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QQll The costs for each modification alternative are shown in table 14. All alternative modifications with dam raises are based on costs for concrete parapet wall raises except those for Alternative 8, where dam crest raises were considered singly with no other modifications to the project. For this alternative, earthfill dam raise procedures were also costed to yield an approximate range of costs. Additionally, table 16 shows the lowest cost plan for each class of alternative along with other factors for evaluation. An exception is the dam raise alternative where the costs for a range of raises from 9 to 19 feet are shown. The cost of the highest dam raise would be one-half to one quarter of the cost of any other alternative. TENTATIVE fLAN SELECTION Table 16 compares each alternative against the evaluation factors that were just discussed. Where several plans were developed for one class of alternative, the plan with the lowest cost is displayed in table 16. For the dam crest raise alternative, however, all levels of taise are displayed. An "X" in table 16 indicates the alternative receives a favorable evaluation for that factor. Widening the existing spillway would protect the dam from 100 percent of the PMF, while avoiding any additional damage from releases down Cherry Creek. Sand and Toll Gate Creeks are another matter, however. Figure 3 shows that the widened spillway would divert substantially greater flows into the adjacent stream system. The increased flows would occur over the full range of spillway operations, and this prospect undoubtedly would elicit strong objections from property owners along Meadowbrook, West Toll Gate, Toll Gate, and Sand Creeks. The spillway widening would produce a significant environmental impact through disruption of the vegetation and wildlife habitat associated with the present 70