Newsletter and Technical Publications
<Municipal Solid Waste Management>
6.4 Sound technical options
|Sound practices for MSW landfills
- leachate management and environmental impact minimization
- gas management and risk reduction
- secure access and maintenance of gate records
- compaction and daily cover
- documented operating procedures, and worker training and safety
- establishment and maintenance of good community relations
- closure and post-closure planning
In Planning a landfill it is useful to think about the facility in terms of
four key phases from initial concept to final closure. These phases are:
- Construction, operation, and environmental monitoring
- Closure and post-closure.
The key considerations for sound management of the facility are listed in the
adjoining box. Attention to these issues is important for achieving safe and
effective MSWM at the landfill. Such sound management can be enhanced by the
judicious use of resources at each phase of landfill development.
Siting can be one of the most difficult processes in the landfill process.
The main considerations are:
- public involvement in the siting process
- hydro-geology/cover material
- proximity to airports
Capacity. In the siting process, the available land area is a key
consideration. In order to minimize the transaction costs associated with
design, permitting, siting, and closure and post-closure requirements, it is
desirable to have a facility that will operate for at least two to three years.
In practice, many short-term facilities turn into long-term facilities, so it is
important that all aspects of the siting process be observed even when planning
a short-term controlled dump. Ideally, a site should be sought with sufficient
capacity for 10 - 20 years of operation, particularly in the case of sanitary
Higher environmental standards are increasing the construction, operation,
and closure costs of landfills. In combination with a landfill capacity crisis
in some countries, these factors are leading to the construction of regional
landfills that can respond to environmental concerns in a cost-effective way.
Such regional landfills serve a larger region than would normally be served by a
municipal landfill. These considerations apply in developing countries as well
as industrialized ones. The construction and use of transfer stations will
reduce the higher transport costs brought about by the use of more distant,
Public involvement. Public opposition can be strong and protracted.
The planner must be prepared to involve potentially affected communities in the
siting process. He or she must establish a dialog and working relationship with
representatives from the candidate communities and address their concerns in the
design and implementation of the landfill plan.
Hydro-geology. It is desirable to take advantage of the geology of a
site. In particular, the types of soil and rock underlying the landfill and the
thickness of each soil layer can restrict the migration of the leachate toward
groundwater and reduce the concentration of contaminants. For example, clay
soils significantly slow the migration of leachate and can reduce the
concentration of heavy metal contaminants. A bedding of igneous rock also serves
to contain leachate. Sand, on the other hand, will do little to slow leachate
migration and has little capacity to remove contaminants.
Cover material. The availability of cover material is also an
important consideration in the siting decision. As discussed in the section on
landfill operations below, the compacted MSW must be covered by 15-30
centimeters of soil at the end of each day's operations. This creates a large
demand for cover material and can lead to prohibitive costs if this soil has to
be trucked over distances far from the landfill site. Characteristics of
suitable cover material are summarized in the section on cell operations below.
|Siting guidelines related to hydro-geology
Do not site landfills:
- in wetlands or in an area with a high water table;
- in floodplains;
- in areas that are close to drinking water supplies; or
- along geological faults or areas which experience frequent seismic
Do site landfills:
- above clay soils;
- above igneous rock; and
- where cover material is available nearby.
|Unmanaged leachate is a serious problem at dumps throughout the
world. The leachate from this dump in Accra flows directly into a canal.
(credit: Raymond Asmani-Boateng)
|This uncontrolled dump is situated immediately next to Laguna Lake,
in the Philippines, which planner are hoping to use as part of Manila's
drinking water supply.
(credit: Antonio Fernandez)
Access. To contain hauling costs and discourage the use of illegal
dump sites, it is important that a landfill be located reasonably close to the
area it is designed to serve. At the same time, siting a landfill too close to a
populated area will expose local residents to the environmental and health
threats that landfills may pose. Since urban areas are growing rapidly,
especially in developing countries, an area near the edge of existing
settlements will very likely be too close to populated areas in the foreseeable
future. The ideal location would therefore be sufficiently far from the city to
allow for future population growth, but close enough to be reasonably
In many cases, the use of transfer stations within a city can facilitate the
siting of a landfill at a greater distance from population centers. The
Collection and transfer part of the Sound Practices section addresses the issue
of transfer stations in further detail. The roads that provide access to a
landfill must be adequate to handle the types and quantity of vehicles that will
be used. Planning a landfill requires evaluation of existing and new roads, and
must include provision for maintenance of the roads needed to reach the site.
