2018-11-05_GENERAL DOCUMENTS - C1981044

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Williams Fork Mines Prepared by: R. Reilley M.S. GISP C1981044 5 November 2018 25 Compliance with the Basic Standards for Ground Water (Regulation 41 of the Colorado Water Quality Control Commission) Section 4.05.13(1) of the Regulations requires the establishment of one or more ground water points of compliance (wells) for an operation which has the potential to negatively impact the quality of ground water. The mine monitors the Middle Sandstone in well TR-7a and the Williams Fork alluvium in well AVF-5. The TR-7a well is within the expected bedrock flowpath of mine leachate, should the mine discharge leachate to bedrock units. The AVF-5 well is within the expected alluvial flowpath of leachate, should the mine discharge leachate to Williams Fork River alluvium. AVF-5 is also within the expected flow path of pumped mine water, should mine water adversely impact the alluvial water. Both wells meet the qualifications of a compliance point, as those qualifications are listed in Section 4.05.13(1)(b). Monitoring data from both wells indicate the mine has not caused an exceedance of the Basic Standards for Ground Water with the exception of Manganese levels in AVF-5 which is often above the Basic Standards for Groundwater drinking limit. However, according to section 2.04.7 of the permit, dissolved solids, iron, lead, manganese and sulfate often exceed the drinking water standards naturally. Observed Surface Water Impacts Discharges from the 5 and 6 Mines have not caused measurable depletion of stream flows in the mine vicinity. If all of the mine inflows during active mining (approximately 2 cfs) came from the Williams Fork and Yampa Rivers, it would be too small of a depletion to detect in those rivers’ 7-day/10-year low flows. Monitoring data in the annual hydrology reports from 1981 through 2017 indicate the Williams Fork Mines have not significantly impacted the water quality of the Williams Fork River. G. No surface water is proposed to be discharged into, or directed into, underground mine workings. H. MCM does not plan to convert any monitoring wells to water supply wells. I. Stream Buffer Zones - Rule 4.05.18 The Williams Fork Mines included several structures located within 100 feet of the perennial Williams Fork River. These structures consisted of a coal storage silo (demolished in 2018), a 48-inch cross country conveyor (demolished in 2017), waste water ponds, No. 5 Mine dewatering wells and associated substation and access road, haul road bridge, well 259 and pond HR-P1, and rail road at tail track end (demolished in 2017). The conveyor was an enclosed structure as it crossed the river and the highway, therefore minimizing disturbance to the stream. The coal storage silo was a concrete structure utilized to load railroad cars. These variances from the 100-foot buffer zone for perennial streams have been granted by the Division upon finding: 1) that the original stream channel will be restored; 2) during and after mining, the water quantity and quality from the stream section from within 100 feet of the surface coal