PROJ00370

• Contract/PO #: FS0031X
• Contractor Name: Yampa Project DNR 1972
• Contract Type: Miscellaneous
• Water District: 0
• County: Moffat
• Loan Projects - Doc Type: Feasibility Study

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deposits also showed up at high elevations near the high water I ine at

the east bank of the reservoir at the' location shown on Fig. 1.

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Although the terrace deposits are pervious a~d offer easy passage of

water, the location of such deposits are mostly within the river course.

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The underlying Lance Formation will prevent seepage loss. . Superficial

inspection gives the impression that the Lance Formation forms a tight

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closure around the entire reservoi r and the chance of leakage through

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the terrace deposits is rather small.

However, we cannot rule out entirely the possibil ity of losing water

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from the terrace deposits at high elevation along the bank. In the

estimate for the construction of the dam and reservoir, provision should

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be made for the lining of the reservoir with impervious material at

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specific locations. At most, we estimate that less than 5% of the

reservoir will need such.treatment.

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Lance Formation: Bedrock in the area is identified as the Lance Formation.

It consists of interbedded light buff sandstone and grey shale and mostly

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consists of the fine grained sandstone. The sandstone formation is

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exposed at many places along the bank. The upper few feet of the sandstone

is highly weathered and fractured, but at a lower depth probably 2 to 3

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feet below the surface the sandstone formation is intact and should provide

good resistance to seepage of water. 'Seams and fissures may be present

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in the Lance Formation which will allow losing probably a minimal amount

of water in the reservoir.

In general, we do not foresee any problem in increasing the height

of the high water level from 6342 feet to 6375 feet. We believe the bank
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of the reservoir should be impervious and allow a minimal loss of water.