EPA regulations have significantly reduced stormwater runoff pol-lution from industry and agriculture. The remaining battleground in many areas is urban runoff — lawns, streets, parking lots, and roofs all contribute their share of debris and pollutants, and the sheer number and variety poses a real challenge.
With more than 60 inches of annual rainfall, the City of Boynton Beach, Fla., needed a comprehensive plan to ensure stormwater quality. “The creation of a formal Stormwater Utility, supported by fees based on our customers’ equivalent residential units (ERUs), has helped the city with the financial resources to do what we had to do,” says Paul Fleming, PMP, senior project manager for the Boynton Beach Utilities Department’s Engineering Division since 2001.
ERU fees, along with additional federal and local funds, provided the means to address the problem on several fronts. Included were upgrades to existing stormwater infrastructure, integration of a GIS mapping system, public education, and widespread installation of a simple but effective filtration device.
Fleming considers the filters one of the most important contributors to stormwater pollution reduction for Boynton Beach, on Florida’s Atlantic Coast.
One part of the plan
Fleming’s department serves 16 square miles in the city, plus 11 square miles of surrounding area. The city’s population is 65,000, with 30,000 more people living in the outlying areas.
Besides filtration, Boynton Beach employs a range of stormwater quality improvement measures common to similar communities. As part of its stormwater quality improvement program, when other utility-related infrastructure improvements are constructed, the city also renovates decades-old swales that have become clogged or sedimented over time. Five new stormwater wet retention ponds have been constructed.
More attention is being paid to wetlands and mangrove preservation along the coast. “Many of the city’s older intra-coastal neighborhoods were not master planned for stormwater management,” Fleming says. “As we become more aware of our urban environment, we see how we’re affecting these ecosystems.”
GIS was another step forward. The current system is based on the widely used ArcGIS platform by ESRI. GIS has helped significantly. “Boynton Beach is an established Florida city, and we’ve been playing catch-up on this,” Fleming says. “We’re going from sketches and memory to a proper underground utility atlas.” In the near future, all that data will be migrated to the Orion GIS platform, also by ESRI, to enable more web-based functionality.
Meanwhile, stormwater filters have made a significant impact on pollutants by attacking urban runoff at its entry points. The city selected SNOUT filters, manufactured by Best Management Products Inc. (BMP) of Lyme, Conn.
Archimedes rules
Easily retrofit in existing stormwater sumps, the filters help segregate debris and pollutants from the outflow. “One of our consultants recommended this device, and we could see immediately it had the potential to help us comply with a significant component of our NPDES MS4 permit requirements,” Fleming says.
The filters use the physics of flotation to remove debris and pollutants. Back in 250 B.C., Greek scientist Archimedes showed how objects more dense than water sink, and those less dense than water float.
When the SNOUT filter is attached over an outflow pipe in a stormwater catch basin or sump, it creates a baffle that selects outflow from the middle stratum of water. Debris and pollutants stay largely above or below that point, and they remain in the sump for later removal.
Fleming notes that in the past, the city fabricated similar baffles onsite, using aluminum or fiberglass. “But when we looked at the costs of fabrication compared to an off-the-shelf alternative, and at the cost of maintenance, we come out ahead using the BMP product,” he says. “Cost, fabrication and instal-lation time, ease of use, adaptability, and durability all figure in.”
More to come
For dissolved or suspended pollutants that make it past the barrier, an accessory, the Bio-Skirt, can be attached at the inlet. It consists of a series of synthetic fabric strips impregnated with diatomaceous earth, providing catch points where bacteria and hydrocarbons are adsorbed. It continues working as long as the fabric is intact.
“It’s not a catalyst, since there’s no real chemical reaction occurring, but it’s similar to a catalytic process in that nothing gets used up, and it keeps doing the job as long as it’s there,” says T.J. Mullen, BMP president.” Other accessories include flow deflectors that improve settling in the sumps, and odor control filters that attach to a built-in anti-siphon vent.
The unit comes in sizes to fit around all common outlet diameters. They are fastened in place using six to eight anchor bolts. The included gasket is set, and the unit is bolted in place.
The filter units are designed to fit over any existing pipe — not into it. That results in a minimal restriction to outflow. The units are lightweight marine-grade fiberglass — one worker can set a 36-inch model in place. Field data so far suggests a life expectancy of more than 10 years.
Cleaners on call
Fleming has seen no failures. He has more than 30 units in place and plans to deploy another 25 soon in an area now under infrastructure redevelopment. The city specifies the filter in all new Utilities Department work.
Fleming and his staff can’t enforce the use of filters in new residential subdivisions, where infrastructure is the developer’s responsibility. But they specify out-flow water quality equivalent to what the city achieves with filters. This helps ensure that, as urban growth continues, as it inevitably will, stormwater quality is maintained and improved.
The filter-equipped basins require periodic cleaning. Boynton Beach has a fleet of four combination trucks, two of which are dedicated to stormwater cleanout. The others are dedicated to sanitary sewer cleaning, although Fleming’s department can tap them as needed. With two trucks on a more- or-less daily cleanout schedule, the Utilities Department stays ahead of problems.
Stormwater crew members can reach down with one hand, do a quarter-turn on the access port, pop that off, insert the combination truck jet hose into the pipe, jet the sedimentation and debris back into the sump, and vac the debris out.
With filtration, Fleming is seeing a reduction of pollution and debris in stormwater outflow, as measured by visual inspection and EPA-mandated testing. “I’d like to say we have hard data on the performance, but we haven’t yet quantified the impact of these units,” he says. “I can’t tell you how many tons of debris we’ve removed from the drainage structure sumps, but I can say they’re doing the job.”
He observes that the units capture a large percentage of the floatables. In conjunction with the drainage structure sumps, a similarly large percentage of the sediment is kept out of the city’s exfiltration systems.
In some high runoff areas, filters are installed in series on adjacent sumps and catch basins. Under most conditions, the downstream unit is barely taxed. Because the Southeast U.S. has been in an extended drought, the biggest tests may be yet to come.
Bigger picture
Besides taking care of storm-water in Boynton Beach, Fleming is a member of the Florida Stormwater Association, with a seat on the Education Committee. In this capacity, he works with Chris Roschek, engineering division manager and NPDES representative, on analytic studies of pre- and post-development runoff.
“We’ll be focusing on things like bed loading; silt, dirt and debris chemistry; and particle size and distribution characteristics, to finally get some hard data on the effectiveness of the city’s storm-water systems,” he says. “We’re firm believers in environmental stewardship, something that should be high on everyone’s list.
“Both the city and utilities management are committed to doing everything we can to ensure air and water quality, working in an integrated way with agencies at the local and national level, like NDPES, EPA, the South Florida Water Management District, and the Florida Stormwater Associ-ation. This provides tremendous benefits as we continue to develop our urban areas. And we’re already seeing positive results.”
The Boynton Beach Storm-water Utility was created in the late 1990s to generate the revenue required to meet those lofty goals. Many older cities in the region do not yet have such a funding mechanism in place. Fleming and his colleagues are extremely proud of their accomplishment, and of what it has allowed them to do. Now, the city known as the “Gateway to the Gulf Stream” is helping its namesake remain a clean stream.
