2022-06-24_PERMIT FILE - C1980007A (2)

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West Elk Mine was relocated in 1998 from the east side of the train load -out to an area west of the load -out between the two sets of tracks. The relocated sediment pond is constructed with concrete and is preceded by an oil skimmer and a sediment trap. The current design detail for this pond can be found in Exhibit 66. The RPE area has also been treated independently of the other surface facilities. The RPE area is located to the east of the lower refuse disposal area and east of Sylvester Gulch. The sediment pond has been designed to completely contain the runoff from a 100 -year, 24-hour storm event. The design detail for this pond, the clean water diversion ditches, and sediment ditches can be found in Exhibit 70. DCW-2, the ditch immediately south of the haul road above the Lower Refuse Pile, serves as the clean water diversion ditch for the Lower Refuse Pile (LRP). It diverts undisturbed runoff from flowing over the LRP area and diverts it to sediment pond MB -5E. Runoff from the Lower Refuse Pile is collected in perimeter ditches D2R-1, D2R-la, and D2R-3, which are all sized for the 100 -year, 24-hour storm event. During construction of the West Elk Mine, a spring was located on the site where the substation was to be built. In order to stabilize the substation pad, a french drain system and collection pipe were constructed to dewater it. As shown in Exhibit 43 and on Map 54, a 6 -inch PVC pipe collects the water and drains it into culvert C1 -6A. MCC has designed and constructed several other french drains around the mine site, as approved by the CDRMS, to improve stability. These french drains are shown on Map 54. Sediment traps were constructed below the breaker building to pre -treat (i.e., settle) wash -down water prior to flowing down to pond MB -2R. The locations of these sediment traps are shown on Map 54. MCC also utilizes sediment traps above the inlets to ponds MB -3 and MB -4. General Requirements for Sedimentation Control Facilities All storm drainage/sediment control ponds have been designed in accordance with the requirements of the CMLRB Regulations for Coal Mining. In addition, all inspection, construction and maintenance procedures conform to the requirements of these regulations. Flow meters have been installed on all mine water intakes and discharges to measure flows. Sedimentation ponds MB -3, MB -4, MB -5E, SG -1 and RPE ponds have gated dewatering systems located above the sediment level. Refer to the designs in Exhibit 43, 47A, 48 and Exhibit 66. The dewatering system for SG -1 is shown in Exhibit 66. Sedimentation Pond Operation The following discussions describe significant features associated with and the operations of each of the sedimentation and water storage ponds located at the West Elk Mine. MCC typically 10 collects a pre -discharge sample from the sediment ponds to determine if the discharge will be in compliance with MCC's NPDES permit, prior to opening the gate to discharge the pond. The pre -discharge sample is typically analyzed for total suspended solids. 1.05-33 Rev. 06/05, 01/06, 03/06, 04106& 05/06- PRIG; 01/09- MR350; 04/09- TR116;; 05/09- MR354; 08/09- TR119