The Chthonic Mrs.5000

A Guest Dispatch from the Underworld, by Legendary Blogwife Mrs.5000!

Maybe you’re not a person who spends a lot of time thinking about Combined Sewer Overflows, but here in Portland they’re actually kind of a big deal. When it rains heavily (i.e. fall, winter and spring), the sewer system can’t handle the influx of stormwater added to the sewage, and untreated wastewater is dumped directly into the Willamette River. This was standard practice when the sewer lines first started going in eighty or ninety years ago. Today it is considered icky. For the last twenty years or so, The City That Works has been doing a number of things to keep stormwater out of the system in the first place, disconnecting downspouts and requiring new buildings to handle run-off on-site with techniques like stormwater planters and dry wells. The big expensive piece of the solution involves two massive underground pipes, one on each side of the Willamette, to transport the remaining overflow to a pumping station and thence to a treatment plant before it’s allowed to join the Columbia.

A few weeks ago I read in The Oregonian that the East Side Big Pipe was nearing completion, and anyone interested could enter a lottery to get a tour. Of course I liked the idea of standing inside the new Great Bowel that will soon be carrying away our diluted sewage. So I entered my name. And, lo and behold, I was one of a hundred lucky citizens chosen to take the tour!

Last Friday morning found me checking in under a small blue tent near the Opera Shaft, where I was issued a hard hat, reflective vest, gloves and safety glasses. I was part of a group of eighteen citizen-tourists who ushered into a large construction trailer, where we got a safety briefing and an overview of the East Side Big Pipe project. The pipe is about six miles long, and its inside diameter is 22 feet. You’ll be happy to know it’s ahead of schedule and under budget! We also saw a scale model of the TBM, or tunnel boring machine (not a boring tunnel machine, I hope you agree).

It was good to see the model, since the TBM was at the end of the tunnel about two miles away, and we wouldn’t be visiting it. The working end of the TBM really was painted the cheery yellow, red and blue you see on the model, at least when first delivered, but as the project manager pointed out, digging underground for mile after mile really plays havoc with a paint job. You can note it’s not pointy like some giant drill bit to dig through rock, but more like a rotary disc sander. The tunnel goes through wet gravel, about a hundred feet below the water table, and every aspect of its construction is designed to keep that water out. Tunneling through wet is a big deal (think catastrophic failure of sandcastles), and this is one of the first projects of this kind in the United States. Much of the technology comes from Germany. The front end of the TBM grinds away in a pressurized slurry, while its human operators guide its progress via computers, and the extracted material slurps and rattles through two pipes to the tunnel entrance.

This is what that tunnel entrance looks like when you are leaning down over the side railing making sure your hardhat doesn’t slip off:

It’s called the Opera Shaft, not because it would be a cool place to stage the Ring of the Nibelung, but because it’s right next to the headquarters of the Portland Opera. We didn’t take the stairs, luckily, but squished into a ten-person elevator that reminded me a little of an autoclave.

Now here’s a photo showing what it’s like for a surface-dweller at the bottom of a cylinder 70 feet in diameter and 120 feet underground:

It’s not unlike one of the artist James Turrell’s skyspaces. As industrial-era humans, most of us don’t spend a lot of time in cylindrical spaces, and they strike me as inherently ceremonial. Except in this case it’s a very noisy worksite, with people and heavy objects moving about, so it’s not conducive to meditation.

The circular form is also of course a strong sensible way to put tunnels together. As a pipe it will prove ideal for the conveyance of future smelly liquids. Right now it is doing a capital job of keeping all the groundwater out. In the picture above, we are standing on a catwalk inside the Big Pipe itself, looking north. (You can see the two smallish pipes that carry extracted earth up out of the tunnel.) Over three years ago, the TBM was lowered in sections down the Opera Shaft and began digging its four-mile route north. Every five feet, gasketed concrete segments were put in place to extend the tunnel while keeping it watertight. When the northern route was finished, the TBM was hauled out of the northernmost shaft, barged down the Willamette, and lowered back down the Opera Shaft again to dig two miles south. Here’s the beginning of the south part of the tunnel, showing the temporary construction railway and, at the top, a big ventilation duct. It looks like a train tunnel now, but think of it as a culvert 22 feet wide:

And that was pretty much the end of the tour. Far more explanation of the project and its construction than I have room for, plenty of time to gawk, take photos, and be just slightly in the way of people trying to work. We got to hear the airhorn warning that heavy objects were in motion overhead, and took appropriate measures. We went back up in the elevator and returned our safety gear for the next group to use.

In coming weeks, now that digging is complete, the TBM and all the rails, conduits, ducts and other machinery inside the Big Pipe will be removed. The small shrine to St. Barbara (patron saint of miners)....

...will be removed from above the tunnel’s south entrance, everything will be taken out of the shaft, and the top of the last short section of pipe now open to the sky will be closed in. The Opera Shaft itself will then be filled in, since it was designed to provide access only during construction.

Goodbye Opera Shaft! It was a pleasure to tour you. Good luck to the Big Pipe, which will be carrying our stormwater surges and effluent for decades to come. It was lovely to see you when you were clean and dry.