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As environmental legislation is becoming more and more inclusive, integrated and strategic; risk assessment approaches also need to be adapted to remain responsive and representative. Although various risk assessment approaches have been adopted for landfill waste disposal sites, there are still wide-ranging knowledge gaps and limitations which need addressing by developing a holistic risk assessment methodology. This paper presents a framework of such a risk analysis methodology for landfill leachate in an integrated fashion, thereby attempting to bridge these knowledge gaps. The framework or structure does not only draw together various sections and sub-sections of the holistic risk assessment in one place but also categorises and arranges them in a logical sequence from start to end. The paper also outlines a holistic computer model corresponding to the holistic risk assessment framework.
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*T. E. Butt 1 ; N. Mair 2 and A. J. D. Ingles 3
*(1). Sustainable Buildings Research Group (SBRG), University of Greenwich, Avery Hill
Campus, Bexley Road, Eltham, London. PostCode: SE9 2PQ. England, UK.
Mob: 07817139170; Email:
(2). Environmental Leadership Ltd., 440 St Helens Road, Bolton. PostCode: BL3 3RS. England,
(3). Information Manager, Information Services, University of Abertay Dundee, Bell Street,
Dundee. Postcode: DD1 1HG. Scotland, UK.
As environmental legislation is becoming more and more inclusive, integrated and strategic; risk
assessment approaches also need to be adapted to remain responsive and representative.
Although various risk assessment approaches have been adopted for landfill waste disposal sites,
there are still wide-ranging knowledge gaps and limitations which need addressing by
developing a holistic risk assessment methodology. This paper presents a framework of such a
risk analysis methodology for landfill leachate in an integrated fashion, thereby attempting to
bridge these knowledge gaps. The framework or structure does not only draw together various
sections and sub-sections of the holistic risk assessment in one place but also categorises and
arranges them in a logical sequence from start to end. The paper also outlines a holistic computer
model corresponding to the holistic risk assessment framework.
Current risk assessment approaches specifically for landfills do not appear to have a holistic
system which includes all modules and sub-modules of individual constituents of risk assessment
such as baseline study, hazard identification and categorisation, hazards’ concentration
assessment, exposure assessment with exposure quantification, pollutant migration analysis,
significance assessment, uncertainty assessment, hazard indices, carcinogenic risks, and non-
carcinogenic risks. (8, 26).
On the contrary, environmental legislation is increasingly becoming inclusive and integrated. For
instance, the Water Framework Directive includes new requirements for protection and
restoration not only of ground waters but also surface waters and dependent ecological systems
(1, 27). Similarly, the Landfill Directive and Regulations take it even beyond surface and ground
waters only, thereby, including air, soil, global environment, greenhouse gases, and human
health (28, 29, 30, 31, 32, 33). Another directive, generally referred to as Habitat Directive (34),
brings a legal obligation to combat hazards in order to guard and enhance natural habitats and
wild fauna and flora. On the basis of these environmental legislation, which are becoming more
holistic than ever before, it can be concluded that an even more holistic approach towards risk
analysis is required. Therefore, the main objective of this paper is to attempt to present an overall
framework or structure of such a holistic risk assessment methodology in which all parts and
sub-parts of risk assessment are categorically and sequentially drawn together. A corresponding
computer-model is also outlined. The term ‘holistic’ in this paper implies an overall umbrella
encompassing or encapsulating all aspects and factors of risk assessment of landfill leachate
from beginning to finish. However, these aspects and factors are not covered in detail due to
Risk Management (RM) consists of two main factors i.e. the Risk Assessment / Analysis (RA)
and the Risk Reduction (RR) (See Figure 1). RA is further divided into two parts Hazard
Assessment (HA) and Risk Estimation (R Esti). The output of HA is an input to R Esti. In a
given RA, the HA process predominantly involves identification, categorisation and significance
analysis of all potential hazards, pathways and receptors based upon the preliminary
investigation or baseline study. Where as the R Esti is regarding consideration of the likelihood
of hazards hitting receptor(s) or estimating probability of happening of an undesired event. The
process of using the outcome of a risk analysis to investigate risk control options, and actions
taken to mitigate hazards and unwanted consequences is called Risk Reduction, which thereby
accomplishes the whole RM exercise. This paper focuses on RA and not RR. Therefore,
constituents of HA and R Esti, which together form a total RA system, are developed and
described in the following sections of the paper.
