A Practical Guide to Environmental Risk Assessment for ... · A Practical Guide to Environmental Risk Assessment for Waste Management Facilities Guidance Note 25 Version 2 National

A Practical Guide to EnvironmentalRisk Assessmentfor Waste Management Facilities

Simon Pollard, Dave Purchase and Sue Herbert

Guidance Note: 25 8 November 2000

Title: A Practical Guide toEnvironmental Risk Assessmentfor Waste Management Facilities

Guidance Note 25Version: 2

Approval Signature Date

Distribution: Environment Agency & External

Dr Jimi Irwin 8 November 2000

A Practical Guide to Environmental Risk Assessment for Waste Management FacilitiesGuidance Note 25 Version 2

National Centre for Risk Analysis and Options Appraisal Page i

Keywords: waste management licensing, environmental risk assessment

Links to Duties and Powers: Environmental Protection Act Part II, sections 35(3), (4), (5),(8), 36(3), 37 & 42(1); Waste Management Licensing Regulations, regulation 19, Schedule 4,paragraphs 4(1)(a), 6.

Public Domain References: see bibliography

Internal References: see bibliography

Contact Details:Simon Pollard, Risk Analysis Manager, National Centre for Risk Analysis and OptionsAppraisal, Steel House, 11 Tothill Street, London, SW1H 9NF; Tel: 020 7664 6832; Fax: 0207664 6836; email: [email protected]

David Purchase, Regional Waste Licensing Manager, North West Region, P.O. Box 12,Richard Fairclough House, Knutsford Road, Warrington, WA4 1HG; Tel: 07768 276931;Fax: 01925 242209; email: [email protected]

Status: Environment Agency, External

Acknowledgements: The Agency acknowledges contributions from the following in thepreparation of Version 2:

Agency staff:Dave Bliss, Ian Brindley, Karen Byrom, Charlotte Danvers, Bill Darbyshire, Steve Eland,Peter Elliott, Dave Fleming, Jan Gronow, Mike Harget, Jill Leather, Mark Maleham, TonyMarsland, David Parr, Brian Payne, Pandora Rene, Jonathan Smith, Mark Stringer andHoward Thorp.

Industry – the Environmental Services Association Risk Assessment Sub-group:Beth Bracewell (Sita), Pat Corker (Aspinwall), Francis Crozier (Entec), Lesley Heaseman(Chair) (M J Carter and Associates), Nick Holmes (ESA), Graham Peacock (Biffa), JonWeetman (Shanks), Chris Young (WRc).

The Agency further acknowledges the contributions and feedback received from Agency staffin the development of the Shell Licensing Kits and training in their use.

This Guidance Note replaces Version 1 (issued as Version 1.1, Consultation Draft forComment, 8 March 1999). The Environment Agency officers, servants or agents accept noliability whatsoever for any loss or damage arising from the interpretation or use ofinformation, or reliance upon the views, contained herein.


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EXECUTIVE SUMMARY

This document provides technical guidance to Environment Agency staff and to applicants onthe practical environmental risk assessment tools that can be used in the waste managementlicensing process to assist in the design and operation of sites to prevent pollution. It shouldbe used alongside the DETR/EA Guidelines for Environmental Risk Assessment andManagement (DETR, Environment Agency and Institute for Environment and Health, 2000),that provide general guidance on the Agency’s expectations of risk assessment work. Itsupports the Agency’s Licensing Process, the Library of Licence Conditions and WorkingPlan Specifications and the Shell Licensing Kits that have been derived from the Library toapply to specific types of waste management facility. The tools described fit within the tieredapproach to environmental risk assessment which is adopted by the Agency (Figure 1). Theguidance is arranged in the following sections:

1. IntroductionIntroduces the concept and stages of environmental risk assessment. Describes the contextand coverage of the principal guidance documents on environmental risk assessment asapplied to waste management facilities, including this guidance.

2. The approach to risk assessment and risk management.Describes the ‘source-pathway-receptor’ approach as the basis for risk assessment, and therisk assessment and risk management questions which are being asked and answered at eachtier and stage of the assessment. Explains the relationship between risk assessment and riskmanagement systems. Links this approach to options appraisal and cost benefit assessments,and to other permitting regimes for waste management installations (PPC permitting andLandfill Directive).

3. The use of risk assessment in waste management licensing.Describes the relationship between the tiered approach to risk assessment and risk-basedlicensing, based on the Agency’s licensing tools – the Licensing Process, the Library and theShell Licensing Kits – and the resulting products of the process – the licence conditions andthe working plan. Explains what an applicant should provide in terms of a risk assessmentand working plan. Includes an Agency decision flowchart for the use of the Shells.

4. Developing the conceptual model.Explains the importance of good problem definition, and the development of a goodconceptual model as the basis for a risk assessment, and how it is carried out and developedthrough Tier 1, 2 and 3 assessments.

5. Tier 1: Screening of environmental risks.Explains what Tier 1 screening assessment is, based on the ‘source-pathway-receptor’approach, and describes its use in the form of the Shell Risk Assessments which form thebasis of the Shell Licensing Kits. Discusses the use of scoring in the rating and prioritisationof risks and risk management systems.

6. Tiers 2 and 3: Detailed environmental risk assessment.Outlines the types of detailed assessments which may be carried out under Tiers 2 and 3.

The descriptions given of these techniques are not prescriptive, but summarise the generalphilosophy and approach of each technique. Examples of these approaches are given in the


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appendices. The approach described in this guidance allows for flexibility in selection ofspecific risk assessment tools, within the overall good practice framework described. Furtherinformation on the Agency’s general approach to environmental risk assessment can be foundin DETR, Environment Agency and Institute for Environment and Health (2000) and thereferences in the bibliography.

Figure 1: Tiered Approach to Environmental Risk Assessment and Management(after DETR, Environment Agency and Institute for Environment and Health (2000)

Problem Formulation

Risk Prioritisation Hazard Identification

Identification ofConsequences

Magnitude of Consequences

Probability of Consequences

Significance of the Risk

** SSttaaggeess wwiitthh eeaacchh tt iieerr ooffRRiisskk AAsssseessssmmeenntt

Economics Technology

Social Issues Management

Risk Management

Tier 1 Risk Screening *

Tier 2 Generic QuantitativeRisk Assessment *

Tier 3 Tailored QuantitativeRisk Assessment *

OOppttiioonnss AApppprraa iissaall

Tiered approaches to riskassessment allow application oftools in proportion to thecomplexity and priority of the risk.They also help in ensuringproblems are properly defined andscoped out prior to the applicationof numerical methods. This is theapproach promoted in the revisedDETR/EA Guidance onEnvironmental Risk assessment andRisk Management (DETR,Environment Agency and Institutefor Environment and Health, 2000).

Collect data & iterateprocesses wherenecessary


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CONTENTS1 INTRODUCTION............................................................................................................1

1.1 What is environmental risk assessment? ..............................................................................................................1

1.2 Scope and Context of this Guide............................................................................................................................1

1.3 Further information and guidance ........................................................................................................................2

2 THE APPROACH TO RISK ASSESSMENT AND RISK MANAGEMENT...........7

2.1 Introduction...............................................................................................................................................................7

2.2 The ‘source-pathway-receptor’ concept as the basis for risk assessments.....................................................7

2.3 Options appraisal and risk management decisions......................................................................................... 10

2.4 Risk management measures for waste management facilities ....................................................................... 11

2.5 Primary and residual risk management ............................................................................................................ 11

2.6 The need to consider risk management measures for the site as a whole.................................................... 12

2.7 Where do costs and benefits fit in?..................................................................................................................... 12

2.8 Environmental risk assessments for licensing in relation to those for PPC permits and the LandfillDirective............................................................................................................................................................................. 13

3 THE USE OF RISK ASSESSMENT IN WASTE MANAGEMENT LICENSING15

3.1 Risk assessment and waste management regulation ....................................................................................... 15

3.2 Environmental risk assessment questions for waste management licensing: stages, tiers, tools andtechniques.......................................................................................................................................................................... 15

3.3 Waste management licences and risk-based conditions................................................................................. 16

3.4 The Library of Licence Conditions and Shell Licensing Kits ........................................................................ 17

3.5 The tiered approach in relation to the Library and Shells ............................................................................. 18

3.6 What should an applicant provide?.................................................................................................................... 21

3.7 Licence conditions, risk assessments, risk management systems and working plans................................ 21

4 DEVELOPING THE CONCEPTUAL MODEL........................................................23

5 TIER 1: SCREENING OF ENVIRONMENTAL RISKS.........................................27

5.1 Introduction............................................................................................................................................................ 27

5.2 Screening of environmental risks for waste management sites ..................................................................... 27

5.3 Shell Risk Assessments.......................................................................................................................................... 28

5.4 The ‘source’ of environmental risks................................................................................................................... 29

5.5 Hazardous events and pathways......................................................................................................................... 30

5.6 Environmental receptors...................................................................................................................................... 31

5.7 The environmental risks that are assessed........................................................................................................ 31

5.8 The risk management systems that may be required, and default standards.............................................. 31

5.9 Site-specific variation from the default risk management requirements...................................................... 31

5 . 1 0 Scoring, rating and prioritisation of environmental risks......................................................................... 33

6 TIERS 2 AND 3: DETAILED ENVIRONMENTAL RISK ASSESSMENT...........35


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6.1 Detailed quantitative risk assessments............................................................................................................... 35

6.2 Tier 2: Generic Quantitative Risk Assessment ................................................................................................ 37

6.3 Tier 3: Tailored risk assessment........................................................................................................................ 37

6.4 Event and fault tree analysis................................................................................................................................ 38

6.5 The selection of appropriate data for tailored risk assessment..................................................................... 40

7 GLOSSARY....................................................................................................................41

8 BIBLIOGRAPHY..........................................................................................................44

9 APPENDICES ................................................................................................................46

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1 INTRODUCTION

1.1 What is environmental risk assessment?

Risk assessment is a management tool that aids decision-making and which is used widelywithin regulation, business and finance. It involves the separate consideration of thelikelihood and the consequences of an event, for the purposes of making decisions about thenature and significance of any risks, and how best to manage any unacceptable risks. It is anactivity which is familiar to and performed by us all, albeit intuitively. Environmental riskassessment requires an understanding of the source of a hazard to, or from, the environment,the characteristics of an environmental receptor that may be at risk from that hazard, and themeans, or pathway, by which the receptor may be affected by that hazard.

Environmental risk assessment is fundamental to all phases of development of wastemanagement facilities, from the strategic planning level through to the licensing of anindividual facility (see the Environment Agency policy on the location and impact of wastemanagement facilities given in Environment Agency, 2000j). At the strategic level, riskassessment informs decisions about land use, and subsequently underpins assessment of theenvironmental impact associated with the site location that is considered through thedevelopment planning process. In the context of waste management licensing, environmentalrisk assessment is used to enable the operator and the Agency to identify whether and whatrisk management options, or mitigation measures, are required to adequately prevent, control,minimise and/or mitigate the identified risks to the environment from that site. Thesemeasures are normally stipulated as licence conditions or in the working plan.

Environmental risk assessment is essential for all waste management facilities and the riskinformation gained will be key to regulatory decisions made by the Agency and others.

1.2 Scope and Context of this Guide

This Guide describes the current Agency approach and supporting tools for environmentalrisk assessment in waste management licensing. It explains the use of some practical toolsthat will assist licence applicants and Agency officers in carrying out and reviewing riskassessments, so that they can identify and define the engineered and operating systems thatwill be necessary and appropriate to ensure that any unacceptable risks are managedeffectively.

The Guide does not represent a specification for work, nor does it aim to be prescriptive or toset out how standards themselves are defined by the Agency. It should be used alongsideother Agency licensing tools and guidance, taking into account relevant statutory and bestpractice guidance, to inform the decision-making process. Applicants have flexibility in theirselection of specific techniques and professional judgement will be required of Agency staffand applicants as to what level of detail is required. Guidance on this is included.

Whilst this Guide focuses on risk assessment for the licensing phase of development of awaste management facility, readers must bear in mind that, in the same way that licensing isnot carried out in isolation from the outcome of the planning process, risk assessment forlicensing should not be divorced from earlier risk assessments carried out for planningpurposes. The principles and approach to risk assessment, described in this Guide, areequally applicable to risk assessment at the planning phase, although the level of detail of a



risk assessment required at the licensing phase will often be greater. Risk assessment is aniterative, developing activity, and that carried out for licensing purposes should always buildon and take account of earlier risk assessment findings.

Table 1, based on that included in the Environment Agency policy on the location and impactof waste management facilities (Environment Agency, 2000j), provides a brief overview ofthe level of risk assessment typically required for the different phases of development of awaste management facility. This table is not intended to be prescriptive, but to indicate howthe requirements of risk assessment change, and increase in detail, through the process ofplanning and developing a facility. Figure 2 develops this further to show that the focus ofthe risk assessment work (or effort) changes through these development phases from themacro scale where the interest is in land use and major issues such as site location,fundamental design principles, to the micro scale, where the effort is spent on ensuring thatdetailed design and operational matters are adequate.

1.3 Further information and guidance

The Department of the Environment, Transport and the Regions (DETR) and theEnvironment Agency have produced a range of guidance to support the use of environmentalrisk assessment, both in general and also with specific application to waste managementregulation. These will be of assistance to users of this document. The context and coverageof some of the principal documents is shown in Figure 3. The following documents areparticularly noted.

• For those unfamiliar with the practical aspects and basic terminology of environmentalrisk assessment, the Environment Agency has produced a general document ‘IntroducingEnvironmental Risk Assessment’ (Environment Agency, 2000a).

• Information and general guidance on the tiered approach to environmental riskassessment and the practical considerations involved can be found in ‘Guidelines forEnvironmental Risk Assessment and Risk Management’ (DETR, Environment Agencyand Institute for Environment and Health, 2000). This Guide adopts and supports theprinciples described in the Guidelines.

• Guidance on risk assessment requirements for planning purposes is being developed bythe Environment Agency (e.g. Environment Agency, 2000g).

• With respect to the specific requirements of Regulation 15 of the Waste ManagementLicensing Regulations 1994 (assessment of the impact on groundwater), the Agency hasissued separate guidance (Environment Agency 1999a).



Table 1 : Overview of waste management facility development phases and environmental risk assessment

D E V E L O P M E N T P H A S E KEY ISSUESCONSIDERED

LEVEL OF RISK ASSESSMENT 1 ASSESSMENT TOOLS

PHASE 1:Strategic planning, e.g.:• Waste local plans• Mineral local plans

• Site location• Basic function (e.g.

broad types of waste,overall capacity)

Risk screening (Identify major hazards andreceptors)

• Maps of location of major and minor aquifers(vulnerability maps) – eventually locations of“groundwater bodies” under the WaterFramework Directive;

• Catchment protection zones (e.g. GroundwaterSource Protection Zone 3, Dee catchment);

• Floodplain maps;• Statutory conservation zones (SSSI etc).

PHASE 2A:Pre-planning assessments –scoping and screeningassessments for EnvironmentalImpact Assessment Regulations.

Fundamental elements ofdesign and operation.

Risk screening (Identify all hazards andreceptors)

• As above, but all groundwater protectionzones, mapped conservation areas etc.

• Scoping guidance.

PHASE 2B:Planning applications 2;and Stage 1 PPC applications(where appropriate)

Operational principles, sitelayout, major constructionelements e.g. type of landfilllining. Initial design withoutbenefit of planningconditions.

Tiered risk assessment on major elementsof design, construction and operation.(Assess all pathways and impacts)

• Site specific assessment – site investigations,local mapping etc.

• Risk assessment guidance and tools (e.g.LandSim)

PHASE 3:Environmental authorisations 2;e.g. Waste management sitelicence, IPC, PPC

Detailed design taking intoaccount planning conditions,formal feedback fromAgency etc.

• Review and/or identify all hazards andreceptors

• Tiered risk assessment on detaileddesign, construction and operation.(Assess all pathways and impacts)

• Site specific assessment, as above.• Risk assessment for waste management

licensing (this guidance, Shell RiskAssessments and, for example, LandSim).



Notes:1. See DETR, Environment Agency and Institute for Environment & Health, 2000.2. Planning applications and environmental authorisations may be progressed in parallel.



