Jacobs Modernizing Combined Sewer Overflow Infrastructure to Improve Water Quality and Benefit Local Virginia Communities

Did you know that deep beneath the oldest parts of Alexandria, Virginia, there’s a sewer system that dates to the 1800s?

Working with AlexRenew, the wastewater treatment authority for Alexandria and parts of Fairfax County, we’re supporting a transformative project, RiverRenew, aimed at modernizing infrastructure and reducing pollution to improve water quality for the benefit of the community. 

We’ve worked with AlexRenew for more than 25 years, including on its Envision Platinum Nutrient Management Facility. Now, as the design consultant on the RiverRenew project, we’re responsible for technical leadership, and delivery of design on a new state-of-the-art combined sewer overflow system designed to prevent millions of gallons of sewage from entering the Potomac River, Hunting Creek and Hooffs Run during heavy rainfall events.

From wet-weather troubles… 

The existing combined sewer system in Alexandria collects both rainwater and sewage that’s transported to AlexRenew’s water resource recovery facility for treatment. On dry days, wastewater is transported to the facility smoothly. When it’s rainy though, the system’s pipe capacity is often exceeded, causing what’s known as a combined sewer overflow (CSO), where wastewater and rainwater overflows discharge into local waterways.

To reduce the frequency and volume of sewage overflows and improve water quality, in 2020, the AlexRenew Board awarded the RiverRenew Tunnel System design-build contract to Traylor-Shea Joint Venture (TSJV), with Jacobs playing a critical role as the design consultant and engineer of record for the 2-mile (3.2-kilometer) long, 12 foot (3.9 meter) internal diameter tunnel, two drop shafts to channel flow into the tunnel, a deep pump station, other sewer infrastructure and completely new building facilities at the AlexRenew site.

In March 2024, the project marked a significant milestone, breaking through with a custom-built tunnel boring machine, nicknamed Hazel, which  simultaneously excavated and constructed the tunnel. 

… to a cleaner, healthier tomorrow

Constructing major underground infrastructure upgrades in one of America’s oldest communities isn’t without its challenges. Jacobs Project Manager Samer Sadek and other members of the TSJV team spoke with the North American Tunneling Journal about the unique complexities of the RiverRenew tunnel system’s design and construction. 

“Every site and location had its unique challenges, so the design and construction process is completely different from one location to the other,” Samer says in the article. 

For example, our design needed to consider several unique types of geologic conditions, including stiff clays, terrace formations and alluvium formations along the tunnel alignment. The design also needed to be durable and resilient to its underground location, so that it can serve the community well into the future. 

To aid in the complex design, we’re leveraging our suite of Digital OneWater solutions, including the Replica™ platform for hydraulics, controls and process modeling. We’re also creating a digital twin to train plant operators and experiment with new operating scenarios.

"Designing a program of this size requires a meticulous balance of innovation, precision and collaboration,” says Samer.“ The RiverRenew project exemplifies how intricate planning and engineering combine to address the multifaceted challenges of modern water management in one of America’s oldest cities. Working with AlexRenew and our partners, we’re navigating these complexities and look forward to delivering a sustainable, resilient solution that will benefit the community for generations to come."

Our project director and Jacobs’ global cross market director of tunnel and ground engineering, Mark Johnson, is a local resident and is particularly invested in improving the northern Virginia community’s environmental and public health.

“I understand the importance of CSO tunnel projects like these to local communities and the environment that we live in. It’s not just infrastructure,” Mark shares. “For example, at one of the drop shaft sites on the RiverRenew project, we’ll be covering the shaft and diversion structures with a park that will connect the community to the Potomac River waterfront.”

Before we started the project, Mark says, an unused warehouse with a chain-link fence around it sat on the location and there was no access for those who lived nearby to reach the water. When the project’s complete, the community will have a beautiful park to enjoy spending time by the waterfront. 

AlexRenew’s Nutrient Management Facility marked the first facility in Virginia and only one of 11 in North America to achieve Envision’s top distinction on its Sustainable Infrastructure framework. The RiverRenew project is continuing that commitment to the environment and is on track to achieve Envision certification and a certification from the LEED building rating system. 

The RiverRenew tunnel system, when complete in 2026, will ultimately capture, store and transport millions of gallons of sewage and stormwater to a treatment plant where it will be cleaned and treated before being returned to the Potomac River.