Presentation Outline
The Landfilling Process
Definition of Terms
 Landfills are the physical facilities used for the disposal of
residual solid wastes in the surface soils of the earth
 Landfilling is the process by which the residual solid waste is
placed in a landfill. Landfilling includes monitoring of the
incoming waste stream, placement and compaction of the
waste, installation of landfill environmental monitoring and
control facilities
 Cell is used to describe the volume of material placed in a
landfill during one operating period, usually one day. A cell
includes the solid waste deposited and the daily cover material
surrounding it
 Daily cover usually consists of 6-12 in of native soil or
alternative materials such as compost that are applied to the
working of the landfill at the end of each operating period
 A Lift is a complete layer of cells over the active area of the
landfill
 A bench is commonly used where the height of the landfill will
exceed 50 to 75 ft.
The Landfilling Process
The Landfilling Process
 The final cover layer is applied to the entire landfill surface after
all landfilling operations are complete.
 The final cover usually consists of multiple layers of soil and/or
geomembrane materials designed to enhance surface drainage,
intercept percolating water, and support surface vegetation
 Leachate is the liquid that is collected at the bottom of a landfill
 Landfill gas is the mixture of gases found within a landfill. The
bulk of landfill gas consists of CH4 , CO2, Nitrogen, O2, NH3 and
trace organic compounds
 Landfill Liners are materials ( both natural and manufactured)
that are used to line the bottom area and below-grade sides of a
landfill. Liners usually consist of layer of compacted clay and/or
geomembrane material designed to prevent migration of landfill
leachate and landfill gas.
 Landfill control facilities include liners, landfill leachate and gas
collection and extraction systems and daily and final cover layers
The Landfilling Process
 Environmental Monitoring involves the activities associated
with collection and analysis of water and air samples that are
used to monitor the movement of landfill leachate and gases at
the landfill site.
 Landfill closure describes the steps that must be taken to close
and secure a landfill site once the filling operation has been
completed
 Post closure care refers to the activates associated with longterm monitoring and maintenance of the completed landfill
(typically 30 – 50 years)
The Landfilling Process
Overview of landfill planning, design and operation
The Landfilling Process
The development of a modern landfill is illustrated in Fig. 11-4
The Landfilling Process
Preparation of the site for landfilling
 First Step: preparation of the site for landfill construction
o Existing site drainage must be modified to route any runoff
away from the intended landfill area
o Construction of access roads and weighing facilities and
installation of fences
 Second Step: development of a landfill
o Excavation and preparation of the landfill bottom and
subsurface sides
The Landfilling Process
Post Closure Management
 Monitoring and Maintenance of the completed landfill must
continue by law for some time after closure ( 30 – 50 years)
 Landfill surface must be maintained and repaired to enhance
drainage, control systems must be operated and the pollution
detection system must be maintained and operated
Reactions Occurring in landfills
 Solid wastes placed in landfills undergo a number of
simultaneous and interrelated biological, chemical ( e.g.
dissolution, evaporation, oxidation – reduction) and physical
changes
The Landfilling Process
Concerns with the landfilling of Solid Wastes
 the uncontrolled release of landfill gases that might migrate off
site and cause odor and other potentially dangerous conditions
 the impact of the uncontrolled discharge of landfill gases on
the green house effect in the atmosphere
 the uncontrolled release leach ate that might migrate down to
underlying groundwater or to surface water
 the breeding and hard boring of diseases vectors in
improperly managed landfill
 the health and the environmental impact associated with the
release of the trace gases arising from the hazardous materials
that were often placed in the landfill
 the objectives for the design and operation of a modern landfill
is to eliminate or minimize the impacts associated with these
concerns
Landfill Classification, Types and Method
 The most widely accepted classification system used for
landfills are
o Hazardous waste
o Designated waste
o Municipal Solid Waste
 Types of Landfill
o conventional landfill for commingled MSW
o landfills for milled solid waste
o monofills for designated or specialized waste
o landfills designed to maximize gas production
o Landfill as integrated treatment units
o landfill in wetland areas
Landfill Classification, Types and Method
 Landfilling Methods
o the principal methods used for the landfilling of MSW are
• excavated cell/trench
• area
• canyon/depression
Landfill Classification, Types and Method
Commonly used landfilling methods a: excavated cell b: area c:
canyon/depression
Landfill Siting Considerations
 Factors that must be considered in evaluating potential sites for
long term disposal of solid waste include:
o haul distance
o location restrictions
o available land area ( see example 11-1)
o site access
o soil conditions and topography
o climatological conditions
o surface water hydrology
o Geologic and hydrogeologic conditions
o local environmental conditions
o Potential ultimate uses for the completed site
 Final selection of a disposal site usually is based on the results
of a detailed site-survey, engineering design and cost studies
and an environmental impact assessment. It is interesting that
the up-front development cost for new landfills in california
now vary from 10 million to 20 million before the first load of
waste is placed in the landfill.
