PROJ00077

• Contract/PO #: FS0008X
• Contractor Name: Longmont, City of
• Contract Type: Loan
• Water District: 0
• County: Boulder
• Loan Projects - Doc Type: Feasibility Study

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faces, respectively.
The worst deterior~ion is within a one-to five-foot thick zone located
35 feet below the dam crest between Stations 0+30 and 0+80. This area probably
represents a poorly constructed lift. Holes up to two feet deep are present and
water was observed flowing through this zone at 50 gpm with only on~~foot of
reservoir head.
One-inch diameter twisted steel rebar is exposed in several locations_of
the upstream face. The design specifications called for six to twelve inches of
embedment within the concrete.
There are several open and eroded horizontal lift joints. The design
specifications called for one-foot lifts but lift thicknesses appear to range
from two to four feet. There are no signs of major continuous vertical discon-
tinuities such as radial cracks caused by temperature stresses. There are
several peculiar five to ten foot long curvilinear cracks that dip between 200
to 450 from horizontal. These appear to represent the contact between concrete
pours at a single lift. The uncured concrete was simply allowed to slump.
Calcium carbonate leach stains are common on the downstream face. Black
asphalt stains on the upstream face are the only evidence of the repair work
performed in 1952.
The concrete is "cyclopean" concrete in that it contains large aggregate
known as "plumbstones". The "plumbstones" generally range from 0.5 to 2.0 feet
in diameter and are exposed in several locations on the dam faces. They were
placed closer to each other and to the dam faces than what was specified (see
Appendix C) or what is considered good practice.
Drilling Information
A total of 30 feet of six-inch diameter core and 110 feet of two-inch
diameter core were drilled within three holes. The six-inch diameter core was

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