Waste

The Over-Under on ADC

From sprays to membranes, use of alternate daily cover is increasing.

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Credit: New Waste Concepts
In the heavily regulated business of landfill management, where the daily cover of working cells is required, a 6-inch layer of soil is the standard for overnight cover. “It’s the expected solution,” says Joel Lanz, president, LSC Environmental Products LLC. “Soil is already approved and people are already using it.”

But as with everything, there are drawbacks. In the case of soil, it’s loss of airspace. “Bulky soils take up space in the landfill,” explains Lanz. While the minimum requirement is 6 inches, he says 16 is the average because the soil is difficult to spread evenly. Using a heavy layer of soil can strain an already tight budget.

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Credit: Epi-Global
Enviro Cover system from EPI Global

Soil can be expensive, particularly when considering the cost of daily operations. The use of “big yellow iron”—equipment like excavators, articulated Cats, and bulldozers—to spread (not to mention the necessary manpower) adds to the price.

“We perform a cost-benefit analysis,” announces Lanz, “to compare operating costs.” In order to determine the most efficient option, they look at the type of equipment used, the cost of fuel, how long the equipment runs, and hourly maintenance costs. The also consider emissions and best practices.

Dirt uses up a lot of space. Alternatives typically save on airspace, as well as on daily operations. The problem is that landfills don’t experience airspace until they’re ready to close a cell, Lanz points out—but they do experience fuel savings on day one with ADCs.

Milton Knight, CEO, New Waste Concepts, maintains that ADCs can result in operational savings of 60%, due to less labor time and less overtime since it doesn’t take as long as spreading dirt, less fuel usage, fewer hours on yellow iron equipment (which means the lifetime of the equipment is extended), and prolonged life of the cell. “This argument does not apply where the site is getting RGC,” he clarifies.

Other options include spray-applied slurries, tarps, RGM (revenue-generated materials where a landfill is paid to take “dirty soil”), and soil from the next cell(s) you’re digging (not just a borrow area).

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Introducing ADC
Since the Subtitle D adoption in 1987 allowed Alternative Daily Cover, there have been options. “It’s a significant change from a regulatory point of view,” says Knight, “and from a user’s point of view.”

Whether soil or something else is chosen, all materials used on the surface of the active cell are intended to do the same thing: control vectors, fires, odors, blowing litter, and scavenging—although Knight says that ADCs themselves don’t impact vectors. “You have to add things.” In fairness, he adds, soil doesn’t do the greatest job controlling vectors either. “Flies burrow and birds pick.”

New Waste Concepts
Nevertheless, ADCs have advantages over soil. ADCs can reduce leachate and the amount of water intrusion because they are not as permeable as soil or other products, says J.D. Mohr, business development and marketing executive, Epi Global Environmental Products.

Another benefit of ADCs is odor control. Landfill odor is often the result of hydrogen sulfide, volatile organic carbons, odorous mercaptans, and water vapor that escapes from the cell, although Mohr recognizes that identifying the specific source of an odor can become complicated if there are too few gas collection wells or too much sludge received.

A non-reusable geosynthetic film made of polyethylene is an impermeable material with no interconnected pores through which gas or fluids can flow. Because fluid molecules move slowly through the film as a vapor phase, via molecular solubility and diffusion known as permeation, Mohr explains water vapor droplets collect on the underside of the film instead of dissipating into the environment. This allows landfill gas to flow more freely through soil barriers as it washes away with weather, shifts, and cracks over unconsolidated subsurfaces.

Epi Global offers an Enviro Cover system that produces airspace savings, is quick to apply, and provides complete coverage. “There’s no blowing litter,” emphasizes Mohr, adding that the trucks can dump on it, eliminating any delay caused by pulling back a tarp. “It’s a non-reusable geo-synthetic film—kind of a plastic film that’s used as an ADC that you can put the next day’s waste on top of.”

