3. Identification and Characterisation of Exposure Groups and

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NNL 8856 Issue 3
LLWR Lifetime Project: Data for Exposure
Groups and for
Future Human Actions and Disruptive Events
MTA/P0022/2007-4: Issue 3
A Report to the National Nuclear Laboratory
from
Mike Thorne and Associates Limited
Abbotsleigh
Kebroyd Mount
Ripponden
Halifax
West Yorkshire
HX6 3JA
July 2009
MTA/P0022/2007-4: Issue 3
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NNL 8856 Issue 3
Executive Summary
This report relates to the identification, selection and characterisation of exposure
groups for the operational period and Potentially Exposed Groups (PEGs) for the
post-closure period relevant to radiological impact assessments of the Low-Level
Waste Repository (LLWR) near the village of Drigg, Cumbria under both present and
potential future climate and landscape conditions.
Based on previous work, a well-defined methodology for the identification and
characterisation of exposure groups and PEGs has been developed. This comprises
the following steps:
1) Define the context in which the exposure groups or PEGs are present and
provide outline descriptions of them;
2) Identify the pathways of exposure relevant to each exposure group or PEG;
3) Define the exposure groups or PEGs in terms of present-day population
groups;
4) Select point estimate reference parameter values and uncertainty ranges for
adult members of each exposure group or PEG to achieve relative
homogeneity of characteristics;
5) Select point estimate reference parameter values and uncertainty ranges for
children and infants associated with each exposure group or PEG;
6) Audit local resource use and range of uncertainty for each PEG.
Application of this methodology resulted in a set of nine groups relevant to the
groundwater, gas and facility degradation pathways from closure through to the end of
termination due to the effects of coastal processes.
The nine groups of relevance were identified as:
• Occupational users of the storm beach and intertidal zone;
• Recreational users of the storm beach and intertidal zone;
• Casual and recreational users of the facility cap area;
• Agricultural smallholders making use of the cap area;
• Users of water abstracted from a well downstream of the facility;
• Users of the East-West and Drigg streams and of the Site South area;
• Users of the estuary and lagoon;
• Occupational users of Ravenglass Bay;
• Recreational users of Ravenglass Bay.
Agricultural smallholders making use of the cap area are also identified as the likely
users of water abstracted from a well downstream of the facility. Such an agricultural
smallholder group was discussed in the context of inadvertent human intrusion in the
2002 PCSC. As the approach adopted then for inadvertent human intrusion remains
applicable, the smallholder PEG is discussed in the human intrusion context.
For each of the remaining seven groups, the following general pathways were
considered:
• External exposures to contaminated soils, sediments and water bodies;
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•
Ingestion of contaminated soils and sediments, water, plant products and animal
products;
• Inhalation of contaminated soils and sediments and radioactive gases (including
radon, thoron and their progeny).
The groups identified have some similarities with the Analogue PEGs adopted in the
2002 PCSC, but also some substantial differences. These differences reflect the
shorter timescale now considered and the greater emphasis that is placed on the
potential disruption of the facility by coastal processes.
A further difference from the 2002 PCSC arises in the specification of parameter
values for each exposure group or PEG. In the 2002 PCSC, point estimates only were
given. However, in this analysis, both reference point estimates and reasonable
ranges are provided to facilitate the undertaking of sensitivity studies. Also, although
the principal assessment calculations are still to be undertaken for adults, reference
parameter values and ranges are also given for 10-year-old children and 1-year-old
infants in all appropriate cases to facilitate comparisons between age groups.
In defining ranges for exposure group or PEG characteristics, correlations between
those characteristics have been recognised. Therefore, rather than specifying ranges of
values for all of the parameters directly, in some cases, formulae have been developed
to represent the relationships between parameters and ranges have been specified for
secondary parameters used in those formulae.
In respect of inadvertent human intrusion, a stylised approach was adopted in the
2002 PCSC and no good reason was identified for adopting a different approach.
In suitably generalised terms, three modes of intrusion are distinguished:
• Small: Representative of the type of disturbance that might be caused by the
drilling of boreholes during site investigation;
• Medium: Representative of the type of disturbance that might be caused by
impact from an aircraft crash, a trial pit excavated on the site of the disposal
facility, or a limited bulk excavation, e.g. associated with the construction of
an isolated dwelling;
• Large: Representative of large-scale excavations associated with major
construction projects or, potentially, archaeological investigations at the site.
PEGs have been identified for each of these modes of intrusion. In each case,
identification of the appropriate PEG had to take into account two main categories of
exposure:
• Type A: Individuals involved directly or indirectly in the activity giving rise to
the intrusion;
• Type B: Site inhabitants exposed to wastes dispersed on the site as a
consequence of the intrusion.
In principle, there will be only a single most-exposed PEG for each mode of intrusion.
However, in practice, without undertaking specific calculations, it is not always
possible to determine whether the most exposed PEG will be the intruder, an associate
or a site inhabitant. For this reason, potential PEGs for each type of exposure were
defined for generalised large intrusions. For generalised small and medium
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intrusions, it was clear that Type A dominates so only this type of exposure has been
addressed. The characteristics of the site inhabitant PEG were also considered
appropriate to an agricultural smallholder making use of the cap area.
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Contents
Executive Summary.................................................................................................................................iv
1. Introduction ....................................................................................................................................... 1
1.1 Background ................................................................................................................................ 1
1.2 Scope and Structure of the Report.............................................................................................. 2
2. Methodology for the Identification and Characterisation of Exposure Groups................................. 5
2.1 The Methodology Adopted in the 2002 Operational Environmental Safety Case ..................... 5
2.2 The Methodology Adopted in the 2002 Post-closure Safety Case ........................................... 10
2.3 Climate and Landscape Evolution Scenarios ........................................................................... 15
2.3.1
The Storm Beach and Intertidal Zone............................................................................. 16
2.3.2
The Cliff ......................................................................................................................... 16
2.3.3
Carl Crag Bay ................................................................................................................. 17
2.3.4
Barn Scar Headland ........................................................................................................ 17
2.3.5
Drigg Dunes and Drigg Point ......................................................................................... 17
2.3.6
Area 1 ............................................................................................................................. 17
2.3.7
Site North........................................................................................................................ 18
2.3.8
Site South........................................................................................................................ 18
2.3.9
The Irt Estuary ................................................................................................................ 19
2.3.10
The Barrier Lagoon......................................................................................................... 19
2.3.11
Ravenglass Bay............................................................................................................... 19
2.3.12
Timescales ...................................................................................................................... 20
2.4 Identification of Exposure Groups and PEGs .......................................................................... 21
2.4.1
Exposure Groups for the Operational Phase ................................................................... 21
2.4.2
PEGs for the Post-closure Phase..................................................................................... 23
2.5 Methodologies Adopted for PEG Identification and Characterisation for Future Environmental
Safety Cases ............................................................................................................................. 24
2.5.1
Defining the Context in which PEGs are Present ........................................................... 25
2.5.2
Representation of All Relevant Pathways....................................................................... 25
2.5.3
Identification of PEGs .................................................................................................... 26
2.5.4
Relative Homogeneity .................................................................................................... 27
2.5.5
Residence in, and Utilisation of Materials from, the Contaminated Area ...................... 27
2.5.6
Age Groups..................................................................................................................... 28
2.5.7
Use of Standard Data ...................................................................................................... 28
2.5.8
Use of Point Values ........................................................................................................ 28
2.5.9
Other Considerations ...................................................................................................... 28
2.5.10
Steps of the Methodology ............................................................................................... 28
3. Identification and Characterisation of Exposure Groups and Potentially Exposed Groups ............ 30
3.1 From the Present Day through to and During Facility Disruption ........................................... 30
3.1.1
Identification of Pathways of Exposure.......................................................................... 30
3.1.2
Definition of Exposure Groups and PEGs as Population Groups................................... 34
3.1.2.1
Analogue PEGs in the 2002 PCSC ....................................................................... 34
3.1.2.2
Exposure Groups and PEGs defined in this Study ................................................ 37
3.1.3
Selection of Point Estimate Parameter Values and Ranges for the Characterisation of
Members of Exposure Groups and PEGs ....................................................................................... 38
3.1.3.1
External Exposure to Soil and Sediment ............................................................... 39
3.1.3.2
External Exposure to Water Bodies ...................................................................... 41
3.1.3.3
Ingestion of Soil and Sediment ............................................................................. 42
3.1.3.4
Ingestion of Water................................................................................................. 43
3.1.3.5
Ingestion of Plant Products ................................................................................... 44
3.1.3.6
Ingestion of Animal Products................................................................................ 46
3.1.3.7
Inhalation of Soil and Sediment ............................................................................ 47
3.1.3.8
Inhalation of Radioactive Gases............................................................................ 48
3.1.3.9
Compilation of Reference Values ......................................................................... 48
3.1.4
Local Resource Use and Ranges of Uncertainty............................................................. 50
3.2 For Inadvertent Human Intrusion over the Period from Closure to Facility Disruption........... 52
3.2.1
Approach Adopted in the 2002 PCSC ............................................................................ 52
3.2.2
Characteristics of PEGs for Inadvertent Human Intrusion ............................................. 55
3.3 Smallholder PEGs located on the Cap ..................................................................................... 60
4. Conclusions ..................................................................................................................................... 61
5. References ....................................................................................................................................... 63
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1.
Introduction
This report has been prepared by Mike Thorne and Associates Ltd for Nexia Solutions
Ltd. It relates to the identification, selection and characterisation of Exposure Groups
relevant to radiological impact assessments of the Low-Level Waste Repository
(LLWR) near the village of Drigg, Cumbria under both present and potential future
climate and landscape conditions. The Exposure Groups apply to the operational
phase of the LLWR which covers the period from the present day, through closure of
the site (planned for 2050AD) to 2150 AD, following an assumed period of 100 y
over which knowledge of the site is retained. After 2150 AD, knowledge of the site is
assumed to be lost and beyond this time, the post-closure phase is considered to
persist, during which Potentially Exposed Groups (PEGs) are used to assess any
subsequent risks to humans. PEGs are used instead of Exposure Groups because the
habits of the human receptors are less well established and hypothetical population
groups are envisaged in the context of climatic and landscape changes for site and its
environs recently developed by Thorne and Kane (2007).
The report also provides data for future human actions and disruptive events based on
the methodology of the 2002 PCSC superimposed on the new climate and landscape
change scenarios that have been developed in recent work (Thorne and Kane, 2007).
The timing and characteristics of these actions and events is considered in the context
of the post-closure phase.
1.1
Background
The Environment Agency (EA) has issued a new Authorisation for operations at the
Low-Level Waste Repository (LLWR) which has an effective date of 1st May 2006
(Defra, 2006; Environment Agency, 2006).
The authorisation followed a review of the previous authorisations for the site and was
informed by, but not limited to, a review of the 2002 Operational and Post-closure
Environmental Safety Cases submitted by BNFL (BNFL, 2002a; 2002b). The
outcome was a single new authorisation encompassing all aspects regulated by the EA
under the Radioactive Substances Act 1993. One of the key schedules within the
Authorisation, Schedule 9, is a list of improvement and additional information
requirements placed on the operator.
To satisfy the Schedule 9 requirements, the LLWR Site Licence Company (SLC) has
initiated a significant programme of work, called the Lifetime Project, in support of
the Lifetime Plan of the LLWR (Randall et al., 2006). This report concerns a study
undertaken within the R&D component of the Lifetime Project, relating to the
identification of exposure groups under potential patterns of future climate change and
consequent landscape change at the LLWR site. The work is intended to inform
various aspects of the Lifetime Project, including:
• Optimisation studies;
• Radiological capacity studies;
• Evaluation of radiological impacts on humans;
• Evaluation of non-radiological impacts on humans.
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This work does not inform ecological assessments of non-human biota which have
been undertaken recently (Eden and Barber, 2007).
In the context of optimisation studies, it is noted that by 1 May 2008, the LLWR Site
Licence Company (SLC) is required to provide the EA with a full report of a
comprehensive review of national and international developments on best practice for
minimising the impacts from all waste disposals on the site. This is to include a
comprehensive review of options for reducing the peak risks from deposition of solid
wastes on the site, where those risks arise from potential site termination events and
potential future human actions.
By 2011, the LLWR SLC is required to update the Environmental Safety Cases for
the site covering the period up to withdrawal of control and thereafter. In undertaking
this updating, radiological safety assessment studies covering the operational and
post-closure phases are essential inputs. These studies will need to incorporate new or
revised information from a number of areas (such as the information on exposure
groups provided in this report) and assess the implications of this information for
radiological safety.
1.2
Scope and Structure of the Report
This report relates to the identification, selection and characterisation of exposure
groups for use in the operational and post-closure radiological impact assessment
described in Section 1. The identified and characterised exposure groups are those
that are relevant to all climate and landscape combinations that are applicable in the
various assessment scenarios from the present day operational phase and throughout
the post-closure phase. The combinations of climatic and landscape characteristics to
be addressed mainly in assessments of the post-closure phase are provided by Thorne
and Kane (2007).
Unlike the 2002 Operational Environmental Safety Case (OESC) and Post Closure
Safety Case (PCSC) which were considered separately, subsequent Environmental
Safety Cases for the LLWR will consider these aspects together to ensure consistency
and, in part, address issues previously raised by the Environment Agency (EA). Thus,
for the climate and landscape change scenarios provided by Thorne and Kane (2007)
and bearing in mind issues raised by the EA, there is a requirement to:
•
Define and apply the methodology for the selection of exposure groups for the
operational phase and PEGs for the post-closure phase;
• Define the habits of the exposure groups and PEGs, covering occupancy and
ingestion/inhalation exposure pathways, and associated parameter values.
The exposure groups and PEGs apply for releases of radionuclides in groundwater
and gaseous form. However, it was recognised that the LLWR facility could be
disrupted by either natural events or by inadvertent human intrusion, which is
assumed to be prevented from taking place until the post-closure phase. Therefore,
the requirement was augmented to include the provision of data for future human
actions and disruptive events based on the methodology of the 2002 PCSC
superimposed on the new climate and landscape change scenarios. In practice, the
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PEGs for natural disruptive events relate closely to those for the groundwater and gas
pathways, and are considered together with them in this report.
In identifying and selecting the PEGs, and in defining the habits of those exposure
groups in quantitative terms, extensive reference is made to earlier work by Thorne
and Kane (2006) for UK Nirex Ltd and to the recommendations of Smith and Jones
(2003). The application of these publications to the LLWR was briefly considered in
Thorne (2007). Thus, the main work involved in this study has been the adaptation of
that information to the climatic and landscape situations identified by Thorne and
Kane (2007) as being of relevance.
The work on future human actions and disruptive events is primarily an adaptation of
existing information from the 2002 PCSC (Halcrow, 1998; Thorne and Halcrow,
2003) to the same set of climate and landscape situations. The use of this information
in the 2002 PCSC is discussed in Egan (2003), Penfold (2003), and Penfold and
Cooper (2003), with a follow-up study on alternative assumptions in Penfold (2004).
In Section 2, the methodology adopted for the selection and characterisation of
exposure groups and PEGs is described. In Sections 2.1 and 2.2, the methodologies
adopted for the 2002 OESC and PCSC respectively are summarised and pertinent
issues raised by the EA are considered. Application of these methodologies requires
an understanding of the climatic and landscape characteristics applicable at the LLWR
site at various times from the present day onwards until termination processes affect
the facility and truncate the period over which quantitative assessments are
undertaken. This information is provided in Thorne and Kane (2007), and is
summarised in Sections 2.3 and 2.4. The information provided in Sections 2.1 to 2.4
provide the basis for describing how the methodology has been updated and adapted
for application in the forthcoming assessments described in Section 1.1. This
updating and adaptation is described in Section 2.5.
The methodology set out in Section 2.5 is applied in Section 3, particularly in terms of
the identification and characterisation of PEGs. A major difference between the
analysis described here and that reported in support of the 2002 PCSC is that a much
greater emphasis is placed on the first few thousand years after repository closure.
This is because it is projected that, in the absence of protective measures, the site will
be destroyed by coastal processes on a timescale of a few thousand years. In turn, this
means that PEGs associated with termination events are characterised in more detail
than was considered appropriate in the 2002 PCSC, as these events are now given
greater emphasis as a key aspect of the site evolution scenario.
It must be emphasised that part of the basis of the assessment is that no specific
actions are taken to prevent coastal erosion and inundation of the LLWR site. This
allows a baseline evaluation of the implications of such a policy. In practice, such
actions could be taken and optimisation studies are likely to be undertaken to evaluate
the benefits and detriments of various approaches to intervention. For such studies, it
seems likely that some adaptation of the PEG characteristics given in this report will
be required. Sufficient background is given on the basis for PEG identification and
characterisation to facilitate such adaptation, as required.
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In Section 3.1, exposure groups and PEGs appropriate to the gradual evolution of the
site between closure and its destruction by coastal processes are identified and
characterised. Here and subsequently, identification is the process of defining the
group in descriptive terms. In contrast, characterisation is the process of defining
their habits and behaviour in quantitative terms, i.e. through the specification of
consumption rates of environmental materials such as drinking water, food, soil and
sediment, inhalation characteristics, and occupancy of contaminated areas.
Next, in Section 3.2, the additional PEGs associated with inadvertent human intrusion
into the facility or its immediate environment in the period before its destruction by
coastal processes are identified and characterised. Whereas inadvertent intrusion
during the period over which the facility is intact is regarded as a low probability
event and the scenario is imposed on the normal evolution scenario at different
possible times of occurrence, inadvertent intrusion during facility destruction is
regarded as an integral part of the overall scenario and occurs over the specific time
interval during which the destruction occurs. Indeed, rather than being considered as
inadvertent intrusion, it is treated as access to waste debris and particulates degraded
from such debris during the termination process.
In Section 3.3, a brief account is given of a smallholder PEG that is relevant in the
context of ‘bath-tubbing’ of the facility or in the case of abstraction of water from a
well or borehole located in a plume of contaminated groundwater.
Finally, Section 4 provides conclusions in terms of a summary of the types of
exposure groups and PEGs that should be included in the forthcoming assessments.
In addition, brief comments are provided on distinctions between the approach that
has been used to define PEGs in this report and that adopted in the 2002 PCSC.
Bibliographic details of references cited in the report are given in Section 5.
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2.
Methodology for the Identification and
Characterisation of Exposure Groups
In this Section, the methodology for identifying exposure groups for the 2002 OESC
and PEGs for the 2002 PCSC are described in Sections 2.1 and 2.2, respectively.
