You’re tooling along the Interstate, and before you know it, the visibility drops down to zero. Not from fog, driving rain or blowing snow, but from a huge cloud of dust.
This isn’t a hypothetical scenario; it really happened. Just this past April, clouds of blowing dust near San Simon, Arizona, forced a 60-mile stretch of I-10 to be closed at least seven times within a five-week period. The source was a 2,000-acre agricultural field that a farmer had cleared, but hadn’t yet planted.
Visibility was so poor that it caused several collisions. State workers spent days watering the field down, to no avail. Soilworks, LLC, of Chandler, Arizona, a manufacturer of biodegradable, engineered copolymer soil-stabilizing products, was called in by the state’s Department of Environmental Quality (ADEQ).
The company sent 45,000 gallons of a biodegradable liquid copolymer product called ‘Gorilla-Snot.’ It was applied to a 600- acre section of the field next to the freeway. This proved to be the fix.
We’ll never be done fighting dust. On a celestial body with an atmosphere, it’s inevitable. We can wet it down, block it, blanket over it, or coat it with sticky substances, but as long as we continue to drive and build things, dust will be there.
Why so much fuss over dust? Besides obscuring vision, it represents valuable topsoil that’s being lost. It has a grinding-down effect on machinery, muddies bodies of water and carries pollutants into them, and, perhaps worst of all, settles into people’s lungs.
When you think dust, think “PM-10.” In 1987, the U.S. EPA replaced an earlier air quality standard with PM-10.
It’s shorthand for “particulate matter having a diameter of 10 microns or less,” equivalent to 0.0004 inches, or one-seventh the width of a human hair. Particles that size can easily enter the lungs; that’s why the EPA limits our exposure to them.
“Some of the really tiny ones, 2.5 microns and smaller, can cause respiratory and even heart issues, as they can get down into the very smallest, deepest air sacs,” said Kimberly Butler, enforcement and compliance director for the Maricopa County, Arizona AQD (Air Quality Department). “It’s very difficult to cough them back up again.”
That’s why the EPA is currently reviewing whether or not to set a new, stricter standard, which would be called “PM-2.5.”
Matt Pugh is a project manager/ senior construction manager at Amec Foster Wheeler in Wilmington, North Carolina, a company that works with energy production and mining sites worldwide. He says that before you start doing anything on a site, you first need to establish a “sequence of construction.”
It’s a plan and schedule of all the steps involved, usually specified by a project’s engineer. “It should be a very good, detailed sequence that will clearly spell out the limits of what you’re allowed to do. This will reduce the amount of soil you’ll be exposing, thus minimizing the environmental impact.”
Such a plan should specify which BMPs (best management practices) will be used. The sequence of construction is critical, especially on big projects. Not only must every piece of dust and erosion control be thought through carefully, the BMPs must also be budgeted-for adequately.
Pugh has seen what can happen on sites where sequencing, also called staging, didn’t happen, or was simply ignored. “On this one large earth-moving project, we had a contractor who wanted to do things his own way—however he wanted to do them.”
“So, he deviated from the sequence, and had four different haul roads going, instead of just one. Trucks and pans (scrapers) were rolling in from all directions, creating a dust bowl.”
The inspector was not pleased. “He said, ‘This is part of your erosion control permit; you can’t have fugitive dust emissions all over your L.O.D. (limit of disturbance),’” said Pugh. He then proceeded to create a video record showing all of that dust blowing over the property line.
The solution was to establish one dedicated, graveled haul road, with a maintenance water tanker stationed on it, spraying continuously in the 100-degree weather. The contractor could have avoided all of that, if he’d just stuck to the plan.
Water and other BMPs
Water is what’s used the most for temporary stabilization. It’s environmentally safe, and usually readily available, unless a severe drought limits access. “When you’re on an active site with a dust problem, water is your friend,” said Pugh. But use too much of it, and you can create another problem.
Excess water can form rills and erode the soil.
The problem with water, of course, is that it evaporates. “If it’s 70 degrees, one application can last all day, depending on what you’re doing,” said Pugh. “But on a really hot day, it might only last 30 minutes.” Something stronger and less ephemeral is then needed.
Some of the same BMPs used for soil-erosion prevention are also used for dust control. Wetted straw wattles or bales, wet burlap and plastic tarps are used over dirt or debris piles. Bonded fiber matrix (BFM), a type of hydromulch, can also be sprayed over them.
Silt fencing is the most commonly used BMP, ubiquitous on most construction sites. These geotextile fabric barriers are fairly inexpensive, and can be erected quickly.
To work well, silt fencing should be installed at right angles to the prevailing winds. It must be maintained diligently, because it can fill up fast, be knocked down, or develop holes or gaps. Fencing that’s filled up with silt can be a source of dust in itself.
Breezes can also be blocked with boards or fabric-covered chainlink fencing. Other common BMPs include stone check dams and rocklined or paved access-road entrances and exits.
Oily substances coat dust extremely well. Old timers can remember when waste motor oil was sprayed on roads. Of course, that’s not done anymore, for environmental reasons. Fortunately, there are lots of other dust-control tools in addition to water that are also environmentally friendly.
Commonly used spray-on solutions include calcium and magnesium chloride, soybean oil, guar gum, anionic asphalt emulsions, latex emulsions and resin-water emulsions.
Calcium chloride is one of the most widely used and cost-effective sprayed-on dust control solutions. It’s hygroscopic, drawing moisture out of the air, so it can stay damp for very long periods of time. When dry, it creates a smooth, hard-packed surface that accumulates with repeated applications.
GP Dust Control, Brighton, Michigan, has a contract to maintain the privately-owned gravel roads in the southeastern part of the state. The company uses calcium chloride to coat the many miles of privately-maintained roads; in the winter, they use it for snow removal. The company is busy right now applying it on roads near Lake Michigan.