StrategicPlanning

Figure 2: Risk Assessment Effort related to Waste Management Facility DevelopmentPhases

ScopingAssessmentTier 1

Tier 2

Tier 3

Licensing

PlanningApplication

RiskAssessment

Scale of Analysis

WasteManagementFacilityDevelopmentPhases

STRATEGIC PLANNING

Legend:

Scale: Macro – e.g. Site location, basic function Intermediate – e.g. Site layout, major construction elements Micro – e.g. Material specifications, operation details

T3

T2

T1

Scale

Mac

ro

Mic

ro

LICENSING

T3

T2

T1

Scale

Mac

ro

Mic

ro

PLANNING

Macro Micro

Mac

ro

Mic

roScale

T3

T2

T1

Risk Assessment Effort

Tie

r

Intermediate



Figure 3: Context and coverage of principal guidance documents on environmentalrisk assessment as applied to waste management licensing

DETR, EnvironmentAgency & Institute forEnvironment andHealth, 2000. Guidanceon Environmental RiskAssessment and RiskManagement.

EnvironmentAgency, 2000g (inpreparation). ScopingGuidance on theEnvironmentalImpact Assessmentof Projects.

EnvironmentAgency, 2000a.IntroducingEnvironmentalRisk Assessment .

Genericguidance onprinciples ofenvironmentalrisk assessmentfor publicdomainenvironmentalrisk assessments

EnvironmentAgency, 2000.A Practical Guideto EnvironmentalRisk Assessmentfor WasteManagementFacilities (GN25)(this guidance).

Environment Agency,1998. InterimFramework Policy forLandfill Engineering.

Environment Agency,1999. Interim InternalGuidance onInterpretation andApplication ofRegulation 15.

Department of theEnvironment,1994a. Circular11/94;Department of theEnvironment,1995. W asteManagement Paper26B.

Leafletintroducinggeneralprinciples fornon-specialists

Environment Agency, 1999b &2000c. Library of Licence Conditionsand Working Plan Specifications.

Site-specific riskassessment forwaste managementsite(Not guidance.Document suppliedto Agency in supportof application, or byAgency in supportof Agencymodification)

Translation ofgeneral principlesto wastemanagementlicensing

Guidance on the use ofsimple risk assessmenttemplates for ‘standard’ sites

Simple riskassessmenttemplates forstandard sitecategories

Site-specific risk assessmentfor waste management site:operators document, whichmay be produced fromagreed template, or modifiedwith more detailedassessment

Environment Agency,2000d. Shell RiskLicensing Kits: Guidanceon their Derivation,Content and Use.

Environment Agency,2000d. IndividualShell Risk Assessmentpacks for selected sitecategories from therange A1-A25.

DETR statutoryguidancerelevant to riskassessment

Guidance onspecific riskassessmentssupporting theuse of theLibrary

Frameworkandguidance forapplicationof riskassessmentin use ofLibrary

Guidance onrisk assessmentrequirementsfor planningpurposes



2 THE APPROACH TO RISK ASSESSMENT AND RISK MANAGEMENT

2.1 Introduction

Environmental risk assessment and risk management typically involves answers being soughtto the following questions:

• ‘What environmental hazards are present and what are their properties?’• ‘How might the receptors become exposed to the hazards and what is the probability and

scale of exposure?’• ‘Given exposure occurs at the above probability and magnitude, what is the probability

and scale of harm?’• ‘How significant is the risk and what are the uncertainties?’• ‘What needs to be done to prevent, control or minimise the risks?’

The Agency adopts a tiered approach to answering these questions, in accordance with goodpractice, which is described in its general guidance on environmental risk assessment andmanagement (DETR, Environment Agency and Institute for Environment and Health, 2000).This is outlined in Figure 1, and indicates that assessment and appraisal effort should betargeted where risks or uncertainties are high. Early risk screening and prioritisation avoidsunnecessary detail and allows the level of approach to be matched to the needs of theproblem. If the risk management decision cannot be made based on an initial screeningassessment, then more detailed approaches are used, focusing on the key risks identified. Theemphasis is on:

i) understanding the environmental setting;ii) using simple, qualitative tools; andiii) applying greater levels of sophistication according to need.

However, it is important that all risk assessments, whether simple or complex, are carried outin a robust, systematic and transparent manner.

2.2 The ‘source-pathway-receptor’ concept as the basis for risk assessments

Fundamental to the good practice framework for risk assessment shown in Figure 1 is thesource-pathway-receptor approach. For a risk to exist, there must be an identified orplausible relationship between the three individual components of:

• source – i.e. the hazardous substance or material• receptor – i.e. the entity (e.g. human, water body, ecosystem, building, etc) that is

vulnerable to the adverse effects of the hazardous substance or material• pathway – i.e. the mechanism by which the receptor and source can come into contact

(e.g. by a hazardous event or action on site giving rise to a release of the hazardoussubstance or material to atmosphere or to ground).

The ‘source’ for waste management facilities is defined by the hazardous properties of thewaste types and operations to which they will be subjected on the proposed site. (It may alsoinclude the events which lead to the hazards associated with those wastes and/or operationsbeing transferred into the environment, although, as used in this guidance, it is more



appropriate to link such ‘hazardous events’ with the ‘pathways’ by which the hazards aretransferred.)

The environmental ‘receptors’ (or ‘targets’) are those entities which are liable to be adverselyaffected by the identified hazards transferred from the defined ‘source’ into the environmentby the identified ‘pathways’. These include, but are not necessarily restricted to:• People outside the site boundary. (People within the site boundary are only considered

where they may be trespassers or others who have gained unauthorised access – ‘sitesecurity’ requirements are imposed to prevent this situation occurring. People who arelegitimately on site - including site staff and other people who are authorised or doingother legitimate business - are covered specifically by the Health and Safety at Work Act1974 and are not considered in the environmental risk assessment);

• Properties outside the site boundary, including public and private property and placeswhere the public have access – this may also include livestock or other animals which arekept (rather than wild) outside the site boundary (or within the site boundary);

• Ecosystems, especially habitats designated in accordance with the Habitats Directive, andother designated sites;

• Surface water in the vicinity of the site;• Groundwater in the vicinity of the site;• Atmosphere, which is a receptor in regard to the risk of global warming.

The ‘pathways’ for a defined source of environmental hazards are the means by which theidentified hazards are transferred into the environment, and thence to any defined ‘receptors’in the environment. ‘Hazardous events’ and the ‘pathways’ by which the resulting hazardsare transferred into the environment are intimately linked. They include the following‘environmental pathways’:• Direct emissions of heat and shock due to fire or explosion;• Releases of polluting emissions by one or more of the following routes:

- air (or atmosphere) as pathway (it may also be a receptor for certain risks – seebelow);

- ground (including via services);- water (surface water and groundwater are receptors in their own right – see below);

• Other vectors for environmental hazards:- dust- pests;- scavengers;- litter;- noise.

If humans (or animals) are exposed to hazardous substances or emissions via one or more ofthe above environmental pathways, harm to their health may occur through a number of‘exposure pathways’. Typically these may include: inhalation or ingestion of, or dermalcontact with, hazardous substances; and the direct effects of heat and shock in the case offires or explosions. Humans may also suffer harmful effects on health through seriousdetriment to the amenity of their locality.

The type and magnitude of the harmful effects will depend upon the dose received, theparticular ‘dose-response’ relationships for those hazardous substances, and other more



specific factors such as the sensitivities of the individuals. The resulting effects on healthmay be direct or indirect, acute or chronic.

The assessment of the risks of harm from exposures to hazardous substances and emissions isvery complex and subject to wide variability between individuals. It is not specificallyconsidered except in some more detailed and complex Tier 2 and Tier 3 risk assessments,although it may form the basis of certain environmental quality criteria or targets. In Tier 1and many Tier 2 and 3 assessments, it is sufficient for the assessment to identify whether ornot a significant exposure of identified human or animal receptors is likely to occur, in orderto decide whether or not risk management measures need to be provided.

Box 1 provides an example of the source-pathway-receptor approach for a landfill generatinglandfill gas.

Box 1: Example of ‘source-pathway-receptor’ approach.

Consider the case of methane gas emanating from an active landfill site. Methane representsan explosion hazard between certain defined concentrations in confined spaces. Methaneemanating from the source (the active landfill site) at sufficient pressure poses a high risk ofharm (injury, loss of life and damage to property) to receptors in the vicinity of the site(persons and buildings) where the likelihood (or probability) of concentrations building up tothe lower explosive limit is high, due to the presence of suitable environmental pathways forlandfill gas migration and ingress into buildings (such as permeable ground strata ormanmade drains, conduits, etc).

The ‘source’ in this example is the biodegradable, methanogenic waste within the landfillsite, which is generating methane gas. The potential ‘pathways’ are the permeable groundstrata, or manmade drains, conduits, etc, around the landfill site. The potential ‘receptors’ arethe buildings and their occupants in the vicinity of the site.

If the risk assessment identifies that the risk exists from methane to nearby housing, theAgency will stipulate in the licence conditions that the operator provides and maintainsspecified systems to manage the identified risks from landfill gas emanating from the site; forexample, that they:

a) provide, operate and maintain a landfill gas management system that meets defineddesign and performance standards (for example, this may include a membrane aroundthe waste to contain landfill gases, a landfill gas collection system, and a landfill gasflaring or energy recovery system); and

b) provide monitoring points and boreholes for landfill gas around the site in suchpositions that landfill gas migrating through the ground strata from the site can bedetected; and

c) carry out a defined programme of monitoring landfill gas at those monitoring points,including analysis and reporting of the results and the carrying out of defined actionsif the measured levels of landfill gas exceed defined values.

The operator will then provide the necessary information on the systems that they willprovide and maintain to meet these requirements, in their working plan and other supportingdocumentation.



If it can be shown for a particular site, that there is no plausible connection or pathwaybetween potential releases from a specified hazardous source (e.g. a specified treatmentoperation being carried out on specified wastes with one or more environmentally hazardousproperties) and environmental receptors which are known or expected to exist in the vicinityof the site, then the situation cannot be considered to present a risk as there is no realisticsource-pathway-receptor relationship.

A decision that a realistic source-pathway-receptor relationship exists does not always meanthat there must be firm evidence of the presence of all three components: source, pathway andreceptor. However, it must be evident that the source has hazardous properties that have thepotential to adversely affect the receptors in question. Furthermore, the presence of thereceptors must be proven or be a realistic possibility. It may not always be possible to provethe presence of a pathway linking the two, but again this must be a realistic likelihood ratherthan a theoretical possibility.

In making decisions about source-pathway-receptor relationships for waste managementfacilities, the Agency will give consideration to being precautionary in the light of expectedchanges and events over the lifetime of the facility, which may result in the nature of therelationship changing with time. Decisions will be made on a site-specific basis, bearing inmind the need to be both proportionate and precautionary.

If a plausible source-pathway-receptor relationship is identified for a particular site, this willnormally be taken by the Agency to demonstrate the need for appropriate risk managementmeasures to prevent the anticipated risks being realised. In many cases, robust decisionsabout the presence of a plausible source-pathway-receptor relationship will be sufficient fordecision-making about the need for risk management measures. It may not be necessary,desirable or cost-effective to resort to more detailed quantitative assessments of theprobability and scale of risks involved, except in cases (such as the design of landfill linersystems) where it may be necessary to enable detailed design of the risk managementmeasures.

This is the basis of the tiered approach to risk assessment shown in Figure 1, that the level ofeffort put into assessing risk reflects the priority of the risk and how any risks would be dealtwith. For many waste management facilities, it will be more appropriate to put most effortinto design and management of the facility, provided that robust initial decisions are madeabout source-pathway-receptor relationships. Guidance on Tier 1 risk assessments (and theuse of the Agency’s Tier 1 Shell Risk Assessment tools) is given in Chapter 5, and on Tier 2and Tier 3 assessments in Chapter 6.

2.3 Options appraisal and risk management decisions

The purpose of carrying out an environmental risk assessment is to inform a risk managementdecision; that is, to determine what risk management measures need to be taken to preventand control the identified risks.

There may be more than one way of managing the identified risks, and the decision as towhich is the best option may need to be informed by an appraisal of their relative costs andbenefits. Waste licensing decisions include a qualitative consideration of likely costs and



benefits through the application of the test of reasonableness, and this is discussed in moredetail in section 2.7.

The applicant or operator will normally have assessed the different design options for a givenfacility at the stage of conceptual/outline design, prior to their licence application. Thedecision on whether the proposed waste management facility represents the best practicableenvironmental option (BPEO) will generally be made at the planning stage. Where a detailedoptions appraisal is required at this stage it may need to take into account relevant factors oftechnology, economics, social issues and management. This document does not includeguidance on such detailed options appraisals, since these are generally not required for thepurpose of preparing licence conditions.

If there are circumstances where a detailed options appraisal is required at the licensing ormodifications stage, then specialist guidance should be sought. As with the tiered approachto risk assessment, the approach taken should be proportional to the outcome, meaning thatthe resources required to undertake the options appraisal should not be disproportionate to thecosts and benefits of the decision.

2.4 Risk management measures for waste management facilities

Detailed guidance on the risk management measures covered by specific licence conditionsand working plan specifications is given in the Library of Licence Conditions and WorkingPlan Specifications (Environment Agency, 2000c) and in the Shell Licensing Kits which arederived from it (Environment Agency, 2000 d). (These are described in section 3.4.)

The complexity of the measures needed will depend upon the type and level of risks that thewaste management operations in question present to the environment. The measures neededto prevent and control the risks may be relatively simple, such as operational proceduresrequiring simple actions and documentation, or relatively complex, such as engineeredsystems requiring fully documented and quality assured stages of design, construction, testingand validation, operation and maintenance.

An example of the former would be waste acceptance and control procedures for a transferstation handling inert, non-hazardous or low hazard, non-special wastes. An example of thelatter would be the systems underlying the provision of an engineered site liner for a landfill,or of a groundwater monitoring programme for a landfill. These will place different levels ofdemand on supporting systems such as record-keeping, and the training and competence ofsite staff.

If the risk management provisions (simple or complex) are to be effective, they must bespecified and carried out to an appropriate and auditable standard. Risk managementprovisions to prevent emissions to the environment will usually consist of a combination ofoperational procedures and controls, engineered containment of emissions, and, as relevantand appropriate, monitoring of emissions with actions to control and minimise any emissionsthat do occur.

2.5 Primary and residual risk management

It is important to recognise that, where risk management measures are provided, thereremains a risk that these will fail to perform to the required performance standard. This is



referred to in the Library and Shell risk assessment approaches as the ‘residual risk’; that is,the risk to the environment posed by the identified hazard, taking into account the primaryrisk management measures that will be provided.

Such failures can occur due to faults in design, installation, and operation (includingmaintenance). The causes of faults and failures may include failures in hardware, software,and procedures; and will often include an element of human error. It is essential thatprovision be made to minimise the likelihood of residual risks so as to ensure that therequired standard of environmental protection is realised throughout the life of the site. Thenecessary ‘residual risk management’ should be provided so as to prevent such failuresgiving rise to significant functional failure of the primary risk management system underconsideration. Typically, this will be provided by the following measures:• during the design stage, through the site investigations and risk assessments supporting

the design process, the use of recognised design standards, and adherence to a formaliseddesign quality assurance process;

• during the installation stage, through adherence to a formalised construction qualityassurance process, supported where appropriate by a testing/commissioning stage;

• during the operational stage, through adherence to documented operational proceduresand maintenance programmes, supported by:- monitoring of the process performance and emissions; and- documented procedures for dealing with deviations from defined performance and

emission standards; and- periodic reviews of performance against the environmental emission standards and of

the environmental risk management systems for the site.

2.6 The need to consider risk management measures for the site as a whole

It will be evident from the preceding discussion that risk management measures, both for thesite and for particular operations, should be regarded as an integrated whole. A change to onepart or element of the system, such as the design standards, or the quality and content ofrecord-keeping, or the training and competence of staff, will potentially change theeffectiveness or performance of the risk management system as a whole. This means that anyproposed changes to any part of a risk management system should be assessed for their effecton the overall performance of the risk management measures, to ensure that the necessarystandards of environmental protection are maintained for that system and for the overall siteoperations.

This is the reason that the licence conditions set a requirement for proposed changes to theworking plan to be supported by a review of the relevant risk assessments, and to be pre-notified to and, where necessary, approved by the Agency before implementation.

2.7 Where do costs and benefits fit in?

Under Section 39 of the Environment Act, the Agency has a duty to take account of likelycosts and benefits in deciding whether or not to exercise its powers, and in deciding how toexercise those powers. It is important to note that this duty:

i) does not supersede the Agency’s obligations to discharge specific duties, comply withlegal requirements or meet objectives; and



ii) does not require the consideration of costs and benefits to involve their quantification ormoneterisation.

