Third Indian Geotechnical Society: Ferroco Terzaghi Oration Design

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Indian Geotechnical Journal ISSN 0971-9555Volume 42Number 4 Indian Geotech J (2012) 42:223-256DOI 10.1007/s40098-012-0024-4

Third Indian Geotechnical Society:Ferroco Terzaghi Oration Design andConstruction of Barrier Systems toMinimize Environmental Impacts Due toMunicipal Solid Waste Leachate and GasR. Kerry Rowe

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INVITED PAPER

Third Indian Geotechnical Society: Ferroco Terzaghi OrationDesign and Construction of Barrier Systems to MinimizeEnvironmental Impacts Due to Municipal Solid Waste Leachateand Gas

R. Kerry Rowe

Received: 27 August 2012 / Accepted: 2 September 2012 / Published online: 9 October 2012

� Indian Geotechnical Society 2012

Abstract Based on case histories and the latest research,

this paper examines municipal solid waste landfills as a

system comprised of three primary subsystems (the

hydrogeology and barrier system below the waste; the

waste and landfill operations; and the landfill cover and

landfill gas control system) that exists in a broader social/

regulatory/administrative/economic system. Issues dis-

cussed include the effects of waste type and waste man-

agement risks, landfill leachate and leachate collection,

landfill gas and gas collection, the hydrogeology and bar-

rier subsystem required to contain contaminants in leachate

and landfill gas from escape by both advection and diffu-

sion, the dependence of a landfill design on the type and

amount of waste and the operational model, materials

specifications, and construction issues. Lessons to be learnt

from the past problems are discussed together with the

implications for modern waste management. The success

of modern systems are noted together with the need to

maintain vigilance and avoid complacency with respect to

landfill siting, design, approval, construction, operations,

after-use, and in approving subsequent surrounding land

use. The importance of considering the interactions

between the different components of the landfill system is

discussed in the context of the need to ensure that changes

in terms of waste stream or modes of landfill operations are

carefully researched and considered in developing designs

to provide long-term environmental protection.

Keywords Waste management � Landfills �Geomembranes � Geosynthetic clay liner �

Compacted clay liner � Landfill gas � Leachate �Leachate collection

Abbreviations

AL Attenuation layer

b Half-width of a wrinkle (m)

BPA Bisphenol-A

CL Clay liner (either CCL or GCL)

CCL Compacted clay liner

COD Chemical oxygen demand

DCM Dichloromethane

DDT Dichlorodiphenyltrichloroethane

Dg Diffusion coefficient in a geomembrane (m2/s)

EVOH Ethylene vinyl alcohol

GCL Geosynthetic clay liner

GMB Geomembrane

ha Height of potentiometric surface above aquifer

(m)

HA Thickness of attenuation layer (m)

HL Thickness of clay liner (m)

hw Leachate head on liner (m)

i Hydraulic gradient (-)

is Hydraulic gradient across CL and AL (-)

HDPE High density polyethylene

k Hydraulic conductivity/permeability (m/s)

kA Hydraulic conductivity of AL (m/s)

kL Hydraulic conductivity of clay liner (m/s)

ks Harmonic mean hydraulic conductivity of CL

and AL (m/s)

L Length of connected wrinkle (m)

LLDPE Linear low density polyethylene

lphd Litres per hectare per day

MSW Municipal solid waste

PBDE Polybrominated diphenyl ether

R. K. Rowe (&)

GeoEngineering Centre at Queen’s-RMC, Queen’s University,

Ellis Hall, Kingston, ON K7L 3N6, Canada

e-mail: [email protected]

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Indian Geotech J (October–December 2012) 42(4):223–256

DOI 10.1007/s40098-012-0024-4

Author's personal copy

PCB Polychlorinated biphenyls

PCE Perchloroethylene (tetrachloroethene)

Pg Permeation coefficient (m2/s)

Q Leakage (m3/s or lphd)

ro Radius of a hole in a GMB (m)

Sgf Partitioning coefficient (-)

TSS Total suspended solids

h Geomembrane/clay liner interface transmissivity

(m2/s)

Introduction

Human-kind has been generating and disposing of waste

throughout its history; a fact of great value to archaeologists

seeking to understand our past. When the volumes of waste

and the concentration of people near the waste was low, the

potential impacts on public health and the environment of

dumping in a ‘‘hole in the ground’’ were low. As populations

increased and became concentrated in towns and cities, the

importance of collecting and safely disposing of this waste

(be it garbage or sewage) increased. This need increased

further with the development of modern chemicals and

products some of which were found to be toxic to humans

and/or the environment (polychlorinated biphenyls (PCBs),

dichlorodiphenyltrichloroethane (DDT), tetrachloroethene/

perchloroethylene (PCE), being three well known examples).

During the last 60–70 years of the twentieth century and

even into the twenty-first century, disposal of waste in largely

unengineered dumps has caused problems due to subsequent

contamination of ground and surface water (Fig. 1) as well as

the escape of landfill gas. Development around, or in some

cases over, old dumps without the recognition of the risk

posed by these dumps has resulted in unacceptable impacts

on the public near these sites as well as to the environment.

‘‘Those who cannot remember the past, are condemned

to repeat it’’ [161]. These words and the many subsequent

variants of them such as ‘‘Those who fail to learn from the

mistakes of their predecessors are destined to repeat them’’

are worth keeping in mind in any discussion of waste

disposal and site after-use in the second decade of the

twenty-first century. The issues surrounding waste disposal

are both technical and social. While there are still inter-

esting research questions to be addressed, we already know

a great deal. Given what we know today, the contaminant

impact of landfills can be kept to negligible levels provided

that what we know, including the lessons of the past, are

considered in all phases of landfill development: siting,

design, approval, construction, operations, and after-use,

and in approving subsequent surrounding land use. There

are lessons to be learnt from the past problems that have

greatly influenced technical aspects of modern waste

disposal practice in many parts of the world. This paper

will discuss some of these lessons and the implications for

modern waste management. It will discuss the movement

over the last 20–30 years to engineered municipal solid

waste (MSW) landfills and the benefits that can be realized

by this move. For example, in much of both the developed

and developing world, new landfills are often required to

have a barrier system below the waste to control the release

of contaminants to environmentally acceptable levels.

Barrier systems generally include, as a minimum with

suitable hydrogeology, a leachate collection system which

minimizes the leachate head (i.e., the driving force for

leakage) acting on the underlying natural or engineered

liner. The leachate collection system often involves a filter/

separator (e.g., the geotextile in Fig. 2) between the waste

and a granular drainage layer that contains a series of

perforated pipes to transmit leachate to the point where it is

removed. The liner or liner system provides resistance to

the advective migration of contaminants (leakage due to a

hydraulic/pressure gradient) and the diffusion of contami-

nants (i.e., the movements of contaminants in a liquid or

gas phase due to a concentration gradient—see [143] for

details).

The barrier system may involve a single liner or a

double liner with a secondary leachate collection system

(also called a leak detection system) between the two liners

(Fig. 2). In either case, the liner will commonly be com-

prised of a protection layer on top of a composite liner.

Fig. 1 Leachate leaking from an unlined dump in an old sand

extraction pit can contaminate both surface water and groundwater

224 Indian Geotech J (October–December 2012) 42(4):223–256

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The protection layer is intended to minimize the damage

from overlying granular drainage materials and the com-

posite liner provides resistance to advective/diffusive

migration of contaminants. The composite liner [143]

involves a geomembrane (GMB: typically 1.5–2 mm thick

high density polyethylene, HDPE) overlying a geosynthetic

clay liner (GCL: about 5–10 mm thick layer of low per-

meability clay, called bentonite, encased between two

geotextiles) or a compacted clay liner (CCL:

600–1200 mm thick). When the GCL hydrates by uptake

of moisture from the adjacent soil it can have very low

hydraulic conductivity (permeability). If the CCL is con-

structed using appropriate soil and compacted correctly, it

can have a low hydraulic conductivity. As well as con-

trolling the leakage of leachate and the diffusion of con-

taminants in the leachate, the liner system also controls the

escape of landfill gas to the subsurface, especially on the

side slopes below waste.

As indicated by Rowe [112, 115] and Mitchell et al.

[89], when properly constructed, barrier systems can be

highly effective in providing excellent protection to the

environment and the public. However a primary objective

of this paper is to highlight the need for vigilance not only

in the regulation of the required presence of basic com-

ponents of such a system (e.g., drainage layer, liner) but in

the detailed design, construction, and operation of MSW

landfills. Post closure care and monitoring of these facili-

ties are also essential to provide long-term protection to

public health and the environment but are not discussed in

any detail in this paper.

A landfill with an engineered barrier system can be

expected to provided superior environmental protection to

an unengineered site, but this paper advances the thesis that

to achieve the full potential environmental protection of an

‘‘engineered landfill’’ more is required than simply a design

drawing showing a leachate collections system and liner.

The lessons from the past extend beyond the need for some

barrier system as part of the design. This paper will argue

that: (a) the liner system needs to be designed recognising

all the potential contaminant transport mechanisms; (b) the

barrier system that is needed will depend on the type and

amount of waste, and how the landfill is to be operated;

(c) not all drainage layers, geomembranes and clay liners

are the same—the system’s long-term performance may be

highly dependent on the choice of materials used in the

barrier system; (d) good construction quality is essential

and this requires qualified installers and good construction

quality control and assurance; (e) the system performance

will be dependent on how the landfill is operated and the

controls placed on the waste that is disposed to ensure that

they are compatible with the design; and finally (f) the final

cover, gas control and appropriate site aftercare and mon-

itoring are critical to ensuring long-term protection. Sub-

sequent sections of this paper will address these issues.

The development and application of landfill technology

varies substantially from one part of the world to another

and indeed it can vary from one part of a country to

another. This paper has a North American bias simply

because that is where there is the greatest breadth of doc-

umented experience (both good and bad). However it is

also intended to act as a guide to the development of

landfill technology in other parts of the world. It deals with

issues ranging from very basic to the most sophisticated

considerations. The basic considerations are well establish

in some parts of the world but are in the process of being

developed and implemented in other parts of the world.

The paper highlights issues that those developing regula-

tions and implementing a waste management strategy may

wish to consider. Many of these issues are social issues.

Waste management, with a particular focus in this paper on

landfill integrity/safety, is dependent on more than the

engineering per se: it depends upon the social environment

and a whole network of people (e.g., engineers, regulators,

politicians, contactors, the public) in all phases of design,

implementation, and care. At the other end of the spectrum,

the paper discusses many sophisticated technical details

and findings arising from the most recent (2012) research

that may seem daunting to many; however awareness is a

key starting point for development of the expertise that is

needed worldwide to address these issues.

Waste and Waste Management Risks

Until the 1980s there was little distinction between types of

waste [78]. All waste (liquid and solid hazardous, MSW,

industrial and commercial waste, ash, etc.) was dumped

without much consideration to the implications of the

containment required for different types of waste. In

Waste

Foundationlayer

Compactedclay liner

Geotextile

Geosynthetic protection

Geomembrane

Geosynthetic clay liner

Geotextile

Geosynthetic protection

Geomembrane

Secondary leachate collection

Primary leachate collection}

}

Fig. 2 Schematic showing one possible double composite liner

barrier system (the foundation layer shown here is often omitted)

Indian Geotech J (October–December 2012) 42(4):223–256 225

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particular, the potentially hazardous nature of, and the risks

associated with the uncontrolled disposal of, many useful

man-made chemicals (especially chlorinated chemicals

such as PCBs, DDT, PCE, etc.) were not really appreciated.

Frequently different types of waste such as MSW and

drums of liquid hazardous waste (e.g., dry cleaning fluid,

PCE), paint stripers and degreasing fluids like dichloro-

methane (DCM) were disposed in the same hole in the

ground as old washing machines and rotten tomatoes.

Unfortunately, even if the drums in which the liquid haz-

ardous waste was contained were intact when disposed,

they eventually corrode and the contents will escape. This

led to many problems (e.g., see the Love Canal case

described later). As a result of these problems, it was learnt

that: (a) it was especially unwise to dispose of liquid

hazardous waste, (b) waste generally required some form

of containment to reduce the potential for contamination of

ground and surface waters (Fig. 2), and (c) the level of

containment would depend on the risk associated with the

type of waste and hence it was undesirable to mix different

types of waste such as hazardous waste and MSW, MSW

and construction waste etc. Today many countries have

regulations that classify waste and limit the types of waste

that can be disposed in different types of landfills (with

some wastes, such as PCBs with a concentration above

a minimal level, being banned from landfill disposal

altogether).

The classification and controls on waste disposal com-

bined with the development of modern barrier systems and

active gas collection have very substantially reduced the

risks associated with landfilling waste (some of which are

illustrated by the cases discussed later). In parallel there

has been growing interest in the 3Rs (reduce, reuse, and

recycle). Source reduction is the most desirable approach to

minimizing the amount of waste to be disposed. Unfortu-

nately, in many countries source reduction of MSW (e.g.,

packaging materials) encounters implementation problems

and there is resistance to significant reduction [77]. Reus-

ing is highly desirable where practical but again in the

context of MSW encounters many challenges. Recycling

has become popular in many counties as a perceived pri-

mary means of reducing the amount of waste that requires

landfilling [1, 68, 80, 88, 169]. For example in many parts

of North America it is common to put out a ‘‘blue box’’

with recyclable materials (beverage containers, some

plastics, paper etc.). For some materials this makes perfect

sense (e.g., aluminum cans), however for others careful

consideration needs to be given to the total environmental

impact of recycling. For example, the Centre for Sustain-

ability at Aquinas Collage makes the following claim:

‘‘Because most products are not designed to be recycled

today, a great deal of energy is required to reprocess

materials for re-use. Generally, this energy comes from

non-renewable fossil fuel sources that pollute the air and

landscape, or from nuclear power plants that produce

radioactive waste. By-product emissions from current

recycling operations often release hazardous wastes into

the environment. For example, steel smelters have become

a large source of dioxin emissions. Furthermore, only one

or two additional uses are obtained from recycled products

today and the resulting product is often of lesser quality’’

(http://www.centerforsustainability.org/resources.php?category=

40&root=). Also there is the question of whether there is a

market for the recycled material. Sadly, much that is col-

lected for recycling ultimately ends up in a landfill because

of the lack of an adequate market for the materials; this

type of recycling is undesirable both environmentally and

economically. Not only does ineffective recycling not

remove the materials for which there is no market from the

waste stream, it can also reduce pressure for source

reduction because people believe that the materials are

being recycled.

At the other end of the spectrum, there are still many

parts of the world where there is no sorting of garbage at

the source and ‘‘recycling’’ is done manually on the land-

fill/dump by people for whom this is a source of subsis-

tence. Evolution to a safer mode of waste management also

requires consideration of the social implications.

There is a growing movement to remove organic

material from landfilled waste. This has advantages in

terms of reducing the organic matter that gives rise to

landfill gas and leachate (which can accelerate clogging of

leachate collection systems as discussed later) while also

reducing one source of heat that can affect the performance

of landfill liners; however there are challenges. Compost-

ing is a common means of removing organic waste [49] but

one needs to be sure that the composing facility is ade-

quately lined such that it will not cause pollution to ground

and surface water that its removal from a landfill is

intended to avoid. Unfortunately, composting facilities

often do not receive the level of design, construction, and

operations regulation and inspection that is warranted when

conducted on a large/commercial scale.

In some parts of the world, incineration is gaining

popularity as a means of managing waste and obtaining

‘‘energy from waste’’ [26, 101]. However while incinera-

tion reduces the volume of waste it does so by converting

the mass of waste to ash and gases. The ash needs a final

resting place and often that is a landfill [55, 156]. The ash

contains concentrated constituents (e.g., heavy metals) that

need to be well contained in an appropriately designed

landfill, and constituents (e.g., calcium) that can accelerate

the clogging of leachate collections systems in a landfill—

especially when co-disposed with MSW containing organic

matter. Hydration of the ash can also generate substantial

heat that has the potential of damaging modern liner


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http://www.centerforsustainability.org/resources.php?category=40&root=

http://www.centerforsustainability.org/resources.php?category=40&root=

systems (discussed later). Unfortunately the risks associ-

ated with disposing of incinerator ash are not well enough

recognised and in many cases the landfills being used are

not being engineered to account for the nature of the waste

(although it is possible to do so).