Accessibility notwithstanding, the geological considerations described above
are paramount in ensuring the environmental soundness of a landfill. Even when
it is necessary to site a landfill far from a city, the expense that results
from additional road construction and increased hauling costs may well be less
than the cost of remediating a contaminated drinking water supply.
Proximity to airports. A landfill should not be sited closer than two
kilometers from the nearest airport. Birds converging at the landfill may pose a
problem for aircraft and the landfill may pose other problems for airport
operations if the facilities are located too close to each other. The required
separation may be larger depending on the size and type of the landfill and of
Other considerations. A landfill that is sited in a gently sloping
area will facilitate leachate collection. Landfills should not be sited: (a) in
very windy areas, where it would be difficult to control wastes; (b) near
existing gas, sewer, water, or electrical lines, unless the landfill definitely
does not present a problem to such infrastructure; or (c) near residential
areas, churches, schools, etc.
Sound practice involves the evaluation of several candidate sites and the
selection of the final site from a prioritized list of such sites. The
accompanying table presents a simpli-fied ranking scheme to aid the site
In estimating the capacity and NIMBY factors the planner should consider
projected population growth and future trends in land development in the area.
It is not uncommon for an initially isolated site covering an extensive area to
find itself constrained by burgeoning urban development, confronted by hostile
residential neighbors, and restricted from expanding to its planned capacity.
Land use restrictions and zoning by the city planning department can help to
minimize such conflicts. Municipal authorities should integrate these
commitments into the initial landfill site plan wherever possible.
An environmental risk assessment (EnRA) should be made once the final site is
selected. This assessment should analyze rigorously both environmental and human
health aspects of the landfill proposal. The actual content of such an EnRA will
depend on local regulations. However, at minimum, the EnRA should detail the
risks to ground and surface water from the facility, the risks from gaseous
emissions, the impact of vermin, traffic, litter, and noise on the area, and the
potential for recovery of the land after the site has completed the post-closure
These general guidelines apply equally to controlled dump and sanitary
landfill facilities. In the case where an existing open dump is to be upgraded
to a controlled dump or sanitary landfill, the siting decision has already been
made. In this case the planner applies the above procedure to the areas for
proposed expansion of the existing site.
The reader may find several references that provide greater detail on the
landfill (and other MSWM facility) siting process. Among these, The Solid Waste
Handbook (McGraw-Hill) and the classic textbook by Tchobanoglous et al. contain
understandable, general guidelines.
|Items for consideration at the design stage
- public/private ownership/operation
- monitoring and control of leachate
- monitoring and control of landfill gas
- access and tipping area
- pre-processing and waste picker policy
- operations and safety manuals
- closure and post-closure plans
- community relations program
The design of a landfill will significantly affect its safety, cost, and
effectiveness over the lifetime of the facility. Key items requiring attention
in the design stage are listed in the adjoining box.
These considerations may have different implications for controlled dumps and
sanitary landfill facilities. The facility should be designed to operate
effectively given the mix of capital, labor, and expertise available to its
owners. Thus, labor-intensive controlled dumps should be designed where capital
is severely limited, labor is available at low cost, and there is a shortage of
expertise and infrastructure to service a highly mechanized facility. Such
conditions prevail in the cities of many developing countries. However, an
appropriately designed facility can still avail such cities of safe and
In the case of the controlled dump, planned capacity may not be protected by
zoning and land use restriction guarantees provided by municipal authorities.
Therefore, the landfill planner must use the designated site strategically to
minimize the risk of future incursion by municipal development and maximize the
total area available for landfilling over the lifetime of the facility.
Strategies may include acquisition of property surrounding the landfill site or
working inward from the border deemed most susceptible to urban growth.
For the sanitary landfill, capacity is often granted by regulatory permits on
an incremental basis. Thus, rather than declaring the capacity of the entire
site at the initial design stage, the planner develops it in two- to five-year
increments once the overall site meets the required zoning and land use
requirements. This practice allows the landfill owner to selectively develop the
property with the flexibility to convert it to more lucrative alternative land
uses that may develop over time. This is particularly applicable to private
landfill owners. In the case of municipal facility owners, incremental
development may also be advisable for the same reasons. However, municipal
planners must also ensure that appropriate sites with the required capacity are
always available for future needs.
Public/private ownership and operation
In most developing countries landfills are owned and operated by local
governments or other public agencies. This is often a function of the
substantial capital investment required to construct such facilities. Where
proven expertise is available in the private sector, municipal planners should
explore the option of privatizing landfill operations on a contractual basis.
