Utilizing airspace often boils down to an eclectic mix of personalized priorities and strategies.

By Penelope Grenoble O'Malley

That's the end-all and be-all of the whole thing: Use the least amount of airspace possible to get the same amount of trash in the hole. —Mickey Cereoli, Bomag Americas

It's not just digging a hole and throwing stuff in. You've got to do it right ... —Lesley Bailey, Al-jon Inc.

Although we might deny it, it seems the more complex the problem, the more we aim for a one-stop solution. But a challenge as complicated as managing a landfill to maximize airspace requires balancing constantly shifting priorities. Just when you think you've got your ducks lined up, something intervenes and they scatter. "Perhaps," says Abdul Mulla Saleh of Camp Dresser & McKee in Tampa, FL, "you're taking in 200 tons a day and everything's going fine, then all of a sudden you're getting 300 tons a day. More fresh waste means more decomposition and more gas and the next thing you know you're rethinking your alternative daily cover."

Maybe the weather changes and litter ends up on lawns 5 miles away—or the residential neighborhood down the road has grown 5 miles closer. Maybe the new guy on the compactor doesn't take his job as seriously as he should, but you have no way of verifying the effects of his lackadaisical attitude. The truth is it's all related. The wrong cover laid down incorrectly can affect your compaction rate, which affects density, which in the long run can affect the way a landfill subsides, which affects, guess what? And not only are there no one-size-fits-all solutions, it seems personal preference, in league with operational circumstances, often ends up the prime decision-making driver.

"A lot of people talk about compaction," says Mickey Cereoli, national sales manager for landfill and stabilization for Bomag Americas, "but a lot of people confuse compaction with compression. When you compress something you're doing nothing more than squeezing it together by exerting an excessive amount of weight. Typically when you release whatever's holding what's been compressed, it pretty much jumps back to its original size.

"Trash only weighs 400 to 600 pounds a cubic yard in its normal state. We'd ultimately like to put this away at somewhere between 1,400 and 1,500 pounds per cubic yard, which means we're going to want to reduce what we've got about 3 to 4:1, and make it stay that way without bands or ties. To do this we have to break the material down and manipulate it to where it fits together better and penetrate it with teeth to constantly tuck it in. There's no natural way to make four milk jugs fit next to a sheet of plywood tightly. Simply putting weight on it by rolling over it won't do."

It's the interface with the trash, Cereoli reminds us, that counts. "The functions you want from your compactor wheel are demolition—breaking up larger pieces—and traction, which is vital, especially when you're working on slopes," says Lesley Bailey, vice president of sales for the Solid Waste Division at Al-jon Inc. in Ottumwa, IA. "Taller teeth are definitely a trend, 8 to even 10 inches. The position of the teeth is also important, closer together for C&D [construction and demolition], farther apart if you're going to be in something that's soupy or sticky like MSW. More cleats give you better wear life.

"Trash is not a consistent medium. You can have one wheel on a telephone pole or concrete, another on a bag of wet, sloppy trash. So you need both demolition and traction." Nor does Bailey think bigger is always or necessarily better. "What we're seeing is a trend toward heavy but maneuverable machines with enough power to handle whatever daily volume is coming in. A smaller machine with a 48-inch wheelbase produces more ground pressure than a heavier, bigger machine with a 55-inch wheelbase, which by virtue of its larger wheel size doesn't produce as much ground pressure."

But Waste Market Manager Murl Kelley at Caterpillar Inc. notes that too narrow a wheel can also work against productivity. "Let's use an extreme example. Say I replace a 55-inch wheel with a 24-inch wheel. The theory for doing this is the weight of the machine is spread over a narrow width, which will give you higher density. But the problem is you haven't covered all the trash. What you want is a wheel width that matches the weight and horsepower of your machine. Also, if you've got too narrow a wheel, you can sink in to the point that you're dragging the belly pan across the trash."

What comes next is good operational techniques. "Keep the working face as small as possible," Bailey says. "If you're got material spread all over, you're not going to compact it as well, regardless of the kind of equipment you're using. Use equipment that's matched to a site. A huge machine on a small face is only going to cause traffic jams and won't be able to maneuver."

"Compaction is the action, density is the measure," says Mark Williams, head of research and development for Systems Development at GeoLogic Computer Systems in Saranac, MI, which provides a range of landfill hardware/software solutions. "There's no measurement associated with compaction, whereas density is the number of pounds of trash you can fit into a given cubic yard. The ability to measure density as you're working can increase your capacity between 10% and 20%, which can sometimes save a landfill."