Landfill Siting Considerations
Composition and Characteristic, Generation,
Movement , and Control of Landfill Gases
Composition and Characteristics of landfill gas
 landfill gas is composed of a number of gases that are present in large
amounts ( the principal gases) and a number of gases that are present
in very small amounts ( the trace gases)
 The principal gases are produced from the decomposition of the
organic fraction of MSW. Some of the trace gases are toxic and could
present risks to public health
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Generation of the Principal Landfill Gases
 the generation of the principal landfill gases is thought to occur in
five sequential phases
 Phase 1 – initial adjustment
 Phase 2 – transition phase
 Phase 3- Acid phase
 Phase 4 – methane fermentation phase
 Phase 5 – maturation phase
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Duration of Phases
 the duration of individual phases in the production of landfill gas will
vary depending on the distribution of
o Organic components in landfill
o the availability of nutrients
o the moisture contents of waste
o the moisture routing through the fill
o the degree of initial compaction
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Variation in Gas Production with Time
 under normal conditions, the rate of decomposition, as measured by
gas production, reaches a peak within the first 2 years and then slowly
tapers off , continuing in many cases for periods up to 25 years or
more.
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Sources of Trace Gases
 Trace constituents in landfill gases have two basic sources. They may
be brought to the landfill with the incoming waste or they may be
produced by biotic and abiotic reactions occurring within a landfill.
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Movement of Landfill Gas
 Under normal conditions, gases produced in soils are released to the
atmosphere by means of molecular diffusion
 in the case of an active landfill, the internal pressure is usually
greater than atmospheric pressure and landfill gas will be released by
both convective ( pressure – driven) flow and diffusion.
 other factors influencing the movement of landfill gases include the
sorption of the gases into liquid or solid components and the
generation or consumption of a gas component through chemical
reactions or biological activity.
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Upward migration of landfill gas
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Movement of Trace Gases
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Passive Control of Landfill Gases
 The movement of landfill gases is controlled to
o reduce atmospheric emissions
o minimize the release of odorous emissions
o minimize subsurface gas migration
o allow for the recovery of energy from methane
 Control system can be classified as passive or active
 In passive control system, the pressure of the gas that is generated
within the landfill serves as the driving force for the movement of the
gas
 In active gas control system, energy in the form of an induced vacuum
is used to control the flow of gas
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Passive Control of Landfill Gases
 The movement of landfill gases is controlled to
o reduce atmospheric emissions
o minimize the release of odorous emissions
o minimize subsurface gas migration
o allow for the recovery of energy from methane
 Control system can be classified as passive or active
 In passive control system, the pressure of the gas that is generated
within the landfill serves as the driving force for the movement of the
gas
 In active gas control system, energy in the form of an induced vacuum
is used to control the flow of gas
 For both the principal and trace gases, passive control can be
achieved during times and when the production of the principal gases
is limited, passive controls are not very effective because the
molecular diffusion will be the predominant transport mechanisms
 Control of VOC emissions may necessitate the use of both passive and
active gas control system
Composition and Characteristic, Generation,
Movement , and Control of Landfill
 The passive methods for the control of landfill gases include:
o Pressure relief vents/ flares in landfill cover
o Perimeter interceptor trenches
o Perimeter barrier trench or slurry wall
o Impermeable barriers within landfills
o Use of sorptive barriers within landfills for trace gases
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill gas
 Active Control System
o Perimeter gas extraction and odor control wells
o Perimeter gas extraction trenches
