Drain Inlet Development To Manage Stormwater
Written by Bradford Bucknum, Communications Manager, SBN.
Good design is slow. Effective collaboration takes time, too when you set out to manage stormwater.
My colleague Sara Pevaroff Schuh, founding principal of Philadelphia-based SALT Design Studio says, “Quality fights to be a full partner at the table with quick.” She’s right.
It may seem like an all too costly endeavor to return to the drawing board often, but the familiar cliche rings true–you either pay now or pay later.
Fabco and ACF work together to manage stormwater
Rob Woodman, Senior Stormwater Engineer at ACF Environmental, witnessed the benefits of a time-intensive collaborative design process first hand when designing a new product for the Philadelphia Water Department’s (PWD) city inlets to manage stormwater.
PWD needed a solution. They noticed safety concerns and inefficiencies during maintenance procedures for the filter bags used in storm drain inlets to manage stormwater. These “green” inlets are an integral component of Philadelphia’s Green City, Clean Waters program, an initiative that uses green stormwater infrastructure (GSI) to manage stormwater and reduce the volume of stormwater runoff and associated pollution entering Philadelphia’s waterways.
According to new research from the Sustainable Business Network of Greater Philadelphia (SBN), the twenty-five-year nature-based stormwater management plan is an inspiring example of the triple bottom line (people, planet, profit) in action. Their June 2019 report, “The Economic, Social, and Environmental Case for Green City, Clean Waters: An Update,” highlights a correlation between a nature-based approach to stormwater management with lower crime and health costs and billions of dollars in economic impact.
The plan is bold, effective, and has put Philadelphia on the map as a leader in GSI, but its continued success depends on the city’s commitment to maintaining the systems and mechanisms of the plan.
PWD’s Green Stormwater Operations Unit (GSO) is responsible for the inspection, maintenance and repair of PWD’s GSI. The Unit’s supervisor, Gerald Bright, reached out to ACF Environmental in search of a product that would improve upon the existing means of pre-treating city inlets to manage stormwater. The existing wall-mounted units used to pretreat these inlet types lacked suitable capacity and were difficult to install and remove.
Woodman recollected, “Maintenance staff would lay in the roadway, attempting to scoop sediment out of the filter bag by hand through narrow curb openings. The product was not working for them and there was not an existing product that would adequately fulfill their goals relating to performance and maintenance needs better than they had already installed. A solution would have to be developed specifically for them, to satisfy their requirements and not put them at risk in the field.”
The only other option to hand-scooping sediment out of the bags was to remove the 4-foot long filter bags from the inlet, but because of the design of the product and the inlet, this was nearly impossible without dumping sediment into the drains because the only opening was a 24-inch diameter manhole and the 4-foot long bag could not fit through without being tipped at a steep angle. Bright needed ACF Environmental to develop and implement a more maintenance-friendly solution.
ACF Environmental carries a variety of inlet protection products that target pollutants in various types of drains and catch basins; however, after listening to PWD’s concerns, both parties initiated a collaborative design process to create the ideal solution.
Conventionally, a company designs a product and then shops it out to a customer, but this design process was unique because ACF Environmental and PWD invited maintenance workers to join the discussions.
“Everyone had a voice at the table,” said Woodman. “By listening and including all team members in the process, we could brainstorm and develop ideas for a product that did not exist in the marketplace yet.”
New product design can be both time-consuming and challenging. It takes patience for designers to revisit the drawing board with each issue. After each round of prototyping, the ACF Environmental team met with various staff members of PWD to review the progress and determine necessary modifications. Woodman stated, “Feedback from all team members was considered a gift–whether they were a maintenance worker or the Senior Design Engineer. We discussed every piece of feedback.”
ACF Environmental completed a prototype for a new high-flow geotextile filter bag that would resolve issues with the existing filter bags, including premature failure both in place and during maintenance. The existing filter bags tore easily and maintenance workers needed to replace them every few months even though the expected lifespan was over a year. Geotextile bags would tear along the centerline seams when the weight of the accumulated sediment applied stress to the seam.
