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Hayden Gulch Loadout <br />Truck Loop Pond -Storage Capacity Demonstration <br />2,000,000 ton/year Rail Car Unloading/Truck Haul Operation <br />Objective: Demonstrate that the Truck Loop Pond satisfies the requirements of Rule 4.05.9, <br />including Rule 4.05.9 (2)(b) which specifies that the impoundment contain runoff <br />from the 10-year, 24-hour storm event and Rule 4.05.9(2)(c)(ii) which specifies <br />that the spillway system be designed for the 25-year, 24-hour storm event. <br />Methodology: SEDCAD 4 (Schwab, 2004) <br />Assumptions and Inputs: <br />Watershed: No new areas of disturbance. All construction activities associated with <br />2,000,000 ton per year unloading/haulage system will occur within the <br />previously disturbed facilities area boundary. <br />Contributing area, digitized directly from Exhibit 12-2, is 4.86 acres. <br />Water use: <br />• A11 vehicle washing off site at trucking contractors facility <br />• Anticipate that the coal stockpile watered once per day for 15 minutes <br />using 300 gpm water cannon -total daily application = 4,500 gallons. <br />• Assume all water drains to ponds, no evaporation or infiltration loss. <br />This is a conservative approach. <br />• Stockpile footprint approximately 0.49 acres; approximately 0.29 acres <br />of stockpile located within Rai] Loop Pond watershed. <br />• Consequently, of total daily water application, 59% or 2,655 gallons per <br />day (0.008 ac-ft) drains to Rail Loop Pond (this is a conservative value). <br />• All conveyor transfer points drain to Rail Loop Pond. <br />• Dust suppression on access road will be infrequent watering, chemical <br />surfactants may also be used. <br />• The average pan evaporation rate for the northwest Colorado is <br />approximately 2.2 feet per year or 0.006 feet per day (from Evaporation <br />Atlas for the Contiguous 48 United States, U.S. Department of <br />Commerce, 1982). This rate is similar to the conservative estimate of <br />0.008 ac-ft per day of baseflow to the pond. Consequently, expected <br />daily water use associated the facility operations will not cause a <br />significant change in the volume of water stored in the pond. <br />Hydrology_ 10-year, 24-hour ppt event = 1.7 inches (from existing permit information) <br />25-year, 24 hour ppt event = 2.1 inches (from existing permit information) <br />Type II storm distribufion <br />Runoff slopes and lengths were digitized directly from Exhibit 12-2 <br />TA-O6 12-iB.l Aevised OS/OS <br />