The “Hazel” tunnel machine to solve Alexandria’s sewer problems | Pollution & Solutions

The circular face of a 380 ton machine looked a bit too clean for the job he was assigned to do on a hot July morning. Soon, its cheerful blue facade would be plunged 100 feet below the Earth’s surface, where the giant worm-shaped craft will spend months plowing its way through the earth beneath the city of Alexandria, Virginia. , leaving a water retention tunnel in its wake. .

The 2-mile tunnel will store polluted stormwater until it can be treated at Alexandria Renew Enterprises, or AlexRenew, the water treatment plant that took on the $615 million project. The effort, which is expected to be completed by mid-2025, will prevent millions of gallons of sewage-contaminated overflows from entering the Potomac River and its tributaries.

“I’ll tell you one thing, people understand sewage,” said Nancy Stoner, president of the Potomac Riverkeeper Network, at an event christening the tunnel boring machine in action. “They know they don’t want it in their water and they don’t want to swim in it. The investment is worth it. »

Like many centuries-old sewage treatment systems in the country, the one in Alexandria captures both sewage and stormwater in its pipes. To prevent sewage backups, the system was designed to divert overflows during rainy weather to the nearest body of water, sending untreated sewage directly into the stream or river. This is called a combined sewer overflow system.

A new tunnel boring machine sits next to one of two large shafts that will help reduce sewage and stormwater overflows in Alexandria, Virginia. One shaft will be used to lower the TBM into place, and the other will transport dirt and other materials to the surface.

The city-imposed 2025 deadline to limit these overflows seemed virtually impossible to meet when it was first demanded by state lawmakers, who deemed the previous 2035 target not soon enough. At the time, the Virginia cities of Richmond and Lexington had projects underway to greatly reduce stormwater overflows mixed with sewage. Across the Potomac River from Alexandria, the District of Columbia had already been engaged for several years in a $2.7 billion project to build 18 miles of water storage tunnels by 2030.

The 2017 General Assembly Act left Alexandria with what could be one of the fastest timelines in the nation to resolve overflow issues. (Lawmakers then sent the city additional funds to help get the job done.) AlexRenew assumed responsibility for the project in 2018, taking over what utility chief executive and CEO Karen Pallansch called ” largest infrastructure project our city has seen.

“It’s pretty much an impossible schedule, but the team made it unlikely,” Pallansch said. “If one little thing goes wrong, we can’t make it happen.”

Tunnel boring baptism

Karen Pallansch, Managing Director and CEO of AlexRenew, speaks at the christening of a new tunnel boring machine, dubbed “Hazel”.

So far, despite a federal government shutdown, pandemic and supply chain issues, “we’ve figured out how to get things done” and stay on track, Pallansch added.

In addition to building a custom-built tunnel boring machine, AlexRenew is building additional pumping stations and increasing treatment capacity at the plant, which currently processes approximately 13 billion gallons of wastewater per year. In total, this RiverRenew project will prevent an additional 120 million gallons of sewage-laden stormwater from entering waterways each year, Pallansch said.

The tunnel boring machine, custom-built by a German manufacturer, was named “Hazel” – after Chicago-based environmental justice advocate Hazel Johnson – during a naming ceremony on July 14. About 500 people voting in a online naming contest chose Hazel from the names of women who included an abolitionist from Alexandria and civil servants.

Pallansch traced the tradition of naming tunnellers after women to the 1800s, when, in the absence of modern safety protocols, underground workers turned to Saint Barbara, the patron saint of miners, for protection.

Below the name “Hazel” painted on the side of the tunnel boring machine were a series of handprints that officials could sign while the structure was above ground. Hazel’s bar was ceremonially named by smashing glass bottles filled with treated sewage.

tunnel boring machine

Guests attend a christening ceremony July 14, 2022 for a new tunnel boring machine in Alexandria, Virginia. Dubbed “Hazel,” the machine will create a tunnel that will store sewage-contaminated runoff and divert it to a treatment plant.

One hand featured a tribute to Kerry Donnelly, a former Alexandria major and AlexRenew board member who died the day before the event. Pallansch, who considered Donnelly a mentor, said he was so committed to the tunnel project that he nicknamed the machine the “rocket”.

Current Alexandria Mayor Justin Wilson said he couldn’t think of a more appropriate ‘bold undertaking’ as a tribute to Donnelly’s legacy than the fast-built tunnel project he and others took on. gathered to celebrate that day.

“This work is generational,” Wilson said. “This is going to impact our region and our community for generations to come.”

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