Chattanooga Wastewater System Built for Peak Flow

Tennessee utility takes on consent decree and rebuilds its system to handle any weather.

Chattanooga Wastewater System Built for Peak Flow

Public Works crew member Steven Bach switches Godwin pumps on-site after an overnight overflow.

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The wastewater system infrastructure in Chattanooga, Tennessee, is undergoing a massive makeover, mostly to boost the system’s ability to handle a high volume of stormwater and wastewater during heavy rain events.

Sanitary sewer overflows caught the attention of the Environmental Protection Agency several years back, and Chattanooga is actively tackling that issue under the terms of a 2013 consent decree agreement with the EPA, Tennessee and the Tennessee Clean Water Network.

The agreement includes both a list of issues that must be addressed and penalties including $800,000 to be spent on a supplemental environmental project, $238,000 for a state environmental project and a $238,000 civil penalty paid to the U.S. 

This consent decree is not the city’s first run-in with the EPA. Fifty years ago, Chattanooga had the distinction of having the worst air quality of any city in America. The town came together through public and private partnership to clean up the air, with great success. 

In 2014 and 2015, Outside magazine named Chattanooga “Best Town” for its quantity and quality of adventure playgrounds and its vibrant neighborhoods. Today, the city hopes to accomplish the same turnaround with its water resources.

System snapshot

The Chattanooga wastewater collections system covers 505 square miles and serves approximately 400,000 people. It comprises 1,263 miles of gravity sewers, 26,000 manholes, 72 pump stations and one regional wastewater treatment plant.

The Moccasin Bend Wastewater Treatment Plant treats 140 mgd with a peak hydraulic capacity of 220 mgd, and it produces 70,000 wet tons of biosolids per year. 

Two projects tackled and completed at the treatment plant include the construction of two new secondary clarifiers and their associated piping, valves and instrumentation, as well as the rehabilitation and upgrade of influent grit detritors and related splitter box. Both projects will improve the capacity of the plant and help reduce SSOs. 

Jeffrey Rose, director of the Waste Resources Division for the city of Chattanooga Department of Public Works, says many of the system’s pump stations hadn’t been rehabbed for decades. The consent decree turned out to be a good excuse to tackle so many of the much-needed upgrades. 

For example, the Citico Pump Station received an overhaul of its pumps, valves, electrical and instrumentation equipment while the Combined Sewer Overflow Treatment Facility got new pumps, piping, valves and instrumentation. 

Along with improvements to the Citico Pump Station itself, there will also be a backup emergency submersible pump and a permanent emergency standby generator. 

Getting to work

Like many cities, inflow and infiltration is an ongoing problem in Chattanooga, and it contributes to the SSO problem being addressed. 

Some of the largest-diameter interceptor and main pipes are being rehabilitated using CIPP trenchless technology. Rose says many of these pipes run along creeks and rivers, so they take in significant water. 

To date, 1.1 million linear feet of pipe have been inspected, and 300,000 linear feet have been rehabilitated. Besides the pipe, 4,500 manholes have been inspected and 2,000 have been rehabbed. The total goal for rehabilitation is 500,000 linear feet of pipe and 2,400 manholes.

“Lining these pipes gives us a pretty good payback almost immediately,” Rose says.

Chattanooga has an interjurisdictional agreement program with its municipal satellite sewer systems that require each satellite to do its own rehab, respond to I&I issues and meet a 3:1 peak flow rate. Rose says when they identify an issue or violation through smoke tests and CCTV inspections, the satellites address the problems promptly.

The utility also upgraded a series of equalization basins that hold about 70 million gallons. These basins were set up decades ago during a time when many industrial customers were dumping high-strength waste. Rose says many of those industries have gone away, and the ones that are left are controlling their wastewater better. As a result, the basins rarely have more than 5 feet of water in them. 

The majority of these basins had blower lines and diffusers. They were swapped out with surface aerators, eliminating one of the highest uses of electricity the plant had. 

Speaking of electricity, Chattanooga is also working to improve its solids quality and enhance methane production and capture. The plan is that the methane can be used one day as part of a yet-to-be-determined energy project. They will also start building a 10-acre solar farm they estimate will supply with 10% of their electrical demand. 