These sections also describe key issues raised by the EA in relation to these
methodologies which required addressing in taking this work forward. A number of
these issues could be dealt with by considering the exposure groups associated with
the operational and post-closure phases in sequence. To achieve this requires a
description of the changing environment that these exposure groups will interact with,
and so, in Section 2.3, there is reference to a number of recent climate and landscape
change scenarios for the LLWR and its environs from Thorne and Kane (2007). As
all of the scenarios lead to a termination of the existence of LLWR site at various
times, through coastal erosion, the spatial components of each scenario on which the
exposure groups are based tend to be consistent across all scenarios and are explicitly
described in Section 2.3.
At the end of Section 2.3, there is a discussion of timescales for the onset and
completion of site termination for reference in relating to the definition of exposure
groups and habits for the operational assessment of the site in Section 2.4.1 and the
definition of PEGs and habits for the post-closure phase of the assessment in Section
2.4.2.
2.1
The Methodology Adopted in the 2002 Operational
Environmental Safety Case
In the 2002 Operational Environmental Safety Case (OESC) (BNFL, 2002a), the
assessment was based mainly on key exposure pathways for aerial and liquid
discharges from the LLWR site rather than on exposure groups. The 2002 OESC
was undertaken independently from the 2002 PCSC using separate models, though the
groundwater network model for the 2002 PCSC was adapted for use in assessing
groundwater discharges as part of the OESC.
The 2002 OESC covered the period up to 2149 AD, i.e. until just before the end of
management control. Three key time points were considered within that interval:
• 2005 AD: Vault 8 full;
• 2050 AD: Disposals complete;
• 2100 AD: Post-closure engineering features complete.
The OESC was based on authorised aerial and liquid effluent discharges from the
LLWR site, comprising:
• Aerial discharges (from trenches 1 to 7, Vault 8 and the Drigg Grouting
Facility (DGF));
• Liquid discharges (by marine pipeline to the Irish Sea).
For aerial discharges, assessments using atmospheric Gaussian plume modelling were
undertaken. Exposure groups were considered to be located at two properties (1 and
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2) close to the site, a nearby farm (property 3) and a coal yard at the distances shown
in Table 1.
Source
DGF
Effective height (m)
Exposure Group
Property 1
Property 2
Property 3
Food Production
Coal Yard
High Volume Air
Sampler
Source
Effective height (m)
Exposure Group
Property 1
Property 2
Property 3
Trench
Trench
1
2
<5m
<5m
<5m
Distance from source (m)
351
365
580
949
570
233
718
532
504
718
532
504
1017
614
295
718
1054
1294
Future Vaults 1
<5m
Distance from source (m)
750
500
675
Trench
3
<5m
Trench
4
<5m
Vault
8.1
<5m
Vault
8.2
<5m
451
328
411
411
425
1166
256
576
435
435
665
948
706
269
649
649
191
1440
754
340
722
722
202
1462
Future Vaults 2
<5m
Future Vaults 3
<5m
750
650
700
750
800
750
Table 1: Exposure Group Distances used in the 2002 OESC
To characterise the behaviour of the exposure group, inhabitants were assumed to
consume food produced from the fields of property 3 and spent all their time at their
location. For discharges during 2005, the food consumption rates were taken from the
MAFF/NRPB advice of the time considering the two most likely foods that will be
consumed and produced locally (milk and root vegetables including potatoes) at 97.5th
percentile rates (Byrom et al., 1995). Also, other foodstuffs, as listed in Table 2, were
taken to be consumed at mean rates (Byrom et al., 1995).
Food
Milk
Beef
Mutton
Liver
Green vegetables
Root vegetables
Fruit
Poultry
Eggs
Adult
240
15
8
5.5
35
130
20
10
8.5
Consumption Rate (kg a-1)
Child
240
15
4
3
15
95
15
5.5
6.5
Infant
320
3
0.8
1
5
45
9
2
5
Table 2: Consumption Rates used in the Discharge Assessment for 2005
For future discharges, consumption rates were adopted that were consistent with the
2002 PCSC and are shown in Table 3.
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Food
Milk
Beef
Mutton
Liver
Green vegetables
Root vegetables
Fruit
Poultry
Eggs
Adult
600
15
8
5.5
35
130
20
16
8.5
Consumption Rate (kg a-1)
Child
510
15
4
3
15
95
15
9.5
6.5
Infant
590
3
0.8
1
5
45
9
2
5
Table 3: Consumption rates used in an Assessment of Projected Discharges over
the Period 2050- 2149
Occupancy and breathing rates associated with the exposure groups are shown in
Table 4 for both 2005 and the period 2050-2149. These are consistent with the 2002
PCSC.
Quantity
Occupancy
Fraction of time indoors
Breathing rate (m3 d-1)
Fractional occupancy indoors at home
Fractional occupancy of beach
Residual fractional outdoor occupancy
Indoor breathing rate (m3 d-1)
Outdoor breathing rate (m3 d-1)
Adult
Data for 2005
1
0.5
19.9
Data for PCSC
0.5
0.14
0.4
10.32
28.8
Child
Infant
1
0.5
15.6
1
0.9
5.18
0.8
0.14
0.1
8.4
24
0.94
0.06
0.04
5.28
5.28
Table 4: Occupancy, Fraction of Time Spent Indoors and Breathing Rates1
For liquid discharges to the Irish Sea, assessments using a compartment-based model
were used. These simulated the long-term dispersion of radionuclides in the Irish Sea
by annually averaged advection and dispersion. Doses were calculated to a critical
group of West Cumbria seafood consumers on the basis of ingestion of marine biota
taken from specific regions of the model. This critical group was determined by habit
surveys to be adults that live along the western coast of Cumbria and consume
seafood collected along the Cumbrian coastline between Whitehaven and Ravenglass.
The consumption rate values used for 2005 were averaged from habit data given by
MAFF/FSA and SEPA between 1996 and 2000 to provide a longer-term average
(Table 5). External exposure over contaminated sediments was also averaged in the
same manner.
1
Fractional occupancies sum to 1.04. This is as reported and probably arises because occupancy of the
cap has been incorrectly added to residual fractional outdoor occupancy in each case.
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Pathway
Fish consumption
Crab consumption
Lobster consumption
Winkle consumption
Mussel consumption
External exposure
1996
25
7.2
4.8
7.2
4.8
420
1997
37
8.5
6.8
1.68
2.52
1000
1998
45
23.8
4.2
4.5
10.5
1100
1999
43
19.2
4.8
12.5
12.5
1000
2000
31
8
8
8.5
8.5
1000
Average
36.2
13.3
5.7
6.9
7.8
904
Table 5: Habit Data for the West Cumbrian Critical Group
(kg a-1 or h a-1). (Data taken from the RIFE series of reports, see, e.g. RIFE-4,
RIFE-5 and references therein.)
For 2050 and 2100 AD, the estimated consumption rates from the 2002 PCSC were
adopted, as shown in Table 6. This critical group made use of a wider range of
pathways than those considered for the West Cumbria seafood-consuming group.
These extra pathways were seaweed consumption and inadvertent ingestion of
sediment.
Rates (kg a-1 or h a-1)
60
10
10
5
5
50
0.0365
880
Pathway
Fish consumption
Crab consumption
Lobster consumption
Winkle consumption
Mussel consumption
Seaweed consumption
Sediment ingestion
External exposure
Table 6: Habit Data for the West Cumbrian Critical Group for 2050 Onward
Besides assessing authorised effluent discharges, the 2002 OESC also assessed:
• The impact from the Drigg stream;
• The impact from Drigg groundwater;
• The impact of direct radiation exposure (shine) from the site;
• The impact on Drigg biota.
In the context of this report, the impact from the Drigg stream was based on
monitored radionuclide concentrations there and a side calculation of exposure from
consuming water directly from the stream and milk from cows that were taken to
drink stream water. The impact from groundwater was based on predicted
radionuclide concentrations at a number of abstraction points. Direct shine was
estimated based on Thermo-Luminescent Dosimeter (TLD) measurements at locations
close to the site. The impact on Drigg biota is outside the remit of this report and is
not discussed further.
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The Environment Agency in their assessment of the 2002 OESC raised a number of
issues2, of which the following are pertinent to the context of defining exposure
groups:
OESC_003
Definition of Exposed Groups;
OESC_004
Scope, Purpose and Objectives of the OESC;
OESC_010
Management of Uncertainty;
OESC_012
Assessment of Prospective Public Doses.
The issue OESC_003 relates to the fact that the 2002 OESC was mainly based on key
exposure pathways rather than identifiable exposure groups. To address this issue, it
is required that exposure groups should be specifically defined for the operational
phase of forthcoming assessments, particularly for aerial effluent discharges and the
Drigg stream assessment. For the aerial discharges, the EA requested that more
exposure pathways for locally grown fruit and vegetables at each of the properties be
considered. For the Drigg stream assessment, the EA specified that exposure
pathways in addition to drinking water and cow’s milk need to be considered.
Issue OESC_004 relates to the fact that the scope and purpose of the 2002 OESC were
not clearly defined. In future assessments, the EA expected BNFL to address:
• The questions that the OESC is attempting to answer;
• How and where the Principles and Requirements set out in Environment Agency
et al. (1997) are addressed;
• The broad methodological approach adopted for the dose assessments;
• Whether the empirical data are of sufficient quality to justify the modelling
approach;
• Bias, uncertainty and variability in the choice of assumptions and data;
• How the OESC output influences site strategy and operations.
This report addresses issues relating to the broad methodological approach adopted in
dose assessments. In particular, consistency and continuity between the pre-closure
and post-closure assessments is achieved. The adequacy of available data on human
habits and behaviour are assessed, and bias, uncertainty and variability in the
underlying assumptions and data are evaluated.
Issue OESC_010 recognises that uncertainty was not systematically addressed in the
2002 OESC, though this was done for the 2002 PCSC. This was largely due to the
fact that, in most cases, the doses obtained from the 2002 OESC tended to be lower
than the dose constraint. The exception was the groundwater pathway (drinking
water), which was re-assessed as being below the dose constraint by Willans et al.
(2003). Nevertheless, future operational assessments need to consider such
uncertainties, e.g. in respect of styles and rates of coastal erosion and the nature and
characteristics of the local hydrogeological system.
2
These issues are set out in the Environment Agency Report ‘Review of the 2002 Environmental
Safety Cases for the LLW Repository at Drigg: Issue Assessment Forms’.
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Issue OESC_12 mentions that prospective public doses were not assessed in the 2002
OESC and considers that these need to be considered in future assessments covering
the operational period. This matter is relevant here to the extent that exposure groups
need to be defined for the whole of the operational period.
2.2 The Methodology Adopted in the 2002 Post-closure
Safety Case
In Thorne et al. (2003), it was emphasised that PEGs can be defined that make
maximum reasonable use of local contaminated resources or that are considered
particularly appropriate to the environs of the site under both present-day and future
climatic conditions. Both types of PEG were addressed in Thorne and Kane (2003).
These two types of PEGs were termed Local Resource Dominated and Analogue
PEGs, respectively.
Local Resource Dominated PEGs were identified and
characterised in order to give a cautious over-estimate of radiation exposure and risk.
Analogue PEGs were those considered particularly appropriate to the environs of the
site under both present-day and future climatic conditions. However, they were also
cautious in terms of assessed radiation exposure and risk, in that they were defined to
be located in the most highly contaminated area and to make substantial use of local
resources. Following comment from the EA, it seems that emphasis should be placed
on Analogue PEGs in future assessments (see below). This is reflected in the
emphasis given to Analogue PEGs in the present report.
The principles by which PEGs were defined in the 2002 PCSC were set out in Table
2.1 of Thorne and Kane (2003). This information is reproduced here as Table 7.
These principles remain valid and are adopted as a basis for the methodology used in
this study.
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Item
a
b
c
d
e
f
g
h
i
j
k
l
m
n
Principle
The Reference Biospheres concept and methodology will be used in the 2002 Drigg PCRSA. PEGs will be selected in the
context of such Reference Biospheres.
The characteristics of the PEGs selected in the context of Reference Biospheres will be such that all potentially relevant
pathways of exposure will be represented. However, PEGs will not be characterised to the same degree of detail as would
typically be employed in characterising present-day critical groups in the context of radioactive waste discharges.
One or more PEGs will be selected for each Reference Biosphere and scoping calculations will be used to identify which of
these should be taken forward for detailed analysis on the basis of the highest calculated radiological risk.
For the 2002 Drigg PCRSA, PEGs will be defined such that they are relatively homogeneous with respect to radiation
exposure.
At annual individual risks of the order of, or less than, the risk target, up to a factor of ten heterogeneity of exposure is
acceptable within a PEG. At substantially larger annual individual risks, the degree of heterogeneity should be less.3
Reasonable homogeneity of exposure does not necessarily imply that the representative member of a PEG is restricted to
residence in, and utilisation of materials from, the area in which environmental concentrations of radionuclides are highest.
However, the degree of utilisation of contaminated local resources will be estimated. In addition, an estimate will be made of
the number of individuals comprising each PEG.
The quantity to be compared with the risk target is the annual risk to an adult individual in any one year.
The diet and lifestyle of PEGs will be based on observed past and present behaviour, either in the region where the repository
is to be located or in analogue regions appropriate to different future environmental conditions.
In defining PEGs, human actions that imply knowledge of the presence of a radioactive waste repository will be excluded
from consideration.
PEGs will be defined in terms of broad characteristics likely to substantially affect radiation exposure. These broad
characteristics will be based on existing UK, overseas and international experience relating to both solid radioactive waste
disposal and discharges of radioactive effluents to the environment.
Assessment calculations will compute annual individual risk to the representative member of a PEG summed over all
situations that could give rise to exposure to that PEG. The major contributions to total risk will be clearly displayed. The
annual individual risks to be summed are those arising at specified times post-closure and not the peak risk from each
situation irrespective of its time of occurrence.
Assessment calculations for each situation will be for defined Reference Biosphere/PEG combinations characterised by
single (point) values of the associated uncertain biosphere /PEG parameters. The robustness of these calculations will be
examined in sensitivity studies in which values of the key biosphere and PEG parameters will be systematically varied. Due
to the uncertainties associated with potential future human actions, it is not considered appropriate to attempt to calculate
risks by sampling from distributions of values for biosphere and PEG parameters.
Results will be presented for each PEG separately. It is not appropriate to combine risks associated with different PEGs, as
PEGs are defined with sufficiently broad characteristics (see (j) above) that any given individual can be considered to be a
member of a single PEG only.
In general, when selecting parameter values to characterise representative members of PEGs, typical occupancies and
consumption rates will be used. However, consideration will be given to the size of the group or community from which the
PEG is drawn. If the group or community is sufficiently large that high occupancy or consumption rate individuals are likely
to be present at any one time, above-average occupancy or consumption rate data will be used.
Table 7: Principles for the Definition of Potential Exposure Groups for use in the
2002 PCSC (from Thorne and Kane, 2003)
These various principles were based on a set developed previously for application in
safety assessments undertaken by UK Nirex Ltd (Thorne, 2000). In Thorne and Kane
(2003) additional commentary was included on the application of the principles in
Table 7 to the LLWR. This additional commentary is reproduced in Table 8. It is
included mainly for reference in subsequent sections of this report and does not need
to be studied in detail for an appreciation of the following discussion.
The EA in their assessment of the previous 2002 PCSC raised a number of issues of
which the following is pertinent in the context of defining PEGs:
BIO_006: Selection and characterisation of exposed groups.
3
The risk target is the value of one per million per year proposed in the guidance on requirements for
authorisation issued by the environment agencies (Environment Agency et al., 1997).
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In issue BIO_006, there is specific reference to the Guidance on Requirements for
Authorisation (GRA; Environment Agency et al., 1997) paragraphs 6.5 to 6.8 and
6.19 to 6.20 that describe the requirement that the assessment of radiological dose or
risk to members of the public is approached by identifying exposure groups. The EA
recommended in future, that BNFL (or any subsequent Assessor) should:
1.
Account explicitly for uncertainties in the properties and characteristics of
transport pathways (e.g. using probabilistic techniques) in order to calculate
the expectation values of dose and risk to PEGs for comparison with the
design target.
2.
Calculate doses to PEGs exposed to individual pathways, to clarify the key
routes for radionuclides to reach the accessible environment and give rise to
doses.
3.
Use the same assumptions as to the habits and characteristics of PEGs in
calculations of doses arising from both the groundwater and gas pathways.
4.
Base its safety case on calculated risks to reasonable PEGs and not on
arguments concerning inappropriate and undemonstrated conservatisms.
Taking each issue in turn, the climate and landscape change scenarios to be used as a
framework to address uncertainties are described in Section 2.3. These scenarios
provide for ranges of sea level and coastal erosion rates that directly affect the
characteristics and evolution of the transport pathways for the radionuclides.
Mapping the envisaged habits of the PEGs to landscape regions associated with these
pathways will provide a range of dose and risk estimates for the PEGs for comparison
with the relevant dose or risk criteria.
In addition to expressing doses and risks summed over a number of exposure
pathways that characterise the exposure group, a range of doses and risks will be
provided for individual exposure pathways for the climate and landscape change
sceanrios described. This will allow a study of the contributions of individual
exposure pathways to the overall dose or risk for particular assumptions as to habits
and behaviour. This requirement does not impact strongly on the characterisation of
exposure groups, as this characterisation is necessarily undertaken for each pathway
of exposure. Rather, it is a matter relating to the manipulation and presentation of
results obtained in assessment studies.
In the 2002 PCSC, the habits and characteristics of the PEGs were not entirely
consistent when combined in joint consideration of the groundwater and gas
pathways. This was because greater emphasis was placed on the habits of the PEGs
associated with the groundwater pathway to the point that additional habits associated
the gas pathway could not be precisely reconciled when they were considered at a
later time. This issue is now resolved by considering groundwater and gas pathways
together in the definition of PEGs.
The last issue relates to the unease felt by the EA in respect of the use of Local
Resource Dominated PEGs in the 2002 PCSC, as these made maximal use of the
contaminated resources and received the largest risks. These were considered to
represent an unduly cautious basis for assessment. Local Resource Dominated PEGs
are not considered further in this study and only Analogue PEGs are taken forward for
future use.
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Item
a
b
Principle
The use of scenarios and prescribed landscape descriptions in the 2002 PCSC is very much in the spirit of defining Reference
Biospheres. The simplifications inherent in such landscape descriptions represent a balance between the perceived need to
take potential environmental changes into account and the recognition that it is not currently possible to generate a justified
mechanistic description of landscape evolution. PEGs can be defined in the context of such landscapes and can be
characterised by their degree of utilisation of the contaminated environmental media located therein. This approach is
endorsed, for example, by the International Atomic Energy Agency’s BIOMASS Theme 1 Reference Biospheres
Methodology and illustrated in Example Reference Biosphere 2 (BIOMASS, 2003).
