Councilmember Clark left office on April 14, 2015.
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Category: Interesting jobs I’m glad someone else has

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Things are hectic as the year winds down, so I’ve not been good about posting to the blog. There’s plenty going on — 520 bridge details, text amendments in South Lake Union, wrapping up mid-rise and high-rise zoning code changes — and I’ll try to do better.

In that vein, I wanted to share yesterday’s surprising factoid. I’m the alternate Seattle member on the Regional Water Quality Committee. This is the group that meets over in King County Council Chambers and includes representatives from King County Council, suburban cities, local sewer districts and Seattle City Council. Usually Councilmembers Richard Conlin and Tim Burgess attend. Richard is off this week (hiking in some beautiful place, I’m sure) so I attended in his place yesterday for a vote requesting financial policies be developed before the County proceeds with any reclaimed water program.

But that’s not the riveting part. The second to last item on the agenda was an update on construction of the new Brightwater Treatment Plant. (I still want to meet the person who came up with the name “brightwater” for a sewage treatment plant.) Brightwater is big, complicated, contentious, and expensive. It’s the kind of project where once you make it past all the political and legal hurdles, you really need for absolutely nothing to go wrong. The price tag to all of us is in the billions.

There are four tunnel segments being bored deep underground to move treated water west to “outfall” into Puget Sound. The machines are like long canisters with turning, munching blades on the lead end. The blades turn, the machines munches and the canister inches forward through silt, clay, and rock. All the debris gets pushed out behind the machine and taken out back at the main tunnel access point to be loaded into trucks. The machines are big enough in diameter so that some of the resulting piping can be as much as five feet in diameter.

This summer and fall two boring machines failed. Both have had more wear and tear on the rims of the cutting end of the machine than anticipated and both need repairs before boring can continue. So, how do you repair a busted tunnel boring machine that’s 300 feet under a school parking lot (in the case of one machine) or people’s houses (in the case of the other)? Well, you move the second one further forward until it’s under an intersection. At both locations you drill and pump out the water that’s in the ground around the lead end of the machine so you reduce the pressure on the machine. (I hadn’t thought about this previously, but the machines are down far enough that pressure is an issue.) Then real live people work their way through the tunnel length the machine already made, they move through the machine and pop out the front of it to repair the rims. Depending upon the pressure they could work as many as five hours at a time down there and then spend an hour decompressing.

Wow. For a point of comparison that may be helpful to some people, the Beacon Hill Light Rail Station is approximately 160 feet down. The Brightwater tunnel boring machine repair people go down almost twice as far and then through the tunnel to get to their target.

Thanks, TBM repair people!

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