In April of 2020, engineers from Kier and Wright of Livermore, California, reached out to Contech to assist them with their Storm Water Quality Control Plan for a large warehouse project in Stockton, CA. Contech was asked to review their stormwater design to help make it more efficient and cost-effective.
The original design utilized traditional bioretention planters throughout the site. When Contech engineers looked at the layout and the size of the drainage areas, it became apparent that the Filterra Biofiltration system would be the perfect alternative to traditional bioretention. Filterra is similar in cross-section to traditional bioretention. However, the unique engineered soil media allows the system to operate much more efficiently than traditional bioretention, offering equal or better water quality at a fraction of the size.
The biggest engineering challenge was the size of some of the treatment areas. Some of the treatment areas were required to treat several acres of impervious surfaces, including one that was treating approximately 11 acres. A traditional bioretention basin for this area would have required nearly 22,000 square feet (½ acre), taking up a great deal of real estate, not to mention the added demand for irrigation and maintenance. Using Filterra in that location required only 500 square feet. A savings of 21,500 square feet.
Filterra is typically provided in a precast vault with all of the internal components pre-installed. However, given the size of this basin, using a precast vault was not practical due to its size and weight. In this case, Filterra Bioscape was used. Filterra Bioscape utilizes all the Filterra components but without the concrete structure, allowing for multiple inlets and installation directly into a basin.
There are 31 individual drainage areas on the site, each treated with a Filterra Bioscape system placed in the parking lot medians. The treated and overflow water is routed to a stormwater trunkline running through the property. The sizes of the Filterra systems ranged from 20 square feet to nearly 500 square feet. Many of the Filterra systems are planted with landscaping plants surrounding them to help them blend with the landscaping.
Teichert Construction worked closely with Contech’s local Stormwater Consultant, Sales Engineer, and Field Operations team to ensure proper construction and installation of the units in April of 2021. After seeing how efficient Filterra was at meeting water quality requirements, the engineer replicated the design for two additional warehouse projects in the vicinity.
In October 2021, approximately six months after the Filterra systems were installed, the region experienced what was termed an “atmospheric river,” bringing much-needed rain to the region. The storm intensity was more than a 100-year storm which put the Filterra systems and the overall design to the test. Ensuring there is enough overflow capacity to route peak flows around the units is essential to prevent washout of the biofiltration area and prevent localized flooding.
Two weeks after the storm, Contech's local team visited the site to inspect the Filterra systems. Upon inspection, it was clear that the systems had performed as designed. Maintenance was performed in the Spring of 2022 by a local Contech Certified Maintenance Provider as part of the complimentary one-year service agreement. The maintenance included inspecting the system, removing trash, replacing the mulch, and pruning the vegetation.
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