BOARD AGENDA MEMORANDUM
Government Code § 84308 Applies: Yes ☐ No ☒
(If “YES” Complete Attachment A - Gov. Code § 84308)
SUBJECT:
Title
Receive an Update on the Anderson Dam Tunnel Project.
End
RECOMMENDATION:
Recommendation
Receive an Update on the Anderson Dam Tunnel Project.
Body
SUMMARY:
Background
The Anderson Dam Tunnel Project (ADTP), Project No. 91864006, is currently being constructed and includes building a diversion system to augment the existing outlet, consisting of a new diversion tunnel, an outlet structure, a micro-tunnel lake tap, and modifications to Coyote Creek just downstream of the base of the dam. Once completed, the ADTP will serve as the Stage 1 Diversion System to divert inflows from the reservoir to Coyote Creek during the beginning of the Anderson Dam Seismic Retrofit Project (ADSRP). All of the ADTP elements, except for the micro-tunnel lake tap portion, will be incorporated into the final configuration of the ADSRP.
On April 27, 2021, Valley Water’s Board of Directors awarded the construction contract for the ADTP to the top-ranked best-value proposer, Flatiron West, Inc. (Contractor), in the sum of $161,140,321 and approved a contingency amount of $40,000,000 (25% of the contract price).
On January 28, 2025, the Board of Directors approved an increase of $40,000,000 to the construction contract contingency sum, bringing the total construction contract contingency to $80,000,000.
Project Construction
Several major elements of the ADTP construction have been completed to date, including:
• Tunnel Excavation and Initial Lining
Tunnel excavation and initial lining of the tunnel were completed in April 2024. The Contractor used conventional mining methods, including drilling and blasting the rock to complete the excavation. The initial lining installed to support the excavation consists of an 8-inch thick layer of fiber-reinforced shotcrete (spray-applied concrete) and steel support arches spaced every 3 to 5 feet.
• Microtunnel and Lake Tap
Conclusion of tunneling and tapping into the reservoir was completed in August 2024. A micro-tunnel boring machine (MTBM) drilled through the last 350 feet of tunnel into the reservoir about 30 feet under the water surface. Sections of 8-foot diameter steel pipe were driven into the ground behind the MTBM in this portion of the tunnel.
• Diversion Outlet Structure (DOS) Construction
Construction of the DOS outside the downstream tunnel portal was completed in June 2024. The DOS will be used to house the two large fixed-cone valves that control flows through the tunnel and dissipate the energy of the releases by reducing the velocity of the water. The foundation, walls, and roof of the structure are made of thick, reinforced concrete sections that were placed in multiple stages.
• North Channel Extension
Work to reopen the North Channel was completed in November 2024. The work included excavation, grading, and rock placement for over 1,600 linear feet starting outside the DOS to reconnect this historic creek channel back to Coyote Creek. A concrete labyrinth weir was also installed in the channel to dissipate the energy and control high flows to be released from Anderson Reservoir.
The remaining major construction elements to be completed include:
• South Channel Weir Construction
Improvement of the South Channel by constructing a new concrete weir, with a notch for low-flow passage. This weir will work in conjunction with the North Channel Weir to control flow releases from Anderson Reservoir in this reach of Coyote Creek.
• Final Tunnel Lining Installation
Construction of the final tunnel lining. There are three distinct structural systems that will be used for the final tunnel lining:
o Continuous Reinforced Concrete - a 24-inch thick, horseshoe-shaped arch, walls, and floor
o Articulating Joint Concrete Sections - a similar 24-inch thick reinforced concrete structure with heavier reinforcement and gaps between sections every five or ten feet designed to independently displace if ground movements occur.
o Steel Pipe with Concrete Backfill - about 450 linear feet of 13-foot diameter steel pipe will be installed at the downstream end of the tunnel that exits the portal. The annular space will be backfilled with concrete.
• Diversion Outlet Structure (DOS) Large Diameter Pipe and Valve Installation
Installation of the large diameter steel pipes and valves in the DOS. As the 13-foot diameter steel pipe exits the tunnel, it bifurcates into two 11-foot diameter steel pipes. Each of the 11-foot diameter pipes have a butterfly valve and fixed cone valve to control flow releases and dissipate energy into the DOS.
