Minimizing Volume and Saving Costs
These high capital costs and low operating costs combine to create a unique business model. Overall profitability depends on the ratio of disposal airspace to landfill footprint area. Each acre of the landfill’s footprint represents a capital cost in terms of liner or final cover construction. Each cubic yard of available disposal airspace represents an amount of disposed waste whose weight was measured at the entrance truck scale and paid for on a per-ton basis. Simply put, the more waste that can be crammed into an acre of landfill, the greater profit the landfill operator will achieve.
There are two ways, one direct and the other indirect, to increase the amount of waste disposed of in each available cubic yard of airspace. The direct way is to compact the deposited waste into as small a volume as possible, increasing its in-place density as much as possible. This maximizes the mount of tons per volume in the landfill. Since landfill earnings are on a per-ton basis (as measured by the truck scales), compaction of the waste changes the equation from volume per area to tons per area.
The indirect method is to minimize the amount of airspace that is not used directly by disposed waste. Not every cubic yard of airspace, even in the most efficiently run landfill, is given over to waste. All states require the use of daily and intermediate cover to overlay deposited waste. This requirement for daily cover application is rooted in Subtitle D of the Resource Conservation and Recovery Act (RCRA). Specifically, the regulation required by RCRA are given in Title 40 of the Code of Federal regulations, 40 CFR-“Protection of Environment,” Chapter I-Environmental Protection Agency, Subchapter I-Solid Wastes, Parts 239 through 282. The regulation mandating the use of daily cover is found in Part 258, Subpart 21:
Part 258.21 Cover Material Requirement
- Except as provided in paragraph (b) of this section, the owners or operators of all MSWLF units must cover disposed solid waste with six inches of earthen material at the end of each operating day, or at more frequent intervals if necessary, to control disease vectors, fires, odors, blowing litter, and scavenging.
- Alternative materials of an alternative thickness (other than at least 6 inches of earthen material) may be approved by the Director of an approved State if the owner or operator demonstrates that the alternative material and thickness control disease vectors, fires, odors, blowing litter, and scavenging without presenting a threat to human health and the environment.
- The Director of an approved State may grant a temporary waiver from the requirement of paragraph (a) and (b) of this section if the owner or operator demonstrates that there are extreme seasonal climatic conditions that make meeting such requirements impractical.
- The Director of an Approved State may establish alternative frequencies for cover requirements in paragraphs (a) and (b) of this section, after public review and comment, for any owners or operators of MSWLFs that dispose of 20 tons of municipal solid waste per day or less, based on an annual average. Any alternative requirements established under this paragraph must:
Consider the unique characteristics of small communities;
- Take into account climatic and hydrogeologic conditions; and
- Be protective of human health and the environment.
Daily cover must be applied to all exposed waste by the end of the working day. Daily cover material cannot be organic and putrescible, cannot consist of large objects that would interfere with coverage and application, and cannot be municipal solid waste or any other kind of waste unless approval is granted by state regulators.
Why Use ADC?
Over the operational lifetime of a landfill, the amount of airspace given over to standard earthen daily cover can be significant, as high as 10% to 20% of the landfill’s overall airspace. By not utilizing the standard daily cover of 6 inches of earthen material spread out over the current workface, the effective disposal volume of the landfill can be increase proportionally. In addition to the direct effects of more immediately available profit from pure waste disposal, not having to use standard earthen daily cover extends the lifetime of the current disposal cell and the landfill as a whole.
This can provide an indirect benefit of delaying the additional capital costs of subsequent cell construction and final cover installation. Delaying the cost of building the next cell from year 10 of the landfill’s operational lifetime to year 12 may not seem significant, but this delay decreases the present value of these outlays, greatly improving the overall financial health of the site.
It is paragraph 2 of Subpart 21 that allows for the use of alternate forms of daily cover in terms of alternate materials and alternate thicknesses-provided the operator can show the proposed alternate daily cover (ADC) meets the performance requirements of standard earthen cover in terms of controlling “disease vectors, fires, odors, blowing litter, and scavenging” and as long as the proposed ADC poses no threat to human health or the environment. In other words, ADC must provide complete coverage over the workface without allowing waste to protrude to the surface, be nonflammable, adhere to the waste surface so that neither itself nor the waste it is covering could form windblown dust or litter, keep out disease vectors and scavengers (such as rats, birds, insects), and contain odors generated by the waste without generating odors itself.
