Fugitive Dust Control and Road Stabilization
Whether fugitive dust comes from mining activities, country roads, open land, or elsewhere, federal governments in North America and in other countries around the world have been tightening their dust control regulations.
At the same time, concerns about the environment are spurring companies that develop dust control as well as soil stabilization products to come up with increasingly creative and sophisticated solutions.
In many situations, analyzing miniscule specks of dust is the first step in determining the potential damage they can cause both to the environment and to the health of those who live in the environment. The first profile below shows how a portable version of a wind tunnel combined with another portable piece of equipment detected not only the mass of dust particles, which determines how far they can spread, but also their size, which determines how deeply they are inhaled.
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Stakeholders have an increasing number of effective, environmentally friendly dust control and road stabilization products to choose from. Often one product may serve both purposes when it’s applied differently.
The last four profiles show successful dust control applications and soil stabilization applications in open pit mines, country roads, and a generating station in the Arizona desert.
Measuring Fugitive Dust at the Canadian Oil Sands
When Xiaoliang Wang, a research professor at the Desert Research Institute (DRI) in Reno, NV, was funded to measure fugitive dust at the Athabasca Oil Sands Region, also known as the Canadian oil sands, choosing the instrument to measure the dust was easy. He chose the one he invented.
“I worked for TSI [TSI Inc. in Shoreview, MN] from about 2005 to 2009,” says Wang. “One of my projects was developing a particle monitor for workplace safety. At that time, TSI’s DustTrak measured only the mass concentration of dust particles. I was asked to design something to measure their sizes and masses simultaneously. I came up with an instrument that separates dust particles into different sizes.”
Credit: XIAOLIANG WANG
The DustTrak DRX, Wang’s fugitive dust sampling system
And, in fact, the DustTrak DRX is named for him: Wang’s nickname around the office is Dr. X, for Xiaoliang.
The monitor is the only one in the industry that can measure both the mass and the size of dust particles at the same time. This is important because users can see both how far the dust will travel (larger masses fall quickly and small ones travel farther) and the dust’s health effects (smaller sizes penetrate deeper in the respiratory tract). The monitor also allows analysis of the chemical composition of the dust, which reveals its toxicity.
The DustTrak DRX is very easy to use and very durable, he says. “When we built it, we had a drop test. We literally kicked the case down the stairs. Some parts came loose, so we changed the design.”
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Wang took along DRI’s Portable In-Situ Wind Erosion Laboratory (PI-SWERL), which was invented by his colleagues, including Vic R. Etyemezian. Unlike the traditional method of measuring wind erosion, with a wind tunnel that requires a large flat surface and a large fan, the PI-SWERL is a portable instrument with a rotating blade that creates a shear force to simulate different wind speeds. Dust particles become suspended in the air and are measured by the DustTrak DRX and collected on the filters.
The oil sands dust emission characterization project took place between 2012 and 2014 at 64 sites in the vicinity of Ft. McMurray and Ft. McKay. The two cities are approximately 35 miles apart in a north-south direction. The sites included oil sands mining facilities, quarry operations, and roadways. The soil types include gravel, silt, sand, and clays.
The project was sponsored by the Canada Wood Buffalo Environmental Association (WBEA). The association is now a partner of the Environmental Monitoring and Science Division of Alberta Environment and Parks.
“The WBEA was looking for third-party scientists to try to understand the pollution and to protect the environment,” says Wang. “Dust plumes are everywhere, especially on high wind days.”
Another reason for the testing was concern about the health effects on the First Nation people (native Americans) as well as the ecosystem in the area, he says. Wang measured fugitive dust in the air and soil. He used the DustTrak DRX to quantify the amounts that were emitted under different wind speeds as well as to quantify the effectiveness of applying water to the roads to reduce dust emissions. The testing also helped the oil companies to comply with regulations regarding the concentrations of dust for worker safety and to see how effective their current dust control measures were.
