Greenville expands wastewater infrastructure with 5,950-ft underground tunnel
City of Greenville
Greenville, SC's consistent population growth put a strain on its wastewater management systems and risked creating environmentally damaging sewer overflows. The city built a 5,950-foot underground tunnel to add wastewater management capacity and accommodate future population growth.
Revolving loan funds
In Progress/Under Construction since 2018
Greenville risked experiencing frequent sewer overflows due to the strain population growth had on the city’s wastewater system.
The City of Greenville, South Carolina, is among the fastest-growing communities in the entire United States. Between 2010 and 2019, it added more residents than almost every county in South Carolina.
While population growth is great for bringing new economic opportunities to Greenville, it puts additional strain on infrastructure that tends to go unnoticed, like wastewater systems. In Greenville, the existing sewer line was already near capacity, with the population expected to continue growing. Greenville residents had already experienced sewer overflows when the system’s capacity was exceeded during wet weather events, and the projected population growth was certain to make overflows a more regular occurrence unless additional capacity was built. In addition to being unsightly, overflows also pose a direct threat to water quality, the environment, and economic development.
The city’s wastewater treatment and conveyance services are performed by Renewable Water Resources (ReWa), which immediately began looking into ways to add capacity to the city’s wastewater management system with the last impact and with the lowest lifecycle costs. Many of the original pipes were built in the 1920s and 1950s, so the most obvious choice was to rebuild the sewer system running through downtown Greenville, given its age and inadequate capacity. However, ReWa noted that many of the system’s pipes are in locations that would prove to be very disruptive to the community and add environmental risk during construction.
After evaluating 18 solutions, it was decided that a new tunnel would be built 100 feet underground to add capacity to the wastewater system with minor disruption to the community. The project - nicknamed “Dig Greenville” - would better equip Greenville to handle and mitigate the impacts of wastewater overflows during peak wet weather events. The flow of wastewater through the 7-foot diameter tunnel would be powered primarily by gravity without the need for maintenance-intensive mechanical equipment. Although this type of project was new for Greenville, it had been used in highly urbanized cities before.
The project “will help sustain future growth, especially in the urban area of greater Greenville,” said Greenville County Council Vice Chairman Butch Kirven, District 27. “Growth goes where the infrastructure is, mainly sewer lines, and there are some areas in the county that need to grow. There are other areas that don't need to grow as fast.”
With a plan in place, ReWa and Greenville needed to find a partner to help manage the construction process for the $39 million project.
Building an underground tunnel helped Greenville add wastewater management capacity to support future growth and avoid sewer overflows.
Facing such a major undertaking, ReWa wanted to partner with a company that had experience with big projects in the water sector similar to Dig Greenville. With the city’s economic development at risk, ReWa brought in Black & Veatch to design and manage the construction of the 5,950-foot tunnel. Funding for the project is administered through revolving funds from the South Carolina Department of Health and Environmental Controls and partially funded through the United States Environmental Protection Agency.
The 130-person project team focused on planning, safety, controlling construction impacts, and community outreach to accomplish the project’s goals. The construction was split into stages: blasting to clear the shaft, digging the starter tunnel, and building the main tunnel using a tunnel boring machine (TBM). The final stage before site restoration was to install new pipes and complete sewer connections. With the tunnel in place, Greenville anticipates having enough wastewater management capacity to serve the city decades into the future.
“About five years ago, the city felt it had some serious issues in the downtown area to address in regards to sewer capacity,” Greenville Mayor Knox White said. The tunnel "definitely puts not just the downtown, but rather the whole city in a better position for the future.”
Taking a proactive approach to the project’s work proved to be key when the team’s geotechnical investigation discovered that the initial plan to drill couldn’t be accomplished due to soil and different types of rock in the tunnel zone. The project team pivoted by designing and building a starter tunnel that was excavated using 41 blasts over a 9-month period. The approach was also beneficial when it came to controlling the impacts of the construction, despite operating in several high-profile areas of Greenville’s downtown corridor. The project team made use of odor and groundwater control plus continuous monitoring of noise, dust, and blast vibrations to mitigate the effects of the work on residents and the city landscape.
Community engagement was a big element of the project and ReWa held 25 community events and created 120 social media posts on social media platforms to keep the public informed of the project’s scope and status. One engagement strategy even involved working with a local elementary school where students constructed a lego tunnel for their lego city. Additionally, tours of the project by ReWa and consistent community engagement from planning through construction fostered strong relations with stakeholders.
When completed, Dig Greenville will help support the city’s continued population growth and economic development.
The Dig Greenville tunnel will help Greenville support future population growth for decades with expanded wastewater conveyance capacity
The city avoided sewer overflows from occurring more frequently during wet weather events by building additional wastewater capacity
Greenville prioritized environmental health by designing the tunnel to convey wastewater using primarily gravity instead of mechanical equipment
The city kept the community informed of the project’s scope and status through 25 community events and 120 social media posts
The Dig Greenville project can stand as an example for other cities to replicate in prioritizing low-impact, sustainable projects to accommodate a growing population
Despite being 5,950 feet long and 7 feet in diameter, the tunnel is mostly invisible to the surrounding community apart from an entry shaft at each end.
Who Should Consider
Communities looking for ways to prioritize environmental health and minimal disruption to the community with wastewater expansions that accommodate population growth.
Winner, Project of the Year - APWA
Winner, Project of the Year - Underground Construction Association
Government Project Team
- Knox White, Mayor
- Butch Kirven, Greenville County Council Vice Chairman District 27
Last UpdatedJul 18th, 2022
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