PROJ00504

• Contract/PO #: C153334
• Contractor Name: Henry Waneka Mutual Reservoir Company c/o City of
• Contract Type: Loan
• Water District: 6
• County: Boulder
• Bill Number: FSA
• Loan Projects - Doc Type: Feasibility Study

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ohown on Figure-VI and is based upon obtabing the property in the flood pool

in addition to the property required for the larger structures. An

auxiliary dike would be constructed most of the way around the reservoir,

including along the Public Service Company access road at the southeast

portion of the reservoir.

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Due to the poor foundation conditions, the proposed embankment includes

the internal drainage system as described under the Rehabilitation section

of this report. The slope stability analysis (Figure-VIII) on the en-

largement embankment resulted in a factor of safety of around 2.5. The

discussion of the critical circle for the rehabilitation alternative is also

applicable for the enlargement alternative. During final design, steeper

embankment slopes should be investigated to reduce the conservatism in the

factor of safety.

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4 - Seepage Control

The quantity of seepage through the embankment was estimated in Section

V-B-4(b) of this report and found to be as much as 15 AF/year. The wide

variation in the estimated quantity was due to unknown foundation/embank-

ment conditions as well as the actual permeability values. To adequately

define the necessary seepage parameters, such that the quantity can be

more accurately defined, an expensive drilling and testing program would

be required, which is beyond the scope of the feasibility analysis.

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Several methods for reducing the seepage quantity were considered

including a core material cut-off into the bedrock, an impermeable membrane

and cut-off into the bedrock, and a slurry trench cut-off into the bedrock.

Due to the depth of the bedrock (from 15 to 25 feet below original

ground) and the length of the embankment (in excess of 2,000 feet), the

cost of the alternatives were all found to be in excess of $100,000. If

the seepage amount is reduced by 10 AF, then the cost per acre-feet is

$10,000 or more, which was considered excessive based on today's prices.

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