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~ -.,J 00 ~ A 1989 Survey report provides a summary of the work by theBuRec and private consulting fIrms, and presents the results of further investigations (5). This Survey report describes the results of extensive aquifer testing of wells close to the Pool and provides some insight into the regional flow patterns of bedrock ground water in the area. Information from all the described reports were utilized in this study, but the 1989 Survey report, because it is a summary of previous reports and describes testing of wells in the area, is referenced the most. The analyses in this report rely on data obtained from the drilling and testing of the Wright Well and the Redstone Well to develop conclusions regarding well development impacts on spring flow, but considers data and concepts presented in the many BuRec reports and the Survey study. The location of the Wright and Redstone Wells is shown in Figure 2. The Wright Well was constructed by Wright Water Engineers in 1981 in a effort to tap into the geothenna1 resources; the Redstone Well was also drilled in 1981 by the Redstone Corporation for the same purpose. Flow testing of the Redstone Well and measurements of drawdown in the Wright Well permitted calculation of data that were used to quantify potential impacts of developing ground water on the Yampa Spring and other springs in the area. LOCAL HYDROGEOLOGIC SETTING Principal Geologic Units Glenwood Springs, in northwestern Colorado, lies alljacent to several uplifted areas and structural basins including the White River,Plateau to the north, Lookout Mountain, and the Grand Hogback to the southeast and southwest. Figure 2 is a surface geologic map of the Glenwood Springs area as modifIed by other reports (5, 6). Geologic units of interest include the Leadville, Belden Formation (Belden), and the Evaporite, shown as MI, Pbm and Pev on Figure 2. A generalized geologic section at the Pool area is presented in Figure 3. The principal bedrock source of ground water in the Glenwood Springs area is the Leadville. It is largely a limestone and dolomite unit that contains minor amounts of shale. The Leadville can be cavernous, the result of fracturing from structural movement and solution by ground water slowly percolating through the unit. These caverns and solution cavities are interconnected and can transport large amounts of ground water. A detailed description of the hydrogeology of the Leadville and other geologic units of interest can be found in Appendix A -4- I Bishop-Brogden Associates. Inc.