3.1 The Hazard Assessment (HA)
3.1.1 Baseline Study (BS)
The Baseline Study is defined as the most preliminary step of risk analysis in which all basic
information / data is gathered, organised and analysed. It is also the step on which the rest of the
risk assessment process is based. For landfill leachate, the BS has to take account of a wide range
of information and subjects that are categorised into eight modules as follows: 1) Geology, 2)
Hydrology, 3) Hydrogeology, 4) Topography, 5) Meteorology, 6) Geography, 7) Site
Management and 8) Human Influences. (1, 2, 8, 9, 10, 11, 12). See Figure 1 for more details.
3.1.2 Hazard Identification and Categorisation (H Iden)
From the perspective of risk analysis the definition of the term hazard has been stretched beyond
being a substance only. It is defined as follows: a hazard means anything such as a substance, a
property, a process or even a layout / setting that may cause harm(s) or has a potential to cause
harm(s) (13, 14).
Hazard Identification and Categorisation (H Iden) is the second stage of RA and is divided into
four modules below: H Iden Quantity
In the H Iden Quantity module, a risk assessor is expected to estimate the quantity of leachate in
a given site. The quantity of leachate itself is deemed as a hazard in this module. H Iden Quality
After leachate quantity has been worked out, a risk assessor can switch to the H Iden Quality
module of RA. In this module, hazards posed by leachate in terms of its qualities are
characterised. This module is further categorised into two sub-modules namely, pollutants and
properties. The former comprises the hazardous substances (such as lead, mercury, phenols,
cresols, toluene, xylene, cobalt, barium), which may exist in a given leachate. The latter, unlike
substances existing in leachate in physical form, deals with properties of leachate e.g. BOD, pH
value, age of leachate, hardness. In the H Iden Quality module, a risk assessor can also
categorise leachate quality hazards into groups of carcinogenic and non-carcinogenic. H Iden Process and / or Layout Hazard
In this module, a risk assessor is expected to consider items such as groundwater level
fluctuation, heavy rain, liners and capping failure or no liners and capping used, fissures in
bedrock, high porosity of bedrock. All such items are to be considered in context of process and /
or layout hazards posing risk or adding more to the degree of overall risk. Necessary information
on all such items will come from the eight modules of the BS. H Iden Harms
The last and fourth module of H Iden is Harms, which implies damage, loss, hurt, or injury. This
module is not about hazards themselves. It specifies potential harms that could result from the
hazards which would have already been identified in the above three modules of the H Iden for a
given landfill.
3.1.3 Exposure Assessment (Ex A)
In Ex A, all possible hazards at the pollutant source, pathways and environmental receptors are
identified and categorised. In addition, exposures of the identified receptors to the identified
hazards through the identified pathways are measured. Ex A is classified into four modules as
follows: Source Identification and Categorisation (Sorc Iden)
In Sorc Iden module, a given landfill is identified as a pollutant source. This module also allows
the identification and categorisation of a given site into different portions in a number of ways.
For instance, which parts of a given waste disposal site are active, post closed and / or in design /
planning stage; which cells have similar dimensions; etc. A risk assessor can also identify,
geometrically, an equivalent and effective centre point in a given site body. The distances to the
receptors and exposure media can be measured from this centre point, as a site generally does not
have regular dimensions.
