The landfill course
This months lesson covers equipment,
safety, operational strategies, and operator training..
Operating procedures at a sanitary
landfill are determined by many factors, which vary from site. The landfill operational
plan prepared as a part of the desing procedure serves as the primary resource document,
providing the technical details of the landfill and procedures for constructing tre
various engineered elements.
Since a landfill is constructed and operated over number of years, it is important that personnel continually consult the plan to assure conformance with the plan okver the long term. If operating produceres must be noted so that an accurate record is maintained. Changes in operating procedures often need regulatory agency approval, and careful planing is necessary to make a smooth transition to a revised operating plan.
After receiving the required site desing approvals from the appropriate authorities, preparation and construction of the site can begin. Table 1 lists the steps to be completed for site preparation and construction. However , at a given site, the steps may not necessarily follow the exact order shown.T
Site Preparation and Construction Steps
Development of the complete landfill may be divided into
stages, some of which are completed many years after the opening of the site. As with
other construction projects, all the work should be documented. While commonly overlooked
in landfill construction, documentation can be invaluable when questions arise in the
future regarding the adequacy of site construction. Documentation is important for proving
to regulatory authorities and local committees of concerned citizens that design standards
are actually being implemented. Also, good documentation can case repairs if they become
Guidelines shown in Table 2 list important considerations when placing the landfill into operation.
Equipment at sanitary landfills falls into five functional
categories: site construction, waste movement and compaction, cover transport, placement
and compaction, and support functions.
Landfill site construction is often done by contractors employed by the site developer. Whether the work is done by contractors or site personnel, good construction management and coordination of equipment is essential. Conventional earth moving equipment, including scrapers, bulldozers, excavators, trucks, and graders, is usually employed. Specialized equipment is needed for the installation of geosynthetic Tabl
and soil liners. This includes specially adapted tractors
and cranes for moving synthetic liner material and compaction equipment for placement of
soil liners at the desired permeability.
Waste movement is usually confined to the spreading of wastes on the working face with compactors or dozers after the wastes are deposited by the truck. Movement over long distances is inefficient with this equipment.
Figure 1 shows a typical operation. Periodically, usually daily, the compacted waste is covered with earth and a new cell is started. An alternative to soil cover is the use of manufactured foams or temporary blankets. Foams require specialized application equipment to spray the material onto the compacted waste. Blankets can be lifted into place with a crane, or specially equipped tracked excavator, and then removed the following day before waste placement begins.
At some sites, wastes may be deposited at the top of the working face, making it easier to spread the wastes over the face. Litter control nay be more of a problem when this procedure is used.
Selection of type, size, quantity, and combination of machines required to spread, compact, and cover waste depends on the following factors:
The amount of waste produced by a community is the major
variable in selecting the appropriate size machine. Table 3 shows equipment needs by
population and waste generation amounts.
The type of waste to be handled strongly influences the machines to be used. Proper machines can be selected after identifying major solid waste components for a community. For example, at a site receiving a high proportion of hard-to-compact, heavy industrial waste (bricks and concrete), a compactor might not achieve normal compaction densities and the pushing and gripping ability of a track-type tractor may be needed.
However, a small track-type tractor has more difficulty compacting bulky wastes than a landfill compactor. Landfills accepting only shredded wastes are operated much like landfills handling unprocessed wastes, although there may be less need for daily soil cover, and there will usually be less trouble with waste compaction. Landfills handling baled wastes have substantially different operating procedures and requirements. Not only are soil cover requirements often less stringent, but the bales can be handled with forklifts or similar types of equipment, without the need for compaction equipment.
Degree of compaction is a critical parameter for extending
the useful life of a landfill. For achieving high in-place waste densities, a compactor
may be necessary. A minimun in-place compaction density of 1,000 pounds per cubic yard is
The number of passes that the machine should make over the wastes to achieve optimum compaction depends upon machine wheel pressure, waste compressibility, land and fuel requirements, labor costs, and work load. Generally, three to five passes are recommended to achieve optimum inplace waste densities.
Although additional passes will compact the waste to a greater extent, the return on the effort diminishes beyond six passes. An experienced operator will know if additional passes will result in greater compaction.
The graphs in Figure 2 show the relationship between waste layer thickness, number of passes, and the compacted waste density found in a field test for a particular type of machine and operating procedure. Each landfill will have different results, but the shape of the curves will he similar.
Note the rapid decrease in density after a thickness of about 1 1/2 feet. Thus, the most efficient solid waste compaction should be in a number of thin layers up to the total cell thickness and not in layers greater than two feet thick.
The working face slope will also affect the degree of compaction achieved. As the slope increases, vertical compaction pressure decreases. The highest degree of compaction is achieved at the grade with the least slope However, the feasibility of flat working face grades has to be weighed against the larger area over which the solid wastes must be spread.
Steel-wheeled compactors are designed specifically for
compacting solid wastes. Wheels are studded with load concentrators of various designs.
This equipment gives maximum compaction of solid wastes. Steel-wheeled compactors are best
suited to medium or large sanitary landfills.
A variety of attachments may be added to give the versatility required in small one-machine operations. This equipment is best used on level or gently sloping surfaces, and will not perform as well as tracked equipment on steep slopes or under wet conditions.
A loader-type front-end blade can add to the versatility of these machines. This attachment will allow excavation and carrying of soil for cover material. Cover material can be moved distances of up to 300 feet economically.
Track-type tractors may be used for site preparation as well as road construction and maintenance. Ripper attachments are available and can increase usefulness in frost conditions or unconsolidated soil. These machines work well in wet conditions due to high traction.
