2017-03-17_REVISION - C1982056 (3)

Home Browse Search

Peabod 1111 ENERGY Twentymile Coal, LLC RECEIVED MAR 17 2Q17 Division of Recla►11WOOI Mining & Safety 29515 Routt County Road 27 Oak Creek, CO 80467 970 879.3800 Ms. Tabetha Lynch, Environmental Protection Specialist March 16, 2017 Division of Reclamation, Mining, and Safety 1313 Sherman Street, Room 215 Denver, Colorado 80203 (303) 866-3567 X 8120 RE: Twentymile Coal, LLC - Foidel Creek Mine (Permit No. C-82-056), Minor Revision (MR17-306) — Sandstone Sub Thickener Underflow Borehole and Pipeline Dear Ms. Lynch: Twentymile Coal, LLC (TC) had previously submitted and received approval for a Minor Revision (MR]7-303) for a test borehole to be used to evaluate the condition of the No. I Entry of the 3SW Gateroad, as a possible location for an additional thickener underflow borehole. Over the weekend, our underground crews observed water in the vicinity of the 9 -Right and 10 -Right seals adjacent to our Main entries. hi this area, ongoing monitoring of the pooled mine water indicates significant (approximately 70 feet) freeboard, so it is unlikely that the observed water is from a pooled mine water source. Given this consideration, it is likely that the observed water is coming from the thickener underflow discharge in 8 -Right, and that a blockage in the area of 8 -Right is causing the discharge water to back-up and move laterally through the caved gob, parallel to the stop -line adjacent to the Main Entries. In order to address this situation, we need to shift the thickener underflow discharge to another location. As a temporary measure, we plan to shift the discharge to the existing approved 1 MN Replacement Thickener Underflow Borehole (MR10-243). We previously experienced a minor blockage of this borehole, but expect that it can be used for a short period of time until another borehole can be established. As a back-up plan, we will re -excavate the incised holding basin adjacent to the Area 1 Pit (refer to page 2.05-32.3), which was previously approved and utilized when we encountered a similar problem with the original 1MN Thickener Underflow Borehole, to provide a buffer for temporary placement of underflow slurry, if needed. The excavated soil rnaterialsl will be bermed around the perimeter of the basin for future use in backfilling the excavation, any dewatered co I fines which may need to be excavated will be placed o� the existing coal refuse pile. It is anticipated th t a layer of dewatered and consolidated coal fines will be left in the basin as a low -permeability layer to minimize infiltration. As a long-term solution, and assuming that the test borehole confirms favorable conditions, we request emergency approval to convert the test borehole to a thickener underflow borehole and install a connecting pipeline that will extend approximately 1,200 feet from the existing thickener underflow pipeline at the 1MN Borehole location to the Sandstone Sub Borehole location (3SW Gateroad). If the test borehole does not indicate favorable conditions, TC will probably proceed with the approved plan for the WMD Thickener Underflow Borehole and Pipeline JR 16-86). Conversion of the test borehole to a thickener underflow borehole will not require any additional surface disturbance or change the access or drainage control considerations already addressed and approved for MR] 7- 303. The test borehole will be bored out to 22 to 24 inches for the surface casing and 12 to 15 inches for the finished borehole, a 16 to 18 inch surface casing will be set land cemented to a depth of approximately 60 feet, a 8 to 11 inch borehole casing will be set and cemented to a depth of approximately 420 feet, and an 8 -foot covered CMP manhole with lightening protection will be set in-place to protect the well -head. Any mud pit(s) will be allowed to dry -out, will be backfilled with excavated material, and the surface area around the manhole will be graded, and the pad and access will be graveled to control erosion and runoff. When the borehole is no