This option should be weighed carefully as it involves issues of cost recovery
and the payment of fees for tipping privileges at the landfill. There are
several references on the privatization of municipal services in the literature.
The municipal planner should read these with due attention to their feasibility
for the local situation.
Monitoring and control of leachate
Leachate management is a key factor in safe landfill design and operation. The
natural decomposition of MSW, in combination with rain infiltration into the
site, causes potentially toxic contaminants to flow toward the bottom of the
landfill. The wetter the climate, the greater the potential risks of groundwater
and surface water contamination from the landfill. As explained above, the
geology of a site can exacerbate or reduce the amount of leachate that enters
A variety of wastes can contribute contaminants to landfill leachate. Paint
pigments and household batteries can release heavy metal contaminants. Household
hazardous waste (e.g., paint products, garden pesticides, automotive products)
and hazardous wastes from commercial and industrial generators can release
organic chemical contaminants.
A sanitary landfill contains engineering features to prevent the release of
hazardous substances to the environment. Natural or synthetic materials are
often used to line the bottom and sides of landfills to prevent the migration of
leachate into nearby groundwater and surface water. Many landfills use liners
constructed from two feet or more of compacted clay. Other liners consist of
thin sheets of plastic made from a variety of synthetic materials. Any type of
liner, however, could fail to contain leachate. Natural and synthetic liners can
crack, particularly if improperly installed, or can lose strength over time. In
an effort to improve the containment of leachate, more than one liner or a mix
of natural and synthetic liners, called a composite liner, is a recommended
To minimize the production of leachate, covering material should be applied
after each dayÕs MSW is spread. When a landfill is closed, a final cover is
applied. These covers are discussed below.
Leachate collection and treatment. Leachate retained by the liner will
accumulate and possibly leak through the liner unless it is removed by a
leachate collection system. Leachate collection systems are installed above the
liner and usually consist of a perforated piping system which collects and
carries the leachate to a storage tank. Periodically, leachate must be removed
from the storage tank and treated or disposed of. The most common leachate
management methods are: discharge to a wastewater treatment plant, on-site
treatment followed by discharge to sewerage or surface water (depending on the
quality of the treated leachate), and recirculation back into the landfill. All
of these options generally require a pumping system. They require considerable
maintenance due to the corrosive nature of the leachate.
Leachate recirculation. Recirculating leachate over waste in landfills
has been shown to increase the quantity (by nearly a factor of 10) and quality
of methane gas for recovery as well as possibly reduce the concentration of
contaminants in leachate and enhance the settling of the waste. There is now
considerable experience with such bioreactor landfills in the US, Europe, and
Brazil. In a country like Brazil, with a warm climate and highly organic MSW,
landfill cells stabilize within three to five years. Landfill gas recovery for
energy is feasible, and the cells can be excavated after five years and the
space reused. The humus-like material that is excavated (about 65%) can be
recycled as compost, and the remaining material used for daily or final cover of
the next cells.
As a substitute for a leachate treatment system, leachate reinjection may be
particularly appropriate for areas with low rainfall, since leachate production
in those areas is more dependent on the humidity of the waste than on the
infiltration of rain. In some instances, this technology can be more
cost-effective than other leachate treatment systems.
Leachate recirculation is a relatively new technique of leachate management.
As a management technique its goal is to stabilize the waste through accelerated
and controlled decomposition, accompanied by methane recovery. This is in
contrast to standard landfill technology, which focuses more on isolation.
Possible drawbacks of leachate recirculation include clogging of leachate
collection systems, increasing the release of leachate to the environment (even
though the main effect is the opposite), and increasing odor problems. After
weighing these advantages and disadvantages, federal regulators in the US
decided to allow leachate recirculation only at landfills that have a composite
liner and a leachate collection system that meets specified performance
requirements. In developing countries, however, the trade-offs may be different.
Inexpensive methods of leachate control. The state-of-the-art liners
and leachate collection systems described above are too expensive for many
developing countries. There are three practices that are much cheaper and that
may be practical in some situations.
- As described in the description of transfer stations (see
Collection and transfer in the Sound Practices section), MSW in an area with
low rainfall can be partially dried at transfer stations prior to
landfilling. This will reduce the leachate produced at the landfill itself.
- For areas where pre-drying is impractical or where the soil conducts water
very well (and where leachate runoff would therefore be a major problem), it
may be necessary to site a landfill in an area with a steeper grade than
would otherwise be chosen. In conjunction with a well-distributed leachate
collection system, this can reduce the dangers of water table contamination.