4 Pathway Identification and Categorisation (P Iden)
In the P Iden module a risk assessor identifies all possible pathways connecting a given landfill
with likely receptors in a given scenario. The main focus of this module is the identification of
all links between the two ends of each pathway, i.e. between a given site (the pollutant source)
and the considered receptor. Receptor or Target Identification and Categorisation (T Iden)
In the T Iden module, a risk assessor categorically specifies all likely environmental receptors
that could be affected by hazards of a given landfill site. These will not be only humans, but
other potential terrestrial and aquatic flora and fauna. Also, receptors may not necessarily be
only living, but could also be non-living such as atmosphere, lithosphere / land, hydrosphere,
buildings, structures. These receptors could be either off-site or on-site. Exposure Quantification (Ex Quan)
In the fourth and last module entitled Ex Quan, there are a number of ways to quantify exposure
e.g. exposure equations. Exposure routes, through which hazards could enter a given receptor
boundary, have been divided into four types. These are ingestion, dermal contact, inhalation and
‘others if any’. The first three routes are applicable to living receptors, such as humans,
mammals, etc. The fourth route is to provide a facility to the risk assessor to account for
exposure routes other than the three. This fourth route is particularly useful in cases of non-living
receptors e.g. a leachate polluted aquifer feeding into a river.
3.1.4 Concentration Assessment (CA)
Like Ex A, Concentration Assessment is also a fundamental stage of a risk assessment process in
which concentrations of all possible hazards are estimated or measured in four categories
described below: Source Concentration Analysis (Sorc C)
In this module, concentrations of leachate quality hazards within the landfill body, which were
identified earlier in the H Iden module, are quantified and described.
5 Pathway Concentration Analysis (PC)
PC is further divided into two sub-modules, Pre Ex MC and Ex MC, representing Pre-Exposure
Medium Concentration Assessment and Exposure Medium Concentration Assessment,
respectively. The former sub-module involves concentration analysis of hazards in all the links
of a given pathway that lie between the pollutant source (i.e. landfill body) and the exposure
medium of a given receptor. The latter sub-module (Ex MC) deals specifically with the exposure
medium to which a given target is exposed directly. (18). Receptor or Target Concentration Analysis (TC)
The TC module is categorised into three sub-modules namely, TCi (Target Concentration
Initial or background concentration), Intk C (Intake Concentration i.e. hazard concentration
entering boundaries of a given receptor) and TCf (Receptor or Target Concentration Final).
The first two when summed up using a mass balance approach gives the value of the final
concentration of a given hazard in the target (i.e. TCf). Critical Concentration Analysis (Cri C)
However, Critical Concentrations are preferably obtained directly from legislation and
regulations. They may also be determined from items such as Reference Dose (RfD) and Unit
Cancer Risk (UCR) in the literature, depending upon characteristics of a given scenario and that
of a given receptor / target in particular (18). Once Cri C and TCf values are established for
hazards, the RA process then can exceed the HA remit and lead further to the R Esti stage of the
holistic framework.
3.2 Risk Estimation (R Esti)
3.2.1 Migration Assessment (Migra A)
Migration Assessment is that constituent of the RA framework which considers transfer and fate
of (pollutant and / or property) hazards of leachate via various media / links of pathways from
the pollutant source up to environmental receptors. This constituent addresses migration in two
modules. Firstly, leachate migration as a physical phenomenon itself (involving e.g. dispersion,
advection, retardation) and, secondly, attenuation of leachate quality hazards as it migrates
(covering e.g. sorption, cation exchange reactions, dilution).
3.2.2 Significance Assessment (Sig A)
Significance Assessment is an aspect that is integrated to the framework to allow the risk
assessor to establish which modules, sub-modules and / or parameters are important to be
considered and which ones are insignificant to be dropped out / eliminated from the risk analysis
process of a given landfill.
3.2.3 Uncertainty Assessment (UA)
Immeasurable or non-estimated risk is called uncertainty. Uncertainties can arise from several
sources, including natural or inherent variability over space and time, variability in the accuracy
of measurements and data manipulation, and knowledge gaps due to lack of data. (4). Like Sig
A, UA is also involved in all modules, sub-modules and / or parameters of the framework.
