Laserfiche WebLink
6. Powderhom provides the SEDCAD+ Basin Capacity for Pond#12. The Division <br />compazed the capacity (ac-ft) depicted on page RSN-49 to [he Pond #12 Map on page RSN-47. <br />The Division came up with a much lazger pond volume (4X lazger) than what is depicted in the <br />SEDCAD+ model. Powderhorn shows a 1.66 ac-ft pond below the emergency spillway <br />elevation, where the Division estimates a 6.22 ac-ft pond below the emergency spillway. See <br />attached SEDCAD+ Basin Capacity Utility for clarification. Please clarify this discrepancy with <br />the Division. <br />7. On page RSN-48, Powderhorn depicts the emergency spillway pipe leading from Pond <br />#12 to Pond #5. Please provide the elevation of the pipe as it enters Pond #5. Please also <br />provide the Division with the elevation of the two culverts leading into Pond #5 (12" CMP and <br />18" CMP). <br />8. Rule 4.05.6(11)(g) requires those faces of embankments including the surrounding azeas <br />disturbed by construction will be vegetated or stabilized by other means. The Division is <br />concerned of the stability of the embankment that is adjacent to Coal Canyon Drainage. The <br />operator has estimated significant runoff through Coal Canyon Drainage that could jeopardize the <br />out slope of the embankment if it is not protected. Please inform the Division how the out slope <br />of the pond embankment will be stabilized from the estimated flows in Coal Canyon Drainage. <br />9. Rule 4.05.6(11)(k) states that sedimentation ponds not meeting the size criteria of 30 CFR <br />77.216(a)(1989), shall have a minimum safety factor of 1.3 for a normal pool with steady state <br />seepage saturation conditions. The operator needs to demonstrate a safety factor of 1.3 of the <br />embankment at a pool level of 4,802.6' with steady state seepage saturation conditions. Please <br />provide this demonstration to the Division. <br />10. On page RSN-48, Powderhorn has two reference elevations that aze incorrect. The <br />reference elevation 4,900' should read 4,800' and 4,890' should read 4,790'. The lowest elevation <br />of the embankment upstream toe might also be added to the profile to eliminate any assumptions. <br />Please correct these reference elevations on page RSN-48. <br />If you or the operator have any questions, please let me know. <br />c:\wp51\misc\970307 <br />m:\coal\esc\970310 <br />