2013-01-29_PERMIT FILE - C1981010A

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permit area, A pit in the No Name, Johnson and East Pyeatt drainages, and A East pit in the Flume drainage. Trapper does not anticipate recharge to the shallow aquifer systems to be adversely affected by mining operations in the Third White Sandstone. Short term localized disruptions may occur with respect to the Third White Sandstone. However, Trapper predicts the post-mining recharge to this unit will equal or exceed the pre-mining rate due to the enhanced permeability associated with the backfill materials. Seasonal fluctuations in the recharge rate will exist similar to pre-mine variations. The Second White Sandstone projected outcrop lies to the north of the northernmost extent of the mine pits in the Pyeatt and Flume drainage areas of Trapper Mine. The Second White Sandstone is most likely recharged at its outcrop which, at its closest point, is found approximately 4000 feet down-gradient of the northern edge of planned mining in the Pyeatt drainage (see Map M32). Mining has very little potential to influence the groundwater system of the Second White Sandstone throughout the project area and should not decrease the quantity of water the Second White Sandstone yields to the Pyeatt shallow alluvial aquifer. This aquifer's recharge should not be affected by mining. Water levels in the Second White Sandstone in Pyeatt and Flume Gulches should not be affected by mining. If spoil springs develop at the north end of A pit near Pyeatt Gulch, mining could marginally increase the quantity of surface water flow available to recharge the Second White Sandstone. The additional quantity would be expected to be negligible. Aquifer Restoration: Restoration of the Upper Williams Fork aquifers that the mine will penetrate will be mainly governed by the permeability of the backfilled spoils in the mined areas. Radian (1981) measured a range in spoil permeabilities of 6.48 to 115.4 gpd/square foot. Tables 2.7-21 and 2.7-21b provide aquifer test summary information for a number of wells at Trapper. The spoil (backfill) aquifer permeabilities vary from 0.46 to 4.83 ft/day (see Table 2.7-21 b). These data indicate that the spoils will probably be more permeable than the existing aquifers. The spoil aquifer within each pit is likely to act as one aquifer system whereas pre- mine conditions are characterized by the function of several distinct aquifer units separated by confining beds or relatively impermeable layers. Spoil springs may develop in the bottoms of drainages at the down-gradient contact of spoils and non- mined areas. The spoil spring elevations will limit the buildup of water levels in the spoil aquifer in their area. The Trapper mine plan will enable spoil springs to occur at several locations on the north side of Ashmore Pit. Spoil Springs have not developed to date in the backfill of the Derringer and Enfield Pits 4-238 PO 01(2 (rJ