Landfill compaction dos and don’ts

Effective landfill compaction maximizes the amount of waste that can be placed in a minimal amount of space. In short, it’s all about airspace and density.

It’s also about costs. Failure to maximize airspace shortens the lifespan of a landfill, resulting in added costs related to emissions, water control and the resources it takes to build a new cell with a liner.

“It’s important to look at the lifespan of a landfill,” says Martin Mattsson, director of key account sales for waste and recycling at Sweden-based Volvo. That requires considering limited airspace and getting the right density of material.

Dale Mills, vice president of sales and managing partner for Jeffersonville, Indiana-based Macpactor Inc., likes to use the analogy of stuffing $100 bills into a suitcase to explain the importance of density. “You’re going to try to compact those bills so you can get more in.” Compacting trash at a landfill is like putting “as much garbage in the suitcase as possible.” And, while you wouldn’t want to shred those $100 bills, you can shred garbage for even better compaction.

In addition to increasing landfill space, achieving optimal compaction has many other benefits:

• decreasing operational and labor costs;
• minimizing environmental impact;
• improving safety;
• creating a base for equipment access roads;
• stabilizing slopes by working to eliminate uneven settlement and landslides;
• containing leachate by eliminating low spots that collect water and preventing water from seeping through the cell; and
• reducing fire risk by reducing air pockets.

Bad compaction, on the other hand, shortens the lifespan of a cell. As Mattsson points out, it also impedes the work of gas systems used to fuel fleets and power homes.

So, how do you achieve maximum compaction? Attaining peak compaction comes with some dos and don’ts—as well as some advice from the experts.

The right equipment

In some regions, environmental regulations require compaction, but whether or not it’s required, it’s standard procedure at nearly all landfills. The proper compaction technique includes shredding the material, pushing it to mix and blend it, placing it to fill any voids, and compacting it to maximize space. This requires a small fleet of equipment.

Equipment selection begins with the size and number of compactors needed at the site.

“The number of tons a day, as well as peak tonnage—the busy times of day—determine which model and size of machinery you need,” Mattsson explains. Municipal solid waste (MSW) at landfills has an average density of 550 to 650 pounds per cubic yard, so it’s important to size equipment accordingly.

Some landfills use a steel-wheeled/drum compactor to shred and compact the material in the waste stream. Typically, the preferred minimum operating weight is more than 45,000 pounds. A compactor should not be used on slopes with grades steeper than 25 percent.

While landfill compactors often are equipped with blades that can push large volumes of waste, they are not the best piece of equipment for moving material because they lack grip on loose refuse.

Track-type tractors, or dozers, typically are used to spread thin layers of waste over the working face of a cell and to deposit daily cover. Fitted with steel tracks, they have a better grip than compactors and can also chop and shred waste.

“A compactor is not a dozer, and a dozer is not a compactor,” Mattsson says, underscoring the importance of selecting the right equipment for the job. “A dozer moves and places material; a compactor runs over it and compacts it.”

Although possible to do, compacting with a dozer is not recommended because of inefficiency. Dozers are better at pushing material dumped by collection trucks and spreading layers on the working face.

Tips, cleats, cleat patterns and cleat guards

Mattsson says a properly equipped landfill compactor is required. Volvo offers a purpose-built compactor, the LC450, that can be equipped according to the landfill’s demands. “The material dictates cleats and cleat patterns; that’s most important,” he says.

Some landfills are 100 percent construction and demolition (C&D) or MSW. Others have a mix of materials, including sludge, though Mattsson cautions that residential waste should never be mixed with C&D debris.

C&D requires more cleats to break up the material without wearing out the wheels. Tips should break, separate and puncture the material into the landfill. To get the best results, “you need the right configuration for the weight of the machine,” he says.

Placement also is important. The type of garbage will determine where the pattern of the tip is located on the wheel.

Tips also should have “good height” and be shaped the right way, Mills says. He advises running tips low—4 inches or less— before replacing. Much lower, he says, and you’ll lose traction.

“The compactor slips and uses more fuel. It won’t compact properly, so you’ll lose compaction and density,” Mills says.

Design impacts efficiency. “Some companies build cheap, chopper-type wheels,” Mills says, explaining that this type was the original wheel for the logging industry. “They chop, but they don’t compact due to the big blade that flips the material up.”

For better separation and puncturing, Macpactor builds tips at a natural angle of repose. “Think of a conveyor belt with a pile of sand at the end,” Mills says. “It falls in a natural slope or angle. We build tips at that angle.” Because it’s not a straight-up wedge cleat, chopper or twist cleat (which has a pocket that catches dirt), the material gets off the tip easily.

One thing that doesn’t come off so easily is the wire wrap found in items including fishing line and mattresses. “It’s a big issue because it slows down the machine,” Mills says. “It cuts into the wheels and destroys them.”

Cleat guards prevent material from wrapping around the inside of the wheel. “Other companies use a ‘pizza cutter’ wall to divert material away from the machine,” Mills elaborates. “They have gaps. When big pieces of cable get stuck, they can snap axles. [The] guards work great. Our patented design turns it into a cleat for additional traction, which adds compaction.”

Choice of wheels

The material at a landfill also can guide the choice of wheels. The type of material can vary geographically, as can the soil. Mills notes that clay soil (common in Louisiana) and sludge (water waste) pack on the wheels, creating a smooth drum that doesn’t compact material. 

Reduced wheel width increases pressure and compaction. Therefore, mobile equipment with two drums instead of four wheels is less effective. Reduced wheel size increases pressure but not necessarily compaction. Narrow wheels can break free and spin more easily if the sheer force of the wheel is higher than the compacted waste.

The least expensive wheels cost about $50,000 and last only 5,000 hours, Mills estimates. “Cheap wheels with 8-to-9-inch tips last about 6,000 hours, depending on the type of material the tip is made of,” he says.

Macpactor wheels cost $80,000, but last 12,000 hours or more. “We out-wear other manufacturers two to three times on wheel life. That saves money over the life of the machine,” Mills says.

He mentions one customer who saved $100,000 by buying Macpactor wheels. “It allows you to capitalize on the expense,” Mills adds. “If wheels last 12,000 hours, you can rebuild for half the price.”

The standard for wheel replacement used to be 5 inches. Mills says it’s now 4.5 inches or less—at a cost of $50,000 to $60,000.

Blade types

Dozers that are equipped with large- capacity blades can increase productivity, but there’s more to it than just size. “What kind of blade—straight or semi-U—makes a difference,” Mattsson says.

Macpactor offers a choice of semi-U blades and the M-blade. The semi-U can contain waste within a concave “U” design, helping minimize waste escaping around the sides of the blade and instead directing it under the compaction wheels. It also can position cover material more accurately when attached to a compactor or dozer.

The multiangled M-shaped blade features a strong, rigid construction that stands up to the tough environment.

The safety factor

Increasing landfill density is an important factor in improving safety, both at the landfill and in the surrounding areas, because it reduces fire risk, fugitive odors and rodents.

Safety is a crucial element in the equipment, as well. “Slip-and-fall is the biggest safety issue,” Mattsson confirms.

In keeping with Volvo’s focus on safety, he points out features that are incorporated into its compactor:

• ground-level fuel, filter and service access points for easier and safer maintenance;
• LED lighting; and
• orange handrails at the three points of contact on entry, as well as points to hold while cleaning the windows.

Ultimately, Mattsson says, waste applications are tough for heavy equipment; they should be less so for operators.

The author is a freelance journalist based in Indianapolis. This article was originally published in MSW Management.