2021-12-09_REVISION - C1981010 (7)

Home Browse Search

90W. Such a plume would not be expected to form until several years,possibly decades, after the pit is reclaimed. The Third White Sandstone is monitored in the area of the possible plume in well GP-9, and the alluvium is monitored with the Coy well. Monitoring data from both wells indicate that a plume has not reached these wells. Well GC-2 completed in the P White Sandstone up gradient of well GP-9 has shown evidence of the predicted plume with elevated TDS levels and sulfate levels that initially increased over time but have since stabilized and appear to be decreasing. Other wells down-gradient of spoil backfill such as well P-8 completed in the Third White Sandstone and well GD-2 completed in the R aquifer are also showing signs of elevated TDS/Sulfate likely leaching from backfilled spoils. TDS Levels in well P-8 appear to have stabilized after a large increase in 1995 but are remaining above baseline levels. TDS/Sulfate levels in the alluvial wells have fluctuated significantly over the years but appear to be within natural levels according to TMI's 2020 annual hydrology report. Surface Water Impacts Within the area of the proposed SL23 bond release,surface water flows through three different watersheds and includes discharges through three active NPDES outfalls. The three active discharge points are all covered under NPDES Permit C00032115 and located in the following gulches: Middle Pyeatt(NPDES 09),Horse (NPDES 24),and Oak(NPDES 17). All runoff is tributary to the Yampa River. Surface water consistently discharges only through Johnson,No Name, and East Pyeatt. The remaining discharge points seldom if ever record surface water runoff. Throughout the sampling history of the discharge points,no violations of C00032115 standards have occurred. Seasonal excursions of TSS and total iron occasionally occur during spring snowmelt or, as a result of an intense precipitation event. Also on occasion, seasonal excursions of pH occur. Any pH excursions are quickly mitigated by Trapper Mine with the addition of CO2. Division reviews indicate that there have been no significant water quality problems at Trapper's discharge points. No known spoil springs appear to be present on any of the reclaimed lands proposed for bond release in SL23. Spoil springs that were present at the down gradient contact of spoils and non-mined areas in East Pyeatt and Oak Gulches were previously Phase III released. 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 Control Commission's Basic Standards for Ground Water(Rule 41). Any ground water in alluvial deposits in the bond release area meets the classification of Limited Use and Quality because the alluvial water is of such small volume in the thin, laterally discontinuous deposits present that it is not currently used and is unlikely to be used in the future. The Basic Standards for Ground Water have no water quality standards for the Limited Use and Quality classification. Division reviews indicate that there have been no significant ground water quality problems in the monitored formations. Protection of Ground Water Recharge Capacity On a local scale,the disturbed area does not significantly divert ground water flows to surface water Permit Number. C1981010 Page 14 of 16