Most folks would agree that alternative daily cover is a good thing for landfills. If used properly, it can save soil, save airspace, and ultimately, save money.

By Neal Bolton

That's what you'd call a "general truth." So is saying that you need a shotgun to hunt ducks. But whether you are covering trash or shooting ducks, a general truth won't do. You need to get specific.

If you want to hunt ducks, you'll need to decide where to go, when to go, and who to go with. Will you sit in a duck blind or sneak along a riverbank? What kind of shotgun will you use? Lots of decisions must be made before you can arrive at the desired end result.

This month, many of us in the landfill business will attend WasteExpo. We'll get together, swap stories, and tell each other all we know about landfills. Much of the discussion will be of the general-truth variety. As far as that goes, depending on who's doing the talking, a lot of it might simply be general.

But when you return home and decide to apply some of those general truths you've learned, you'll have to get specific. You'll have to make decisions.

Before you can decide what type of alternative daily cover (ADC) you want for your landfill, or indeed whether you want to use ADC at all, you'll have to evaluate the costs and benefits. And, because the decision might not be entirely based on economics, you will also need to look at the pros and cons of various types of ADC.

What kind of regulatory, environmental, or operational issues must you consider? Do you want it to last for a day, a week, or a month? Are you looking for a short-term economic boost or a long-term investment? Do you want to spray it, roll it, foam it, or spread it? Do you want to purchase a manufactured ADC or find an alternative use for part of your wastestream? Finally, do you have the information necessary to apply a dollar figure and decide what kind of ADC is best?

As you can see, before you can make these ADC-related decisions, you'll have to pass the point of generalities and head into detailed specifics. Here are some ideas to help you get there.

Most ADC manufacturers have a very good understanding of their product. They can explain its particular savings, benefits, and ease of application. And, if they are doing their job, you'll quickly understand all of the reasons why their material has been so successful at other landfills. They'll be able to show you how much airspace and money their ADC product can save at yours. It's a safe bet that, when it comes to ADC, the typical ADC manufacturer/representative knows more about the product than the typical landfill manager does.

This is why, when it comes to selecting an ADC product, many landfill managers turn first to ADC manufacturers for direction. As a result, the landfill's choice of ADC might be based more on what has worked best at other landfills than on what would be best for yours. This is because, while most manufacturers have a very good understanding of their product - its application and benefits - they probably don't know as much about your landfill as you do.

Going to the manufacturer can be a great second step, but it probably shouldn't be your first. Remember, there's a difference between getting the best ADC product and getting the ADC product that's best for your landfill.

Why Use ADC?

Before you select a specific type of ADC, make sure you understand why you want to use ADC in the first place. Doing it because "it's the right thing to do" or because someone said you should isn't enough. Let's talk about some of the reasons that landfills use ADC. View Table 1. ADC Ranking Criteria

Economic Issues

Sure, at most every landfill, saving money is a major goal and a critical part of any decision - including whether or not to use ADC. So how much money can you save by switching to ADC? Let's take a look.

AIRSPACE

As you might have guessed, the most significant economic savings will probably be related to airspace. Historically, most landfills have used soil for daily cover. That soil takes up space that could otherwise be filled with trash. Using less soil saves airspace - and saves money.

Every cubic yard of airspace that's not filled with soil is a cubic yard that can be filled with trash to generate revenue. So doesn't it follow that every cubic yard saved is worth the price you'd sell it for? Not exactly. That calculation must include a deduction of the cost to provide the airspace and an adjustment for the time value of money. In terms of revenue, the benefit of ADC must be based on net revenue. Also, you won't be selling that saved airspace until near the end of your landfill's life. Consider this example:

Suppose that a landfill has 1,500,000 yd.³ of airspace. Of that total, 500,000 yd.³ is earmarked for cover soil and 1,000,000 yd.³ can be "sold" for trash. The facility has 10 years of remaining life (based on filling 100,000 yd.³/yr. with waste and 50,000 yd.³/yr. with soil). If, by using ADC, soil use drops to 400,000 yd.³, then the landfill would have 1,100,000 yd.³ that could be sold for trash - and an additional year of remaining life. Let's also assume that the landfill sells airspace for $16.30 per landfill yd.³

Does that mean that switching to ADC saved the landfill 100,000 yd.³ valued at $16.30/yd.³? Nope. Remember, just because airspace sells for $16.30/ yd.³ doesn't mean it's all profit. We must subtract the cost of providing that airspace.