Gases from incineration go up the stack. These gases

can be hazardous and, if not extremely well controlled by

equipment (e.g., scrubbers), can be released to the atmo-

sphere. If hazardous gases or particulates are released, the

speed at which they can impact on humans is many orders

of magnitude faster than the possible escape of gas or

leachate from a modern landfill. Thus there is much less

time to react and implement contingency measure to avoid

an impact on the public. The preface of the 2nd edition the

Report of the British Society for Ecological Medicine on

‘‘The Health Effects of Waste Incinerators’’ [178] states:

‘‘Since the publication of this report, important new data

has been published strengthening the evidence that fine

particulate pollution plays an important role in both car-

diovascular and cerebrovascular mortality…and demon-

strating that the danger is greater than previously realised.

More data has also been released on the dangers to health

of ultrafine particulates and about the risks of other pol-

lutants released from incinerators. With each publication

the hazards of incineration are becoming more obvious and

more difficult to ignore…We also highlight recent research

which has demonstrated the very high releases of dioxin

that arise during start-up and shutdown of incinerators.

This is especially worrying as most assumptions about the

safety of modern incinerators are based only on emissions

which occur during standard operating conditions. Of equal

concern is the likelihood that these dangerously high

emissions will not be detected by present monitoring sys-

tems for dioxins.’’

While there are risks associated with landfills (as illus-

trated in later sections), these risks and the environmental

impacts need to be evaluated in comparison with the risks

and environmental impacts of alternative means of dis-

posal. The risks and environmental impacts of all methods

of waste management (be it recycling, compositing,

incineration, landfill etc.) can be mitigated if they are

adequately recognised and dealt with by appropriate

designs, construction, operations, maintenance, monitoring

and contingency measures. This paper deals with landfills;

however, similar consideration needs to be given to other

forms of waste management.

This paper deals with the disposal of waste once it

reaches the landfill. Often, social forces seek to place the

landfill as far away from the source (e.g., the town or city

generating the waste) as possible to minimize potential

effects on the residents (or a subgroup thereof). For

example, the City of Toronto trucked up to about 1Mt of

waste per year from downtown Toronto (Canada) over

400 km to Michigan (U.S.A.) between 2002 and the end of

2010, and about 200 km to the Green Lane landfill near

London, (Ontario, Canada) since January 2011. A risk

assessment with which the writer was involved found that

the greatest risk to human health and safety of disposing of

waste in a modern landfill is not from the escape of gases or

leachate from the landfill, but rather the risk associated

with transporting it considerable distances. In addition, the

environmental implications such as the use of fossil fuels

and associated air pollution need to be considered before a

decision is made to transport waste considerable distances,

especially by road.

Landfill Leachate and Leachate Collection

Although other factors can contribute to leachate genera-

tion, in a lined MSW landfill, leachate is primarily gener-

ated by (a) the percolation of rainwater through the daily,

intermediate and final cover and then through the waste,

and (b) water released by biodegradation of organic waste.

The resulting leachate is mostly water but contains [143]

organic matter which generates organic acids (e.g., acetic,

butyric, and propanoic acids) as it biodegrades, metals

(predominantly sodium, from sodium chloride, but also

calcium, iron, aluminium and very low concentrations of

heavy metals etc.), suspended solids (e.g., soil particles,

bacteria), volatile organic compounds (e.g., benzene, tol-

uene, ethylbenzene, xylenes, DCM, etc.) and other trace

constituents some of which are discussed below. The ces-

sation of land-disposal of liquid hazardous waste, as well as

the cessation of the co-disposal of hazardous waste with

MSW, has led to a reduction in the concentrations of many

of the most toxic chemicals (e.g. PCE, benzene, vinyl

chloride, lead, mercury, cadmium, etc.) from typical levels

found in old dumps to very low levels in the MSW leachate

from modern landfills. That said, leachate still has the

potential to impact groundwater and surface water quality

and needs to be prevented from escaping in anything but

negligible amounts (i.e., amounts that would have no

impact on human health or the environment).

Current barrier systems for MSW landfills were developed

to deal with the contaminants of known concern in the

1990s like salts, heavy metals and hydrocarbons [e.g., 95].

However, there are several new classes of contaminants for

which there is recent and growing concern about their

potential release into the environment. These contaminants

of emerging concern are either relatively new or recently

identified in the waste stream. Little has been documented

regarding the effectiveness of current barrier systems

for controlling these contaminants of emerging concern

although this is the subject of ongoing research [e.g., 157,

170]. Examples of contaminants of emerging concern


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include nanoparticles whose toxicity is currently under

investigation but is largely unknown [e.g., 62], leached

chemical additives such as bisphenol-A (BPA) which is

used in many plastic products and is believed to be an

endocrine disruptor that may mimic human estrogen at low

concentrations [75, 171], and polybrominated diphenyl

ether (PBDE) which is an additive flame retardant in

plastics, foams and fabrics that may leach out of waste and

may cause liver, thyroid, and neurodevelopmental toxicity

(US EPA). Both BPA and PBDE have been recently found

in significant concentrations in MSW leachate [3, 93].

Modern landfills have a leachate collection system that

is intended to (a) collect most, if not all, of the leachate

generated by the landfill and (b) minimize the build-up

of leachate in the waste which, if allowed to occur, would

increase the driving force for the advective movement

(leakage) of contaminants from the landfill out into the

groundwater or surface water and also impact on gas col-

lection. Leachate typically flows down through the waste

and when it reaches the drainage layer below the waste, it

is intended to flow laterally through the void space between

the solid particles in the granular drainage layer (e.g.,

gravel) to plastic (usually high density polyethylene,

HDPE) collector pipes. These pipes are a key component of

the collection system and are perforated to allow leachate

entry. The pipes transmit the leachate by gravity to sumps

which are usually pumped to remove the leachate from the

landfill for treatment.

The nutrients in the leachate encourage bacterial growth

within the waste, in geotextile filters, in granular drainage

layers, and in the leachate collection pipes. Clogging of the

leachate collection system involves the filling of the void

space between the fibres of a geotextile filter or solid

particles (e.g. sand or gravel, Fig. 3) in the drainage layer,

and the build up of clog material in the perforation of

collection pipes or in the pipes themselves due to a com-

bination of biological, chemical and physical events. For

MSW landfills, clogging is microbiologically induced

[27, 106]. The reduction in void space caused by biofilm

growth [27, 35, 36, 47, 138, 139, 141, 180, 182] reduces the

hydraulic conductivity and hence the capacity to laterally

transmit leachate for a given gradient [33, 179]. There is a

consequent increase in the height of the leachate mound

within the landfill, maintaining flow to the drainage points,

but this also can increase leakage through the liner,

potentially resulting in increased contaminant migration

through the barrier system and into the groundwater and, if

the mound is high enough, impacting surface water by

leachate seepage from the side slopes of the landfill.

Leachate characteristics are generally based on leachate

collected at the sump after it has passed through the col-

lection system. However this leachate has been changed by

the bio-geochemical processes in the leachate collection

system [e.g., 81, 83, 112, 138, 139] and except for con-

servative chemicals such as chloride, the concentrations

measured in leachate from the sump do not represent the

leachate entering the system. Thus clogging studies per-

formed with leachate that has passed through the leachate

collection system are likely to underestimate, and in some

cases grossly underestimate, the clogging that would

actually occur if the leachate entering the collection system

had been used.

Leachate wells are often proposed as a contingency

measure in the event that the leachate collection system

clogs and an unacceptable head develops on the liner.

However unless there are a very large number of wells,

leachate wells have limited capacity to control the leachate

head because of the steep drawdown curve near the well

means that they tend to only influence a very local zone

around the well, especially if there is a significant thickness

of waste [e.g., 128]. Clogging around the wells further

decreases their effectiveness with time. Thus, while

leachate wells do represent a possible contingency mea-

sure, they should not be seen as a justification for designing

a leachate collection system that is likely to clog (e.g., one

with a sand drainage layer).

Landfill Gas

Landfill gas is generated by the biodegradation of putres-

cible waste. It is predominantly comprised of methane and

carbon dioxide although it will also contain low concen-

trations of other gases. Due to the sensitivity of the nose to

very low concentrations of some components of landfill gas

like hydrogen sulphide (also known as rotten egg gas),

odour complaints can occur near landfill sites even if there

is no significant subsurface migration of landfill gas.

Landfill gas can also contain low concentrations of

potentially hazardous volatile organic compounds (e.g.,

benzene, vinyl chloride, DCM, etc.).

Fig. 3 Coarse gravel that has been cemented together and voids

largely filled by biologically induced clog material


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For landfill gas to move (migrate) any significant dis-

tance, it needs a path that provides relatively little resis-

tance to its movement. Gas will move most easily

in situations where there is an unsaturated granular soil or

fractured clay or rock with continuous space in the pores

through which the gas can migrate. If the pores in the soil

are filled with water, as in a saturated soil or a compacted

clay liner, the water provides resistance to the advective

movement of the gas. Thus for a landfill in a thick low

permeability clay deposit there will be little lateral

migration of the gas except by diffusion (discussed later).

There is greater potential for gas to escape laterally for a

landfill in an unsaturated uniform sand or fractured rock

deposit, however even in this case lateral migration will be

limited because it is relatively easy for the gas to escape to

the atmosphere. Significant subsurface migration of landfill

gas is usually associated with hydrogeological environ-

ments where there is a relatively coarse unsaturated gran-

ular soil (e.g., sands, gravels) or fractured soil or rock layer

with an overlying layer of less permeable material (e.g.,

clay, sandy clay, clayey sand, or even silt and sandy silt)

that contains an essentially continuous liquid water phase

in its pores and provides greater resistance to the vertical

migration of the gas than the coarser granular soil does to

lateral migration.

Gas will only migrate if there is a suitable path and the

gas pressures in the landfill exceed the pressures in the soil/

rock outside the waste (e.g., if the gas pressures in the

waste are not adequately controlled). Gas migration from a

landfill can be exacerbated by changes in atmospheric

pressure. For example, if the gas pressure in the landfill is

close to average atmospheric pressure, a drop in air pres-

sure may induce gas migration that would not occur at high

atmospheric pressure.

Landfills usually require buffer areas (i.e., areas with-

out construction) between a landfill and residential

developments to reduce nuisance effects (e.g., noise,

odour, etc.), to minimize problems with lateral migration

of landfill gas, and to allow room for monitoring (and

remediation if needed). The size of buffer required may

depend on the hydrogeology, the level of engineering

design, and the findings from monitoring. The larger the

buffer the greater the probability that either the confined

layers/lenses that may act as gas conduits will terminate,

preventing further lateral migration, or the confining layer

will terminate allowing the landfill gas to escape to the

atmosphere. When structures (e.g., houses) are too close

to a landfill, there is a risk that if the lower permeability

soil confining the landfill gas terminates below a house

(either naturally or because it is excavated as part of

construction of the house or services for the house) then

landfill gas can migrate upward and into the house either

directly or through services leading to the house. A spark-

triggered explosion can occur if the gas builds up to

explosive levels (5–15 % v/v methane in air). There are a

number of cases reported in the literature [e.g., 58, 61,

177, 183] where gas migrated from landfills to homes and

where, in some cases, explosions occurred.

Just as landfill gas can migrate through the subsoil it can

also migrate through manmade structures such as the

granular material used below asphalt in roads and espe-

cially in granular bedding used for sewers and other ser-

vices for a subdivision, or through pipes used for services if

there are holes to allow gas an entry and exit. Services

represent long and potentially uniform unsaturated fea-

tures. If the buffer zone is too small and excavation for

these services intersects a landfill gas bearing layer, the

permeable materials often used as bedding for the services

(and indeed the services themselves if not well sealed)

could act as a conduit for transmitting landfill gas from the

natural conduit to even quite remote portions of a subdi-

vision potentially affecting houses that would not have

otherwise been affected. This can significantly extend the

potential zone of influence of the landfill gas away from the

landfill boundary. Just as gas can enter manmade linear

features from natural unsaturated soil (e.g., sand), landfill

gas can also potentially migrate from the manmade con-

duits back into the hydrogeological environment (e.g.,

another area of unsaturated sand) and hence to locations

away from the services. Also, construction of services and

roads too close to a landfill can potentially increase the risk

of landfill gas migration by draining (drawing down) the

water levels near the road or services, thereby desaturating

the confined granular soil and allowing easy landfill gas

migration in a hydrogeological unit that would not have

otherwise permitted significant lateral migration.

The subsurface migration of landfill gas at a given

landfill site may be affected by the hydrogeology of the

area, the size of buffers zones around the landfill, the

presence/absence/effectiveness of a liner, leachate collec-

tion system, gas collection system, cover over the waste,

services and roads near the landfill, and other engineered

measures such as a gas cut-off or interception trench

around the landfill.

A Landfill as a System

Rowe [114] argued that a landfill is a system, and ensuring

good long-term environmental protection requires both

understanding the interactions between the different com-

ponents of the system (and various subsystems) as well as

designing the landfill as a system rather than an agglom-

eration of components. The following sections, and in

particular the case studies presented in the next section,

will provide additional evidence in support of that thesis.


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Expanding on Rowe [114], from a technical perspective,

a landfill is comprised of three primary subsystems: (i) the

hydrogeology and barrier system below the waste (this

includes side slopes below waste); (ii) the waste and

landfill operations; and (iii) the landfill cover and landfill

gas control system. In addition, the landfill exists within a

social/regulatory/administrative/economic system and this

system can override technical knowledge. It is essential

that landfill owners, municipalities, and governments (who

establish and administer landfill regulations) look beyond

short-term economic/social/political issues to what is nee-

ded to provide long-term environmental protection. A lack

of appreciation of technical issues and risks by landfill

owners can result in short-term decisions on the basis of

minimizing costs that result in significant subsequent

environmental/human impacts and substantial long-term

economic costs. Although essential, it is not enough to

have good regulations; there must also be the level of

staffing with appropriate expertise needed to ensure that the

regulations are being followed and enforced. This is par-

ticularly critical in economic recessions when owners and

various levels of government seek to reduce costs (e.g., by

reducing the level of investigation, design, review of

design, inspection during construction, operational con-

trols, closure costs, and post-closure monitoring) without

taking a long-term view of risks and costs that may result

from these short-term decisions.

Based on what we know today, it is possible to design

landfills that can be expected to ensure suitable environ-

mental protection for the contaminating lifespan of the

landfill (i.e., the period of time during which the landfill

will produce contaminants at levels that could have unac-

ceptable impacts if they were discharged into the sur-

rounding environment; see [143], but doing so requires a

socio-political system willing to do so.

Lessons from the Past

This section will discuss two cases in some detail since

they resulted in the evacuation of residents from around the

site of a former landfill/dump and both illustrate the need to

consider the interaction of essentially unengineered dumps

with subsequent development around the dump. Other

cases, discussed in much less detail, give examples of

problems that have occurred with respect to specific engi-

neering issues such as leachate collection and stability.

Case 1—Impact of Leachate/Contaminated

Groundwater on Nearby Residents

One of the best known examples of problems associated

with old waste disposal practice relates to Love Canal near

Niagara Falls in New York, USA. Originally intended to

move water from the Niagara River to a proposed hydro-

electric plant, the Love Canal project was terminated in

1896 leaving an unneeded ‘‘hole in the ground’’ that was

about 900 m long, 12–30 m wide and 2.4–4.6 m deep [31].

