CIRIA C665 London, 2007 Assessing risks posed by hazardous ground gases to buildings S Wilson EPG Ltd S Oliver Millard Consulting H Mallett Buro Happold H Hutchings Enviros Consulting Ltd G Card Card Geotechnics Ltd Classic House, 174–180 Old Street, London EC1V 9BP TELEPHONE 020 7549 3300 FAX 020 7253 0523 EMAIL [email protected]WEBSITE www.ciria.org
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Assessing risks posed by hazardous ground gases to buildings
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Published by CIRIA, Classic House, 174–180 Old Street, London EC1V 9BP, UK
This publication is designed to provide accurate and authoritative information on the subject mattercovered. It is sold and/or distributed with the understanding that neither the authors nor the publisher isthereby engaged in rendering a specific legal or any other professional service. While every effort hasbeen made to ensure the accuracy and completeness of the publication, no warranty or fitness isprovided or implied, and the authors and publisher shall have neither liability nor responsibility to anyperson or entity with respect to any loss or damage arising from its use.
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Ground, landfill andsoil gas risk assessment,methane, carbondioxide, hazardousground gas, siteinvestigation, detection,measurement andmonitoring techniques,interpreting resultsfrom gas investigation
Classification
AVAILABILITY Unrestricted
CONTENT Advice/guidance
STATUS Committee-guided
USER Land owners, developers (commercialand residential), professional advisors/consultants (both engineering andenvironmental), builders andcontractors, regulators (EnvironmentAgency, Local Authority, buildingcontrol) and other professional andnon-specialist stakeholders
Summary
Following the high profile gas explosions at Loscoe and Abbeystead during the 1980s, anumber of reports were published in the 1990s on the measurement of ground gases,the assessment of risk such gases may present along with the measures that can beemployed to mitigate these risks. More recent guidance has focused on licensed landfillsites but there is a need for up-to-date guidance relevant to existing or planneddevelopment.
With government policy encouraging redevelopment on brownfield sites, includingthose sites where there is a potential for the presence of elevated concentrations ofpotentially hazardous ground gases, the lack of clarity in the existing guidance hasbecome more apparent. The resulting uncertainty is compounded by the lack ofcurrency with respect to guidance on the methods of investigation, the adequacy ofmonitoring, the methods of risk assessment, and the selection of options forremediation. There is evidence that this current lack of clear and up-to-date guidanceis leading to inappropriate, over- and under-conservative design, consequent resourceinefficiencies and potentially unacceptable levels of risk.
This book gives up-to-date advice on all these aspects. The guidance it containsconsolidates good practice in investigation, the collection of relevant data andmonitoring programmes in a risk-based approach to gas contaminated land. A step-wiseapproach to risk assessment is described. Two semi-quantitative methods are set out forthe assessment of risk:
1 For low rise housing with a ventilated under floor void at minimum 150 mm.
2 For all other development types.
Both methods utilise the concept of “traffic lights” to identify levels of risk. Themitigation and management of potentially unacceptable risk is described with referenceto both passive and active systems of gas control (as well as brief reference to sourceremoval etc).
Post development monitoring to confirm predicted behaviour is increasingly importantin the remediation of contaminated land. However, in terms of development on oradjacent to gassing land, particularly for housing development, it is recognised thatparticular circumstances apply such that long-term/post construction monitoring wouldnot normally extend beyond the point of sale or occupation of the development.
This guidance aims to ensure a consistent approach to decision making, particularlywith respect to the need for, and scope of, remedial/protective design measures whileremaining flexible enough to be relevant to site-specific and development variabilities.
