2013-04-10_PERMIT FILE - C1981019 (82)

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RULE 2 PERMITS Rule 2.05.6(3)(b)(iii) requires determination of probable hydrologic consequences for the proposed 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 proposed activities must be anticipated. Summary of the Probable Hydrologic Consequences The anticipated probable hydrologic consequences of mining coal as proposed in this application are: • Springs near the Little Collom X and Collom Lite pits might experience increased and /or decreased flow. • The Little Collom X and Collom Lite pits, facilities pad, and spoil pile will eliminate several seeps and springs. • Dewatering of the Little Collom X pit is not anticipated, but dewatering of the Collom Lite pit is probable. • Hydraulic conductivity within the backfilled pit will be higher than in the adjacent unmined areas. • Springtime peak flow in the West Fork of Jubb Creek may be reduced by up to 42 percent during and after mining. This estimate is highly uncertain and likely very conservative due to limited monitoring data, low flow rates, uncertain recharge basin boundaries for the affected springs causing the decrease, and tendency of spring/seep flows from the upper watershed to reinfiltrate into the valley fill. The West Fork of Jubb Creek does not produce baseflow. Actual effects are likely to be less significant than the percentage change reported here. • 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. 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. Springs within Little Collom Gulch that will be eliminated by the mining operations include SPRLC -01, SPRLC -02, SPRLC -03, VI 1, and V29. Additionally, V1, V 10, and V32 (West Fork of Jubb Creek) may be impacted by mining activities via potential elimination of portions of their recharge areas. Additional springs in the Collom Gulch and Jubb Creek drainages are unlikely to be affected, due to their location upgradient/updip, cross -dip, or on the opposite side of an incised stream channel of the proposed mining. Table 2.05.6 -4 lists the springs and seeps found in the vicinity of the proposed mining areas. The locations of the investigated springs and seeps are presented on Mao l OB Collom — Rule 2, Page 133 Revision Date: 9/28/11 Revision No.: PR -03