The hole was widened, deepened and the unlined dump

was filled with approximately 21,000 tonnes of chemical

wastes between 1942 and 1953. These wastes were repor-

ted to include alkaline chemicals, fatty acids, and numerous

chlorinated hydrocarbons [12] such as 2,3,7,8-tetrachloro-

dibenzo-p-dioxin (2,3,7,8-TCDD) which is a highly toxic

by-product of 2,4,5-trichlorophenol production [31]. The

waste was covered with soil and vegetated. The local

school district then sought to acquire the land to build a

new school. It is reported that the owner initially refused to

sell because of the risks due to the presence of the waste

chemicals. However, the school district still wished to

acquire the property, which included land in which

chemicals had been disposed [187], and so in 1953 the

owner agreed to sell the land for $1 subject to a clause

indicating that there were dangers associated with building

on the site [12]. Notwithstanding the warning, it is reported

that excavation for the school commenced on the site and

workers discovered two areas filled with drums containing

chemical wastes where the school was to have been loca-

ted. In response, the school was moved about 25 m from

this location [32]. The school was completed in 1955. The

school district sold the land not required for the school to

private developers and the Niagara Falls Housing Author-

ity, apparently without advising them of the risks [168].

The City of Niagara Falls had sewers constructed in the

area in 1957 to allow homes to be built on land adjacent to

the dump site. During construction of the gravel sewer beds

and water lines, it is reported that construction crews broke

through the (fractured) clay adjacent to the dump [168,

187]. In addition, part of the clay cover was reported to

have been removed so the soil could be used elsewhere.

These actions would be expected to have both (a) increased

the accumulation of rainwater in the dump, and (b) created

a path for contaminated water and chemicals leaking from

the drums to migrate through the clay and be conducted

through the bedding of the sewers and water pipes in the

subdivision. It is understood that the chemical dump was

not monitored. The subsequent construction of an

expressway near the dump changed the groundwater flow

conditions, reducing the potential for flow to the Niagara

River. Subsequently, high rainfall in 1962 caused signifi-

cant flows from the dump and puddles of oil or coloured

liquid were reported in yards and basements in the area

[12].

Although there were signs of problems at least as early

as 1962, it was not until about 1976 that Love Canal began

to attract the attention of the local press and in 1978 health


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issues heightened the concerns. The concerns included:

(a) waste subsidence and exposure of drums; (b) contami-

nated water ponding in backyards adjacent to the dump;

(c) unpleasant chemical odours; (d) movement of con-

taminants into the basements of houses close to the landfill;

and (e) movement of contaminants into and through the

local sewer system. In addition, there were concerns being

raised regarding health problems which included greater

than statistical norms for spontaneous abortions, birth

defects, and low birth weight of infants in the area [31, 92].

In 1978, President Carter declared a State-of-Emergency at

Love Canal. The school was closed and 236 families were

evacuated from homes around the landfill. A containment

plan was implemented for part of the site and further

investigations were initiated. The results of preliminary

studies of 36 area residents indicated that 11 had chro-

mosomal abnormalities [31]. These results prompted a

second State-of-Emergency in 1980. Ultimately, over 700

families were relocated [100].

The investigation prompted by the State-of-Emergency

indicated [31] that the geology of the site involved an

overburden layer of fill, silty sand, and sandy silt underlain

by a fractured silty clay, underlain by a soft silty clay,

underlain by glacial till, and finally underlain by fractured

bedrock. The hydrogeologic studies showed that a leachate

mound in the dump had given rise to radial groundwater

flow through the overburden soils and downwards towards

the bedrock. Dense non-aqueous phase liquids (DNAPLs)

were observed in the fractured silty clay layer. Cohen et al.

[31] suggested that home owner’s sump pumps likely had

induced the movement of contaminants towards the base-

ments. In a similar manner, the sewers below the water

table may have both provided a pathway for contaminant

migration and induced a gradient towards the sewers that

contributed to the movement of contaminants into the

sewers and hence around the subdivision.

An eight year long health study of former residents of

the Love Canal area initiated in 1996 [92] found, inter alia,

that ‘‘rates of congenital malformations were twice that

expected compared to the external standard populations, a

difference that exceeded the range of rates expected by

chance alone. In addition, the internal comparisons

revealed that malformations were positively associated

with potential exposure as a child.’’

In an article on free-market environmentalism, Stroup

[168] made the following comment: ‘‘Only when the waste

site was taken over by local government—under threat of

eminent domain, for the cost of one dollar, and in spite of

warnings by Hooker about the chemicals—was the site

mistreated in ways that led to chemical leakage. The

government decision makers lacked personal or corporate

liability for their decisions. They built a school on part of

the site, removed part of the protective clay cap to use as

fill dirt for another school site, and sold off the remaining

part of the Love Canal site to a developer, without warning

him of the dangers as Hooker had warned them. The local

government also punched holes in the impermeable (sic)

clay walls to build water lines and a highway. This allowed

the toxic wastes to escape when rainwater, no longer kept

out by the partially removed clay cap, washed them

through the gaps created in the walls.

The school district owning the land had a laudable but

narrow goal: it wanted to provide education cheaply for

district children. Government decision makers are seldom

held accountable for broader social goals in the way that

private owners are by liability rules and potential profits.

Of course, mistakes can be made by anyone, including

private parties, but the decision maker whose private

wealth is on the line tends to be more circumspect. The

liability that holds private decision makers accountable is

largely missing in the public sector.’’

Case 2—Impact of Landfill Gas on Nearby Residents

Some 30 years after President Carter’s 1978 declaration of

a State-of-Emergency at Love Canal and the evacuation of

236 families from around the dump in Niagara Falls made

headlines in the USA, the headline of a major Melbourne

(Australia) newspaper read: ‘‘Gas threat forces residents to

flee’’, and the related article indicated, inter alia, that:

‘‘more than 200 Cranbourne residents were last night told

to evacuate their homes because of dangerous levels of

methane gas. The residents of Brookland Greens estate

were told by the State Government’s Emergency Response

Team that there was an unacceptable risk to their safety if

they remained in their homes…It is estimated about 400

houses in 20 streets are affected by the gas, which comes

from a nearby tip. The meeting was called by Casey

Council after methane gas readings of up to 60 % were

detected in the walls of some homes in the area. A pam-

phlet distributed to residents earlier said methane gas could

explode at levels between 5 and 15 %.’’ [79].

Two days later the headline in the same paper read:

‘‘Planning tribunal knew of gas risk: EPA’’ and the article

[69] indicated, inter alia, that ‘‘A government inquiry will

try to find out how dangerous gas came to leak from a

council tip into a Cranbourne housing estate, exposing

residents to an explosion risk. The State Government is

expected to announce on Monday a full investigation into

the leaching methane, which in places has reached beyond

flammable levels of 5–15 % in the Brookland Greens esta-

te…The EPA and the council objected in 2002 to the last

stage of the development in the area next to the tip, which

closed in 2005. But that objection was overturned in 2004 by

the Victorian Civil and Administrative Tribunal…The Cran-

bourne landfill site lacked modern design features such as


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cell liners, leachate collection pipes and a leachate drainage

layer, the EPA said. The submission also detailed a history

of complaints about the site and advice to the tribunal that

the gas extraction system was inadequate. ‘Based on the

EPA’s past experience with the Cranbourne landfill, I would

anticipate that should a reduction in the buffer distance be

approved, a significant increase in adverse impact on the

community…is likely to result’ the EPA…said in the

submission.’’

The government enquiry referenced in the article above

resulted in a report [94] upon which the information pre-

sented below was based. This is a complex case with many

factors bearing on the final outcome. What follows is a

summary of the key issues with respect to the points to be

made in this paper.

In 1992 the Victorian Environment Protection Authority

(EPA) issued a works permit for the Stevenson Road

Landfill (SRL) in the Shire of Cranbourne (6)1 on the

outskirts of Melbourne, Australia. A former sand pit (141),

the site was to be developed as a MSW landfill accepting

putrescible waste. The EPA intended that the site be lined

with compacted clay to assist in controlling leachate and

landfill gas (7). The Shire objected to the requirement of a

liner on the grounds that it would be expensive ($500,000)

to install (13). After discussions with the Shire and its

consultant, the EPA approved the landfill site as a

hydraulic containment site whereby leachate is controlled

by an inward flow of groundwater by maintaining the

leachate level below the groundwater level outside the

landfill (217–218). At the time that the landfill was

approved, the landfill was to be located in a rural area with

an existing dump on the east side, a race track on the south

side, farm land on the west side and a sand extraction pit on

the north side. The nearest residence when the landfill was

proposed was more than 500 m away and more than 200 m

from the final site as constructed and even as late as 2004

there were no residences within 200 m of the landfill

(Illustration 5).

The landfill was to have a leachate underdrain to control

leachate levels (219). When the landfill was constructed in

1995 it appears that the leachate underdrainage system was

omitted (17). The landfill began to accept waste in 1996

and relied on pumping leachate from two sumps to control

the leachate head (467). By 2000 when the first (of four)

and southernmost cell was closed, problems with leachate

mounding/seeps had been identified (475). In 2003

groundwater was found to be polluted by leachate (476).

Furthermore, monitoring was not adequate for identifying

whether the leachate was being controlled to a level that

would ensure an inward gradient (480) in accordance with

the design as a hydraulic containment site (217–218). In

2003, the bubbling of landfill gas in monitoring wells was

also causing problems with leachate monitoring (481) and

it was noted that the level of leachate relative to the base of

the northern cells could not be established because the

depth to the bottom of these cells was unknown at the time

(482). Subsequently it was estimated that the depth of the

northern cells was about 35 m as compared to about 14 m

specified in the works approval (612). The extra about

20 m in depth over the approved amount substantially

increased the waste available to generate gas (650). Prob-

lems controlling leachate levels were reported to have been

ongoing and still present in September 2008 (513) when

residents were evacuated from the estate.

In 2000, the landfill license was revised to require a gas

collection system to be installed and operated (518). In

May 2002 the license was amended again to be more

explicit regarding the nature of gas collection in both the

closed and active cells (519). In March 2002 an agreement

was reached with a company to install a gas collection

system in the landfill (554). However, the primary objec-

tive of the gas collection system was to extract gas for

energy (544). An expert witness interviewed by the

Ombudsman was the former National Advisor for Landfills

for the United Kingdom Environment Agency. He com-

mented ‘‘that landfill gas utilisation can compromise

migration control.’’ He said some companies ‘‘design a gas

system for the energy they can get out of it, not for control’’

(549). The gas system came into operation in November

2002 (560). Low volumes of gas were collected and in

March 2003 there was not sufficient volume for energy

generation (561). Nevertheless, odour problems prompted

the EPA to issue an Infringement Notice in June 2003

(562). In August 2003, an investigation into the cause of

the gas collection problems indicated, inter alia, that the

flare for burning gas was not operational and that gas

collection was impeded by high leachate levels which

blocked gas collection pipes (567). The company con-

ducting the investigation recommended lowering water

(leachate) levels across the site (569), however, the

Ombusman concluded that the ‘‘evidence suggest(s),

however, water levels in the site were not in fact lowered

as…recommended’’ (570), and problems with gas collec-

tion continued through to April 2005 (572). Five additional

vertical wells were installed in the northern portion of the

site in May 2006 (577) and another 20 in July 2006 (578).

The haste in installing these wells in 2006 was prompted by

the observation of gas bubbling off-site (in a portion of the

estate being serviced for residential construction west of

the northern portion of the site) (578–579). Additional gas

wells were installed in the southern portion of the site in

April 2007 (580). Dual gas and leachate wells were also

1 References in brackets relate to the paragraph number in the

Ombusdmen’s Report [94] from which the information was obtained.


123


introduced (581). These changes increased gas collection

but an independent evaluation of the effectiveness of the

system conducted for the EPA in February 2008 indicated

‘‘that the system was not operating adequately to prevent

off-site emissions of landfill gas’’ and in September, the

UK expert hired by the EPA indicted that the gas system

was ‘‘53 % ineffective’’ (584). The Ombudsman noted

‘‘whether the failure of the gas extraction system was due

to overly high leachate levels, poor design, or poor con-

struction was unclear’’ (586).

In addition to the problems noted above, there was

evidence to suggest that waste delivered to the site gener-

ally was not inspected and that prohibited waste (e.g.,

‘‘catering and general waste from international and

domestic flights’’, ‘‘paint, milk and alcohol’’) was some-

times dumped at the landfill because of a ten-fold cost

savings versus that required for deep burial (606–609).

The Ombudsman concluded that the site operations and

post-closure ‘‘was characterised by significant environ-

mental issues including largely uncontrolled and over-

abundant leachate and poorly controlled gas. Contributing

to these outcomes were the following general administra-

tive problems: poor contract management; lack of

accountability; poor knowledge management; (and) poor

performance of statutory duty,’’ (42). Problems with

operations resulted in the EPA issuing a Notice of Con-

travention in 2001 (64).

In 1999 a private developer began construction of a res-

idential estate (Brookland Greens) to the west of the landfill

and applied to have land closer to the landfill rezoned for

residential development which included land within the

buffer zone (i.e., 200 m from the landfill boundary) (883). In

2000, the developer agreed that no homes were to be built

within a 200 m buffer of the landfill (89) although the def-

inition of where the point to which the distance would be

measured was unclear (935–936). In April 2002, the

developer applied to construct residences on land within

200 m of the landfill by defining the buffer as 200 m from

the active tipping face (940–941). ‘‘Both the City…and the

EPA opposed any reduction in the buffer for the landfill for

obvious and compelling reasons although neither referred to

the actual risks, including potential explosions, posed to

residents by laterally migrating methane gas from an unlined

landfill in sandy geological conditions’’ (948). On 3–5 May

2004 the ‘‘Victorian Civil and Administrative Tribunal

hearing considered a planning permit to develop…land sit-

uated within the 200 m landfill buffer’’. On 6 May 2004 it

issued an interim decision in favour of the developer’s

definition of the buffer (1054) which allowed ‘‘development

to proceed with some houses being built along the boundary

of the landfill within two to three metres of where putres-

cible waste had been deposited’’ (1057). Following the

decision, the City ‘‘progressively approved further planning

applications’’ by the developer ‘‘within the buffer zone as

the tipping face moved north, resulting in the buffer zone

being completely built out’’ (1064). In June 2005 the landfill

ceased operation after about 1.1 million tonnes of waste had

been placed at the site (143). In March 2006 workers con-

structing drainage in an as yet undeveloped part of the estate

reported the presence of methane in ‘‘bubbling puddles’’

(109). The gas was observed ‘‘approximately 150 m from

the north west corner of the landfill’’ (1143) and was

observed where they had reportedly excavated clay to allow

construction of a drainage system as part of the development

and where puddles had formed after rainfall (1143–1145).

Around the same period, bubbling had also been observed in

a pond on undeveloped land (about 30 m) north of the site

(1148) and bubbling with a slight odour was also observed at

another location west of the landfill about 50–60 m from the

landfill boundary and 1–2 m off where drainage lines were

being installed (1150).

At the time that the gas bubbling 150 m west of the

northwest corner of the landfill was observed, this location

had not been approved for development (1161–1170). The

Ombudsman commented that ‘‘despite these and other

warnings that migrating methane posed a threat to the

residents of the…Estate, the City…proceeded to approve

further building work on the estate in May 2006’’ (113) and

that ‘‘it is concerning that a methane reading of 63 % was

recorded in a wall cavity in a home…in August 2008 which

is located in the Stage 20 development where the gas had

been observed in March 2006’’ (1169). Although the

development was not stopped, the City indicated that it did

‘‘implement a monitoring program for houses in the estate

and established an Emergency Response Plan to deal with

any methane detection in a home. The monitoring program

successfully detected methane in…(the home in question)

and a response was initiated with the Council’s Emergency

Response Plan’’ (1170). In January 2007, the EPA issued a

Pollution Abatement Notice to the City regarding the now-

closed landfill (1172) which required the City ‘‘to develop

a landfill gas management plan and conduct an environ-

mental audit to assess the effect of landfill gas on residents

of the estate’’ (1172). In July 2007, the environmental audit

warned of ‘‘an ‘imminent environmental hazard’ and an

‘unacceptable risk’ to residents, due to the presence of

methane in the estate’’ (110) and indicated that ‘‘immediate

action is required to reduce the current risk’’ (1184). In

August 2007, a follow-up gas risk assessment indicated

that the City had developed a landfill management plan and

that the remedial measures involved ‘‘greater and more

efficient extraction of landfill gas and in installation of a

gas interception trench on the north and north-west side of

the landfill. The available data indicate that these measures

are not currently effective at controlling off-site landfill gas

migration and the risk profile is more significant than that


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observed in February–March 2007. The most significant

risk of adverse impacts of landfill gas is from accumulation

and possible explosion in underground structures and

dwellings within 50 m of the landfill’’ (1185).

