Managing Odour Risk at Landfill Sites:
Main Report
P McKendry, J H Looney, A McKenzie
MSE
First Published 2002
ISSN 1478-0143
Copyright of this document remains with
MSE Ltd & Viridis © 2002
This project was funded by SITA (UK) Ltd
under the Landfill Tax Credit Scheme. The
full report entitled “Managing Odour Risk at
Landfills – Main Report” is available for
download from the following web sites:
Viridis (www.viridis.co.uk) and MSE
(www.mse-environmental.co.uk).
Viridis was the Entrust Approved
Environmental Body (AEB) responsible for
the project and the work was undertaken by
Millennium Science & Engineering Ltd
(MSE).
The authors wish to acknowledge the
assistance of the Environment Agency in
reviewing the air dispersion modelling
aspects of the project.
MSE is committed to optimising energy
efficiency, reducing waste and promoting
recycling and re-use. In support of these
goals, this report has been printed on
recycled paper, comprising 100% postconsumer waste, manufactured using a TCF
(totally chlorine free) process
TABLE OF CONTENTS
TABLE OF CONTENTS
i
Abbreviations
iv
Summary of Conclusions
v
1.
1.2
1.3
Preface
History
Related Landfill Tax Funded Projects
1
1
1
2.1
2.2
2.3
2.4
2.5
2.6
Introduction
Waste Management Context
Regulatory Framework
Planning Controls
Waste Management Licensing
Regulatory Guidance
Public Acceptability
1
1
2
2
3
3
3
3.1
3.2
3.3
Odour and Odour Measurement
Olfactory Response and Odour
Odour Measurement
Odorous Compounds in Landfill Gas
4
4
5
5
4.1
4.2
4.3
4.4
4.5
Landfill Odour Sources
Introduction
Waste Transport Vehicles
Landfilled Wastes
Leachate
Landfill Gas
7
7
7
8
8
9
5.1
5.2
5.3
5.4
5.5
5.6
Site descriptions
Introduction
Waste Input/Waste Types
Site Design and Operational Regime
Terrain
Proximity to Habitation
Potential Off-Site Odour Sources
9
9
9
10
10
11
11
6.1
6.2
6.3
6.4
Odour Complaints Data and Questionnaire
Odour Complaints
Odour Questionnaire
Analysis of Survey Results
Alternative Potential Odour Sources
12
12
12
13
14
7.1
7.2
7.3
7.4
Regional Wind Flow Patterns
Physics of Wind Flow
Terrain
Air Dispersion Models
Application to Landfills
14
14
15
20
21
2.
3.
4.
5.
6.
7.
i
8.
8.1
8.2
8.3
8.4
8.5
Monitoring of Emissions
Definition of Source Terms
Monitoring Procedure
Measurement of Emission Rates
Sources Monitored
Monitoring Programme
21
21
22
22
25
26
9.1
9.2
9.3
9.4
9.5
9.6
Air Dispersion Modelling and Results
Graphical Outputs
General Effects
Location Specific Effects
Site Specific Interactions
Probability of Odour Events
Summary and Conclusions
26
26
27
32
39
39
44
10.1
10.2
10.3
10.4
10.5
10.6
Management System Tool
Introduction
Odour Control Guidance
IPPC, BAT and Odour
Mitigation Options -- General
Mitigation Options – Specific
Further Work
45
45
45
45
51
53
55
11.1
11.2
11.3
11.4
11.5
Conclusions
Study Background
Odour, Measurement and Complaints Data
Landfill Odour Sources and Measurement of Emissions
Air Dispersion Modelling
Management Options
55
55
55
55
56
56
References
57
9.
10.
11.
12.
Appendix 1 Guidance on Odour and Odour Control
Appendix 2 Odours and BAT
Appendix 3 Properties of Selected Mercaptans and Hydrogen Sulphide
Appendix 4 Calculations and Conversions
Appendix 5 Details of Site Characteristics
Appendix 6 Odour Questionnaire
Appendix 7 Emissions Monitoring Protocol
Appendix 8 Measurement of Emission Rates
ii
Figures and Tables
Figure 1: Normal distribution of the sense of smell within a population
4
Figure 2: Comparison of the ODT for selected LFG trace components and their reported
concentration in LFG
6
Figure 3: Two stages of the anaerobic decomposition of complex organic wastes
9
Figures 4 – 7: Regional Wind Flow at Site V2 at a height of 10m
16
Figure 8: Wind Flow over Landfill Flank (or Escarpment)
19
Figure 9: Schematic of Flux Tent
22
Figures 10 – 17: Wind speed variation
28
Figures 18 – 20: Surface Roughness
29
Figures 21 – 26: Wind Direction without Terrain
30
Figure 27: Fluctuations with Terrain
32
Figures 28 – 34: Wind Direction and Terrain H1
33
Figures 35 – 42: Wind Direction and Terrain V2
32
Figures 43 – 48: Wind Speed and Terrain H1
34
Figures 49 – 60: Wind Direction, Wind Speed and Terrain V2
37
Figure 61: Annual Wind Rose, Site P3, 2001.
40
Figure 62: Annual Wind Rose, Site V2, 1997
41
Figure 63: Annual Wind Rose, Site H1, 1999
42
Table 1:
Table 2:
Table 3:
Table 4:
Table 5:
Table 6:
Table 7:
Table 8:
Table 9:
Table 10:
Table 11:
Table 12:
Table 13:
Table 14:
ODT of Selected LFG Trace Components
Selected Sulphur Containing Compounds in LFG (50% methane)
Waste streams accepted by sites and total annual input (m3)
Summary of Site Design Characteristics
Summary of Questionnaire Statistics
Beaufort Scale-Specifications and Equivalent Speeds
Roughness values for different land use surfaces
Measured Emission Values for Methane from Landfill Odour Sources
Calculated Mass Emission Rate for Methyl Mercaptan
Combinations of Typical Emission Sources (based on Mercaptans) and the
Cumulative Emission Rates
Cumulative Effect of Combined Controlling Factors on Percentage
Exposure to Odours
Odour Risk Assessment Matrix
Odour Control: Design and Operational Management Options
Specific Operational Options to Reduce Odour Impacts
iii
5
6
10
10
13
14
21
23
24
25
43
46
47
54
Abbreviations
BAT
Best Available Techniques
EA
Environment Agency
EHO
Environmental Health Officer
FID
Flame Ionisation Detector
IPPC
Integrated Pollution Prevention and Control
LFD
Landfill Directive
LFG
Landfill Gas
MSE
Millennium Science & Engineering Ltd
ODT
Odour Detection Threshold
ORT
Odour Recognition Threshold
OT
Odour Threshold
OU
Odour Unit
PPC
Pollution Prevention and Control
STW
Sewage Treatment Works
VFA
Volatile Fatty Acids
WMP
Waste Management Paper
iv
Summary of Conclusions
subsequently produce an off-site odour footprint or
plume leading to a complaint.
• The management of odours from landfills is an
aspect of landfill operations and management that
is of continuing concern to both the public, and the
regulatory authorities and waste management
companies.
• To provide input data on odour emission rates for
air dispersion modelling, fieldwork was undertaken
to measure directly methane emission rates from a
range of landfill surface and point sources using
flux devices. Equivalent odour omission rates
were deduced from published data on the
composition of landfill gas and the ratio of
methane to odorous compounds. It was assumed
that these ratios were constant for the purposes of
the dispersion modeling.
• To identify and assess management techniques for
controlling odour risk at potential receptors, a
study was initiated comprising the comparison of
historic complaints and site operations records; the
field measurement of methane emission rates (as a
proxy for odorous emissions) from landfill sources;
collecting data on public perceptions of odour; and
extensive air dispersion modelling using the data
gained from the preceding tasks.
• The results of the dispersion modelling confirmed
that the key factors associated with odour events
are the total odour emission rate from a site, the
topographic setting of the site, location of potential
receptors and the interaction between wind speed,
direction and topography.
• The objective of the study was to produce guidance
on odour control for site managers by identifying
the key parameters associated with odour and
prioritising the effectiveness of existing odour
control techniques and practices. Six landfill sites
with different waste inputs and geographic
locations within England were selected for the
study.
• Management of odours by prevention commences
at the site selection stage, where the location of
sensitive receptors and the interaction between
wind speed and direction and the adjacent
topography should be taken account using air
dispersion modeling.
• A public questionnaire was used to obtain both
generic and site specific information from potential
receptors local to the sites about odours and odour
events. The common findings within the responses
confirmed the basic assumptions used in the
subsequent air dispersion modelling that low wind
speeds, and early morning/late evening were the
atmospheric and temporal conditions most likely to
produce odour events. The questionnaire results
also presented anecdotal evidence for odour events
occurring during damp/foggy conditions.
• Once selected, all site operational activities are
potential sources of odours; from the delivery of
wastes;
delays in burying odorous wastes,
trenching into mature waste for installing gas
collection pipework and the recirculation of
leachate; the number of venting gas wells or open
leachate chambers; to the area of side wall flanks
and the effectiveness of the gas management
system.
• The questionnaire findings indicated that landfill
gas and leachate were the most common sources of
odours and that the public may be experiencing
odours more often than actually reported,
suggesting that odour is a persistent low level
problem with intermittent high levels leading to
complaints.
• Mitigation measures that limit the extent of the offsite odour footprint are based on reducing the
odour emission rate by decreasing the rate of
odorous emissions from a source; by increasing
the depth of cover materials and/or changing the
type of cover material on landfill surfaces;
abstracting odorous compounds by connecting all
chambers and wells to the active gas management
system; by introducing features that increase the
surface roughness of the terrain such as bunds,
hedges and solid fences to promote the mixing of
laminar air flows containing odours providing
dilution of odorous air flows.
• It was hoped to be able to correlate historic data on
odour
complaints
with
the
details
of
contemporaneous site activities and practices.
However insufficient data was available from
either the regulatory complaints records or records
of site activities to enable this approach to be used.
The conclusion is that there is a need to improve
greatly the level of detail when logging complaints
and similarly for the level of detail contained in the
Site Diary, if these data are to be of subsequent
value when investigating the sources of odour
complaints.
• Based on site location, wind speed and direction
and the specific local terrain, the probability of a
fixed receptor experiencing an odour event can be
estimated approximately.
Application of this
process at the impact assessment stage of site
selection would significantly mitigate against
future odour problems.
• Air dispersion modelling was used to identify the
pattern of air movement over the landfill and
across the adjacent terrain. The entrainment of
landfill derived odours within the air mass can
• Prevention and mitigation of odours during
operations can be achieved by correct site selection
v
• monitored; direct field measurement of typical
odorous compounds; establishing the effectiveness
of gas management systems by direct
measurement; and assessing the effect of landform
design and phasing on the potential for off-site
odour events.
and the combined application of existing site
operational and management techniques.
• Suggestions for further work include: establishing
a database of emission rates for various landfill
surfaces and other emission sources, including
leachate aeration lagoons; defining the atmospheric
conditions under which this emission rate was
vi
1.
management, as applied to the design and the
management of landfill sites.
Preface
The work undertaken and reported in this and other
supporting documentation was funded through the
Landfill Tax Credit Scheme. The project was carried out
under the auspices of the Environment Body Viridis, with
Landfill Tax funding provided by SITA Trust and the
balance by SITA Holding (UK) Ltd. Millennium Science
& Engineering Ltd undertook the work
1.3
Related Landfill Tax Funded Projects
Six odour related studies have been funded under the
Landfill Tax Credit Scheme at the time of this report
(Eventure and TG Trust 2000A - E).
These previous studies have investigated odour aspects
such as identifying sources, odour sampling and
measurements and developing cost effective means of
monitoring odorous constituents.
1.2
2.
Introduction
2.1
Waste Management Context
Odours have long been associated with waste
management activities, a natural and inevitable
consequence of the biological and chemical processes
that occur during the decomposition of putrescible
wastes. While not all odours result from the biological
processes occurring in putrescible wastes e.g. odours
from inorganic chemical wastes, the majority of odours
are associated with the aerobic and anaerobic
decomposition processes that organic wastes undergo
when either landfilled or treated by processes such as
composting.
History
Waste management activities of all types – recycling
facilities, transfer stations, composting facilities and
landfill sites – are all potential sources of a wide range of
amenity complaints, such as dust, noise, vectors, vehicle
movements and odour. Of these complaints, odour has
become the most common in recent years and a cause of
concern for nearby residents. Landfill companies have
been in discussion with the Environment Agency (EA)
and Local Planning Authorities regarding the issue of
odour from landfill sites and the increasing number of
public complaints that have been received (TG Trust
2000A).
The dictionary definition of odour is defined in two ways:
•
characteristic property of a substance which
makes it perceptible to the sense of smell
•
a smell, whether pleasant or unpleasant i.e.
either a fragrance or stench
It is the perceptibility of an odour, as determined by its
concentration in ambient air and its apparent fragrance or
stench that causes difficulties. The ability to detect a
smell or the sense of smell varies greatly between people,
such that some may detect a smell when others cannot.
These differences in human response make the
determination of acceptable levels of odour or smell, as
measured by its concentration in air, difficult to quantify.
The limiting concentration in air below which a smell or
odour cannot be detected is called the Odour Detection
Threshold (ODT) of that substance.
The potential sources of odour from landfill sites are well
documented but accurate and quantitative modelling of
these odour sources to enable predictive assessment of
their likely impact has not hitherto been rigorously
applied. The lack of modelling has been partly due to the
inability of existing air dispersion software to cope with
the small-scale effects associated with a typical landfill
site and the variety of odour emission sources.
Appropriate new generation air dispersion modelling
software is now available which can deal with a wider
range of meteorological conditions; local terrain and
topographic features; small-scale odour releases such as
point, line and diffuse odour emissions and; specific sitebased events, such as a ‘puff’ release of odorous gas.
While odours from waste management and other
industrial activities may historically have been accepted
as a normal part of that activity, this is not the case today.
The number of odour complaints arising from a wide
range of industrial activities has increased markedly in
recent years, especially with respect to waste
management facilities and particularly landfill sites.
Millennium Science & Engineering Ltd (MSE) proposed
the concept of a formal odour risk management
programme to determine effective ways to identify and
quantify sources, link transfer paths to receptors and to
establish cost-effective solutions for odour mitigation and
The term odour as used in the context of this project
refers only to its effect on amenity and not as a potential
risk to human health via chemical or microbiological
1
term ‘harm’ is defined in Section 29 of EPA 90 as
including, in the case of man, offence to any of his senses
or harm to his property. In Schedule 4, Paragraph 4, the
Regulations require inter alia in relation to the disposal
and recovery of waste, that processes do not cause
nuisances through odour.
toxicity. It is understood that the EA Landfill Gas Task
and Finish Group is considering the potential harm to
human health of landfill gas. It is also accepted that there
are potential health risks from sources other than landfill
gas. The modelling here is applicable however to other
uses e.g. investigations into health effects.
2.2
Part III of the EPA 1990 enables Environmental Health
Officers to control any odour that a waste management
facility might cause that is prejudicial to health or a
nuisance to the public. In Scotland nuisance is dealt with
under the Public Health (Scotland) Act 1897.
Regulatory Framework
European Legislation
The Framework Directive on Waste (Directive
75/442/EEC, as amended by Directive 91/156/EEC)
identifies waste management activities that need to be
properly controlled so that inter alia waste is recovered
and disposed of without endangering human health and
without using processes or methods which could harm
the environment and in particular:
•
without risk to water, air, soil, plants and
animals
•
without adversely affecting the countryside or
places of special interest
•
without causing a nuisance through noise or
odours
The LFD introduced measures to prevent or reduce
negative effects on the environment and risks posed to
human health due to waste and landfills. In particular
these effects cover the pollution of surface water,
groundwater, soil, air and include impacts on the global
environment with respect to emissions of landfill gas as
well.
Implementation of the LFD’s requirements in England
and Wales took place under the Landfill Regulations
2001, operating under the Pollution Prevention and
Control (PPC) Act 1998, which implements the EC
Directive 96/61 on IPPC. The objectives of PPC and the
LDF are complementary with the reasons for
implementing the Directive in this way including:
The regulation of odour from waste management
facilities is within the remit of the EA and the planning
authority (including Environmental Health Officers –
EHO’s), where odour nuisance will be a material
consideration in the determination of a planning
application. Wherever bulk quantities of waste are
handled, kept, treated or disposed of there is potential for
the generation of offensive odours. Geology, economics,
logistics (e.g. transport systems) etc. often result in waste
management facilities being situated close to residential,
commercial, industrial or amenity areas.
In addition development pressures can and do, result in
residential developments being constructed within close
proximity to existing waste management facilities. It is
reasonable that members of the public going about their
normal living, working or leisure activities should expect
landfill-site management to minimise odour events,
thereby experiencing no adverse impact on amenity.
•
A set of regulations and accompanying
guidance giving increased consistency and
clarity of interpretation and application of the
Directive
•
Incorporating landfills into an integrated
environmental protection regime
•
Economies of scale to be achieved by avoiding
the need to duplicate effort on operating and
maintaining two regimes for landfill sites with
the corresponding need for two sets of guidance
and training
Landfills come under Section 5.2 of the Pollution
Prevention and Control Regulations 2000, “Disposal of
Waste by Landfill” if they receive more than 10 tonnes of
waste in any day or with a total capacity of more than
25,000 tonnes, excluding landfills taking inert waste only.
The EA has a duty to ensure that the deposit, recovery
and disposal of controlled waste do not take place in a
manner likely to cause pollution of the environment or
harm to human health. Links are maintained with other
authorities such as local authorities (in their role as
planning and environmental health authorities) and the
Health and Safety Executive to ensure that all interested
parties are involved.
The PPC Regulations require the Operator to describe the
main activities generating odour and/or sources of odour,
the location of the nearest odour-sensitive receptors,
describe any relevant environmental surveys which have
been undertaken and the techniques for controlling
odorous emissions.
United Kingdom Legislation
The potential impacts of odour are raised initially as part
of the planning process. On submission of an application
for a waste management facility, an environmental
impact assessment should be, where applicable,
undertaken assessing the possible effects of odour arising
from the facility and identify suitable mitigation
measures. Operational controls are considered under the
2.3
The Landfill Directive’s 1999/31/EC (LFD) requirements
have been transposed into UK national law via the
Environmental Protection Act 1990 (EPA 90) and the
Waste Management Licensing Regulations 1994. The
2
Planning Controls
sector and identifies the various stages at which issues
associated with odours (from whatever source) need to be
addressed i.e. at the landfill development stage where the
risks posed by the development must be assessed through
waste acceptance, operational controls to landfill gas
management. Section 2.3.9 of IPPC S5.02 refers
specifically to odour issues (See Appendix 2 for a copy of
this section).
Waste Management Licensing regime administered by
the EA but amenity effects such as dust, noise and odour
are usually also addressed at the planning stage.
The EA is a statutory consultee in the planning process
for waste facilities and will make known its comments
about the proposed facility, including the possible effects
of odour. Detailed descriptions of the operational
practices that might lead to odour events and means of
providing subsequent controls are dealt with by the EA in
the application for a Waste Management Permits, which
enables the consented facility to be operated.
2.4
The aim of the proposed internal guidance is to provide
EA officers with the relevant background to this issue and
to engender a nationally consistent approach to the
control of odour through the licensing system and
subsequent monitoring activities.
Waste Management Licensing
The Guidance proposes that:
The EA is responsible for issuing the operational licence
for the facility. Guidance on licence requirements is
provided in Waste Management Paper 4 (WMP4).
WMP4 identifies the expected operational standards.
Issuing a licence condition that seeks to eliminate all
odours arising from a waste management facility is
unlikely to be effective. Adequate and effective odour
controls require the combined use of a number of
management and operational controls.
The EA issued a Library of Licence Conditions (EA,
1999). Application of a number of these conditions will
be required to achieve the desired objective of adequate
odour control. The basis of the approach used in setting
the Licence Conditions is that of Environmental Risk
Assessment and Risk Management.
The licence
conditions must address the environmental risks arising
from site operations and ensure that the objective of
prevention of pollution of the environment is achieved.
This objective includes prevention of harm to human
health and prevention of serious detriment to the amenities
of the locality. Condition 6.020, “Control of Odours”,
specifically addresses those aspects that need to be covered
in the Working Plan to ensure the control of odours.
all new licence applications are assessed with
regard to odours via a risk assessment
undertaken by the applicant or operator, bearing
in mind that some sites may have already
provided odour assessments as part of their
planning permission process
•
the risk assessment will be used to define the
approach to odour control within the licence
•
the impact of odour on the surrounding
environment is considered as part of routine site
inspections
•
odour is primarily controlled at source by good
operational practices, the correct use and
maintenance of plant and operator training
•
odour controls are considered in consultation
with other relevant regulatory authorities
Details of the practical measures identified in the various
guidance documents are presented in Sections 10.2 and
10.3 of this report.
The consultation document recognises that the provision
and maintenance of measures to control odours will need
to take into consideration a number of factors that are
likely to give rise to offensive odours. License conditions
seeking to control the detection of odours beyond the site
boundary should take account of the location of the
nearest odour receptors and of the proximity of
commercial or industrial activities adjacent to the landfill
site and their potential impacts.
A Licence requirement is for a site diary to be maintained
as a means of demonstrating the adequate running of the
site with respect to pollution prevention, harm to human
health and serious detriment to the amenity. The diary
should be a source of information to enable correlation
between odour complaints and site activities undertaken
at the time of the event.
2.5
•
In March 2002, the EA commissioned an R&D Project
(Proposal No 1E(02)20) to provide guidance on best
practice measurement and assessment of odour (and
noise) at waste management facilities with particular
reference to amenity issues. At the time of publication of
this report, no date had been set for publication of the
R&D Project report.
Regulatory Guidance
Guidance on odour control can be found in various
documents notably; the WMP series, including WMP
26A and B (Appendix 1), WMP27; IPPC S5.02. In July
2001, draft guidance entitled “Internal Guidance for the
Regulation of Odour at Waste Management Facilities
under Waste Management Licensing Regulations” was
issued for external consultation. Responses were due by
9 November 2001 but at the time of this report, no final
guidance had been produced.
2.6
Public Acceptability
As indicated previously public acceptance of odours from
industrial activities has decreased and is especially so in
respect of odours from waste management facilities. A
recent study of complaints associated with 46 UK landfill
IPPC S5.02 was issued in November 2001. Section 1.7
of IPPC S5.02 provides an overview of activities in this
3
sensitivities of detection. The sensory perception of
odorants involves four components:
sites (TG Trust 4, 2000A) found that odour was by far the
most significant cause of complaint, accounting for 59%
of all complaints made over a five year period at 20 of the
sites surveyed. Notwithstanding these results, not all sites
receive odour complaints. The absence of odour
complaints could indicate either that adequate controls
are in place or that people generally do not complain.
Obnoxious or bad odours emanating from a landfill may
have a number of effects, including: general annoyance;
loss of amenity (e.g. forcing someone out of their
garden); loss of appetite and/or sleep; and may affect
social activities (e.g. spoil dinner parties etc.). In
addition, the public may link any odour to potential health
fears, or perceived effects such as increased awareness of
colds, asthma or other respiratory ailments and this may
result in fears regarding the nature of ‘toxic’ or
‘dangerous’ inputs into the associated landfill. The public
may also associate repeated, or continual, odour episodes
with a loss of value in their property.
Odour and Odour Measurement
3.1
Olfactory Response and Odour
Detectability:
the theoretical minimum
concentration of odorant stimulus for detection in
a specified percentage of the population (usually 50%)
•
Intensity:
sensation
•
Odorant character: what the odour smells like
•
Hedonic tone:
relative
unpleasantness of the odour
perceived strength of the odour
or
Human response to odorant perception follows a number
of characteristic patterns associated with sensory
functions. Olfactory acuity in the general population
follows a normal distribution with 96% of people having
a ‘normal’ sense of smell and 2% each having either an
acute sense or a reduced sense of smell. While sensitivity
is normally distributed amongst the population it is not
constant across odorants or individuals, leading to a wide
variation in conditions leading to an odour complaint.
Measurement of odour is a difficult and complex process.
While the concentration of a chemical producing an
odour can be quantified, the impact of the odour on
human receptors is largely subjective, depending on the
type and nature of the smell produced and individual
Figure 1:
pleasantness
Human response to odorant perception follows a number
of characteristic patterns associated with sensory
functions. For a substance to be detected by the human
olfactory system, it must lie within a certain size range,
corresponding to a molecular weight (MW) between 15300 (Environment Agency, July 2001). The substance
must also be soluble in water and lipids, to enable it to
penetrate the mucous layer covering the smell detector
cells. For example, hydrogen sulphide with a MW of 34
is odorous, while sucrose with a MW of 342 is not
odorous.
Human response to odour is highly subjective. Some
people are particularly sensitive and may object to odours
that others may not be able to detect. People may also
become sensitised or de-sensitised to an odour, depending
on the nature of the odour itself, the frequency and
strength of exposure and their personal associations with
the odour. Even nominally pleasant odours can become a
nuisance over time.
3.
•
Normal distribution of the sense of smell within a population
4
3.2
Odour Measurement
establishment of an odour panel or the associated odour
sample control measures. A review of olfactory studies
produced by the American Industrial Hygiene
Association (AIHA, 1997) has produced a list of ‘A’
rated ODT data from the studies reviewed and these data
was used in the present study.
Measurement of the concentration of an odorant
compound is a straightforward process. Samples of LFG
are collected and analysed by appropriate chemical
methods to identify the particular odorant compound
required. However, the perception of odour is more
complex. One recognised and established method of
assessing odour is the determination of the number of
Odour Units (OU) for a substance. OUs are determined
using an odour panel, a panel of 5-10 people exposed to
changing concentrations of the odorant.
