Disposal of Solid Wastes and Residual Matter Chapter 11

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 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


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 long-term monitoring and maintenance of the completed landfill (typically 30 – 50 years)


Overview of landfill planning, design and operation


The development of a modern landfill is illustrated in Fig. 11-4


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


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


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 wasteo landfills designed to maximize gas production o Landfill as integrated treatment units o landfill in wetland areas


Landfilling Methods o the principal methods used for the landfilling of MSW are

• excavated cell/trench• area • canyon/depression


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


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


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


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.


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.


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.


Upward migration of landfill gas


Movement of Trace Gases


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


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 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)


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


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


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


Preparation of Landfill Water Balance


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:


Estimation of Vertical Seepage of Leachate


Hydraulic Equivalency


Breakthrough Time


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 includeo 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


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.


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.


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


Table 11-16


Table 11-17


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 exampleo The clay layer and the geomemrane serve as a composite

barrier to the movement of leachate and landfill gaso 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


(Fig.11-36)


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


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


Leachate Management Option A number of alternatives have been used to manage the leachate

collected from landfills includingo 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


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


Fig. 11-49


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


Table 11-19


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


General Feature of Landfill cover Insert Fig. 11-52


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:

Structural and Settlement Characteristics of Landfill

The extent of settlement depends on the:o Waste decompositiono 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)


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


Table 11-22


Fig. 11-58


Fig. 11-59


Gas Monitoring in the Vadose Zone

See Fig 11-60


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


Fig. 11-61


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


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 of landfill Sites


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 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

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Disposal of Solid Wastes and Residual Matter Chapter 11

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