2013-12-13_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. At each of these locations, a drill -pad and required drainage structures have been constructed. Buried thickener underflow pipelines have been or will be installed between the existing washplant facilities and the thickener underflow boreholes. The locations of both 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 will involve 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 (6RT Borehole only), minor fill placement (if required) and grading to establish level drill -pads and improve the existing light -use road (6Rt Borehole only), placement of gravel as surfacing for the light -use road, excavation of temporary cuttings pits on the drill -pads, drilling and casing of the boreholes, and installation of protective access manholes. On completion of drilling and casing operations, the cuttings pits will be allowed to dry-out, material excavated from the pits will be replaced and graded, and the pad surface will be graveled to control erosion and sediment and provide an all- weather operating surface. The completed thickener underflow borehole installations will include the light -use road (6RT only), a soil material stockpile (pad and road); the drill -pad (1MN — 25 x 180 feet, 6RT- 70 x 70 feet, 7RT 100 x 75 feet); the 6- to 8 -inch cased boreholes, 16 -inch cemented surface casings, and a covered 8 -foot diameter CMP culvert manholes with lightening protection. With timing and weather constraints, portions of the pipeline may be temporarily installed on the surface, to be buried when ground conditions are more favorable. Pipeline installation will involve removal and windrowing of soil materials from the pipeline construction corridor (maximum - 40 -foot wide); trenching in most areas; placement of suitable bedding materials; placement, connection, and pressure testing of the pipelines; backfilling and compaction of suitable fill materials around and over the pipelines; backfilling and compaction of the trench; regrading; replacement of soil materials; and revegetation of all disturbed areas. Where the pipelines pass under RCR27, the Twentymile Mine railroad spur, and Foidel Creek, the pipeline trench will be expanded to provide room for horizontal boring equipment, and the pipelines will either be trenched or bored under these features. Because pipeline placement and construction of portions of the 6RT and 7RT pads will necessarily involve activities within the Foidel Creek buffer zone, TC is requesting a temporary variance for pipeline construction and a longer -term variance for the limited pad areas from the regulatory requirements for operations within a buffer zone. The pipelines will be a double HDPE pipe system in critical areas, with a 6 to 8 -inch carrier pipe inside a larger (maximum size - 12 -inch diameter) containment pipe, buried approximately 5 -feet deep. The 1MN pipeline will extend approximately 1,800 feet, with the 6RT pipeline extending approximately 8,000 feet, and continuing another 1,600 feet to 7RT. 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 and pipe -tees for the moisture detection system will be located at key points along the pipeline routes. During construction, and for the minor surface structures that will remain during mining, drainage and sediment control will be provided by Alternative Sediment Controls (ASC's) consisting of combined Best Management Practice (BMP) measures. BMP's for the construction activities include: • Minimizing the area of surface disturbance • Scheduling of construction activities during the dry summer or early winter periods • Placement of staked straw wattles downgradient of all surface disturbance areas to intercept any surface runoff and trap associated suspended solids • Installation of the Foidel Creek, RCR27, and railroad spur pipeline crossings as either trenched or bored /jacked pipeline crossings under Foidel Creek, RCR27 and the railroad spur (if trenched, TC will obtain required CDPHE -WQCD Temporary Construction Discharge Permit and will complete required USACE notification • Soil replacement and stabilization with either the standard rangeland or riparian seed mixtures (as appropriate) in a timely manner following completion of construction activities MR13 -270 2.05 -84.6 11/21/13