The actual grade required would depend on the conductivity of the soil, the
stability of the graded surface, and other site- specific engineering
considerations. The use of steeper grading, along with the denser placement
of leachate collection pipes, will add to the cost of a landfill. However,
these changes may be far less expensive than importing, transporting, and
applying clay or synthetic liners.
- To avoid the initial expense and ongoing maintenance requirements of
pumping leachate, leachate can be collected in a concrete-lined holding
pond, constructed downhill from the landfill. The best option in many cases
is then to allow the leachate to evaporate as much as possible. The handling
of the leachate residue must be considered in weighing this option. There is
experience with this in the treatment of wastewater that may be adapted to
leachate ponds in developing countries. In arid areas, the pond, or a set of
cascading ponds, should be designed to maximize the surface area of the
collected leachate, in order to maximize the rate of evaporation. In order
to avoid the risk of overflow into surface water supplies, such ponds must
be large enough to handle all of the expected leachate and rainfall. During
rainy times, the holding pond solution may not work as well or at all, since
evaporation may not counteract the combination of leachate and rainfall.
Even in this circumstance, however, the leachate from an overflowing pond
will be diluted by rainfall.
At controlled dumps monitoring operations may involve the scheduled
withdrawal of samples to test for indicator contaminants such as bacteria, heavy
metal ions, and toxic organic acids. The EnRA should establish the background
concentration of these substances as a basis for evaluating performance
standards for the landfill.
Monitoring operations at sanitary landfills may involve computerized
statistical sampling and automatic reporting of results at the regulatory
agency. Such systems are costly and require skilled personnel to use correctly
and to maintain. The choice of system is dependent on the capital and human
resources available to the landfill owner/operator and the requirements of local
|Necessary conditions for economic capturing of landfill gas
- sufficient methane is generated;
- capital is available for processing the gas;
- there is local demand for natural gas or a means to transport it
- the market price for natural gas is relatively high.
Monitoring and control of landfill gas
Landfill gas is primarily a mixture of methane and carbon dioxide produced by
the decomposition of organic matter in the MSW. Landfill gas is highly flammable
and poses a risk of explosion if not properly managed. Gas management is
generally required at sanitary landfills. At controlled dumps, there should at
least be monitoring to determine if dangerous amounts of gas are being released.
A low-cost design to handle landfill gas may consist of buried vertical
perforated pipes, using the natural pressure of the gas to collect and vent or
flare it at the surface. This is called a passive collection system. More costly
active collection systems utilize a buried network of pipes and pumping to trap
the gas. The gas is then processed and used for process heat or electricity
generation. Because landfill gas is potentially explosive, pressurized
collection is risky and expensive.
|A poorly managed leachate pond at a Thai dump
(credit: Chris Furedy)
|A gravity-fed leachate plant downhill from Tiger's Cave dump in
Guangzhou. The plant has had numerous technical problems.
(credit: Chris Furedy)
The accompanying box lists the conditions under which it may be economically
feasible to recover methane from a landfill. Generally, all of these conditions
must be met. From an environmental perspective, collecting and using methane is
ideal because it captures the energy value in the gas and prevents the release
of a greenhouse gas to the atmosphere. However, in many situations, not all of
the conditions stated above are fulfilled, and landfill gas recovery is not
The technical feasibility of recovering economical quantities of methane gas
depends on several factors. Perhaps the most important factor is the composition
of the MSW. The production of methane gas depends on a relatively high
percentage of organic MSW as well as proper nutrients, bacteria, pH, and a high
moisture content. The size of the landfill must be large enough and contain
enough MSW to produce economically recoverable quantities of methane. Generally,
landfills that have a capacity of at least one million tons should produce
enough methane to support recovery operations. The age of the landfill is also
important because it can take anywhere from several months to a few years after
the disposal of MSW before sufficient methane is produced. Early methane
production can be enhanced by using uncompacted waste as the first layer of a
landfill, thus allowing it to compost more quickly.
The engineering components of a landfill may also increase the quantity of
methane gas that can be recovered. Landfill liners help keep methane from
escaping from the landfill and help maintain the anaerobic conditions necessary
for methane production. Similarly, a daily cover that keeps methane from
escaping and inhibits the introduction of air into the landfill can increase the
rate of methane production. Other factors, such as the geology of the landfill
site, also play an important role. However, landfills that do not have
engineered liners or covers and landfills sited in porous soils can still
produce significant quantities of methane gas.
|This plant is part of the landfill gas capture system in Izmir,
Turkey. The gas will be used to generate electricity.
