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<br />the workings flood and the cone of depression flattens out. From monitoring of the coal <br />seam water level at other locations, the applicant estimated that water levels in the mine <br />will recover to an elevation approximatelyl0 feet below the East Portal. <br />If the mine were to discharge from the East Portal at the current rate of mine inflow, the <br />discharge would subsequently be diluted by the relatively large flow of the Purgatoire <br />River to levels below receiving stream standards for all constituents. To further improve <br />the water quality of the slurry water, the applicant will convert from sulfuric acid to <br />hydrochloric acid in the thickener process to reduce the dissolved metals in the slurry <br />water. <br />Once the mine workings are flooded, the water quality of the mixed mine water is <br />expected to meet the Colorado Water Quality Control Commissioner's Ground Water <br />Standards. The current water quality of the underground mine is used as the baseline <br />water quality, as pre-mining baseline water quality is not available from this 43-year-old <br />mine. <br />The slurry backfill operation has an estimated life of 5 years. Mine workings will be <br />monitored for water quality and recovery of the formation aquifer. Monitoring informa- <br />tion, backfill volumes, and water quality will be reported in the annual hydrology report. <br />The slurry backfill operation has been designed to minimize adverse impacts to the <br />hydrologic balance. <br />There will be a number of benefits resulting from disposal of coal fines underground. <br />First, underground disposal of coal fines will increase the stability of the coal refuse pile. <br />Currently the coal fines are disposed in the refuse pile. The fines often create disposal <br />problems because when they are recovered from the preparation plant, they are saturated <br />and do not dry well due to their fine-grained nature. In this state, the fines do not <br />compact and create a stability problem in the refuse pile if not handled properly. Second, <br />underground disposal of coal fines will extend the life of the coal refuse pile, reducing the <br />immediacy for construction of a new disposal area. Third, underground disposal of the <br />fines may diminish the magnitude of subsidence, if any were to occur, in the mains. The <br />filling of the void spaces in the mains with coal fines will give some support to the roof if <br />subsidence should occur. <br />Due to the continuing use of most of the surface facilities, much of the disturbed area will <br />not be cleared of structures and reclaimed until the completion of mining. When actual <br />coal extraction ceased, the portals were temporarily sealed. Backfilling and final sealing <br />has not occurred at this time (February 19991. The bench areas will be graded to the <br />approximate original contour. The disturbed areas will be topsoiled to the extent topsoil is <br />available, then seeded and mulched to establish a vegetative cover of a variety consistent <br />with surrounding vegetation. The stream channel diversion of the Middle Fork of the <br />Purgatoire River, which was approved under Permit Revision #1, is permanent and will <br />remain as constructed. Monitoring has demonstrated that this work was successful and <br />the reconstructed channel is stable. <br />9 <br />