Urban stormwater runoff is one of the leading causes of water pollution because it carries pollutants such as oil, grease, pesticides, fertilizer, animal waste, trash, debris, and other substances through storm drains and into lakes, rivers, and other bodies of water.
The National Pollutant Discharge Elimination System (NPDES) program regulates discharge from municipal separate storm sewer systems, construction sites, and industrial sites. According to regulations, operators may be required to obtain an NPDES permit before discharging stormwater.
Soaking It Up
The Ultra-Urban Filter from AbTech Industries is a proprietary, low-cost best management practice designed to meet NPDES requirements for nonpoint-source pollution control, says AbTech’s Todd Megronigle. When paired with the Smart Sponge, consisting of an innovative polymer technology designed to filter, absorb, encapsulate, and solidify petroleum hydrocarbons and other contaminants, it can screen pollutants before they enter the storm drain.
The Ultra-Urban Filter with Smart Sponge treats stormwater runoff for municipal and industrial sites, parking lots, and commercial and residential developments, removing trash, debris, oil, bacteria, heavy metals, and phosphorous at a reduction rate of greater than 80% for total suspended solids, oil, and gas. Specifically:
- Trash and debris: 80%
- Sediment: 60%–90%
- Oil and grease: 90%–99%
- Bacteria: 80%–99%
- Phosphates: 60%–95%
- Heavy metals: 60%–90% (cadmium, chromium, copper, lead, zinc, selenium)
“We’re not monitoring effluent now,” says Megronigle, “but it’s rated greater than 80% on sediment removal, and greater than 90% on oil and grease removal. Sites can do a chemical analysis by melting down the polymers to determine the specific types and amount of sediments.”
Developed at the University of Arkansas at Little Rock and exclusively licensed by AbTech, the Ultra-Urban Filter removes hydrocarbons and can reduce coliform bacteria. An installation of 275 units in Norwalk, CT, resulted in a 75% reduction in hydrocarbons and bacteria, according to field testing. Three rounds of cleaning also yielded 37,976 pounds of trash and debris. Megronigle recommends cleaning the filters every few months to remove solids.
Similarly, Long Beach, CA, which installed 1,900 units, removed 91,963 pounds of trash, debris, sediment, oil, grease, and organics from the storm flow over a three-year period.
Smart Sponge changes the molecular properties of oil into a stable solid, which can then be disposed as non-hazardous waste, explains Megronigle: “It permanently binds oil.” This prevents it from leaching back into the environment.
It doesn’t degrade over time and can be reused, with an average lifespan of one to three years, depending on location. The Charlotte, NC, airport fueling center, which Megronigle says spills diesel fuel around the clock, replaces its Smart Sponges yearly, while a rural church parking lot customer changes them only every 15 years.
When Easton, MD, acquired about a half-dozen Ultra-Urban Filters to filter downtown-area runoff containing trash, debris, oil, grease, and sediment, city officials were so pleased that a few months later, they bought 250 more. In the three years since then, they have begun replacing them at a rate of 85 a year, or roughly one-third annually.
The units are easy to install and maintain, can be molded into various shapes and sizes, and can be retrofitted to any curb opening-style catch basin. Megronigle explains that a mounting bracket bolts into the base of the catch basin and the modular system clips on. The Curb Opening Series UUFs are designed for catch basins with an open-throat curb opening instead of a metal grate. The Drain Opening Series UUF can be fitted to any catch basin with a metal grate by fabricating stainless collars, regardless of dimensions.
One way to keep dirt and debris out of the storm drain system is to capture it upstream from the storm drain inlets. Rock and sand bags are commonly used for this purpose, but can get broken or deteriorate, creating a mess on the street or causing more pollution when the material goes down the drain. “Just ask any vacuum truck operator how difficult and noisy it is to remove rocks from a drain pipe,” says Bob Hanson, owner/president of Gator Guard Environmental Products Inc.
Gator Guard Weighted Gutter Wattles are completely different, he says. Three feet long and 4 inches tall, they weigh 20 pounds each. Sand that is triple-wrapped in geotextile inside a sleeve is used for weight and flexibility. “The ASTM clean coarse sand is contained in a 6-mil plastic tube, which is wrapped in tough monofilament geotextile, sewn shut, and then foam strips are strapped to the top for height,” explains Hanson. “This inner component is then sewn inside a geotextile outer sleeve, which has soft nonwoven geotextile loosely sewn on the bottom to conform to the irregularities of asphalt and concrete.”
The Gutter Wattles are placed diagonally across a gutter at a 45-degree angle, with one end pressed against the curb. As dirty runoff flows along the gutter, the wattles create a small “pond,” where the dirt has time to settle out of the calm water. “You need a still pond area to drop the particles out,” reiterates Hanson.