The ODT was used in favour of the ORT for two reasons:
while an odour may not be identifiable, its characteristics
may still be considered to be a nuisance; and the
pragmatic reason that there no suitable data on ORT
could be sourced compared with ODT data.
The approach of using the chemical concentration at the
ODT rather than OUs has the additional benefit of using a
parameter that could subsequently be measured in the
field with suitable equipment to give real-time
measurements. However this approach takes account of
any synergistic effects between chemicals.
The concentration at which 50% of the panel can detect
the smell is deemed the Odour Detection Threshold
(ODT) and by definition has an odour unit (OU) value of
1. The concentration at which 50% of the panel can
recognise the smell is termed the Odour Recognition
Threshold (ORT). Measurement of these thresholds is
expressed in OU, the number of dilutions of the starting
concentration required before the odour can no longer be
detected. It is also possible to measure the actual
concentration of the odorant chemical present in the
sample at the ODT.
3.3
Over 300 trace compounds have been identified in LFG.
Unpleasant odours are usually associated with the
sulphur-containing compounds, primarily mercaptans and
sulphides. The vast range of trace compounds measured
in LFG is a reflection of both the anaerobic
decomposition processes taking place in the waste mass
and the wide range of chemicals introduced via the
industrial and commercial waste streams.
It can be seen that while the OU method takes account of
variations in human olfactory acuity, it is a time
consuming process and therefore a costly process. The
costs incurred involve the collection of gas samples,
forming a panel of 5-10 persons and running successive
dilutions and panel testing of the odour samples as
necessary, until the 50% detection threshold is achieved.
A list of common odorant compounds with low ODTs
found typically in LFG, the reported range of
concentrations in LFG and their ODT concentrations is
presented in Table 1 and Figure 2 below. The range of
reported ODT values represents only the minimum value
and does not indicate the range of concentrations at which
compounds can be detected.
To maximise the quantity of work that could be
undertaken for the agreed budget, it was decided to use
the technically valid but simpler approach of basing the
odour dispersion modelling on the chemical
concentration of the odorant species determined at its
ODT. This approach is simpler, as is does not require the
Odorant Compound
Butanoic acid
Butyl Mercaptan
Diethyl disulphide
Dimethyl disulphide
Dimethyl sulphide
Ethyl mercaptan
Methyl mercaptan
Ethyl butanoate
Hydrogen sulphide
Methyl butanoate
Propyl mercaptan
Xylene
Odorous Compounds in Landfill Gas
Reported Concentration
in LFG*
(mg m-3)
0.1
0.01
0.1
0.02
0.02
0.1
0.005
0.1
0.0005
0.2
0.05
0.0015
-
210
16.1
1.0
40
135
120
430
350
97,152
125
2.1
1100
Reported ODT Range**
(mg m-3)
0.0000029
0.006
0.0003
0.00023
0.00033
0.00025
0.0000003
0.00003
0.0001
0.0019
0.0000025
0.0002
* based on average of LFG literature derived values
** AIHA 1999 and AEAT 1994 & 1997
Table 1: ODT of Selected LFG Trace Components
5
-
9
12
0.02
12
0.6
0.001
0.02
0.28
2.8
0.077
0.00014
100
Butyl Mercaptan
Ethyl Mercaptan
Methyl Mercaptan
Propyl Mercaptan
10
00
10
00
0
10
00
00
10
0
10
1
0.
1
0.
01
0.
00
1
0.
00
00
00
1
0.
00
00
01
0.
00
00
1
0.
00
01
Hydrogen Sulphide
Concentration (m g / m 3)
Literature minimum ODT Range
Reported Concentration in LFG
Figure 2:
NB: Data from Table 1
Comparison of the ODT for selected LFG trace components and their reported concentration in LFG
Offensive, sulphur-based odorant compounds found in
LFG typically have the lowest ODT concentrations,
making them the most likely source of unpleasant odours
in LFG (for a given concentration). Table 2 presents the
reported concentrations found in LFG for four sulphurcontaining compounds, part of the mercaptan series
(Appendix 3). The four mercaptans, methyl-. butyl-,
ethyl- and propyl mercaptan (also known as
methanethiol, butanethiol, ethanethiol and propanethiol),
are all found in LFG at concentrations well above their
ODT. Hydrogen sulphide, also widely found in LFG, is
included for comparison.
It can be seen clearly that there is a broad range of
reported odorant concentrations and ODT values. Such
variations in the range of intrinsic key odour data makes
it certain that odour complaints from LFG will vary
greatly from one seemingly identical site to another. In
addition extrinsic factors such as the extent of capping,
the type and extent of the gas control system and its
efficacy, the surrounding terrain and features etc. will
influence the potential for odour events.
As a
consequence the comparison of odour issues between
sites is a complex matter.
Reported Values (mgm-3)
Sulphur Containing
Compounds
Min Value*
Odorant to
Methane Ratio***
Max Value Average Value**
Methyl mercaptan
0.01
430
36
3.17 x 10
-6
Ethyl mercaptan
0.10
120
11
2.98 x 10
-6
Butyl mercaptan
0.01
13
2.1
2.95 x 10
-6
Propyl mercaptan
0.05
2.1
0.88
6.45x10
Hydrogen sulphide
0.00
97152
1210
1.62 x 10
-6
-4
-3
* Value <0.01mgm reported as 0.00
** based on average of literature derived values
-3
*** assumes 50% methane and unit concentration of 1mgm (Appendix 4.7)
Table 2: Selected Sulphur Containing Compounds in LFG (50% methane)
Using the reported concentrations of these compounds (or
any other compound of interest) in LFG, the ratio of the
odorant species to methane can be calculated. Based on
this calculated ratio the equivalent mass emission rate of
the odorant can be deduced from the measured methane
emission rate. The odorant ratio will change depending
6
Landfill odours can vary from ‘pleasant’ to ‘unpleasant’
but it is the impacts of ‘unpleasant’ or ‘offensive’ odours
that are the focus of this study.
on the actual concentration assumed. Comparison with
other published data (AEA, 1994; AEA, 1997; AIHA,
1997) shows that there is considerable variation in the
reported concentration of the odorant compounds at the
ODT, with differences of several orders of magnitude
reported for the same compound.
The wide variation in the value of ODT and the range of
odorant concentrations measured in LFG highlights the
difficulties of investigating odour complaints and
analysing odour sources. The reported range of ODT for
typical odorant species in landfill odours often overlap,
leading to difficulties of identifying whether the odour
source was landfill gas or leachate in origin.
In this situation the use of OU has an advantage over the
use of chemical concentrations, as OU measure the
overall ‘odour’ experienced. However OU do not allow
identification of the individual chemicals contributing to
the odour, which can be useful information in terms of
identifying the specific sources contributing to the odour.
Using this first-order approach of assuming the typical
values reported in the literature, enabled reasonable
values to be used for this initial dispersion modelling
study. However it is recognised that the use of such
typical data could result in under- or over-estimation of
the actual concentrations and it is strongly recommended
that site specific measurements of landfill gas or actual
field measurements of odorants be used whenever
possible.
It was appreciated that other odorant species will also be
present and may interact with the mercaptan compounds
assumed for the study. However it was both beyond the
scope of the present study to consider possible
interactions between different odorants and the resulting
cumulative effects and also inappropriate for an initial
study of this type.
4.
Landfill Odour Sources
4.1
Introduction
All waste management facilities and especially landfill
sites produce odours. The collection, transport and
handling of wastes combined with the effects of
temperature, time and rainfall makes it inevitable that the
decomposition of the organic matter will commence
before the waste is disposed to landfill.
Landfill sites present many different sources and
opportunities for odours to be generated. The application
of design, operational and management techniques can
reduce the impact of odours. In determining appropriate
odour control and mitigation measures, it is imperative
that the source of the odour is identified correctly.
Remedial action applied to the incorrect source of odour does
not achieve the desired result and incurs costs for no benefit.
7
4.2
Waste Transport Vehicles
of large molecules, such as carbohydrates, into smaller
molecules via the process of hydrolysis. Under the action
of anaerobic processes within the waste mass, the
degradation products from hydrolysis undergo further
breakdown by acetogenesis.
Odour complaints can begin with the delivery of waste to
the site by the collection vehicle. Waste collection
schemes, particularly those for household wastes, occur
either once a week or once a fortnight. Prior to the waste
being collected for disposal, the waste may already be 7
to 14 days old. If the waste is stored within a container,
such as wheelie bin, the air temperature within the
container can approach 45oC if located in direct sunlight,
encouraging the microbiological breakdown of materials
and the production of odorous compounds.
Acetogenesis produces a series of acids such as butyric,
proprionic and acetic acids, termed volatile fatty acids
(VFAs). Under the anaerobic conditions existing at this
stage, oxidised materials present as, for example
sulphates, will be reduced to sulphides, producing another
series of odorous compounds.
The conversion of the products of hydrolysis into LFG
can be represented as a two stage process, shown
schematically in figure 3 below:
Once collected from residential and commercial
properties, putrescible wastes may be delivered to transfer
stations for bulking up and onward movement to a
landfill for disposal. The waste may be stored for some
days before final despatch to landfill e.g. Bank Holiday
period. Under these conditions the microbiological
decomposition processes already commenced in the
collection receptacle will develop further and ensure that
odorous degradation products will be present during
subsequent transport to landfill.
These materials are highly odiferous and unless
methanogenic processes are established that convert the
VFAs into methane and carbon dioxide e.g. LFG, or they
are adequately contained, they will themselves act as a
potent source of highly odorous emissions. The sulphide
degradation are unaffected by methanogenisis and remain
odorous, becoming an integral part of the LFG
subsequently produced.
Transport of odorous decaying wastes through residential
areas on route to the landfill will create an odour pathway
that will sensitise occupants along the route. Subsequent
odour complaints generated may in fact be related largely
to the delivery of wastes and not solely to the landfilling
process.
4.3
The odour characteristics of leachate vary with its age.
Leachate at the VFA stage is termed young leachate,
typically a black odorous liquid with a high COD and
BOD. Over time as methanogenisis is established, the
aged leachate loses its COD and BOD, as LFG is formed.
In parallel the odorous nature of the leachate also reduces.
Landfilled Wastes
In addition to the VFAs, other odiferous compounds have
a high solubility in water, allowing dissolution in leachate
to a greater or lesser extent. Dissolution in leachate
enables the transport of odorous chemicals to locations
and situations where they might be released, leading to
the odour impacts remote from where leachate is
produced. Examples include:
Odours associated with the landfilling of wastes can
originate from both the delivery of odorous wastes and
the result of decomposition processes taking place in the
landfilled waste mass. Identifying correctly the odour
source is an essential part of designing appropriate
remedial measures. Not all landfill-derived odours are
necessarily offensive but in this study only offensive
odours are considered. The same dispersion and dilution
effects apply equally to both offensive and inoffensive
odours.
Fresh waste odours are usually typified by esters and
alcohols compared to aged wastes, where putrefaction
processes have been established and putrid sulphur-based
mercaptans and sulphides tend to dominate the odour
mix.
4.4
Leachate
The action of water on putrescible or organic wastes leads
to the generation of a liquid effluent termed landfill
leachate. Leachate is formed by the gradual breakdown
8
•
aeration lagoons that can produce ‘puffs’ of
odour as the aerators agitate the leachate and
release dissolved odorous compounds
•
off-site disposal via a public sewer running
through a residential area, where the agitation
of the leachate as it passes along the sewer can
lead to the release of dissolved odorous
compounds, the odour exiting via manholes
along the route, unless removed or pre-treated
beforehand
Acid Forming
Bacteria
Complex
Organics
i.e. waste
Methane Forming
Bacteria
Organic Acids
First Stage
Figure 3:
4.5
CH4 and CO2
Second Stage
Two stages of the anaerobic decomposition of complex organic wastes
Landfill Gas
used. If adequate abstraction is not achieved, the pressure
under which LFG is produced can lead to fugitive surface
emissions. For this combination of factors, flanks are
suggested as being an important source of fugitive LFG
emissions and hence odours. On some sites, flanks may
represent the most important source of odours, dependant
on the configuration of the active working area.
Young leachate is the feedstock material or precursor for
the formation of LFG. Unless methanogenic conditions
are established for the subsequent conversion of the
VFA’s generated in young leachate, the result will be
large quantities of an odiferous leachate, with minimal
production of LFG. In most situations sufficient
methanogenisis takes place to enable the production of
LFG, making emissions of LFG a major source of landfill
odours.
The major components of LFG are methane and carbon
dioxide, with a small amount of nitrogen. The three bulk
components typically total over 99% of LFG, none of
which are odorous. Importantly however is the presence
of small amounts of trace gases and compounds, which
are odorous.
5.
Site descriptions
5.1
Introduction
Six sites form the basis of the study, located to cover
England from the north to the south. The six sites are
treated separately with regard to emissions data, odour
surveys, odour complaints and odour questionnaires,
For dispersion modelling purposes the six sites fall within
three simple classification groups determined by the
surrounding terrain. Assuming that the final landform is
represented as a small hill, the three categories can be
described simplistically as:
Over 300 compounds have been detected in LFG,
consisting of both offensive and inoffensive odorous
compounds. The mobile nature of LFG and its
generation within the waste mass under pressure provides
a driving force for its movement both through and out of
the landfilled waste mass, which can be controlled by gas
collection and management systems.
•
hill on a plain
•
hill on a hill
•
hill in a valley
The intrinsic characteristics of the daily cover
soils/materials, in terms of thickness and soil type, the
infiltration of rainfall and the degree of compaction of the
waste are all factors that determine how readily LFG will
exit the site. Extrinsic factors such as the extent and
effectiveness of the gas management system will
determine how much LFG is available to exit the site.
Typical emission sources are gas wells and leachate
chambers not under abstraction, excavations in the waste
mass and uncapped landfill surfaces, especially flanks.
Three of the sites equated to the hill on a plain scenario
(hereon referred to as sites P1, P2 and P3 ); one is a hill on
a hill (H1); and two sites are represented by a hill in a
valley (V1 and V2). Details of the terrain surrounding the
sites and site descriptions is covered in later sections and
is included in Appendix 5.
Flanks can and often represent a significant area of an
active site. Due to the steepness of the slopes (often 1:2
and greater), flanks are difficult to both compact and to
place an adequate thickness of daily or temporary cover
soils. Placement of gas wells close to the top of flanks is
liable to cause the ingress of air into the waste via the
porous flank surface, if high abstraction pressures are
Table 3 summarises the waste quantities and waste
streams accepted by each of the study sites. All sites
accepted domestic and non-hazardous commercial or
industrial waste. Three of the six accepted special or
hazardous waste. Only one of the sites accepted liquid,
sludge’s or other waste types. A more detailed discussion
5.2
9
Waste Input/Waste Types
of the waste inputs and waste streams is included in
Appendix 5.
Site
Design Characteristic
P1
P2
P3
H1
V1
V2
350,000
430,000
200,000
130,000
140,000
80,000
50
140
26
27
21
9
Domestic
Non-hazardous Commercial /
Industrial
Special / Hazardous
Liquids / Sludges
Other
3
Annual Input (m )
Total Site Area (ha)
3
Table 3: Waste streams accepted by sites and total annual input (m )
Site
Design Characteristic
P2
P1
Dilute & Disperse (Active*/Restored**)
Engineered Containment with Composite Liner
(Active*/Restored**)
/
X/
X/X
/X
P3
H1
V1
V2
/
X/X
X/
X/
X/X
/
Clay Final Cap
/X
X
Geomembrane Final Cap
/X
X
X
Gas Wells
Power Generation
X
Flare
X
Leachate primary treatment and discharge to
sewer
X
Leachate removed from site by another method
X
X
X
X
X
X
X
*
Active: The current area of waste disposal and all other areas not as yet restored (including those with final clay,
Geomembrane or other capping)
**
Restored: Surface capped and returned to planned final cover (grassed)
Table 4: Summary of Site Design Characteristics
5.3
Site Design and Operational Regime
Sites P1, P2 and P3 were all located on river or coastal
flood plains. As such, there was little topographic
variation surrounding the sites and in all cases, the landfill
site forming the largest topographic feature in the
proximity of the sites.
The wide age range of the sites involved in the study
meant that site designs included dilute and disperse
systems, engineered containment and combinations of the
above. All sites conformed to current design standards
and operational good practice, including the installation
of gas abstraction and leachate collection systems. The
site design characteristics are summarized in Table 4
above.
5.4
H1 was located at an altitude of approximately 50m AOD
in an area of rolling hills rising up to 90m AOD. The site
was located on a ridge that formed the margin between
the coastal plain and the inland hills.
Terrain
Sites V1 and V2 were both located in an area of rolling
terrain with a height of up to 130m AOD. Both of the
sites were positioned on the valley floor at approximately
80m AOD.
The terrain of the six sites can be classified into three
distinct groupings. As indicated previously, for the
purposes of dispersion modelling these were a hill on a
plain, a hill on a hill and a hill in a valley.
10
5.5
Proximity to Habitation
The sites selected differed greatly in the extent of and
their proximity to sensitive receptors. Receptors included
residential, industrial and commercial, including a
supermarket and a kindergarten. The closest receptor to
any of the sites was a kindergarten located at the entrance
to P1. Conversely, complaints had been received over 2
km away from both sites P2 and H1. A more detailed
discussion of the proximity of the sites to habitation is
included in Appendix 5.
5.6
Potential Off-Site Odour Sources
All of the sites were situated in areas where agricultural
practices were undertaken. In particular, V2 was located
in close proximity to an area where regular application of
slurry to land occurred.
P1 was situated in close proximity to a number of
chemical manufacturing facilities and sites that make use
of solvents. In addition, odours associated with the
estuary were also possible. Similar estuarine odours were
possible at P2.
Odour issues are complicated at P2 due to the very close
proximity of a sewerage treatment works (STW) located
adjacent to the landfill site. Furthermore, the site
accepted the sludge-cake from the STW, with the cake
being transferred in open containers. Problems had arisen
in the past regarding the determination of the odour
source as a result of this close proximity. A poultry farm
was also located approximately 350m to the north of the
site, giving the local area around the site multiple odour
sources. Differentiation of the various odours and
attribution of the likely (multiple) sources is a complex
issue, requiring significant effort.
11
6.
to human health and serious detriment to the
amenity.
Odour Complaints Data and
Questionnaire
•
6.1
Odour Complaints
Management of complaints by and feedback from the
public about landfill operations, including odours, are an
essential part of ensuring that waste management
activities are properly managed. The public have a right
to expect facilities to be managed in accordance with
good practice and to be compliant with the requirements
of the regulatory regime under which they operate. The
conventional routes for the public to register complaints
are via the Environmental Health Department, the EA
and or directly to the site.
Whilst all the sites diaries were in compliance, the
Licence requirements do not specify a level of recorded
detail that would be of value to odour investigations. The
lack of suitably detailed site records precluded the
detailed comparison of site activities with odour
complaints and only a limited analysis could usefully be
undertaken. To facilitate the investigation of odour
complaints and as part of good operational practice, each
site should have an operational weather station. The
specification of the station should include the logging of
wind speed, wind direction, precipitation, relative
humidity and the net radiation. The logged data can be
used in combination with the full meteorological data set
required for air dispersion modelling purposes to provide
site specific data.
Odour complaints should be seen by site operators in a
positive light, helping to identify conditions that they may
be unaware of either during or outside of normal
operating hours. Once alerted to such events, operators
can investigate the cause and take appropriate action(s).
Inspections by the regulatory body, the EA, can only
obtain a snap-shot in time of site activities and their
potential impacts. In terms of odour, a 30-minute
inspection once per week (for example) represents less
than 0.3% of a year and the likelihood of experiencing an
odour event during an inspection is small.
Of the sites involved in the study, all except Site P1 had
received complaints in the previous 12-18 months. The
inclusion of Site P1 was to identify what differences may
have accounted for the absence of any odour complaints,
Odour receptors around the site, such as
industrial/commercial activities are present for perhaps
25-30% of the year, while residents can be present 100%
of the year. Site operators are likely to be present for
about 30-35% of the year, making residents the receptors
most likely to experience any odour events. The effects
of still/calm weather conditions that occur primarily at
night or in the early morning, also makes it more likely
that residents will experience any odours emanating from
the site.
6.2
Odour Questionnaire
Central to any investigation of odour complaints is the
experience of the receptors and complainants. To obtain
information from local residents and complainants about
odour issues and odour events, a questionnaire was
prepared and sent to a random selection of residents in the
areas around four of the sites from where complaints had
been received (see Appendix 6).
As part of this study it was intended that historic
complaints and operational data would be compared via a
detailed analysis with meteorological data. However, a
number of factors limited this comparison. The lack of
definition of the time that a complaint was lodged
prevented cross-comparison with meteorological
conditions and site activities. The location of the
complaint, due to a requirement for maintaining
complainant confidentiality, was often limited to a
postcode area or road name. The area covered by a
postcode or road name varied from few hundred square
meters to many thousands e.g. urban versus rural.
The purpose of the questionnaire was to obtain a
combination of generic and site specific data, to enable a
comparison of complaints records with site operations
and weather conditions at the time. The format of the
questionnaire covered the length of time odour events had
been experienced, weather at the time, time of day/year,
characteristics of the odour, complaints history, who
complained to and any general concerns.
Responses were sent back (return self-addressed, replypaid envelope) on an anonymous basis, to encourage
people to respond frankly. A request was made for a
name and contact address if the respondent wished to be
involved in any follow-up exercise. The number of
questionnaires issued reflected the population density
around the sites.
All landfill sites are required to maintain a site dairy as
part of their Licence. The purpose of the diary is to
record major site activities. Details of the Licence
requirement are specified as:
•
Use: The site diary may be required to include
details of, for example: times on and off site of
the
designated
Technically
Competent
Manager(s) for the site; details of complaints
received and actions taken; and times/dates of
scheduled monitoring and maintenance.
The structure of the questionnaire was designed to
attempt to differentiate between the various factors which
could contribute to odour, such as weather, time of year
etc., to see if odour events were associated with seasonal
activities associated with farming i.e. spreading of slurry
Objective: To provide a daily on-site record
that will demonstrate adequate running of the
site with respect to pollution prevention, harm
12
Analysis of the questionnaire returns data provided some
useful generic data but also reinforced the confused
nature and perception of odour and odour events held by
the general public. Listed below are general findings
applicable to all the sites:
or fertilisers etc. Similarly for other adjacent industrial
activities that could lead to odour events, including
specific daily or weekly activities such as the cleaning of
plant and equipment, batch processes being
loaded/unloaded etc.
6.3
Analysis of Survey Results
Historically responses to mailshot questionnaires are not
usually very successful, for a variety of reasons, such as
lack of interest, insufficient time to complete, complexity
of the questionnaire etc.
As with any mailed
questionnaire, the respondents understanding of some
questions differed from that intended and the lack of
replies or non-specific replies to other questions meant
that data was incomplete.
It can be concluded that the only means of obtaining
complete and full details would be to undertake face-toface consultations with those sent the questionnaires. In
the event, 57% of those responding expressed an interest
in becoming involved in any further studies.
Despite the length of the questionnaire – 25 questions (a
full analysis of the returned questionnaires is presented in
Appendix 6) – the standard of response was good. The
overall success of the questionnaire approach in this
instance could be judged by an overall 40% return rate
against the total of 135 questionnaires despatched to the
four locations (Table 5).
•
Short term odour event (few hours duration)
•
Once per week or greater frequency
•
Usually a longstanding issue, commencing at
site opening
•
Worst time of day for odour events are
mornings and/or evenings (however this is
when more residents are at home or outside)
•
Odours detected generally under still/foggy
conditions
•
Odour strength typically moderate/strong
•
Apart from animal manure smell, generally
rotten food/putrid/pungent
•
Most people do not complain about odours
The survey found that most people did not bother to
complain about landfill operations, including odours even
when experienced. This suggests possibly either the
limited scale of the problem or a feeling that complaining
will be of no value. The value of a Site Liaison
Committee should not be underestimated. The high
questionnaire response rate (85%) at H1, where a liaison
committee exists, suggests an openness and willingness
to contribute to a programme that seeks to minimise the
environmental impact of the landfill operations and where
the views of the public are listened to and addressed.
Public complaints should be seen as an essential part of
ensuring that waste management activities are properly
managed.
While the overall return rate for all the questionnaires was
40%, the return rate varied between the four sites.
Unsurprisingly perhaps, the lowest return rate came from
Site P1, the site with no odour complaints. The return for
Site H1 reflected on-going odour issues currently being
dealt with by a joint Operator/EA team. No obvious
reason(s) could be identified to explain the lack of odour
issues associated with what appear to be similar sites
being operated in the same way taking the same waste
streams. Once again odour proves to be a complex issue,
not always easily delineated by obvious causal factors.
Questionnaire Statistics
Site*
Number
Sent
Number of
Replies
% Replying
% Replying Wishing to be
Involved Further
P1
40
8
20
12
P2
50
21
42
57
P3
25
8
32
75
H1
20
17
85
76
135
54
40
57
TOTAL
*
Note: Questionnaires were not distributed at either site V1 or V2 due to a number of logistical
issues
Table 5: Summary of Questionnaire Statistics
13
6.4
Alternative Potential Odour Sources
other sites could compound and/or confuse odour
complaint issues.
Of the sites covered by the study, sites P1, P2, P3 and V2
were located within an agricultural or semi-agricultural
environment. Farming activities taking place around the
sites included poultry farming, animal grazing, the
cultivation of crops and the use and/or storage of farm
generated animal slurry and wastes. Each of these
activities are likely to produce an odour event period or
periods during the course of the year, which may lead to a
complaint incorrectly attributed to the landfill site.
