I just remembered that Hanford monitors the City of Richland water intake area (the water going to the water treatment plant for potable water use) for contamination measurements which they do on a regular basis, I have seen the set up personally since I used to help maintain the Irrigation pump for Leslie Groves Park which is in the same intake area.
The latest pump for Irrigation was a 40 Horsepower delivering 450 PGM but I never ran it above 400 PGM to prevent Cavitation and maintain stable pressure at around 90 PSI.
The water was always safe for use even the Richland Wastewater is daily sampled for a variety of contaminants before it gets discharged back into the river which I have seen the Monthly charts showing that 99.98% of the time nothing gets above the minimum safe level.
Have no idea what goes on in the Portland area but the Rivers giant flow greatly diluted the contamination.
Every year in June The Columbia river for about 2-3 weeks empties more water into the ocean than any other river in the world.
None of that massive river flow really affects small neighboring communities that draw water from elsewhere. And in the case of SAVANAH river plant, the awful unthinkable stuff is already happening in terms of ground and river water contamination.