In its waste licensing decisions, the Agency has a duty to prevent pollution of theenvironment, harm to human health and serious detriment to amenities of the locality.

Licence conditions prepared using the Library or Shells are aimed at satisfying this duty andmeeting the statutory guidance (Department of the Environment, 1994a) which states thatconditions should be:• proportionate in their requirements to the risks involved and the benefits to be obtained;• goal-based, having defined objectives and specified standards and, where appropriate,

specifying the means to their fulfilment;but should not:• serve as an end in themselves;• be over-prescriptive; or• impose an unjustifiable or disproportionate burden on the licence holder, especially small

businesses.

Risk management offers the benefit of risk reduction, so risks can be characterised withreference to the costs of implementing measures to mitigate them. A level of judgement onthe test of reasonableness is therefore required on the part of the regulator when preparinglicence conditions, and also when preparing subsequent licence modifications.

2.8 Environmental risk assessments for licensing in relation to those for PPC permits and theLandfill Directive

The Pollution Prevention and Control (England and Wales) Regulations 2000 (SI 2000 No.1973) came into force on 1 August 2000. A number of types of waste managementinstallations, as defined in Chapter 5 of Schedule 1 of the Regulations, will need to beregulated under the PPC regime instead of the waste management licensing regime. Existinglicences for these types of installations will be replaced by PPC permits in accordance withthe programme defined in Schedule 3 to the Regulations.

As such, these installations will then be subject to assessments of whether they satisfy therequirements of the ‘best available techniques’ (or ‘BAT’) criterion, as defined in Regulation3. The Agency is currently developing guidance on an assessment methodology (the ‘E2’guidance and methodology) for this purpose. This will be developed, so far as practicable, tobe consistent with the relevant related methodologies under planning legislation (EIAs) andthe Control of Major Hazards (COMAH) Regulations. It will incorporate:

i) a stage to assess and compare options, to determine the best practicable environmentaloption (BPEO) for a proposed installation, consistent with the planning stage; and

ii) an environmental impact assessment stage to determine, for those options where thetechnical standards for BAT are not defined or else an alternative is sought, whether thepreferred option satisfies the BAT requirement.

Consistent with the Agency’s tiered approach and the approach for waste managementlicensing covered by this guidance, the PPC ‘E2’ approach will incorporate screeningassessments as a basis, although it may be that, due to the nature of the requirements under



the PPC regime, this will lead to a greater degree of use of detailed technical assessments ofthe Tier 2 and Tier 3 type. This is not likely to significantly affect the guidance given in thisdocument for those sites which remain within the waste management licensing regime.

The EU Landfill Directive comes into force on 16 July 2001, and is expected to be introducedin England and Wales through the PPC regime. All landfills will be required to adhere tonew requirements regarding their design and operation, and over a period of time all landfillwaste management licences will be replaced with PPC permits that comply with the LandfillDirective requirements. The Agency is developing further guidance on risk assessmentrequirements for landfills under the Landfill Directive and this document will be revised, asappropriate, in due course.



3 THE USE OF RISK ASSESSMENT IN WASTE MANAGEMENTLICENSING

3.1 Risk assessment and waste management regulation

The siting, operation and decommissioning of waste management facilities carries certainrisks that are assessed at various times within a facility’s life, from design throughconstruction and operation to decommissioning and licence surrender. Environmental riskassessment can be applied at the following stages:• at the strategic planning, pre-planning and planning stages (through submission of

environmental impact assessments and environmental statement s, including riskassessments; if detailed options appraisals are necessary they will usually be carried out atthese stages);

• during the process of waste management licensing (through the use of the Library andShells, and including requirements for a ‘Regulation 15’ assessment) (this process may becarried out in parallel to the planning application);

• during the site supervision stage (through the use of the Agency Site InspectionMethodology and the use of the Operator Pollution Risk Appraisal (OPRA for Waste)technique for prioritising inspections on a risk assessment basis – these arecomplementary to and consistent with the Library and Shell risk assessment tools)

• prior to modification of the licence or amendment of the working plan, resulting fromchanges to operation (through the use of the Library and Shells, and includingrequirements for a ‘Regulation 15’ assessment); and

• prior to site completion/closure and licence surrender (through the Licence Surrenderprocess, using the supporting risk assessment guidance for that process).

Procedural and technical guidance is provided by the various waste management papers andAgency documents, to which readers are referred. The scope and methodology of the riskassessment will be dictated by the specific requirements of each stage and the purpose forwhich the assessment is being carried out. While it should not automatically be presumed thata risk assessment undertaken for one stage will necessarily be adequate for another, there willusually be a degree of overlap, and opportunities should be taken to make use of valid andreliable assessments of risks which have been produced at earlier stages and which are ofrelevance to waste management licensing. In particular, the potential to screen risks duringany environmental impact assessment (EIA) carried out at the planning stage should beregarded as a valuable opportunity to undertake work of relevance to licensing the site.Similar opportunities should be sought through the preparation of site-specific riskassessments supporting a ‘Regulation 15’ assessment for facilities where List I and IIsubstances are of relevance.

3.2 Environmental risk assessment questions for waste management licensing: stages, tiers, toolsand techniques

Environmental risk assessment for waste management licensing should not be carried outeither for its own sake or in isolation, but in order to assist the making of risk managementdecisions in a cost-effective manner. The practical objective is to provide answers to thequestions of:



i) what risk management measures are required for a particular site; and henceii) what needs to be specified in the licence conditions and described in the working plan.

Appendix 1 provides a breakdown of these into the following questions:

A. What is the nature of the site (including the waste management operations) and its environmentalsetting?

B. Is there a risk to the environment from the waste management operations on this site?

B1. What hazards are present and what are their properties?

B2: What are the potential environmental consequences that may arise from the identified hazards?

B3. What is the magnitude of the consequences for the identified potential receptors?

B4. How might the receptors become exposed to the hazards?

B5. What is the probability of the hazard occurring?

B6: What is the probability of the receptors becoming exposed to the hazard?

B7: What is the probability of harm resulting from exposure to the hazard?

B8. How significant is the risk?

B9. What are the uncertainties? (Is a more detailed risk assessment needed?)

C. What are the options for management of the identified risks?

D. What needs to be done to minimise the environmental risks?

E. Does the risk assessment need to be reviewed or revised?

The table in Appendix 1 indicates how, in addressing these questions:a) the tiered approach to risk assessment and the identification of appropriate risk

management measures would be applied at Phase 3 (Environmental authorisation: wastemanagement licensing – see Table 1); and

b) hazard identification, risk assessment and identification of appropriate risk managementmeasures would be carried out using the tools and techniques appropriate for wastemanagement licensing,

The table includes an example of how a Shell Risk Assessment approach would be applied(as explained in the following sections and Chapter 5) in the case of a waste transfer stationhandling household, industrial and commercial wastes, for the particular hazard of wasteswhich are likely to produce emissions of dust to atmosphere.

3.3 Waste management licences and risk-based conditions

A waste management licence is issued with conditions attached. The conditions relate to theactivities the licence authorises; and the precautions to be taken and/or works to be carriedout in connection with, or in consequence of those activities. Requirements may therefore be



imposed in the licence, to be complied with before the activities authorised by the licencehave begun, or after they have ceased.

The objective of a waste management licence is to ensure that the licensed facility does notcause either pollution of the environment or harm to human health and does not becomeseriously detrimental to the amenity of the locality. The Agency aims to set licenceconditions which specify (to the level of detail necessary to meet this objective) the riskmanagement provisions and the standards they must meet. It is a basic requirement of wastemanagement licensing that licence conditions should be specific to the site in question. Thisdoes not obviate the use of templates, or the use of benchmark requirements for typical sitesas default standards, provided that the process is supported by a risk assessment of thesources, pathways and receptors of environmental risk for the site in question in relation to itsspecific environment.

Use of the Library and Shell tools enables the Agency to set licence conditions based on theassessed environmental risks at the specific site in question. The licence conditions willrequire an appropriate type and level of engineered and operational systems to be providedthat will prevent, control and minimise those risks to acceptable standards.

3.4 The Library of Licence Conditions and Shell Licensing Kits

The Library provides tools for:• the production of risk-based site-specific licence conditions, based on the use of Library

Condition Templates; and• the production and assessment of working plans, based on the use of Working Plan

Specifications.

Licences drafted using the Library and this guidance contain a “customised” set of conditionsreflecting the environmental risks identified from a site-specific risk assessment. However,the Library is a complex tool applicable to the full range of waste management operationsthat span the whole spectrum of environmental risk. The work involved in preparing,assessing, consulting and finalising the site-specific risk assessment, the working plan and thelicence conditions, can be complex and demanding on resources.

As experience of using the Library and the Licensing Process has grown it has becomeapparent that there are opportunities for streamlining the process. As a consequence ShellLicensing Kits are being developed and issued in order to provide optional ‘starter packs’ fortypical sites in certain categories falling within the Agency’s site classification system (A1 toA24). This classification is currently used by the Agency for waste management licensingprocess records and Agency OPMs, for the site inspection methodology and OPRA forWaste, and for waste strategy site classifications.

Each Shell Licensing Kit is intended to stand alone, without recourse to the Library or itssupporting guidance unless necessary for particular issues. Each kit includes, specific to thecategory of site covered:• Guidance notes on the derivation, content and use of the Shell Licensing Kit.• A Shell Risk Assessment pack, based on a generic Tier 1 screening risk assessment for a

typical site in that category, which is used by the applicant to produce a risk assessment



which is specific to their proposed site, and which identifies the risk managementprovisions that will be required and will be described in the working plan. (The structureof the Shell Risk Assessment is discussed in more detail in Section 5.)

• A specification of the information needed in the working plan for a typical site in thatcategory (based on the Shell Risk Assessment), which is used by the applicant to producethe site-specific working plan, describing the risk management systems that will beprovided on the basis of the site-specific risk assessment.

• A template of the licence conditions for a typical site in that category (derived from therelevant Library condition templates), which is used by the Agency to prepare the site-specific licence conditions, taking into account the applicant’s site-specific riskassessment and working plan.

The Shell approach permits a degree of flexibility in how the specified standards can bedelivered. In producing site-specific conditions, variations from the shell licence templatecan be accommodated provided that they are justified on the basis of the site-specific riskassessment and recorded in the audit trail documentation. This will provide the necessarysupport for the resulting site-specific licence.

Each site/application will still require individual decisions to be made specifically in respectof it. However, properly used, shell licensing kits will enable significant streamlining of therisk assessment and licence drafting processes. They will also assist in ensuring thatoperating standards required for sites of the same type are consistent, whilst still allowinglicences to reflect site-specific differences, e.g. in risk management requirements.

3.5 The tiered approach in relation to the Library and Shells

The Library of Licence Conditions includes an Index of Library Conditions, which provides atabular framework, based on the type of facility and the waste management operations, foridentifying:• the Library Condition templates which will need to be included in the licence; and for

risk-based conditions• the risk management provisions which the condition will cover in its requirements; and• the level of risk assessment which is required for the site.

Application of the Library risk assessment framework allows for the fact that acomprehensive risk assessment for any single waste site may require more than one tier ofapproach, according to the issues under study. This allows for an increasing focus on thoseaspects of the facility that present a higher risk and may require more detailed assessment.The framework does not prescribe the risk assessment tools that should be used within eachtier, but does suggest the applicability of Tier 1-type screening tools, and more detailed Tier2-type generic and Tier 3-type tailored risk assessments based on quantified modellingtechniques (refer to Figures 1 and 2). The framework indicates a level of risk assessment thatwould normally be required but it is recognised that site-specific issues may override andplace more onerous requirements on specific installations. Application of individual riskassessment tools within the overall framework is at the discretion of the applicant.

Figure 4 shows how the use of the Library and Shell Kits fits into the Agency’s tieredapproach to risk assessment (as outlined in Figure 1). The Agency decision process for usingShell Licensing Kits in processing an application is shown in the flowchart in Figure 5.



Figure 4: Tiered Environmental Risk Assessment Approach applied toWaste Management Licensing

Pre-application tools:Development of conceptual model, and scoping of site design,operation, & environment (some of this will have been carriedout during the statutory planning process)

Tier 1: Risk screening assessment(using Shell Risk Assessment pack where available)

Tier 2: Generic quantitative RA

Tier 3:Tailored quantitative RA

Use of Shell Licensing Kit tools:Shell Licence Template;Shell Working Plan;Shell Financial ProvisionAssessment;Shell Audit Trail.

Risk assessment outcome: Site-specific risk assessment

Need tocompare riskmanagementoptions

Complex risks

Iteration andreview of riskassessment orriskmanagementstandards,whererequired

Use of Library tools:Licence Condition Templates;Working Plan Specifications ;Financial ProvisionAssessment;Library Audit Trail.

Site-specificvariations,whererequired

Review of sitedesign andoperation, wherenecessary

Licence and working plan preparation output:Site-specific: Risk management systems;

Working plan;Licence conditions;Financial provision assessment;Licence conditions audit trail.

Risk scoring,ranking &

prioritisation(see section 5.10)

Default riskmanagement standards

Deviations from ShellRisk Assessment; &/orneed for detailedquantitative assessment

Risk assessment tools

Tailored riskmanagement standards

Ranked riskmanagementoptions

Ranked riskmanagementoptions



2 Agency DecisionsPre-application

discussions Has a Shell Kit been issued tocover this type of site? Use Library of Licence Conditions &

supporting guidanceFollow full process for use of Library

Does the applicant/operator wantto follow the Shell Licensing Kitfor this application?

Yes

No

Yes

No

No

Assessment ofapplication – Shell

Working Plan

Provide applicant with copy ofappropriate Kit andexplain its use

Yes

Does the risk assessmentcompleted by theapplicant/operator (Section 2 ofthe pack) fit the site and proposedoperations?

• Identify relevant deviations from‘fit’;

• As appropriate (see guidance) eithercarry out or require operator to carryout risk assessment to necessary levelof detail

Assessment ofapplication – ShellRisk Assessment

pack

Do the risk management systemstandards accepted or proposed bythe applicant/operator (Section 2 ofthe pack) provide the necessarylevel of environmental protection?

• Identify relevant site-specificstandards;

• As appropriate (see guidance) eitherprovide or require operator to providejustification for site-specific standard

No

Yes

Does the working plan provide thenecessary information in thenecessary form?

No

Yes

• Identify necessary amendments;• Require operator to provide

amended working plan section(s)

Do the Shell licence conditionsrequire site-specific variations(other than the standard inserts)?

Drafting of licenceconditions – ShellLicence Template

• Identify necessary variations;• Carry out justified amendments;• Use Library Condition Templates

for any justified additional conditions;• Record changes in audit trail

Finalising licenceconditions – Shell

Audit Trail

Yes

Finalise and quality assure licenceconditions, and complete audittrail

No

Assessing financialprovision – Shell

Financial ProvisionAssessment

Agency Actions

Completion of the following actionsshould, subject to satisfactoryoutcome, be followed by returning tothe ‘Decision’ chain

Do the applicant’s financialprovisions give the necessary levelof cover?

Application received

Yes

No

• Identify necessary amendments;• Require operator to provide

amended financial provision

• Process financial provision

Figure 5: Decision flowchart for the use of Shell Licensing Kits in applications



3.6 What should an applicant provide?

The Agency requires a specific risk assessment to be submitted for all applications for awaste management licence. This must be developed according to the principles and goodpractice set out in this guidance and must be site-specific.

The Agency expects applicants will wish to work through the tiered approach outlined inFigures 1 and 4, using the Library risk assessment framework or, where a Shell Licensing Kitis available, the relevant Shell Risk Assessment tool. It is expected that risk assessmentsundertaken in support of Environmental Impact Assessments (EIA’s) and the relevantplanning application will be used to inform this process, where they have been carried out.

The degree of sophistication of the risk assessment should reflect the particular conditions ofthe site. However, all environmental risk assessments should be based upon reasonablescenarios, data and assumptions. The development of a clear conceptual model (see Section4) is critical to the analysis.

Tier 1 risk screening assessments may be sufficient where these give a clear demonstration ofthe anticipated level of risk and that the proposed risk management provisions are fit forpurpose, giving the required standard of environmental protection (see Section 5). This mayinclude, where justified, an assessment that the hazard and associated risks are soinsignificant, that they do not require prevention, control, or monitoring. (The available ShellRisk Assessments have been developed to fulfil these requirements for the categories of siteto which they apply – see Section 5.) The output of the Tier 1 assessment should be astatement with justification, of the risks identified and a specification of appropriate riskmanagement provisions. The statement should include details of any significant uncertaintyor disagreement over the required standards or their justification, and proposals for resolvingthese.

