2016-11-18_PERMIT FILE - C1981019A (7)

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RULE 2 PERMITS 2.05.6 (3)(a) Protection of the Hydrologic Balance Surface Water Surface water will be protected in the mining areas by stormwater management as described in Section 2.05.3(4) of this permit revision application and in the Stormwater Management Plan portion of the Stormwater Discharge Permit and as shown on Map 33B. Protection includes the use of diversion ditches to route surface water around the mining impact areas and stormwater impoundments downstream of the mining impact areas. Similar features will be included in the Lower Wilson mining area, with one or two impoundments likely to be used to catch surface water runoff from that impact area. Current surface water rights will not be impacted by mining operations at Lower Wilson or South Taylor. There is no expected long-term measurable impact to the quantity of surface water in Wilson, Taylor, or Good Spring creeks or any of their tributaries. Surface water amounts that will be used in mining operations will be within the water rights owned by Colowyo. Surface water quality of the three creeks is calculated to only be marginally impacted by mining activities. This marginal impact, described in the Probable Hydrologic Consequences section (Section 2.05.6 (3)(b)(iii) below), will be due to meteoric water being captured in and evaporated from the mine pit during operations, and meteoric water contacting an increased surface area of soil in the vadose zone and 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 alluvial/colluvial aquifers 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 alluvial -aquifers 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 shallow alluvial aquifers, beneficial -use wells in the Colorado Division of Water Resources well database within several miles, down gradient of the mining impact areas (Map 11 B). South Taylor/Lower Wilson— Rule 2, Page 79 Revision Date: 11/18/16 Revision No.: MR -163