Filterra systems can be used successfully in cold-weather environments when they are properly designed, installed, and maintained. A common concern is whether the biofiltration media will freeze. In practice, if conditions are cold enough for the media to become fully frozen, there is typically limited stormwater runoff occurring at that time. As snow and ice begin to melt, systems designed with adequate drainage and appropriate pretreatment generally recover and resume normal function. For additional information on this topic, please refer to this blog post - Biofiltration in Cold Climates: Risks, Realities, and Proven Design Strategies.

The required elevation difference, or hydraulic drop, for a Filterra system varies depending on the applicable regulatory approval, system configuration, and site conditions. A typical Filterra system requires approximately 30 inches of elevation difference from inlet to outlet. Shallow configurations may be available for certain applications. Contact your local Contech Stormwater Consultant to evaluate your site and determine the appropriate configuration

The project engineer or landscape architect typically specifies the plant for the site. Contech can provide guidance and a list of pre-approved plants suitable for different hardiness zones. If a preferred plant is not included on the pre-approved plant list, Contech can review it for acceptance on a project-specific basis. 

Filterra systems use double-shredded wood or bark mulch that meets Contech’s specification requirements. The mulch can typically be sourced from local landscape material suppliers. For full mulch specifications, contact your local Contech representative.

The Filterra system can be designed outside of a precast structure as a Bioscape configuration.

Yes. Filterra can be used in a raised planter configuration when stormwater can enter at the top of the media and mulch layer and discharge from the bottom of the system. In these applications, the top of the vault may be placed above grade, typically using a cast-in-place configuration. Standard precast Filterra systems are typically installed with the top of the unit flush with finished grade.

A Filterra open-top vault configuration can be manufactured and delivered as a more complete system, with internal components and, depending on vault size, stone and media preinstalled. This can simplify installation, improve quality control, and reduce the amount of field assembly required. Vault-less Filterra Bioscape systems integrate well into landscaped areas and can provide greater layout flexibility, but typically require more on-site installation of internal components, stone, and media.

Trees and plants in a Filterra bioretention system do not need to be replaced on a fixed schedule. With proper species selection and routine maintenance, trees can often last 10–20 years or more.

Plants should only be replaced when they show signs of disease, pest infestation, or decline that cannot be corrected through maintenance.

For a complete list of recommended plants, please visit: https://www.conteches.com/technical-guides/search/?filter=OOIA4XCWXG

Yes, it is possible, but it depends on the elevation and the location of the pipe inlet relative to the curb.  Typically, if both are needed, we recommend a Filterra Peak Diversion configuration.

The Filterra with Sediment Chamber is a special configuration for the state of Maryland. For information about Filterra with Sediment Chamber, we recommend you contact Contech’s local Stormwater Consultant in Maryland, noted below. 

Matthew Griffin, P.E. (Maryland)
Stormwater Area Manager
901 Elkridge Landing Road, Suite 350|Linthicum Heights, MD 21090
Primary (Mobile) Telephone 410.736.2134 Secondary Telephone 443.457.1503 
[email protected]

The maximum treatment flow rate of the Filterra system is up to 324”/hr per TAPE approval. The maximum bypass flow rate varies based on system configuration.

Many Georgia municipalities offer stormwater utility fee credits for implementing Best Management Practices (BMPs) that reduce runoff volume and improve water quality. 

Since Filterra is a high-performance bioretention system designed to treat stormwater runoff and improve water quality, it may qualify for such credits. However, eligibility and the amount of credit can vary by jurisdiction. It is recommended that you consult your local Contech Stormwater Consultant for specifics. 

Contech provides installation guides, maintenance guides, and plant lists for the Filterra System. These guides can be found in our technical Documents Library by clicking here. 

Yes, the Filterra system can be installed above grade.  For these applications, it is recommended to use a cast-in-place vault.

The standard depth of a Filterra system depends on the specific configuration. In some cases, adjustments may be possible; however, the required media profile, including the underdrain stone, engineered media, and mulch layer, must be maintained to comply with applicable approvals and performance requirements. Please contact your Contech Stormwater Consultant to review project-specific constraints and available configuration options.

Yes. When comparing pollutant removal data, Filterra has demonstrated performance that is generally consistent with or better than conventional bioretention systems for many common stormwater pollutants, and has been certified by the Washington State Department of Ecology for Basic (TSS), Phosphorus and Metals Treatment.  Based on information from the International Stormwater BMP Database, conventional biofilters may meet TAPE Basic Treatment requirements, but do not generally meet nutrient and dissolved metals performance levels.