(Reader photo from a brown-water situation earlier this month)
By Tracy Record
West Seattle Blog editor
After months of intermittent but intense West Seattle brown-water incidents that we’ve been covering – going back to last fall – the city is making plans for a major operation to try to attack the underlying problem: Rust in the pipes.
The rust isn’t unusual and isn’t unhealthy, Seattle Public Utilities stresses – but there shouldn’t be this much of it stirred up when something happens such as a hydrant opening or pipe break, and it should clear faster (as commenters have pointed out, it often lingers longer than they were told it would).
So SPU is planning a “unidirectional flush” – something that utility managers say hasn’t been done anywhere in the city in more than a decade.
It’s not one big operation at one time but will play out over the course of months. We got an early briefing during a visit to the SPU Operations Control Center, following up on our recent behind-the-scenes look at how water safety and quality is monitored.
We met there with drinking water quality director Wylie Harper and other SPU water managers, including operations director Dave Muto. First, some context. Two-thirds of the 1,800 miles of pipeline in SPU territory is unlined cast iron – and this is the primary source of what discolors the water in certain circumstances:
If there’s a pipe break/leak, if a hydrant is operated (including fire incidents), if something in the operational system requires a flow reversal, it could “stir things up … that’s part of the nature of the system.”
While SPU refers to it as sediment, it’s rust from those cast-iron pipes.
Harper says it’s not that the utility never flushes pipes – “it’s usually been more ‘spot flushing’,” compared to what’s in the works now, a “much more thoroughly planned and comprehensive effort,” at multiple locations involving a “large portion of the system.” It’s “hugely time-consuming and complex to do this,” so they’ve been having planning meetings.
They will start at the source – a tank, a transmission line, a large feeder main (12″ wide or larger), “working so that sediment is pushed from the source to the outer edges of the pressure zone, with valve closure along the way.” That means some effects at homes/businesses while it’s happening, and they promise you will get an advance alert when it’s scheduled to happen in your area.
Explaining how this works, they explained that West Seattle has “three planning zones” for water delivery, largely related to topography and how the water is delivered. The zone that’s primarily being focused on for this upcoming operation is known as 498 (the beige area in the map above), and Harper says “60 or 70 piping segments have been picked out” for the unidirectional flushing operation, starting in the north, where more problems have been reported in recent months. (We learn while at SPU that we too are in the 498 zone, toward its south, served by an unlined-cast-iron main, but we can’t recall having had a discoloration problem in the 20-plus years we’ve lived in the same place.)
This is all an intricate operation to be sure it doesn’t cause more problems than it solves. “To do it the right way … there’s a fair amount of technique involved,” Harper explains: A certain velocity – three to five feet per second – will suspend (the) rust and move it out. If it’s too slow, it’s not good. Too fast, not good” – that could break off “rust nodules” that have formed inside the pipes over the decades. So they have mapped out which hydrants, which pipe sections will be involved. And they plan to do most of the work late at night, when it will have less of an impact on customers, and when the pressure is higher because use is lower.
Following up post-visit with SPU spokesperson Ingrid Goodwin, we obtained more explanation: “The flushing needs to occur sequentially. So, when one flush is complete, crews will move to the next location. At this point, we are still determining how many crews will be required. It will likely be up to three, 2-person crews ( so 2 to 6 people) working in the field M-F, from about 11 pm to 5 am. Daytime flushing may occur at some point, as well. We estimate that it could take 3 to 6 months to flush all of West Seattle. However, once we get started in April, we’ll have a better idea of how long it’s actually going to take to complete.”
According to Harper, they’ll be able to measure the results via water-quality parameters. As for how customers will know it was a success – the primary result would be any future discoloration (for the same reasons, pipe breaks, hydrant uses, etc.) clears more quickly. Harper is careful to stress it doesn’t mean discoloration will never happen again – “we still have unlined cast iron pipe … what flushing WILL do is remove some of the sediment, so the intensity (of discoloration) is less.” Though the pipes are up to ~90 years old, removing and replacing them on a large scale isn’t an option, according to Harper. For one, they still, in general, “function properly,” with a “leak rate better than the industry average, fewer links per mile … and the pipe wall itself is robust.”
Also stressed: The reason for this is aesthetics, not a health risk, unlike the last time this kind of flushing was done, out of concern about coliform bacteria in the early ’90s. But the aesthetic concern is enough that they’ve decided to do this – “a lot of this is driven by customer interest and recent calls,” Harper said.
What happens to the water that’s “flushed”? Another question we asked Goodwin post-interview: “During flushing, water valves are closed to direct the water through designated parts of our main lines and flushed out of opened hydrants. The water is drained to either the combined or separate storm drain systems. Water that goes to the combined system (wastewater and drainage) ends up at the treatment plant. Water that goes to the separated system is dechlorinated onsite and flows to receiving bodies of water.”
One more note from Harper – he said they would like to do more in the future; other areas of the city have unlined cast-iron piping such as North Ballard and Green Lake, and “might benefit,” according to Harper.
In the meantime, watch for the first round of formal announcements from SPU about the flushing operation in about a week. (added) Goodwin told us, “We are planning to mail a public notice, FAQ and map to customers by the end of next week (by April 8). This information will go to the first group of neighborhoods in West Seattle that are scheduled to have the water mains on their streets flushed. These will be the neighborhoods in the northern part of the 498 zone.”
And if you experience discolored water (as did residents in Fairmount Springs after a truck took out a hydrant last night) – call SPU’s 24-hour hotline, 206-386-1800. Speaking of which:
COMING UP ON WSB: Within a few days, we’ll publish part 2 of the report on our visit to the Operations Center will take a look at what happens when you call in a complaint as well as more extensive background on where your water comes from and what happens to it along the way, including a behind-the-scenes look at the center – which includes controls for facilities of all sizes, as well as the call centers where operators talk with SPU customers reporting problems (photo above), calling with questions, etc.
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