Landfill Airspace: a Holistic Approach

All landfills are similar; but then again, they aren’t. Some landfills are simply more efficient and more competitive than others. One important characteristic of a competitive landfill is the ability to use airspace effectively-important because it results in reduced operating costs, deferred capital costs, and a more competitive bottom line.

Sure, there are variations in wastestream, site conditions, local weather patterns, and other important criteria, but after filtering through all of those issues, we find that high-performance landfills aren’t competitive by accident; they are competitive on purpose.

They are competitive because someone-usually a manager-has created an efficient system, in much the same way that a skilled coach builds a winning team. Here’s a bit of insight: Great players may occasionally win a game, but great teams consistently win championships. And it’s this kind of team-based, holistic approach that you must adopt if you want to have a competitive landfill.

Every landfill functions as a collaboration between lots of people performing individual tasks that are interrelated. And when each part meshes properly with the others, they work together like the parts in a well-oiled machine.

We aren’t just talking about the relationship between the dozer pushing trash…and compactor packing it. The reach is much broader. Performance in the field-in the form of, say, improving the airspace utilization factor (AUF)-can translate into longer landfill life and better amortization of such major capital expenditures as liners and closure/post-closure. Savings here are then translated back to the operation in the form of better training, more efficient equipment, which further improves the operation and provides even more big picture savings…you get the idea.

Once this process gets going, it becomes a sort of perpetual energy machine-landfill style.

Sounds pretty good, doesn’t it? We’ll look at how these concepts might be applied.

I often tell our clients, “Every day you’re building something, you’re headed somewhere…and, good or bad, you’ll eventually get there. Let’s make sure we’re headed toward the right goal.”

This first requires an understanding of the difference between strategy and tactics.

Strategic Versus Tactical
The difference between defining your ultimate goals and taking the specific steps required to achieve them is the difference between strategic and tactical. Strategic goals establish the big picture of where we want to end up. One example of a strategy might be to position your landfill so that it can be competitive and serve as a regional facility. With this in mind, you have laid out a direction in terms of how much land you’ll need, how much capacity it must provide, type of access, planning horizon, etc. Or maybe your landfill will only serve a small community, so it doesn’t have to be as big or require the infrastructure that you would need for a regional facility. These are strategic plans.

Once you have the strategy, we must determine the tactics necessary to achieve those goals. Both of these things must be done in order for the system to work. You can’t have good tactics if you don’t know what the big picture goal is, and you cannot hope to achieve big picture goals with poor tactics.

To be competitive, your strategy and your tactics must work together.

Integrating all Aspects
In general terms, the plan for a landfill often includes maximizing airspace, extending the life of the landfill for as long as possible and operating safely and efficiently. It also includes doing these things for the least overall cost. Great goals, to be sure, but way too general-and as a result, the buck gets passed around but never really stops.

Let’s take, for example, the goal of airspace consumption, which can be simplified to this statement: “Airspace consumption should be minimized.”

This typically starts as a management goal that gets transferred to the design engineers and, ultimately, to the landfill crew.

But landfills that minimize airspace consumption do so by aligning strategy and tactics. Here’s an example of where to start this process.

Pushing
The process of pushing waste-from where it’s dumped to the active cell-is a critical part of waste compaction. It establishes the tone of the operation by placing the appropriate type of waste in the right location within the cell-at the right time. In this context, the pushing process does affect the waste compaction process.

Let’s first look at the length of the push. Obviously, longer pushes take more time and cost more money (in dozer cost). But those longer pushes also create more mess-a mess that will eventually have to be cleaned up and covered with soil. The result: longer pushes  add up to more soil, and more soil adds up to more wasted airspace.

Another example of how pushing impacts airspace is related to the depth of each layer of waste placed in the cell. In general, thin layers are better than thick layers, because the compactor’s ability to compact waste rests more on the action of the teeth…than on the weight of the compactor. Though both are important factors, placing the waste in thin layers to provide good access for the teeth will result in greater density. So, when pushing, the dozer should spread the waste in thin layers.

There are many other considerations at the pushing stage of the operation-things that will affect how efficiently you utilize your airspace. Here’s another-less obvious-consideration.

Sweep the Deck (Tipping Pad)
Most people think that pushing waste is a simple process-if they think about it at all. You just lower the blade, move forward, and push trash to the face. “Ah, Grasshopper…there is more to the story.”

Consider what happens when a mixed load-containing stucco, shingles, plaster, or sheetrock-is dumped on the deck. These materials are difficult for the dozer blade to gather and push because the pieces are flat and heavy. So, in order to clean this material off the deck, the dozer operator must drop the blade just a bit lower than normal. This cleans the deck, but also causes the dozer blade to scrape soil off the deck…and push it into the cell. And as the deck erodes, more soil is brought in to replace it…and the cycle continues. In the process, airspace is wasted-a surprisingly large quantity.