By September 2008, residential housing had been

‘‘constructed right up to the landfill site boundary’’ (598

and Illustration 2). On 31 August 2008 methane was

detected at very high levels (63 % v/v) within a house in

the estate and on 9 September 2008 the EPA ‘‘deter-

mined that landfill gas migrating from the landfill rep-

resented an imminent danger (to residents) and

recommended that urgent action take place, including

recommending relocation of affected residents’’ (1278).

Short-term mitigation measures ‘‘were implemented to

minimize the risk to residents in the estate’’ (1324). The

emergency continued throughout October 2008 but by

the end of October the level of risk had reduced (1396)

and on 31 October 2008 residents were informed that it

was safe for them to return/stay in their homes, with

some recommendation regarding actions that they could

take to minimise risk since there was still gas in the

ground across the estate (1399). Activities to control gas

in the estate are ongoing.

The Ombudsman was critical of most of the parties

involved with the landfill. Of particular note are the com-

ments with respect to the Shire (which subsequently

became the City) who was both the landfill owner and the

body responsible for approving development around the

landfill. The Ombudsman concluded, inter alia, that ‘‘the

Shire failed to have regard to environment protection in

two ways: It did not recognise its own role in protecting the

environment. It sought to affect the role of the EPA in

protecting the environment.’’ (20), and ‘‘in its narrow focus

on the economics of landfilling, the Shire failed to take

account of other factors, namely environmental standards’’

(22).

With regard to conflict of interest, the Ombudsman

concluded that the City ‘‘failed to adequately address its

conflict of interest as an owner of the landfill and the

responsible authority for making planning decisions about

residential development adjacent to the landfill,’’ (95).

With regard to appreciating the risk to residents, the

Ombudsman stated that ‘‘Throughout my investigation

I observed contrasting views concerning the level of risk

to residents in the estate caused by the leaking methane.

I appreciate that given the unusual nature of the emergency

and lack of past experience in Australia with leaking

methane gas from a landfill, there would be differing views

regarding the level of risk posed to residents in the estate.

However it appears that, of the many agencies involved in

the emergency, the City’s…perception of risk to the resi-

dents was significantly less than that of the EPA, the CFA

(Country Fire Authority) and the independent experts

despite the weight of expert advice,’’ (115). ‘‘When one of

the technical consultants engaged by the City…informed

the EPA about his concerns in relation to the risk to the

residents posed by the methane, the Acting Executive

Officer for the City…responded by downplaying the advice

and sought to discredit the consultant for ‘breaking

ranks’,’’ (116). ‘‘Also it appears that the City…officers

downplayed the advice of the international advisory group

assembled by the EPA, including one landfill gas expert

who described the landfill as one of the worst sites he had

ever seen with the potential for explosion and/or asphyxi-

ation,’’ (117).

With regard to the cost of the problem, the Ombuds-

man’s summary states that: ‘‘I understand that the City…in

the 2008–2009 financial year alone committed $21 mil-

lion’’ (Australian, about $22 million US) ‘‘to a range of

measures aimed at mitigating the risk of landfill gas leaking

into the estate. In the long term, the total cost of rehabili-

tating the landfill is expected to exceed $100 million. This

stands in stark contrast to the 1992 estimated cost of

$500,000 to line the landfill as a preventative measure to

protect people and the environment, which the Shire…rejected on the basis of expense’’ (133).

No doubt many critiqued by the Ombudsman would not

agree with some of his opinions/conclusions (including

those noted above). This is a complex case and the sum-

mary above only addresses some aspects relevant to this

paper. For example, the Ombudsman opined at various

points in his report that there was poor record keeping, the

responsibilities for action were unclear, there were poorly

written contracts, there was conflict over who exactly was

responsible for various issues, and ‘‘a failure to effectively

manage contracts (which) contributed to very poor results

at the landfill’’ (660). It is not the objective of this paper to

discuss the merits of any of his views. However the fact

that the methane gas unquestionably escaped the landfill

site and caused the evacuation of residents highlights the

need for caution in the design, construction, operation, and

closure of landfills as well as the need for an appreciation

of the potential risks associated with development close to

a landfill without a buffer that is adequate given the local

hydrogeology, the level of engineering of the landfill, and

the nature of the waste disposed in the landfill.

Some Field Cases Related to Leachate Collection

The field performance of leachate collection systems has

been examined in detail by Rowe [112] and Rowe and Yu

[133] and the reader is referred to these two papers for

more details and cases than are presented here. The fol-

lowing cases have been selected because they illustrate a

number of points to be made in this paper and only the

essential details are presented here.


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Brune et al. [27] reported that when waste was placed

very rapidly (about 10–20 m/a) at the Altwarmbuchen

Landfill, there was an intensive acetogenic phase of

decomposition. The reduction potential (Eh), presence of

sulphide in all the drains, and gas analysis all indicated

anaerobic conditions. Newer portions of the landfill had

acidic leachate (pH 5.9, COD = 51,000 mg/L, BOD5 =

23,300 mg/L, BOD5/COD = 0.46, calcium = 3,530 mg/

L, iron = 1,150 mg/L, drain temperature = 25–40 �C),

while older portions were neutral to slightly alkaline

(pH 7–8, COD = 10,000 mg/L, BOD5 = 1,000 mg/L,

BOD5/COD = 0.1). The clogging was particularly intense

even though the leachate pipes were flushed at least

annually. Between cleanings, clog deposits extended across

the bottom of the pipes from one side to the other. This

landfill accepted sewage sludge which likely contributed to

the rate of clogging.

Excavation of the leachate drainage system at the

Geldern Pont MSW landfill [27] found large areas where

the sandy gravel (80 % 2–9 mm gravel and 20 % sand)

drainage layer was clogged to between 1/3 and 2/3 of its

thickness and the hydraulic conductivity was reduced to as

low as about 10-8 m/s.

Koerner and Koerner [64] reported that a perforated

collection pipe wrapped with a geotextile (heat bonded

nonwoven, apparent opening size = 0.15 mm, permittiv-

ity = 1.1 s-1) in a layer of 6–30 mm gravel experienced a

significant reduction in flow after 1 year and the develop-

ment of a high leachate mound. Due to clogging, the

hydraulic conductivity of the gravel had reduced from an

initial 2.5 9 10-1–2 9 10-7 m/s, while that of the geo-

textile had reduced from 4 9 10-4–3 9 10-8 m/s.

It is not just drainage systems in MSW that experience

clogging. For example, Koerner and Koerner [64] also

reported that the blanket underdrain at an industrial landfill

with solids and sludge (slurry fines with 70 % of particles

finer than 0.15 mm) ceased collecting fluid after only

6 months, resulting in the build-up of a high leachate mound.

The underdrain had a sand (0.075–4 mm) protection layer

over a geotextile (apparent opening size = 0.19 mm) over a

pea gravel (1–20 mm) drainage layer with 100 mm diameter

HDPE perforated pipe wrapped in needle punched nonwoven

geotextile (apparent opening size = 0.19 mm, permittiv-

ity = 1.8 s-1). The continuous geotextile between the sand

and gravel was performing well with about a five-fold

reduction in hydraulic conductivity to about 9 9 10-5 m/s

and the pea gravel had not experienced significant clogging.

The cause of the problem was the geotextile wrapped around

the perforated pipe, which had clogged excessively and

experienced a five order of magnitude reduction in hydraulic

conductivity to about 4 9 10-8 m/s.

Rowe [110] reported that a 64.4-ha landfill located just

east of Toronto, Canada, which became operational in

1975, had accepted about 15 Mt of MSW waste and about 2

Mt of sewage sludge at the time of closure. It has a

100–150 mm thick sand bentonite liner and a leachate

collection system comprised of perforated leachate col-

lection pipes, surrounded by 5–10 mm pea gravel with a

radius of 0.5 m, at a spacing of 50 m in newer portions of

the landfill and 200 m in older portions of the landfill. By

1987 the leachate mounded was as much as 20 m above the

liner. The leachate header plugged in 1988 and in 1990 a

bypass was installed to divert leachate around a plugged

section of the perimeter drain. Despite this change the

volume of leachate collected by the collection system was

small and in 1991 less than 6 % of the estimated

129,300 m3 of leachate being generated annually was

being collected (with consequent groundwater contamina-

tion issues). Modelling by Rowe and Yu [134] has shown

that the leachate mounding can be explained by clogging of

the pea gravel around the pipes.

Rowe [112] describes the Keele Valley Landfill located

just north of Toronto in some detail. It has an approxi-

mately 1.2 m thick compacted clayey till liner with a

hydraulic conductivity of less than 10-10 m/s [60]. The

landfill was constructed in four stages. In each stage, the

liner was covered by a 0.3 m desiccation protection layer

of sand.

In Stages 1 and 2, the primary leachate collection system

is comprised of lateral finger (French) drains (50 mm,

relatively uniform gravel and 1.2 m2 cross-sectional area)

at a spacing of about 65 m sloping towards the main col-

lection pipes (spacing 200 m). The waste placement in

Stage 1 started in 1983 [8] and an exhumation in Stage 1

after 4.25 years of landfilling [60] showed that the diffu-

sion profile started at the top of the sand blanket. This

implies negligible horizontal or vertical flow in the sand.

The sand blanket had ceased to transmit leachate (except

by diffusion) and appeared to have clogged within about

the top 5 cm very early after waste was placed. Monitoring

[8, 112] indicated that the leachate head between the finger

drains in Stage 1 was about 0.5 m in 1985 and gradually

increased to about 1.2 m in 1987. It remained at about

1.2 m from 1987 until 1992. Over the next ten years

(1992–2002), the leachate head increased to about 8.4 m.

After 2002, the head decreased slightly due to the closure

of the landfill and construction of the final cover which

reduced infiltration and hence the volume of leachate

generated. Rowe and Yu [134] have modeled this sequence

of events and shown that it can be explained by clogging of

the gravel around the finger drains to a hydraulic conduc-

tivity less than that of the waste in about 1992 (i.e., in less

than 9 years).

In Stages 3 and 4, there is a 0.3 m thick continuous

drainage blanket of 50 mm gravel over the 0.3 m thick

sand desiccation protection layer. The waste is generally


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placed directly on the gravel drainage layer although in a

few locations there is a slit-film geotextile between the

waste and gravel. Fleming et al. [47] examined the leachate

collection gravel in Stage 4 in 1995, after it had been in

place for 4–5 years. They reported clogging in the lower

portion of the gravel, which had reduced the hydraulic

conductivity by about three orders of magnitude to about

10-4 m/s. However, due to the high initial hydraulic con-

ductivity of the gravel, the layer was still controlling the

leachate head to below the maximum design value (0.3 m),

as it still is today (some 20 years after it was placed). They

also reported that where there was a filter/separator layer

between the waste and drainage layer, there was less

clogging of drainage media relative to locations where

there was no filter/separator. This is in stark contrast to the

performance of the other collection systems described

above and illustrates the value of having a continuous layer

of relatively uniform coarse gravel as a drainage layer.

Fleming et al. [48] reported a perimeter drain system

installed in 2004 at the edge of an old MSW landfill that

failed within 3 years of installation. The drainage system,

which was placed 3–5 m below ground surface in a trench

excavated to below the water table, comprised a 300 mm

perforated HDPE pipe wrapped in a lightweight heat-bonded

nonwoven geotextile surrounded and covered by a sand

(D90 = 1 mm, D50 = 0.2–0.4 mm, D10 = 0.1–0.2 mm)

backfill. The clogging was attributed to the growth of

microbial biofilm and precipitation of iron oxides and

hydroxides due to oxidation of iron rich leachate contami-

nated groundwater from the landfill. Most of the perforations

in the pipe were at least partially blocked and those near the

invert were completely blocked. By 2007, the nature of the

design and the reduction in hydraulic conductivity of the

geotextile had resulted in leachate-contaminated ground-

water bypassing the drain and contaminating a nearby creek.

In summary, these examples illustrate the importance

of considering the potential for clogging in the design of

leachate collection systems and that clogging can reduce

hydraulic conductivity of both granular materials and

geotextiles to of the order of 10-8–10-7 m/s and that

unless the system is well designed this can cause exces-

sive leachate mounding with consequent contaminant

escape. However, it has also been demonstrated that a

drainage layer with coarse uniform gravel has given good

performance and that, used wisely, geotextiles can be

beneficial to the performance of the leachate collection

system.

Some Field Cases Related to Stability

Although most landfills are constructed without stability

problems, there have been failures. The most common

failures are associated with veneer failures in leachate

collection layers before waste placement and in landfill

covers. These may be related to poor design, poor con-

struction, and/or operational issues. The geotechnical

engineering behind designing to avoid most veneer failures

which are associated with poor drainage (excessive pore

pressures and seepage drag forces) and inadequate inter-

face shear strength is well known [e.g., 66]. Rowe [111]

discusses four cases where there were failures of leachate

collection layers on slopes ranging from 4:1 (H:V) to 2.5:1.

Three of the cases were attributed to the low hydraulic

conductivity of the drainage material (one because the

initial hydraulic conductivity of the as-placed material was

too low and two cases because of the accumulation of fines

in the gravel) which caused an increase in seepage forces

and consequent failure. The fourth case was related to

climatic conditions.

Final cover failures involving sliding of the materials

above the geomembrane are often associated with inade-

quate drainage to control pore pressures.

A factor that may be neglected in the design of final

covers is the potential effect of landfill gas pressures below

a low permeability cover. For example, Benson et al. [11]

describe a case where, about 9 months after it was con-

structed, there was a veneer failure of a 4.25-ha section of

final cover on a 4:1 slope. The cover was over MSW where

operations involved ‘‘vigorous’’ recirculation of leachate.

The cover above the waste comprised, from bottom up: a

600 mm thick layer of silty clay, a GCL, a textured 1 mm

thick linear low density polyethylene (LLDPE) geomem-

brane, a geocomposite drainage layer, 760 mm of sand, and

150 mm of topsoil. A forensic investigation found that

elevated landfill gas pressure beneath the cover reduced the

effective normal stress and resulted in slope failure due to

inadequate shearing resistance between the geomembrane

and GCL. In addition, the study indicated that the slope

would have been stable if gas pressures had been main-

tained near atmospheric. The elevated gas pressure was

attributed to inadequate gas collection associated with

excess leachate in the gas collection wells due to the

recirculation of leachate and, in part, due to inoperative

leachate extraction pumps in the gas extraction wells.

There have been a number of failures where a slide was

associated a failure plane related to liner construction.

Examples include the Kettleman Hills slide [28] and the

French slide [96]. The French slide demonstrated how

construction conditions which differ from those assumed in

design (in this case the wetting of the clay liner by rainfall

before placing the geomembrane) can give rise to failures if

not anticipated and dealt with in either the design itself or

the construction documents and construction monitoring.

