On the day after that massive water-main break at 24th/Kenyon cut water service to thousands and flooded half a dozen apartments (WSB coverage here), we asked Seattle Public Utilities some followup questions. This evening, we received the answers from SPU spokesperson Sabrina Register. So here’s what we’ve learned:
What caused the break? SPU says they don’t know yet. We mentioned that a construction project’s been under way in the area – the Natural Drainage Systems-related work reported here in June – but Register says that crew was working half a block away when the main ruptured.
How old is the main, and why did the break result in such a geyser, when many breaks don’t? Register says SPU records show the main was installed in 1925 and re-lined with cement-mortar lining in 1983 “to extend its life against internal pipe corrosion.” The average age of SPU pipes, she says, is about 70 years. As for why the water erupted with such force: “The water main that broke is a 24-inch diameter pipe, which has a much greater carrying capacity than our typical 8-inch or 12-inch diameter pipes. Additionally, the pipe is under more pressure than many other pipes in the water system. The added pressure in the pipe has to do with the area of the city the pipe serves and the pipe’s elevation relative to the area served. The pipe serves water at around 130 pounds per square inch, compared to more typical pressures in many water pipes of under 80 pounds per square inch.”
Any recent leaks reported (as a commenter had suggested)? “Since 1983, there have been a handful of small (called pinhole) leaks, consistent with a pipe of that age, but no major leaks have been reported. Construction inspectors on the site reported no leaks observed during the construction project.”
How much water was lost before it was shut off? SPU estimates about two million gallons.
What happens now? “SPU has been on site to determine when and how to best replace the section of pipe. SPU temporarily has taken the water main off-line, which does not impact customers’ service. Only a handful of residential customers were connected to the main and crews have been able to provide temporary service to these customers.” To be specific, she says, four houses were connected directly to this main and those were the last to get their service back, restored today.
Repair logistics? “With an active construction site just feet away, close coordination is needed for the complicated work. It may be several weeks before crews are able to replace the broken section of pipe. We are still assessing the pipe and developing a plan to fix it, but crews will have to replace at least a ten-foot section of pipe.” The repairs are expected to be complicated because “the break is extensive and horizontal, which often requires crews to cut out a section of pipe and replace.”
What’s being done for the people whose apartments were flooded? “SPU staff are reaching out to the handful of customers who were displaced yesterday when the water main broke, working with them on the claims process.”