Articles / October 10, 2024

Music City Makeover: New Equalization Facility Helps Nashville Wrestle with Water Overflows

Long-time residents of Nashville still reel when remembering the flooding that occurred during the weekend of May 1-2, 2010, when 13.57 inches of rain was measured in a 36-hour period. The two-day rainfall total doubled the previous 48-hour rainfall record, and the human and financial consequences proved devastating. The storm killed 11 people in the Nashville area, including one victim whose body was found nearly five months after the flood. Nearly 11,000 properties were damaged or destroyed, and 10,000 people were displaced. The flood caused more than $2 billion in private property damage and $120 million in public infrastructure damage.

The mighty Cumberland River, which stretches for 688 miles through Tennessee and Kentucky, crested at 51.86 feet, nearly 12 feet above flood stage. Riverfront Park, one of the region’s most-popular tourist destinations—perched along the river in downtown Nashville—is home to concerts, restaurants and entertainment and was among the areas that witnessed significant destruction.

One year after the flood, the Clean Water Nashville Overflow Abatement Program was created to improve the city’s wastewater infrastructure. The program is an initiative led by Metro Water Services, the U.S. Environmental Protection Agency, and the Tennessee Department of Environment and Conservation.

“Nashville is a lot like a lot of other cities that have aging infrastructure,’’ explains Kimberly Martin, program manager for Clean Water Nashville. “We’re a high-growth area now, which has added some complexities to the program.”

The Clean Water Nashville program covers more than 70 projects, varying in size and scope. Earlier this year, workers completed the Gibson Creek Equalization Facility. The $18.9 million project includes a 10-million-gallon pre-stressed concrete tank and a 22-million-gallon-per-day pump station. Construction began in August 2021 and was completed in February 2024.

“The primary goal of the project is to improve the infrastructure due to a growing population and increase flow,’’ says Thomas Ward, assistant project manager at Reeves Young, the general contractor for the project.

Design drawings detail the Gibson Creek Equalization Facility project. (Image Credit: Metro Water Services of Nashville and Davidson County, Tennessee)

Equalization Projects

The Gibson Creek project was one of several in which Clean Water Nashville constructed equalization facilities. Equalization tanks are designed to buffer flows to a wastewater treatment plant with variants in influent flow due to diurnal variation and wet-weather events. Mixing is required in the basins to maintain solids in suspension, preventing deposition and equalizing load to the treatment plant.

Waste treatment is most effective when conditions are constant. Inconsistent flow rates or batch dumping, which occurs when wastewater is gathered, treated and then discharged at one time, create changes that affect the biological environment. It also creates the need for constant modification of chemicals.

Equalization minimizes the modifications required for treatment and results in superior operation of the process. It also reduces the amount of capital expenditures for supporting equipment. Equalization tanks also play a key role in rainwater overflow and excess sewage. The tanks prevent untreated wastewater from overflowing into nearby rivers and streams.

In 2022, another Tennessee community constructed an equalization station with three large storage tanks that hold up to 30 million gallons of wastewater.

The project included construction of a 10-million-gallon pre-stressed concrete tank and a 22-million gallon-per-day pump station. (Photos by Luis Corone)

“When Chattanooga was hit with a 10-year rain event that flooded streets, parking lots and buildings, one very important thing did not happen,’’ notes Mark Heinzer, director of the Moccasin Bend Environmental Campus. “Not one gallon of untreated wastewater overflowed into the Tennessee River, thanks to (Chattanooga’s) new wet-water equalization station. Instead, 18 million gallons of wastewater and rainwater overflow was pumped into tanks and later slowly released into our treatment plant for purification.”

The project was part of upgrades planned by Clean Water Nashville to improve infrastructure and decrease sewer overflows. (Photos by Luis Coronel)

Surprisingly, Nashville receives more rain than most other U.S. cities. More than 56 inches of rain douse The Music City each year, putting it in the top 10 among major U.S. cities. Nashville receives more annual precipitation than Seattle, Tampa and Jacksonville, two Florida coastal communities that often experience hurricanes.

