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Permit Revision 11(Pit-11) <br /> Performance of the Trapper Mine East Buzzard Sediment Control System <br /> East Buzzard impoundments#1 and#2 were originally certified during the year 1987.The design files <br /> from this time period indicate that a watershed area of 340.9 acres reported to this structure.With the <br /> completion of reclamation activities and Phase III bond release in the associated watershed,these <br /> impoundments were reclaimed <br /> As a part of the PR-11 submittal,Trapper Mine has applied to re-disturb and newly disturb portions of <br /> the East Buzzard watershed in order to access coal reserves in C pit and West I pit. Under the proposed <br /> mining plan,the worst-case disturbance acreage will total 82.9 acres.The total watershed area reporting <br /> to the East Buzzard ponds is 573.8 acres.This acreage includes the watershed that flowed into Far East <br /> Buzzard.These two watersheds have been combined; Far East Buzzard dam is no longer a part of the <br /> drainage and sediment control plan for this area. <br /> In order to provide adequate drainage and sediment control to treat runoff from the proposed <br /> disturbed areas,Trapper will construct an impoundment(East Buzzard #3). <br /> For the worst-case year 2024,the areas and associated curve numbers for the watershed are as follows: <br /> Area Description Acres Curve Number <br /> Active Mining 82.9 87 <br /> Reclaimed—2+Years Growth 306.4 67 <br /> Undisturbed 184.5 49 <br /> Total 573.8 72 <br /> The composite curve number of 72 is a run-off weighted average. <br /> SEDCAD software was used to model the hydrology and sedimentology for this system. In order to <br /> comply with current regulations,the impoundment modeling must result in a 10-year, 24-hour peak <br /> settleable effluent concentration less than 0.5 ml/I at the system sampling point(below East Buzzard <br /> #3). In addition,the freeboard resulting from the peak stage of a 25-year, 24-hour event must be at least <br /> one foot. The model was run for a 10-year, 24-hour rainfall event and a 25-year,24-hour rainfall event. <br /> A summary of the relevant results is shown below: <br /> East Buzzard #3, 10-year, 24-hour event peak outflow settleable concentration (MI/1) 0.00 <br /> East Buzzard #3 Top of Dam Elevation 6250.0 <br /> East Buzzard#3 25-year, 24-hour event peak stage 6248.3 <br /> East Buzzard#3 25-year, 24-hour event freeboard (ft) 1.7 <br /> The performance of the East Buzzard sediment control system, as modeled, meets the requirements of <br /> the Regulations of The Colorado Mined Land Reclamation Board for Coal Mining,Section 4.05 <br />