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DEM Adds Three Proprietary Stormwater Runoff Treatment Devices to Pretreatment Approved List

PROVIDENCE The Rhode Island Department of Environmental Management (DEM) is announcing that it has added three more proprietary stormwater treatment devices to its pretreatment approved list: the Jellyfish Filter, the Stormceptor, and the Cascade Separator. The Jellyfish Filter has been granted recertification as a water quality best management practice (BMP) while the Stormceptor and Cascade Separator have been recertified for use as a pretreatment device in Rhode Island.

"Increased development across the Narragansett Bay watershed has made stormwater runoff the biggest source of pollution to our coastal waters," said DEM Acting Director Terry Gray. "Cleaner beaches and shellfish beds start with better stormwater control in our municipalities. I appreciate the efforts of DEM's Office of Water Resources in evaluating and approving essential green infrastructure technology to help mitigate the scourge of stormwater."

Precipitation in an urban or suburban area that does not evaporate or soak into the ground but instead runs across the land and into the nearest waterway is stormwater runoff. This runoff holds harmful pollutants like fertilizer, pet waste, chemical contaminants like pesticides, leaking fuel, motor oil, litter, and sediment such as dirt and sand. This mix of nutrients and contaminants can fuel the growth of harmful algae blooms that reduce oxygen levels and cloud the water, blocking sunlight from reaching underwater vegetation. It can cause beach closures, shellfish closures, and many other water quality related problems if left un-treated.

The Jellyfish Filter uses high surface area filter fabric cartridges, which can be removed for cleaning, to treat stormwater. It is a high flow-rate, compact device that is ideal for urban sites with limited amounts of space for stormwater BMPs. The approved models include the Offline and Peak Diversion configurations, and the re-certification is effective for five years. The Stormceptor is a hydrodynamic separator that uses swirl technology to separate sediment and has a space to store captured hydrocarbons. Its recertification is effective for five years. The Cascade Separator is certified as an approved pretreatment device that's also effective for five years starting Oct. 12, 2021.

The products are sold by Contech Engineered Solutions LLC, which showed via third-party testing that the Jellyfish Filter can remove at least 85% of total suspended solids, 30% of total nitrogen, 50% of total phosphorus, and 60% of pathogens from stormwater runoff. Contech also has shown via third-party testing that the Stormceptor and Cascade Separator are able to remove at least 25% of total suspended solids from stormwater runoff. These products are intended for commercial and municipal use.

Proprietary devices that are approved as water quality BMPs in Rhode Island must be designed to treat the first inch of stormwater runoff produced by a site's impervious surfaces (such as roadways, roofs, and parking lots) during a rainfall event. Similarly, pre-treatment devices must pre-treat the first inch of stormwater runoff. Treating the first inch of runoff from impervious surfaces is essential because it provides treatment for approximately 90% of annual rainfall events which ensures that treatment devices capture the "first flush" of a storm, where most of the pollutants can be found. Approved proprietary devices also must be designed, built, and maintained to meet the conditions specified in their technology-specific DEM certification letter.

The review of the proprietary stormwater treatment technology applications is conducted by members of the DEM Office of Water Resource's stormwater engineering program along with members of the RI Department of Transportation and Coastal Resources Management Council. DEM is proud to promote and contribute to the advancement of stormwater treatment technology in hopes of protecting Rhode Island's precious water resources by minimizing the environmental impact caused by land development. The list of DEM approved proprietary stormwater technologies and their associated certification letters are available here. For additional information on the DEM stormwater technology review program, contact Christopher Dill, E.I.T. by email or 401-222-4700 ext. 2777404.

For more information about DEM divisions and programs, visit or follow us on Facebook, Twitter (@RhodeIslandDEM), or Instagram (@rhodeisland.dem) for timely updates.

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  • Department or agency: Department of Environmental Management
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  • Release date: 12-24-2021

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