Future Water Supply

Cascade currently contracts with Seattle Public Utilities (Seattle) to provide drinking water to its seven member agencies. In 2009, Cascade purchased Puget Sound Energy’s former White River – Lake Tapps Reservoir system as future, municipal drinking water supply.

Cascade’s supply contract with Seattle is a declining block agreement, which begins to decline in 2039. Without a contract extension with Seattle, or a new supply contract with Tacoma or other supplier, Cascade needs to develop and put the Lake Tapps Reservoir in service by 2042.

In May 2024, Cascade’s Board of Directors approved a resolution which directs Cascade to negotiate a supply contract with Tacoma. Cascade expects to take water from Tacoma starting in 2041 to replace the declining Seattle supply.

A new contract with Tacoma would allow Cascade to defer developing the Lake Tapps Reservoir until at least the 2060s. By that time, Cascade will need a new water treatment plant and other major infrastructure.

A new Tacoma contract would require development of the Tacoma-Cascade Pipeline (TCP) to connect Cascade to Tacoma’s water system. At approximately $1.0 billion, the TCP will be the largest project undertaken by Cascade and will include the following project elements: the Central Pipeline segment, the North Pipeline segment, the Bellevue-Kirkland-Redmond (BKR) Pipeline, a pipeline that runs parallel to the Bellevue-Issaquah Pipeline (BIP), booster pump station(s), storage facility(s), and connections.

Pending development of the plans listed below, alternatives for the Central and North Pipeline segments combined may total approximately 25-30 miles, ranging from 24” to 66” in diameter, and would deliver up to 35 mgd of water from Tacoma’s Pipeline 5.

Cascade will rely heavily on the consulting community to manage, plan, and design the TCP and to support environmental review, permitting, and property acquisition. Between 2025 and 2040, Cascade plans to secure the following services either as stand-alone contracts or a combination of contracts:

• Program and engineering support services to provide strategic and tactical program and engineering support services to Cascade through the duration of the project. This includes development of a Project Execution Plan, a Project Procurement Plan, and other documents as required. (The selected firm and their sub-consultants for this consulting contract will be prohibited from proposing and performing follow-on work, either as a prime or sub-consultant, on the Design team.)
• Development of an Operations and Flow Allocation Plan that identifies the amount of water and methods of transfer from the TCP to Cascade’s member agencies’ distribution systems. This plan forms the basis for system requirements and the development of the Facilities Plan.
• Development of a Facilities Plan (or Project Scope Statement) that forms the basis and requirements for the project design.
• Franchise and right-of-way support services to evaluate potential permanent and temporary real property needs and alternatives and (following design and environmental and permitting review) assist in acquiring all real property rights that are needed for the project.
• Design, environmental and permitting services for the Central and North Pipeline segments and associated facilities and connections.
• Construction management services for the Central and North Pipeline segments and associated facilities and connections.

Construction would start in 2030 for the Central Pipeline segment and the mid-2030s for the North Pipeline segment. Design and construction of the Intown Transmission Pipes and other infrastructure (BKR Pipeline, Parallel BIP, booster pump station(s), storage facility(s), and connections) will commence in the 2040s.

For more information about the TCP Project, click on these links:

• Estimated TCP and Lake Tapps Reservoir project timelines
• Upcoming TCP consultant contracting opportunities

Questions? Contact Henry Chen, Engineering and Capital Projects Director, at hchen@cascadewater.org or (425) 283-0367.