o Perimeter air injection wells (Air curtain system)
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Active Control of Landfill Gas with Vertical and Horizontal Gas
Extraction Wells
 Both vertical and horizontal gas wells have been used for the
extraction of landfill gas from within landfills
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Composition and Characteristic, Generation,
Movement , and Control of Landfill
Management of Landfill Gas
 Flaring of Landfill Gases
 Landfill Gas Energy Recovery Systems
 Gas Purification and Recovery
o Physical adsorption
o chemical adsorption
o membrane separation
Composition, Formation, Movement and Control of
Leachate in Landfill
 Leachate may be defined as liquid that has percolated through
the solid waste and has extracted dissolved or suspended
materials
 In most landfills, leachates is composed of the liquid that has
entered the landfill from external sources such as surface
drainage, rainfall, groundwater and the liquid produced from
the decomposition of the wastes
Composition of Leachate
 Representative data on the characteristics of leachate are
reported in Table 11-13
 Typical physical, chemical and biological monitoring parameters
that are used to characterized the leachate are summarized in
Table 11-4
Composition, Formation, Movement and Control of
Leachate in Landfill
Composition, Formation, Movement and Control of
Leachate in Landfill
Composition, Formation, Movement and Control of
Leachate in Landfill
Water Balance and Leachate Generation in Landfills
 The water balance involves summing the amounts of water
entering the landfill and subtracting the amounts of water
consumed in chemical reactions and the quantity leaving as
water vapor
 The components that make up the water balance for a landfill
cell are identified in Fig. 11-31 (Insert)
 The principal sources include the following
o Water entering from above
o Water entering in solid waste
o Water entering in cover material
o Water leaving from below
o Water consumed in the formation of landfill gas
o Water lost as water vapor
o Other water losses and gains
Composition, Formation, Movement and Control of
Leachate in Landfill
Composition, Formation, Movement and Control of
Leachate in Landfill
 Preparation of Landfill Water Balance
Composition, Formation, Movement and Control of
Leachate in Landfill
Movement of leachate in Unlined Landfills
 Under normal conditions, leachate is found in the bottom of
landfills
 From there its movement in unlined landfills is downward
through the underlying strata, although some lateral
movement may also occur, depending on the characteristics of
the surrounding material.
 The rate of seepage of leachate from the bottom of a landfill
can be estimated using Darcy’s law, which can be expressed as
follows:
Composition, Formation, Movement and Control of
Leachate in Landfill
Estimation of Vertical Seepage of Leachate
Composition, Formation, Movement and Control of
Leachate in Landfill
Hydraulic Equivalency
Composition, Formation, Movement and Control of
Leachate in Landfill
 Breakthrough Time
Composition, Formation, Movement and Control of
Leachate in Landfill
Fate of Constituents in Leachate in Subsurface Migration
 Mechanisms that are operative in the attenuation of the
concentration found in the leachate as the leachate migrate
through the subsurface soil include
o mechanical filtration
o precipitation
o co precipitation
o sorption ( including ion exchange)
o gaseous exchange
o dilution and dispersion
o microbial activity
 The fate of heavy metals and trace organic, the two
constituents of greatest interest, is considered in the following
discussion
Composition, Formation, Movement and Control of
Leachate in Landfill
Heavy Metals
 In general, heavy metals are removed by ion exchange
reactions as leachate travles through the soil
 The ability of soil to retain the heavy metals found in the
leachate is a function of Cation Exchange Capacity (CEC) of the
soil
 The total CEC of a soil is defined as the number of meq of
cations that 100 grams of soil will adsorb
 The CEC of a soil depends on the amount of minerals and
organic colloidal matter present in the soil matrix
 It can be concluded that with a properly designed landfill cover
and clay liner, heavy metals should not pose a problem.
Composition, Formation, Movement and Control of
Leachate in Landfill
Trace Organics
 Adsorption is the most common way in which the organic
constituents in leachate are removed as it moves through the
porous medium
 Retardation of the organic constituents found in leachate is
important because the retained material can be subjected to
biological and chemical conversion reactions.
