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Deep Dig: Huge Tunnel Boring Machine Goes After Pollution | News

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Deep Dig: Huge Tunnel Boring Machine Goes After Pollution

WASHINGTON, DC (WUSA9) -- DC is dumping $2.6 billion into a hole in the ground.


Right now, a $30 million steel and concrete caterpillar is gnawing at the earth six days a week, 24 hours a day about 120 feet down. It's DC's biggest construction project since Metro and you probably never noticed.

The Lady Bird tunnel boring machine is building the first of more than 13 miles of tunnels, so the city can end the century-old practice of dumping raw sewage into our rivers during many rainstorms.

Lady Bird is about a quarter mile in from a ten story shaft at the Blue Plains Advanced Wastewater Treatment Plant and she's headed toward Nationals Park. Crews are about 70 feet below the Potomac off the Navy Research Lab.

Lady Bird stretches out about a football field and a half. She's like a giant assembly line chomping into the earth six feet at a time.

Out front is a 26 foot cutting head... trailing behind is everything to allow workers to survive down there. She builds the tunnel behind her from pre-cast concrete segments that weigh as much as 24,000 lbs a piece. She then pushes off the tunnel walls with four ton hydraulic jacks to take her next bite of soil.

The tunnel's designed to solve a problem that's plagued the city since the Civil War. When it rains, storm water mixes with everything you flush down the drain, routinely flooding some neighborhoods -- and spewing billions of gallons of raw sewage and runoff into the Potomac, Rock Creek and the Anacostia.

"So the solution we have to come up with is how to handle that peak flow, in the big storms, when its coursing off the streets," says DC Water General Manager George Hawkins. "Where do we put all that flow in something big enough?"

What's big enough to capture more than 90% percent of the pollution is a network of tunnels that's likely to take 20 years to finish.

We watched operator Mark Griffith as he drove Lady Bird with the help of a laser, and GPS control points in the tunnel shafts, that keep him within an inch of the designated route. "It's basically like looking through the scope of a rifle," says Griffith, pointing to a monitor that puts crosshairs where he needs to go.

The cutting head is pressurized to keep the earth from collapsing. So if workers need to get up front to put on a new blade or remove an unexpectedly large stone, they have to climb into an airlock, equalize the pressure, and then climb through a hatch like a deep sea diver.

The muck is sent back through the tunnel on a conveyor belt and run to the surface in giant buckets. There are about 100 dump truck loads of muck coming up everyday.

But when they're done, workers will have gone a long way to once again making the rivers of the nation's capital fishable and swimmable.

DC Water customers are paying for the vast majority of the tunnel. Rates have gone up 50% in the last few years -- to an average of $65 a month for a single family home. DC Water's GM George Hawkins says if people in the rest of the watershed reduce pollution too, the payoff will be a much healthier Chesapeake Bay.