Science on the Horizon
Sustainable dust control is quickly becoming a reality.
When it comes to dust, the effects from the hand of nature may appear a bit more dramatic than those generated by the activities of humans. The catastrophic eruption of Mount Krakatoa in 1883 blasted an immeasurable quantity dust 4 miles into the atmosphere, where it persisted for up to four years, blocking sunlight and drifting to span the globe, lowering temperatures by a full degree. The great dust storm of November 12–13, 1933, started in the plains of the United States and caused discoloration of snow a half continent away in New England, where, according to reports of the time, it deposited 25 tons of dust per square mile. However, dust tossed up from roads, industrial sites, farms, and practically any other site perturbed by humans does have its impact; it can travel vast distances over extended periods of time. And it can get into, and practically ruin, pretty much anything.
Bethany Williams, a biologist for the US Geological Service, explains that dust can act as a vehicle to carry contaminants like metals into roadside streams, and the dust itself can contribute to sediment loads in aquatic habitats.
“There are obvious health concerns with PM10 and PM2.5 dust [smaller than 10 and 2.5 micrometers, respectively], and road dust makes a substantial contribution to both of those categories. Several studies show it can cause crop injury and inhibit photosynthesis if plant leaves are coated with dust, and at least one study indicated that dust on forage crops can cause excessive tooth wear for livestock,” Williams says. “There are very good reasons to keep dust out of the roadside habitat as much as possible.”
And the animals in their own way may let on precisely how they feel about dust in their environment. Alan Sarver says ranchers in the Dakotas have complained that their sheep and other livestock turn up their snouts to grazing anywhere near dusty gravel roadsides.
Sarver, who operates Z&S Dust Control, providing dust control services along rural roads in places like McKenzie County, ND, has seen his business boom in the past few years—not because of the sensitive palates of sheep and cattle, but because of the voracious appetite the rest of us have for oil.
The oil fields in North Dakota are booming, thanks to the Bakken Formation, a petroleum-rich geological feature stretching over parts of the Dakotas and Montana. Advances in hydrofracking and horizontal drilling techniques, and an oil market that makes the investment worthwhile, has some experts comparing events in the Dakotas today to the early days of the historic Texas oil rush.
What it means to Sarver is tons more dust-churning traffic on McKenzie County’s gravel roads.
“Just a few years ago,” he says, “you would have seen maybe 30 to 40 or 50 farm-to-market trucks per day, but now it’s more than 1,000 vehicles, running 24 hours a day—and all of them semis.” Sarver says not even an asphalt paved road could hold up long to that kind of onslaught.
To illustrate the severity of the dust problem, Sarver says, the governor of North Dakota recently offered to take reporters up in helicopters “just to show them. From the distance you can see dust in the air. There is just so much traffic, and even after all the roads that they‘re shooting, it’s not enough; you can literally see it. When you get within 50 miles you can see it on the horizon.”
Although gravel has long been the preferred road-surfacing material used in the county, Sarver’s company serviced a scant 12 miles of road in the area just a few years back. However, in 2011 that figure jumped to 80 miles, and he expects that his contracts will balloon to more than 500 lane miles in the coming year, with no end in sight.
“They are short of everything,” Sarver says, and that has been good for business.
And although it takes a tanker load of brine to control the dust and stabilize each mile of road, Sarver feels he can rely on ample supplies of magnesium chloride to keep his fleet of five applicator trucks and 17 nurse trucks humming, laying their 5,000-gallon, 20-foot-wide swath of brine down the center of every mile of road he is contracted to service.
He selected North American Salt’s DustGard from the wide variety of dust control materials on the market. He says the magnesium chloride brine, derived from the Great Salt Lake in the process of extracting potash for fertilizer, represents a good example of a green product: It is plentiful, natural, and economical compared with some proprietary dust-control materials on the market, with “no additional costs other than transport.”
And, he says, it works with nature, absorbing humidity from the air to stabilize the road surface. “Mag chloride is very hygroscopic. That’s one of the reasons it works so well,” Sarver says. “If you look at it in the early morning, it looks dark; if you look at it around noon, it’s lighter; in the evening it’s darker again, because it’s attracting the moisture again.” And this process repeats every day as long as the product remains on the road.
Sarver says gravel roads and magnesium chloride stabilization treatments are a good match for transportation needs in the region. “The whole of South Dakota has a population of less than one million. You could say, ‘If you paved it once you’d be done with it,’ but there’s not enough money in the tax base even to do that, and then there is the maintenance.”
He notes that in some cases, communities in the region that have invested in asphalt roads have become discouraged by the maintenance they require. As a result, Sarver says, “In a lot of places they are turning asphalt roads back into gravel roads, and we’re putting on mag chloride.”
