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._. ,: .. . TR-22 ADEQUACY REVIEW 1. Please address within the text of the application how Powderhorn will determine when and what quantity of flocculant and sulfuric acid will be added to Pond #12. 2. Please inform the Division as to how Powderhorn predicted the amount of mine water discharge leading into Pond #12. What is this number based on, and what will be done if more inflow is encountered? 3. On page 13-7, Powderhorn states, ° ... as an added precaution, the emergency spillway dumps into Pond 5 which will allow additional settling capacity below the primary spillway of Pond 5.' The operator needs to demonstrate that Pond #5 will be able to store and/or treat the additional mine water from Pond #12. The NPDES permit will also need to be revised to allow mine water dischazge and use of floculants in Pond #5. Please provide the Division with designs demonstrating that sediment pond #5 can safely store or treat the ... ,., mine water from Pond #12. 4. Powderhorn provides the SEDCAD+ Basin Capacity for Pond#12. The Division compared the capacity (ac-ft) depicted on page RSN-49 to the Pond #12 Map on page RSN- 47. The Division came up with a much lazger pond volume (4X larger) than what is depicted in the SEDCAD+ model. Powderhorn shows a 1.66 ac-ft pond below the emergency spillway elevation, where the Division estimates a 6.22 ac-ft pond below the emergency spillway. See attached SEDCAD+ Basin Capacity Utility for clarification. Please clarify this discrepancy with the Division. 5. On page RSN-48, Powderhorn depicts the emergency spillway pipe leading from Pond #12 to Pond #5. Please provide the elevation of the pipe as it enters Pond #5. Please also provide the Division with the elevation of the two culverts leading into Pond #5 (12" CMP and 18" CMP). ~ 1 ~-- - 6. Rule 4.05.6(1 l)(g) requires those faces of embankments including the surrounding - azeas disturbed by construction will be vegetated or stabilized by other means. The Division is concerned of the stability of the embankment that is adjacent to Coal Canyon Drainage. The operator has estimated significant runoff through Coal Canyon Drainage that could jeopardize the out slope of the embankment if it is not protected. Please inform the Division how the out slope of the pond embankment will be stabilized from the estimated flows in Coal Canyon Drainage. 7. Rule 4.05.6(11)(k) states that sedimentation ponds not meeting the size criteria of 30 CFR 77.216(a)(1989), shall have a minimum safety factor of 1.3 for a normal pool with steady state seepage saturation conditions. The operator needs to demonstrate a safety factor of 13 of the embankment at a pool level of 4,802.6' with steady state seepage saturation conditions. Please provide this demonstration to the Division.