Dubbed “Hazel,” theis tunnel boring machine will create a tunnel that will store sewage-tainted stormwater runoff and divert it to a treatment plant. Photo: Whitney Pipkin

Massive Alexandria Tunnel Machine to Save Potomac from Sewage Problems

By Whitney Pipkin, Bay Journal News Service

The circular face of a 380-ton machine looked a little too clean for the work it was being commissioned to do on a hot July morning. Soon, its cheery-blue façade would be plunged 100 feet beneath the Earth’s surface, where the giant earthworm-shaped contraption will spend months eating its way through the dirt beneath the city of Alexandria, Va., leaving a water-holding 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’s taken on the $615 million project. The effort, which should be completed by mid-2025, will prevent millions of gallons of sewage-tainted overflows from entering the Potomac River and its tributaries.

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

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

 The tunnel-boring machine sits beside one of two wide shafts that will help reduce sewage-stormwater overflows in Alexandria. Photo: Whitney Pipkin

The city’s mandated 2025 deadline for curbing such overflows seemed virtually impossible to meet when it was first required by state legislators, who ruled that the previous 2035 goal was not soon enough. At the time, the Virginia cities of Richmond and Lexington had projects to sharply reduce overflows of sewage-mingled stormwater well under way. Across the Potomac River from Alexandria, the District of Columbia already was several years into a $2.7 billion project to build 18 miles of water-storing tunnels by 2030.

The General Assembly’s 2017 law left Alexandria with what may be one of the fastest timeframes in the country for addressing overflow problems. (Legislators later sent the city additional money to help do the work.) AlexRenew assumed responsibility for the project in 2018, taking on what the utility’s general manager and CEO, Karen Pallansch, called “the largest infrastructure project our city has seen.”

“It is pretty much an impossible schedule, but the team made it only improbable,” Pallansch said. “If one little thing goes wrong, we won’t be able to make it.”

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

In addition to building a custom tunnel-boring machine, AlexRenew is constructing additional pump stations and increasing treatment capacity at the plant, which currently processes about 13 billion gallons of wastewater per year. In all, 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 July 14 christening ceremony. About 500 people voting in an online naming contest chose Hazel among names of women that included an Alexandria abolitionist and public servants.

Pallansch traced the tradition of naming tunnel-boring machines after women to the 1800s, when, in the absence of modern safety protocols, underground workers turned to St. Barbara, the patron 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 aboveground. Hazel’s helm was ceremonially christened by breaking glass bottles filled with treated wastewater.

“This work is generational,” said Alexandria Mayor Justin Wilson. “It’s going to have an impact on our region and community for generations to come.”