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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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DOI 10.1007/s40098-012-0024-4
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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
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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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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.
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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
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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)
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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
240 Indian Geotech J (October–December 2012) 42(4):223–256
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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
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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]
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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.
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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
244 Indian Geotech J (October–December 2012) 42(4):223–256
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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
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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
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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
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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
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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
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• 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
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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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