Residents in the Denali Avenue area were without water for about five hours Wednesday after a cast-iron water main on that street broke.
Ketchikan Public Utilities Water Division Manager John Kleinegger said, “Fortunately, the six-inch cast-iron main snapped cleanly like a pencil would break, and didn’t hydraulically lift the asphalt pavement, which can occur, too. This was a fairly simple repair. The apparent cause seems to be differential settlement that stressed the cast-iron pipe to the point that it broke.”
The uneven settlement was the result of organic material, such as wood, used as fill when the pipe was installed in 1969. That organic material rotted, causing uneven support for the old pipe.
He said cast iron pipes, while better than the wood-stave pipes that Ketchikan originally used, are fairly fragile and don’t stand up well to stress. KPU is slowly replacing its five miles of aging water pipes with new mains made of special plastic.
“It’s chemically inert, withstands corrosion, doesn’t break due to differential settlement. It’s just actually a much better product,” he said.
Kleinegger said Wednesday’s leak was reported by a resident who saw more water than usual in the gutter. Crews then went out to find the source of the problem.
“We have a sophisticated amplification system that you can actually listen to a leak,” he said. “As you go along the surface, where you know the pipe is, as you get closer to where you believe the break is, the sound will of course get louder and louder, and as you move past the break it will go down in amplitude.”
Using that system, he said repair crews were able to find the break fairly quickly.
Kleinegger said that crews repaired the broken pipe with a stainless steel band, and everyone was back in service by 7 p.m.
