PROJ01931 ‎(2)‎

• Contract/PO #: C153471
• Contractor Name: Frederick, Town of
• Contract Type: Loan
• Water District: 0
• County: Weld
• Loan Projects - Doc Type: Approval Letter

Agenda Item 19b

.. . ,

Town of Frederick - Milavec Lake Rehabilitation
January 22-23. 2003

maintenance. Therefore, the cost savings to the Town would beat least $42,000 per year per 100
acres of Town property irrigated with raw water.

If the Town acquires additional water rights, the raw water irrigation system may also be used to
serve entities or customers in the future other than the! Town. This would further enhance the
economic value of the project. Also, the proposed project will result in the reservoir capacity being
increased by approximately 275 acre-feet from an existing capacity of 775 acre-feet to post-project
capacity of 1,050 acre-feet. This increase in capacity" as well as the conversion to "lined storage",
will also increase the long-term value of the reservoir to the Town. The current project annual
demand of 450 acre-feet is less than the 60 percent of the 768 acre-feet total adjudicated storage
decree, and will be less than half of the total reservoir storage volume after the project. In the
future, Milavec Lake could also potentially serve as a secondary or "peaking" potable water source
to supplement CWCWD.

Proiect Description

The September 2002 RMC Seepage Investigation Study evaluated three construction alternatives
for reducing seepage, including preliminary-level cost estimates for comparison purposes. The
alternatives were:

1. Partial Slurry Wall (1a) -$524,000 or Full Perimeter Slurry Wall (1b) - $674,000
2. Partial Slope Liner (2a) - $728,000 or Full PerimE~ter Slope Liner (2b) - $$927,000
3. Construction of Toe Drain Pumpback System - $120,000

Alternative No.1: Would provide a hydraulic cut-oil of the higher permeability sands underlying
the dam foundation by construction of a 20-23 foot (vertical) bentonite slurry wall, constructed inside
the reservoir about 20 feet from the upstream toe of the dam.

Alternative 1 a includes a slurry wall only along the north, east and south sides of the dam.
Alternative 1 bincludes a slurry wall around the entire perimeter of the lake.

Alternative No.2: Would provide a hydraulic cut-off of the higher permeability sands underlying the
dam foundation by construction of a 20-23 foot (vertical) compacted clay slope liner, constructed
inside the reservoir about 25 feet from the upstream toe of the dam (for construction and stability
purposes.)

Alternative 2a includes a slope liner only along the north, east and south sides of the dam.
Alternative 2b includes a slope liner around the entire perimeter of the lake.

Alternative No.3: Provides for construction of a deep toe drain gallery along the downstream -
slope of a portion of the dam, where seepage water would be collected in manholes and pumped
back into the reservoir.

The selected alternative. Alternative 2b. Full Slooe Liner, was selected and approved by the
Town Board. The design proposes to extend a low permeability compacted clay slope liner from
the existing upstream clay liner down to the underlling natural clay. The clay liner would tie into the
upstream face by construction a clay cap. Approximately 5,700 linear feet of liner with an average
depth of 20 feet would be constructed. Excavation for the clay liner, when hauled off-site will result
in 240,000 cubic yards of sandy material being removed and reservoir storage increased by ~ 50
acre-feet. In addition, geotechnical investigations indicated that the reservoir bottom consists

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