A chimera is a mythical creature that combines two different animals, an example being the Griffin, which is half lion and half eagle. A municipal solid waste landfill is also something of a chimera, being half construction site and half industrial facility. As such, a landfill has a very unique financial setup. Typically, a landfill requires extensive site investigation and expensive capital costs to construct and eventually cap its disposal cells (not to mention non-landfill capital costs associated with security, support buildings, etc.). Landfills tend to be very complex and expensive to construct. However, the actual waste disposal operations are relatively simple and straightforward. Waste is hauled in, deposited at the current working face, spread, and compacted. On a per-unit (ton of waste received) basis, waste disposal operations are relatively inexpensive.
The result is a business with high fixed costs associated with the capital outlays needed to establish the basic infrastructure that allows operations to begin. In this manner, landfills are not that much different than any other construction site. In addition to the high fixed costs, landfills tend to have low per-unit operating costs that can result in healthy profitability once operations exceed the site’s breakeven point. To simplify, a landfill’s costs (for the most part) are a function of its aerial extent, since capital costs (construction and capping) are based on the acreage of the disposal area. Furthermore, a landfill’s profitability is a function of the waste disposal volume. Maximizing profits involves maximizing the amount of airspace that can be utilized for each acre of disposal area.
This is how alternate daily cover (ADC) material can be used to positively affect a landfill’s bottom line. Unlike the soil cover layers mandated by regulations, ADC utilizes little or no airspace. All the volume that would otherwise be taken up by soil cover layers can be freed up for waste disposal. Over years and decades of landfill operations, the accumulated airspace can be significant, with volumes as high as 10% to 15% of the landfill’s total volume. Furthermore, by effectively increasing the airspace available in the current disposal cell, the lifetime of the cell can be extended by months or years. This pushes back the need to build the next disposal cell to a later date, effectively reducing the site’s capital costs on a present value basis. Either way, ADC is both a time saver and a money maker.
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Photo: Rusmar
Rusmar’s system lays down a wide swath of foam. |
Regulatory Requirements
Subtitle D of the Resource Conservation and Recovery Act (RCRA) deals with the management and disposal of nonhazardous municipal solid waste (MSW). The regulatory framework established by RCRA is provided in Title 40 of the Code of Federal regulations (40 CFR—“Protection of Environment”). Under 40 CFR, Chapter I—Environmental Protection Agency, Subchapter I—Solid Wastes (Parts 239–282) details the regulatory standards and requirements for MSW landfill operations. Specifically, the requirements for covering deposited waste at the end of the work day are described as follows:
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 six 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:
(1) Consider the unique characteristics of small communities;
(2) Take into account climatic and hydrogeologic conditions; and
(3) Be protective of human health and the environment.
The state environmental agencies that serve as the enforcement arm of American environmental policy (aka an “Approved State”) must mandate regulations that are at least as stringent as those established by the federal government. As such, landfill permitting, construction, and operation must meet or exceed these regulatory standards. The section of Part 258 quoted above allows for the use of alternate daily cover materials instead of the basic 6 inches of soil, but effectively requires two sets of standards. The first deals with operational performance of the cover material itself (“to control disease vectors, fires, odors, blowing litter, and scavenging”), while the second requires that alternative application schedules specifically protect human health and the environment, which can be taken as being applicable to all covers and application schedules. In short, an alternate daily cover must meet or exceed the same performance standards as 6 inches of daily cover soil without itself directly or indirectly presenting a threat to the environment.
For areas of deposited waste that will be exposed (neither receiving additional deposited waste on top of their exposed surfaces nor installing a final cap and cover system on these surfaces) will usually be required to receive intermediate cover. Ohio Administrative Code regulation 3745-27-19 provides a good example of the standards required for intermediate cover:
(G) Intermediate cover
- To minimize infiltration, the owner or operator shall apply intermediate cover to all filled areas of a sanitary landfill facility where additional waste is not to be deposited for at least thirty days. The director may approve the use of some alternate time period, if the owner or operator can demonstrate to the satisfaction of the director that, by use of the alternate time period, infiltration will not be increased.
