Water main breaks are a standard part of the job in the winter time. The reason they break is due to freezing temperatures but maybe not in the way most people think. The water mains, themselves, do not freeze as they are well below the 36” frost line for our geographic region. Our water mains have a least 48” of soil cover on top of them and in some cases, even more protecting them from freezing.
When the sewer systems were installed in the 1970’s & 1980’s, sewer contractors had to excavate soil in order to install the new sewer lines. Much of this excavation went much deeper than the already existing water mains. When the soil was back filled, it settled over time and eventually left voids under the water mains. These may not be physical voids but the soil under the pipe is not compacted tightly, like it may be above the pipe.
So, as the ground freezes, it expands and creates an increased pressure on top of the water main, pressing downward into these now existing voids. The pipes, made of iron, are not very flexible and can only take so much downward pressure from the expanding soil before they crack, usually vertically. Many times you can notice the street or ground heaving upward after consistent sub freezing temperatures. The same heaving is happening downward towards the water main. There is usually an outbreak of leaks as temperatures are consistently cold pressing down and then another round of leaks as the ground thaws and constricts.
The district has been repairing 30-50 water main breaks a year since the early 1980’s. This is a common occurrence for all districts that have had sewer systems installed within their town. Naturally, some leaks happen due to the age of the pipe, but those leaks are few and far between. These type of main leaks will continue to happen for generations to come as there are at least 9,000 sewer connections in our town, in addition to the thousands of crossings at each intersection of each road.