2013-07-09_REVISION - C1981010 (7)

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predicted subsurface saturation elevation (section 4.3.4.6 of permit application). Almost all of the waste ash material will be coal combustion ash and sludge from the Craig power plant. The main elemental components of the combustion wastes are barium, calcium, iron, magnesium, potassium, silicon, and titanium. Adequate ground water monitoring is in place to detect any ground water problems early -on so mitigation measures can be implemented. Drawdown of water levels in aquifers - The original permit application predicted that the excavation of pits at the Trapper Mine could temporarily draw down water levels in local aquifers by a few feet at a distance of one mile from the permit boundary (page 4 -226 of permit application). The predictions proved inaccurate as no draw -downs were detected in wells at those distances. Observed draw -downs have been temporary and are limited to the immediate vicinity of the pits. The operator expects such limited draw -downs to continue with future mining. Draw -downs may be so limited because the mine is on the up -dip edge (near the drainage divide) of the local hydrologic basin. Impact on aquifer recharge capacity - The proposed mining operation will have little if any effects on the post- mining recharge capacity. The applicant's studies concluded that the recharge capacity of the reclaimed spoils will actually be slightly higher than the pre -mine condition. The applicant estimated the pre - mining infiltration rate to be approximately 10 -5 to 10 -6 cm /sec (0.34 to 0.034 inches per day). Reclaimed spoils are expected to have an infiltration rate of 10 -3 to 10 -4 cm /sec (34 to 3.4 inches per day). The mine activities should not impact any regional aquifers except the Third White Sandstone. Mined strata dip far beneath the Yampa River alluvial aquifer and communication between these strata and the alluvial aquifer is negligible. Potential impact to domestic wells — Section 4.8.2.2 of the permit discusses potential drawdown impacts to adjacent wells. Based on Trappers analysis, drawdown has the potential to impact two wells during the current permit term. A mitigation plan is in place if drawdown affects the water users. A groundwater monitoring program discussed in section 4.8.3.2 of the permit and point of compliance wells are in place. Surface Water Impacts During mining in a drainage, runoff may temporarily increase during the time period the ground surface is denuded. Much of the increased runoff will be contained by the pits and the required sediment control system of ditches and ponds. Spring snowmelt will cause the ponds to discharge, although the levels of total suspended solids in snowmelt runoff will be substantially below pre -mine levels in most cases due to settling in the sediment ponds. Pit pumping will also cause some drainage systems to discharge on a regular basis but this water is of generally acceptable quality for stock watering and other agricultural purposes and no problems are projected due to this discharge. Once vegetation is re- established throughout a drainage, runoff in the drainage may decrease below pre- Trapper Mine 26 July 9, 2013