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With both Washplants I and II operating, the thickener underflow is typically a 15 to 25 percent solids, 300 to 550
<br />gpm slurry mixture of rock and coal fines (28 mesh x 0). Exhibit 9C, Underflow Chemical Characterization,
<br />provides data on selected chemical constituents found in the thickener underflow. The water quality of the slurry is
<br />consistent with that of typical spoils water generated at the adjacent CYCC surface mine. The slurry mixture is
<br />piped to the sealed mine workings in the EMD, where the fines settle -out, and the decant water flows to a sump and
<br />is recycled back to the washplants. At the full coal fines refuse discharge rate, approximately 1.6MM ft; of coal
<br />fines storage is required on an annual basis. The EMD has approximately 110MM ft3 of coal fines storage capacity
<br />remaining (approximately 70 -years capacity). In anticipation of future mining of the underlying Wolf Creek Coal
<br />Seam, TC shifted underground coal fines slurry placement to sealed mine workings in the Southwest Mining
<br />District (SWMD), which provides approximately 61MM ft3 of coal fines storage capacity (approximately 30 -years
<br />capacity). Map 23 shows the EMD, WMD and SWMD areas that have been or will be filled with fine refuse
<br />material.
<br />With the addition of thickener underflow boreholes at the 6RT, 7RT, 2MN, 12, 14, 15, 16, & 17 -Left, and SWMD
<br />locations, it will be possible to pump the fine coal refuse slurry from the washplants through the
<br />1MN/SWMD/WMD or the 2MN/6RT/7RT pipelines to the corresponding boreholes. The 1MN/SWMD/WMD
<br />pipeline consists of two 6 -inch HDPE pipelines extending approximately 1,800 feet to an 8 -inch cased mine
<br />borehole, located near the former CYCC Mine Office Building ("Brown Palace", see Map 24 for location of
<br />pipeline and borehole). The two thickener underflow pipelines replace the previously used 6 -inch PVC line from
<br />Washplant I, which was cut-off, capped, and abandoned in-place. The approximately 7,130 foot original SWMD
<br />pipeline will connect to the existing 1MN pipeline and extend to 2SW, plus an additional 2,800 foot pipeline to
<br />1 SW borehole. The WMD pipeline tees off the SWMD pipeline and the pipeline will parallel RCR27 for an
<br />additional 5,800 feet, extending to the northwest, crossing under Fish Creek, and then a tee will be installed to route
<br />the thickener either 1,940 feet to the 12 -Left borehole or 7,245 feet through 14, 15, and 16 -Left boreholes on to the
<br />17 -Left borehole. A boost station will be on the 2SW Borehole pad to provide sufficient pumping capacity to
<br />efficiently move the coal fines slurry through the pipeline network to reach all of the designated locations (1 SW,
<br />12, 14, 15, 16 and 17 -Left) allowing TC to re-route the slurry if needed. The 6RT/7RT/2MN pipeline will extend
<br />approximately 9,600 feet to 7RT. All of the newer (installed subsequent to the 1MN pipeline) pipeline installations
<br />will be a double HDPE pipe system, with a 6 to 8 inch carrier pipe inside a larger (maximum size - 12 -inch
<br />diameter) containment pipe. Electronic moisture sensors, along with pump controls, and shut-off valves will provide
<br />for timely detection, shut-off, and isolation of the pipeline in the event of pipeline leakage. Access/inspection
<br />manholes will be located at key points along the pipeline routes. The pipelines will be buried at a depth of
<br />approximately 5 feet and traverse both previously disturbed and un -disturbed areas. Installation of the thickener
<br />underflow pipelines typically involves:
<br />• Placement of temporary BMP's for drainage and sediment control from pipeline and construction areas
<br />• Removal and windrowing of soils materials from any new disturbance areas
<br />• Excavation of the pipeline trench, with temporary placement of excavated material adjacent to the trench
<br />• Excavation of boring/jacking pits on the edge of Haulroad B-2 and an existing drainage ditch on the north
<br />side of the existing railroad spur (as shown on Figure 49K -F1) and boring/jacking of 24 -inch secondary
<br />containment culvert under existing Foidel Creek road„Fish Creek, Fish Creek Tributary, Foidel Creek, and
<br />the railroad spur
<br />• Bedding and placement of the thickener underflow pipelines (carrier and containment system) in the trench,
<br />and installation of intermediate access/monitoring manhole(s)
<br />• Installation of moisture sensors, and connection of the pipelines to the thickener underflow systems from
<br />the Washplant I and II Thickeners, along with associated pump controls and shut-off valves, and pressure
<br />testing of the pipeline
<br />• Controlled backfilling and compaction of excavated material in the trench
<br />• Surface grading, soil material replacement, seeding with TCC's temporary stabilization seed mixture, and
<br />placement of temporary BMPs to control runoff and erosion until vegetation was reestablished for all
<br />project disturbance areas
<br />The thickener underflow borehole surface casings extend approximately 4 feet above grade, and are capped and
<br />locked. The borehole casing range anywhere between 310 feet to 1408 feet into the sealed and abandoned mine
<br />TRI 8-90 2.05-97.7 04/05/18
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