The ABCs of ADC

Running a landfill is macho stuff. Garbage trucks roar into the site and dump garbage on the ground. Bulldozers shove it off the deck. And steel-wheeled compactors crush it, rip it, and shred it. The sweat, the dust, the smell. Hey, this is the real thing. Then at the end of the day, the cell is covered with a thin layer of…uh…fluff?…plastic?…foam?

What’s the deal? Have we traded in our “big iron” image for a foam applicator? If John Wayne were still alive, would he head off into the sunset riding a llama? Like it or not boys, we’ve got to face it: The landfill business is changing. As landfills become ever more competitive, greater numbers of them are reducing their dependency on cover soil by using some form of alternative daily cover (ADC). ADC is any regulator-approved material that can replace soil as a daily cover material. The primary purpose of ADC is to reduce the amount of dirt going into the landfill, thereby saving more airspace for garbage.

However, some landfills use ADC to avoid the dust associated with hauling soil. Consider this: Many landfills work hard to achieve a 3:1 cover ratio; some never do that well. This means that after the time and expense of developing a usable landfill, we “feel good” (??) about using 25% or more of its capacity for soil. That’s 25% right off the top. And we don’t just give it away—we pay to haul the soil there!

If you’re still covering with dirt and haven’t seriously considered ADC, read on to learn how some of your peers are using less and saving more. And perhaps surprisingly, you’ll read why some landfills have opted to continue using soil instead of switching to ADC.

ADC isn’t new; it’s not a phenomenon of the 1990s. I know of one central California landfill that was using ADC back in the 1970s. At that time airspace was not a major concern for landfills. But even then, the landfill operators recognized that it cost money to haul dirt. So as an alternative to daily soil cover, the landfill set aside all of the brush and tree trimmings that came into the site (back then the term greenwaste wasn’t in vogue). Then at the end of the day, they’d spread it on the face and track-walk it with the dozer. They called it “brushin’ the garbage.”

Types of ADC: How to Decide?

Alternative daily covers are like blue jeans: there’s a size, style, and price to suit just about everyone. Here’s a quick rundown on some of the more common types of ADC.

Geosynthetic ADC. Geosynthetic covers (tarps and films) are probably the most commonly used ADC material. They are inexpensive and placed manually (by hand) and/or mechanically. Films are typically placed across the landfill, and sand or soil is sprinkled on top to hold them in place. Tarps are often placed by hand, especially at small landfills. At other sites, tarps are placed mechanically by using a spreader bar or a mechanical spool.

Diverted-Waste ADC. Diverted wastes such as auto-shredder waste and greenwaste are often used as ADC. One of the major benefits of using a waste material as an ADC is that it provides a use for materials that might otherwise go into the landfill as waste. In fact, many landfills actually receive recycling “credit” for using diverted waste materials as ADC. One drawback is that greenwaste provides virtually no fire protection.

A common form of ADC, greenwaste includes chipped or shredded yardwaste and tree trimmings. In many areas of the country, greenwaste is often a recyclable material without a market. Today, there are many facilities in the United States that divert greenwaste out of the wastestream with a desire to recycle it, only to find that there is no viable market. As a result, waste might go right back into the landfill. Using it as ADC will, in a sense, recycle it because doing so saves landfill space that might otherwise be filled with soil. Additionally, landfills may actually receive recycling credit (toward a mandatory recycling goal) if they use greenwaste as ADC.

What many people don’t realize is that whereas woodwaste as ADC represented 7-12% of the total wastestream in the early 1990s, today diverted-waste ADC often represents 30% of the incoming wastestream—in essence, too much of a good thing. Often the driving force behind overuse of ADC is subsidies or diversion credit for recycling. Some landfills are trying to attract as much woodwaste as possible, labeling it as “ADC,” and putting it into the landfill. On the other hand, some landfills are dirt “poor,” and for them it makes sense to stockpile as much cover as possible. So for some sites, stockpiled ADC makes sense.

Foams. Foams have been around for several years. They can provide quick coverage, use virtually no airspace, and provide good protection against infiltration and vectors. However, foams normally require specialized application equipment. The foam covers I’ve seen are sprayed onto the garbage through a row of spray nozzles (similar to a boot truck applying road oil), with a spray wand, or with a large monitor or “swivel gun.”