Failures associated with general shear failures during the

expansion of existing landfills (e.g., Maine slide reported

by Reynolds [105]) or the Cincinnati slide reported by


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Stark and Evans [165] or the Beirolas slide in Lisbon

reported by Santayana and Pinto [162] all demonstrate the

need for a good geotechnical investigation and analysis for

any landfill construction or expansion. Other less well

documented failures (e.g., the failure of the Bulbul Landfill

at Kwazulu-Natel in South Africa on 8/9/97) have been

triggered by the addition of liquids to the waste (including

recirculation of leachate) which increased pore pressures

on the interface between materials at the base of the landfill

and thereby decreased the shear strength to the point where

a failure occurred.

In summary, these cases highlight the need for a good

geotechnical investigations and design when dealing with

all facets of landfill stability. They also indicate the

importance of considering how conditions can change (e.g.,

moisture can increasing the density of waste, increasing

pore pressures, reducing interface friction, etc.) either due

to natural climatic events (e.g., rainfall) of operational

decisions (e.g. adding fluid to waste) and reduce stability.

Hydrogeology and Barrier Subsystem

The migration of contaminants below the ground surface is

controlled by the hydrogeology and the barrier system

between it and the waste. In environments where there is

thick low permeability clay, the engineered barrier system

could be minimal (e.g., a leachate collection system). If the

hydrogeology involves permeable zones (e.g., sand, gravel,

fractured soil or rock), a more elaborate system is generally

required for the reasons illustrated by the cases discussed in

the previous section, and will typically involve at least a

leachate collection system and primary liner. For small

landfills, the primary liner will typically involve a protec-

tion layer and a geomembrane, clay liner or, most com-

monly (for reasons discussed below), a composite liner

comprised of a geomembrane and clay liner. For large

landfills a double liner (e.g. Fig. 2) is usually required to

provide adequate containment.

Leachate Collection and Control of Head on Liner

As discussed earlier, the driving force for subsurface

leachate escape (leakage) is the height of the leachate head,

hw, on the liner. The leachate collection system controls

this head but its long-term performance is highly dependent

on the nature of the leachate, the thickness of the drainage

layer, the grain size distribution of the granular material

used, and the spacing and maintenance of the leachate

collection pipes as illustrated by laboratory and field

studies referenced in earlier sections and by state-of-the-art

modelling techniques [e.g., 33, 34, 37, 38, 118, 181, 186].

These studies show that the greater the mass loading on the

collection system as represented by the combination of

leachate flow and the concentrations of total suspended

solids (TSS), organic matter (COD), and cations such as

calcium and iron, the faster will be the clogging and the

more robust the collection system needs to be. As a con-

sequence, some regulators may specify the type of drainage

material, thickness and pipe spacing required to achieve a

given service life (time to clogging). For example, Ontario

Regulation 232 [95] indicates that for a leachate collection

system for a normal MSW landfill (i.e., no leachate recir-

culation, no co-disposal of ash or sludge) to have a service

life of C100 years the drainage layer must meet certain

criteria which include: ‘‘The pipes must be bedded in a

continuous layer of stones (gravel) that extends completely

across the base of the waste fill zone and that has a mini-

mum thickness of 0.3 m on the base side slopes and a

minimum thickness of 0.5 m elsewhere. The stones must

have a D85 of not less than 37 mm, a D10 of not less than

19 mm, a uniformity coefficient (D60/D10) of less than 2.0,

and, when measured by weight, not more than 1.0 per cent

of the stones may pass the US #200 sieve. A suitable

geotextile or graded granular separator must be installed

between the stone layer and the overlying waste and

between the stone layer and any underlying soil or liner.

The perforated leachate collection pipes must be made of

high density polyethylene (HDPE), with a minimum

internal diameter of 150 mm and with perforations not less

than 12 mm in diameter…The perforated leachate collec-

tion pipes must be placed across the base of the waste fill

zone, excluding the base side slopes, and spaced so that the

drainage path before leachate can potentially intercept a

collection pipe is not more than 50 m in length.’’

Regulations/guidelines such as those indicated above are

supported by the latest research for traditional MSW land-

fills. However, a change in operating conditions could

change the effectiveness of such a system. For example, the

co-disposal of ash (e.g., from incineration of MSW) con-

taining significant amounts of calcium (6–29 % of total ash

depending on type of ash; [55]) and iron (0.4–15 % of total

ash depending on type of ash; [55]) has the potential to

increase the clogging of leachate collection systems if

mobilized by acids (e.g., as generated by the biodegradation

of MSW). An additional environmental concern is the level

of leachable lead (2.3–65 % w/w of the total content) and

molybdenum (9–19 % w/w of the total content) from fly ash

and acid gas scrubbing residues [55]. Yet these factors

generally are not fully appreciated in the design of leachate

collection systems for MSW where ash is being co-disposed.

Likewise, the effects of increasing the mass loading asso-

ciated with operating landfills as bioreactors has not, in the

writer’s opinion, been adequately researched and hence

considered in the design of leachate collection systems for

these facilities. These comments are not meant to imply that


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suitable systems could not be designed but, rather, that more

data is needed to aid in the design of suitable systems to

ensure adequate long-term performance.

Tire shreds have been proposed as an environmentally

(and economically) ‘‘friendly’’ alternative to gravel as a

drainage layer since they need to be disposed in any event and

in many areas suitable gravel is either not readily available or

expensive. Unfortunately, tire shreds are highly compressible

and far more prone to clogging than relatively uniform coarse

gravel [127]. Consequently, while they may be suitable in

non-critical areas with low stress, they are not suitable as a

replacement for gravel in MSW landfills in critical areas.

The propensity for geotextiles to experience a reduction

in hydraulic conductivity due to clogging has raised debate

regarding their use in a leachate collection system. Cer-

tainly the evidence (see previous section on field cases) is

clear that leachate pipes should not be wrapped in geo-

textile. However, both the field data (see previous section)

and laboratory studies [82] suggest that a suitable geotex-

tile between the waste and the gravel drainage layer can

improve the long-term performance of the gravel drainage

layer without significant perched leachate mounding for

normal MSW landfill operations (the effects of factors such

as leachate recirculation, operation as a bioreactor, co-

disposal of combustion waste such as incinerator ash and

scrubbing residues, and co-disposal of sewage sludge have

not been adequately evaluated at the time of writing).

In some cases, operational considerations favour

allowing leachate to build up in the leachate collection

system thereby saturating the layer. While there may be

some advantages to doing so, there are also risks. Most

significantly, both field and laboratory research suggests

that clogging is much faster in saturated gravel than

unsaturated gravel [46, 47, 83, 84] and hence, to maximize

the long-term performance of the leachate collection sys-

tem, it would appear prudent not to allow the leachate

collection to saturate whenever it can be avoided.

In summary, there is now a good understanding of what is

required to ensure good long-term performance of leachate

collection systems for normal MSW landfills with the appro-

priate use of HDPE drainage pipe, a relatively uniform

coarse gravel drainage layer, and a suitable geotextile filter

between the waste and the gravel. However more research is

required to develop designs that can confidently be expected

to give good long-term performance when incinerator ash or

other non-typical curb-side waste is disposed in MSW land-

fills, or when significant moisture is added to the waste (i.e.,

in excess of about 0.2 m3/m2/year).

Leakage Through Liners

The leakage through bottom liners has been extensively

discussed by Rowe [115] and is only briefly reviewed here.

For a single liner, the leakage (advective transport) will

depend on the local hydrogeology, the nature of the liner

that is present, and the leachate level (head) above the

liner. For a primary liner in a double lined system (Fig. 2)

it will depend on the nature of the liner that is present and

the leachate level (head) above the liner. For a geomem-

brane resting on a relatively permeable layer (be it soil or a

secondary leachate collection/leak detection system), the

leakage is controlled by Bernoulli’s equation and the

number and size of holes.

To illustrate the effectiveness of different liners at

controlling leakage, consider a primary liner underlain by a

secondary leachate collection (leak detection) layer where

the leachate head on the liner is 0.3 m (a typical design

value) and there is no head directly below the liner (due to

the free draining secondary leachate collection system). For

the case of an average size hole (radius 5.64 mm; see [115]

for discussion of hole size) in a geomembrane, even one

hole per hectare can result in a relatively large leakage of

12,600 lphd (litres per hectare per day) for a typical design

leachate head of 0.3 m (Table 1). For a compacted clay

liner (CCL) or geosynthetic clay liner (GCL) used alone,

the leakage depends on the hydraulic gradient and

hydraulic conductivity. Liners are often specified to have

hydraulic conductivities of 1 9 10-9 and 5 9 10-11 m/s for

a CCL and GCL, respectively, and for these values the leakage

though a typical (0.01 m thick) GCL and (0.6 m thick) CCL

Table 1 Calculated leakage, Q, through selected primary liners in a

double lined system for hw = 0.3 m and no head below the liner

Case kL (m/s) Q (lphd)

Geomembranea – 12,600

GCLb 5x10-11 1,300

CCLc 1x10-9 1,300

GCLb 2x10-10 5,400

CCLc 1x10-8 13,000

Wrinkle L (m) 100 200 700

Geomembrane/CCLd,e 1x10-9 83 170 580

1x10-8 270 530 1,860

Geomembrane/GCLd,f 5x10-11 3 6 21

2x10-10 9 17 61

Based in part on information published in [115]a Based on Bernoulli’s equation with one hole/ha, ro = 5.64 mm

(area of hole = 100 mm2)b GCL thickness HL = 0.01 mc CCL thickness HL = 0.6 md Using Eq. 1 and geometry as per schematic in Fig. 6 with

2b = 0.1 m, hole ro = 5.64 mm; assuming a hole in one connected

wrinkle of length L per hectare, ha = 0, HA = 0; calculated leakages

have been roundede h = 1.6x10-8 m2/sf h = 2x10-11 m2/s


123


are both about 1300 lphd (i.e., about one order of magnitude

lower than for the geomembrane alone). However, CCLs are

not always compacted as specified and both CCLs and GCLs

can experience chemical interaction with landfill leachate

(especially salts) as discussed by many authors and as sum-

marized by Rowe et al. [143]. If one adopts a reasonable upper

bound (higher values are possible in extreme cases) hydraulic

conductivities of 2 9 10-10 and 1 9 10-8 m/s for a GCL and

CCL, respectively, then the leakage (Table 1) increases in

proportion to the increase in hydraulic conductivity to

5,600 lphd for the GCL and 13,000 lphd for the CCL and the

leakage approaches, or is similar to, that of the geomembrane

alone.

After a geomembrane is placed, heating by the sun can

result in thermal expansion that gives rise to wrinkles

(Figs. 4, 5). Techniques for quantifying wrinkling have

been developed [172] and used to examine, inter alia, the

effect of restrained area and time of day/geomembrane

temperature on the interconnected length and width of wrinkles [29, 155]. While a geomembrane may have many

wrinkles, the ones that matter are those present at the time

when the geomembrane is covered by the leachate col-

lection layer since, if they have a height exceeding about

3 cm at that time, they are more likely to remain after

being covered (see discussion in [115]. Rowe [111] pro-

vided a simple equation for calculating the leakage through

a composite liner with a wrinkle (Fig. 6):

Q ¼ L 2bk þ 2ðkDh½ Þ0:5�hd=D ð1Þ

where Q is the leakage (m3/s), L is the length of the con-

nected wrinkle (m); 2b is the width of the wrinkle (m); k is

either the hydraulic conductivity (m/s) of the clay liner

(CL), kL, if there is no attenuation layer (AL), or the har-

monic mean of the CL and AL hydraulic conductivities, ks,

if there is an AL; h is the transmissivity of the GMB/CL

interface (m2/s); hd = (hw ? HL ? HA - ha; see Fig. 6) is

the head loss across the composite liner (m); and

D = HL ? HA is the thickness of the CL and AL (m). The

likely length, L, and width, 2b, of wrinkles and the inter-

face transmissivity, h, between the geomembrane and CL

for different conditions are discussed by Rowe [115] and

the interested reader is referred to that paper for details.

A geomembrane may have a number of holes (2.5–5 per

hectare is often assumed if there is high level of construction

quality control) but if they do not align with wrinkles the

leakage through a few small holes per hectare is negligible

for the conditions considered here; thus the critical holes are

those that are on, or hydraulically connected to, wrinkles.

Assuming a composite liner with one wrinkle with a hole

per hectare, the leakage can be calculated for wrinkle

lengths of 100, 200, and 700 m as given in Table 1.

For a composite liner with a geomembrane and CCL

having a hydraulic conductivity of 1 9 10-9 m/s, the

leakage for this range of wrinkle lengths was between 83

Fig. 4 Interconnecting wrinkle along and across a geomembrane

provides a potential conduit for leakage if there is a hole in, or close

to, a wrinkle

Fig. 5 Wrinkle network

Fig. 6 Schematic showing leakage through a wrinkle of length L and

width 2b with a hole of radius ro. (After Rowe 2012, Short and long-

term leakage through composite liners. Can Geotech J 49(2):141–169)


123


and 580 lphd (corresponding to an average Darcy flux of

0.003–0.02 m/a). These values are substantially less (even

for a 700 m wrinkle) than the leakage for a geomembrane

alone (12,600 lphd) or a CCL alone (1,300 lphd).

With good construction and a short connected wrinkle

(L B 100 m) the leakage is low enough that diffusion is

important as a transport mechanism relative to leakage. An

increase in hydraulic conductivity of the CCL by a factor of

ten (to 1 9 10-8 m/s) increases leakage—but by less than

a factor of four, showing that the composite liner action

is a significant factor in improving liner performance by

reducing leakage.

For a composite liner consisting of a geomembrane and

a GCL having a hydraulic conductivity of 5 9 10-11 m/s,

the leakage for this range of wrinkle lengths was between 3

and 21 lphd (corresponding to an average Darcy flux of

0.0001–0.0008 m/a), which are in the diffusion-controlled

range and the actual leakage is negligibly small. Even with

an increase in hydraulic conductivity to 2 9 10-10 m/s due

to clay-leachate interaction the leakage of 9–61 lphd

(average Darcy fluxes of 0.0003–0.002 m/a) are still small

and remain in the diffusion-controlled to diffusion-domi-

nated range. This highlights the value of a composite liner

with a GCL.

Landfill gas can also leak though liners under certain

circumstances. Here, the driving force is the gas pressure

in the landfill; if the gas pressure exceeds the air pressure

outside the liner there is potential for gas migration.

A single geomembrane liner would have to be perfectly

intact to control the migration of gas if there is an

unsaturated permeable zone below the geomembrane.

Thus, a single geomembrane in a primary liner of a

double-lined system has the potential to transmit gas to the

secondary leachate collection (leak detection) system and

its migration beyond that point will depend on the nature

of the secondary liner.

If intact (without significant macrostructure; e.g., see

[136]) and saturated or at a high degree of saturation (i.e.,

C95 %), a compacted clay liner can be expected to provide

excellent resistance to gas leakage. However, it is essential

that the clay liner be protected from desiccation after it is

placed—this is especially critical on side slopes where it is

more difficult to construct the liner without macrostructure

and where exposure conditions are such that the liner may

be exposed for longer and hence be more prone to possible

desiccation.

A saturated GCL is also an excellent barrier to gas,

although its gas permeability increases significantly as the

degree of saturation decreases [15, 16, 42]. Thus to be

effective as a gas barrier, it is important that the GCL

remain saturated or at a relatively high degree of saturation.

A composite liner (a geomembrane and either a GCL or

CCL) can potentially provide an excellent barrier to the

escape (leakage) of landfill gas to the subsurface. A hole in

the geomembrane will allow gas to reach the clay liner and

the leakage will depend on the gas transmissivity of the

geomembrane/clay liner interface [e.g., 17] and the gas

permeability of the clay liner. The leakage of gas through a

hole in a geomembrane in direct contact with the clay liner

can be calculated [e.g., 19]. As for leachate, holes in

wrinkles pose the greatest potential for gas to leak through

the geomembrane since the wrinkle can distribute the gas

over the entire area of any interconnected wrinkle with a

hole. The leakage can be calculated in a manner similar to

that for leachate using appropriate gas pressures, gas

interface transmissivity, and gas permeability. This could

be particularly important on side slopes, where the clay

liner is often most vulnerable and where unsaturated

hydrogeology is most common.

