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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
<br /> slurry mixture of rock and coal fines (28 mesh x 0). Exhibit 9C, Underflow Chemical Characterization, provides data
<br /> on selected chemical constituents found in the thickener underflow. The water quality of the slurry is consistent with
<br /> that of typical spoils water generated at the adjacent CYCC surface mine. The slurry mixture is piped to the sealed mine
<br /> workings in the EMD, where the fines settle-out, and the decant water flows to a sump and is recycled back to the
<br /> washplants. At the full coal fines refuse discharge rate,approximately 1.6MM ft3 of coal fines storage is required on an
<br /> annual basis. The EMD has approximately 110MM ft3 of coal fines storage capacity remaining(approximately 70-years
<br /> capacity). In anticipation of future mining of the underlying Wolf Creek Coal Seam,TC shifted underground coal fines
<br /> slurry placement to sealed mine workings in the Southwest Mining District (SWMD), which provides approximately
<br /> 61MM ft3 of coal fines storage capacity(approximately 30-years capacity). Map 23 shows the EMD,WMD and SWMD
<br /> areas that have been or will be filled with fine refuse 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 1MN/SWMD/WMD or
<br /> the 2MN/6RT/7RT pipelines to the corresponding boreholes. The 1MN/SWMD/WMD pipeline consists of two 6-inch
<br /> HDPE pipelines extending approximately 1,800 feet to an 8-inch cased mine borehole, located near the former CYCC
<br /> Mine Office Building("Brown Palace", see Map 24 for location of pipeline and borehole). The two thickener underflow
<br /> pipelines replace the previously used 6-inch PVC line from Washplant I,which was cut-off, capped, and abandoned in-
<br /> place. The approximately 7,130 foot original SWMD pipeline will connect to the existing 1MN pipeline and extend to
<br /> 2SW,plus an additional 2,800 foot pipeline to 1 SW borehole. The WMD pipeline tees off the SWMD pipeline and the
<br /> pipeline will parallel RCR27 for an additional 5,800 feet, extending to the northwest, crossing under Fish Creek, and
<br /> then a tee will be installed to route the thickener either 1,940 feet to the 12-Left borehole or 7,245 feet through 14, 15,
<br /> and 16-Left boreholes on to the 17-Left borehole. A boost station was placed on the 2SW Borehole pad to provide
<br /> sufficient pumping capacity to efficiently move the coal fines slurry through the pipeline network to reach all of the
<br /> designated locations (I SW, 12, 14, 15, 16 and 17-Left) allowing TC to re-route the slurry if needed. A 10' X 18' pre-
<br /> fabricated master control building and an 18' X 32' addition will be added to the existing pump station building to house
<br /> an additional pump system to assist the second pipeline. The 6RT/7RT/2MN pipeline will extend approximately 9,600
<br /> feet to 7RT. All of the newer(installed subsequent to the 1 MN pipeline)pipeline installations will be a double HDPE
<br /> pipe system, with a 6 to 8 inch carrier pipe inside a larger (maximum size - 12-inch diameter) containment pipe.
<br /> Electronic moisture sensors,along with pump controls,and shut-off valves will provide for timely detection, shut-off,and
<br /> isolation of the pipeline in the event of pipeline leakage. Access/inspection manholes will be located at key points along
<br /> the pipeline routes. The pipelines will be buried at a depth of approximately 5 feet and traverse both previously disturbed
<br /> and un-disturbed areas. Installation of the thickener 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 side
<br /> of the existing railroad spur(as shown on Figure 49K-F 1)and boring/j acking of 24-inch secondary containment
<br /> culvert under existing Foidel Creek road„Fish Creek,Fish Creek Tributary,Foidel Creek, and the railroad spur
<br /> • Bedding and placement of the thickener underflow pipelines(carrier and containment system)in the trench,and
<br /> installation of intermediate access/monitoring manhole(s)
<br /> • Installation of moisture sensors, and connection of the pipelines to the thickener underflow systems from the
<br /> Washplant I and II Thickeners,along with associated pump controls and shut-off valves,and pressure testing of
<br /> 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 project
<br /> 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 /> MR19-312 2.05-97.7 03/11/19
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