2009-09-21_REVISION - C1981010 - Laserfiche WebLink

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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 - During the review for Permit Revision PR- 01, the Division raised the issue that any degradation of water quality in the Lux well, a well that is owned by one of Trapper's neighbors, could push the well's water quality beyond the secondary drinking water standards because the pre- mining quality of the well's water barely met those standards. Monitoring was required and has been incorporated into Trapper's groundwater monitoring plan. 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- mining levels as surface water infiltrates more easily into the subsurface which has been disaggregated by mining. The most noticeable change in surface water quality will likely be an increase in the levels of total dissolved solids (mainly calcium sulfate) contributed by springs that discharge from the mined-out pits that have been back-filled with spoil and from fill structures (K-Pit Buttress Fill and Horse Gulch Fill). Following reclamation, each spoil-filled pit and fill structure will likely develop a flowing spring on the ground surface at the down-slope end of the pit or fill. The pit or fill effluent that discharges from a spring will be composed of water that is rich in the minerals that are dissolved from the spoil which fill the mined-out pit or that was used to construct the fill. The effluent discharging from a spoil spring or fill spring will flow downslope to the nearest drainage channel. Trapper Mine 27 September 21, 2009