Laserfiche WebLink
MRY.30 '97 4~19PM DMG,GJCT 1 303 2410336 P. 12 <br />TR-22 ADEQUACY REVIEW <br />1. Please address within the text of the application how Powdcrlwrn will determine when <br />and what quantity of flocculent and sulfuric acid will be added to Pond #I2. <br />2. Please inform the Division as to how Powderhorn predicted the amount of thine water <br />discharge leading into Pond #12. What is this number based on, and what will be done if <br />more inflow is encountered? <br />3. On page 13-7, Powderhorn states, ' ... as an added precaution, the emergency <br />spillway dumps into Pond 5 which will allow additional setiliag capacity below U1e primary <br />spillway of Pond 5." The operator needs to demons~atc that Pond #5 will be able to store <br />and/or treat the additional mine water from Pond #12. The NPDlS permit will also need to <br />be revisfd to allow mine water discharge and use of fltxttlants in Pond #5. Please provide <br />the Division with designs demonstrating that sediment pond #5 can safely store or treat the <br />mine wafer from Pond a'f12. <br />4. Powderhorn provides the S1;DCAD+ Basin Capacity for Pond#12. The Division <br />compared the capacity (ac-ft) depicted on page RSN-49 to the Pond #12 Map on page RSN- <br />47. The Division came up with a much larger pond volume (4X larger) than what is depicted <br />in the SEDCAD+ model. Powderhorn shows a 1.66 ac-ft pond below the emergency <br />spillway elevation, where the Division estimates a G.22 ac-Cl pond belvw the emergency <br />spillway. See attached SEDCAD+ Basin Capacity Utility for clarificatirm. Please clarify <br />this discrepancy with the Division. <br />5. Oa page RSN-48, Powderhorn depicts the emergency spillway pipe leading from Pond <br />f/12 to Poud #5. Please provide the elevation of the pipe as it enters Pond A!5. Please also <br />provide the Division with ffie elevation of the two culverts leading into Pond #5 (12" CMP <br />and 18" CMP). <br />6. Rule 4.05.6(11)(g) requires those faces of embankments including the surrounding <br />areas disturbed by construction will be vegetated or stabilized by oU1er means. The Division <br />is concerned of the stability of the embanlanent tliat is adjacent tv Coal Canyon Drainage. <br />The operator has estimated significant runoff through Coal Canyon Drainage that eni.ld <br />jeopardize the out slope of the embankment if it is not protected. Please inform the ?division <br />how the out slope of the pond embankment will be stabilized froth the estimated flow; in <br />Coal Catt}•on Drainage. <br />7. Rule 4.05.6(11)(k) states that sedimentation ponds not moeting the size criteria of 30 <br />CFR 77.216(a)(1989), shall Lave a minimum safety factor of 1.3 for a normal pool with <br />steady state seepage saturation conditions. The operator needs to demonstrate a safety factor <br />of 1.3 of the embankment at a pool level of 4,802.6' with steady state seepage saturation <br />conditions. Please provide this demonstration to the Division. <br />Z~- <br />