Columbia River Outfall and Effluent Pipeline Project

This project builds on decades of planning to ensure we can meet the region’s long-term wastewater treatment needs and continue safeguarding public health, environmental quality and our community’s economic future. The project will upgrade the transmission pipeline from the Salmon Creek Wastewater Treatment Plant to the Columbia River and improve water quality in the Columbia River.

Project Benefits

The project will:

  • Ensure continued reliable service at a stable, affordable rate by planning for the long-term and avoiding the increased cost of isolated improvements.
  • Support planned growth within the community.
  • Ensure adequate mixing and dilution of treated wastewater discharged into the Columbia River.
  • Manage shoreline stability at the discharge point.
  • Enable future decommissioning of Ridgefield’s aging wastewater treatment plant and outfall into Lake River (after additional projects are in place).

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Contact Us

Adrienne DeDona, Public Outreach Manager, can be contacted at (360) 903-4792.

Project information can be provided in other formats or languages upon request.

Project Overview

Columbia River Outfall and Effluent Pipeline Project Map

The project will build a replacement pipeline between the Salmon Creek Wastewater Treatment Plant and the Columbia River, as well as an improved discharge assembly at the river.

The Salmon Creek Wastewater Treatment Plant treats wastewater from approximately 100,000 Clark County residents. All wastewater received at the plant is treated to a high standard. Clean water, or effluent, is conveyed and discharged into the Columbia River via a 30-inch pipeline and submerged diffuser. The conveyance pipeline and diffuser were built in 1974 and need to be replaced. The Columbia River Outfall and Effluent Pipeline project will plan and build a larger transmission pipeline and improved discharge system.

The new conveyance pipeline will be big enough to ensure continued reliable service at a stable, affordable rate by planning for the longterm and avoiding the increased cost of isolated improvements.

The pipeline and diffuser are needed for future increased plant capacity to support planned growth in the community, as well as to ensure adequate mixing and dilution of treated water discharged into the Columbia River. The project will also reduce ongoing maintenance at the discharge location and allow future decommissioning of Ridgefield’s aging wastewater treatment plant.

The information in this web page is also available as a fact sheet (PDF, 2.36 MB).

Preliminary Design and Preferred Pipeline Route

The first two tasks of this project are to determine the preliminary design and preferred route for the new conveyance pipeline. This step in the process has been in discussion for over two decades and is nearing completion.

The emerging preferred route and location that has been identified is parallel to the existing effluent pipeline. However, planning the route for the new conveyance pipeline is complicated because it must cross private property, the Burlington Northern Santa Fe Railway, existing utility lines, Salmon Creek, Lake River, and two road rights of way. A variety of permits will need to be obtained before construction can begin. We are negotiating with property owners for easements. The community will be kept informed as the design process moves forward.

Diffuser Diagram

An improved diffuser under the Columbia River will ensure that increased discharge of treated water is mixed efficiently and will not harm the environment.

Improved Water Quality: Discharge Mechanism

The Columbia River has been designated by The Department of Ecology as impaired due to high temperature, presence of bacteria, and low oxygen. In order to address the Columbia River’s water quality issues, an improved river discharge assembly, called a diffuser, will be built at the end of the effluent conveyance pipeline. We’ve worked closely with the Department of Ecology to determine the best location and design for the outfall (discharge location). The diffuser and replacement pipe will improve Columbia River water quality by better diluting and mixing discharges of treated water. The mixing zone will meet stringent standards set by the Department of Ecology to ensure clean water for swimming, boating, fishing, and aquatic resources.

Aligning Planning Considerations with Community Values

Special care is being taken to make sure that construction, installation, and operation of the new effluent pipeline and outfall will be environmentally sound, cost-effective, fiscally responsible, and address neighbor and ratepayer concerns. The new pipeline will require minimal energy and maintenance to operate. The existing pipeline will be retained to facilitate continuous treatment plant operation during the transition and routine maintenance.


In 2014, the Alliance adopted a comprehensive Capital Plan that brings the partners’ facility assets, including the Salmon Creek Wastewater Treatment Plant and discharge facilities, under Alliance ownership. Planning and design costs for the Columbia River Outfall and Effluent Pipeline Project are covered in the Capital Plan.

In total, the project is anticipated to cost $20–25 million. Those costs are allocated to the local agencies that own the capacity within the facility – the City of Battle Ground and the Clark Regional Wastewater District. The City and the District have included the project costs in long range financial planning efforts to ensure affordability of rates and charges.

Diffuser Diagram

Reliable, expandable sewer service is essential to our economy and the health of our communities and environment.

Planning for the Future

It’s important to plan for the future. Our community expects dependable, affordable sewer services that are essential to our quality of life. Our personal health, the community’s economic health, and the health of our rivers and environment depend in large part on treating the wastewater we all generate so that it can be returned safely to the environment. To effectively meet our growing need, the Alliance is already underway with this Phase 5 expansion project.

The Phase 5 expansion will take place over several years and will be performed as two separate and independent projects. In addition to designing, planning and constructing the Columbia River Outfall and Effluent pipeline, the Alliance will conduct a capacity analysis that will evaluate existing operations and recognize ways to increase the plant’s treatment capacity to 17 million gallons per day without changing physical infrastructure. As part of this capacity analysis, an odor containment and treatment system will be built to serve the Preliminary and Primary Treatment Facilities at the plant.

Staying ahead of the reliability and resiliency needs is vitally important. By proactively planning now, the Alliance ensures that ample wastewater treatment facilities will be in place to continue to provide reliable service at an affordable cost well into our future.

Design Work is Underway, Though Construction is Years Off

We are completing information and data gathering to verify pipeline location and design. This includes surveying, geotechnical exploration, environmental analysis, and determining permit and easement needs. As planning and design progress, cost estimates will also be updated.

There is a great deal that needs to be completed before construction can begin, including detailed design and engineering, acquisition of the necessary permits and easements, and selecting a construction contractor.


Outfall Project Schedule

Stay Up to Date

Throughout the project, interested community members can follow progress and provide feedback through this website, and at public events. The event schedule will be posted online.