Where a Tier 1 analysis provides insufficient understanding of the risks, a Tier 2 or Tier 3assessment should be carried out, as appropriate (see Section 6). The output should be adescription of the identified risks according to significance, identification of those risksrequiring control or reduction and details of the proposed risk management measures. Itshould provide sufficient understanding of the contributing factors to establish the variousoptions for managing the risk (see Figure 1 and section 2.3).

3.7 Licence conditions, risk assessments, risk management systems and working plans

In licence conditions prepared using the Library or Shells, Condition 1.1 sets limits for thewaste management operations that may be carried out on the site under the licence, andcondition 1.2 sets limits on the wastes that may be received on the site and subjected to thoseoperations, in terms of the types of waste and their environmentally hazardous properties.

The specification of the operations and of the waste types and hazards, taken together,characterise the source of the risks to the environment that will be posed by the site. Theytherefore determine the measures that will be necessary to prevent and manage those risks tothe environment, and the scope of the other licence conditions that will be necessary. Thoseother licence conditions will define the risk management systems that must be provided bythe operator, and will set the performance standards that those systems must meet. The



working plan will therefore need to describe the site operations and risk management systemsto a level of detail that shows, clearly and convincingly, that those requirements andstandards will be met.

The licence conditions and sub-conditions prepared using the Library or Shell templates willfall into two basic types:• conditions that set absolute standards which include specifying the means by which they

shall be achieved; and• conditions that set a standard but specify the means by which it shall be achieved by

including a reference to specified section(s) of the working plan.

Although the working plan is produced by the operator and is their document, those sectionsspecifically referenced in the licence conditions become an operational and enforceable partof any licence issued. The Agency therefore approves those referenced sections of theworking plan prior to the issue of a licence. The licence conditions will also include:

• a general requirement that any proposed changes to those referenced sections of theworking plan must be supported by an assessment of their effect on the environmentalrisks of the site, and notified to the Agency before they are implemented; and

• a specific requirement for those sections of the working plan which are identified asdescribing environmentally significant risk management provisions, that the changes areapproved by the Agency before they are implemented.

The environmental risk assessment of the site therefore becomes a ‘living document’ which iskept under review throughout the life of the site.



4 DEVELOPING THE CONCEPTUAL MODEL

Fundamental to environmental risk assessment is the problem definition (or formulation)stage, which enables a clear picture to be established of the site and its environment, basedupon the nature of the site (including the wastes to be received and handled, and the wastemanagement operations to be carried out) and its environmental situation (including thepotentially vulnerable environmental receptors in the vicinity of the site).

Irrespective of the tier of the assessment being undertaken, the first key steps are to identifythe hazards and consequences that might arise. The hazards for a waste management facilitycan be readily identified from knowledge of the types of wastes to be accepted and theprocesses they will undergo at the facility, be they treatment, storage, disposal, etc.

Then, it is critical to have an understanding of the circumstances of exposure – what or whois exposed to which hazards and by what means; i.e. the receptors and the pathways. Theassessor should ‘draw a picture’ of the site and its environment, which will enable them toidentify and analyse:

• the sources of environmental hazard that the site will present during its operations;• the potential events and pathways by which the environment will be exposed to those

hazards;• the potential receptors or targets who will be impacted by those hazards; and• the potential consequences to or effects upon those receptors or targets.

This will usually be achieved by literally sketching out and then refining drawings andplan(s) of the site, which show the proposed, or existing, waste management facility and itsenvironment. This will enable the assessor to develop a valid and reliable model (a‘conceptual model’) of the site, its hazards and its environment. The model may be basedsolely on plans and/or diagrams, but will more usually include a table or spreadsheet whichidentifies the sources of environmental hazards that the site will present, the potentialpathways and the potential receptors, and helps the assessor to screen and assess theenvironmental risks with confidence. (DETR, Environment Agency and Institute forEnvironment & Health, 2000.)

The plans, diagrams and models will be progressively developed through the Tier 1 screeningassessment, and may be further refined, by data collection, for example, to support detailedquantified assessments at Tier 2 and Tier 3. The final, site-specific environmental riskassessment is based on a combined pictorial and analytical model of the site that reliablyrepresents the site and its environment to the required levels of detail and accuracy. Theplans and models will typically develop through the following stages:

• Pre-licensing application discussions to develop the conceptual model for a site may bebased initially upon outline plans and designs. These may start out as outline sketchesand develop from there. They will usually be developed in support of the planningapplication.



Conceptual pictures and models are a useful starting point for scoping the site and itsenvironment. Figure 6 shows examples of simple conceptual models for landfillcatchments (taken from Environment Agency, 2000k – in preparation).

• By the time the licence application is being submitted for consideration, the conceptualmodel will need to be based upon a detailed scale plan of the site and its surroundings.

Site-specific scale drawings and plans are usually essential for a Tier 1 screeningassessment to be carried out, in order to ensure that the model used is relevant, valid andreliable for the site in question. These will usually be available in the form of the outlineor detailed plans and designs that the applicant has produced for their planningapplication. The applicant may also have developed an environmental risk assessmentmodel to support an EIA submitted with the planning application.

Figure 7 shows an example of the sort of site-specific plan (in this case, of a combinedlandfill and transfer station) that could be used. Examples of environmental receptors thatmay be relevant to the site-specific risk assessment are indicated on the conceptual planby ‘call-out boxes’. These would be taken into consideration in the Tier 1 risk screeningassessment (see Chapter 5). The risk management measures which are assessed as beingnecessary to prevent harm to these receptors would then be incorporated in the detaileddesign and plans for the site, as the conceptual model is developed.

• The plans and model are then refined as the risk assessor (Agency and/or applicant)reviews the risk assessment against the actual site and its environment. This developmentprogresses as necessary through the various tiers of assessment, until understandingdevelops to the level appropriate to the risk management decision.

• The plans and model for a site must be developed on the basis of the actual site and itsenvironment, and while desk-based studies and reviews may provide some of the basis,site-based inspections and reviews are essential. While development of the site-specificmodel and assessment should be led by the applicant/operator, it should be based uponactive discussion with the Agency officer dealing with the application, who should alsoconsult the Agency officer who is or will be responsible for inspecting the site against itslicence conditions.

Further guidance on developing conceptual models (with specific application to modellingcontaminant transport processes in the subsurface) is provided in Environment Agency,2000h.



Figure 6: Examples of conceptual models - simplified landfill catchment drawings.


Sewerconnection

Perimeter fence

Transferstation

Figure 7: Example of a conceptual plan of a combined landfill and transfer station, indicating examples of potentialenvironmental receptors

Perimeter fence

Claybund

Exemptarea

Screener

Concretepad

Gate

Wheelspinner

Mainroad

Wheel wash

Weighbridges& office

Carpark

Site office &laboratory Quarantine

storagelagoon

Leachatelagoon

m0 10 20 30 40 50

Phase 2 landfill – compositelined

Phase 1 landfill – compositelined

Farm house & barns

Bays

People & Property; e.g.inhabitants, workers, school,hospital, factory, offices.

People & Property;e.g. inhabitants,houses.

People & Property;e.g. inhabitants,workers, buildings,livestock.

Ecosystems;e.g. designatedHabitat, SSSI.

Surface water

River / stream

Groundwaterbelow & invicinity of site

1

2

3



5 TIER 1: SCREENING OF ENVIRONMENTAL RISKS

5.1 Introduction

This chapter explains what Tier 1 screening assessment is, based on the ‘source-pathway-receptor’ approach, and describes its use in the form of the Shell Risk Assessments whichform the basis of the Shell Licensing Kits. Examples and relevant tables are given,supported by Appendix 1, 2, 3 and 4. It discusses the use of scoring in the rating andprioritisation of risks and risk management systems. An example is given in Appendix 5.

5.2 Screening of environmental risks for waste management sites

A typical screening assessment of the environmental risks of a site consists of a qualitativeassessment which identifies:• what risks there are to the environment from the proposed site operations• what standards of environmental protection are required to manage those risks• which, if any, of the identified environmental risks require a more detailed technical risk

assessment:a) to resolve uncertainty over the identification or significance of the risk; and/orb) to determine the necessary standards of environmental protection.

Screening assessments should be based upon a conceptual model which analyses the ‘source-pathway-receptor’ links for the site, and, as described in Section 4, this model usually takesthe form of a table, matrix or spreadsheet. This identifies the sources of the hazards, thepathways through which those hazards may be transmitted into the environment and bywhich they might reach the things we wish to protect (i.e. the environmental receptors).

Situations in which either a source, a pathway or a receptor will not be present, or where thelikelihood of them becoming connected is justifiably negligible, can be screened out. Wherethere is significant uncertainty concerning the presence or connection of a source, pathwayor receptor, then the situation should not be screened out without further investigation ormore detailed assessment.

In waste management licensing, the identification of a plausible or likely link between thesource of an environmental hazard via a potential pathway to a potential receptor isconsidered to be sufficient to warrant risk management measures being stipulated in thelicence conditions, unless the site-specific risk assessment demonstrates that, for the site inquestion, the environmental risk is so low that such measures are unnecessary.

The scope, type and standard of risk management measures that will be required will dependupon the environmental hazard and upon the identified environmental risks. In wastemanagement licensing, many sites will fall within typical categories (such as various types oftransfer stations) where the activities they carry out and the environmental risks they give riseto are known and understood well enough that the risk management provisions they willtypically require can be identified and specified as ‘default risk management standards’.These are standards that will normally be required in default of any more detailed site-specific assessments indicating that either a lesser or a higher standard of risk management



provision is required for that particular site. This is the level of assessment that is providedthrough the Shell Risk Assessment approach.

As uncertainty increases however, and the likelihood of severe consequences become lessclear, a more detailed assessment of the source-pathway-receptor is necessary to understandthe nature of the risks and how to avoid, or manage them. The Shell Risk Assessmentapproach can be used to identify where these more detailed assessments are needed.

5.3 Shell Risk Assessments

Shell Risk Assessments are Tier 1 screening assessments. These are for use in definedcircumstances by the applicant/operator and by the Agency in producing a site-specific riskassessment in support of the licence application or a licence modification.

Each Shell Risk Assessment is based on: a ‘typical site’ for the category of site in question(for example, A11: Household, Commercial and Industrial waste transfer station), which isdefined in terms of:• the waste categories that will typically be permitted on that category of site, including

references to the relevant Level 1 waste categories listed in the UK Waste ClassificationScheme (UKCWS); and

• the waste management operations that will typically be permitted on that category of site,which will fall within the general classifications of storage (or keeping), treatment(including physical, chemical, biological and combinations thereof) and disposal(including treatment operations which are an inherent part of the disposal), and which willalso include the handling operations which are inherently associated with thoseoperations.

(The waste operations will be classified within the licence conditions with reference, whereapplicable, to the ‘Waste disposal’ and ‘Waste recovery’ classification list (the ‘D’ and ‘R’list) which is given in the Waste Management Licensing Regulations 1994, Schedule 4, PartsIII and IV.)

‘Typical sites’ can be regarded as those which provide a good fit with the shell riskassessment, the shell licence conditions and working plan. A ‘good fit’ is defined as whereneither the applicant’s risk assessment nor the Agency’s evaluation of that risk assessment,justify either:a) detailed quantitative risk assessments to be carried out; orb) significant variations in the risk management provisions from those described in the

working plan or from the default standards; orc) significant variations from the default standards specified in the shell licence

conditions.

Appendix 2 provides an example from the Shell Licensing Kits used by the Agency.

Hazards and risks can be ranked or scored using qualitative indicators, such as ‘high’,‘medium’, or ‘low’, and this can be useful in helping to identify the type and degree of riskmanagement measures that are appropriate in a particular case. Box 2 explains how thisworks in the Shell Risk Assessment tools.



Box 2: Rating of environmental risks in the Shell Risk Assessment tools.

Each Shell Risk Assessment tool has been constructed upon the basis of a generic assessmentof whether, for a defined ‘typical site’ of that type, the ‘source risk’ (the risk that the site willgive rise to hazardous releases or emissions) is ‘high’, ‘medium’, ‘low’ or ‘insignificant’.This is done on the basis of a generic conceptual model of the type and amount of each wastehandled, its associated hazardous properties, and the waste management activities to which itis subjected.

Where the Shell Risk Assessment identifies a ‘source risk’, it also generically identifies theplausible or likely environmental pathways for the identified releases and the plausible orlikely ‘receptors at risk’ from those releases (people, properties, groundwater, surface water,etc). The presence of a receptor for that risk indicates that a risk management system isrequired. The vulnerability and proximity of receptors is not assessed or scored as ‘high’,‘medium’, ‘low’ or ‘insignificant’ in the Shell Risk Assessment.

The Shell Risk Assessment specifies the default risk management measures that areconsidered as being appropriate for such a ‘typical site’, taking into account whether the‘source risk’ is assessed to be ‘high’, ‘medium’, ‘low’ or ‘insignificant’. These measures arespecified to generic standards for that type of site to reduce the identified risks throughappropriate requirements for:• engineered containment• operational procedures• monitoring• action plans and remediation measures.

Either the Agency or the applicant may carry out a more detailed assessment to show that forthe site in question these are such as to justify either higher or lower standards of riskmanagement than those specified in the default requirements for the generic ‘typical site’.This may be based on a detailed assessment of the vulnerability and proximity of receptorsfor the site in question.

Thus, the Shell Risk Assessment tool establishes a decision-making framework appropriate tothat type of site, in which a ‘Yes/No’ decision can be made for each hazard, as to whetherthere is a linkage and hence a risk. A ‘Yes’ answer indicates that the identified riskmanagement systems need to be provided for that site to the standards specified as a default,and a ‘No’ indicates that they do not need to be provided. This can be regarded as thesimplest form of scoring system for risk, equivalent to assigning a ‘binary’ score of 1 or 0.Where there is uncertainty or disagreement over whether the answer is ‘Yes’ or ‘No’ then amore detailed assessment is needed to resolve the question.

5.4 The ‘source’ of environmental risks

The ‘source’ is analysed in terms of the hazardous properties of the waste types andoperations to which they will be subjected on the proposed site. The hazards are listed inAppendix 3, and are those resulting from:



a) specific properties of special wastes, classified using the codes for special wastehazardous properties: H1 to H14 (as defined in the Special Waste Regulations 1996(as amended)); and

b) hazardous properties of wastes (whether special or non-special) which are not coveredby the above, but which could give rise to an environmental risk – these includeproperties which are covered by the appropriate ‘difficult waste’ codes for property(H15 to H20) and form (F1 to F6) as listed in the UK Waste Classification Scheme(Environment Agency, 1998); and

c) other waste operation related hazards, such as noise, which are not covered by theabove, which are within the terms of reference of the licence and which could giverise to an environmental risk.

The ‘Source’ definition also includes under each hazard classification, the relevant riskphrases and the UK Waste Classification first level waste categories which include wasteswhich may display those hazards.

5.5 Hazardous events and pathways

The hazardous events and pathways that are assessed are (see section 2.2):

• Direct emissions of heat and shock due to fire or explosion;• Releases of polluting emissions by one or more of the following routes:

- air (or atmosphere) as pathway (it may also be a receptor for certain risks – seebelow);

- ground (including via services);- water (surface water and groundwater are receptors in their own right – see below);

• Other vectors for environmental hazards:- dust- pests;- scavengers;- litter;- noise.

As discussed in section 2.2, if humans (or animals) are exposed to hazardous substances oremissions via one or more of the above environmental pathways, harm to their health mayoccur through a number of ‘exposure pathways’. Typically these may include: inhalation oringestion of, or dermal contact with, hazardous substances; and the direct effects of heat andshock in the case of fires or explosions. Humans may also suffer harmful effects on healththrough serious detriment to the amenity of their locality.

These ‘exposure pathways’ are not explicitly assessed in Tier 1 Shell Risk Assessments. It issufficient for the assessment to identify whether or not a significant exposure of identifiedhuman or animal receptors is likely to occur, in order to decide whether or not riskmanagement measures need to be provided.



