PROJ00235

• Contract/PO #: C153633
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: HB 91-1006
• Loan Projects - Doc Type: Feasibility Study

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2.

Partial Deoth Slurry Wall. A partial depth slurry wall will reduce the phreatic levels in
the embankment and will thus Increase the stability, but may not significantly reduce the
seepage losses from the reservoir. To reduce phreatic levels in the embankment, a
partial depth slurry wall should penetrate the foundation one to two times the
embankment height. This would involve the construction of slurry walls varying from
approximately 20 to 80 feet deep through the embankment. This is less than the 50
percent cutoff described in Section 5.3.5.

3.

Full C1av Liner. A clay liner constructed on the upstream face of the embankment and
on the full reservoir bottom would significantly reduce seepage losses from the reservoir
as well as lower the phreatic levels in the embankment and increase the stability. A
borrow source for clay liner material was not identified during our investigation and is
not likely avanable near the site. For cost estimation purposes, we have estimated that
clay liner material will need to be brought in from an off-site borrow source with a 75
mile round trip haul, and will be mixed with on-site materials in a ratio of 40 percent
import to 60 percent native materials. The mixture will then be spread and compacted
in lifts to a three-foot thickness. A two-foot-thick protective layer of on-site sands and
gravels will need to be placed over the clay liner. Existing riprap slope protection on
the upstream face will need to be removed and replaced for this option.

4.

Partial C1av Liner. A clay liner constructed on the upstream face of the embankment
and on part of the reservoir bottom may reduce the effectiveness of partial blanketing
of the reservoir bottom is difficult to predict the seepage losses, lower phreatic levels
within the embankment, and increase the stability. We have assumed that a partial
clay blanket would start at the dam crest and would range from 100 feet wide along
the dike to 350 feet wide at the maximum section. The thickness and construction
techniques for a partial clay liner would be similar to those for a full clay liner,
discussed above.

5.

Partial Svnthetic Liner. Due to the lack of natural cohesive material on site, a partial
liner could be constructed using synthetic liner materials. The areal extent of such a
partial liner would be similar to that of a partial clay liner, discussed above. The
synthetic liner should be covered with a two-foot thick protective layer of the natural on-
site materials. In addition, to minimize the risk of puncturing, a one-foot thick cushion
of select fill (l-inch maximum size) should be placed underneath the liner. To stabilize

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