(credit: Chris Furedy)
Access and tipping area
Fencing should be designed to restrict unauthorized access to the landfill and
to keep out vermin and stray animals. Ideally, a vegetative hedge should be
planted along the perimeter of the site (the plant Jatropha curcas L. is a good
candidate for tropical countries) followed by a buffer zone several feet wide.
The fence may be erected within the hedge. If possible the perimeter of the
facility should be patrolled to minimize vandalism.
A staffed gate should be the point of entry to the facility for vehicles and
any waste pickers. Separate provisions must be made for access to emergency
vehicles and equipment. Ideally, the gate should be equipped with scales for the
weighing of vehicles as they enter and exit the facility. This provides a record
of the tonnage of material entering the facility. Weighscales are an essential
element of a sound municipal MSWM system, as they provide critical information
for planning purposes and for operational management of collection vehicles.
|Weighbridge at a new landfill in Bandung. Accurate assessment of the
quantity of waste dumped is critical in MSWM planning.
(credit: Chris Furedy)
In the case of the controlled dump, the designer may forego mechanical scales
when the total expected gate receipt of waste is less than 200 tons per day.
Manual scales or calibrated tables of weight-to-volume for delivery vehicles may
be used to provide estimated gate receipts in these cases.
Ideally, the tipping area should be at the working cell. This entails the
design of access roads to these locations within the site. This may not be
possible at controlled dumps and smaller sanitary landfills, either due to a
lack of resources for road construction or the lack of maneuvering room for the
delivery vehicles. In such cases tipping may occur close to the gate area and
the load transported to the working cell by smaller vehicles or muscle-powered
Pre-processing and waste picker policy
The landfill is the least efficient alternative for materials recovery
operations since the waste is usually well mixed by the time it arrives there
and the cost of transporting the material to the landfill has already been
incurred. Nevertheless, where composting is desirable at the landfill and/or
waste picking activity is permitted, sorting of the waste should occur close to
the gate or tipping area rather than at the working cell. This reduces the risks
to sorters from the equipment and activity at the active cell. It also reduces
the amount of material that has to be transported to the cell. Such activities
reduce the volume of material to be landfilled and prolong the life of the
Where waste picking is the established policy, the process can be most
efficiently managed by the awarding of permits for the recovery of materials or
for the conduction of on-site composting operations. Such permits would
facilitate more ready control of waste picker activity and their accountability
to the facility owner. The issue of waste pickers is discussed in greater detail
Where mechanical equipment, such as compactors and bulldozers, is used in
landfill operations, waste picking activity should be restricted to separate
resource recovery facilities or prohibited altogether from the site. Waste
picking policy should be established during the design phase of the facility so
that alternatives may be provided for the displaced workers and operating
procedures set for safe landfill operations.
Operations and safety manuals
These manuals should be prepared or acquired during the design phase of the
landfill. This permits their content to be specifically tailored to the
processes for which the facility is designed. Several handbooks and manuals on
landfill operations are available and the planner should tailor these to the
specific needs of the site. Clear operating procedures and well-trained workers
are vital to safe and effective landfill operations.
Closure and post-closure plans are required in the permitting process of most
sanitary landfills. Their essential elements are:
- plans for the sealing and application of final cover (including
vegetation) to the site;
- plans for long-term leachate and gas management system monitoring;
- plans for long-term ground and surface water monitoring;
- financial assurance guarantees to the local or state government; and
- land use restrictions for the site
In the case of controlled dumps in most developing countries, closure and
post-closure plans are not prepared. Facilities are not required to make
financial allowances for these activities. However, the provision of ongoing
monitoring and control of the facility after its useful life is an unavoidable
reality of landfill management. It is necessary to monitor these facilities to
ensure their continued safety to the health of surrounding communities and the
environment for periods that may exceed 30 years after their closure. Cost
recovery programs may be instituted during the operation of the facility to
provide funding for these activities. Alternatively, taxes or other
revenue-raising options may be employed to secure the required funds.
This is vital if the landfill is to win community support over its lifetime. The
designer should establish a program for ongoing dialog with the community. This
should be based on transparency in landfill operations and procedures and a
commitment to addressing community concerns. Some facilities offer give-backs to
their host community. These include free street paving to compensate for the
heavy vehicles in transit to the landfill. Another option is the waiving of
tipping fees to residents of the host community. Community relations begins with
the first consideration of the landfill site, and the formal program should be
incorporated into the design of the landfill management plan.
|Leaflets like this one are very useful in educating the public about
(credit: Bangkok Municipal Administration)
Construction, operation, environmental monitoring, and special wastes
The amount and type of construction depends on the class of landfill, on
physical conditions at the site, and on local regulatory requirements.
