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abandoned mine workings in the SWMD. The 6RT Thickener Underflow Borehole installation will be located <br />southeast of the intersection of Routt County Roads 27 (RCR27) and 33 (RCR33), on the north side of Foidel Creek <br />and the Twentymile Mine railroad spur. The Thickener Underflow Borehole will extend approximately 540 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. At both locations, a drill -pad and required drainage structures will be constructed. Buried thickener <br />underflow pipelines will be installed between the existing washplant facilities and the two thickener underflow <br />boreholes. The locations of both the thickener underflow boreholes and the associated pipelines are shown on the <br />Surface Facilities and Freshwater Systems Map, Map 24 (1/4). <br />Installation of the thickener underflow boreholes will involve placement of construction erosion controls (silt fence <br />and/or straw wattles), removal and windrowing of available soil materials from pad areas and the road margins (6RT <br />Borehole only), grading to establish level drill -pads and improve the existing light -use road (6Rt Borehole only), <br />placement of gravel as surfacing for the light -use road, excavation of temporary cuttings pits on the drill -pads, drilling <br />and casing of the boreholes, and installation of protective access manholes. On completion of drilling and casing <br />operations, the cuttings pits will be allowed to dry-out, material excavated from the pits will be replaced and graded, <br />and the pad surface will be graveled to control erosion and sediment and provide an all- weather operating surface. <br />The completed thickener underflow borehole installations will include the light -use road (6RT only), a soil material <br />stockpile (pad and road); the drill -pad (1MN — 25 x 180 feet, 6RT- 70 x 70 feet); the 6 -inch cased boreholes, 14 -inch <br />cemented surface casings, and a covered 8 -foot diameter CUT culvert manholes with lightening protection. <br />Pipeline installation will involve removal and windrowing of soil materials from the pipeline construction corridor <br />(maximum - 40 -foot wide); trenching in most areas; placement of suitable bedding materials; placement, <br />connection, and pressure testing of the pipelines; backfilling and compaction of suitable fill materials around and <br />over the pipelines; baclfilling and compaction of the trench; regrading; replacement of soil materials; and <br />revegetation of all disturbed areas. Where the pipelines pass under RCR27, the Twentymile Mine railroad spur, <br />and Foidel Creek, the pipeline trench will be expanded to provide room for horizontal boring equipment, and the <br />pipelines will either be trenched or bored under these features. Because pipeline placement will necessarily involve <br />activities within the Foidel Creek buffer zone, TCC is requesting a temporary variance from the regulatory <br />requirements for operations within a buffer zone. The pipelines will be a double HDPE pipe system in critical <br />areas, with a 6 to 8 -inch carrier pipe inside a larger (maximum size - 10 -inch diameter) containment pipe, buried <br />approximately 5 -feet deep. The 1MN pipeline will extend approximately 1,800 feet, with the 6RT pipeline <br />extending approximately 8,000 feet. Electronic moisture sensors, along with pump controls, and shut -off valves will <br />provide for timely detection, shut -off, and isolation of the pipeline in the event of pipeline leakage. Access/inspection <br />manholes 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 (BUT) <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 />• Placement of staked straw wattles downgradient of all surface disturbance areas to intercept any surface runoff <br />and trap associated suspended solids <br />• Installation of the Foidel Creek, RCR27, and railroad spur pipeline crossings as either trenched or bored/jacked <br />pipeline crossings under Foidel Creek, RCR27 and the railroad spur (if trenched, TC will obtain required <br />CDPHE -WQCD Temporary Construction Discharge Permit and will complete required USACE notification <br />• Soil replacement and stabilization with either the standard rangeland or riparian seed mixtures (as appropriate) <br />in a timely manner following completion of construction activities <br />Construction- related surface disturbance will be limited to soil removal and windrowing from the pipeline trench <br />alignments and stockpiling for the borehole pad areas, excavation of the trenches and temporary stockpiling of <br />excavated material adjacent to the trenches, minor cut/fill grading to establish the borehole drill -pads and excavation of <br />temporary cuttings pits, and excavation of temporary pits (within existing disturbance areas) for pipeline boring or <br />jacking operations at the Foidel Creek, RCR27, and railroad spur pipeline crossings. <br />MR 10 -248 2.05 -84.6 09127/10 <br />