3.2.4 Risk Characterisation (R Cha)
The Risk Characterisation is the final step in the RA framework. At this stage the assessments of
exposures and hazards’ concentrations carried out in the HA process, are summarised and
integrated into quantitative and qualitative expressions of risk. (12). R Cha is divided into three
modules: Hazard Index
HI is the ratio between a hazard’s final concentration in a target body and the corresponding
critical concentration. Mathematically:
HI = TCf / Cri C Eq 1
Unlike the other two modules of R Cha (i.e. Carcinogenic Risk and Non-carcinogenic Risk,
discussed below), while working out HI values in this module, no discrimination between
carcinogenic and non-carcinogenic hazards is made. However, if a given receptor is, for
example, a human or mammal for which classification between carcinogenic and non-
carcinogenic hazards makes sense, the other two modules of R Cha can be considered.
Once HI values have been worked out for all contaminants in a given landfill scenario, then a
risk assessor can identify the ones which have values more than unity as those hazards would be
the ones with concentrations beyond safe levels. Carcinogenic Risk
A carcinogenic risk is the probability or chance of a receptor / target to develop cancer over a
given time scale. Carcinogenic risk can mathematically be expressed as follows:
R = TCf x UCR Eq 2
Where, R is a carcinogenic risk, TCf is final concentration of the carcinogen in the target body,
and UCR is the Unit Cancer Risk. Non-carcinogenic Risk
A non-carcinogenic risk is the likelihood or chance of a receptor / target to suffer a non-cancer
adverse health affect (such as skin infection, headache) over a given time scale.
Non-carcinogenic risk is generally indicated by means of Hazard Index (HI). However, Cri C for
non-carcinogens can be used for quantitative risk assessments as follows (23):
R = PF (TCf – Cri C) Eq. 3
Where, R is a non-carcinogenic risk, PF is the potency factor of the slope of the dose-response
curve, TCf is the final concentration of the non-carcinogen in the target body and, Cri C is the
reference dose i.e. RfD for the non-carcinogen.
There is a requirement not only for a quantitative hazard and risk assessment methodology for
landfills with a holistic approach, but also for an electronic representation of this methodology in
the form of a computer model that is more readily useable than simply a documented procedure.
The underlying context of the model development was decided, based upon the needs of a risk
assessment system specifically for landfill leachate. The model also allows for maximum, most
likely or mean and minimum values for various parameters, where appropriate, to assist in
establishing worst case, most likey and least bad risk scenarios. However, due to given brevity of
the paper, format and functions of the holistic computer model is presented to a substantially
limited extent below.
Figure 2 shows the main front page of the RAM (risk assessment methodology) model. The
overall structure in the model is developed in the same style as the holistic RAM framework
itself, as explained in the previous section of the paper. Keeping in view variations in nature, size
and function of different factors of the methodology, the format of all modules, sub-modules and
parameters of the model have been developed in a similar pattern to the possible best degree in
order to achieve symmetry among modules and sub-modules for convenience and traceability.
An example of this pattern is explained below where HI module of the RAM model is described
(i.e. Figure 7). The mutual data and / or information transfer amongst the modules and sub-
modules of the RAM model is designed to take place automatically as well as by choice of the
model user. The model is also flexible to take information externally from other appropriate
models and methods
When the button ‘Baseline Study (BS)’ on the main front page (shown in Figure 2) is pressed, a
form as depicted in Figure 3 will open. This form possesses links to all the eight modules of the
BS. The model user can put all the relevant data and information in these eight modules for use
in the subsequent stages of the risk assessment process. Similarly, other constituents including H
Iden (Figure 4), Ex A (Figure 5), CA (Figure 6), and Migra A (Figure 7) can be reached by
pressing their respective button in the main font page of the RAM model. Due to brevity,
individual as well as mutual functionalities of these stages of RAM are not described further.
However, out of the last stage of RA, one module i.e. Hazard Indices is described below to
deliver a flavour of how the model operates and yields results in what format.
