Willamette Water Supply System Commission

“The WWSS Commission is a partnership formed under ORS Chapter 190 between the following parties: Tualatin Valley Water District and the cities of Hillsboro and Beaverton.”

“The Willamette Water Supply System Commission is responsible to oversee the design, permitting, funding, construction, ownership, operation, management, repair and replacement, and, as reasonable, providing information to the WWSS Partners in support of their procuring financing for the WWSS in order to supply potable water to TVWD, Hillsboro, Beaverton, and other potential municipal water providers.”

“920 SW 6 Avenue, Suite 600 Portland, Oregon 97204 PH 503.222.9518 www.geosyntec.com Memorandum Date: March 30, 2026 To: Christina Walter and Jill Chomycia, Willamette Water Supply Program From: Jacob Krall, Geosyntec Consultants, Inc. Subject: Thermal Trading Annual Report for 2026 INTRODUCTION The Willamette Water Supply System Commission (WWSS Commission) is an Oregon intergovernmentalentityformedbyTualatinValleyWaterDistrict(TVWD),theCityofHillsboro, and the City of Beaverton. The WWSS Commission was formed to build the Willamette Water Supply System (WWSS) in response to planned growth in their service areas. The WWSS will provide an additional resilient water supply for Washington County. When complete, the WWSS will be one of Oregon’s most seismically-resilient water systems—built to better withstand natural disasters, protect public health, and speed regional economic recovery through restoring critical services more quickly. The Willamette River, one of Oregon’s largest rivers, is the WWSS’s new supply source. The raw water intake is located at the Willamette River Water Treatment Plant in Wilsonville. From there, raw water will be pumped to the WWSS Water Treatment Plant, a new state-of-the-art water filtration plant where multiple treatment processes will produce high quality drinking water. Drinking water will be pumped to reservoir facilities on Cooper Mountain, then will be gravity- fed to additional storage and customers in the TVWD, Hillsboro, and Beaverton service areas. The new system will be completed in 2026. On October 23, 2020, the Oregon Department of Environmental Quality (DEQ) approved a Thermal Trading Plan (TTP) to fulfill the temperature offset requirement of the Clean Water Act (CWA),Section401WaterQualityCertification(WQC)asitpertainstotheWWSS.Theapproved TTP modeled the required thermal offset requiredat the full withdrawal capacitytobe 30.2 million kilocalories per day (MMKcal/day). The maximum withdrawal will be reported in each annual report and compared to the credits achieved.”

“Water Treatment Plant Tualatin Valley Water District (TVWD), the City of Hillsboro and the City of Beaverton are developing the Willamette Water Supply System. The new system will draw water from the mid-Willamette River at Wilsonville and, once treated, deliver it to their customers. The Willamette Water Supply Program is being funded by TVWD, Hillsboro and Beaverton ratepayers. Plant Location and Capacity Construction of a new, seismically resilient water treatment plant (WTP) is essential to the new water system. It will be located in the Tonquin Employment Area near the intersection of SW 124th Avenue and SW Tualatin-Sherwood Road. The site is within the Urban Growth Boundary and the City of Sherwood. In addition to playing a critical role in improving the region’s ability to recover after a large earthquake, other benefits include: • Improving travel for the public—by building a new east-west road crossing 124th Avenue that connects Tualatin and Sherwood • Enhancing emergency preparedness—by creating an emergency facility capable of producing drinking water for emergency responders and the community within 48 hours of a major seismic event • Providing educational opportunities—through a public overlook of a preserved natural area, and other educational features The WTP will occupy about 20 acres. Approximately 20 additional acres are earmarked for roadway improvements, setbacks and habitat preservation. The site meets several important criteria including that it is geologically stable, is slated for future development, is of adequate size, and allows opportunities to conserve wetland and upland habitat. The stable soils on this site mean the WTP will have superior seismic resiliency and will be better able to withstand a catastrophic natural disaster. The new WTP will initially produce up to 60 million gallons of water per day (mgd) but will be designed for a maximum of 120 mgd. Water Treatment Process The new WTP will be designed to utilize similar processes as another plant utilizing the same source water, the existing Willamette River Water Treatment Plant (WRWTP), which has been delivering safe and reliable water to Wilsonville and Sherwood residents since April 2002. The new WTP will utilize multiple treatment steps to meet drinking water standards Learn More including enhanced coagulation sedimentation, ozonation, ultraviolet light, OurReliableWater.org granulated activated carbon, sand filtration, and chlorine disinfection (learn 503-941-4570 more at www.ourreliablewater.org/quality-water-after-filtration) Timeline [email protected] Design and permitting is underway. Construction is anticipated to begin around 2022, with the plant beginning operations in 2026. U_04142021”

“The Willamette Water Supply System (WWSS) Water Treatment Plant (WTP_1.0) is a new, seismically resilient water treatment plant with an initial treated water capacity of 60 million gallons per day. WTP_1.0 is in the City of Sherwood in Washington County, Oregon. The water treatment plant construction will require participation from many subcontractors and suppliers.”

“Construction is nearly 91 percent complete on the WTP_1.0 Project. At the height of construction, about 300 workers that represent hundreds of local and regional businesses will provide the skills and expertise to complete the work. Dozens of other companies will provide the goods and materials to support the effort.”

“The new WTP will initially produce up to 60 million gallons of water per day (mgd) but will be designed for a maximum of 120 mgd.”