Managing stormwater runoff on bridge decks has become a
more prevalent issue as concerns about the quality of receiving
water bodies is on the rise. Pollutants such as trash and debris,
heavy metals, oil and grease, and particulates are constantly
found on the bridge deck, as are sand, gravel and chemicals used
for deicing.
Previously, stormwater runoff on bridges such as the Burnside
and Broadway bridges in Portland, OR, would be directed
away from bridge decks through scuppers or storm drains
with horizontal piping off the bridge or directly into the
river. These piping systems have long posed significant
maintenance challenges, as horizontal pipes and traditional
catch basins tend to clog with debris. Additionally, transportation authorities have been hesitant to install any
stormwater management system that would require significant traffic disruption or bridge closure for regular
maintenance.
The Challenge
When Chuck Maggio, P.E., a Project Manager in Multnomah County’s Bridge Section, was tasked with replacing
the outdated stormwater systems on the Burnside and Broadway Bridges, his goal was to eliminate both
direct discharges into the Willamette River as well as the horizontal pipes that were prone to clogging. Maggio
investigated the feasibility of using a combination of traditional catch basins and piping to direct discharge
either into the river or into the City of Portland’s existing sewer system.
The Solution
After considering the available options, Multnomah County chose to replace the outdated stormwater systems
on each bridge with the Stormwater Management StormFilter®. The StormFilter is available in a variety of
configurations to meet site constraints. To allow installation right in the bridge deck, Maggio selected the
CatchBasin StormFilter. This compact system features a three-in-one design that combines a catch basin, a
high flow bypass device, and a StormFilter into one structure.
Easy access from the bridge deck makes maintaining the CatchBasin StormFilter quick and easy — maintaining
each system takes less than 20 minutes. Additionally, with point-of-entry treatment the CatchBasin StormFilter
treats sheet flow as it enters the system and then allows discharge to the river at the outlet.
“This system provided a catch basin where solids settle out,” said Maggio. “Filtration is a big benefit. We’re actually
treating the water and discharging it straight into the river. The CatchBasin StormFilter provided a design that fit
easily into the existing bridge structure and a BMP that was easy to maintain. The StormFilter system allowed us
to filter the water and direct it back into the river without the need for extensive piping, which would have had an
impact on the visual quality of the bridge —plus be a maintenance problem,” added Maggio.
Fourteen CatchBasin StormFilters were installed on the Burnside Bridge, replacing the existing system that routed
stormwater runoff off the bridge or to the nearest intersection and an inlet to the storm sewer system. On the
Broadway Bridge, ten CatchBasin StormFilters were installed during the deck replacement and microsilic overlay,
including two that treat stormwater runoff from the lift span. Perlite, a naturally occurring puffed volcanic ash
often used in gardening, was the media chosen for the systems on the Burnside and Broadway bridges. The highly
porous nature, multicellular structure, and rough edges of Perlite make it very effective for removing suspended
solids (TSS) and oil and grease.
The CatchBasin StormFilter was designed to address the constraints of the bridge deck. “The StormFilter did not
require a great deal of modification to the bridge structure to support them,” said Maggio. “They easily fit between
the stringers of the bridge.”
Flexibility in the CatchBasin StormFilter design allowed it to fit in an opening in the deck. This allows maintenance
to be completed from the deck surface while allowing for easy replacement in the future. The company also
provided information on the StormFilter’s pollutant removal efficiency that was used during discussions with the
National Marine Fisheries Service and the Oregon Department of Environmental Quality. On the Broadway Bridge,
the CatchBasin StormFilters that treat runoff from the lift span are mounted underneath the deck on the pier. A
manhole installed directly above the units provides easy access for maintenance and cleaning.
The Result
Traffic disruption during maintenance is minimal. On a bridge like the Burnside Bridge, with its long, straight
sightlines, maintenance does not require a complete lane closure. Signs are posted warning traffic of road work
and a limited lane closure ahead. Then the crew simply positions an arrow truck behind the vactor truck to alert
drivers, and the operation quickly moves from system to system down one side of the bridge and up the other.
On bridges like the Broadway, where sight is limited due to a curve in the roadway and the grade of the bridge
deck, cones are used to block off one lane for safety. Minimal maintenance time allows the crews to complete
maintenance between the morning and the evening rush hours.
Tony Lester, Bridge Maintenance Supervisor, noted the system’s compact design and ease of access from the
bridge deck as factors that make it easy to maintain. While he recognizes that replacing the StormFilter cartridge
adds an additional step not required when maintaining traditional catch basins or scuppers, he believes that the
advantages of filtration outweigh any additional effort. “With other systems the stormwater is going directly into
the river,” said Lester, “It’s more involved but obviously, that’s putting all those pollutants — unfiltered, uncleaned
— right into the river. So this is the way of the future.”
The three-in-one system design allows the maintenance crews to clean the catch basin portion of the system at a
different frequency than the StormFilter Cartridge. “We change these filters every year, but because the catch basin
[chamber] is separate from the filter chamber…we can still clean the catch basins and get the debris out without
having to put new filters in, and that’s kind of nice,” said Lester.