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<br />with sediment control and storm runoff modeling at Colowyo, and without significant evidence <br />demonstrating that current models overestimate actual storm runoff, I am not in favor of <br />changing curve number values that were previously agreed upon with the Division through <br />extensive meetings, discussions and revisions. <br />Current permit language resulted from TR-56 approved on or about October 2003. Initially, <br />TR-56 revised materials totally excluded the permit text section in Exhibit 7 titled <br />Methodologies and Assumptions for Sedimentation Pond Evaluations. Through adequacy <br />review, this deficiency was noted by the Division and in a response to the Divisions adequacy <br />letter dated August 7, 2003 Colowyo responded "The methodologies and assumptions <br />section, previously included as the introduction to the pond design information in Volume 2C <br />has been reviewed, revised as appropriate, and is provided with these responses for insertion <br />as the introduction to the updated pond designs in Volume 2D." How it was revised is not <br />known and no further questions were raised by the Division. <br />An additional problem was discovered upon review of the revised materials proposed for TR- <br />73. Under the section 1.9 Base Flow, permit language reads "Base flows were not used in <br />any other pond design calculations [excepting West Pit and Streeter]. Discharge of collected <br />water from the open pits, as a result of pumping, will not be permitted during a storm event <br />equal to or greater than the 10-year, 24-hour storm event." This language is not correct and <br />should be changed to "less than or equal to the 10-year, 24-hour storm event." No <br />effluent limitations regarding sediment apply for storm events in excess of the 10-year, 24- <br />hour event making the current language meaningless. Whether this language was added or <br />revised during TR-56 is not known but regardless this is a glaring problem that needs to be <br />resolved. <br />Some minor changes in text were also noted and I have highlighted those for future <br />reference. I have not included any adequacy comments at this time until we can discuss the <br />purpose and intent of this revision. Let me know when you want to discuss.