New stormwater filter bag with easy maintenance access

A case study on including maintenance teams in stormwater BMP product design.

Would you ever lay down in a busy street to look down the storm drain? What if you found out your maintenance team was doing this regularly? Yikes!

No, this isn’t the beginning of IT by Stephen King, but instead a case study on new stormwater BMP product development and the benefits of including the end user (maintenance teams) in the design.

BACKGROUND: The City of Philadelphia and Philadelphia Water Department (PWD) is ahead of the “green streets” game with their Green City, Clean Water program. The program is responsible for managing the first inch of stormwater on 9,500 acres of impervious surfaces (with streets representing 38% of these surfaces) and embraces a variety of Best Management Practices (BMP) products. Some of the products involved include storm drain filter bags, tree trenches, bump outs, and rain guardians.

THE PROBLEM: It was brought to the PWDs attention that their maintenance staff was hand-scooping sediment out of filter bags while laying in busy roads as the standard maintenance processes were failing.  Their current drain filter bags (known as “green inlet filters”) would often tear, or the frames would collapse, dumping the very sediment they captured into the drain they were protecting when the team attempted to remove them. These were only a few of the eyebrow raising concerns from safety to effectiveness with their current storm drain filter bags that sparked the immediate need for a different green inlet filtration device solution.

Our team was brought on board to assist the PWD in identifying a different product that would better meet their needs. Unfortunately, due to the city’s standard storm drain design and filtration requirements, there was not an adequate product available on the market. Our team felt that this was unacceptable and partnered with the PWD and Fabco Industries on a new design.

COLLABORATING THROUGHOUT THE DESIGN PROCESS: The design process was unique because the maintenance team was invited to join the discussions. This collaborative approach was critical to ensuring the design met necessary specs while also allowing for a safe and efficient maintenance process.

The two-fold design included a high-flow geotextile filter bag and a new heavy-duty aluminum frame. The high-flow geotextile filter bag had to be strong enough to be removed and dragged to the emptying site when full without tearing. In order to accomplish this, a woven monofilament geotextile middle filtration layer was selected for the filtering element with polyethylene mesh added on both sides to provide protection of the filtration layer during maintenance. Our team was also able to develop the new bag with no centerline seam to eliminate the issue of the seam ripping open when lifted out of the drain and improved the bag to frame connection points.

Once the bag design was finalized, Fabco Industries (a Long Island, New York based stormwater filtration and product innovation company with a specialty in metal) worked on new aluminum frames that would not bend or break due to the weight of the bag when removed. In addition, the new frame also reduced the number of anchors into the wall, allowing for a faster installation with less parts and offered adjustability to accommodate drain size variations.

THE FINISHED PRODUCT: We’re excited to announce that the new green inlet filter series, known as the “PWD StormSacks,” were unveiled in December 2018 and are currently being installed in inlets throughout Philadelphia, Pennsylvania!

The PWD StormSack series of green inlet filter devices includes 2’x4’ Green Highway inlet filters for both 3-sided and 4-sided flanged castings, the unique 2’x4’ Green City inlet filter that is set behind the curb line, a “6-foot dual” green inlet filter for combination drain structures, and an innovative domed overflow/beehive grate filter that deploys a circular high-flow geotextile bag on an expanding ring device.

CONTINUED IMPACT: Many cities are closely following Philadelphia’s trailblazing Green City, Clean Waters Program – New York City being one. Following the completion of the PWD StormSack, the NYC DEP and their consultants reached out to us for assistance in developing custom inlet protection devices for their right-of-way (ROW) bioswales and infiltration trench designs that meet their performance and maintenance needs. Stay tuned for more information on this design!

IN THE NEWS: A more detailed version of this case study was featured on the Sustainable Business Network’s Green Stormwater Infrastructure Partners site. To view the article, click here.

This story was also published in Informed Infrastructure’s May 2020 issue, and can be viewed by clicking here.

PWD Stormsack - Type M - stormwater filtration