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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 />Spur and will be accessed by a short (550 feet) access road from the existing mine road. The Thickener Underflow
<br />Borehole will extend approximately 150 feet from the surface into the existing active 2MN No. 6 Mine Entry. From
<br />this location, the coal slurry will be piped underground approximately 2,650 feet and 3,850 feet, respectively, to
<br />horizontal boreholes into the sealed 7 -Right and 8 -Right Panels in the Eastern Mining District (EMD).
<br />At each of these locations, a drill -pad and required drainage structures have been constructed. Buried thickener
<br />underflow pipelines have been or will be installed between the existing washplant facilities and the thickener
<br />underflow boreholes. The locations of both the thickener underflow boreholes and the associated pipelines are shown
<br />on the Surface Facilities and Freshwater Systems Map, Map 24 (1/4). Design information for the thickener underflow
<br />boreholes and pipelines is provided in Exhibits 49K and 495.
<br />Installation of the thickener underflow boreholes involves placement of construction erosion controls (silt fence and /or
<br />straw wattles), removal and windrowing of available soil materials from pad areas and the road margins (6RT
<br />Borehole only), minor fill placement (if required) and grading to establish level drill -pads and improve the existing
<br />light -use road (6Rt Borehole only), placement of gravel as surfacing for the light -use road, excavation of temporary
<br />cuttings pits on the drill -pads, drilling and casing of the boreholes, and installation of protective access manholes. On
<br />completion of drilling and casing operations, the cuttings pits are allowed to dry-out, material excavated from the pits
<br />is replaced and graded, and the pad surface is graveled to control erosion and sediment and provide an all- weatlier
<br />operating surface. The completed thickener underflow borehole installations include an access road, a soil material
<br />stockpile (pad and road); the drill -pad (1MN — 25 x 180 feet, 6RT- 70 x 70 feet, 7RT 100 x 75 feet, 2 -MN 75 x 75
<br />feet); the 6- to 12 -inch cased boreholes, 16 -inch cemented surface casings, and a covered 8 -foot diameter CMP culvert
<br />manholes with lightening protection.
<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 />room for horizontal boring equipment, and the pipelines will either be trenched or bored under these features.
<br />Because pipeline placement and construction of portions of the 6RT and 7RT pads will necessarily involve
<br />activities within the Foidel Creek buffer zone, TC is requesting a temporary variance for pipeline construction and a
<br />longer -term variance for the limited pad areas from the regulatory requirements for operations within a buffer zone.
<br />The pipelines will be a double HDPE pipe system in critical areas, with a 6 to 8 -inch carrier pipe inside a larger
<br />(maximum size - 12 -inch diameter) containment pipe, buried approximately 5 -feet deep. The 1MN pipeline will
<br />extend approximately 1,800 feet, with the 6RT pipeline extending approximately 8,000 feet, and continuing another
<br />1,600 feet to 7RT. The 6RT /7RT pipeline is immediately adjacent to the 2MN Borehole, so only a short connecting
<br />pipe was necessary. Electronic moisture sensors, along with pump controls, and shut -off valves will provide for
<br />timely detection, shut -off, and isolation of the pipeline in the event of pipeline leakage. Access /inspection manholes
<br />and pipe -tees for the moisture detection system will be located at key points along the pipeline routes.
<br />During construction, and for the minor surface structures that will remain during mining, drainage and sediment control
<br />will be provided by Alternative Sediment Controls (ASC's) consisting of combined Best Management Practice (BMP)
<br />measures. BMP's for the construction activities include:
<br />Minimizing the area of surface disturbance
<br />Scheduling of construction activities during the dry summer or early winter periods
<br />MR13 -273 2.05 -84.6 12/06/13
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