Two models are available. The smaller 700 model is suitable for 600 tons per day or less and mounts to the front of a dozer. The larger ECB 800 has its own self-propelled motor/carrier system. Deployers use dirt, sandy soil, or aggregate as ballast. The mixture goes into the hopper and the machine distributes it to pin down the plastic, which has a thickness of 1.25 mil (or 1.75 mil if there are animals such as deer or birds in the area), Mohr explains.

Tarps
Southwestern Sales Company produces a safer, more labor-efficient tarp deployment system for landfills receiving daily tonnages from 100 tons to more than 6,000 tons, according to Shannon Harrop, Southwestern Sales Co., tarpARMOR. The tarpARMOR TDS Tarp Deployment System requires only one operator, whereas competitive machines require an additional spotter to be on the ground to engage removable spools.

“The application and removal of tarps with the TDS machine is a simple process,” says Harrop.

He says the TDS system is optimized to provide the most cost-effective solution for daily cover. Designed as a modular solution, the tarpARMOR TDS30HS machine can incrementally add 12,840 square feet of tarp coverage per machine because it can be equipped with one to four tarps measuring 30 feet by 107 feet.

The TDS machine is a self-contained apparatus that includes alternate daily cover tarps, support frame, rotating spool, and a self-powered gasoline or diesel hydraulic power unit. Spool direction is controlled via a handheld wireless remote control. The machine is lifted and moved by existing landfill equipment.

“Each TDS machine functions independently and provides 12,840 square feet of coverage,” reiterates Harrop. “The tarps can cover an area of 120 feet by 107 feet in less than 20 minutes with one operator.”

Another cost-saving measure is the use of durable woven polypropylene in tarpLOX-equipped tarps. The TDS can be supplied with up to four of them, each equipped with patented tarpLOX ballast cables and full-length 3/8-inch side chains. “The tarpLOX cable system will support and maintain the tarps at their full 30-foot width of coverage and not bunch to the middle of the spool and reduce tarp coverage like competitive machines,” explains Harrop.

Harrop says there is no appreciable environmental concern with tarps and nothing is left in the landfill to decompose. “The only consumable for the product is the tarp. With proper use and care, the average life expectancy of TDS tarps (which are made from recyclable polypropylene) is two years.” The operational life of the TDS machine itself is at least 10 years when following recommended maintenance procedures.

Safe at Any Speed
Tarps are a quick—and safe—way to cover the working face of a landfill, states Marlon Yarborough, sales and marketing manager for Tarpomatic. “No one has to walk on trash; the tarps are mechanically applied,” he points out. He says they are also the “least cost” method of cover.

A machine that fits onto a dozer or compactor deploys the tarps rapidly. Available in three sizes, Yarborough says the most common tarps fit a 40-foot machine. Up to 300 feet of weighted tarp fit on a spool, but mid-size and larger landfills may need more. For them, Yarborough says a new spool can be picked up in two minutes.

Tuff Tarps made of high-density woven polyethylene (a heavier fabric) feature a water-resistant, flame-retardant coating and can be reused—typically for 24–36 months. Weights are sewn into pockets on the outside perimeter for a 3/8-inch chain. The patented cable keeper works reusable 3/8-inch cable into the cross pockets.

“The advantages outweigh the disadvantages,” says Yarborough. “It’s the least expensive method and one of the safest.”

Credit: Tarpomatic
Deploying Tarpomatic’s Tuff Tarp

Spray It, Don’t Say It
A lot of people use tarps, Lanz says, but tarps have one use only and are approved for daily cover only. “They are a single-use item. They must be put on and taken off every day.” Conversely, LSC’s Posi-Shell is a multi-use product that can be used as an ADC, as an intermediate cover, and for hydroseeding. “It can be different things, depending on how thick or thin it is.”

