Sep 07, 2021

California Mixed-Use Development Plan Utilizes Bioretention System

This case study originally appeared in SWS September 2021 issue as "California Mixed-Use Development Plan Utilizes Bioretention System"

storm-water-runoff

Contech Engineered Solutions

www.conteches.com  •  800.338.1122

Avion Burbank is a 60-acre master-planned, mixed-use development located in Burbank, California. The development is immense and includes 17 buildings and 1.25 million square feet of space.

According to the city's MS4 permit requirements, a low impact development (LID) plan was submitted by OMP to the city of Burbank Community Development director. The LID Plan was required because the project would alter 50% or more of the impervious surfaces of a previously existing development that was not subject to post-construction storm water quality control requirements. Therefore, the project was classified as a "Planning Priority Project" and was required to comply with regulations that call for treatment of all storm water runoff generated at the site.

Since infiltration of storm water runoff was determined to be infeasible due to groundwater contamination, the LID plan included the use of bioretention, as required by Attachment H of the Los Angeles County MS4 permit. Given the tremendous amount of runoff needed to be treated, the engineer of record (EOR) selected the Filterra Bioretention system. Filterra is an approved alternative to Attachment H of the Los Angeles County MS4 Permit. With its high flow media, Filterra provides a high level of treatment in a much smaller footprint than traditional bioretention. Given the value of land, the smaller treatment footprint was a significant benefit to the developer. The smaller footprint will also reduce long-term maintenance costs.

Engineering for the treatment of storm water from more than 1 million square feet of impervious surfaces was a challenge. Storm water design engineers at Contech needed to treat at least 93% of the average annual runoff volume to provide treatment on par with a properly sized conventional biofilter. To accomplish this, engineers utilized clusters of parallel Offline Filterra systems of various sizes (44 units in total) with the largest being 22 inches by 8 inches. The Filterra systems provide the necessary treatment and enhance the site's aesthetics. Planted with native vegetation, they provide a visible reminder to the occupants of the developer's commitment to sustainability.

The EOR incorporated two CDS hydrodynamic separators into the drainage system to provide pretreatment for the Filterra systems. After being pretreated by the CDS systems, a pipe manifold from the storm drain distributes flow as evenly as possible throughout multiple Filterra systems allowing each system in the cluster to operate in parallel. This helps prevent any one system from providing a majority of the treatment and maximizes the maintenance interval.

As clusters of systems were manufactured, they were shipped and installed at 10 units per construction day. Since most of the units were too heavy to ship with the media installed inside the vaults, Contech worked with GJ Gentry to provide the Filterra media the day after delivering the vaults. A Contech field representative was on site to guide GJ Gentry during the delivery and installation of the vaults and media. Contech activated the Filterra systems, which included installing the vegetation and mulch, once the site had been stabilized.

To date, this is Contech's largest single phased Filterra project in history. The aggressive schedule the Contech team needed to meet displayed the knowledge and efficiency of everyone involved and proved the team's dedication to meeting customer's needs. During the design phase, the storm water consultant reviewed site plans with the EOR and provided preliminary product recommendations. At the same time, the storm water design engineer developed site-specific drawings. When it was time for construction, the project coordinator managed all the manufacturing and delivery details with the contractor, while the field consultants provided site supervision. The team's consistent interface with the general contractor, sub-contractor and distribution partner resulted in tremendous success.

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