After subtracting an estimated $10/yd.³ for providing the airspace, the landfill would net $6.30/yd.³ But we're not done yet. Remember, ADC or no ADC, the landfill will be selling airspace for the next 10 years. It's not until the 11th year that it sells the airspace gained by switching to ADC.

Because of the time value of money, getting $6.30/yd.³ in year 11 is not worth nearly that much in today's dollars. Assuming an interest rate of 5%, the net revenue from year 11 is worth about $3.68/yd.³ - or a total of approximately $368,000.

Also, if the landfill plans to construct a liner during its remaining lifetime, then the time value of money may favor a switch to ADC. If by using ADC the landfill could postpone the date of liner construction, then present value of that liner's cost will decrease.

AVOIDED HAULING COSTS

In our example, the landfill would use 100,000 yd.³ less soil. Thus it might appear that ADC would save the cost of hauling that soil. If the soil were located off-site, it would. However, if the soil has to be excavated to make room for the additional 100,000 yd.³ of waste, then the soil still has to be moved and there is still a hauling cost. In that case, switching to ADC might not provide any savings in regard to hauling cost.

As we've talked about the economic benefits of ADC, you might have gotten the impression that I'm trying to downgrade the benefits of using ADC - you know, reducing the savings based on the time value of money, or possibly discounting altogether (in some instances) the avoided hauling costs. But rest assured that I am indeed a big supporter of ADC. The fact is, it's hard to find a landfill that wouldn't benefit from using ADC.

While we're talking about things like airspace and hauling costs, and lest you think I'm serving up the "lite" version of ADC savings, one other thing needs to be cleared up. That is the fallacy of 6 in. of daily cover. Talk to landfill operators, read through federal and state regulations, or look at the assumptions used to justify using ADC, and you'll quickly get the idea that daily cover is 6 in. of soil. If you think daily cover and 6 in. of soil are one and the same, you had better think again.

Most landfills use more than 6 in. of soil for daily cover - a lot more. If you don't believe it, do your own calculation. Here's how:

• Track the quantity of soil you bring in to cover a daily cell. For example, if you bring in 12 scraper loads, each with a payload of 20 yd.³, that's 240 yd.³
• Multiply by 27 to convert yd.³ to ft.³: 240 × 27 = 6,480
• Then calculate the surface area of the cell: Let's say it's 150 ft. × 200 ft. = 3,000 ft.²
• Finally, divide the volume of soil by the area of the cell.
• The resulting answer is the average depth of soil: 6,480 ft.³÷ 3,000 ft.² = 2.16 ft.

If your landfill is like most other landfills, you'll find that you're placing much more than 6 in. of soil. This doesn't mean that you're doing a poor job. It's just showing the difference between theory and practice. It also shows that switching to ADC will save considerably more than a theoretical 6 in. a day.

When it comes to economics, some folks look at cost per square foot. Others look at cost per ton of waste. Still others compare different ADC materials based on cost per day, month, or year. When you get right down to it, the cost units matter a lot less than the assumptions that go into them. If a bull weighs 2,000 lb., 907 kg, or 32,000 oz., no matter how you look at it, it's still a ton of bull.

The key is to compare the costs of various types of ADC in a fair and equal manner. If you use a certain interest rate for financing one type of ADC, use the same rate for all others. Try to standardize the amortization period for each. If that's not possible, bring all the costs back to present value. Learn enough about each type of ADC to ensure that the costs you're using to compare Foam X to Spray Y to Film Z are fair and also that the quantities will actually provide adequate coverage.

But keep in mind that deciding to switch to ADC is not just an economic question.

Other Issues

Many landfills are sold on ADC based on its ability to save airspace and money. Those are important factors, but they are by no means the only factors. The selection of a specific type of ADC will impact more than your bottom line. You might even find that the lowest-cost ADC is not necessarily the best one for your landfill. Let's look at some other important issues.

REGULATORY

Although regulatory agencies typically recognize the advantages of ADC, there is wide variation in regard to what's acceptable - and what isn't. For this reason, start your evaluation of ADC material by talking with your regulator/inspector. But also keep in mind that rules can change and variances are possible. So, even if your preferred ADC isn't allowed under the current regulations, it might  be possible to negotiate a workable compromise with the regulators. Just don't be unreasonable - like the manager of a coastal landfill who wanted to use seagulls as ADC. Nice try.

