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• <br />In addition, there are a number of extenuating circumstances <br />regarding the design assumptions for the South Collection Ditch <br />system which should probably be considered in assessment of this <br />NOV. The "joint Colowyo and DMG modelling" referred to in <br />Colowyo's request for vacation was the subject of extended debate <br />and has never yet been resolved to the satisfaction of hydrologists <br />on our staff or myself. <br />Regardless of the outcome of that debate, a major factor in the <br />problems generated by the storm was that topsoil had been stripped <br />from a sizable area uphill from the ditch in the fall of 1992 in <br />preparation for a new pit. "Worst case" assumptions in the ditch <br />sizing assumed interception of disturbed area runoff by the pit. <br />Since the pit was not in place, the ditch apparently received much <br />more runoff than anticipated in the modelling exercises. <br />I do not believe the evidence submitted by the operator at this <br />time is sufficient to justify the conclusions in their request for <br />vacation. I also feel that the circumstances discussed above <br />should be factored into any consideration of vacation of this NOV. <br />Pending presentation of that evidence and discussion of the <br />circumstances in greater detail (at an assessment conference), I <br />recommend that this NOV not be vacated at this time. <br />cc: Steve Renner <br />David Berry <br />Janet Binns <br />c:\wp51\61093 <br />