The project went very well, he says. The data showed that most of the dust was caused by heavy vehicles and digging on unpaved surfaces. Gusty winds generate high-concentration but short-duration dust emissions. Wang points out that although lower winds generate less dust per event, their contribution to dust concentrations cannot be ignored due to their more frequent occurrence. Surface watering proved effective in reducing dust emissions, potentially between 50 and 99%.
Credit: SJT CHEMICALS & REAGENTS
Inside the mine after using PennzSuppress D
The dust contains minerals such as aluminum, calcium, and iron. Some dusts are also high in polycyclic aromatic hydrocarbons (PAHs), quite a few of which are carcinogenic. Pollutants associated with dust deposit on snow, water, lichen, and blueberries grown in the region.
The data will help local governments design and evaluate dust control strategies. It also can help modelers, who traditionally have used assumptions based on older and not necessarily local studies to estimate the amount of fugitive dust emissions and how far it travels. They can enter Wang’s data into their models to make more accurate estimates.
Wang still gets emails from researchers asking for the data, he says. “Someone doing studies on lichen as biomarkers found lots of dust inside them and wanted to know if it came in from the air or the water. This is something this research is trying to find out. We don’t know the answer yet.”
Open Pit Mines in Northern Mexico
Some open pit mines in northern Mexico contain up to 62 miles of unpaved road 26 to 130 feet wide. They support trucks and other vehicles weighing approximately 180 to 390 tons—so heavy that they would pulverize asphalt or concrete roads in a day. Each road has an average of eight passes per hour, for a total average of 300 passes per day.
“The trucks stir up a lot of dust,” says Gerardo Alvarez Muzquiz, president of SJT Chemicals & Reagents Inc. in Laredo, TX, which services roads inside mines and does road remediation. “They cause visibility problems, which cause accidents, as well as health problems for the workers.” In addition, the dirt becomes mud after it rains, causing the roads to become very slippery.
These large mines, as well as some smaller ones, are owned by many large companies, primarily Grupo Mexico and Grupo Acerero del Norte, says Muzquiz. About seven years ago, the Mexican government tightened up air quality regulations. It now restricts dust emissions to 210 micrograms of dust per cubic meter of air.
One of the mines that Muzquiz is working with still uses water trucks. Crews have to spray the main roads in the mine 10 to 15 times per day to keep the dust down. The other mines switched to PennzSuppress D, a resin from PennzSuppress, based in Lago Vista, TX.
PennzSuppress D is used around the world for dust control as well as for soil and surface road stabilization. Non-toxic and environmentally friendly, it’s the first dust suppressant to be certified by the California Environmental Protection Agency (EPA).
PennzSuppress D is sprayed from a water truck. The initial application depends on the material and condition of the road, notes Muzquiz, but is approximately one part PennzSuppress D to 10 parts water.
Maintenance applications are more diluted, typically one part PennzSuppress D to 25–30 parts water. The frequency is based on the number of vehicles using the roads per day and the amount of time they take. Trucks apply maintenance applications an average of once every 12 days.
The results are immediate, says Muzquiz. The amount of airborne dust in these mines is down to approximately 50 micrograms per cubic meter of air, well within Mexico’s air quality regulations. Accidents are down, first because visibility is improved, and second because the application process congeals dirt particles so rain doesn’t penetrate and the roads are no longer slippery. It also improves the quality of workers’ health.
“In addition, PennzSuppress D is much more efficient than water,” he says. “It requires fewer applications, so it cuts down on traffic and lets the mines operate with less downtime.”
Coolidge Generating Station
In late 2015, Pinal County, AZ announced its upcoming fugitive dust regulations for PM10; before the regulations were finalized, the Coolidge Generating Station had a dust control application in place.
“We decided to be proactive,” says Kimberly Myers, the environmental specialist at the facility. “We take our commitment to protecting the environment and compliance very seriously.”
