2016-12-23_PERMIT FILE - C1982056A (3)

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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 gpm slurry mixture of rock and coal fines (28 mesh x 0). Exhibit 9C, Underflow Chemical Characterization, provides data on selected chemical constituents found in the thickener underflow. The water quality of the slurry is consistent with that of typical spoils water generated at the adjacent CYCC surface mine. The slurry mixture is piped to the sealed mine workings in the EMD, where the fines settle -out, and the decant water flows to a sump and is recycled back to the washplants. At the full coal fines refuse discharge rate, approximately 1.6MM ft3 of coal fines storage is required on an annual basis. The EMD has approximately 1 l OMM ft3 of coal fines storage capacity remaining (approximately 70 -years capacity). In anticipation of future mining of the underlying Wolf Creek Coal Seam, TC shifted underground coal fines slurry placement to sealed mine workings in the Southwest Mining District (SWMD), which provides approximately 61 MM ft3 of coal fines storage capacity (approximately 30 -years capacity). Map 23 shows the EMD and SWMD areas that have been or will be filled with fine refuse material. With the addition of new thickener underflow boreholes at the 6RT, 7RT, 2MN, and SWMD locations, it will be possible to pump the fine coal refuse slurry from the washplants through the 1MN/SWMD or the 2MN/6RT/7RT pipelines to the corresponding boreholes. The 1 MN/SWMD pipeline consists of two 6 -inch HDPE pipelines extending approximately 1,800 feet to an 8 -inch cased mine borehole, located near the former CYCC Mine Office Building ("Brown Palace", see Map 24 for location of pipeline and borehole). The two Thickener Underflow Pipelines replace the previously used 6 -inch PVC line from Washplant I, which was cut-off, capped, and abandoned in-place. Tile approximately 7,700 foot SWMD pipeline will connect to the existing 1MN pipeline. The 6RT/7RT/2MN pipeline will extend approximately 9,600 feet to 7RT. All of the newer (installed subsequent to the 1 MN pipeline) pipeline installations will be a double HDPE pipe system in critical areas, with a 6 to 8 inch carrier pipe inside a larger (maximum size - 12 -inch diameter) containment pipe. Electronic moisture sensors, along with pump controls, and shut-off valves will provide for timely detection, shut-off, and isolation of the pipeline in the event of pipeline leakage. Access/inspection manholes will be located at key points along the pipeline routes. The pipelines will be buried at a depth of approximately 5 feet and traverse both previously disturbed and un -disturbed areas. Installation of the thickener underflow pipelines typically involves: • Placement of temporary BMP's for drainage and sediment control from pipeline and construction areas • Removal and windrowing of soils materials from any new disturbance areas • Excavation of the pipeline trench, with temporary placement of excavated material adjacent to the trench • Excavation of boring/jacking pits on the edge of Haulroad B-2 and an existing drainage ditch on the north side of the existing railroad spur (as shown on Figure 49K -FI) and boring/jacking of 24 -inch secondary containment culvert under existing Foidel Creek road crossing culverts and railroad spur • Bedding and placement of the thickener underflow pipelines (carrier and containment system) in the trench, and installation of intermediate access/monitoring manhole(s) • Installation of moisture sensors, and connection of the pipelines to the thickener underflow systems from the Washplant I and II Thickeners, along with associated pump controls and shut-off valves, and pressure testing of the pipeline • Controlled backfilling and compaction of excavated material in the trench • Surface grading, soil material replacement, seeding with TCC's temporary stabilization seed mixture, and placement of temporary BMPs to control runoff and erosion until vegetation was reestablished for all project disturbance areas The thickener underflow borehole surface casings extend approximately 4 feet above grade, and are capped and locked. The borehole casing extends approximately 310 feet into sealed and abandoned mine workings into 1MN, 750 to 850 feet into the SWMD, and 510 feet into 6RT, 850 feet into 7RT, and 150 feet into 2MN, discharging on the mine floor, where the fines settle -out and the decant drains to the decant sumps, where submersible pumps recycle the water back to the surface. The water is retained by coal barriers, as shown on the underground mine workings map. The barriers for the refuse storage areas are minimum 250 -foot wide coal barriers between the EMD and the Northern Mining District, and the SWMD and the Western Mining District, respectively. These barriers currently retain accumulated water from mine inflows and contain a submersible pumps at the low points for mine dewatering. These pumps will be used to recycle water back to the surface for washplant make-up water or underground for dust suppression, or the TR16-86 2.05-97.7 09/02/16