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Twentymile Mine railroad spur. The 6RT Thickener Underflow Borehole extends approximately 540 feet from the <br />surface into the sealed EMD mine workings. An existing light -use road extends approximately 250 feet from RCR33 <br />to this location. The 7RT Thickener Underflow Borehole installation will be located east of both the intersection of <br />Routt County Roads 27 (RCR27) and 33 (RCR33) and the 6RT Borehole, on the north side of Foidel Creek and the <br />Twentymile Mine railroad spur. The 7RT Thickener Underflow Borehole will extend approximately 850 feet from <br />the surface into the sealed EMD mine workings. The 2MN Thickener Underflow Borehole installation will be located <br />near the north edge of the existing Mine Facilities Area, between the existing Weld Shop and the Twentymile Railroad <br />Spic- and will be accessed by a short (550 feet) access road from the existing mine road. The 2MN Thickener <br />Underflow Borehole will extend approximately 150 feet from the surface into the existing active 21VIN No. 6 Mine <br />Entry. From this location, the coal slung will be piped underground approximately 2,650 feet and 3,850 feet, <br />respectively, to horizontal boreholes into the sealed 7 -Right and 8 -Right Panels in the Eastern Mining District (EMD). <br />Two additional thickener underflow boreholes will be added in the SWMD in 2016 and 2017. The SWMD Thickener <br />Underflow Borehole will be located near the Fish Creek Borehole road where it joins RCR27. Two alternate borehole <br />locations have been identified, only one of which will be constructed and developed. Tile first location I (in Panel <br />2SW) is located on the west side of RCR27 between the west entrance and the Fish Creek Borehole road, and has <br />been selected for construction. The second location (in Panel 1 SW) is located on the east side of RCR27 and would <br />be accessed from the Fish Creek Borehole road. The additional SWMD Thickener Underflow Borehole will extend <br />fi-om the surface into the sealed SWMD mine workings a maximum of approximately 850 feet. TC also plans a test <br />borehole (Sandstone Sub Test Borehole) to evaluate conditions in the 3SW Gateroad (WMD) for a future thickener <br />underflow borehole. The test hole will be located on the existing Sandstone Substation pad, and will be directionally <br />drilled to intersect the 3SW Gateroad at a depth of approximately 420 -feet. If conditions in this area are favorable, TC <br />will convert the test borehole to a thickener underflow borehole, which will involve boring the test hole out to 22 to <br />24 inches for the surface casing and 12 to 15 inches for the finished borehole, setting and cementing a 16 to 18 inch <br />surface casing to a depth of approximately 60 feet, setting and cementing a 8 to 11 inch borehole casing to a depth <br />of approximately 420 feet, and setting an 8 -foot covered CMP manhole with lightening protection in-place to <br />protect the well -head. <br />At each of these locations (except the Sandstone Sub location, where a pad already exists), a drill -pad and required <br />drainage structures were or will be constructed. Buried thickener underflow pipelines have been or will be installed <br />between the existing washplant facilities and the thickener underflow boreholes. The locations of both the thickener <br />underflow boreholes and the associated pipelines are shown on the Surface Facilities and Freshwater Systems Map, <br />Map 24 (1/4). Design information for the thickener underflow boreholes and pipelines is provided in Exhibits 49K and <br />49S. <br />Installation of the thickener underflow boreholes generally involves placement of construction erosion controls (silt <br />fence and/or straw wattles), removal and windrowing of available soil materials from pad areas and the road <br />margins, grading to establish level drill -pads and construct or improve roads, placement of gravel as surfacing for the <br />light -use road, excavation of temporary cuttings pits on the drill -pads, drilling and casing of the boreholes, and <br />installation of protective access manholes. On completion of drilling and casing operations, the cuttings pits are <br />allowed to dry -out, material excavated from the pits is replaced and graded, and the pad surface is graveled to control <br />erosion and sediment and provide an all-weather operating surface. The completed thickener underflow borehole <br />installations include light -use road access, one or more soil material stockpiles (pad and road); the drill -pad (I MN — <br />25 x 180 feet, 6RT- 70 x 70 feet, 7RT — 100 x 75 feet, 2MN — 75 x 75 feet, 1 SWMD -- 250 x 170 feet max., <br />Sandstone Sub — 75 x 75 feet); the 6- to 12 -inch cased boreholes, 16 to 18 -inch cemented surface casings, and covered <br />8 -foot diameter CMP culvert manholes with lightning protection. The Sandstone Sub Borehole, because it will be <br />completed on the existing substation pad, will not require soil handling, an access road, pad construction, or surface <br />casing or a manhole, and drainage will be contained on the pad by a constructed berm. <br />With timing and weather constraints, portions of the pipeline may be temporarily installed on the surface, to be <br />buried when ground conditions are more favorable. Pipeline installation will involve removal and windrowing of <br />soil materials from the pipeline construction corridor (maximum - 40 -foot wide); trenching in most areas: <br />placement of suitable bedding materials; placement, connection, and pressure testing of the pipelines; backfilling <br />and compaction of suitable fill materials around and over the pipelines; backfilling and compaction of the trench; <br />regrading; replacement of soil materials; and revegetation of all disturbed areas. Where the pipelines pass under <br />RCR27. the Twentymile Mine railroad spur, and Foidel Creek, the pipeline trench will be expanded to provide <br />TR 17-87 2.05-84.6 03/14/17 <br />