To compute density you need to know volume and weight. To achieve the proper density requires the right lift thickness and the correct number of passes. Conventional wisdom has it (and in this case it happens to be right) that the amount of trash compacted in a given space is a function of how many passes the compacter makes and the thickness of the lift. "On the first pass we get a certain performance for the wheel and the tooth and the weight because we have the footprint of all four wheels supporting the weight of the machine," Kelley says. "The second pass we have less of that footprint supporting the machine, the third even less. On residential trash in the United States, more than four passes is probably a waste of time. On the first pass you're getting 80% of 100% maximum density, the second pass you're probably getting up to 85%, the third pass, 90% to 92%, and the fourth pass you might not get any more increase than 1% or 2%.

"If you've got all the time in the world, the best thing you can do to achieve maximum density is thin lifts, the thinner the better. Work on a level slope and make more passes." While Kelley wants to see lifts of no more than 2 feet, Williams would like 1-foot lifts, which he says contribute to increased density in more ways than one. "I can tell you we've measured many, many landfills and most of what we see is differential subsidence. You drive over it with an ATV equipped with GPS [global positioning system] and you see it's settled more in one area than another. Maybe the moisture content was better when you were working in one area. Maybe you got better compaction for some reason. Maybe whatever was coming in on a given day was better. But if you could reach this point of what I call practical refusal every day—the point of declining returns from your compactor—you'd have a better chance of having subsidence that's equal. And here's the point: You may not only get a higher density out of the trash, but you could actually increase your volume because you know how much the landfill is likely to settle based on your daily measurements—and you can fill to compensate for that."

At Camp Dresser & McKee, Mullah Saleh agrees that when it comes to filling up the space, you have to take into account both initial and settled volume. "If you don't compact the material well, that volume may settle in the future and you won't get the density you want when you put more trash on top of it."

The experts agree that GPS-equipped dozers and compactors are the way to uniform compaction, increased density, slope maintenance, and consistent subsidence. Sometimes referred to as machine control, GPS systems that have been adapted for landfills such as Caterpillar's CAES (Computer Aided Earthmoving System) originated in the grading and excavation industry. "GPS increases the operator's efficiency to know where he's been and how many times he's been over a given area," Kelley says. "Because he can't really eyeball it as well as he thinks, particularly if other people are on the same trash. We see this as providing a better tool for management than building a bigger machine or putting funnier-looking teeth on our wheels. It's a way to get more out of your machines. We also see landfill managers using GPS for excavation. Each site seems to have learned where it's the most valuable for them: engineering and design, maximizing density and management of the machine on trash, or controlling cover material and the working-face slope."

Bruce Carlson, president of Carlson Software in Maysville, KY, which designs machine-control software, agrees. "The real challenge I see in landfills is slope control," he says. "The designers typically do a good job in designing the slopes to get maximum airspace, but building them to that design is what's critical. Any time you get more gradual than the maximum slope you're trying to hit, you're hurting yourself.

"We advise clients to go to machine control so they can get real-time information on the compaction they're actually doing," Carlson continues. "Sometimes with one pass you'll drop the width of your forearm, the next pass the width of four fingers. GPS is accurate to about the width of one of your fingers. It allows you to see that you've not gone down as far as you thought you did on a given pass, or that you've got as much compaction as you're going to get and you're wasting time doing anything more.

"We're talking about real-time GPS, where you have a base at the landfill office and a rover receiver and antenna mounted on the compactor. Software like ours does the analysis for you, coloring the number of passes, detecting and presenting how much you're dropping. One person using a computer can monitor multiple pieces of equipment. And although your idea may be that six passes will do it, maybe your GPS data will tell you you're not going to get the last ounce out until you do seven."

"When you compress a landfill," Williams says, "you would like to have the way it implodes or falls in on itself controlled. You don't want one area falling in faster than another, because this deforms the surface of the landfill, which you then have to repair. If you build a history of what you're doing by using GPS, you can project settlement."

Bill Anderson, engineering manager for the Rhode Island Resource Recovery Corporation (4,000 tons a day, 98% of the state's waste) says he can't see running a landfill without GPS. "It's a time saver … it's an air saver. You survey in the morning, you survey at night, you know how much tonnage you took in a day, and you know your density and your occupied airspace. With the back pack units we have we can tell within centimeter accuracy where we are on the landfill and project volumes." Anderson now uses his annual flyover for long-term planning and is also looking at machine control. All new compactors and dozers will come equipped with GPS.