Potentially significant pathways of exposure have been identified in a succession of assessments over the last two decades.
In addition, a formal exploration of potential routes of exposure has been undertaken in BIOMASS (2003). A key point is
that PEGs should not be characterised in great detail, e.g. in respect of consumption of specific foodstuffs. (For comparison,
in the definition of critical groups used in retrospective assessments of the radiological impacts from liquid and atmospheric
discharges of radioactive wastes, specific foodstuffs, e.g. winkles, are often represented explicitly.) This suggests that
exposures can be characterised at the following simplified level:
•
•
•
External exposures to contaminated soils, sediments and water bodies;
Ingestion of contaminated soils and sediments, water, plant products and animal products;
Inhalation of contaminated soils and sediments and radioactive gases (including radon, thoron and their progeny).
Ingestion of plant products needs only to consider terrestrial and freshwater plants. Terrestrial plants should only be
distinguished into broad classes. Cereals, fruit, green vegetables and root vegetables would seem to be sufficient, with other
foods aggregated into these classes. Similarly, for animal products, a broad division into milk, meat and offal would seem
adequate. Distinctions between animal types are of limited importance, with distinctions in transfer factors typically
substantially offset by differences in consumption of contaminated materials. Marine foodstuffs include the range of seafoods
currently or recently obtained in the area.
c
d
e
It is noted that for Local Resource Dominated PEGs the aim is to ensure that maximum reasonable use is made of all
potentially contaminated local resources by all relevant pathways, as there is a need to ensure that possible contributions to
dose are not neglected. (This can mean that consumption rates of some types of foodstuff are not as high as for Analogue
PEGs with a more restricted diet.) For Analogue PEGs, it is generally appropriate to consider only a more limited set of
relevant pathways. Indeed, one consideration in the definition of Analogue PEGs is to make as great a distinction as possible
between the different PEGs relevant to a specific context. If this is done, it is more readily determined, from inspection of
the results obtained, what the radiological impact would be on alternative PEGs with intermediate or mixed characteristics.
As described above, both Local Resource Dominated PEGs and Analogue PEGs are characterised and several may be carried
forward to define the range of radiological risks that may arise, subject to some cautious constraints on location and
utilisation of local resources. In the context of Local Resource Dominated PEGs, in some situations it will not be
immediately clear what characteristics of the PEG will dominate in determining the radiation dose received by a
representative member of that PEG. Therefore, more than one potential Local Resource Dominated PEG may have to be
studied in preliminary scoping calculations in order to determine which should be adopted.
This is a standard component of the BNFL approach and is taken into account when defining the size of the group, so that all
members of the group can make intensive use of local resources (see also item (f)). The variety of resources utilised and the
degree of intensity of use will be determined by whether a Local Resource Dominated or Analogue PEG is under
consideration.
Relatively high conditional individual risks may arise for releases from the LLWR, so the lower degree of heterogeneity may
be appropriate. However, following ICRP, the minimum degree of heterogeneity that should be used is a factor of three, i.e.
a factor of about 1.7 in either direction from the representative value.
Table 8: Additional Comments on the Definition of Potential Exposure Groups
for use in the 2002 PCSC. This table is based on Thorne and Kane (2003), but
deleting some text and updating references.
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Item
f
Principle
This principle applies both to Local Resource Dominated and Analogue PEGs. For Local Resource Dominated PEGs, a
prescription consistent with this principle and also with the requirement to make maximum reasonable use of the most
contaminated resources is as follows.
•
•
Define the utilisation Uj of each environmental medium j, where utilisation is either mass per unit time (kg y-1) for
ingestion or fractional occupancy for inhalation and external exposure.
Calculate the annual effective dose, E (Sv), using:
E=
SkfijUjCijk
where
•
fij is the fraction of the utilisation of environmental medium j from compartment i;
Sk is a conversion factor with units of Sv Bq-1 for ingestion and Sv y-1 per Bq kg-1 for inhalation
and external exposure;
Cijk (Bq kg-1) is the concentration of radionuclide k in medium j in compartment i; and
the summation is over radionuclides (k), compartments (i) and media (j).
Maximise E by adjusting the values of fij subject to the constraint that NfijUj is less than the total amount of medium j
available from compartment i and N is the number of people in the PEG.
Where Sk is for inhalation, it is defined as the product of the volume of air breathed per year (m3 y-1), the load of the
environmental medium in air (kg m-3) and the intake to effective dose factor by inhalation (Sv Bq-1).
This approach ensures that maximal use is made of local resources, in the sense that the effective dose is maximised. By
summing over radionuclides, it recognises that the worst case for one radionuclide is not necessarily the worst case for
another.
It is emphasised that the above prescription is a statement of what the assessment is aiming to achieve. In practice, values of
fij will be selected prior to the calculation of annual effective doses. However, the results obtained using such prior
assignment will then be examined to determine whether changes to the values would more closely approximate the above
optimum. This is reasonably straightforward, as the fundamental equation can be rewritten as:
E=
SkfijUjCijk =
Hij =
SkUjCijk
fijHij
where
g
h
i
j
k
Values of Hij can be obtained from the exposure equations employed in the various assessment models used, the definition of
the PEG in terms of overall utilisation of environmental media and the computations of concentrations. Therefore, no new
transport calculations are required to adjust values of fij to maximise E.
This principle applies both to Local Resource Dominated and Analogue PEGs. Although adult individuals are adopted as a
basis for such comparisons, sensitivity studies for other age groups may also be informative. For this reason, representative
children and infants are defined for each Local Resource Dominated PEG. Only adults are defined for Analogue PEGs, but
the data for children and infants given for Local Resource Dominated PEGs can be used to generate corresponding data for
Analogue PEGs, as required.
For the 2002 PCSC, present behaviour was studied for the area in the immediate vicinity of the site and for the climatic
analogue regions that were used in developing the landscape models for the various states. In addition, recent past behaviour
in the immediate vicinity of the site and in analogue regions was studied by reference to documentary records. This principle
applies to both Local Resource Dominated and Analogue PEGs. For Local Resource Dominated PEGs, the emphasis is on
maximising exposure by considering extremes of plausible behaviour, whereas for Analogue PEGs, the emphasis is on using
the observed information more directly, but with a desire to maximise the contrasts between the groups.
This does not preclude consideration of actions that arise from knowledge of the presence of a human artefact (the engineered
facility). It is only the knowledge that radioactive materials are present that results in an action being excluded from
consideration. The principle is not intended to address response to the identification of radioactive materials, e.g. through
institution of long-term controls on access to the site, if such materials are discovered subsequent the post-closure
management period. For the purpose of the 2002 PCSC, no account was taken of such responses in the quantitative
evaluation of the radiological performance of the facility. However, the potential for such response was considered when
addressing the issue of provision of sub-surface markers describing the nature of the facility.
To a large extent, this point has already been addressed. The main additional matter is that it implies that characteristics can
be based on syntheses of information from a variety of sources, such as BIOMASS (2003).
The main issue is the definition of situations. It seems reasonable to take each state in each scenario as a different situation.
Furthermore, it is also appropriate to take the scenarios to be mutually exclusive and not to define PEGs that are common to
more than one scenario. This precludes aggregating risks across scenarios or having to assign probabilities of occurrence to
the different scenarios. Special considerations apply in defining situations for intrusion [see Appendix C of Thorne (2000)
for discussion of this point]. Note that a PEG may be exposed by more than one pathway, e.g. release of radionuclides in
both gas and groundwater. In these circumstances, risks from the different pathways should be summed. Summation over
co-existing pathways of exposure is a distinct issue from summing over alternative, mutually exclusive situations.
Table 8 Continued
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Item
l
m
n
Principle
The use of point values for parameters was endorsed in the BIOMASS programme (BIOMASS, 2003).
This point is relatively self-evident and does not require elaboration. However, it is noted that Analogue PEGs are defined to
be as distinct from each other as possible. Therefore, other Analogue PEGs can be defined that are intermediate between, or
have characteristics of more than one of, the Analogue PEGs studied. However, these further PEGs are distinct groups and
calculations of risk for these groups is not the combination of risks for the different PEGs, even though the numerical
computations are similar.
This comment applies to Local Resource Dominated and Analogue PEGs.
Table 8 Continued
The application of these principles to future assessment calculations is addressed in
Sections 2.4 and 2.5, in the context of the climate and landscape evolution scenarios
described in Section 2.3.
2.3
Climate and Landscape Evolution Scenarios
In Thorne and Kane (2007), eight evolution pathways are identified and described.
These relate the three sea-level change scenarios. The A4a evolution pathways relate
to a continuation of climatic conditions similar to those at the present day. The
B3/B4V1 evolution pathways relate to a greenhouse-warmed world, but with
increases in global sea-level close to the minimum that is projected to occur. The
B3/B4V2 evolution pathways, in contrast, relate to a greenhouse-warmed world in
which increases in global sea-level are close to the maximum that may occur. Further
distinctions between the evolution pathways are made in terms of the overall sediment
budget of the system. Details of the eight evolution pathways are provided in Table 9.
Evolution
Pathway
A4aHc
A4aOc
B3/B4V1si
B3/B4V1sc
B3/B4V1ud
B3/B4V2si
B3/B4V2sc
B3/B4V2ud
Description
Continuation of the present-day coastal process system without additional forcing. No
rise in sea level and no change in hydrologically effective rainfall.
Continuation of the present-day coastal process system without additional forcing, but
with Barn Scar ceasing to act as a headland. No rise in sea level and no change in
hydrologically effective rainfall.
Lowest rate of sea-level rise, self-regulating coastline, positive sediment budget. Major
change in geography, with the Ravenglass estuary being replaced by a barrier-lagoon
complex.
Lowest rate of sea-level rise, self-regulating coastline, balanced sediment budget.
Essentially an accelerated version of A4aOc with an increased rate of cliff recession.
Lowest rate of sea-level rise, negative feedbacks not evident, negative sediment budget
results in rapid erosion.
Highest rate of sea-level rise, self-regulating coastline, positive sediment budget. An
accelerated version of B3/B4V1si. Major change in geography, with the Ravenglass
estuary being replaced by a barrier-lagoon complex.
Highest rate of sea-level rise, self-regulating coastline, balanced sediment budget. An
accelerated version of B3/B4V1sc.
Highest rate of sea-level rise, negative feedbacks not evident, negative sediment budget
results in rapid erosion. An accelerated version of B3/B4V1ud.
Table 9: The Eight Evolution Pathways addressed
As discussed by Thorne and Kane (2007), for each of these evolution pathways, there
are a limited number of components of the landscape in which a substantial amount of
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radioactive contamination can occur either directly or indirectly. These landscape
components comprise:
• An intertidal zone;
• The storm beach;
• The cliff;
• Carl Crag bay;
• Barn Scar headland;
• Drigg Dunes;
• Drigg Point;
• Area 1 (the tract of land between Carl Crag and the site boundary);
• Site North;
• Site South;
• The Irt Estuary;
• A Barrier Lagoon
• Ravenglass Bay.
Thorne and Kane (2007) describe each of these landscape elements in turn from the
point of view of PEG identification. That discussion is reproduced below. Note that
it does not distinguish between the various scenarios for landscape evolution. This is
because those scenarios are primarily distinguished by differences in rates and
patterns of transport of water, sediments and radionuclides, rather than by differences
between the types of community and individual that would occupy, or make use of,
the contaminated environmental media.
In the discussion below, there is reference to PEGs as opposed to exposure groups
because the landscape changes as described are more aligned to the timescales of the
post-closure phase. Landscape changes over the short term (up to 2150 AD) are
addressed in Section 2.4.1, in considering exposure groups for the operational phase.
2.3.1 The Storm Beach and Intertidal Zone
It is appropriate to combine the storm beach with the intertidal zone, as there is no
strong demarcation between them and individuals involved in leisure and
occupational activities would be expected to utilise both areas. The intertidal zone
will clearly become contaminated during termination events, and it may become
contaminated at an earlier stage, as the receding cliff line encounters plumes of
radioactivity developing from the disposed wastes. Therefore, a relevant PEG is one
that makes use of the intertidal zone for recreational or occupational purposes.
Although the extent to which the area is used, e.g. for the launch of boats, will depend
somewhat on whether a bay is present (see Section 2.2.3), making distinctions
between PEG characteristics depending upon evolution scenario is thought to be an
over-refinement of the analysis and it seems reasonable to develop a single set of
PEGs, including both recreational and occupational groups, characteristic of a
reasonably open, west-facing, accessible, rural area of coastline.
2.3.2 The Cliff
Although the cliff may not erode exactly on the same line in each of the evolution
pathways and its detailed pattern of recession will be affected by the relative
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resistance of the environmental media, engineered structures and wastes through
which it passes, it seems a reasonable approximation for assessment modelling to take
it to retreat parallel to the site boundary and at a constant rate during the period over
which site termination occurs. This simplification does not pretend to a greater
understanding of the variable resistance of the environmental media than exists at the
present day, and provides a baseline against which studies of alternatives for
protecting the site from erosion can be assessed.
No PEGs are associated specifically with the cliff, but PEGs that use the intertidal
zone would be expected also to access the cliff face.
2.3.3 Carl Crag Bay
Carl Crag bay only exists in A4aHc. In the other evolution pathways, it is replaced by
a stretch of open coastline. However, whether the local coastline is open or
constitutes a bay, it is the PEG defined for the intertidal zone that will make use of the
area.
2.3.4 Barn Scar Headland
The Barn Scar headland is of importance as a control on landscape evolution and not
as a location at which a PEG would be located.
2.3.5 Drigg Dunes and Drigg Point
Although the Drigg Dunes exert an important control on the landscape through their
till core and as a source of blown sand, they are not associated with contaminant
transport pathways in their own right. Their degree of contamination during
termination will be small compared with the intertidal zone, so there is no specific
requirement to identify PEGs that make use of the dune area. If there were a need to
make calculations to illustrate the magnitude of radiological impacts from occupancy
of this area, Thorne and Kane (2007) suggested that it will be sufficient to partition
the occupancies developed for the intertidal zone PEGs between the intertidal area
and the Drigg Dunes.
2.3.6 Area 1
Area 1 comprises the region between Carl Crag and the site boundary. It is of
relevance because flow and transport pathways run beneath this area. Although
discharges to this area are not confirmed at the present day, the potential for
discharges in evolving future conditions is a matter that has to be explored through
hydrogeological modelling under the changed boundary conditions that will exist,
notably the altered geometry of the area and the modified position of the saline
interface zone.
In A4aHc, A4aOc, B3/B4V1sc, B3/B4V1ud and B3/B4V2sc, the area reduces to a
small triangle of dune and heath by the time of onset of termination. In B3/B4V1si
and B3/B4V2si, the evolution of the area is much the same, but there is also much
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blown sand present and extensive dune development. In B3/B4V2ud, Area 1 is
entirely eroded away prior to termination.
Area 1 is of limited interest with respect to occupancy over the period through to
termination and it is not clear that any significant degree of contamination of the area
would be expected over that period. Thorne and Kane (2007) comment that if it were
necessary to consider a PEG present in that area, the same approach as recommended
for the Drigg Dunes could be adopted, i.e. the occupancies developed for the intertidal
zone PEGs could be partitioned between the intertidal area and Area 1.
2.3.7 Site North
Site North comprises the cap which can be covered in blown sand and is associated
with dune and heath vegetation that advances across the site. It is entirely eroded
away during termination. The amount of blown sand varies from high (e.g.
B3/B4V1si) to low (e.g. B3/B4V1ud).
The Site North area is identified as a potential location of gaseous discharges and of
wastes exhumed due to human intrusion. Potential ‘bath-tubbing’ pathways would
also involve Area 1 and Site South. In the absence of intrusion, utilisation of this area
would be expected to be limited to casual recreational activities. However, it is
feasible that a smallholding might be developed in this area and that a domestic
dwelling associated with such a smallholding could abstract water from a well or
borehole downstream of the facility.
2.3.8 Site South
In A4aHc, A4aOc, B3/B4V1ud and B3/B4V2ud, this area is characterised as heath
and salt marsh subject to inundation. There is overgrown wetland along the line of
the Drigg Stream and the area is entirely eroded away during termination. In
B3/B4V1ud, part of the area becomes included within the estuary prior to termination
and becomes part of Ravenglass Bay during termination. In B3/B4V2ud, early
formation of Ravenglass Bay intrudes across the area prior to termination.
In B3/B4V1si, Site South is dominated by blown sand. It is initially subject to
inundation with overgrown wetland along the line of the Drigg Stream. Around 1000
a AP, a lagoon occupies part of the area extending up along the line of the Drigg
Stream. Before 2000 a AP, the roll back of the Drigg Dunes infills the lagoon, and
dune and heath vegetation is present. The area is entirely eroded out during
termination as Ravenglass Bay forms. In B3/B4V2si, the evolution is similar, but
with lagoon occupancy occurring at 200 - 500 a AP and roll back of the Drigg Dunes
occurring before 1000 a AP.
In B3/B4V1sc and B3/B4V2sc, recession of the Drigg Dunes buries the Drigg Stream
and raises the level of the ground surface. Dune and heath vegetation is present. No
inundation of the area occurs, because the River Irt is diverted further inland and
eastward. The area is entirely eroded away during termination as Ravenglass Bay
forms.
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Site South is associated with a transport pathway, primarily via the Drigg and E-W
Streams, but also via near-surface groundwater pathways. Such pathways may be
engineered out and stream pathways will cease following roll over of the Drigg Dunes
in those evolution pathways for which this occurs. Discharges could occur to an
estuary (B3/B4V1ud), a lagoon (B3/B4V1si and B3/B4V2si) or to Ravenglass Bay
(e.g. B3/B4V2ud, B3B4V1sc, B3B4V2sc). PEGs are required relating to use of the
streams, use of areas of land potentially contaminated by groundwater pathways and
use of the estuary, lagoon or Ravenglass Bay.
2.3.9 The Irt Estuary
In A4aHc, A4aOc, B3/B4V1sc and B3/B4V2sc, the Irt estuary has a changed
geometry, but the same ecology as at present. During termination, the River Irt
realigns to pass directly south-east of the site to the sea. The existing estuary area is
converted to a full maritime bay. By the end of termination, the bay extends well
inland.
In B3/B4V1si, the Irt estuary ceases to exist before 1000 a AP and is replaced by a
barrier lagoon (see below). In B3/B4V2si, the evolution is similar, but more rapid,
with replacement by a barrier lagoon occurring at 200 - 500 a AP.
