Rehabbing regional sewer pipes protects a valuable public asset

Date: Monday, February 8, 2016

Did you brush your teeth or flush the toilet this morning? If so, you are most likely a user of the Metropolitan Council’s regional wastewater collection system.

Workers install a new dual force main along Highway 101 in Hennepin County.Few elements of a thriving metropolitan region are less glamorous than wastewater infrastructure. Yet few things are more vital to our daily life. Just consider a plugged kitchen sink or toilet on Thanksgiving.

Residents of the Twin Cities metro area are fortunate that early civic leaders built one of the nation’s most effective and cost-efficient regional sanitary sewer systems – one that has kept ahead of growth and responded as needed to changing times.

But more than 100 years after the first sewers were laid in Minneapolis and Saint Paul, time has taken a toll on parts of the infrastructure. And the whole system grows older with each passing year.

Systematic sewer rehab underway

Graph shows when gravity interceptors in the seven-county metro were constructed: 2%25 between 1886 - 1900; 3%25 between 1901 - 1920;11%25 between 1921 - 1940; 12%25 between 1941-1960; 44%25 between 1961 -1980; 16%25 between 1981 - 2000; and 12%25 between 2001 - present.That’s why the Council is deeply engaged in a systematic, detailed rehabilitation program of regional interceptor sewers that is designed to keep these sewers strong and reliable for the next 100 years – even while the region adds 27,000 new residents every year.

Council Chair Adam Duininck is a champion of the long-range program. “Few residents have to think much about our wastewater system, and that’s as it should be,” he said.

“But we take sanitary sewers very seriously – on both a daily level and planning decades ahead to serve regional growth,” Duininck said. “Ultimately, our mission is to protect public health and the environment, and we’re also committed to making sure we get the most value for our investment, which is significant.”

Duininck said the Council’s long-range program demonstrates good stewardship of the public’s resources. “The investments will help us sustain our quality of life and the region’s vitality for decades to come.”

Some sewers still in use date to 1880s

The Council’s wastewater collection system is a complex, high-tech underground labyrinth.

Photo from the 1936 Minneapolis Journal shows KSTP interviewing workers in the giant wastewater (sewage) interceptor, then under construction, that connects Minneapolis and Saint Paul to the Metro Wastewater Treatment Plant south of Saint Paul on the Mississippi River. The interceptor, 200 feet below ground along some of its length, is still functioning.It includes 610 miles of large collector sewers (aka interceptors), which have an average diameter of 36 to 48 inches. The largest one is 14 feet in diameter. These pipes convey 250 millions of flow every day from locally owned sewers.

The system also includes 200 flow meter stations, 60 pumping stations and eight treatment plants. About 600 employees are responsible for the massive system, which is monitored 24/7.

The total value of the regional investment is estimated at $6.7 billion.

It’s an intricate system working hard against time. Nearly 75% of the conveyance system was built before 1980, and 28% before 1960. Some sewers still in use date to their original installation around 1880. The average life of a concrete sewer that conveys flow by gravity is about 80 years. Other sewers that convey flow under pressure last only about 40 years.

In addition to their age, regional interceptor sewers are usually more than 20 feet deep and not easily accessible for repair and rehabilitation. In fact, the deepest sewer is about 200 feet below ground in Saint Paul. Several interceptors cross under rivers.

The interceptors mostly range in size from 24 to 48 inches in diameter. But some are as large as 14 feet in diameter.

Maintaining high reliability, helping communities plan ahead

Bryce Pickart, assistant general manager of Metropolitan Council Environmental Services (MCES), said the ongoing rehabilitation program is essential to preserving the system and maintaining high reliability.

One method of interceptor rehabilitation is known as “cured in place pipe.” With this method, a lining is installed inside an existing pipe and hardened in place.“We serve more than 2.5 million people in 108 communities across the region,” Pickart said. “We have a comprehensive program to evaluate the condition of our assets, and have developed a purposeful, rational plan over many years to rehabilitate or replace the oldest or most-deteriorated facilities first.

“Our program assures that we continue protecting the public health and the environment, and also provide capacity to serve our growing population,” Pickart said.

It won’t be inexpensive, and as a result municipal wastewater charges are expected to rise gradually in the decades ahead. To maintain the system, Pickart said the Council will need to invest about $100 million per year in the interceptor system.

Another goal of long-range planning is maintaining consistent and predictable rates, so municipalities can plan ahead for their share of costs.

 “Our rates likely will need to increase to pay for future debt, but we’re very proud of our record and plan to build further on that legacy,” he said.

MCES is a national model among large regional wastewater systems of similar size and funding, with rates that are 40% less than national averages.

Collaboration with MnDOT, counties and cities minimizes construction impacts

By planning interceptor rehabilitation projects and working with local, county and state agencies, the impact on residents and businesses in the cities affected can be minimized.

In the past few years, the Council completed major sewer projects in South St. Paul, Hopkins, Excelsior and Wayzata. A new crossing under the Mississippi River was just finished between Brooklyn Park and Fridley. In each case, good communication and cooperation between the Council, its contractors and the cities helped keep residents informed and complaints to a minimum.

Currently, the Council is working with Hennepin County and the City of Richfield to complete an interceptor rehab project along 66th Street on either side of Nicollet Avenue prior to reconstruction of the roadway in 2017-2019.

Better outreach to residents reduces disruption

ES General Manager Leisa Thompson said ES staff have worked hard in the past decade to improve advance communications with the residents impacted by its projects, like this one.

“We have more advanced assessment techniques, better rehabilitation designs, and improved construction techniques, but I think the biggest impact for communities is our improved community outreach,” she said.

“Years ago we had typically had one community open house at the start of a project,” she said. “Now we have numerous outreach meetings and more ways to engage with local residents, which has paid off in a big way.”

More information

To learn more about the Council's sewer planning and construction work, see



Posted In: Wastewater & Water

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