Almost every year, the city asks about 300 homes whose pipes are notorious for freezing to run their water throughout the winter,??Duluth???s chief engineer of utilities??Eric Shaffer??said.
???This year, in addition to that, we had about 350 houses freeze up that were not on our list because it was so cold. And then, during March, we started to get water mains actually freezing,??? he said.
Water mains are the large diameter pipes that are buried beneath the streets. ??Service lines are the small diameter pipes that pump the water from the main lines to businesses and homes.
???That???s below our normal average,??? Jacobson said. ???In the winters in the past, we???ve normally had over 100.???
During an average winter, the majority of these breaks happen to service lines. This year, however,??most of the 75 breaks were along main lines, Jacobson said.
The reason for this change, Jacobson said, was the early snowfall in December.
???Even though we had a very cold winter, the snow cover was a blessing in disguise,??? Jacobson said. ???It insulated a lot of our underground utilities other than the ones that were exposed.???
The snow insulates service lines because they typically run through unplowed areas, like yards. In snow-covered areas, the frost depths reached a shallow 1-2 feet, Jacobson said.
In plowed areas like streets where the main lines flow, however, the frost was able to reach down 7 to 8 feet ??? the same depth that most main lines are buried, Jacobson said. As the ground freezes, it expands and shifts, and this jarring movement can stress the main pipes to the point of breaking.
???It???s like taking a stick and snapping it in two,??? Jacobson said. ???That???s what the ground does to the pipe.???
The viscous spring thaw
Not only are pipes prone to fracturing when the ground is freezing, but they???re even more susceptible when the ground is thawing.
???In a regular year, March and April are our worst times,??? Shaffer said about water line breaks. ???As the frost starts to come back out and thaw, it moves the soil quite a bit and it???ll take those 100-year-old pipes that are brittle ??? made out of cast iron ???and it moves them. That???ll cause them to break.???
But the spring thaw didn???t come in March and is only slowly starting to make its way into the ground this April.
???We just had one service freeze yesterday because the frost is deep,??? Shaffer said last Wednesday. ???(The frost) hasn???t come out yet.???
A slow thaw is the ideal situation because it means gentle, gradual movements in the soil and less impact on the pipes, Shaffer said. But he???s not so sure it???ll play out quite so smoothly.
???We???re pretty much ready every day for it,??? he said about the spring thaw breaks.
When a pipe leaks or breaks in the winter, it???s easy to catch because the escaping water sticks out like a sore thumb in a frozen environment. Spotting the same situation in the springtime, however, is a different scenario.
???The streets are wet. The sidewalks are wet. If there???s a leaky water line under the street and it???s leaking onto the street, it???s hard to distinguish that water main break from normal spring run off,??? Duluth???s stormwater coordinator??Chris Kleist??said about spring. ???So, it???s hard to detect them.???
The healing process
When a break does happen, the city repairs it immediately to avoid danger.
???When sections of town are without water, they don???t have fire service protection,??? Kleist explained. ???So, if there???s a fire, those fire trucks couldn???t get the water to fight it.???
Another safety hazard is the road ice that can form from the leaking water, Kleist said.
When a leak or break happens, Duluth???s Utility Operations first locates where the water is coming from and then uses excavators to dig up ground to access the break.
Once the break is exposed, they mend the hole by either patching it or attaching an entirely new piece of pipe depending on the type of break.
The future of Duluth???s water lines
Eventually, Duluth hopes to replace these pipes with newer, more flexible ones, Kleist said.
???We have a very old infrastructure. Our water system, our sanitary sewer and our storm sewers ??? some of those pipes are over 100 years old. We???re trying to replace sections of pipe as we can,??? he said.
Although the older, cast iron water lines are strong and have lasted much longer than their life expectancies, they aren???t flexible enough for Duluth???s harsh and variable environment, Kleist said.
Most of the newer, pipes are ???ductile iron,??? while a few are ???high density plastic.??? Both are ???able to move a little bit with the ground,??? he said.
As for fixing the water line problem on Orange Street, Shaffer has a more intensive plan.
???Someday we???ll have enough money; we???ll go dig it up to put it deeper,??? he said.