CSO Advisory: Localized heavy rains leads to a combined sewer overflow to the Willamette River

Press Release

May 2 Update: This combined sewer overflow (CSO) advisory has expired 48 hours after the overflow ended or at about 4:00 p.m. May 2.

May 1 Update: The CSO started at 3:33 p.m. and ended at 3:40 p.m on April 30. The total volume of the overflow was an estimated 4,080 gallons. The public is advised to avoid contact with the river for 48 hours after the CSO has ended because of increased bacteria in the water.

Heavy rains led to a combined sewer overflow (CSO) to the Willamette River from an outfall located between the Cathedral Park Boat Ramp and St. Johns Bridge. The overflow began around 4:30 p.m. The volume of combined sewage that reached the river is unknown at this time. Avoid contact with river water downstream of this location.
During an overflow and for 48 hours afterward, the public is advised to avoid contact with the river because of increased bacteria in the water. The river’s water quality is safe for recreation during all other times.

A CSO is about 80 percent stormwater and 20 percent sewage. 

CSOs are rare and can occur during periods of heavy rain or snowfall.

Since completing the Big Pipe project in 2011, the 20-year $1.4 billion program to reduce overflows, the number of CSOs has dropped by 94 percent to the Willamette River and 99 percent to the Columbia Slough. 

Before the project, CSOs occurred to the Willamette River from multiple outfalls an average of 50 times a year, with some instances lasting days. Today, overflows occur an average of four times per winter season, and once every three summers.

The Big Pipe system refers to a series of improvements, from disconnecting downspouts on homes to allow rainwater to be absorbed naturally in the ground to the construction of big pipes on both sides of the river and along the slough to store and convey large quantities of flows to the Columbia Boulevard Wastewater Treatment Plant.

Find out more about the Big Pipe and CSOs.

Follow updates on Twitter @BESPortland.

-  ### - 

Environmental Services is Portland’s sewer and stormwater utility. We protect public health and our environment by collecting and recovering resources from the city’s wastewater, managing stormwater, and restoring and protecting Portland’s rivers, streams, and watersheds. portland.gov/BES/news