2017-04-17_REVISION - C1982056 - Laserfiche WebLink

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Installation of the 1 SW & 12 -Left Thickener Underflow Boreholes will involve placement of construction erosion controls (silt fence and/or straw wattles), removal and stockpiling of soil materials and the limited vegetation from the pad areas and road (12 -Left only), construction of the designed drainage structures (ditches and rock sumps), minor cut and fill grading to establish the access road and level drill pads, minor road and drainage improvements for the 1 SW borehole, placement of gravel surfacing on the roads and pad areas, excavation of temporary cuttings pits on the drill pads, and drilling and casing of the boreholes. 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 gravel surfacing will be extended for the affected areas to control erosion and sediment and provide an all-weather operating surface. The completed thickener underflow borehole installations will include the light -use road access, soil material stockpiles, the leveled drill pads (maximum 175' x 175'), 14 -inch diameter cemented surface casings (60 feet deep), 12.25 -inch diameter cased boreholes, and covered 8 -foot diameter CMP manholes with lightning protection. Partial or full reclamation of the thickener underflow borehole disturbance will include, as appropriate, removal of the manhole structures, plugging and sealing of the boreholes consistent with State Engineer requirements, removal of pad and road surfacing materials, grading of pad and road areas to a stable configuration that blends with the surrounding terrain, replacement of soil materials, and revegetation with the approved rangeland seed mix. Given that the thickener underflow boreholes will be enclosed within the manhole structures, it will not be necessary to maintain the full pad areas used for drilling. As appropriate, TC may reclaim portions of the pad areas, leaving only the light -use access roads and a limited area around the manholes for inspection and maintenance access. The pipeline installations will involve removal and windrowing of soil materials for the 40 -foot maximum width pipeline construction areas; 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 trenches; re -grading; and replacement of soil materials and re -vegetation of all disturbed areas. Parts of the pipeline disturbance will occur within the same disturbance corridor previously used for mine roads and or County Roads. The 1 SW Pipeline will extend to the Northeast approximately 2,930 feet from the 2SW Borehole, and will be extended under RCR27 by boring or jacking that segment of the pipeline. These activities are addressed by a "Utility Construction" permit from the Routt County Road & Bridge Department. The 12 -Left Pipeli e will tee off this pipeline, and extend approximately 7 700 feet to the northwest to the 12 -Left Borehole location, paralleling RCR27. Where it crosses Fish Cre k, the 12 -Left pipeline will be jacked or bored under Fish Creek. The pipeline will be a double walled H PE pipe system, with a 8 -inch carrier pipe inside a 12 -inch containment pipe, buried approximately 5 -feet deep. Electronic moisture sensors in the interstice between the inner and outer pipe connected to the pump controls and shut-off valves will provide for timely leak detection and spill prevention. Access/Inspection manholes will be established at key points along the pipeline route. It is anticipated that a maximum of 10 manholes will be placed along the new pipeline disturbance corridors. The new thickener underflow boreholes are upwards of 15,000 feet from the source of the slurry, and the current thickener underflow pump does not have the capacity to reliably pump the slurry over that distance. To aid in the pumping TC plans to install a pump boost station along the first section of the SWMD pipeline between the 1MN pipeline and 2SW boreh le. The pump boost station will be located near the West Truck Scales at the west entrance to the Mine Facilities Area. The pump boost station will consist of a one -foot thick, 20 x 20 foot concrete pad, a pre -fabricated pump building, the booster pump and piping connections, and a drop -line from a nearby power -pole with electrical connections and pump controls.