2020-03-24_PERMIT FILE - C1981019A (2)

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RULE 2 PERMITS 2.05.6 (3)(b)(i & ii) Hydrologic Controls Surface water and groundwater drainage from the mining areas will be controlled as described in Section 2.05.3(4) and Section 4.05.Surface water flow will be diverted around the mining operations and into sediment ponds. Stormwater that enters the mining operations and water that occurs on the mining operations will be allowed to evaporate or infiltrate, or will be routed into these surface structures. 2.05.6 (3)(b)(iii) Probable Hydrologic Consequences Rule 2.05.6(3)(b)(iii) requires determination of probable hydrologic consequences for the mining operations. This rule indicates that these consequences must be defined for both the permit area and adjacent areas, for quantity and quality of surface and ground waters. Baseline conditions must be established, and possible impacts from the activities must be anticipated. Summary of the Probable Hydrologic Consequences — South Taylor Pit The anticipated probable hydrologic consequences of mining coal in the South Taylor area are: • Springs near the South Taylor Pit might experience increased and/or decreased flow. • The South Taylor pit will eliminate several seeps and springs. • Dewatering of the pit is not anticipated. • Hydraulic transmissivity within the backfilled pit will be higher than the adjacent unmined areas. • Base flow in Good Spring Creek will be reduced by up to 7% during and for 45 years after mining. • Total dissolved solids in the base flow of Good Spring Creek will increase by 1.6% to 13.5% for several hundred years after mining has been completed, with sulfate the dominant increasing ion. • Base flows of Taylor Creek will not be reduced, and peak flow of Taylor Creek will be reduced 2% by the South Taylor pit. • No other statistically significant changes to surface water quality or quantity are anticipated. These consequences are discussed in the following subsections. Potential Impacts to Springs and Seeps Springs in the Colowyo Mine area result from three general sources: 1) typified by a relatively deep soil accumulation immediately upslope and shallow bedrock downslope of the point of discharge, 2) discharge within valley bottom deposits, and 3) from sheer bedrock faces on hillsides (CDM 1985b). The first two of these sources may mask or contribute to bedrock sources of the springs. The seeps and low volume springs flow generally in response to snowpack accumulation and subsequent melting resulting in seasonal flows. A total of 8 springs, which maintained flow for the month of July, contribute to base flows in the receiving streams adjacent to South Taylor, and were determined as a critical component of the hydrologic balance. Seeps and springs relevant to this permit revision are shown on Map 10. The majority of the springs, with bedrock sources, appear to be contact springs. A contact spring results from the infiltration of water from the surface to a porous zone (such as sandstone) above a horizontal hydrologic barrier (such as shale) where the water preferentially flows along the contact to the exposure. This type of spring is common in areas where alternating sequences of lithologies exist that exhibit differential hydraulic conductivities, such as the Williams Fork Formation. South Taylor/Lower Wilson — Rule 2, Page 79 Revision Date: 4/7/17 Revision No.: RN -07