“We’ve had a very dry winter,” said Marcel Bouhana, owner and president. “The dust is so bad that the homes—and the trees in front of them—are coated with thick layers of gray dust. When people pull out of their driveways, they can’t see a thing.”
Tall-oil pitch and lignin sulfonate, both byproducts of paper processing, are widely used. Since they’re derived from trees, they’re biodegradable. However, one of the disadvantages of lignin and other pinetar derivatives is an odor that some find objectionable. Lignin can also clog sprayer nozzles.
But lignin is the only BMP you’re allowed to use in certain areas, such as forest roads controlled by the Bureau of Land Management.
“There are lots of issues, such as the longevity of the coatings, or the cost, that will determine what kinds of tackifiers we’ll use for dust control,” said Sam Stribling, CEO of 814 Solutions, LLC, a seeding and erosion-control company in Albuquerque, New Mexico.
“It all depends on our customers’ needs. For instance, if they have environmental concerns, we might use tall-oil pitch. It’s a little more conducive to vegetative growth, is environmentally friendly, and can last quite long. It’s one of the best things out there, but it’s not necessarily the cheapest.”
A whole other class of BMPs made of synthetic polymers has been developed over the last 20 years or so.
They can provide long-lasting dust control, and though synthetic, they’re biodegradable.
Some of these products work as soil stabilizers, forming a three-dimensional bond with the soil. Others work more on the surface, containing adhesives that glue soil particles together, creating a hard crust. “They become as hard as cement,” said Chad Falkenberg, Soilworks’ chairman, founder and CEO. “You can drive on these surfaces, and they won’t break down. They contain their own sunblock, so they don’t photodegrade. Unlike lignin and tall-oil pitch, which are water-soluble, they’re resistant to the weather.”
How long will these sealants last?
Falkenberg says that the longevity of a polymer coating is proportional to how much is used, and how well the site is prepped, but it can remain effective from several weeks to several years. In the case of that stretch of I-10, he estimates that the surface will hold up for six to twelve months.
Of course, there’s nothing better for keeping dirt in place than plant roots. When permanent stabilization is needed, such as after construction is finished, a dusty or disturbed area should be hydroseeded.
There’s no ‘silver bullet’ BMP that’s the answer to every single dust-control problem, according to Bob Vitale, CEO of Canton, Ohio’s Midwest Industrial Supply. “The polymer emulsions and acrylics are simply hard to beat, when you’ve cleared and graded 500 acres or more, and need the surface to last for six months or longer.”
“They’re also good to use on roads.
But in many instances, other chemistries would work better. It’s important to know what’ll be best in a particular situation; what’s going to last the longest, versus the cost. You don’t want to spend a lot of money creating a beautiful dust-control situation, and then traffic comes along and chews it up.”
Control the access
Construction-site access roads can be major sources of mud and dust, both within the site and beyond. When mud gets caked onto vehicle and equipment tires and dragged offsite onto the public roads, it’s called ‘trackout.’ When it dries, it creates fugitive dust.
To limit trackout, a good construction sequence should specify just one haul road. Covering the surface with rocks and gravel will keep down blowing dust, and also knock mud off tires.
An additional tire washout area might be needed as well. If it’s allowed by local regulations, some temporary access roads can be paved with asphalt. When the project is done, the road surface is ground off and disposed of properly.
Ideally, construction sites should be closed to the public. “Those big, graded-out areas are great places for people to go drive their ATVs,” said Butler. This kicks up the dust you’ve worked so hard to keep down. So, you have to think about what might happen on the weekends, too.
Your regulatory climate may vary
There’s a great deal of variation in regulatory enforcement across the country. Some worksites rarely get visited by inspectors working for local or federal environmental agencies. However, if you’re working in an area that’s considered environmentally sensitive, such as the Chesapeake Bay watershed, you can expect a lot more oversight.
Pugh says violations are to be avoided at all costs, as they’re project- and job-killers. “In some jurisdictions, like North Carolina, I believe the limit is six minutes of fugitive dust in one hour. If an inspector sees too much of it migrating off your site, he’ll issue a Notice of Violation, and shut your project down.”
Bouhana constantly gets ‘panic calls’ from contractors being threatened with a shutdown. Usually, the construction sites are in heavily populated city centers. “They should have gotten a quote from a dust-control contractor before they even started those jobs. The dust coming off those sites can be unbearable.”
Dry conditions certainly don’t help. In the desert, dry is the norm. It’s not surprising that Arizona’s Maricopa County (Phoenix area) has some of the most stringent dust-control regulations in the country.
“In the early 2000s, we were determined to be in ‘severe non-attainment’ with the EPA’s health standard for particulate matter, PM- 10,” said Butler. “When that happened, we had to come up with some very strict rules.”
They included a requirement that certain construction personnel, such as site superintendents, water truck and water pull drivers, must pass a number of dust-control training and certification classes.
“As the regulations were becoming stricter, we needed to make sure that everyone understood what they were, and why they were implemented,” Butler said. “When people are educated about the reasons for doing something, they’re more likely to do it.”
The classes worked. The compliance rate soared to 92 or 93 percent from the previous rate of only 50 to 60 percent. According to Butler, contractors will even call AQD and say, “We’re having a dust problem; can you talk us through it?” There’s a strong incentive to comply, because not doing so can bring some mighty stiff penalties, up to $10,000 per day per violation.
At its most basic level, dust control is about safety—for drivers, for the environment, for people’s lungs. Working in dust control makes you a guardian of people’s health. And, as long as our planet has an atmosphere, you’ll never lack for work.