5.6 Environmental receptors

The environmental receptors that are assessed are (see section 2.2):

• People outside the site boundary. (People within the site boundary are only consideredwhere they may be trespassers or others who have gained unauthorised access – ‘sitesecurity’ requirements are imposed to prevent this situation occurring. People who arelegitimately on site - including site staff and other people who are authorised or doingother legitimate business - are covered specifically by the Health and Safety at Work Act1974 and are not considered in the environmental risk assessment);

• Properties outside the site boundary, including public and private property and placeswhere the public have access – this may also include livestock or other animals which arekept (rather than wild) outside the site boundary (or within the site boundary);

• Ecosystems, especially habitats designated in accordance with the Habitats Directive, andother designated sites;

• Surface water in the vicinity of the site;• Groundwater in the vicinity of the site;• Atmosphere, which is a receptor in regard to the risk of global warming.

5.7 The environmental risks that are assessed

The risks that are assessed are environmental pollution risks, including harm to human health.Serious detriment to the local amenity is included where it straddles the line between amenityand environmental pollution; that is, where the detriment is such that a source-pathway-receptor relationship is identified that is likely to have an adverse effect on human health; e.g.dust or odour emissions, pest infestations.

5.8 The risk management systems that may be required, and default standards

The environmental risk management systems that are specified are those that will typically berequired for sites that ‘fit’ the shell risk assessment. These include provisions, such asmaintenance, monitoring, etc, which will typically be required to manage and minimise the‘residual risks’ arising from failure of ‘first lines of defence’ such as engineered sitecontainment and drainage systems.

These are included as default standards in the corresponding shell licence conditions for thatcategory of site, which are identified in the assessment table. They represent a reasonableprecautionary standard; to deviate from this standard would require a detailed risk assessmentto justify a different standard from the default.

5.9 Site-specific variation from the default risk management requirements

Each Shell Risk Assessment includes guidance on when the Agency officer dealing with theapplication and reviewing the applicant’s completed risk assessment should considerimposing a requirement for additional or higher levels of risk management, because the riskpresented by the site in question may be higher than that for the ‘typical site’ of that type.This may be because:i) the wastes which are handled by the site are atypical and exhibit hazardous properties

which are atypically high; or



ii) the waste management operations are atypical and the risks of hazardous releases oremissions is atypically high; or

iii) the environmental receptors are atypically vulnerable to hazardous releases or emissions interms of their sensitivity (e.g. hospitals) and/or their proximity to the site.

Where appropriate, the relevant ‘OPRA for Waste’ (Environment Agency 2000e) riskassessment criteria are referred to for guidance and as an aid to the decision (the relevantOPRA assessment criteria are given in Appendix 4). These should only be used as indicativeguidance, and will not be a substitute for more specific consideration of the receptorspotentially at risk.

Where receptors are identified as being highly sensitive to the hazard, or at high vulnerabilityor risk of exposure, more detailed modelling and assessment may be required in order toidentify and specify appropriate risk management standards, or to resolve uncertainty ordisagreement over those proposed.

The Agency officer dealing with the application should consult the Agency officer who is orwill be responsible for inspecting the site against its licence conditions on this, as they will befamiliar with the use of OPRA for such sites and with the presence of potentially vulnerablereceptors in the vicinity of the site. This should take place at the same time as the conceptualmodel for the site is being reviewed on the site (see Section 4).

For example, for a waste transfer station where the Tier 1 assessment identifies receptors athigh risk of exposure which include:

a) domestic dwellings, schools, hospitals, SSSIs or designated Habitats, then:• a covered building which provides containment of aerial emissions may need to be

considered as a necessary requirement rather than an option; and• for some hazards, scientific monitoring of aerial emissions may need to be considered

as a necessary requirement.(the need to consider this may be indicated by an OPRA Environmental Appraisal target-based score for Human Dwellings, Population Density and Environmental Targets whichis equal to or greater than 15); or

b) a groundwater protection zone (GPZ) or vulnerable major aquifer, then scientificmonitoring of groundwater quality may need to be considered as a necessary requirement,(the need to consider this may be indicated by an OPRA Source score which is equal to orgreater than 15, combined with an Environmental Appraisal target-based score forGroundwater which is equal to or greater than 10); or

c) a surface water body which is of high quality, then scientific monitoring of surface waterquality may need to be considered as a necessary requirement, (the need to consider thismay be indicated by an OPRA Source score which is equal to or greater than 15,combined with an Environmental Appraisal target-based score for Surface Water which isequal to or greater than 10).

The OPRA score is only indicative and will not in itself provide sufficient justification for theAgency to impose such requirements. If a need for scientific monitoring or another higherlevel of risk management is identified for a site, then the Agency should justify that need andthe standards required on the basis of a more detailed risk assessment regarding that riskmanagement provision. Where scientific monitoring is so justified by the assessment, the



necessary conditions should be added to the shell-derived, site-specific licence conditions.The applicant should be required to provide working plan sections detailing the relevant riskmanagement systems, for referencing to these licence conditions, or else the Agency mayprescribe detailed requirements. Area referral to Region is recommended in thesecircumstances.

5.10 Scoring, rating and prioritisation of environmental risks

Within waste management regulation the identification of a plausible or likely connectionbetween a source, pathway and receptor is usually sufficient to warrant risk managementmeasures (in the absence of a detailed assessment justifying otherwise), and the prioritisationof risks is not applied within Shell Risk Assessments. This is because risk managementmeasures may not be common across different types of risk. For example, the provision of arisk management system to prevent and control, for example, landfill gas emissions, wouldnot justify a failure to provide a risk management system to prevent and control dustemissions. (This does not prevent the same risk management system from providingprevention and control for different hazards, where this is appropriate; in this example, thelandfill cap will, on completion, provide some of the protection from both landfill gas anddust hazards. But the risk and the management system provided must be assessed on theirown merits in each case.)

Hazards and risks can be ranked or scored using qualitative indicators, such as ‘high’,‘medium’, or ‘low’, and this can be useful in helping to identify the type and degree of riskmanagement measures that are appropriate in a particular case. Box 2 in section 5.3explained how this works in the example of the Shell Risk Assessment tools.

The use of semi-quantitative indicators to score probability and consequence and to rankrisks, can assist where there is a need to understand whether the risks in question are drivenby the probability of their occurrence or by their consequences if they do occur. This may beuseful where there is a need to compare different approaches to risk management or to scopeout more detailed studies. However, scoring systems (particularly those employingnumerical scales, such as 1-5) are liable to convey a spurious impression of scientificprecision, and should only be employed where their use can be shown to add value to thedecision or inform it in a way that would not be obtained by considering the actual risks tothe identified receptors, and the actual specifications of the system that will be required tomanage those risks to a defined and enforceable standard.

Risk prioritisation requires a separate consideration of probability and consequence. In mostinstances this can follow on from the source-pathway-receptor analysis used in the screeningassessment or Shell Risk Assessment. The hazard and source characteristics and thesensitivity of the receptor dictate the consequences. Probability is usually dominated by theavailability of the linkage between the source and receptor.

The benefit of rating and prioritisation is to distinguish between low probability, lowconsequence risks and high probability, high consequence risks. The latter will usuallyrequire some further level of analysis, although this is not to infer that low probability, lowconsequence risks will not need to be addressed.

The following points need to be borne in mind when considering the use of a rating andprioritisation assessment:



• Rating and prioritisation approaches usually incorporate a numerical scoring system thatreflects the magnitude of the probability or consequences of adverse effects occurring at alocation. At this level of assessment scoring systems are arbitrary. Scores can not reflectabsolute risk and scoring systems need to be simple, clear, easy to follow andreproducible. Critically, they should never assume a degree of sophistication in theirdesign beyond what they can deliver in terms of distinguishing between risks.

• They should never be used to estimate or infer ‘absolute’ levels of risk that are thencompared with risk criteria or to test the effectiveness of detailed risk managementoptions.

• The value of prioritising risks within a band (for example, for ranking all risks in order ofthe highest to the lowest), is of limited value if all risks must be addressed. This willusually be the case in setting conditions for waste management licenses. This is becauseit will not be acceptable to omit risk management requirements from the licenceconditions on the grounds that, based on a scoring and ranking assessment, the risk inquestion comes low on the rank ordering list or is ‘relatively insignificant’.

• More sophisticated tools are available for detailed estimates of risk, and scoring systemsimplying high levels of ‘precision’ should not be employed, given the relative nature ofrisk prioritisation. Where different scales are used for scoring (e.g. 1-5 vs. 1-30), theseshould be properly justified.

An example of a risk rating assessment is given in Appendix 5, in which it can be seen thatthe scoring system used and the results obtained do not add significant value to the qualitativeassessment or to the risk management and licensing decisions.

In general:• Risk rating systems can:

- distinguish between risks posed by facilities or situations of a generic type;- allow prioritisation of risks from risk scores, usually through the separation of

probability and consequence;- allow comparisons between situations with similar risk, but with different ‘driving’

factors;- accommodate simple ‘what if’ questions;- allow fast screening of numerous facilities or situations;- prioritise and focus further risk assessment effort;- support the identification of high risk situations which may develop after

authorisation or licensing.

• Risk rating systems cannot:- provide absolute estimations of risk; scores are relative- provide a degree of resolution beyond that inherent to the subjectivity of the scoring

system; scores are best ‘banded’ in ranges;- be applied without training.

A good example of the valid use of risk rating and prioritisation features in the ‘OPRA forWaste’ scheme (Environment Agency, 2000e) and the features of such schemes are detailedin the National Centre for Risk Analysis and Options Appraisal’s Guidance Note on RiskRating Systems (GN17) (Environment Agency, 1999c).



6 TIERS 2 AND 3: DETAILED ENVIRONMENTAL RISK ASSESSMENT

6.1 Detailed quantitative risk assessments

Where there is potential for linkages to exist, and the Tier 1 screening assessment/Shell RiskAssessment indicates that those linkages need a more detailed assessment, the source-pathway-receptor analysis may be developed to include the following:• construction of a source (contaminant, hazard), pathway, receptor table for the facility or

situation under study, paying specific attention to the completion of discrete linkages(hazard identification);

• an evaluation of the actual or potential connectivity of these components (exposureassessment);

• consideration of the relative likelihood and scale of exposure and scale of consequencesby reference to the nature of the hazard (potency), availability of the pathway andsensitivity of the receptor (risk estimation);

• classification of the relative magnitude of the risk together with a justification for theassignment of risk class (risk characterisation).

For example, the temporal and seasonal aspects may be important for a particular hazard anda particular site. Problems with exposure to dust may be identified as an issue, especially inthe summer months, which requires detailed exposure assessment in order to justify arequirement for environmental monitoring points to measure dust emissions. Likewise, theperformance of a liner system needs to be assessed beyond the working lifetime of a site.The development of a more detailed assessment may be justified in these cases, to identifywhether increased standards of protection will be necessary. These aspects usually involveconsiderable uncertainty and a precautionary approach is usually adopted where the risks areidentified as significant.

Detailed quantitative risk assessments are required where either:• the Tier 1 screening assessments indicate that they are necessary for that site due to its

particular circumstances (for example: the need for and design of engineeredcontainment for a landfill will normally require detailed risk assessment); or

• the applicant/operator wishes to justify more relaxed standards of risk management thanare indicated in relevant standards or Agency guidance as being typically required for theidentified environmental risks, due to site-specific factors (for example: operationsinvolving the handling, storage or treatment of non-inert wastes will normally require anengineered site surface providing containment and sealed drainage – theapplicant/operator may be able to provide a detailed assessment of the site and itsenvironment for consideration by the Agency, which indicates that there is no significantrisk to either groundwater or surface water from their proposed operations and that alower standard of site surface containment and drainage is acceptable); or

• the Agency wishes to impose more rigorous standards of risk management than areindicated in relevant standards or Agency guidance as being typically required for thoseenvironmental risks, due to site-specific factors (for example: operations involving thehandling, storage or treatment of non-inert wastes will not normally require eithergroundwater monitoring or surface water monitoring where an engineered site surfaceproviding containment and sealed drainage is provided – the Agency may, by providing adetailed assessment of the site and its environment, show that there is a significant risk to



either groundwater or surface water from the proposed operations, even with suchengineered containment and drainage, and that appropriate monitoring is required).

If a detailed risk assessment is to be conducted, a principal consideration is the type of riskbeing assessed. At the licensing stage, the Agency is usually concerned with three maintypes of situation:• the risk of an initiating event that may result in a release (e.g. the failure of a landfill gas

extraction system; or the puncture of a landfill liner);• the risk of exposure to the wider environment following a release (e.g. loss of a drinking

water supply due to contamination from an leachate plume released from a landfill site);and

• the risk of harm resulting from exposure (e.g. risks to human or ecological health as aresult of exposure to asphyxiant gases).

Within the context of a tiered approach, these types of risk require the use of quite distinctrisk assessment tools. Systems with engineering features (engineering landfills, cappingsystems) are amenable to ‘fault and event tree analysis’ that assesses the performancecharacteristics and the root cause(s) of failure; whereas environmental exposures oftenrequire ‘distribution modelling’, which attempts to characterise the transport of contaminantsin the environment by reference to numerical models. Risks of harm, beyond the reference toenvironmental standards, require a more detailed understanding and evaluation of physical,chemical or biological damage.

Quantitative risk assessment is used for high priority, complex risks and is a specialist area ofexpertise. A variety of numerical models and computer software, such as LANDSIM, havebeen developed to assist in the quantification of risks from waste management sites. Twoapproaches are possible:• Tier 2 generic risk assessment: where a representative numerical model is used to

simulate the facility under study in order to assess the nature and level of risks involvedand to inform the general type of risk management measures required; and

• Tier 3 tailored risk assessment where attempts are made to tailor the generic modelspecifically to the site under study, using assumptions and input parameters that reflectthe site-specific conditions.

Both Tier 2 and Tier 3 assessments involve a quantitative assessment of the risks that apply tothe particular waste management facility. The principal difference between the two tiers isthe extent to which the assumptions built into the model and the input parameters are genericor site-specific. In a Tier 2 assessment most of the assumptions will be generic, chosen aspart of the model development to be representative of ‘typical’ conditions (cf. the Tier 1 ShellRisk Assessment approach). This has the advantage that the assessment is easier and quickerto complete than a Tier 3 assessment, requiring less site-specific data. However, because theassumptions are largely generic, the extent to which the assessment exactly models the sitecircumstances will be less than for a Tier 3 assessment.

Use of either generic or tailored risk assessment approaches requires that:• inputs are matched to outputs when carrying out simulations using the model; that is, the

user of the model understands the means and manner in which the selection of the inputvariables will affect the relevant outputs – failure to understand this relationship will tendto lead to the situation of ‘garbage in-garbage out’ in the modelling;



• the data used as inputs to the model is justified and referenced; and• the data ranges are not subject to bias which will distort the resulting outputs.

6.2 Tier 2: Generic Quantitative Risk Assessment

Generic quantitative risk assessment adopts models representative of a general situation; eg.the generalised engineered landfill. For example, LANDSIM is a performance assessmentmodel for landfills and is capable of selecting from a wide range of liner types, landfillgeometries, drainage systems and leachate strengths to estimate contaminant breakthroughcurves. However, it does not represent any actual site under consideration per se because ofthe site-specific complexities, and it should be used with caution (e.g. does it fit theconceptual model of the site?). Use of the model is explained elsewhere (EnvironmentAgency, 1996). An example is given in outline in Appendix 6.

The value of these approaches is that they:• allow adoption of recognised equations in a probabilistic mode;• allow an intrinsic handling of uncertainty;• formalise the decision-making approach;• facilitate a full assessment of all possible outcomes within the constraints of the model

that has been set up;• provide an assessment more meaningful than a qualitative treatment in isolation;• allow sensitivity analyses of components of risk; and• allow and promote discussion of expert judgement issues.

Most generic models operate in predictive mode and are concerned with improving anunderstanding of how a system behaves rather than being over-concerned with the accuracyof output. They provide a more accurate means of assessing risks than a Tier 1 assessment,and they are an aid to selecting and designing risk management measures. With appropriateuse, the pattern of results generated from these generic models should not be so divergentfrom a tailored risk assessment that radically different decisions would have been made; overcell design, for example.

6.3 Tier 3: Tailored risk assessment

Tailored risk assessment extends use of the generic tool to include site-specific assumptionsand input parameters. Adoption is usually restricted to complex, high priority cases, such asradioactive waste repositories, for example. Where used, it will often involve construction ofone of several models linked together. This level of risk assessment is a highly specialisedand expert activity.

