May-June 2005

Going the Distance

Short- and long-term dust control solutions

Fugitive dust is becoming a problem as large as its particles are small. Whether it’s blown from a new construction site or shaken off the top of a coal pile, fine particle pollution can reduce the efficiency of equipment and the physical condition of project managers, site workers, and nearby residents.

“Just the dust itself is a concern for health reasons, particularly [for] those who suffer from asthma,” says Cheryl Detloff, chief chemist at Midwest Industrial Supply based in Canton, OH, referring to the damage that can be done when dust is inhaled. “Dust can also carry potential toxins. It depends on what the source is. Dust from a farmer’s field could be carrying pesticides. Coal dust could be carrying carcinogens.”

Fugitive dust can also reduce visibility both on the road and on the runway, and dust near water areas can be a problem as well. “It’s hard to quantify how much dust lands on water, in potential drinking water sources,” she explains.

According to the EPA, fine particles 2.5 micrometers in diameter—smaller than the human hair—have been associated with serious health problems, including heart attacks and chronic bronchitis. The agency is seeking state cooperation to reduce fine particle pollution within their regions.

Controlling fine particles in the short term and for the long haul ultimately depends on how the applications of environmentally appropriate dust control products are carried out.

Stability on Rural Roads
Finding a solution that can handle the conditions on Utah roadways is the main criterion Utah’s Department of Transportation (UDOT) uses when choosing a method of dust control.

“UDOT uses magnesium chloride brine (30%) for dust palliative in our yards and on one of our two gravel-surfaced roads,” says Lynn Bernhard, maintenance methods engineer with UDOT based in Salt Lake City. “We like the magnesium chloride because it is hygroscopic and keeps dust particles bound to the road. The road we use it on is situated on a south-facing slope in a very dry location just north of Mexican Hat, UT, where the surface dries out quickly. It's easy to apply since we use our anti-icing sprayer to apply the liquid.

“Long-term stabilization would involve a plan to apply heavier applications. Our short-term dust control is on a very steep—15% grade—road where the material tends to migrate downhill under traffic.”

Magnesium chloride is used for dust control in areas where the department doesn’t want vegetation to grow, “such as along guardrails, in front of crash cushions, around roadside delineators,” he explains. “Our goal is to reestablish vegetation as soon as possible in areas that will not be disturbed again. Revegetation does require specialized equipment to reseed large areas. Small areas can be done efficiently by hand. Mag chloride is more expensive in the long run for controlling dust than vegetation, but for short-term use where plants cannot establish themselves, it is the best solution for our climate. We are a little different than many states because most of our state experiences hot, very dry conditions. Seeds have a tough time surviving after they germinate during some months.”

Other reasons his department chose magnesium chloride brine is because the UDOT crews were familiar with its use, and it’s easily available, explains Bernhard.

“Being somewhat ‘mistake-proof’ also makes magnesium chloride a good choice,” he says. “We like the fact that we do not have to grade the road as frequently to redistribute the gravel.”

Because water evaporates quickly, it can be difficult to use as a dust control method on unpaved roads. Calcium chloride is frequently used to control dust in this environment.

“The chemical absorbs water from its environment,” explains Mark Slotwinski with the calcium chloride division of General Chemical, based in Amherstburg, ON, Canada. “Basically what it does is it controls the moisture in your gravel road and makes the moisture very resistant to evaporation.”

One application, when the chemical is sprayed on the road from a pressurized spray system at the back of a tanker truck, can stabilize an area for approximately four months. Its environmental friendliness is appealing as well. “Calcium chloride is a non-hazardous chemical,” says Slotwinski. “It’s not regulated by DOTs.”

Dan Williams, a winter and roadside maintenance specialist with Montana’s Department of Transportation (MDT) based in Helena, says his department primarily uses magnesium and calcium chlorides for dust control on construction projects. “When there is very little clay or 200-mesh material in the aggregate mix, some folks prefer chlorides with lignin,” says Williams. “MDT uses chlorides for surface stabilizing of aggregate and dust control only. As little as one application of one half gallon per square yard will meet our goals. For major long-term projects, geotextiles, engineer-designed gravel mixes for underlayment stabilizing, slope angle control, and hydroseeding are used.”