Construction issues include:
- construction of access roads
- erection of fences, gates, and the tipping area
- site preparation for the diversion of precipitation and the control of
- installation of the leachate and gas monitoring systems
- installation of the leachate and gas treatment systems
- construction of administrative offices, physical plant, and other
buildings at the facility
- preparation of the general working area, including:
- land clearing, grading, and excavation
- compaction of the base and application of the liner
- installation of the leachate collection system.
It is useful to define some common terms when discussing landfill operations.
A cell is the basic unit by which a landfill is developed. It is the
general area where incoming waste is tipped, spread, compacted and covered. A
basic cell consists of a base of synthetic or soil liner, compacted MSW and a
compacted cover layer of soil. Cells range in height from two to three meters.
The landfill is filled with waste following an ordered cell by cell sequence.
Special cells in the landfill may be reserved for materials such as medical
waste or construction and demolition debris. The dimensions of a cell depend on
the type of equipment being used, the planned use of the cell and the dimensions
of the overall site.
A lift is the completed layer of compacted waste in the cell. MSW is
laid down in rows 25 to 75 centimeters thick. This layer is then compacted
either by multiple passes of a manual roller or a mechanical compactor. A second
layer of waste is then spread upon the first and subsequently compacted. The
process is continued until the desired height of the lift is attained. As noted
above, this ranges from two to three meters. The completed lift is covered with
a layer of soil that is 15 to 30 centimeters thick when compacted. This
completed lift and cover material constitute a cell. Compaction increases the
capacity of the landfill. Mechanical compactors achieve densities of 500-900
kilograms per cubic meter. Manual rollers, likely to be found at controlled
dumps, will achieve significantly less than this. The planner should obtain
information on the compaction capabilities of any equipment that is under
The working face is the length and width of the row in which the waste
is being deposited. The width should be twice the width of the spreader (or
twice the width of the row of rakes in manual spreading). The length should be
adjusted so that the lift will be at its maximum height at the end of the day's
Some landfills use multiple lifts. Thus, when one cell is completed, another
is placed above it. This second level of cells is not begun until the first
level is filled with cells at the same level. It is customary to stack cells
into a final pyramidal structure. The final cell in the stack is covered with
soil that is 60 centimeters thick when compacted. When stacked cells are
employed, the final slope should be chosen to facilitate the runoff of
precipitation while ensuring the stability of the structure.
In addition to the area method of landfilling described above, two other
means of laying down waste are also employed: the ramp and trench methods. Both
the area and ramp methods are good for sites where the terrain (hilly or rocky)
is unsuitable for excavation of trenches (the area method where no excavation is
possible, the ramp method where only some is possible). Both methods require
cover material to be trucked in. The trench method is used where excavation is
possible. In this method the excavated soil may be used as cover material.
Operations at the landfill may be classified into three main areas:
- gate operations
- cell operations
Gate operations include weighing and recording gate receipts, tipping
(if direct access to the working cell is not available), pre-processing
(including materials recovery and composting if practiced at the site), and the
transportation of the tipped waste to the lift site at the working cell.
Cell operations include:
tipping: either of waste directly transported by the haul vehicle or of
residues preprocessed at the gate area and transported to the cell.
spreading and compacting: This may be done manually by workers with
rakes and weighted rollers. Mechanical spreaders and compactors are also
available. These achieve much higher compaction than manual means. However this
equipment is costly and requires specialized maintenance. For many cities in
developing countries, manual spreading and compacting is a sound practice. The
reader is directed to the waste management literature for further details on
spreading and compacting operations and equipment.
daily cover: It is important to cover new MSW at the end of the day
with a layer of soil or compost. This can sometimes be done by applying a 15-30
centimeter layer of soil that was excavated earlier or by using fine
construction and demolition residue handled elsewhere at the site. This daily
cover is used to control disease vectors such as rats and insects, reduce
blowing of waste and odors, and slow down the infiltration of rainwater. It also
results in more gas generation, which may or may not be desirable. This practice
also makes waste picking much more difficult. In Europe, both dried sewage
sludge and low-grade compost are used for daily cover. A mulch made of pulped
paper is also sometimes sprayed on. In some cases, a removable tarp can be used.
