Dust-control solutions when paving is not an option

By Linda Robinson

Idaho's Ada County Highway District was searching for a compromise with local Boise hikers, bikers, and foothills enthusiasts over how to control the fugitive-dust problem on the unpaved, washed-out North 8^th Street extension. The controversy over the rural road had begun when the highway district decided to pave it for easier maintenance and to prevent the erosion that occurs every spring from snowmelt runoff. Boise residents who use the road for outdoor sports and hiking were adamant that they wanted to retain the rustic feel of the area and to discourage motor vehicle traffic on the road.

A task force, made up of the City of Boise, the Bureau of Land Management, the United States Forest Service, and other agencies, searched for some common ground with the residents. It was more than happy, says Craig Quintana of the Ada County Highway District, when one local resident suggested Soil-Sement as a paving alternative.

Soil-Sement provided a workable solution for both sides of the 8^th Street debate. For the highway district, the polymer emulsion will act to prevent washboards from forming by creating a hardened surface and will control dust on the road. Environmentally concerned citizens like the soil additive's nontoxic, nonflammable, and nonpolluting characteristics. "It looks like we might come up with a win-win situation, and it's not paving," says Boise City Councilwoman Paula Forney. "It solves the drainage issues and saves everybody money too."

In October, work crews began to apply the dust suppressant, manufactured by Midwest Industrial Supply Inc. in Canton, OH, to approximately 1.1 mi. of the Boise foothills road. If it passes the freeze-thaw cycles of Idaho's harsh winter climate, the highway district will apply more of the dust-control material on unpaved roads around the Treasure Valley area.

The first application cost around $13,000, and each year the highway district will need to apply a $4,000 maintenance coating. The highway district says the savings are huge compared to the $30,000 it has been spending to maintain the pastoral atmosphere of the foothills road each year. Soil-Sement has been tested, evaluated, and certified by some leading advocates of environmental technologies, including San Diego State University, the California Environmental Technology Certification, the Engineer Research and Development Institute, the Desert Research Institute, and the Arizona Department of Emergency and Military Affairs.

Used for dust control, erosion control, and soil stabilization on unpaved roads, building pads, parking lots, fields, and other off-road motor vehicle parks, the product has a molecular structure that allows bonding and cohesion with small soil particles, resulting in a strong surface sealant.

What Size Is Your Dust?

Soil-Sement dust suppressant was applied to 1.1 mi. of a Boise foothills road in an effort to control dust and spring runoff erosion.

It can be relaxing to watch dust particles slide down a sunbeam streaming through the window on a summer day, but for people with asthma or allergies, it might not be very healthy. Dust has been the subject of many USEPA studies and recently was found to be a cause of irritation to upper-respiratory airways and the reason behind increased emergency room visits and hospital admissions. But for the most part, this visible form of dust is considered larger particulate matter and not associated with severe health risks. The dust we all take for granted as part of life, especially those living in a desert environment, has a particle size greater than 10 microns and is more a nuisance than a threat.

Atmospheric dust, or PM10 fugitive dust, on the other hand, has been shown to be associated with severe health problems. The National Ambient Air Quality Standards addresses particulate matter no greater than 10 micrometers in aerodynamic diameter, otherwise known as PM10. Under the Clean Air Act, PM10 fugitive dust must be controlled using the best available control measures. Made of the tiniest particles of soil and other air pollutants, PM10 particles can make their way down into the alveoli of the lungs.

EPA studies have identified exposure to PM10 and PM2.5 as the cause of several critical health problems, including higher incidences of critical asthma episodes, low-lung respiratory infections, and other respiratory distresses. In an air pollution study, researchers from New York University and Brigham Young University recently found that in a population of 500,000 adults nationwide, deaths from lung cancer increased 8% for every 10 micrograms of fine particulate matter (PM2.5) per cubic meter. Studies such as these have caused a degree of controversy in the last few years since EPA issued new standards that tightened the PM10 regulations to include PM2.5.

Protecting Your Employees, Your Equipment, and Your Checkbook

Arizona has developed some of the strictest state regulations in the country, and violations, especially in Maricopa County, can be austere. Maricopa County, which includes Phoenix, one of the country's fastest-growing cities, is one of the most studied metropolitan areas for fugitive dust. When EPA inspectors discovered violations in 1999, final settlements on seven cited violations added up to penalties more than $120,000.

Under Maricopa County air pollution rules, parties held responsible for permits, including a dust-control plan, are the property owner, lessee, developer, and general contractors. That means if the general contractor on a construction job site fails to comply with the earthmoving permits or the dust-control plan, the developer and other parties may be held responsible. Enforcement follows two basic processes:

• A business or a person found to be in violation of federal, state, or Maricopa County air-quality laws and regulations will receive a Notice of Violation (NOV).
• If compliance is not met within a reasonable time after the NOV, then an Order of Abatement will be issued.