In addition to the direct and indirect advantages of utilizing an ADC for conserving space, improving your cover ratio, and reducing the costs of operating equipment used to excavate, transport, and apply soil as a daily cover, the improvement of the “in place specific density of the waste” is another benefit which can be illustrated by the experience of the Veolia’s Blue Haze Landfill in the UK, managed by Steve West, a Veolia Environmental employee, along with David Goodwin, the site engineer. Their research showed the following results (as quoted by Milton F. Knight of New Waste Concepts, Inc.):
- Prior to using the ADC, the site was recording “in place specific density of waste” at about 0.7 metric tonnes per cubic meter, which converts to about 1,153 pounds per cubic yard. Upon the outset of using the ADC, they witnessed initially a decline in the “in place-specific density” of the waste from .7 to about .65 metric tonnes per cubic meter. However, within three months of beginning the use of NWC’s ProGuard IIB ADC, they began to see continued and consistent improvement in the “in place-specific density of the waste” being put into the landfill.
- Over a period of two years, the in place-specific density of waste grew from its low of .59 to 1.2. The equivalent number in pounds or American tons per cubic yard was or is 2,024 pounds, or 2.024 tons.
- Part of the reason for this dramatic change that has been theorized by site management and the site engineer is in part due to the improved flow of leachate and gas throughout the waste mass, as well as improved and accelerated degradation of the waste, technically called stabilization of the waste.
ADC Materials: Types and Standards
Approval may be granted to inorganic waste such as industrial or residual waste of varying thicknesses, provided the waste meets the performance characteristics of 6 inches of soil cover. Examples of wastes used as ADC include contaminated soil, foundry sand, coal combustion bottom ash, slag, and certain industrial residuals such as filter cakes. Unsuitable alternate daily cover materials include dusty material that can easily become dried out and pose a windblown dust hazard. Also unsuitable are materials that could be a potential odor source. Restricted use can be made of materials that could generate contaminated runoff, provided the runoff is properly contained and directed to the landfill’s leachate collection layer.
Also usually considered unsuitable for alternate daily cover materials are tires or tire chips (due to potential fire hazard), fly ash (which poses a blown dust hazard), automobile recycling fluff (possessing contaminants such as asbestos, polychlorinated biphenyls, and mercury), construction-and-demolition debris fines (blown dust and asbestos fibers).
Unsuitable conditions may also inhibit or hinder the use of ADC. For example, most ADCs have restrictions placed on their use by extreme weather conditions, such as high winds, heavy rain, hail storms, freezing temperatures, or any combination of these. Spray foams can be blown away from the working face, and tarps can be torn by high winds. Such practical limitations may also become part of a permit requirement should the state regulator become involved in the decision to allow the use of ADC.
By definition, ADC only has to last 24 hours. Foams, for example, can last only a few hours depending on their type and application. Heavy (40-mil and thicker) high-density polyethylene (HDPE) geomembranes used as tarps can last for months with constant reuse each day. For these reasons, certain types of ADC may have their use limited both in area and duration. Waste surface exposed for more than 30 days would have to receive intermediate cover (usually defined as 12 inches of soil cover).
A tarp deployment system can extend landfill life and save thousands of dollars in labor and materials.
Non-cement or non-mortar-based ADC applications can be easily sprayed over a workface as either daily, intermediate, or long-term environmental cover material.
In any case, a waste used as alternate daily cover must meet the standards provided in ASTM D 6826 “Standard Specification for Sprayed Slurries, Foams and Indigenous Materials Used As Alternative Daily Cover for Municipal Solid Waste Landfills” and ASTM D 7008 “Standard Specification for Geosynthetic Alternative Daily Covers.” These specifications provide or reference methodologies for determining if the proposed waste material meets performance requirements for being non-flammable (ASTM D 4982 “Standard Test Methods for Flammability Potential Screening Analysis of Waste” and NFPA Method 1 “Standard Methods of Fire Tests for Flame Propagation of Textiles and Films”), and control odors (ASTM E 96 “Test Methods for Water Vapor Transmission of Materials”).