The types of risk assessment tools that are likely to be applied in tailored risk assessmentinclude the use of fault and event tree analysis and the use of groundwater distributionmodels to predict the travel time and characteristics of contaminant plumes following release.The use of event and fault tree analysis and the selection of appropriate data for riskassessment are outlined in sections 6.4 and 6.5 respectively. Specialist assistance should besought for any tailored risk assessment.



6.4 Event and fault tree analysis

Event and fault tree analysis is used for assessing the risks of an initial release, usually fromcontainment. There are two basis approaches, both of which calculate the probability of theevent by considering the causes of the incident. The first involves the use of historical,statistical data on the failure of containment. The second approach uses a method called‘synthesis analysis’, to break the system down into contributing factors and causes.

There is a general problem of demonstrating very low probability; that is, in obtaining astatistically meaningful estimate of rare or accidental events. It is therefore valuable tocollect event data over time, as much of this is useful in reliability and availability studies.This type of information is valuable for testing results from synthesis analysis againsthistorical data to determine whether the approaches used lead to comparable predictions.

When historical performance data are not sufficient, ‘synthesis analysis ’ is used. The twomost common methods used are fault trees and event trees. These techniques are initiallyqualitative in nature, although they provide the basis for quantitative analysis, if required.They can be made highly site-specific, being tailored to the system being analysed. They canidentify event scenarios that have not been realised in the past, which allows for theintroduction of risk reduction measures to reduce the likelihood of an event taking place inthe future.

In fault tree analysis the aim is to select an undesired event (such as a failure of containment,usually called the top event) and trace it back to the possible causes, which can be componentfailures, human errors or any other possible events that can lead to the fault. The causes arerelated using simple logic relationships (i.e. AND/OR ‘gates’) to allow for the construction ofa logical structure that models the failure of the system (Figure 8 gives an example of theway a fault tree is constructed). The technique produces a list of the events that could lead tothe fault (i.e. top event) being realised.

Event tree analysis operates in the opposite way. The starting point is an initiating event (thefailure of a leachate treatment system, for example) and the technique is often used to followthe consequences of such an event.

Fault tree and event tree analyses still require data to quantify the contributory causes.Quantification often involves value judgements made on the basis of professional expertise,which can be difficult to justify when not substantiated by historical records.


National Centre for Risk Analysis and Options Appraisal Page 39 Figure 8: Tools and techniques for environmental risk assessment: fault tree example

Release to groundwater

Release to ground

Groundwaterpresent

Release to ground viahardstanding

Release to unsurfaced ground

Emittingwaste

Operatorerror

Emittingwaste

Operatorerror

Leak

Emittingwaste

Leak insystem

Maintenanceerror

Release to ground via impermeable pavement &sealed drainage

oror

&

& &&

&

Top event

Logic gate(‘AND’ gate)

Logic gate(‘OR’ gate)

Intermediateevent

Baseevent



6.5 The selection of appropriate data for tailored risk assessment.

Early dialogue between operators and the Agency on the scoping of a tailored risk assessmentis valuable. It may cover aspects such as:• assumptions within a conceptual model;• agreeing receptors that should be considered at different stages of proposal development;

the appropriateness of default values; and• appropriate level of site investigation required to support the risk assessment.

Tools such as LANDSIM used for tailored risk assessment should be considered as within abroad spectrum of possible risk assessment tools and should never be seen as providing ‘theanswer’ to all problems. In situations where the hydrogeology is complex and the aquaticenvironment is particularly sensitive, for example, more complex assessment tools are almostcertainly a necessity. Conversely, if the site hydrogeology and sensitivity do not warrant adetailed treatment, the risk assessor may be able to reach a robust decision on the basis of lessintensive risk assessment process.

By necessity, numerical models demand numerous assumptions. They are only tools and theassumptions need to be understood in order to properly interpret the results. The predictionsfrom a tailored assessment should always be considered in the light of input data quality,model assumptions, uncertainty within the conceptual model and parameter sensitivityanalysis. Only then is it possible to reach a robust decision whether to accept the predictedrisks, to refine the model by collecting more data, or to move to a more complex assessmenttool.



7 GLOSSARY

Conceptual model: a risk assessment tool consisting of a presentation in visual (sketches,drawings, plans) and written form (tables, matrices, spreadsheets) of the hypothesisedrelationships between sources, pathways and receptors for a site in its environmental setting.A conceptual model represents the problem under study and is used as the basis on which todevelop a site specific risk assessment. The level of detail required of the model will dependupon the complexity of the risk assessment. The model is not static and will oftenmodification as new information about the risks becomes apparent and more sophisticatedlevels of analysis are applied.

Consequences: the effects (or impacts) of a particular situation, action or event. Impactsmay be positive (benefits) or negative (costs, or harms). Risk assessments usually focus onassessing the potential negative consequences (the harm) that may result from the realisationof identified hazards.

Environmental risk assessment : the systematic identification, assessment, estimation andcharacterisation of risks to or from the environment from a particular event, activity,operation, process or design. Environmental risk assessments are carried out and reported bysuitably qualified or competent persons, to a defined scope, using recognised tools andtechniques.

Harm: the damage to a receptor that results when a hazard is realised.

Hazard: a property or situation that in particular circumstances could lead to harm.

Impact: see Consequences.

Receptors : identified individuals, environmental populations or components, structures,assets and property that may potentially be exposed to an identified hazard, and that mayconsequently suffer harm.

Probability: the likelihood of an event occurring, or expression of chance usually denotedmathematically either as:• the ratio or percentage of the occurrence of a particular event as one among a number of

possible events (e.g. a 20%, or one in five chance); or• the frequency of occurrence of a particular event in a given period of time (e.g. an annual

probability of one in a million).

Pathways: the routes or means by which defined hazards may potentially realise theirconsequences at the receptors.

Risk: a combination of the probability, or frequency, of occurrence of a defined hazard andthe magnitude of the consequences of the occurrence.

Scope : the agreed boundaries of the risk assessment and the risks to be assessed within thoseboundaries.



Source : the activity or operation taking place on the site from which a particular hazard mayarise.





8 BIBLIOGRAPHY

Department of the Environment, 1994a. Circular 11/94 in relation to The WasteManagement Licensing Regulations 1994. The Stationery Office, Norwich, London.

Department of the Environment, 1994b. Waste Management Paper No 4 (WMP 4) Licensingof Waste Management Facilities. The Stationery Office, Norwich. (Revised in DETR,2000.)

Department of the Environment, 1995. A Guide to Risk Assessment and Risk Managementfor Environmental Protection. The Stationery Office, Norwich, London.

Department of the Environment. Waste Management Paper No 26A (WMP26A) LandfillCompletion. The Stationery Office, Norwich.

Department of the Environment. Waste Management Paper No 26B (WMP26B) LandfillDesign, Construction and Operational Practice. The Stationery Office, Norwich.

Department of the Environment. Waste Management Paper No 27 (WMP27) Landfill Gas.The Stationery Office, Norwich.

DETR, 2000. Waste Management Paper No 4 (WMP 4)(Revised) Licensing of WasteManagement Facilities. The Stationery Office, Norwich.

DETR, Environment Agency and Institute for Environment and Health, 2000. Guidelines forEnvironmental Risk Assessment and Management, Revised Guidance, DETR,Environment Agency and Institute for Environment and Health. The Stationery Office,Norwich.

Environment Agency, 1997. A Guide to Risk Analysis at the National Centre for RiskAnalysis and Options Appraisal. Environment Agency, London.

Environment Agency, 1998. Interim Framework Policy for Landfill Engineering.Environment Agency, Bristol

Environment Agency, 1999a. Interim Internal Guidance on Interpretation and Application ofRegulation 15. Environment Agency, Bristol.

Environment Agency, 1999b. Library of Licence Conditions & Working Plan Specifications,Volumes 1 & 2, Edition 2. Environment Agency, Bristol. (Being replaced byEnvironment Agency, 2000b).

Environment Agency, 1999c. Guidance Note on Risk Rating Systems (GN17). NationalCentre for Risk Analysis and Options Appraisal, Environment Agency, London.

Environment Agency, 2000a. Introducing Environmental Risk Assessment. National Centrefor Risk Analysis and Options Appraisal, Environment Agency, London.

Environment Agency, 2000b. Licensing Process Handbook. Environment Agency, BristolEnvironment Agency, 2000c. Library of Licence Conditions & Working Plan Specifications,

Edition 3. Environment Agency, BristolEnvironment Agency, 2000d. Shell Licensing Kits (available for various site categories).

Environment Agency, BristolEnvironment Agency, 2000e. Waste Management Licensing. Risk Assessment Inspection

Frequencies. Operator and Pollution Risk Appraisal for waste “OPRA for Waste”. Version2.0. Environment Agency, Bristol.

Environment Agency, 2000f. Licensed Waste Management Facility Site InspectionMethodology and Consistent Scoring Guidance. Version 2.0. Environment Agency,Bristol.

Environment Agency, 2000g (in preparation). Scoping Guidance on the EnvironmentalImpact Assessment of Projects. National Centre for Risk Analysis and Options Appraisal,Environment Agency, London.



Environment Agency, 2000h. Guide to good practice for the development of conceptualmodels and the selection and application of mathematical models of contaminant transportprocesses in the subsurface. NGWCLC Report NC/99/38. National Groundwater andContaminated Land Centre, Environment Agency, Solihull.

Environment Agency, 2000j (in preparation). Environment Agency Policy: The location andimpact assessment of waste management facilities (with particular emphasis on landfillsites and the protection of controlled waters). Environment Agency, Bristol.

Environment Agency, 2000k (in preparation). Guidance on monitoring of landfill eachate,groundwater and surface water. R&D report (R&D project HOCO_232). EnvironmentAgency, Bristol.

European Environment Agency, 1998. Environmental Risk Assessment: Approaches,Experiences and Information Sources, Copenhagen.

Environment Agency, 1996. LandSim: Landfill performance simulation by Monte Carlomethod. LandSim manual, ref CWM 094/96. (prepared by Golder Associates (UK) Ltd).Environment Agency, Bristol.

Gronow, JN & Harris, RC, 1996. LandSim: a regulatory tool for the assessment of landfillsite design. In: Wastes Management, February 1996.



9 APPENDICES





Appendix 1: Environmental risk assessment questions, stages, tiers and techniques – waste management licensing

(See Chapter 3, section 3.2.)

As indicated in Chapter 1, Table 1, the following risk assessment stages and questions may be addressed at the appropriate level of detailthrough the relevant Tier 1, 2 or 3 assessments at Phase 1 (Strategic planning), Phase 2 (Individual planning) and/or Phase 3 (Environmentalauthorisation).

This table indicates how:c) the tiered approach to risk assessment and the identification of appropriate risk management measures would be applied at Phase 3

(Environmental authorisation – waste management licensing), based on the example of a waste transfer station handling household, industrialand commercial wastes, for the particular hazard of wastes which are likely to produce emissions of dust to atmosphere;

d) hazard identification, risk assessment and identification of appropriate risk management measures would be carried out using the tools andtechniques appropriate for waste management licensing, using the example of a Shell Risk Assessment approach for this category of site (asexplained in this chapter and Chapter 5).

This approach would be used either to review an environmental risk assessment provided in support of the relevant planning application, or toidentify and assess the relevant hazards where such an environmental risk assessment was not available.



Stage1 Question Tier Tools & techniques - licensing Example - licensing SeeChapter

Conceptualmodelling &scoping theboundaries of theenvironmentalrisk assessment

A. What is the nature of thesite (including the wastemanagementoperations) and itsenvironmental setting?

Problemformulation ordefinition

Drawing pictures, plans anddiagrams of the site andits environmentalsetting; and developing a‘source-pathway-receptor’ model;

supported by site visit &/orinspection.

Household, industrial and commercial wastetransfer station. (Category A11 site)

4

Environmentalriskassessment;

(or review ofenvironmental riskassessmentprovided insupport ofplanningapplication).

B. Is there a risk to theenvironment from thewaste managementoperations on this site?

Tier 1: Riskscreening

Source-pathway-receptortable;Agency tool: Shell RiskAssessment;supported by site inspection&/or investigation.

Category A11 Shell Licensing Kit: Shell RiskAssessment pack.

5

Tier 2 &Tier 3:Quantitativeriskassessments

Generic and tailoredquantitative risk assessments

Only where necessary to resolve uncertainty ordisagreement over Tier 1 (Shell) riskassessment and/or risk management measuresrequired. (See below.)

6

Stage 1:Hazardidentification

B1. What hazards are presentand what are their properties?

Tier 1 Source characterisation:• inventory of wastes handled

and stored• identification of

environmentally hazardousproperties

• description of waste

Category A11 ‘typical’ site:• Waste handled and stored - UKCWS first

level waste categories:21: Inert22: General and biodegradable24: Contaminated general

• Environmentally hazardous properties (see

5




management operations. SRA) - example:Solid wastes which contain significantproportions of dusts, fibres, powders orparticulates

• Waste management operations:- receipt- handling- storage- simple physical treatment (e.g. sorting,

compaction to reduce volume)- despatch

Stage 2:Identification ofconsequences

B2: What are the potentialenvironmental consequencesthat may arise form theidentified hazards?

Tier 1 Identification of potentialconsequences (harm/damage topotential environmentalreceptors)

Environmental receptors liable to be adverselyaffected by releases or emissions of dusts(including fibres, powders and particulates) fromthe site:• People:

harm to health by inhalation of dust, etc;• Properties:

damage to property and loss of amenitycaused by deposition of particulates;

• Ecosystems:environmental damage as a result of falloutcausing “smothering” effects.

5

Stage 3:Estimation of themagnitude of theconsequences

B3. What is the magnitude ofthe consequences for theidentified potential receptors?

Tier 1 Identification of:• the spatial scale of the

consequences• the temporal scale of the

consequences• the time to onset of the

consequences

This is implicit in the Shell Risk Assessment forthe identified hazards; e.g. in this example:

Consequences of dust emissions:• spatial scale:

- receptors within likely zone of effect; i.e.- aerial dispersion plume for aerial

dispersion and deposition of dusts,etc

• people:

5




- temporal scale: exposed receptors (i.e.not intergenerational)

- time to onset:- immediate harmful effects on quality

of life- immediate and delayed harmful effects

on health• properties:

- temporal scale: exposed receptors- time to onset:

- immediate and longer term damage• ecosystems:

- temporal scale: exposed receptors- time to onset:

- immediate harmful effects onecosystem

- longterm damage to ecosystem

Tier 2 or 3 Detailed quantified modellingand assessment ofconsequences. (See Stage 5,question B7 below.)

(See Stage 5, question B7 below.) 6

Stage 4:Estimation of theprobability of theconsequences

B4. How might the receptorsbecome exposed to thehazards?

Tier 1 Identification andcharacterisation of:• potential release scenarios

during normal operations,abnormal operations andaccidents; and

• consequent pathwaysbetween releases andreceptors.

Release to air of dusts, fibres, powders orparticulates, either directly from wastesexhibiting these properties or as a result of thewaste handling activities on the site. Aerialdispersion of dusts, etc, beyond the siteboundary.

5

B5. What is the probability ofthe hazard occurring?

Tier 1 Estimation of probability ofhazard occurring

In the Shell Risk Assessments, these probabilitiesare estimated or characterised as being either‘high’, ‘medium’, ‘low’ or

5




insignificant/negligible’, on the basis of thelikelihood of the permitted waste types havingthe identified hazardous property, and theoperations to which those waste types will besubmitted. For the example in question:

• Probability of waste handled andstored containing significantproportions of dusts, fibres,powders or particulates:

- Category 21: Inert wastes = High;- Category 22: General and biodegradable

= Medium- Category 24: Contaminated general =

Medium

• Probability of waste management operationsgenerating dust emissions from thesewastes:

- Receipt = Low- Handling = High- Storage = Medium- Simple physical treatment (e.g. sorting,

compaction to reduce volume) = High- Despatch = Low

Tier 2 or 3 Detailed quantified modellingand estimation of probabilityand magnitude of releasesduring normal and abnormaloperations, using fault tree andevent tree analysis.

Only where necessary to resolve uncertainty ordisagreement over Tier 1 (Shell) riskassessment and/or risk management measuresrequired.

6




B6: What is the probability ofthe receptors becomingexposed to the hazard?

Tier 1 Identification of likely orplausible pathways

If there is no actual or potential connectionbetween the hazard and the identified receptors,then there is no risk to those receptors from thathazard.