Maricopa County is not the only metropolitan area that is firm about enforcing the Clean Air Act, but it is among the most comprehensive. Other cities have strict compliance regulations and will issue penalties for violations, and EPA inspectors continue to ascertain more noncompliance areas. Penalties have to be strict to bring these areas into compliance. For instance, the Maricopa County Air Pollution Control Penalty Policy is used to set penalties for both criminal and civil complaints, and the range is a whopping $2,500-$10,000/day per violation, depending on the circumstances.

How Is PM10 Created?

Substantial amounts of atmospheric dust are generated when aggregates are pulverized by mechanical crushing action - for example, the pressure of a tire on an unpaved road. The more dust that is created and lost to the atmosphere, the less stable the road becomes as it loses the fine material. This leaves spaces between the larger aggregates, which allows them to shift and creates washboards, holes, and a general deterioration of the road base. Sites prone to this kind of soil weathering include new-home subdivisions, construction sites, aggregate storage piles, and agricultural operations.

After dealing with dust problems for several years at Lower Valley Turf Farm, Tom and Sandy Vanaken decided enough was enough. The sod farm, located in Terrebonne, OR, had a stretch of unpaved road approximately 1.75 mi. long of heavy volcanic pumice soil. Sandy says that with her allergies, the dust clouds made her miserable, and in March the Vanakens worked with Round Butte Seed to get EnviRoad's Earthbind applied to the road. "As far as farm traffic on the road, it's definitely helped us a lot," Sandy says. "It was absolutely worth the money, and we will be doing it again."

Earthbind is tank-mixed and diluted with water to be sprayed on the unpaved surface, where it provides a cohesive material to bind the dust particles. The parent company got its start in the 1970s when the family-owned and -operated business began applying lignin and magnesium chloride products for the US Forest Service in the Pacific Northwest. As concern for the environment grew, so did research that eventually launched Earthbind at the EnviRoad facility in Portland, OR. There the challenge was to develop a product that would meet the need for environmentally safe dust-control and soil stabilization.

Wind Erosion and Sandblasting Airplanes

Earthbind being applied with a pressurized spreader bar.

Half of the road is applied with Earthbind; traffic can immediately start using the treated road.

Other mechanical forces that break up a road base with applied pressure include heavy construction equipment, blades, scrapers, and multiple wheelbases. Additionally, wind is a contributing factor, especially in arid, desert regions. At speeds of 12 mph or greater, particles crush against each other; the smaller particles become airborne and can be blown with greater force for several hundred yards. In the same way that sandblasting does, blowing dust of this magnitude can cause damage to equipment, including trucks and airplanes.

At the King County Airport (Boeing Field) in Seattle, WA, Christine Thedens became concerned about the wind-blown dust coming off a previously designed art park at the airport. Originally, Ruby Chow Park had used ivy as its main ground cover. But when ivy became listed on the state's noxious-weed list, the entire area was sprayed out. "When it was taken out it left huge areas of bare ground and weeds," says Thedens, the perimeter lead for landscaping at Boeing Field.

Thedens had a twofold mission. She needed to suppress the dust blowing off the bare ground, but she also wanted to quickly establish more permanent turf and ground cover in the form of flowers and trees. To solve her problem she turned to Michael Alms, president of Growing Solutions Inc. in Eugene, OR.

Growing Solutions manufactures "compost tea" systems designed for areas as small as 5 ac. up to large industrial units and 100-ac. farms. Municipalities, golf courses, and organic farms have used the system, which is also popular among greenhouses and nurseries in the Northwest.

"In our system, we extract microorganisms and nutrients from high-quality compost. When these extracts - or compost tea - are applied to the soil, the aggregate structure is improved, allowing for an increase in water retention and improved drainage," explains Alms. "These conditions in turn provide an optimum environment for root growth, soil stability, and plant health."

For the King County Airport, Thedens says it has had a dramatic impact. She spent her first year mixing the compost tea, worm castings, and a proprietary catalyst agent in large garbage cans and applying it to the soil with buckets. But that was the old way, she says. The compost tea proved itself, and the airport purchased a Growing Solutions 12-gal. machine and a small spraying unit. The machine produces 120 gal. at a time of mixed solution for the park and flower strips around the airport.

"We've been able to get great dust suppression because of the depth of the roots on our plants and the better-quality soil," Thedens says emphatically. "And dust suppression is very important at the airport because of the problems it can cause for the planes."

