2024-03-12_REVISION - C1981022 (18)

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I. Stream Buffer Zones 1. The Division has approved surface and underground mining activities within 100 feet or through perennial streams. This decision was based on a finding that on Hubbard Creek, the original stream channel will be restored, water quality and quantity shall not be adversely affected, and appropriate riparian vegetation will be reestablished. On the North Fork of the Gunnison, the decision was based on the fact that the original stream channel would not be affected, and water quality and quantity would not be adversely affected. The buffer zone variance was granted for the areas located at the stream crossing and pre-law bench area at the lower Hubbard Creek site and the topsoil stockpile at the upper Hubbard Creek site. The buffer zone variances on the North Fork of the Gunnison are located at the alluvial well and leach fields just above and below the town of Somerset [4.05.18(1)]. K. Probable Hydrologic Consequences This section reviews the Probable Hydrologic Consequences (PHC) of mining at the Somerset Mine, Sanborn Creek, and Elk Creek Mine locations. The review includes the probable consequences which will result from the three mines. The Cumulative Hydrologic Impact Assessment(CHIA)for the North Fork of the Gunnison River contains a detailed analysis of the cumulative impacts of all currently permitted mine activities within the North Fork of the Gunnison River drainage basin. The CHIA document is available for review at the Division office. This PHC is based upon information contained within the PAP for Permit No. C-1981-022 (Somerset Mine, Sanborn Creek Mine, and Elk Creek Mine) and upon the analyses contained within the CHIA for the North Fork Gunnison River. The PHC separately addresses potential effects on groundwater and surface water. 1. Effects on Groundwater Mining of the Elk Creek Mine will have some impact on the groundwater regime within the immediate area of the proposed operation, but, as with the Somerset and Sanborn Creek Mines, the impact will not cause material damage to the ground water regime. Though the Sanborn Creek operation mined both the B and C seams that had been mined before at the old Somerset Mine, the Sanborn Creek Mine was not connected to the old workings and was protected by a 100-foot buffer. The old Somerset mine is thought to be flooded and that buffer was apparently successful in protecting the newer operation from inundation from the old workings. The 100-foot buffer was maintained by advance drilling to find the location of the old workings. Mine water inflow into the Sanborn Creek workings is estimated to be 425 gpm or less. The old Somerset Mine had an inflow rate of 0.15667 gpm/acre 26