Moving forward

The next step for Chattanooga is installing equalization stations to further reduce SSO events in specific locations. The aboveground stations have been a touchy point with the public, according to Rose. 

While Chattanooga tries to locate the stations on out-of-the-way property owned by the city, sometimes they have to purchase land close to people’s homes or businesses. Even though the stations contain very diluted stormwater and wastewater and they drain out within 48 hours, it’s challenging to get people to approve an installation in their backyard, so to speak.

The utility is building new storage tanks that will handle 30 million gallons right near the plant, just 1/4 of a mile away. These tanks will eliminate the most significant overflow, the West Bank overflow, which the EPA specifically highlighted in the consent decree. Between the rehabilitation of pipes and manholes and those tanks, that overflow is expected to be eliminated. 

While fixing problems to meet the consent decree is a high priority, Chattanooga has also been making safety improvements. One such improvement was a change at the treatment plant from chlorine gas for disinfection to bleach. Given the plant’s proximity to downtown Chattanooga, this change reduces the potential threat of an accident that would affect many residents. 

Public communication

Primary funding for all projects has come from a series of loans through Tennessee’s State Revolving Fund Loan Program, which administers Tennessee’s Clean Water State Revolving Fund Loan Program. Rose says they have been able to get more money than they originally asked for because they go to the SRF with shovel-ready projects and ask if there’s any extra money not being used. 

“If they do have it, they’ll help us. We work together to make it happen,” he says. 

Chattanooga has also been raising sewer rates for the last six or seven years, yet Rose says the City Council and the public have been supportive. He attributes that support to a strong communication program.

Early in the process, the utility’s main message to the City Council was that the work had to get done because the EPA was making them do it. However, communication is now also aimed at the people of Chattanooga and the message promotes a clean environment, eliminating sewer overflows and the overall benefit to the city.

They’ve branded the effort to comply with the consent decree Clear Chattanooga and now promote its 3R Approach, which stands for restore, repair and replace.

“It’s given the public more visibility into what we’re doing, which is always good,” Rose says. “We want to make sure people hear what we’re doing with their money; it’s a lot of money.”

As for that particularly touchy point of underground storage tanks, communication is vital. Rose says people simply want to be heard and they want to know why specific properties were selected. He and his team developed an animation to show precisely what those wet-weather storage facilities do and why they are needed in the neighborhood.

“It’s pretty cool. People see it and say, ‘Oh, I get it now,’” Rose says.

Clean future

Chattanooga sits right on the Tennessee River and boasts a 13-mile riverwalk providing visitors with not only a view, but plenty of outdoor activities, restaurants, the country’s first freshwater aquarium, a sculpture garden and more.

The city is committed to using the natural resources such as the Tennessee River as the foundations for revitalizing downtown and restoring the relationship between natural resources and a great midsized city, making this cleanup effort very good for Chattanooga. Rose is confident they’ll succeed.

“If we can clean up our air, we can clean our water too.”

Planting a partnership

The Chattanooga (Tennessee) Public Works Department is turning to the community for help soaking up some of the city’s stormwater runoff.

The RainSmart program encourages homeowners to install rain barrels, rain gardens and vegetated bioswales on their property to capture stormwater runoff. In return, the city will reimburse eligible projects up to $1,000.

Once an interested homeowner fills out an application, the city will assess the property and advise where to place the garden and help calculate the appropriate size of the garden. They will also discuss planting options and give the property owner an estimation of their reimbursement amount.

Then, the property must pass a percolation test and the homeowner needs to submit plans to get the final go-ahead. Homeowners have the option to tackle the project themselves or work with a landscaper. For those going the DIY route, the city provides a guide and templates to help create the garden or bioswale plan.

Chattanooga is also using these installation projects as a water-quality teaching moment. Here, the homeowner can choose to co-host a “workshop” with the Public Works Department. Once the garden’s structural work is complete, workshop attendees help with the planting and mulching while water-quality specialists teach them about rain gardens, water quality and the RainSmart program.

There have been 15 rain gardens installed since the program’s inception four years ago, and 14 rain barrels received reimbursement since that option was offered in 2018. Of the 15 gardens installed, three have been used as workshops.


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