Water Quality Filter FAQs

The RWQF is used in conjunction with the Marlee Float Skimmer to meet Post-Construction Water Quality requirements in stormwater basins. It is installed after completion of construction as part of the conversion to the permanent pond. In most cases, the Marlee Float skimmer will already be installed as part of the sediment basin function of the pond during the construction phase.

The RWQF is a two-stage system. The outer stage/skirt is a woven polypropylene (Mirafi FW 402) with an AOS of 40 and flow rate of 145 gpm/sf. This acts as a screen to remove debris and larger sediment particles. The inner stage is a non-woven material – Adsorb-IT. It is a 12 oz fabric with AOS of 100-150 and flow rate of 151 gpm/sf. The inner stage is made of two layers of Adsorb-IT. Each layer is slit every 6 inches and the layers are offset so water weaves through the fabric, creating more surface contact. Each skirt hangs +/- 36” deep below the skimmer and has floatation built into the skirt so it is self–supporting. The bottom is open so the filter will never completely blind off or clog. The flow rate of the skimmer is not enough to pull sediment particles from 3’ below the skimmer to be discharged – we let gravity do the job.

The RWQF is used in detention ponds/stormwater basins and can be used on any site that needs to meet water quality requirements related to Total Suspended Solids (TSS) removal.

The Marlee Float Skimmer and RWQF are relatively easy to install. We are working to establish a national network of certified installers to make sure the products are installed correctly to insure they function properly. We will provide the list of certified installers on our website as these are established. We also provide installation videos for contractors that are not familiar with the product but want to do the installation.

In areas that will experience significant freezing of 6” or more of ice in the ponds, the outlet structure should incorporate an alternative drain. We recommend using a perforated riser with a valve. The filter should also be inspected after thawing to confirm it has not been damaged.

We have tutorial videos on our website and YouTube channel to go over this in detail. You will model the skimmer as part of the pond outlet structure in Hydraflow Hydrographs, HydroCAD or other modeling software. The Filters are sized based on the maximum flow rate of the skimmer and will not impact the flow rate so you just need to specify the proper size filter to go with the skimmer. This will confirm you are meeting a 90% TSS removal rate.

The Marlee Float Skimmer is made of HDPE so it will have a 20+ year life. The filters will need to have periodic cleaning and replacement. This will vary based on pond conditions. We recommend replacing the filter every two years. This is based on our prototypes that were used in a pond for two years with minimal maintenance and were still functioning when removed.

Yes! TRI Environmental tested the RWQF in conjunction with the Marlee Float Skimmer in accordance with ASTM C1746 standards. ASTM C1746 is a standard for testing sediment retention efficiency. Based upon the ASTM requirements, it was determined that the skimmer and filter system would remove 90% TSS. Most States require removal of 80% or 85% TSS so the RWQF exceeds requirements in most areas.

We have not tested the RWQF system for other pollutants, however, one of the materials we use for the filter is the Adsorb-It fabric and it has been tested and shown to be effective at removing hydrocarbons, metals and other pollutants. The Adsorb-It material we use has also been treated with an anti-microbial that may help in
removal of bacteria. The Adsorb-IT data is also available on our website as part of the Engineer’s Pack download.

Traditional water quality designs in sediment basins require a “first flush” volume to be released slowly, typically over 24 hours or more, to allow for settling of sediment particles prior to discharge. The RWQF system uses filtration to treat the stormwater. The filter can be sized to accommodate higher flow rates, which allows water to be released faster, which in turn results in smaller pond volumes being required.

In addition, traditional methods are not effective in treating small storm events because they rely on ponding and time for settlement. Small storm events have minimal ponding in the basin, therefore, they have minimal time for settlement. However, the RWQF system provides filtration for 100% of the rainfall that is managed by the skimmer.

Most States and MS4s do not have an approved list of products. Some states do have approved list and we are working on obtaining those approvals at this time and will provide them on our website as they are received. In many cases, states and MS4s have standards for use of “Alternative BMPs”, “MTDs” or “Proprietary Products” that can be followed.

No. We have not applied for approval with either program. However, there is a new national program called STEPP (Stormwater Testing and Evaluation for Products and Practices) that has been started and will be establishing national standards. STEPP will utilize ASTM Standards as the basis for their program and the RWQF system has already been testing in accordance with ASTM standards. Once the STEPP program develops standards for filtration-based devices, we will apply for STEPP Certification. It is expected STEPP will have this out later this year.