In the Shell Risk Assessments, if there is a likelyor plausible connection between the hazardsource and the identified receptors, then it isassumed that there is a risk to those receptorsfrom that hazard, and that appropriate riskmanagement measures are required (see ‘RiskManagement decision’, question D, below).

5

Tier 2 or 3 Detailed quantified modellingand estimation of probabilityand degree of exposure; using,for example, models such asLandSim, Helga, etc.

Modelling required in this example only wherenecessary:- to resolve uncertainty or disagreement over

the identification of likely or plausiblepathways at the Tier 1 (Shell) riskassessment level; and/or

- where highly sensitive receptors areidentified as being at high vulnerability orrisk of exposure, in order to identify andspecify risk management standards otherthan those generally accepted as bestpractice or specified as default standards.

In this example, this may apply where identifiedreceptors include domestic dwellings, schools,hospitals, SSSIs or designated Habitats whichare identified at Tier 1 as being at high risk ofexposure to the hazard.

6

B7: What is the probability ofharm resulting from exposureto the hazard?

Tier 1 Estimation of the likelihood ofharm resulting from exposure tothe hazard

In the Shell Risk Assessments, if there is a likelyor plausible connection between the hazardsource and the identified receptors, then it is

5




assumed that there is a significant likelihood ofharm to those receptors (see question B6 above),and that appropriate risk management measuresare required (see ‘Risk Management decision’,question D, below).

Tier 2 or 3 Detailed quantified modellingof exposure-harm relationship.This depends upon likelysusceptibility of individualreceptors to the hazard and theamount or duration ofexposure. This is oftensimplified in terms of a dose-response relationship, relatingexposure to magnitude of harmfor certain receptor types. Theuncertainty is high forprobabilistic assessments ofindividual cases, and mostassessments take the magnitudeof harm to be a direct result ofexposure.

May be necessary where highly sensitivereceptors are identified as being at highvulnerability or risk of exposure, in ordereither:

- to identify and specify risk managementstandards other than those generallyaccepted as best practice or specified asdefault standards; or

- (for the Agency) to justify rejection of theapplication.

Examples may include domestic dwellings,schools, hospitals, SSSIs or designated Habitatswhich are identified at Stage 4 as being at highrisk of exposure to the hazard.

6

Stage 5:Evaluating thesignificance ofa risk

B8. How significant is therisk?

Tier 1 Risk evaluation andcharacterisation; i.e. making avalue judgement as to theacceptability of the identifiedand assessed risks and the needfor risk management measures.

In waste management licensing, theidentification of a plausible or likely linkbetween the source of an environmental hazardvia a potential pathway to a potential receptor isconsidered to be sufficient to warrant riskmanagement measures being stipulated in thelicence conditions, unless a more detailedtechnical assessment demonstrates that, for thesite in question, the environmental risk is so lowthat such measures are unnecessary.

5




Tier 2 or 3 Comparison against or withreference to pre-existingmeasures, such as toxicologicalthresholds, environmentalquality standards, or othersocial, ethical or politicalstandards.

This may involve the use offormalised quantitativeapproaches, such as ‘look-uptables’ or the HSE ‘tolerabilityof risk’ (TOR) framework.

Where necessary to provide a quantifiedassessment for:- comparison and evaluation against a

defined environmental quality standard orequivalent; and/or

- to identify and specify risk managementstandards other than those generallyaccepted as best practice or specified asdefault standards; or

- (for the Agency) to justify rejection of theapplication.

6

B9. What are theuncertainties?Is a more detailed riskassessment needed?

Tier 1 Review of site and operationsagainst Shell Risk Assessment,to produce site-specific riskassessment.

Use of the Shell Risk Assessment pack toproduce a site-specific risk assessment shouldidentify those areas where:a) the site in question and its environmental

situation are significantly at variance fromthe ‘typical site’ forming the basis of theShell Risk Assessment; and/or

b) there is disagreement or uncertainty over therisk assessed and the risk managementmeasures required; and hence

c) a more detailed risk assessment is needed,either by the applicant or by the Agency.

5

Tier 2 or 3 Sensitivity analysis anduncertainty assessment.

May be necessary where a Tier 2 or Tier 3 riskassessment is provided

6

Options appraisal C. What are the options formanagement of theidentified risks?

Tier 1 Risk scoring, ranking andprioritisation (see Figure 4).

Where more than one risk management system isavailable to control the identified risks to theassessed standards, then a risk scoring, rankingand prioritisation approach may be useful toidentify the preferred risk management option.

5.10




Optionsappraisal

(see Figure 1)

Options appraisal framework(see DETR, EnvironmentAgency and Institute forEnvironment & Health, 2000)

In waste management licensing, the majordesign options for the site will have beendetermined at the Phase 1 and 2 planning stages(see Table 1), with reference to the BestPracticable Environmental Option (BPEO). Atthe Phase 3 stage of environmentalauthorisation, the types and standards of riskmanagement measures required will usually bedetermined by reference to generally acceptedor defined ‘best practice’, except whereotherwise defined and justified through either:- a risk scoring, ranking and prioritisation

assessment; or- a Tier 2 or Tier 3 quantitative risk

assessment.

2.3

Risk management D. What needs to be done tominimise the environmentalrisks?There are 3 main riskmanagement options:1. reject the proposal

altogether because itposes unacceptable risks;

2. accept whatever risk isimposed;

3. reduce the risk in someway, by doing one ormore of the following:

a) modifying the receivingenvironment or hazard;

b) modifying or avoidingexposure; or

c) modifying the effects orconsequences of the risk.

Riskmanagement (seeFigures 1& 4)

In waste management licensing:1. rejection of an application

on the basis ofunacceptable risk willusually need to be justifiedby a Tier 2 or Tier 3 riskassessment supported by ademonstration that theassessed risks cannot beadequately reduced bypracticable design changesand/or risk managementmeasures;

2. acceptance of whateverrisk is imposed will usuallyneed to be justified by aTier 1, 2 or 3 riskassessment showing thatthe risk is insignificant anddoes not require any

In waste management licensing, theidentification of a plausible or likely linkbetween the source of an environmental hazardvia a potential pathway to a potential receptor isconsidered to be sufficient to warrant riskmanagement measures being stipulated in thelicence conditions, unless a more detailedtechnical assessment demonstrates that, for thesite in question, the environmental risk is so lowthat such measures are unnecessary. For theexample in question, the generic risk assessmentof the hazard is that:

The risks of dust emissions are adequatelycontrolled through primary and residual riskmanagement provisions specified in the ShellRisk Assessment and Shell Licence Template.

The measures that will typically be required as‘best practice’ in managing this risk will be, as

5




specific risk managementmeasures;

3. reducing the risk willusually be achievedthrough risk managementmeasures which do one ormore of the following:

i) reduce the ‘source risk’through restrictingwaste types and wasteoperations;

ii) reduce or restrict theexposure pathways,through engineered andoperationalcontainment;

iii) control and minimisereleases and emissions,through monitoring andaction plans.

specified in the Shell Risk Assessment and theShell Licence Template:

i) Waste acceptance procedures - exclusion ofwastes consisting solely or mainly ofpowders

ii) Waste control procedures- wastes which arelikely to contain significant proportions ofdusts, fibres, powders or particulates areonly permitted if they are either:

• received in sealed containers and stored insealed containers and in areas providedwith impermeable pavement and sealeddrainage; or

• stored in covered buildings providingcontainment of aerial emissions; or

• stored in roofed areas provided with apermanent water supply and bowseringequipment, and impermeable pavement andsealed drainage.

Storage of these wastes in covered buildingsproviding aerial containment may be therequired option when the identified receptors inthe vicinity of the site include domesticdwellings, schools, hospitals, SSSIs ordesignated Habitats which are identified atStage 4 as being at high risk of exposure to thehazard.

Variation from these standards requiresjustification by an appropriate Tier 1, 2 or 3 riskassessment.




Risk based review E. Does the risk assessmentneed to be reviewed orrevised?

Tier 1, 2 or 3, asappropriate.

As appropriate, in accordancewith the above.

Risk assessments should be reviewed, andrevised as necessary:a) in order to resolve uncertainty in the results

of the risk assessment and/or the standardsand/or detail of the risk managementmeasures provided;

b) when modifications or changes areproposed in the standards, design oroperation of the facility or any of the riskmanagement measures provided;

c) on a periodic basis, taking into account theenvironmental performance of the facilityand changes in regulatory standards andbest practice.

Notes:

1. Stages 1 to 5 are as described in DETR, Environment Agency and Institute for Environment & Health, 2000.





Appendix 2: Example of a source-pathway-receptor table for contaminated run-off from a transfer station handling household,industrial and commercial wastes

Source Hazardousevents &Pathways

Potentialreceptors

Generic risk assessment for thewaste types handled on typical sitesof category

Environmental risk management measures necessary to controlassessed risks: default ‘best practice’ standards for typical sites ofthis category

Shell licencetemplateconditions

Solid wasteswhich arelikely toproducecontaminatedor pollutingrun-off.

Risk phrases:Risk ofcontaminatedrun-off.

Example wastetypes (UKWCcategories):21, 22, 23, 24,25, 26, 27, 28,29, 30

Release ofcontaminatedsite run-offfrom Category21, 22 and 24wastes to theenvironmentvia ground,groundwaterand surfacewater.

Properties.Ecosystems.Surface water.Ground water.(People viaabovereceptors.)

Non-special waste types fallingwithin the Category 21: Inert wastes:• Insignificant risk of pollution of

groundwater.• Low/medium risk of pollution of

adjacent surface water courses orbodies due to run-off from the sitecarrying suspended solids;consequent low/medium risk toecosystems.

• Low/medium risk of run-off ontoadjacent properties.

Non-special waste types fallingwithin the Category 22 and 24 wastetypes:• Medium/high risk of pollution of

groundwater.• Medium/high risk of pollution of

adjacent surface water courses orbodies; consequent medium/highrisk to ecosystems.

• Medium/high risk of run-off ontoand contamination of adjacentproperties.

Primary risk management systems:Provision of engineered site containment and drainage system.Waste control procedures:

• Inert (Category 21) wastes only permitted if stored in areas witheither:

- hardstanding and drainage that prevents run-off from thewaste into adjacent surface water bodies or storm waterdrains; or

- an impermeable pavement and sealed drainage.

• General and biodegradable (Category 22) and contaminatedgeneral (Category 24) wastes only permitted if stored in areaswith impermeable pavement and sealed drainage and either:

- received in sealed containers and stored in sealedcontainers; or

- stored in covered shelters or roofed areas; or- stored in bays.

Residual risk management systems:Control and remediation of spillages of waste.

Groundwater monitoring systems:Groundwater monitoring should only be given consideration as anecessary requirement when a site-specific risk assessmentdemonstrates significant risk to groundwater in the vicinity of the site(this risk assessment should be provided by the Agency in the firstinstance). This should be given consideration where the site is situatedwithin a groundwater protection zone (GPZ) or on a vulnerable majoraquifer. It may be indicated by an OPRA Source score which is equal

2.1.

4.6.

(supportedbyengineeredcontainmentunder 2.1)

4.2


National Centre for Risk Analysis and Options Appriasal Page 61

Source Hazardousevents &Pathways

Potentialreceptors

Generic risk assessment for thewaste types handled on typical sitesof category

Environmental risk management measures necessary to controlassessed risks: default ‘best practice’ standards for typical sites ofthis category

Shell licencetemplateconditions

to or greater than 15, combined with an Environmental Appraisaltarget-based score for Groundwater which is equal to or greater than10.

Surface water monitoring systems:Surface water monitoring should only be given consideration as anecessary requirement when a site-specific risk assessmentdemonstrates significant risk to surface water in the vicinity of the site(this risk assessment should be provided by the Agency in the firstinstance). This should be given consideration where the site is situatedin the vicinity of a surface water body which is of high quality. It maybe indicated by an OPRA Source score which is equal to or greaterthan 15, combined with an Environmental Appraisal target-based scorefor Surface Water which is equal to or greater than 10.


National Centre for Risk Analysis and Options Appriasal Page 62



Appendix 3: Sources of environmental hazard used in Library and Shell RiskAssessments

Special wastes which have any of the following classifications and properties:H1: Explosive. Substances or preparations which may explode under the effect of a flame orwhich are more sensitive to shock or friction than dinitrobenzine.

H2: Oxidising. Substances and preparations which exhibit highly exothermic reactions when incontact with other substances, particularly flammable substances.

H3-A: Highly Flammable.i) Liquid substances and preparations having a flash point below 21°C (including extremely

flammable liquids);ii) substances and preparations which may become hot and finally catch fire in contact with

air at ambient temperature without application of energy;iii) solid substances and preparations which may readily catch fire after brief contact with a

source of ignition and which continue to burn or to be consumed after the removal of theignition source;

iv) gaseous substances and preparations which are flammable in air at normal pressure;v) substances or preparations which, in contact with water or damp air, evolve highly

flammable gases in dangerous quantities.

H3-B: Flammable. Liquid substances and preparations having a flash point equal to or greaterthan 21°C and less than or equal to 55°C.

H4: Irritant. Non-corrosive substances and preparations which, through immediate, prolongedor repeated contact with the skin or mucous membrane, can cause inflammation.

H5: Harmful. Substances and preparations which, if they are inhaled or ingested or if theypenetrate the skin, may involve limited health risks

H6: Toxic.

H7: Carcinogenic. Substances and preparations which, if they are ingested or if they penetratethe skin, may induce cancer or increase its incidence.

H8: Corrosive. Substances and preparations which may destroy living tissue on contact.

H9: Infectious. Substances containing micro-organisms or their toxins which are known orreliably believed to cause disease in man or other living animals.

H10: Teratogenic. Substances and preparations which, if they are inhaled or ingested or if theypenetrate the skin, may induce non-hereditary congenital malformations or increase theirincidence.

H11: Mutagenic. Substances and preparations which, if they are inhaled or ingested or if theypenetrate the skin, may induce hereditary genetic defects or increase their incidence.



H12: Substances or preparations which release toxic or very toxic gases in contact withwater, air or an acid.

H13: Substances and preparations capable by any means, after disposal, of yielding anothersubstance, e.g. a leachate, which possess any of the characteristics listed above.

H14: Ecotoxic. Substances and preparations which present or may present immediate or delayedrisks for one or more sectors of the environment.

Wastes (special or non-special) which have any of the following properties:Finely divided metal (H15)

Dust or powder (H16; i.e. wastes which are in powder form F1).

Solid wastes which are likely to give rise to significant amounts of dusts, fibres, powders orparticulates, (i.e. wastes which can give rise to H16 hazards, but which are not in form F1:Powdery/powder when delivered).

Pressurised gas (H17; including gaseous wastes, form F6).

Odorous (H18); including wastes which are likely to give rise to harmful or offensive odours.

Sharp (H19)

Light (H20), including wastes which are likely to give rise to significant quantities of litter.

Solid wastes (F2) which are likely to give rise to contaminated or polluting run-off.

Viscous/ paste wastes (F3) or Sludge wastes (F4) or Liquid wastes (F5) which are likely to becontaminated or polluting.

Combustible wastes (such as wood, paper, plastic); these are wastes which consist of or containsubstances not falling into the Special wastes ‘H3-A Highly flammable’ or ‘H3-B Flammable’classifications as such, but which are capable of self sustained burning in air, once ignited.

Wastes which are likely to attract pests.

Wastes which are likely to attract scavengers.

Wastes or waste operations which are likely to give rise to mud or debris.

Waste operations which are likely to give rise to loud and persistent/recurring noise.



Appendix 4: OPRA Environmental Appraisal criteria referred to in Shell RiskAssessment approach

[Note: The following examples have been extracted from Environment Agency, 2000e.]

Screening risk assessments of aerial emissions:

Human Dwellings. Population Density And Environmental Targets This attempts tocategorise the likelihood of an event occurring by reference to the distancefrom the site and the consequence of an incident by considering sensitivity. The largest scorefor the site is to be incorporated within the model for the purposes of considering risks tohuman dwellings and/or environmental targets. In terms of sensitivity the followingcategories are considered:

(i) High – domestic dwellings, schools, hospitals and SSSIs (or equivalent) and beaches;(ii) Medium – offices, industrial units, footpaths, major highways and local

environmental areas; and(iii) Low – minor roads and public open space.

In this way, the system attempts to categorise not only the sensitivity of a receptor but alsothe amount each is likely to be used.

