Clearing the Air…and Keeping It That Way
In 1306, King Edward I of England proclaimed the first air-quality law. He prohibited the burning of coal in craftsmen’s furnaces because of its smell. Airborne coal particles still produce an unpleasant smell; however, we now know they also constitute a threat to human health.
And it isn’t just coal.
Any particulates that are 10 microns in diameter or smaller can enter the lungs and cause serious health problems, such as asthma and decreased lung function. They also can contribute to heart attacks and premature death in people with heart or lung disease, according to EPA.
The EPA has standards for six categories of pollutants: particulate matter less than 10 microns in diameter (PM10 and PM2.5), sulfur dioxide, nitrogen dioxide, ozone, carbon monoxide, and lead. Coal dust ranges from 1 to 100 microns, but metallurgical dust ranges from 0.1 to 1,000; ground limestone from 10 to 1,000; cement dust from 3 to 100; and vehicle emissions from 1 to 150 microns.
In this country, the first air-quality regulations were enacted in the late 1800s. It wasn’t until 1947, though, when people in Los Angeles could see only three blocks down the street and suffered from serious health effects, that California passed an air pollution law, the first in the country.
In 1955, the federal government passed the Air Pollution Control Act, which was soon renamed the Clean Air Act. The act declared that air pollution was a danger to public health and welfare and mandated federal research programs to investigate its effects, but it left the responsibility for controlling air pollution to the states and local governments.
In 1970, President Nixon created the Environmental Protection Agency, which emphasized strict enforcement of air pollution laws. The key is to keep the particles from becoming airborne. There are a number of techniques to achieve this, depending on the site conditions.
Areas such as construction sites and landfills, where the surface is disturbed on a regular basis, require only short-term, temporary dust suppression. Plain water sprayed on these sites with a hose or from a water truck or a hydroseeding machine at the end of the day may be sufficient to keep the dust down.
Other sites, such as unpaved roads, mining sites, industrial sites, and dirt stockpiles on construction sites, might require an additive to stabilize the soil for longer periods of time. Some of these applications dry clear and often include wood fiber to show the coverage area.
Additives may be hygroscopic, to attract and hold water molecules from the surrounding environment. They may contain salts, such as zinc chloride, calcium chloride, potassium hydroxide, and sodium hydroxide. They may be resins, which attach themselves to the dust and cluster it into particles. They may be tackifiers, which bind soil particles together, like the plant-based tackifier guar or a polymer mixture.
These additives are usually mixed with water and sprayed on with a water truck or with hydroseeding equipment. Some also can be spread dry on the ground, tilled into the soil, and compacted.
On all sites, the application rate and frequency depend on the site conditions, such as the amount of wind, moisture in the soil, and disturbance of the soil, including traffic. When the weather is hot, dry, or windy, or when the soil is disturbed more often-or any combination of these-the applications have to be repeated more frequently.
The following three profiles illustrate the use of three different applications on three very different sites: a busy landfill in Hawaii, a gravel road in California, and a tailings pond at a gold mine in the Nevada desert.
PVT Land Co. Ltd.
You never know what you’ll find in a landfill.
Buried in a landfill in Waianae, on the island of Oahu in Hawaii, are an 18-story concrete building, a 40-foot ship, an old bus from England, whole spools of copper from the days when copper was cheap, and 200 drums of boat resin that would be worth close to a quarter of a million dollars if the resin wasn’t dried solid.
“I know it’s solid,” says Stephen Joseph, general manager of the PVT Land Co. Ltd., an integrated solid waste facility. “I opened every drum. We aren’t allowed to accept liquids.”
Every year PVT processes 200,000 to 300,000 tons of construction-and-demolition waste, as well as materials that contain asbestos and soils contaminated with petroleum. The company recycles 60% to 80% of the materials it receives.
Recently it began working on an innovative project to recycle part of the landfill itself. The plan began about five years ago.
“When you’re on an island in the middle of the Pacific, you have to plan for everything,” Joseph says.
On the island, where the prices of land and oil are both very high and there are no sources of natural gas or oil, Joseph has been tracking the cost of oil. At the same time, the company has been burying such materials as wood, paper, plastic, cloth, rubber, and scrap metals, which can be converted to methane and other burnable gasses, separately from the materials it cannot recycle.
When oil went up to $100 per barrel, everything became possible, he says. Now, the company is digging up and retrieving the convertible materials.
“You don’t make money on recycling the metal, but we can take the other materials and recycle them to the renewable energy facilities. It makes a lot of sense. It covers our costs and gives us a little income.”
It also increases the longevity of the landfill, which is nearing permitted capacity. “It’s become a very renewable landfill,” he says. “We’ll be sending out 600 tons a day, and it could be up to 800 tons. We think we can recycle 40% of the materials buried in the landfill.”
