science environment

Portland Water Bureau Has Location, Technology In Mind For New Filtration Plant

By Amelia Templeton (OPB)
Aug. 15, 2018 8:05 p.m.

The Portland Water Bureau has identified a likely location for a new treatment plant for the city’s drinking water, which comes from the pristine Bull Run Watershed east of Portland.

The bureau has until 2027 to design and build the plant under an agreement it reached with the Oregon Health Authority last year after testing found a tiny microbe, cryptosporidium, in the city’s water source.


Some forms of the microbial pathogen can cause serious and even fatal illness in humans, while other varieties don’t appear to easily infect people.

The preferred site for the plant is a 95 acre parcel of land in the unincorporated community of Cottrell, roughly halfway between Gresham and the Bull Run Watershed.

The water bureau acquired the property decades ago, anticipating that as federal drinking water regulations changed it might need to build a treatment plant.

Director Mike Stuhr says the site is surrounded by farms and nurseries. It has the appropriate zoning for a plant and is at an elevation that will help maintain the flow of water through Portland’s pipes. Portland’s water system is almost entirely gravity fed.

“It’s a little early to predict, but one of my goals is gravity’s cheap, gravity is free, nobody’s figured out to bill us for it yet. So we want to maintain as much of the gravity system as possible,” Stuhr said.

Stuhr and bureau staff presented the Portland City Council with an update on plans for the treatment facility this week.

The bureau has also identified a preferred technology for the plant: a granular media filtration system.

It’s the most common type of treatment used by large water systems in North America. Granular systems typically use a combination of sand and anthracite, a type of coal, to filter out sediment and microbes.


The bureau wants the new plant to have the capacity to treat 140 to 160 million gallons per day, based on the projected daily demand for water through 2045.

The water bureau has not developed an updated cost estimate for the plant, but pressed by Commissioner Nick Fish, Stuhr said the technology the bureau prefers should put costs at the low end of an initial estimate of $350 to $500 million.

But Stuhr cautioned that a number of factors make it difficult to predict construction costs, including new tariffs that have created uncertainty around the future price of steel.

“I can say generally, from listening to my staff talk, we’re seeing increasing prices,” Stuhr told OPB.

Next week, the water bureau will ask the city council to authorize two major decisions related to the multi-million dollar construction project.

The bureau wants to hire the environmental engineering firm Brown and Caldwell to assist with high-level project planning and design oversight decisions.

The bureau is also seeking approval to use alternative criteria to evaluate bids for the construction project.

That would allow it to select a general contractor based on qualifications, as opposed to the lowest cost, according to the bureau.

Portland’s City Council voted unanimously in 2017 to direct the water bureau to pursue plans to build a filtration plant for the city’s drinking water.

Up until that year, Portland had been the only large city in the country with a variance from EPA rules that require treatment of surface water sources for several microbial pathogens.

Portland received the variance on the basis of the extraordinary environmental protection of its water source, the Bull Run Watershed, and testing that established little presence of cryptosporidium in the city’s reservoirs and their surroundings.

In 2017, routine testing began regularly detecting very small amounts of cryptosporidium in the city’s water supply. While no public health outbreak of cryptosporidosis was detected, the Oregon Health Authority announced it was revoking the water bureau's special variance.

In addition to removing any cryptosporidium from the water supply, a treatment plant will also remove sediment from the water. Bureau staff say that will make the city’s drinking water system more resilient to climate change and to natural disasters like wildfires and earthquakes.