Seismic-Savvy Infrastructure: The Story Behind Wilsonville’s Raw Water Facilities Project

The Raw Water Facilities Project (RWF_1.0) is the critical first link in the Willamette Water Supply Program (WWSP), a regional partnership providing safe, reliable drinking water for growing communities in Washington County, Oregon. Located at the Willamette River Water Treatment Plant in Wilsonville, RWF_1.0 upgrades and expands key infrastructure, including pump stations, intake structures, fish screens, and a 66-inch raw water pipeline, all while strengthening seismic resiliency so water delivery can continue even after a major earthquake. Beyond technical excellence, the project protects public health, supports regional growth, and demonstrates forward-thinking engineering that balances innovation, safety, and sustainability. It is more than infrastructure – it is a foundation for community resilience that will serve hundreds of thousands of residents for generations.

Project Goals/Overview

The Willamette Water Supply Program (WWSP) is a partnership between the Tualatin Valley Water District, the City of Hillsboro, and the City of Beaverton established to develop a seismically resilient water supply for growing communities in Washington County, Oregon. The Raw Water Facilities Project (RWF_1.0) establishes the new water source of this $1.6 billion regional system, which will draw from the mid-Willamette River to provide safe, reliable drinking water to hundreds of thousands of residents.

Located in Wilsonville at the existing Willamette River Water Treatment Plant, RWF_1.0 was designed to enhance the reliability, capacity, and seismic resiliency of the water intake and pumping facilities that supply the new Willamette Water Supply System. Improvements included upgrades to the existing pump station and intake caisson to increase pumping capacity and resiliency, construction of a new electrical building and standby power system, seismic stabilization of the Willamette River bank, installation of new fish screens, and construction of a 66-inch-diameter raw water pipeline extending from the pump station to connect with the next project phase (PLM_1.1).

These upgrades were designed to increase capacity for future water needs and to make sure water delivery can continue even after a natural disaster, such as a major Cascadia Subduction Zone earthquake. RWF_1.0 is a cornerstone of the WWSP program’s resilience strategy, supporting seismic resilience of the system at its source.

Uniqueness and/or Innovative Application of New or Existing Techniques

RWF_1.0 presented significant engineering challenges: retrofitting and expanding an existing facility located within a narrow riverbank site bounded by the Willamette River and critical infrastructure. The project was delivered with the Construction Manager/General Contractor (CMGC) model, enabling early collaboration between the design team, contractor, owner, and peer reviewers and emphasizing constructability and reducing changes during construction.

WWSP established program-wide seismic design guidelines and minimum design requirements based on the 2013 Oregon Resilience Plan. These guidelines set ambitious Level of Service (LOS) goals that required 100% operational capacity within 24 hours following a magnitude 9.0 Cascadia Subduction Zone event and five days of fully independent operation. To meet these goals, the Black & Veatch (B&V) and GRI team conducted a seismic resiliency and recovery by design analysis, systematically identifying and mitigating risks to operations, recovery, and public safety. This process defined performance objectives for critical structures and equipment, backup systems, and lifeline utilities, making sure that each component could continue operation or be rapidly restored after a major seismic event.

A critical input to the system-wide resiliency and recovery study was to provide best estimates of seismically induced soil movements at critical infrastructure locations throughout the site (including the steeply sloping Willamette Riverbanks). GRI’s geotechnical engineers employed a range of innovative techniques to achieve these design objectives. The approach included an extensive subsurface exploration program with on-land and in-water borings, cone penetration testing, and Cyclic Direct Simple Shear (CDSS) laboratory testing to provide the necessary calibrated inputs for advanced slope stability and numerical modeling using the Fast Lagrangian Analysis of Continua (FLAC) software. The modeling used site-specific testing and calibration to evaluate the potential for liquefaction, lateral spreading, and the potential ranges and pattern of deformations that could impact the existing caisson and new and existing pipelines structure during a 2,475-year Cascadia event. The CDSS testing was focused on better estimating the behavior of the fine-grained silty soils, which have a wide range of potential seismic behavior and are a critical university and industry research topic in the last decade. This testing was completed at GRI’s in-house laboratory, allowing the team to directly measure how the site’s soils would behave during strong earthquake shaking and significantly reduce conservatism that was considered during earlier design phases. In tandem, B&V performed soil-structure interaction finite element modeling of the new welded steel water pipeline to determine it could withstand up to 7 inches of lateral ground deformation without losing integrity. B&V also designed structural retrofits and seismic restraints for the pump building and equipment to prevent overstress during seismic events. This collaborative, data-driven process allowed the team to optimize resiliency and set the standard for future seismic design in the Pacific Northwest.

To meet the tight deformation criteria identified for seismic resiliency, GRI designed a unique ground improvement system using angled jet grouting and deep soil mixing (DSM) within an exceptionally constrained footprint between the existing caisson and the steep riverbank. The design was refined into three ground improvement geometries, starting at the caisson and moving along the pipeline alignment, and was calibrated to different allowable deformation thresholds established by the design team for each controlling structure or improvement. This innovative design avoided working below the river’s ordinary high-water mark, which eliminated the need for additional environmental permitting and protected the environmentally sensitive riverfront and forested area that would have been otherwise removed.