Other Materials. Other materials used as ADC include sludges, compost, petroleum-contaminated soil, shredded tires, and foundry waste. These types of materials are effectively being used at many landfills, but in some cases, special handling or testing might be required in order to receive regulatory approval. For example, to use petroleum-contaminated soils, you’ll likely have to perform some testing to determine the concentration of the contaminants, particularly heavy metals. In some cases, regulators may also require a more intensive surface water control plan.

With all things considered, if your site can use some form of ADC, it will likely be worth the effort it takes to implement it. Nearly every landfill I have been involved with as a landfill operations consultant could benefit from using ADC. In order to determine which type of ADC will work best at your landfill, you must consider such site-specific conditions as:

• Type of garbage
• Size of cell
• Convenience
• Wind conditions
• Cost/economics
• Local enforcement agency concerns/preferences
• Precipitation factors
• Specific vector problems

What you’ll see reflected in this article’s case studies is that every landfill is unique in terms of the type of ADC that works best. There is no “one size fits all.” Before you select a form of ADC, take the time to look around and see what other landfills in your area are using. Find out what they like and don’t like.

Who’s Using What?

Thomasville, GA. John Wood, operations engineer at the city’s landfill, sums up ADC benefits in one word: airspace. According to Wood, with most landfills now built on costly liners, “The entire equation centers on volume of airspace and the cost to provide it.”

They initially looked into purchasing a mechanical tarp placement system but have found that the mechanical systems do not justify their need for the landfill’s particular application. Instead, using a home-built spreader bar mounted on a Cat 320L excavator, the crew can efficiently deploy and remove the tarp. Says Wood, “Tarp life is primarily a function of operator care in placement and removal…lifting with the excavator provides longer tarp life than dragging the tarp on and off.” The system must be working. After nearly a year of use, the original tarps are still in service.

Notes Wood, “Odor is slightly more noticeable when using ADC in place of soil. However, because of the landfill’s remote location and lack of neighbors, the odor is not a significant concern.”

Santa Ynez, CA. David Stubchaer, site manager and civil engineer at Santa Barbara County’s Foxen Canyon Landfill, says, “We began using ADC to extend the landfill’s life.”

The 90-tpd landfill had been mainly covered with soil. But in order to coordinate the closure of the landfill with the opening of a planned transfer station, extending the life of the landfill became an important issue. A spray-on foam ADC was decided against, explains Stubchaer. “The site was too small to justify the foam machine. Also, to avoid bare spots, we had to apply the foam from two directions. The tarps were more economical. We found the foam to be messy, especially during windy conditions.

“Placing and removing the tarps takes only 10 to 15 minutes,” he says. The tarps are pretty tough, though they can be ripped if the operators become careless. According to Stubchaer, in order to prevent tarp damage, track-walking the waste prior to placing the tarps is vital.

To obtain approval from the California Integrated Waste Management Board, Foxen Canyon Landfill had to go through a pilot or “demonstration” program with the tarps. Prior to regulatory approval, the tarps had to meet certain performance standards in regard to litter control, vector control, and surface-water protection. As part of the approval, Foxen Canyon can leave tarps in place for up to seven days. Remarks Stubchaer, “The landfill gets a little smelly after seven days with a tarp, but the ability to cover once a week gives us a lot of flexibility.”

“Aside from ripping a tarp if we become careless, the only problem we’ve experienced is associated with wind. The tarps are weighted with integral cables, but we often use old tires to help hold down the tarp.”

Foxen Canyon Landfill typically uses three 40- x 100-ft. tarps to cover its active area.

Santa Barbara, CA. Brian Chaney, refuse leader at Santa Barbara County’s Tajiguas Landfill, says, “We recently switched from foam to a tarp system. We were not allowed to use foam if the weather forecast predicted a 30 percent or greater chance of rain. With the tarps, rain isn’t a problem.”

