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October 23, 2020 C-1980-007/West Elk Mine LDS <br />Inspection Topic Summary <br />NOTE: Y=Inspected N=Not Inspected R=Comments Noted V=Violation Issued NA=Not Applicable <br />N - Air Resource Protection <br />N - Availability of Records <br />N - Backfill & Grading <br />N - Excess Spoil and Dev. Waste <br />N - Explosives <br />N - Fish & Wildlife <br />N - Hydrologic Balance <br />N - Gen. Compliance With Mine Plan <br />N - Other <br />N - Processing Waste <br />N - Roads <br />N - Reclamation Success <br />N - Revegetation <br />V - Subsidence <br />N - Slides and Other Damage <br />R - Support Facilities On -site <br />N - Signs and Markers <br />N - Support Facilities Not On -site <br />N - Special Categories Of Mining <br />N - Topsoil <br />COMMENTS <br />This was a partial inspection by Leigh Simmons of the Division of Reclamation, Mining and Safety <br />(Division). Kathy Welt and John Poulos of Mountain Coal Company (MCC) accompanied the inspection. The <br />weather was clear, dry and cold. The mine was active. <br />SUBSIDENCEE - Rule 4.20: <br />MCC had previously notified the Division of subsidence that had occurred during the afternoon of <br />Monday October 13th, as a result of development mining under South Prong Creek. A hole, approximately 40' <br />across, had opened up on the surface, just upstream of the confluence with the North Fork of South Prong Creek, <br />causing water from the creek to flow into the mine workings. MCC staff had responded immediately, setting up <br />pumps and a temporary diversion during the night. Stream flow was initially estimated at 100 gallons per minute <br />(022 cfs), and later measured at 160 gallons per minute (0.36 cfs). The stream flow had been successfully diverted <br />around the subsidence hole by the morning of Tuesday October 14th. <br />Minor Revisions 450 and 452 were submitted on October 14th and 16th respectively, to permit the <br />disturbance associated with repairing the damage. Technical Revision 148 was submitted on October 30th, to <br />permit the design of the restoration of South Prong Creek. <br />The main focus of the inspection was the damaged area, the associated disturbance, and the ongoing <br />repairs. At the time of the inspection the water in the creek had been directed into a lined sump, which gravity <br />drained into a 16" pipe. The 16" pipe split into two 6" pipes, only one of which was in use. The other pipe was <br />available to provide capacity in case of increased stream flows. A second sump had been constructed just <br />downstream of the first, which allowed a small electric pump to be used to pump the small amount of water that <br />ran under the lining to be pumped back up to the first sump through a hosepipe as necessary. <br />Topsoil had been salvaged from a borrow area adjacent to the subsidence and stockpiled. The perimeter of <br />the disturbance had been protected with a silt fence. The topsoil stockpiles had been marked with sign posts, and <br />protected with mulch and straw wattles. Cobbles and large boulders had been set aside. The subsided area had <br />been filled with native material from the borrow area, compacted in 2' lifts. A 6-8" thick bentonite cap had then <br />been made in place. <br />According to Mr. Poulos, the subsidence of the creek had occurred when the roof of the western -most of <br />five entries in the Sunset Mains South had caved, as development was progressing from north to south. The entries <br />Number of Partial Inspection this Fiscal Year: 5 <br />Number of Complete Inspections this Fiscal Year: 1 <br />Page 2 of 24 <br />