Commercial Availability
Far more practical, and usually more easily available, than alternate daily covers consisting of waste materials are commercially available products specifically designed for alternate daily cover applications. These include foam, spray-on slurry, reusable geosynthetics, and non-reusable geosynthetics.
Tarpomatic has a new addition to its line of tarp-based ADC materials, the Cable Keeper. These fixtures attach on both sides of the Tarp so that the cables cannot come out. These cables connect to their patented Automatic Tarping Machine (ATM). The ATM attaches to a piece of heavy equipment (front-end loader, bulldozer, etc.), which allows for easy deployment as the equipment backs over the work face, leaving the tarp anchored in place. Each ATM is customized to allow for easy attachment and quick removal from the equipment being used to deploy 40-foot-wide tarp panels. Operated by means of convenient in-cab controls, the ATM uses a hydraulic drive motor to wind and unwind the tarp’s spool with varying speed controlling allowing the spooling rate to match the ground speed of the equipment. The equipment operator can raise or lower the spool to avoid large objects and more easily deploy tarps on uneven terrain.
Airspace Saver has a full-scale tarp shop that can make any type of cover. Airspace utilizes several types of fabrics from heavy-duty flame-resistant fabrics down to lightweight economical fabrics. All seams and edges are sewn together using 2-inch seatbelt webbing with hookup points on all four sides and corners. All tarps are customized, made per order and manufactured for any design. Airspace Saver also makes compost covers, environmental tarps, and trailer covers. Its landfill ADC tarps are made from a high-density woven polyethylene-coated fabric manufactured by Fabrene Inc. Each tarp is manufactured to a custom width with polyester web straps with high tensile strengths (6,000 pounds) used to reinforce the edge and seams. Steel D-rings are set every 12 feet around the perimeter and corners of the tarp. The company offers an option of inserting heavy chain sewn into pockets around the perimeter to weigh down the tarp in high-wind applications. Operationally, these tarps meet all the functional requirements for daily cover, being water-resistant, flame-retardant, durable, cost-effective, flexible (can be installed either by machine or by personnel), and easily anchored, controlling vectors and suppressing odors.
Rusmar’s third-generation AC-667SE Soil Equivalent Foam is more than a landfill cover material. Beyond providing a superior ADC medium, it produces a thick, long-lasting, viscous foam barrier for immediate control of odors, surface fire dangers, windblown litter, rodents, mosquitoes, other disease vectors, and scavengers. The material is applied by the PFU 400/25 or PFU 1600/40 towed trailer systems providing air-compressor, storage, and foam-generating equipment, as well as a 200-foot hose and spray nozzle.
The Enviro Cover Systems division of EPI Environmental Products Inc. manufactures an efficient and cost-effective film-type ADC tarp (Enviro Cover) that is also environmentally friendly. Not only does it minimize airspace utilization, the film itself is degradable. Therefore, it can be left in place after each use, eliminating the need for labor-intensive removal and storage as required by conventional reusable tarps. After burial, the Enviro Cover will degrade and not block leachate percolation down through the waste or form gas pockets in the waste mass. In addition to its signature degradable film, EPI manufactures and supplies the Enviro Cover Deployer equipment for applying the cover. As the EPI tarp is unrolled onto the surface, the deployer simultaneously dispenses a sufficient release of ballast (anchoring material), regulated in a manner to suit the application ensuring stability and proper placement. Together, the cover, the deployer and the method of application make up the Enviro Cover System. The system can be used to deploy intermediate cover for landfills, as well as daily cover applications.
