The Bureau of Environmental Service, which operates Portland’s sewer system, is advising people to avoid contact with the river for at least 48 hours after the overflows end because of increased bacteria in the water. There is no estimate when they will end because of the continuing rain.
A combined sewer overflow is about 80 percent stormwater and 20 percent sanitary sewage. They used to occur much more frequently, but the $1.4 billion Big Pipe project completed in 2011 reduced them by 94 percent to the Willamette River and 99 percent to the Columbia Slough.
Despite that, CSOs — as they are commonly called — can still happen during especially heavy rains. According to the National Weather Service, more than two inches fell in Portland on Saturday and the storm system called an atmospheric river may continue to bring periods of rain to the Portland area through Sunday.
Read the whole story at the Portland Tribune.