2010-11-19_PERMIT FILE - C1992081A (3)

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Sediment and Water Control Facilities Plan There are two sedimentation ponds located within the permit boundary. The ponds were originally designed and constructed by Morrison-Knudsen Company in May 1980 for the previous operator/permittee, H-G Coal Company. The ponds have been referred to as "Truck Loop Pondl (Pond "A", Outfall 006)" and "Rail Loop Pond2 (Pond "B", Outfall 007)". HGTI identifies the ponds as "Truck Loop Pond" and "Rail Loop Pond" - the ponds are permitted by the Colorado Water Quality Control Division as industrial wastewater treatment facilities under Permit No. COG-850008. Exhibit 12-2 shows locations and contributing drainage areas for both ponds. The Rail Loop Pond was modified in 1985. A permit revision was submitted (by the previous operator/permittee) to replace the culvert spillway with a trapezoidal spillway constructed of fabriform. Certification reports for this pond modification are presented in Appendix 12-1A, Pond Certifications. The Truck Loop Pond was modified by the previous operator/permittee in June 1992. This modification was performed to meet CDRMS regulations regarding separate pipe spillways. A 12-inch diameter culvert was installed above the existing 24-inch diameter culvert spillway. Certification reports for this pond modification are presented in Appendix 12-1A, Pond Certifications. Capacity tables for the two ponds are shown on Exhibit 12-3 for the Truck Loop Pond and, Exhibit 12-4 for the Rail Loop Pond. Per Exhibit 12-3, the Truck Loop Pond has an as-built storage capacity of 1.11 acre-feet at the principal spillway elevation (24-inch drop inlet pipe), and 1.56 acre-feet at the invert of the emergency spillway (12-inch straight pipe). As shown on Exhibit 12-4, the Rail Loop Pond has an as-built storage capacity of 1.69 acre- feet at the invert of the combination principal and emergency (trapezoidal) spillway. Area-stage information was compiled from an October 1992 aerial photography survey, a 1991 sediment survey and, for the Rail Loop Pond only, a 1997 as-built survey. Certification of these as-built drawings is limited to storage capacities only and is not intended to verify design and/or construction standards. Design and construction certifications were completed by the previous operator/owner and are referenced above. Truck Loop Pond Appendix 12-1, Sediment Control and Pond Design, presents a SEDCAD 4 modeling demonstration that shows the existing storage capacity (0.97 acre-feet) is adequate to detain runoff from the truck dump watershed area generated by the 10-year, 24-hour storm event and, that the as-built pond configuration meets the requirements of Rules 4.05.6 and 4.05.9. MR-16 2 Revised 11/07