Williams says MDT looked for a product that had a good purchase price and availability, good longevity and comparatively good application rates, and maintained good air and water quality above and below ground. Another factor was whether the product could be reworked after an application for “changing construction conditions, weather, and temperature restrictions.” It was only after these considerations were weighed that the organization decided to use chloride-based dust control products.

Tom Oxford, owner of Oxford Inc. in Moyie Springs, ID, which distributes and applies dust control products, also uses calcium chloride, particularly on the region’s forestry roads, where replacing gravel can be difficult.

“I use 77% flake calcium chloride and 94% mini pellets (manufactured by Dow Chemical),” he says. “If you had a mining project or a larger timber sale over the course of a couple of years, put down two pounds per three square yards. Generally just place it over [the site]. You pre-water … then spread the dry product on it with applicator boxes we have specifically for that.”

Photo: Enviroseal Corp.

Finally, he waters over the product, and he says the customer will end up with “two or three inches of dust-free compacted surfaces, a nice tight road to run on.”

He also likes dust control products for their erosion control properties, particularly on roads in his area where the upkeep and expense involved with pavement rules that out as a consideration for many rural roads. He prefers a solid dust control product. “When you put a liquid down, you can’t keep it all on the road; it’s going to run off into the ditch somewhere,” notes Oxford. “I like the dry product because it all stays right where you put it.”

When applying a dust control product to a site, he tries to apply as closely as possible to the area where the work is immediately taking place. “We try and stay as close behind the blade as we can—just so long as you’re there before the road gets really compacted. The chloride penetrates faster and easier.”

Maintaining Military Dust Control Needs
Ruth Sparks, an integrated training area management coordinator at Fort Irwin, CA, the Army’s national training center, needs dust control that can handle some of the country’s driest natural conditions. “We use it on tank trails and other heavily used vehicle trails,” says Sparks. “We’ve used it in our aviation areas, which are usually helicopter sites, to reduce brown-outs as they land and take off. That includes both areas around an actual airfield as well as sites out in the field where they are doing refuel operations as part of their training.”

The sites, all located on 643,000 acres in the Mojave Desert, are continuously in use, and dust control that can adapt to the environment is essential. “The product that we use up here is Soil-Sement,” says Sparks. “The logistics of using large quantities of water in the desert is just not feasible.”

The land management contractor performed a comparative analysis of a variety of products nine years ago before choosing Soil-Sement from Midwest Industrial Supply. The product, Sparks says, “retained a little bit of flexibility, a little bit of give” in an area where heavy vehicles are used. “It didn’t seem to be as brittle as some of the other things that we were using and [we also chose it] because of the environmental considerations. It was pretty benign. We do applications twice a year. Most of it is done from a spraybar off the back of a truck.”

Air quality is a prime consideration here, because some of the area’s trails are located near residential areas. Local water quality standards must be met as well. Paving was not an option in most of the training areas, many of which replicate the environments the military personnel will encounter overseas. “Not everything will be paved,” says Sparks.

Photo: Enviroseal Corp.

Another company familiar with meeting the harsh environmental needs of the military is Enviroseal Corporation based in Port St. Lucie, FL. “We have done extensive testing with the US Army Corps of Engineers in both fixed-wing [aircraft] and helicopter testing. We ship in 275-gallon IBC totes [containers for transporting liquids] that are easily adaptable for military applications. Construction of an airfield runway in the middle of the desert in 24 hours is now possible using the in situ material,” says Andy Stevens, vice president of Enviroseal, who adds that the company has filled orders for use during the war in Iraq. “Our LDC (liquid dust control) is an acrylic-based product that binds fine soil particles together two ways. In cohesive soil, it is adsorbed by the soil particle. In non-cohesive soil, it is encapsulated around the soil particle. In both instances, the soil particles adhere to larger soil particles to bind them together.”

