The landfill industry has accepted alternative daily cover as a normal, often expected component of progressive, modern operations.

By Neal Bolton

Certainly, based on the economic benefits of saving airspace and reducing soil costs, alternative daily cover (ADC) makes sense. In fact, finding a modern landfill that wouldn’t save money by using ADC would be about as difficult as finding a landfill that didn’t have birds or litter.

And that leads us to another aspect of ADC that has often been overshadowed by the issue of airspace. In many cases, ADC can also provide significant environmental benefits for landfills. Remember, the original purpose of daily cover was not simply to put dirt on garbage, but to use cover soil to accomplish several environmental objectives including the prevention of litter, fires, dust control, disease vectors (i.e., flies, rats, mice, etc.), birds, odors, and infiltration (i.e., rain or snow).

Also, from a subjective standpoint, cover soil helps keep landfills looking sanitary.

It is these things that daily cover soil—or ADC material—has historically accomplished. So why then is the justification for using ADC so often based solely on its ability to save airspace? Probably for the same reason that we solicit bids for liners, tractors, and engineering services—because in the competitive landfill market, money talks. And it is saying, “cut costs, be competitive, or go out of business.” And so, the primary focus comes back to saving money.

That’s all fine and dandy, but if that’s our only perspective, we’re leaving too many other perks on the table. Let’s back up a bit and evaluate ADC from a broader perspective. When we do, we may be surprised to find hidden benefits, some of which may even help contribute to a better bottom line.

We’ll start by reviewing some of the various types of ADC materials used by landfills

Types of ADC
There are many types of ADC. Some are manufactured specifically for use as ADC while others are simply a by-product of some other process. Manufactured ADC materials include tarps, film, foam, and sprays. Other types of ADC include ground up or shredded green waste or wood waste, chipped tires, residual wastes (i.e., auto shredder fluff), inert wastes, certain types of construction and demolition waste, contaminated soil, and a host of other materials.

Tarps
A variety of ADC materials fall under this heading. Most tarps are constructed of woven or non-woven material and are available in several widths, lengths, and thicknesses to match a specific landfill’s need and budget. Some tarp manufacturers also offer tarps in different colors, like green and brown, to help minimize their visual impact.

There are several methods of placing tarps. Some landfills, especially smaller landfills, place tarps manually by dragging them into place with a machine and perhaps pulling the edges by hand. This is a very inexpensive way to place tarps, but dragging them across trash will shorten their effective life due to rips and tears. Safety issues related to medical sharps, nails, and other hazards may also arise if workers are required to walk on exposed trash. Landfills that have an excavator may use a spreader bar to place tarps. This method is safer and less likely to damage the tarps. However, it also takes a bit of finesse to place them, especially when it’s windy.

One of the safest and most efficient methods is to use a mechanical tarping machine like the ones manufactured by Tarp-O-Matic or Mercer Motor Works.

While tarps offer the benefit of repetitive use, some landfills prefer to use film-type ADC for exactly the opposite reason.

Film
Many landfills prefer to use film as ADC because it offers many of the benefits of tarps without the need to remove it every morning. Being able to leave the film in place saves time and allows the crew to immediately begin placing waste as it arrives the next morning. Using film also eliminates certain problems associated with removing tarps.

For example, Bob Jordan, solid waste manager of the North Star Borough Landfill in Fairbanks, AK, cites difficulties in removing snow-covered tarps as one of the reasons they prefer to use film.

Sprays
Like film, spray-type ADC offers the benefit of being a one-step process. It goes on and that’s it. There is nothing to remove the next morning. Sprays offer the added benefit of being able to reach areas that might be inaccessible for tarps, film, or foam machines.

There are a number of spray-on ADC products available for landfills. These materials are mixed with water and then sprayed on the surface of the trash in much the same way that hydro-seeders apply seed, mulch, and/or chemicals.

Spray materials can consist of cellulose fibers, cement, and/or a variety of other non-hazardous chemicals depending on the manufacturer. Some landfills have modified the recipe to meet their site-specific needs.

Foam
Foam-type ADC is applied directly from a track-mounted unit via a series of nozzles on a spray bar. Foam offers many of the same benefits of spray-type ADC, but the foam application process is less affected by high winds.

Processed Waste
When it comes to various types of ADC, the greatest diversity falls under the category of processed waste. Processed waste includes ground up green waste, wood waste, shredded tires, auto-shredder waste, and other waste materials.

All ADC materials can save airspace and minimize the amount and cost of soil used for daily cover. However, when it comes to the ability to meet the environmental requirements of daily cover, there are differences.

Environmental Performance
We’ve looked at various types of ADC, but let’s examine how these materials perform in terms of preventing the environmental problems listed earlier. To do this, we’ll discuss some general pros and cons of different types of ADC and also look at some specific examples of how certain types of ADC perform under a range of conditions.

Litter
One of the primary uses of daily cover, and of course ADC, is to prevent litter. In that regard, virtually all types of ADC will prevent litter by simply covering the waste. However, a more revealing question may be: under what conditions does a particular landfill produce litter and what type of ADC might be most effective at preventing it?

