2020-06-25_REVISION - C1981019 (6)

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RULE 2 PERMITS thereby theoretically increasing the mass of dissolved solids entering the groundwater. These dissolved solids in groundwater will eventually enter the surface water system, with a theoretical increase in dissolved solids in the surface water. This increase is calculated to be small enough to have no impact on the current or projected surface water uses in Wilson, Taylor, or Good Spring creek drainages. Groundwater Groundwater in the vicinity of the Lower Wilson and South Taylor mining areas is restricted to perched aquifers of limited extent within bedrock of the Williams Fork Formation, the Trout Creek aquifer (a bedrock aquifer of regional extent), and valley fill deposits as described in Section 2.04.7. The Williams Fork Formation aquifers have no beneficial use owing to their limited extent and minimal production. The Trout Creek Sandstone is a sandstone unit underlying most of the permit area and extending across much of northwestern Colorado. It contains water of useable quantity and quality as demonstrated by beneficial wells near the permit area. The Trout Creek Sandstone is beneath the mining impact areas and is separated from these impacts by clay and claystone layers within the Williams Fork Formation (see Section 2.04.5 and 2.04.6). A borehole intersecting the Trout Creek (84-B-TC - NW'/4, NE'/4, Sec. 19, T3N, R93W) was installed between the Lower Wilson and South Taylor mining areas. The Trout Creek formation was dry at this location, since the sandstone in this area outcrops to the west and is above any recharge source. With the dip of the strata to the north and east, the Trout Creek Sandstone, and overlying strata, do not become saturated until (1) the strata dips below the valley floor and (2) the elevation of the appropriate strata equals the elevation of surface water in Wilson and Good Spring Creek. Based on this information, mining is anticipated to have no impact on the Trout Creek aquifer. Groundwater in the shallow valley fill of Good Spring Creek is calculated to be marginally impacted by surface mining activities at South Taylor as described in the Probable Hydrologic Consequences. There are no registered beneficial-use wells in the Colorado Division of Water Resources well database within several miles, down gradient of the mining impact areas (Map I IB). 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)(111) 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. South Taylor/Lower Wilson—Rule 2,Page 77 Revision Date: 6/22/20 Revision No.: MR-220