CIRIA C665 iii
Foreword
A series of guidance documents were published for the construction industry as part ofCIRIA’s 1990s research programme Methane and associated hazards to construction. Thesepublications provided advice on the following:
� the occurrence and hazards of methane; CIRIA R130 Methane: its occurrence andhazards in construction (Hooker and Bannon, 1993)
� detection, measurement and monitoring techniques; CIRIA R131 The measurement ofmethane and other gases from the ground (Crowhurst and Manchester, 1993)
� interpreting measurements from gas investigations; CIRIA R151 Interpretingmeasurements of gas in the ground (Harries et al, 1995)
� protecting development from methane; CIRIA R149 Protecting development frommethane (Card, 1996)
� strategies of investigating sites for methane CIRIA R150 Methane investigationstrategies (Raybould et al, 1995)
� the assessment of risk CIRIA R152 Risk assessment for methane and other gases from theground (O’Riordan and Milloy, 1995).
This book aims to clarify and update this earlier guidance, while being consistent withmore high profile generic advice (eg the Environment Agency Model Procedures). Theguidance aims to consolidate good practice in a risk-based approach to gascontaminated land and to ensure a consistent approach to decision making whileremaining flexible enough to be relevant to site-specific and development variabilities.
CIRIA C665iv
Acknowledgements
The book was written by S Wilson (EPG Ltd), S Oliver, H Mallett, H Hutchings(Enviros Consulting Ltd) and G B Card (Card Geotechnics Ltd) under contract toCIRIA.
The authors
Steve Wilson, MSc BEng CEng CEnv CSci MICE MCIWEM FGSSteve is the technical director of the Environmental Protection Group Limited and hasextensive experience of risk assessment and remediation on contaminated sites,particularly on ground gas and vapours. He works as consultant to all sectors of theindustry and often provides advice to local authorities on ground gas issues.
Sarah Oliver, BSc MResSarah Oliver is a senior environmental consultant at Millard Consulting. She hassubstantial experience working on contaminated land projects with particularexperience on landfill gas projects. Sarah acted as the main researcher and later projectmanager for the preparation of this guidance.
Hugh Mallett BSc MSc C.Geol SiLCHugh Mallett was a project director at Enviros Consulting during the preparation forthe guidance and has since joined Buro Happold. Hugh has extensive experiencemany aspects of contaminated land and held overall responsibility for the delivery ofthe guide.
Heidi Hutchings BSc MSc AIEMAHeidi is a consulting group manager within the Land and Water team at EnvirosConsulting Ltd, involved in the project management, investigation and assessment ofcontaminated land prior to acquisition, reclamation or redevelopment. Heidi startedher career 13 years ago as a landfill gas monitoring technician and since then hasdesigned and implemented remedial works for a number of proposed and existing sitesconstructed on former landfills. Heidi also acted as project manager in the preparationof this guidance.
Geoff Card, PhD BSc CEng FICE EurIng CGeol CSi FGSGeoff is the founding director of Card Geotechnics Limited. Geoff has some 35 yearsexperience in geotechnical engineering and contaminated land development and workson major projects both in the UK and overseas. He is the author of CIRIA publicationR149 Protecting development from methane and associated gases (CIRIA, 1996).
This project was funded by: English Partnerships, Roger Bullivant, Card GeotechnicsLimited, Fairview Estates Ltd, RSK Group Plc, Taylor Woodrow, NHBC, A. ProctorGroup, Waterman Group and CIRIA Core Members.
CIRIA, Enviros Consulting Ltd and the project team are grateful for help given to thisproject by the funders, by the members of the Steering Group, David Barry of DLBEnvironmental Ltd and by many individuals and organisations who were consulted.