Distance High Medium Low<50 metres 20 15 10≥50<250m 15 10 5≥250<500m 10 5 1≥500m 5 1 1

Screening risk assessments of emissions of contaminated liquids to groundwater:

Groundwater It has not been possible to generate a matrix of probability against severity forthis section as little site specific data is known. Therefore, it has been decided to use theGroundwater Vulnerability maps which identify the vulnerability of groundwater tocontamination across the country in a similar manner. This has been based on the distributionof aquifers, the physico-chemical properties of overlying soils and the characteristics of stratain the unsaturated zone. It provides a consistent means of screening hydrogeologicalsignificance. A further group was added as inclusion within a Groundwater Protection Zone(‘GPZ’) highlights actual use of the groundwater in the vicinity of the site (please note that atpresent not all GPZ’s have been mapped.) Depending on the size of the licensed abstraction,thought must be given to whether or not it should be included for this purpose as if it werewithin a GPZ even if the abstraction is too small to be formally quantified as such.

Designation Rank/pointsWithin GPZ 15Major 10Minor 5Non-aquifer 1



Screening risk assessments of emissions of contaminated liquids to surface water:

Surface water The following system is based on the River Ecosystem Classification (RE)which has been assigned by the Environment Agency. This classification is based on anidentification of what work needs to be undertaken to meet the specified target. Thisinformation is available from the relevant Local Environment Action Plan document. Theconsequence has been subdivided into the following sections based upon the RiverEcosystem Classification, High (RE1 and RE2), Medium (RE3 and RE4) and Low (RE5).The consequence should be based on current RE classification. The distance to the surfacewater target should be calculated from the edge of the site although there should beconsideration of site specific factors. Where the pathway to the surface water is direct i.e.via an outfall pipe then it should be assumed that the distance to the pipe is the distance tosurface water i.e. adjacent rather than 250m. Also where no RE classification exists then thenearest downstream one should be used. For estuaries the nearest upstream RE classificationshould be used. where two RE classifications exist in similar proximity to the site thenconsideration should be given to the most likely route of any discharge and the approariateclassification inserted. The general assumptions in this section are that a canal is notgenerally in hydraulic continuity with the groundwater and unless there is a direct dischargeto the canal from the facility then it should have the score halved. All ponds, streams andrivers etc qualify for consideration as surface water.

Distance High Medium LowAdjacent 15 10 7<50 metres 10 7 3≥50<250m 5 3 1≥250 1 1 1



Appendix 5: Risk prioritisation assessment example

(See section 5.10 for guidance on the uses and shortcomings of this type of assessment.)

In this example, all identified risks are rated and prioritised through a scoring system, with those of most risk to the environment or humanhealth showing a higher score. The risk comprises two elements, the probability and the consequences, which are semi-quantitatively estimatedand combined to produce a risk factor. For each estimated risk, appropriate protective measures, controls and action plans are identified, alongwith an assessment of their mitigating effects. These are combined with the assessed risk factor to produce a mitigated risk factor for each risk..

The scoring system is defined as follows:-

Probability of hazard occurring: Consequences of hazard to theenvironment or human health:

Mitigation to risk:

0 Never1 Annually or less frequently2 Monthly or less frequently3 Weekly or less frequently4 Daily or less frequently5 More frequently than daily

0 Harmless5 Almost harmless10 Some harm15 Harmful20 Very harmful25 Extremely harmful

1 Ineffective or non existent2 Partly effective3 Effective4 Very effective5 Entirely effective

Risk factor = Probability x Consequence

Mitigated Risk Factor = Risk factor ÷ Mitigation factor



H a z a r d P a t h w a y a n d R e c e p t o r ProbabilityofHazard

C o n s e q u e n c eo f H a z a r d

R i s k f a c t o r( = P r o b a b i l i t yxC o n s e q u e n c e )

P r o t e c t i v e M e a s u r e s / C o n t r o l s( M i t i g a t i o n )

M i t i g a t i o nf a c t o r

M i t i g a t e d R i s kF a c t o r( = R i s k f a c t o r÷ M i t i g a t i o nf a c t o r )

Contaminationof surfacewaters byrunoff fromwaste storageareas.

Contaminated runoff from rapidlybiodegradable wastes, such aspaper, cardboard, entering surfacewater systems or ground water viasurface drainage, site ditches.

4 10 40 Storage in specified areas onimpermeable pavement, withsealed drainage system. Limiton maximum storage times toreduce potential forbiodegradation. Storage ofunsorted wastes within enclosedbuilding or of segregated wastesin enclosed containers.

5 8

Contaminated runoff from moreslowly biodegradable wastes,such as wood, green waste.

2 10 20 Storage in specified areas onimpermeable pavement, withsealed drainage system.

4 5

Contaminated runoff from non-biodegradable wastes, such assoils, concrete, hardcore.

1 10 10 Storage in specified areas onhardstanding. Wastes non-biodegradable or inert.

2 5

Contaminationof surfacewater, or breachof leachate/surface waterdischargeconsent limits

Acceptance of wastes outside sitedesign limits (unacceptablewastes), resulting in storage oninappropriate areas,contamination of surface waterresources or leachate quality inexcess of consent limits.

2 15 30 Implementation of wasteacceptance and control systems,including assessment of wastesprior to delivery, on siteinspection and waste handlingprotocols.

5 6

Inhalation ofdust

Generation of dusts by wastedischarge, handling and wind.Inhalation by site operatives andhumans at site boundary ofnuisance dusts only due torestricted range of wastes.

5 10 50 Undertake operations involvingcommercial, industrial andunsorted wastes within enclosedbuilding, with ventilation.Implementation of dustsuppression measures includingwater sprays/ sprinkler systems.Use of concrete hardstandingfor external materials storage.

4 12.5









Nuisanceodours

Windborne odours frombiodegradable wastes, detectableat site boundary by generalpublic. Greater perception ofnuisance than actual harm itself.

5 5 25 All operations involving storageof biodegradable wastes (exceptsorted wood) to be undertakeninside building. Limit onmaximum storage time forbiodegradable wastes to preventadvanced stage ofbiodegradation.

5 5

Unacceptablenoise levels

Noise generation by use ofrecycling equipment and plantmovement. Impacts uponresidential properties and personsin vicinity of site boundary.Greater perception of nuisancethan actual harm itself.

5 5 25 Wastes sorting and primaryactivities to be undertakeninside enclosed building,reducing impact at siteboundary. Secondary activities(crushing/wood chipping)undertaken outside will only beperiodic when sufficientmaterials are available foractivities. Screening aroundrecycling area will attenuatenoise. Operations will berestricted to PlanningPermission hours, limitingduration of impact.

5 5

Attraction ofpests to site,spread ofdisease.

Attraction of pests to site due tostorage of biodegradable wastes.Small quantities of contaminationby food may exist. Spread ofdisease by rats and flies topersons outside site. Alsonuisance to residents near site.

3 10 30 Site not accepting domesticwastes or waste types likely toinclude large quantities of foodwastes. Storage of relevantwastes types within buildingwill deter pests. Use ofspecialist pest controlcontractor.

3 10









Bird nuisance Attraction of birds to site due tostorage of biodegradable wastes.Small quantities of contaminationby food may exist. Nuisance toresidents near to site and possiblespread of litter and disease.Greater perception of nuisancethan actual harm itself.

5 5 25 Site not accepting domesticwastes or waste types likely toinclude large quantities of foodwastes. Storage of relevantwaste types within building willeffectively exclude birds fromcontact with waste and deterpresence.

5 5

Litter nuisance Spread of windblown litter (paper,cardboard, plastics, etc.) toadjoining parts of the site andbeyond site boundary. Visualamenity impact. Hygiene issues.Greater perception of nuisancethan actual harm itself.

4 5 20 Storage of relevant waste typeswithin an enclosed building orof appropriate sorted materialsin enclosed containers on site.Site inspections for presence oflitter and clearance of anyfound. Sheeting and netting ofdelivery vehicles.

5 4



Appendix 6: Quantitative assessments: Imaginary Landfill, England

Imaginary Landfill was constructed to receive industrial waste with limited putresciblecontent from a nearby town. Completed in the early 1990’s, it includes a composite liner andis relatively small in size. An extension to the landfill is now proposed and the EnvironmentAgency requires that as part of the waste management licensing process a Regulation 15assessment be carried out to predict the likely impact on groundwater and compliance againstthe requirements of the Groundwater Directive. Separate risk assessments are to beundertaken for other processes including migration of, and exposure to landfill gases,construction and durability of engineered barriers and leachate management systems, andimpacts on ecological systems including a nearby site of special scientific interest (SSSI).

The landfill is underlain by strata that are classified as Minor Aquifer by the EnvironmentAgency, and consists of inter-bedded clays, silts and sands. Hydraulic continuity is assumedbetween the sandstone horizons on the basis of the hydraulic response to local pumping tests,which indicate a (saturated) aquifer hydraulic conductivity between 1.0 E-5 m/s and 3.4 E-6m/s. Laboratory analysis of samples indicates sediments have a cation exchange capacity of5-15 meq/100g, and reaction efficiency between 5 and 15%. Faulting is generally absent.

The regional hydraulic gradient is 0.05 towards the south-east. On-site permeability testingand laboratory testing of unsaturated cores indicate an hydraulic conductivity of about 1.0E-7m/s to 1.0E-9 m/s depending on the lithology tested. Porosity does not exceed 30% and themoisture content of core samples lies between 5 and 7%. The winter watertable lies at anaverage of 15m below the site and effective rainfall is estimated at approximately 250 mm/aon the basis of MORECS data.

Watertable

InfiltrationMonitoring

borehole

Listsubstance

Waste

Assess impactsfor List II

substances atborehole

Layeredaquifer

Assess impacts forList 1 substances atentry to watertable



Following conceptualisation of the site, surroundings and processes it has been agreedbetween the Agency and the developer that LandSim is an appropriate assessment tool in thisinstance. As part of data collection for inclusion in the LandSim assessment, existing leachatechemistry from the previous phase of landfilling was undertaken and compared withpublished data that relate to the anticipated waste stream. In addition a List I screen wasundertaken (as described in the Agency’s interpretation on Reg15), and trichloroetheneidentified as being present in elevated concentrations. Examination of landfill recordssuggests this originates from the industrial waste received at the site. The operator’sconsultant has carried out a Landsim assessment on the existing site as a first stage and asummary of the input data is given in Table A6.1. The landfill has been modelled assuming aporous medium with no accounting for retardation. It has been agreed that the compliancepoint for licence conditions shall be shall be a monitoring borehole immediately down-gradient of the site, while predictive assessments for List II substances and non-listedsubstances will be made for a point beneath the site. Assessments of List I substances will bemade against the predicted impact on groundwater quality as the leachate enters thewatertable directly beneath the landfill.

The LandSim assessment models the performance of the landfill under normal conditions, i.e.it assumes that the engineering performs as designed throughout the operational life of thesite. An additional assessment of risks associated with catastrophic failure of the site wasundertaken using qualitative methods. In this instance, an assessment was made of thelikelihood and consequence of the HDPE tearing due to ground instability, and of a largepuncture of the basal liner during waste deposit by, for example, a scaffolding pole.

Table A6.1: Summary of Imaginary Landfill data for LandSim

Min value Most likelyvalue

Max Value Justification

INFILTRATION (mm/a) 45 50 55 Capped landfill

LEACHATE SOURCE:

Leachate Inventory (mg/l)ammoniacal_N 4 200 500 Based on Robinson 1995chloride 40 2300 7800 & on-site leachate data.mercury 0.00004 0.00009 0.002trichloroethene 0 0.1 0.2

Drainage System (piped)Specified Head on EBS (m) 0 1 licence requirement

Engineered Barrier SystemK of mineral lower liner (m/s) 1.00E-10 1.00E-09 1.00E-08 LandSim default valuesMembrane defects (/hectare)Pin holes 0 25 25Holes 0 5 5Tears 0 0.1 2Design thickness of liner 1mVariability in liner thickness 5%

Width (m) Length(m)

Number Top area (m2) Base area (m2)

CellGeometry

100 120 1 18000 12000



Table A6.1: Summary of Imaginary Landfill data for LandSim (cont’d)

Min value Max Value Justification

UNSATURATED PATHWAYPARAMETERS:

Length (m): 14 16 Depth to watertable from boreholesMoisture content (%) 5 7 Laboratory analysisK (m/s) 1.00E-09 1.00E-07 Lab analysis & on-site measurementsPorosity 0.05 0.3 Laboratory analysisLongitudinal dispersivity 0 1 Default values (0.1 × pathway length)Transverse dispersivity 0 0.1 Default values (0.01 × pathway)CEC (meq/kg) 50 150 Sand/Silt/Clay strataReaction Efficiency 0.05 0.15

VERTICAL PATHWAY (assumed negligible):

Pathway length (m) 0 0.0001 Unconfined aquifer

AQUIFER PATHWAY PARAMETERS:Length (m) 0 160 Receptor south-east corner of site (List

II); receiving GW (List I)Width (m) 140 160 Cell width parallel to flowMixing Zone (m) 5 15 Borehole logsPorosity 0.1 0.3 Laboratory analysesRegional gradient 0.01 0.05 [NB: 0.05 most likely]K (m/s) 3.4E-06 1.00E-05 Pumping test resultsLongitudinal dispersivity 0 10 Default values (0.1 × pathway length)Transverse dispersivity 0 1 Default values (0.01 × pathway length)

CALCULATION SETTINGS: Key:Number of iterations 5000 CEC: Cation Exchange CapacityTimeslices at (years): 30, 100, 300, 1000 K: Hydraulic Conductivity

The results from the LandSim model are summarised in Table A6.2. Although there are smallvariations in concentrations between each run the results appear acceptable for mostcompounds. The exceptions are ammoniacal nitrogen and trichloroethene (TCE).

Table A6.2: Predicted Contaminant Concentrations in Groundwater, Imaginary Landfill(Selected confidence limits)

Time Concentrations Predicted(years) Ammonical_N (mg/l) Chloride (mg/l) Mercury (mg/l) Trichloroethene (mg/l)

95%-ile 99%-ile 95%-ile 99%-ile 95%-ile 99%-ile 95%-ile 99%-ile30 1.00E-30 1.00E-30 3.94E+01 1.34E+02 1.00E-30 1.00E-30 6.23E-04 6.66E-03

100 1.00E-30 1.00E-30 5.59E+01 1.51E+02 1.00E-30 1.00E-30 1.13E-03 7.43E-03300 1.00E-30 5.68E+00 5.75E+01 1.53E+02 1.00E-30 1.00E-30 1.25E-03 7.64E-03

1000 1.00E-30 1.06E-01 5.75E+01 1.53E+02 1.00E-30 1.00E-30 1.25E-03 7.64E-03Infinity 1.00E-30 1.23E+01 3.94E+01 1.34E+02 1.00E-30 1.00E-30 6.23E-04 6.66E-03

Ammonia exceeds the maximum admissible concentration in groundwater at 300 years andinfinity (at a 99 percentile confidence limit). There is a domestic abstraction 200m from thesite and the Environment Agency will therefore need to be satisfied that the ammoniacal



nitrogen concentration will remain below drinking water standards (0.5 mg/l) a short distancedown-gradient of the landfill site. An appropriate contaminant transport model would need tobe used for this purpose. If drinking water standards are not achieved an improvedcontainment system or a reduction in the putrescible waste would be required before theAgency would accept any extension to the site.

Trichloroethene is predicted at a maximum of 1.25E-03 mg/l at the 95%ile confidence limit.This equates to 1.25 µg/l, which although below the drinking water standard of 30 µg/l, isstill discernible against background quality and could represent a discharge of List Isubstances. Following further discussion between the developer and the Agency, it wasagreed that LandSim did not include all the mechanisms that might be expected to affect thefate and transport of TCE in the subsurface. TCE is biodegradable under anaerobic conditionsand adsorbs to organic material, and these conditions are known to exist below the landfillwhere leachate has entered the unsaturated zone. In order to validate the model, thepredictions were compared against existing monitoring data collected from the existing cell.Although TCE is found in the leachate within the site, there has never been any TCErecorded in the groundwater monitoring boreholes. As a result, it was agreed that thepredicted leakage of TCE though the engineered barrier would be unlikely to cause adischarge of list I substances to groundwater, provided that the engineered barrier performedas modelled.

Comprehensive and clear reports were submitted to the Environment Agency as part of thesubmission for a waste management licence. The conceptual model was clearly described anddrawings and cross sections clearly annotated. All input laboratory and literature derived dataused in the quantitative modelling process were fully documented and justified.

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