Controlling Fugitive Dust on Roadways
Climate, traffic, and road composition help determine what to use.
By Carol Brzozowski
Anyone whose work involves earthmoving activities, construction, or mining knows the problems fugitive dust can cause—from poor visibility to respiratory problems to simply causing a nuisance to people downwind. They're probably familiar with some of the remedies, too, from water trucks to dust-suppressing products. However, dust control is also an issue in places we don't often consider, and some of the work done to solve the more unusual problems in other arenas ends up benefiting the construction and erosion control industries as well.
The military has been dealing with dust control for decades, particularly at airfields. The action of helicopter blades, for example, generates a tremendous amount of dust, particularly in the arid environments of Iraq and Afghanistan, where many are deployed, as well as in desert training sites such as Twentynine Palms, CA, and Yuma, AZ. With an increase in training and operations overseas, the issue became a priority shortly after the wars in Afghanistan and Iraq started.
"The natural sands, dust, and silts that exist in those regions are easily kicked up by the aircraft we are using," explains Barry Spargo, branch head at the Naval Research Laboratory (NRL) in Washington, DC. "We were challenged to come up with solutions for reducing the amount of dust that is created during helicopter landings and takeoffs in the theater and in training for the Marine Corps and the Navy."
Although air quality is part of the equation, dust control becomes more urgent in this type of environment. "While this is an environmental issue and it's something that the Navy continues to address, it's also an operating and maintenance problem and a safety problem," Spargo says. "Whenever you are kicking up significant amounts of dust and dirt, you diminish the visibility significantly and also increase the intake of these particles into engines, so you get engine wear and blade wear. It's a pretty significant problem."
In addressing it, NRL considered the variety of commercial products on the market and how they might be redesigned to meet the needs of the military. "They have to be environmentally friendly and easy to use, and they have to have a low logistical footprint," Spargo says.
NRL drew on research and testing that had already been done, including work at the US Army Corp of Engineers' Waterways Experiment station in Vicksburg, MS, which has been a leader in looking at soil stabilization and soil composition and handling construction-type issues. "Those were the folks who ran some of the testing on behalf of the Marine Corps to evaluate the quality of the different products," Spargo says. The Army Research and Development Center also had performed a study evaluating various dust-control products, resulting in the award of a Department of Defense (DOD) contract to Soilworks. The company's Soiltac, a copolymer emulsion soil-stabilization and dust-control product, is being used in Iraq. The Army and Marines are also using Soilworks's Durasoil, a synthetic organic dust-control agent, at their domestic training sites.
Taking into account the different operational requirements of the various services, NRL developed a sucrose-based dust-control product (known commercially as Surtac) to address dust-control issues in the military as a whole. The technology has been licensed by Soilworks, which manufactures and distributes it to the DOD. When the product is incorporated into the soil and compacted, it provides six months to a year of stabilization; a maintenance coat is required once a year. "This is going to be very dependent upon the environmental conditions and what kind of traffic that particular area is experiencing," Spargo notes. "Those numbers vary significantly based on where you are and who is using the area."
|A Moby Dick drive-through wheel washer in operation at Indy Recycling in Ohio.
Around the country, dust-control issues are escalating, leading to lawsuits and stop-work orders on large construction projects. The EPA is increasingly clamping down on the problem, which is not only a visual annoyance, but a health issue as well in terms of aggravating respiratory problems.
Roads remain a common source of dust problems, and many municipalities report that residential complaints of dust are the catalyst for dust-control actions. Consider Chardon Township in Ohio.
Don Mohney, a road foreman with the township, explains that dry weather had been causing a dust problem on three roads, as well as traffic on a road that wasn't being treated with anything. The heavily trafficked clay-based roads have severe hills, curves, potholes, and washboarding conditions. The township wanted to control dust on the roads and reduce complaints of chemical splashing on cars.
"We have used just about everything available over the years," Mohney says. "I've been here for 23 years. Years ago, we used calcium chloride, and it basically would turn a road to mush if you put too much down, or it would turn the road soft, mucky, and muddy. You would get stuck in it with that."
Mohney recalls that the township reverted to reprocessed used oil obtained through a local company. "We used them for quite a few years, but you never knew what you were getting each time you called them out," he says. "It would either last a week and be gone, or it would take three weeks to soak in, and then we'd get constant complaints about it being on people's vehicles."
Finally, another company presented a solution to the township: a polymer resin, mixed from four to seven parts to one part water. "I found it to be a good product," Mohney says. "We had only about one complaint a year; somebody would get it on their car because they were following the truck right down the road as they put it down, not giving it any time to soak in, and we could only tell them a little kerosene or gasoline would get it off."
The product not only stopped the dust on a dirt and gravel road but also bound the road so that it appeared almost like an asphalt road as the summer wore on.
