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I I I I I I I I I I I I I I I I I I I Hourglass Reservoir has high seepage losses, based on the single simplified seepage loss investigation. Apparent losses at elevalion 9356.8 feet (24.0 gage) appear to be in the order of seven acre-feet per day, or 200 acre-feet per month. Losses will be greater at higher reservoir levels. Very little of the reservoir seepage loss returns to the stream channel above the measuring flume below the dam and ~ cannot be ered~ed as a measured release from the dam. Such a high seepage loss precludes use of the reservoir for long term water slorage, particularly at the higher reservoir levels. The reservoir should continue to be used as ~ now is. That is, to briefly store excess water from Comanche Dam and release ~ downstream as needed on a year-to-year basis. Option 1 - Downstream Drainage Conslructlon, bringing the dam up to present safety standards is recommended for final design and construction at a feasibility level construction cost of 328,075 thousand dollars. This Is the minimum rehabilitation to adequately improve dam safety, This recommendation Is based on our understanding that add~lonal useable reservoir capacity can probably be developed for less cost al other Greeley reservoirs. Option 2 - Partial Depth Slurry Wall Includes a partial slurry well seepage cutoff In addition to the safely improvements included in Plan 1. The estimated cost of construction is 1,346,975 dollars. Such cost for a potenllal savings of a few hundred acre-feet of waler per year Is not considered to be economically altraclive al present. If Ihe cost of waler does rise 10 justify a partial cutoff. ~ can be placed at any time after completion of Option 1 for 995,500 dollars, No new water supply will be crealed under Option 1. The safety of the dam will be brought up to current standards, Now that inflows from Comanche Dam can be measured, seepage losses In Hourglass Reservoir can and should be more accurately determined during future reservoir operation. The foregoing construction costs are for construction only, not Including contingency, engineering, price escalation and interest. See Table 6.1 for these costs.