2010-06-08_PERMIT FILE - C1982056A (2)

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completed from the same pad used for the original borehole. The 6RT Thickener Underflow Borehole installation will be located southeast of the intersection of Routt County Roads 27 (RCR27) and 33 (RCR33), on the north side of Foidel Creek and the Twentymile Mine railroad spur. The Thickener Underflow Borehole will extend • approximately 540 from the surface into the sealed EMD mine workings. An existing light -use road extends approximately 250 feet from RCR33 to this location. At both locations, a drill -pad and required drainage structures will be constructed. Buried thickener underflow pipelines will be installed between the existing washplant facilities and the two 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). 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), 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. General drilling and completion practices will involve drilling a nominal 14.75 -inch drillhole, and placing and grouting a 14 -inch maximum diameter (O.D.) steel surface casing to bedrock. A nominal 6.25 -inch pilot hole will then be drilled within the surface casing to within 15 feet above the targeted surveyed mine entry. The pilot hole will then be rearried to a nominal 11 -inch diameter, and 8 -inch I.D. casing will be placed and grouted in the borehole, as a carrier pipe for the thickener underflow slurry. While the mine is evacuated (MSHA requirement), the borehole will be completed into the sealed and abandoned mine workings. Given problems with the original casing in the 1Ml\l Borehole, TC plans to install either a high- strength, abrasion/corrosion resistance casing in the 1MN Replacement Borehole or a wear liner, cap all monitoring stand - pipes, incorporate provision for controlled drainage and containment of any accumulated fluids in the secondary containment pipe, and implement a regular borehole and pipeline inspection program. 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); the 6 -inch cased boreholes, 14 -inch cemented surface casings, and a covered 8 -foot diameter CMP culvert manholes with lightening protection. 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 be bored under these features. Because pipeline placement will necessarily involve activities within the Foidel Creek buffer zone, TCC is requesting a temporary variance 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 - 10 -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. 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 MR10243 2.05 -84.6 05/31/10