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April 10, 2018
<br />Ms. Tabetha Lynch, Environmental Protection Specialist
<br />Division of Reclamation, Mining, and Safety
<br />1313 Sherman Street, Room 215
<br />Denver, Colorado 80203
<br />(303) 866-3567 X 8147
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<br />Twentymile Coal, LLC
<br />Foidel Creek Mine
<br />29515 RCR 27
<br />Oak Creek, CO 80467
<br />970.879.3800
<br />RE: Twentymile Coal, LLC - Foidel Creek Mine (Permit No. C-82-056), Technical Revision (TR18-90)
<br />WMD 14, 15, 16 & 17 -Left Thickener Underflow Boreholes, Pads and Pipelines
<br />Dear Ms. Lynch:
<br />Twentymile Coal, LLC (TC) requests CDRMS approval of a Technical Revision to our existing approved Permit
<br />for construction, operation, and reclamation of four new Thickener Underflow (TUF) boreholes, drill pads,
<br />additional pipelines, and associated ancillary equipment and facilities in the Western Mining District (WMD) -
<br />Panels 14, 15, 16, & 17 -Left. The new thickener underflow installations are needed both as backup for the current
<br />system, and ultimately, to replace the 2SW and 12 -Left, which are currently being used, if and when either of these
<br />boreholes are no longer functional.
<br />The 14, 15, 16, & 17 -Left TUF boreholes will be located north of the 12 -Left TUF borehole. All of the locations
<br />will be within 300 feet from Routt County Road 27. TUF boreholes 14 -Left & 15 -Left will be accessed using one
<br />County Road driveway with a light use road going between the two pads. TC has applied for a driveway permit
<br />through Routt County. TUF 16 -Left & 17 -Left will be accessed using the existing driveway that is used to access
<br />the existing 16 -Left Pad. To access the 16 -Left TUF location a short light use road will be built off of the existing
<br />16 -Left pad access road. The 17 -Left borehole will be located on the reclaimed site of the 17 -Left WMD
<br />Stabilization borehole at the start of the 16 -left pad access road. All boreholes will be drilled into the inby opening
<br />of their associated panel; the depths are 1,370 feet, 1381 feet, 1408 feet, and 1405 feet respectively.
<br />Installation of the new WMD Thickener Underflow Boreholes will involve placement of construction erosion
<br />controls (silt fence and/or straw wattles), removal and stockpiling of soil materials and the limited vegetation from
<br />the pad areas and newly disturbed roads, construction of the designed drainage structures (ditches and rock sumps),
<br />minor cut and fill grading to establish the access road and level drill pads, placement of gravel surfacing on the
<br />roads and pad areas, excavation of temporary cuttings pits on the drill pads, and drilling and casing of the
<br />boreholes. On completion of drilling and casing operations, the cuttings pits will be allowed to dry -out, material
<br />excavated from the pits will be replaced and graded, and gravel surfacing will be extended for the affected areas to
<br />control erosion and sediment and provide an all-weather operating surface. The completed thickener underflow
<br />borehole installations will include the light -use road access, soil material stockpiles, the leveled drill pads
<br />(maximum 200' x 200'), 14 -inch diameter cemented surface casings (60 feet deep), 12.25 -inch diameter cased
<br />boreholes, and covered 8 -foot diameter CMP manholes with lightning protection.
<br />Partial or full reclamation of the thickener underflow borehole disturbances will include, as appropriate, removal of
<br />the manhole structures, plugging and sealing of the boreholes consistent with State Engineer requirements, removal
<br />of pad and road surfacing materials, grading of pad and road areas to a stable configuration that blends with the
<br />surrounding terrain, replacement of soil materials, and revegetation with the approved rangeland seed mix. Given
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