The proximity of possible alternative sources of odour
makes a clear differentiation of odour sources difficult,
especially as the data available from both the EA/EHO
complaints records and the landfill site diary contained
insufficient detail to enable a clear view to be formed as
to the likely cause of the odour.
The lesson to be learnt is that more accurate and detailed
records need to be maintained by both the site operator
and the regulatory bodies if an objective assessment is to
be made as to contributory source or sources of odour
complaints.
At site V2, a regular occurrence was the movement of
animal slurry along a road adjacent to the site that ran
past a residential area. Immediately after the movement
of this material on days when the wind was blowing in
the appropriate direction, evidence indicated that odour
complaints were recorded.
P1 was located in close proximity to an industrial estate,
which included a paint manufacturer, other chemical
processes and a range of light industries. P2 was located
adjacent to a major Sewage Treatment Works. The
presence of this alternative odour source further
complicated the issue as the landfill site accepted the
sewage cake produced by the Sewage Treatment Works.
Two of the sites, V1 and V2, were also situated in a
locality with a number of other landfill sites. As such,
operational and managerial issues associated with these
Force
Description
7.
Regional Wind Flow Patterns
7.1
Physics of Wind Flow
Wind is the movement of atmospheric air from a region
of high pressure to one of lower pressure. Wind strength
is measured in terms of velocity, m/s, but is usually
characterized by its visual effects, the two measurements
being linked by the Beaufort Scale. Table 6 gives the
relationship between wind speed in m/s and the observed
visual effects.
Equivalent Speed at 10 m Above
Ground
Effects
Miles Per Hour
0
calm
smoke rises vertically
Meters Per
Second
Mea
n
Limits
Mea
n
Limits
0
<1
0.0
<0.2
1
light air
wind direction shown by smoke drift
2
1
-
3
0.8
0.3 - 1.5
2
light breeze
wind felt on face, leaves rustle
5
4
-
7
2.4
1.6 - 3.3
3
gentle breeze
leaves/small twigs move
10
8
- 12
4.3
3.4 - 5.4
4
moderate breeze
raises dust and loose paper
15
13
- 18
6.7
5.5 - 7.9
5
fresh breeze
small trees begin to sway
21
19
- 24
9.3
8.0 - 10.7
6
strong breeze
large branches move
28
25
- 31
12.3
10.8 - 13.8
7
near gale
whole trees move
35
32
- 38
15.5
13.9 - 17.1
8
gale
breaks twigs off trees
42
39
- 46
18.9
17.2 - 20.7
9
strong gale
slight structural damage
50
47
- 54
22.6
20.8 - 24.4
10
storm
trees uprooted considerable damage
59
55
- 63
26.4
24.5 - 28.4
11
violent storm
widespread damage
68
64
- 72
30.5
28.5 - 32.6
12
hurricane
-
-
>32.7
-
>73
Table 6: Beaufort Scale-Specifications and Equivalent Speeds
14
7.2
The maximum wind speed likely to occur at a given
location is needed for many structural engineering
purposes, such as the design of buildings and other
structures. The UK Meteorological Office provides wind
data based on hourly mean and hourly gust data, for every
hour, at each of the 140 anemograph stations across the
UK. These records enable the hourly mean and gust data,
as determined at a standard height above ground level (10
m), to be calculated. Using this reference wind data a site
design wind speed and direction can be calculated, as can
the number of days above a specific, or threshold, wind
speed.
Once a reference wind speed has been calculated for the
general area of the site, correction factors can be applied
to determine a design wind speed for the site. The usual
engineering requirement is the extreme mean hourly wind
speed at a particular height, calculated using the Kfactors, which takes account of surface roughness at and
upwind of the site. The design wind speed forms the
basis of subsequent engineering calculations when taking
account of forces generated due to the wind. The
methodology upon which this calculation is based
assumes that the wind speed follows a Weibull
distribution, which describes the wind speed variation
with time at a location. This technique can be applied to
specific sectors, enabling threshold exceedance to be
determined for particular wind directions that may be of
interest e.g. local housing or other sensitive receptors.
Based on this site design speed and direction, the effects
of height above ground, surface roughness up and down
wind of the site and the surrounding terrain can be
calculated. This calculation uses a series of factors – Kfactors – that are used to determine the design wind speed
at the specific site under consideration.
The benefit of undertaking this exercise at the site
selection stage, is that it provides an indication of the
magnitude of possible wind-related effects, such as
wind-borne litter problem and odour, enabling mitigation
measures to be included at the environmental assessment
phase. Whilst on its own this evaluation exercise is
unlikely to lead to the de-selection of a proposed landfill
site, it may lead to a re-think of the proposed phasing plan
for filling and to changes in site operational practices,
which could include more effective mitigation and
abatement techniques.
Between ground level and a height well above the surface
of the Earth, the gradient height, a wind speed gradient
exists. Surface features on the Earth induce drag forces,
hindering wind movement but this effect reduces with
increasing height until wind moves along lines of equal
pressure, the gradient wind speed. The region between
ground-level and the gradient height is termed the
atmospheric boundary layer (ABL).
As wind speed at any point in the ABL is dependent on
the gradient speed, which in turn is influenced by
geographical location, it cannot be easily measured. To
accommodate this, wind speeds measured near the
ground are used as reference values. Factors which affect
the wind speed in the ABL include;
•
geographical location i.e. the reference wind
speed
•
surrounding terrain
•
surface roughness
•
height of the point ground level
Terrain
Terrain effects
Terrain features, such as hills and ridges, valleys and
escarpments or slopes, have an influence on the wind
speed as it passes over them (Figures 4-7). The
magnitude of this effect is dependent on the upwind slope
of the particular feature:
Temporal factors are also important, such as the average
interval between occurrences of a particular wind speed
and the time period over which the maximum wind speed
is averaged, which is usually one hour.
15
•
for a gradual change, no net effect on the ABL
will occur
•
for features such as cliffs and slopes, the effects
depend on the slope angle, α, with 17o being a
break point.
Figures 4 – 7: Regional Wind Flow at Site V2 at a height of 10m
-1
Site V2; Wind Speed 0.8ms ; Surface Roughness: 0.5m. NB Axis in Km
Figure 4: Wind Direction 900
Figure 5: Wind Direction 1800
0.35
0.55
0.75
0.95
1.15
Wind Speed (m/s)
+ Site Location
16
1.35
1.55
Figure 6: Wind Direction 2700
Figure 7: Wind Direction 3600
0.35
0.55
0.75
0.95
1.15
Wind Speed (m/s)
+ Site Location
17
1.35
1.55
A shallow slope, α<17o, will produce a reduction in the
approach wind speed to a minimum value at the foot of
the slope, increasing to its maximum value near the crest
of the slope, before decelerating to a constant value
downwind (Figure 8a). The ratio of the maximum crest
speed to the constant downwind speed is 1.6, at a height
of 10 m above ground for α = 17o.
the air mass speeds up and moves up a slope, the pressure
above the surface is reduced, enhancing the emission of
LFG through the porous surface. The vortex effect noted
in 7.2.5 ensures that any surface emission is captured
within the moving air mass, enabling the trapped odorant
compounds to move off-site with the air body moving
across the site.
As α increases above 17o, flow up the slope produces
separation of the air-flow upwind of the base of the slope
and upwind of the crest, resulting in a reverse flow of air
in each location, or as it is more commonly known, a
vortex (Figure 8b). Because the air-flow in a vortex is
circulating, it provides an upward force which will tend to
cause odorous compounds (or solids such as litter and
dust) to become entrained in the air mass. Flow down the
slope creates a vortex only at the base and not at the crest
(Figure 8c).
While increasing the velocity of the air moving over the
surface also increases the abstraction rate of the surface
emission (by increasing the negative pressure over the
surface), the resulting increased turbulence enhances the
mixing and dilution of any odorant compounds released.
The worst-case conditions for odour dispersion will be
experienced at low wind speeds, where the mixing effect
is reduced but so also is the abstraction effect. The
quantification of any enhanced odour abstraction was not
part of this study but would be a useful topic for future
study.
In addition to above effects on air flow, the same
processes causing changes in the air flow also induce
pressure changes over the surface of the land mass. As
18
WIND
Decelerates
Accelerates
Decelerates
α < 17o
(A) Flow up shallow escarpment
WIND
Decelerates
Accelerates
Decelerates
Downwind separation
bubble
α > 17o
Upwind separation
bubble
(B) Flow up steep escarpment
WIND
No Change
α > 17o
Separation bubble
(C) Flow down steep escarpment
Figure 8: Wind Flow over Landfill Flank (or Escarpment)
19
7.3
Air Dispersion Models
scale fluctuations in concentration. The accepted average
time period of 15 minutes for modelling SOX emissions,
for comparison with the National Air Quality Standards,
has been verified by field measurements. The same 15minute time period has therefore been adopted for the
modelling of odours.
Air dispersion models describe the movement of gas and
particulate emissions as a function of the prevailing
meteorological conditions. New generation air dispersion
models, such as AEROMOD and ADMS, use the MoninObukhov relationship to describe meteorological
conditions rather than relying only on Pasquil
atmospheric stability conditions. The new generation
model ADMS version 3.1 was the dispersion modelling
software used in this study. ADMS has been developed
by three organisations, CERC, the Meteorological Office
and National Power (subsequently the University of
Surrey) and its development has been determined and
reviewed in detail by sponsors who have supported part
of the development (including the EA, HSE, DEFRA
(formerly MAFF) and many more).
Air dispersion models can be used in a variety of ways
for design and “what if”, or sensitivity, studies. For
example, to:
The ADMS model has been extensively validated against
field data sets and has constantly been supported by a
management committee with representatives from
industry and government organisations and is widely by
industry and regulators alike.
•
calculate the mean hourly and gust speeds at a
site for a specific reference wind speed
•
determine the effect on selected wind
properties of changing the input variables
•
reduce/correct measured wind properties to
values corresponding to specific standard
conditions.
Air dispersion models provide the designer/analyst with
the ability to try out several “what if” scenarios, taking
full account of local, site specific conditions, such as;
The EA has recently issued its LFG risk assessment
software called GASSIM.
GASSIM assesses the
environmental impact of the bulk and trace species in
LFG on the global atmosphere, the local environment and
exposure to humans from atmospheric dispersion and
lateral migration.
Environmental transport is simulated for terrestrial lateral
migration by a one dimensional advection-diffusion
equation, and for atmospheric dispersion using the NRPB
R91 (Gaussian plume) model. The model determines the
concentrations of the various species in the unsaturated
subsurface and in the air, including wet and dry
deposition for on-site and off-site receptors at various
vectors plotted on a wind rose.
•
ground roughness at the site
•
upwind variations in ground roughness
•
height above the ground
•
topographic effects of the location of the site on
a hill, ridge, cliff or slope.
Roughness and Terrain Effects
An important modelling option influencing dispersion is
Surface Roughness, which represents the characteristic
roughness length of the land surrounding the source,
based on land use. Roughness reflects the micro-scale
effects, which refer to the location and size of buildings
and the nature of the ground surface e.g. pastoral, arable,
woodland etc (Table 7). The lower the roughness length,
the lower the resistance to dispersion or ability to
generate turbulence and mixing and therefore the higher
the average concentrations experienced.
The NRPB R91 model does not accommodate the micro
and macro-scale terrain effects that new generation air
dispersion models (inter alia ADMS or AERMOD) can
deal with and which are most applicable to investigating
odour effects at landfill sites.
The air dispersion model employed models a wide range
of buoyant and passive releases to atmosphere either
individually or in combination. The effects of buildings,
terrain and coastlines on dispersion can be taken into
account. ADMS is unique amongst air dispersion models
as it is the only tool of its kind which models short time
20
Land Use
Roughness Length (m)*
Sea
Short Grass
Open Grassland
Root Crops
Agricultural Areas
Parkland, Open Suburbia
Cities, Woodlands
Large Urban Areas
0.001
0.005
0.02
0.01
0.2 – 0.3
0.5
1.0
1.5
*Roughness length does not equate to the magnitude of the land use feature
Table 7: Roughness values for different land use surfaces
New generation air dispersion models can model
complex terrain situations where it is used for estimating
airflow and dispersion over hills and changes in surface
roughness. Local topographic features include macroscale effects, such as hills and valleys. The effects of
these features on wind speed and wind direction can be
seen in Figures 4 to 7.
complaints e.g. timed aeration of leachate, venting LFG via a
leachate chamber or gas well, or excavating in waste.
Input data
Three input data are required for modelling as follows:
Meteorological data
Atmospheric pollution is affected by meteorological
factors. The key input parameters required for air
dispersion modelling are:
•
Mean wind speed at specific height
•
Surface sensible heat flux or cloud cover
•
Wind direction
•
Boundary layer height
Source emission
•
Meteorological
•
Terrain
The source emission inputs can arise from a combination
of landfill emissions i.e. exposed landfill surfaces, gas
flares, gas engine exhausts, gas wells etc.
Key
parameters for these emissions are the velocity and
temperature of the emission and the mass concentration
of odorant in the gas stream. Both the emission rate and
odorant concentration can be either measured or derived
from published data. Due to the wide range of surface
emission rates that can occur, it is recommended that the
actual emission rates for methane are measured, rather
than relying on published data.
This data is required in an hourly sequential format.
The meteorological data are entered into the system using
a prepared meteorological file supplied by the
Meteorological Office. The meteorological input module
of ADMS and other air dispersion models reads the data
from the meteorological input dataset and uses the preprocessing algorithms to estimate values of the boundary
layer and related meteorological quantities required for
running the dispersion model.
7.4
•
The meteorological and terrain data for the site are
purchased as data packages from the Meteorological
Office and Ordinance Survey respectively.
8.
Monitoring of Emissions
8.1
Definition of Source Terms
Application to Landfills
Source term
Emission sources
Dispersion modelling requires the value of the mass
emission rate of the gas to be modelled in gs-1, called the
source term. The source term defines the mass of
material released from the emission source per unit time,
which is then dispersed in accordance with the
meteorological and terrain conditions.
The ability of new generation air dispersion models to
deal with local, small-scale topographic features makes
them especially appropriate for dealing with landfills and
other waste management sites. The effect of specific
features such as landform phases, soil bunds, walls,
fences etc. on odour dispersion can all be modelled. The
models can deal with point, line and diffuse emissions
sources and with constant and ‘puff event’ emissions,
typical of many landfill activities that could lead to odour
Comparison of emission rates requires normalisation of
the emission rate expressed in gs-1m-2. The emission rate
from two sources may be similar in terms of the overall
21
Emissions from surfaces were determined using both a
large-scale flux box (4.1m2), termed a flux tent, and a
small-scale flux box (0.15m2). The measurement mode
can be either static or dynamic, the former being less
accurate in absolute terms but providing a result in a
much shorter time. To obtain the largest number of
measurements in a given timescale, the static mode
operation was used (Appendix 8).
mass emission rate but the contribution per unit area may
be significantly different.
8.2
Monitoring Procedure
A standard monitoring procedure was established for onsite visits and the collection of emissions data. The
procedure included a methane surface emission and
odour site walk-over survey, a site boundary odour
survey, measurement of on-site meteorological conditions
and the measurement of surface and point emissions
using both large- and small-scale flux chambers
(Appendix 7).
8.3
Landfill surfaces are by nature heterogeneous, with
surface cracks and variations in cover material thickness
producing wide variations in the emission of landfill
gases. Due to the smaller surface area of a typical flux
box e.g. <0.5m2, it is recommended that the larger flux
tent should be used wherever practicable, to ensure the
increased probability of inclusion of potential surface
defects.
Measurement of Emission Rates
Flux measurement
Surface of tent
Monitoring
Point
Landfill
Surface
Edge dug into surface
Figure 9: Schematic of Flux Tent
Flux measurement data
However it is not always possible to use the large-scale
flux tent due to uneven ground surface or accessibility,
such as cell flanks. When using a device with a smaller
surface area, the subsequent measurements may exclude
surface defects, which can have significant mass emission
rates. To compensate for the reduced area of coverage,
larger numbers of measurements are required to provide
representative data.
Data on flux measurements for methane emissions from
landfill sites is limited. Published data (Bond et al, 2000)
provides values for emission rates from landfill surfaces.
Inevitably the results show a wide variation in the
emission value between different types of landfill surface
and the type of emission source. In this study the field
determination of the emission rate was based on
measuring the time rate of change of concentration of
methane in the flux tent. Subsequent calculations
produced a methane flux value in gm-2s-1 (see Appendix 4
for details). Table 8 compares emission rate data from
the current study and published sources.
Figure 9 shows the schematic arrangement of a flux tent
used to measure the methane emission rate from a landfill
surface. Figure 9 applies equally to both large- and
small-scale fixed volume flux boxes.
22
Odour Source
Methane Flux Rates
(mg m-2 s-1 – areas, or mg s-1 – point sources*)
Current Study Range
(Average)
Active working area
-2
n/a
4.2x10
-1
Daily cover
3.1x10
Flank –temporary cover
(Sandy)
1.2x10
Flank –temporary cover
(Clayey Soil)
1.0x10
Temporary Cap (Sandy)
6.0x10
Temporary Cap (Soil)
6.2x10
Restored (Capped)
Freely venting gas well
Range of Reported Values
(Bond et al, 2000)
n/a
-2
–
Man-hole cover over 1.2m
*
diameter leachate chamber
2.4x10
5.0x10
-2
2.2x10
n/a
-3
*
2
n/a
0
-2
5.0x10
0.0
*
-1
3
-3
–
4.0x10
–
4.0x10
-2
4.6x10
3
-5
5.0x10
–
–
1.0x10
4.1x10
n/a
n/a
* Single observation: not to be regarded as typical
Table 8: Measured Emission Values for Methane from Landfill Odour Sources
23
0
-2
The emission rates were calculated as a function of an
assumed odorant concentration expressed in mgm-3 of
LFG. The concentration of the odorant in LFG is not a
constant but a dynamic and variable quantum. The mass
emission rate modelled for each site was assumed to
represent the cumulative output from all sources. Based
on the reported concentrations in LFG, a concentration of
10mgm-3 in LFG was assumed for the purposes of the
modelling. Table 9 gives the mass emission rates for
methyl mercaptan based on the odorant ratio in Table 2
(scaled up to reflect the concentration assumed) and the
methane flux rates in Table 8.
Comparison of the data between the current study and
reported values shows that they are generally of the same
order of magnitude for the same emission source. The
number of significant figures should really be reported as
one, or even on an order of magnitude basis, due to the
need to undertake significant numbers of measurements
to provide increased accuracy of the data. While it was
not the purpose of this study to provide data of such
accuracy, two significant figures are reported to help
differentiate the data values.
The difference in emission rate between flanks with
sandy or clayey soil cover is ascribed to differences in the
homogeneity of the soils. Clayey soils can be ‘lumpy’
and unless well-compacted have the potential to produce
large open spaces between the lumps, providing discrete
pathways for subsurface emissions. While inherently
more porous, sandy soils are likely to be more uniformly
dispersed and overall give a more homogenous emission
surface with few large, discrete emission pathways.
The total mass emission from a site could comprise a
combination of different sources with each at a different
emission rate (Table 10). The emission rate used in the
dispersion modelling could comprise a variety of
potential emission sources, such as a single point source
or multiple point sources, a linear source, or the
combined emission from a number of sources. Table 10
gives examples of the combined effect of different types
of sources that could contribute to the overall mass
emission rate of odorous compounds from a landfill.
The ‘potential’ emission rate of the odorant can be
determined by using the odorant to methane ratio derived
in Table 1, which is then used as input data for dispersion
modelling.
Applying this ratio-approach enables
methane to be used as an indicator species for highly
odorous compounds such as methanethiol, ethanethiol,
butanethiol and propanethiol.
The data in Table 10 identifies the importance of
distinguishing between the various types of emission
sources so that appropriate remedial and mitigation
measures can be applied. The same approach could be
applied to other odorant species of interest to produce
equivalent emissions data for subsequent use in air
dispersion modelling.
The uncertainty with this approach is the actual
concentration of the odorant in the specific gas stream, as
the odorant ratio quoted in Table 1 is based on a nominal
1mg m-3 compound concentration. The uncertainty can
be resolved by taking actual measurements of the odorant
species present in the specific gas stream, allowing the
more readily measured methane concentration to be used
as an indicator species. Such measurements did not form
part of this initial study.
Emission Source
Flank
In this study, no account is taken of the potential for the
cumulative effect on odour due to the presence of
different odorant species. It is believed that there will be
a compounding effect on the odour experienced by
receptors due to the presence of multiple odorant species
but such investigations were not part of this study.
Methane Mass Emission (mgm2 -1
s )
-1
3.2x10
-1
9.8x10
-2
1.9x10
-3
1.3x10
3
1.3x10
1.0x10
Daily cover (Sandy)
3.1x10
Temporary Cap (Sandy)
Restored (Capped)
6.0x10
4.0x10
Freely venting gas well*
Odorant Compound Mass
Emission Rate (mgm-2s-1)
(assumes 10mgm-3 in LFG)
4.0x10
-6
-6
-6
-7
Table 9: Calculated Mass Emission Rate for Methyl Mercaptan
24
-1
Emission
Rate
(gs-1)
-5
1
2
5x10
-5
5x10
3
5x10
4
5x10
5
6x10
6
5x10
7
1.5x10
-5
-5
-5
-5
-4
Source
Flank
Flank
Restored
Surface
Daily
Cover
1 x Open
Pipe
Flank
Restored
Surface
1 x Open
Pipe
Flank
Cover Material
Characteristics
Area
(m2)
Methyl Mercaptan
Flux Rate
(Area sources: mgs-1m2
, Point sources: mgs-1)
Temporary Cover
Temporary Cover
15,600
5,200
3.2x10
-6
9.6x10
-6
10
30
Grassed
154,000
1.3x10
-7
10
5,100
9.8x10
-6
10
-
6.5x10
-2
5
5,000
6.4x10
-6
20
-7
20
-1
10
-6
10
Daily Cover
Open Well-pipe
Temporary Cover
Grassed
108,000
2.6x10
-
1.3x10
Open Pipework
Temporary Cover
5000
3.2x10
Concentration (mg)
of Odorous
compound in 1m3
LFG
Table 10: Combinations of Typical Emission Sources (based on Mercaptans) and the Cumulative Emission Rates
methane concentrations near to these levels would
indicate the potential for an off-site odour event to arise.
It can be seen from the Table that to achieve the assumed
mass emission rate used in the modelling study that the
necessary surface areas are not significantly large and are
in fact typical of many sites. The inclusion of a single
venting gas well can be seen to be very significant, a
single well exceeding the assumed mass emission rate.
Increasing the concentration of the odorant in LFG
increases the odorant mass emission in direct proportion.
In reality emissions will be produced by a multiplicity of
sources, making it likely that a significant mass emission
will be produced, sufficient to create an odour event
under suitable conditions.
It should be noted that while odorant emissions from
grassed restored (clay capped) surfaces are included in
Table 10 for illustrative purposes, no odours were
detected. Methane emissions were measured but it
appears that the odorant compound(s) had been removed,
possibly by adsorption onto the humic or clay materials in
the soil. Using the empirical observations noted above,
no odour was detected at methane concentrations well
above 25ppm being emitted from the grassed restored
surface. Odours were however detected from ungrassed
areas of the same clay capped surface, suggesting that
emissions arose from cracks in the clay cap, which may
have allowed direct continuity with the underlying
wastes.
Empirical Observation
It became apparent during the fieldwork at the sites
involved in the study, that two distinct odours could be
detected. Further work associated these odours with
‘leachate’ and ‘LFG’ sources.
Based on field
measurements, an empirical relationship was quantified
between the detection of these odours and the measured
ambient concentration of methane at nose level:
•
Leachate Source
– 25ppm CH4
•
LFG Source
– 50 - 75 ppm CH4
8.4
Sources Monitored
Sources to be monitored were identified as a result of
initial site investigations and during the site boundary and
site walkover surveys.
The emissions monitoring
equipment imposed limitations regarding the areas where
monitoring could be satisfactorily and safely undertaken.
The flux tent required a relatively even ground surface
into which it was possible to trench the tent. Point
sources were required to be either covered by the flux
tent, such as a leachate well cover at ground level, or that
enabled a bag to be placed over the emission source, such
as open gas wells pipes.
These observed values were both repeatable for the same
source on the same site and reproducible for the same
type of source on different sites. The demarcation
between the odour not being detected and being detected
was clear-cut. The deduced numerical values were
confirmed by two different investigators, giving validity
to the objectivity of the observation. Future action would
be to identify the compounds associated with these
odours using field equipment.
The sources to be monitored at each site were classified
into area and point sources as follows:
•
Tipping Area
•
Restored
•
Daily Cover
•
Flank
•
Temporary
•
Leachate Well
Capping
•
Gas Well
•
Final/Permanent •
Open Pipe
Capping
When undertaking on-site methane emission surveys,
methane concentrations near to these limits could be used
as a direct indication of the pending onset of detectable
on-site odours. The same situation applies equally to
boundary and off-site surveys, where the measurement of
25
The results of the air dispersion modelling runs were
plotted using Surfer 8 and standardised so that the source
was located in the centre of 6 x 6km grid covering both
the site and the surrounding receptors. The modelling
grid was the finest possible using the model and
represented a 99X99 grid, which produces a grid spacing
of 60.6m. The axis labels have been simplified, thereby
replacing the ordinance survey standard reference system
and the x-y intercept is therefore not necessarily (0,0).