- Intermediate cover material shall be nonputrescible and have low permeability to water, good compactability, cohesiveness, and relatively uniform texture, and shall not contain large objects in such quantities as may interfere with its application and intended purpose. A soil layer, a minimum of twelve inches thick, consisting of well-compacted loam, silt loam, clay loam, silty clay loam, silty clay or some combination thereof, shall be used. The owner or operator may use other materials or thicknesses for intermediate cover if the owner or operator can demonstrate the satisfaction of the director that the proposed intermediate cover material or thickness provides comparable and adequate protection.
- Prior to the placement of the next layer of waste in that area, intermediate cover in an area shall be removed or otherwise prepared as necessary so as not to impede the flow of leachate to the leachate management system within the limits of waste placement.
- The owner or operator shall perform measures to protect the intermediate cover from erosion.
Note that the “30 days” limit for maximum exposure duration probably derives from the 40 CFR Part 256.60 Closure Criteria requirement for starting final closure within 30 days of final receipt of wastes. In either case, the requirement is recognition of the need to minimize exposure time for waste. Daily cover, whether standard soil or some alternative material, is meant as only a short-term protection and safeguard. Daily cover is intended to prevent fly emergence from landfill materials; to minimize disease vectors by limiting contact between waste and disease carriers (birds, rodents, and insects); to control blown litter, odors, and air emissions by preventing direct contact by the wind with the deposited waste; to promote runoff by reducing percolation of precipitation into the waste; to reduce the risk of fire by smothering external sparks or flames; and generally to improve the landfill’s aesthetics. This last function is of great importance and not to be dismissed simply because it has no practical operational applicability. In an industry where perceptions can shape public and political attitudes towards a landfill, aesthetics may be the most important function of all.
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Photo: Landfill Service Corp.
Posi-Shell is a cement-mortar-based spray-on cover. |
Crunching the Numbers
While aesthetics and public relations are important, the bottom line remains the bottom line. This can be illustrated by means of a hypothetical example of a typical landfill that charges a $30 per ton tipping fee at the gate.
Assume that this is a moderately large landfill with a disposal area extending over 100 acres, with a roughly square shape of about 2,000 feet by 2,000 feet. As with most landfills, its maximum allowable height is limited by local height restrictions and its maximum depth defined by its underlying hydrogeology. As a result, the final waste disposal grades and the liner grades established by excavating below existing terrain result in an average waste thickness of 100 feet (though this varies considerably across the landfill and from cell to cell). The hypothetical landfill’s 10,000 acre-feet of disposal airspace would be equivalent to approximately 16,130,000 cubic yards (at 1,613 cubic yards per acre-foot).
Further assume that the hypothetical landfill receives an average of 1,000 tons (2,000,000 pounds) per day. MSW arrives at the landfill with a density of 15 to 25 pounds per cubic foot. Once the waste has been deposited it is spread out over the current working face in a loose lift 2 to 3 feet thick. After spreading, waste compactors make several passes (usually three to five) over the loose layer to achieve optimum density. Once spread out over the working face and compacted, the volume of the waste should be halved and its density doubled to 30 to 50 per cubic foot.
Assuming that the compaction efforts at the hypothetical landfill result in an average in-place density of 40 pounds per cubic foot (0.54 tons per cubic yard), the landfill would have a maximum waste disposal capacity of 8,700,000 tons. At an average waste receipt of 1,000 tons per day, the landfill would have an operational lifetime of almost 28 years. Additionally, the landfill’s waste disposal operations would utilize 50,000 cubic feet (about 1,850 cubic yards) of airspace each day.
The required operational area of the current working face is a function of the productivity of the waste compactor(s) and the rate that waste is deposited on the landfill. With a waste compactor of moderate size (an operating weight of 70,000–100,000 pounds and an engine of 300–400 horsepower) 1,000 tons per day could require a quarter-acre working face, though there are many site conditions and geometry factors that will affect this size.
