Geren Island Water Treatment Plant – Ozone Contact Basin

Project Completed: Scheduled completion in Spring 2024

City of Salem

The City of Salem owns and operates the Geren Island Water Treatment Plant near Stayton, Oregon, and has used it for generations to provide safe drinking water to the City and surrounding municipal areas. The treatment plant receives water from the North Santiam River and has utilized a roughing filter, acres of slow-sand filtration basins, and chlorine disinfection to continuously treat the water in compliance with the Surface Water Treatment Rule. Unfortunately, in 2018, a combination of environmental factors introduced cyanotoxins into the source water, and this historical treatment process was not able to remove these from the system and the only solution for several weeks was providing bottled water or water trucked in from other sources to serve the entire population. To address this issue in the future and ensure safe—and resilient—drinking water resources, the City invested over $50 million in the design and construction of an ozone treatment facility at the treatment plant. This treatment utilizes a powerful disinfectant called ozone to aid the roughing and slow-sand filters in destroying the cyanotoxins that filtration cannot remove.  

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Combined with the tried-and-true slow-sand filtration method, ozone treatment (another proven method) delivers excellent results in eliminating cyanotoxins. Some additional benefits of ozone treatment include treatment against other harmful organisms in the surface water, such as giardia and cryptosporidium, more stable year-round maintenance, a reduction in the amount of chlorine used, working harmoniously alongside the other treatment steps, and leaving no trace of ozone in the final water product. In addition to the Ozone Facility, the City and Carollo Engineers have also made another $50 million in improvements to the plant, including the replacement of the slow-sand underfilters, cleaning and resanding of the filter beds, and the construction of a 30-foot-diameter Ranney collector well to utilize as a source of water when the turbidity levels in the river exceed the levels that can be adequately treated in the roughing filter.

A photo of a duct bank crossing at a project site


Our construction management team is providing ongoing project construction management and inspection services during the more-than-three-year construction of the water treatment plant improvements, and has been responsible for managing the construction of all phases and facets of the $100 million project.

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Our team made specific recommendations to improve and streamline the project's construction while safeguarding all stakeholders' interests. We also managed material submittals, delivery ticket checks, concrete form and pour inspections, project material and equipment deliveries, and project-related correspondence. Partway through the project, the collector well became a part of the project. Our team provided additional support on schedule items, sequencing, and addressing construction issues with the contractor on starting and completing this phase. Through our expertise and involvement in construction management, the project is being finished efficiently and cost-effectively, and the City and contractor have maintained a good working relationship. The City's operation and water delivery system were minimally disrupted, and the residents of Salem and the surrounding municipalities will have a safe and reliable system for decades to come.

Our construction managers are instrumental in maintaining tight quality control standards, managing submittals, tickets, concrete, project material and equipment, and most of the project-related correspondence.