Soil may be king of the daily landfill covers, but significant challengers to the throne have arrived. Alternative daily covers (ADC) are more than just soil proxies; they must be capable of meeting regulatory requirements, including controlling odors, preventing day-lighting of waste, reducing access to the wastes by vectors and controlling wind-blown litter. That's a tall order for these foams, tarps, degradable films and hard-shell covers that now are eroding soil's 40-year reign as the standard daily cover.
As the costs associated with opening new landfills mount, the value of airspace has increased as well, and the six inches of dirt which typically has been employed can equal thousands of dollars in lost revenue over the site's life.
While Federal regulations mandate daily covers, it often is the purview of individual states to determine which ADC is acceptable. In the past, state agencies have conducted studies to determine the operational characteristics of specific methods to establish regulations and guidelines.
Many materials that are by-products from waste diversion or other waste-handling activities, such as ground yard wastes, construction and demolition debris, auto fluff and other inert materials, may be used as ADCs. While the use of such material may count toward diversion goals, it's debatable whether this use actually can be construed as "recycling."
Recognizing ADCs as a burgeoning market, many companies have developed products to match the demand, but a particular method's performance still is dictated by the physical and economic characteristics of the environment in which it is used.
Topping Off With Tarps One of the simpler ADCs to use is a tarp, a fixed-size fabric or plastic product that is rolled or dragged out over the working face and secured by weighted objects, such as tires, chains or sandbags. The following morning, tarps are collected and stored for reuse; if handled properly, a tarp may last up to 24 months.
"The biggest concern of daily covers is that people must walk on the working face and drag these tarps around," notes Marlon Yarborough of Airspace Saver Daily Covers, Prairieville, La. "I've noticed a trend towards mechanical equipment [for deploying tarps] coming for years."
With mechanical deployment, a machine attaches to the front of either a bulldozer or compactor that rolls out large tarp panels.
Such a machine has "its own engine and hydraulic system and allows the operator to have full control," says Mike Slutz of Tarp-O-Matic Inc., Canton, Ohio.
In addition to promoting employee safety, these machines can increase time efficiency as well. For example, according to Slutz, a 128-foot tarp can be rolled out in less than a minute, and a 10,000-square foot landfill can be covered in 10 minutes mechanically.
Degradable plastic films, new on the ADC front, are designed to be installed permanently over the working face. Various components help them degrade through either heat, ultra-violet light or a combination of both so as not to create leachate barriers. Their advantage is that they only have to be handled once and can be installed either by hand or machine.
"Since waste will go on top of the alternate daily cover at the end of the day, it must be able to break down so it doesn't create a hydraulic barrier that would inhibit the flow of leachate and methane freely throughout the cross section of the landfill," says Don Hildebrandt of EPI Environmental Projects Inc., Woodland, Calif.
Installation of thin films is similar to taping up a package: The material is extended either by machine or hand at the top or bottom of the landfill face and then rolled down to the opposite end. The edges are secured, and the next row is overlayed slightly on the first, and the process is repeated.
"Generally, a machine is required for two reasons: It expedites the process and it dispenses soil or other ballast across the film as it's being unrolled to keep the film in place," explains Jim Kynor of In-Line Plastics Co., Houston. "The film is a thin mil and needs to be wetted down in order to prevent blowing and also to ensure proper coverage and protection against migrating animals."
The machine is attached to the blade of a bulldozer or compactor and is controlled from the cab. The machine is designed to deploy the plastic film as the bulldozer moves across the face. A ballast dispensing system is used to deposit the ballast automatically along the edge of the film as it is laid out.
The non-water soluble film is usable in most weather conditions, but heavy rains can be problematic due to possible erosion of the windrows of soil or fractured material that is placed on top of the film, reports Hildebrandt.
The working face's size may be a factor in determining films' economic feasibility. "The ideal conditions [for films] would be on landfills with a working face of 1,000 feet or greater, which maximize efficiencies by allowing operators to use the machine," reports Kynor. "On a smaller working face, they would have to deploy it by hand. It's really the size of the working face which maximizes the effectiveness."
Spray On A third category of ADC products includes both soft- and hard-shelled covers that are applied with a sprayer. These products usually are delivered in dry-bulk, stored on-site in silos, then mixed with water and applied using a pump which either sprays the product through a hand-held or vehicle-mounted nozzle or through a vehicle-mounted spray manifold. Most manufacturers offer storage and spraying equipment designed to optimize distribution.
The characteristics of these covers vary: Some remain wet and fluffy like shaving cream, while others form a hard, durable shell. While all these covers can meet most of the environmental conditions present, from cold winter conditions in the North, to hot summers in the desert, heavy rainfall tends to be problematic for foam products, according to Tim Johnson of New Waste Concepts, Erie, Mich.
If you're expecting heavy rain, you might want to use a product that will get hard and not be affected by rain either during or after the application, Johnson advises. Once such products dry and solidify, if remoistened, they won't become to a liquid state, he notes.
"Heavy rain is our biggest challenge," reports Larry Hawes of Rusmar, West Chester, Pa. "If a heavy rain fall is forecast for the coverage time, you should err on the side of caution and not use [foam]."
With foams, once the material is worked the next morning, it crushes into a fine powder. "Picture stepping on shaving cream; [the foam] is absorbed into the waste," describes Hawes. "Foam is typically 96 percent air by volume so you're crushing a lot of air out of it. We've not had any instances of slippage or any problems with equipment or anything running over it after the fact."
Some manufacturers make different mixtures for different applications, such as daily cover, intermediate cover or erosion control. "The harder foams form a cover which are durable enough to last up to several months, adds Joe Missavage of Landfill Service Corp., Appalachia, N.Y.
Working The Alternatives As with any new program, it is important to conduct as much research as possible prior to committing to one type of ADC over another. Most manufacturers offer programs in which operators can test these products in actual day-to-day operations. "Test-driving" different ADC types allow operators to evaluate performance characteristics and to gain hands-on experience. Other suggestions when weighing one method against another include:
* Grill the manufacturer. How easy is this product to apply? What are the storage and handling requirements? Is field support available if there is a problem? What kinds of financing programs - such as rentals, leases and free use of applicator equipment in exchange for purchasing minimum quantities - are offered?
* Request a list of users and call for their insight into that particular method's strengths and weaknesses.
* Include local regulatory agencies in the evaluation process so that they can understand how the ADC is going to perform at a site under their jurisdiction. Striving for greater efficiency and cost savings in landfill operations demands that the smart operator consider ADCs. While the dollars-and-cents cost comparisons may be confusing among product claims, the savings in sellable airspace and dirt handling may make ADCs an alternative you can't afford not to cover.