OPERATING STYLE

Economics are important, regulations impose limits, but every landfill is still unique. Be sure to consider your operating style when selecting an ADC material for your landfill. Local preferences, traditions, and attitudes vary.

Several years ago, I conducted a cursory survey of landfill managers, asking how they selected ADC materials.

One manager said that his landfill used two types of materials: tarps and foam. His reason? During windy conditions, when the tarps were hard to place, the foam could be blown and drifted into place easily. During calm days, they would use the tarps.

Another landfill manager also used the same two materials. Why? During windy conditions, when the foam was hard to place and made a big mess, the tarps could be placed easily by raising one edge and letting the wind lift and set the tarp in place. Go figure.

LABOR AND EQUIPMENT

When selecting an ADC material, consider how it will work in terms of your available workforce and equipment. What machines will be required? How many work-hours will it take each day to apply it? Also, even if you have adequate resources, will the scheduling of ADC placement/removal conflict with other required activities at the landfill?

A landfill manager once told me that he had tried tarps but had to quit because the early-morning truck drivers kept dumping their loads on the tarps. As a result, the tarps were quickly destroyed and discarded.

Another manager of a small rural landfill said that even though his was a one-person operation, he used tarps successfully. When I asked how one person could place and remove the tarps, he replied, "He doesn't have to. The truck drivers remove the tarps in the morning...and then help the landfill operator place them at the end of the day."

DIVERSION

Many materials that would otherwise end up in the landfill's wastestream can be used as ADC. Wood waste, greenwaste, or even construction debris is often used as ADC; in addition to providing a low-cost material, using waste materials for ADC can help boost your landfill's diversion rates.

ENVIRONMENTAL

Landfills are unique and each has its own environmental issues. Matching those issues to a specific type of ADC is important. Remember, there are always pros and cons. You might gain in one area but give somewhere else. Here are some examples of how a landfill might select certain ADC materials to deal with specific issues

Minimize infiltration. A landfill that receives lots of rainfall and as a result generates lots of leachate might decide to use an impermeable ADC material. Although there are materials that can effectively shed water, consider how well they will perform in regard to vector control, fire protection, and cost.

Discourage digging animals. Many types of ADC will discourage animals from digging through to the waste. For example, tarps, film, and some spray products will do a good job of keeping birds out of the trash. Fewer products will effectively keep larger animals from digging through. For discouraging dogs, coyotes, or javelina from digging, greenwaste, woodwaste, or construction and demolition materials (e.g., shingles) are often most effective. Many landfills are having problems with bears digging through the cover. If anyone has a practical solution (other than a bearskin rug), please pass it on.

Reduce odors. If you want to reduce odors, you'll need to select an ADC that can provide a fairly impermeable seal. In this case, shredded greenwaste or woodwaste won't work too well. There are just too many voids. Chances are you'll be looking at tarps, sprays, or film.

Vector control. When it comes to controlling flies, you might find that spray-on ADC products, film, and tarps all work. But depending on the type of waste you receive, how long the ADC is left in place, and the weather conditions, one type of ADC might work better than another.

To help you define what type of ADC is best for your landfill, we've put together a table that can help you rank the economic and noneconomic performance of various ADC materials (see Table 1). This is just an example, and because every landfill is unique, you'll likely want to modify the table to match your specific needs.

To help you get from generalities to specifics, this table has been posted, along with a spreadsheet (to calculate how much soil you are currently using), on the Web site listed here:  a spreadsheet (to calculate how much soil you are currently using) has been posted on the Web site listed here: www.forester.net/mw_0405_airspace_estimate.html.

The Final Analysis

When it comes to ADC materials, there are many options out there. But what's best for one landfill might not be best for another. If you're considering a switch to ADC, start by identifying what your landfill's needs are. Brainstorm with your crew, your engineer, and your regulator. Then talk to ADC users and ADC manufacturers. These folks can provide you with lots of information. And the more you know, the better decision you'll be able to make.

By doing some diligent research up front, you'll enjoy the benefits that come with finding the ADC material that's best for your landfill.

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 - May/June 2004