Winds are another thing. During certain times of the year, Tajiguas is plagued with what’s known locally as “sundowner” winds. Caused by inland warming, these strong thermal winds rip across the landfill toward the ocean. To keep them from blowing away, the tarps are weighted with steel chain along the edge, and steel cable is sewn across them at 25-ft. intervals. Even so, in high winds the tarps are “a pain in the neck,” according to Chaney. “Our Tarp-O-Matic works pretty good, although when winds exceed 40 miles per hour, we have to resort to using soil and wood chips for cover.

“We have three spools with three tarps on each spool. These are our working tarps. Normally we use two to six tarps per day, depending on our cell configuration. Including old tarps and spares, we have around 15 40- by 100-foot tarps on-site.”

At 800 tpd, Tajiguas is one of the largest landfills on California’s central coast. Since the landfill is located along the scenic coast highway and within sight of the Pacific Ocean, when it comes to achievement standards, its ADC must really perform.

Fresno, CA. Fresno County’s American Avenue Disposal Site (1,700 tpd) is, according to Senior Engineer Francis Coward, a balanced site. “Because our site is balanced [ratio of waste to soil], we do not currently use ADC. We have tested various types of ADC, including tarps and film. However, at this time, because we have no-where else to put soil, we don’t see a benefit to using ADC.”

Other landfills report that they’ve made a similar choice not to use ADC. However, some of those “balanced” landfills that elect not to use ADC might benefit by raising their base grades, using ADC in place of soil, and thus avoiding the cost of moving the extra soil. As another option, they might consider excavating to deeper base grades, stockpiling the soil off-site, and using ADC. “Stockpiling excess soil off-site, along with using ADC, might help us to create more usable airspace and cut costs,” Coward points out.

Lamesa, TX. Says Neal Welch of the Lamesa Landfill, “Using tarps saves us a tremendous amount of airspace.” Similar to most small landfills (the Lamesa Landfill receives 20 tpd), when soil is used as daily cover, it may represent up to 50% of usable airspace.

Raising the bar in regard to teamwork, Lamesa Landfill’s tarps, manufactured by THOR Tarp, are removed in the morning by the refuse truck drivers, then placed on the waste at the end of the day by the same truck drivers.

This is a bright example of working together compared to landfills that report truck drivers dumping on top of the tarps if the landfill crew doesn’t get them off in time.

Welch says that placing and removing their 50- x 100-ft. tarps takes about 10 minutes. “With this size of tarp, our guys can walk along the covered edge when handling tarps and don’t have to walk on exposed garbage. By being careful, we’re still using our original tarps from four years ago. We’ve only had to make one repair.

“We have checked on foam, but because of the winds we sometimes get here in west Texas, we opted for tarps. We usually place tires along the edge of the tarps to help hold them in place.

“We have a good relationship with our local enforcement agency [inspector]. On exceptionally windy days, we are allowed to tarp loads where they’re dumped, then wait until the next day to push them.”

Louisville, KY. From the Outer Loop Recycling & Disposal Facility in Louisville, KY, manager Rick Barr reports that they are currently using tarps as ADC. “We pull them into place with the dozer and/or the compactor. Typically it takes two to four tarps to cover the face. We rotate in a new tarp every month or so.”

Barr, who recently came to Louisville from the Earthmovers Landfill in Elkhart, IN, says, “We used wood chips for ADC and various other uses around the landfill. They worked quite well as a temporary road base, especially during wet weather.

“At Earthmovers Landfill, we gained a 20 percent savings in landfill life by using a variety of materials for ADC: wood chips, foundry waste, auto-shredder fluff, and compost tailings. In Indiana, our permit allowed us to go from seven to 21 days before placing additional waste, depending on what type of ADC we used. For example, wood chips were good for seven days and foundry waste was good for 21 days. We didn’t use tarps at Earthmovers because of the snow. It’s hard to remove a tarp when it’s covered with snow.

“currently we’re in the process of seeking approval to use some of these same kinds of materials here at Outer Loop Recycling & Disposal Facility. This will give us a lot more flexibility when it comes to managing our waste-stream and saving airspace.”

Tinton Falls, NJ. In New Jersey, the Monmouth County Reclamation Center uses the Rusmar foam system for ADC. “We operate a 1,700-tons-per-day balefill,” says Superintendent John Gray. The Monmouth County site also receives some unbaled waste-mostly bulky waste and construction/demolition debris. “The unbaled waste is spread on top of the bales and used as a leveling course. In the past we used soil [and] tried tarps, but in the end we selected the Rusmar foam system. We’ve used foam for about four years. We stopped using tarps because of wind problems.