A Flexible Rule of Thumb
Because gravel cannot be expected to all be uniform in quality, Sarver says,
“You have to be able to take the worst gravel and make it work.” However, he says that figuring out the precise application of magnesium chloride to do that requires a certain amount of finesse. “It would be nice if there were a rule of thumb, but if you take gravel from one side of a pit, and then from a different side of the same pit, it will be different.
“We have a standard that works for most areas. We like to put down thirty-five-hundredths of a gallon per square yard, and that works almost all the time. But being in the business for 32 years, you get a feeling for what will work with the gravel in different areas—that, and the past track record, what we’ve had to do in the past to make it work.
“There are places where maybe a quarter of a gallon is all they’ll need, but sometimes they’ll end up putting a quarter gallon down maybe twice a year—once in the spring, once in the fall.” He says knowing when to reapply is a matter of keeping a good eye on how well each stretch of road holds up. “When it starts wearing out, you’ll start getting a little dust, then a little more dust, and pretty soon you can’t tell if you even treated it at all, because you’ve let it go too long.”
Although Sarver considers magnesium chloride an environmentally friendly material, he concedes it can cause problems if it is not used properly, a view Bethany Williams shares. To minimize hazards, she says, users should pay careful attention to material safety data sheets provided with the products and follow manufacturer recommendations.
Going a bit further to minimize any negative impacts and manage costs for his clients, Sarver has equipped his vehicles with computerized applicators paired with GPS systems so they can tell where they have sprayed and where they haven’t.
“They keep tolerances so you know when you’ve come to the end of the job. It shows you, for instance, that you put down 4,732 gallons and it’s within the specs called for by the contract.”
Although Williams says EPA has reported recently that 52% of PM10 in the air, and about 21% of PM2.5 emissions, were associated with roads, Julie Mamula of Midwest Industrial Supply says almost any industry can benefit from implementing dust control practices, including steel mills with yards that are unpaved, mines, or natural resource extraction operations with miles of access roads and haul roads. Among other applications that could benefit from dust control, she includes such diverse operations as mine tailings ponds or ash ponds maintained by utilities. She says dust control products such as a treatment called SoilSement, which her company markets, can even be used to protect such fuel supplies as stockpiled coal from weathering and waste due to spontaneous oxidation or combustion.
If a contest were held for dirtiest job in the city, the demolition contract would certainly be a contender. But to handle the dust from this dirtiest of tasks, many contractors rely on the most basic dust control material imaginable: ordinary water. It is likely that at any given time, somewhere in any large city, one could find any number of construction workers wearing their hardhats and orange vests, standing in a puddle with fire hose or even a garden hose, attempting to dampen down a pile of debris to curtail dust, while a crane or bulldozer punches away at a nearby wall.
Photo: DUST CONTROL TECHNOLOGY
Demolition of an obsolete athletic facility at Bradley University
Contending With a Dirty Job
Although water might be the most environmentally acceptable, universally available, and generally economical dust control application, Dave Schielein, president of IronHustler Excavating (IHX), a major demolition contractor based in Peoria, IL, says hosing down a dust hazard sometimes simply creates a mess, and he didn’t think that technique would be good enough when it came time to bring down an obsolete athletic facility at Bradley University.
LeRoy Neilson, utilities supervisor at the residential campus of 6,000 students just a short walk from the heart of downtown Peoria, says the administration had indicated from the planning stages of the project that controlling fugitive dust emissions would take a high priority.
Schielein adds that, in addition to being a labor-intensive operation, hosing down rubble can contribute to runoff problems that the project team would also have to address, and because demolition contractors pay by the ton at the landfill, hauling off debris weighed down with water can add a significant amount to the cost of a project.
Schielein proposed a different solution: the DustBoss, an automated dust-suppression system that continuously emits a fine mist of ordinary water for dust suppression with minimal supervision.
Rick Felde, a spokesperson for the manufacturer of DustBoss, Dust Control Technology, says the DustBoss can control dust over a 125,000-square-foot site and can easily be moved about or simply aimed in another direction to cover activities in specific areas of the site.
He says the equipment can be conveniently powered by standard electrical voltage to emit a continuous spray of water, atomized by its special “water fracturing” technology, creating a dust-trapping mist over the demolition zone where it is aimed. In addition, he says, the spray can be augmented with any additives deemed necessary to achieve various project goals.