Project Schedule
The ADSRP FERC Order received in February 2020 stated that Valley Water should advance the low-level outlet tunnel portion of the project immediately as a risk reduction measure. The project team advanced the design for the tunnel as a separate package for construction. When the ADTP contract was awarded, several permits and design elements had not been fully approved. This decision was consistent with the need to build the tunnel as soon as possible.
Due to the delay in notice to proceed based on final permits and design changes through final review by various regulatory agencies, the ADTP has experienced several delays resulting in contract time extensions. Some additional design changes occurred during construction based on differing site conditions and resulted in substantial project delays as well.
Table 1 below summarizes each time extension which included a time impact analysis of the project schedule.
Table 1 - Project Schedule Extensions and Completion Dates
|
Time Impact Analysis (TIA) |
Contract time extension in calendar days |
Construction Contract Completion Date |
|
Original Contract Completion Date (Start 6/28/2021) |
- |
3/4/2024 |
|
TIA-01 (Delay to issue Notice to Proceed 2A) |
79 |
5/15/2024 |
|
TIA-02 (HLOW Drop Shaft design changes) |
166 |
11/4/2024 |
|
TIA-03 (Diversion Outlet Structure excavation design changes) |
56 |
12/30/2024 |
|
TIA-04 (Tunnel Excavation differing site conditions) |
25 |
1/24/2025 |
|
TIA-05 (North Channel design changes) |
236 |
9/17/2025 |
|
TIA-06 (Tunnel Final Lining Changes) |
443 |
12/4/2026 |
|
Total |
1,005 |
|
Project Cost
There have been several changes to the construction contract cost due to various reasons. Many of the cost increases are associated with the contract time extensions summarized above. When the duration of the contract is extended by changes directed by Valley Water or differing site conditions, the Contractor can claim additional overhead costs and other additional charges for the extended contract time. There have also been other differing site conditions related to the dredging, overruns on certain bid item unit quantities, and design changes to improve compatibility with the ADSRP. Significant credits have been applied to the total contract amount as well due to design changes that reduced the scope of work for the Contractor. All cost changes have been presented as Contract Change Orders throughout the life of the ADTP. Table 2 below summarizes the current construction contract cost and amount billed to date (through April 2025 billing).
Table 2 - ADTP Construction Contract Amount and Remaining Balance
|
|
Contract Amount |
Total Billed |
Balance Remaining |
|
Original Contract |
$ 161,140,321 |
$ 125,911,004 |
$ 35,229,317 |
|
Change Orders (includes Pending) |
$ 58,355,786 |
$ 27,673,312 |
$ 30,682,474 |
|
Total Contract |
$ 219,496,107 |
$ 153,584,316 |
$ 65,911,791 |
The original contract cost contingency of $40,000,000 was established when the contract was awarded. After several cost increases and schedule extensions, Staff recommended an increase to the contract cost contingency for a total of $80,000,000 which the Board of Directors approved as noted above in the Background section. Based on Contract Change Orders executed and pending to date totaling $58,355,786, the remaining contract contingency is $21,644,214. There are additional anticipated cost changes that will reduce the remaining contingency once finalized.
ENVIRONMENTAL JUSTICE IMPACT:
There are no Environmental Justice impacts associated with this item. However, the Environmental Justice Impacts of the Project will be assessed and addressed in future Project board actions related to the Project execution.
FINANCIAL IMPACT:
The Anderson Dam Tunnel Project (ADTP), Project No. 91864006, is included in the Capital Improvement Program (CIP) Fiscal Years (FY) 2025-29 Five-Year Plan. There are no financial impacts associated with this item.
CEQA:
The recommended action does not constitute a project under CEQA because it does not have the potential to result in a direct or reasonably foreseeable indirect physical change in the environment.
ATTACHMENTS:
Attachment 1: PowerPoint
UNCLASSIFIED MANAGER:
Manager
Ryan McCarter, 408-630-2983