Heavy rain. No combined sewer overflow (CSO)
During the storm from March 11 to March 14, 1.3 inches of rain fell in Portland. The Willamette River Big Pipes managed the storm and no combined sewage overflowed to the river.
Wastewater Collection and Treatment
The Columbia Boulevard Wastewater Treatment Plant normally processes an average of 70-million gallons a day. On March 13, the plant processed 241-million gallons.
The plant processed a total of 509 million gallons from March 11 to March 13. That's enough water to fill nearly 5,560 semi-truck tank trailers.
One inch of rain within 12 hours can be enough to cause a combined sewer overflow to the Willamette River. The 1.3-inches of rain from this storm over three days did not exceed that level and the Willamette River big pipes safely conveyed all the wastewater to the treatment plant. There was no overflow to the river.
At the peak of the storm, the 16-foot diameter West Side Big Pipe and the 22-foot diameter East Side Big Pipe together reached only 32% capacity. The Big Pipes stored about 198 million gallons of wastewater, a combination of stormwater and sanitary sewage, and conveyed it all to the Columbia Boulevard Wastewater Treatment Plant.
After the heaviest rain on March 13, it took about 24 hours to pump out all the wastewater stored in the big pipes.
With every inch of rain, Portland's 1,700 green street planters collect and filter about 3.8 million gallons of stormwater runoff, and allow water to soak into the earth to replenish groundwater.
During the March 11 - March 13 storm, green streets managed an estimated 4.9-million gallons of stormwater.