2016-05-19_PERMIT FILE - C1982056 (10)

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V V V VCENGINEERING nil SKN LINE 120 %I) — LARAMIE, N'1 82070 - (307) 742-0031 FAX (307) 721-2913 MEMO TO: MIKE BERDINF„ MANAGER - TECHNICAL RESOURCES "I'WI;N'I YMILE COAL, LLC FROM: .Il IS I'IN "I ERFEHR, P.E. SUBJECT: I IYDROLOGIC/HYDRAULIC ANALYSIS FOR 9E UTILITY BOREHOLE PAD AND \('CESS ROAD DATE: MAY 11. ?016 This Memo documents hydrologic and hydraulic evaluation of culverts and diversion ditches for the 9E Utility Borehole Pad and Access Road to be constructed by Peabody Energy, Twentymile Coal, LLC (Figure 1). The analysis modeled the upgradient hydrology and sized the proposed culverts and diversion ditches utilizing SEDCAD. Twentymile Coal uses 24 -inch diameter CMP culverts as a minimum for maintenance and cleaning. The 24 -inch culvert is larger than what is required to pass the runoff from a 10 -year, 24-hour precipitation event for all four locations: 9E Culvert 1, 9E Culvert 2, 9E Culvert 3 and 9E Culvert 4. The SEDCAD model was used to determine the diversion ditch depths with a minimum freeboard of 0.3 feet (Figure 2). Grades for each diversion ditch were determined from the existing site topography. The diversion ditches shall be constructed as v -shaped ditches to a minimum depth of 1.0 foot with 2:1 (horizontal: vertical) side slopes. Watershed soil and cover information used for the SEDCAD modeling were taken from the Topsoil Stockpiles Along 18 Right Shaft Access Road project (WET, Inc. 2005). WET obtained the data from site photos and a soil investigation report (Habitat Management. Inc. October, 2003. Fish Creek Shaft & Access Road Soil Investigation, ROUtt County. Colorado, Twentymile Coal Company Permit 982056). All culverts and diversion ditches were modeled for the 10 -year, 24-hour storm event with a precipitation depth of 1.8 inches. All SEDCAD modeling completed for this analysis are provided under Attachment 1. 1/1