C150293 Approval Letter - Laserfiche WebLink

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NoRh Sterling Irrigation District May 12, 2009 (UPDATED May 22, 2009) Page 4 of 6 Agenda Item 17d 1. The no-action alternative; 2. Enlarge .the current spillway only; 3. Enlarge the current spillway and increase the dam freeboard with a parapet wall; 4. Enlarge the current spillway and increase the dam freeboard with soil; 5. Enlarge the current spillway, increase the dam height to increase freeboard and create additional storage. Alternative No. 1 was considered unacceptable since it means the Reservoir storage would be restricted by the SEO. Alternative No. 2 was ruled out because enlarging the spillway alone would require a substantial amount of earthmoving without addressing the dam crest. Alternative No. 3 was ruled out due to the cost of construction of the parapet wall. Selected Alternative No. 4 was selected because with additional freeboard, the width of the spillway is significantly less, therefore requiring less ea.rth work and at the same time addresses the dam crest issue and spillway issue. Alternative No. S was ruled out predominately due to cost but also due to the inability to attract partners in the increased storage. The selected alternative, Alternative No. 4, consists of widening the current auxiliary spillway from 530 feet to 915 feet, lowering the crest of the auxiliary spillway by 0.5 feet (to match the primary spillway), and raising the dam crest approximately 2.5 feet. Also included in the Project is the construction of a seepage collection system on the downstream slope of the dam. W.W. Wheeler and Associates, Inc. performed the design of the spillway. The design is currently being reviewed by the SEO. Construction is expected to begin in the summer/fall of 2009 with a 90 day construction window. The District obtained a cost estimate from Cornerstone Construction of Sterling, Colorado, which is presented in Table 2. TABLE 2 PROJECT COST Construction $ 999,350 Engineerin $ 48,000 Contin enc $ 157,100 TOTAL $ 1,204,450