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Crossroads Parkway

City of Industry, California

Stormwater Treatment


City of Industry


PBLA Engineering, Inc.


Kana Pipeline


October 2017

Technical Description:

  •  (7) Filterra Offline Systems

The Los Angeles Region MS4 Permit is very specific regarding post-construction stormwater management options. The current LA County MS4 permit, (Order R4-2012-0175) requires that biofiltration systems on land development projects either be designed and sized according to “Attachment H - Bioretention / Biofiltration Design Criteria” or be approved by the Executive Officer of the Regional Board as providing equivalent performance. With the cost of land in Southern California ever increasing, the challenge of designing and implementing cost-effective and regulatory compliant projects also increases.

In an effort to reduce the BMP footprint, decrease construction costs, and reduce long-term costs on future projects, Contech Engineered Solutions pursued an alternative approval to Attachment H with the Filterra Bioretention System. Filterra is similar to bioretention in its function and application, but has been optimized for high volume/flow treatment and high pollutant removal.

A study by Geosyntec evaluated equivalent performance between conventional biofiltration BMPs meeting the criteria of the MS4 Permit and Filterra systems as an alternate biofiltration BMP. Equivalency was determined based on the factors that influence the performance of Stormwater BMPs including capture efficiency, volume reduction, and concentration reduction. The Crossroads Parkway Campus Building is one of the first projects to propose and gain approval from the Executive Officer of the Regional Board for an alternative approval to Attachment H.

The City of Industry is an almost entirely industrialized suburb of Los Angeles County. Stormwater runoff from the neighborhood and commercial areas convey a variety of pollutant discharges into the local storm drain systems.  These systems feed into the San Gabriel River Watershed which connects the City to the Pacific Ocean via the Los Angeles River. As a contributing source of stormwater discharge to Southern California’s tourism heavy beaches, achieving compliance under the Los Angeles Regional MS4 Permit was a high priority.

With an accelerated deadline and a relatively small amount of footprint available, the City of Industry and PBLA Engineering, Inc. selected the Filterra Biofiltration system to capture and treat the site’s trash, debris, sediments, and metals. These fit within a footprint far more compact than traditional biofiltration sized per Attachment H. Contech provided support to both the City and the engineering team in navigating the approval process required by the Regional Water Quality Control Board.

Seven Filterra Offline systems were installed of various sizes. The Filterra Offline configuration is the most economical and simplest configuration. It utilizes a downstream catch basin or curb inlet for bypass flows allowing for the shallowest profile and most flexible design of any of the Filterra configurations.

Contech Stormwater Design Engineers assisted PBLA by providing product specific engineering calculations to properly size the units and meet the strict regulatory requirements. Contech supported the contractor through a tight installation schedule to ensure a timely and proper installation. A Contech Certified Maintenance Provider was on-site to perform the planting of the vegetation and activation of the system.

“The Contech team was a big help on this project," said Steve Levisee, PE, Principal-PBLA Engineering, Inc.. "The sizing calculations they provided, their knowledge and understanding of the regulations, and their overall responsiveness to my technical questions made the process of specifying Filterra an easy one.”

Since installation, the plants in the Filterra units are thriving, enhancing the appearance of the largely industrial site while removing pollutants.

Technical Description:

  •  (7) Filterra Offline Systems

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