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Hernandez, Alysha From: Burgmaier, Susan Sent: Monday, March 05, 2012 3:26 PM To: Bowles, Brock Cc: Brown, Sandy; DRMS- Coal -Admin Subject: Bowie No. 2 Mine (C1996083) TR -72 Preliminary Adquacy Review Brock — I have completed my preliminary adequacy review of the surface water related proposals in the TR -72 application, and have the following comments to forward to the operator. 1. The revised Sedcad modeling provided by Bowie Resources, LLC (BRL) indicates that the additional disturbance created with the gob pile expansion will result in increased runoff to Pond F. Accordingly, the sediment storage of the pond must be reduced by half to accommodate the additional runoff volume. BRL has revised the model assuming there will be one year of sediment storage, down from the original plan for two years' storage. In reviewing the quarterly sediment pond reports provided by BRL since Pond F was constructed, BRL has reached the maximum sediment capacity and been required to clean Pond F annually. If BRL increases the disturbed area and subsequent runoff volume as predicted in the proposed gob pile expansion plan, BRL would need to clean the pond on average every six months. The Division is concerned that this increased frequency may not be manageable long term, and is inconsistent with Rule 4.05.6(3)(a), requiring "...adequate sediment storage volume and periodic sediment removal to effect compliance with Rule 4.05.2(7)." BRL should consider options for increasing the volume of the pond. 2. Page App. B -7 , the flow characteristics for the Pond F Steel Flume, show a side slope of 1.5:1. The currently approved design shows aside slope of 0:1, which is consistent with the currently installed flume. Please revise the design to reflect the existing sideslopes of 0:1. 3. Also on page App. B -7, the required peak discharge is listed as 35.52 CFS. The Sedcad run shows a peak discharge of 54.47 CFS. Please also revise this figure to 54.47, as shown in the Sedcad model output (page App. B -40). 4. With the existing configuration of the Pond F flume, the capacity is 54.54 CFS. The proposed gob pile expansion will result in a peak flow of 54.47 CFS, near maximum capacity of the flume, with insufficient freeboard. BRL will need to revise the design and propose a larger flume to ensure that the required freeboard of 0.3' is maintained at peak discharge. Should you or the operator have questions or need additional information, please let me know. Susan L. Burgmaier Environmental Protection Specialist Colorado Division of Reclamation, Mining and Safety 1313 Sherman Street, Room 215 Denver CO 80203 303 - 866 -3567 x 8111