The Great Capture: Trapping Pollutants

June 6, 2015

Florida Park Revitalized
Kissimmee Lakefront Park in Kissimmee, FL, desperately needed revitalization. New facilities and buildings were planned and built, and paved surfaces were restored. Another big part of the project was installation of stormwater treatment best management practices (BMPs).

The park covers about 25 acres, situated between the downtown urban area of Kissimmee and East Lake Tohopekaliga. The lake, famous for bass fishing and bird habitat, is a resource that needed to be protected from pollution and trash. The Lake Front Park is heavily visited by local residents and by travelers to nearby Disney World.

A 42-inch pipe passed through the park, draining stormwater from downtown Kissimmee into the lake. For this project, a Suntree Technologies Nutrient Separating Baffle Box was retrofitted into the existing pipe. The SkimBoss Filtration System was also added. The project plan was to use these products to create a treatment train.

Two areas make up the treatment zone—first, a hydrodynamic separator for gross pollutant removal, and second, a filtration system to capture dissolved pollutants. The hydrodynamic separator being first in the line means that the filtration media will work more efficiently and last longer without being clogged by large particles.

Gross pollutant removal is handled by the Nutrient Separating Baffle Box. The box is designed to fit in line with existing pipe, making it easy to use in a retrofit project. The screen system captures and holds leaves and litter and will keep them contained even during peak flows. The system continues to perform under large flows with minimal head loss, even when the screens are filled with debris. The separation of the organic matter from the water prevents nutrients from leaching into the runoff.

The sediment settles to the bottom of the box and is prevented from escaping in future flows. A proprietary turbulence deflector system calms the water and allows even extra-fine particles to settle. The chamber can hold up to thousands of pounds of debris, depending on the size installed.

Credit: Suntree Technologies
Kissimmee Lakefront Park

The Nutrient Separating Baffle Box is installed easily because the interior parts are already in place when it arrives at the job site. Various sizes are available and should be chosen depending on the size of inlet pipe.

Once the stormwater has flowed through the Nutrient Separating Baffle Box, it passes through the SkimBoss Filtration System. The SkimBoss provides media filtration in line with flows without the usual head loss. The SkimBoss is resistant to clogging because of the fluidized media bed. During dry periods, the media settles to the bottom with about 2 inches of space at the top of the chamber. Once water begins to flow, the media shifts and any clogs are broken up. The hydraulics of the system creates pressure to force the water up through the media bed, providing the filtration. Any solids that remain in the stormwater settle to the space below the media chambers. If heavier flows occur, the SkimBoss rises until the hydraulic pressure on inflow and outflow equalizes. The media continues to filter the flow, and louvers on the media vessel backflush the media. Once the flow decreases, the SkimBoss returns to its normal position.

The media used in the Kissimmee Lake Front Park project was Bold and Gold, a media developed by the University of Central Florida (UCF) Stormwater Management Academy. According to Martin Wanielista, professor at the academy, the biggest challenge was to develop media that would have minimum residence time for the removal of nitrogen and a lifetime for the removal of phosphorus. Bold and Gold not only filters the stormwater but also has sorbent surfaces that capture dissolved pollutants. Many other systems trap only pollutants that are attached to sediment. The media is highly effective and fairly inexpensive. It does not have to be replaced often, but can be washed off with a hose and used again. The effective use is up to 20 years.

Students from UCF Stormwater Management Academy performed water flow and quality measurements before and after installation at Kissimmee Lake Front Park and monitored samples for total suspended solids (TSS), total nitrogen (TN), and total phosphorus (TP). The results:

  • Average 67% of TN removed
  • Average 79% of TP removed
  • Average 81% of TSS removed

An interesting addition to the Kissimmee Lake Front Park project was the addition of a Suntree observation lid. The large clear cover allows the public to look inside and see the system components. The ability to see stormwater treatment in action greatly increases awareness of the importance of clean water practices. The city of Kissimmee won the Florida Stormwater Association’s Outstanding Treatment and Public Education Award for this project in 2014.

