PROJ01828

• Contract/PO #: C153749
• Contractor Name: DeWeese-Dye Ditch and Reservoir Company
• Contract Type: Loan
• Water District: 12
• County: Custer
• Loan Projects - Doc Type: Contract Documents

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Ms. Honey R. Moschetti, President

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December 19, 1994

Based on our visual inspection, it appears that the condition of the dam and appurtenances is
good, except for the two concrete raise sections. Consistent with previous inspections by the
SEO and others, it appears that the dam safety issue of greatest concern is the poor condition of
the upper 12 feet of the dam, representing the two concrete raises constructed in the 1930' s. The
concrete in this portion of the dam is exhibiting considerable deterioration, generally in the form
of spalling and pattern cracking. This deterioration is probably the result of freeze-thaw
weathering and erosion due to overtopping flows. These effects can be initiated and accelerated
by poor concrete quality and poor placement techniques. The surface deterioration was observed
to extend as far as six inches or more below the original surface of the concrete, exposing the
steel reinforcement in some areas. The lower raise section appears to be in generally poorer
condition than the upper raise section, probably due in large part to lower quality concrete.
Deterioration of the concrete in the lower raise is reported to extend as much as 18 inches.
Concrete cores obtained and tested in 1986 indicate that the concrete in the lower raise section
has compressive strengths i_n_!~~~g~ of 95()"to- 1,400 po~s per square inch (psi). Tests of
the concrete iii.-ilie- upper-raise section indicated compressive strengths of between 3,300 and
5,600 psi. Numerous areas of efflorescence were noted on the surface of the concrete, indicating
that water is seeping through the concrete. This seepage could be the result of cracks extending
through the section, or a relatively porous concrete.

Other items noted during our visual inspection included:

1. Seepage through the foundation rock in the left abutment, and at the downstream toe
of the dam to the right of the outlet works.

2. Minor efflorescence on the masonry downstream face of the original dam.

DATA REVIEW

A vailable Data

Available data regarding the design, construction and past performance of the dam is limited.
The following documents were reviewed:

1. SEO dam safety inspection reports, dating from as early as 1973, and various
correspondence between the SEO and the DeWeese-Dye Ditch and Reservoir Co.

2. A National Dam Safety Program Phase I Inspection Report, prepared in 1980 by
International Engineering Co., Inc.

3. A reservoir capacity survey performed in 1992 by Great Divide Engineering and
Surveying.

94311\DDREPORT L'"