From Water to Mud and Grit

Other options are available to control fugitive dust, some more permanent than others. Reducing wind speeds by planting windbreaks or other plant cover helps prevent wind erosion and controls flying dust debris. Preventing dust from blowing from aggregate and soil storage piles might involve installing fences, building berms, or simply parking heavy trucks and construction equipment in a position that surrounds the pile. These types of wind barriers will only reduce, not replace, the need for watering or using chemical stabilizers.

Watering programs and chemical stabilizers are common dust-control measures. Although water is usually readily available and often considered to be the least expensive measure, it usually provides very temporary control, depending on the soil and climate at the site. Other problems associated with water use can actually make it more costly than other methods. For example, for equipment such as rock quarry crushers, water can create problems when it's used in amounts needed to control the dust problem. Dust coming off the crushers can be so thick that to try to suppress it with water alone would cause clogged screens and downtime at the plant. Additionally, the grit caused by water is abrasive to equipment and increases maintenance costs.

Maryland-based Martin Marietta Magnesia Specialties produces a foam-based product that avoids some of the problems caused by using water alone. Dust-Buster is sprayed on the large rocks going into the crushers so that the resulting end product is already treated; hence, less dust coming off at the end of the line.

"Relatively speaking, this is a short-term control on the end product," explains Martin Marietta's Lin Midyett. "It will dissipate after a period of time. In a few days it will be gone."

Dust-Buster works by increasing the surface area of a small amount of water used and depolarizing that water. By creating literally millions of tiny bubbles of foam, the quarry uses possibly one-fifth to one-tenth of what it would otherwise use in a water-spray program.

Options: What Works and Is Affordable

When developing dust-control options for unpaved roads, things to consider include how long the road will be operational and the volume and type of traffic it is expected to bear. There are basically three groups of control options, including restricting vehicle traffic, improving the road surface, and applying surface treatments, such as dust suppressants. Restrictions might include setting speed limits or limiting the weight or number of vehicles that may pass on the road. These measures have shown to provide moderate emission reductions when they are strictly enforced. Paving is a surface improvement that works well but is so costly that it often becomes unaffordable, and in some cases, such as the Boise 8^th Street example, it's undesirable for other reasons. Paved roads also generally create more stormwater runoff. Chemical dust suppressants offer the least expensive and most efficient option. Reapplication rates vary and are a major item to address in the development of a dust-control plan.

Chemical stabilization treatments suppress dust by changing the physical characteristics of the soil surface. The effectiveness of these treatments is highly dependent on applicators strictly following the manufacturer's label directions. Each dust suppressant has its own restrictions on dilution rates, application rates, amount of time between applications, climatic conditions during application, and size, speed, and amount of vehicular traffic between applications. EPA field tests have demonstrated that when applied correctly, chemical dust suppressants provide, on average, about 80% control efficiency of PM10.

Anthony Mariniello of the North Andover, MA, Rohm and Haas office notes that education about the correct application of the company's polymer products has become a major focus over the last few years. "We want to make certain that the product is used properly so customers will get the effectiveness. We would rather they not use our product than use it incorrectly."

PaveCryl Suppress Emulsion is one of the Rohm and Haas products used for dust suppression. The vinyl/acrylic emulsion provides penetration and bonding when it is applied to fine or granular materials. "Basically it goes down wet, and then the water evaporates and the product hardens," Mariniello explains. "If they scarify the ground and mix and roll [the PaveCryl] in native soil, it can last as much as several years, with one-year topical touch-ups."

When PaveCryl is used for road stabilization, if potholes do begin to emerge, the holes can simply be filled in with a mixture of native soil and the emulsion; it adheres to the surrounding surface and becomes part of the treated road. The lower viscosity of PaveCryl Suppress Emulsion compared to other vinyl/acrylic copolymers allows for easier transfer from tank trucks to bulk storage equipment. Less handling results in less foam generation and less of the polymer drying in the transfer lines.

"PaveCryl Suppress Emulsion will actually cure, depending on the weather conditions, in a few hours, and it doesn't change the color of the soil," Mariniello notes. "Twenty minutes after application, you can't tell it's down."

Maricopa County Department of Transportation Tests and Results

Using various techniques, Maricopa County Department of Transportation conducted tests on dust palliative products with soil-stabilizing qualities. These tests were all done on low-volume roads, and it should be noted that under different traffic conditions the results might vary significantly. The use of product names does not constitute endorsement of any particular product, and they only are used in the context of the test results.

Frequent contributor Linda Robinson is a journalist specializing in agriculture and land-use planning.

EC - March/April 2003