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. . Mr. J. William McDonald October 17. 1989 Page 2 During the last eighteen months. the District has been conducting additional studies needed to satisfy Eagle County 1041 permitting requirements. These studies include a water quality and stream flow monitoring program and a detailed evaluation of aquatic habit conditions in Gore Creek. Though these studies are not yet complete, we have learned that it would be desirable to modify the operation of Black Lakes, as described in the District's Augmentation Plan (Case No. 82C~28), in order to more effectively mitigate aquatic impacts associated with future additional diversions from Gore Creek. Operation Proposed in the Augmentation Plan In conjunction with the Augmentation Plan. the 300 acre feet of storage in Black Lakes, is to be operated to augment municipal diversions when streamflows in Gore Creek at the Vail Gage are at or below 16 cfs from May 1 to September 30 (summer) and 6 cfs from October 1 to April 30 (winter). (The Vail Gage is located just upstream from the outfall of the Vail Wastewater Treatment Plant at the Forest Road bridge.) However. the District is required to replace only those municipal diversions in excess of 4.35 cfs, and releases from storage in Black Lakes are required only to the extent necessary to return the stream flow to 16 cfs in summer or 6 cfs in winter or the natural flow. whichever is less. The District retains the right to use water released from storage in Black Lakes downstream from the confluence of Gore Creek and the Eagle River. Background Information from Recent Studies Since late September of 1988, the District has been monitoring water quality and stream flows at up to twelve stations on Gore Creek and Black Gore Creek. The winter of 1988-89 was generally considered to be representative of unusually low flow conditions because of the dry fall, below average snowpack, and very cold temperatures. Even under these conditions, it was found that streamflows at the Vail Gage did not drop below the 6 cfs level that could have triggered releases of water stored in Black Lakes. The lowest measured flow at the Vail Gage was 6.6 cfs on March I, 1989. Under the operational criteria proposed in the Augmentation Plan, water would not have been released from Black Lakes even though the stream flow in Gore Creek below the municipal well field on March I, 1989 was estimated at only 2.6 cfs. Recognizing the limitations of only one season of data. it does appear that streamflows in Gore Creek recover from the municipal diversions at the well field more rapidly than realized when the Augmentation Plan was negotiated. If this past winter is any indication