FOLLOWUP: Here’s what more we found out about West Seattle’s big water-main break

(WSB photo, Monday)

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.

(WSB photo, this morning)

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.”

16 Replies to "FOLLOWUP: Here's what more we found out about West Seattle's big water-main break"

  • Lauren August 16, 2022 (8:24 pm)

    We lost all water when this happened yesterday (Gatewood) but since it’s been turned back on, our water pressure is quite low. Low enough that it’s a challenge even taking a shower. Just wondering if this happened to anyone else who lost water yesterday? 

    • Patrick August 16, 2022 (8:55 pm)

      Same over in the Roxhill area. Water is back but the pressure is noticeably lower. Still usable but not great. 

  • John Smith August 16, 2022 (9:34 pm)

    It sounds like this main is more of a distribution line, I suspect that we will have lower water pressure until this main is repaired. I also suspect that a contract will have to be let for the repair. This repair seems beyond the capabilities of the water department (the name these days is SPU Water Line of Business) employees/equipment.

    • John Smith August 16, 2022 (10:37 pm)

      It looks like this 24″ water line crosses Longfellow Creek at the location of the break, adding an entire new level/dimension of bureaucracy to the time required until a repair can be done. The construction at the site was/is being done to improve salmon habitat. If I were in charge, I would immediately let an emergency contract waiving environmental rules/regulations for the duration of the repair (with common sense oil/fuel pollution prohibited). Now is the best time to do the repairs since (according to at least one comment on this blog) the level of Longfellow Creek was double or triple its normal flow during the uncontrolled portion of the break. Any damage to salmon habitat/fry/eggs/whatever has already occurred.

      • John Smith August 16, 2022 (11:59 pm)

        A visual double or triple increase in the Longfellow Creek flow during the uncontrolled period of the break means probably close to an 8 times to 16 times increase in the amount of flow in Longfellow Creek downstream of the break. Radius (radius is half the diameter) is the important/significant factor because flow/volume increases exponentially with the radius. Although I have never seen Longfellow Creek, it seems likely that it is generally confined to a narrow channel.  IOW (In Other Words), Longfellow Creek is probably shaped more like a circular cross section rather than broad and shallow.

        • Jethro Marx August 17, 2022 (10:02 am)

          No, this creek is mostly wide and shallow, and those of us who love it would like to see the repairs done right, without any special environmental exemptions.

          • John Smith August 19, 2022 (12:03 am)

            Jethro Marx, the damage has already been done downstream of the break. In addition to hydraulic scouring resulting from the temporary high flow, AFAIK (As Far As I Know) the water in the SPU water pipes has chlorine. For less catastrophic (than this one) water main breaks, the water department places large tablets (I think they are calcium) in the flowing water from the leak in order to (at least attempt to) neutralize the chlorine. In a break of this magnitude, the equivalent amount of calcium tablets required would be measured in gravel truck loads, not tablets.

  • John August 17, 2022 (2:44 am)

    I don’t know if you guys can link it or not I can’t seem to find it for some reason but this reminds me of a number of years ago a water main broke in the Fauntleroy area and washed out a hillside. I believe it was at the end of Cambridge street

  • Another One August 17, 2022 (1:41 pm)

    Only minor leaks yet the area east of the creek along the water main has always been very wet and marshy. Could be a coincidence but I wonder. 

  • Holly August 17, 2022 (4:19 pm)

    A lot of aged pipes just like in Bellevue where the homeowners near Somerset lost their house due to bad pipes.

  • Mj August 17, 2022 (10:15 pm)

    I’m curious if this break and water re-routing is causing a slight drop in water pressure in other areas of WS?  When watering earlier today the water pressure seamed to be a bit lower.

    • John Smith August 18, 2022 (12:54 am)

      Mj,Scroll back/up to read my earlier posts to this comment thread.

    • Midnight Cowboy August 18, 2022 (9:46 pm)

      I live around Alaska Junction area I noticed that water pressure, especially on my 2nd floor bath, is about a quarter percent lower.   I thought I might have forgetten to turn off a faucet.   Aug 18.  Any neighbors nearby with similar issue?

  • John Smith August 18, 2022 (2:53 am)

    The water department (SPU Water Line of Business) spokesperson should report/explain every day what is being done to fix this break.

  • Mj August 18, 2022 (7:09 am)

    John Smith – thank you 

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