It’s said that an automobile should have its oil changed every 3,000 miles. Landfill equipment has its own service and maintenance schedule. The landfill itself has a maintenance schedule with activities that have to be performed daily, monthly, quarterly, and annually.

By Daniel P. Duffy

It is a mistake to consider a landfill to be a static mass of earth and refuse. A landfill consists of multiple mechanical systems that can wear out or fail if not properly maintained and serviced. Furthermore, the workface needs to be properly maintained to keep waste disposal operations running smoothly and efficiently.

Daily maintenance revolves around the landfill’s current workface where waste is being deposited. The landfill operator must maintain his workface properly so as to minimize dust, blown litter, disease vectors, and odor. The easiest way to achieve all of these goals is to properly use daily cover. Daily cover becomes easier to apply if waste is carefully confined and properly compacted into the smallest area possible. In order to assure that waste compaction and placement is within operational norms, the operator should track weekly, if possible, the airspace utilized by waste disposal operations. Inclement weather and winter conditions add to an already difficult job and require their own operational procedures.

In addition to operational maintenance, the landfill operator is responsible for long-term maintenance of existing landfill structures. Those areas that have already received final cap and cover should be inspected for damage, erosion, and failed vegetation—at least quarterly. The stormwater runoff control structures and sedimentation controls should be inspected even more often, especially after a major storm event. Landfill mechanical systems, such as the landfill gas management system and the leachate extraction system, should be inspected and serviced as required by the manufacturer to ensure that they remain in good working order.

Maintaining the Workface
The workface is the heart of landfill operations. All other services, systems, and functions exist to support its operation and to ensure that disposal operations are performed as efficiently as possible and do not adversely affect the environment. Like any other work place, a neat landfill workface is a safer work area with fewer opportunities for accident and injury.

The first item on an operator’s to-do list is to minimize dust. Dust minimization is usually required by law or the permit conditions dealing with site operations. This primarily involves maintaining the access roads leading to the current workface. Access roads should be considered as extensions to the workface. If an operator does not maintain the access roads, he won’t get there from anywhere. Most roads on the landfill are not paved. They are typically dirt roads or, at best, have gravel surfaces. Roads used as a route to the workface need to be sprayed regularly, preferably with reclaimed water from the landfill’s surface-water management system, to minimize dust. At no time should leachate or any other contaminated liquid be used to spray access roads. Some states allow the use of oil to minimize dust, but this is poor practice as it can lead to slick surfaces and contaminated runoff. Occasionally, states with stricter standards will require the use of potable water for dust control. Commercially available and approved chemical treatments for holding down dust are available and, though more expensive, may actually cut overall application costs by reducing the number of passes required to achieve the same level of dust suppression.

Water can also be sprayed (in limited quantities) at the workface and the dumping pad to minimize dust, but care should be taken not to introduce excessive moisture back into the landfill. Such moisture will return eventually as leachate. This is a potentially serious problem during the initial stages of a disposal cell’s operation when there is little waste to absorb moisture and prevent leachate head build-up on the liner. Certain waste loads (like ash) will be inherently dusty. Instead of applying large amounts of water on these loads, the best practice is to push as much regular waste over the dusty waste and bury it as quickly as possible.

Applications of dust-suppressant liquids should be performed either with a water spray truck or with a sprinkler hose. The spray truck is appropriate for applications along the access roads or over broad areas. Hose applications should be reserved for spot applications in a limited area or on parts of the workface that a spray truck cannot access. Since the operational goal of dust suppression is to maximize safety by maximizing visibility (the environmental goal is to minimize air pollution), safety precautions should be taken during dust suppression. These precautions include, at minimum, maintaining good eye and ear contact with nearby pedestrians, equipment, and trucks (situational awareness), yielding right of way to these same trucks and equipment, and completing each pass in a regular manner without shortcuts or sudden, unexpected changes in direction.

