Filterra Bioretention Systems: FAQ : Support, Stormwater Solutions

By: Filterra  09-12-2011
Keywords: Stormwater Treatment

Engineer Support

Can Filterra treatment systems be placed in succession?

Yes, as long as they are not all used to treat the same drainage area. If two or more units are placed in succession to treat the same overall surface area, the first unit will receive an overabundant amount of sediment and could require an alternate maintenance schedule. Filterra should be considered living systems and each unit requires its own specified drainage area.

Can I pipe directly into a Filterra unit?

Standard Filterra is a stand alone system that accepts surface sheet flow from both streets and parking lots. Standard Filterra requires an additional high flow bypass structure, or other means of relief, downstream from the units.  Roof Drain Filterra accepts piped in flow from roof leaders, and selected other piped in applications, and includes an internal bypass feature. Filterra should never be used as a junction box for other pipes outside of each Filterra’s respective drainage areas.

Why can’t Filterra receive runoff in a “head-on” fashion?

Water flow should approach the Filterra system parallel to the structure so that water flows in a linear pattern in front of the throat. During extreme storm events, excess water should continue to flow in front of Filterra to a bypass inlet or other relief. When water flows into the Filterra system “head-on” it may cause system damage (media erosion or suspension) and may eject collected trash back into the parking lot or roadway.

Can a Filterra unit be modified to meet spacing constraints on my project?

Yes. Although Filterra manufacturing facilities stock standard sized units, we have the capability to fabricate units with both modified lengths and widths in order to accommodate certain project constraints. Each modified unit will need to be designed and reviewed by Filterra staff prior to final approval and fabrication. 

I have a shallow existing inlet on my project, can the overall depth of Filterra be modified to fit?

Yes. Filterra has been used on projects where the overall depth of the unit was modified in order to provide stormwater treatment in retrofit applications. There are certain restrictions regarding plant selection and overall design. Please contact a Filterra representative for more details.

What are the overall dimensions of a Filterra Unit?

Unit dimensions listed on all Filterra documents (plans, drawings, Engineer Design Assistance Kits, sales sheets, etc) refer to the internal dimensions of the Filterra unit. Our vaults are precasted with 6-inch thick walls which would make the overall outside dimension of each unit an additional foot in both horizontal directions. A standard 6’x6’ Filterra has an actual outside dimension of 7’x7’.

Why does Filterra need to review the site plans?

Part of Filterra’s standard operating procedure is to review each system specified on a set of plans. This is to ensure that certain design criteria (proper sizing, cross-linear flow, higher flow line elevation than its bypass, positive slope, etc.) are met. Our plan review staff will make every effort to review your plans within three (3) business days of receiving them.

Filterra also conducts a mandatory review of all purchasing contractors set of plans. This is to ensure that all units are still sited and sized within our design specifications, with proper piping and fabrication. The Filterra staff works extensively on all aspects of the project, from design to maintaining each BMP after installation. 

Keywords: Stormwater Treatment

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