"It was an exceptional product at a good price," Mohney notes. "They sold the company and the customers to Midwest Industrial Supply, and we've been with them for two years." He notes that the new product, EK-35, is somewhat different because it doesn't need to be mixed with water. The product is formulated with synthetic fluids and rosins, and controls dust and stabilizes soil.
In road experiments in Chardon, dust kicked up into the air 10 feet by a vehicle traveling 35 to 40 mph. After an initial application of EK-35 at the same speeds, the dust would rise 5 to 10 feet and settle back down within 20 feet of the particles' origin. Midwest Industrial Supply designed application rates by the tenth of a mile for each of the roads to address areas such as hills, curves, areas with moisture, and places where vehicles left asphalt for dirt roads. The initial application of the product over 2 miles of three individual roads was in early July 2003, with maintenance applications in late July and September.
"We've used it on those three roads and the yard and it's worked out well," Mohney notes. "We haven't had a single complaint. Even though it really doesn't kill the dust all the way, you can still go down the road after they've done it. What's good about it is you can actually follow their truck as they are putting it down and it will get on your car, but it will wash right off with soap and water."
|A Moby Dick Quick wheel washer helps control dust at OmniSource in Ohio.
For Chardon Township, it's also an economical choice. The township's budget for dust control is $14,470, with any job more than $15,000 having to be bid out by the township, so Mohney had to insist the project be done at that rate. He is pleased with the return on the investment.
As for application rates, Mohney asks Midwest to provide coverage twice a year—once before June 1, because the town has a large-scale trash collection on that day and doesn't want a lot of dust resulting from it.
"I try to get it done one more time during the year for two reasons—not just for dust, but to help bind up the road so it'll hold for me in the winter when I'm plowing," Mohney says. "When you get the road bound up, you're not pushing off all your gravel in the low end of the ditch when you plow, so it's a good idea."
Some entities like to be proactive, such as Bay County, MI. Jim Orris, a general superintendent with the Bay County maintenance department, says the county uses calcium chloride for a number of purposes, including gravel stabilization, to "jump start" salt to work at lower temperatures during the winter and for dust control.
"Gravel is made up of clay, sand, and crushed stone," Orris says, adding that crushed limestone, which makes the road hard, also needs to be controlled so it doesn't become airborne. Calcium chloride is a salt that attracts moisture from the air and acts as a "chemical magnet" to tightly bind matter, controlling dust. "When it's bound together, it acts to distribute the weight," Orris explains. "Well-bound road gravel makes like a solid surface, like concrete, to spread out the weight of the vehicles so they don't get buried to the axels."
Orris says the county would most likely put calcium chloride on roads for that reason, even if it weren't for the dust-control benefit. However, he notes, "It's real easy to sell because of the dust control."
The frequency of application depends on the concentration being used, how it's applied, the weather, how much moisture is in the air, and how much traffic is on the roads. It can be applied yearly, or up to eight times a year in urban places such as Detroit, Orris points out. The county grades a road and then applies a 38% concentration of calcium chloride over the freshly graded surface; the road absorbs it and traffic packs it down.
Orris previously had worked in another county where calcium chloride was used in different concentrations and frequencies; Bay County uses one concentration and one or two applications.
Orris explains that a vein of the mineral runs through the middle of Michigan. Hot water is pumped down into the vein and the material is brought up. "That material can be applied at a 26% concentration of salts—it's like a 21% to 23% calcium chloride. There are some magnesium chloride and other assertive chlorides and salts in there," Orris says. "They bring it up at a lower concentration and then distill it to raise the concentration. Their primary product is a 38% concentration, though they sell various other concentrations." The product also is further distilled for other uses.
Bay County uses products from Dow Chemical Co., the world's largest producer of calcium chloride, largely because it is based Midland, MI. "I have to admit that part of that is because calcium chloride comes from Michigan, and when you are dealing with things with such a low cost per gallon as this stuff is, transportation is a very large consideration. When you are close to the source, it makes it quite efficient," Orris says.
In the county where Orris previously worked, a subcontractor who had to maintain a long gravel road, including providing dust control, utilized a variety of products, many of which had a hefty price tag attached. "I have had experience with just about everything I know of that's on the market or in the trade magazines, and calcium chloride by far provided the best performance at the most economical price," he says.
Often, dust-control products are used in conjunction with other methods to achieve optimal results. Such is the case at OmniSource, the largest privately owned scrap-recycling company in the country, with facilities throughout the Midwest and South. The company buys and processes ferrous and non-ferrous metals for final shipment to consumers, mills, and foundries throughout the country.