The 6 inches of soil placed as daily cover would then consume 5,400 cubic feet (about 200 cubic yards). Therefore, of the total airspace consumed each day, a little over 2,000 cubic yards, approximately 10% is consumed by cover soil instead of profitable waste disposal. For our hypothetical landfill, 10% of its total volume would be 1,613,000 cubic yards, equivalent to 871,000 tons. At a tipping fee of $30 per ton, this represents a loss of gross revenue equal to $26,131,000 (equal to average gross revenue losses of almost $1 million a year).
Applications and Types of Alternate Daily Cover
We can all agree that this represents a significant revenue loss. The goal then is to utilize a non-soil material for daily cover, material that can be easily removed and/or not consume measureable amounts of airspace. There are five broad categories of alternate daily cover to choose from:
- Disposable sheets of thin plastic film
- Reusable tarps or sheets made from high density polyethylene (HDPE)
- Reusable tarps made from heavy geotextile
- Spray applications using inorganic chemicals and concrete
- Spray applications that utilize such organic materials as pulped paper
Tarps and sheets can be rolled out over the current work face manually, but it is usually more efficient and cost effective to utilize a mechanical tarp-deployment mechanism. Mechanical deployment reduces wear and tear on the tarp and takes less time. Disposable sheets are to be deliberately torn up at the start of the next working day by means of track walking with a dozer. This action makes the tarps permeable to the downward passage of moisture and prevents leachate lenses from forming above them in the waste.
Sheets and tarps can sometimes be difficult to place, given that waste contains many sharp objects that can catch or tear the sheet during deployment. Spray-on ADC is an alternative to tarps and sheets. Spray-on ADC is a slurry mix of water, cementitious binder, adhesive additives and bulking fiber. Once sprayed over the working face with a high-pressure hose it dries out to form a decomposable (if organic) or easily breakable (if inorganic) paper-mache-like crust over the waste surface. Spray-on ADC also has operational limitations and often cannot be effectively deployed during high winds or in low temperatures. Otherwise, they can be a labor-saving addition to the landfill’s equipment fleet.
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Photo: EPI Environmental Products Inc.
EPI’s plastic film is biodegradable. |
Manufacturers and Suppliers
Airspace Saver Daily Cover of Ponchatoula, LA, supplies an alternate daily cover tarp manufactured by Sassco Supply. The company uses a fabric manufactured by Fabrene Inc. The tarp can be manufactured to specified widths. Each tarp is serviced by a series of high-tensile strength (6,000-pound yield strength) polyester web straps. These straps are sewn onto every material seam as well as around the perimeter to improve the strength of the tarp. Steel D-rings are then securely sewn into the tarp around its edges, at intervals of 12 feet and on all corners. Additionally, a heavy cable or chain can be sewn into a pocket around the edge of the tarp to further strengthen it against tear failure and provide additional weight to allow its use during periods of high winds.
AmCon Environmental Inc. of Somerset, KY, manufactures Beltech 113 alternate daily cover tarps made of woven polypropylene fabric. Available sizes range from 50 feet by 50 feet to 150 feet by 150 feet. The polypropylene fabric is flame resistant and minimizes moisture infiltration. Its tight weave helps to reduce oxygen infiltration and the escape of noxious odors. The 8-ounce-per-square-yard fabric is further reinforced by 15,000-pound-tensile-strength nylon webbing quadruple stitched with polyester thread around exterior of tarp with reinforced corners. This reduces damage due to stress and allows for easy placement with standard landfill equipment.
EPI Environmental Products Inc. of Vancouver, BC, is a proponent and leader of oxo-biodegradable plastic additive technology. It has developed a degradable plastic film that can be utilized as alternate daily cover (Enviro Cover) or as stretch wrap for compacted MSW bales (Enviro Wrap). Enviro Cover is a degradable polyethylene film categorized as a “nonreusable geosynthetic.” It does not require removal or retrieval once it is placed on the working face to provide daily cover. It degrades upon the exposure to sunlight, heat and/or mechanical stress. Prior to degradation, it has sufficient tear and puncture resistance, and elongation characteristics that allow it to be used as ADC without initial tearing. Since it is degradable, it will not interfere with normal landfill gas and liquid flows within a landfill, avoiding leachate lenses and gas bubbles.