CIRIA C665 v
Following CIRIA’s usual practice, the research study was guided by a Steering Groupwhich comprised:
Mr R Johnson (chairman) Mouchel Parkman
Mr P Atchison PA Geotechnical
Dr B Baker Independent Consultant
Dr R Boyle RSK Group Plc (now with English Partnerships)
Mr S Cassie Worley Parsons Komex
Mr P Charles CIRIA
Mr R Dixon English Partnerships
Mr M Corban A. Proctor Group
Mr C Douglas A. Proctor Group
Mr R Douglas SEPA
Dr B Gregory Golders Associates
Mr R Hartless BRE
Mr I Heasman Taylor Wimpey Development Ltd
Mr J Keenlyside Environment Agency (now with Jacobs UK Ltd)
Mr R Lotherington Fairview Estates Ltd
Ms C MacLeod Arcadis Geraghty & Miller International
Mr S Moreby Gloucester City Council
Mr C Nelson Zurich
Mr M Rafferty NHBC
Mr N Rake Roger Bullivant
Mr D Rudland Halcrow
Mr R Shipman ODPM
Mr P Witherington RSK Group Plc
CIRIA’s project manager for this guide was Miss J Kwan.
Case study 4.1 Significance of response zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Case study 5.1 Example of typical gas monitoring round . . . . . . . . . . . . . . . . . . . . . .61
CIRIA C665 xi
Glossary
Aerobic A process that involves oxygen.
Anaerobic In the absence of oxygen.
Asphyxiant A vapour or gas which causes unconsciousness or death bysuffocation (lack of oxygen).
BOD A measure of the potential for a polluting liquid to removeoxygen from the receiving water by biological or biochemicaloxidation processes.
Borehole A hole drilled in or outside the wastes in order to obtainsamples. Also used as a means of venting or withdrawing gas.
Brownfield sites A term generally used to describe previously developed land,which may or may not be contaminated.
Catalyst A substance which speeds up a chemical reaction without itselfundergoing any permanent change.
COD A measure of the potential for a polluting liquid to removeoxygen from the receiving water by chemical oxidationprocesses (COD is always higher than BOD).
Combustion A chemical process of oxidation that occurs at a rate fastenough to produce heat and usually light, in the form ofeither a glow or flames.
Cover Material used to cover solid wastes deposited in landfills.
Concentration The proportion of the total volume of void space occupied bya particular gas.
Conceptual site model A representation of the characterisation of a site indiagrammatical and/or written form that shows the possiblerelationships between the contaminants, pathway andreceptors. This shows the potential risks that the site posesgiven the intended operations and future use on the site.
Development Works of construction, which may be buildings or civilengineering structures above or below ground, and includingancillary works, installations and open spaces associated withthe structures.
Explosion The bursting or rupture of an enclosure or a container due tothe development of internal pressure from deflagration.
Factor of safety This is used to provide a design margin over the theoreticaldesign capacity to allow for uncertainty in the riskmanagement process. The uncertainty could be any one of anumber of the components of the risk management process,including calculations, material performance etc. The value ofthe safety factor is related to the lack of confidence in theprocess.
Flammable A substance capable of supporting combustion in air.
Flux Movement of gas.
CIRIA C665xii
Gas One of three states of matter, characterised by very lowdensity and viscosity (relative to liquids and solids), withcomplete molecular mobility and indefinite expansion tooccupy with almost complete uniformity the whole of anycontainer.
Gas An analytical technique which can be used to identify andchromatography quantify substances according to the relative rate at which
they separate out when passed through a specific medium
Gas flow rate The volume of gas moving through a permeable medium oremanating from a standpipe per unit of time.
Gas generation Volume of gas produced per unit mass or volume of waste perunit time.
Gas screening Gas concentrations (%) multiplied by the measured boreholeflow value rate (litres per hour).
Ground gases A general term to include all gases (ie including VOCs orvapours) occurring and generated within the ground whetherfrom made ground or natural deposits.
Hazard A situation that could occur during the lifetime of a product,building or area and that has the potential for human injury,damage to property or the environment or economic loss.
Hazardous ground Gas generated from ground which can cause adverse impactgases to human health, structures and the environment.
Hydrocarbon A compound containing carbon and hydrogen only.
Ionisation The process of changing a particle with no charge into onewith a positive or negative charge, by the removal or additionof electrons.