In summary, composite liners (a geomembrane and

either a GCL or CCL) can be very effective barriers to the

advective movement (leakage) of both leachate and landfill

gas. To ensure good performance the geomembrane needs

to be constructed with relatively few holes and the number

of wrinkles at the time the liner is covered should be kept

low. The GCL needs to be able to uptake and retain

moisture so that when it is needed to act as a liner it has a

high degree of saturation. The CCL needs to be appropri-

ately constructed and should not be permitted to desiccate.

Diffusion Through Liners

For well-designed and constructed liners and a well-func-

tioning leachate collection system that controls the head to

0.3 m or less, leakage will be sufficiently low that diffusion

may be an important, and for very good liners, the domi-

nant, transport mechanism [103, 107, 108, 143, 163]. When

considering diffusion in the aqueous phase, chloride is

usually the first contaminant considered because it is pre-

valent in MSW leachate at a relatively high concentration

and is conservative (i.e., it does not biodegrade or sorb to

the clay). Figure 7 shows that the diffusion of chloride

though clay with no advection (flow) is similar for several

salt solutions with a diffusion coefficient (at room tem-

perature) of about 5.9 9 10-10 m2/s [7]. The diffusion

coefficient obtained for advective flow (Darcy flux of

1 9 10-9 m/s) in the same direction as the diffusive gra-

dient of 5.7 9 10-10 m2/s [135] is, to experimental accu-

racy, the same as that for pure diffusion. Diffusion tests on

compacted clay with advective flow in the opposite direc-

tion to the diffusive gradient (Fig. 8; Darcy flux of

-8 9 10-9 m/s; [138, 139]) gave a very similar diffusion

coefficient of 5.4 9 10-10 m2/s. This illustrates that

mechanical dispersion is negligible at realistic advective

velocities (leakages) through clay and these tests (and other

tests; [143] indicate a relatively narrow range of diffusion


123


coefficients for chloride in compacted or natural clay lin-

ers. Volatile organic compounds (e.g., benzene, DCM) will

also diffuse in the aqueous phase through a clay liner with a

diffusion coefficient of similar magnitude to that for

chloride, but the migration of these contaminants can be

retarded by sorption and biodegradation. For example,

Rowe et al. [137] reported a slightly higher diffusion

coefficient for DCM than chloride at room temperature

(8 9 10-10 m2/s) for a relatively soft clay (i.e., near the

surface where it could swell), but because of retardation of

DCM by organic matter in the soil and biodegradation

of DCM as it diffused through the soft clay, the rate of

migration of chloride through a CCL or natural clay liner

normally would be higher than for DCM. For these reasons,

when dealing with a compacted or natural clay liner alone,

chloride is usually the critical contaminant (i.e., if the

diffusive migration of chloride is controlled to a negligible

level then other non-volatile contaminants normally will be

controlled to negligible levels), although calculations can

be performed for a range of contaminants to confirm this

for each situation (some parameters used in Ontario,

Canada are given in [95]).

Chloride and VOCs can also diffuse through GCLs [70,

72] and VOCs only can experience limited sorption [72,

73, 144]. The diffusion coefficient for GCLs is much more

dependent on the bulk void ratio (and hence stress level)

than for CCLs with a variation of about an order of mag-

nitude from around 3 9 10-10 m2/s at 20 kPa to

0.4 9 10-10 m2/s at 350 kPa for the GCL tested by Lake

and Rowe [70]. These values are lower than for compacted

clay, but the GCL is also relatively thin (typically about

0.01 m for a GCL compared to 0.6–1.2 m for a CCL) and

so the diffusive flux through a GCL alone is similar to or

larger than for a CCL alone. Thus, to give a similar dif-

fusive flux and contaminant attenuation as a CCL, the GCL

must be combined with an attenuation layer with a thick-

ness similar to the thickness of the CCL. The diffusion of

gases through a GCL has been reviewed by Bouazza [15,

16] and is highly dependent on the degree of saturation.

The diffusion of contaminants through an HDPE geo-

membrane is governed by a partitioning coefficient Sgf,

which is analogous to Henry’s coefficient and reflects the

ratio of the equilibrium concentration in the geomembrane

to that in the adjacent fluid (be it liquid or gas) and the

diffusion coefficient in the geomembrane, Dg. Under steady

state conditions, the flux of a contaminant from one side of

the geomembrane to the other is given by Fick’s first law:

f ¼ �Pgdcf

dzð2Þ

where

Pg ¼ Sgf Dg ð3Þ

and f is the flux of the contaminant of interest through the

geomembrane, Pg is the permeation coefficient, dcf /dz is

the change in concentration from the fluid on one side

of the geomembrane to that on the other side divided by

the thickness of the geomembrane, Sgf is the partitioning

coefficient, and Dg is diffusion coefficient in the

geomembrane. There are various ways of establishing

the partitioning, diffusion and permeation coefficients,

Fig. 8 Downward chloride diffusion with upward flow (upward

Darcy Flux 0.25 m/a). After Rowe RK, Caers CJ, Reynolds G, Chan

C (2000) Design and construction of barrier system for the Halton

Landfill. Can Geotech J 37(3):662–675. �Canadian Science Publish-

ing or its licensors

Fig. 7 Normalized chloride pore-water concentration versus depth

for the single-salt solution diffusion test conducted with various

solutions. C = concentration at t = 15 days, Co = initial chloride

concentration in the source solution, Cb = initial chloride concentra-

tion in the soil pore water. After Barone FS, Yanful EK, Quigley RM,

Rowe RK (1989). Effect of multiple contaminant migration on

diffusion and adsorption of some domestic waste contaminants in a

natural clayey soil. Can Geotech J 26(2):189–198. �Canadian Science

Publishing or its licensors


123


however the approach that best matches reality uses a two-

compartment diffusion cell [158] with a geomembrane

between the source and receptor compartments and where

contaminant diffusion is monitored from the source to the

receptor. At equilibrium, Sgf can be deduced from mass

balance considerations. Both Dg and Sgf can be deduced by

fitting the observed variation of the source and receptor

concentrations with time to a theoretical solution that

considers the appropriate boundary conditions, partitioning

(phase change) and transport through the geomembrane

[e.g., 123].

HDPE geomembranes are a remarkably good diffusion

barrier to the majority of contaminants in MSW landfill

leachate. For example, the concentration in the receptor

divided by the source concentration (c/co expressed in %)

obtained from a two-compartment diffusion test on a 2 mm

thick HDPE geomembrane that has been running for almost

20 years are presented in Fig. 9. The results shown are

controlled by the detection limit, which has varied over the

past 20 years, and the concentration in the receptor has been

below the latest detection limit of 250 lg/L (c/co & 0.01 %)

since January 2011. Based on this data, the permeation

coefficient, Pg, can be inferred to be less than 4 9 10-18 m2/s,

or about 100,000,000 times less than that through compacted

clay. The previous estimate of Pg B 3 9 10-17 m2/s repor-

ted by Rowe [112] was based on about 12 years of data at a

time when the detection limit was 500 lg/L (c/co & 0.02 %),

and the approximately ten fold reduction in the upper bound

estimate of Pg is a result primarily of a lower detection limit

in 2012 than in 2005, but also the fact that the test has been

running for about 7 years longer at the time of writing. For

these contaminants, the impact due to diffusion though the

intact geomembrane will be negligible over the service life of

the geomembrane.

There are, however, some contaminants for which a

standard geomembrane is not a good diffusion barrier—

notably VOCs such as benzene, DCM, etc. [43, 85, 86, 97,

102, 153, 158, 184]. For LLDPE and HDPE, the perme-

ation coefficients of VOCs in leachate (Table 2) are up to

about one order of magnitude less than that for a CCL or

GCL. However, the geomembrane thickness is only about

20 % that of a GCL and 1–3 % that of a CCL, and hence

the traditional geomembrane alone provides relatively little

resistance to diffusive flux of these contaminants. Aging of

a geomembrane has been shown [57] to reduce the diffu-

sion and permeation coefficients of an HDPE geomem-

brane. Modelling [116] indicates that while this is

advantageous, the change is not sufficient to address the

limitation of HDPE as a diffusion barrier for VOCs and the

combined presence of a clay liner and an attenuation layer

normally is needed to control the escape of these

contaminants.

To address this limitation for situations where there are

elevated levels of VOCs and insufficient attenuation

capacity in the hydrogeology (e.g., if the soil outside the

barrier system is unsaturated granular material or fractured

clay or rock), enhanced products such as fluorinated HDPE

[151, 152, 153, 160] or co-extruded geomembranes with an

ethylene vinyl alcohol (EVOH) inner core and either

LLDPE or HDPE outer layers can reduce permeation

coefficients with respect to VOCs by an order of magnitude

(Table 2) or potentially more [86].

Most research has been conducted for diffusion from the

aqueous phase. However, there is also potential for diffu-

sion from the gaseous phase. McWatters and Rowe [85, 86]

Fig. 9 Chloride concentrations in receptor as percentage of source

concentration for several two-compartment diffusion tests on 2 mm

thick HDPE with an aqueous sodium chloride source after 19.3 years.

Note values shown represent the detection limit for a given cell and

hence are an upper bound to the actual concentration. Where only one

data point is shown at a given time, all cells had values below the

same detection limit. Thus the value of Pg shown (Pg = Sgf Dg where

Sgf = 0.0008; Dg = 5 9 10-15 m2/s) represents an upper bound to

the permeation coefficient and not the actual value. No measurable

change has occurred in the source concentration in almost 20 years

Table 2 Comparison of aqueous phase permeation coefficients for three types of geomembrane

Permeation coefficient, Pg (m2/s) Benzene Toluene Ethylbenzene m&p-Xylene o-Xylene

LLDPE 0.7–1 9 10-10 1.1–1.8 9 10-10 0.8–1.6 9 10-10 0.9–1.4 9 10-10 0.8–1.1 9 10-10

HDPE 0.1 9 10-10 0.3 9 10-10 0.5 9 10-10 0.6 9 10-10 0.4 9 10-10

LLDPE/EVOH 0.02 9 10-10 0.03 9 10-10 0.06 9 10-10 0.05 9 10-10 0.04 9 10-10

Adapted from [86]


123


found that the diffusion coefficient is not dependant on the

phase. The partitioning coefficient, with respect to the

concentration in the vapour phase, Sgf*, can be related to

that in the aqueous phase, Sgf, by Henry’s law:

S�gf ¼ kSgf ð4Þ

and similarly the permeation coefficient from the gaseous

phase, Pg*, can be related to that in the aqueous phase, Pg,

by:

P�g ¼ kPg ð5Þ

where k is the Henry’s law coefficient specific to each

contaminant and temperature [85, 86].

Stark and Choi [164] examined the diffusion of methane

found in landfill gas and concluded that the gas permeation

coefficients are low enough that very little methane diffu-

sion would be expected through a PVC, LLDPE, or HDPE

geomembranes if they were intact.

In summary, standard HDPE geomembranes are excel-

lent barriers to the diffusion of ions (e.g., chloride, sodium

etc.) and some gases (e.g., methane) but not to VOCs found

in leachate and landfill gas. The geomembrane needs to be

used in conjunction with a clay liner and suitable thickness

of attenuation layer to control the diffusion of VOCs. For a

GCL to be equivalent to a CCL as a diffusion barrier it

needs to be used with a suitable attenuation layer (typically

about the same thickness as the CCL). If diffusion of VOCs

can not be controlled to sufficiently low levels in this way,

enhanced (co-extruded HDPE/EVOH/HDPE) geomem-

branes are available that have a much greater resistance to

the diffusion of VOCs than traditional HDPE.

Interaction Between Leachate Collection System

and Liner–Liner Protection

The leachate collection system is an essential component of

the barrier system, as described above; however, the coarse

gravel that is desirable to extend the service life of the

leachate collection system can induce significant strains in

the geomembrane [21, 52, 53] that will shorten the service

life of the geomembrane and cause thinning of an under-

lying GCL [39, 40]. Thus, improving the performance of

one component of the system (the drainage layer) can

reduce the performance of another component (the com-

posite liner) unless special care is taken to avoid that

undesirable outcome. This problem can be avoided by

including an appropriate protection layer between the

drainage layer and the geomembrane. Geotextiles are

commonly used. However, the research cited above has

shown that the geotextile needs to be very substantial (in

excess of 2000 g/m2) to protect against coarse gravel and a

pressure as low as 250 kPa. The best protection layer

appears to be a sand layer, not as a component of the

drainage system but simply as a protection layer. Research

has suggested that a sand protection layer has the added

benefit of extending the service life of the geomembrane in

ways other than just reducing the strain [130, 131].

An adequate protection layer is also required with the

use of a geonet or tire shreds/chips since both can induce

strains in the geomembrane and tire shreds can puncture

the geomembrane if there is any wire remaining with the

shreds. In addition, if a GCL is used in a primary composite

liner for a double-lined landfill then the GCL needs to be

protected from thinning due to localized strains induced by

the drainage layer [41] and from intrusion of the GCL into

the drainage layer [76, 112].

In summary, the long-term performance of a geomem-

brane and GCL can be compromised it they are not ade-

quately protected against local indentations and the

associated strains that can be induced by adjacent materials

(e.g., gravel, geonets).

Service Life of Geomembranes

As noted earlier, a geomembrane can be an excellent bar-

rier to fluids—provided it does not have too many holes,

especially holes in long wrinkles. This requires good con-

struction quality (see later discussion) and good operations

that do not damage the geomembrane. Adequate protection

is an important component of minimizing the risk of

damage during operations. For example, Rowe et al. [142]

and Lake and Rowe [74] describe a composite (1.5 mm

HDPE geomembrane over a 3 m thick CCL) for a leachate

lagoon that was decommissioned after 14 years of service.

The geomembrane had been left exposed (i.e., with no

protection) during its lifetime. At the time it was decom-

missioned, there were wrinkles (Fig. 10) and a total of 82

cracks, holes, and patches (repaired holes) in the about

1500 m2 geomembrane (i.e., 528 defects per hectare over

the 14-year period of operation). Of these, 30 % (180

defects per hectare) were below the leachate level and

when the leachate was removed, walking on the geo-

membrane was like walking on a waterbed due to the

abundance of fluid between the geomembrane and the

CCL. Thus, at decommissioning the geomembrane was no

longer effective as a barrier and the question remained as to

when operations (e.g., cleaning of sludge from the bottom

of the lagoon) had compromised the geomembrane per-

formance. To address this question, the migration of vari-

ous constituents of the leachate was examined with

chloride being the primary indicator since it had migrated

1.7 m into the clay liner in 14 years (Fig. 11). The forensic

investigation indicated that for this low hydraulic conduc-

tivity CCL (2 9 10-10 m/s), diffusion was the dominant

transport mechanism (D = 7 9 10-10 m2/s) and that the

geomembrane had been effective for less than 6 years.


123


Fortunately, the CCL had prevented any escape of con-

taminants. This case illustrates how a lack of understanding

of the need to avoid damage to the geomembrane during

operations compromised the value of installing the geo-

membrane. While this is an extreme case, it does highlight

the need for operators to understand the basis of a design

and avoid damaging the geomembrane liner after it has

been placed and approved.

Assuming good construction and operations, the service

life of a geomembrane liner used in a MSW landfill will

depend, inter alia, on temperature and time–temperature

history, the chemical composition of the leachate, and the

geomembrane properties [e.g., 90, 126, 132, 145, 146, 148,

159]. This research is based on tests in which a geomem-

brane is immersed in the fluid of interest. It has been shown

[130, 131, 149], however, that the exposure conditions can

greatly affect the service life. The development of geo-

synthetic landfill liner simulators [23, 149] offers an

opportunity to explore the interactions between the differ-

ent factors influencing geomembrane service life. The

results from experiments that examine all three stages of

the service life will become available for the first time over

the next few years. In the meantime, the reader interested

in the service life of geomembranes in landfill applications

are referred to the references cited above and Rowe [112,

115].