In B3/B4V1ud and B3/B4V2ud, rapid erosion of the spit causes realignment of the Irt
estuary and early formation of Ravenglass Bay prior to termination.
Transport pathways will exist to the Irt Estuary via the Drigg Stream. Furthermore,
the estuary may accumulate debris or particles derived from debris during and after
termination. Therefore, PEGs are required that specifically make use of the estuarine
environment. The estuary can be converted to a lagoon or bay in some evolution
pathways and radionuclides retained in the estuary can be transferred to these
alternative environments, which also need to have PEGs associated with them.
2.3.10
The Barrier Lagoon
The barrier lagoon only forms in B3/B4V1si and B3/B4V2si. It forms after the
barrier across the estuary is complete and may be either brackish or freshwater. Water
ponds behind the barrier and seeps through, occasionally washing over. Periodic
breaks in the barrier are sealed by storm action bringing sediment ashore.
Sedimentation occurs in the lagoon and marshy areas develop.
Contamination of the lagoon occurs via Site South. Contaminants will mix in the
lagoon and seep through the barrier to the sea. The barrier lagoon is likely to evolve
rapidly during termination and may break down before termination is complete. As
noted in Section 2.3.9, the barrier lagoon should have PEGs specifically associated
with it.
2.3.11
Ravenglass Bay
In A4aHc, A4aOc, B3/B4V1sc and B3/B4V2sc, Ravenglass Bay is likely to form at a
late stage during termination. Debris from the site is washed out to sea by the River
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Irt at the mouth of its estuary, by now located immediately south-east of the site.
Debris may return to accumulate in the bay.
In B3/B4V1si and B3/B4V2si, Ravenglass Bay will form eventually after the barrierlagoon system fails after recession of the barrier as far as physically possible.
However, bay formation is not expected before termination is complete or largely
complete.
In B3/B4V1ud, Ravenglass Bay forms prior to termination. Debris from the site may
accumulate in the bay. Bay formation is relatively rapid, with less sediment, less
extensive drying areas and deeper waters than in other B3/B4V1 evolution pathways.
A similar evolutionary pathway is followed in B3/B4V2ud. Again bay formation is
relatively rapid, with less sediment, less extensive drying areas and deeper waters than
in other B3/B4V2 evolution pathways. As noted in Section 2.2.9, Ravenglass Bay
should have PEGs specifically associated with it.
2.3.12
Timescales
In giving consideration to the characteristics of the exposure groups and PEGs to be
defined, it is important to emphasise the relatively short timescales involved. This is
illustrated in Table 10, taken from Thorne and Kane (2007). This shows the time at
which cliff retreat and inundation first breach the site boundary (T1), the time at
which the site has been completely destroyed (T2), and the period over which the
majority of bulk erosion of the vaults and trenches occurs. It is emphasised that these
timescales are indicative, as there are considerable uncertainties in the amount, timing
and rate of sea-level rise, and in the resistance of the coast to erosion under any
particular pattern of sea-level rise.
Evolution
Pathway
A4aHc
A4aOc
B3/B4V1si
B3/B4V1sc
B3/B4V1ud
B3/B4V2si
B3/B4V2sc
B3/B4V2ud
T1 (Years
AP)
Beginning of
Bulk Erosion
(Years AP)
End of Bulk
Erosion
(Years AP)
T2 (Years
AP)
1500
2500
2000
1500
1000
1000
900
750
1500
2500
2000
1500
1000
1000
900
750
4500
3500
3000
2400
1800
1400
1200
1000
4500
5000
3000
2400
1800
1400
1200
1000
Period of
Bulk
Erosion
(Years)
3000
1000
1000
900
800
400
300
250
Table 10: Period and Duration of Bulk Erosion for Each Evolution Pathway
The interval of bulk erosion is only significantly shorter than the period of bulk
erosion for the A4aHc evolution pathway. This arises from the substantial change in
the shape of the cliffline for this pathway. The period of bulk erosion is similar for
the A4aOc evolution pathway, which does not take account of sea-level rise, and the
B3/B4V1 pathways, which have a lower-bound estimate of sea-level rise for the
greenhouse-warming scenarios. However, for B3/B4V2 evolution pathways, the
period of bulk erosion is reduced from ~ 1000 years to 250 to 400 years. It is
emphasised that the amount and pattern of sea-level rise is substantially uncertain, so
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intermediate scenarios can be envisaged in which the period of bulk erosion
commences between 750 and 2500 years AP and takes between 250 and 3000 years.
Overall, PEGs need to be defined for a period of between 750 and 2500 years
covering the period up to the start of bulk erosion and also for a period of between
250 and 3000 years over which bulk erosion takes place.
2.4
Identification of Exposure Groups and PEGs
2.4.1 Exposure Groups for the Operational Phase
Considering the previous landscape change information for the short term up to 2150
AD, exposure groups are identified in Table 11. Missing from the table are the
Barrier Lagoon and Ravenglass Bay areas, which will not apply during this period.
Over this interval, varying degrees of coastal erosion as exemplified by the various
landscape change scenarios of the site will have occurred, but termination of the site is
still in the future. This identification has been informed by a consideration of the
exposure pathways identified in the 2002 OESC and issues raised by the EA, in
particular OESC_003 and OESC_004 (as described in Section 2.1).
Also implicitly taken into account are the climate change scenarios A4a and B3/B4
occurring over the next few decades and the effect climate may play on the habits of
the present-day exposure groups. From Thorne and Kane (2007), for the A4a
scenario, a temperate climate with similar temperature and precipitation will prevail
for the next 150 years, whereas for the B3/B4 scenario (with global warming) the
mean annual temperature may increase by up to 3 °C. As regards mean annual
precipitation for the B3/B4 scenario, relative to the present day value or around 1000
mm a-1, the rate could either increase to around 1200 mm a-1 or decrease to around
850 mm a-1.
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Area
Storm beach and intertidal zone
Cliff
Exposure Groups
Recreational and occupational.
None, but Exposure Groups defined for the storm
beach and intertidal zone would be expected to
access the cliff face.
None, but Exposure Groups defined for the storm
beach and intertidal zone would be expected to
make use of this area.
None, but Exposure Groups defined for the storm
beach and intertidal zone might make use of this
area. If so, it will be sufficient to partition the
occupancies developed for the intertidal zone
PEGs between the intertidal area and the Drigg
Dunes.
Exposure Group potentially for aerial discharges
from current and future operations.
No Exposure Groups on site itself, though
Exposure Groups (around perimeter of Site North)
for aerial discharges from current and future
operations need to be considered. It can be
assumed that this region will be unaffected by
liquid discharges.
No Exposure Group on site itself, though
Exposure Groups (around perimeter of Site South)
for aerial discharges need to be considered. For
the public assuming that near-surface discharges
to the Drigg stream and surrounding water courses
are engineered out, there will only be residual
levels from previous operations. Exposure Groups
may be applicable to the Irt Estuary due to
envisaged groundwater discharges to the coastal
region and resulting tidal actions.
Carl Crag bay or corresponding length of open
coastline
Drigg Dunes and Drigg Point
Area 1
Site North
Site South/ Irt Estuary
Table 11: Identification of Required Exposure Groups
Thus the various Exposure Groups that require characterisation are:
• Occupational users of the storm beach and intertidal zone;
• Recreational users of the storm beach and intertidal zone;
• Users of the East-West and Drigg streams and of the Site South area;
• Users of the Irt Estuary.
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2.4.2 PEGs for the Post-closure Phase
From the summary presented in Sections 2.3.1 to 2.3.11, the PEGs listed in Table 12
are identified as being required.
Area
Storm beach and intertidal zone
Cliff
PEGs
Recreational and occupational.
None, but PEGs defined for the storm beach and
intertidal zone would be expected to access the
cliff face.
None, but PEGs defined for the storm beach and
intertidal zone would be expected to make use of
this area.
None, but PEGs defined for the storm beach and
intertidal zone might make use of this area. If so,
it will be sufficient to partition the occupancies
developed for the intertidal zone PEGs between
the intertidal area and the Drigg Dunes.
None, but if it were necessary to consider a PEG
present in this area, the same approach as
recommended for the Drigg Dunes could be
adopted, i.e. the occupancies developed for the
intertidal zone PEGs could be partitioned between
the intertidal area and Area 1. This would only
arise if the degree of contamination of Area 1 was
greater than that of the intertidal zone, and this is
considered to be highly unlikely.
PEGs are required for casual and recreational
activities, and for inadvertent human intrusion.
Also, a smallholding could be developed on the
cap area and a well could be sunk close to the
facility and intercept contaminated groundwater.
PEGs are required relating to use of the streams,
use of areas of land potentially contaminated by
groundwater pathways and use of the estuary,
lagoon or Ravenglass Bay.
Carl Crag bay or corresponding length of open
coastline
Drigg Dunes and Drigg Point
Area 1
Site North
Site South/Irt estuary/Barrier-lagoon/Ravenglass
Bay
Table 12: Identification of Required PEGs
Thus, the various PEGs that are required are:
• Occupational users of the storm beach and intertidal zone;
• Recreational users of the storm beach and intertidal zone;
• Casual and recreational users of the facility cap area;
• Agricultural smallholders making use of the cap area;
• Users of water abstracted from a well downstream of the facility;
• Inadvertent intruders into the facility;
• Individuals making use of the cap area subsequent to inadvertent intrusion;
• Users of the East-West and Drigg streams and of the Site South area;
• Users of the estuary and lagoon;
• Occupational users of Ravenglass Bay;
• Recreational users of Ravenglass Bay.
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Users of the estuary and lagoon have been placed together, noting that these are both
fresh to brackish water bodies of substantial spatial extent. It seems likely that the
main distinctions that will arise will relate to radionuclide transport in these two
different types of water body rather than in the habits and behaviour of individuals
making extensive use of them. Although users of Ravenglass Bay have been
explicitly listed, their habits and behaviour should be similar to users of the storm
beach and intertidal zone, as both sets of individuals access a broadly similar
environment. As the storm beach and intertidal zone is likely to be the more highly
contaminated of the two environments, it seems appropriate to give the PEGs
associated with that region priority in definition, and to define those associated with
Ravenglass Bay identically, so that comparisons can be made between radiological
impacts in the two areas without introducing differences between PEG characteristics
as a confounding factor.
It is noted that PEGs present on the cap could be exposed due to releases of
radioactive gases or as a result of build-up of water in the facility (‘bath-tubbing’)
giving rise to contamination of the overlying soil. In this context, it is emphasised
that the potential for bath-tubbing may be limited through engineering measures, so
this route of exposure may, in practice, be of little radiological significance.
A PEG associated with abstraction of water from a well has been included. Although
this has been associated with Site North in Table 12, in practice it might be
constructed anywhere downstream of the repository where it could intersect a plume
of contaminated groundwater. The probability of such a well existing within the
plume area at any time will depend on the spatial extent of the plume and the potential
requirement for water use. It will also depend on the quality of the water that can be
abstracted. The limited area between the facility and the coast, and the poor quality of
the land both imply that well construction and use will be less likely than in good
quality agricultural areas, notably in the drier parts of the UK. Nevertheless, the
presence of such a well cannot be excluded from consideration. The most likely
intensive use of water from such a well is by a smallholder and their family. Thus, a
smallholder PEG is required both for residence on the cap and for utilisation of well
water.
It is emphasised that this report does not address the likelihood of a well being present
within the contaminant plume. This is more appropriately addressed in the context of
the assessment calculations when information is available on the potential spatial and
temporal development of a plume of contaminated groundwater.
2.5
Methodologies Adopted for PEG Identification and
Characterisation for Future Environmental Safety Cases
The following subsections cover formal methodologies for identifying, in a more
quantitative manner, PEGs and their characteristics or habits for assessment studies of
the LLWR site, particularly during the post-closure phase when all prior knowledge of
the site has been lost. These methodologies are framed using the principles for the
definition of PEGs for use in the 2002 PCSC (Table 1) and output from BIOMASS
(2003) and BIOCLIM (2004).
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2.5.1 Defining the Context in which PEGs are Present
By defining a limited set of landscape evolution pathways (Section 2.3), a reference
biosphere concept is adopted, in the sense that the small number of pathways selected
are intended to span the range of potential patterns of evolution and provide wellcharacterised landscape contexts within which radiological impact assessment
calculations can be undertaken. The main distinction from the BIOMASS (2003)
methodology is that termination is seen as a continuous transitional process rather
than a biosphere state. In this sense, the methodology more closely relates to the
states and transitions approach adopted in BIOCLIM (2004). In this case, there is
only a single climatic state prior to the termination transition.
Following the BIOMASS or BIOCLIM methodologies, biosphere characteristics and
changes in those characteristics would be systematically identified and described by
distinguishing the biosphere into major components, and by using interaction matrices
and transition diagrams to characterise the relationships between those various
components. However, this type of analysis is primarily relevant to the identification
and characterisation of radionuclide transport pathways. For the purpose of PEG
identification and characterisation, the main consideration is to disaggregate the
environment into spatial components and to identify which of those components could
become contaminated to a significant degree. PEGs can then be defined that make
reasonable, maximal use of those components. The disaggregation of the biosphere
into components has been addressed in Section 2.3.
The main impact of climate change in defining the landscapes in which the PEGs will
be present comes indirectly through changes in sea level. In the A4a landscape
evolution pathways, climatic conditions are identical to those at the present day
throughout. In the B3/B4 landscape evolution pathways, the climate is considerably
warmer than at the present day. However, the warming is considered to take place
mainly over the next 100 to 200 years, so by the time that post-closure institutional
control is assumed to be lost, the climate will have achieved much of its projected
warming. As greenhouse-induced warming is expected to persist for many millennia
(Thorne and Kane, 2007), it is appropriate to consider that the greenhouse-warmed
climate persists almost unchanged throughout the pre-termination and termination
periods.
Overall, the principle of adopting the Reference Biospheres concept (Table 7, item a)
has been fully achieved. The comment made in Table 8, relating to the 2002 PCSC,
remains applicable, i.e. the use of scenarios and prescribed landscape evolution
descriptions is very much in the spirit of defining Reference Biospheres.
As the identification and characterisation of the context in which the PEGs are present
has been completed in Section 2.3, this matter does not need to be addressed further in
the application of the methodology set out in Section 3.
2.5.2 Representation of All Relevant Pathways
Item b of Table 7 calls for all potentially relevant pathways of exposure to be
represented, but not to the same degree of detail as would typically be employed in
characterising present-day critical groups in the context of radioactive waste
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discharges. Item b of Table 8 proposes that exposure pathways can be suitably
characterised as:
• External exposures to contaminated soils, sediments and water bodies;
• Ingestion of contaminated soils and sediments, water, plant products and animal
products;
• Inhalation of contaminated soils and sediments and radioactive gases (including
radon, thoron and their progeny).
The proposed distinction of plant and animal products uses a simple, generalised
classification scheme distinguishing only between:
• Freshwater plants:
• Freshwater fish:
• Terrestrial plants: cereals, fruit, green vegetables, root vegetables and tubers;
• Terrestrial animal products: milk, meat and offal;
• Estuarine and lagoon fish, crustaceans and molluscs;
• Marine fish, crustaceans and molluscs.
With respect to animal products, distinctions between animal types are neglected (see
Table 8). For assessment modelling purposes, it is considered appropriate to take total
milk, meat and offal consumption as if all the food products were obtained from
cattle. This arises because the higher transfer factors observed for smaller animals are
compensated for by their smaller intakes of food and hence their smaller intakes of
radionuclides in a landscape contaminated at a particular level.
In applying the methodology, a matrix is drawn up of the various PEGs along one axis
and the various exposure pathways along the other. Pathways that are included or
excluded for each PEG are indicated in the matrix, and a brief justification for each
decision is provided (see Section 3.1).
2.5.3 Identification of PEGs
Item c of Table 7 identifies the need to select one or more PEGs for each Reference
Biosphere and to undertake scoping calculations to identify which of these should be
taken forward for detailed analysis. Table 8 identifies that in the 2002 PCSC both
Local Resource Dominated and Analogue PEGs were characterised. In view of the
relatively short period of a few thousand years that will be covered in future
assessments, it is assumed that there will not be a reversion to primitive conditions
over the period of interest. Therefore, the emphasis is placed on defining Analogue
PEGs based on present-day habits and behaviour, either local to the facility for
present-day climatic conditions, or at analogue locations for greenhouse-warmed
conditions. This is in line with the EA view that Local Resource Dominated PEGs
incorporate unduly pessimistic assumptions concerning potential exposures. Thus, in
Section 3, the various PEGs described in outline in Section 2.2 are defined more
closely in terms of present-day population groups.
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2.5.4 Relative Homogeneity
In item d of Table 7, it was required that PEGs should be identified such that they
were relatively homogeneous with respect to radiation exposure. It was further noted
that (item e), at individual risks of the order of, or less than, the risk target of 1 10-6
per year, up to a factor of ten inhomogeneity of exposure is acceptable, but that, at
substantially larger individual risks, the degree of inhomogeneity should be less. In
Table 8, it was clarified that the minimum degree of heterogeneity that should be used
is a factor of three, i.e. a factor of about 1.7 in either direction from the representative
value.
In practice, relative homogeneity of radiation exposure cannot be determined without
spatially distributed estimates of radionuclide concentrations in environmental media
and it may not be appropriate to attempt to estimate such spatially distributed
concentrations over an extended post-closure period. Therefore, relative homogeneity
of habits and behaviour relating to the occupancy of the most contaminated areas and
consumption of the most contaminated food and water has been adopted instead.
Relative homogeneity of habits and behaviour is achieved through the selection of
appropriate parameter values to represent the habits and behaviour of representative
members of PEGs, as described in Section 3. In defining those habits and behaviour,
item h from Table 7 is taken into account, i.e. the diet and lifestyle of the PEG is
based on observed past and present behaviour, either in the region of the LLWR or in
an analogue region appropriate to future environmental conditions.
2.5.5 Residence in, and Utilisation of Materials from, the
Contaminated Area
Item f of Table 7 points out that reasonable homogeneity of exposure does not
necessarily require that the representative member of a PEG is restricted to residence
in and utilisation of materials from, the area in which environmental concentrations of
radionuclides are highest. However, it does require that the degree of residence or
utilisation should be estimated.
In this analysis, an emphasis is placed on Analogue PEGs and it is important to
evaluate their use of local resources. This is done in Section 3, where an audit of local
resource use relative to total use is presented for each PEG.