Intrinsically safe Of an instrument (or equipment) which does not generate anignition source within the gas atmosphere being monitored(usually indicated by BSI accreditation).
Landfill Waste or other materials deposited into or onto the land.After implementation of the Control of Pollution Act (1974),landfills became licensed and engineered.
Landfill gas Gas generated from licensed, unlicensed, operating or non-operating landfill sites.
Leachate The result of liquid seeping through a landfill and beingcontaminated by substances in the deposited waste.
LEL The lower limit of flammability, that is the minimumpercentage by volume of a mixture of gas in air which willpropagate a flame in a confined space, at normal atmospherictemperature and pressure.
Limits of Concentration range bounded by LEL and UEL (see flammability Abbreviations) within which a gas or vapour is flammable at
normal atmospheric temperature and pressure.
Loscoe A village in Derbyshire where a house was destroyed by alandfill gas explosion in 1986.
Made ground Ground where there are deposits that have not been formedthrough natural geological processes. These may comprisecombination of natural deposits together with products andmaterials, and waste produced by man.
CIRIA C665 xiii
Mercaptans A group of organic compounds containing sulphur whichhave strong and unpleasant odours.
Methanogenic Methane producing.
OEL Limits related to personal exposure to substances hazardousto health in the air of the workplace.
Organic waste Waste which contains a significant proportion of carbonaceousmaterials and is degradable waste (for example vegetablematter).
Oxidation Reaction of species with an oxidant – normally, but notnecessarily, “oxygen” from the air.
Paramagnetic The property of substance which, when placed in a magneticfield, causes a greater concentration of the lines of themagnetic force within itself than in the surrounding magneticfield.
Passive control The control of gas emission by provision of engineeredventing pathways (for example wells and vent trenches)without mechanical aid.
Permeability A measure of the ability of a medium to allow a fluid (gas orliquid) to pass through it.
Photo-ionisation The ejection of an electron from an atom by quantum ofelectromagnetic energy.
Radius of influence Area where changes happen.
Response zone The perforated section of standpipe which allows gas in theunsaturated zone to enter a standpipe.
Recirculation Method undertaken to measure the rate of gas recovery in aborehole.
Risk The chance of a defined hazard occurring and achieving itspotential.
Sampling Collection of a portion of material for experimentation suchthat the material taken is representative of the whole.
Sensitive receptors Property and structures which are more likely to be affectedby a gas hazard either by virtue of their location orconstruction.
Soil gases Gases present between soil particles or other sources whichare generated from manmade and natural occurring activities.In this publication, soil gases have been used to describe allpotential gases emission from the ground, including VOCs orvapours.
Solubility The mass of the dissolved solid or gas which will saturate aunit volume of a solvent under stated conditions.
Source- This describes the linkage between the source of contaminationpathway- receptor and the pathway through which receptors can come into
contact with contaminants.
Standpipe A rigid tube inserted into the ground which allows thesampling of gas and water (usually in a borehole).
Surface emission Volume of gas escaping from a unit area of ground in a unitrate of time.
CIRIA C665xiv
UEL The upper limit of flammability, that is the maximumpercentage by volume of a mixture of gas in air, at normalatmospheric temperature and pressure, which will propagateflame in a confined space.
Vapour Gases generated from volatile hydrocarbons.
Void space The space between solid particles, occupied by a gas.
Zone of influence The volume of ground surrounding a standpipe or other gasinvestigation installation which can or is being influenced bythe use or control of that installation.
