Tunnelling for RiverRenew, a wastewater project in Alexandria, Virginia, has been completed.

TBM Hazel, which was launched in November 2022, broke through last week after building a 3.2km tunnel under Old Town Alexandria and the Potomac River.

The 4.47m diameter Herrenknecht TBM broke through in a 30.5m-deep shaft, south of Oronoco Bay. The shaft will collect combined sewage overflows from an existing outfall and direct the flows through the new tunnel to Alexandria’s wastewater treatment provider, AlexRenew. The wastewater will be treated and returned to the Potomac River.

Completing excavation of the new Waterfront Tunnel marks the integration of AlexRenew’s wastewater plant with all four of the city’s combined sewer outfalls that date back to the 1860s.

“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,” said AlexRenew general manager and CEO Justin Carl.

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