The integration of multiple structural design codes and the program’s project-specific performance criteria within a single project was equally innovative. The existing pump station retrofit was governed by American Society of Civil Engineers (ASCE) 41, while new structures such as the electrical building were designed to ASCE 7-16. These codes and program-specific design requirements include different seismic hazard levels and performance expectations, so integrating the three of them was relatively novel and presented a unique challenge. The design team collaborated closely with the seismic peer review panel to create unified, project-specific seismic design criteria that have since been adopted program-wide as the standard for future WWSP facilities.

Future Value to the Engineering Profession and Enhanced Public Awareness of and Enthusiasm for the Role of Engineering

RWF_1.0 provides a replicable model for seismically resilient water infrastructure design and interdisciplinary collaboration. Its design solutions, particularly the integrated use of ASCE 7 and ASCE 41 standards with project-specific performance expectations, advanced soil-structure modeling, and unique site-specific ground improvement, has helped set a precedent for engineers to address retrofit and expansion challenges for critical infrastructure. In this regard, the integrated design, analysis, and recovery framework developed here is transferable to other utilities preparing for seismic risks, advancing the profession’s ability to safeguard essential services in the event of natural disasters.

The WWSP’s emphasis on elevated seismic standards, peer review, and public communication has also brought awareness to the vital role of engineering in community resilience. While much of the work will never be seen by the public, its benefits are profound: establishing and protecting a functioning water supply for hundreds of thousands of residents while the community grows, even after a major earthquake. The project demonstrates how forward-thinking infrastructure design can protect public health, economic stability, and emergency response capacity in the face of seismic risk.

Social, Economic, and Sustainable Development Considerations

RWF_1.0 directly addresses a critical community need: securing a reliable and seismically resilient water source for a growing population for now and for the future. By reinforcing the intake structure, stabilizing the riverbank, and implementing stringent seismic design criteria, the facilities will remain operational following a major earthquake, protecting public health and safety.

Environmental considerations were central to the design process and solutions. GRI’s ground improvement design minimized disturbance to the riverbank and preserved natural habitats. B&V incorporated energy-efficient pumping and backup systems that allow five days of independent operation, supporting both resilience and sustainability goals. The improved facilities also increase pumping efficiency and provide long service life, contributing long-term sustainability.

Economically, RWF_1.0 represents a major investment in resilient infrastructure that also supports regional growth. The CMGC delivery method enabled early collaboration among the owner, CMGC, and the B&V and GRI team for constructability reviews and value engineering. This process yielded significant cost savings, including a roughly $8 million reduction in ground improvement cost from the Engineer’s Estimate, while maintaining or improving performance standards. Beyond construction savings, the facility’s ability to remain operational after such a massive event as a Cascadia Subduction Zone earthquake will play a vital role in the region’s economic rebound.

Complexity

Few portions of the WWSP presented more technical and logistical complexity than RWF_1.0. The site’s limited footprint, bounded by the river, existing facilities, and a public park, demanded innovative design and construction staging. Construction required coordination with ongoing operations at the adjacent Wilsonville Water Treatment Plant and temporary park closures to protect public safety. The project also included a trenchless crossing across Arrowhead Creek to maintain site access across the existing bridge and to minimize disturbance in the creek.

Subsurface conditions included fine-grained, potentially liquefiable soils that posed a risk of slope failure toward the river during a Cascadia Subduction Zone earthquake. GRI developed detailed 2D numerical models to evaluate soil-structure interaction, guided by site-specific cyclic laboratory data, while B&V’s finite element analysis verified structural and pipeline performance underground deformation scenarios. When analysis revealed that pump equipment verticality, rather than structural demands, governed certain design parameters, the team pivoted to develop customized deformation criteria for each project feature. This iterative, multi-disciplinary design process required close coordination among the owner, civil, geotechnical, structural, and construction teams, an effort that exemplified engineering ingenuity and adaptability.

Successful Fulfillment of Client/Owner Needs

From project initiation through construction, the RWF_1.0 team maintained a strong partnership with the WWSP, City of Wilsonville, the Owner’s Representative, and the Contractor. Early involvement in peer review and basis-of-design development meant that all parties shared a common understanding of the site’s constraints and seismic performance objectives from the outset. The CMGC delivery approach facilitated timely feedback and constructability input that informed design refinements and mitigated risk. B&V coordinated with the owner and City to plan water treatment plant outages required for system tie-ins. The outage planning exercise developed redundancy and contingency strategies that maintained continuous water supply and minimized service disruptions.

The final design met the owner’s objectives for safety, resilience, constructability, and cost control. The project was delivered on schedule and under budget. The contributions of the B&V and GRI team addressed the site’s geotechnical and seismic complexities and established the technical framework for future WWSP facilities, laying the groundwork for a resilient water system that will serve the community for generations. RWF_1.0 demonstrates engineering excellence in technical complexity, innovation, collaboration, and public service. As the critical initial link to a new regional water system source, it has set a national standard for seismic resilience efforts for water infrastructure projects.