Composition, Formation, Movement and Control of
Leachate in Landfill
Control of Leachate in landfills
 liners are now commonly used to limit or eliminate the
movement of leachate and landfill gases from the landfill site
 The use of combination composite geomembrane and clay
liners is gaining in popularity
 The characteristics, advantages and disadvantages of the geo –
memembranes liners are summarized in Table 11-16
 Typical specifications for geomembrane liners are given in Table
11-17
Composition, Formation, Movement and Control of
Leachate in Landfill
Table 11-16
Composition, Formation, Movement and Control of
Leachate in Landfill
Table 11-17
Composition, Formation, Movement and Control of
Leachate in Landfill
Liner System for MSW
 There are many types of liner designs (refer to Fig.11-36 and
37)
 Typically, the liner system consists of multilayer liner where
each of the various layers has a specific function , for example
o The clay layer and the geomemrane serve as a composite
barrier to the movement of leachate and landfill gas
o The sand or the gravel layer serves as a collection and
drainage layer for any leachate that may be generated
within the landfill
o The geotextile is used to minimize the intermixing of the
soil and sand or gravel layers
o The final soil layer is used to protect the drainage and
barrier layers
Composition, Formation, Movement and Control of
Leachate in Landfill
 (Fig.11-36)
Composition, Formation, Movement and Control of
Leachate in Landfill
Composition, Formation, Movement and Control of
Leachate in Landfill
Liner System for Monofills
 Liner system for monofills
usually comprise two
geomembrane, each is provided with a drainage layer and a
leachate collection system
 The leachate collection system is placed between the first and
second liner as well as below the lower liner
 In many installations, a thick clay layer is used below the two
geomembrane for added protection
Construction of Clay Liner
 The clay tends to form cracks due to desiccation. It is critical
that the clay liner not be allowed to dry out as it is being placed
 Another problem that has been encountered when clays of
different types have been used is cracking due to differential
swelling. To avoid differential swelling only one type of clay
must be used in the construction of the liner
Composition, Formation, Movement and Control of
Leachate in Landfill
Leachate Collection System
 The design of a leachate collection system involves:
o The selection of the type of the liner system to be used
o The development of the grading plan including the
placement of the leachate collection, drainage channels
and pipelines for the removal of leachate
o The layout and design of the leachate removal, collection
and holding facilities
Composition, Formation, Movement and Control of
Leachate in Landfill
Leachate Management Option
 A number of alternatives have been used to manage the leachate
collected from landfills including
o Leachate Recycling
o Leachate Evaporation
o Treatment followed by disposal
o Discharge to municipal wastewater collection systems
Selection of treatment facilities
 The type of treatment facilities used will depend primarily on the
characteristics of the leachate and secondarily on the geographic and
physical location of the landfill
 Leachate characteristics of concern include TDS, COD, SO4-2, heavy
metal and nonspecific toxic constituents
 Leachate containing extremely high TDS concentrations (e.g., 50,000
mg/l) may be difficult to treat biologically. High COD values faver
anaerobic treatment . High sulfate concentrations may limit the use of
anaerobic treatment process because of the production of odors from
the biological reduction of sulfate to sulfide
Composition, Formation, Movement and Control of
Leachate in Landfill
Composition, Formation, Movement and Control of
Leachate in Landfill
Fig. 11-46
Surface Water Management
Surface Water Control System
 Elimination or reduction of the amount of surface water that
enters the landfill is important in the design of the landfill
because surface water is the major contributor to the total
volume of leachate
Surface Water Drainage Facilities
 In those locations where stormwater runoff can enter the
landfill, the site must be graded appropriately and designed
drainage facilities must be installed
 Examples of the types of drainage facilities used to protect
landfills are illustrated in Fig. 11-49
Surface Water Management
Fig. 11-49
Surface Water Management
Intermediate Cover Layers
 The purpose of the intermediate cover layer may be
summarized as following
o Eliminate the harboring of disease vectors
o Enhancing the aesthetic appearance of the landfill site
o Limit the amount of surface infiltration
Materials Used for Intermediate Cover Layers
 Refer to Table 11-19
Surface Water Management
Table 11-19
Surface Water Management
Final Cover Layers
 The primary purpose of the final landfill cover are
o To minimize the infiltration of water from rainfall after the landfill
has been completed
o To limit the uncontrolled release of landfill gases
o To suppress the proliferation of vectors
o To limit the potential for fires
o To provide a suitable surface for the re-vegetation of the site
o To serve as the central element in the reclamation of the site
 To meet these purposes the landfill cover must
o withstand climatic extremes
o resist water and wind direction
o resists the effects of differential landfill settlement caused by the
release of the landfill gases, compression of the wastes and the
foundation of the soil
o resist failure due to landfilling operations
o resist deformations caused by earthquakes
o withstand alterations to cover material caused by constituents in
the landfill gas
o resist the disruptions caused by plants, burrowing animals,
worms and insects
Surface Water Management
General Feature of Landfill cover
Insert Fig. 11-52
Surface Water Management
Surface Water Management
Determination of Percolation Rate Through Intermediate and
Final Cover Layers
 Estimation of the percolation of rainwater is usually
accomplished using one of many available hydrologic
simulation programs . Percolation can also be estimated using a
standard hydrological water balance. Referring to Fig.54, one
can calculate the water balance for a soil landfill cover by the
following expression:
Surface Water Management
Surface Water Management
Surface Water Management
Structural and Settlement Characteristics of
Landfill
 The extent of settlement depends on the:
o Waste decomposition
o Characteristics of the waste
o the effects of consolidation when water and air are forced
out of compacted solid waste
o Overburden Pressure ( height)
 the following relationship can be used to estimate the
increase in the specific weight of the waste as a function
of the overburden pressure
 Representative data on the degree of settlement to be
expected in a landfill as a function of the initial compaction are
shown in Fig. 11-56
Structural and Settlement Characteristics of
Landfill
Fig. 11-56
Environmental Quality Monitoring At Landfills
 Environmental monitoring is conducted at landfills to ensure
that no contaminants that may affect the public health and the
surrounding environment are released from the landfill
 The monitoring required may be divided into three general
categories
o vadoz zone for gases and liquid
o groundwater monitoring
o air quality monitoring
 Environmental monitoring involves the use of both sampling
and non sampling methods.