The natural gas–fired power generating station is owned and operated by TransCanada Corp. and provides enough electricity for 575,000 homes in the state. The site covers approximately 100 acres. Until the regulations were announced, employees drove the facility’s ATVs across the approximately 60 acres of undeveloped land. The only maintenance was the pulling of weeds, which also disturbed the soil.
The regulations say owners and operators of open areas and vacant lots must not cause or allow fugitive dust emissions to exceed 20% as measured by a visual inspection, a method approved by the EPA for large areas.
TransCanada sent out three requests for bids to carry out the dust suppression project and chose Soilworks LLC of Scottsdale, AZ.
The company’s product, Gorilla-Snot, was the least environmentally intrusive and the most cost-friendly, says Myers.
Gorilla-Snot is a biodegradable, copolymer-based dust palliative. It forms a colorless crust that remains permeable and controls both PM10 and PM2.5 particulate matter generation.
Instead of having ATVs drive on the open land, Soilworks’ contractors put gravel roads in areas of high traffic. On the rest of the site, they did minimal grading of a couple of eroded areas, mixed the Gorilla-Snot with water, and sprayed it with water trucks. It dried within 24 hours. The entire project took one week to complete.
The generating station sprays for weeds four times a year instead of pulling them, which also leaves the land undisturbed.
“The results are very distinctive,” says Myers. “Arizona has some extremely high wind days. We used to see dust generation off our facility. Now we can see dust being generated by the farms around us and it practically stops at the fence line.”
Pinal County regulators have inspected the site twice. They were so impressed the second time, in December 2016, that they asked Myers to do a presentation for other county stakeholders at their Air Quality Compliance Assistance Seminar.
“The presentation went well,” she says. “Several people came up and asked questions after. Many people use water for dust control. I don’t think a lot of them track how much water costs.”
Soilworks’ contractors reapplied the Gorilla-Snot in early 2017 at same rate as the first application. “The biggest cost is the mobilization of these people to come out,” says Myers. “I decided the full-strength original application was the most practical.”
Soilworks has been great to work with, she adds. “The facility has had no fugitive dust emissions since the first application of the Gorilla-Snot, and Soilworks indicated that we may be able to go 24 to 36 months before we need another application.”
Tapering in as the dirt road meets the new asphalt road
Road Stabilization in Gilliam County, OR
In small, rural Gilliam County, OR, blowing dust comes mostly from farm and ranch traffic on the gravel roads, says Dewey Kennedy, road master for the county road department.
There are 428 miles of road in the county, which lies on the Columbia River at the northern edge of the state. Some 310 miles are gravel. Of the 118 miles of pavement, 12 have been paved in the last six years with EBS-RA (Earthbind), a polymer modified asphalt emulsion from EnviRoad in Portland, OR, and with recycled asphalt.
“It looks like the same asphalt as on the highway, but it’s applied cold,” explains Kennedy. “In this area, we can be three hours from the asphalt plant. By the time we got it to our roads, it wasn’t hot anymore. We were hauling asphalt on the road, grading, and shaping, and we weren’t getting a smooth finish.”
Earthbind is an environmentally friendly emulsion that may be combined with crushed asphalt or reject rock. It binds loose soil or aggregate particles together to strengthen and waterproof the road base. It won’t wash off roads after it’s been cured. It also can be used on gravel roads as a dust suppressant.
The county grinds asphalt pavement that’s been removed from local roads. Kennedy has stockpiled enough to pave another 28 miles of road when his budget permits.
Using a local material saves money on trucking costs, and grinding it allows the county to be in control of the gradations of the rock, allowing it to use less of the emulsion, which also saves on costs.
“Asphalt isn’t an exact science,” says Kennedy. “The amount of Earthbind you need depends on the gradations of the grindings. Most of our gradations are uniform all the way across: five-eights inches minus. We’re only adding around two percent Earthbind, weightwise.”