CIRIA C665 xv
Abbreviations
ALARP As low as reasonably practicable
AGS Association of Geotechnical and Geoenvironmental Specialists
BOD Biochemical oxygen demand
BRE Building Research Establishment
BS British Standard
BSI British Standards Institute
CIRIA Construction Industry Research and Information Association
CLEA Contaminated land exposure assessment model
COD Chemical oxygen demand
CQA Construction quality assurance
Defra Department for Environment, Food and Rural Affairs
DETR Department of Environment, Transport and the Regions
DNAPL Dense non-aqueous phase liquids
DoE Department of the Environment
DPM Damp proof membrane
DQRA Detailed quantitative risk assessment
EA Environment Agency
EAL Environment assessment limit
EIC Environmental Industry Commision
GSV Gas screening value
HDPE High density polyethylene
HPA Health Protection Agency
HSE Health and Safety Executive
LDPE Low density polyethylene
LEL Lower explosive limit
LNAPL Light non-aqueous phase liquids
NAPL non-aqueous phase liquids
NHBC National House Building Council
NICOLE Network for Industrially Contaminated Land in Europe
NRPB National Radiological Protection Board
OEL Occupational exposure limit
PPC Pollution prevention control
ppm Parts per million
SEPA Scottish Environmental Protection Agency
CIRIA C665xvi
SNIFFER Scotland and Northern Ireland Forum for Environmental Research
UEL Upper explosive limit
USEPA United States Environmental Protection Agency
WEL Workplace exposure limit
VOC Volatile organic compounds
CIRIA C665 xvii
CIRIA C665xviii
1 Introduction
1.1 BACKGROUND
Recent government policy has encouraged redevelopment (both residential andcommercial) on brownfield sites including those where there is a potential presence ofelevated concentrations of hazardous ground gases. Local authority duties under PartIIA of the Environmental Protection Act 1990 have also led to recognition of existingdevelopment which may be similarly located.
A number of reports were published in the early- to mid-1990s on the measurement ofsoil gases, the assessment of the risk such gases might present together with themeasures that can be employed to mitigate such risks. More recent guidance hastended to focus on licensed landfill sites. Consequently, many construction professionalsnow engaged in the investigation and assessment of such sites have found a lack ofclarity in the various guidance documents. This uncertainty is compounded by the lackof currency in the guidance with respect to methods of investigation, the adequacy ofmonitoring, risk assessment and remediation. Furthermore, there is evidence that thecurrent lack of clear and up-to-date guidance is leading to inappropriate, over- andunder-conservative design and consequent resource inefficiencies. This book providesup-to-date advice on all of these aspects and is relevant to both residential andcommercial development, to existing properties and to the design of new build.
This publication and the advice it contains has been prepared to be generally consistentwith CLR11 Model Procedures for the management of land contamination (Defra andEnvironment Agency, 2004a). The guidance presented here aims to consolidate goodpractice in the risk-based approach to gas contaminated land and to ensure a consistentapproach to decision making while remaining flexible enough to be relevant to site-specific and development variabilities.
1.2 LEGISLATIVE FRAMEWORK
This publication provides technical guidance in an area where there is a complex mixof documentation related to legislative and regulatory procedures. It is not the purposeof this publication to describe in detail all regulations. However, it is important torecognise the context into which the guidance has to be employed.
Government policy is based upon a “suitable for use approach”, which is relevant toboth the current and proposed future use of land. When considering the current use ofland, Part IIA of the Environment Protection Act 1990 provides the regulatory regime.The presence of hazardous ground gases could provide the “source” in a “pollutantlinkage” which could lead the regulator (local authority or Environment Agency) todetermine that considerable harm is being caused, or there is a significant possibility ofsuch harm being caused to people, buildings or the environment. Under suchcircumstances, the regulator would determine the land to be “contaminated land”under the provisions of the Act, setting out the process of remediation as described inthe DETR Circular 02/2000 Statutory guidance on contaminated land (DETR, 2000a).
CIRIA C665 1
In planning and development control of planned future use, Planning Policy Statement23 Planning and Pollution Control (ODPM, 2004b) requires developers to undertakelandfill gas risk assessments sufficient to demonstrate to the local planning authoritythat the proposals adequately mitigate any potential hazards associated with groundcontamination, including gas. As described above, the Model Procedures provide atechnical framework for applying a risk management process when dealing with landaffected by contamination (including soil gas). The necessity of the risk assessment andrisk management is also reiterated in a 2003 consultation document Building developmenton or within 250 metres of a landfill site (Environment Agency, 2003b).