Blown litter is similar to dust in its safety and environmental impacts, but it is controlled in a completely different fashion. In many ways, litter is worse. While even a heavy cloud of dust will eventually settle to the ground and disappear, blown litter will create an unsightly mess well beyond the boundaries of the landfill site. Like dust control, minimizing blown litter is often a permit requirement.

The first step in minimizing blown litter is to attack the problem at its source by keeping the waste confined in as small a workface as possible. The optimum workface size is a function of the number of waste compactors operating at the workface, which in turn is a function of the amount of waste received each work day. Proper compaction immediately after deposition is a must. This usually involves the pushing of waste uphill by the compactors to get the full force of the compactors’ weight and operating speed applied to the waste mass. Though not always possible, it is good practice to have the open workface downwind of the waste tipping area so that any blown litter gets blown into the workface instead of out of the landfill. Even better is to have the workface alee of the wind so blowing at the workface does not occur at all. Once the waste is compacted in place, a new load of waste should be immediately spread and compacted above it. If no additional waste is available, or if it is at the end of the work day, cover material (either synthetic membranes and sheets, or six inches of soil) should be placed over exposed areas of the workface that received waste.

If litter is not properly contained at the workface, there are secondary methods of control. First and foremost are litter-control fences and netting. Fences can be as small as wooden snow fences installed around the perimeter of the disposal area. More extensive netting can be strung between tall poles. The poles should be anchored in heavy tires and/or concrete blocks that provide stability while allowing their relocation using heavy equipment to other parts of the landfill. Their actual location will depend upon current wind conditions and the configuration of the workface. Should litter make it past the control fences, there remains the old standby—manual labor. Litter pick-up is a necessity at nearly every landfill, even those with stringent blown-litter controls. Litter crews are also needed to remove caught litter from the fencing itself. Removal of litter from the fencing reduces the force of the wind on the fence, and prevents the fence from being overturned by a strong gust. When all else fails, water can be applied to loose waste to make it adhere to the workface.

After dust and blowing litter, the third landfill maintenance headache is disease vectors. Vectors are any potentially disease carrying animals, birds, or insects (rats, deer, mosquitoes, flies, seagulls, etc.). Oddly enough, deer are attracted to landfills since leachate tends to taste like salt. An improperly maintained workface attracts deer like a very large salt lick. And while rats naturally carry diseases, deer can also spread disease and do serious damage to the landfill’s structural components. Deer hooves are notorious for the damage they can do to exposed sections of geosynthetic membranes and textiles.

Seagulls and other birds can often become so numerous (even at landfills far inland) that extraordinary means are required to chase them away. Explosive canons are the preferred method (if the neighbors don’t mind all the noise) and should be set to blow at regular intervals. Even more exotic are radio-controlled robotic falcons that swoop through flocks hovering over the landfill. Not only are bird droppings extremely unpleasant, the birds themselves pose a strike hazard to airplanes (which explains the Subtitle D landfill-to-airport setback distance requirements). Landfills near major urban areas tend to have a zero tolerance policy for birds. Bird nuisance and most other vectors can be greatly minimized by the proper application of daily cover and by keeping the workface to the smallest size possible.

Last but not least is landfill odor control. A well-maintained landfill isn’t just about avoiding unsightliness, it’s also about impacts to the people downwind of the landfill. While it may be practically impossible to eliminate landfill odors, a great deal can be done to minimize this problem and its associated public relations challenges. An isolated location, as most landfills have, usually results in few odor complaints. Perfumes are also available in what can only be described as large, economy-size containers. They are designed to send an aerosol mist into the sky above the workface at regular intervals. Odor control foams that can be sprayed directly onto the waste are also available.

This brings us back to proper applications of daily cover material. At the end of each working day, the site operator should place daily cover over the entire current workface. This gives the landfill a better appearance, prevents the breeding of disease vectors (insects and rodents), minimizes odors, and prevents windblown debris. The standard material used for daily cover is locally available soil. Usually, this soil is a stockpile leftover from landfill cell construction operations. Cover soil is spread loosely over the workface and is not compacted in place.