Jim Shollenberger, a Toledo, OH–based director of engineering and environmental safety for OmniSource, says dealing with ferrous materials means dealing with heavy loads. "The material handling is all done by crawler cranes and large front-end loaders. As a result, typical stone beds get pulverized. The crawler cranes are very abrasive to the surface, and typical topical applications of emulsified asphalt or a calcium chloride solution would serve the purpose temporarily but would not solve the problem.
"Since we are a commodity-based business, we focus our capital more toward the process rather than typical improvements on roads. You don't get the capital to do that simply because the environment we are dealing with— the front-end loaders, crawlers, cranes—just tear up concrete."
The company had been running into problems even with topical applications and continuous mechanical sweeping. "Mechanical sweeping just cannot do the job alone," Shollenberger says. "The content of the roadbed is very high in silt. What happens is that basically you have the equivalent of a baby powder that gets onto the streets. Mechanical sweeping methods just can't get it up; all it does is smear it." When that dries, the traffic on the state road kicks up a lot of turbulence, he says.
When plumes of clouds come off of the roadbed, calls go out to regulatory agencies from residential areas adjacent to the OmniSource facility. "As a result, we are still in the throes of getting through a series of notices of violations from Toledo for fugitive dust violations and mud drag-outs," Shollenberger says.
He notes that one of the company's Georgia facilities had a person stationed at the truck scale area to hose down the wheels as trucks went by because of similar problems. "Using that as an idea, I started looking around for wheel-washer installations," he says. "We went with a plan of putting a wheel washer in and getting the trucks going through it. Regardless of how thick the dust is, as the trucks run through the wheel washer, prior to hard surfacing, it'll cut down the amount of the material being dragged out into the street."
His company learned about managing the water and created a close-loop system in which the water used is recycled. The dust, which essentially becomes mud, is collected and disposed of in the yard's waste system. The Moby Dick wheel washing system from Frutiger is used in conjunction with topical applications to address the dust-control problem.
OmniSource is working with SynTech Products in Toledo, which has supplied the chemical and has developed and tracked the dust-mitigation efforts of the newly installed wheel washer at the facility. SynTech also has helped OmniSource develop dust-suppression work practice standards, review compliance with National Ambient Air Quality Standards, develop a comprehensive dust-control compliance and emission-reduction plan, and develop a "good neighbor" policy to promote environmental stewardship in the use of dust suppressants.
"It could be a tough thing to put a true number on [the wheel-washing dust mitigation], because you are dealing with climatic situations—sometimes it's wet, sometimes it's dry," Shollenberger says. "[SynTech] is trying to get a handle on the efficiency of what we are actually pulling off the vehicles. All I know is when I look at the discharge end of the drag tank, I'm seeing what is actually mud at that point, but it's material that would ordinarily find its way on our hard surfacing and then out to the street."
Shollenberger says the company also is finding that silt is being picked up, which the mechanical sweeping could not do.
"In the past, we had to use calcium chloride on our hard surfaces, and we're still doing that on our entryways," he says. "We don't get it out into the street, but we keep it on our entryways and use it as a means to coagulate the ‘baby powder' to allow the mechanical sweeper to pick it up. Otherwise, it would just smear around."
He says the traditional means of dust control have been the use of emulsified asphalt or different types of topical application dust suppressants. "But there hasn't been a jump to try to do something in the area of washing," he says. "Our industry has had numerous operational seminars, and we get into discussions on environmental issues. When it comes to the issue of dust, it all goes back to hiring a sweeper. The sweeper you have to pay for every day."
Using the wheel-washing unit enables the company to pump and spray water in a stream from 48 inches down that knocks the material off, Shollenberger says. He hopes to be able to run the operation into winter months; he finds that topical applications are ineffective during winter because of the snow and ice.
OmniSource uses a SynTech polymer to help solidify the sediments and encourage separation so the company can continue to recycle the water. It also uses PetroTac, and a calcium chloride flake product on hard surfaces.
"It clustered up, and if you look at the surface, the PetroTac does bind itself, but in a very short period of time, due to whatever the dynamics are in there, the silt gets worked up and sticks to the tires and goes out. You really have to wait until the yard gets to a certain degree to apply it again," Shollenberger says.
He hopes that using the wheel washer will cut down on the dust presence in the yard and the continuous expense associated with addressing that. "Ultimately, we are attempting to make a cost reduction and be more effective by putting this equipment in. Mechanical sweeping is only good for certain granular sizes. When you get down to the smaller baby-powder size, mechanical sweepers or the vacuum sweepers simply just poof it up in the air."
Neighbors are complaining that the sweeping is doing no good and is actually making the dust problem worse, Shollenberger notes. "This is an attempt to try to control those smaller particles by washing them off the vehicle and collecting them while they are damp and trying to reduce the cost of mechanical sweeping and other mechanical means that we are using."
Journalist Carol Brzozowski writes on erosion control and technology.