2020-08-20_PERMIT FILE - C1980007A

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data, a detailed assessment of mining impacts of the past water year as well as potential mining impacts for the upcoming water year. Until the AHRs are submitted each year, copies of all raw monitoring data for the previous water year are maintained on file at Mountain Coal Company's offices. To date, there has been no historical evidence that coal mining has affected stream flows or the water chemistry of springs and groundwater. Except for shallow groundwater systems, which may be impacted by the refuse piles, the potential for coal mining to affect the chemical character of groundwater discharges is extremely low. Mining induced water level changes have been observed in some F, E, and B seam monitoring well hydrographs; however, these changes have not corresponded with influxes of water into mine workings. No chemical abnormalities, which can be attributed to mining, were observed in the historical monitoring data and there is no reason to anticipate that mining will affect water quality in the future. Monitoring has also shown that groundwater systems in the Rollins Sandstone are not areally extensive and are not in hydrodynamic communication with each other (localized in fractures) and as such, the Rollins Sandstone is not an aquifer. As could be expected, there are no users of Rollins Sandstone water in the vicinity of the mine. Mitigation of Hydrologic Impacts The F seam pillar retreat mining and B Seam longwall mining caused subsidence in the North Fork of the Gunnison River drainage basin after mining occurred. The E seam and B seam longwall mining has and will cause subsidence in the Minnesota Creek drainage basin. The impacts of subsidence with respect to hydrology have been and are expected to continue to be minimal. Adjudicated water augmentation plans, replacement water rights and surface and in -mine storage rights have been established to aid in mitigating water losses that have resulted from mining subsidence and mitigate any impacts to other adjudicated water rights. To date, mining has not required water rights mitigations or implementation of the water augmentation plan as described below. Water that may be encountered during mining that requires discharge will be pumped from the mine to the approved NPDES/CDPS discharge points at the mine water treatment ponds (outfall 017) or Pond MB -5E (outfall 004/009). Mine water quality can be treated in these ponds if necessary prior to being discharged in compliance with CDPS permit requirements. Groundwater that is intercepted in the F seam mine near the Sylvester Gulch fan is of sufficient quality to discharge directly to the receiving water in Sylvester Gulch (outfall 011). MCC's water withdrawals from the North Fork of the Gunnison River for the mine's uses are not expected to cause any impact since they are a small percentage of stream flow even during low flow conditions. MCC also leases augmentation water to replace the amount of all water pumped for use by the mine during periods of time (typically June through October) when senior water rights place a call on the river water, causing all junior water rights without augmentation water to cease pumping or diversions. This period of call, as well as augmentation water flows, is administered by the local Water Commissioner of the Colorado Division of Water Resources. 2.05-72 Rev. 11/96- PR07, 04/06 -PRIG; 12/14- TR136, 08/16-TR139, 08/18- PR15