Maybe nobody else cares, but my wife and I got curious over the weekend why the city's water mains break in cold weather, since we were left without water for several hours Saturday night. We live in a neighborhood of old houses with poorly insulated pipes. Most people leave their taps running when the temperature dips much below 28. So if all of our household taps are running up and down the block, how does the water in the main freeze?
Charles Stringer, assistant director of Dallas Water Utilities, generously took time out of a busy day today -- there have been more than 100 water main breaks since Wednesday, most caused by the deep freeze -- to answer my stupid questions. First, he said, the water in the main doesn't freeze very often. It's the sudden differential between soil temperature outside the pipe and water temperature inside that cracks old cast-iron pipes.
The three to four hours it takes to fix a main is easy to understand, once Stringer explains the process. First, the city must dispatch a valve crew to shut off the water to the main. There's a valve about every block, but pipe crosses and intersections can raise the number of valves that need to be closed to as many as four or five for one leak. All of those have to be found and shut down.
The place where the water surfaces may not be the place where the main is broken, Stringer said. So now you have to get a get a leak detection crew in to find the leak. He said the city uses sophisticated sonar-type equipment, but DWU also has very experienced people on the crew who can bore down with a T-handle auger and get down on the ground with their ear to the hole and determine which way the leaking water is flowing. The water listeners!
Once DWU knows where to dig, it has to contact the electrical and gas utilities to make sure it won't be digging through any of their stuff. Then the water crew can excavate.
Stronger said cast-iron mains are the worst. The city hasn't installed the old cast-iron stuff since 1940, but a lot of it is still out there. When the repair crew does dig down to a break, they fix it with bolted compression couplings, usually of a more modern metal composite. Then it's easy. Shovel the dirt back in. Turn the valves back on.
And somewhere in East Dallas, two crabby people in an old house are saying to each other, "Well, it's about time!"