Water flows through the porous geotextile at a rate of 100 gallons a minute per square foot. Depending on the flow, “fairly clean water” will flow through the gutter wattle or around the street end of the wattle. After it dries, the wattle is set aside so the dirt can be swept up. “Fine clays plug it up, so it filters slowly,” says Hanson. If water goes over the top due to heavy rain, water flows into the ponding area, which allows it to settle.
“With four layers of tough, UV-resistant geotextile under the soft sand tube, these gutter wattles should last five years and survive reuse on many jobs without a leak,” says Hanson. “Although they cost more, they will save time and money while actually keeping our streams clean.”
The reusable wattles can be connected end-to-end to fit the site, and a lifting strap makes them easy to move—a benefit for temporary use while construction sites are open. “Housing sites are typical,” he says, because they are required to catch runoff before it goes into the storm drain. Trackout from construction sites deposits dirt on the streets, which eventually washes off and runs into the gutter and then into the storm drain and typically heads to the rivers and reservoirs.
In addition to Weighted Gutter Wattles, Gator Guard makes 6-inch-by-12-foot Weighted Wattles for direct use on asphalt and concrete. They weigh 50 pounds each and connect end-to-end to contain sediment and construction debris on streets and parking lots.
Another product, Gator Guard’s 6-inch-by-25-foot Sediment Control Wattles, provides effective perimeter control because the wattles slow construction-site runoff to settle out the dirt while “clean-ish” water passes through or over the wattle, ultimately protecting storm drains. “Gator Guard foam-filled wattles weigh only 10 pounds each, including installation nails, and can be easily removed and reused,” says Hanson. Because the apron is nailed to the ground and covered with an inch of dirt, it is essentially sealed to the ground, preventing underflow washouts. The low profile allows easy access to the construction site, and they do survive tires and tracks.
The foam-filled wattles were tested at San Diego University. Compared with straw wattles on a 3:1 slope in the Los Angeles basin, they produced only 1 kilogram of dirt runoff versus 20 kilograms from straw.
The lightweight geotextile is made up of a monofilament like fishing line, consisting of strong strands. Compared with parachute material, it is stiff, thick, and strong. However, it conforms to contours and will “pop” back up if it’s driven over by construction equipment. “This allows free access to the site, as opposed to using silt fence,” points out Hanson.
New Geotextiles Capture Contaminants
For the past 30 years, silt fence has been commonly used all over the US as perimeter sediment control on construction sites, but it prohibits construction vehicles from accessing a job site. For about 10 years, compost filter sock—a tubular device filled with organic materials—has been used, says Michael Zock, technical consultant with MKB. This more expensive option constitutes the “vast majority of perimeter control in Pennsylvania” and other areas, he says. “It’s a cultural thing per site because terrain and fish streams need a higher level of protection.”
Compost filter sock (CFS) continues to be increasingly used in the US, but is still outranked by silt fence. In 2017, Siltron estimates that the total amount of installed CFS in the US was 30–40 million linear feet, with silt fence totaling more than 400 million linear feet.
Typical silt fence works by ponding sediment-laden water, allowing dirt and debris to settle out as the water slowly passes through the geotextile in a process called seepage. CFS, on the other hand, has high hydraulic flow that pulls the sediment toward the device, where it accumulates against an inside edge, reducing hydraulic flow to create a ponding effect that results in increasing the height of the sediment-laden water and ultimately leads to further sediment accumulation.
Zock says CFS is better than typical silt fence because it removes more sediment and pollutants such as hydrocarbons, which silt fence does not do. Studies indicate that tubular perimeter control devices filled with biomass such as straw or composted wood material do a good job of capturing construction-site pollutants including motor oil, hydraulic fluid, diesel fuel, and grease. These devices also typically last longer and fail less often. Silt fence failures include fabric tearing or ripping off the stakes, or stakes breaking or falling over. Zock believes that using a ponding-only textile puts too much stress on the containment system, leading to failure.
That’s not to say that CFS is immune from failures, however. If filter media particle size is too small, it can lead to poor hydraulic flow, overtopping, or blowouts. Weak nettings can fail. Improper installation can result in CFS being undercut.
A new product was released in January. Siltron Diamond Sock is a high-performance perimeter three-layer composite geotextile, or dewatering bag, for inlet protection. Designed to address the shortcomings of typical “ponding-only” silt fence geotextile, it captures sediment and pollutants such as diesel, grease, motor oil, and bar and chain oil from construction equipment.
Zock says MKB has been working with the Pennsylvania Department of Environmental Protection, awaiting publication of DEP’s findings after third-party field-testing by TRI Environmental and monitoring usage at Traditions of America, a residential facility.
Weighing 33 ounces per square yard, the lightweight geotextile material has a tensile strength that is “off the charts,” proclaims Zock. Layers are needle-punched together for added strength. “It’s a better textile with a better outcome. It’s a game-changer.”
