The city of Duluth has been contending with a flurry of water-main breaks made worse by several days of subzero temperatures.
Through Tuesday morning, the city had experienced 25 water-main breaks so far in 2021, most coming within the past 10 to 12 days.
“This is typical for what happens when temperatures drop to minus-20 and stay here for a couple days,” said Eric Shaffer, the city’s chief engineer of utilities.
The city features 435 miles of underground water piping, most of it cast-iron pipe, along with 55 miles of newer plastic pipe. The cast-iron pipe falls into two categories: higher-grade pipe from the 1880s, and thinner, more brittle cast-iron pipe from the 1950s and ’60s.
When a water main breaks, it’s because the frost works down deeper into the ground, forcing the old cast-iron pipe to shift, Shaffer said.
Workers close off the two nearest valves to isolate the failing pipe in order to fix the breaks.
“Normally, we go down and put a repair clamp on it,” Shaffer said, describing how the clamp wraps around the pipe and includes a rubber gasket tightened around the break. When breaks split the pipe longitudinally, workers cut out the section and put in a replacement piece.
The average repair takes eight to 10 hours, with much of the time spent digging the hole to access the break.
“We try to keep the shutdown as small as possible,” Shaffer said, though not every block in the city was designed to feature shut-off valves, so some breaks are more impactful than others.
Regardless, the city doesn’t want residents going too long without water.
“Our target is to always have the water back on before you get up to go to work,” Shaffer said.
The city is in the process of phasing in a water-rate increase through 2023. With the increase, the city is attempting to put in 4 miles, or 1%, of new pipe every year. Also, any street reconstruction projects include the addition of new plastic water mains that are immune to the corrosion that’s undermining the cast-iron piping.
“Our system is plagued with corrosion issues, caused by the clay solids in the ground,” Shaffer said, explaining the steady diet of corrosion-related leaks the city deals with every summer, most of it related to the thinner cast-iron pipe installed during the last century.
The city is targeting the worst pipes, the ones that break the most, for replacement first.
Progress is already showing. The city used to experience upward of 160 water-main breaks annually.
That figure fell to 72 last year.
“We’ve done a good job on the number of breaks in the city overall,” Shaffer said. “The number of breaks continues to go down. We’re staying on top of it, and getting as much pipe replaced as we can. We want to stop having people out of water.”
Duluth water-main breaks
Year — No. of breaks
2021 — 25 (through Tuesday morning)
2020 — 72
2019 — 114
2018 — 96
2017 — 70
2016 — 48
2015 — 142
2014 — 147
2013 — 139
2012 — 112
2011 — 103