In Figure 2, when the link ‘Hazard Indices (HI)’ is clicked, the form shown in Figure 8 can be
reached. In this form, the button ‘What is HI?’ will open another form where details have been
set out on what HI is, its mathematical expression, and other implications are also pointed out
with respect to the RAM model. This form once benefited from can be closed. The links
‘Significance Assessment’ and ‘Uncertainty Assessment’ lead to other discreet forms where
relevant information, presumptions (if any), and explanations around significance and
uncertainties can be laid down by the model user / risk assessor. The link ‘Measuring HI’ in the
form (Figure 8) leads to the form which is exhibited in Figure 9, and is discussed below.
In order to execute the measuring of HI values, the form entitled ‘HI_Measuring’ and shown in
Figure 9, is provided in the model. The button ‘What specific Pathway and Target?’ leads to a
form where the risk assessor can record which iteration of the RAM model is being applied to
which specific environmental receptor and via which pathway. The HI itself is a dimensionless
entity therefore does not have any units. However, the link ‘Units’ opens a form in case the risk
assessor wants to mention units of HI numerator (TCf) and denominator (Cri C), thereby making
sure that the units of the two items are the same. The link ‘General Description’ is to access the
form where the format and all functions of the HI_Measuring form (shown in Figure 9) are
explained as an ‘on-hand’ help for the RAM model user. The ‘Specific Description’ link is to
reach a form where the risk assessor can describe site-specific details regarding any worth
mentioning aspects of hazard indices.
During various stages of RAM model application, a user would have identified hazards,
pathways, receptors, critical concentrations (Cri C), and final target concentrations (TCf) in
maximum, most likely and minimum values. These information will automatically appear or link
up with the HI_Measuring form, as appropriate. Once the button “HI Workout is pressed
(Figure 9), all TCf values will be divided by the corresponding Cri C values to workout HI
values for worst case, most likely and least bad scenarios for each of these three groups of
hazards i.e. non-toxic, carcinogenic, and non-carcinogenic. If sum of HI in any of the nine HI
columns is more than unity it would imply there is at least one scenario where TCf exceeds Cri
C, and the unacceptable risk of this case would need being controlled such that the ratio becomes
less than unity. Also where HI ratios are greater than unity, the model shows them highlighted in
red (though in this paper it appears black for the print is black and white).
The paper presents a ‘total’ framework of holistic risk assessment that clearly establishes and
places together all parts, sub-parts, modules, sub-modules and parameters of risk analysis in a
sequential and categorical manner. A corresponding computer model is also outlined. This
holistic framework may provide stronger bases to perform risk analysis and consequently risk
management, where risk assessment is increasingly becoming a legal requirement in different
countries (5, 6, 7). This study may play an effective role in landfill planning permission, landfill
siting, design and construction as well as hazard mitigation measures. This research can also
underpin Environmental Impact Assessment (EIA) and Statement to identify impacts and the
degree of impacts on the environment and its various species. Due to the degree of holism that
this framework offers, issues of environmental integration, for instance, raised by the Water
Framework Directive and Habitats Directive, may well be taken into account. Moreover, this
framework can provide more degree of consistency in risk assessments, thereby making it more
feasible to compare estimated risks between different site locations for a proposed landfill, as
well as various scenarios for the same landfill at the same location. Thus, this can also assist in
locating a landfill where overall environmental risks are least. This research work is a step in the
direction of a more categorical, sequential, integrated and holistic risk analysis.
Figure 1: The Holistic Framework of Risk Assessment and Management – Shaded boxes are parts of RA (Concluded, adapted and further developed from 3, 11,
15, 16, 17, 19, 20, 21, 22, 23, 24, 25)
1. BS
(IV). R Cntrl
R Mana
R Reduc
2. H Iden
4. CA
(III). R Eva
1. Conse Eva
3. Costs Eva
2. Opt Estb
Tech Eva
Socio Eva
R Commu R Percp
Sorc C PC
Cri C
Pre Ex MC
T Iden
P Iden Ex Quan
Sorc Iden
Ex MCi
Ex MCr
Ex MCf
Intk C
(II). R Esti
3. UA
4. R Cha
2. Sig A
1. Migra A
R Carci
R Non-carci
1. Opt Dsgn
3. R Monit
2. Opt Imple
4. Corrective
Process and / or Layout H
Quantity Quality
CE Reactions
Hori Migra
if any
Sta Parti
Hyd Topo
Natural Envi
Built Envi
Wind S&D
C&S Deg
t (wet & dry bulbs)
Site Mana
Site Engg
Waste Mana
Envi Monit
Site Type
Site Location
Other Site Operations
such as documentation
Site History
Atmo Waters
Litho Waters
Preci ET Intcp Runoff
Perco WCIng
like hydrau-
lic gradient,
logical Zones
Zones, e.g.
