradient of the land proposed for release. Surface Water Impacts Within the area of the proposed SL -17 bond release, surface water flows through eight different watersheds. This includes discharges through eight active NPDES outfalls. The eight active discharge points are all covered under NPDES Permit CO -0032115 and are in the following gulches: Johnson, No Name, Coyote, Middle Pyeatt, East Pyeatt, Deer, West Pyeatt, and Oak. All runoff is primarily tributary to the Yampa River, with a small amount from Deer Gulch going to the Williams Fork. Surface water consistently discharges only through Johnson, No Name, East Pyeatt, and Oak Gulches. The remaining discharge points seldom if ever record surface water runoff. Throughout the sampling history of these discharge points, no violations of CO -0032115 standards have occurred. Recent Division reviews of AHRs (from 2001 to 2015) indicate that there have been no significant water quality problems at these discharge points. No known spoil springs appear to be present on any of the reclaimed lands proposed for bond release in SL -17. Spoil springs that were present at the down -gradient contact of spoils and non -mined areas in Johnson and No Name Gulches were Phase III released in SL -4. Compliance with Basic Standards for Ground Water The absence of leachate plume development in the bedrock units indicates that for bedrock units in and adjacent to the bond release area, the mine operator is in compliance with the Colorado Water Quality Trapper Mine Page 12 November, 2016 Phase III Bond Release (SL -17)