St. Paul has long separated its sanitary sewers from its storm water system, but that doesn’t mean clear water never seeps into wastewater pipes.

Root intrusion and aging infrastructure lend themselves to cracks in the system, and when clear storm water and groundwater infiltrate wastewater collection, they take up important space in wastewater pipes needed for future real estate development. Excessive clear water can create sewage backups into homes, as well as dirty overflows into lakes and creeks.

After extended rainfall, some city sewer systems will be full of as much clear water as wastewater.

“The average amount of (inflow and infiltration) is anywhere from 10 to 20 percent, but we’ve seen some communities where it’s as much as 70 percent, and in some cases can even double,” said Kyle Colvin, manager of engineering programs within the Metropolitan Council’s Environmental Services division.

To help combat the problem, the Met Council has awarded a three-year, $500,000 grant to the city of St. Paul to showcase how local government can work with private property owners on the issue, in this case within a 10-block stretch of the West Side Flats area of the city. Within the designated area, the city has already begun free inspections of the sanitary sewers extending from people’s homes, which would ordinarily cost $300 to $500 per inspection. Repairs, if necessary, would take place in 2020 at free or reduced cost.

Roughly 80 percent of clear water entering the wastewater collection system comes from private sources, an issue expected to become even more critical as the region’s population grows.

“The St. Paul demonstration will be one of the first to accurately quantify the reduction created by specific repairs because of the targeted area of the project,” the Met Council said in a statement.

A 2016 Met Council task force determined that funding a local demonstration project would be the best way to obtain data on the problem and pave the way for other municipalities to follow. St. Paul’s three-year proposal won a competitive grant process in 2018.

The St. Paul project will focus on private pipes, called “service laterals,” that bring wastewater from homes and businesses to the city wastewater pipe in the street.

The city has already reached out to the property owners on the West Side Flats, a growing residential area across the Mississippi River from downtown St. Paul, and installed flow meters throughout the 10-block project zone from George Street to Annapolis Street, between Manomim Avenue and Ohio Street. Sewer service pipe inspections are underway. Part of the grant funding will pay to repair faulty sewer pipes.

Some cities, such as Golden Valley and West St. Paul, have reduced the problem from private property by requiring inspections and repairs of private service lines when a house is sold. Related Articles Minneapolis man pleads guilty to torching University Avenue business during May unrest

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Kenny Blumenfeld, a climatologist with the Minnesota Department of Natural Resources, has informed the Met Council that climate changes have added to the issue. On average, annual rainfall in the Twin Cities has increased from 26 inches in the 1940s-1970s to 31 inches in the 1980s-2000s, and has kept going up in the past decade.

The alternative to reducing the issues would be to build even bigger sewer pipes and expand treatment plants. That would “cost billions of dollars and cause unnecessary disruption to communities and transportation systems,” Jeannine Clancy, assistant general manager for Met Council Environmental Services, said in a statement. “Addressing (the problem) on private property is the most cost-effective solution.”

To reduce inflow and infiltration, the Met Council urges homeowners to have their sewer service laterals inspected, to check to make sure that sump pumps are pumping water outside their home and not into the wastewater system, and to disconnect gutters and downspouts that may be discharging storm water directly into the sewer service instead of the storm water system. The Met Council has put more information online at tinyurl.com/MetCouncilInflow.