Daily cover operations become much easier when the waste is properly compacted. Here we come to the foundation of all workface management. Everything else is made easier by proper waste compaction. Once the waste has been spread out over the current workface, each compactor makes three to five passes. More passes won’t result in further volume decreases, so they would be wasted effort.

Winter and Inclement Weather Operations
Winter and inclement weather operations present unique challenges to the landfill operator. While snow can hide exposed waste, it doesn’t serve as an adequate cover. In fact, its effects are almost completely negative. Everything—people and machines—slows down in winter conditions. Though the cold weather eliminates most disease vectors and reduces the decomposition that creates odors, winds are worse, which tends to blow more dust and litter during dry spells while making the placement of daily cover more difficult. On rare occasions, very severe weather may even shut down a landfill for a day.

During wet spells, dust and blowing litter are minimized by nature, but new problems occur. Wet and cold conditions can reduce access roads into a goopy mess with ever-deepening tire ruts, unsafe driving and operating conditions, and the new problem of mud tracked onto paved roads both on and off the site. Often, a dozer or scraper is required to back-blade the surface of unpaved roads in wintertime. But this is only a temporary solution, since ruts begin again in the new surface even if temperatures are well below freezing. An effective alternative to repeated back-blading is the use of corduroy road surfaces. However, these temporary road surfaces are expensive and only useful for tire vehicles (they tend to get torn up by tractor-tread equipment movement). Lastly, icy conditions may require the use of road salt and other de-icing chemicals. Care should be taken when applying these so that runoff from the melting ice and snow does not impact nearby groundwater monitoring wells and result in a false contamination reading for the groundwater.

Tracking Airspace Utilization
Tracking airspace utilization with regular surveys of the workface and the current waste disposal cell is important for proper landfill maintenance for several reasons. First, it gives the operator accurate information on how well the waste is being compacted. By comparing weekly tonnage receipts with airspace calculated between the workface surface at the start of the week and the surface at the end of the week, an accurate measurement of in-place density can be made. By comparing current densities with historic norms, the operator can determine if proper compaction is being achieved and if the landfill volume is being efficiently utilized. Allowances should be made for special conditions, such as the initial lift of waste (which is never compacted) disposed in a cell and the disposal of essentially non-compactable waste, such as fly ash or foundry sand. Secondly, area surveys can be used to determine the size, slope, and extent of the actual workface. This will tell the operator if the workface is as minimal as possible given operational norms. In turn, this provides the information necessary to calculate daily cover application rates. Thirdly, workface surveys provide a planning tool for the choreography of heavy equipment in the disposal cell. An operator can review the survey map and determine the operating location of each compactor and the approach routes, tipping points, and exit routes of the waste delivery trucks.

Methods for tracking airspace can be simple or high tech. Simple methods include vertical yardsticks anchored in orange traffic cones. These are placed around the workface at regular intervals. Hand measurements can determine weekly changes in waste depth. Tape-measure measurements of the yardstick locations can be used to determine the area of the current workface. A more high-tech approach would utilize a GPS survey station set on an established, fixed benchmark with known northing, easting, and elevation. Once the stationary unit has been established and the height of its antenna above the benchmark measured, the rover antenna is used to establish three more local benchmarks to triangulate the site. The rover antenna can then be used to perform location and elevation shots across the workface and disposal cell. The points can be used to create 3D surfaces, perform volume calculations, generate contour maps, and draw site cross-sections.

Keeping a Complete Cap and Cover
Once operations in a disposal cell are complete, those portions of the disposed waste that have achieved final grades will receive a final cap and cover. The outermost layer of the final cap and cover is a vegetative soil layer 6 inches to 12 inches thick supporting a complete growth of grass cover. The layer is exposed to the elements and is subject to erosion and gullying until the vegetative cover is complete. The operator is responsible for ensuring that the cover’s integrity is preserved and eroded areas repaired and reseeded as needed.