The ratings of some soils commonly used as cover material are summarized in
the following table.
|The most basic controlled dump site should still have a site office
for checking vehicles and their loads.
(credit: Chris Furedy)
Administration includes site permits and regulatory compliance, worker
training and safety, public relations, permitting franchisees, record keeping,
accounting, and all other clerical duties associated with the operation of an
industrial facility. The success of the landfill depends on a strong
administration that is committed to adequate financing of the facility,
transparency in its operations, and accessibility of information to the public.
These factors promote good technical and safety performance of the landfill.
Numerous texts provide details on all aspects of landfill operations. Topics
range from the selection and use of equipment to the establishment of tipping
fees for cost recovery. The reader is advised to consult these in planning for
Monitoring of leachate and gas migration from the landfill is necessary to
determine their impacts on surface and ground water and air quality,
The landfill operator should monitor for the presence of heavy metals in
potentially affected surface and ground waters. If these are unacceptably above
the background concentrations (determined by the environmental risk assessment)
landfill leachate could be the source of the problem. At controlled dumps simple
withdrawal from test wells dug at 5, 10, and 15 meters from the site along the
path of groundwater flow can give a profile of the groundwater contamination and
the extent of its attenuation by natural processes.
The landfill operator should also monitor for landfill gas on the site. If
dangerous concentrations are present, this gas must be collected and either
vented or flared, if it is not to be used. At controlled dumps, test vents may
be sunk at the North, East, South, and West corners of the facility in the
buffer zone. These can serve as a low-cost test for the migration of landfill
gas off the site.
In the case of sanitary landfills, the permitting process generally specifies
a more detailed monitoring program. Where such provisions are absent, the
facility owner should install a reliable system based on available resources.
This will permit the operator to react to problems as they occur and reduce the
risk of injury or damage from escaping gas or leachate contamination.
Special wastes include medical waste, household hazardous wastes, tires, used
oil, construction and demolition debris, human excreta, and sewage sludge. The
management of these wastes is covered in the next section of this Source Book.
Their coverage here addresses sound technical options for their disposal at the
landfill. In all cases the first option would be to redirect the waste to the
appropriate facility. Some sanitary landfills are prohibited from accepting
several of these components as a matter of regulatory policy. However, for many
other landfills, particularly controlled dumps in developing countries, the
facility is the final and only legitimate destination for these special wastes.
Medical waste: The first option would be to redirect medical waste to
an appropriate incinerator or other treatment facility. If not possible, these
wastes should be buried in a separate cell at the landfill and covered with
lime. Special care should given to the management of leachate from these cells.
Household hazardous waste (HHW): Special handling of HHW is only
required if it is delivered to the landfill as a separate load from regular MSW.
In such cases, management at the landfill begins with documentation of the
shipmentÕs source, contents, and transporter. In other cases HHW mixed with the
regular MSW stream is processed according to routine operations. Ideally, the
landfill should have a posted policy of not accepting special loads of HHW.
However this may not always be possible. For HHW consignments, such as
deliveries from HHW collection programs, the first option is to redirect the
consignment to an appropriate hazardous waste treatment, storage, or disposal
facility. If no such facility is available, as is the case in many developing
countries, then separate collection of HHW is not sound MSWM policy. These
components are likely to pose less risk to health and the environment if they
remain diluted in the general MSW stream. The landfill operator has the option
of storing the waste until an appropriate hazardous waste treatment, storage, or
disposal facility becomes available or mixing and diluting it with incoming MSW
for disposal. Depending on the exact nature of the waste, the regulatory
environment, and the outcome of consultation with municipal and state
authorities and community groups, the operator must choose the lesser of these
two evils. Under no conditions should chemically incompatible materials be
stored together. If no other options are available, solvents and other
potentially explosive materials should be destroyed by burning at the site.
If the landfill operator is uncertain about the chemistry of a HHW consignment,
he/she should immediately seek professional advice.
Tires: Tires should not be disposed of with regular MSW. They do not
remain compacted and adversely affect the structural stability of the completed
cell. Open storage poses a fire hazard. It also poses a health hazard as a
breeding ground for mosquitoes. If possible, the tires should be shredded to
reduce their volume and used creatively around the site. Some such uses include
terracing for erosion control and padding and bumpers on gates and heavy
machinery. The unused material should be disposed of in a separate section of
Used oil: Used oil should be rejected by the landfill operator. It is
unsafe to keep for long- term storage and is highly polluting of ground and
surface water if it leaks in the landfill.
