Laserfiche WebLink
INTAKE SHAFT FACILITY <br />DRAINAGE AND SEDIMENT CONTROL SYSTEM DESIGN <br />Peabody Energy Twentymile Coa] Company (TCC) proposes to construct a new intake <br />shaft facility within the Twentymile Coal-Foidel Creek Mine located in Routt County, <br />Colorado. The purpose of this analysis is to remodel the hydrology and sedimentology of <br />the site runoff to design azero-discharging sediment pond that completely contains the <br />100-year, 24-hour rainfall runoff event with a minimum of 1.0 foot of remaining <br />freeboard. The hydrologic and hydraulic modeling was conducted using SEDCAD*"' 4 <br />(guild Date 2000.09.07). Watershed soil and cover information were taken from site <br />photos and a soil investigation report (Habitat Management, Inc. October, 2003. Fish <br />Creek Shafi & Access Road Soil Investigation, Routt County, Colorado, Twentymile <br />Coal Company Permit #82056). Since the most up-gradient boundary of the facility is <br />located on a watershed divide, no up-gradient drainage ditches aze required to collect <br />runoff from undisturbed areas. <br />The runoff from the 11.04-acre disturbed azea will be collected in a small sediment pond <br />both directly and via two down-gradient drainage ditches (designed in a previous Mazch <br />2005 submittal). The pond will be constructed as an incised impoundment with a surface <br />area of approximately 0.566 acres. The maximum depth of the pond will be 5.17 feet. <br />The maximum capacity of the pond will be 1.97 acre feet. The pond will completely <br />contain three years of sediment runoff volume (0.02 acre-feet) plus the rainfall runoff <br />from the 100-year, 24-how event (1.426 acre-feet), and still maintain 1.01 feet of <br />freeboazd. <br />The following is submitted to demonstrate that the sediment pond will effectively contain <br />the surface water and sediment runofffrom the intake shaft facility. <br />DESIGN PARAMETERS: <br />Intake Shaft Facility Sediment Pond <br />Combined watershed area = 11.04 ac <br />100-yeaz, 24-how storm = 2.6 inches <br />25-year, 24-how storrn = 2.1 inches <br />CN = 89 {compacted road base pad -hydrologic soil group D) <br />Three-yeaz sediment storage volume = 0.02 ac-fi <br />The following sediment pond elevation-area data were input to SEDCAD: <br />Elevation (feet) Area ac Capaci (ac-fil <br />6,730.52 0.000 0.000 <br />6,730.69 0.150 0.008 <br />6,730.80 0.162 0.026 <br />6,731.69 0.270 0.216 <br />~ 6,732.69 0.422 0.559 <br />6,733.69 0.46] 1.000 <br /> <br />