(October 19, 2017) – A combined sewer overflow (CSO) occurred this evening from a single location - the SE Alder Pump Station that is slated to be taken offline later this month to improve and expand its capacity.

Triggered by heavy rains, the CSO began at 7:32 p.m. and ended 14 minutes later, discharging about 23,000 gallons of stormwater mixed with sewage to the Willamette River.The pump station also overflowed in September for four minutes. The SE Alder Street Pump Station is located at SE Alder Street and Water Avenue. https://goo.gl/maps/kmdmYw57pD22. 

A CSO is about 80 percent stormwater and 20 percent sewage. The pump station, built in 1952, is scheduled to be taken offline later this month for two years of construction. The upgrades will improve reliability and increase pumping capacity to prevent sewage releases into buildings and streets as well as overflows to the river. During construction, the combined sewage and stormwater flows will be diverted to other pipes in the system and the  likelihood of CSOs from this location will decrease.  For more information on the project, please visit: https://www.portlandoregon.gov/bes/72747.

CSOs are rare, but when they occur the public is advised to avoid contact with the river for about 48 hours due to increased bacteria in the water. In this case, the public is advised to avoid contact with the Willamette River from the Morrison Bridge to the Columbia River confluence until this advisory is lifted. Areas upstream are not subject to this advisory.

Since completing the Big Pipe project in 2011, a 20-year $1.4 billion program to reduce overflows, the number of CSOs have been reduced 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.

For more information about CSO events, what they are and why they occur, visit https://www.portlandoregon.gov/bes/article/565061.

The Bureau of Environmental Services provides city residents with programs to protect water quality and public health, including wastewater collection and treatment, sewer construction and maintenance, stormwater management, and stream and watershed restoration. Visit www.portlandoregon.gov/bes and follow us on Twitter for news @besportland.

Media contact: Diane Dulken 503.823.6724 diane.dulken@portlandoregon.gov