Construction and demolition debris: This is largely inert material.
Where possible it should be handled at a separate cell in the landfill, both to
facilitate possible future recovery and because such debris does not require the
same leachate management efforts as other wastes. Laborers may recover masonry
blocks, wood, and metal for resale, although this should not be done at the
working lift. Where gravel and stone bits are present in sufficient quantity
they may also be used as cover material at the landfill. However, special
processing to separate this material involves costly screening machinery which
may be beyond the means of most controlled dumps.
Excreta and sewage sludge: Ideally these wastes should be dried before
delivery to the landfill. They should be handled by specially trained and
equipped workers. At the landfill they are mixed and disposed of with the
regular MSW. Where facilities are available, composting is a resource recovery
option for these wastes.
Closure and post-closure
In a regulated system, closure and post- closure (CPC) plans are required to
obtain the landfill operating permit. Thus CPC plans are prepared during the
design of the landfill. Since financial assurance is a requirement of such
plans, provisions should be made at that time for financing these inevitable
operations. CPC planning is new to many developing countries. However, as
discussed in the section on landfill design, closure and post-closure are
important phases in the management of a landfill. They should be explicitly
included in its planning. This applies equally to controlled dumps and sanitary
landfills. It also applies to planning for the financing of these operations and
to the identification of the party responsible for their implementation. In the
case of a publicly owned facility, the agency responsible for operating the
landfill would be a prime candidate for CPC operations. In the case of a
privately owned facility, CPC operations are the owner's responsibility.
CPC operations include the following: sealing and application of final
cover: A final impervious layer of clay and/or synthetic material is used to cap
the landfill after operations have ceased. A layer of soil is applied above this
cap and vegetation is planted to control erosion and improve the aesthetics of
the site. The final cover should be constructed to minimize the incursion of
precipitation into the landfill by maximizing its runoff and diversion from the
site. At controlled dumps where clay or synthetic liners are not an option, the
landfill may be capped with soil compacted by multiple passes of the weighted
roller or mechanical compactor. In this case, grading and drainage are important
to divert precipitation. Vegetative cover and other techniques to control
erosion are also important low-cost needs.
|This once-objectionable dump site in New Delhi has been planted with
trees and shrubs and now provides a breathing space in the growing city.
(credit: Chris Furedy)
leachate and gas management and monitoring: Leachate and gas will
continue to be produced long after daily operations have ceased at the landfill.
Thus, the management systems must be maintained for the period specified in the
regulations or until monitoring tests of the leachate and gas emissions indicate
that their quantity and/or composition have declined to acceptable levels. This
long-term responsibility can seem like an undue burden to the facility operator.
However, these programs can significantly reduce the risks of environmental and
health damage from uncontrolled leachate and gas migration. Where they prevent
the need for costly remedial actions, the savings from post-closure
environmental controls can be quite large. This is because landfill remediation
is costly. Even at controlled dumps, every effort should be made to maintain the
basic systems discussed earlier in the design and the lift operation sections of
this text. These systems also contribute to long-term risk reduction and savings
from avoided remediation.
ground and surface water monitoring: These programs are generally
required at sanitary landfills during the post-closure period. They are
generally not required at controlled dumps. In either case they can provide
early warning of potential contamination due to leachate from the closed
landfill. This allows for timely interventions.
financial assurance guarantees: These are required for privately owned
sanitary landfills in OECD countries. For municipally owned sanitary landfills
and for controlled dumps, it is still sound practice for these provisions to be
made explicitly at the time that the landfill is designed. This forces the owner
to allocate funds for CPC activities, either through the generation of income
from tipping fees, from the sale of bonds, or by appropriations from public
funds. Municipal taxes (either direct or indirect) may be the source of such
funds. However, in many developing countries such funds are not retained by the
municipality and must be procured from the treasury of the central government.
Without firm institutional commitments the supply of these funds can be
unreliable. This can subsequently jeopardize the entire CPC program.
land use restrictions for the site: land at the landfill will continue
to subside for several years after closure. Additionally, sites without
long-term gas management will continue to pose a threat of fires and explosion.
While the site is under CPC management it should be restricted from other land
uses. When the CPC period is over, tests should be conducted to ensure that the
site is structurally stable and safe from chemical hazards. The outcome of these
tests should determine the future uses of the site. In areas of high population
density and limited open land, former landfill sites are frequently used for
secondary, usually recreational, purposes. In some cases, these sites may be
paved and used for residential, commercial, or industrial development.