In summary, it is essential not only that the geomem-

brane be correctly installed but also that it should not be

damaged during operations if it is to give good long-term

performance. Assuming it is properly installed and not

damaged by operations, the length of time that the geo-

membrane will remain an effective barrier to leakage (its

service life) will depend on factors such as the temperature

and time–temperature history of the geomembrane, the

chemical composition of the leachate, and the geomem-

brane properties. Studies have indicated that this service

life could range from millennia to less than a decade

depending on these conditions. The available data for good

quality 1.5–2.0 mm HDPE geomembrane used in normal

MSW landfills where the liner temperature is less than

40 �C is likely to a couple of centuries and potentially

much longer.

Modelling Transport Through Barrier Systems

Much has been written on the modelling of contaminant

transport through barrier systems ranging from clay liners

[e.g., 119–121] to composite liners [e.g., 45, 98, 143]

including consideration of the effect of service lives of the

components of the system (e.g., leachate collection layers,

geomembrane liners) on contaminant transport [122], the

effect of uncertainty regarding parameters [124], landfill

temperature [117], and aging of the geomembrane [116].

The interested reader is referred to the cited references.

The key point for this paper is that techniques exist, and

have been well tested, for predicting advective–diffusive

migration of contaminants through barriers systems. These

techniques can consider factors such as changes in tem-

perature with time and the service life of the components of

Fig. 10 Photo of geomembrane in a leachate lagoon composite liner

at decommissioning after 14 years

Fig. 11 Chloride concentration profile through the compacted clay

liner based on samples from five boreholes together with prediction of

pore-fluid concentration for different assumed geomembrane service

lives. After [142]. Rowe RK, Sangam HP, Lake CB (2003) Evaluation

of an HDPE geomembrane after 14 years as a leachate lagoon liner.

Can Geotech J 40(3):536–550. �Canadian Science Publishing or its

licensors


123


the system to allow a reasonable assessment of the likely

long-term performance of a given design; there is no need

to guess. Some regulations [e.g. 95] require the use of these

techniques for large landfills (waste volume [290000 m3/

ha) and in the writers opinion this should be more generally

required.

Design Dependence on Waste Type, Amount,

and Operational Model

Even for typical MSW, the contaminating lifespan is a

function of the thickness of the waste or mass of waste per

unit area [109, 143] and it follows that the barrier system

required for a given hydrogeology is likely to be more

extensive for a landfill with a large mass of waste per unit

area than for a landfill with a small mass of waste per unit

area, as reflected in Ontario Regulation 232 [95], which

requires a double liner when a landfill exceeds a certain

size (waste volume 100,000–140,000 m3/ha depending on

groundwater conditions) but is generally not recognised in

many other jurisdictions.

The nature of the waste disposed in the landfill can

greatly affect the temperature on or near the liner (Table 3;

[115]). For normal MSW, having liner temperatures in the

30–40 �C range, one can expect a good HDPE geomem-

brane to have a service life of a couple of centuries or more

as noted earlier [112, 115]. Most regulations were devel-

oped with this application in mind [e.g., 95]. However,

when other waste is co-disposed with the MSW, liner

temperatures can range from 50 to greater than 85 �C and

the service life can be reduced to decades (or in some cases

less). Likewise, the co-disposal of combustion waste

(incinerator ash) not only affects the leachate collection

system, it can also give rise to significant (46–90 �C) liner

temperatures (Table 3). For these cases, a typical liner

system (as shown in Fig. 2) may not be sufficient. Various

strategies can be adopted to control the liner temperature

[e.g., 56, 125, 150] and maintain an adequate geomem-

brane service life but they need to be implemented in the

design stage and cannot be easily retrofitted; thus the nature

of the waste must be considered in the design and con-

trolled to be consistent with the design to ensure good long-

term performance.

The way the landfill is operated will also affect the liner

temperature. There are many benefits (e.g., increasing the

amount of waste that can be disposed in approved landfill

contours, more efficient gas collection and energy gener-

ation, reducing the cost of leachate management) associ-

ated with recirculation of leachate; however, it also

introduces many challenges that must be anticipated at the

design stage. These challenges include problems with gas

collection, cover stability and landfill stability discussed

earlier, as well as increasing liner temperature (Table 3),

which can substantially reduce the service life of the liner

system.

In summary, one needs to consider the type of waste

and the mode of operation at the design stage. Once the

barrier system is established for a proposed waste type and

mode of operation (e.g., with or without leachate recir-

culation), the nature of the waste and operations must be

maintained consistent with the design assumptions.

Unfortunately, most regulations were developed before

these factors were anticipated and do not (yet) address the

need to design the barrier system to be consistent with the

nature of the waste being disposed (beyond the restrictions

Table 3 Temperature on (or near) liners for different environments

Environment Temperatures (oC) References

Normal MSW landfills (limited moisture addition) 30–40 [27, 65, 91, 112], Author’s files

Wet landfills (e.g. bioreactor landfills) where there is a

significant amount of moisture

40–60 [67, 185], Author’s files

Unusual MSW landfillsa 60–80a Author’s files

50–60b

Ash monofills 46 [63]

50–90a Author’s files

65–70b

MSW with aluminum production waste and leachate

recirculation

85c to [143d [166]

Based on Rowe [115]a No monitors on liner so liner temperature is unknown, temperature given is in waste about 3 m above linerb Leachate temperaturec Temperature in leachate collection pipesd Temperature in waste


123


on hazardous, industrial, and commercial waste in MSW

landfills). Landfills with barrier systems that will give

excellent long-term performance of normal MSW landfills

may give problems in the same time frame (decades) as

the two cases discussed in detail earlier if used to dispose

of non-typical MSW waste. Barriers could be designed for

these wastes but they are likely to be different to the

conventional MSW design and should be based on

appropriate research.

Landfill Cover and Gas Collection System

The landfill cover and gas collection system controls both

the entry of water (which generates leachate) and the

escape of landfill gas. To minimize the leakage of landfill

gas to the atmosphere, the cover will include a liner system

to provide resistance to gas escape and a gas collection

system, which reduces the driving force (pressure) for gas

escape. In addition to the liner and gas collection system,

there may also be a moisture distribution system to provide

moisture to the waste to encourage biodegradation and gas

generation.

Bonaparte and Yanful [13] describe the basic consider-

ations with respect to the design of covers for waste and

Staub et al. [167] describe a model to assess the environ-

mental impact of cover systems on MSW landfill emis-

sions. Since the cover liner system is often similar to that in

the bottom liner, many of the same issues discussed above

for bottom liners and below with respect to material

selection and construction also apply to covers and are not

repeated here. For covers, the effect of climate on clay

liners requires particular attention since they will be

exposed to climatic effects for a long period of time (unlike

base liners which should be covered quickly to protect the

liner from climatic effects). Compacted clay liners are

prone to cracking (due to both wet-dry and freeze–thaw

cycles) which will increase the hydraulic conductivity and

hence the infiltration entering the waste and gas leaving the

landfill—especially if there is no geomembrane to provide

composite action. GCLs are also susceptible to the effects

of climate but have the advantage of having some self-

healing capacity provided that the combination of cation

exchange, drying, and low stress do not prevent significant

self-healing as has been observed in some cases [e.g., 10,

87]. These issues can be addressed with careful design and

maintenance of the cover.

As noted in earlier sections, some critical considerations

in the design of low permeability covers are ensuring good

drainage of water above and below the cover to avoid

excess pore pressures that can result in a loss of stability

and avoiding a build-up of gas pressures (even local gas

pressures) below the cover.

Materials Specification

A critical aspect of design is specifying appropriate mate-

rials. As already discussed with respect to leachate col-

lection systems, the selection of an appropriate drainage

material is critical to good long-term performance in MSW

landfills. The selection of a suitable soil is critical to good

performance of a compacted clay liner [143]. Likewise, the

selection of an appropriate HDPE geomembrane and geo-

synthetic clay liner is critical to the system’s long-term

performance and there can be substantial differences

between products. Standard specifications such as GRI-

GM13 or GRI-GCL3 [50, 51] represent a basic starting

point—but they are minimum requirements and while they

are sufficient for some applications, a geomembrane or

GCL that meets these specifications may not be adequate

for other applications (e.g., some applications with elevated

temperatures or covers where cation exchange may be

expected). There are a wide range of HDPE geomembranes

and GCLs on the market and many manufacturers have a

range of products. With respect to geomembranes, the resin

and antioxidant package used may have a significant

impact on the geomembrane’s long-term performance in

landfill applications. GCLs may differ in terms of the

bentonite used (e.g., natural sodium bentonite, calcium

bentonite, activated sodium bentonite, polymer enhanced

bentonite), the mass of bentonite per unit area, the method

of GCL manufacture, the cover and carrier geotextiles, and

the presence of a polymer coating on the GCL, all of which

can affect the GCL’s performance in critical applications

[e.g., 71, 99, 113, 115, 129]. For example, Bouazza and

Vangpaisal [18] indicate that the gas permeability of GCLs

may vary by several orders of magnitude depending on the

distribution of needle-punched fibres, highlighting the fact

that not all needle punched GCLs are the same. While

many GCLs may meet the requirement of GRI-GM13

(e.g., having a hydraulic conductivity B5 9 10-11 m/s as

per ASTM D5887 [4] and swell index C24 mL/2 g as per

ASTM D5890 [5]) for the virgin material, they may

respond very differently in some landfill applications (e.g.,

in covers, over drainage layers, when used in a composite

liner that is left exposed for some time, etc.); space does

not permit a detailed discussion of these issues in this paper

and the reader is referred to the relevant literature.

The interactions between materials need to be consid-

ered in specifying materials that will work together in a

system such as the level of protection needed for a given

drainage layer and liner as discussed earlier, the interface

properties between components of a composite liner [e.g.,

6, 30, 44], the potential for stones in a CCL affecting an

overlying geomembrane [e.g., 22], etc.

While caution is required in selecting the appropriate

materials for a given application, it should be emphasised


123


that suitable materials that are available may be more

expensive than alternatives because the features that offer

better performance cost more than the cheapest available

materials. When cost becomes an issue, the lessons from

the past highlighted earlier should be remembered; what is

cheap in the short-term may be a very expensive solution in

the intermediate- to long-term.

Not only should the correct material be specified for a

given application, the materials delivered to the site should

be checked for conformance with the specification. For

example, Guyonnet et al. [54] examined a number of GCLs

with bentonite from different regions (North America,

Europe, India, and Australia) and found that when the

GCLs were permeated with synthetic leachate at 100 kPa,

the hydraulic conductivity values were less than

5 9 10-11 m/s for 5 of 6 GCLs but 1 9 10-10 m/s for one

case. A manufacturer claimed that a GCL contained natural

bentonite but, in fact, it was activated bentonite. Guyonnet

et al. [54] also report that a GCL claiming to contain

bentonite had less than 30 % smectite (the active clay

mineral in bentonite) and the predominant clay mineral was

kaolinite (which does not provided the same low perme-

ability as smectite which predominates in true bentonite).

The key point is that the geomembrane and GCL should

be selected based on its engineering requirements and once

selected inferior alternatives should not be permitted.

Details such as the type and mass of cover and carrier

geotextiles, and the amount and quality of the bentonite in

a GCL and the resin and antioxidants used in a geomem-

brane can be critical to long-term performance. Also once

specified vigilance is required to ensure that the materials

delivered to the site met the specification.

Construction Issues

Good construction quality is essential to good performance

on a landfill barrier or cover/gas collection system. While

perhaps obvious, this may nevertheless be overlooked.

Although space does not permit a detailed discussion of

construction issues, the following is intended to highlight

its importance and flag some issues discussed in more

detail elsewhere.

While the construction of leachate collection systems

and CCLs and the installation of geomembranes and GCLs

(amongst other things) may seem simple, there are very

important details that need attention to ensure good per-

formance. For example, if excessive fines are allowed to

migrate into a drainage layer (Fig. 12) they can compro-

mise the performance of a well-designed system. The

construction of a low permeability CCL requires careful

attention to the construction water content and the equip-

ment used for compaction [e.g., 136, 143] in a way dif-

ferent from what is required for good road construction

where most contractors have experience. Geomembranes

and GCLs require qualified installers (e.g., to ensure good

welds, to correctly install GCLs overlaps, and to ensure

that penetrations for pipes, etc. are correctly sealed—a

common problem). In addition, the construction of com-

posite liners requires careful attention to issues such as

minimizing wrinkles at the time the geomembrane is

covered [29, 115, 155], hydration of GCLs [e.g., 2, 104],

minimizing the risk of shrinkage of GCLs [e.g., 14, 24, 25,

59, 115, 147, 152, 154, 175, 176], and minimizing the risk

of desiccation of a CCL below a geomembrane [9, 20,

115].

Some Lessons from Landfill History

The two primary cases discussed in detail earlier have

many differences but also some similarities. Both cases

involve technical issues, but also issues concerning: (a) the

knowledge and responsibilities of public authorities that

are dealing both with waste itself and the land above and

surrounding landfills; (b) the risks of ‘‘saving money’’ in

ways that will ultimately increase risks to the public and

the environment and cost a great deal more than was saved;

(c) the need for good communications; and (d) the need for

good record keeping, all of which are critical. Some of the

lessons that can be drawn from these cases and others cases

noted above but not discussed in detail include:

• There are risks associated with human contact with

contaminated water and gas from waste disposal sites.

These risks can be minimized by appropriate siting,

design, construction, and operation of an engineered

landfill facility, and by the control of the nature of the

waste in a given class of waste disposal facility.

• There is a high risk associated with the disposal of

liquid hazardous waste in a landfill (even if in sealed

barrels). Today many jurisdictions do not permit theFig. 12 Fines produced during transport of washed relatively

uniform gravel to a landfill site


123


disposal of liquid hazardous wastes in landfills; only

solid stabilized residue. Processes for the reduction in

the amount of hazardous liquid waste generated,

techniques for solidifying liquid waste, and alternative

techniques for destroying (rather than landfilling)

certain hazardous wastes (e.g., PCBs) have been

developed. Municipal waste landfills should have

restrictions on the waste accepted. For example,

concentrated hazardous wastes are not acceptable in

these landfills and must be sent to a hazardous waste

facility. Hazardous waste landfills generally require a

higher level of hydrogeological predictability and

protection and/or higher levels of engineering than

small MSW landfills, although large MSW landfills

may require engineering similar to that for hazardous

waste.

• The is a high risk of ground and surface water

contamination arising from placing waste in an unlined

dump with little or no leachate control, especially if the

hydrogeology is unsuitable for controlling contaminant

migration. For example, there is a high potential for

contaminant migration through fractures in clay layers

and rock. Under some circumstances (e.g., unsaturated

conditions) fractures also can be a path for lateral

migration of landfill gas. Leachate can readily flow

through saturated granular layers and landfill gas can

readily migrate through unsaturated granular layers.

• Of particular concern for landfill gas migration is a

hydrogeological environment where there is a perched

water table above an unsaturated granular or fractured

zone that will limit the gas escape to the atmosphere

and encourage lateral migration of landfill gas in the

unsaturated zone.

• While leachate contaminated groundwater poses a

threat to human health by its use for drinking water

or in food preparation, contaminated groundwater may

contain contaminants that will volatilize and hence

cause potential problems due to uptake through the

respiratory system (e.g., if contaminated groundwater

moves into a basement due to a sump pump drawing the

contaminated water towards the home; or if contami-

nated groundwater is used to shower). This risk is

mitigated by controlling to a negligible level the mass

of volatile organic compounds (VOCs) present in the

landfill and by construction of an appropriate barrier

system.

