2008-07-25_GENERAL DOCUMENTS - C1981010 (2)

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place to detect any ground water problems early-on so mitigative 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-' cm/sec (0.034 to 0.34 inches per day). Reclaimed spoils are expected to have an infiltration rate of 10-3 to 104 cm/sec (3.4 to 34 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. During the review for Permit Revision PR-01, the Division raised the issue that any degradation of water quality in a well that is owned by one of Trapper's neighbors, the Lux well, 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 sulfate) contributed by springs that discharge from the mined-out pits that have been back-filled with spoils. Following reclamation, each Trapper Mine 24 July 25, 2008