Waianae is on the lee, or dry, side of the island. It’s windy most of the time, rainfall is typically just 10 to 14 inches per year, and temperatures can reach 95 degrees.
PVT uses conventional water trucks containing mostly brackish, salty water for dust control on roads and high-traffic areas on the site. Company officials were looking for a solution that was both effective and mobile for the workface of the landfill, where dust is created by the day-to-day operations.
Waste material is dumped, sorted, moved, compacted, and at the end of the day covered with fill dirt. Concrete, asphalt, and rock are crushed to use for the roads and as riprap to prevent erosion. Materials to be recycled are excavated and run through a separator and a shredder. Five to 10 trucks are operating at any given time.
Joseph visited a coal-fired power generation facility on the island that was using a DustBoss DB-60 from Dust Control Technology in Peoria, IL. It kept the coal dust down with just a fine mist of water, was versatile and mobile, and had a large coverage area. PVT bought one about four years ago.
The DB-60 looks like a small cannon and is mounted with a generator on a flatbed truck. When it arrived at the landfill, Dust Control Technology technicians set up the spray pattern, the elevation of the throw angle, and the droplet size-25 microns because of the very fine dust at the landfill. The settings can be changed and additives or surfactants can be added to the water, but PVT crews haven’t changed anything.
“It’s been so effective and useful just the way it is,” Joseph says. “We’ve definitely noticed a difference with DustBoss. It really knocks down the dust.”
Crews run the DustBoss between four to eight hours per day on average. They fill it up once from a water tank in the morning and from a small water truck during the day. It uses approximately 1,000 gallons of water per hour, which the company pumps from its own wells.
“Ideally, we like to keep the workface about 30 feet wide, but it can be variable in size,” Joseph says. “If it’s windy, we cut back so we don’t have so much surface exposed.”
The machine usually stays in one place for the day. Crews store it with their other equipment at night and reposition it the next day. “When we start a new day, it’s often in a different area,” he says. “The fact that it’s mobile and we can reposition it makes it really nice.”
Joseph and the crews have noticed a number of side benefits of the DustBoss’s fan-driven misting system. “The guys working around it say it really cools the air, by about 15 to 20 degrees,” he says.
The company also delivers wood to recyclers, and this wood has to have a limited amount of moisture in it. The mist adds the right amount of moisture content without getting the material too wet.
And in October, right before the rainy season, PVT crews plant rye grass to prevent soil erosion. If they need to supplement the rainfall, they set up the DustBoss to mist the area. It doesn’t matter if the grass dies before it goes to seed, Joseph says, because the stalks trap seeds of Buffalo grass, which grows in the area and also prevents erosion.
“We try to be environmentally conscious and not impact our neighbors,” he says. “You always have to have a plan.”
Treating an Access Road in Santa Barbara County
A long, dusty access road in Santa Barbara County, CA, leads from a paved county road to a ranching operation. Along the way, the easement crosses three properties, two of them wineries.
“The road has been in existence for 30 years,” says Robert Sjoquist, of S&S Seeds in Carpinteria, CA. “The owner had been using water to try to keep the dust down, but neighbors complained, and he’s been cited a few times. It’s particularly bad when there’s traffic or when it’s dry and windy.”
The area, in Santa Ynez Canyon near Vandenberg Air Force Base, is very dry and windy. Some 10 to 12 vehicles, from farm equipment to cars, travel the 1.8-mile gravel road every day. In addition to being a nuisance, the dust settled on the grapes in the wineries and caused problems during the harvest.
When the owner wanted to widen the access road where it meets the county road, county officials told him they were looking hard at the new dust control standards and that he would have to mitigate the dust for three to six months at a time.
“I’d just met someone from the county at a trade show at the Earl Warren Showgrounds, and he suggested that the owner call me,” Sjoquist says.
S&S is a wholesale company that provides wildflower, grass, and California native plant seeds for reclamation, erosion control, and landscape projects as well as products for other projects, such as dust control. Sjoquist recommended the additive Soilfloc, from Hydrosorb Inc. in Orange, CA. “It’s very economical,” he says. “You need to apply about a third less than you do with other products, and Hydrosorb is a good company that stands behind its products.”
The owner already had experimented with a number of products, with no success, but he bought a 5-gallon pail of Soilfloc DC 90 to test it out. Then he bought a 55-gallon drum.
Soilfloc is a polyacrylamide polymer that reduces free dust by aggregating soil particles, which makes them larger and heavier and therefore more resistant to becoming airborne. It also reduces water- and wind-induced erosion. It’s environmentally friendly and biodegradable. With continued use, the soil structure will change and reapplication will be necessary only when dust reappears.
“The owner has his own water truck that he used to water the road with,” Sjoquist says. The tank holds about 1,500 gallons of water, and a bar across the back of the truck has 20 to 30 water jets. He pours the 5-gallon pails of Soilfloc straight into the tank. With the drum, he uses a scavenger pump to pump it in. The truck has no agitator, but driving down the gravel road provides plenty of mixing.
