2014-10-15_PERMIT FILE - C1982056A (7)

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(b) Each plan shall describe the source and quality of waste to be stored area to be backfilled percent of the mine void to be filled method of constructing ground retaining walls, influence of the backfilling operation on active underground mine operations surface area to be supported by the backfill and the anticipated occurrence of surface effects following backfilling. (c) The applicant shall describe the source of hydraulic transport medium method of dewatering the placed backfill retainment of water underground treatment of water if released to surface streams, and the effect on the hydrologic re i (d) The plan shall describe each permanent monitoring well to be located in the backfilled area the stratum underlying the mined coal, and gradient from the backfilled area. (e) The requirements of 2.05.3 shall also apply to pneumatic backfilling_ operations, except where the operations are exempted by the Division from requirements specifying hydrologic monitoring I: D.YZ�J�6YJ TC returns the thickener underflow generated at both Washplants I and II to the abandoned and sealed underground mine workings. When Washplant I initially began operations, the thickener underflow was partially dewatered using a filter- press, and this material was then combined with the coarse refuse and hauled to the Refuse Pile for placement. Due to handling and placement problems, TC modified the fine refuse handling method, and began pumping the thickener underflow into the abandoned mine workings in the Eastern Mining District (EMD), as opposed to mixing it with the coarse refuse for placement on the Refuse Pile. 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 was historically piped to the sealed mine workings in the EMD, where the fines would settle -out, and the decant water would flow to a sump and be 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 I OMM ft3 of coal fines storage capacity remaining (approximately 70 -years capacity). In anticipation of possible 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 61MM ft3 of coal fines storage capacity (approximately 30 -years capacity). Map 23 shows the EMD and SMD areas that have been or will be filled with fine refuse material. With the addition of new thickener underflow boreholes at the 6RT and 7RT locations, it will be possible to pump the fine coal refuse slurry from the washplants through either the 1MN or the 6RT /7RT pipelines to the corresponding boreholes. The IRT 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. The 6RT /7RT pipeline will be a double HDPE pipe system in critical areas, with a 6.625 -inch carrier pipe inside a larger (maximum size - 12 -inch diameter) containment pipe, extending approximately 9,600 feet. 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 two thickener underflow pipelines involved: • Placement of temporary BMP's for drainage and sediment control for pipeline and borehole construction areas • Removal and windrowing or stockpiling of soils materials from any new disturbance areas • Grading of the drill -pads for the thickener underflow boreholes MR13 -270 2.05 -97.3 11/06/13