Posi-Shell is applied as a spray. “The landfill needs applicator from LSC or a hydroseeder: some sort of mixing and spraying unit,” explains Lanz. Water is added to the powder to form what looks like chocolate pudding when mixed. Lanz says the water can come from a pond or a well, and that some landfills can even get leachate tested and approved for use.

Trash can be added the day after application. Although it forms a hard, durable coating, there’s no need to remove the covering each day; Lanz says compaction breaks up the shell. He claims that a landfill lasts 15–20% longer because of the space savings from Posi-Shell.

Epi Global produces a non-reusable geosynthetic ADC. This Enviro Cover film is simple to apply, using a loader, dozer, or self-propelled Cat engine, Mohr says. Several sites are experiencing operational improvements and reduced cost, he reports. “If the site is covering with soil, we can compete.”

The industry considers it a new mousetrap, Mohr continues. “It’s just becoming accepted.” Thanks to an additive from their parent company—TDPA (totally degradable plastic additive) that meets ASTM standards—it breaks down or degrades so there’s no need to remove it.

Slurry with the Fringe on Top?
New Waste Concepts’ Knight classifies ADCs:

  • RGCs
  • Tarps, which should be upgraded to be made fire-retardant
  • EPI biodegradable plastic, also known as rollable, digestible plastic
  • Foam
  • Spray-on slurries: basic and cementitious—Posi Shell, Topcoat, WasteCover, ProGuard, and ConCover (NWC)

The cost for slurry-based materials is down, Knight reports. “The price per square foot is less than one cent (from two cents). The customer didn’t ask for it, but benefitted from a price war.”

However, he says, the visual quality and thickness are also down. He holds the customer ultimately responsible for that because, he says, customers diluted the mixtures which impacted the quality, so the industry went back to a bag system to preserve quality. In fact, he says, the state regulator contacted New Waste about a site that used a diluted mix. The regulator required the site owner to keep a record of their coverage after that. The problem is, Knight says, because state budgets have been cut back, regulators have less time to monitor landfills.

HydraGuard is a mix of vinyl acetate and acrylic polymers blended so that they easily soak into a variety of soils in order to achieve at least an inch of penetration. Once the liquid mixture dries and hardens, it creates a semi-impermeable layer that allows stormwater penetration as well as the passing of gas, vapor, and VOCs. It’s also beneficial for erosion and dust control.

The difference between this and other sprayable slurries is that instead of sitting on top of the soil, it penetrates. Geomembranes and special fabric coatings require additional maintenance, according to New Waste, and can be washed out in areas where stormwater gets underneath them. That doesn’t occur with HydraGuard because it becomes part of the soil surface. It “locks up” 1–2 inches of the surface layer of soil into its barrier, reducing water penetration 75%–85%. It lasts 12–13 months.

Trends
Regulators are approving more revenue-generating cover, Knight states. It’s attractive to landfill owners because of reduced tipping fees and ADCs. “Private landfills contract to pick up waste, so their investment in the landfill is fixed.”

A greater range of RGC materials have become sources of regulatory-approved ADC, Knight continues. That spectrum of ADC material can be added to increase durability without a lot of money, providing flexibility and options. “Thus, the landfill is paid for its cover material. We are seeing a greater range of these going to the MSW landfill that might have previously gone to other lower classified landfills.”

Lanz believes that daily cover trends are “holding steady.” Of the “couple thousand landfills,” he says 50% use ADC and 50% use soil. “But,” he adds, “we’re picking up new customers every year. The trend is a move toward ADC. We don’t lose customers; they don’t go back to soil.”

An even bigger trend Lanz sees is more alternative intermediate cover, which requires a 12-inch cover.

As with anything, Mohr notes, there are trade-offs when purchasing an ADC. Each site has unique variables that dictate how it performs with a daily cover.

Landfills are often understaffed. Using more labor-efficient ADCs allows them to reassign employees to other areas. When ADC can also reduce operating costs, save time, and reduce odor and blowing litter, they can be a sensible investment.  MSW_bug_web

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