In this context, it is noted that the selection of parameter values for characterising
representative members of PEGs will take into account the requirement in item n of
Table 7 that, in general, typical occupancies and consumption rates should be used.
However, again following the recommendation in item n, if the group or community
is sufficiently large that high occupancy or consumption rate individuals are likely to
be present at any one time, above-average occupancy or consumption rates will be
used. Special considerations apply to the smallholder PEG, as noted in Section 3.
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2.5.6 Age Groups
In item g of Table 7, it is stated that the annual risk to be compared with the risk target
is that to an adult individual in any one year. Table 7 further comments that although
adult individuals are adopted as a basis for such comparisons, sensitivity studies for
other age groups may also be informative. For this reason, representative children and
infants are characterised as well as representative adults. It is noted that exposure of
the embryo, foetus and breast-fed infant may also require consideration. In this
context the primary requirements are details of the diet and occupancy of the pregnant
woman or nursing mother. As a basis for comparison, these are taken as identical to
those of the reference adult, i.e. changes in behaviour during pregnancy and breast
feeding are neglected.
2.5.7 Use of Standard Data
Item j of Table 7 requires that PEGs should be defined in terms of broad
characteristics likely to substantially affect radiation exposure. This is largely
addressed in Section 2.5.2. However, item j also requires that those broad
characteristics should be based on existing UK, overseas and international experience
relating to both solid radioactive waste disposal and discharges of radioactive
effluents to the environment. This requirement is implemented by relying, as far as
possible, on values recommended by authoritative bodies, such as HPA-RPD, unless
there are specific reasons arising from the landscape description to adopt alternative
values.
2.5.8 Use of Point Values
Item l of Table 7 requires assessment calculations to be undertaken using single
(point) values of PEG characteristics. Thus, point values of PEG characteristics are
recommended in Section 3. However, item l of Table 7 also requires that the
robustness of the calculations shall be examined in sensitivity studies. To facilitate
this, recommendations are provided in Section 3 as to ranges over which PEG
parameters should be systematically varied. Provision of these ranges also helps to
explicitly address issues relating to the relative homogeneity of the PEG (Section
2.3.4).
2.5.9 Other Considerations
Other principles set out in Table 7 and commented upon in Table 8 relate to the
assessment calculations undertaken for representative members of PEGs. They do not
impinge on the identification and characterisation of PEGs. Therefore, they are not
considered further herein.
2.5.10
Steps of the Methodology
Based on the above discussion, the following methodological steps are identified:
1) Define the context in which the exposure groups or PEGs are present and
provide outline descriptions of them (addressed in Section 2.3);
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2) Identify the pathways of exposure relevant to each exposure group or PEG;
3) Define the exposure groups or PEGs in terms of present-day population
groups;
4) Select point estimate reference parameter values and uncertainty ranges for
adult members of each exposure group or PEG to achieve relative
homogeneity of characteristics;
5) Select point estimate reference parameter values and uncertainty ranges for
children and infants associated with each exposure group or PEG;
6) Audit local resource use and range of uncertainty for each exposure group
or PEG.
In undertaking these six steps, the various detailed considerations set out in Sections
2.5.1 to 2.5.8 are required to be taken into account.
This methodology is applied explicitly in Section 3.1, which relates to exposure
groups or PEGs defined for groundwater-mediated and gas pathways prior to
termination and during the termination process, and also to PEGs exposed to debris
and particulate contaminated material as a result of the termination process. Thus,
consistency between pathways, and between the operational and post-closure phases,
is achieved, as required by the EA. The principles set out in Tables 7 and 8 were also
applied in relation to inadvertent human intrusion in the 2002 PCSC. The PEGs
identified there did not require modification, so the text describing them is largely
taken from the 2002 PCSC and is provided in Section 3.2.
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3.
Identification and Characterisation of Exposure
Groups and Potentially Exposed Groups
3.1
From the Present Day through to and During Facility
Disruption
3.1.1 Identification of Pathways of Exposure
Excluding PEGs associated with inadvertent human intrusion, the exposure groups
and PEGs identified in Sections 2.4.1 and 2.4.2 comprise:
• Occupational users of the storm beach and intertidal zone;
• Recreational users of the storm beach and intertidal zone;
• Casual and recreational users of the facility cap area;
• Agricultural smallholders making use of the cap area;
• Users of water abstracted from a well downstream of the facility;
• Users of the East-West and Drigg streams and of the Site South area;
• Users of the estuary and lagoon;
• Occupational users of Ravenglass Bay;
• Recreational users of Ravenglass Bay.
It should be noted that the exposure groups identified for the operational phase are a
subset of the PEGs identified for the post-closure phase. The differences between
these periods reside in the projected concentrations of radionuclides in environmental
media, arising from the different routes of release of relevance, rather than in the
habits and behaviour of the exposed groups and PEGs. Thus, by defining identical
habits and behaviour, consistency between the operational and post-closure safety
assessment calculations is achieved. In this context, it is noted that many of the
parameter values and ranges recommended later in this section were developed for
use in discharge assessments and have been adapted to the post-closure context.
Thus, again, consistency between the two periods is achieved.
Agricultural smallholders making use of the cap area are also identified as the likely
users of water abstracted from a well downstream of the facility. Such an agricultural
smallholder group was discussed in the context of inadvertent human intrusion in the
2002 PCSC. As the approach adopted for inadvertent human intrusion remains
applicable, the smallholder PEG is discussed in the human intrusion context (Section
3.2.2).
For each of the remaining seven groups, the following general pathways have to be
considered:
• External exposures to contaminated soils, sediments and water bodies;
• Ingestion of contaminated soils and sediments, water, plant products and animal
products;
• Inhalation of contaminated soils and sediments and radioactive gases (including
radon, thoron and their progeny).
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An audit of the potential significance of each pathway for each group is presented in
Table 13. Note that comments on individual entries are given in footnotes below the
table.
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PEG
Occupational users of
the storm beach and
intertidal zone
Recreational users of
the storm beach and
intertidal zone
Casual and recreational
users of the facility cap
area
Users of the East-West
and Drigg streams and
of the Site South area
Users of the estuary
and lagoon
Users of Ravenglass
Bay
Pathway
External to soil and sediment
External to water bodies
Ingestion of soil and sediment
Ingestion of water
Ingestion of plant products
Ingestion of animal products
Inhalation of soil and sediment
Inhalation of radioactive gases
External to soil and sediment
External to water bodies
Ingestion of soil and sediment
Ingestion of water
Ingestion of plant products
Ingestion of animal products
Inhalation of soil and sediment
Inhalation of radioactive gases
External to soil and sediment
External to water bodies
Ingestion of soil and sediment
Ingestion of water
Ingestion of plant products
Ingestion of animal products
Inhalation of soil and sediment
Inhalation of radioactive gases
External to soil and sediment
External to water bodies
Ingestion of soil and sediment
Ingestion of water
Ingestion of plant products
Ingestion of animal products
Inhalation of soil and sediment
Inhalation of radioactive gases
External to soil and sediment
External to water bodies
Ingestion of soil and sediment
Ingestion of water
Ingestion of plant products
Ingestion of animal products
Inhalation of soil and sediment
Inhalation of radioactive gases
External to soil and sediment
External to water bodies
Ingestion of soil and sediment
Ingestion of water
Ingestion of plant products
Ingestion of animal products
Inhalation of soil and sediment
Inhalation of radioactive gases
Included
Y
Y
Y
Y
N
Y
Y
N
Y
Y
Y
Y
N
N
Y
N
Y
N
Y
N
N
N
Y
Y
Y
N
Y
Y
N
Y
Y
N
Y
Y
Y
Y
N
Y
Y
N
Y
Y
Y
Y
N
Y
Y
N
Comment
a
b
c
d
e
f
g
h
a
b
c
d
e
i
g
h
j
k
l
m
n
n
o
p
q
r
s
t
u
v
w
x
y
z
s
aa
ab
ac
w
x
ad
ae
s
d
e
af
g
ag
Table 13: Identification of Pathways associated with Exposure Groups and PEGs
(Footnotes to Table 13 are given on the following page.)
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Identifier
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
aa
ab
ac
ad
ae
af
ag
Comment
Waste debris and particles incorporated in the storm beach and intertidal area. Wastes
exposed at the cliff face.
From swimming, boating and exposure close to the shoreline. Likely to be of less
radiological significance that external exposure to materials in the cliff and beach.
Inadvertent ingestion of particulate material mainly from the intertidal area.
Inadvertent ingestion of small quantities of seawater mainly when swimming.
Negligible development of edible vegetation in the area. Assume no collection of
edible macrophytic algae (seaweed) from the shoreline, but this could be included as a
variant, unusual pathway calculation.
Occupational group, so consumption of locally caught fish and shellfish is included.
Resuspension of small particles from the beach.
Possibility of radon and thoron exhaled from wastes, but gas pathways are of limited
significance even for individuals exposed on the cap area.
Recreational users, assumed not to be involved in harvesting fish and shellfish, as this
pathway is addressed through the occupational users.
Cap materials could become contaminated, e.g. in bath-tubbing scenarios.
No substantial water bodies present in the area.
Inadvertent ingestion of contaminated cap materials.
Water for drinking is not anticipated to be obtained from the local area of the facility.
Cap area not suitable for agricultural activities and becomes less so as the cliff line
moves toward the site.
Due to resuspension of contaminated cap materials.
Pathway of specific interest, as evolved bulk and trace radioactive gases may be
released through the cap structure.
General area may become contaminated through groundwater discharge and overbank flooding.
Streams are not spatially extensive, so external exposure will be dominated by that
due to soils and sediments.
Inadvertent ingestion.
Limited casual use of the streams, e.g. by campers.
Area is associated with salt marsh, heath vegetation or blown sand. It is not used for
agriculture, except possibly some cattle and sheep grazing.
Only for those evolution pathways for which salt marsh may be present.
Due to resuspension of contaminated soil and sediment.
Very limited gas release from uranium and thorium series radionuclides migrating in
groundwater and surface water.
General from sediments in the vicinity of the estuary or lagoon.
From swimming, boating and exposure close to the shoreline. Swimming is likely to
be of less significance than in the open ocean, but boating may be more intensively
pursued in the enclosed waters of a lagoon.
Estuary or lagoon water is not likely to be of suitable quality for drinking, but
inadvertent ingestion may occur during recreational activities.
Not an agricultural area. Freshwater plants and macrophytic algae not assumed to be
taken from the estuary or lagoon for food consumption. This pathway could be
explored as a variant, as required.
Fish, molluscs and crustaceans taken from the estuary or lagoon.
Mainly from intertidal sediments.
From swimming, boating and exposure close to the shoreline.
Consumption of locally caught fish and shellfish is included.
Very limited gas release from uranium and thorium series radionuclides migrating as
debris, particulate material or dissolved in seawater.
Footnotes to Table 13
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3.1.2 Definition of Exposure Groups and PEGs as Population
Groups
Having identified the exposure pathways that need to be considered for each exposure
group and PEG, the next requirement is to characterise each such group in terms of
present-day population groups. It is at this stage that a link can be made with the data
used in the 2002 PCSC (Thorne and Kane, 2003) and with exposure group
information that has been used previously or has been recommended for use
elsewhere.
3.1.2.1 Analogue PEGs in the 2002 PCSC
For the 2002 PCSC, Analogue PEGs were defined through to the far future. Given
the shorter-term assessment now being developed, not all of these Analogue PEGs are
appropriate. However, those defined for the period at, or soon after, closure of the
facility remain potentially relevant. These comprise:
•
In-shore fishermen;
•
Coastal livestock farmers;
•
Estuary livestock farmers;
•
Coastal horticulturists;
•
Irt Estuary houseboat dwellers;
•
Drigg villagers;
•
Coastal villagers.
The general characteristics of the area relevant to conditions at closure for which these
Analogue PEGs were defined were described by Thorne and Kane (2003).
Fishing and livestock farming were taken to be the main rural, food producing
activities compatible with the present day environment in coastal West Cumbria. The
agro-climatic analogue for West Cumbria during the at-closure state was taken to be
coastal land in the vicinity of Plymouth, Devon (reflecting a limited amount of
anthropogenic climate warming by the time of closure). The agricultural statistics
reveal a more diversified agricultural economy than that of West Cumbria.
Specifically, cereals, pigs and poultry are present, but are not recorded for West
Cumbria today. Also, there is a reduced emphasis on livestock in general, and an
increased emphasis on horticulture and mixed farming. However, whilst this pattern
was anticipated to become characteristic of much of the coastal plain, it was thought
that the area most affected by sea-to-land transfer would probably be largely
unaffected. The essential characteristics of this area were taken to be attributable to
coastal processes and features that limit the potential for agricultural activity. These
processes and features were considered characteristic of the geographical and
landscape setting and not particularly sensitive to changes in climate.
Cereals for human consumption were not expected to be grown in the area most
affected by sea-to-land transfer and this land was taken to continue to be used mostly
as rough summer grazing. Water supplies were taken to be uncontaminated, although
it was noted that surface waters may be affected by sea-to-land transfers. It was noted
that there is little if any commercial horticultural or fruit production at present in the
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area most affected by sea-to-land transfer, but there is no reason why such production
should not occur on a small scale.
Characteristics of the individual Analogue PEGs, as provided by Thorne and Kane
(2003) are set out below.
In-shore Fishermen
The in-shore fishermen PEG was deemed to be based at Seascale, although
Ravenglass is an alternative, and perhaps more likely, location. Seascale was chosen
as the location because it is most exposed to sea spray. The fishing boats are shorelaunched and their range is limited. The group derives a living by a combination of
netting, shore-based line fishing and from harvesting crabs and lobsters, winkles and
mussels. The group members consume seaweed in the form of laverbread. Group
members were deemed to spend their time at sea, on the foreshore or within the area
most affected by sea-to-land transfers. Apart from marine foods that they were taken
to consume at a high level, all their other foods were deemed to be uncontaminated, so
as to achieve maximum distinction between groups. Their drinking water was also
deemed to be uncontaminated.
In practice, in-shore fishermen could well consume contaminated terrestrial
foodstuffs.
However, an uncontaminated source was assumed to maximise
distinctions between the Analogue PEGs.
Coastal Livestock Farmers
The coastal livestock farmers PEG was deemed to be located between the site and
coast because this is the zone most likely to be affected by sea-to-land transfer. They
were taken to spend some 20 hours a day on an annual basis in this area. This takes
account of holidays, trading away from the site and other off-model activities. The
area of livestock grazing includes the area between the site and Seascale. Lowland
cattle and sheep best describes the most likely livestock enterprise at Drigg, but it was
assumed cautiously that dairy cows are also grazed on potentially contaminated land.
It was also cautiously assumed that the livestock obtain all their dietary intake
requirements throughout the year from grazing coastal grasslands. In practice, they
would spend only part of the year by the coast and would spend much of their time
grazing further inland. A proportion of their diet would also take the form of
concentrates and silage, especially over winter. It was cautiously assumed that the
livestock obtain all their water from sources contaminated by sea-to-land transfer.
The farmers were assumed to consume at a high rate the full range of dairy, beef and
sheep products. To make the greatest possible distinction from the in-shore fishermen
PEG, fish consumption rates were set to zero.
Estuary Livestock Farmers
The estuary livestock farmers were deemed to live at Saltcoats and were cautiously
assumed to spend 20 hours per day on an annual basis on and around the salt marsh
and tide-washed pasture. This included 4 hours per day off-model. The livestock
graze the salt marsh and tide-washed pasture for half of the year. This is assumed to
correspond to the highest level of access to these lands. Soil consumption by animals
whilst grazing the salt marsh is high. The animals drink from local streams and
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drainage ditches at Drigg Stream levels of radionuclide concentration. Other
assumptions regarding the livestock were the same as for coastal livestock farmers
and the same conservatisms applied. Inadvertent sediment consumption by humans
was taken to be from salt-marsh soils. To make the greatest possible distinction from
the in-shore fishermen PEG, fish consumption rates were set to zero.
Coastal Horticulturists
Coastal horticulturists were deemed to be located between the site and the coast,
because this is the zone most likely to be affected by sea-to-land transfer. They spend
some 20 hours per day on an annual basis in this area. It was assumed that the soils
have been improved for the purposes of horticulture and that sufficient inputs are
available to produce good and consistent yields of salad crops, fruit and vegetables,
flowers and ornamental plants. Greenhouse cultivation might be expected as part of
the enterprise, but this assumption would strongly offset the impact of sea-to-land
transfer – the only contamination pathway considered during the at closure state.
Irrigation would also be an expected practice and the most likely reliable source
during the summer would be a public water supply. However, well waters might be
used. The PEG has a high rate of consumption of its own produce.
Irt Estuary Houseboat Dwellers
The Irt Estuary houseboat dwellers PEG was deemed to live on the mudflats in the
vicinity of Saltcoats. They spend some 20 hours each day on an annual basis in the
vicinity of the estuary and foreshore. They are not employed within the potentially
contaminated area and include a number of elderly, but active individuals. They do
not consume locally produced foods other than marine fish, shellfish and seaweed.
They do not consume contaminated waters. They do inadvertently consume sediment
from the mudflats and foreshore in the course of their domestic and recreational
activities.
Drigg Villagers
As the title suggests, the PEG is deemed to live in Drigg village, away from the area
most affected by sea-to-land transfer. They are rural, agricultural workers who are
largely self-sufficient in terms of locally produced foodstuffs, part of which derives
from contaminated land. As such, the socio-economic context for this group is
historical. They consume mean levels of fish all of which comes from local coastal
waters and mean levels of vegetables and selected animal products, half of which
comes from areas affected by sea-to-land transfer. They use the foreshore
recreationally. The village has a public drinking water supply.
Coastal Villagers
As the title suggests, the coastal villagers PEG was deemed to live in Seascale village
where they are close to the shoreline and in the area most affected by sea-to-land
transfer. They are rural, agricultural workers who are largely self-sufficient in terms
of locally produced foodstuffs. As such, the socio-economic context for this group is
historical. They consume mean levels of fish, all of which comes from Irish Sea
waters and mean levels of vegetables and selected animal products, all of which
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comes from areas affected by sea-to-land transfer. They use the foreshore
recreationally. The village has a public drinking water supply.
3.1.2.2 Exposure Groups and PEGs defined in this Study
Although the various PEGs identified by Thorne and Kane (2003) do not bear a oneto-one correspondence with the exposure groups and PEGs identified in this report,
some of the assumptions and data remain of relevance. The relationships between the
Analogue PEGs used previously and the PEGs defined in this study are set out below.
Occupational Users of the Storm Beach and Intertidal Zone
This group is closely related to the In-shore Fishermen PEG described previously.
