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The Lake Oswego Tigard Water Partnership collaborated with local neighborhood associations to develop a Good Neighbor Plan to ensure consideration of community feedback during each of the project phases. Photo: Slayden Constructors

A $69 million project more than doubles capacity and incorporates energy-efficient and sustainable features.

Constructed in 1968, the original Lake Oswego Water Treatment Plant treated water from the Clackamas River in Oregon at a capacity of 10 million gallons per day (mgd). Periodic updates were made to the facility, with an expansion to 16 mgd in the 1980s, but it still lacked the size and technology to meet the growing needs of the cities of Lake Oswego and Tigard.

To improve overall water supply, the two Oregon cities devised a plan to upgrade and expand the wastewater treatment facility that would produce a larger quantity of high-quality drinking water and incorporate energy-efficient and sustainable features and operations.

At 16 mgd, the City of Lake Oswego’s existing treatment plant was undersized for present and projected future growth in the two communities, making expansion to 38 mgd capacity necessary. Working in collaboration, the two cities developed a plan for upgrading and expanding the facility and created a process for engaging nearby community members. Seeking their ongoing feedback and ensuring it was considered in the plan were critical pieces of the project’s success.

Maintaining existing plant operations during construction was another top priority for the project team, as it would require careful planning and considerations throughout the course of the project to ensure the community’s water supply remained consistent and properly treated.

Additionally, the plant needed to implement an updated treatment process, increased energy efficiency, incorporate renewable energy components, and address the plant’s seismic vulnerability.

Forging a partnership

In 2008, the communities of Lake Oswego and Tigard formed a partnership with the intent to share drinking water resources and the project cost. Tigard had previously leaned on the City of Portland for water, but long sought ownership of its own secure water source to maintain control over the price it paid and to ensure an adequate water supply for the future. In an effort to keep water rates affordable for residents in both communities, the Lake Oswego Tigard Water Partnership was formed. Dividing the cost of planning, designing, and constructing a new water treatment plant secured the long-term water needs at a more manageable cost for both cities.

Under the partnership agreement, the City of Lake Oswego managed and built the water improvements with oversights from a combined Lake Oswego and Tigard Council Committee, providing guidance when necessary.

Following the design phase with Stantec, the partnership contracted with Slayden Constructors, part of Stantec Construction Group, to build the expanded and upgraded plant via a $69 million budget.

Incorporating community feedback

The partnership collaborated with local neighborhood associations to develop a Good Neighbor Plan to ensure consideration of community feedback during each of the project phases — design, construction, and ongoing operations — and a process for two-way communications.

Aesthetically pleasing buildings, landscaping, and visual buffers gave the facility a residential look and feel. Photo: Slayden Constructors

The plan was developed during a 20-month period and incorporated more than 20 community meetings, tours, and open houses. Efforts to mitigate the impacts on nearby neighbors during construction and ongoing operations phases were identified and implemented into the plan, ensuring the plant remains a good neighbor into the future.

Aesthetically pleasing buildings, landscaping, and visual buffers — like planting more than 300 trees and 25,000 native plants and shrubs — gave the facility a residential look and feel. Integration of public amenities, such as pathways, a two-acre park-like setting, and rain garden, improved the area’s interconnectedness and encouraged ongoing public access at the site. The final product was an expanded wastewater treatment plant that truly blended with the neighborhood and incorporated innovative community features.

The plan and its purpose to create a more collaborative process played a significant role in the final output of the treatment plant, with much of the community feedback incorporated throughout the project’s life.

Maintaining existing operations

The new facilities were constructed around the existing facilities through a three-phase process. After completion of each phase, demolition of existing structures occurred, all while ensuring the existing plant remained operational. Construction of the numerous water-holding structures required considerable modifications and additions to buried process pipe throughout the site. As a result, all connections had to be carefully sequenced and planned to ensure existing processes were not interrupted. Many of the new buildings were constructed only several feet away from existing structures, requiring constant coordination between teams.

To plan for this careful coordination of the interconnections between the old and new buildings, the structures were 3D modeled in Revit, which allowed the team to virtually simulate how the two structures would coexist. Working from the Revit model, Slayden developed a set of sequence drawings that mapped out the key requirements for each phase of the project. The owner, contractor, and engineering teams used these documents to coordinate the work.

State-of-the-art water treatment system

The new plant incorporates a state-of-the-art water treatment process known as conventional filtration plus ozone. The ozone used in the process removes more impurities from the water supply than traditional treatment methods. It effectively eliminates taste- and odor-causing compounds and provides an additional barrier for protecting public health.

Additional benefits of the process include:

  • produces pleasant tasting water year-round;
  • reduces the amount of chlorine needed for disinfection; and
  • meets emerging concerns for pathogens, algal toxins, and pharmaceuticals

Energy efficient and seismically reliable features

Process pipe connections throughout the site had to be carefully sequenced and planned to ensure existing processes were not interrupted. Photo: Slayden Constructors

Energy efficient elements such as LED lighting and solar panels were installed at the plant to meet the partnership’s desire to utilize green design features. The addition of garden roofs, swales, and pervious surfaces reduce stormwater runoff and lower heating and cooling costs at the facility.

During construction, the partnership, Slayden, and other contractors utilized sustainable operational practices when available to mitigate the project’s impact on the environment and nearby neighbors.

Studies predicting a major earthquake in the Pacific Northwest led the partnership to design and construct more seismically sound infrastructure throughout the facility. Facilities and associated pipelines at the treatment plant are supported by 1,150 deep reinforced concrete piles — 56,000 linear feet of support — making the facility able to withstand most earthquakes.

Slayden Constructors worked closely with the partnership, design engineer, and other contractors to ensure the project met the appropriate needs and time requirements. The solutions-driven approach adopted by all parties was crucial in making the overall Lake Oswego Water Treatment project a success.


Steve Flett, vice president – preconstruction services at Slayden Constructors, Inc. (http://slayden.com), has more than 26 years of experience in construction. He is responsible for marketing and oversight of project pursuits for new opportunities leading to preconstruction tasks including but not limited to design and constructability reviews, value engineering, work strategies and sequencing, estimating, work package development, and client relations. Jeff Wall, construction manager at Slayden Constructors, Inc., has more than 25 years of experience. He has estimated and managed construction in Oregon, California, and Washington, including responsibility for the scheduling, planning, opening, and closing projects. His past projects include heavy civil, water and wastewater treatment plants, and fish facilities. Wall has completed 26 water and wastewater treatment plants totaling more than $300 million.

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