 Sampling methods involve the collection of a sample for
analysis. The nonsampling methods are used to detect chemical
and physical changes in the environment as a function of an
indirect measurement such as a change in electrical current (
See Table 11-22)
Environmental Quality Monitoring At Landfills
Vadose Zone Monitoring
 An important characteristics of the vadose zone is that the pore
spaces are not filled with water, and that the small amount of
water that are present coexist with air ( see Fig. 11-58)
 Vadose zone monitoring at landfills involves both liquids and
gases
Liquid Monitoring in the Vadose zone
 The sampling devices used for sample extraction in the
unsaturated zones are called suction lysimeters . Three
commonly used classes of lysimeter are
o the ceramic cup ( see fig. 11-59)
o the hollow fiber
o the membrane filter
Environmental Quality Monitoring At Landfills
Table 11-22
Environmental Quality Monitoring At Landfills
Fig. 11-58
Environmental Quality Monitoring At Landfills
Fig. 11-59
Environmental Quality Monitoring At Landfills
Gas Monitoring in the Vadose Zone
See Fig 11-60
Environmental Quality Monitoring At Landfills
Groundwater Monitoring
 Monitoring of groundwater is necessary to detect changes in
water quality that may be caused by the escape of leachate and
landfill gases
 Both down and up gradient wells are required to detect any
contamination of the underground aquifer by the leachate from
the landfill ( see Fig. 11-61)
 To obtain a representative sample, purged must be made
Environmental Quality Monitoring At Landfills
Fig. 11-61
Environmental Quality Monitoring At Landfills
Landfill Air Quality Monitoring
 Air quality monitoring at landfills involves
o the monitoring of ambient air quality at and around the
landfill site
o the monitoring of landfill gases extracted from the landfill
o the monitoring of the off gases from any gas processing or
treatment facilities
Monitoring Ambient Air Quality
 Ambient air quality is monitored at landfill sites to detect the
possible movement of gaseous contaminants from the
boundaries
 Gas sampling devices can be divided into three categories
o Passive
o Grab
o Active
Environmental Quality Monitoring At Landfills
Monitoring Extracted Landfill Gas
 landfill gas is monitored to assess the composition of the gas
and to determine the presence of constituents that may pose a
health or environmental risk
Monitoring Off-gases
 Monitoring off – gases from treatment and energy recovery
facilities is done to determine compliance with local air
pollution control requirements
Layout and Preliminary Design of Landfills
 Among the important topics that must be considered in an engineering
design report are the following
o layout of the landfill site
o types of waste that must be handled and the degree of
compactability of solid waste component (See Table 11-24 and
example 11-5)
o the need for a convenience transfer station
o Cover Material ( see example 11-6)
o estimation of landfill capacity
o evaluation of geology and hydrology of the site (See Fig. 11-66)
o selection of the leachate control facilites
o selection of the landfill gas control facilities
o layout of surface drainage facilities
o aesthetic design considerations
o monitoring facilities
o determination of equipment requirements
o development of an operation plant
o Final use or uses to be made of completed site
 Important factors that must be considered in the design of landfills are
reported in Table 11-23
Layout and Preliminary Design of Landfills
Layout and Preliminary Design of Landfills
Layout of landfill Sites
Layout and Preliminary Design of Landfills
Layout and Preliminary Design of Landfills
Layout and Preliminary Design of Landfills
Insert Fig. 11-66
Landfill Operation
 The development of a workable operating schedule ( depends on
factors such as traffic patterns, commercial and public access, etc.), a
filling plan for the placement of solid waste, landfill operating records
( See Fig.11-71) and billing information, a load inspection plan for
hazardous wastes ( see Fig. 11-72) and site safety and security plans
are important elements of a landfill operation
 Other factors that must be considered in the operation of a landfill
are reported in Table 11-27
Landfill Operation
Table 11-27
Landfill Operation
Landfill Operation
Landfill Closure and Postclosure Care
Landfill closure and postclosure care includes the following
 Development of long-Term Closure Plan
 Cover and landscape design
 Control of landfill Gases
 Collection and treatment of leachate
 Environmental monitoring systems
 Routine inspection
 Infrastructure maintenance