“When the pump station gets overloaded and there is too much wastewater coming through, the system will divert it to an equalization tank until it settles down,’’ says Ward. “Then the wastewater will drain back into the regular system. It prevents the storm system from getting backed up. These tanks are fairly common and help the system handle the flow.”

Other Improvements

Workers constructed a wide range of other improvements at Gibson Creek. The Reeves Young team improved the existing pump station facility to address settlement and cracking issues and coping repairs. The plan also called for the construction of a new flow-diversion structure vault, flow-metering vault, equalization pump station and foundation work such as piles, slabs, beams, walls and miscellaneous concrete work.

Workers also built electrical motor control centers with a standby power-generation system and architectural buildings. The project also called for general site work, including paving, grading, drainage, fencing and signage, and installation of a sewer pipe and manhole.

“We dealt with flooding several times while we were in construction,’’ explains Ward. “In that case, there’s nothing you can do except wait for it to subside. We’d just be dewatering into the Cumberland River and it would flood again. You have to wait until the water settles down, and sometimes that can take about a week. It’s something that we experience quite a bit during some of the wetter months.”

Population Explosion

Besides being prone to flooding, Nashville also needed infrastructure improvements to maintain pace with a surge in population. Earlier this year, the Nashville Area Chamber of Commerce reported the region increased by more than 31,500 residents in 2023.

Increasing population, however, also requires critical infrastructure improvements. Clean Water Nashville established its Overflow Abatement Program to address sewer capacity issues, improve infrastructure and reduce health risks associated with exposure to bacteria and contaminants.

Undoubtedly, Nashville’s sewer system needed a major upgrade. “Nashville had no wastewater treatment until 1958,’’ Clean Water Nashville Program Director Ron Taylor said in an interview with WKRN. “Everything went straight to the water untreated.”

The original system dates back to the late 1800s and consisted of a combined sewer system in which both sanitary sewage and stormwater was funneled into one piping system. Combined sewer systems were common in cities during the 1800s to address public-health problems caused by lack of proper sanitation. City planners later transitioned to separate sanitary and storm sewers.

The city began treating wastewater in the 20th century, and stormwater treatment plants improved water quality. Pipelines were constructed to convey sanitary sewage along with stormwater to treatment plants to improve water quality. Intense rainfall often leads to flows of stormwater in the combined sewer system that exceed treatment plant capacity. In some instances, stormwater was discharged without treatment.

In addition, separate sanitary systems and piping deteriorate over time, and the volume of rainwater can overwhelm aging sewer systems.

Common Problem

Nashville isn’t alone among U.S. cities trying to improve its wastewater infrastructure. In May 2024, the Environmental Protection Agency reported that the nation will need at least $630 billion over the next 20 years to protect the nation’s waterbodies.

Tennessee, however, has shown signs of improvement. A 2022 report from the American Society of Civil Engineers gave the state a “C” on its most recent report card. The state received a “C+” grade for its stormwater infrastructure and a “C-” grade for its wastewater infrastructure. The report said “capacity enhancements were accomplished at the expense of maintenance, as evidence by combined sewer overflows that result in sewer tap moratoriums.”

The project includes 15 doors from BILCO, which allow access to valve vaults, a wet well and diversion structures. (Photos by Luis Coronel)

Wastewater infrastructure owners reported a $5.9 billion, 13-year funding gap for needed capacity and to bring the systems back to a state of good repair. Even with significant investments and improvements, however, there’s no guarantee that Nashville’s wastewater management infrastructure won’t be overwhelmed by a generational flood. Even with improvements in place, a 2021 flood killed seven people in Nashville.

The floods in 2010 devastated the city and are not easily forgotten. Clean Water Nashville is committed to improving the city’s infrastructure to mitigate any future deadly storms.

“The program to improve the wastewater system infrastructure will provide lasting benefits for future generations, improve water quality and provide a clean, healthier environment for our citizens,’’ the agency said on its website.

About Thomas Renner

Thomas Renner writes on building, construction and other trade-industry topics for publications throughout the United States; email: trenner@catalystmc.com.