Building control bodies such as Local Authority Building Control (LABC) andapproved inspectors enforce compliance with the Building Regulations. Practicalguidance with respect to the Building Regulations is provided by a series of ApprovedDocuments, one of which, Approved Document Part C Site preparation and resistance tocontaminants and moisture (ODPM, 2004a) aims to protect the health, safety and welfareof people in and around buildings, and includes requirements to protect buildings andsurrounding areas from contamination including gas from the ground. The ApprovedDocument includes a brief description of sources of soil gases, the risk assessmentprocess and options for remediation.
Although this current CIRIA guidance is not designed to address the issues associatedwith gas derived from licensed landfills, recent publications related to landfills providesome useful and relevant information. In particular Guidance on the management oflandfill gas (Environment Agency, 2004a) relates to the assessment of risks from landfillgases and provides a general overview of the process.
1.3 SCOPE AND OBJECTIVES
This publication is designed to provide up-to-date, practical and pragmatic advice onthe assessment and mitigation of potentially hazardous ground gases with respect tobuildings and their occupants. The advice covers both residential and commercialdevelopment and is focused on proposals for new build. However, it is also relevant toexisting buildings and structures which may have been constructed without properrecognition of their foundation on a potentially hazardous gas regime. So the advice inthis publication will be relevant to the regulator’s assessment in carrying out dutiesunder Part IIA of the Environmental Protection Act 1990.
The focus of this study has been on methane and carbon dioxide, although much of thetext is also relevant to consideration of other contamination present in the vapourphase. However, it is not within the scope of this publication to address the specificissues of measurement, risk assessment and remediation of the wide variety of vapoursthat could be encountered in geo-environmental investigations. Where appropriate toboth methane/carbon dioxide and to other contaminants in the vapour phase, genericcomment has been made or advice given. However, it should be recognised that thepresence of particular contaminants in the vapour phase will require specificconsideration during investigation, risk assessment and in remediation. Such specificconsideration is outside of the scope of this document.
The emphasis of this guide is on gases generated from the ground. Some of these arehazardous to human beings and the environment. Soil gas is a term that is used tospecifically define gas present between soil particles.
CIRIA C6652
The specific objectives of this guidance were to ensure that:
1 Valid data describing the gas regime are obtained:
a From appropriately designed and executed site investigation(s).
b From an appropriately designed and implemented monitoring programme.
2 The extent of uncertainty resulting from any limitations in the investigation andmonitoring programme is properly recognised, and reflected in the risk assessmentand design of remediation.
3 An appropriately rigorous, consistent and transparent strategy for the assessment ofthe risks posed by the soil gas regime is undertaken.
4 An appropriate strategy is developed for the mitigation of potentially unacceptablelevels of risk in the:
a Assessment of the need for and scope of remediation.
b Design of any such remediation.
c Validation of approved remedial measures.
1.4 METHODOLOGY
The research undertaken to produce this publication comprised five tasks:
1 An initial scoping study.
2 The determination of good practice for the definition of the ground gas regime.
3 Identification of good practice in the risk assessment of ground gases.
4 Derivation of mitigation measures for the assessed level of risk.
5 Drawing this all together into practical guidance.
Existing guidance and information was examined by means of a focused andcomprehensive literature search (see Bibliography). The state of current good practicewas determined by means of a questionnaire survey sent to all members of the steeringgroup, and members of both the AGS and the EIC. Consultation has been carried outwith a total of some 100 organisations with expertise or experience of the assessment ofrisks associated with soil gases. This research took as its starting point and benefitedfrom the results of the ground-breaking research in this area published mainly in theearly- and mid-1990s. A number of the key references are identified in thebibliography.
