C150331 Feasibility Study

• Contract/PO #: C150331
• Contractor Name: North Delta Irrigation Company
• Contract Type: Loan
• Water District: 40
• County: Delta
• Loan Projects - Doc Type: Feasibility Study

WestWater Engineering
2516 FORESIGHT CIRCLE, #1 GRAND JUNCTION, COLORADO 81505 [phone] FAX [phone]
April 3, 2012
Ryan Edwards, P.E„ Project Manager
Finance Section
Colorado Water Conservation Board
1313 Sherman Street, Room 721
Denver, Colorado 80203
RE: NDIC Tunnel Repair Project
Contract Number Cl 5033 1
Dear Ryan,
Pursuant to the March 20, 2012 combined CWCB loan and WSRA grant approval for the North
Delta irrigation Company(NDIC) tunnel repair project, the described scope of work should be
amended to include not only the basic tunnel rehabilitation with heat fused slipline pipe, that is
represented as Bid Schedule I on the Tunnel Rehabilitation and Canal System Upgrades Plans
and Specifications prepared by WestWater Engineering dated March 2012, but also Phase 1 of
Bid Schedule 2 of the same set of Plans and Specifications. Construction of the combination of
Bid Schedule 1 and Bid Schedule 2 Phase I will meet all project objectives, that include tunnel
repair, protection of the tunnel against further failures, and to deliver at least 80% of the decreed
water right to the approximately 171 headgates downstream from the project.
Without Bid Schedule 2 Phase 1, the NDIC will be unable to deliver a large portion of its decreed
water right to approximately 94% of its shareholders. Construction of Bid Schedule I alone
would reduce the flow delivery capacity to the majority of shareholders by about 50% to 60%,
which is insufficient during peak ET months of the growing season. Without extension of the
tunnel toe drains of Bid Schedule 2 Phase 1, recommendations of the project's geotechnical
Engineer to prevent generation of a hydrostatic head along the tunnel will not be met. Without
the 60-inch ADS west canal pipe and appurtenances of Bid Schedule 2 Phase 1, discharge from
the tunnel would flow freely to Highway 65 right-of-way rather than be contained in the canal
system. Furthermore, the east canal 60-inch ADS pipe of Bid Schedule 2 Phase 1 provides the
hydraulic conditions needed for the design tunnel flow conveyance capacity. Without the piped
tunnel approach, the NDIC cannot safely raise the water level to the extent required, without
implementing alternatives to the canal pipe for stabilizing an apparent weakened embankment.
Finally, without the Flow Control Structure of Bid Schedule 2 Phase 1, the NDIC will have no
operational control to manually regulate, divert or otherwise control flow that is conveyed
directly upstream to the tunnel.
Because of the many important functions of the canal pipe and appurtenances described in Bid
Schedule 2 Phase 1, it is our recommendation to include at least these minimum canal system
upgrades as integral components for tunnel rehabilitation work under Bid Schedule I, to be
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