Neilson says dust control needs do vary based on conditions on the worksite, but that in the case of the athletic facility, any hazardous materials had been mitigated before the start of demolition work, greatly simplifying matters. Nonetheless, even with a good system in place to suppress the dust, it became necessary once in a while to replace the filters on the air-handler equipment serving campus facilities near the work zone.
Schielein says that after using the DustBoss on numerous job sites, he’s heard few complaints. In fact, on one particular job in Sterling, IL, when onlookers called to complain of an ominous cloud gathering over the work zone, it turned out to be nothing more than the fine mists of water being sprayed up by the DustBoss itself, glinting in the sun’s rays.
“When city officials realize we’ll be using a DustBoss, they are relieved, and it makes it easier to get approval for projects,” Shielein says.
Although having the right technology onsite is of great importance, Neilson adds that successful control of fugitive dust on an urban demolition project is “all about communications.” He says project personnel should “try to keep vigilant watch over the daily activities at the site.”
“We had a small team on staff here at the university that worked directly with the contractors for oversight and coordination to monitor what was going on, so if we ever did see anything that started to get out of control we could quickly respond and notify the contractors to cease activities and get it under control. It was probably the best tool that we had going for us,” Neilson says.
Today, he says, the site of the demolition has been transformed into “a beautiful landscaped area, and you would never know that we had a construction project going on not too long ago.”
Randy Teague, the director of public works operations for Douglas County, CO, says many of his dust control activities are related to protecting life and limb. “On some of the main rural arterials in the county, the dust plumes would get so great that when two cars would pass each other it was actually a safety concern,” he says.
He believes dust control has already evolved from a convenience to a necessity, but that because of the increasing concern over the environmental impacts of dust, it may soon evolve into a science.
In an informal way, his department is making a contribution to that science with its studies comparing the performance of some of the treatment options it uses on local roads. In an ongoing project, Teague says, Douglas County has been running a comparison between its traditional dust control applications, which use a 70% magnesium chloride and 30% lignin sulfinate blend, with durablend, EnviroTech’s proprietary dust-suppression product, which the county has begun using on areas with low traffic volume.
According to Jeff Collins of EnviroTech, the company produces a suite of dust control products ranging from Xhesion, a non-chloride-based dust control material, to durablend, a magnesium-chloride-based dust suppressant enhanced with a proprietary polymer to reduce the mobility of the magnesium chloride through the soil.
Because that the residents of the bedroom communities surrounding Denver have a keen awareness of sustainability issues, Teague says, the ecological impact of dust control practices, and of magnesium chloride in particular, has been a critical issue for the department—“especially in subdivisions with ponderosa pine trees.”
“We have found that the 70–30 blend, might have migrated in the past and damaged ponderosa pines. Typically, these are trees that are right next to the roadway, sometimes as close as the ditch. In those areas where we have subdivisions with trees, it has been very important to people that we not damage those trees.”
Collins says durablend stays on the road longer and doesn’t penetrate as deep as traditional brine, “so it concentrates the magnesium chloride closer to the surface than a traditional brine would,” cutting down on the risk of magnesium chloride exposures by reducing the volume of the application.
For instance, he says where a traditional blend would require 1 half-gallon per square yard, “with the durablend you would put it down at 1 quarter-gallon per square yard in most cases, for a topical application.”
He notes that in some situations the application rate will be different—for example, on a new road with new gravel where there is no residual buildup. Teague says his crews in the Douglas County test project applied durablend at a rate of rate of three-quarters of a gallon per square yard and milled it in to a depth of 3 inches, following that with a topical of 1 quarter-gallon per square yard.
The technique has been getting “very positive” reviews from the public. “Where we’re using it, the public acceptance has been outstanding,” Teague says.
“We’ve treated roads for upward of 15 years now using different methods,” he notes. Some methods, he says, “got so sloppy that at times, after a rain, that you literally couldn’t drive up the roadway, but with this process it’s got to the point that we rarely get complaints anymore.”
And in tests on stretches of road that had never before been treated, Teague says, an analysis done through Colorado State University demonstrated that with the use of durablend the chloride levels did not increase. “Actually, in the testing they went down, so it kind of made us feel good that we were putting down a material that, at least so far, has shown it doesn’t build up in tree bark or tree flesh.”
A Refuge for Science
Williams of the USGS says Colorado is one of the sites she visited along with researchers while “looking into the dust issue in general.” She says a lot of concern exists there about dust because EPA has identified a number of non-attainment areas and has mandated regulations to reduce the amount of dust. In addition, she says, “Citizen concern about the effects of dust and the effects of chlorides is higher in Colorado than some of the other places we visited.” But, she says, it’s not just ordinary citizens who are concerned.