At a typical landfill, this one scenario can waste several (scraper/truck) loads of soil per day. This can add up to hundreds of thousands of cubic yards of soil-and wasted airspace-over the life of the landfill. Off the shelf, wasted…gone.

This chronic loss of airspace can be greatly reduced by making one simple change. Instruct the spotter to place those “hard-to-gather” loads close to the face-in order to avoid long pushes. And also instruct the spotter to prep those loads by double stacking with a sweeper load-something such as soft trash or brush. This allows the dozer operator to push the prep-load (with the blade held above the deck) and allow the soft load to sweep the messy load into the cell.

As you’re seeing, achieving optimum waste compaction is not just about the compactor…but you sure can’t ignore it either.

Waste Compaction
Your landfill compactor is the single most important bullet in your compaction arsenal. Use it wisely.

While this includes the processes of segregating trash, spreading in thin lifts, etc., most of what you need to know about waste compaction can be boiled down to one simple instruction: Put lots of big teeth into the trash.

Again, like pushing trash to the cell-the concept is simple, but the application is a bit more involved. Here are some ways to put more big teeth into the trash.

Have more big teeth– The first step, logically, is to make sure your machines have more big teeth. It’s surprising to see compactors operating in the trash, when they are better suited to be rolling asphalt. What I mean is this: The teeth are so far gone that you can’t really call them teeth. It’s more like they’re trying to gum their way to compaction density.

There is a rule of thumb: The lifetime cost of a machine can be three to five times the purchase price-let’s call it four times. This includes purchase cost, interest, insurance, fuel, repairs, maintenance, etc. So if you purchase a new compactor for $800,000, it will end up costing you $3.2 million. Does it make sense to spend that kind of money for a compactor-with the intent of compacting trash-and then not equip it to do the job? Would you buy a power saw…and run it with a worn-out blade? No, it doesn’t make sense-use the tool right or don’t have it in the first place.

Pack flat– Working flat (sometimes referred to as flat-packing) is the most effective way to increase the number of compactor tooth penetrations. It’s all a matter of velocity.

The compactor will generally move faster on a flat area than on a steep slope. That means more wheel revolutions…and more teeth into the trash per day. This is a big deal. At a typical landfill, the change from working on a slope to working flat can add several hundred-thousand tooth penetrations per day. In some cases, benefit is as dramatic as adding another compactor…simply by working flat.

Make long runs– This is another subtle factor, but one that can provide a big payoff. Again, it’s all about putting more teeth into the trash.

Consider the typical cycle of a compactor. It is: roll (forward), decelerate, stop, accelerate, roll (backward), decelerate, stop…over and over again. But if the compactor is making short runs, it will spend a greater percentage of its time decelerating, stopping, and accelerating than if it operated on a long run.

If you have the room to lengthen the compactor’s run, do it. Of course the tradeoff is that the open face may be a bit longer…but if it isn’t creating other issues (e.g., litter, odor, vectors, etc.), you will increase your compaction rate.

Get support from the pusher-When we conduct efficiency studies at landfills, we often include activity sampling. This is simply a measure of what how the machines, including the compactor, are spending their time. And we typically find that the compactor is spending too much time pushing trash…and too little time compacting it.

Let the pusher-typically a dozer or loader-do the heavy work of pushing and spreading, which allows the compactor to spend more of its time compacting. Remember, if the compactor’s wheels aren’t rolling, they aren’t compacting.

Match hours to tonnage– Landfills are as unique as fingerprints in terms of the type of waste received…and how it arrives. That specific profile of inbound tonnage should be matched by your compactor(s). There is a sweet spot when it comes to optimizing the compactor’s effort-a point of diminishing return. Running the compactor too much gains little additional airspace…but wastes fuel. Not running it enough wastes airspace.

To find that optimal point, you can conduct a compactor productivity test, where you create a site-specific production curve for your compactor(s). Another, somewhat less scientific option is to compact each layer of trash until it feels tight …then stop.

Soil reduction– Excessive use of soil has been and still is the primary cause of wasted airspace at landfills. There are many way to mitigate this problem, but properly using alternative daily cover (ADC) is the best.

To get a handle on soil use at your landfill, you must first monitor soil use. Weigh inbound loads of soil and/or count scraper or truck loads brought in from your borrow pit. Following the lead of Subtitle D and state regulations, many landfill operators will say that they cover the trash with 6 inches of daily cover soil. No, they probably don’t. We’ve evaluated hundreds of cover soil operations, and it’s virtually impossible to use only 6 inches of soil…and cover the trash.

