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Peabodu <br />March 5, 2019 <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 <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 (TR19-93) <br />Wash Plant Additional Thickener Tank Design Modification <br />Dear Ms. Lynch: <br />Twentymile Coal, LLC (TC) requests CDRMS approval of a Technical Revision to our existing approved Permit <br />for a modification to the foundation design of the second Thickener tank (TR18-91) at the west side of the Wash <br />Plant facilities. <br />The design modification addresses a change to the foundation support design of the thickener tank. The existing <br />permitted plan called out the use of 108 concrete pilings to be drilled into the bedrock to support the foundation of <br />the thickener tank. The new modification will be replacing the 108 pilings with 4 feet of devised compacted fill to a <br />compacted rating of 950 o or better. This fill is equivalent to the pilings and was an alternative offered by the <br />engineering firm hired to design the thickener tank. During the placement of the compacted free draining fill <br />material, limestone was placed on the northwest side of the proposed thickener tank at a depth of around 15 feet to <br />help relieve any hydrostatic pressures that may exist due to the shallow water table. The ground water will be <br />allowed to drain through the limestone to a perforated pipe that will drain to pond D. To also assist in water control <br />a french drain will be placed on the South side of the pump building to divert any runoff water from entering the <br />pad area. <br />Detailed design, operations, and reclamation information for the proposed activities is provided as both revised <br />PAP text and exhibits; and revised maps, reflecting the location and configuration of the new facilities. New and <br />revised PAP materials are identified by the attached Summary of Revisions. -Additions. <br />We would like to proceed with this project ASAP to avoid any operation delays. We, therefore, appreciate your <br />consideration, cooperation, and assistance in facilitating timely review and approval of this Technical Revision <br />application. After you have opportunity to review the accompanying information, please feel free to contact me <br />with any questions or to discuss submittal materials or related matters. <br />Sincer 1 , <br />OF <br />V '" kuvmk- <br />Miranda Kawcak <br />Environmental Engineer <br />mblomquist@peabodyenergy.com <br />970-870-2718 <br />cc: Ed Brady ITC <br />Jerry Nettleton <br />