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<br />Seneca ^-W. PR-2 <br />February ?F, 199y <br />Pace 6 <br />36. No response needed. <br />37. Response accepted. <br />33. The review of this permit revision is nearing completion. An updated bond estimate is <br />necessary. <br />General Comments <br />39. Response accepted. <br />40. Concerning the postmine channel designs, all of the typical channel designs have varying <br />channel slopes, e.g. channel PNI-1 slope varies from 5% to 25%, yet according to the <br />figures, velocity remains constant, total depth remains the same etc. This does not appear <br />to be accurate because if one parameter is changed, the other parameters will change <br />accordingly. Drawing 20-5.9 shows the channel profiles for each projected ditch, and <br />when channel velocities are calculated for any given length, especially those in excess of <br />20%, all velocities exceed the permissible non-erosive velocities. For example PM-1 at <br />28.1% for a flow of 2.7cfs has a velocity of 8.46 fps, and a flow depth of .33 ft. A <br />vegetated channel cannot withstand this erosive velocity, therefore the channel must be <br />protected, yet nowhere in the designs is any riprap called for. All of these channel <br />designs need to be re-engineered to reflect any significant changes in any single <br />pazameter. Please ensure that channel velocities do not exceed the erosive velocities <br />associated with any given soil type or channel protection method. <br />41. Response accepted. <br />42. Response accepted. <br />The decision date for this permit revision is March 8, 1999. It is unlikely a decision will be <br />made by then, so it will be necessary for SCC to request an extension to the deadline. If you <br />have any questions regarding this letter, please feel free to contact me. <br />Since/rely, <br />Sandra L. Brown <br />Environmental Protection Specialist <br />Enclosure <br />