Although there are likely more than 2 million miles of unpaved roads in United States, Williams says, the proportion of unpaved roads on federal lands is 85%, and that includes many roads in national wildlife refuges managed by the US Fish and Wildlife Service (USFWS). While these areas often need some form of dust control, because the USFWS had so little information on the potential environmental impacts of the products available for that purpose, Williams says, “they have been under a near moratorium on chemical dust suppression since 2005.” The agency’s road coordinator “did not feel good about putting out products unless there was some controlled scientific studies of whether or not there were likely to be any adverse impacts,” she adds.
In response, the USGS initiated a new study, which Williams believes is perhaps the first of its kind, to apply a scientific approach to evaluate and compare the potential environmental impact of various dust control options.
Although the study is targeted specifically for USFWS, Williams, who leads the research team, says, “Our intention is that it will have broader impact on the dust control industry as a whole, because the sort of environmental data that we’re gathering could be used by anyone.”
While there have been, over the years, a number of scientific environmental studies of chloride-based dust suppressants, accompanied by science-based recommendations for their proper use, what distinguishes the current study is its focus on emerging categories of non-chloride dust control products.
Williams says it has been a bit of a challenge narrowing down the focus of study to cover the appropriate products. “It’s really kind of tough, because when we talk about dust control products we talk about it as if it’s a homogenous category of some kind, but it’s not really. Almost every conceivable substance has been used for dust control at some point in the history of unpaved roads. Some of the products are water soluble and some are not; some work with the charges on clay particles; some just coat the fine material—for instance, some of the hydrocarbon products work like that; some draw water to the road; and some simply glue the fine material in the road together to form a crust. There are lots of different ways these products work, and that was a challenge for us. We were dealing with a wide variety of products that behave very differently in the environment and could have very different effects on organisms and plants.”
To close in on the important data, the project will proceed in three phases. The first phase is an aquatic toxicity screen, which Williams says will examine 15 different products from different vendors and across different product categories. Standardized tests with the rainbow trout, a common test organism, will be used “to see, in the worst-case scenario, if these products entered a roadside stream or wetland, whether they might have a toxic effect.”
Phase two includes a toxicity screen expanded to cover additional species, and phase three includes plans to move the study into the field for 12 months, something Williams says she is “really excited about.”
“Ultimately, we care about what the potential impacts of these products are in a real-world setting. So we’ll take several of the products that we’ve identified as having low toxicity in the laboratory tests, and we’ll apply them in the field as they would be applied under real-world conditions, with surveys of roadside organisms and plants before, during, and after the applications to see if there are any effects.”
Williams says the initial report will be published later this year and will be available to anyone interested. But she believes many stakeholders will be eager to see the results of the field portion of the study, which will run for 12 additional months, “so they can add that to the lab data to help guide product selection.”
While awaiting the scientific results, Williams says, “The most important thing a county road supervisor, a refuge manager, or an applicator could do, both to maximize the value they are getting from the products they use and to minimize the environmental impact potential, is choose the appropriate product for their setting, and have their soils tested by a contract laboratory to make sure they are choosing a product that is good for their particular type of road.” For example, Julie Mamula says her company, Midwest Industrial Supply, offers such testing services to its customers if they can supply a 5-gallon sample of the material to be treated.
Sarver says there are many good reasons to optimize dust control procedures for gravel roads. Without dust control, he says, “you’re going to lose an inch of gravel a year.” Under those conditions, road managers will have to regravel periodically. “That’s awfully expensive, and they’ve got to be careful because there are fewer and fewer gravel pits all the time, and good gravel is getting hard to find.”
Randy Teague agrees and says his department realized some surprising benefits from its dust control projects. Before implementing dust control procedures, the department found itself regrading its gravel roads every two weeks, but dust control and road stabilization measures reduce the level of required maintenance considerably. In addition, Teague says, “We have found that when you do dust suppression, the gravel doesn’t get chewed up as badly during grading. Every time you grade a road, you break down the rock and it gets smaller and smaller until you get to the point that you don’t have any of the larger three-quarter-inch material left.” He says dust suppression and stabilization “protects the gravel, so we don’t have to add gravel to the road bed as often.” And that saves money.
But Teague says it is also important that citizens understand that dust is a part of the underpinning of any good gravel road. “Dust is inherent in gravel,” he says. “You have to have the fines in there to keep the gravel together—to keep it compacted. And it’s that same dust, those same fine particles, that get airborne when it gets dry. Some people feel that the gravel shouldn’t produce dust. That’s been, maybe, our biggest frustration, when people move on to a gravel road and expect for there not to be any dust.”
Writer David C. Richardson is a frequent contributor to Forester publications.