Based on a negotiation between design-driven requirements (flow rate and particle size) and maintenance-driven requirements (volume of capture and bypass capacity), they selected a woven monofilament geotextile middle filtration layer for the filtering element. They added polyethylene mesh on both sides of the woven monofilament geotextile to provide additional protection from tearing when the unit was cleaned in place with a vacuum or removed from the inlet (which often included workers dragging the sediment-laden unit to the emptying location).
ACF Environmental could develop the new high-flow geotextile bag with no centerline seam and improve the bag to frame connection points.
Once ACF Environmental’s manufacturing and design teams completed the bag, they brought on Fabco Industries–a Long Island, New York-based stormwater filtration and product innovation company–who specializes in metal fabrication to design to finalize the unique PWD specific aluminum frames.
PWD was experiencing issues with their current metal frames bending or breaking during maintenance causing sediment and trash to fall into the drains. It was critical that the new frame could support the load of a full filter bag during removal. The new frame accomplished this and reduced the number of wall anchors required during installation. Each of the new frames also provided adjustability so maintenance workers could accommodate minor conflicts and drain size variations in the field to manage stormwater.
In December 2018, ACF Environmental and PWD unveiled the new green inlet filter series, known as PWD StormSacks. PWD will install inlets throughout the City in the coming months. PWD’s maintenance staff no longer has to lay in the street because StormSacks are easy to remove and can be cleaned with a vacuum.
Bright stated, “The new StormSack product was a marked improvement over existing products in regard to capacity, durability, and ease of maintenance. It allowed us to maintain City inlets using mechanized equipment as we do for other inlet types, which will no doubt result in an uptick in productivity for our Inlet Pretreatment Maintenance crews.”
“Using feedback from all members of the team, including feedback from key program maintenance consultants like AKRF, we developed a safer, more efficient process for inlet maintenance by producing a high-performance, long-lasting and cost-effective set of inlet filters,” said Woodman. “Collaboration is a crucial element of innovation.”
Many cities are paying attention to Philadelphia’s trailblazing Green City, Clean Waters Program, including New York City. After the installation of the PWD StormSack, the NYC DEP and their assigned consultants reached out to ACF Environmental for help in developing inlet protection devices for their right-of-way (ROW) bioswales and infiltration trench designs that meet their performance and maintenance needs to manage stormwater.
“What we have realized through working with a series of cities now, is that every city is unique, and with that, calls for unique solutions. From a design side – we consider the obvious variables like the size of tributary areas to drains, the size of drain grates/castings, and pollutants.
Sometimes the main concern is more than sediment or trash,” said Woodman. “There are other pieces to the puzzle though, which include a city’s experiences with inlet protection, their maintenance capabilities (including available equipment), desired frequency of maintenance, aesthetics, public perception, and a variety of key program personnel opinions and perspectives. A collaborative process is the only way to have a positive impact on the long-term performance, success, and cost of ownership for green infrastructure programs.”
PWD will closely monitor the enhanced performance and optimized maintenance processes their new PWD Stormsack will provide. Just as all voices were heard during the design process, ACF Environmental expects that tweaks will continue to be made as additional lessons and feedback from the field return to the team. They plan to continue to collaborate on and evolve the PWD filter bag solutions to manage stormwater.
Referencing an earlier edition of the Green Streets, Clean Waters design manual, Howard Neukrug, the former PWD commissioner, said, “The key to the success of green streets is to develop a seamless process whereby stormwater management, street engineering, and landscape design come together to produce a functional, attractive and cost-efficient project.”
This is clear through the design process of the new PWD StormSack. It is worth it to put in the time to protect the performance of these systems as well as the public investment in GSI, especially since the social, economic, and environmental return on investment for a nature-based approach is necessary and welcomed in Philadelphia and beyond.