Dust can be a problem anywhere in the country. Here are three examples that illustrate three different types of problems and three different approaches.
Dealing With Dust in Albuquerque
Pat Wylie and partner Bob Sparling operate Sparling Construction Company, which does heavy earthmoving and paving and utility projects in and around Albuquerque, NM. Jobs can range in size from about 3 to 60 ac.
They know well the challenges of controlling dust in a dry climate. Many of their projects involve easily eroded soils. They also deal with strong winds in the spring that can blow continuously for a week or longer and powerful winds from frequent thunderstorms in the summer. During one two-week period this past spring, sustained winds limited work to just a few hours on most days.
Water is their main dust control tool. If a site allows it, they set up sprinkler irrigation to prewet areas before moving any dirt. Once earthmoving equipment starts to roll, so do the water trucks. For example, in areas where soil is very light and erodible, a 6,000-gal. tanker truck is assigned to every 23-yd. scraper, applying water ahead of the earthmover. On heavier, more stable soils, that same tanker can often keep soil moist for as many as three 23-yd. scrapers.
“Once we begin clearing vegetation, the water truck covers the entire bare area to aid compaction and develop a crust that will help keep dust down,” describes Wylie. “We water continuously throughout an eight- or 10-hour shift. We can’t afford to stop because we’d lose our moisture and compaction. Then, if we got strong winds, we wouldn’t be able to control the dust.
“We try not to strip vegetation too far ahead of ourselves. Once the soil is disturbed, you have to keep watering it to maintain a crust, otherwise controlling the dust would be a lost cause. On days when the wind is too strong, we shut down and run only the water trucks in the hope of being ahead the next morning if the winds subside.”
Haul roads receive water treatment continuously throughout the work day too. Because these routes change daily, it’s not economical to use dust palliatives on them, Wylie notes.
Water is also used to control dust on open ground near sensitive areas such as existing homes, parks, golf courses, and streets.
Wylie is concerned that the clear water that Albuquerque contractors use to control dust might or might not recharge local aquifers. “I wish we had a gray-water system here, as in some areas, so we could use reclaimed water for controlling dust,” he remarks.
Other dust control tools include snow fences and hay-bale barriers. On some jobs, existing buildings upwind of a project help block the wind.
“Controlling dust the way we do is expensive,” admits Wylie. “But we don’t want to cause problems for neighbors around our projects. It’s important to be flexible and able to adapt to rapidly changing weather conditions. Everyone in this business seems to be production-driven. Sometimes I’ve found you’re better off to stop working, however, because if you continue, you’ll create dust that blows onto someone else.”
Controlling Dust at the Big Dig
When it comes to moving dirt, you’ll have to look long and hard to find a project that will move more than the “Big Dig” in Boston, MA. The 13-year Central Artery/Tunnel Project is designed to reduce traffic congestion by improving the flow of cars and trucks through the heart of the city. It will replace the existing elevated freeway with 161 lane-miles of highway in a 7.5-mi.-long corridor. About half of this roadway will be in tunnels. By the time the project is completed in 2004, grading and excavating contractors will have removed 13 million yd.3 of earth. Most of this material is being used to build a public park on an island in Boston’s harbor once used as a landfill.
To meet PM10 standards throughout the project, the Massachusetts Highway Department developed specifications that, among other things, require contractors to control dust at all times, including nonworking hours, weekends, and holidays. Based on the project’s specifications for construction dust control, contractors must have an approved plan for controlling wind-blown and vehicle-created dust on all exposed areas and unpaved roadways. The PM10 levels at the construction sites are monitored closely from June 1 through October 31, when most dust problems occur.
Some of the dust control measures include:
- Wheel-Wash Stations. Located at points where vehicles exit a construction site, they’re designed to reduce dirt and mud tracked onto public roadways by trucks and other vehicles. Wheels and underbodies of vehicles are cleaned with handheld spray washers. Material that might still be tracked onto the road is removed using hand brooms and vacuum sweepers.
- Street Cleaning. Because they’re more effective in removing smaller, finer soil particles, vacuum sweepers have replaced conventional broom sweepers.
- Perimeter Dust Barriers. Sheets of plywood or wind-screen material (such as that used around tennis courts) attached to chainlink fencing is placed atop jersey traffic barriers to help contain wind-blown dirt within the construction zone.
- Load Covers. Loads of dirt in trucks are covered with tarps before leaving a construction site to prevent material from blowing off when traveling on public roads.
- Stockpile Protection. Water or dust surfactants can be used to wet and bond dirt particles on stockpiles; otherwise they must be covered with polyethylene tarps.
“Overall, the Central Artery/Tunnel Project dust control program has been very effective in meeting PM10 standards during construction,” reports Alex Kasprak, the project’s senior air-quality engineer. “We’ve found that any one method by itself won’t work effectively on a project such as this, which has a number of different work zones. As a result, you have to fine-tune mitigation measures. For example, if you apply too much water on construction areas, you could end up with more mud being tracked onto paved roads than a street sweeper can handle. Everything has to work in unison.”
Solving a Problem With Blowing Sand
In the spring of 1998, land developer Bob Coy of Stuart, FL, was searching for a solution to a problem he had never faced before: irate neighbors complaining about fine particles of sand being blown into their homes and swimming pools from one of his residential projects.
Crews were installing streets and utilities in the 30-ac. subdivision. The source of those particles-Coy calls them white sugar sand-were open areas that had been disturbed during construction.
“It was an abnormal situation,” he says. “We had never had winds in this area that bad before. The pressure to stop the sand from blowing was really on us.”
First, he tried planting a mixture of rye grass and other grasses with a mechanical seeder. The grass didn’t grow because of the poor soils, Coy recalls. Next, he tried spraying water from an artificial lake he had dug on the site earlier. “The soil would dry out in a few hours. Then the winds would come along, and we had the same problem all over again.”
Finally, at the suggestion of Erosion Control Supply Source Inc. of Palm City, FL, he treated the bare areas with an acrylic copolymer dust suppressant. “Results were immediate,” Coy states. “The treatment worked marvelously.”
By mistake, the dust control product had not been applied as intended with a mixture of grasses and fertilizer. That was corrected with a second treatment. He reports that the product kept the dust down for six to seven weeks until the grass grew enough to limit any blowing soil.“That product saved the day,” says Coy. “The county was ready to shut down the job.”