Most of the thousand miles of water pipes that snake through Minneapolis are close to a century old, including the downtown pipe that broke Tuesday, sending 90,000 gallons of water gushing into the streets near Target Center.
That pipe is so old that it was built the same year — 1889 — that North Dakota and South Dakota became states and the Eiffel Tower was finished in Paris.
But city water officials insist that the age of the pipes is not linked to any serious problems and matters far less than other conditions, such as the type of soil in which the pipes are embedded.
“Age is not an indication of bad pipe,” said Mark Ebert, general foreman for city water distribution.
This week’s incident — the second prominent water main break so far this year, and one of about 40 yearly — shut down the sports arena, along with Life Time Fitness and Hubert’s Bar and Grill, for most of the day as crews worked to repair a giant sinkhole on 2nd Avenue N. between 6th and 7th Streets.
In St. Paul, which has up to 1,200 miles of water mains, breaks have averaged 140 to 150 in each of the past 20 years. But that number has been shrinking, and last year the city recorded a low of 105 breaks, said Steve Schneider, general manager of St. Paul Regional Water Services.
He attributed the downward trend to the city’s annual replacement program, which aims to replace 11 to 12 miles of mains in a long-term effort to renew St. Paul’s underground infrastructure every 100 years. Minneapolis’ replacement program is comparable.
Like Minneapolis, the vast majority of pipes replaced in St. Paul are made of cast iron, which is more corrosive than newer materials such as ductile iron and plastic. Last winter, a 16-inch cast iron water main broke overnight in downtown St. Paul, sending 1.75 million gallons of water down several blocks in the Lowertown area. Months later, it’s still unclear exactly what led to that break, Schneider said.
“It was a split that nobody here with all our years of experience had ever seen before, on both sides of the pipe and 8 feet long,” he said. “That type of break is typically caused by a pressure surge, but no one was working on the water system. We really don’t know what happened and probably never will.”
Crews will take a closer look at the pipe and the nearby soil conditions when they replace a three-block section of Lowertown water mains this fall, he said.
In Minneapolis, Ebert said the cast iron pipe that recently broke had deteriorated during a process called electrolysis, where a naturally occurring reaction between the metal and the soil softened the main and “you get just a chunk of metal popping out with the escalating pressure.”
About 800 miles of the city’s water pipes were installed before 1920, and the very oldest were built in the 1870s in the Mill District along the Mississippi River.
Grainy soil best
Minneapolis expects to spend $6.4 million on water distribution improvements this year, up from $5.3 million the two previous years, although that increase is driven by plans to replace hydrants and upgrade water meters.
Grainy soil can help a water main last hundreds of years, while clay soil leads to more breaks, said Marie Asgian, supervisor of Minneapolis water distribution.
Most of the city’s pipes are made of cast iron, which accumulates mineral deposits that build up from rust on the inside, discoloring the water and reducing the water volume. To remedy the problem, the city scrapes off the buildup and adds a ⅛-inch-thick cement lining to 8 to 10 miles of pipe annually.
That treatment is for stable pipes.