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_; <br />• ~, <br />The second SEDCAD design (stripping 89 acres) also depicts a three foot span <br />between the spillways. The As-built reveals that there is only 1.61 acre feet storage <br />between the primary and emergency spillways. The required design calls for 2.44 <br />acre feet (68.6 stripped acres) and 3.29 acre feet (89 stripped acres). <br />Comparing the approved pond design submitted under TR-33 and the As-Built Map, <br />it appears that the sediment pond may discharge through the emergency spillway <br />during the ]0-year 24-hour precipitation event. According to the design, the peak <br />stage is two feet above the height of the primary spillway (SW#1). If this is the case, <br />the peak stage after the storm event would then be at the elevation of the emergency <br />spillway, and possibly discharging. Neither the pond design or Rule 4.05.6(4) allow <br />for the runoff from the 10-year 24-hour precipitation event to discharge through the <br />emergency spillway. <br />In the occurrence of the 25-year 24-hour precipitation event, water may overtop the <br />pond embankment. The SEDCAD design for the East Taylor Pond reveals that the <br />stage of the emergency spillway has a storage capacity of 11.62. The As-Built Map <br />reveals a storage capacity of 8.88 acre feet at the height of the emergenry spillway. <br />As noted above, the 10-year 24-hour event may discharge through the emergency <br />spillway. This does not leave enough capacity to safely pass the 25-year 24-hour <br />precipitation event through the emergency spillway. <br />Colowyo submitted a certified letter signed and stamped by Steve Hinltemeyer, <br />certifying that the pond was built in accordance to design specifications and using <br />proper procedures used in the construction of earthen embanlanen[s. According to <br />the As-Built Map submitted after the certified statement, the pond was not <br />constructed as designed under TR-33. In light of the design, it appears that the <br />constructed pond will not properly discharge the 10-year 24-hour or 25-year 24-hour <br />precipitation event. <br />Colowyo must address these issues with the Division and/or MSHA prior to any <br />mining disturbance from which runoff would be contained or directed to the East <br />Taylor Pond. Colowyo must demonstrate that the existing pond will safely contain <br />or treat the 10-year 24-hour precipitation event and safely pass the 25-year 24-hour <br />precipitation event. <br />If you have any questions, please do not hesitate to call. <br />Sincerely, <br />Erica S. Crosby <br />Environmental Protection Specialist <br />c: \wp51 \ col owyo \ 951025 <br />