According to TRI Environmental, Siltron demonstrates the highest sediment removal rate and produces the highest seepage rate for a fencing geotextile (97.8% and 1.51 gallons per minute per square foot, respectively, per ASTM 5141 testing).
Fiber and filter water in the core bind with viscous construction-site pollutants like oil, hydraulic fluid, and radiator fluid. It can be power-washed and reused, and has a long life, with one-and-a-half-year-old samples not exhibiting any weathering. “They are 100% at 5,000 hours,” he notes.
Their strength translates to high puncture, tear, and ball-burst testing numbers. Zock says the nonwoven, locked-together composite is a better water filter with good water throughput, and it doesn’t sag. It requires less maintenance and repairs, contributing to a quicker return on investment and lower cost, as well as less pollution. Siltron also has higher UV resistance than most silt fence.
Installation is quick and easy, with clips—which is why Zock contacted Denis Friezner, director of engineering and founder of Hydra TMDL Systems Inc.
Friezner is the inventor of the stainless steel automatic retractable screen gate to prevent trash from entering storm drains. Developed in response to a request from the City of Los Angeles for a system that could keep trash from entering the catch basin inlet during dry weather but still be able to open when water reached 50% of the curb height during rain events, the Hydra ARS system—and 10,000 connecting pipe screens—accomplished phase two of the city’s trash TMDL (total maximum daily load) compliance.
Los Angeles approved the storm drain gate as a 94% capture device, and the connector pipe screen as a 100% full-capture device. Available in a one-piece radius or a rectangular screen, the pipe screen fits any size vault outlet pipe and can be used as a standalone device or in conjunction with the Hydra ARS. Together, they keep debris in the catch basin and resist clogging.
Since then, Friezner has refined the low-cost system that effectively prevents 98% of trash from entering the storm drain. Most storm drain gates use a locking mechanism that unlocks when the water hits a prescribed height, but often, the gates don’t open, the mechanism fails, and the gate stays open, or something gets stuck under the gate. The blades on the ARS system work independently, so even if something gets stuck under some of the blades, the others will still close. The individual blades move trash away from the storm drain opening. Having independent blades results in less damage from impacts than having one perforated steel panel.
Blade deflection is adjusted depending on location and compliance requirements, unlike other adjustable systems that rely on curb height measurements—which can lead to flooding if inaccurate—or non-adjustable systems. The Hydra Never Jam tensioner rotates a hidden adjustment wheel to increase or decrease the pressure required to open the blades. How far the system opens can also be adjusted, which is particularly useful for high-debris areas or hillside locations. There are no height or width restrictions; the blades can fit into any size vault opening.
The only part of the ARS system that opens is the area receiving the most volume of water; other portions remain closed to reduce the amount of debris entering the storm drain. Other systems are completely open or completely closed.
The ARS system is made from a durable polymer that is recyclable and has no scrap value, making it theft-resistant. “The material absorbs hydrocarbons and has a good flow rate,” says Friezner. “There’s no need to buy another system; this marries storm and erosion control.”
That’s important because, as Friezner points out, every city in America must become compliant with federal laws about reducing trash and debris entering storm drains or forfeit federal funds. Hawaii is not worried about trash, he adds—its concern is sediment and debris because “construction runoff is killing the reef.”
“Los Angeles was the first city to be compliant,” he says. It achieved the goal through a 10% reduction per year and, he believes, because they used his stainless steel system, which helped them achieve a 60% reduction in just the first year.
This system replaces baskets in storm drains for leaves and trash. “Baskets get heavy,” observes Friezner, “and you have to hand-shovel for removal. Mine are compartmentalized for lighter weight.” Made of the same material, his stainless steel baskets feature overflow holes to avoid flooding.
An additional material that Friezner expects to test for mold and gases in Hawaii and California and is currently testing at Penn State is a high-performance, pollution-preventing, three-layer composite fencing geotextile from Diamond Sock. Diamond Sock, owned by MKB, builds fences for sediment runoff on hills and construction sites that have a high flow rate.
The material absorbs hydrocarbons, pesticides, and oils. Hydrocarbons and oils wick down and can be pressure-washed out so the material can be reused or thrown away. It’s ideal for capturing sediment during construction or for filtering debris, volatile organic compounds, and nitrates as part of post-construction stormwater management. “It’s mostly for erosion and sediment control,” explains Zock. “We sent it to Denis [Friezner] to fit over his device because it has spring-loaded ‘fingers’ that we thought would work with our material.”
Diamond Sock fits over the ARS device. Friezner says that removing the MKB prototype is like “pulling a liner out of a trash can.”
Being able to contain and properly discard trash, debris, sediment, and other pollutants enables cities and municipalities to protect the waterways and all the aquatic life that depends