Linear sources, such as a leachate collection trench at the
toe of a flank, or open sources such as a leachate holding
lagoon were not considered as part of this study, due to
the measurement difficulties involved. Measurement of
emissions from such sources should be addressed in
future studies to determine the significance of these
sources.
8.5
Monitoring Programme
The odour dispersion plume is based upon an ODT of 3
x10-7 mg m-3, which corresponds to the lowest reported
value for methyl mercaptan (Table 1). Other values
reported for methyl mercaptan are orders of magnitude
greater. The lowest value was adopted to model the
greatest spatial extent of an odour plume arising from a
source. The next lowest ODT relates to propyl mercaptan
with an ODT of 2.5x10-6 mg m-3 a factor of 10 times
higher compared with methyl mercaptan. The ODT
values in Table 1 have been either validated or accepted
as best estimates by the respective authors of the reports.
Monitoring for odours took place between January 2002
and June 2002. Due to restrictions on site access and
safety, on-site monitoring occurred only during site
working hours. Where possible or practicable, off-site
surveys were conducted around the site and in the vicinity
of local sensitive receptors.
Initial site surveys were targeted on those days when
conditions were expected to favour odour events
occurring i.e. calm, still conditions. However, with the
winter and spring of 2002 being both wetter and more
windy than expected, the monitoring period was
prolonged to attempt to capture such conditions.
9.
Air Dispersion Modelling and
Results
9.1
Graphical Outputs
As indicated in 8.2.14, l any odorant compound can be
used as input data and the odour plume dispersion
modelled utilising the appropriate ODT for that
compound. The importance of the ODT is that it
represents the concentration of an odorant compound that
may produce an odour complaint. The specificity of the
odour compound becomes important when identifying
the odour source e.g. LFG, leachate, or other highly
odiferous wastes to enable appropriate design,
remediation or mitigation measures to be devised.
Air dispersion modelling requires a number of input
variables to be able to generate accurate outputs. The
principal inputs are meteorological parameters,
topographical data, source emission rates, source
definition and estimation of the surface roughness
coefficient. All of these factors have an effect on the
dispersion of odours derived from landfill sources.
For the purposes of this study, to produce a ‘worst case’
scenario, it was assumed that the odorant species was
methyl mercaptan, because of its low ODT and
potentially ‘high’ concentration in LFG compared with
other similar odorant species.
Still, calm or foggy meteorological conditions produce
the ideal conditions for off-site odour events to occur i.e.
no mixing or dilution of odours and sensitive receptors
more likely to experience an odour event. For the
purpose of this research the modelling runs were targeted
to replicate these ideal meteorological conditions i.e. low
wind speeds and from a direction most likely to impact
upon known sensitive receptors. ADMS can model a
minimum wind speed of 0.75 ms-1, and consequently the
ideal meteorological conditions most likely to produce
off-site odours could not be modelled. A minimum wind
speed of 0.8ms-1 was chosen to simulate the worst-case
conditions for an odour event to occur. Lower wind
speeds of approximately 0.4 ms-1 or less may result in
odour being detected at greater distances off-site than
were observed during this study. The limitations of the
model prevented this from being assessed.
In some instances the plotted odour dispersion plume
extends beyond the boundary of the chart, which is
particularly obvious at low wind speeds. It should be
noted that the charts have been plotted to demonstrate the
‘worst-case’ for an off-site odour event whilst balancing
the need for graphical clarity and continuity. As such
some of the plots extend beyond the designated
boundaries. This enables direct comparison of the plots,
demonstrating the magnitude of the effect of conditions
that are more turbulent and favourable to mixing and
therefore odour dilution.
The concentration contours (or extent of the odour
footprint) indicate the extent of the area that could
experience that concentration of odorant over the
specified time period. It does not mean that all of that
area will experience that concentration all of the time or
even at the same time. The average time period used in
this study for modelling odour was 15 minutes.
The terrain data was based on a 20km X 20km grid and
the grid spacing used for producing the modelling outputs
was a 64 X 64 grid, producing a grid spacing off about
300m. It is now possible to obtain 5km square terrain
data, which will enable a smaller grid spacing to be
obtained.
During this 15 minute period it is assumed that both the
odorant emission rate and the meteorological conditions
remain constant. Fluctuations in the meteorological data
are taken into account by using statistically derived
26
assumed emission value is considered a modest estimate,
that is not a worst-case value, that could apply to many
landfills taking putrescible wastes. The emission rate
equates to a total flank area of about 15,000m2 with
typical levels of cover and an assumed odorant flux rate
of 3.2x10-6 gm-2s-1. Depending on the particular site, the
actual emission rate could easily increase many-fold due
to the combination of the area of the emission source, the
flux rate and the odorant concentration in LFG. Site
specific measurements and data are needed to provide a
more accurate analysis for a given site.
fluctuations within the sampled meteorological data.
ADMS makes use of these data to simulate changes in
the meteorological conditions which will affect the
dispersion of odour and hence the extent of the odour
concentration footprint. The fluctuation periods modelled
were, 5, 2, and 1 minutes and 1 second. The fluctuations
component enables short-term events such as opening
either a leachate or gas well to be modelled, which may
result in more intense odour events occurring.
9.2
General Effects
Factors that have a general effect on air dispersion
modelling are:
•
Odorant emission rate
•
Wind speed
•
Surface roughness
•
Wind direction
•
Terrain
•
Fluctuations in the meteorological conditions
Wind Speed
The significant effect of wind speed on the dispersion of
odour from a source is clearly demonstrated in Figures
10-17. The model run in this instance does not take
account of any topographical interactions. It is clearly
visible that as wind speed increases, the amount of
dispersion also increases. This has the effect of
decreasing the area of the footprint that receptors would
be exposed to under these conditions. Based on a 3x107
mgm-3 ODT, the odour dispersion plume can be seen to
extend beyond the limits of the chart e.g. at 1ms-1, the
plume extends 10.3km from the source.
Odorant Emission Rate
For modelling purposes a fixed odorant emission rate of
5x10-5 gs-1 was assumed for all modelling runs. The
27
Figures 10 – 17: Wind speed variation
-1
o
-5
-1
Site P3; Surface Roughness: 0.3ms ; Wind Direction: 0 ; Emission Rate: 5x10 gs .
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
-1
2
3
5
4
6
-1
Figure 10: Wind Speed 1ms
Figure 11: Wind Speed 1.5ms
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
-1
2
3
5
4
6
-1
Figure 12: Wind Speed 2ms
Figure 13: Wind Speed 2.5ms
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
-1
2
3
5
4
6
-1
Figure 14: Wind Speed 3ms
Figure 15: Wind Speed 4ms
NB.: Axis in Km;
-7
-7
Footprint represents odour threshold values from literature: ___ 3x10 , _ _ 3x10
• Receptors
+ Source
28
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
-1
2
3
5
4
6
-1
Figure 16: Wind Speed 5ms
Figure 17: Wind Speed 6ms
NB.: Axis in Km;
-7
-7
Footprint represents odour threshold values from literature: ___ 3x10 , _ _ 3x10
• Receptors
+ Source
Surface Roughness
boundary layer also increases, leading to dilution of
odorous emissions through mixing with the moving air
stream. The result is that the odour footprint decreases in
size as the surface roughness increases.
Increasing the surface roughness has a similar effect to
increasing the wind speed (Figures 18-20). As the
roughness increases, turbulence in the atmospheric
Figures 18 – 20: Surface Roughness
o
-5
-1
Site P3; Wind Speed: 0.8m; Wind Direction: 0 ; Emission Rate: 5x10 gs .
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
1
6
Figure 18: Surface Roughness 0.3m
2
3
5
4
6
Figure 19: Surface Roughness 0.5m
NB.: Axis in Km;
-7
-7
Footprint represents odour threshold values from literature: ___ 3x10 , _ _ 3x10
• Receptors
+ Source
29
6
5
4
3
2
1
1
2
3
5
4
6
Figure 20: Surface Roughness 1.0m
NB.: Axis in Km;
-7
-7
Footprint represents odour threshold values from literature: ___ 3x10 , _ _ 3x10
• Receptors
+ Source
Wind Direction
not cause a greater degree of dispersion to occur, merely
that the odour dispersion plume will shift direction
accordingly to always be parallel to the direction.
Modelling the effect of wind direction on dispersion is of
little relevance without the inclusion of terrain. Figures
21-26 demonstrate that changing the wind direction will
Figures 21 – 26: Wind Direction without Terrain
-1
-5
-1
Site H1; Wind Speed 1.5ms ; Surface Roughness: 0.5m; Emission Rate: 5x10 gs .
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
0
2
3
5
4
6
0
Figure 21: Wind Direction 200
Figure 22: Wind Direction 210
NB.: Axis in Km;
-7
-7
Footprint represents odour threshold values from literature: ___ 3x10 , _ _ 3x10
• Receptors
+ Source
30
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
0
2
3
4
5
6
0
Figure 23: Wind Direction 220
Figure 24: Wind Direction 230
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
0
2
3
4
5
6
0
Figure 25: Wind Direction 240
Figure 26: Wind Direction 250
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
Fluctuations
minute fluctuation period shown on each Figure indicates
that the odour footprint is approximately 500m greater in
overall width than scenarios where fluctuations were not
taken into account. Modelling a fluctuation of 1 second
did not markedly increase the area of the odour footprint.
The effect of this will depend on the dispersion of
receptors around the site. In an urban area, the odour
plume with an increased width will inevitably expose a
greater number of receptors to an odour.
The effect of running the Fluctuations component of
ADMS (Figure 27), indicates that for these particular
conditions there was little difference between the outputs
for fluctuations of between 1 second, 1, 2 and 5 minutes.
The 1 and 2 minute fluctuations events are not indicated
on Figures 27, as a measure to maintain the simplicity
and clarity. The result of modelling the meteorological
fluctuations indicates that the 15 minute average
underestimates the area of potential odour impact. The 5
31
Figure 27: Fluctuations with Terrain
Site V2; Wind Speed 0.8ms-1; Surface Roughness: 0.5m; Emission Rate: 5x10-5 gs-1.
6
5
4
3
2
1
1
2
3
4
6
5
0
Figure 27: Wind Direction 200
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
____ No Fluctuation
_ _ _ 5min Fluctuation
…… 1sec Fluctuation
9.3
Location Specific Effects
combination of parameters, ADMS required a minimum
wind speed of 1.5ms-1 in order to successfully model
these conditions. In this instance the hill NW of the site
causes the airflow to divert to the SE to the extent that the
air mass is diverted almost perpendicular to the primary
wind direction (Figure 32). Figures 21-26 and 29-34 are
directly comparable as they represent the same
meteorological and surface roughness conditions, the
only difference being the inclusion of terrain data in the
latter set.
The inclusion of topographic data within the model and
its interaction with wind direction and wind speed has a
marked effect on the direction of odour dispersal.
The digital elevation model (DEM) used within the
model is shown in Figure 28, with a sample of the
resultant outputs demonstrated in Figures 29-34. These
Figures represent H1, the hill on a hill scenario, for the
5x10-5 gs-1 odorant emission rate. Due to the particular
32
Figures 28 – 34: Wind Direction and Terrain H1
-1
-5
-1
Site H1; Wind Speed 1.5ms ; Surface Roughness: 0.5m; Emission Rate: 5x10 gs .
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
1
6
2
3
4
5
6
Figure 29: DEM & Wind Direction 2000
Figure 28: DEM for H1
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
0
2
3
4
5
6
Figure 31: DEM & Wind Direction 2200
Figure 30: DEM & Wind Direction 210
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
0
2
3
4
5
6
Figure 33: DEM & Wind Direction 2400
Figure 32: DEM & Wind Direction 230
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
33
6
5
4
3
2
1
2
1
3
5
4
6
Figure 34: DEM & Wind Direction 2500
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
The hill in a valley scenario V2 produces a comparable set
of results. The impact of terrain on the movement of air
and the dispersion of odour around V2 is clearly affected
by the local terrain. The 5x10-5 gs-1 odorant emission rate
was modelled for a surface roughness of 0.5 with a wind
speed of 0.8ms-1 and a varied wind direction. Figures 35
and 39 represent the DEM for V2, with the results shown
in Figures 36-38 and 40-42. The latter Figures provide a
clearer understanding of the air movement over the
locality. Figures 36 and 37 indicate that the air is
channelled through the narrowing of two hills to the E of
the site and into the lower ground beyond. Figure 35
indicates that approximately 1km SE of the source there
is also a slight low point on the hillcrest. Figure 42
suggests that a NW wind will target directly for this low
point and into the valley beyond. The results shown in
the Figures may be interpreted as the air mass moving
along the path of least resistance, following the line of
least change in terrain.
Figures 35 – 42: Wind Direction and Terrain V2
-1
-5
-1
Site V2; Wind Speed 0.8ms ; Surface Roughness: 0.5m; Emission Rate: 5x10 gs .
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
5
6
1
2
3
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
32
4
5
6
Figure 36: DEM & Wind Direction 2500
Figure 35: DEM for V2
6
6
5
5
4
4
3
3
2
2
1
1
1
2
3
4
6
5
1
0
2
3
4
6
5
0
Figure 37: DEM & Wind Direction 260
Figure 38: DEM & Wind Direction 300
Figure 39: 3D DEM for V2
Figure 40: 3D DEM & Wind Direction 2500
Figure 41: 3D DEM & Wind Direction 2600
Figure 42: 3D DEM & Wind Direction 3000
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
1.5ms-1 (Figure 44), the odour footprint is deflected
considerably to almost 90o from the original wind
direction. As the wind speed increases further (Figures
45-48) the odour footprint progressively realigns to the
original wind direction. Whilst this example is specific to
this site, the results are indicative of the complex and
diverse interactions between wind speed, direction and
the underlying terrain that can arise
As discussed previously (9.2.3) odour dispersal is also a
function of the wind speed. The interaction between the
topographical features and wind speed are indicated in
Figures 43-48, with the wind direction of 230o, surface
roughness of 0.5 and an odorant emission rate of 5x10-5
gs-1 maintained constant. In the Figures the wind speed
varies from 1 to 6 ms-1. For site H1, the particular site
characteristics result in almost no odour leaving the site at
a wind speed of 1ms-1. As the wind speed increases to
35
.
Figures 43 – 48: Wind Speed and Terrain H1
o
-5
-1
Site H1; Wind Direction 230 ; Surface Roughness: 0.5m; Emission Rate: 5x10 gs .
Figure 43: DEM & Wind Speed 1.0ms-1
Figure 44: DEM & Wind Speed 1.5ms-1
Figure 45: DEM & Wind Speed 2.0ms-1
Figure 46: DEM & Wind Speed 2.5ms-1
Figure 47: DEM & Wind Speed 4.0ms-1
Figure 48: DEM & Wind Speed 6.0ms-1
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
speed is increased from 0.8 ms-1 to 2ms-1, the odour
footprint increases in area, reaching an area increasingly
distant from the source. However, at a wind speed of
approximately 2.5ms-1, the odour footprint reaches its
furthest extent and then retreats towards the source as the
wind speed continues to increase
A duplicate study to H1 was undertaken for site V2 to
assess the location specific interaction between wind
speed and terrain. The scenarios are a derivative of those
defined in 9.2.6. For a particular wind direction, the wind
speed was progressively increased from 0.8ms-1 to 6ms-1
(Figures 49-60). The Figures indicate that as the wind
.
36
Figures 49 – 60: Wind Direction, Wind Speed and Terrain V2
-5
-1
Site V2; Surface Roughness: 0.5m; Emission Rate: 5x10 gs .
Figure 49: DEM, Wind Direction 250o &
Wind Speed 1.0ms-1
Figure 50: DEM, Wind Direction 260o &
Wind Speed 1.0ms-1
Figure 51: DEM, Wind Direction 300o &
Wind Speed 1.0ms-1
Figure 52: DEM, Wind Direction 250o &
Wind Speed 1.5ms-1
Figure 53: DEM, Wind Direction 260o &
Wind Speed 1.5ms-1
Figure 54: DEM, Wind Direction 300o &
Wind Speed 1.5ms-1
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
37
Figure 55: DEM, Wind Direction 250o &
Wind Speed 2.0ms-1
Figure 56: DEM, Wind Direction 260o &
Wind Speed 2.0ms-1
Figure 57: DEM, Wind Direction 300o &
Wind Speed 2.0ms-1
Figure 58: DEM, Wind Direction 250o &
Wind Speed 2.5ms-1
Figure 59: DEM, Wind Direction 250o &
Wind Speed 4.0ms-1
Figure 60: DEM, Wind Direction 250o &
Wind Speed 6.0ms-1
NB.: Axis in Km;
-7
Footprint represents odour threshold values from literature: ___ 3x10
• Receptors
+ Source
38
9.4
Site Specific Interactions
At V2 the presence of the ridge to the N of the site
prevents the prevailing SW wind creating odours impacts
in the populated area just to the N of the ridge. At low
wind speeds the air mass is diverted SE down the valley,
while at higher wind speeds increased turbulence ensures
that by the time the SW air mass reaches the populated
area that sufficient dilution has taken place to prevent the
ODT being achieved.
Sites P3, H1 and V2 were chosen to represent three types
of topographic location to provide a generic set of data
able to be used for landfills with similar terrain. The
results presented in 9.3 reflect the general impacts due to
the interaction between terrain and wind direction.
For sites P3, H1 and V2, Figures 10, 32, and 49 represent
the ‘worst-case’ scenarios to create an off-site odour
event i.e. the wind direction and wind speed were
manipulated to deliberately target the receptors.
9.5
Probability of Odour Events
Risk assessment involves the identification of pathways
that link sources and receptors. The modelling work has
identified a number of site based odour sources and their
subsequent impact on sensitive receptors via airflow
across the site. The worst conditions to produce an offsite odour event were modelled i.e. a low wind speed
event in the direction of receptors.
Due to the lack of topographic features within the
landscape around site P3, the odour dispersion plume is
dominated by the wind direction and not by any
topographic effects associated with air mass deflection.
Figures 10-17 clearly demonstrate this. Even at low wind
speeds there is no apparent deflection of the air caused by
a N wind. By running various permutations on and about
the site, no abnormal variations could be achieved.
However, the worst-case conditions modelled account
only for a proportion of the overall meteorological
conditions experienced at and around the site. Figures 61
to 63 summarise the annual meteorological data upon
which the three generic landfill-type models were based.
The wind rose represents the proportion of time that the
wind blows from a given direction at a particular wind
speed over a period of a year at a fixed location.
Further confirmation of the importance of terrain is
clearly evident when comparing Figures 21-26 and 29-34
for site H1. Site H1 is complex in terms of its
geographical position on the crest of a hill that forms the
interface between the coastal plain and the inland hills.
Under the conditions modelled and shown in the Figures,
the site is fortunate not to have receptors in close
proximity located in the area affected by the diversion of
the SW air mass due to the interaction of terrain and wind
direction i.e. to the SE of the site.
In all three instances, the predominant wind direction, as
to be expected for the UK, was between a S and W
direction, with these directions contributing the strongest
wind speeds.
39
Wind Rose - Frequency Distribution
P3, 2001
N
3.54
6.34
2.81
11.25
2.15
2.23
3.24
W
11.68
0.02
4.57
E
4.53
9.05
5.84
7.58
6.32
8.20
10.54
S
Calms included at center.
Rings drawn at 5% intervals.
Wind flow is FROM the directions shown.
0.10% of observations were missing.
0.1 1
2
3
4
6
Wind Speed ( Meters Per Second)
PERCENT OCCURRENCE: Wind Speed ( Meters Per Second) PERCENT OCCURRENCE: Wind Speed ( Meters Per Second)
LOWER BOUND OF CATEGORY
LOWER BOUND OF CATEGORY
DIR
0.1
1
2
3
4
6
0.1
1
2
3
4
6
DIR
N 0.28 0.73 0.63 0.44 0.43 0.30
S 0.26 0.93 0.89 1.63 2.90 1.58
NNE 0.30 0.58 0.52 0.30 0.19 0.26
SSW 0.20 0.81 1.05 1.18 1.58 1.49
NE 0.19 0.33 0.47 0.41 0.67 0.16
SW 0.31 0.71 1.09 1.15 2.05 2.28
ENE 0.16 0.50 0.59 0.61 0.88 0.50
WSW 0.17 0.90 0.96 1.27 1.89 3.86
E 0.31 0.71 1.30 0.93 1.14 0.18
W 0.25 0.85 1.33 1.64 3.07 4.53
ESE 0.33 0.82 1.30 1.04 0.80 0.25
WNW 0.30 1.07 1.87 1.75 3.48 2.78
SE 0.28 1.21 1.15 1.14 1.26 0.80
NW 0.18 1.40 1.51 1.68 1.04 0.52
SSE 0.28 0.81 1.29 1.65 3.70 2.81
NNW 0.20 0.75 1.05 0.75 0.55 0.24
TOTAL OBS = 8784 MISSING OBS = 9
CALM OBS = 2 PERCENT CALM = 0.02
Figure 61: Annual Wind Rose, Site P3, 2001.
40
Wind Rose - Frequency Distribution
V2, 1997
N
4.43
5.82
4.45
2.41
5.76
10.08
2.64
W
4.68
3.01
6.61
5.27
E
1.52
1.07
2.84
11.50
9.78
17.02
S
Calms included at center.
Rings drawn at 5% intervals.
Wind flow is FROM the directions shown.
1.10% of observations were missing.
0.1 1
2
3
4
6
Wind Speed ( Meters Per Second)
PERCENT OCCURRENCE: Wind Speed ( Meters Per Second) PERCENT OCCURRENCE: Wind Speed ( Meters Per Second)
LOWER BOUND OF CATEGORY
LOWER BOUND OF CATEGORY
DIR
DIR
0.1
1
2
3
4
6
0.1
1
2
3
4
6
N 1.23 0.68 1.52 1.13 0.86 0.40
S 2.12 1.53 2.26 1.75 1.66 0.47
NNE 0.73 0.34 0.88 1.11 1.11 0.29
SSW 2.71 1.90 3.95 3.50 3.17 1.79
NE 0.43 0.22 0.75 1.10 1.96 1.30
SW 0.89 0.97 2.01 2.12 2.98 2.52
ENE 1.02 0.94 1.93 1.85 2.67 1.68
WSW 0.50 0.51 1.12 1.19 1.05 0.90
E 1.21 1.11 1.53 1.47 1.00 0.29
W 0.56 0.29 0.78 0.71 1.20 1.15
ESE 0.47 0.14 0.39 0.42 0.10 0.00
WNW 0.47 0.25 0.45 0.43 0.51 0.53
SE 0.19 0.13 0.33 0.23 0.16 0.03
NW 0.45 0.16 0.62 0.35 0.43 0.40
SSE 0.30 0.26 0.98 0.68 0.53 0.09
NNW 0.46 0.48 1.12 1.07 0.99 0.31
TOTAL OBS = 8760 MISSING OBS = 96
CALM OBS = 264 PERCENT CALM = 3.01
Figure 62: Annual Wind Rose, Site V2, 1997
41
Wind Rose - Frequency Distribution
H1, 1999
N
6.03
4.63
3.25
4.99
4.21
8.78
2.96
W
11.67
7.63
3.50
E
1.15
2.10
10.92
3.34
6.00
10.22
8.28
S
Calms included at center.
Rings drawn at 5% intervals.
Wind flow is FROM the directions shown.
0.39% of observations were missing.
0.1 1
2
3
4
6
Wind Speed ( Meters Per Second)
PERCENT OCCURRENCE: Wind Speed ( Meters Per Second) PERCENT OCCURRENCE: Wind Speed ( Meters Per Second)
LOWER BOUND OF CATEGORY
LOWER BOUND OF CATEGORY
DIR
DIR
0.1
1
2
3
4
6
0.1
1
2
3
4
6
N 1.74 0.30 0.83 0.97 1.37 0.82
S 0.42 0.34 0.98 1.48 2.73 2.32
NNE 0.58 0.11 0.32 0.62 0.99 0.63
SSW 0.25 0.31 0.59 0.82 1.46 2.57
NE 0.59 0.22 0.55 0.67 1.34 0.84
SW 0.45 0.26 0.80 1.04 3.45 4.22
ENE 0.23 0.13 0.47 0.63 0.86 0.65
WSW 0.48 0.45 1.16 1.68 3.78 3.38
E 0.48 0.25 0.68 0.66 0.99 0.43
W 1.27 0.55 1.43 1.93 3.64 2.85
ESE 0.16 0.11 0.18 0.34 0.27 0.08
WNW 0.92 0.30 0.98 1.60 2.45 2.52
SE 0.29 0.19 0.40 0.34 0.54 0.34
NW 1.50 0.32 0.70 0.83 1.26 0.39
SSE 0.33 0.27 0.59 0.89 0.84 0.41
NNW 1.90 0.37 0.68 0.51 0.59 0.58
TOTAL OBS = 8760 MISSING OBS = 34
CALM OBS = 668 PERCENT CALM = 7.63
Figure 63: Annual Wind Rose, Site H1, 1999
42
The occurrence of an off-site odour event is primarily a
function of the number and location of sources coupled
with a significant emission rate. Without a source, an
odour event will not arise from landfill activities.
For the remaining 8.5% of the year, the wind direction
will be towards the receptors but will not necessarily
cause an odour event to be experienced. Figure 15
suggests that a wind of 4ms-1 from 25o would not impact
a receptor. Figure 17 shows that a northerly wind of 6ms1
will be close to a receptor but will not actually cause
exposure to odour. A wind from the NNW would,
however, potentially have an impact on the same
receptor. The result of this is that the proportion of the
overall of time that wind speed and direction favour an
odour event decreases to 7.5% of the year.
