When a Louisiana developer had to place a sewer treatment plant in a small and cozy shaped space, precast concrete provided the solution.
By Deborah R. Huso – Photos courtesy Gainey’s Concrete Products
When Equity Construction of Monroe, La., set out to develop a sewer treatment plant for a subdivision in Hammond, the firm had several major challenges to overcome, not the least of which was a very tight place in which to locate the plant. Looking something like a trapezoid, the area allotted for the plant within the St. Paul Estate subdivision measured roughly 77 feet by 34 feet, had a 30-degree angle on one side, and was located directly adjacent to a pre-existing gas line and newly completed homes.
Equity considered building a conventional aboveground plant with steel, but that option proved more expensive, and the steel plant didn’t have the flexibility to fit the space. The above-ground plant would have also been unsightly to residents of adjacent houses. “Who wants a sewage treatment plant right next to their house?” asks Greg Roache, president of Gainey’s Concrete Products, which supplied both the precast concrete components and the installation for the underground treatment facility. “The developer didn’t want residents of the subdivision to have to look at the plant,” explains Roache, “and we also had to work
around a nearby gas line. It was really an odd piece of property.”
Precast Fits the Space (and the Bill)
Steel also would have represented a greater expense. Gainey’s designed thin-walled cells for the plant at half the price of a steel tank. “We were able to design a custom 30,000-gallon-a-day plant for considerably less than an off-the-shelf steel equivalent,” Roache notes. Dale Edwards, project manager for Equity Construction, estimates that choosing concrete over steel ultimately saved 30 percent on total project costs.
“It also allowed us to shift the components around to fit the area,” Edwards adds. “An above-ground plant wouldn’t have permitted that. We couldn’t have rearranged the configuration.” Edwards says the space was so tight that, in retrospect, he is not certain an above-ground steel plant could have even worked.
The precast plant was designed to meet Equity’s specifications, meaning it would have to be capable of servicing 30,000 gallons per day for up to 75 three-bedroom homes. All of the homes in St. Paul Estates are designed as rental homes for low-income families, meaning the developer, Standard Enterprises of Monroe, wanted to fit as many homes (and the equipment to service them) in as small a space as possible.
“This is a unique developer,” Roache says. “Post- Katrina, everybody wanted to be a developer and create subdivisions, sell the homes and make quick money.” Roache says after the real estate bubble burst, a lot of these subdivisions and their developers found themselves in serious trouble. But Standard Enterprises’ approach has been very different. “These are rental homes. They’re single-family, and they rent for $500 a month. If a family leases a home for 20 years, then they can buy it for $6,000.”
The builder had also anticipated the need for a grease interceptor in the subdivision. “But the grease interceptor was requested for the project after the plant designs were already made,” Roache says.
Clay Barrilleaux, CEO of Density Utilities, the firm that maintains the treatment plant, suggested the grease interceptor. “We felt it was necessary since the plant was serving the entire subdivision,” Barrilleaux explains. Once again precast concrete came to the rescue. Because Gainey’s could build a grease interceptor of any size to fit any space, it was able to
build a thin, long structure that fit the minimal leftover space on the site.
The St. Paul Estates plant also has another unique feature: a tertiary filter imported from Czechoslovakia.
Because of the small area in which the plant was located, the developer didn’t have the luxury of space for a drainage field. For this system’s size, Roache estimates a conventional treatment system would have required an area the size of a football field. The special filter allows for the reduction of sewage content by two-thirds in the final process of treatment, thereby easily meeting their discharge limits required by Louisiana Department of Environmental Quality (LADEQ).
The lift station and treatment system at St. Paul would have been especially hard on a steel plant. “When you deal with a lift station, you’re dealing with raw sewage without oxygen, which allows anaerobic bacteria to eat it,” Roache explains. “But it also eats up the steel terribly if the plant is underground.” That would have meant the only option for St. Paul had the builder selected a steel plant would have been an aboveground operation that would have been visible to the subdivision’s residents.
“Precast likes the ground,” Roache says, “and it lasts in the ground.” He says he knows of 25-year-old precast concrete treatment plants that look as new as the day they were installed.
Roache says steel plants, if placed below ground, are also a major environmental concern because they disintegrate quickly. “They’re easier to install, but if nobody replaces them, soon you’ve got raw sewage leaching into the soil.” If a plant uses chlorine, that introduces yet another deterioration factor for steel.
Precast Reduces Maintenance Concerns
“Steel experiences extreme corrosion,” says Barrilleaux. “Some plants get corroded to the point that you can’t even continue their use for fear they’ll fall apart.” On the other hand, he says he’s seen precast concrete plants that have been abandoned 20 years that still work once re-commissioned.
Barrilleaux says steel plants operate well, but they can be unsightly because they’re high above the ground. That also means more dangerous working conditions for people like Barrilleaux who maintain them.
“With concrete, you’re working 6 inches off the ground. It’s easier, and it’s safer,” he says. That also means the residents of St. Paul Estates won’t have to look at the plant. “It’s low to the ground. It increases the visual appeal of the subdivision. The ability to keep the sewer treatment plant out of sight and out of mind is very important in instances like this where the homes are close to the plant.”
Roache says staging the pieces was definitely challenging given the fact that houses were already built close to the plant site by the time the precast concrete cells were ready for installation. “But we were able to install the plant, two lift stations, sample port and tertiary filter retaining wall (41 pieces) in three days,” he adds, “and that really cuts down on the price.” All precast components of the plant were built in Gainey’s factory in about 15 days, and the time of the project from order to installation took just three months. Edwards says a steel plant typically takes at least four months to build, and he was on a time schedule with the St. Paul Estates project, needing the plant up and running by Sept. 1.
Lisa Roache, vice president of sales for Gainey’s Concrete Products, says the St. Paul Estates project was one of the company’s most challenging. To make all the treatment plant cells work in a small space with an odd shape, Gainey’s had to do a lot of planning before beginning construction. “It was like putting a jigsaw puzzle together,” she says. “We had to make sure all the holes from one cell to the next lined up.” She’s grateful for the daily interaction Gainey’s had with Equity Construction. “An hour spent in planning can save days on the construction site,” she adds.
Precast is also easier to maintain, according to Barrilleaux, who also services plants made with shotcrete and steel as well. “Installation is quick,” he says. “You dig the hole, (set a limestone base), put the plant in, and it’s a done deal. You don’t have to worry about the weather.”
“Done right, precast is the most durable and least expensive option for sewer treatment plants,” Roache says. Project engineer Bryan Butler, vice president of Ballard CLC, says that precast is the ideal option in any project with constraints because it offers so much flexibility.
Barrilleaux agrees, though he cautions against jumping on the precast bandwagon without considering the factory that’s producing it. “Consider your precast provider carefully. Don’t necessarily go with the cheapest.”
Deborah Huso is a freelance writer who covers home design and restoration, sustainable building and design, and home construction.