Kym Industries Inc. of Slocum, AL, manufacture tarps made from heavy-duty but lightweight coated polypropylene material for use as alternate daily cover. Ease of transportation is provided by standard reinforced webbing and secured loops. Thei company’s vinyl-coated fabrics come in weights ranging from 10 ounces to 22 ounces per square yard. They are able to manufacture tarps to any size specification, and each tarp includes webbing all around the hems, vinyl reinforced pockets, double stitching, and grommets all around at standard spacing intervals.
The Landfill Service Corp. of Apalachin, NY, manufactures the Posi-Shell Cover System, a spray-on alternate daily cover. Posi-Shell is a cement-mortar-based, spray-on cover material, similar to stucco in its visual and physical characteristics. It meets and exceeds regulatory requirements for daily cover performance, minimizing vectors, fires, odors, blowing litter, and dust. The Posi-Shell Cover System consists of a liquid base (which can be either water or leachate), Posi-Pak P-100 Fibers, and the PSM-200 Setting Agent combined with Portland cement. Its color can be changed by adding various dyes to the mixture. For landfills permitted to accept it, latex paint can become an additive to the Posi-Shell mix, lending further strength and durability. Unlike paper or wood mulch based ADCs, once cured, Posi-Shell continues to exceed regulatory requirements for flammability while it forms a durable, fire-resistant crust that resists wind and water erosion. Posi-Shell’s mixture can be modified to allow its use as short-term overnight cover, intermediate cover for erosion and odor control, and long-term cover for stockpiles and compost. When used as daily cover, additional waste can be deposited on the previous Posi-Shell surface the next day, since the crust it forms is easily broken up by equipment movement and waste disposal operations. This feature of Posi-Shell makes it an ideal enhancement for bioreactive landfills as moisture more readily migrates below the surface to accelerate the decomposition process.
Mechanical tarping systems are the business of Mercer Motor Works LLC of Mercer, ME. Mercer’s deployment system reduces labor costs with a one-man operation that can lay 9,000 square feet of tarp in less than 10 minutes by remote control from inside the existing landfill equipment. Two landfill-specific systems are available, the TDS-30 and the TDS-30 HC. The TDS-30 weighs around 3,000 pounds and can easily be used in landfills having high sludge content or otherwise requiring low ground-pressure equipment due to its frame legs having shoes welded on to support the TDS-30 in soft or muddy ground conditions. The frame itself is made of heavy-duty gauge steel and able to support at least three 6.5-ounce, coated polypropylene tarps, each 30 feet wide by 100 feet long, ballasted and with chain sewn in pockets. Its engine is a 5.5-horsepower Honda gas-powered engine powering a hydraulic system that operates the TDS-30 spool, which deploys the tarps. The TDS-30 comes with a manual control and a heavy-duty remote-control unit for retracting and extending controls for rolling and unrolling the tarp covering system. Easily adapted to existing landfill equipment, the TDS-30 can be moved and operated from D4- to D8-class bulldozers or CAT 826 to CAT 836 compactors. The TDS-30 HC is the heavier version, weighing in at 4,000 pounds and each capable of deploying four ballasted tarps.
New Waste Concepts of Perrysburg, OH, provides a wide range of daily, intermediate, and long-term covers as well as cover additives, seeding stimulants, odor controls, bird controls, and dust controls. Primarily a manufacturer of non-cement-based spray-on alternate cover applications, New Waste Concepts product lines provide easy-to-apply cover applications and their support equipment. The company’s Topguard daily cover application consists of a blend of polymers and recycled fibers combined into one dry component that eliminates the need for mixing two separate ingredients. Proguard SB alternate daily cover, also a blend of polymers and recycled fibers, is a heavier version with a higher viscosity. The two-component version, Proguard IIB, has been formulated to meet all Subtitle D requirements and also acts as an effective odor barrier against hydrogen sulfide and other gases, such as radon and volatile organic compounds. A more durable version of this product is Proguard IIB+, which incorporates a higher chemical content and a fiber matrix that allows the material to adhere to the working face more effectively. ConCover SW is the company’s longer-term, intermediate cover application, providing cover for seven to 60 days.
