PROJ00455

• Contract/PO #: C153583
• Contractor Name: Ute Water Conservancy District
• Water District: 0
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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Groundwater is not anticipated at the proposed excavation depths along the S.H. 65 and 1-70
portions of the bypass pipeline route. Shallow to at-surface groundwater conditions are expected
along the portion of the pipeline in the Plateau Creek and Colorado River flood plains.

5.0 TUNNEL ALTERNATIVES

5.1 General

The purpose of this section is to describe the investigations performed to evaluate various tunnel
alternatives for replacement of the existing Plateau Tunnel. The proposed tunnel has been
suggested as an alternative to a pipeline corridor being considered to increase the capacity of the
existing pipeline system. The proposed tunnel is located in close proximity to the existing Plateau
Tunnel immediately southwest of the junction of Interstate 70 and State Highway 65 approximately
20 miles east of Grand Junction, Colorado. This section outlines the geologic conditions and
permit, design, and construction and maintenance considerations associated with a tunnel. A cost
estimate has been prepared for each of the various alternatives and a general project schedule is
outlined.

5.2 Geologic Conditions

The regional geologic conditions in the vicinity of the Plateau Tunnel are characterized by a nearly
flat lying sequence of sandstones and interbedded shales with a regional dip of approximately six
degrees to the north-northeast. The rocks of the area are part of the Hunter Canyon Formation
which is the stratigraphic equivalent of the Mesa Verde Formation in southern Colorado. The
Hunter Canyon Formation consists primarily of sandstone and minor interbedded shales. Also
included in the Hunter Canyon Formation are thin coal units. The soil conditions at the tunnel site
consist of thin colluvial soils directly overlying bedrock. The bedrock is exposed on all near-vertical
faces and is overlain by a thin colluvial soil cover reaching an average thickness of approximately
two to five feet on the benches and gentler slopes. The bedrock exposed at the site consists of
sandstone and interbedded shales. The thickness of the sandstone units reaches up to tens of feet
and the thickness of the interbedded shales varies from one to two inches up to approximately three
feet. Groundwater in the vicinity of the proposed tunnel is anticipated to consist of shallow,
perched zones with relatively low storage volume if present at all.

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