• Landfill gas poses a risk of explosion or asphyxiation if

it migrates away from a landfill and accumulates in a

structure or underground services. However, even

in situations where this is not a concern (e.g., if there

are no nearby structures or services) landfill gas can

cause contamination of groundwater (e.g., VOCs in the

gas can partition to the groundwater according to

Henry’s law). The latter risk is mitigated by controlling

to a negligible level the mass of VOCs present in the

landfill and by construction of an appropriate barrier

system.

• An appropriate hydrogeological investigation is

required prior to siting a landfill. In addition, landfills

typically require either a suitable natural hydrogeolog-

ical barrier (e.g., thick intact clay) or one or more

engineered liners (e.g., clay or composite with a

geomembrane over clay such as shown in Fig. 2).

• In some circumstances, leachate migration can be

controlled in the absence of an engineered liner by

having an adequate leachate collection system inducing

hydraulic containment [143]; however, this will not

prevent the lateral migration of landfill gas. Hydraulic

control can be a very effective measure to minimize the

potential for contaminants migrating away from a

landfill if a liner is also provided to limit groundwater

inflow [e.g., 140] and, together with gas control

measures, to minimize gas escape.

• An engineered cover is required for a landfill. The

cover should be designed to minimize the risk of:

(a) erosion exposing waste; and (b) leachate seeps

contaminating surface water. The cover may also be

designed to control the amount of leachate generated

and aid in gas collection.

• Water (including rainwater, surface water or ground-

water) entering landfilled waste is likely to increase the

risk of leachate migration to surface and/or groundwa-

ter if there is not an adequate leachate and groundwater

control system. Thus, there is the need for modern

landfills to include a suitable leachate collection system

to collect and remove leachate, thereby controlling the

head acting on any liner system and minimizing the risk

of leachate seeps. In the case of low potential ground-

water flows into the waste, the leachate collection

system may be sufficient to control the groundwater. If

there is potential for significant groundwater inflow, a

separate groundwater control system and liner will be

required in addition to the leachate collection system.

• While a low permeability cover can reduce the amount

of leachate generated, it can also increase the risk of

lateral migration of landfill gas if there are not adequate

engineering controls in place to capture the gas and

prevent its escape into the hydrogeological envi-

ronment.

• A high leachate head in a landfill not only increases the

risk of groundwater contamination, it also reduces gas

collection efficiency and increases the risk of landfill

gas migration beyond the landfill if there are no other

adequate engineering controls.

• A well-functioning continuous leachate drainage and

collection system on both the base and side slopes is


123


necessary for ensuring a low leachate mound on the

liner.

• The effectiveness of a leachate collection system can be

reduced by biological/chemical/physical clogging. This

can occur in MSW and industrial waste landfills, and or

landfills developed solely for ash (ash monofills).

Clogging can occur under both anaerobic and aerobic

conditions.

• Clogging begins as a soft biofilm, which can readily be

cleaned from inside pipes, but then develops into a hard

clog of predominantly calcium carbonate. The hard

clog, once established, is extremely difficult to remove

from pipes. To all practical purposes, the clog within

the granular drainage layer cannot be removed.

• Clogging of the leachate collection system in a MSW

landfill is accelerated by rapid placement of waste and

high levels of organic matter in the waste. In several

cases, significant clog deposition has occurred in the

leachate pipes between annual cleaning.

• Pea gravel and sand can readily clog and experience a

reduction in hydraulic conductivity to the order of

10-8–10-7 m/s. Under certain conditions the hydraulic

conductivity of 6–30 mm gravel around a leachate

collection pipe can be reduced by six orders of

magnitude to about 2 9 10-7 m/s and that of a

geotextile wrapped around the pipe by four orders of

magnitude to 3 9 10-8 m/s.

• The rate of clogging of a granular underdrain is highly

dependent on the grain size and grain size distribution

of the granular material; a relatively uniform and large

particle size is likely to give the best long-term

performance of the drainage layer.

• Geotextiles should not be used to wrap leachate collection

pipes but have been effectively used as a continuous

separator/filter layer above the drainage gravel.

• The reduction of hydraulic conductivity of a drainage

material around pipes (e.g., finger drains) or in

continuous drainage layer to of the order of 10-7

–10-8 m/s will allow the development of a significant

leachate mound, thereby increasing the driving force

causing leakage, but will not provide significant

resistance to the outward leakage of contaminants

through the base of the landfill.

• Finger (sometimes called French) drains do not provide

an effective leachate collection system.

• A continuous drainage layer of relatively uniform

coarse-grained gravel has been found most effective for

long-term control of leachate head on the liner. Other

beneficial factors for extending the functional life of

these systems include minimizing movement of partic-

ulate material into the granular material (e.g., having a

suitable filter above the gravel) and regular cleaning of

perforated pipes.

• Even with an effective leachate on collection system,

lined landfills with low permeability covers can have

problems due to perched leachate on low permeability

layers (e.g., daily or intermediate cover and some types

of waste), especially in situations where there is

recirculation of leachate. This has been observed to

decrease gas collection efficiency leading to elevated

gas pressures.

• Gas pressures beneath a low permeability landfill cover

can cause failures. This illustrates the importance of

maintaining adequate gas collection and relieving gas

pressure in MSW landfills, especially for landfills

where the gas generation rates have been increased by

recirculation of leachate or the operation of the landfill

as bioreactors.

• Consideration should be given to installing a transmis-

sive gas collection layer below a low permeability

cover [e.g., 173, 174] that can ensure gas pressures

below the cover are low enough not to reduce the

stability of the final cover and avoid geomembrane

aneurisms such as that shown in Fig. 13.

• There is a need to avoid veneer stability problems in

(a) leachate collection layers before waste is placed,

and (b) final covers, by selecting appropriate materials

including ensuring that drainage layers (e.g., leachate

collection layers and drainage layers above geomem-

branes in final covers) have suitable hydraulic con-

ductivity/transmissivity (e.g., relatively uniform gravel

rather than sand). In addition, there is a need for a

design and construction plan that will minimize accu-

mulation of fines in the drainage layer, and appropriate

consideration to the potential impact of climatic

conditions (e.g., heavy rainfall, freezing conditions)

on veneer stability.

• Slope stability problems and failure of lined landfills

during active operations have been caused by the

addition of moisture (e.g., leachate reticulation, co-

disposal of liquids with solid waste).

Fig. 13 Aneurism in a geomembrane in a final cover due to excess

gas pressure below the geomembrane


123


• Stability problems can be minimized by ensuing: (a) a

proper geotechnical investigation of the subsoil prop-

erties; (b) carefully considering all potential failure

mechanisms; (c) avoiding optimism regarding geotech-

nical properties when the data is not consistent with that

optimism; (d) considering the effect of moisture in

terms of increasing the unit weight of the waste and

decreasing the shear strength of components of the liner

system; (e) selection of materials with the appropriate

strength/interface properties (including appropriate lab-

oratory tests) and considering the fact that different

components of the system will reach peak strength at

different times and that key components of the system

may be at post-peak or even residual strength at the

critical time; (f) appropriate stability analyses;

(g) appropriate construction quality control and assur-

ance to ensure that the system is installed as designed;

(h) considering stability at all stages in construction

(e.g., considering the effect of excavation at the toe of

existing waste on stability); (i) developing landfill

expansion plans that clearly define allowable conditions

for construction of the expansion area and a means of

monitoring adherence to the development plans;

(j) avoiding co-disposal of liquid waste or injection of

other moisture (e.g., recirculation of leachate) without

fully assessing the potential impact on both stability

and geoenvironmental protection; (k) considering the

effect of unusual weather (e.g., heavy rainfall, ice, etc.)

on stability; and (l) having contingency plans in the

event of changed conditions occurring during construc-

tion (e.g., excessive rain, unexpected foundations

conditions, etc.) that include alternatives so that waste

can be diverted if problems arise.

• Landfills (both closed and active) require an adequate

buffer zone between the waste and any urban develop-

ment. Amongst other things, this buffer provides a zone

for monitoring and if necessary the installation of

contingency measures.

• The construction of sealed roads and buried services

(sewer, storm water, water, electricity, etc.) too close to

a landfill can provide a conduit for any leachate or gas

escaping the landfill to readily migrate in the urban area

and have a much greater impact than would have

occurred had the development not encroached too close

to the landfill. This indicates the need to consider not

only the existing but foreseeable future conditions

when evaluating the suitability of a proposed site and

design. When planning new developments, there is also

a need to consider how the development may impact

the performance of any existing waste disposal site.

• History has shown that the difficulties and costs of

remediation after contaminants have escaped from a

landfill are very high. However, even today some

landfills are being designed with insufficient engineer-

ing or with too little attention to detail in the construc-

tion and operation.

• For society there is a long-term economic benefit to

selecting, designing and operating a site that is

designed and constructed to provide environmental

protection for the contaminating lifespan of the facility.

For large facilities and/or sensitive environments this

will usually involve a double lined landfill.

• When failures occur, considerable money is spent on

many experts to evaluate why the failure occurred.

More expert peer review at the design and construction

stage would be a good investment—especially for

situations where there is insufficient time, staff, or

expertise for expert regulatory peer review of proposal

before a design is approved.

Concluding Comments

The available evidence indicates that technical knowledge

regarding the design, construction, and operation of

municipal solid waste landfills is sufficient to control the

contaminant impact (from both leachate and gas) to neg-

ligible levels. Very high quality barrier systems have been

designed and constructed, and have been performing

extremely well for decades. Well-designed, constructed

and operated landfills can be expected to perform very well

for many centuries. Unfortunately, this does not apply to all

landfills. To ensure good long-term performance, it is

important to consider why those landfills that are working

well are in fact doing so, and not to extrapolate this per-

formance to other landfills without careful consideration

of the similarities and differences in conditions in all

phases of landfill development: siting, design, approval,

construction, operations, after-use, and in approving sub-

sequent surrounding land use.

Based on case histories and the latest research, it is

concluded that a municipal solid waste landfill is a system

comprised of three primary subsystems: (i) the hydroge-

ology and barrier system below the waste (this includes

side slopes below waste); (ii) the waste and landfill oper-

ations; and (iii) the landfill cover and landfill gas control

system. In addition, the landfill exists within a social/reg-

ulatory/administrative/economic system and this system

can override technical knowledge. Past experience indi-

cates that it is essential that landfill owners, municipalities,

and governments (who control regulators) look beyond

short-term economic/social/political issues to what is nee-

ded to provide long-term environmental protection. A lack

of appreciation of technical issues and risks by landfill

owners can result in short-term decisions based on

minimizing costs or maximizing short-term return on


123


investment that can result in significant subsequent envi-

ronmental/human impacts and substantial economic costs.

To ensure long-term environmental protection, it is

essential to understand the interactions between the dif-

ferent components of the system (and various subsystems)

and to design a total system rather than an agglomeration of

components. In this context, this paper has sought to

highlight that with respect to MSW landfills:

• Past problems could be anticipated and avoided by

appropriate attention to siting, design, approval, con-

struction, operations, and after-use, and in approving

subsequent surrounding land use. Many of the lessons

that can be learnt from past problems have been

itemized in this paper.

• The bottom liner and cover need to be designed to

minimize both advective and diffusive migration of

contaminants from both the aqueous and gaseous

phases.

• While different elements of a barrier system have

strengths and weaknesses, an appropriate combination

of materials and understanding of their interactions can

provide an excellent barrier to the escape of contam-

inants both in leachate and landfill gas.

• The barrier system that is needed to provide adequate

environmental protection will vary from one landfill to

another depending on site conditions, the type and

amount of waste, and how the landfill is to be operated.

For example, the temperature on a liner can be greatly

affected by whether the wastes accepted include

components other than conventional municipal curb-

side waste and by activities such as recirculation of

leachate. Unless specially designed to accommodate

elevated temperatures, temperatures above those typical

for normal MSW landfills (B40 �C) can substantially

reduce the long-term effectiveness of typical liners.

• Not all drainage materials, geomembranes and clay

liners will provide the same performance and the

system’s long-term performance may be highly depen-

dent on the choice of materials used in the barrier

system.

• Good construction quality is essential and this requires

qualified installers and good construction quality con-

trol and assurance.

• The system’s performance will be dependent on how

the landfill is operated and the controls placed on the

waste that is disposed to ensure that they are compatible

with the design.

• The final cover, effective landfill gas control, and

appropriate site aftercare and monitoring are critical to

ensuring long-term protection.

• Although essential, it is not enough to have good

regulations; there must also be the level of staffing with

appropriate expertise needed to ensure that the regulations

are being followed and enforced, including in times of

economic recession when there is pressure to reduce costs.

While there are risks associated with landfills, these

risks and the environmental impacts need to be evaluated in

the context of the risks and environmental impacts of

alternative means of disposal. With attention to issues such

as those addressed in this paper, problems that have arisen

from the dumps of the past can be avoided and very safe

and secure landfill sites can be constructed to provide

excellent long-term environmental protection. Landfilling

can be both a safe and cost-effective component of a waste

disposal strategy.

Acknowledgments The research presented in this paper was funded

by the Natural Science and Engineering Research Council of Canada

(NSERC). The author is very grateful to: his colleagues in the Geo-

Engineering Centre at Queen’s-RMC, especially Drs. Richard

Brachman, Andy Take and Greg Siemens, and Grace Hsuan from

Drexel University; industrial partners, Terrafix Geosynthetics Inc.,

Solmax International, Ontario Ministry of Environment, AECOM,

AMEC Earth and Environmental, Golder Associates Ltd., Canadian

Nuclear Safety Commission, CTT Group, Knight Piesold and Thiel

Engineering for their advice and support with various aspects of this

research that forms the basis for much of the information presented;

many past and present graduate students whose co-authored papers

are referenced as well as F. Abdelaal, M. Chappel, A. Ewais, D.

Jones, P. Sahali and Y. Yu for their contributions to as yet unpub-

lished research and R. Thiel for Fig. 13 and many valuable discus-

sions. The author is also very grateful for the assistance of D. Jones

and Y. Yu in the preparation of the paper and to Drs. M. Hird, A.

Mabrouk and Y. Yu and to D. Jones, R. Thiel, and A. Verge for their

review of the manuscript. The views expressed herein are those of the

author and not necessarily those of the people who have assisted with

the research or review of the manuscript.

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Author Biography

R. Kerry Rowe is a member of

the GeoEngineering Centre at

Queen’s RMC. Prior to joining

Queen’s in 2000, Professor

Rowe was educated at the Uni-

versity of Sydney—BSc (1973),

BE (Hons I, 1975), PhD (1979),

DEng (1993). He was employed

by the Australian Government

Department of Construction in

Sydney, Australia for eight

years before immigrating to

Canada where he first spent 21

years at the University of Wes-

tern Ontario. He then moved to

Queen’s University in Kingston where he served 10 years as Vice

Principal (research) being responsible for the administration of all

research conducted at the university (everything from cancer research

to particle astrophysics to the humanities) and now holds the Canada

Research Chair in Geotechnical and Geoenvironmental Engineering.

Author of 260 refereed journal papers, three books, 14 book chapters

and more than 270 full conference papers, he has extensive research

and consulting experience in the geotechnical and geoenvironmental

engineering field. His research is reflected in landfill regulations in

Canada and around the world. He has been recognized by numerous

awards, including being a former NSERC Steacie Fellow, a Killam

Prize winner, and he was selected to present the 45th Rankine Lecture

in March 2005 and the 7th Casagrande Lecture in 2011. He is a fellow

of the UK Royal Academy of Engineering, both the Royal Society of

Canada and the Canadian Academy of Engineering as well as Pro-

fessional Societies in Australia, Canada and USA. He is past president

of the International Geosynthetics Society, the Canadian Geotechnical

Society and the Engineering Institute of Canada.


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http://www.nesgeorgia.org/files/free_market_environmentalism.pdf

http://www.nesgeorgia.org/files/free_market_environmentalism.pdf


http://www.ecomed.org.uk/content/IncineratorReport_v3.pdf

http://www.ecomed.org.uk/content/IncineratorReport_v3.pdf

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