That group was taken to derive a living by a combination of netting, shore-based line
fishing and from harvesting crabs and lobsters, winkles and mussels. The group
members consume seaweed in the form of laverbread. Group members were deemed
to spend their time at sea, on the foreshore or within the area most affected by sea-toland transfers. Apart from marine foods that they were taken to consume at a high
level, all their other foods were deemed to be uncontaminated. The main distinction
is that laverbread consumption is now treated as a variant on the characteristics of the
group, rather than as an intrinsic part of its behaviour.4
Recreational Users of the Storm Beach and Intertidal Zone
This group does not bear a close relationship to any of the Analogue PEGs considered
previously. It includes individuals who make extensive use of the beach for activities
such as dog walking, swimming, surfing and sun-bathing.
Casual and Recreational Users of the Facility Cap Area
None of the Analogue PEGs included in the 2002 PCSC was assumed to make use of
the cap area. However, the Local Resource Dominated PEGs were assumed to access
the cap for one hour per day, through use of a permissive footpath for dog walking.
Bearing in mind that the Site North area is associated with dunes, blown sand and
heath vegetation, this remains a reasonable assumption for the likely degree of access
to the area, though dog walking may not be the only reason, e.g. sun-bathing may also
occur as Site North becomes an integral part of the beach and cliff regime.
Smallholders located on the Facility Cap Area
None of the Analogue PEGs included in the 2002 PCSC was assumed to make use of
the cap area. However, use of the cap area by smallholders was included in the
assessment of inadvertent human intrusion (see Section 3.2.2). Also, abstraction of
well water was included in the assessment.
4
Clyne et al. (2004) have identified two additional pathways that it may be appropriate to take into
account in supplementary calculations. Four people were identified who regularly used seaweed
collected from Drigg, Seamills and Seascale beaches as a fertiliser on their vegetable gardens. Also,
two farmers were identified removing sand from two beaches in the survey area. One used this
material to repair farm lanes and tracks as a regular activity and the other used sand from Braystones
Beach to fill in walls on his farm.
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Users of the East-West and Drigg Streams and of the Site South Area
The primary reason for accessing this area is to use it for grazing of salt marsh for
pasture or for recreational purposes. Grazing of the salt marsh was included for
Estuary Livestock Farmers, but a specific recreational PEG was not defined for this
area.
Users of the Estuary and Lagoon
In this case, there is a close relationship with the Irt Estuary houseboat dwellers PEG
that was deemed to live on the mudflats in the vicinity of Saltcoats. These individuals
were taken to spend some 20 hours each day on an annual basis in the vicinity of the
estuary and foreshore. Also, they did not consume locally produced foods other than
marine fish, shellfish and seaweed, and did not consume contaminated waters. They
did inadvertently consume sediment from the mudflats and foreshore in the course of
their domestic and recreational activities.
Users of Ravenglass Bay
These could be similar to the occupational and recreation users of the storm beach and
intertidal zone. Also, the group has similarities with the Analogue PEG of Coastal
Villagers. Theses were deemed to live in Seascale village where they would be close
to the shoreline and in the area most affected by sea-to-land transfer. However,
translocating them along the coast to a new settlement at Ravenglass Bay seems
plausible. They were taken to be rural, agricultural workers who are largely selfsufficient in terms of locally produced foodstuffs. They were also taken to consume
mean levels of fish, all of which comes from Irish Sea waters and mean levels of
vegetables and selected animal products, all of which comes from areas affected by
sea-to-land transfer. They were taken to use the foreshore recreationally.
3.1.3 Selection of Point Estimate Parameter Values and Ranges for
the Characterisation of Members of Exposure Groups and
PEGs
Although for assessment studies, it is important to consider all the pathways by which
an exposure group or PEG might be exposed (as shown in Table 13), for the purpose
of estimating parameter values, it is more convenient to discuss matters on a pathwayby-pathway basis. This is because the information that is required to be reviewed and
the judgements that have to be made differ considerably between the various
pathways. Furthermore, although the selection of parameter values for adults on the
one hand and children and infants on the other are identified as distinct steps in the
methodology, in practice, the commonality of relevant considerations mean that it is
convenient to discuss all age groups together. Thus, in the main part of this section,
the discussion is structured on a pathway-by-pathway basis. However, the section
concludes with a summary table that presents the recommended point values by
exposure group or PEG and age group. As the ranges of some of the quantities are
correlated with each other, they are not presented in the summary table and the reader
should consult the following text to determine how self-consistent sets of values
should be obtained.
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It is emphasised that the inclusion of parameter value ranges does not imply that
radiological impacts should be calculated sampling over uncertainties in PEG
characteristics. As pointed out in item l of Table 7, an approach is adopted in which
PEG characteristics are specified in terms of point estimates of the relevant
parameters. The reason for inclusion of parameter value ranges is so that sensitivity
calculations can be undertaken to determine the robustness of the results of the
reference calculations relative to changes in the input data.
3.1.3.1 External Exposure to Soil and Sediment
In this case, the only quantity of relevance is the occupancy of the contaminated soils
and sediments. For coastal areas, this matter has been discussed in detail by Smith
and Jones (2003). Their compilation is based on site-specific habit surveys
undertaken in the UK relevant to a range of substrates in beach and inter-tidal areas,
and to both occupational and leisure activities. Data from their report are summarised
in Table 14. Note that the data given in this report were originally developed for
operational assessments.
Substrate/Group
Mud and sand
Mud
Saltmarsh
Sand and rock
Sand/Coal
Bait Diggers
Angling
Maximum
Occupancy (h a-1)
1,900
3,300
1,900
1,100
3,000
950
1,000
Comments
Data from Rosyth
Boat dwelling on the Ribble Estuary near Springfield
Farmers, Rockliffe, Cumbria
Fishermen, Sellafield
Coal gatherers
Sellafield
Angling over beaches and handling sediment,
Sellafield
Table 14: Occupancy of Beach and Inter-tidal Areas from UK Surveys
On the basis of these data, Smith and Jones (2003) recommended a generic critical
group value of 2,000 h a-1.
Critical group occupancies tend to result from occupational use of beach or bank
areas, or from occupancy of houseboats. However, use of beaches and the foreshore
may also occur to a less degree by members of the public. In this context, Smith and
Jones (2003) distinguished two sub-groups. There are those who occasionally visit
the beach due to its vicinity to their home or holiday locations, and those who use the
beach as part of a leisure activity, such as fishing or diving.
Smith and Jones (2003) estimate beach occupancies for members of the general
population on two main sources of information. The first was a survey of the
occupancies of residents and visitors at 19 sites on the West Cumbrian coast. The
other survey was carried out to investigate the impact of Sellafield discharges on the
levels of radioactivity in tide-washed land along rivers in Dumfries and Galloway.
The occupancy values for residents in West Cumbria were found to range from
around 12 to 300 h a-1, whereas the occupancy of inter-tidal pastures was 20 to 400 h
a-1. Smith and Jones (2003) commented that a reasonable estimate of non-leisure use
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of beaches by residents of 30 h a-1 was found from the Cumbrian data. They state that
this value is also appropriate for visitor occupancy that is likely to include some beach
leisure activities. These data apply to adults. Although values for children and
infants have to be inferred, Smith and Jones (2003) concluded that a leisure-related
value of 30 h y-1 is also appropriate for children and infants.
Activity
Walking
Wildfowling
Fishing (haaf-netters)
Horse riding
Ornithology
Gardening, cycling, sports
Occupancy (h a-1)
150
200
320
240
80
150
Table 15: Recreational Use of Tidally Washed Pasture in Dumfries and
Galloway
The survey in West Cumbria also suggested that occupancy of 300 h a-1 is
representative for a small sub-group of the resident population who participated in
activities such as dog walking, jogging or cycling on beach areas. Farmers who
grazed animals on tidally washed pastures accounted for the higher occupancies of
350 to 400 h a-1 in the Dumfries and Galloway survey.
Smith and Jones (2003) also noted some supporting information. A survey for the
Countryside Commission for Scotland on the use of two recognised coastal
recreational locations at Longniddry and Gullane on the Firth of Forth near Edinburgh
supported an occupancy value of 30 h a-1 for coastal usage by the general population.
Also, the local Environmental Health Department made observations of the inter-tidal
area between Skerton Bridge and Carlisle Bridge in 1990. People were seen in only 6
of 142 observations in this area, indicating how rarely it is occupied.
In respect of the various PEGs identified in Table 13, the occupancy values shown in
Table 16 are recommended for adults. Note that these occupancies include a
contribution from exposure on or in the water body. A correction to take account of
this is introduced in Section 3.1.3.2. For children and infants, occupational activities
are not appropriate. For the recreational groups, the reference value should be
reduced from 300 h a-1 to 30 h a-1, as recommended by Smith and Jones (2003). In
these cases, the ranges should also be reduced by a factor of ten to conform to the
scaling of the reference value. For users of the estuary and lagoon, no reduction in the
reference value and range should be made, as the values relate to dwelling on boats.
However, it is emphasised that boats are more likely to be occupied by older people
than by families.
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Reference
Value (h a-1)
2000
Range (h a-1)
Basis
1000 to 3000
300
80 to 300
Casual and
recreational use of
the facility cap
area
Users of the Site
South area
300
80 to 300
300
80 to 400
Users of the
estuary and lagoon
3300
300 to 8000
Occupational
users of
Ravenglass Bay
Recreational users
of Ravenglass Bay
2000
1000 to 3000
Reference value is the generic
recommendation of Smith and Jones (2003).
Range is based on rounded values from
Table 14, excluding boat dwellers.
Reference value is a West Cumbrian
estimate for a small sub-group of the
population engaged in dog-walking, jogging
or cycling on beach areas. Lower bound of
range is for ornithology from Table 15.
As for recreational use of the storm beach
and intertidal zone. This corresponds quite
closely to the value of 1 h d-1 used in the
2002 PCSC.
Casual and recreational use, but with the
upper end of the range extended to include
data for farmers grazing animals on tide
washed pastures.
Reference value is from boat dwellers on
the Ribble Estuary. Range is from
recreational use through to permanent
residence on a boat with only limited time
spent away from the area.
As for the storm beach and intertidal zone.
300
80 to 300
Group
Occupational
users of the storm
beach and
intertidal zone
Recreational users
of the storm beach
and intertidal zone
Table 16: Adult Occupancies for External Exposure
3.1.3.2 External Exposure to Water Bodies
No detailed guidance is available on external exposure to water bodies. This category
of exposure includes contributions from swimming, boating and being present
adjacent to the water body. A reasonable basis is that no more than about half the
time of occupational or recreational use of a beach or foreshore area is likely to be
spent on or in the water. Thus, rather than specifying the period of external exposure
to water bodies directly, it is defined as a fraction, f, of the overall occupancy values
given in Table 16. Recommended f values and ranges are given in Table 17. These
values apply to adults, children and infants. They are applied in the formulae:
Os = (1 - f)Oext
Ow = f Oext
where Os is the external occupancy on soils and sediments;
Ow is the external occupancy to water bodies;
Oext is the total external occupancy, as discussed in Section 3.1.3.1.
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Group
Occupational users of
the storm beach and
intertidal zone
Recreational users of
the storm beach and
intertidal zone
Reference Value
0.25
Range
0.0 to 0.5
0.25
0.0 to 0.5
Casual and recreational
use of the facility cap
area
Users of the Site South
area
0.0
0.0 to 0.0
0.0
0.0 to 0.0
Users of the estuary
and lagoon
0.25
0.0 to 0.5
Occupational users of
Ravenglass Bay
Recreational users of
Ravenglass Bay
0.25
0.0 to 0.5
0.25
0.0 to 0.5
Basis
Reference value is
arithmetic mean of
range. Some
individuals, e.g. dog
walkers, will not be
exposed to the water
body.
No relevant water
bodies.
Streams are not
sufficiently large to be
considered as water
bodies in this context.
Reference value is
arithmetic mean of
range. Range takes
into account that some
boats may be beached
at all times, whereas
others will be afloat at
high tide.
As for the storm beach
and intertidal zone.
Table 17: Partitioning of External Occupancy between Exposure to Soils and
Sediments and Exposure to Water Bodies
In selecting a value of f, it should be kept in mind that external exposure rates will
typically be higher over soils and sediments than over (or in) water bodies, so key
sensitivity studies may require f to be reduced rather than increased.
3.1.3.3 Ingestion of Soil and Sediment
Generic data for rates of ingestion of sand and soil are provided by Smith and Jones
(2003). These data are based on a study by van Wijnen et al. (1990) on the soil
ingestion habits of children aged between 6 months and 5 years. This work provides
soil ingestion rates under normal and extreme (camping) conditions.
Hourly ingestion rates are derived in order to estimate ingestion related to time spent
in a given location. Hourly ingestion rates for small fractions of the year spent at a
particular location were calculated taking account of the consideration that ingestion
is likely to occur mainly outdoors. The average daily rates and hourly rates given by
Smith and Jones (2003) are compiled in Table 18.
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Age Group
1 year old
5 year old
10 year old
15 year old
Adult
Average (mg d-1)
100
50
30
20
10
Critical (mg d-1)
300
200
100
50
30
Hourly (mg h-1)
50
20
10
5
5
Table 18: Ingestion Rates of Soil and Sand estimated by Smith and Jones (2003)
It is of interest to compare the rates given in Table 18 with those recommended by the
US NCRP (1999), for assessments of contaminated land, based on an extensive
review of the primary literature (see also Simon, 1998). These values are 50 to 100
mg d-1 for an adult and 100 to 200 mg d-1 for a child, with periods of exposure
typically of 180 to 360 days per year. These values are in good agreement with the
recommendations of Smith and Jones (2003).
Rather than specifying ingestion rates directly, it is recommended that the values of
Os (h a-1) computed using the relationship Os = (1 - f)Oext are used to estimate annual
intake rates of soil and sediment by inadvertent ingestion. Thus, intake rates are given
by:
Is = OsR
where Is (mg a-1) is the ingestion rate; and
R (mg h-1) is the age-dependent hourly ingestion rate.
In the assessment, the age groups considered are 1-year-old, 10-year-old and adult.
Thus, the values of R adopted are 50, 10 and 5 mg h-1, respectively.
This approach is modified for the estuary/lagoon group, as exposure to the water body
may be from within a boat. In this case, Oext is used to estimate the sediment
ingestion rate. It is emphasised that this could be an over-estimate, as the hourly rates
are not intended for use with long periods of exposure.
3.1.3.4 Ingestion of Water
In contrast to most radiological impact assessments, a contaminated water source is
not considered to be the primary source of drinking water for the PEGs of interest,
except for the user of well water discussed in Section 3.3. Water is either consumed
accidentally, e.g. in swimming, or through occasional use of a local stream, e.g. when
camping.
The occasional use of water from streams is relatively readily estimated, though very
uncertain. Total fluid consumption, which is around 1.0 to 2.4 litres per day in adults
(ICRP, 1975, Table 127) is not very relevant in this context. More relevant are daily
rates of consumption of tap water (0.045 to 0.73 litres per day for adults, but with
values within this range also recorded for children) and water-based drinks (0.32 to
1.45 litres per day for adults, but with values within this range also recorded for
children) (ICRP, 1975, Table 127). Overall, it seems reasonable to suppose that about
1 litre per day might be extracted from a stream for drinking by an adult. Thus, for 10
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days of use of the stream per year, the total intake would be 10 litres. A similar value
might apply to a 10-year-old child. However, it seems unlikely that a 1-year-old
would be permitted to consume stream water, even after treatment by boiling or with
sterilisation tablets.
Inadvertent ingestion of water during swimming does not seem to have been studied.
Assuming that one or two mouthfuls (~ 0.02 litres) are swallowed on each occasion
and that swimming occurs on a few tens of occasions per year, the total consumption
might be up to ~ 1 litre per year. This value would apply to adults and 10-year-old
children. It seems reasonable to assume that inadvertent ingestion by 1-year-old
infants does not occur.
Based on the above discussion, recommended water intake rates are as listed in Table
19.
Group
Reference Value
(Litres per year)
1.0
Range (Litres per
year)
0.0 to 3.0
1.0
0.0 to 3.0
Casual and recreational
use of the facility cap
area
Users of the Site South
area
0.0
0.0 to 0.0
10.0
1.0 to 20.0
Users of the estuary
and lagoon
Occupational users of
Ravenglass Bay
Recreational users of
Ravenglass Bay
1.0
0.0 to 3.0
1.0
0.0 to 3.0
1.0
0.0 to 3.0
Occupational users of
the storm beach and
intertidal zone
Recreational users of
the storm beach and
intertidal zone
Basis
Reference value given
in text. Inadvertent
consumption rates are
unlikely to range as
high as deliberate
consumption rates
during camping.
No relevant water
bodies.
Reference value given
in text. Range based
on 1 to 20 days of
typical use per year.
As for the storm beach
and intertidal zone.
Inadvertent
consumption may be
rather greater for
swimming in the sea
rather than in the
lagoon or estuary, but
there is not an adequate
basis for making any
distinction between
these areas.
Table 19: Water Consumption by Adults and 10-Year-Old Children
(Consumption rates by 1-year-old infants are taken as zero.)
3.1.3.5 Ingestion of Plant Products
Ingestion of plant products is not identified as a pathway for any of the PEGs of
relevance. However, it is noted that macrophytic algae (seaweed) collected from the
shoreline could be considered in variant calculations and that this pathway has been
included in previous operational assessments. If this was done, the relevant
consumption rate for adults could be up to 50 kg a-1. This was the value used for the
Local Resource Dominated PEG in the 2002 PCSC (Thorne and Kane, 2003, Table
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4.1; see also Table 6, as the same value was used for the operational assessment at
2050 AD). It was based on the laverbread consumption rate at Sellafield given in the
RIFE-4 (1999) and RIFE-5 (2000) reports.
For 10-year-old children, the adult rate can be scaled by a factor of 0.7 to give 35 kg
a-1 (Thorne and Kane, 2003). For infants, zero consumption can be assumed (Thorne
and Kane, 2003).
Although not relevant to any of the exposure groups or PEGs addressed in this report,
it is noted that some areas of agricultural land might be contaminated by sea-to-land
transfers. If this were the case, then consumption rates of terrestrial foods would be
required. Also, agricultural pathways are relevant in respect of the consumption of
animal products from animals drinking contaminated stream water. Generalised
values suitable for use in post-closure radiological assessments have been
recommended by Thorne and Kane (2006). These values are based on observations at
the present day and are equally applicable to the operational period. They are
reproduced in Table 20. Although derived for an inland community, they are judged
also to be appropriate to a near-coastal agricultural community affected by sea spray.
