From closets and kitchens to land in Manhattan and coastal communities, it seems there's never enough space. And, making the most of what's available has become a science.
Just ask any landfill operator. When it comes to maximizing landfill airspace, they often rely on the usual suspects: compaction fleets, efficient use of daily cover, GPS and bioreactors. But it's how operators combine those techniques and adapt them to their specific circumstances that keep things interesting.
The Right Machine for the Job
Of course, using the proper equipment remains one of the most effective ways to maximize compaction. After all, you wouldn't send in a gardening spade to do an excavator's job. Just ask the crew at the Ames Environmental Landfill, a 21-acre construction and demolition (C&D) debris landfill in Ames, Iowa, that accepts approximately 12,000 tons of waste per year. With the landfill nearing capacity in 2005, site officials began looking into replacing the loaders they were using both to spread and compact the waste.
After being granted a vertical expansion, they purchased a used Terex Trashmaster 370 compactor. One year later, the site upgraded to a new 390E model from the vendor. Monica Fedeler, who manages Ames Environmental's office, says the compactors have extended the life of the landfill — which otherwise already would have closed — to 2010. “We would have a lot more life left to the landfill if we would have switched [to compactors] earlier,” she says.
The change resulted, in part, from the weight, wheel design and single-pass coverage that helped better compact the material, Fedeler says. And because the compactor crushes the C&D debris so finely, the landfill also now uses approximately 60 percent less dirt as a cover. (The site applies a thin layer once a week.) The denser compaction also has reduced the amount of shingle wrappers and paper blowing around the site by about 90 percent, she says.
Responsible for overseeing 36 landfills across the country on behalf of Folsom, Calif.-based Waste Connections, Scott Schreiber relies on an array of heavy equipment that includes products from Al-Jon, Caterpillar and Bomag to get the job done. Typically, a bulldozer will sweep the load from the tipping face to the working face, where the waste is spread into a 1- to 2-foot layer. A compactor featuring steel wheels with thick cleats and chopper blades will pass over it three to four times, moving in different directions. Schreiber, director of landfill operations for the company, notes the larger landfills have a separate vehicle for each stage of the process.
The specific type of compactor used depends on the scale and composition of the site. For a C&D-type waste landfill and sites with a slope, it's a four-wheel configuration. If the area is large and flat, Schreiber prefers a three-wheel configuration.
Probably every landfill manager will say that weight and wheel design are major considerations when choosing a compactor. Yet, there are other, less-obvious features that help to maximize compaction. For Schreiber, general performance is key. “It doesn't matter how big it is if it doesn't run,” he says. “We are looking for high uptime and few chronic repairs.”
Steven Pendry, landfill superintendent for High Point, N.C., always considers a more indirect feature: operator comfort. “We want him to be happy,” says Pendry, who has been relying on compactors for nearly 30 years. “He'll do a better job than someone who's uncomfortable.” So springing for a model with air conditioning may be worth it. Fedeler adds that more modern controls also can make the job easier for an operator and prevent errors.
Pendry, whose landfill consists of about half industrial waste and half residential MSW, also blends the materials for maximum capacity. He estimates the landfill achieves a compaction of 1,400 tons per cubic yard. That figure is based on an annual flyover performed every year. An engineering firm does the calculations as required by the state near the end of June. They calculate the tonnage going into the landfill and then use the topography to determine the density.
To make compaction as efficient as possible, some landfills are also using GPS, which goes a step further toward reducing human error. But many landfills continue to operate without it. “It's definitely worth the investment for larger landfills,” Pendry says. “We just can't justify the added cost.” Ames Environmental also isn't using GPS. Waste Connections, however, is testing the technology at one of its sites and is considering extending it to other landfills.
What Lies Beneath — and On Top
For operations that already are satisfied with their equipment, there are plenty of other things they can do to improve compaction. It may not be high tech or glamorous, but Schreiber says the landfills he oversees focus on stripping the daily cover of dirt before dumping any new loads, a process that only takes about 20 minutes in the morning. While he's been employing the practice for years now, he says he still knows of many landfills that do not.
And conserving landfill airspace isn't the only benefit he sees. “When you peel it off, you can reuse it, too,” Schreiber says. “You save money from conserving airspace and soil.”
In general, minimizing the amount of daily cover used can be an effective tactic. According to Schreiber, you don't want the cover to comprise any more than 12 to 18 percent of the landfill based on proportion. Pendry agrees. His landfill uses Tarpomatic tarping machines daily. “They let us start from where we left off,” he says.
Beneath the surface, bioreaction — the practice of recirculating leachate and possibly other sources of moisture — can help decompose the waste more quickly. The U.S. Environmental Protection Agency estimates that bioreaction can result in a 15 to 30 percent gain in landfill space. Increased capacity is just one of the benefits of bioreactors, which can also include methane gas management, better handling of leachate and shorter closure times.
While this technology likely will be more prevalent in years to come, some operators are using the approach now, including Houston-based Waste Management, which is involved in bioreactor projects in the United States and Canada.
Schreiber says Waste Connections also is recirculating leachate at many of its landfills, aside from those in the West. “In the West, there's no leachate to recirculate,” he says. The practice remains more common in areas with greater rainfall, like Florida.
Pendry says bioreaction isn't a possibility for his landfill in North Carolina, because it isn't double-lined. “We rely on nature's own for moisture,” he says. He adds that, fortunately, they rarely get so much rain that it causes a problem for their compaction operations. “That usually only happens after a very heavy downpour.” In that case, the daily workface needs to be “re-established.”
Jennifer Grzeskowiak, a former managing editor of Waste Age, is a contributing writer based in Laguna Beach, Calif.