In our experience, where we’ve measured the surface area of the cell and the volume of soil used, the depth is always greater. Based on our studies, the average depth of daily cover soil is 16 inches. That’s 267% more soil than is required by regulation.

Yes, there are ways to do a better job of prepping the waste and placing soil. And while your numbers can improve, they’ll never be great. The only way to make dramatic reductions in cover soil use is with ADC.

Tarps, film, spray, foam, waste-derived ADC…take your pick. If you’re currently using ADC, you probably have a good perspective of the benefits. But if not, visit other landfills that are. When used properly, ADC can put you on a much higher level of performance in regard to AUF success.

One of the keys to using ADC effectively is to create daily or multi-day cells that allow you to increase the surface area covered with ADC…and decrease the surface area requiring soil cover. Determining the optimum cell geometry at your landfill can pay off handsomely in terms of reducing soil use and saving airspace.

OK, we’ve looked at several factors that can affect airspace consumption. The processes of pushing, packing, and covering all play a role. But there are other things that impact airspace-things more dependent on a computer chip than on diesel fuel. We’re talking about the planning component.

Short-Term Fill Sequencing
Most landfills would benefit from having a short-term fill sequence plan, so why is it that most landfills don’t have one? I believe the reason is this: They don’t see the benefit. This takes us back to where we started: The holistic approach where operations impact planning…and vice-versa.

If you’ve ever had to construct a sliver fill on an outside slope or make a killer-long push to fill an outlying corner of your landfill, you’ve paid the price of not having a short-term plan.

Conversely, if you agree with the previously discussed concepts of pushing short, packing flat, making long runs, building optimum cell geometry, and maximizing the use of ADC, then you just convinced yourself to develop a short-term fill sequencing plan.

Because a properly designed, short-term fill sequence plan will address all of these issues-and more. It tells you where you are going, and when you’ll get there. It identifies lift thickness, cell geometry, push distance, etc.

And on a this short-term basis-usually a year or so-the plan sets the stage for the operation…and the improved operation establishes a leaner rate of airspace consumption…which is, in turn, reflected in the plans (i.e., in the volume calculations).

Long-Term Development
The same inter-relationship takes place between operations and the long-term site development plan. When your landfill was designed, there was an estimated excavation volume, fill volume, overall site capacity, and expected life. And all of these were based on the designer’s best guess at the time.

Accordingly, you’ve made scheduling and financial plans for liner construction, closure, post-closure and for an expansion, a transfer station, or “whatever comes next…”

Now, here we come with the ability to increase efficiency and slow the rate of airspace consumption. This means you can defer development costs for liner, closure and post-closure. It means your closure funding payment gets reduced. It means the landfill will last years longer than anticipated. How does that sound?

So, as the operation creates a platform that improves the long-term development of the landfill-the plan begins to support the operation too.

By optimizing the soil excavation schedule, you can create practical areas to stockpile excess soil…this leads to surcharging, settlement, and more airspace.

By establishing long-term access roads and drainage facilities, the operation knows the plan and so spends less time and money making improvements that will be outdated in a year or two.

By using less daily cover soil within the landfill mass, leachate and gas can be more easily collected, thereby reducing operational conflicts related to unplanned repairs/modifications.

The operation enhances the fill sequence plan-which in turn improves long-term planning-that turns around and makes the operation more efficient. It’s holistic. It’s symbiotic. It’s…well, you get the drift.

Three Things You Must Do to Conserve Airspace
Evaluate and improve operations-In order to bring your operation to a higher level of performance, you’ll need to find those parts of the operation that affect airspace consumption. We covered a brief list of some common factors, but the list is much longer, and it’s unique for every landfill.

This can be done with one word: “Why?” Question every part of your operation. Ask and re-ask why are we doing something a certain way? Is there a better way? Why are we doing it in the first place? Ask, ask…ask. The answers may surprise you.

Establish procedures-As you identify things you can do to save airspace, lock it in. Create a procedure so that everyone does it the same way…every time. Yes, I know that conditions change every day and some flexibility is necessary-right: it’s a landfill. But when you find a way to increase waste compaction, use less soil, or streamline the operation, make it part of your landfill’s normal operation.

Incorporate operations into plans…and plans into operations-Finally, revise the assumptions that your landfill’s plans were based on. You are now the operations expert for your landfill. Share what you’ve learned and apply the new benchmarks for airspace consumption to your existing and future plans.

These things are all part of the process of managing airspace. By developing a culture of continual process improvement at your landfill you can keep your operation dynamic and competitive. It’s not necessary that you understand all of these concepts right now; just take the first step by improving one aspect of the operation.