Imagine a Coca-Cola can stretched to 240 feet in diameter and nearly five stories tall.
Now imagine two of them rising from the landscape along Interstate 75.
For months, motorists have driven past the towering concrete structures near South Chickamauga Creek, watching them gradually take shape. Most people never get a closer look.
Recently, however, the city of Chattanooga pulled back the curtain on one of the region’s largest infrastructure projects, inviting media members, elected officials and community leaders inside the massive wet-weather equalization tanks under construction as part of the Environmental and Economic Infrastructure Improvements program, known as e2i2.
The tour offered a rare opportunity to step inside a facility designed to solve a problem most residents rarely think about: what happens to millions of gallons of wastewater when heavy rain overwhelms the sewer system.
When completed in 2027, the project will include two equalization stations capable of storing approximately 30 million gallons of excess wastewater during heavy rain, helping reduce sanitary sewer overflows, improve water quality in South Chickamauga Creek and protect the Tennessee River watershed.
“People driving past on I-75 notice these structures going up,” Chattanooga Wastewater Department Administrator Mark Heinzer told visitors before the tour. “But they don’t realize what’s actually taking shape. From the highway, all you see are two massive concrete cylinders rising above the landscape. Today, you’ll get a chance to step inside one of these enormous tanks – something very few people will have the opportunity to do.”
Building capacity for a growing region
The project sits at the boundary between the city of Chattanooga’s wastewater system and the Hamilton County Water & Wastewater Treatment Authority system, making it a joint effort between the two agencies.
Officials say that partnership has been essential to delivering a project intended to benefit the entire region.
The equalization stations will function as giant holding facilities during storms. Rather than allowing excess flow to overwhelm the wastewater network, the system will temporarily store wastewater until treatment capacity becomes available. Once the system stabilizes, the stored flow will gradually be released and treated.
The investment is a key component of Clear Chattanooga, the city’s long-term initiative to modernize aging wastewater infrastructure, reduce sewer overflows and prepare for future growth.
“This project has brought together multiple agencies, contractors and stakeholders,” Heinzer said. “As the city’s first wastewater design-build project, delivered in partnership with the Industrial Development Board, it’s allowed us to move more efficiently while creating infrastructure that will serve the community for decades to come.”
The scale of the undertaking extends beyond environmental benefits. According to city officials, the project has generated approximately $39 million in local economic investment, including more than $27.7 million awarded to area subcontractors, consultants and vendors.
Tight squeeze into a giant space
The most memorable part of the tour began with an unexpectedly small entrance.
Visitors entered the tank through a manway opening measuring just 2 feet, 9 inches high by 4 feet, 5 inches wide.
After ducking through the opening, the space opened into something cavernous.
The unfinished interior stretched outward in every direction, voices echoing across the concrete floor as the curved walls rose toward a massive domed roof overhead.
Standing inside, it became easier to understand the sheer scale of a structure designed to hold more than 15 million gallons of wastewater.
Each tank features a 240-foot interior diameter and sidewalls approximately 46 feet high. Together, the two tanks at the West Chickamauga site will provide more than 30 million gallons of storage capacity.
Yet the engineering hidden within the walls might be even more impressive than the size.
Engineering a modern reservoir
Unlike traditional cast-in-place concrete tanks, the equalization tanks use a prestressed concrete design intended to maximize strength, durability and efficiency.
The floor consists of an 18-inch-thick reinforced concrete slab containing roughly 3,000 cubic yards of concrete. Above it rises a wall system unlike anything visible from the outside.
Embedded within the wall is a steel diaphragm that creates a watertight seal. Layers of shotcrete, reinforcing steel and prestressing wire surround it.
The secret lies in the wire.
Steve Jay, senior project manager for Brasfield & Gorrie, says approximately 450 miles of quarter-inch prestressing wire are wrapped around each tank under roughly 4,000 pounds of tension.
The result is a structure that becomes stronger through compression.
The approach provides significant advantages over conventional construction.
“Compared to conventional tank construction, it’s an efficient, cost-effective approach with exceptional longevity,” Jay explained.
Following the flow
The tanks represent only one component of a larger system.
The tour also included visits to the diversion structure, pump station and electrical building, each playing a critical role in managing wastewater during storm events.
When heavy rainfall increases flow throughout the sewer network, wastewater will be diverted into the equalization system and pumped into storage.
Inside the tanks, flow will enter through a 24-inch standpipe. At the center sits a sump designed to collect stored wastewater once treatment capacity becomes available.
Operators at the Moccasin Bend treatment facility will be able to control precisely how much wastewater is returned to the system.
Automated valves and flow meters will regulate that process, ensuring stored wastewater can be released gradually rather than overwhelming downstream facilities.
The system will also include carbon-bed odor control units positioned at key locations.
Those units will pull potentially odorous air through activated carbon filtration systems, helping minimize impacts on surrounding neighborhoods and recreational areas.
More than concrete and steel
For city leaders and project partners, the infrastructure carries significance beyond engineering.
The South Chickamauga Creek Greenway has been closed for nearly two years while construction proceeds. When the project is complete, officials say the greenway will reopen, restoring public access to one of Chattanooga’s most popular outdoor corridors.
Project leaders also emphasize the role the facility will play in supporting future growth.
“Every water project touches lives – and we take that responsibility seriously,” said Ben Harris, regional vice president for Brasfield & Gorrie. “With the environmental sensitivity and the complexity involved, we’re intentional about building the right relationships and choosing the right methods to get the job done well and safely.”
For Harris, the value of the project extends beyond pipes and pumps.
“These improvements to the city’s wastewater infrastructure are vital to the health of the overall system and Chattanooga’s future,” he continued. “They enhance quality of life. They help make Chattanooga an even better place to live, work and grow. It means cleaner water, healthier neighborhoods and less disruption when the next storm rolls through.”
As Chattanooga continues to expand, projects like this often operate largely out of public view. Residents rarely see the facilities that collect, transport and treat wastewater, even though they’re essential to public health and environmental protection.
That reality made the tour unusual.
For one day, visitors could walk through areas normally hidden behind construction fencing. They could stand inside a tank capable of storing millions of gallons of wastewater, follow the route water will take through the system during major storms and get a closer look at the infrastructure serving the region.
In many ways, that was the purpose of the event: to give residents a better understanding of a major public works project that’s largely out of sight but will have a lasting impact on the community.
As Heinzer reminded the crowd before the tour began, projects like this are the result of years of planning, collaboration and skilled labor.
“Construction of a facility this size requires thousands of hours of planning, engineering, coordination and craftsmanship,” he said. “Every wall, every pipe, every pump and every electrical component has been designed and installed by professionals committed to building infrastructure that will serve this community long after we’re all gone.”