For long-term use, the product should be mixed with the soil.“A simple spray-on application will provide erosion control and temporary dust control. Long-term stabilization requires a solid matrix of the material mixed with our products. Typically, a 6- to 12-inch layer of soil is thoroughly blended, graded, then compacted,” says Stevens. “Depending on the particular application, the effectiveness can only be as good as the intended use.

Stabilizing the Soil and Settling
the Dust at Construction Sites
Stabilizing the soil as a company controls fugitive dust can also maintain the integrity of a construction site. A prime example occurs when a construction company builds a store or other commercial facility and leaves undeveloped land that needs to be stabilized until the property is sold, notes Klif Rader of Desert Mountain Corp. in Farmington, NM. It’s cost-effective for construction companies to grade larger areas at one time before applying the dust and erosion control methods, rather than bringing equipment back to the site more than once to grade in stages.

“What companies are telling me is that they need to grade the site at one time. They have the excavators out there,” says Rader.

Rader provides Soiltac to construction companies, as well as mining companies. “I cap coal piles with it. I use it on roads and undeveloped sites,” he says.

The product can be used for large commercial sites as well as residential applications, according to Chad Falkenberg, president of Soilworks based in Gilbert, AZ. “Soiltac works by bonding soil particles together to create a strong yet flexible matrix. Once cured, it becomes completely transparent, leaving the natural landscape to appear untouched,” he explains. “Soiltac results are based on the application rate used. Modest applications can create a light temporary surface crust that is permeable by water and is useful for dust control needs.”

Application varies with the individual construction company’s schedule. Falkenberg says Soiltac typically lasts for 12 to 24 months with a single application. “It is used for temporary dust control by extending its application rate between 50 to 300 gallons per acre at a highly diluted rate, and applied topically to the site,” he notes. “Soiltac is used for soil stabilization by uniformly mixing it into the ground at a minimum rate of 50 square feet per gallon. Heavy applications can generate results similar to the qualities of cement.”

Getting a product to a construction site for application can sometimes be problematic in arid regions. “Watering is not cost-effective anymore. Water is becoming a very high-demand product,” comments Rader. “Water is getting tougher to get on construction sites.”

Wind blocks are another consideration for construction companies seeking temporary dust control, but are not the most effective protection.

Understanding why the dust problem is occurring and what activities might be exacerbating it is an important step in choosing a dust control method. “One of the things we are going to look at is whether it’s going to stay where it’s put. What forces are acting on the roads, or the coal, that are making the particles airborne?” says David Moore, a dust control engineer at Syntech Products based in Toledo, OH. “If it’s a pile that’s being actively used, can we access the pile using a different method to stop particles from getting airborne?” He notes that how long a product will last is of concern, depending on an area’s traffic and the type of use. “If it’s an open area used for storage, longevity becomes important. We have products that bind the silts to the aggregate, [and products] that bind the silt together. We have products that keep moisture on the roadway so particles don’t become airborne.”

Dust control products are affordable options for construction companies, especially when paving is not an option and revegetating a site will take too long, or when work onsite is still underway. Sometimes, even if paving for permanent control is possible, “companies want to keep a rural look,” notes Rader. “But they don’t want to deal with the dust.”

As air-quality regulations have become more stringent, the company has seen business increase. Rader has also noticed residents in rural areas complain more about dust problems as these areas become more developed. “It’s a trend in our area—people from the city are retiring to a rural area, but they don’t understand why they have dust,” he says.

Photo: Midwest Industrial Supply

Construction companies face a variety of soil types and often favor a single dust control product that works well with several.

“Soil-Sement is very adaptable to most if not all soil types, and it also provides a level of protection that the customer decides. We can design programs around that. [A contractor] can stabilize hundreds of acres and basically walk away from that site until they are ready to build on it,” says Frank Elswick, Midwest Industrial Supply’s western regional manager. “Another part of it is the longevity of the product. It doesn’t leach or wash away.”

