2010-06-02_REVISION - C1982056 - Laserfiche WebLink

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Peabody Twentymile Coal _CVV JUN p ? 1p10 iann, U1V1?Gj? U1 29515 Routt County. Road 27 Oak Creek, CO 80467•-: 970.879.3800 Mr. Jason Musick, Environmental Protection Specialist May 31, 2010 Division of Reclamation, Mining, and Safety 1313 Sherman Street, Room 215 Denver, Colorado 80203 (303) 866-3567 X 8134 RE: Twentymile Coal Company - Foidel Creek Mine (Permit No. C-82-056), Minor Revision (MR10-243) - Replacement Thickener Underflow Borehole Dear Mr. Musick: Twentymile Coal, LLC (TC) requests CDRMS approval of a Minor Revision to our existing approved Permit for installation, operation, and reclamation of a replacement Thickener Underflow Borehole. The replacement Thickener Underflow Borehole will replace the previously constructed borehole (refer to TR07-60), which recently plugged, and could not be rehabilitated. Similar to the existing Thickener Underflow Borehole, the replacement borehole will convey the thickener underflow slurry from the Washplant Thickener(s) through a nominal 14.75-inch O.D.. cased and grouted borehole approximately 310 feet deep, which will carry the slurry to abandoned and sealed underground mine workings in the Southwest Mining District, consistent with existing approved practices. The replacement borehole will be drilled adjacent to the existing Thickener Underflow Borehole, from the existing pad, and is not expected to involve any additional surface disturbance. The north end of the existing Thickener Underflow Pipeline will be partially excavated, shifted to the west, and extended to connect to the replacement borehole. Given our experience with the recent Thickener Underflow Borehole blockage and minor coal slurry discharge, we propose to implement additional safeguards to both prevent, and contain a coal slurry discharge, should one occur. Borehole drilling and completion methods will be essential the same as used for the previously constructed Thickener Underflow Borehole, except that either high-strength, corrosion/abrasion-resistant casing or a wear liner will be used. We also propose to install a float sensor in the manhole for the each thickener underflow borehole to detect any significant liquid accumulation at the wellhead, to cap any inspection/monitoring pipes to prevent leakage under pressure from any fluid that may escape to the secondary containment pipe, to provide a means for controlled discharge and containment of any fluid accumulations, and to implement regular borehole and pipeline inspections. We will continue to utilize differential pressure gauges at either end of the pipelines, double-walled pipe, and moisture sensors, to provide for timel'.y detection of any leakage or pipeline breach, and to protect against any potential leakage or spills. Pump controls and shut-off valves, controlled from a central monitoring and control center, will allow the slurry flow to be cut-off, and the pipelines drained, if necessary for maintenance and repairs. r While the associated disturbance areas will essentially be reclaimed within a reasonable time period following pipeline installation, TC does not consider these areas to be reclaimed for purposes of reporting, since there is some potential that they may be re-disturbed for pipeline repair or maintenance