“The foam is convenient. It takes about 45 minutes per day to spray the face. It also costs less than soil, frees up the excavation equipment to do other work, and uses virtually no airspace.

“Rusmar helped us modify the foam so that it is tacky and will stick to the vertical face of the balefill. As the bales advance, we put foam on the face and put soil on top.”

Brownwood, TX. Tim Airheart, solid waste superintendent at the Brownwood Regional Landfill, states, “At 250 tons per day, ours is a relatively small landfill. Even so, using soil we’d lose about 150 cubic yards of airspace per day. That worked out to over $500,000 per year in lost airspace. ADC saves us a lot of money.

“We started out using film. We leased a machine for two years. One of the benefits of film was that it could be placed on an irregularly shaped cell. Also, because the unit was only 16 feet wide, it was easy to maneuver. “We also tried manually placed tarps for a while but found that we had lots of problems with tearing. Now we’re using a Tarp-O-Matic. It’s simple, easy to use, and keeps people off the garbage. We’re saving an additional $50,000 per year since switching to this system.

“At first the crew didn’t like this system. Because of its width [45 feet], it was hard to handle, especially on steep slopes. However, now that they’re used to it, they can cover in one pass; usually in about 10 minutes.” The Brownwood Regional Landfill typically uses one or two 40- x 100-ft. tarps to cover the face. They have two spools, each with two tarps. One spool serves as a backup. “We get a lot of wind here in central Texas,” Airheart notes, “but with intersewn cable and chain for ballast, the tarps work very well.”

Davis, CA. Lorell Miller, associate civil engineer at the Yolo County Central Landfill, reports, “After looking at various types of ADC, we opted for shredded greenwaste and tarps.”

This 550-tpd landfill is county-owned and contractor-operated. “Greenwaste is generally used during the winter months,” explains Miller, “and tarps and greenwaste are used in combination during fair weather, placed according to schedule of operations. We’ve evaluated film and foam ADC, but the greenwaste and tarps (which last up to six months) are the most economical for us.”

The landfill’s tarps are approved for cover for up to 72 hours. Because of the tonnage, up to eight tarps are used on the face.

Another important factor in the decision to use ADC is soil. At Yolo County Central Landfill, ADC helps to minimize the site’s potential soil shortage.

Appleton, WI. Gary Steede, superintendent at the 1,000-tpd Outagamie County Landfill, has been using foam ADC for a decade and a half. “In 1984 we began using foam. At that time, we used Sani-Foam. Over the years, we’ve tried several different foam systems,” he recalls.

currently the landfill uses Terravest, made by Aqua-Shed Technologies Inc. Says Steede, “For us, it boils down to a combination of price and ease of use. We’ve looked for a system that will provide us with consistent results without having to worry about cell finish. We’ve found the product easy to mix and easy to clean, and we just don’t have the maintenance problems we had with other systems.

“At our landfill, we have specific issues that have led us to the ADC we now use. The clay soils are difficult to spread thin. Six inches of cover more often than not became 18 inches. With snow, tarps didn’t work well. And when we tried tarps, we seemed to have problems with protruding waste, like rebar.

“We figure we’re gaining 30 percent in usable airspace by utilizing the foam system instead of soil.”

When asked about how wind impacts foam application, Steede surprisingly replies, “The wind actually can be a help to us. With a good tailwind, we get much greater range out of our swivel gun. Of course, when spraying into the wind, we have to keep the nozzle pointed down close to the unit.

“It takes two passes to cover with foam. We spray one direction on the way up and the other direction on the way down. We can cover a 10,000- to 15,000-square-foot face in about 20 minutes.”

Selecting the right kind of ADC for your landfill requires a little science and a little art, and in many cases it’s based on good ol’ common sense. Yet, while the answer may be different for each landfill, it’s usually measured in dollars, airspace, and landfill life. In looking at these different landfills that use a variety of cover, it’s clear that ADC truly is an alternative daily co