The EPA is getting tough on stormwater erosion and contaminants. Here’s a look at how precast concrete can successfully meet their requirements.

By Kent Sipes

Stormwater treatment used to be just a matter of channeling excess water safely into a lake or river. And channeling the water “safely” only meant making sure the water volume didn’t damage life or property on its way to the destination. Once it reached the lake or river, it was someone else’s concern. New EPA guidelines have changed all that.

When stormwater runs over a hard, non-porous surface like a parking lot or a street, it washes oil, silt and trash from the surface. Unless the stormwater is filtered, these pollutants may enter the water supply. In the past, this was not as big a problem as it is today, because most stormwater was filtered by running into and through several feet of soil. However, an increase in paved surfaces has created the need for man-made filtration of stormwater.

New EPA guidelines require larger cities and counties to take steps to improve stormwater quality prior to discharge. These steps include public education about stormwater runoff, street sweeping programs to remove trash, regulation of construction sites to minimize erosion, and the production of a “stormwater atlas” that details all components of a stormwater collection and discharge system. The target result is an 85 percent reduction in contaminants that would have otherwise entered the water system.

Here is a look at two stormwater treatment projects that used precast concrete components to solve design and installation challenges. Both projects adapted antiquated stormwater treatment methods to meet modern standards.

Largo, Fla.

The stormwater runoff from a 90-acre basin in Largo, Fla., was a major concern to the city’s Stormwater Program, especially since the site also contained a 25-acre apartment complex. The previous system used in the basin merely drained the water, along with runoff containing hydrocarbons and trash, into the 8th Street discharge point. Since Largo is part of the EPA’s NPDES (National Pollution Discharge Elimination System) Phase 1 program, requiring the city to take proactive measures to improve water quality, the basin was a natural target for a retrofit.

Mike Sepessy, stormwater program manager for the City of Largo, says he faced several challenges in this project. “First, since this was a municipal project, we were operating under a very tight budget. Using precast components helped to greatly reduce our cost,” he says.

“Second, we needed a system that would incorporate two input pipes and a diversion box,” he continues. “Since precast components could be custom-designed for our needs, this was not a problem.” Finally, since there was such a large drainage basin and lots of upstream flow, he needed to use a large stormwater separator system. “Again, custom-designed precast components provided our solution.”

Sepessy adds that the lower cost and increased flexibility of precast concrete components compared to other types of construction helped to solve problems with other above- and below-ground water. “Since the water table here in Florida is only inches below the ground surface, and because excess water on the surface is a constant problem, we needed to use well-pointing equipment and mud pumps. Because we used precast concrete pipes, boxes and walls, we were able to add this other equipment in a cost-effective manner.”

Chris Landt of CDS Technologies, the developer of the project, says, “Since the weir box we needed for the 8th Street Outfall project was so large (10 feet by 8 feet by 8 feet), it helped that the precaster shipped it to us in two pieces with a horizontal seam.” He says this made installation of the box a lot simpler.

“For stormwater treatment systems, it’s just a given that precast is the first choice,” adds Landt. “It lasts longer than anything else and it’s very strong.” In fact, precast concrete can be designed to provide various strengths, depending on the need, and its strength gradually increases over time.

Atlanta

Grant Park, home of the Atlanta Zoo, had a problem with debris washing off its two parking lots into the storm drains. Overloaded storm drains became clogged with leaves and trash, thus excess rainfall had nowhere to go. Water collected in low spots, giving the parking lots a flooded appearance.

Erosion was also a problem in the park. Because of insufficient drainage, recreational fields flooded and washed silt into the stormwater system. Further, the old stormwater collection system used 3-inch clay pipes that were totally inadequate.

The City of Atlanta and contractor Site Engineering Inc. decided to build a retention pond large enough to hold rainfall from a 100-year storm event. They also installed two large precast concrete systems to separate stormwater from trash and oil washing off the lots. The reinforced concrete pipes now carry the filtered runoff to the retention pond.

David Hess, Project Manager for Site Engineering Inc., says, “We were under severe time constraints, because the zoo’s peak attendance occurs between April and September.” His company completed the first lot’s drainage prior to April and began work on the second lot in September. “The use of precast components assisted in completing the critical path in time.” Hess adds that the work was not hampered by the very wet spring, since the installation of precast components isn’t greatly affected by the weather.

Clint Voyles, foreman for Site Engineering, says precast concrete even improved the safety of the job. “Because precast can be immediately installed, the ditches don’t have to be open for as long as with other types of construction.” Since precast concrete pipes don’t require backfill material that’s as costly as the material required for other types of piping, additional cost savings were realized on the project.

Voyles also noted that design changes occurring during the construction phase would have created much more of a problem if precast hadn’t been used. “There were changes made to grades, and the Grant Park Conservancy Organization asked us to save as many of their trees as possible,” he says.

“We had been scheduled to remove 30 to 40 of the large, old-growth trees in the park, but we were able to alter our design and removed only five of the trees,” says Hess. The smaller footprint typical of precast components (compared to other types of construction) helped with the design as well.

Stormwater treatment will continue to be a concern for both established cities and growing population centers, and EPA regulations on water quality will continue to impact both public and private sectors. Precast concrete provides a wealth of flexible, cost-effective solutions for stormwater treatment.

Project Profile

Project Name: 8th St. Outfall

Owner: City of Largo, Fla.

General Contractor: Site Engineering Inc., Atlanta

System Developer: CDS Technologies, Canton, Ga.

Precast Manufacturer: Atlantic Precast, Florida Division, Sarasota, Fla.*

*Atlantic Precast, Florida Division is a certified plant under NPCA’s Quality Assurance/Plant Certification program.

Project Name: Grant Park

Owner: City of Atlanta

General Contractor: Site Engineering Inc., Atlanta

System Developer: CDS Technologies, Canton, Ga.

Precast Manufacturer: Atlantic Precast, Georgia Division, Douglasville, Ga.*

*Atlantic Precast, Georgia Division is a certified plant under NPCA’s Quality Assurance/Plant Certification program.