Event specific parameters such as wind speed and wind
direction impact the effectiveness of the pathway between
the source and the receptor. An odour event will impact
receptors only if suitable conditions exist. If the direction
of the wind is not towards receptors, or if the wind speed
is either too great or too little, there will be no impact
upon the receptors. It is not possible to define what these
conditions are in a generic manner, as each site will have
different characteristics.
Results from the odour questionnaire suggest that odour
events occur largely between early morning and late
evening i.e. between 0600 and 2200, spanning the normal
operation time of the site. Outside of these hours, most
receptors are likely to be asleep, a less receptive state than
when awake. On a pro-rata basis, this further decreases
the proportion of the year for which favourable
meteorological conditions exist to 5.3%.
The distance between source and receptor is a crucial
factor. So too is the terrain within which the site is
located. The characteristics of a site located on an
estuarine or coastal plain have been shown to be
considerably different from a site located on a hill or
within a valley. It is however possible to undertake a
broad assessment of the probability of an odour event to
occur based upon evaluation of the meteorological data
(Appendix 4).
Of the 5.3% of the year when wind conditions favour
odour events, an odour source is also required to be
present. It may be that no activities are present on site
during these favourable wind conditions resulting in no
off-site odour events occurring. Realistically, a site is
likely to have a number of fugitive emissions that occur
during all favourable wind events, the result of which
would be odour events occurring up to a maximum of
5.3% of the year, or once every 20 days on average.
Figures 61 to 63 include a tabular presentation of the
proportion of hourly average wind events that occur for
specific wind directions and speeds. Using this data it is
possible to predict the time occurrence of meteorological
conditions that will impact upon receptors.
For example, the only receptors surrounding site P3 are
located between approximately 155o and 205o (SSE to
SSW) of the site (Figure 10). As such, a wind from
between 25o and 335o clockwise (NNE to NNW) would
not target any of the receptors. Including calm days,
where wind speeds are less than
0.1 ms-1, wind
between NNE and NNW accounts for 91.5% of the year.
Applying the same approach to site H1 and V2, the results
obtained are shown in Table 11.
Site
Controlling
Factor
P3 (%)
Wind
Direction
Wind Speed
8.5
H1(%)
58.3
7.5
5.3
V2 (%)
55.9
37.7
26.7
50.6
35.8
Receptor
Availability
Table 11: Cumulative Effect of Combined Controlling Factors on Percentage Exposure to Odours
43
emission rate is a conservative estimate compared with
the mass emission that could emanate from the sites
included within this study. The 5x10-5 gs-1 emission rate
is equivalent to a cell flank of 160m2 covered with
temporary cover material, a concentration of methyl
mercaptan of 1 mg m-3 in LFG and an odorant flux rate of
3.2x10-4 mgm-2s-1. As the total mass emission rate from
the site was modelled and not the number of sources,
there are numerous permutations that could produce the
same emission rate, examples of which are provided in
Table 10.
Rain has a scrubbing effect on odours, further reducing
the 5.3% proportion the year that odour may have an
impact on receptors. From the meteorological data it was
not possible to quantify the proportion of favourable wind
events that combine with rain scrubbing.
Other
antecedent conditions will also impact emission rates
from landfill surfaces. These include periods of ground
freezing or following prolonged periods of rainfall.
The above analysis assumes that the receptor location is
fixed i.e. a residential property, school etc. If however
the occupant of a residence walked around the site
perimeter, for example walking a dog, they would be
likely to experience odours a larger proportion of the time
than predicted by the above analysis.
Determining a representative odorant mass emission rate
to a high degree of accuracy is both difficult and
inappropriate due to the heterogeneous nature of landfill
surfaces. In view of the variation in emission rates and
reported ODT values, it is perhaps more appropriate to
report and compare results based on their order of
magnitude.
While the previous sections have detailed the probability
of favourable meteorological conditions which can
produce odour events, it should be the aim of all site
operators to at least minimise, or at best remove, all odour
sources.
9.6
As shown in Figures 10 to 12 and others, the odour
footprint can extend a considerable distance from the
source, in some cases up to 10km. The question therefore
arises as to why odour complaints are not reported at this
distance from landfill sites. A number of possible
answers could be responsible.
Summary and Conclusions
Modelling outputs are only as accurate as the defined
parameters, the input data and the complexity and
technical veracity of the mathematical model. The more
accurate the model and the input data, the more accurate
the results and for this reason, ADMS 3.1 was selected.
Firstly, human perception of odour is not homogeneous
within a population. Even if a population had a sense of
smell that was normally distributed, 2% of the population
would have an acutely poor sense and would be able to
detect significantly less than others. As such, not all of
the population exposed may detect, let alone recognise
the odour.
The modelling clearly indicated that those parameters
which increase atmospheric mixing are crucial in the
dispersion of off-site odours. Wind speed and surface
roughness both effect dispersion. At some sites a critical
wind speed could be determined which limited the
maximum extent of odour dispersion. At site V2 this was
approximately 2.5ms-1 while at H1, there is no such
critical wind speed, with the extent of odour dispersion
decreasing as the wind speed increased.
Secondly, the assumed ODT of 3x10-7mgm-3 used for
methyl mercaptan may be too low, leading to an increase
in the lateral extent of the odour footprint. The AIHA
study reports the next detection threshold ODT for
methyl mercaptan as being 103 higher i.e. 10-4mgm-3.
Despite this reported difference in values, the ODT of
3x10-7mgm-3 has been awarded an A-rating based on the
olfactory measurement methodology. Work undertaken
by AEA also supports an ODT of between 10-6 to 107
mgm-3.
An understanding of the local and regional topographic
features and their influence upon the regional wind flow
patterns enables an understanding of site specific
characteristics to be determined.
This is clearly
demonstrated at Site H1 where the odour dispersion
footprint is diverted through 90o from the original wind
direction. No single factor evaluated had a dominant
control on the dispersion of odours from a site.
Figures 7 to 10 show the effect of assuming an ODT of
3x10-6mgm-3. As expected the extent of the odour
footprint at this higher ODT is considerably less than for
the ODT i.e. the odour plume extends approximately 2km
from the source compared to 10km for an ODT of 3x107
mgm-3.
While terrain and wind direction affect the direction of
the odour dispersion plume, wind speed and surface
roughness affect the spatial extent of dispersion by
influencing the mixing of odour releases with the air mass
flowing over the site. In addition to these interactions,
there also exists a relationship between terrain and wind
speed. Figures 4 to 7 show how the wind speed increases
over crests and through valleys whilst decreasing over
shallow gradients, influencing mixing and leading to
subsequent interactions with surface roughness.
Thirdly, there may be an odour concentration level that
complainants regard as a nuisance rather than offensive or
obnoxious and therefore do not complain. This is
supported by the results of the odour questionnaire.
There is also the possibility that other off-site odour
sources may intervene and dominate the landfill-derived
odour.
A constant odorant mass emission rate of 5x10-5 gs-1 was
modelled throughout the different scenarios. This
Section 9.5 details the probability of conditions favouring
odour events, based on average hourly meteorological
44
A summary of the above guidance can be expressed in
the form of a simple risk assessment matrix. The matrix
identifies the key contributory factors, with ranking of the
factors based on a qualitative assessment. Table 12
below outlines an odour risk assessment for sites with
increasing levels of risk.
data. The probability defines the maximum likelihood of
a static receptor experiencing odour events. Note that the
probability of an event could be applied in many different
ways. For example, a probability of 5.3% may apply
equally across each individual day i.e. a total of 60
minutes exposure to an odour event occurring each day of
the year, or two 30 minute exposure periods each day
etc., or a two hour event every second day or part thereof
etc.
10.3 IPPC, BAT and Odour
The implementation of the IPPC Directive and its
application to the landfill sector in the UK with the
enactment of the PPC Act 1998 and the ensuing PPC
Regulations, brings increased requirements for the
permitting of a landfill. Under IPPC a number of aspects
additional to those covered previously under the Waste
Management Licensing regime are regulated, including
noise, vibration, energy use and odours. Additionally the
concept of BAT (Best Available Techniques) applied to
landfill activities requires measures to be taken to
prevent, or where not practicable, to reduce emissions to
air and water.
10. Management System Tool
10.1 Introduction
A key objective of this study was to produce a
management tool for landfill designers and site managers
to assist them with site selection, design and odour
reduction and management.
The design and operational management of landfill sites
is controlled and regulated by various legislative and
regulatory instruments (see Section 2). A number of
landfill design and operational good practice codes exist,
within which key design and operational aspects are
identified that should be applied to landfill activities. The
recognition of these key factors highlighted in the
guidance is to ensure the protection of the environment
and human health and includes amenity aspects such as
litter, dust and odour control.
The Guidance Document S5.02 for the Landfill Sector
provides an indication of those aspects requiring
compliance with BAT. S2.3.9 deals specifically with
odour, while S2.3.3, S2.3.7 and S2.3.8 deal with odours
indirectly via landfill gas, point source and fugitive
emissions to air.
The key aspects of the IPPC guidance relate to:
While the key factors relevant to odour reduction and
control may already be known, the relative importance or
impact of these factors on reducing odour emissions and
assisting odour control has not been prioritised.
•
Types of, location and characteristics of
sensitive receptors
•
Characterisation of odorous
deposited/disposed and generated
10.2 Odour Control Guidance
•
Types of odour release sources
Waste Management Papers 26B and 27 identify the
guidelines and practice that needs to be considered and
addressed in the design and operation of a landfill facility.
The regulatory requirements to be considered at the
design stage and the need for a risk assessment of the
potential for odours to be produced by the proposed
landfill development will help minimise odour production
and the potential for off-site odour events to occur.
•
Structured odour management plan covering:
o
Prevention
o
Control
o
Monitoring
o
Emergency actions
o
Communication arrangements
substances
A summary of potential odour control techniques that can
be used to assist demonstrating compliance with BAT is
presented in Table 13. The list is not meant to be
exhaustive but identifies a range of options to help
prevent and control odours produced by landfill activities.
Activities likely to produce odour begins with delivery of
waste to site, compaction and placement, covering,
capping and restoration and pollution control systems.
In addition to design and operational factors, the guidance
identifies the need to include associated factors such as
the recording of weather and climate data and emphasises
the need for routine monitoring and the recording of any
odour complaints. Appendix 1 gives further details of the
regulatory guidance on odour
The guidance adopts an holistic approach to minimising
odour impacts. Beginning with the initial site design/site
selection stage, an assessment of the potential impacts
follows and continues through to the operational stages of
waste reception and placement, installation of the gas
management system and the capping and restoration of
completed sites. At all stages appropriate techniques and
practices can be adopted to minimise and control odorous
emissions.
45
Table 12: Odour Risk Assessment Matrix
Risk Assessment Factors
Risk
Level
Terrain & Location
•
HIGH
•
•
•
LOW
MODERATE
•
•
Site located up gradient of or
raised above sensitive
receptors
Substantial residential
development within close
proximity of the disposal area
Weather
•
Receptors downwind
of site
•
Interaction of wind
direction and terrain
impacting on
receptors
Sensitive receptors e.g.
schools, hospitals, OAP
homes, recreational, say 250m
•
Receptors located in a valley or
depression adjacent to a site
•
Some sensitive receptors or
residential development within
say 500m of the site
•
Other development present
within 1km
•
Flat terrain
•
Surrounding woodlands and
hedges
•
Few residential receptors
within say 1000m
•
•
•
•
High rainfall.
Receptors mainly
upwind of the site
Waste Types
•
•
•
Large working areas.
•
Spray recirculation of leachate.
•
Large exposed flanks with poor cover.
•
•
Multiple emission sources combine to
create an additive effect
Uncovered storage of young
odorous leachates.
•
•
Poor levels of daily cover
Delivery of odorous wastes
by open vehicle
•
Open leachate chambers
Discharge of odorous
leachates to sewer through
residential areas.
•
No/poor gas abstraction system
•
Leachate methane stripping
exhaust vented to air.
•
Capping programme out of sequence with
installation of gas management
infrastructure
•
Frequent excavations into waste
•
Reduced size of working area.
•
Storage of mature leachate
•
Limited areas of exposed flanks.
•
•
Moderate cell depth/ surface area.
Covered storage tanks with
filtered venting
•
Other odour sources nearby.
•
•
Adequate daily cover
Methane stripping exhaust
vented through bio-filter
•
Limited numbers of open leachate
chambers
•
Gas abstraction system installed
•
Capping programme in line with extension
of gas system
•
No storage of leachates
Wastes likely to react with
leachate e.g. sulphate-based
wastes etc.
•
Domestic and occasional
inputs of specific odorous
wastes indicated above
Moderate rainfall
All receptors upwind
of the site
No wind/terrain
interactions
Leachate Management
Inputs of highly odorous
wastes such as sewage
sludge/ screenings,
food/animal wastes,
paint/chemical wastes,
solvents etc.
•
No significant
interactions between
wind direction and
terrain
Site Operations
•
Largely inert wastes
•
Small working area.
•
Limited quantities of
commercial and industrial
wastes
•
Very limited areas of cell flanks
•
Good levels of temporary and daily cover
•
Gas well spacing based on field
measurements of collection effectiveness
•
Leachate wells under abstraction
•
Several adjacent odour sources.
Low rainfall
46
Table 13: Odour Control: Design and Operational Management Options
Control Aspect
Control Mechanism
Applications
Comments
Site location
Locate site remote from
receptors
•
All sites likely to accept putrescible or odorous
wastes
•
•
Identified at the initial site selection stage of project development
Practically, site selection will need to balance a variety of competing factors
Waste delivery
routing
Route delivery vehicles to
avoid residential and other
sensitive receptors
•
Delivery route arranged to minimise contact with
receptors
Ensure vehicles properly sheeted/covered,
especially if carrying odorous wastes
Avoid delivery of highly odorous wastes when
wind directions adverse
•
•
•
•
Determined at the site selection or planning application stage
Reduces extent of exposure of receptors to the odour source
Limits the magnitude of the odour source term
Odour impact dependent on wind direction, so avoid deliveries when wind directions
likely to impact large numbers of receptors
Wastes bulked up or stored over weekends,
especially during summer for delivery to site
Full containers/skips left on site over weekends
etc.
•
Commencement of waste degradation before disposal produces offensive odours
during delivery to site
Degraded wastes are more odorous than usual and special handling required during
disposal
Wastes with highly offensive odours e.g.
seafood, animal by products etc.
Wastes that may subsequently react to produce
offensive odours e.g. sulphate bearing
Wastes with odours that cannot be contained by
sheeting/covering
•
•
•
Reduces highly odorous sources
Minimises odour exposure during delivery
Highly effective if pre-treatment used
•
•
Stored putrescible
wastes
Prohibition of specific
wastes
Putrescible wastes delivered
from transfer stations/Bank
Holiday periods
•
Prohibit highly odorous
wastes streams unless
suitably pre-treated to
reduce odour
•
•
•
•
•
Placement and
Compaction.
Reduction of odour emission
surface area and reduced
waste porosity
•
•
Working face/area
Cell flanks
•
•
•
Normal good operational practice.
Increased waste density and daily cover reduces the odour emission rate
Simple to achieve
Waste cover
Reduces emission rate via
waste surface and increases
opportunity for bio-filtering
action
•
Adequate depth of daily cover over all
operational areas
Depth of cover maintained over time on
temporary ‘capped’ areas
Type of daily/temporary cover material
important
•
•
Thickness of cover correlates with reduced odour emissions
Sandy and clay cover soils not as effective as loamy-type soils, due to difficulties of
placement
Ability to place and retain cover thickness over time important e.g. rain wash,
placement on cell flanks, movement etc.
Whole site.
Essential part of site operational plan
•
•
•
•
Size of operational
cells.
Odorous waste
disposal
Water balance approach to
prevent imbalance between
odorous acetogenic
leachates and establishment
of methanogenic conditions
Disposal of odorous wastes
in poor (wind) dispersal
conditions.
•
•
•
•
Select disposal area remote from sensitive
receptors
Deep trench and cover immediately with nonodorous wastes
47
•
•
Reduced production of odorous gases at source.
To be used concomitantly with phased capping and installation of gas control
infrastructure
Good practice
•
•
•
•
•
Can be used when adverse wind directions apply if the exposure time is limited
Relatively simple to apply
Effective
Low cost.
Requires careful management.
Control Aspect
Control Mechanism
Applications
Undertaken only when wind
direction suitable and for the
minimum exposure time for
excavated wastes
Avoid odours from deposits
of litter picking/road
sweepings
•
•
Reduced extent of
active working area
Reduces odour emission
source area.
Limit extent of
uncapped areas on
non-operational parts
of the site.
Limiting slope of and
extent of cell flanks.
Excavation into
previously deposited
wastes.
Site housekeeping.
Comments
•
•
Difficult to prevent significant short-term odour releases from decomposed wastes
and landfill gas
Requires careful pre-planning and management
All site areas.
•
•
•
•
Primarily for aesthetic purposes but creates improved perception of operations
Minimal effect on odour emissions
Simple.
Low cost
•
Tipping area.
•
•
•
•
Minimisation of a prime odour source.
Reduced requirement for daily cover
Simple in theory but requires careful management
Difficult to achieve on sites with a wide range of inputs requiring separate disposal
areas
Reduces available area for
uncontrolled gas emissions.
•
All areas with intermediate or temporary cover,
particularly cell flanks.
•
•
•
•
Essential to coordinate with installation of gas control infrastructure
Very effective in reducing LFG emissions
Necessary for the control of site water balance
Requires careful planning to obtain materials when needed
Flank area and slope both
reduced to allow adequate
placement of cover
materials
•
Essential to reduce the extent of a key odour
source
Retro fit difficult to apply
Planned at Working Plan stage
•
Important to plan cell operation and phasing to ensure maximum flank slope of 1: 3
with short length and width
Adequate cover thickness necessary to cope with movement of flank with waste
settlement
Necessary to maintain adequate levels of cover over time
•
•
Installation/repair of landfill gas and leachate
infrastructure
•
•
Odorant
counteractants
Use of odour masking,
neutralising or suppressant
agents
•
•
•
Active working area
Site boundary adjacent to receptors
Specific odorous site activities e.g. leachate
storage tanks or aeration lagoons
•
•
•
Effectiveness not guaranteed
Spray can produce odour complaints
Public concern over the use of sprays potentially masking the presence of harmful
compounds
Landfill gas control
Abstraction of landfill gas
and the destruction of
odorous and potentially
harmful trace compounds
present in landfill gas
•
Installation of gas abstraction wells and
collection pipework infrastructure
Destruction of methane and trace compounds
via gas flare or use as a fuel in a gas engine
powered generator set
•
•
Applicable to all sites producing landfill gas
Operation of the control system is required to ensure adequate environmental
performance, rather than meeting solely the commercial needs of any generation
plant
Gas collection system requires routine balancing to ensure adequate performance
across the site
Whole site, operational
areas and pollution
treatment area.
•
Landfill design requirement for collection
systems
Leachate chambers should be sealed and
under abstraction for gas
Leachate stored for treatment stored in closed
tanks
Aeration lagoons located away from receptors
•
Leachate
management
•
•
•
•
•
•
•
•
•
48
Acetogenic leachates are highly odorous and must be properly managed to avoid
acting as an odour source
Good working practice to cover chambers and place under abstraction
Storage of leachate prior to removal off-site may require chemical dosing to maintain
oxygen levels
Storage tanks require venting during filling and exhaust gas should be passed via a
bio-filter
Aeration of leachate in lagoons can release absorbed odorant gases, producing an
intermittent odour release
Control Aspect
Pollution control
equipment
maintenance
Control Mechanism
All sites with pollution
control plant and equipment
Applications
•
•
•
Engineered capping
layer
Restoration soils
Odour monitoring
Site Diary
Weather station
Comments
Gas flare, engine exhaust, storage tank vents,
lagoon aerators etc.
Maintaining sealing of gas/leachate boreholes
seals as the landfill settles
Maintaining integrity of any onsite pipework due
to settlement of damage by site plant
•
Areas of the site filled to final level
•
•
•
•
Surface containment of
completed cells to keep out
water and keep in odorous
gases
•
Filtration of any gases
passing through a soil
supporting active plant
growth will be attenuated by
chemical/biological means
All sites and all areas of the
site, including any odour
controls and pollution control
infrastructure
•
Necessary on all sites with an engineered clay
capping layer to prevent damage to the cap
•
Soil medium above any cracks/damage to the capping layer which may allow
odorous gases to exit will help to attenuate odour compounds
•
•
Site and boundary walk around
Use of FID to identify potential emission
sources
Identified odour emission sources rectified
Use of specialist equipment to measure
odorous gas concentrations
•
Good practice to continually monitor and measure the performance of odour control
methods
Use of equipment to quantify odour release rates/odour type useful for identifying
possible sources
Simple to undertake and raises awareness of issues
Consultation and liaison with public e.g. via Liaison Committee, is a useful means of
assessing odour impacts and helping to deal with (possibly) unforeseen odour
release sources
•
•
All site activities noted on daily basis
To include sub-contractor activities
•
•
Site specific wind speed and direction, rainfall
and pressure data
•
Record of site activities
Record of local
meteorological data
•
•
•
•
•
•
•
•
•
Communications
Electrical/mechanical items require regular and routine maintenance and calibration
to operate efficiently
Odour emission checks on gas flares and engine exhausts should be undertaken on
a regular basis
Monitoring for fugitive emissions from defective valves and seals, blocked pipework
reducing abstraction efficiency etc. all part of routine maintenance
Consultation with site
operatives and the Public
•
•
•
•
All site operatives and contractors
Local residents
•
49
Achieves a significant reduction in a potential emission source
Capping must be installed to high standard to prevent cracking of the clay cap or
defects in synthetic capping material allowing emission of landfill gas
If gas control or leachate recirculation pipework is installed beneath the capping
layer, remedial works must ensure the continuing integrity of the re-installed cap
Record of all site activities, routine and non-routine that can subsequently be used to
determine if any specific activity lead to an odour complaint
Include all sub-contractor activities involved in potential odour-release activities e.g.
installation of gas wells and pipework, modifications to leachate wells, gas system
monitoring, placement of final capping layer etc.
Provides the ability to assess what weather conditions prevailed at the time of an
odour complaint
Provides data for helping to benchmark future air dispersion modelling studies
Can be used to provide data to assist with atmospheric pressure effects on gas
emissions studies etc.
Raises awareness amongst site operatives of the potential impact of their activities
Routine and regular liaison with the public to learn of their concerns e.g. Site Liaison
committee
A site Open Day would be one means of engaging the public and raising their
awareness of the operational constraints facing landfill operators
10.4 Mitigation Options -- General
that due account is taken of the interactions between terrain
and wind direction and the proximity of potential
receptors.
The items listed in 10.2 –10.3 above can be categorised
into pre-operational and operational stages. The following
considerations should be taken into account and assessed
at each stage of the proposed landfill development and
planning process:
The landform profile, its height and the phasing sequence
of the filling programme needs to be taken into account, to
minimise the effects of wind movement over the landfill
producing enhanced emission rates from odour sources
e.g. the aerofoil effect creating low pressures over landfill
surfaces, enhancing the emission of LFG and odorant
compounds through the porous surface.
Development and initial design stage:
•
initial site selection and location of potential
receptors
•
interactions between terrain and wind direction
and potential effects on receptors
•
site layout, landform profile and phasing of
filling and capping to determine the potential to
create emission sources and their proximity to
receptors
•
location of gas management plant e.g. gas flares
and gas engine exhausts to take account of
potential odour impacts
The location of pollution prevention and treatment
infrastructure, such as landfill gas flares and leachate
lagoons and holding tanks and their construction and
planned operation are also key issues to consider at the
design stage. Combustion plumes from flares or exhausts
may not be as offensive as raw landfill gas but an odour
may still be produced that is deemed objectionable by a
receptor. Interactions with the landform, terrain and
structures on site will all impact on the odour footprint.
Planning and Environmental Impact Assessment
Stage
Planning and environmental impact assessment stage:
•
formal environmental impact assessment of the
selected landfill design and the proposed method
of working and phasing
•
effect of proposed landfill operations to be
assessed for the potential impact on receptors
e.g. size of working area, area of exposed flanks,
capping sequence and timings etc.
•
air dispersion modelling and environmental risk
assessment of odour impacts to confirm design
basis
The preliminary work undertaken at the site selection and
initial design stage should produce a site location and a
landfill facility with minimal potential to create significant
odour impacts. The need for the facility as required under
planning, may dictate the preferred location of potential
sites. However, planning aspects do not necessarily take
account of air dispersion impacts and a balance may need
to be struck between the various planning considerations
of visual, traffic, proximity to ecological sites etc. and the
potential for odour impacts.
The final design can be refined as the formal
environmental impact assessment process is applied and
the detail of potential odour impacts is assessed. Changes
to the phasing sequence and the capping programme can
be assessed to minimise their impacts on odour emissions.
For example, LFG freely-venting over a large area and
dispersing with no odour impact can be focussed to
become a high mass emission rate line or point odour
source, by the placement of a low permeability cap.
Subsequent delays installing the planned gas control
system in that area can lead to increased emissions creating
an odour event.
Operational stage
•
use of acknowledged good operational practices
that reduce site smells and odour impacts
•
account taken during landfilling operations of
the effects of weather conditions on odour
impacts
•
routine monitoring activity to include factual
and interpretative data and reports on odours
Development and Initial Design Stage
The selection of the proposed development site will have
the greatest impact on the potential to create odour events
at receptors. For example, selection of a site with no
receptors within a say 1km, is likely to lead to fewer, if
any, complaints compared to a site with numerous
receptors within several hundred metres.