The success of any spot or general area revegetation effort depends on factors limiting vegetation growth, final site conditions, site preparation, use of mulches, plant selection, type of fertilizers, and seed application methods. For small repair jobs, a hand-cranked seed thrower can be used by one man walking over the repair area. Larger jobs may require significant earthwork to repair the physical damage and broad area hydro seed application. Long-term care of the final cover requires an inspection plan, trained equipment operators, and laborers. For final cover, long-term care lasts as long as it takes for the vegetation to stabilize and provide complete erosion protection—about five to ten years.

Integral to the final cover are the structures used to collect and divert surface-water runoff from the final cover to discharge channels and sediment controls. Drainage control structures should be inspected at least quarterly during landfill operations and at least annually after the landfill closes. In either case, they should be inspected after major rainfall events. Similarly, prolonged dry periods can result in desiccation, cracking of the cover, and the failure of vegetation. Cleaning the structures may not be necessary if the flow velocities in the channels are fast enough to allow for self-cleaning. Sediment build-ups in these channels can be cleaned out with small dozers or backhoes.

Maintenance of the Landfill Mechanical Systems
The landfill is served by two mechanical systems during operation and after closure: (1) methane gas management, and (2) leachate collection and extraction. Decomposing waste produces methane gas. Methane is deadly in confined areas, such as trenches and sumps, as well as being a flammable gas. If not managed properly, it can create serious hazards for the landfill and neighboring structures. For landfills with geomembrane covers, an accumulation of landfill gas can cause the cover to blow up like a balloon. This can cause structural instabilities and usually requires someone to perform the risky and unpleasant task of slitting open the exposed membrane to allow the gas to escape.

Predicting landfill gas production is more art than science. Gross predictions for the overall landfill may be preformed, but unbalanced landfill production depends on unforeseeable operational conditions. Excess use of fill dirt may reduce the overall volume of waste in one disposal cell (reducing methane production) while disposal of highly organic sludges in the next cell may increase gas production above the expected average. The landfill gas extraction wells have to be regularly balanced, both during operations and after closure to compensate for these irregularities. Landfill gas extraction wells come with pressure-measuring ports and ports for taking gas samples for chemical analysis. Once the gas-well information has been examined, the wells can have their pressure, flow velocities, and flow volumes altered by turning a throttle valve in the well stack. In extreme cases, wells can be shut off entirely or new wells added to high gas regions.

Leachate is a byproduct of precipitation (stormwater, snow melt, and moisture from the refuse itself) percolating through the waste until it reaches the leachate collection layer at the bottom of the landfill. The leachate collection layer typically consists of pipes surrounded by gravel set in a highly permeable sand layer. These pipes carry leachate to collection sumps where pumps discharge them through riser pipes to storage tanks, pretreatment systems, or directly to nearby sanitary sewers. The components of the leachate management system should be inspected at least quarterly during operations and at least annually after closure. At regular intervals, the leachate collection pipes will need to be jetted to remove accumulated sediment and biological scum that may reduce the pipes’ flow capacity. The pumps should be replaced and maintained as required by the manufacturer. A good landfill design will have a double-riser pipe arrangement for each leachate collection sump. One riser will have an active leachate extraction pump, while the second will be empty and held in reserve. Occasionally, pumps get caught down in the bottom of the sump and cannot be pulled up the riser. Having a second riser allows the operator to abandon the caught pump in place and insert another pump down the additional riser. The alternative is the very expensive and unpleasant task of digging up waste until the sump is exposed and the pump can be removed.

In conclusion, the operator should consider even the non-mechanical portions of the landfill to be like a mechanical system in constant need of maintenance and regular tune-ups. Failure to do so will have the same effect on the landfill’s performance as lack of maintenance would have on any machinery or equipment. The effort spent maintaining the landfill is worthwhile—paying dividends well past the landfill’s closure.

Daniel P. Duffy, P.E., is an environmental engineer in Cincinnati, OH.

MSW - November/December 2005