Human Influence
Past Future
Top Soil
Other Geo
Volume / Size
Pollu H Proper H
4. Other Eva like
feasibility, policy
A Assessment MC Medium Concentration
Atmo Atmosphere or Atmospheric Meteo Meteorology / Climate
Atmo Waters Atmospheric Waters Migra A Migration Assessment (of pollutants)
Attenu Attenuation Monit Monitoring or Monitor
B Baseline / preliminary Natural Envi Natural Environment
Bio Biological Non-carci Non-carcinogen(s) / Non-carcinogenic
BS Baseline Study Opt Option(s)
Built Envi Built Environment Opt Dsgn Options Design
C Concentration Opt Estb Options Establishment
C&S Degree Degree of Cloudiness and Sunlight P Pathway
Carci Carcinogen(s) / Carcinogenic p Pressure
CA Concentration Assessment P Iden Pathway Identification & Categorisation
CE Cation Exchange Parti Participation or Participate
Cha Characterisation / Characterise PC Pathway Concentration
Che Chemical Perco Percolation
Cntrl Control Perco Percolation
Conta Contaminants Phy Physical
Conse Consequence(s) Pre Ex MC Pre Exposure Medium Concentration
Conse Eva Consequence(s) Evaluation Preci Precipitation
Costs Eva Costs Evaluation Proper Properties
Cri Critical Quan Quantification
Cri C Critical Concentration R Risk
Dispr Dispersion R Cha Risk Characterisation / Characterise
Dil C Dilution Concentration R Cntrl Risk Control
Engg Engineering R Commu Risk Communication
Envi Environment R Esti Risk Estimation
Envi Monit Environmental Monitoring R Eva Risk Evaluation
Estb Establishment R Mana Risk Management
Esti Estimation R Monit Risk Monitoring
ET Evapo-transpiration R Precp Risk Preceptioin
Eva Evaluation(s) R Reduc Risk Reduction
EWEQ Existing Waters Existing Qualities RA Risk Assessment
Ex Exposure Retar Retardation
Ex A Exposure Assessment Satu Ing Saturated Ingress/Phreatic or GW Ingress
Ex MC Exposure Medium Concentration Site Engg Site Engineering
Ex MCi Initial Ex MC Site Mana Site Management
Ex MCr Reaching Ex MC Socio Sociological or Sociology
Ex MCf Final Ex MC Socio Eva Sociological Evaluation
Ex Quan Exposure Quantification Sorc Source
Geo Geology Sorc C Source Concentration
GW Ground Water Sorc Iden Source Identification & Categorisation
H Hazard Sta Stakeholder(s) and public
H Iden Hazard Identification Sta Parti Stakeholder(s) & Public Participation
HA Hazard Assessment Subsurface WC Subsurface Water Course(s)
HI Hazard Index or Indices Surface WC Surface Water Course(s)
Hori Horizontal Migration t Temperature
Humi Migra Humidity and / or Relative Humidity T Receptor / Target
Hyd Hydrology T Iden Target Identification & Categorisation
Hydgeo Hydrogeology TC Target Concentration
Iden Identification & Categorisation TCi Initial / Background Target Concentration
Infiltra Infiltration TCr Reaching Target Concentration
Ing Ingress Tech Eva Technical Evaluation
Intcp Interception (Loss) Topo Topography
Inter Intermediate U Uncertainty or Uncertainties
Inter MC Intermediate Medium Concentration UA Uncertainty Assessment
Intk Intake Unsatu Ing Unsaturated Ingress/Vadoze Water Ingress
Intk C Intake Concentration Verti Migra Vertical Migration
Leach Leachate W Water
Litho Lithosphere or Lithospheric Waste Mana Waste Management
Litho Waters Lithospheric Waters WC Water Course(s)
M Medium or Media Wind S&D Wind Speed and Direction
Mana Management
Figure 2: The Main Front Page or Form of the RAM Computer Model
Figure 3: The Main Front Page / Menu of the ‘BS’ Form in the RAM Model
Figure 4: The Main Front Page / Menu of the ‘H Iden’ Form in the RAM Model
Figure 5: The Main Front Page / Menu of the ‘Ex A’ Form in the RAM Model
Figure 6: The Main Front Page / Menu of the ‘CA’ Form in the RAM Model
Figure 7: The Main Front Page / Menu of the ‘Migra A’ in the RAM Model
Figure 8: The Main Front Page / Menu of the ‘HI’ Form in the RAM Model
Figure 9: Measuring Form of ‘Hazard Indices (HI)’ in the RAM Model