The operational aspects of the timing of capping and the
installation of gas management infrastructure outlined
above are important practical considerations and can have
significant short-term adverse effects on odour emissions.
The effect of changes to the programmed sequence should
be assessed to determine the magnitude of potential odour
impacts on receptors.
The chances of identifying such an ideal site are likely to
be small. Realistically receptors will be much closer to
potential development sites and it is therefore important
It is at this stage that the final air dispersion modelling of
the proposed development can be undertaken to assess the
cumulative effects of landfill operations, gas flare and
50
A site Open Day may be considered as one mechanism to
promote greater openness between the site and the public
and to raise public awareness of the varied range of
activities that take place on an operational landfill site.
engine exhausts, phasing and capping programmes and
location of pollution control infrastructure.
The extent to which measures are taken to prevent,
minimise or mitigate potential odour impacts will be
determined in accordance with BAT. While every
endeavour should be made to reduce odour impacts, the
cost implications of such measures are also a material
consideration when determining the final design.
The application of BAT is also applicable to the
Operations stage and the combination of technology and
techniques to reduce odour effects will also be metered by
the cost implications.
Expenditure of money on
inappropriate measures does not serve any useful purpose
and careful examination of the cause of the problem and
identification of the best solution, or approach, to be
adopted should be undertaken.
Operational Stage
The use of acknowledged and accepted good operational
practices that help prevent and reduce site smells and
odour impacts is an essential aspect of any odour control
programme. Practices and techniques that can assist with
odour control are listed in Table 13.
10.5 Mitigation Options – Specific
Drawing on the general options referred to above in
Section 10.4, specific recommendations for minimising
odour releases during site operations are listed in Table 14.
The recommendations are based on the findings of the
modelling study and general landfill site experience.
Whilst odour control involves a combination of
approaches and no single technique is sufficient, these
options are considered to have the greatest significance on
reducing odour emissions.
Any site activity likely to produce odours should take
account of the effects of weather conditions i.e. wind speed
and wind direction, producing an odour impact on
sensitive receptors.
A site weather station recording appropriate
meteorological data will provide reference data to
determine whether an odour complaint is likely to relate to
the site.
External factors such as the site location, location of
receptors and the surrounding terrain are all extremely
important but cannot be altered for existing operational
sites. There are a limited number of mitigation options
which can be applied to existing sites, such as increasing
the roughness of the adjacent terrain by planting tree bands
or by forming earth bunds or placing fences in strategic
locations.
Keeping a comprehensive site diary at all times, recording
all site activities irrespective of whether or not there is an
apparent impact on odour production, will provide the site
operator with information to determine which site activity
might have been the cause of a reported odour event.
An effective odour-control monitoring programme should
involve routine monitoring activities, which will include
factual and interpretative data, reports on odour emissions,
odour measurements, additional air dispersion modelling
studies etc.
Attention should be paid to all odour complaints, to
identify the source of the odour emission and remedial
actions implemented as appropriate.
A public
communications programme, including establishing a Site
Liaison committee, should be maintained to ensure that a
suitable forum for public comments is made available.
51
terrain and wind direction and the proximity of potential
receptors.
10.6 Mitigation Options -- General
The landform profile, its height and the phasing sequence
of the filling programme needs to be taken into account,
to minimise the effects of wind movement over the
landfill producing enhanced emission rates from odour
sources e.g. the aerofoil effect creating low pressures over
landfill surfaces, enhancing the emission of LFG and
odorant compounds through the porous surface.
The items listed in 10.2 –10.3 above can be categorised
into pre-operational and operational stages.
The
following considerations should be taken into account and
assessed at each stage of the proposed landfill
development and planning process:
Development and initial design stage:
•
initial site selection and location of potential
receptors
•
interactions between terrain and wind direction
and potential effects on receptors
•
site layout, landform profile and phasing of
filling and capping to determine the potential to
create emission sources and their proximity to
receptors
•
location of gas management plant e.g. gas flares
and gas engine exhausts to take account of
potential odour impacts
The location of pollution prevention and treatment
infrastructure, such as landfill gas flares and leachate
lagoons and holding tanks and their construction and
planned operation are also key issues to consider at the
design stage. Combustion plumes from flares or exhausts
may not be as offensive as raw landfill gas but an odour
may still be produced that is deemed objectionable by a
receptor. Interactions with the landform, terrain and
structures on site will all impact on the odour footprint.
Planning and Environmental Impact Assessment
Stage
The preliminary work undertaken at the site selection and
initial design stage should produce a site location and a
landfill facility with minimal potential to create significant
odour impacts. The need for the facility as required under
planning, may dictate the preferred location of potential
sites. However, planning aspects do not necessarily take
account of air dispersion impacts and a balance may need
to be struck between the various planning considerations
of visual, traffic, proximity to ecological sites etc. and the
potential for odour impacts.
Planning and environmental impact assessment stage:
•
formal environmental impact assessment of the
selected landfill design and the proposed
method of working and phasing
•
effect of proposed landfill operations to be
assessed for the potential impact on receptors
e.g. size of working area, area of exposed
flanks, capping sequence and timings etc.
•
air dispersion modelling and environmental risk
assessment of odour impacts to confirm design
basis
The final design can be refined as the formal
environmental impact assessment process is applied and
the detail of potential odour impacts is assessed. Changes
to the phasing sequence and the capping programme can
be assessed to minimise their impacts on odour emissions.
For example, LFG freely-venting over a large area and
dispersing with no odour impact can be focussed to
become a high mass emission rate line or point odour
source, by the placement of a low permeability cap.
Subsequent delays installing the planned gas control
system in that area can lead to increased emissions
creating an odour event.
Operational stage
•
use of acknowledged good operational practices
that reduce site smells and odour impacts
•
account taken during landfilling operations of
the effects of weather conditions on odour
impacts
•
routine monitoring activity to include factual
and interpretative data and reports on odours
The operational aspects of the timing of capping and the
installation of gas management infrastructure outlined
above are important practical considerations and can have
significant short-term adverse effects on odour emissions.
The effect of changes to the programmed sequence should
be assessed to determine the magnitude of potential odour
impacts on receptors.
Development and Initial Design Stage
The selection of the proposed development site will have
the greatest impact on the potential to create odour events
at receptors. For example, selection of a site with no
receptors within a say 1km, is likely to lead to fewer, if
any, complaints compared to a site with numerous
receptors within several hundred metres.
It is at this stage that the final air dispersion modelling of
the proposed development can be undertaken to assess the
cumulative effects of landfill operations, gas flare and
engine exhausts, phasing and capping programmes and
location of pollution control infrastructure.
The chances of identifying such an ideal site are likely to
be small. Realistically receptors will be much closer to
potential development sites and it is therefore important
that due account is taken of the interactions between
52
A site Open Day may be considered as one mechanism to
promote greater openness between the site and the public
and to raise public awareness of the varied range of
activities that take place on an operational landfill site.
The extent to which measures are taken to prevent,
minimise or mitigate potential odour impacts will be
determined in accordance with BAT. While every
endeavour should be made to reduce odour impacts, the
cost implications of such measures are also a material
consideration when determining the final design.
The application of BAT is also applicable to the
Operations stage and the combination of technology and
techniques to reduce odour effects will also be metered by
the cost implications.
Expenditure of money on
inappropriate measures does not serve any useful purpose
and careful examination of the cause of the problem and
identification of the best solution, or approach, to be
adopted should be undertaken.
Operational Stage
The use of acknowledged and accepted good operational
practices that help prevent and reduce site smells and
odour impacts is an essential aspect of any odour control
programme. Practices and techniques that can assist with
odour control are listed in Table 13.
10.7 Mitigation Options – Specific
Any site activity likely to produce odours should take
account of the effects of weather conditions i.e. wind
speed and wind direction, producing an odour impact on
sensitive receptors.
Drawing on the general options referred to above in
Section 10.4, specific recommendations for minimising
odour releases during site operations are listed in Table
14. The recommendations are based on the findings of
the modelling study and general landfill site experience.
Whilst odour control involves a combination of
approaches and no single technique is sufficient, these
options are considered to have the greatest significance on
reducing odour emissions.
A site weather station recording appropriate
meteorological data will provide reference data to
determine whether an odour complaint is likely to relate
to the site.
Keeping a comprehensive site diary at all times, recording
all site activities irrespective of whether or not there is an
apparent impact on odour production, will provide the site
operator with information to determine which site activity
might have been the cause of a reported odour event.
External factors such as the site location, location of
receptors and the surrounding terrain are all extremely
important but cannot be altered for existing operational
sites. There are a limited number of mitigation options
which can be applied to existing sites, such as increasing
the roughness of the adjacent terrain by planting tree
bands or by forming earth bunds or placing fences in
strategic locations.
An effective odour-control monitoring programme should
involve routine monitoring activities, which will include
factual and interpretative data, reports on odour
emissions, odour measurements, additional air dispersion
modelling studies etc.
Attention should be paid to all odour complaints, to
identify the source of the odour emission and remedial
actions implemented as appropriate.
A public
communications programme, including establishing a Site
Liaison committee, should be maintained to ensure that a
suitable forum for public comments is made available.
53
Table 14: Specific Operational Options to Reduce Odour Impacts
Number
Option
Effect
Comments
1
Minimise uncapped
operational area
Reduces the area available
for odour emissions
Odorant emission rates are greatest for surfaces
in operational areas
2
Minimise uncapped final
level areas
Reduces the area available
for odour emissions
Odorant emission rates are greater for surfaces
without a low permeability cap
Minimise size of flanks
Reduces the area available
for odour emissions
Flanks have a high emission rate factor and can
represent a large surface area
4
Minimise slope of flanks to
<1:3
Improved daily cover and
compaction
Steep slopes cannot be properly compacted and
covered with adequate depths of soil, enabling an
easy pathway for LFG emissions.
5
Alter waste deliver route and
improve transport method
Reduces a potential source
of odour complaints prior to
disposal at site
Transport of odorous wastes to site in an
inappropriate manner can sensitise receptors
along the route before placement on site.
6
Cease taking certain highly
odorous wastes
Removes the source of
odour
The apparent financial value of some waste
streams should be judged against the longer-term
amenity issues involved with odour complaints.
Removes odour source
7
Place all leachate
chambers, wells etc. under
active gas abstraction
Well and chamber covers do not form gas-tight
seals and odours will escape. Abstraction under
low pressures will provide a positive means of
capturing odorous compounds and enable
disposal by a safe route i.e. flaring or engine fuel.
Increased density of gas
abstraction wells
Increased chance of
reducing fugitive LFG
emissions
Inter-well spacing determines the collection
efficiency of a gas well system, ensuring that the
waste mass between gas wells is a under
negative pressure at all times.
Determine the effective
capture area of gas wells
Measure the effectiveness
of the LFG well collection
system
Individual gas wells will have specific capture
volumes, dependent on well depth and diameter,
well pipe perforation size and extent, waste type,
waste density, leachate levels, abstraction
pressure, collection pipework size etc.
Monitor the effectiveness of
gas abstraction wells and
the abstraction system
Ensures the continued
performance of the gas
management system
The effectiveness of a gas collection system
varies with time and requires routine monitoring of
key parameters to confirm its continued collection
efficiency.
Ensure gas engine exhausts
are vertical and as high as
feasible
Ensures adequate
dispersion
Combusted LFG can still produce odorous
compounds and maximum dispersion is achieved
by increasing the exhaust height and orientation
Use only shrouded gas
flares
Ensures effective
destruction of odorous
compounds
Similar comments as engine exhausts on
dispersion and important to achieve adequate
odour destruction by maintaining time and
temperature.
Ensure gas is adequately
dewatered before entering
the gas flare
Prevents dispersal of an
odorous substance
Leachate condensate contains dissolved odorous
compounds, which if passed through the flare will
release the odorous compounds without
necessarily achieving the destruction
temperature.
Locate gas engines and gas
flares away from receptors
Removes a source of odour
Location remote from potential receptors removes
a potential odour source.
Leachate storage vessels to
be fully contained
Contains an odour source
15
Young, acidic leachates contain odorous VFAs,
which require full containment to prevent odour
release.
Dosing of leachate stored
for long periods
Removes an odour source
16
Leachates required to be stored should be dosed
with hydrogen peroxide to prevent anoxic
conditions and reduce odours.
Removes an odour source
17
Dosing of leachate if
discharged to sewer without
pre-treatment
As with storage of young leachates, disposal to
sewer without pre-treatment is likely to lead to the
release of dissolved odorous compounds within
the sewer and escape enroute via manhole
covers and vent pipes etc.
Siting of leachate aeration
lagoons
Removes an odour source
As with the siting of gas engine plants
Undertake known highly
odorous activities according
to wind direction (when
possible)
Prevents an odour impact
on sensitive receptors
Unavoidable odorous site activities should only be
undertaken when appropriate weather conditions
prevail e.g. wind direction away from receptors
and wind speed high, to promote mixing and
dilution.
3
8
9
10
11
12
13
14
18
19
54
10.8 Further Work
The objective of the study was to produce guidance on
odour control for site managers by identifying the key
parameters associated with odour and prioritising the
effectiveness of existing odour control techniques and
practices. Six landfill sites with different waste inputs and
geographic locations within England were selected for the
study
Suggestions for further work build on the results of the
study and encompass a number of different aspects.
The establishment of a database of emission rates for
various types of landfill surface and other emission
sources, including leachate aeration lagoons, leachate
surface drains etc. would provide quantitative data to
identify the significance of emission sources, enabling the
prioritisation of resources
11.2
The perception of odour and its measurement is a
complex issue, due to variations in human olfactory
acuity. While taking account of both qualitative and
quantitative factors, the commonly used method of odour
measurement based on OU is time consuming and costly.
An alternative approach is adopted based on measuring
the concentration of the odorant compound at the ODT.
Identification and direct measurement of odorous
compound concentrations in the field is now possible
using portable equipment. Determination of the specific
odorant at a location combined with emission rate data
would provide source term data to enable accurate air
dispersion modelling. Based on the ODT for the odorant
the likely extent of odour events could be more accurately
evaluated. Knowledge of the specific odorant would
assist with the selection of odour suppressant or masking
sprays.
A benefit of the chemical concentration approach is that it
allows a wide range of sensitivities to be modelled, both
in terms of source term emission rates, emission source
areas and the concentration of the odorant in the source
LFG or leachate.
The effect of landform design and phasing on the
potential for off-site odour events should be modelled and
assessed, to help prevent odour events by designing out
specific landform and phasing arrangements that could
lead to off-site odours
A key aspect of investigating odour complaints is to
obtain suitable data from receptors, to enable the
differentiation between real and perceived odour events
and to identify whether there were other contributory
sources to the odour event
Establishing the effectiveness of gas management systems
by simple direct measurement would identify underperforming areas of the gas control system that would
benefit from the application of appropriate remedial
measures. Areas that would benefit particularly from
such testing are cell wall flanks, areas known to be a
source of high odorant emission rates
The finding that the public do not always report odour
events suggests that odour may be a long term chronic
problem with an acceptable persistent low level of odour
and higher levels of odour leading to complaints
11.3 Landfill Odour Sources and Measurement
of Emissions
11. Conclusions
11.1
Odour, Measurement and Complaints Data
All aspects of landfill -- from the delivery of waste, the
type of waste and its placement, the installation of
pollution control infrastructure for LFG and leachate
management and restoration excavation, through to the
operation of pollution control plant, especially LFG flares
and gas engines – are potential sources of odour.
Study Background
The management of landfill odours is an increasingly
significant aspect of landfill operations and management
that is of concern to both the public and regulatory
authorities and waste management companies. Concerns
relate to both loss of amenity and the potential for health
impacts
The maintenance of both accurate site activity records and
detailed complaints records needs to be improved, to
enable these records to be of value when investigating
odour complaints.
Recent odour related studies carried out under the Landfill
Tax Credit Scheme have focussed on examining odour
creation, odour sampling and measurement, identifying
odour constituents and developing cost effective means of
monitoring odorous constituent by chemical finger
printing.
Each site should maintain a weather station logging wind
speed, wind direction, precipitation and relative humidity
to provide site specific metereological data for the
investigation of odour complaints or air dispersion
modelling studies.
To identify and assess management techniques for
controlling odour risk at potential receptors, a study was
initiated comprising the comparison of historic complaints
and site operations records; the field measurement of
methane emission rates (as a proxy for odorous
emissions) from landfill sources; collecting data on
public perceptions of odour; and extensive air dispersion
modelling using the data gained from the preceding tasks
Measurement of odour emission rates can be undertaken
indirectly, using methane as the measured parameter and
relating the odorant emission rate to its composition in
LFG. This approach is useful for sensitivity studies to
model air dispersion scenarios.
55
the location of significant emission sources such as LFG
flares, power generation plant and the effect of changes to
the phasing of site filling operations.
Direct measurement of odorant emission rates at a
specific site is recommended and should be used
wherever practicable for accurate estimation.
The field measurement data for methane emissions was in
accordance with other reported data and confirmed the
suitability of the measurement methods used. The
emissions values determined for the different landfill
surfaces showed the potentially significant impact arising
from uncapped surfaces, especially cell wall flanks.
11.5 Management Options
Considerable guidance exists on managing landfill
operations to minimise odour events. Based on the results
of the air dispersion studies, the impact of emission source
can be identified and then prioritised, to ensure that
appropriate prevention/minimisation/mitigation/remedial
measures are applied
11.4 Air Dispersion Modelling
The movement of an air mass across a surface will
capture odour emissions arising from the surface and
disperse the odour across the surrounding terrain with the
air mass. The modelling of air dispersion can be
undertaken to take account of both micro and macro-scale
topography and terrain effects, as required for odour
dispersion from landfill sites.
Mitigation measures to limit the extent of the off-site
odour footprint are based on two key aspects, reducing the
odour emission rate and reducing the extent/size of the
emission source. In practice this can be achieved in a
number of different ways, such as; by increasing the
depth of cover material; and/or changing the type of
cover material on landfill surfaces; abstracting odorous
compounds by connecting all chambers and wells to the
active gas management system; capping open areas with
a low permeability layer; introducing features that
increase the surface roughness of the terrain such as
bunds, hedges and solid fences to promote the dilution of
odorous air flows
The effect of surface roughness and wind speed on
dispersion can be deduced, with increases in both factors
reducing the size of the downwind odour footprint. The
adjacent terrain has a significant effect on odour
dispersion from a site.
The interaction of terrain and wind direction can produce
significant changes in the odour dispersion of a site,
leading to specific impacts due to the site location. Use of
air dispersion modelling at the site selection stage can
reduce the subsequent potential for odour impacts.
Constant awareness of the implications of poor site
practices leading to the creation of odour events is needed
to ensure that such actions do not lead to problems e.g.
open excavations in waste left for long periods; deposited
waste left uncovered; large areas of uncapped waste with
only daily cover, especially flanks; uncapped newly
installed gas wells; uncovered leachate chambers etc.
Dispersion modelling can be applied equally to emissions
from areal, line and point sources, providing a
management tool to help assess the impact of changes in
56
12. References
AEA Technology, 1994, Odour Measurement and
Control – An Update. (Eds. Woodfield, M and Hall D)
LFG Literature References:
AEA Technology, 1997, Guidance on the Emissions
from Different Types of Landfill Gas Flares, AEA
Technology, Report No. CWM 142/96A
AEA Technology, 1996, The Composition and
Environmental Impact of Household Waste
Derived Landfill Gas, Second Report, CWM
041/88
AEA, 1994, A Report on Investigations of the Sources
of Odour Near Blue Circle Industries Westbury Site,
AEA Technology, Report No. AEA/CS/18325045/013,
1994
AEA Technology, 1997, Guidance on the
Emissions from Different Types of Landfill Gas
Flares, AEA Technology, Report No. CWM
142/96A
American, Industrial Hygiene Association, 1997,
Odour Thresholds for Chemicals with Established
Occupational Health Standards’, AIHA Press, ISBN 0932627-34-X
AEA, 1994, A Report on Investigations of the
Sources of Odour Near Blue Circle Industries
Westbury Site, AEA Technology, Report No.
AEA/CS/18325045/013, 1994
Bond, P, Sellwood, D and Roberts, D, 2000,
Monitoring Methane Emissions from Landfill Covers,
Waste 2000, Warwick
Allen, M.A., Braithwaite, A. and Hills, C.C,
1997, Trace Organic Compounds in Landfill Gas
at Seven UK Waste Disposal Sites, ,
Environmental Science & Technology, (1997)
31,pp 1054-61.
Environment Agency, IPPC General Guidance on
Odour
Allen, M.R., Braithwaite, A. and Hills, C.C,
1996, Analysis of the trace volatile organic
compounds in landfill gas using automated
thermal desorption gas chromatography-mass
spectrophotometry, Intern. J. Environ. Anal.
Chem.,1996, 62, pp 43-52.
Environment Agency, 2001, IPPC S5.02, Guidance
for the Landfill Sector Version 3a
Environment Agency, 2001a, Interim Technical
Guidance for Best Practice Flaring of Landfill Gas,
September 2001
Assmuth, T. and Kalevi, K, 1992, Concentrations
and Toxicological Significance of trace Organic
Compounds in Municipal Solid Waste Landfill
Gas, Chemosphere, 1992, 24, pp 1207-1216.
Environment Agency, 2001c, Technical Guidance on
the management of Landfill Gas
Environment Agency, 2002, R&D Project (Proposal
No 1E(02)20)
Baldwin, G. and Scott, P.E, 1991, Investigations
into Performance of landfill gas flaring systems in
the UK, Proceedings Sardinia 91, 3rd International
Landfill Symposium.
Environment Agency, August 1999, Library of
Licence Conditions and Working Plan Specifications –
Vol. 1: Waste Management Licences, Edition 2, 2
August 1999
Bridges, O. and Bridges, J.W, Comparisons of
Risks from Landfill and Incinerators of Municipal
Solid Waste, University of Surrey.
Environment Agency, July 2001, Internal Guidance
for the Regulation of Odour at Waste Management
Facilities under Waste Management Licensing
Regulations, Version 2.3, Draft for External
Consultation,
Brookes, B.I. And Young, P.J, 1983, The
development of sampling and gas
chromatography~mass spectrophotometry
analytical procedures to identify and determine the
minor organic components of landfill gas, Talanta
(1983) 30: 665-676.
Environment Agency, Scottish Environmental
Protection Agency, NI Service for the Environment
and Heritage, Odour assessment and Control Guidance for regulators and industry
Brosseau, J, and Heitz, M, 1994, Trace gas
compound emissions from municipal landfill
sanitary sites, Atmospheric Environment,1994, 28,
pp 285-293.
Eventure Ltd.: Research at University of Hull into
odour creation and dispersal around landfills
Cernushi, S. and Giuiano, M, 1989, Assessment
techniques for landfill gas emission and
dispersion, Sardinia 89, 2nd International Landfill
Symposium.
57
Science of the Total Environment, 127, pp 201210.
Crouch, E.A.C., Green, L.C. and Zemba, S.G,
1990, Estimation of Risk from landfill gas
emissions, GRCDA 11th International Symposium
on Landfill Gas, Lincolnshire, Illinois, 1990
Colin MacDonald C, 1994, A Report on the
Investigations of the Sources of odour Near Blue
Circle Industries' Westbury Site, August 1994.
Eklund, B. et al, 1998, Characterisation of
Landfill Gas Composition at the Fresh Kills
municipal solid waste landfill,. Environmental
Science & Technology, 1998, 32, pp 2233-2237.
Peterson, T.N, Human Health Risk Assessment of
Landfill Gas Emissions. Peterson, T.N.
ENTEC, 1997, Investigation into odour problems
at Nant-y-Gwyddon Landfill, South East Wales.
Final Report to the Environment Agency Welsh
Region SE Area Environmental Protection.
Report No.97194
Rettenberger G. and Stegmann, 1991, Trace
Elements in Landfill Gas, Sardinia 91 3rd
International Landfill Symposium
Schweigfofler, M. and Niessner, R, 1999,
Determination of siloxanes and VOC in landfill
gas and sewage gas by canister sampling and
GC~MS / AES analysis, Environ. Sci. Technol.,
1999, 33, pp 3680-3685.
ENTEC, 1999, Investigations into Odour
Problems at Trecatti Landfill, South East Wales:
Final Report
ENTEC , 2000, Investigations into Odour
Problems at Nant-y-Gywddon Landfill, South East
Wales: Final Report
Waste Management Paper 26, HMSO, 199?
Young, J.P. and Parker, A, 1980, Waste
Management and Research, 1980, The
Identification and Possible Environmental Impact
of Trace Gases and Vapours in Landfill Gas,
Young, J.P. and Parker, A, pp 213-226.
ETSU, Research and Development of Landfill Gas
Abstraction and Utilisation Equipment ~
Condensate Analysis and Equipment Corrosion:
Volume 3 ~ Site Descriptions and Results, ETSU
B/LF/00150/REP/3
Young, P.J. and Heasman, L.A, 199?, An assessment
of the odour and toxicity of the trace components of
landfill gas, GRCDA 8th International Symposium on
Landfill Gas, San Antonio, Texas.
Goldberg, M.S. et al, 1993, Incidence of Cancer
among Persons Living near a Municipal Solid
Waste Landfill Site in Montreal, Quebec, Archive
of Environmental Health, Nov / Dec (1993), 50,pp
416-424.
TG Trust Ltd. 2000A: Analysis of Neighbourliness
of Landfill Operations
Hoather, H.A. and Wright, P.A, 1989, Landfill
gas: site licensing and risk assessment, Proc.
Dept. Energy Int. Conf. On Landfill Gas and
Anaerobic Digestion of Solid Waste, Chester, UK.
