According to this Oregonian story, a large volume of untreated sewage was discharged into the Willamette this week because of the heavy rains. Thankfully, this kind of story is news nowadays, because historically, discharging sewage into the Willamette was Portland’s sewage handling strategy.
According to my math, 61.9 million gallons of sewage discharge in 3 hours and 45 minutes equals about 620 cubic feet per second, which, put in perspective, is roughly twice the summertime flow of the Tualatin River at West Linn. According to these Portland BES estimates, that’s only about 1/3 of the 1,900 cubic foot per second maximum system-wide expected overflow. In other words, combined system overflows of untreated sewage can get a lot worse than the event we experienced on Wednesday.