Wind
Afternoon Winds. For a landfill that has predictable afternoon winds, one important requirement of any ADC would be that it could be placed in stages. That way, as portions of the daily cell are completed, they could be covered immediately to keep the open face as small as possible. Under these conditions, an ADC material requiring little or no setup effort would be preferred. Wood waste, green waste, or other bulk material that could be stockpiled adjacent to the cell and then used little by little throughout the day would work well. So would any ADC material that didn’t require repeated mixing or multiple mobilizations.

Morning Winds. On the other hand, for a landfill that has predictable morning winds, the most vulnerable period---in terms of litter---would of course be in the morning. In this situation, using an ADC material that didn’t have to be removed avoids exposing the landfill to those morning winds. This doesn’t mean you couldn’t use tarps. In fact, the tarps could be removed in stages. But in terms of keeping the litter in its place, a sacrificial ADC material would be best.

Fire.
There are many potential causes of landfill fires. But regardless of how a fire starts, one of the major risks is that it will spread across the surface of the landfill. One of the primary purposes of daily cover, and thus of ADC, is to minimize the risk of such a fire. Soil will of course prevent—or at least slow—the spread of fire. But what about ADC?

Many types of ADC are fireproof. Some are fire resistant. Others are perhaps more flammable than the waste itself. Let's take a look.

Fireproof ADC materials include contaminated soil and some forms of C&D, such as concrete or stucco. Most foam material is noncombustible, as are some spray-on ADC materials. Many of these materials simply will not burn.

Some films, tarps, and spray-on ADC materials are only fire-resistant to varying degrees and, under the right conditions, will burn.

Finally, chipped or ground up wood waste, green waste, or other organic material can be very flammable. Some sprays or tarps may also be quite flammable.

When considering the fire prevention aspects of different ADC materials, there are two issues: how great a risk does fire pose to your landfill and how serious would it be if a fire occurred?

While it’s true that any landfill could have a fire, some are much more susceptible than others. I’ve conducted surveys showing that some landfills may have several fires per year, and others go many years without a fire. Similarly, some landfill fires are relatively inconsequential, while others are disasters. Management style or operating policies are often important factors in the frequency and seriousness of landfill fires. These things should be considered when selecting a specific type of ADC.

Tarpomatic's Automatic Tarping Machine

Risk and Consequences. At a landfill where fires are rare and the risk of serious complications is low, a fireproof ADC may not be necessary. In this situation, other characteristics such as the ability to shed water or minimize odors may outweigh the slight risk of fire. On the other hand, for a landfill with a history of frequent fires and the potential to cause lots of damage (i.e., upwind of a residential or commercial area), selecting a fireproof ADC material might be the top priority.

Yes, I know that all landfill fires can be serious, but so can other things like infiltration, litter, odor, and birds. In this real world in which we live, there will be trade-offs. It’s up to the landfill staff and regulators to decide what those trade-offs are.

One landfill uses processed shingles as ADC. As you might imagine, this material offers little in the way of fire protection, but the trade-off is that this material discourages wild pigs from rooting around in the landfill at night.

Dust Control
Dust is another one of those things that can slide up or down the priority scale, depending on a landfill’s history, location, and local reputation. Virtually all types of manufactured ADC products do a good job of controlling dust. Most of the dust problems associated with ADC occur during the processing and placement of wood waste, green waste, or C&D.

Disease Vectors
The ability to prevent disease vectors is one of the most important criteria of daily cover and of ADC and, along those lines, virtually any type of ADC material can do the job. But no, you can’t get by this issue either without stepping into a gray zone. Let’s consider some scenarios that might get you leaning one way or another in terms of your ADC choice.

Duration. On a short-term, overnight basis, most types of ADC will prevent disease vectors due to the simple fact that the surface of the waste is covered. However, some folks might be interested to know that alternative daily cover is often expected to perform for longer than a day. It is not uncommon for cells to be covered only with ADC for a week, two weeks, or longer as part of a landfill’s alternating, back-and-forth fill pattern. In these cases, some types of ADC will perform better than others when it comes to preventing disease vectors.

If your operation depends on using ADC for longer than a day or two, you may want to improve its long-term performance by changing the type of ADC you use. You may also use thicker tarps or film, or consider applying a thicker layer of spray-on, foam, or waste-derived ADC.

Species. In some instances, a landfill may be focused on preventing a particular species of disease vector that has been problematic in the past. For example, some waste-derived ADC—wood waste, green waste, tires, etc.—may have enough voids to allow fly larvae to freely develop and emerge if given enough time. If preventing flies is your priority, you’d want to select an ADC material that provided an impenetrable surface. Options may include tarps, film, foam, or sprays. A fine-grained material such as contaminated soil or ash may also work.

Conversely, mice or other similar vermin may be able to access the trash through or under various types of ADC over time. In these cases, you’ll want to select a material that provides a barrier that can’t be chewed or dug through.