Williams reminds us that compaction is only one part of the density equation. "Obviously, daily cover is a waste of airspace," he notes. "Reduction of daily cover by any method—tarps, foams, slurries, films—is a positive."

Mullah Saleh agrees. "ADC [alternative daily cover] will enhance the capacity of the landfill. The key is to be flexible and change with conditions," he says

"By now most people are familiar with alternative daily cover," says Monica Kuhlman, territory manager for Rusmar Inc., which manufactures foam. "Now landfill managers are mixing and matching, depending on what their needs are. One size can't fit all. Foam, for example, is very good at controlling odors and VOCs [volatile organic compounds]."

"Effectively, what ADCs do is offer the possibility to increase density and save space," says Tony Knight at New Waste Concepts in Perrysburg, OH, which offers biodegradable slurries made from polymers and recycled fibers. But trading soil or dirt for space is not enough as far as Knight is concerned. "Operationally, it's not just the 6 inches of soil you're going to save. Let's assume 1,275 pounds per cubic yard as a pretty good average, and 6 inches of soil. With this, what you're going to get is 75% compaction. Add to this the assumption that you're going to spend four hours a day getting the soil to the working face and an hour and a half at the end of the day spreading it over the 10,000 square feet. Plus labor costs. So at the end of the year you would have used 57,777 cubic yards of soil, which you could convert into 36,883 tons of waste multiplied by $32 a ton. So in one year that 6 inches of soil uses up 1,178,667 dollars' worth of airspace."

For most managers, the logic of ADC often takes priority over economics. Bob Jordan, solid waste manager for the Fairbanks, AK, regional landfill, was looking to replace gravel he had to buy for cover. The landfill has a number of challenges, including seasonal tonnage and extreme weather. Currently a 20-acre active cell, Jordan estimates the landfill takes in about 85 cubic yards a day, for 100 tons a year. After experimenting with tarps, which filled up with snow, and foam, which he rejected because of harsh winter conditions, Jordan settled on EPI Environmental Products' biodegradable film as daily cover on his active MSW cell, while continuing to use gravel on his construction and asbestos cell. "Theoretically, we're supposed to have 6 inches of gravel. In reality it's probably 7 to 8 inches in one place and 4 inches in another," he says. "The cost of the gravel and the cost of the EPI product are about the same. The advantage is the space savings. The less gravel I use the more room I can allocate for the garbage that generates revenue."

Jordan says it's difficult to lay the film in cold weather—12 degrees below zero Fahrenheit—and this year's protocol calls for switching back to gravel at 20 degrees. Wind can also make it difficult to lay the panels but it's not impossible with the right amount of ballast (Jordan uses gravel) and the right technique (into the wind).

At the Allen County Landfill in Kansas, Director of Public Works Bill King selected Central Fiber Corporation's Topcoat hydromulch to replace the dirt he was trucking in—and because it keeps newspapers out of revenue-generating space. "Our local chamber of commerce does a paper drive, and every month or so we haul a load of the material to the Topcoat facility where it's manufactured. We provide the transportation, the civic group gets the money, and we keep the newspapers out of our landfill." The Allen County Landfill is a quarry, so lugging in cover was time-consuming and expensive. "You're looking at a $300,000 machine, $7,500 an hour for the machine and operator. Topcoat may cost me $100 a day. It's effective for vector control and for airspace—that's the trick."

In Louisiana, Don Breaux of landfill Solutions LLC in Baton Rouge has 15 of Louisiana's 23 landfills using Waste Cover marketed by Finn Landfill Solutions, a newly created business unit of the Finn Corporation in Fairfield, OH. Finn has just rolled out a full-service line of ADC, odor control, erosion control, and dust control products and equipment. For doubting Thomases, Breaux calculates the value of the facility's airspace, then persuades managers that the 6 inches of dirt they're using amounts to x number of cubic yards of "non-revenue generating space." Breaux says that, typically, his customers are doubling the life of their cells. Waste Cover is a one-bag spray-on system already on the market, but Finn's new ADC product, Enviro-Cap, will be a two-bag product. ADC materials will be contained in one bag, leaving the landfill manager the option of buying the filler locally. Gordan Riddles, Finn national sales manager, says the company aims to be a total solutions supplier, coaching managers to use their mulch-spraying equipment for other applications.

In Bowie, TX, Bowie Industries sees ADC as an up-and-coming market, and has recently come out with a specially designed hydroseeding machine for the landfill industry. Equipped with airplane tires and easily pulled behind a bulldozer, the unit is a stripped-down hydroseeding machine that will cost the same as the conventional model. Sales Manager Larry Barch says he's already sold machines in "dirt-poor" Iowa, where landfill managers are making ADC a priority.