During the period when this project was carried out (January to December 2005),research on related topics was also being carried out by the EIC (which will bepublished as BS 8485 Code of Practice for the characterisation and remediation of ground gasin brownfield development, in the near future) and by the NHBC (Boyle andWitherington, 2007). All the research contractors have cooperated fully to ensure thatthe results of these projects are complementary to, and generally consistent with eachother, and that conflicting advice has not been produced.
1.5 AUDIENCE
This guidance has been written to be relevant to all parties/ stakeholders involved inthe consideration of land and/or development (existing or planned) of land, affected bypotentially hazardous ground gases and vapours. The target audience will include landowners, developers (commercial and residential), professional advisors/consultants
CIRIA C665 3
(both engineering and environmental), builders and contractors, regulators(Environment Agency, local authority building control) and other professional and non-specialist stakeholders.
1.6 STRUCTURE OF THE PUBLICATION
Figure 1.1 illustrates the structured procedure for the assessment of hazardous groundgases. This structure is also reflected in the layout that has been adopted in thispublication. The figure is a flow chart that has taken as its basis the framework from theModel Procedures (Defra and Environment Agency, 2004a). The publication followsthis logical sequence; describing the tasks involved in the development of an initialconceptual site model and its relationship to hazards related to gases, then setting outthe process and techniques necessary to clarify uncertainties or potentially unacceptablerisks identified in this model. The methodologies available to assist in the assessment ofrisk associated with ground gases are then described. The assessed level of risk is thendirectly linked to the need for and scope of remediation, with the options forremediation set out in sequence from simple passive venting measures through to morecomplex multi-barrier and active systems. Guidance is also provided on the long-termmonitoring and management of gas control systems.
The text is supported, where possible, by worked examples and case studies presentedin boxes. “Quick reference” and “example” text boxes provide summarised advice.Detailed advice and information is also presented in a series of supporting appendicesoutside of the main text.
CIRIA C6654
CIRIA C665 5
Figure 1.1 The process of managing risks related to hazardous ground gases
Is post installation/constructionmonitoringrequired?
Source(s) of gas(es)/vapour(s) identified?
Has monitoring beencarried out undervarying conditions
likely to influence thegas vapour regime?
Is data reliable?(eg appropriate response
zones, variable/unrepresentative
groundwater levels)
Are there potentialunacceptable risks?
Have these factorsidentified the potential
presence ofgases/vapour
Has development ofmodel included sitespecific factors thatmay influence gas/
vapour regime?
Carry out phase one desk study
Develop initial conceptual sitemodel and undertake preliminary
risk assessment
Identify further actions to clari-fy potential unacceptable risks
Establish objectives of anyfurther investigations
Review data
Undertake appropriate risk assessmentmodelling. Define gas regime
No further actionrequired
Undertakeadditionalintrusive
investigations
Detailed evaluation ofremedial options
Develop a remedial strategy
Design, implementationand verification of
remedial measures
No further actionrequired
Site characterisation Assessment of risk Determination/validationof remediation
Undertakeadditionalintrusive
investigationsand/or
monitoringand sampling
Results sufficientlyconsistent/reliable
Extent of source(s)established?
Amber RedGreen
No further actionrequired
Does risk assessmentdemonstrate corrective
action required?
Has sufficient databeen obtained to allowthe selection/design ofappropriate remedial
solutions?
Completion/validation report
Reviewamend
remedialstrategy
No
Yes
Yes
Yes
No
No
No
Yes
Yes
Yes
Yes
Yes
YesNo
No
No
No
No
Yes
Yes
No
No
Yes
No
Define the context anset the objectives
Identify feasibleremedial options
Identify remedialobjectives to mitigate
unacceptable risks
Undertake post installation/construction monitoring
Is the monitoringdata acceptable?
Refine conceptual site model
Consider odour and toxicity and incorporateinto risk assessment as appropriateCarry out further investigation