Reef Industries Inc. of Houston, TX, has been manufacturing Griffolyn Landfill Covers since 1957. Its Griffolyn sheets have found a wide range of uses in the environmental field, including use as alternate daily cover tarps: corrosion protection, equipment storage, shipping covers, landfill covers, vapor and moisture barriers, dust and environmental partitions, contaminated soil covers, athletic field covers, greenhouses, and crop protection, to name a few. The sheets themselves are made from internally reinforced three-ply laminate combining two layers of UV-stabilized coextruded polyethylene with a high-strength cord grid. This high-strength reinforced grid provides significant puncture-and-tear resistance with an improved ability to withstand extended exposure to weather and UV degradation. Large panels (greater than an acre in size) can be custom fabricated, while its lightweight material makes even large panels easy to handle. All these characteristics allow Griffolyn to survive longer in the harsh environment of a landfill’s working face.
Enstar’s Tarp Armor brand tarps are supplied by the Southwestern Sales Co. of Rogers, AR. These come in standard sizes of 50 feet by 50 feet and 100 feet by 100 feet (other standard sizes and custom sizes are also available). Their light weight allows for effective manual placement as well installation by equipment. These can be integrated with most automatic tarping machines (ATMs) while being equipped with the company’s patent-pending tarpLOX structural support system. The tarps themselves are made out of polypropylene sheets weighing either 6.5 ounces or 9.4 ounces per square yard. This support system reinforces the tarp corners and provides heavy-duty straps and D-rings on all four edges. Use of the tarpLOX system reduces wear and tear, ensures maximum coverage without telescoping, increases stability in high winds, and minimizes placement time.
Tarpomatic Inc. of Canton, OH, manufactures a patented ATM. It is a mechanism that can attach to the front of most types of heavy equipment, usually waste compactors and dozers, although other equipment can be adapted for the ATM. Ruggedly built, many Tarpomatic ATMs are still in the field after a decade of rough use. It is basically a giant spool suspended from the equipment by means of support arms. The spools deploy the tarp by rolling along directly above the current working face, unrolling the tarp as the equipment backs up over the area. In this manner, a tarp can be easily deployed without pulling and resultant catching, tearing, and abrasion. Tarps can be unwound and rewound at the start of the next working day by means of a variable-speed control system. As a result, the tarp material suffers less wear and tear, adding to its useful life and reducing operating costs. The system is designed to deploy panels 40 feet wide in varying lengths. Easily removable spools allow for quick linking of adjacent tarps to cover larger areas. The equipment operator has complete control over the tarping mechanism by means of a hydraulic motor and engaging system.
The tarpARMOR brand of Alternative Daily Covers (ADCs) is offered by Southwestern Sales Co. of Rogers, AR and is produced in a wide variety of sizes and designs suitable for manual deployment methods or using automatic tarping machines (ATMs). The most common sizes for manual ADCs are 50 feet by 50 feet and 100 feet by 100 feet. Other sizes are available along with a variety of custom features. Standard designs utilize heavy-duty pull straps and D-rings as required for easy manual deployment, or the use of spreader bars. ADCs designed for automatic tarping machines (ATMs) can be order with the patent-pending tarpLOX structural support system. The tarpLOX system reduces wear and tear on both tarp and machine, ensures maximum coverage without telescoping, increases stability in high winds, and minimizes tarp replacement time. All tarpARMOR ADCs are made of abrasion-resistant polypropylene in 6.7-ounce-, 8-ounce-, or 9.4-ounce-per-square-yard panels. Polypropylene passes some fire-retardant tests. Heavier weights and higher fire-retardant materials are available upon request.