RiverRenew Tunnel System Project

As lead partner of the Traylor-Shea Joint Venture, Traylor is constructing the RiverRenew Tunnel System Project for Alexandria Renew Enterprises (AlexRenew) in Alexandria, VA to eliminate combined sewer overflows (CSOs) and improve water quality. The project includes a 2.2-mile-long tunnel, a 6-foot-diameter open-cut sewer pipeline, multiple diversion structures, a pump station, and a wet-weather treatment facility. Once complete, the system will capture and treat 98% of combined sewer flows, reducing overflows from 70 per year to fewer than four and protecting the Potomac River, Hunting Creek, and Hooffs Run.

In March 2024, Hazel, the tunnel boring machine (TBM), completed mining the 11,377-linear-foot Waterfront Tunnel, holing through at the Pendleton Street shaft. Hazel was launched in November 2022 from AlexRenew’s Water Resource Recovery Facility (WRRF), navigated a 90-degree curve, and successfully holed through a flooded shaft near the waterfront. The tunneling process proceeded smoothly under 3-4 bar psi. A key innovation was the use of Multi-Service Vehicles (MSVs) instead of traditional locomotives. These rubber-tired vehicles eliminated the need for rail installation, improving efficiency, saving time and labor, and increasing safety. The MSVs feature automatic drive mode, Strata camera systems, and customizable setups to safely transport tunnel segments, materials, and personnel through the tunnel.

Now that tunneling is complete, the project team has shifted focus to critical structural work. Installation of the internal concrete structures for the pump station is underway, followed by mechanical, electrical, and plumbing work in the fall of 2024. Work has also begun on the permanent liners for the Outfall 002 Drop Shaft and Screening Shaft, while deep foundation drilling for the Pump Station Superstructure is in progress. Additionally, the 2,500-foot Hooffs Run Interceptor pipeline installation is already mitigating combined sewer overflows. The commissioning of this sewer interceptor has provided early control of CSOs, reducing overflow events from Outfall 004 from 45 to fewer than four, significantly improving local water quality.

A key feature of the tunnel system is its high-performance concrete liner, which has a 100-year design life and a thickness of 8.75 inches. As part of the next phase, large pumps and piping, manufactured in Wisconsin and Sweden, will be installed to move water through the system efficiently.

In the final months of the project, the system will be tied into the existing treatment facility, programmed, and tested before commissioning. The team will also complete restoration work, including replanting trees and landscaping to return work areas to their original or improved condition.

Upon completion, the tunnel system will have the capacity to carry 180 million gallons of water per day, significantly enhancing Alexandria’s ability to manage stormwater and wastewater. Commissioning is expected to begin in early 2026.