While it doesn't appear conventional compaction and densification strategies will get a run for their money anytime soon, alternative options for increasing airspace are in the works: landfill mining, obviously, along with accelerating decomposition, and balefills in which the trash comes to the landfill compacted into neat cubes. "It's simple," says Richard Harris of Sierra International Machinery LLC in Bakersfield, CA. "They've been doing this kind of waste handling in Europe for decades because they don't have the luxury of space we've had in North America. What you have is a uniform cube every time, which is much more dense because the baling unit exerts maximum pressure each and every compression. In traditional landfilling you might instruct your operators you want an eighteen in. lift and to run over it five times. And this may occur when you're right there on the spot. But when you're not, they pile up 36 inches and run over it once or twice."

The Monmouth County Reclamation Center in western New Jersey (100 acres, permitted capacity 3,500 tons a day, on average 2,000 tons daily) is this county's largest balefill and has been balefilling since 1997. Always a progressive operation, the county originally shred its waste. "Our shredding operation needed to be upgraded and a public referendum tuned down a resource recovery facility, so we went to baling," says Acting Superintendent Chris Murray. "Baling gave us comparable size reduction, which was our priority. Our curbside recycling throughout the county is pretty good so we dispensed with our original effort to sort out recyclables. Loads are taken in at a tipping facility where they're processed through one of our four conveyors, then into one of the four balers, then loaded onto county-owned trailers and taken to the landfill where the bales are pressed into place using the clamp of a Gradall, which fits them tightly into the landfill.

"One thing I've discovered is our settlement is not as differential as you get with a conventional landfill. If you follow a contour line along a slope and compare it with the prior year, you'll see the settlement is almost one to one. Right now we're staring a program of recirculating leachate and we've found the way the bales go in helps in placing the system. We're also projecting that we'll have less problems with the piping systems creating pockets or watering conditions because settlement is going to happen on a more uniform basis.

"Daily cover is reduced dramatically. We only have to put cover on top of the cell. We go three bails high, roughly 12 feet, and on the top of each cell we put about a foot of daily cover. We use clean sand. When you place sand with traditional landfills, you see that it kind of fills in the voids and so on. When you balefill the sand stays crisp and you grade it right off. On the vertical face, which is basically the advancing of the working face, we foam with Rusmar foam, which has a long duration. They did a lot of research and development with us to come up with something that would adhere to the vertical face. We spray it on at the end of a given day and it has a multi-day coverage capacity."

Murray cites the factors that have made the baling operation effective for Monmouth County: the fact that housing is moving toward the landfill, the landfill's goal of maximizing compaction, and the fact that managers had the track record of the shredding operation to compare to. "There are costs involved, the processing for one thing. Anyone considering it would have to do some level of cost/benefit analysis. We mitigated a lot of the litter you traditionally see with conventional landfills. In a rural area this might not be so important." Murray says next up is evaluating the idea of using ground recycled glass as daily cover, based on processing that makes it shard free and 100 times more permeable than sand.

"Overall," says Harris about the Italian-made Macpresse balers Monmouth County is using, "we're looking at $7 a ton for a balefill and $18 a ton for conventional landfilling. And this doesn't reflect what can be made from recyclables. St. Lucie County, FL, is making enough money off its steel recyclables to pay for the day laborers sorting them."

The baling operation, which takes in 600 tons of Class 1 waste a day, has extended the St. Lucie landfill 20 years. Liquid from the baling process is collected and circulated through the landfill. Like Monmouth County, the St. Lucie facility uses foam as ADC.

Other alternatives are in the wings. At Rusmar, Kuhlman describes a Michigan land mining operation that is accelerating decomposition by mining recyclables and replacing them with sewage sludge (lining the sides of the trenches with Rusmar foam to reduce odor) then refilling with solid waste. And at CDM Mullah Saleh describes a theoretical project that was dropped when a conventional operator bought the landfill site for which it was being designed, but which he thinks may be an ultimate airspace saver. "The project was to have been in four phases, each one about 50 acres or so," says Mullah Saleh. "The idea was that you filled the first 20 or 50 acres, then moved on to the next one and so on. By the time you reach the end, the first phase would be 20 years old and you would go in and recover it—of course you will have a leachate collection and extraction system—then you'd move on to the second phase, and so on. What you would end with would be a perpetual landfill."

Journalist Penelope Grenoble O'Malley is a frequent contributor to environmental publications.

MSW - November/December 2004