2015-08-31_GENERAL DOCUMENTS - C1981010

Home Browse Search

the spoil will be exhausted, and the leachate quality will approach the pre-mining ground water quality. The amount of time necessary for the mineral supply to become exhausted is predicted to be on the order of a few hundred years. Leachate formation from buried ash - The permit's restrictions on waste placement were designed to limit the amount of subsurface water that comes into contact with buried ash. The restrictions require ash to be buried above the 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- -5-6 mining infiltration rate to be approximately 10 to 10 cm/sec (0.34 to 0.034 -3 inches per day). Reclaimed spoils are expected to have an infiltration rate of 10 -4 to 10 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 32 Trapper MineJuly 9, 2013