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An appraisal of the potential impact of the EC Water Framework Directive (WFD) (2000) upon open channel flow measurement.
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At the present time, risk analysis is an effective management tool used by environmental managers to protect the environment from inevitable anthropogenic activities. There are generic elements in environmental risk assessments, which are independent of the subject to which risk analysis is applied. Examples of these elements are: baseline study, hazard identification, hazards' concentration assessment and risk quantification. Another important example of such generic elements is exposure assessment, which is required in a risk analysis process for landfill leachate as it would in any other environmental risk issue. Furthermore, computer models are also being developed to assist risk analysis in different fields. However, in the review of current computer models and literature, particularly regarding landfills, the authors have found no evidence for the existence of a holistic exposure assessment procedure underpinned with a computational method for landfill leachate. This paper, with reference to the relevant literature and models reviewed, discusses the extent to which exposure assessment is absent in landfill risk assessment approaches. The study also indicates a number of factors and features that should be added to the exposure assessment system in order to render it more strategic, thereby enhancing the quantitative risk analysis.
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A risk assessment process can assist in drawing a cost-effective compromise between economic and environmental costs, thereby assuring that the philosophy of 'sustainable development' is adhered to. Nowadays risk analysis is in wide use to effectively manage environmental issues. Risk assessment is also applied to other subjects including health and safety, food, finance, ecology and epidemiology. The literature review of environmental risk assessments in general and risk assessment approaches particularly regarding landfill disposal sites undertaken by the authors, reveals that an integrated risk assessment methodology for landfill gas, leachate or degraded waste does not exist. A range of knowledge gaps is discovered in the literature reviewed to date. From the perspective of landfill leachate, this paper identifies the extent to which various risk analysis aspects are absent in the existing approaches.
Risk assessment is a new research area. The risk assessment research area deals with a wide range of issues other than landfills. Examples of these issues are Radiation, Food Industry, Ecology, Epidemiology, etc. The authors have found that there are generic elements in risk assessment and these elements are independent of the subject areas mentioned above. An important example of these generic elements is the Concentration Assessment of hazards and is equally important from the perspective of landfill risk assessment. Furthermore, in the literature review of landfill risk assessment approaches, no evidence has been discovered of a holistic risk assessment methodology for landfill gas, leachate, or degraded landfill waste. A range of knowledge deficiencies has been found in the literature reviewed to date. One of these deficiencies in knowledge is the lack of a holistic procedure for carrying out Concentration Assessment. From the perspective of landfill leachate, this paper discusses the extent to which the Concentration Assessment of hazards is absent in landfill risk assessment approaches described in the literature reviewed to date, and the elements that should be added to the procedure of the Concentration Assessment in order to enhance the process of risk assessment. The paper also briefly outlines a holistic procedure for the Concentration Assessment and a corresponding computer model for the risk assessment of landfill leachate.