With the soaring costs of landfill construction, maximizing a site's lifespan by aggressively conserving airspace is critical. Many jurisdictions now allow landfills to use materials other than space-taking (and often expensive) soil as daily covers. The challenge for landfill managers is to find an alternative daily cover (ADC) that fits into the site's operation as well as into the budget.
ADCs range from green waste and construction and demolition (C&D) materials to tarps, foams and spray-on materials. But while green waste and C&D materials consume landfill airspace and face continual scrutiny, there are many products that have established themselves as viable, cost-effective options for the landfill manager.
Tarps are a straight-forward ADC, providing a solid barrier to odors and vectors. Current tarps have been designed to resist or minimize punctures and tears; they can be laid out over the working face by hand, with a bulldozer, or with specially designed equipment that can roll out the tarp each night and remove it in the morning.
The typical lifespan for a landfill tarp is between a year and 18 months. Depending on the site and its conditions, some tarps may only last eight months and others two to three years. Tarp sizes can range from 25 feet by 25 feet to 100 feet by 150 feet.
The Ventura Regional Sanitation District's Toland Road Landfill in Santa Paula, Calif., has been using tarps as ADCs for nearly 13 years. The landfill receives 1,500 tons of municipal solid waste (MSW) per day, with roughly 80 percent of the trash coming into the site from transfer trailers, says RayMel Lloyd, solid waste superintendent for the district.
The site currently uses a 120-foot by 120-foot tarp from Airspace Saver Daily Cover. The tarp features a cable on its perimeter and is placed on the working face at the end of each day by bulldozers. Site workers tie ropes to the cable so that the dozers are pulling on the cable instead of the tarp itself. “That has helped us tremendously to prevent tearing,” Lloyd says. He adds that it takes about five minutes to get the tarp in place and that the landfill is getting about a three-year lifespan out of its tarps.
High Point, N.C.'s landfill receives about 400 tons of waste each day. “About 10 years ago, we were looking into how to preserve our airspace,” says Steven Pendry, superintendent of the site. “We knew that dirt was not the most efficient way to conserve airspace, so we started looking at tarps. When we laid out all the costs, it didn't take us long to conclude that the tarps were the way to go.”
The landfill uses the Tarpomatic system to place three tarps over a 100-foot by 100-foot working face at the end of each day. The site overlaps the three tarps to prevent the wind from blowing waste material around the site. “It takes roughly 15 minutes to lay the three out and then to reverse the process in the morning, it takes about 15 minutes to take them up,” Pendry says.
Non-hardening foam is a daily cover that is applied directly to the working face of the landfill to create a temporary barrier that can last anywhere from one to three days, depending on weather conditions and application rates. The foam may be applied either with a truck-mounted device or a self-propelled unit, and in a variety of temperature and weather conditions. The foam retains its resiliency and dissolves once heavy equipment begins working over the waste.
The Robeson Landfill in St. Pauls, N.C., uses a non-hardening foam from Rusmar Inc. The site takes in approximately 100,000 tons per year of MSW, says Steve Edge, solid waste director for the city. Using a self-propelled applicator with a 2,400-gallon tank, one worker is able to apply the foam to the working face in about 20 to 30 minutes, he adds.
“We get a lot of seagulls from the coast, and we found that birds will not land on this material,” Edge says.
Spray-on slurries harden after being applied to a landfill's working face and may be used not only for daily cover but for the intermediate covering of working areas as well. Depending on the manufacturer, the products may consist of either a mix of polymers such as the Pro-Guard and ConCover line of products offered by New Waste Concepts or a cement mortar coating similar to stucco, such as the Posi-Shell System offered by Landfill Service Corp.
Collier County, Fla.'s 280-acre landfill receives between 1,300 to 1,500 tons of MSW per day. For daily cover, the site uses a combination of soil and Posi-Shell, says Daniel Rodriguez, director of solid waste for the county. The combination has been effective at keeping odors under control and keeping birds from picking at the waste. “During the summer months, we have a tendency to use a little bit more soil,” he says. “Over the last 10 months, we've recognized in the neighborhood of $600,000 to $800,000 in savings in soil usage.”
Landfills sometimes need to consider more than just daily cover. Often, they need covers on a more interim basis, such as when they need to protect newly constructed landfill cells from rain infiltration or cover cells that are not currently in use, but where additional settlement of the waste may allow the cells to be used again. These covers are sometimes needed for periods lasting between two and five years.
The Millersville Landfill in Anne Arundel County, Md., recently constructed two new subcells, totaling 11 acres. The county originally debated about whether it should build the two cells at the same time, says Stephen Krajcsik, disposal and maintenance manager for the county.
Eventually, county officials decided they would “get an economy of scale by building both together,” he adds. However, that meant that the county would have to protect portions of the newly constructed cells that were not yet in use.
To protect the liners and the leachate collection systems in the yet-to-be-used areas, which feature 200-foot side slopes, the Millersville Landfill uses polyethylene rain-shed covers from Raven Industries. “As part of the construction project, we covered approximately three-quarters of the 11-acre [construction area] with the protective tarps,” Krajcsik says. “The panels came in large segments, and we basically field-seamed them together.”
“We weren't concerned about having them completely water tight,” Krajcsik adds. “We stitched them, sandbagged them, and they were toed in around the perimeter. As we fill [in the space with waste], we peel them back.”
Lynn Merrill is a contributing writer based in San Bernardino, Calif.