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1,vmmy ?000 C7pnu Tx~ortr~»r/r t Po»d B Ern/»atiar S <br />The watershed for Pond B covets 23.8 acres, comprised mainly of coal stockpiles. Refer to Map 9B. <br />• Pond B is apre-law pond that was constructed wide a single open notch spillway. The spillway was <br />constructed wnh a 3 inch Patshal flume placed at the bottom of the notch (Refer to Figure 4-1, Pond B <br />Spillway). The spillway was modeled as a single spillway, however, SEDCAD4 required inputs for the <br />flume and trapezoidal channel above the flume in order to calculate discharge rates. Refer to <br />SEDCAD4 printouts. <br />Modeling shows the peak Elow Eiom the 10-}'ear, 24-hour storm will discharge through the notch <br />spillway at about 0.1 Eoot above the flume (6867.5). Modeling of the 25-}'ear, 24-hour storm shows <br />that the peak flow will discharge through the notch spillwa}' at an elevation of G8G7.7. Thts results m a <br />freeboard of 2.3 feet. <br />L <br />• <br />The stage/storage relationship used for Pond B and spillway dimensions and elevations was provided <br />by the Epp survey conducted in 1996 and 1999 survey information provided by TCC. <br />As shown on the SEDCAD4 printouts, Pond B has a total volume (up to the trapezoidal portion of <br />the open notch spillway-G7G8.4) of 1.58 acre-feet. <br />The location of Pond Band its corresponding sttbwatersheds are shown on Ivfap 9B, Pond B <br />Watershed. For this analysis, it was conservatively assumed drat the entire watershed was disturbed. <br />Pond B has been in existence Eor many years and lustorical dtscharge monitoring data that has been <br />submitted to the Department shows that the pond is in compliance with water quality [egulations. <br />The structural nature of the Pond was not evaluated as part of this report <br />Montgomery \C'atson Mining Group ' 165 S. Uwon Boulevard, Suite 4l0' Lakewood, Colorado 80228' (30}} 7G}-510 <br />