C150094 Contract

• Contract/PO #: C150094
• Contractor Name: La Plata Water Conservancy District
• Contract Type: Grant
• Water District: 0
• County: La Plata
• Bill Number: HB02-1152
• Loan Projects - Doc Type: Contract Documents

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Exhibit A
Grant for Proposed Feasibility Study of Long Hollow Reservoir and Red Mesa Reservoir Enlargement

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The dam was originally constructed in 1915. After the dam was washed out in a flood in
1929, the dam was rebuilt in 1945 to its current configuration. The reservoir, which is
used for irrigation, is filled annually by natural inflows and a diversion from the La Plata

River. In dry and average years, the reservoir is totally drained to meet irrigation water
demands.

Harris Water Engineering conducted a Red Mesa Reservoir Enlargement Feasibility
Study that focused on assessing the availability of water for filling the enlarged reservoir
to 4,070 AF, to provide both agricultural and domestic water. That study indicated that
the current dam's earth embankment has a height of 59 feet, a length of 420 feet, and a
crest width of 10 feet. The normal storage capacity of the reservoir is 1,172 acre-feet
(AF), with a maximum storage capacity of 1,454 AF. The spillway, located on the left
abutment of the dam, is 35 feet wide and approximately 6 feet deep. The spil1way has a
capacity of2,126 cubic feet per second (cfs). The outlet works, a 2-foot by 4-foot arched
tunnel near the left abutment of the dam, have a capacity of 138 cfs.

The Harris study identified a need to repair the existing outlet tower and enlarge the
spillway, and recommended consideration of the reservoir enlargement since the repair
work would present an opportunity to conduct the enlargement work in an efficient
manner.

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It is important to note that some critical permitting has already been obtained for the
proposed enlargement, As part of the initial feasibility work, a Clean Water Act Section
404 Permit was obtained and the U.S. Fish and Wildlife Service (USFWS) issued a .
biological opinion under Section 7 of the Endangered Species Act. Renewal of this
permit is now being reviewed by the Army Corps of Engineers. A minimal amount of
time has been included in the scope of work and cost estimate for the Section 404, permit
renewal work.

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The Harris Water Engineering study of the Red Mesa Reservoir enlargement relied upon
geological and geotechnical stmlies completed in 1975 by the Soil Conservation Service
(SCS) in cooperation with the La Plata Soil Conservation District. The SCS field
investigation consisted of drilling eight geotechnical test holes to investigate the
condition ofthe abutment of the dam and possible emergency spillway areas; 41 test pits
dug with a backhoe; and the col1ection of six disturbed soil samples for analysis by a
soils laboratory.

WWE has reviewed the SCS files. Although they provide valuable and useab1e
information, the feasibility study will require collection and evaluation of some additional
geotechnical data. Little site-specific information is available relative to topography,
wetlands, hydrology, cultural resources and threatened/endangered species, other than the
endangered fish in the San Juan River. These items have been ineluded as part of the
proposed work plan for this application.

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