The crews try to do all their work when it’s hot and sunny, he says. “We run the grindings into an old tug mill and inject the Earthbind additive. It’s a continuous feed mixer. As the asphalt goes in, paddles force it into the other end. We haul it out and lay it. It cures fast.”
When the road base is cured, crews chip seal to add a protective layer. “Ideally, you chip seal in a five- to seven-year rotation. I’m on a 15- to 20-year cycle. But since we’ve poured it, we’ve had zero maintenance.”
Kennedy didn’t stop there, however.
“One day, Troy [Tindall, executive vice president of Blue Line Transportation Co. in Portland, OR, the distributor of Earthbind] and I were looking at the chip seal and asked, “‘What if we mix the chips in with the Earthbind?'”
Kennedy, Tindall, and others at Blue Line began using the county’s crushed gravel as the aggregate instead of the asphalt grindings. After experimenting, they found that they could pave successfully with it using about 6% Earthbind.
“Troy has been phenomenal to work with,” says Kennedy. “My budget is very small. He’s helped me stretch my dollars as far as possible on this.”
Now the county has begun partnering with Columbia County on the other side of the state. “We sent them out our mill and they’re doing some experimenting,” says Kennedy.
“Earthbind has worked out phenomenally for us,” he says. “Blue Line hired an engineering firm to do tests on it because it’s a new product. They gave it a 30-year lifespan.”
Road Stabilization in Lincoln County, CO
Traffic on Lincoln County roads can be light—until harvest time, when trucks weighing almost 100,000 pounds run over them, says Chris Monks, road supervisor of Road and Bridge District 1 in the county.
“Our problem is that our roads have no subbase. We get potholes all the time.”
In the late 1960s and 1970s, the county sealed the 42 miles of road in District 1 with magnesium chloride 800 and tree sap, then blotted them with dump trucks full of sand. “Mag chloride is almost like crude oil,” says Monks. “It gets soft when the weather is hot. You can leave footprints in it.”
The county used hot mix patches on the potholes through the years, but the patching never seemed to end, he says. “We had to do something.”
About two years ago, Monks started using BaseBind from EnviroTech Services Inc. in Greeley, CO for road stabilization. “We usually do one project a year, up to half a mile,” he says. “It’s all we can afford.”
BaseBind is a combination of biopolymers that agglomerate fine dust particles while providing stabilization in the road’s surface, says Steve Clark, field scientist manager with EnviroTech. The polymers add weather resistance, flexibility, and help maintain moisture in the road, which increases longevity.
BaseBind is a US Department of Agriculture biopreferred product, which has significance when it is used in biologically sensitive areas or around buildings that have LEED certification. It’s very low in chloride and is compatible with a variety of road bases as well as with reclaimed asphalt pavement.
Preparing the sections of road properly is crucial to the success of the stabilization. The process takes approximately one week. First, the county removes the old chip seal and grinds up the top 3 or 4 inches of soil with a piece of equipment that looks like a giant rototiller, he says.
A motor grader pushes the loose soil back and forth across the road with its blade to evenly distribute the soil. It then grades the road so that it slopes down 4 to 6 degrees from the crown for the road to drain properly. Finally, a truck with a rake on the back roughens the soil so it will accept the BaseBind solution.
A tanker drops the BaseBind, 3/4 gallon per one square yard of road, onto the soil. The motor grader returns and pushes the soil back and forth again to mix the solution thoroughly with the soil.
The road undergoes two separate compactions. The first is with a pneumatic roller with small rubber tires, followed by a steel roller that weighs between 1 to 2 tons. Both compactions are necessary for the stability and longevity of the roads, says Clark.
The road cures in a day or two, and the county chip seals with three layers over the next year or two.
“EnviroTech has been great at lending a hand,” says Monks. “We appreciate that. And BaseBind seems to be the best product we’ve found to stabilize the soil. To this day, where we’ve used it, we haven’t had a failure yet.”