Portland Rain Brings Another Sewer Overflow

Avoid the Willamette River north of Willamette Park for the next 48 hours. Portland says all that rain over the past couple of days has led to another sewage overflow into the river.

They say that it was detected at the Southwest Carolina Street outfall last night. It started at 11:47 p.m. and ended at midnight.

The city's Bureau of Environmental Services said this was the fourth overflow of he winter season. The other ones were: Super Bowl Sunday, February 5. due to unusually heavy rains that dropped about 2.5 inches within 24 hours; on January 18, due to a combination of snowmelt and heavy rain; and Thanksgiving Day due to heavy rain.

BES urges people to avoid the water for 48 hours after the end of a sewer overflow event.

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Before the city completed its sewer overflow control program, overflows happened an average of 50 times a year. Today, the combined system overflows to the Willamette River an average of four times per winter and once every three summers.

Portland's combined sewer system carries sewage and stormwater runoff in the same pipes. In December 2011, Portland completed a 20-year program of sewer improvements, including constructing big pipes on both sides of the Willamette River and along the Columbia Slough. The improvements eliminate 99% of CSOs from the slough and 94% from the river.

During heavy storms, the big pipes store large quantities of stormwater and sewage while pumping it to the Columbia Boulevard Wastewater Treatment Plant. During very heavy storms, some combined sewage can overflow. A combined sewer overflow is about 80% stormwater and 20% sanitary sewage.

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Photo Colin Miner