Credit: Eugene Hernandez
Installation of the Wing-Gate ARS in Baltimore’s Fells Point neighborhood

Baltimore Study
The city of Baltimore, in partnership with the Waterfront Partnership of Baltimore Inc., is conducting a pilot study to evaluate the efficiency of the Wing-Gate Automatic Retractable Screen (ARS) from United Storm Water of California.

The devices are automatic retractable curb inlet covers that prevent trash and debris from entering storm drains under dry conditions. The accumulated trash can be picked up by a standard street sweeping vehicle. When water begins to flow, the pressure on the screen face causes the spring-activated screens to open, preventing street flooding because of clogged curb inlets. They close again when the water flow lessens.

Specifications for the Wing-Gate ARS include a curb inlet opening 4 inches high and a depth from street to back wall of the catch basin of at least 6 inches. The units are made from S-304 stainless steel and have ¾-inch holes. They can be custom made to fit each catch basin and are calibrated to open for rain events of 1 to 4 inches, as needed. A 1- to 2-inch gap is left at the top to accommodate overflow. The Wing-Gates open laterally, and they can be pinned open to allow cleaning of the catch basin. If needed, multiple Wing-Gates ARS can be installed in series for extra-long curb inlets. Filters can be added to the catch basins to clean more pollutants out of stormwater before it enters the storm sewers.

For the pilot study in Baltimore, Wing-Gate ARS screens were installed on a street through Baltimore’s historic Fells Point neighborhood. The area is a commercial district full of small stores and restaurants. Waterfront Partnership is responsible for street sweeping in this area.

Credit: Eugene Hernandez
Installation of the Wing-Gate ARS in Baltimore’s Fells Point neighborhood

The installation took place on May 20, 2014, and proceeded on schedule without complications. According to Adam Lindquist, project manager for the Healthy Harbor Initiative, the city has since experienced storms with rain up to 4 inches, and the Wing-Gates ARS screens have worked as planned without problems. He says there have been no complaints from business owners or individuals and no incidents of flooding since the installation. In an extreme 500- to 1,000-year storm event, the area received 3.91 inches of rain in one hour. The Wing-Gates prevented flooding as they were designed to do and then returned to the job of capturing trash.

In May 2014, the Waterfront Partnership of Baltimore installed a gigantic piece of equipment, the Inner Harbor Water Wheel. This end-of-pipe device can pick up 50,000 pounds of trash from the harbor every day and is powered by solar and water current. However, Lindquist hopes that devices such as Wing-Gate ARS screens will someday make the Water Wheel obsolete, so that trash will be intercepted before it reaches the harbor.

Baltimore is also undertaking a large BMP pilot test of 380 storm drain catch basins to be installed with automatic retractable screens and filter units to keep large and small debris out of Chesapeake Bay.

United Storm Water has provided products for numerous California projects and is now expanding across the country. Terry Flury of United Storm Water says pilot studies are also being conducted in Honolulu, HI; Baton Rouge, LA; and Corpus Christie, TX.

Temporary Protection
The Colorado Department of Transportation (DOT) has a huge ongoing project—the reconstruction of I-25. During construction, sediment control was required to meet NPDES permit requirements. The contractor chosen was Southeast Corridor (Kiewit), and the engineering firm was Carter Burgess Engineering. Dandy Products were used on the project.

The inlet protection devices used include Dandy Bags and Dandy Sacks. Both products are brightly colored for easy visibility. They are installed under storm grates. Which one to use depends on how much sediment and debris is expected; the Dandy Sack has a higher capacity. The products filter the stormwater, capturing any sediment in runoff from the construction site. They can be made to conform to the shape of the grate because of their flexible construction.

Maintenance involves brushing off the sediment and debris on the outside of the bags and emptying them if the sediment load has gotten too heavy. If oil-absorbent filters have been used, they should be replaced.

In the Colorado project, construction crews performed careful maintenance of the products and were able to reuse them, moving to the next section of working area. This has saved the project time and money.

The Colorado DOT has conducted performance studies on the Dandy Products and says it will use them on more construction projects throughout the state.

Protecting Maine’s Waterways
A series of waterways in and around South Portland, ME, had not been able to meet required state water-quality standards. The Long Creek Watershed (3.45 square miles) drains into Clark’s Pond, to Fore River, and finally into Casco Bay. Maine Mall Road is one of the main streets in the area and it was chosen for a retrofit project to improve water quality. The area is heavily developed and includes individual properties and public right-of-way sections.

