PROJ00297

• Contract/PO #: C153507
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 87-15
• Loan Projects - Doc Type: Feasibility Study

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3.0 GEOTECHNICAL EVALUATION

3.1 Field Investigation

3.1.1 General

Geotechnical investigations at Comanche Dam were carried out to supplement
work performed previously in 1965 and 1982. The objective was to characterize
the embankment dam and foundati on, i nvesti gate sources of potenti a 1
construction material and obtain soil samples for laboratory testing. The
field investigations consisted of surficial geologic mapping and subsurface
exploration by means of bore holes, test pits, and seismic refraction
surveys. Multi-level standpipe piezometers were installed in each bore hole
upon compl eti on. The work was performed duri ng the months of August and
September, 1986 and October, 1987, directly by or under the supervision of MKE
personnel.

3.1.2 Geologic Mapping

A surficial geologic map is included in Drawing 2024-GIl. Comanche Dam and
Reservoi r is si tuated on a gl aci al morai ne of Plei stocene age composed of
sandy gravel till. The glacial till contains large subrounded erratics to six
feet in di ameter. Lenti cul ar-shaped 1 acustri ne deposits composed of thi nly
bedded fine sand and silt occur within the moraine. These are associated with
shallOl'l lakes that formed from seasonal melting at the edge of the advancing
or receding glacier. The sides of the glaciated valley are composed of
metamorphic and igneous rock of the Idaho Spri ngs Formati on whi ch is of
Preca~brian age. Several quarternary talus deposits of angular boulders occur
at the base of the steeper slopes and terminate within the reservoir.

3.1.3 Subsurface Investigation

The Comanche Dam and Reservoi r were i nvesti gated in 1986 and 1987 by fi ve
rotary bore holes, 23 test pits, and 1750 linear feet of seismic refraction

2084H

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