Landfill Service Corp. manufactures Posi-Shell. This is a unique mineral mortar compound that is sprayed over the workface. As it dries out, it forms a hard crust that meets all the operational requirements for daily or intermediate cover. Once hardened, it prevents erosion, controls odors, and prevents disease vectors and windblown dust or debris. The hardened surface easily crumbles like mortar when track-walked by heavy equipment at the start of the next workday. This creates a porous surface prior to the next day of waste receipts, allowing for the free flow of leachate percolation and gas migration. A variation of the landfill mix can be used in such non-landfill applications as erosion control and slope stabilization for highway construction projects, ditch-lining, dust control, cover for contaminated soil, compost, coal, or cement clinker piles, mining applications, voc suppression, sludge tar lagoons, and similar industrial purposes. Posi-Shell Cover is both durable (surviving over long-term exposure to weather and wind) and nonflammable. The mixture consist of a liquid base, Portland cement, and Posi-Pak P-100 Fibers with a PSM-200 Setting Agent. If large quantities of water are unavailable, leachate can be used as the liquid base of the mixture. Posi-Shell materials come in easy-to-handle bags. Portland cement may be handled in bags or via a bulk storage and transfer silo. This greatly simplifies the requirements for stockpiling and lay-down areas to store materials and equipment.
New Waste Concepts Inc. provides ADC equipment designed to last twice as long as the industry average. The company supplies non-cement or non-mortar based ADC applications that can be easily sprayed over a workface as either daily, intermediate, or long-term environmental cover material. ProGuard SB2, the newest addition to NWC’s line of environmental cover materials, is a two-bag application (chemical and cellulose) and can be applied for less than a penny per square foot by any slurry application machine with any pump (centrifugal or positive displacement). Its ProGuard spectrum of cover products (SB2, IIB, IIB+, and Irish Mix) provides an ever-increasing range of density and viscosity. Tony Knight, CEO of NWC, says, “Watch for NWC’s newest material, ProGuard ULTRA.” Complementing the ProGuard product line are the intermediate and long-term environmental covers that carry the ConCover brand name. The ConCover product line includes ConCover SW, ConCover SW Superplus, ConCover 180 and ConCover 180 NS, which are all suitable for steep slopes and long-term applications under adverse weather conditions. At the high end of durability, is the ConCover 180 standard and NS (non-setting) environmental covers which provide, when NWC’s HydraGuard 42 is added, a very strong impermeable barrier (10-7) that suppresses the escape of odor, gases and VOCs, while minimizing the penetration of oxygen. On relatively smooth exterior surfaces it has been used as a less expensive alternative for temporary seam welded geomembranes, lasting up to three years.
Reef Industries Inc., one of the oldest manufacturers of polyethylene cover tarps (in business since 1957), provides engineered plastic laminates that are resistant to tears, punctures, exposure, weather, and contaminants. Its Griffolyn-reinforced alternative daily landfill covers can minimize stormwater infiltration, leachate formation and suppress odors. The company provides both reusable and sacrificial synthetic covers, whose long-term endurance properties include: UV stabilization to protect the material from degradation, cold-crack resistance to protect against damage in extremely cold temperatures, flexibility allowing for ease of placement, and lightweight strengthened with reinforce polyethylene to resist punctures and tears. Griffolyn shows superior physical characteristics (weight, yield and break strength, tongue and trapezoidal tear resistance, cold resistance, and impact strength). A mesh reinforced material, Griffolyn TX 1200 and TX 1600 provide a low-permeability barrier against moisture transmission. Meeting Class C, ASTM E-1745-97 standard specifications for water vapor retarders used in contact with soil, their long life expectancy allows for repeated use and greater cost savings. Once anchored in place with sand bags, Griffolyn can survive for extended period when exposed to weathering.
Rusmar Inc. of West Chester, PA, has become a leading provider of foam and application equipment for ADC in municipal solid waste. Its AC-667-SE Soil Equivalent Foam is a liquid concentrate composed of a starch-modified hydrolyzed protein surfactant. It is delivered in bulk quantity and diluted with water prior to application. AC-667-SE was developed specifically to meet and/or exceed all the requirements of RCRA, Subtitle D. The foam forms a complete barrier to control disease vectors, odors, fires, and windblown litter, and to prevent scavenging. The foam has been approved for use up to 48 hours and will consume zero airspace when covered with waste. AC-667-SE is applied with a Pneumatic Foam Unit (PFU) 2500/60. The PFU2500/60 is a self-propelled foam machine designed to be driven over the workface while deploying a 12-foot-wide foam blanket.