A watershed management plan was developed over two years, with four municipalities and jurisdictional agencies, conservation groups, and private landowners taking part. The Maine Mall Road project is the first of many planned improvements.

One of the challenges of this project is that utilities, including direct burial cables and high-pressure gas mains, run along the right of way, restricting placement of stormwater BMPs. The decision was made to provide treatment for the high-traffic and high-pollution areas to enhance water quality throughout the watershed.

A variety of stormwater BMPs was used in the project, which was completed in the summer of 2014. The BMPs came from Contech Engineered Solutions. Contech bioretention systems were used in restrictive areas where runoff could be treated. The media in the systems allows for high-volume and high-flow treatment and is effective for pollutant removal. The areas included both planted and unplanted sections, as well as filters along the creek bank under the guardrails.

Upstream areas that were not easily isolated for treatment were deemed good places for installation of Jellyfish Filters. The filters include pretreatment at a high flow level with membrane filtration. The system is compact, with a smaller footprint than most systems, allowing for installation in tight areas. It also has lower long-term maintenance costs.

Folded sections of the membrane inside the cartridge remove fine grit and silt as well as particulate-bound pollutants. A separation skirt captures oil and trash before it gets to the membrane, and larger particles settle to the bottom of the chamber. Vibration removes sediment from the membrane and after a storm, filtered water backwashes the filtration surfaces.

Test results have shown the following removal results:

  • Trash, 99%
  • TSS, 89%
  • TP, 59%
  • TN, 51%
  • Total copper, less than 50%
  • Total zinc, less than 50%

The Jellyfish Filter cartridges are lightweight and easy to replace, even in restricted spaces. After removal, they can be rinsed and reused, and the sump should be vacuum-extracted. Replacement of cartridges depends on the pollutants loading, but should be done about every two to five years.

For the Long Creek Watershed project, 10 bioretention units and three Jellyfish Filters were installed. The engineering firm for the project was Sebago Technics Inc. of South Portland. Robert McSorley, senior project manager with Sebago, says, “The products, timely design, information, and service through design and construction by Contech allowed for the treatment of more critical areas of the watershed. Along with the district, private landowners, and contractors, Contech has helped make this a successful project.”

Cleanup in Maryland
Salisbury, in southeast Maryland, is called the “Crossroads of Delmarva.” The Wicomico River runs through town, and the Riverwalk is a favorite place for locals and visitors. Unfortunately, trash and debris from the nearby watershed was ending up in the river. The city proposed a plan to clean it up.

The products chosen for the project were from KriStar (now part of Oldcastle). The project, which began in 2011 and continued through 2013, was financed with a community block grant.

KriStar’s Net Tech Gross Pollutant Trap (GPT) units were installed on two stormwater outflow pipes. One 24-inch circular GPT was placed beneath the Division Street Bridge next to the Riverwalk. A second 36-inch unit was installed at a nearby outflow pipe. The Net Tech GPT includes a stainless steel pipe extension that has a heavy duty, UV-stabilized polyethylene net attached. The net captures trash and debris that comes out of the pipe. A release mechanism allows the net to detach if the debris load becomes too great. The net is tethered, so if it is released it travels only short way downstream and can be retrieved. When the net is full, it is emptied and reattached. In Salisbury, the Net Tech is clearly visible so the public can see the amount of trash that is collected—a reminder to dispose of trash properly. Adding to the education of the public on stormwater issues is always a plus, and the reality of seeing the trash collected can make a big impact.

The Wicomico River is tidally influenced, so installation had to proceed around the tides. During high tide, the outflow pipes are partially submerged. The upstream storm sewer also had a persistent runoff, so the outflow pipe had to be dewatered during the installation. The contractor was Drainage Protection Systems (DPS).

The next phase of the plan started in May 2012. The city contracted with DPS to install 30 KriStar FloGard Plus catch basin inserts. The FloGard devices, which come in a variety of sizes and shapes, have a filter screen that traps solids and sediment, as well as an absorbent material that captures hydrocarbons. A high-flow bypass allows stormwater to bypass the device when needed, although it retains accumulated sediment and trash. Tests have shown that in street application the FloGard filters remove 80% of total suspended solids, at least 70% of oil and grease, and 40% of total phosphorus.