Track-type loaders are designed similarly to track-type tractors.. Instead of a push blade, they are equipped with a bucket for digging and carrying materials. Track-type loaders are similar to track-type dozers in versatility; they have the added ability of lifting and carrying soil without losing excavating and spreading ability. These machines are not equipped to pull scrapers, limiting hauling to short distances.
Rubber-tired scrapers are efficient for excavating and transporting soil for cover when the cover soil is greater than 1,000 feet from the working face. Where the soil is hard to excavate (e.g., clay or frozen soil), scrapers can be pushed with a bulldozer. Rubber-tired compactors may be needed for clay liner compaction.
Some site operators are replacing their scrapers with trucks, using them in combination with excavators or end loaders. In their opinion, this equipment is better suited to move large quantities of soil greater distances than a scraper. For large projects, off-road trucks with 30-yard capacities are used.
Backhoes are best employed for small, specialized excavation at the landfill, such as leachate collection system excavation. Dump trucks can be useful at landfills for the transportation of cover material in conjunction with other equipment to excavate the earth.
Draglines are also efficient earth movers, but are only able to deposit soil within the area reached by the boom and are not suitable for transporting cover material. They can be used in combination with other pieces of equipment, including loaders and trucks. Draglines are especially efficient at trench-type landfills, where the entire trench is often constructed prior to being used for waste disposal.
Motor graders are useful for road construction and maintenance, construction of berms and drainage ways, and landscaping.
Equipment maintenance is clearly an important task. Regular maintenance can reduce repair problems before more costly and time-consuming repairs are needed. Equipment manufacturers provide instructions for periodic maintenance and will provide assistance with equipment maintenance and repairs. It is imperative that a periodic preventive maintenance program be implemented and supported by a well-equipped maintenance shop.
Cold weather brings many problems in starting and operating machinery, keeping employees comfortable, and obtaining cover material. Equipment manufacturers can offer recommendations for cold weather starting and operating. Cabs, proper clothing, and employee facilities will help improve employee comfort.
Wet weather problems are especially serious with soils that have high silt or clay content. When wet, these soils become very muddy, and provision should be made to continue operation in areas of the fill that are less susceptible to problems.
Wet weather plans should include measures to reduce tracking of mud from the landfill onto the road system and provisions for cleaning trucks.
Litter does not seriously damage the environment, yet it
is perhaps the most persistent operational problem cited by surveys. lts seriousness is
due, in part, to bad public image.
Waste discharging procedures, orientation of the working face to the wind, existence or absence of nearby wind shielding features, and waste type and preparation all play a role in solving the litter control problem. Unloading wastes at the bottom of the working face can help. Here the wind cannot pick up materials as easily as when wastes are deposited at the top of the working face.
If the trench method is used, it is often recommended that the trench be at right angles to the wind. An open landscape will allow the wind to blow unimpeded, thereby increasing the likelihood of litter. Planting trees or constructing berms can reduce the wind velocity and, hence, litter problems. Portable fences are often used to catch the litter, followed by manual cleaning of the litter fence and the area downwind of the working face. The fence should be cleaned at least daily.
An alternative approach, which has been particularly effective at small sites, is to require all wastes to be bagged for pickup.
Dust can also be a nuisance at landfills, both to employees and neighbors. Water wagons can be used to control dust. Calcium chloride is also used for dust control, since it absorbs moisture from the air.
Fires within the waste are best controlled by digging out the combusting material and covering it with dirt. Each equipment operator should have a fire extinguisher readily available. Expensive pieces of equipment should be protected with automatic fire detection and suppression equipment.
Water wagon equipment can be used for fire control. Also, arrangements should be made with local fire-fighters to establish procedures for extinguishing landfill fires.
To maintain an efficient landfill operation, employees
must be carefully selected, trained, and supervised. Proper landfill operation depends on
Along with equipment operators, other necessary employees may include maintenance personnel, a scale operator, laborers, and a supervisor. People will also be needed to keep financial and operating records.
The landfill manager should have experience in operation of an advanced technology landfill and, in addition, receive technical and managerial training. Several institutions and associations conduct training courses for landfill operators. Some state agencies require that the landfill's manager participate in a training program and successfully complete an exam. In addition to several states, the Solid Waste Association of North America conducts courses and offers a certification exam.
Accidents are expensive, with hidden costs often several
times more than the readily apparent costs. Solid waste personnel work in all types of
weather situations, with many different types of heavy equipment, with a variety of
materials presenting diverse hazards, and in many different types of settings.
The types of accidents possible at landfills include direct injury from explosion or fire; inhalation of contaminants and dust; asphyxiation due to workers. entering a poorly vented leachate collection system, manhole, or tank; falls from vehicles; accidents associated with the operation of heavy earth-moving equipment; attempting to repair equipment while the engine is operating; exposure to extreme cold or heat; or traffic accidents at or near the site.
Safety guidelines specific to the operation of the landfill equipment are shown in Table 4. Educational films and written material on safety at the landfill are available from the federal government as well as equipment manufacturers.
Assistance in setting up a safety program is available from insurance companies with workers' compensation programs, the National Safety Council, safety consultants, and federal and state safety programs.
During site construction, a quality control program should
be followed to assure the landfill is built in accordance with the design plans. An
inspector should be on-site to approve construction work as each structure is completed.
Compliance with specifications should be checked by soil tests before waste is placed over
the liner. Grades and elevations can be measured with surveying equipment to
document the as-built features of the landfill.
Some operational records that should be maintained include: waste quantity by tons or, preferably, by volume, since landfill capacity is by volume; cover material used and available; equipment operation and maintenance statistics; landfill costs; labor requirements; safety statistics.; and environmental monitoring data. Data op waste loading with allow the site operator to predict the useful remaining site life of special equipment or personnel requiremets. Financial records are especially important to ensure that the operation is sound.