Precast concrete tanks powered by Contech’s Filterra system provide an optimal solution for a large-scale, mixed-use development in Southern California.
By Mason Nichols
California is massive. Encompassing more than 160,000 square miles, the state boasts a healthy assortment of terrains and ecosystems, including everything from lush forests and towering redwoods to expansive mountain ranges and arid deserts. With a generally temperate climate, ample job opportunities and so much to do and see, it’s no wonder that real estate values across the state are significantly higher when compared to the rest of the United States.
This has forced many developers to get creative in their plans for construction. In Burbank, Calif., Overton Moore Properties (OMP) of Los Angeles planned Avion Burbank, a 60-acre mixed-use development combining creative office, retail, industrial and hotel space via a sustainable campus environment. With 17 buildings and more than 1.25 million square feet to cover, OMP sought an on-site stormwater solution that would minimize the footprint – and costs – while also providing aesthetic appeal and meeting Los Angeles County’s stringent stormwater requirements.
The answer was Filterra, an innovative solution powered by precast concrete and optimized for high-volume treatment and high pollutant removal that requires a minimal footprint.
PUTTING A LID ON IT
Workers set a precast concrete vault at the Avion Burbank mixed-use development.
With sustainable practices becoming an increasing area of focus across the United States, many entities are turning to low-impact developments (LIDs) for stormwater management. Traditional stormwater management systems collect and convey stormwater runoff via storm drains and pipes to a centralized stormwater facility. LIDs, however, leverage site design and special stormwater techniques to mimic the natural processes that “result in the infiltration, evapotranspiration or use of stormwater in order to protect water quality and associated aquatic habitat,” according to the EPA.
Because LIDs boast a slew of economic and environmental benefits and have been so successful in an array of applications in many states, they are “seen in California as an alternative to conventional storm water management,” according to California Water Boards. For these reasons, the LID approach made perfect sense for Avion Burbank. However, to select the optimal system for the development, the engineer of record and all parties involved had to review the LID hierarchy established for the area. According to Tamara Mamon, stormwater consultant for Contech Engineered Solutions, this was a multi-faceted process.
Mamon explained that the first rule in the hierarchy is that if soils are favorable for infiltration, you must infiltrate on-site. This was not the case for Avion Burbank, so the capture and use tier was considered. But requirements for capture and use mandate that any water collected must be discharged within four days following a rain event. This makes capture and use inefficient within most of Los Angeles County because water collected and stored is typically needed in the drier months – not directly after an event.
The next tier to consider was bioretention, and the engineer of record pursued this to treat the 85th percentile storm event described in Los Angeles County’s Multiple Separate Storm Sewer System (MS4) permit. Ultimately, a LID plan leveraging bioretention was selected, which would allow for the control of pollutant loads and runoff volumes to the maximum feasible extent while meeting all the requirements of the MS4 permit.
ENTER FILTERRA
With a plan in place, the project developer and engineer of record next needed a proven system that would maximize treatment and minimize costs. They turned to Filterra, an advanced bioretention solution designed by Contech for high efficiency that requires just a small amount of space.
Filterra system consists of a plant, 3 inches of mulch, 21 inches of engineered media and an underdrain pipe that’s encased in about 6 inches of stone. Stormwater runoff enters the system through a curb inlet or pipe and flows through a specially designed filter media mixture contained in a landscaped precast concrete vault. The filter media captures and immobilizes pollutants, and, ultimately, the runoff flows into an underdrain system at the bottom of the vault, where it is discharged. One specific feature was of considerable importance for the Avion Burbank project.
“The media infiltration rate of Filterra systems is 140 inches per hour, which is significantly higher than traditional biofiltration media,” Mamon said. “Attachment H of Los Angeles County’s MS4 permit specifies that the range should fall between 5-12 inches per hour. This higher rate results in the footprint being reduced significantly when compared to a more traditional system.
“With the cost of land in Los Angeles being so steep, Filterra is a favorable alternative.”
On most projects where Filterra precast concrete vaults have been specified in the past, only two to four units have been needed. But with more than 1.25 million square feet to consider for Avion Burbank, a sizable increase in the number of vaults was needed. To manufacture the nearly 50 units required for the job, Contech turned to longtime partner and NPCA Certified Producer Member Precon Products of Simi Valley, Calif.
GETTING IT DONE
Precon Products and Contech have a long history together, stretching all the way back to when Precon worked with Australian-based CDS in the late 1990s. After Contech purchased CDS in 2006, the two companies continued partnering on a variety of projects, and Precon now serves as the primary precast manufacturer for Contech in California.
This long-standing relationship was critical to success for Avion Burbank, which required close collaboration among all parties to produce the large number of Filterra units needed in the time frame specified. According to Dan Zarraonandia, vice president at Precon Products, an ample array of vaults in varying sizes were manufactured. All vaults were 4 feet deep but ranged in size from 4 feet wide by 6 feet long to 8 feet wide by 22 feet long. The largest vault weighed more than 50,000 pounds and had to be shipped in three separate pieces.
Zarraonandia explained that the tight working relationship between Precon and Contech, along with assistance from the other project partners, was key to Avion Burbank’s success.
“On a project like this, with the vaults being so large, there’s a lot of coordination required between us, Contech and the contractor to ensure that everything shows up on time,” he said. “But with all three of the main parties working in unison, everything went very smoothly.”
This was especially important given the project’s tight timeline, which called for the Filterra vaults to be manufactured and delivered to the Burbank site in just 10 weeks. Once the vaults were manufactured and delivered to the site, the installation process was simple. Workers from GJ Gentry, the contractor for Avion Burbank, excavated the area for the units to be set, made proper piping connections for the inlets and outlets, then backfilled. After installation was completed, large trucks arrived on-site and distributed Filterra’s filtration media via conveyor belt. The final step included planting trees and shrubs and installing tree grates across the precast vaults.
Mamon agreed with Zarraonandia’s assessment of the work, citing the power of collaboration as critical to bringing everything together.
“Working closely with all the parties involved was imperative on this project,” she said. “Up front, I sought out the city of Burbank multiple times during the design phase to ensure that Filterra would be approved in the plan checking process. Our sales engineers were also very communicative with the contractors and distributors to make sure our spec was held and to prevent any delays.”
Crews fill a precast tank with mulch and engineered media at the Avion Burbank development.
Going with the Filterra precast solution offered many advantages beyond price savings. Zarraonandia said that if a cast-in-place system had been selected, the project likely wouldn’t have been possible. Additionally, precast allowed the bioretention system to meet both the high level of quality and tight tolerances needed.
“With precast, you’re up to strength before you ship, and you know the quality before the product goes out there,” Zarraonandia said. “With cast-in-place, if there’s a bad batch of concrete that doesn’t come up to strength and it’s already in the ground, you could have a real disaster.”
MEETING THE NEED
As developers in California and across the North America continue considering alternative stormwater management solutions on projects at scale, precast concrete solutions – including Filterra – stand ready to reduce costs, foster innovation and provide long-term stability. Thanks to tight collaboration between project partners and the benefits of a proven system, the Filterra precast concrete vaults at Avion Burbank will provide reliable and aesthetically pleasing stormwater management at the mixed-use development for years to come.
Mason Nichols is a Grand Rapids, Mich.-based writer and editor who has covered the precast concrete industry since 2013.
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