Maintenance should be done as needed, but the life of the units is about 10 years. Periodic vacuuming of the insert and replacement of the absorbent may be required.

In August 2013, Mayor James Ireton Jr. announced that more FloGard filters had been installed, advancing the plan to cleanup the river. “I am proud of our commitment to the health of the Wicomico River,” he said. “Our Salisbury Public Works employees, from engineers to river cleanup crews, work every day to reduce the amount of trash that makes it to the Wicomico. I thank long-time employee Howard Landon for always knowing when it’s going to rain and when low tide is, for that is when the outfall pipes empty. We have made a commitment to our downtown through these efforts. Salisbury will continue its environmental activism every year by purchasing and installing even more inlet hoods.”

Amanda Polluck, deputy director of public works, says, “The city is completing installation of FloGard units in key areas and [we] are pleased that we will now have over 100 inlet guards installed. Due to our prompt payment practices, the city was able to receive a discount on the units and we have applied that discount to order replacement filter media. The inlet guards and media were funded by community development block grants. The city will continue to budget for additional inlet guards and replacement media going forward.”

Credit: ClearWater Solutions
Two ClearWater units in a single structure at the San Diego International Airport

Airport Employee Parking
Employee parking at the San Diego International Airport covers more than 50 acres. The area needed stormwater runoff filtration to meet total maximum daily loads (TMDLs). A project to reduce pollutants was completed by January 2013; 14 ­ClearWater BMP-01 units from ClearWater Solutions Inc. of Vista, CA, were installed to handle trash, sediment, oil and grease, metals, and bacteria that are present in the runoff.

The biggest challenge for this project was the very high water table, according to Joe Arthur, vice president with ClearWater Solutions. The units were cut down to fit the location to about 24 to 36 inches. The process required a little extra installation time. Grates were then installed on top.

The ClearWater units are made of stainless steel and can be placed inside curb inlets or under sidewalks and parking lot grates. Trash is diverted into trash baskets. Then stormwater entering each unit is forced through screens and allowed to settle three times before release. It is in constant contact with an oil and grease separator. The water passes through a synthetic mesh filter and then through media that is chosen for each site. The media types include natural zeolites, perlite, PathShield, and activated carbon. The media can be changed if another pathogen or pollutant is detected or as new TMDLs are released. The system is designed to be non-scouring, keeping pollutants captured even in the next rain event.

Testing from San Diego State University has shown the following results for the ClearWater BMP:

  • 90–97% of total suspended solids, depending on type of storm and of the type of material in the water
  • 86% oil and grease capture
  • 83% removal of zinc and 81% of lead

Even dissolved metals were removed by the unit, not just metals attached to sediment particles.

Another factor in the choice of a stormwater treatment is the cost. ClearWater BMP-01 came in about 20% lower cost than other systems considered, with lower maintenance costs as well.

Credit: ClearWater Solutions
Diverters direct water and debris to the filters.

At the San Diego airport, three people installed all 14 units in two days. Maintenance for that area, according to Arthur, should take place in March or April each year and just before the rainy season starts in October. Checking the units is also recommended after every 10 to 12 inches of rain. New installations should be checked regularly for the first 90 days to forestall any issues. Trash baskets may have to be emptied more frequently than the rest of the unit requires maintenance.

As the parking area is built out, the finish grade will increase in depth around the grates. A riser ring can be added to keep the structures flush with the pavement, while the filters remain in their original position.

During maintenance, trash should be removed and the settle areas should be cleaned with a vactor truck when they are about half full. The sorbent sock must be replaced when it becomes discolored or hard and the media should be replaced as necessary.

Arthur recommends, for anyone starting a similar project, “Be specific about the structure design and the real needs on the job, as things will vary from site to site or even, in some cases, from structure to structure. These sites are basically living variables that must be defined and addressed on a unit-by-unit basis.”

About the Author

Roberta Baxter

Author Roberta Baxter specializes in science and technology topics.