Like other polymer-based dust control products, Soil-Sement can be used in temporary or long-term maintenance programs. “It’s a polymer binding agent. It soaks into the ground and it adheres the particles together,” explains Midwest’s Julie Mamula. “It’s got a pliable, almost rubbery, surface. Vegetation can grow through it, based on the application rate.”

The difference between polymer and enzyme-based dust control has to do with the different ways they approach performing the same task. Enzyme-based dust control methods depend on the soil’s chemistry, notes Detloff, because they depend upon a chemical reaction. “The polymers are a physical binding together of the soil particles in a matrix,” she says, adding that they are applied loosely and as water evaporates, they bind together.

Meeting Environmental Needs
Although effective dust control helps improve air quality, there are other natural resources that need to be protected from fugitive dust as well—notably water. Although controlling dust might help reduce sedimentation, stormwater runoff from treated surfaces remains a concern, as this runoff may carry substances used for dust control into surface waters.

Photo: Midwest Industrial Supply

Photo: Midwest Industrial Supply

“Calcium chloride and lignins are water soluble, and they remain that way,” explains Detloff. “Those materials will potentially be carried off, or they can leach into groundwater. Then you have asphalt emulsions—once they are dried and cured, for the most part, they are not water soluble and they won’t be carried into runoff.”

Elswick notes that in addition to storm-water requirements, his company looks at fish and game requirements in producing a product as well.

Determining whether something is environmentally safe is a concern shared by many dust control product companies, and one more complex than it first appears.

“The phrase environmentally safe covers a very broad spectrum of issues, including aquatic toxicity, vegetation toxicity, mammalian toxicity, mutigenicity, and so on and so on,” says Joe Althouse, a senior technical service specialist at Dow Chemical Co., based in Ludington, MI. “Layer on top of that the fact that environmental impact is highly situational, depending on the specifics of a particular application. Certain special interest groups will cherry-pick one or two data points and use them as a basis to wave a big environmentally safe or environmentally unsafe flag.

“In my opinion,” says Althouse, “this practice of over-simplification and telling only selected parts of the story is, at best, a disservice to the general public and, at worst, deliberately deceptive with the goal being selfish gain. The environmental safety of a product can be judged to a significant extent by its application history and its end uses. Calcium chloride has been used as a dust control and road stabilization agent across North America for over 80 years without negative impact. It is also used as a calcium supplement for animal feed and as a foliar treatment for various fruit and vegetables. It is used in many food processing applications and is an ingredient in cheese, sports drinks, and other foods.”

Photo: Midwest Industrial Supply

Choosing a company that tests its products to be environmentally compliant and safe is not enough on its own, says Detloff, noting, “The company really needs to look at the application. In 90% of the applications it’s going to be fine, but unless you have a company that looks at the site-specific conditions you could have a problem.”

For example, a customer of Midwest Industrial Supply was considering one of the company’s dust control products for use at a particular site. “But they had a contaminant in the soil that was not bioavailable. It would stay in soil unless something was put in the soil to carry it away or make it more available in the environment,” says Detloff. “Had we not asked the right questions, we would have had problems.”

Environmental policies differ from state to state, as well.

“The EPA has strict requirements that state the maximum levels for chemicals to be considered toxic,” says Falkenberg, who adds that his company has completed a variety of studies using a third party aquatic toxicity testing facility to document Soiltac’s environmental compliance.

One way to make sure a dust control method is working at a site is through careful monitoring. Some environmental engineers, construction company workers, industrial hygienists, and regulatory agency environmental and compliance officers, for example, choose DustTrak aerosol monitors to track dust migration for brief or extended lengths of time during a project.

“The DustTrak aerosol monitor measures PM 10, PM 2.5, PM 1.0, and respirable size fractions in real time,” says Greg Olson, a product manager at TSI Inc. in Shoreview, MN.

Ultimately, though, the manufacturing practices of dust control product companies play a large role in not only keeping our air clean but maintaining the natural environment as well.

“A lot of it depends on the quality control of the manufacturer,” says Detloff. “The industry is not really regulated by anyone. We depend on ourselves to keep honest.”