AmCon Environmental Inc. supplies woven polypropylene ADC tarps. The woven fabric is designed to reduce air infiltration, minimize odor escape, and promote runoff from precipitation (thus minimizing infiltration and leachate formation). These tarps can survive up to a year of exposure, even under adverse weather conditions. Though relatively lightweight (only 8 ounces per square yard), each tarp is reinforced around the edges up to 15,000 pounds of tensile strength. The light weight and reinforcement combine to allow ease of placement without damage.
Layfield Geosynthetics has extensive manufacturing and support facilities (three locations in North America). Layfield’s fabrication plants produce thousands of small covers each year (such as soil remediation liners and covers). The company’s specialty, however, is large covers. Layfield regularly produces storage pile covers from RPE 15 up to 100,000 square feet in a single piece.
Recently acquired by Southwestern Sales, Mercer Motor Works offers the TDS-30 tarp application system for ADCs capable of deploying and removing multiple tarps of various materials in minutes. The TDS-30 can be attached to standard landfill equipment (dozers, compactors, and excavators) with easy operation provided by a remote in-cab controller. Southwestern Sales also supplies Tarplox a structural support system for automated tarping machine tarps. The Tarplox allows for complete coverage, without waste tarp width during application.
Case Histories
Application of New Waste Concept’s ConCover SW to the Crawford County Cell Base Liner Repair, Bucyrus, OH-Crawford County Landfill secured New Dominion Construction Co. to make liner repairs at its site. To make these repairs, the waste above the damaged liner had to be removed and a new liner installed. During this process, 52,500 cubic yards of waste was exposed, forming 3-to-1 slopes and, in some areas, 10- to 12-foot vertical walls of open waste. ConCover SW was used to cover the excavated waste to stop erosion and odor during the three months it took to repair 131,000 square feet of liner. Landfill liner system construction is important to slope stability and critical to leachate circulation. If a slope stability failure is a concern, it is important to act quickly because slope failures usually occur rapidly and with little or no warning, personnel and equipment can be adversely affected. Mike Pascuzzi says, “ConCover SW sprayed over the excavated open-waste vertical walls and slopes worked very well in containing erosion and eliminated odors.” Mike also stated, “we have had an unusual amount of heavy rainstorms, and the ConCover SW has held very well.” Maryanne Miller, EPA site inspector, was impressed with the durability of ConCover SW.
Use of Enviro Cover System at the Puente Hills Landfill in California-At Puente Hills, what mattered for daily cover operation was not airspace, but time and efficiency of application of daily cover. The manipulation of earthen cover, particularly in rainy conditions, could be slow and problematic, and here is where the testing and comparison of ADCs led the facility to the degradable film coverage approach, using a self-propelled, track-mounted film and film-ballast “deployer.” Other options were found to be unacceptable. Spray-on slurries had the very limited life expectancy of only a couple of days in addition to visual concerns.
Reusable tarps were too expensive to be used for a prolonged period. Furthermore, the removal of tarps at the start of each operating day would create an unacceptable workload to the districts when a large number of waste disposal trucks were lining up at the gate for waste disposal in the morning.
The needs for cost reduction and expedited coverage have supplemented the traditional airspace savings and water-shedding benefits of the Enviro Cover technology at Puente Hills. Instead of needing to use multiple earth movers-including scrapers, dozers, and cover soil compactors, with related personnel, diesel fuel, and maintenance costs-the landfill can cut operational expenses and still meet US EPA requirements. The Enviro Cover System provides a surface barrier which sheds around 98% of rainfall over its coverage area, providing tremendous leachate treatment cost savings when left in place for interim periods and graded to drain as appropriate. Like all EPI’s Enviro Covers, Progressive Enviro Cover (PDC), otherwise known as Extended Enviro Cover (EEC), is a degradable geosynthetic alternative daily cover that does not require removal after its use. It has a specially engineered ability to degrade, following an initial performance of durability. Degradation of all Enviro Cover products is programmed to occur through exposure of the film to heat, mechanical stress and/or ultraviolet light. Once the process is initiated, Enviro Cover continues to degrade and becomes brittle and fragmented upon burial, allowing free movement of landfill gas and leachate within the landfill. The film eventually degrades to simple carbon molecules and water. Degradation rates accelerate within the landfill as higher temperatures develop with depth underneath the waste.