A new threat to Twin Cities water quality

  • Article by: EDITORIAL BOARD , Star Tribune
  • Updated: July 3, 2014 - 6:26 PM

Cities, Met Council need to address impact of excessive stormwater.


A manhole cover bounced on a geyser of water at 10th Street and the Nicollet Mall in downtown Minneapolis during one of last month’s rainstorms.

Photo: JEFF WHEELER • Star Tribune file,

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Why does a torrential rainfall compel people to flush the toilet a dozen times, take another shower and wash an extra load of laundry? Obviously, it doesn’t.

How, then, did all that extra water get into the metro area’s sanitary sewer system during June’s relentless rainstorms, so much of it that the system was overwhelmed and forced to discharge raw sewage into local waters, most notably into Lake Minnetonka, temporarily closing several beaches?

The only possible answer is that an extraordinary amount of stormwater and groundwater somehow got into the sanitary sewer pipes, enough to push the normal flow beyond capacity. Indeed, during last month’s first big rainstorm, the system’s two largest treatment plants, in St. Paul and Shakopee, were burdened with triple the usual volume.

Contrary to accusations by some local officials, the fault doesn’t lie solely with the Metropolitan Council, which collects wastewater from local pipes in 107 municipalities and pumps it to seven regional treatment plants. Those metro pipes and plants have plenty of capacity for wastewater. It’s the intrusion of stormwater and groundwater — much of it from individual homeowners — into smaller, local pipes that eventually reaches and overwhelms the larger metro system and triggers the problem.

In Mound, for example, on the west end of Lake Minnetonka, the wastewater flow through local pipes (some operated by the city, some by the council itself) was five times the average rate after the first big rainstorm on June 1, while the flow from adjacent communities (Minnetrista and Spring Park) held steady, according to Met Council measurements. Mound’s discharge accounted for 85 percent of the flow through the regional lift station near Langdon Lake.

How exactly does all of that unwanted water get into the sanitary sewers? Some of it seeps into cracked and broken underground pipes that run between individual houses and the street, and then along local streets. Tree roots have damaged some of those pipes. Others have faulty joints. In low-lying areas of some Lake Minnetonka communities, lake and groundwater levels were so high last month that some of those pipes were actually underwater during the storms, meaning that pressurized water was jetted into the damaged sewer pipes.

Individual houses and businesses pose an even larger problem. Sump pumps are popular devices for keeping basements dry, but instead of pumping water to the yard or to the street as required, some are illegally rigged to discharge water into the sanitary system. Foundation drains, designed to keep basement walls dry, are sometimes similarly rigged. Some homes even channel water from their roofs into the sanitary sewers.

Add all of that together, and you get sewage overflows, filthy lakes and unsafe beaches. If, as climate experts predict, extreme rainstorms are to become a more normal occurrence, then it’s time to fix the stormwater intrusion problem.

Rather than spend billions of dollars to expand the metro system’s capacity to include excessive stormwater, it makes more sense to spend the millions it would take to repair and tighten the local sanitary sewer pipes and to enforce the laws and codes on household drainage systems.

Some metro cities, notably Minneapolis and St. Paul, have done a commendable job of protecting the integrity of their sanitary systems. But many suburbs (see accompanying text) have been reluctant, fearing that homeowners would balk at inspections and repairs that could cost several thousand dollars per household. It’s easy to blame the Met Council, as Mound officials did last month. It’s harder for both sides to admit flaws in their systems and to begin the difficult work of solving the intrusion problem.

For starters, Mound and Met Council officials met last week to launch an investigation to pinpoint weak spots in their pipes and find the private properties that are most likely overloading the system. Other cities should join the ongoing effort, and the Legislature should gear up to find the $120 million it will take to keep excessive stormwater from invading the metro’s wastewater system.

Amid all of the technical jargon at last week’s meeting, Met Council Member Jennifer Munt used five simple words to summarize the problem: “Our lakes are in jeopardy.”


    Metro communities that had excessive stormwater intrusion, January though May, or that suffered exceptionally high flows during June rainstorms were: Arden Hills, Burnsville, Chanhassen, Chaska, Columbia Heights, Excelsior, Forest Lake, Golden Valley, Hopkins, Long Lake, Maple Grove, Maple Plain, Medicine Lake, Minnetrista, Mound, New Hope, Newport, North St. Paul, Orono, Plymouth, St. Bonifacius, St. Paul, Savage, Shoreview, Shorewood, South St. Paul, Victoria, Waconia, West St. Paul, White Bear Township and Wayzata.


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