Quantity
Units
Consumption of local
foods
Domestic fruit
Potatoes
Root vegetables
Potatoes and root
vegetables
Green vegetables
Other domestic
vegetables
Green and other
domestic vegetables
Mushrooms
Honey
Pig meat
Cattle meat
Sheep meat
Offal
Poultry
Game
Oil (non-dairy)
Milk
Butter
Cheese
Other milk products
Butter, cheese and
other milk products
Eggs
Cereals
kg y-1
Adult
Typical
High
Value
Child
Typical
High
Basis
Infant
Typical High
50
50
10
60
150
100
30
110
30
45
6.0
50
95
75
15
85
19
10
5.0
15
60
25
10
35
24
20
60
40
6.0
15.5
15
40
3.5
6.0
9.5
17.5
44
100
22.5
50
8.0
23.5
3.0
2.5
15
15
8.0
5.5
10
6.0
10
95
4.5
8.0
15
20
8.0
7.5
35
40
20
15
25
10
25
210
15
20
40
50
1.5
2.0
8.5
15
4.0
3.0
5.5
4.0
10
110
3.0
4.0
10
15
3.5
5.5
20
25
10
9.0
15
7.5
20
220
8.0
10
30
40
0.6
2.0
1.5
3.0
0.8
1.0
2.0
2.0
130
1.0
2.0
15
15
1.5
5.5
4.0
8.0
2.0
3.5
5.0
5.5
290
3.0
5.0
40
40
8.5
5.0
20
9.0
6.5
4.5
20
7.0
5.0
1.5
15
3.0
Takes 10% of cereals to
be produced locally
Note that aggregated
food groups are shown
in bold. Typical rates
are those for mean
consumers and high
rates are 95th percentile
values. Domestic fruit
consumption rates are
augmented by imported
fruit consumption rates
to allow for imported
fruit being displaced
from the diet by local
fruit in a locally based
economy. Similarly,
other domestic vegetable
consumption rates are
augmented by other
imported vegetable
consumption rates.
Table 20: Parameter Values for Crop Plants and Animal Products
(Based on Table 5.3 of Thorne and Kane (2006))
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3.1.3.6 Ingestion of Animal Products
Ingestion of animal products applies only to the following four of the seven PEGs
under consideration here:
• Occupational users of the storm beach and intertidal zone;
• Users of the Site South area;
• Users of the estuary and lagoon;
• Occupational users of Ravenglass Bay.
For all of these groups, except the users of the Site South area, the foods of relevance
are fish, molluscs and crustaceans caught either in local coastal waters or in the
estuary or lagoon. Here, it is assumed that individuals can fully satisfy their dietary
requirements from catches in these areas. This is considered to be a cautious, but
reasonable assumption.
Generic critical group consumption rates for marine organisms are given by Smith
and Jones (2003). These are listed in Table 21.
Age Group
Adult
10 and 15 year old
1 and 5 year old
Fish
100
20
5
Consumption Rate (kg y-1)
Crustaceans
20
5
0
Molluscs
20
5
0
Table 21: Critical Group Consumption Rates for Marine Foods
As a general rule, critical group consumption rates are about a factor of two to three
larger than typical consumption rates (see, for example, Table 20). Bearing in mind
that the total numbers of individuals in the PEGs are likely to be relatively small, the
generic critical group consumption rates proposed by Smith and Jones (2003) are
toward the top end of the range of uncertainty and rates a factor of three lower would
be toward the bottom of the range of uncertainty. Thus, the rates set out in Table 22
are recommended for use. The ranges of values recommended encompass the values
adopted in recent operational assessments (see Tables 5 and 6).
Age Group
Adult
10-year-old
1-year-old
Reference Consumption Rate (kg y-1) - Range given in parentheses
Fish
Crustaceans
Molluscs
50 (30 - 100)
10 (7 -20)
10 (7 -20)
10 (7 -20)
3 (1 - 5)
3 (1 - 5)
3 (1 - 5)
0
0
Table 22: Recommended Consumption Rates for Marine Foods
It is noted that the lagoon may be freshwater rather than saline. From Thorne and
Kane (2006), appropriate high rates of consumption of freshwater fish are 20, 5 and 1
kg a-1 for adults, children and infants, respectively. Thus, if the lagoon is a freshwater
body, fish consumption rates can be reduced by approximately a factor of five relative
to marine fish consumption rates. It is not clear whether freshwater crustaceans and
molluscs would be available in the lagoon to be collected for food.
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In the case of the Site South area, salt washed pasture may be present. Following the
discussion in Section 3.1.2.1, this is taken to be grazed by cattle. Based on data in
Table 20 and recalling that cattle are used as a surrogate for all animal types (Section
2.5.2), aggregate consumption rates for milk and milk products, meat and offal can be
derived from Table 20. Recommended values are listed in Table 23. Note that the
milk values are for liquid whole milk. Thus, the values for butter, cheese and other
milk products have been scaled by a factor of six to allow for the higher solids
contents in these milk products than in liquid milk (see, e.g. the comments to Table
29). In deriving these values, the reference values are taken as intermediate between
the typical and high values listed, as for marine foods.
Age Group
Adult
10-year-old
1-year-old
Reference Consumption Rate (kg y-1) - Range given in parentheses
Milk and milk
Meat
Offal
products
330 (215 - 510)
80 (54 - 130)
9 (5.5 - 15)
300 (200 - 460)
50 (37 - 78)
5 (3 - 9)
340 (220 - 530)
12 (7 - 19)
2 (1.0 - 3.5)
Table 23: Recommended Consumption Rates for Terrestrial Animal Products
3.1.3.7 Inhalation of Soil and Sediment
Material distributed in soils and sediments may be resuspended due to wind or human
actions. In some contexts, a resuspension factor is used to relate air concentrations to
ground concentrations expressed on an activity per unit area basis (NCRP, 1999).
However, this approach is more suited to surface deposition following a release to air
than it is to contamination distributed over a substantial depth. For the latter, it seems
more appropriate to adopt a mass loading in air approach. For this approach, the
relevant data are the maintained mass concentration of respirable soil or sediment in
air, the breathing rate and the annual occupancy. Annual intakes of soil or sediment
by inhalation are the products of these three quantities. The mass concentration and
breathing rate are discussed below. Annual occupancies are as for external irradiation
and are listed in Table 16.
A detailed comparison of different approaches to assessing the radiological impacts of
resuspension has been undertaken in the context of the international BIOPROTA
programme (Wasiolek et al., 2005). That report draws attention to the potential
influence of factors such as the preferential resuspension of material of smaller grain
size that is both more readily respirable than material of larger grain size and may
exhibit a higher concentration per unit mass of particle-reactive radionuclides because
of its larger specific surface area. However, the extent of information available
relating to material that could be available for resuspension in the present context does
not permit this degree of refinement to be incorporated in the assessment model used.
The simplest mass loading model that can be adopted assumes that all dust in air at a
location is derived from the contaminated area and that the activity concentration in
the resuspended dust is equal to that in the contaminated source. In assessment
studies, mass loadings of 1 10-7 kg m-3 are typically used, though values ranging from
5 10-9 to 5 10-5 kg m-3 were reported in the BIOPROTA study (Wasiolek et al., 2005).
Annual average mass loadings associated with rural and urban environments have
been reported as 2.8 10-8 and 7.5 10-8 kg m-3, respectively (NCRP, 1999), but during
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soil disturbance values can increase dramatically and values behind a tractor have
been reported with a median of 1.5 10-5 kg m-3 and a range of 3 10-7 to 2 10-4 kg m-3
(NCRP, 1999). For comparison, concentrations above a value of 1.5 10-7 kg m-3 are
considered to constitute a nuisance dust problem (NCRP, 1999).
For individuals present in the various areas of interest, only a limited amount of
human-induced disturbance of the substrate may be anticipated. Therefore, the mass
loading of 1 10-7 kg m-3 typically adopted in assessments seems a cautious, but
reasonable, reference basis for calculations. Values two orders of magnitude higher
and lower than this could reasonably be used in sensitivity studies.
Inhalation rates for individuals of different ages can be taken from ICRP Publication
66 (ICRP, 1994). Except in the case of young infants, activities undertaken in the
various areas considered might be expected to be moderately energetic. Therefore,
the following breathing rates are taken from Table 8 of ICRP (1994):
• 1 year old: sitting awake: 0.22 m3 h-1;
• 10 year old: light exercise: 1.12 m3 h-1;
• Adult: light exercise: 1.375 m3 h-1.
Where separate values are listed for males and females in ICRP (1994), the arithmetic
average has been taken.
Because these values are short-term values appropriate to moderately energetic
activities (except in the case of the 1 year old), they are somewhat larger than the
long-term average values given in Table 8 of Smith and Jones (2003). The value
adopted for the 1 year old is identical to that adopted by Smith and Jones (2003). It is
noted that these rates may also be slightly cautious for residents of houseboats on the
estuary or lagoon.
3.1.3.8 Inhalation of Radioactive Gases
This pathway applies only to casual and recreational users of the facility cap area and
to smallholders (see Section 3.2.2). As gas concentrations in air will be computed
directly, the only quantities required are occupancies (given in Section 3.1.3.1) and
breathing rates (given in Section 3.1.3.7).
3.1.3.9 Compilation of Reference Values
Table 24 provides a compilation of reference values for exposure group and PEG
characteristics derived from the data presented in previous subsections.
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Quantity
Units
Reference Value
Adult
Child
Infant
Occupational users of the storm beach and intertidal zone
Occupancy for external exposure to sediment
h a-1
1500
Occupancy for external exposure to water bodies
h a-1
500
Rate of ingestion of sediment
kg a-1
7.5 10-3
Rate of ingestion of water
m3 a-1
1.0 10-3
50
Rate of ingestion of macrophytic algae (variant
kg (f.w.)
calculation only)
a-1
kg (f.w.)
Rate of consumption of marine fish
50
a-1
10
Rate of consumption of marine crustaceans
kg (f.w.)
a-1
10
Rate of consumption of marine molluscs
kg (f.w.)
a-1
Dust load in air
kg m-3
1 10-7
3 -1
Breathing rate
m a
12050
Recreational users of the storm beach and intertidal zone
Occupancy for external exposure to sediment
h a-1
225
22.5
22.5
Occupancy for external exposure to water bodies
h a-1
75
7.5
7.5
Rate of ingestion of sediment
kg a-1
1.13 10-3
2.25 10-4
1.13 10-3
Rate of ingestion of water
m3 a-1
1.0 10-3
1.0 10-3
0
-3
-7
Dust load in air
kg m
1 10
1 10-7
1 10-7
Breathing rate
m3 a-1
12050
9820
1930
Casual and recreational use of the facility cap area
Occupancy for external exposure to soil and
300
30
30
h a-1
sediment
Occupancy for external exposure to water bodies
h a-1
0
0
0
Rate of ingestion of soil or sediment
kg a-1
1.5 10-3
3.0 10-4
1.5 10-3
Rate of ingestion of water
m3 a-1
0
0
0
Dust load in air
kg m-3
1 10-7
1 10-7
1 10-7
Breathing rate
m3 a-1
12050
9820
1930
Users of the Site South area
Occupancy for external exposure to soil and
300
30
30
h a-1
sediment
Occupancy for external exposure to water bodies
h a-1
0
0
0
Rate of ingestion of soil or sediment
kg a-1
1.5 10-3
3.0 10-4
1.5 10-3
Rate of ingestion of water
m3 a-1
1 10-2
1 10-2
0
330
300
340
Rate of consumption of milk and milk products
kg (f.w.)
a-1
80
50
12
Rate of consumption of meat
kg (f.w.)
a-1
9
5
2
Rate of consumption of offal
kg (f.w.)
a-1
Dust load in air
kg m-3
1 10-7
1 10-7
1 10-7
3 -1
Breathing rate
m a
12050
9820
1930
Table 24: Reference Values of Exposure Group and PEG Characteristics
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Quantity
Units
Adult
Reference Value
Child
Infant
Users of the estuary and lagoon
Occupancy for external exposure to sediment
h a-1
2475
Occupancy for external exposure to water bodies
h a-1
825
Rate of ingestion of sediment
kg a-1
1.65 10-2
m3 a-1
1.0 10-3
Rate of ingestion of water
50
Rate of ingestion of macrophytic algae (variant
kg (f.w.)
calculation only)
a-1
50
Rate of consumption of marine fish5
kg (f.w.)
a-1
10
Rate of consumption of marine crustaceans
kg (f.w.)
a-1
10
Rate of consumption of marine molluscs
kg (f.w.)
a-1
Dust load in air
kg m-3
1 10-7
3 -1
Breathing rate
m a
12050
Occupational users of Ravenglass Bay
Occupancy for external exposure to sediment
h a-1
1500
Occupancy for external exposure to water bodies
h a-1
500
Rate of ingestion of sediment
kg a-1
7.5 10-3
Rate of ingestion of water
m3 a-1
1 10-3
50
Rate of ingestion of macrophytic algae (variant
kg (f.w.)
calculation only)
a-1
50
Rate of consumption of marine fish
kg (f.w.)
a-1
10
Rate of consumption of marine crustaceans
kg (f.w.)
a-1
3
Rate of consumption of marine molluscs
kg (f.w.)
a-1
Dust load in air
kg m-3
1 10-7
3 -1
Breathing rate
m a
12050
Recreational users of Ravenglass Bay
Occupancy for external exposure to sediment
h a-1
225
Occupancy for external exposure to water bodies
h a-1
75
Rate of ingestion of sediment
kg a-1
1.13 10-3
Rate of ingestion of water
m3 a-1
1.0 10-3
-3
Dust load in air
kg m
1 10-7
3 -1
Breathing rate
m a
12050
2475
825
3.30 10-2
1.0 10-3
35
2475
825
1.65 10-1
0
0
10
3
3
0
3
0
1 10-7
9820
1 10-7
1930
22.5
7.5
2.25 10-4
1.0 10-3
1 10-7
9820
22.5
7.5
1.13 10-3
0
1 10-7
1930
Table 24 Continued
It should be recalled that there is also a PEG comprising smallholders located on the
cap area and, possibly, using water abstracted from a well or borehole located in the
contaminant plume. That group is discussed further in Sections 3.2.2 and 3.3.
3.1.4 Local Resource Use and Ranges of Uncertainty
The occupancies and rates of ingestion of sediment and water set out in Section 3.1.3
have been derived to be compatible with reasonable use of local resources. Therefore,
the only consideration is whether food consumption rates can be sustained from the
local area. Bearing in mind that the PEG could comprise only a few individuals, this
is not seen as an issue for fish, crustaceans and molluscs taken from the lagoon,
5
Values for fish, crustaceans and molluscs are modified for a freshwater lagoon.
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estuarine and marine environments. However, consideration needs to be given to
whether, in practice, these organisms would be taken from the lagoon and estuary.
In the case of terrestrial food products, these all derive from cattle grazed on saltwashed pasture associated with the Site South. In this case, the issue is not whether
enough of the products could be produced from the area, but the likelihood that the
cattle would only graze this area for part of the year and either graze uncontaminated
areas at other times or be fed uncontaminated feed. These are issues to be addressed
in the biosphere modelling rather than in relation to PEG characteristics.
As to uncertainties, it is appropriate to compare reference with upper bound
occupancies and consumption rates. For occupancies, Table 16 gives ratios of 1.5, 1.0
and 2.4 for the various groups listed. These ranges are limited, so relative
homogeneity is not a major issue. As ingestion rates of soil and sediment are obtained
by scaling these values by point estimates, relative homogeneity is not an issue in this
context. However, it is noted that the ingestion rates are uncertain and that cautious
point estimates have been adopted for assessment purposes.
The rates of ingestion of water are highly uncertain, as only inadvertent and
occasional uses are considered for these seven PEGs. However, this has been
addressed by adopting reference values towards the top end of the reasonable range.
Extreme values are assessed as being no more than a factor of two to three larger
(Table 19).
Ingestion of plant products is not a significant consideration in the assessment. High
rates of ingestion of macrophyte algae (seaweed) are recommended for use in variant
calculations, as required. If calculations for arable land contaminated by sea spray are
required, typical and high consumption rates of plant and animal products are
provided (Table 20). These typical and high rates generally differ by less than a
factor of three. Similarly, reference and maximum rates of consumption of marine
foods (Table 22) and terrestrial animal products (Table 23) differ only by factors ~ 2.
In summary, either the range of variability in parameter values is small, or, where the
variability is larger, cautious assumptions have been made in recommending reference
values. Therefore, it is highly unlikely that a reasonably homogeneous PEG could be
defined, using realistic variations to the reference parameters, that would receive a
substantially higher dose than the PEG defined using the reference parameter values.
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3.2
For Inadvertent Human Intrusion over the Period from
Closure to Facility Disruption
3.2.1 Approach Adopted in the 2002 PCSC
In the 2002 PCSC, it was assumed that inadvertent human intrusion into the LLWR
site can occur at any time after control over the site is relinquished or lost.
Furthermore, it was also assumed that simplified, stylised scenarios for intrusion
should be adopted, following the recommendations of the ICRP (1998). The
approach adopted was described in Egan (2003), Penfold (2003), and Penfold and
Cooper (2003).
It should be noted that consideration has also been given to the potential for disruption
of the facility by other types of external events, e.g. meteorite impact and aircraft
crash. These are of low cumulative probability of occurrence. Furthermore, they are
judged to be of less radiological significance than disruption of the facility by largescale human intrusion (see below) or by coastal erosion (as discussed in previous
sections). For these reasons, other types of disruption of the LLWR are not addressed
further herein.
With respect to the type of human-intrusion scenarios to be adopted, it was decided in
the 2002 PCSC that these should be based on a set of characteristic ‘modes’ of
intrusion, reflecting disruption of the integrity of the facility on different spatial scales
and over varying lengths of time. In suitably generalised terms, three modes of
intrusion were distinguished:
• Small: Representative of the type of disturbance that might be caused by the
drilling of boreholes during site investigation;
• Medium: Representative of the type of disturbance that might be caused by
impact from an aircraft crash, a trial pit excavated on the site of the disposal
facility, or a limited bulk excavation, e.g. associated with the construction of
an isolated dwelling;
• Large: Representative of large-scale excavations associated with major
construction projects or, potentially, archaeological investigations at the site.
PEGs were identified for each of these modes of intrusion. In each case,
identification of the appropriate PEG had to take into account two main categories
of exposure:
• Type A: Individuals involved directly or indirectly in the activity giving rise to
the intrusion;
• Type B: Site inhabitants exposed to wastes dispersed on the site as a
consequence of the intrusion.