Oct 88.
TG Trust Ltd. 2001B: Evaluation of
sampling/measurement methods for trace gas
constituents at concentrations experienced in odour
episodes and preparation of guidance manual
TG Trust Ltd. 2001C: Research most efficient,
reliable and cost effective methods of monitoring
landfill odours in ambient air - to ascertain best
methods for chemically fingerprinting gaseous
emissions from landfill sites
Klemans, W. et al, 1995, Cytogenetic
biomonitoring of a population of children
allegedly exposed to environmental pollutants.
Phase 2: Results of a three year longitudinal study,
Mutation Research (1995) 342: 147-156.
TG Trust Ltd. 2001D: Research the characteristics of
odour contributing constituents in landfill leachate
development of pre-treatment and full treatment
methods for reducing odour
Lakhanisky, T. et al, 1993, Cytogenetic
monitoring of a village population potentially
exposed to a low level of environmental
pollutants. Phase 1: SCE analysis, Mutation
Research (1993) 319, pp 317-323.
TG Trust Ltd. 2001E: Guidance Manual for Landfill
Managers on the Assessment and Control of Landfill
Odours.
Loizidou, M. and Kapetanios, E.G, 1992, Study
on the gaseous Emissions from a landfill, The
58
1
Appendix 1: Regulatory Guidance on Odour and Odour Control
1.1.1
The key guidance document for landfill construction and operations is Waste
Management Papers 26B (Landfill Design, Construction and Operational
Practice) Volumes 1 and 2. Waste Management Paper 27 is presently being
revised and should be issued later in 2002. Interestingly the (current) 1991
version does not have any references to odours, focussing more on monitoring
and control gas measures. This suggests that at that time odours associated
with landfill gas were not deemed to be a major issue.
1.1.2
Within Waste Management Papers 26B the following references relate
directly/indirectly to the production of odours and their environmental impact
and to ways of providing and maintaining satisfactory odour control:
WMP
Section
No. 26B
Landfill Design,
Construction and
Operational
Practice
Vol. 1
Comments
Part 2: Principles &
Approach to
Landfill Design
3.27-3.34
Risk Assessment
3.35-3.55
Design Objectives
Identifies the source-pathway-receptor concept for
investigating a quantifiable impact arising from landfilling.
Primary focus on water pollution and landfill gas migration
(engineered containment) with reference to noise, dust, litter
and visual impacts. No specific reference to odours.
Specifies as a key objective environmental protection,
determined and evaluated by the risk assessment stage
above.
3.46 Table 3.3 identifies the interrelationship between design
and operations for some operational aspects. Gas control
referred to.
6.64-6.78
Landfill Gas
Management
Part 3:
Operation
Section 6.64 refers to one of the primary objectives of a landfill
gas management system being ‘to minimise …beyond the
perimeter of the site ..that the risk of ….. odours…..are
eliminated as far as possible’.
Landfill
8.19
Stipulates that the Site Manual should include inter alia,,
The Site Manual
‘environmental monitoring data including factual
interpretative data and reports for …. odours ….’.
8.22-8.26
8.23 identifies the effect of winds on the efficiency of landfill
operations, including ‘‘prevailing winds and seasonality
taken into account
when designing the sequence and
Weather and
and
Climate Data
direction of tipping so as to minimise the detrimental effects of
odour … on local communities’
8.24 requires that ‘the wind pattern be taken into account
when locating gas vents and combustion exhausts to
avoid exposure of local residents to emissions and potential
odours.’
8.25 suggests that the installation of a simple weather station
be considered.
8.54-8.57
Statutory Nuisance
8.54 states that local authorities are obliged inspect their
areas for nuisance under the Environmental Protection Act
1990 (Part III, s79) and to investigate odour complaints.
8.55-8.56 allows the local authority to serve an Abatement
Notice to the operator, of which failure to comply with is an
offence.
8.57 allows any aggrieved individual to lodge a complaint with
the Magistrates Court. If the Court believes that a Statutory
nuisance exists or is likely to be a recurring event, it can also
issue an Abatement Notice and levy a fine.
No. 26B
Vol. 2
Part 3:
Operation
9.93-9.96
Odours
Landfill
9.93 identifies sources of offensive odours, which includes the
wastes disposed, leachate and leachate treatment systems
odour counteractants and landfill gas.
9.94 states that good landfill practices will greatly reduce
general site smells and reduce impact form odours that could
lead to complaints. Good practice includes:
•
Adequate compaction
•
Speedy disposal and burial of malodorous wastes
•
Effective use of appropriate types of daily cover
•
Progressive capping and restoration
•
Effective landfill gas management
•
Effective leachate management
•
Use of covered trenches for liquid waste disposal
•
Rapid burial of excavated waste
•
Consideration of prevailing wind direction when
planning leachate treatment plants, gas flares and
direction of tipping
9.95 suggests that odour counteractants may themselves be
an offensive odour source
9.96 acknowledges that the quantification of the
environmental impact of odours is difficult and that odour
control should be incorporated into performance monitoring
systems by maintaining complaints records and actions taken
in response.
9.159-9.161
Problems
arising
from landfill gas
9.162-9.163
Trace components
in landfill gas
9.159 categorises potential problems arising from landfill gas
and includes both risks to human health and odour.
9.162 refers to the presence of trace components in landfill
gas that are responsible for unpleasant odours and that some
may represent a health hazard. Odours from landfill gas differ
to those from leachate, which has higher concentrations of
carboxylic acids than landfill gas.
9.163 indicates that dilution in the air above the site is
significant and most compounds present at significant
concentrations at source are usually diluted to below the
toxicity threshold.
9.164
Landfill gas odours
9.168
Objective of landfill
gas management
systems
10.2-10.3
Objectives of the
capping system
9.164 states that odours can cause considerable nuisance as
insufficient dilution to below the odour threshold may not
occur under some weather conditions.
9.168 states that one of the objectives of a gas management
system is to prevent unacceptable risk to human health,
detriment to the environment or nuisance.
10.2 refers to one objective of the capping system as being to
prevent uncontrolled escape of landfill gas.
1.1.3
The practices and techniques referred to in 26B are all good examples of
measures that would minimise the release of odours. Judging by the recent
rise in the level of odour complaints relating to landfill operations it is fair to
assume that either the application of these practices and techniques is not
being rigorously applied and/or the effectiveness of the measures is less than
expected.
1.1.4
IPPC guidance on odour for the landfill sector is contained in IPPC S5.02. The
guidance outlines the indicative requirements likely to be needed to comply
with the application of BAT in terms of odour. S2.3.9 deals specifically with
odour, while S2.3.3, 2.3.7 and 2.3.8 deal with odour indirectly via landfill gas,
point source and fugitive emissions to air.
2
Appendix 2: Odours and BAT
2.1.1
The Environment Agency have issued Technical Guidance Note IPPC S5.02
Guidance for the Landfill Sector, Technical requirements if the Landfill Directive
and Integrated Pollution Protection and Control.
2.1.2
Specific reference to odour is contained in section 2.3.9, a copy of which is
presented below for information.
Technical Guidance Note
IPPC S5.02
Guidance for the Landfill Sector
Technical requirements of the Landfill Directive and
Integrated Pollution Prevention and Control (IPPC)
INTRODUCTION
Materials
Management
inputs
Odour
TECHNIQUES
Activities/
abatement
2.3.9
Ground
water
EMISSIONS
IMPACT
Waste Energy Accidents Noise Monitoring Closure
Installation
issues
Odour
The objectives of PPC and LFD are complementary with respect of odour and can be summarised as
being to prevent harm in the form of offence to man’s senses, or annoyance.
Odour is typically associated with trace components in landfill gas, the handling of odorous wastes and
inadequate emplacement and covering of biodegradable wastes. Given the fugitive nature of odour
emissions, emphasis should be given to preventative measures relating to landfill gas management
(see section 2.3.3) and waste acceptance and emplacement (see sections 2.2.1 and 2.3.6).
Application Form
Question 2.3 (cont.)
Describe the main activities generating odour and/or sources of
odour, the location of the nearest odour-sensitive receptors,
describe any relevant environmental surveys which have been
undertaken and the techniques for controlling odorous
emissions.
With the Application, the Operator should provide:
1.
Information relating to sensitive receptors
• Type of receptor, location relative to the odour sources and, where undertaken, describe
the findings of any assessment of the impact of odorous emissions on the receptors.
• Details of any routine monitoring undertaken to assess odour exposure of receptors
• An overview of any complaints received, what they relate to (source or particular
operation) and remedial action taken.
• A description or copy of any conditions or limits put in place by any regulatory authority
which relate to the receptors (e.g. relating boundary fence or beyond)
2.
A description of the types of odorous substances deposited/disposed of and generated
(intentional and fugitive (unintentional));
- wastes have to be treated before landfill, which in turn should limit wastes which are
inherently odorous.
- the description s hould make the distinction between wastes which are inherently odorous
where the impact is likely to be more immediate and those wastes which may give rise to
odour because of microbiological action in the landfill (organic or inorganic).
3.
A description of the point, linear or area sources of release.
4.
A structured odour management plan including:
• Control measures to prevent or control odour.
• A demonstration/justification that there will not be an odour problem from the emissions under
normal conditions.
• A description or copy of any conditions or limits put in place by any regulatory authority which
relate to the prevention of minimisation of odour.
• Identification of the actions to be taken in the event of abnormal events or conditions which
might lead to odour, or potential odour problems.
• An understanding of the impact in the event of abnormal events or conditions, for example the
failure of a landfill gas flare. This may require modelling the dispersion of odours under such
circumstances.
• Monitoring undertaken.
• Communication with for example local residents if an odour problem arises or is likely to
arise.
Indicative BAT Requirements
BAT for the
control of
odour
Landfill
Directive Article
9(c), 12 (b)
Annex I (5)
44
1.
2.
Measures will be taken to minimise nuisances and hazards arising from the landfill through
emissions of odours.
Where a landfill operation has a low environmental impact with respect to odour (for example by
virtue of its remoteness from sensitive receptors), the Operator may seek to justify in accordance
with BAT criteria (see section 1.1), deviation from measures stated in this section.
Cont.
Version 3a, November 2001
Landfill
INTRODUCTION
Materials
Management
inputs
TECHNIQUES
Activities/
abatement
Ground
water
EMISSIONS
IMPACT
Waste Energy Accidents Noise Monitoring Closure
Installation
issues
Odour
3.
In order to reduce the release of odorous compounds and their impact at sensitive receptors, the
minimisation of odour should be considered in relation to:
- the types of wastes;
- site layout;
- engineering aspects of the operation;
- management procedures;
- and the day-to-day operational practices.
4.
A regular odour impact assessment should be undertaken. The impact assessment should cover
a range of reasonably foreseeable odour generation and receptor exposure scenarios and the
effect of different mitigation options. Assessment should include point sources (for example vents
and flares) as well as linear or area sources (tipping faces, cracks in the cap etc.).
Odour control techniques – good practice
The following landfill-specific techniques should be used to prevent of minimise odorous releases from
the site. Odour control is not a once-off activity and requires a constant re-evaluation of control
techniques and this should form part of the odour management plan.
IPPC
5.
Waste Acceptance
• materials which promote the generation of gases should be excluded. For example,
wastes with a high sulphate or sulphide content should be excluded.
• co-ordination between the gatehouse and operators at the tipping face should take place
where known odorous wastes are to be deposited.
• excavation of waste or removal of cover during for example the installation of gas wells, or
for other operational needs, may give rise to odours,
6.
Covering of wastes.
• Tipping areas should be kept as small as possible to minimise the effects of wind.
• Waste must be covered as soon as possible.
• On areas of intermediate capping, the degree of capping should be sufficient to prevent
the possible release of odours. After the initial tipping and compacting it is likely that the
odours will tend to become more characteristic of anaerobic degradation/landfill gas. This
phase should coincide with an increase in gas abstraction capacity (see section 2.3.3)
7.
Landfill Gas management
• Certain odorous trace compounds in landfill gas have low odour thresholds. These
include organo-sulphur compounds, cyclic compounds, aromatic hydrocarbons, esters and
carboxylic acids, which derive from microbial interactions.
• An effective landfill gas management plan (see Section 2.3.3) in conjunction with good
operational practice (i.e. not leaving odorous waste uncovered) will significantly prevent
such releases. Providing full containment of the waste, including temporary and/or phased
capping of the site, in addition to incorporating an active landfill gas control system are
essential gas control measures. Point source emissions such as those from landfill gas
flares should be considered in the selection and assessment of the control system.
• Landfill gas control systems are not expected to generate significant point source
emissions if well constructed, operated and maintained.
• Passive venting during the early operational stages may give rise to odours and active
extraction systems should be installed to minimise the release of uncontrolled landfill gas
emissions. The passive venting time period should be minimised.
8.
Leachate management
• Odour from a leachate treatment plant should, in most cases, be manageable to prevent
offensive odours beyond the boundary of the site. An enclosed treatment operation is
desirable where the proximity of the operation to receptors is likely to cause nuisance.
• Leachate sumps/wells should be are effectively sealed (retaining access for monitoring
and maintenance) or extracted to abatement equipment.
Version 3a, November 2001
45
INTRODUCTION
Materials
Management
inputs
9.
TECHNIQUES
Activities/
abatement
Ground
water
EMISSIONS
IMPACT
Waste Energy Accidents Noise Monitoring Closure
Installation
issues
Monitoring
• Standard
- Recording or gathering of weather conditions, for example atmospheric pressure and
stability (inversions), rainfall, wind speed and direction and air temperature.
- Checks on gas abstraction rates, integrity of pipe-work and other relevant infrastructures,
filters, adequacy of capping etc should form part of monitoring or periodic inspection by
trained persons
• Reactive
- Olfactory “sniff testing” at the boundary or at some location which is representative of
sensitive receptors.
- Collection and analysis of air samples to identify odour sources.
Main technical guidance
•
•
•
•
46
Odour Assessment and Control – Guidance for Regulators and Industry (see Reference 30).
Interim Guidance on the Flaring of Landfill Gas (see Reference 29);
Guidance on the Management of Landfill Gas (see Reference (see Reference 19);
IPPC General Guidance on Odour (see Reference 31).
Version 3a, November 2001
Landfill
3
Appendix 3: Properties of Selected Mercaptans and Hydrogen Sulphide
3.1.1
Properties of four mercaptans with low ODT and considered to have the most
offensive odorous are shown in Table A2 below. Hydrogen sulphide is also
included due both to its offensive smell and its ubiquitous presence in LFG.
3.1.2
The relationship between increasing MW and increasing BP follows the
increased level of carbon bonding in the compounds.
3.1.3
As the MW of the mercaptans increases the Pv and solubility in water both
decrease, suggesting that methyl mercaptan is likely to be the most available
form of mercaptan
3.1.4
The high aqueous solubility of methyl mercaptan and hydrogen sulphide
indicates that significant quantities of both could dissolve in any aqueous
phase, such as water vapour or leachate and be available to come out of
solution at some later time, such as during aeration in an open lagoon or
movement through a public sewer.
Table A2:
Compound
Physical Properties of Four Selected Mercaptans and Hydrogen Sulphide
Chemical
Formula
Odour
Character
MW
Methyl
Mercaptan
CH4S
Rotten
cabbage
48
Ethyl
Mercaptan
C2H6S
Rotten
cabbage
62
Propyl
Mercaptan
C3H8S
Not
reported
76
Butyl
Mercaptan
C4H10S
Skunk
90
Hydrogen
Sulphide
H2S
Density
Solubility
Pv
0
( C)
(g/ml)
(ppmw @
25 0C)
(mm Hg @
250C)
23300
6
N/a = not available
0.87
35
0.84
0.81
155
55
0.84
34
1.5
6 x 10-5 -1.6
3 x 10-7 - 6 x 10-2
2.5 x 10-4 – 0.2
6.6 x 10-4 – 10-3
2.5 x 10-6 – 1.4 x
10-4
n/a
n/a
2.7 x 10-3 - 3.7 x
-3
10
10-4 -2.8
1.6 x 10-3 x 7 x 10-2
55
4000
-60
AIHA Reported
Range
527
N/a
57
AEA Reported
Range
1516
527
98
Rotten
eggs
Odour Threshold Values (mg m-3))
BP
N/a
4
Appendix 4: Calculations and Conversions
4.1
Flux Rates
4.1.1
Flux rates were calculated as a function of the rate of change in concentration
within a containment device. The concentration of landfill gas contained within
the device was regularly monitored according to the protocol set out in
Appendix 4. The data collected included the following:
•
Fill time (s) for the containment device
•
The change in ppm over the time period
•
Basal area (m2) of the flux device
•
Containment volume (m3) of the flux device
•
Atmospheric pressure (mb) at the start of the day
•
Atmospheric pressure (mb) at the end of the day
4.1.2
Two constants are required to complete the calculations. These are the
molecular weight (MW) of methane (CH4), 16, and the volume occupied by of
one mole of a gas at a specific temperature and pressure. The molar volume
at 0oC is 22.4 litres per mole at standard temperature and pressure. This is
adjusted within the calculations to take into account both temperature and
pressure differences.
4.1.3
The raw data collected required manipulation into an emission rate of gs-1 and
an effluent flux velocity (Efflux) in ms-1 for input into ADMS.
Equation
c
d
e
f
g
h
i
j
Parameter
Temp Adjustment
Pressure Adjustment
Concentration change of CH4 gm-3
Emission Rate CH4 gm-2s-1 Fixed Volume Sources
Emission Rate CH4 gm-2s-1 Variable Volume Sources
Volume of LFG emitted (m3s-1m-2)
Emission Rate of Odorous Compound from fixed volume
source (gm-2s-1)
Emission Rate of Odorous Compound from variable volume
source (gm-2s-1)
4.1.4
The results of the data manipulation are found in Table 1 were transformed into
a usable format using the following calculations.
4.2
Temperature and Pressure Corrections
4.2.1
Temperature and pressure corrections are required in order to take account of
the conditions during monitoring, the molar volume of 22.4 litres is based on
standard temperature and pressure conditions.
4.2.2
Temperature Correction =
Equation c:
o
273 + T C
Temperature Correction =
273
4.2.3
Pressure Correction =
Equation d:
Temperature Correction =
1013
Observed pressure
-3
4.3
Change in CH4 gm
4.3.1
Calculation of the emission rate of methane form the surface of a landfill
requires the
For a fixed containment volume measuring device (ie tent & bin)
Emission Rate =
Change in ppm per volume contained
time (s)
area (m2)
=
x
ppm
m2
m3
s
Calculation of the change in ppm per volume
contained
ppm = ppmtx - ppmt0
Need convert ppm to g/m3, where ppm is a value, #
∴
# ppm vol x 1e-6
x
vol
∴ Equation e
# x 1e-6
mw (g/mole)
mv (l/mole)
x MW x
1000
x
1000l
m3
g/m3
MV
For a variable volume measuring device
4.4
Calculation of CH4 Emission Rates gs-1m-2 for Fixed Volume Sources
4.4.1
Calculation basis for determining methane emission rates for a fixed volume
source e.g. rigid container.
Calculation of CH4 emission rate g/s/m
g/s/m
2
=
2
Equation e
x
3
Containment Vol (m )
Basal Area of measuring
2
device (m )
Time period of monitoring
2
∴ Equation f
g/s/m =
(# x 1e-6 x 1e3 x MW/MV)
x
3
Containment Vol (m )
Basal Area of measuring
2
device (m )
Time period of monitoring
4.5
Calculation of CH4 Emission Rates gs-1m-2 for Variable Volume Sources
4.5.1
Calculation basis for determining the methane emission rate for a source using
a variable volume collector e.g flux tent.
Calculation of CH4 emission rate g/s/m
2
3 -1
Source Emission rate m s
3
Volume (m )
=
=
Voltx – Volto
Time (s)
g/s/m
2
3 -1
= ms x
tx
Equation e
x
Basal Area of measuring
device (m2)
Time period of monitoring
x
Basal Area of measuring
2
device (m )
Time period of monitoring
3
Containment Vol (m )
∴ Equation g
g/s/m
2
3 -1
= ms x
(# x 1e-6 x 1e3 x MW/MV)
3
Containment Vol (m )
4.6
Volume of CH4 Emitted from a Landfill Surface
4.6.1
Calculation of the volume of LFG emitted from the surface into the containment
vessel expressed in m3/m2/s based on an assumed 50% CH4 in LFG.
1) Emission into containment vessel with fixed volume.
= (Change in Conc CH4 ppm)
x (Vol of containment vessel)
(Volume of CH4 in LFG)
Time (s)
2
Basal Area (m )
Change in Vol of CH4 = ppmtx - ppmt0
Vol of CH4 in LFG = 50% = 50 x 10,000 ppm = 5 e5 ppm
Equation h
=
ppm / 1e6
containment
3
volume (m )
x
5e5 / 1e6
time (s)
2
Basal Area (m )
=
3
2
m /m /s
4.7
Odorous Compound Emission Rate gs-1m2
4.7.1
Determination of the ratio of odorous compounds to CH4.
The purpose of this calculation is to define the ratio of odorous compound (ppm) to CH4 (ppm),
expressed as a dimensionless value
Ratio between literature values for specific odorous compounds in mg/m3 and ppm. Based on either
detection or recognition thresholds and expressed as mg/m3/ppm
3
3
mg/m /ppm
= Odour threshold (mg/m )
Odour Threshold (ppm)
NB: values available from literature
3
3
Calculation of the ratio between 1 mg/m of CH4 and x mg/m OC
3
1 ppm CH4 = x mg/m CH4
1 ppm CH4 =
MW CH4
MV (l/mole)
The purpose of this calculation is to define the emission of odorous compound from landfill sources
expressed in g/s
Emission of odorous compound is a proportion of the CH4 emitted from a source
Emission rate known for CH4
Conversion ratio known for odorous compound (OC)
Equation i: Fixed containment volume
Emission Rate of
odorous compound
=
gs
-1
Emission Rate
of CH4
gs
-1
x
conversion ratio OC: CH4
3
3
(mg/m :mg/m )
Equation j: Variable containment volume
Fixed containment volume
Emission Rate of
odorous compound
=
Emission Rate
of CH4
x
conversion ratio OC: CH4
3
3
(mg/m :mg/m )
5
Appendix 5: Details of Site Characteristics
5.1
Waste Input and Waste Types
5.1.1
The sites included within the covered a range of input material types. All
accepted household waste. At P3, approximately 95% of the waste input was
domestic waste. All sites accept non-hazardous commercial or industrial waste.
At P3, this accounted for a small proportion of the overall input. Sites P1, P2 and
V2 accepted special or hazardous wastes. P2 also accepted liquids, sludge’s
and low-level radioactive waste. This is summarized in Table 4.
5.1.2
Waste input quantity and site capacity varied widely across the six sites. P1
accepted 350,000 m3 annually and had a 1.4m m3 void space remaining over
the 50 Ha site. P2 covered 140 Ha and accepted 430,000 m3 in 2001. An
estimated 1m m3 void space was available in the remaining two phases. P3
was entering into its final stage of operation with much of the 2.2m m3 capacity
full. Annual input was approximately 160,000m3 for the 26 Ha site1, of which
95% was of domestic origin.
5.1.3
Sites H1 and V1 accepted non-hazardous commercial and industrial waste and
domestic waste. Site H1 was a 27 Ha site with annual input of 128,000m3 per
year2. The estimated site capacity was 4.5m m3. In comparison, V1, which
covered 80 Ha, accepted 144,000m3 of waste annually3. Site V2 by
comparison was just 8.42 Ha. The site was not receiving waste at the time of
this study as engineering works were being undertaken on site. The total
annual waste input for the last operational year was 80,000m3 4.
5.2
Site Design and Operational Regime
5.2.1
All of the sites, apart from site H1, had at least one phase that relied on dilute
and disperse. H1 opened in 1998 and was designed as a fully contained
landfill. There was a composite liner of clay and geo-membrane. There was a
temporary cap of 30-50cm sandy-clay material on part of the site. The final
restored cap will also be a composite. A gas control system was in place
including a 1000m3/h flare and a 200m3 leachate storage tank. Leachate was
removed from site for treatment and disposal.
5.2.2
P1, relied completely on dilute and disperse and, when complete, will be
restored with a plastic membrane cap. There are two engines installed and
operational that are backed-up by two flares. Leachate was treated on site and
discharged to sewerage.
1
Void space of 160,000m3 based on 200,000T compacted to a placed density of 0.8 T/m3.
Void space of 128,000m3 based on 160,000T compacted to a placed density of 0.8 T/m3.
3
Void space of 144,000m3 based on 180,000T compacted to a placed density of 0.8 T/m3.
4
Waste input of 80,000m3 based on 100,000T compacted to a placed density of 0.8 T/m3.
2
5.2.3
P2 will soon enter phase 4 of its operation. Phases 1 and 2 were dilute and
disperse cells, with 3 and 4 being fully contained with a composite liner. The
site was also part capped with a composite of plastic, clay and soil material.
Liquids were disposed to a lagoon constructed upon the deposited waste and
allowed to migrate through the waste material. Leachate was collected and
removed from site for treatment and disposal. A gas control system was in the
process of being established. Gas wells were installed and sealed on one
restored phase of the site. Due to the absence of further gas system
infrastructure, including pipe works and a flare or engine, the gas wells were
not connected.
5.2.4
All phases of P3 were dilute and disperse and either capped, or to be capped,
with clay to a depth of 0.5m. Leachate was treated on site and discharged to
sewerage. A gas control system, including an engine, was installed and
operating, utilizing gas produced from the restored phases of the site. Until
mid-2002, a combination of daily cover material and a temporary sheet
membrane was used to cover daily waste deposits.
