Why sump pumps may cause sewage backups

Why do sewage spills and backups happen when it rains, and rains and rains? The largest contributing factor: sump pumps that drain into the wastewater sewer instead of the storm water sewer.

This overwhelms the sanitary sewer system and sewage treatment plants. That's what happened earlier this month when the city of Mound got permission to release sewage into Lake Minnetonka to keep waste water from backing up into about 1,000 homes.

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There were between 20 to 30 such releases around the state from those early June storms. Then on June 19, sewage was released into a handful of lakes and streams from another round of storms.

Any drain in your home feeds into the sanitary sewer -- including floor drains, laundry tubs, sinks, bathtubs, and of course toilets.

Sump pump drainage hoses should stay on the outside of the house, draining water into the yard, or even the street, carrying the water along the curb into a storm water drain, said Tim O'Donnell, spokesman for the Metropolitan Council Environmental Services.

"The problem for folks with sump pumps is that sometimes they don't really have a drainage way to get the water to. So it just circulates around their foundation and that's why I think people sometimes resort to just putting it down the drain," said Bryce Pickart, acting general manager of Metropolitan Council Environmental Services.

He said if just one home continuously pumps storm water from its foundation or basement into the sewer system, the amount of water is roughly what 40 homes would be sending down the drain on a typical day.

Communities are making improvements in how storm water is drained, he said. In 2005, the levels of extra water going into the sewage system were higher than now, even though we've had more rain this year than in 2005.

It's hard to measure exactly how much progress is being made, Pickart said. "But we are making progress -- it's just that we really need to make more progress."

The Metropolitan Council is working with 50 metro area cities to improve their flood water drainage, and has offered grants to offset homeowner expenses of changing piping and draining.

Draining rain water or storm water into the sewage system is illegal. The state plumbing code has banned it since the 1960s, however older homes may still have it plumbed incorrectly, O'Donnell said.

"We hope this offers an opportunity to educate communities and property owners about what happens around their homes," Pickart said. "Some of these things people don't think about at all."

O'Donnell advises homeowners to watch this video from the city of Sioux Falls, South Dakota, about how to properly discharge your sump pump.

MPR News reporter Elizabeth Dunbar contributed to this report.