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RESPONSE <br />TCC is planning on returning the thickener underflow generated at the Prep Plant to the abandoned <br />• workings located in the Eastern Mining District. The location of the area to receive the underflow is shown <br />on Map 23. In the plant, the thickener underflow goes to a filter press for dewatering, and this material is <br />then combined with the course refuse and hauled to the refuse pile for placement. It is TCC's intent to <br />pump the thickener underflow into the abandoned mine works as opposed to mixing it with the course <br />refuse for placement in the refuse pile. The thickener underflow is typically a 25 percent solids (17.8 tons <br />per hour), 214 gallons per minute flow mixture of ash and coal fines (28 mesh x 0). The mixture would be <br />piped to the abandoned works located in the EMD, where the fines would settle out and the water would be <br />recycled back to the wash plant via the mine sump for settling. Map 24 shows where the water will be <br />pumped back outside and recycled to the plant. <br />The quality of the thickener underflow that will be piped to the underground workings is typically 25 <br />percent ash and 75 percent coal fines material (28 mesh x 0). Also, Exhibit 9C, Underflow Chemical <br />Chazacterization, provides data on selected chemical constituents found in the underflow. The underflow is <br />moved in a slurry, flowing approximately 214 gallons per minute. The water quality of the slurry is <br />consistent with that of typical spoils water generated at the adjacent CYCC surface mine. It is TCC's intent <br />that the water used to slurry the mixture underground will be recycled to the plant as make-up water. <br />Map 23 shows the area that will be filled with the refuse material over the next 20-year period. The percent <br />of the EMD abandoned workings that will contain these refuse fines, after the typical annual production for <br />a 20-year period, will be 1.63 percent. This is based on 25,000 tons of refuse fines generated per year and <br />600 million cubic feet of storage in the East Mine District (only assumes a 30-foot height in the gob area <br />and permeability of 25 percent). The source of hydraulic transport medium will be water from the <br />thickener underflow. The water/solids mixture will be piped from the wash plant through a 4-inch HDPE <br />pipeline underground for 1,800 feet to the old 4-inch mine water borehole, (see Map 24 for location of <br />• pipelines). The borehole pipe will then be connected to a 4-inch aluminum pipe on the mine floor for the <br />remaining 5,000 feet to the mine gob seal. The pipe will be connected to the existing drainpipe at the seal <br />where it will flow onto the mine floor behind the seals (gob side) and to the bottom of the gob azea. Map <br />23 shows the azea which will receive the underflow material. <br />The water/ solids mixture will be pumped behind the seals where the fines will settle out and the water will <br />travel to the submersible pump for dewatering back to the surface. The water is retained by the coal barrier <br />as shown on the underground mine workings map. <br />The retaining wall for this refuse storage area is a minimum 250-foot wide coal barrier between the EMD <br />and the Northern Mining District. This barrier currently holds mine inflow water and contains a <br />submersible pump at the low point for mine dewatering. This pump will be used to recycle water back to <br />the surface for wash plant make-up water or underground for dust suppression, or the water will be <br />discharged directly into Foidel Creek. TCC understands that before this water can be dischazged directly to <br />Foidel Creek, its existing dichazge pemut will have to be amended to allow for this activity. <br />The water recycling/discharging system required minor changes to the existing water distribution system. <br />Water pumped from the mine exits the mine at Site 109. From this point, the water is piped to the Area 1 <br />Pit where it is retained to allow for settling of sediments and aeration. A pump station has been installed <br />towazds the south end of the pit. Installation involved burying forty-foot beams under the road and <br />extending them over the pit. A platform was constructed on the beams extending over the pit. A <br />submersible pump, along with hosing and piping, is suspended from the platform into the pit. A winch <br />installed on the platform assists in setting the pump at the desired elevation. <br />The water pumped from the Area 1 Pit can go in one of three directions, or a combination of them: 1) Pit to <br />• Prep Plant; 2) Pit to mine water recycling line; and/or 3) Discharge to Foidel Creek. The water pumped <br />from the pit is piped over to a de-sander, located at an old well site. From this point it is piped to the Prep <br />Plant or piped over and tied into the existing mine water line. Aline has been installed from the de-sander <br />back to the pit so that the back-flush water can be returned to the pit. The location of the lines is shown on <br />TROS-49 2.05-97.3 09/22/05 <br />