2018-10-24_PERMIT FILE - C1982056A (2)

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Twentymile Mine railroad spur. The 6RT Thickener Underflow Borehole extends approximately 540 feet from the surface into the sealed EMD mine workings. An existing light -use road extends approximately 250 feet from RCR33 to this location. The 7RT Thickener Underflow Borehole installation will be located east of both the intersection of Routt County Roads 27 (RCR27) and 33 (RCR33) and the 6RT Borehole, on the north side of Foidel Creek and the Twentymile Mine railroad spur. The 7RT Thickener Underflow Borehole will extend approximately 850 feet from the surface into the sealed EMD mine workings. The 2MN Thickener Underflow Borehole installation will be located near the north edge of the existing Mine Facilities Area, between the existing Weld Shop and the Twentymile Railroad Spur and will be accessed by a short (550 feet) access road from the existing mine road. The 2MN Thickener Underflow Borehole will extend approximately 150 feet from the surface into the existing active 2MN No. 6 Mine Entry. From this location, the coal slurry will be piped underground approximately 2,650 feet and 3,850 feet, respectively, to horizontal boreholes into the sealed 7 -Right and 8 -Right Panels in the Eastern Mining District (EMD). An additional thickener underflow borehole was added in the WMD in 2017. The 12 -Left Thickener Underflow Borehole is located off RCR27 just east of the intersection with County Road 37 on the north side of the road. The borehole will extend into the WMD mine workings approximately 1,260 feet in the 12 Left Irby Panel. In 2018 four additional borehole locations were proposed and permitted in the WMD in panels 14, 15, 16, and 17. All four locations are along County Road 27 with 14 -Left and 15 -Left on the East side and 16 -Left and 17 -Left on the west side, all are within 700 feet of County Road 27. All boreholes will be drilled into the inby panel of their associated panel, the depths are 1,370 feet, 1381 feet, 1408 feet, and 1405 feet respectively. Three additional thickener underflow boreholes will be added in the SWMD in 2016 and 2017. The SWMD Thickener Underflow Borehole will be located near the Fish Creek Borehole road where it joins RCR27. Two alternate borehole locations have been identified, only one of which will be initially constructed and developed. The first location 1 (in Panel 2SW) is located on the west side of RCR27 between the west mine entrance and the Fish Creek Borehole road, and has been selected for construction. The second location (in Panel 1SW) is located on the east side of RCR27 and will be accessed from the Fish Creek Borehole road this location was an alternative and will not be constructed at this time but may be a potential site in the future. The SWMD Thickener Underflow Borehole in 2SW will extend from the surface into the sealed SWMD mine workings a maximum of approximately 750 feet. TC also plans a test borehole (Sandstone Sub Test Borehole) to evaluate conditions in the 3SW Gateroad (WMD) for a future thickener underflow borehole. The test hole will be located on the existing Sandstone Substation pad, and will be directionally drilled to intersect the 3SW Gateroad at a depth of approximately 420 -feet. If conditions in this area are favorable, TC will convert the test borehole to a thickener underflow borehole, which will involve boring the test hole out to 22 to 24 inches for the surface casing and 12 to 15 inches for the finished borehole, setting and cementing a 16 to 18 inch surface casing to a depth of approximately 60 feet, setting and cementing a 8 to 11 inch borehole casing to a depth of approximately 420 feet, and setting an 8 -foot covered CMP manhole with lightening protection in-place to protect the well -head. The third borehole will extend approximately 1,060 feet into the 1SW Panel, at a location north of the sandstone cliffs adjacent to the Twentymile Facilities in the SWMD. This borehole will be accessed from the existing ranch road which is used to access the Union Cellular tower from the Fish Creek Road. Minor road improvements to provide for year-round access will include limited grading, placement of water - bars and minor work on the existing ditches, and placement of gravel surfacing materials. In order for the thickener underflow to reach the 1 SW and the 12, 14, 15, 16, & 17 -Left thickener underflow boreholes, a pump boost station was installed at the 2SW borehole pad location. The pump boost station will consist of a one -foot thick, 20 x 20 foot concrete pad, a pre -fabricated pump building, the booster pump and piping connections, and a drop -line from a nearby power -pole with electrical connections and pump controls. At each of these locations (except the Sandstone Sub location, where a pad already exists), a drill -pad and required drainage structures were or will be constructed. Buried thickener underflow pipelines have been or will be installed between the existing washplant facilities and the thickener underflow boreholes. The locations of the thickener underflow boreholes and the associated pipelines are shown on the Surface Facilities and Freshwater Systems Map, Map 24 (1/4). Design information for the thickener underflow boreholes and pipelines is provided in Exhibits 49K and 49S. Installation of the thickener underflow boreholes generally involves placement of construction erosion controls (silt fence and/or straw wattles), removal and windrowing of available soil materials from pad areas and the road margins, construction of designed drainage structures (ditches and rock sumps), grading to establish level drill -pads TR18-90 2.05-84.6 04/05/18