2020-06-24_REVISION - C1981035 (2)

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ENVIRONMENTAL ASSESSMENT If subsidence cracks damage any barbed wire fence within the permit area(a fencepost could be dislodged or strands of barbed wire could be stretched and break or sag), GCCE would repair the fences without charge to the UMU Tribe or would reimburse the UMU Tribe at reasonable costs for any necessary repairs. Potential impacts to structures from subsidence would be short to long term and negligible. Subsidence cracks do not rupture in such a way that the crack would represent an opening that a person or animal could fall into to any depth. Underground coal mining can result in subsidence of overlying rock. Cracks from subsidence extend upwards and can reach the surface. The hydrologic system, both surface and groundwater, could be altered by subsidence. Surface water conveyances could be physically altered by subsidence if elevation differentials result in grade changes and upland runoff patterns could be similarly altered. Subsidence- caused tension cracks could also result in loss of flow to or within these conveyances. Subsidence may locally affect surface soils through slight but non-uniform settling and development of tension cracks. Soil erosion has the potential for becoming accelerated in areas where surface runoff flows into the subsidence surface cracks. Subsidence may locally alter drainage patterns through slight but non-uniform settling and development of tension cracks. This could change infiltration, ponding, erosion/deposition, and runoff characteristics on a very small and local scale but would not be expected to have off-site impacts or otherwise affect streamflow or sediment regimes. Overtime,tension cracks would be likely to fill and seal, particularly in the areas where soils have substantial clay components and overly shale parent materials. Similarly, as small depressions collect runoff, conveyed sediments would deposit and overtime these depressions would fill, causing local topography to reach pre-subsidence uniformity. Cumulative Actions and Effects The CIAA for subsidence includes the Project Area, which includes the existing mine and the LBA where subsidence has the potential to occur. The cumulative impacts would be the removal of coal and minor amounts of possible subsequent subsidence. Approximately 17 mt of coal would be mined in the Project Area under the Proposed Action.This amount is approximately 0.018 percent of the estimated 9.61 billion tons(2006 estimate)in the San Juan Basin coal field.The level of coal production would depend on market demand for cement and associated coal as well as availability of economically recoverable coal reserves in the immediate area. Based on the unsuitability assessments (BLM 1985; SJNF 1983), 46,000 acres are identified as acceptable for further consideration for coal leasing within the TRFO, with an estimated reserve of 1.5 billion tons. Of this estimated reserve, it is unknown how much would reasonably be expected to be developed in the future. No other metal or mineral mines are likely to be developed in the CIAA that could result in subsidence. As such,the cumulative impacts of subsidence from these activities would be minor. Effects of Alternative B—No Action Alternative Direct and Indirect Effects Under the No Action Alternative, the LBA would not be offered for competitive lease sale by BLM, there would be no mining plan modification to be considered and approved by OSMRE and federal coal reserves in the LBA and new private reserves would not be recovered. Therefore, there would be no new subsidence impacts. Dunn Ranch Area Coal Lease by Application COC-78825 and Mine Plan Modification EA 3-32