C153514 Feasibility Study

• Contract/PO #: C153514
• Contractor Name: Farmers Water Development Company
• Contract Type: Loan
• Water District: 60
• County: San Miguel
• Bill Number: SB 87-15
• Loan Projects - Doc Type: Feasibility Study

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The existing air vent system has apparently been inoperable
for some time due to perforation of the header pipe by rust. The
header pipe lies on the upstream embankment slope and connects the
air inlet just downstream of the gate in the intake structure to
the atmosphere at the control tower. The air vent inlet to the
outlet conduit, located in the tunnel roof immediately downstream
of the existing slide gate, was grouted shut during the emergency
repair program of April 1987 to minimize uncontrolled inflow to the
outlet conduit.

5.3 Foundation

Our study of the geologic literature concerning the area
around and beneath Gurley Reservoir indicates that the upper
portion of the Dakota Formation forms the dam foundation and the
impoundment bottom. The majority of the general geologic
information included in this section was obtained from the
following publications: Areal Geology of the Placerville
Quadrangle, San Miguel County, Colorado, USGS Bulletin 1072-E,
1959; and Geology, Structure and Uranium Deposits of the Moab
Quadrangl e, Colorado and Utah, USGS Mi scell aneous Investi gati ons
Series, 1964. The Morrison and Burro Canyon formations which
underlie the Dakota in the stratigraphic column are believed to
have 1 ittl e or no impact on the performance of the dam foundation
due to the great thickness of the Dakota, believed to be as much as
IBO ft, locally. The Mancos Formation, which overlies the Dakota in
the stratigraphic column is exposed to the south of Gurley
Reservoir on the pediment below Lone Cone Mountain. The Mancos is
also exposed locally to the east of Gurley Reservoir. The Mancos
Formation is also believed to have little or no impact on the
performance of the dam foundation as it appears to have been
removed from the embankment area by erosi ve forces duri ng geo1 ogi c
time. The character and typical properties of all three of these
formations are discussed in greater detail in Chapter 5 of the
feaSibility study report included in Appendix A. The approximate
locations of the formation contacts are shown on Figure 3.

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