The compaction of the road determines the percentage of Soilfloc to add to the water: the looser the gravel, the smaller the percentage.
This road is approximately 80% compacted. On the first pass, the owner uses an 8% to 10% solution to soften the soil. Within 24 hours he makes a second pass, using a solution that’s approximately 6%. With this pass, the solution penetrates the surface and binds the soil particles together. It comes out white and frothy, so he can see the area of coverage.
Once the solution dries, “it basically creates a clear cap,” Sjoquist says. “It turns the road surface and a couple of inches into the ground into a welded surface that doesn’t break when a vehicle goes over it.”
Soilfloc should be reapplied two to four times a year. The owner reapplies it every three to six months, depending on the amount of use and the weather. He applies it more frequently in the summer when the weather is drier, when it’s windier, and after a large storm with shearing rain.
Because the road is an easement, he doesn’t revegetate as an additional dust control measure.
“Initially the owner was concerned about the cost of the Soilfloc,” Sjoquist says, but it he found a number of benefits that more than compensate for it.
He doesn’t have to drive an old truck down a bumpy gravel road two or three times a week and spend as much money as he used to on gas and water, just to see the road dry up again the next day. He doesn’t have to drag the road a couple of times a year to smooth out the ruts. And he spends less time worrying about the issue.
“One of his neighbors works for the county,” he says. “He noticed that there’s less dust, and he’s recommended it for the county to use.”
A Gold Mine in Turquoise Ridge
At Turquoise Ridge, NV, Barrick Mines drills for gold in open-pit and underground mines. The company transports the ore to a mill, where the gold is extracted, and takes the waste soil, or tailings, to a tailings pond.
Barrick, which operates and is 75% owner of the mine, first places a plastic liner on the pond, which can be as large as 100 to 150 acres. The tailings are dumped 10-15 feet deep on top, says Jay Selby, president and owner of Selby’s Soil Erosion Control Co. Inc. in Newcastle, CA.
“It looks like moon dirt,” he says. There are chemicals from the mining and milling processes that Barrick doesn’t want to get into the water table, but the riskier issue is dust.
In the winter, snow covers the pond. In the spring, the snow melts and the pond fills up with water, creating a slurry. By late spring, though, the water recedes back down and the soil is exposed to the hot, dry desert winds.
“That’s when dust becomes a problem,” says Selby. “The high desert has prevailing winds almost year round, and the high winds pick up the soil.”
Selby’s, which performs dust and erosion control services, has been hydroseeding these tailings ponds for five years. The company uses Soiltac from Soilworks in Chandler, AZ, distributed by Horizon, which is also in Chandler.
“We’ve tried various other products,” Selby says. “Soiltac seems to be the most consistent, with the most durability.”
Soilworks created and manufactures Soiltac, which can be used for both dust control and soil stabilization. It’s a liquid polymer mixture that is PM10 and PM2.5 dust compliant, nonhazardous, and biodegradable.
“It has a gluey look and feel,” says Selby. The Soiltac molecules bond with the dust, and as the water dissipates, they form a flexible, durable, and water-resistant mass. Once it is cured, Soiltac becomes transparent.
According to Soilworks, Soiltac can remain effective from weeks to several years, depending on the application rate. At the mine, Selby’s always use the same application rate, which lasts from 12 to 18 months.
The mine, on the eastern edge of the Osgood Mountains in northern Nevada, is in the middle of nowhere, Selby says, and the pond his company treats is inaccessible with any equipment.
Crews drive their 4,000-gallon hydroseeding machine some 70 miles off the last paved road and park at the mine. They put the Soiltac in the machine and use the agitation system to mix it with water. “We also mix in a little wood fiber, mainly to just give our guys a visual,” he says. “When it dries, it dries clear, and it’s easier to monitor if the product is still intact.”
Workers then haul out several thousands of feet of hose and lug it around the perimeter of the 150-acre pond. The only access to the tailings pond is around the perimeter, so “we chase the pond as it recedes. We do the perimeter in early June, then closer to the middle in August or September.”
Even in the summer, crews have to work around the weather. Sometimes the winds are too high, and occasionally the area gets freak rainstorms, Selby says.
Selby’s has a number of hydroseeding machines, but its crews use one from Apex when they work on the mines because all the moving parts are fully enclosed, a Mine Safety and Health Administration (MSHA) safety regulation.
“To be able to work for these mining guys, we do a lot of work behind the scenes,” Selby says. “All of our crews and equipment are MSHA certified, and we have a great safety record.”
After 10 years or so, Barrick restores the land to a natural landscape, leaving rocks, nooks, and other habitats for the desert fauna and flora.
“Barrick Mines is the leader in being proactive in treating these areas,” Selby says. “They have a lot of integrity and don’t mind spending money to get the job done properly.”
