Frequently Asked Questions

How do I know what type of plant to use?

Filterra has created a plant list for each region that describes the sun exposure, hardy range, plant spread and height to help a client best select their plant species. We have also created hardy zone specific plant lists if clients are interested in selecting plants by hardy zones. These lists are preferred if you are already aware of the project site. 

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How many plant replacements have occured since Filterra began commercial sales?

With over 1,200 Filterra systems installed since 2003, less than 1 % of the Filterra plants have been replaced. Of all the plant deaths to date, the majority of them have been from physical damage due to mowers. A few plants have also been stolen. 

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What is the life expectancy of Filterra plants?

The plant should live to its life expectancy. The plant comes from the nursery with nutrients in the potting mix that help it through its establishment period. Overtime those nutrients are used up, but the plant constantly receives nutrients from the stormwater runoff that help maintain the health of the plant. Some plants are also very adaptable to their growing conditions, and the plants on our approved list meet this criterion due to their drought tolerance. There is no reason why a plant living in the landscape outside of a Filterra unit should live longer than the same plant in the Filterra.

We do not recommend plant heights more than 15-25 feet tall to prevent the Filterra unit from becoming root bound. We use plants with a shallow fibrous root system that do not exhibit an aggressive root system. The plant may not grow as fast because it does not receive regular doses of fertilizer to enhance growth rate like some landscape plants, but there are enough nutrients from stormwater runoff to provide sufficient nourishment to maintain plant growth and survival. As long as the units receive proper maintenance (usually twice a year), there should not be any factors causing plant death.

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What is the plants role in pollutant removal?

Through phytoremediation (the use of plants to remove pollutants through the uptake of nutrients and metals by plant roots into the biomass of the plant), contaminants are removed from stormwater runoff. Plants can accumulate metals in the cell tissue to make them less toxic. Nitrogen amd phosphorus are used by the plant to grow more cells. Organic matter is used as an energy source and metabolized into water and carbon dioxide. This means that as the plant grows or increases in biomass, so does the system’s capacity to capture and process more pollutants. 

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What types of records are kept for maintenance?

Filterra keeps a record of maintenance performed on each unit while under such contract. These records include: a photograph of each unit and maintenance detail (amount and type of sediment and trash removed, plant height, width, and evaluation, and additional field notes observed). These records are available to the owner or any inspector upon request.

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Who takes care of the units after installation?

A 1 year maintenance agreement is included with the purchase of each unit. This maintenance agreement begins the day the unit is activated, or becomes operational. Filterra also offers an extended maintenance agreement to continue to maintain the units after the first year. If no agreement is been reached, it is ultimately the site owner’s responsibility to provide regular scheduled maintenance that conforms to the manufacturer’s specifications.

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What training does Filterra provide for maintenance?

Filterra has developed a training DVD which covers all aspects of the maintenance steps needed to meet our specifications. Along with this instructional DVD, Filterra field crew representatives are available to perform on-site maintenance training and answer any necessary questions. There may be charges accrued for performing this maintenance on the installed Filterra unit.

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How are the units maintained?

Maintenance is simple, safe and inexpensive. It typically takes less than 30 minutes to maintain 1 unit. Trash and heavy sediments accumulate on top of the mulch and is typically all that is removed. This waste is easily removed and disposed of in trash bags or buckets. Fresh mulch is then replaced on top of the engineered media and not removed until the next maintenance visit. Hardwood mulch is a highly effective and an inexpensive pretreatment layer that protects not only the engineered media but also the plant in all weather conditions.

Filterra currently includes a 1-year maintenance agreement with the purchase of each unit. The maintenance agreement begins when the system is placed in full operation (complete system installed: curb and gutter and transitions in place, temporary throat protection removed by the Supplier, and plant installation).

Materials and services included in the 1-year maintenance agreement are:

  • Overall unit inspection
  • Additional mulch as needed
  • Addition of engineered media as needed
  • Pruning as needed (usually seasonal)
  • Visual inspections with appropriate service at six month intervals
  • Removal of sediment, litter, and foreign debris
  • Maintenance records updated and stored (reports available upon request)

It is the responsibility of the owner to provide adequate irrigation year-round to the plant within the Filterra system.

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How long of a lead time do I need to order my units?

A standard Filterra unit needs 7-10 days to fabricate, assemble and ship. This required time can vary based of the type and number of units needed on your site. Filterra keeps a variety of standard units in stock which reduces the required lead time for delivery. All units requiring modification may require additional time before delivery.

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When is the tree/shrub planted in the Filterra?

Filterra units are only activated by authorized Filterra personnel after the area around each installed unit has been stabilized and cleaned (full landscaping, grass cover, final paving and street sweeping completed). Activation is used to describe how each unit is opened up and placed into full operation. During activation all internal protective fabric and wood is removed, as well as the tree grate covering and protective throat board. Finally, the selected plant and mulch layers are installed. 

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When does maintenance begin on my units?

Filterra maintenance period begins on the day which the unit was opened up, or activated. Filterra will perform all required maintenance as scheduled for the first year, which is included in the purchase agreement.

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Do I need to supply erosion control during construction?

No, Filterra units are assembled with its own erosion control. E&S measures are taken with the combination of silt fabric and wooden planks and should only be removed by an authorized Filterra representative after installation.

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Do I remove the boards from the units?

The only boards which should be removed are the 2x4 wooden planks set between the Filterra box and top slab used as protection during shipment. The remaining boards should remain in tact during installation and will be removed during ‘activation’ of the unit by an authorized Filterra representative.

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Do I need a crane to set your product?

Standard Filterra units with installed media range in weight from 15,000 to over 32,000 pounds. Larger units are typically installed using a crane. Off loading and installation are the responsibilities of the purchasing contractor. It is recommended that all units are lifted with, at minimum, a 7-foot spreader bar. Unit weight charts are available and provided to the contractor.

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Is Filterra shipped with the media already installed?

Unless otherwise specified by the purchasing contractor, all Filterra products are shipped with the media installed. On project sites where more than two Filterra units are being shipped, the purchasing contractor can request that each unit be delivered without the media installed (empty boxes). Please note there will be price adjustments to compensate for field installation of the underdrain stone and filter media.

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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.

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Can I pipe directly into a Filterra unit?

Filterra is a stand alone system that accepts surface sheet flow runoff from both streets and parking lots and are not designed to be used as junction boxes. 

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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.

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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. 

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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.

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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’.

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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. 

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Quick Links

  • Request DAKit: Design assistance stormwater
  • Gallery of pollutant removal and stormwater treatment images
    • Photo Gallery Photo Gallery Photo Gallery Photo Gallery Photo Gallery
  • How the Filterra Stormwater Bioretention Management System works