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Highland Ditch Company November 8. 2005 (Revised November 17,2005) Page 2 of 4 Agenda Item 23a Feasibility Study The feasibility study was prepared by Duane Smith of Smith Geotechnical of Fort Collins on behalf of the Company. The study was prepared in accordance with the CWCB guidelines and includes preliminary engineering design and cost estimates. The project has been approved by SEO for construction. The Hiahland Ditch Company The Company is a mutual ditch company registered in the State of Colorado. The Company was incorporated in 1872 and has been in continuous existence and operation since its inception. The first water deliveries were from direct flow rights from the Saint Vrain River at the turn of the century and shortly thereafter the Company began construction of several storage reservoirs. The Company's reservoirs total approximately 12,800 AF of storage capacity and are located in Boulder and Weld County. The system also includes approximately 26 miles of supply ditch and approximately 15 miles of extension and lateral ditches. The Company owns direct flow rights from the Saint Vrain River and also owns 40 units of CBT water. The average annual delivery amount of water by the Company from 1995 to 2004 is 32,552 AF. Water Riahts The Company's decreed water right for Foothills Reservoir has an appropriation date of July 13, 1910, Priority No. 11, Third Series, for 4,340 acre-feet of water to a decreed gage height of 45 feet. A conditional refill decree was issued with a date of December 31, 1929, with an appropriation number of 23S, Third Series. This decree was later canceled by the District Court in 1965 due to lack of evidence showing diligence. Foothills Reservoir is utilized to store water from the Saint Vrain River during the spring runoff. The reservoir is filled through a supply canal by an exchange in the river system to allow the Company to withdraw water at its main diversion structure near Lyons. Proiect Description Based on the results of extensive geotechnical investigation and a drilling and sampling program, the Company has decided to repair the dam by cutting off seepage in the upper portion of the dam. Three alternatives were evaluated to determine the most feasible method to accomplish this goal: ALTERNATIVE 1 - Clay Core Trench $600,000 Includes excavating a core trench into the center of the dam to a depth up to 35 feet below the dam crest. This alternative will cutoff the seepage in the zone it pierces and will also add considerable stability to the dam by removing and replacing the poorly compacted shale found in the dam. ALTERNATIVE 2 - Bentonite Slurry Trench $758,355 This alternative considered excavating a cutoff trench through the dam to bedrock using bentonite slurry trench methods. The trench would be placed near the centerline of the dam and would be approximately 18-inches in width. The slurry trench would develop a low permeability barrier to seepage but would not significantly increase the sliding stability of the dam. The uncompacted shale layers in the dam would not be impacted or modified by this construction.