2009-05-22_GENERAL DOCUMENTS - C1981044

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12) The No. 9 Mine will not refill to the surface, but will refill to an equilibrium level between the Twentymile Sandstone and the overlying White Sandstone. 13) The No. 9 Mine portal backfill area is too small to generate enough leachate to have a measurable effect on nearby aquifers. Observed Hydrologic Impacts The monitoring plan contained in the permit application has been designed to verify the permittee's projected hydrologic impacts of mining. Section 2.05 of the permit application includes a description of the observed hydrologic impacts caused by mining at the Eagle Mine Complex. Each year BTU EC assesses the on-going impacts to the hydrologic system in its annual hydrologic report. Observed impacts are summarized below. Observed Ground Water Impacts Mine Inflows and Discharges Water is pumped from the underground mine workings to the ground surface at the No. 5 Mine well and the 7 North Angle well. Annual hydrology reports show the total discharge for the 5 and 6 Mines was a fairly constant 600 gpm during active mining in the early 1990s. After mining ceased in 1995, sumped water was pumped down. In 1997 and 1998, pumping became intermittent, averaging less than 1 gpm. In 2008, pumping was approaching an average annual rate of 1,100 gpm. The pumped mine water is discharged to the Williams Fork River at NPDES outfalls 003 (5 Mine well) and 024 (7 North Angle well). A total of more than 630 million gallons of water were discharged in the most recent reporting year, 2008. Monitoring data through 2008 collected at the outfalls indicate the mine water is consistently alkaline, with total dissolved solids less than 1800 mg/l, and low concentrations of iron and manganese. Trout Creek Sandstone Annual hydrology reports as recent as 2008 indicate no continuing mining-caused change in the Trout Creek Sandstone potentiometric surface or water quality. The water level in the Trout Creek Sandstone monitoring well (No. 5 Mine well) dropped 200 ft. during 1989 and 1990. The drop probably was caused by pumping of the three mine water supply wells completed in the Trout Creek, rather than by mining in the overlying E and F coal seams. The water level fully recovered in 1991 and then fluctuated 200 ft. in 1998. The fluctuation is probably not related to dewatering in the overlying E and F seams because the base of the E coal seam is above the current water level in the No. 5 Mine well. The water level in the No. 5 well stabilized in 1999 through 2000. Monitoring of the well was suspended in 2001 through 2003 as part of the temporary cessation monitoring plan. Since monitoring was resumed the water level has remained relatively stable. Historical field conductivity data for the Trout Creek Sandstone wells indicate no adverse water quality impacts related to mining. Eagle Mine Complex 24 Permit Renewal 05 C-1981-044 May 22, 2009