5.2.5
The restored phases of sites V1 and V2 were engineered for dilute and
disperse. At V1, the recently completed phase was capped with a combination
of a bentonite mat plus an additional 400mm of sandy/silt material from the onsite quarry. Further material will be used to bring this phase to a restored state.
V2 was capped with overlapped HDPE. Both the recently active and soon to be
constructed phases were designed to be fully contained with a composite liner.
Leachate was collected and removed from both sites for treatment and
disposal. Both sites operate gas systems, both of which had recently been
extended into newly completed phases. V1 operated a single flare. V2
operated an installed engine that was backed-up by two additional flares.
5.3
Topography
5.3.1
The six sites were classified into three distinct groupings based upon their
surrounding topography. For the purposes of dispersion modelling these were:
•
a hill on a plain
•
a hill on a hill
•
a hill in a valley
5.3.2
Sites P1, P2 and P3 were all located on river or coastal flood plains. There was
little topographic variation surrounding the sites and in all cases, the landfill site
formed the largest topographic feature in the proximity of the sites.
5.3.3
H1 was located at an altitude of approximately 50m AOD in an area of rolling
hills up to 90m AOD. The site was located on a ridge that formed the margin
between the coastal plain and inland hill forms. As such, this site was classified
in this study as representing a hill on a hill.
5.3.4
Sites V1 and V2 are both located in an area of rolling topography. The
maximum height of the surrounding hills is approximately 130m AOD. Both of
the sites were positioned on a valley floor at approximately 80m AOD. These
sites were classified as representing a hill within a valley
5.4
Proximity to Habitation
5.4.1
Over recent years, development of residential and industrial areas has
increasingly encroached upon P1. A kindergarten and supermarket were
located adjacent to the landfill, separated only by an access road to a sports
centre. Beyond these, there was a series of housing developments and a
primary school. The school was less than 400m from the site.
5.4.2
P2 was located in a semi-rural landscape. A village was located 1.3 Km to the
north and another 2.2 Km to east. In addition to these, there was a hotel
complex located 900m north east of the site. There was also a number of
individual buildings scattered around the north of the site.
5.4.3
P3 was located in a semi-rural landscape and within 50m of a farm. There are
other residential properties approximately 900m south and 1 Km south west of
the site.
5.4.4
H1 was located within 100m of local residents. These properties were the
present outer-residential area of a town. Other properties were situated 250m
east of the site. To the south west and west of the site there were a number of
individual dwellings, although these were over 700m from the site. A large
housing development was located 1.2 Km directly south of the site.
5.4.5
V1 was surrounded to the south by large residential properties and to the east
by smaller dwellings. These were approximately 300m and 400m respectively
from the site boundary. North east of the site, and within just a few meters of
the site boundary was located a school.
5.4.6
500m to the north of V2 there was a hotel located on a hill ridge line. To the
east, there was a village approximately 250m from the site boundary and to the
west a village approximately 600m. To the west there were other individual
properties within 250m of the site
5.5
Off-Site Odour Sources
5.5.1
Sites P1, P2, P3 and V2 were located within an agricultural or semi-agricultural
environment. In particular, V2 was located in close proximity to an area where
regular application of slurry to land occurred.
5.5.2
P1 was situated in close proximity to a number of chemical manufacturing
facilities and sites that make use of solvents. In addition, odours associated
with the estuary were possible. Similar estuarine odours were possible at P2.
5.5.3
Odour issues are complicated at P2 as a sewerage treatment works (STW) was
located adjacent to the landfill site. Furthermore, the site accepted the sludgecake from the STW, with the cake transferred in open containers. Problems
had arisen in the past regarding the determination of the odour source as a
result of this close proximity. A poultry farm was located approximately 350m
to the north of the site.
6
Appendix 6: Odour Questionnaire
6.1
The Questionnaire
6.1.1
A questionnaire was issued to local residents surrounding the site.
number of questionnaires distributed was based on two factors:
•
History of complaints
•
Number of potential receptors within 2km of the site
o If small number of receptors, all households received a
questionnaire
o
6.1.2
The
If large, a random sample of households received a
questionnaire
A copy of the questionnaire can be found on the following pages.
ODOUR QUESTIONNAIRE FOR MEMBERS OF THE PUBLIC
Thank you taking the time to complete this questionnaire. Your assistance will help develop means to
minimise odour nuisance attributed to landfill operations in the UK.
1.
Do you experience odour events from external sources?
2.
Do you think you can identify the source (or sources) of the odour?
NO
3.
If yes to 2, what do believe is/are the most likely source(s)? If more than one please state.
4.
Is the odour event a regular occurrence?
5.
If yes, how regular are the odour events?
Once a week
More often
Less often
6.
How long have you been experiencing odour events?
7.
How long does the odour event tend to last?
8.
Is there a specific time of day when the odours occur?
9.
If yes, what time of day?
Late Morning
NO
YES
YES
Once a day
Early Morning
YES
NO
Once a month
YES
Afternoon
Evening
NO
Night
10. Is the odour associated with particular weather conditions?
YES
NO
11. If yes, which of the following best describes the weather at the time?
Still
Fog
Windy
Rain
Other
Any/All
12. Is there a particular time (or times) of year that odour events tend to occur?
Winter
Spring
Summer
Autumn
13. In your opinion, when is the worst time of day for odours? Worst month or season?
14. Please describe the odour in your own words.
15. Where do you normally encounter the odour? (in your home, in the garden, in the street etc.)
MSE055/ODOUR QUESTIONNAIRE
APRIL 02
16. Could any of the following words be used to describe the odour. If more than one type of
odour, please double/triple tick the best words:
STRENGTH OF SMELL:
Faint
Moderate
Strong
Overpowering
Occasional – few times
Intermittent - more
Continuous for x
minutes
PRESENCE OF SMELL
There then gone
TYPE OF SMELL: - I still think you need to group these to match the types you expect for gas, waste,
leachate, other?
Sulphurous
Sweet
Fruity
Gassy
Lemon-like
Fruity
Pungent
Less sulphurous
Acrid/sour
Rotten cabbage
Putrid
Rotten food
Ammonia
Animal manure
Agricultural
Rotten eggs
Acidic
Solvent/petrol
Disinfectant
Oily
Sickly sweet
Sugary
Pungent
Sulphurous
Ammonia
Farmyard
Petrol-like
Oily
17. Do the majority of the odours appear to come from the same source?
18. Is it always the same smell?
19. Has the odour nuisance varied over time?
YES
Are you after here, scales of minutes, hours, days, weeks, months, seasons, years???
20. If yes, what was the timescale and how did it change?
NO
…………………………………………………………………………………………………………….
…………………………………………………………………………………………………………….
….……………………………………………………………………………………………………….…
……………………………………………………………………………………………………………
……………………………………………………………………………………………………………..
21. Would you/have you complained about the odour?
YES
NO
22. Who would/have you complained to?
Environmental
Health Dept.
Environment
Agency
MSE055/ODOUR QUESTIONNAIRE
Site
Operator
Parish
Council
Residents
Association
Site Liaison
Group
APRIL 02
23. Do you feel that those you complained to responded adequately to your complaints/ concerns?
YES
Add if not what else have you done, is this an ongoing issue
24. Were you aware that the landfill has a Site Liaison group?
YES
NO
NO
25. Do you have any other concerns regarding odours? If so, what are they?
…………………………………………………………………………………………………………….
………………………………………………………………………………………….
….………………………………………………………………………………………
…………………………………………………………………………………………
consider following on separate sheet
If you would like to be contacted regarding further involvement in the project, write your name, contact
address and telephone number below:
NAME:
……………………………………………………………………………………………………
ADDRESS:
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
……………………………………………………………………………………………………
TELEPHONE:
……………………………………………………………………………………………………
Please return the questionnaire in the stamped self-addressed envelope provided. Thank you for
your help with this project.
MSE055/ODOUR QUESTIONNAIRE
APRIL 02
6.2
Evaluation Methodology
6.2.1
The return rate for each of the four sites varied, as indicated in Table A3 below.
The reasons for the varying return rates reflected many factors, such as the
complaints history associated with the site, the adjacent industrial surroundings,
the proximity of residential dwellings and the socio-economic category of those
residential occupants. All but the complaints history and industrial surroundings
were beyond the scope of the study and were not investigated.
Table A3: Numbers of questionnaires sent and returned
SITE
QUESTIONNAIRE
Number
Sent
Number of
Replies
%
Replying
% Replying Wishing to be
Involved Further
P1
40
8
20
12
P2
50
21
42
57
P3
25
8
32
75
H1
20
17
85
76
TOTAL
135
54
40
57
6.2.2
On this basis, the high return rate for sites P2 and H1 reflects the socioeconomic status of the adjacent residences and history of complaints. The
lower return rates for P1 reflects the absence of any complaints history and the
industrial surroundings of the site, while the limited complaints history for site P3
is reflected in the low response to the questionnaire.
6.2.3
To produce a general body of data, the results for the four sites were
accumulated to provide a single set of responses. While this action resulted in
the loss of some site-specific detail, the small number of returns for some sites
made the statistical value of those results of limited value.
6.3
Questionnaire responses
6.3.1
The questions contained in the questionnaire and the responses received
(expressed as a %) are presented in Table A3 above.
6.3.2
The results of the questionnaire are discussed below on a per question basis:
•
Q1: Only 1 in 3 people experienced an odour event from whatever
source. This could be interpreted that either the sensitivity of people
to odours is limited or that people will accept a background level of
odour which occasionally is exceeded, possibly leading to a
complaint being made.
•
Q2: Of those experiencing an odour event, only 1 in 3 felt that they
could identify the source of the odour. This suggests that either
landfills may not be the major source, or that people’s association of
particular processes with the odours produced is limited.
•
Q3: Of those who felt they could identify the source of the odour,
over half associated the odour with the landfill site. The visible
activity and odour associated with waste being transported to sites
may act to sensitise people to associating the site rather than the
transport of the waste as the odour source.
•
Q4: Two thirds of respondents experienced regular odour events.
•
Q5: Over half of the odour events occurred with a frequency of more
than once a week. The high frequency could be due either the site
or to the transport of waste to the site.
•
Q6: Odours had been experienced essentially since the opening of
the landfill site. The change in any pre-existing background odour is
likely to be due to the operation of the landfill site.
•
Q7: The duration of the odour was generally of a few hours. Such a
response supports the case for waste delivery being the major cause
of odours, as other landfill activities and processes are usually of
longer duration.
•
Q8: Overall there appears to be no specific time of day for odours to
occur.
•
Q9: For those who did find a specific time of day for odours, the
calm, still conditions associated with early morning/evening. are to
be expected, as these represent stable atmospheric conditions.
Under stable conditions the absence of any turbulence or mixing
means that no/limited dilution of the air mass containing any odours
will take place. The odorous air mass leaving the site can move as a
fixed body of air for hundreds and even thousands of metres before
dispersion and mixing takes place, caused by physical obstructions
such as hedges, trees, traffic moving along roads etc.
•
Q10: Similar non specific result as with the time of day.
•
Q11: Still/foggy/wet weather represents the same stable
atmospheric conditions as early mornings/evenings and odours are
to be expected.
•
Q12: No apparent pattern related to seasonal effects but a slight
bias to wards summer. Increased time spent outside or windows
being open may help to explain an apparent increase in odour.
•
Q13: Reinforcing the findings of Q9.
•
Q14: The full range of odour descriptors for offensive or obnoxious
odours.
•
Q15: Suggests that the odour source is extensive and not due to
‘home’ related sources e.g. drains.
•
Q16: Odour strength was generally moderate to strong, suggesting
either a local source or a more remote source with a significant
emission rate. Based on the odour descriptors used in the odour
wheel in the Agency odour guidance document, the responses
covered all of the descriptors.
•
Q17: Most respondents believed that the same source was
responsible for all of the odours.
•
Q18: The odour remained the same over time.
•
Q19: Approximately half the respondents felt that the odour
nuisance had varied over time, suggesting a change in site
operations or engineering activities such as capping, installation of
gas control systems, leachate treatment operations etc.
•
Q20: No time-specific response, suggesting that there was no
specific event associated with any change in the odour nuisance.
•
Q21: Surprisingly about half of the people had not/would not
complain in the event of experiencing odours. This could suggest
that odour events are either not frequent enough or of sufficient
strength to lead to a significant adverse amenity impact.
•
Q22: In the event of making a complaint, there was no obvious body
to approach. In light of this apparent dilemma facing prospective
complainants. it is important that odour complaints are centralised so
that accurate records can be maintained.
•
Q23: People generally did not feel that their complaints had been
adequately dealt with by the receiving ‘body’. Be it the Agency, EHO
or the Site Operator, better feedback is needed to assuage
complainants concerns.
•
Q24: Only half of the complainants were aware that the landfill sites
involved in the study operated a Site Liaison group. Liaison groups
are an effective forum for residents, Site Operators and the
Regulators to meet to air and discuss site issues and concerns. In
some cases it may be appropriate to review the composition of the
Site Liaison group to ensure that it adequately reflects local needs.
•
Q25: The major concern associated with odours was the potential
for health effects. This may reflect increased public awareness of
waste management activities and a heightened appreciation of
potential environmental impacts. The waste management industry
and the appropriate regulatory bodies should develop a (combined)
programme of research and effective public consultation to identify
any potential adverse impacts and to then take appropriate steps to
ensure the mitigation of any such adverse impacts.
Public
confidence in waste management needs to be maintained.
6.3.3
While the questionnaire was undertaken on an anonymous basis, any
respondent could request to be involved in any further studies and 57%
indicated a willingness to do so by providing their name and address. Such a
high level of response could be interpreted either as an interest in their local
environment or a willingness to become engaged in the debate.
6.4
Analysis of site operations records and complaints records
6.4.1
All landfill sites are required to maintain a site dairy as part of their Licence.
The purpose of the diary is to record major site activities. The relevant
requirement is LCGN/7 [400]: SITE DIARY, in the Library of Licence Conditions
and Working Plan Specifications Library Conditions Guidance and Templates
Volume 1: Waste Management Licences.
6.4.2
The details of the requirement are specified as:
•
Objective: To provide a daily on-site record that will demonstrate
adequate running of the site with respect to pollution prevention,
harm to human health and serious detriment to the amenity.
•
Use: The site diary may be required to include details of, for
example: times on and off site of the designated Technically
Competent Manager(s) for the site; details of complaints received
and actions taken; and times/dates of scheduled monitoring and
maintenance.
6.4.3
Whilst all the site diaries were in regulatory compliance, it can be seen that the
Licence requirements do not specifically require a level of recorded detail that
would be of much value to odour investigations.
6.4.4
Equally the level of detail recorded by the regulatory bodies about odour
complaints was not comprehensive, making the data of limited value in odour
investigations. The lack of both suitably detailed site and complaints records
precluded the direct comparison of site activities with odour complaints as
initially planned and no useful analysis was undertaken.
6.5
Identification of alternative potential odour sources
6.5.1
Each site had also specific issues that were reflected in the returns. While the
landfill was usually the perceived/actual focus of odour complaints, some sites
had nearby industrial/agricultural activity that was also considered by the
complainants as a possible cause of odour events (section 6.5). It was not
possible within the scope of the study to undertaken any quantitative studies to
differentiate between other potential odour sources. One clear example was a
‘hot plastic’ smell experienced by one respondent, which could clearly be
associated with an adjacent plastics moulding factory adjacent to the site. The
respondent attributed the source of the odour to the landfill site, as the site was
clearly evident, while the plastics factory was suitable anonymous in the
adjacent industrial estate.
6.5.2
Farming activities took place near to most of the sites and odour events
associated with spreading of slurry or fertilisers were noted to be a likely cause
of some complaints. However the seasonal nature of these particular activities
in this study made it clear that they could be responsible for only some of the
complaints. Dependent on the type of farming activity i.e. chicken raising, dairy
or pig units, odours similar to those associated with landfill activities could arise
on a regular basis.
6.5.3
Other industrial activities produce odours similar to landfill derived odours,
exemplified by WTW. Anaerobic treatment of sewage sludge produces
identical odours to LFG, as the production of LFG is also an anaerobic process.
Site B was adjacent to a WTW and it was clear from direct experience that on a
periodic basis the WWT was source of the odour. These odour events were
associated with the transport of filter cake from the Works to the landfill site for
disposal. Odours with characteristics similar to landfill derived odours can
make it difficult for residents and regulators alike to be able to differentiate
between the possible source of odour release, without extensive investigation
and supporting documentation.
6.5.4
It is on these occasions that the value of a comprehensive site diary or other
records of site activities and observations can prove to be invaluable. An on
site-weather station to collect site-specific weather data provides valuable
information that can be used to investigate reported odour events.
6.6
Discussion
6.6.1
The data collected via the questionnaires enables some useful insights to be
determined. It was not the specific purpose of the questionnaire to provide a
statistically valid set of data but to obtain a general view of the key features and
concerns associated with the sites as seen by the residents. Dealing
successfully with odour issues is a combination of the application of appropriate
scientific and engineering measures together with an awareness of public
perceptions.
6.6.2
The statement that odours commenced with the opening of the site is self
evident, as once wastes are placed the nature of the background odour in the
area will change. However, for some people even if odours are controlled and
the inevitable odour events are infrequent, the mere presence of the often
unwanted site can lead to a heightened perception of, or sensitivity to, odours,
be they real or imagined. The merest hint of an odour, from whatever source,
could be sufficient to lead to an odour complaint. In such cases, it will be
extremely difficult to avoid odour complaints.
6.6.3
The limited time scale of the odour event fits in with both changing atmospheric
effects i.e. calm early morning conditions giving way to turbulence as the land
surface heats up and routine site based activities such as the arrival of
collection vehicles etc. Non-routine activities such as the excavation of wastes,
work on gas wells ands leachate chambers etc. are usually of a short-term
nature i.e. less than a day.
6.6.4
The nature and strength of an odour is a subjective assessment (section 3.3).
In some instances responses from nearby residents reported a significant
difference in both the nature and strength of the odour. Both observations
could be explained by the effect of dilution (section 7) but the proximity of the
residents suggests that the differences were largely subjective rather than
actual concentration differences.
6.6.5
The finding that many people had not complained of previous odour events is
interesting and can be interpreted in a number of ways. It could be concluded
that people will tolerate a low level background of odour associated with landfill
sites and only complain when an exceptional event leads to an increased level
of odour or production of a different odour. In a less positive interpretation,
sites that apparently have no odour issues actually do but the public do not feel
that complaining will achieve any beneficial result. If the latter were the case,
then public faith in the ‘regulatory’ system in its broadest sense is low and
people do not feel it worthwhile to complain, as nothing will be gained.
6.6.6
The willingness of people to tolerate a background level of odour does vary
across the country. The more industrialised areas appear to have a greater
tolerance of odour and other emissions i.e. incinerators and EfW plants, than
do those areas which are primarily ‘green belt’. Sites located in these green
belt residential areas are likely to experience a greater level of complaints than
their industrial region counterparts, albeit for the same wastes, operational
standards and site conditions.
6.6.7
Of the sites covered by the study, sites P2, P3 and V2 are located within an
agricultural or semi-agricultural environment. Farming activities taking place
around the sites included poultry farming, animal grazing, the cultivation of
crops and the use and/or storage of farm generated animal slurry and wastes.
Each of these activities is likely to produce an odour event period or periods
during the course of the year, which may lead to a complaint incorrectly
attributed to the landfill site.
6.6.8
At site V2 a regular occurrence was the movement of animal slurry along a road
adjacent to the site that ran past a residential area. Immediately after the
movement of this material on days when the wind was blowing in the
appropriate direction, prima facie evidence indicated that odour complaints
were recorded.
6.6.9
Site P1 is located in close proximity to an industrial estate, which includes a
paint manufacturer, other chemical processes and a range of light industries.
Site P2 is located adjacent to a major WWT facility. The presence of this
alternative odour source further complicates the issue as the landfill site
accepts the sewage cake produced by the WWT. Two of the sites, H1 and H2,
are also situated in a locality with a number of other landfill sites. As such,
operational and managerial issues associated with these other sites will
compound and/or confuse odour complaint issues.
6.6.10
The proximity of possible alternative sources of odour makes a clear
differentiation of odour sources difficult, especially as the data available from
both the Agency/EHO complaints records and the Site Diary have insufficient
detail to enable a clear view to be formed as to the likely cause of the odour
event.
6.6.11
The lesson to be learnt is that accurate and detailed records need to
maintained by both the site operator and the regulatory bodies if an objective
assessment is to be made as to contributory source or sources of odour
complaints.
7
Appendix 7: Emissions Monitoring Protocol
7.1.1
Standard procedures were established for on-site visits and the collection of
emissions data. This included the requirement for a site walk over survey, a
site perimeter survey, monitoring of onsite meteorological conditions and
monitoring of emissions using a flux tent.
7.1.2
On site meteorological conditions were monitored at the start, end and
repeatedly throughout the survey period. This included wind speed, direction,
temperature and atmospheric pressure.
Data collected onsite was
supplemented by data available from the BBC Weather website.
7.1.3
A site perimeter survey was conducted during each site visit using a Flame
Ionisation Detector (FID). FID readings were recorded, including the maximum
and approximate mean value. Odour characteristic, intensity and, where the
odour was particularly unpleasant, the hedonic tone was also noted. The
perimeter survey included central areas of the site with specific features of
interest, such as flanks or particularly odorous leachate or gas wells.
7.1.4
The sites were divided into areas based on potential source types. Area
sources including flanks, restored and/or vegetated ground, temporary capping,
daily cover, and active tipping areas were all identified and classified on their
specific characteristics such as composition. Point sources were also targeted
with measurements taken both from and within the vicinity of these features.
Monitoring was only possible where practical or where safe to do so. A number
of flanks were too steep to enable safe working practices to be undertaken.
7.1.5
Repeat visits to site sought to take repeat flux measurements from the sources
previously monitored. The transient nature of landfilling operations resulted in
repeat measurements being taken where possible in exact or similar locations
8
8.1.1
Appendix 8: Measurement of Emission Rates
Emissions from surfaces were determined using a variation of flux box. The
measurement mode can be either static or dynamic, the former being less
accurate in absolute terms but providing a result in a shorter time. In this study,
three types of a flux box were used:
•
Static Flux Tent
•
Static Flux Bin
•
Static Flux Bag
8.1.2
It is recommended that the flux tent should be used wherever possible for
landfill applications. Landfill surfaces are by nature heterogeneous with surface
cracks and variations in cover material thickness producing wide variations in
the emission of landfill gases. Unless significant numbers of measurements
are taken using the smaller surface area flux box (typically 0.5-0.7m2)
measurements are liable to exclude surface defects, which have significant
mass emission rates.
8.1.3
The flux tent used in this study had an area of 4m2, enabling it to cover 6-8
times the surface area of a standard flux box. The perimeter of the tent was
marked and dug out to a depth of approximately 15cm where possible (Figure
5, Schematic of Flux Tent). The depth to which it was possible to dig to was
highly dependant on the covering material. Where the surface cover was
comprised of fine sandy-clay material, it was easier to create a deeper, even
cut into the cover than where the cover contained inert hardcore. The outer
plastic liner of the tent was placed into the trench and backfilled to create a
seal. A monitoring outlet pipe was laid under the plastic liner and sealed to
prevent escape of gas from the tent.
8.1.4
Measurements were taken every two minutes using the FID for the first eight
minutes and thereafter every four minutes. Monitoring occurred until the
concentration of flammable gas contained ceased increasing to any significant
extent. On occasions when little change in concentration of flammable gas
was observed within the device, monitoring periods were extended.
8.1.5
The flux bin was an 80 litre bin with a basal area of 0.15m2. This was adopted
on the same principles as the flux tent. However, being smaller in size than the
flux tent, the bin served as a means of monitoring emission rates at locations
where the tent was unable to get due to both the tents size and the requirement
to dig the tent in.
8.1.6
The flux bag constituted placing a bag over the open end of a point source,
either a gas well or an open pipe (present during visit to site P2), with a
monitoring outlet. The bag was fully deflated, sealed around the pipe, and
allowed to fill. Measurements were taken every two minutes until either the bag
was full or when the concentration of flammable gas contained ceased
increasing.
8.1.7
There are many limitations to the methodology adopted. First of these is the
static nature of the system. As the containment vessels (tent, bin or bag) fill, a
back pressure is created, therefore discouraging further emissions from
entering the device. Secondly, the inability to create a complete seal around
the base of either the tent or the bin further limits the reliability and accuracy of
the system
8.1.8
The basal area to volume ratio of the bin compared to the tent is far less
favourable. This ratio for the tent and bin are 2.7 m2/m3 and 1.7 m2/m3
respectively. Due to the variable volume nature of the flux bag and the variable
area of the source, it is not possible to give an accurate ratio for this device.
8.1.9
The smaller area of the flux bin required a greater number of measurements
need to be taken in order that the results were representative of the whole
surface area. This was however compensated by the time with which it is
possible to set up the flux bin compared to the flux tent.
8.1.10
An additional weak point of the system was coupling between the monitoring
equipment, the FID, and the flux device. The inability to create a perfect seal
may have enabled dilution of the sample removed from the bin.
8.1.11
Despite all of these limitations, it was believed that the methodology was
capable of calculating emission rates within the correct order of magnitude.
Table 9 would suggest that this is the case. This level of accuracy was
accepted due to the variable nature of the landfill system.
MSE Millennium Science & Engineering Ltd
21 The Steadings Business Centre, Maisemore, Glos. GL2 8EY
T +44 (0)1452 41 21 51
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www.mse-environmental.co.uk