For larger critters like skunks or coyotes, you’ll need a substantial barrier that they can’t crawl under or rip through. In these cases, weighted tarps, or coarse C&D may work best. Again, you’ll have to match durability and effectiveness to the species of disease vector you’re dealing with.

Remember, flies, rats, coyotes, and essentially every other disease vector, are coming to your landfill because it provides a food source. Trash will always contain food. To discourage vectors, you must make accessing it so difficult that it’s not worth the effort. Be creative. Change the thickness, schedule or method of placement. In some cases you may not need to change the type of ADC you use, only the way that you use it.

Birds
Birds typically don’t represent a specific environmental threat, but they sure can make a landfill look unsanitary. When used properly, most types of ADC will discourage birds by providing a barrier between the birds and the food they are attracted to. Some landfills report that, over a period of days, some persistent birds may get through film or spray-on ADC.

Odors
All landfill's produce odors, but not all landfills have odor problems. The difference depends on perception. If local residents and downwind property owners are complaining about landfill odors, or if the landfill has received regulatory violations for odors, then there is an odor problem.

When it comes to preventing odors, not all ADC materials are created equal. Green waste, wood waste, chipped tires, auto shredder waste, and other types of porous ADC material are relatively ineffective at controlling odors.

However, before you rush out and change to another type of ADC in an effort to solve your landfill’s odor problem, it's a good idea to make sure that you've clearly identified the source of the odor. While it is true that the active face can be the cause, odors are often a result of leachate seeps, leachate storage ponds, an inadequate landfill gas control system, or improper management of certain types of inbound waste such as sludge, cannery waste, or dead animals.

Odors are most effectively controlled by ADC materials that provide an impervious cover. These would include foam, film, and some types of tarps and spray-on ADC. For maximum effectiveness, foam and spray-on material must be placed so as to assure full coverage.

Despite the fact that most ADC users began using ADC to save airspace and minimize soil use, they often benefit in other ways. For example, according to Jordan, “We have been using Enviro Cover [manufactured by EPI] film material as ADC for the past two years. Our primary purpose was to save airspace and minimize our use of cover soil.” However, he also states that, “from an operational standpoint, it takes less time to cover with film.”

At the North Star Borough Landfill, odors are not an issue. And while the lack of odors could not be attributed directly to the use of film, its odor-containing ability is much greater than the gravel that they otherwise used for daily cover. Maybe there is no odor problem because of the ADC … or maybe there just is no odor problem period. In either case I say if it's working, don't mess with it.

Infiltration
Infiltration of water into the waste can contribute to a landfill’s leachate problems. Certain types of ADC material can do a much better job than soil at preventing infiltration. According to ASTM D 6523, “certain foams can shed water during moderate rains, once cured.” So, too, will some spray-on materials. In order to be effective, these materials must be applied so as to provide complete coverage. Some users of spray-on ADC report having to spray from two directions to obtain full coverage. Of course this would depend on the type of trash and the amount of effort put into finishing the surface of the cell. The smoother the cell’s surface, the easier it is to cover with spray-on ADC.

This ASTM spec also states that film sheds water “effectively” and tarps shed water “very effectively.” If you use film or tarps, and if preventing infiltration is a priority, remember to place these materials so that the seams run vertically (up and down slope). If you must have horizontal seams, be sure that they overlap like shingles so that the water can run off.

When selecting an ADC material for a specific purpose, make sure that you don't become so focused that you ignore other important issues. For example, a landfill that receives lots of precipitation may consider an ADC material’s ability to prevent infiltration to be the top priority. Along those lines, it may be tempting to use film, tarps, or other impervious material exclusively. And, while this may certainly minimize infiltration, it could also expose the landfill to other risks, such as a fire.

EPI's Enviro Cover System

To ensure that you are not barring the front door from one environmental issue while leaving the back window open to another, it’s a good idea to discuss your ADC choices with other landfill operators, regulators, and consultants. Strategize. Look at your landfill’s strengths and weaknesses. Consider using more than one type of ADC so that you can maintain an edge as the seasons or conditions change.

Performance Standards
When it comes to environmental protection, remember that the initial goal of daily cover was not simply to require landfill operators to put dirt on trash. The foundational intent was to minimize or prevent the environmental problems we've been discussing.

In that regard, as you weigh the pros and cons of various types of ADC, remember that you are dealing with performance standards. Keep an open mind in regard to what might work best for your landfill. According to Bob Jordan, “It was the employees that brought the Enviro Cover system to our attention.” And certainly it makes sense that the folks who work at the landfill every day will have a good idea of what the issues and priorities are.

The A to Z
Matching site conditions and environmental priorities to one or more specific types of ADC can help a landfill perform better environmentally, while at the same time accomplishing those original goals of saving airspace and using less soil. If you’re going to use ADC, it makes sense to select one that offers the most benefits.

Neal Bolton is a consultant specializing in landfill operations and management. He is principal of Blue Ridge Services in Atascadero, CA, and author of The Handbook of Landfill Operations.

MSW - September/October 2005