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S <br />receiving stream standards. To further improve the water quality of the slurry water, <br />Basin Resources will change from sulfuric acid to hydrochloric acid in the thickener <br />process to reduce the dissolved metals in the slurry water. <br />Once the mine workings are flooded, the water quality of the mixed mine water is <br />expelled 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 benefits to the disposal of the coal fines underground. First, underground <br />disposal of coal fines will increase the stability of the coal refuse pile. Currently the coal <br />fines are disposed in the refuse pile. The fines often create disposal problems because <br />when they are recovered from the preparation plant, they are saturated and do not dry <br />well due to their fine-grained nature. In this state, the fines do not compact and create a <br />stability problem in the refuse pile if not handled properly. Second, underground <br />disposal of coal fines will extend the life of the coal refuse pile, reducing the immediacy <br />for the construction of a new disposal area. Third, underground disposal of the fines <br />may diminish the magnitude of subsidence in the mains. The filling of the void spaces <br />in the mains with coal fines will give some support to the roof if subsidence should <br />occur. <br />M:bSSlammMddendum.d ih <br />_z_ <br />