AlexRenew completes tunnel to support a brighter future for the Potomac River

The RiverRenew Tunnel Program in Alexandria, VA announced the breakthrough of its tunnel boring machine (TBM) named Hazel on its 3.2 km (2 mile) long, 30 m (100 ft) combined sewer overflow (CSO) tunnel.

The TBM began boring in November 2022. Over the last 16 months, Hazel and her highly skilled crews have been carefully constructing a 3.2-km (2.2-mile) long tunnel under Old Town Alexandria and the Potomac River.

Hazel, named after environmental activist, Hazel Johnson, is a state-of-the-art TBM, weighing in at 380 tons and longer than one-and-a-half football fields. This shaft will collect combined sewage overflows from an existing outfall and direct these flows to AlexRenew through the new 3.6-m (12-ft) wide, 30-m (100-ft) deep tunnel. The tunnel largely follows Alexandria’s waterfront before taking a sharp easterly bend in Jones Point Park, and then it’s a relatively straight shot back to AlexRenew below Church Street. This milestone signifies a crucial connection point, as it marks the integration of AlexRenew’s wastewater plant with all four of Alexandria’s combined sewer outfalls that date back to the 1860’s.

“The collective efforts of our team to achieve this momentous milestone are nothing short of awe-inspiring. Their dedication and perseverance pave the way for a brighter future for the Potomac River,” says Justin Carl, General Manager and chief executive officer of AlexRenew.

The ambitious project was recently granted a one-year extension by the Virginia General Assembly due to delays associated with Hazel’s manufacturing and shipping in late 2022. The project’s remaining efforts include the completion of a smaller sewer line along Hooffs Run, fitting out the massive drop shafts, and constructing a 12-story underground pumping station at AlexRenew. Work is anticipated to last through 2025.

“While Hazel is just a machine, she has embodied the heart and grit of our team, and like her namesake, has set a foundation for a healthier environment for our community, wildlife, and future generations,” said Carl.

See more industry-related articles in Tunneling & Underground Construction online.