In principle, there will be only a single most exposed PEG for each mode of intrusion.
However, in practice, without undertaking specific calculations, it is not always
possible to determine whether the most exposed PEG will be the intruder, an associate
or a site inhabitant. For this reason, potential PEGs for each type of exposure were
defined for generalised large intrusions. For generalised small and medium
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intrusions, it was clear that Type A dominates so only this type of exposure was
addressed.
As simplified, stylised scenarios were addressed for human intrusion, the concept of
Analogue PEGs was considered to be of limited relevance in the 2002 PCSC.
However, it was commented that it could be useful to undertake studies of some
detailed scenarios of human intrusion to compare the radiological impacts with those
estimated for the simplified, stylised scenarios. This is particularly relevant to
exposures of site inhabitants. In the simplified, stylised scenarios, radiological
impacts to site inhabitants were calculated on the assumption of dispersion of the
active material into a specified volume of top soil and general utilisation of that
material. However, in an assessment of a detailed scenario of a particular type of site
development, it would be appropriate to consider the uses to which the excavated
material would be put in a typical instance of such a development. This might be for
purposes such as general landscaping or the construction of bunds. Such uses would
typically be associated with only a limited number of exposure pathways, at least in
the short term.
Again, because simplified, stylised scenarios were adopted, it was considered
appropriate to provide descriptions of them in the following very general terms.
Small
Investigative boreholes would typically be to prove bedrock, or to a depth of about 10
m to characterise the geotechnical properties of superficial strata. Other boreholes for
pumping tests could extend up to 20 m into bedrock. Boreholes for small-scale water
supply would typically extend to depths of no more than a few tens of metres. The
potential use of water from such wells is discussed further in Section 3.2.2. Largescale abstraction wells that could extend to depths of 100 m or more are considered to
be highly unlikely to be located in the vicinity of the facility, because of its situation
close to the coast. Such wells would be expected to be located further inland. The
volume of samples removed from the site during borehole investigations would
typically be 0.2 to 1.2 m3, with 0.05 to 0.1 m3 of the material examined in the
laboratory. Shell and auger and/or rotary drilling techniques would be used for
construction, which would typically take 1 to 4 days. Boreholes would typically be
backfilled with excavated material (Halcrow, 1998).
Medium
Trial pits would typically be constructed to a depth of 4.5 m below ground surface.
Typically, only about 1 m3 of material would be removed from site in trial pit
investigations, with 0.05 to 0.1 m3 examined in the laboratory (Halcrow, 1998). It is
assumed that most of the material removed from trial pits would be used to backfill
them on completion of the site investigation. Craters resulting from aircraft crashes
are also likely to be only a few metres deep. Selected samples and items from the
immediate vicinity of the crater would be investigated on site, or in a laboratory, as
part of the investigation into the cause of the crash. These samples and items might
originate from the disposed wastes. Individual dwellings would include trenching for
services and foundations to a depth of about 2 m; such excavations would be unlikely
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to penetrate to the wastes while the cap remained substantially intact. Construction of
cellars is appropriately considered in the context of large excavations (see below).
Large
A wide variety of large-scale excavations could be undertaken. A useful illustration
that can be used as the basis of a stylised scenario is the construction of a computer
and paper archive storage facility (Halcrow, 1998). For this, the key activity is
basement excavation/construction. This would involve the creation of an open
excavation to 5.75 m below ground surface, construction of a basement slab and
retaining walls, and backfilling around the basement. A total of 15,000 m3 of material
would be removed, which would be used for landscaping on site.
An alternative scenario could involve the construction of a milking parlour with
underground silage effluent tank, slurry reception pit and settlement tanks.
Excavation would be to a maximum depth of 4.75 m below ground surface and a total
of about 250 m3 of material would be removed (Halcrow, 1998). A similar volume
could be associated with the construction of cellars for an isolated house.
Generalising, large excavations can reasonably be taken to be to depths of 4 to 6 m,
and to have excavated volumes of between 250 and 15,000 m3. A reasonable stylised
reference case is a depth of 5 m and a volume of 2,000 m3. This implies an excavated
area of 400 m2. It is appropriate to assume that all the excavated material is used on
site for landscaping and related purposes.
The EA in their assessment of human intrusion adopted in the 2002 PCSC raised an
issue of relevance in DIS_002: Human intrusion assessment. There, they made
particular reference to the GRA paragraphs 6.18 and 8.16.
Paragraph 6.18 describes the need to consider a number of PEGs over a suitable range
of circumstances in order to identify the group at highest risk. It also requires the
developer to present the range of possible doses that each PEG could receive. In the
context of PEG habits and behaviour, this is addressed by providing information on
ranges of variability in characteristics that can be propagated through the assessment.
Paragraph 8.16 also relates to the possibility that some uncertainties could be
eliminated from further consideration by making simple deterministic assumptions
based on reasoned arguments. It gives the specific example that to deal with future
human behaviour the developer should present assessments in terms of impacts on
PEGs based on observed past and present human behaviour. This approach is adopted
in the development of stylised reference cases for inadvertent human intrusion, as
discussed above.
The general approach to defining PEGs for human intrusion adopted in the 2002
PCSC is considered to remain relevant. Therefore, the characteristics of those PEGs
can be taken directly from the analysis performed at that time. Those characteristics
are described in Section 3.2.2.
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3.2.2 Characteristics of PEGs for Inadvertent Human Intrusion
Small intrusions comprise boreholes to depths of at most a few tens of metres. Only
very small amounts of active material would be distributed on site, so the PEG is
taken to be individuals exposed during excavation or while examining excavated
material in a laboratory. Similar remarks apply to the trial pits considered
representative of medium intrusions. However, for large intrusions, it is necessary to
consider both those exposed while carrying out the excavation and those exposed
from occupancy of the site once intrusion has occurred.
Stylised scenarios are used for intrusion. Therefore, although details of individual site
uses are discussed below, this is solely for the purpose of providing a context for the
simplified approaches to analysis that are adopted in practice.
For small and medium intrusions, the primary pathways of exposure are identified as:
• External irradiation;
• Ingestion of contaminated excavated material;
• Inhalation of resuspended contaminated dust;
• Inhalation of radon and its short-lived progeny.
The last of these pathways is more relevant to the laboratory worker, as radon will be
rapidly dispersed when released to outdoor air from a small amount of excavated
material.
For the excavation worker and laboratory worker, the key parameters governing
exposure are the time spent in the vicinity of the excavated material, the rate of
ingestion of dust and breathing rate.
NCRP (1999) estimated a typical rate of ingestion of soil by adults of 0.1 g d-1 and
this value was used in the 2002 PCSC. For comparison, Smith and Jones (2003) gave
estimates for rates of ingestion of soil and sand based on a study related to ingestion
by children aged between 6 months and 5 years under normal and extreme (camping)
conditions. Corresponding values for older ages were estimated assuming an
exponential decrease in soil ingestion with each year of life up to the age of 18. Rates
of ingestion recommended by Smith and Jones (2003) are listed in Table 25. Note
that this is an expanded version of Table 18 and is provided here for convenience of
discussion.
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Age Group
1-year-old
5-year-old
10-year-old
15-year-old
Adult
mg d-1
100
50
30
20
10
Average
Ingestion Rate
Critical6
-1
mg d
kg y-1
300
4.4 10-2
200
3.5 10-2
100
1.8 10-2
50
8.8 10-3
30
8.3 10-3
kg y-1
3.7 10-2
1.8 10-2
1.1 10-2
7.3 10-3
3.7 10-3
Hourly
mg h-1
50
20
10
5
5
Table 25: Representative Soil Ingestion Rates
(reproduced from Smith and Jones, 2003)
The hourly values listed are for small periods of time spent outdoors in particular
locations where the situation is such that ingestion of soil could occur. It seems
reasonable to apply these short-term rates to excavation and laboratory workers. For
an eight hour working day, this gives an ingestion rate of 0.04 g d-1, somewhat smaller
than the value used in the 2002 PCSC.
On the basis of the above recommendations, and bearing in mind that the NCRP
(1999) value includes both occupational and non-occupational components, an
ingestion rate of 0.005 g h-1 during occupational exposure is adopted here. However,
it is emphasised that the rate could be close to zero in clean laboratory conditions and
could be an order of magnitude higher for workers on a construction site.
Smith and Jones (2003) cited ICRP (1994) in specifying inhalation rates for workers
undertaking ‘heavy’ and ‘light’ work. Heavy workers are explicitly stated to include
construction workers and farm workers. They also noted that the rate of breathing of
3.0 m3 h-1 for heavy exercise that is given in ICRP (1994) is appropriate for periods of
no more than two hours per day for firemen, construction workers, athletes and other
groups. The volumes of air inhaled at work recommended by Smith and Jones (2003)
are shown in Table 26.
Air Breathed (m3)
Activity and Duration
Light work (5.5 h light exercise
+ 2.5 h rest, sitting)
Heavy work (7 h light exercise +
1 h heavy exercise)
Light work
9.6
Heavy work
-
-
13.5
Table 26: Volumes of Air Inhaled at Work (from Smith and Jones, 2003)
Thus, a typical inhalation rate for workers involved in light work is 1.2 m3 h-1. For
heavy work, the corresponding value is 1.7 m3 h-1. The value for light work is
considered appropriate for laboratory workers and those involved in supervisory
activities in the field. The value for heavy work is considered appropriate to
individuals undertaking field activities such as drilling.
6
Critical ingestion rates given in Smith and Jones (2003) in units of kg y-1 are inconsistent with those
given in mg d-1. The mg d-1 values are taken as definitive.
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Thus, it only remains to estimate exposure times. This was carried out by Halcrow
(1998) for a number of site investigation scenarios. Results are set out in Tables 27
and 28. The various site developments were identified as possible in an expert
elicitation study and detailed designs, e.g. for agricultural buildings and hotels, were
then drawn up by Halcrow (1998) based on optimal use of the site area for these
various activities. Based on these detailed designs, it was straightforward to estimate
the resources required for development, as set out in Tables 27 and 28.
Staff
Developer
Client
Consulting
Engineer
Engineer/ Project
Manager
Geotechnical
Engineer
Ass. Geotechnical
Engineer
Contractor
Contracts Manager
Agent
Drilling Manager
Geologist
Technician
Shell Auger Driller
Shell Auger: 2nd
Man
Rotary Driller
Rotary: 2nd Man
Mech. Exc. Driver
Delivery Driver
Total Time in Contact with Material (h) for Different Proposed Site Developments
Golf
Hotel
Sports
Light
Agricultural
Computer
Water
Course
Centre
Industry
Centre
Abstraction
Marina
1
0
0
2
1
1
0
0
5
0
0
9
5
6
0
0
57
2
2
107
66
71
2
2
0
22
48
251
153
166
64
104
0
76
0
152
162
0
0
0
2
0
26
0
22
22
0
2
0
54
0
50
50
9
143
90
286
304
209
209
5
88
55
175
186
158
158
6
95
59
190
201
191
191
0
2
0
74
0
18
18
0
2
0
119
0
104
104
171
171
0
19
0
0
7
4
7
7
4
4
0
0
113
36
14
14
24
22
7
7
15
24
0
0
65
4
25
25
5
4
Table 27: Exposure Times for Ground Investigation Fieldwork
(from Halcrow, 1998)
Staff
Consulting
Engineer
Engineer/ Project
Manager
Geotechnical
Engineer
Ass. Geotechnical
Engineer
Lab. Testing
Contractor
Laboratory Manager
Laboratory
Technician
Skip Driver
Total Time in Contact with Material (h) for Different Proposed Site Developments
Water
Agricultural
Computer
Light
Hotel
Sports
Golf
Abstraction
Centre
Industry
Centre
Course
Marina
0
0
0
0
0
0
0
0
0
0
0
2
1
1
0
0
0
0
0
8
5
5
0
0
1
6
2
12
5
24
10
48
6
30
6
30
5
24
5
24
0
2
4
8
5
5
4
4
Table 28: Exposure Times for Laboratory Testing
(from Halcrow, 1998)
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From these data, it seems reasonable to adopt generalised exposure times of 100 hours
(range 20 to 300 hours) for contact with material during drilling and 20 hours (range 6
to 48 hours) for contact with the material in a laboratory.
Note that the above exposure times and derived ingestion rates apply to the sum of
small and medium intrusions, as these would almost always occur together. Table 27
shows that exposures of drillers are likely to be more prolonged than those of the
drivers of mechanical excavators involved in trial pitting, and Table 28 does not
distinguish examination of samples from boreholes and trial pits.
The analysis presented above relates to site-investigation activities directly associated
with site development. However, intrusions into the wastes may also result from
archaeological activities undertaken before the potentially toxic nature of the wastes is
recognised. In this case, the pathways of exposure are very similar to those for
excavation workers. Therefore, consideration has to be given mainly to the duration
of exposure as the amount of dust likely to be ingested is taken to be directly
proportional to the exposure duration.
Typically, archaeological digs involve mainly student labour and take place over the
summer vacation. Considering a student who works on the dig for ten weeks at 40
hours per week, the total exposure time would be around 400 hours. This suggests
that archaeological investigations can reasonably be encompassed in the excavation
worker scenario by increasing the upper limit on exposure time in sensitivity studies
from 300 to 400 hours.
For large excavations, it is useful to note that the excavation time to produce about
250 m3 of underground space for an agricultural development was 12.25 hours, i.e. a
rate of 20.4 m3 h-1. For a computer building, 15,000 m3 of underground space was
estimated to be excavated and engineered in 470 hours, i.e. a rate of 31.9 m3 h-1
(Halcrow, 1998). Overall, a rate of 25 m3 h-1 seems reasonable as a generic value.
For the stylised reference case of 2,000 m3, this implies an exposure time for
excavation of 80 h, or 10 man days.7 Thus, for construction workers, the relevant
parameters for the PEG are a time of 80 h for both external exposure and inhalation,
ingestion of 0.4 g of dust (with average concentrations of radionuclides to be
determined by modelling), and a breathing rate of 1.7 m3 h-1.
For subsequent exposure, a simple stylised calculation mixes the 2,000 m3 of
excavated material into a superficial soil layer. Heavy loading of this layer is not
appropriate or soil qualities may be substantially degraded. Taking a 10% loading, a
total of 20,000 m3 of contaminated soil is created. Spread at a typical plough depth of
0.3 m, this would result in a contaminated area of approximately 67,000 m2, or 6.7
hectares. This would be sufficient to support a small farm, with both livestock and a
‘kitchen garden’. It is noted that this route of contamination would be expected to
result in far higher exposures than the abstraction of water from a small-scale
domestic borehole and its use for drinking water and/or irrigation. However, it may
7
Note that it is not considered appropriate to make the stylised reference case a worst case in terms of
volume excavated, as it is supposed to represent the whole class of large excavations, in the same sense
that a reference person is taken to be representative of a critical group with diverse, but similar,
characteristics. Somewhat higher exposures will occur for larger excavations, but, conversely,
somewhat lower exposures will occur for small excavations.
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be useful to make a calculation of exposures by this route for comparative purposes.
If such an assessment were made, the rate of water consumption should be taken as
around 1 litre d-1 for adults (see Section 3.1.3.4).
For an area of this size, four groups are identified as being of potential interest. Each
is based on a single family and is defined as set out below, taking resource
requirements into account:
A. The smallholder with 4 to 12 hectares of land who keeps several head of cattle and
uses them to provide meat and milk products.8
B. The smallholder with 1 to 3 hectares of land who keeps a single cow for milk
production only.9
C. The smallholder with 0.5 to 1 hectare of land who keeps two goats for milk
production only.
D. The kitchen gardener who grows his own vegetables and fruit on 0.05 hectare.
Consumption rates for each of these groups (identified by the area of land utilised) are
set out in Table 29.
Characteristic
Group identifier
Land Area
Green and other domestic vegetable consumption
Potato and root vegetable consumption
Garden fruit consumption
Cattle milk and milk product consumption
Cattle meat consumption
Cattle offal consumption
Goat milk and milk product consumption
Units
ha
kg y-1
kg y-1
kg y-1
l y-1
kg y-1
kg y-1
l y-1
A
8
44
60
50
215
62.5
5.5
0
Value for Each Group
B
C
D
2
0.75
0.05
44
44
44
60
60
60
50
50
50
215
0
0
0
0
0
0
0
0
0
215
0
Table 29: Characteristics of Smallholder and Kitchen Gardener PEGs relevant
to Human Intrusion10
8
A dairy cow consumes ~ 100 kg d-1 of fresh forage (IAEA, 1994). Therefore, about 3 ha would be
required per animal. This could be reduced somewhat by growing high yield fodder crops. However,
an area of at least 1 ha is indicated. Furthermore, to maintain continuity of supply, several animals
would have to be kept.
9
The animal is considered to be bought from a local farmer and is eventually disposed of without being
used for meat products by the family.
10
Green vegetable, root vegetable and garden fruit consumption are the typical values for adults from
Table 5.3 of Thorne and Kane (2006). Cattle milk and milk product consumption is also based on data
from Table 5.3 of Thorne and Kane (2006). It again relates to typical consumption rates by adults and
comprises 95 l y-1 of liquid milk plus 20 kg y-1 of milk products converted on the basis that 6 litres of
milk are required to produce 1 kg of butter, cheese or other milk products. This is an approximate
conversion based on milk comprising 13% milk solids and allowing for the presence of water in some
milk products, such as yoghurt. Cattle meat consumption assumes that pig, sheep, goat, poultry and
game meat plus egg consumption is small, but is compensated for by increased cattle meat
consumption. The total consumption of these products by adult typical rate consumers is also taken
from Table 5.3 of Thorne and Kane (2006), as is the consumption of offal. Goat milk and milk product
consumption are taken as identical to cow milk and milk product consumption, as direct replacement is
envisaged. However, consumption could be rather less because of the greater richness of goat milk.
Note that relevant data from Table 5.3 of Thorne and Kane (2006) are reproduced in Table 20 of this
report. Typical rates of consumption are used because this is a small group, but it is noted that the
description of the group is such that its members would be expected to make at least moderately
intensive use of plants that they had grown or animals that they had reared.
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It is not obvious which of these groups should be taken as the most exposed PEG.
Group D occupies the smallest land area, so if the radionuclides are dispersed over
only a small area, it will experience the highest average concentrations. However, it
is only exposed to contaminated plant-based foods. Group C is particularly
interesting, as it occupies a relatively limited area and consumes the milk of goats,
which is enriched in some trace elements relative to cows’ milk. Groups A and B
occupy the largest areas, tending to lead to lower average concentrations of
radionuclides. However, they are associated with the greatest diversity of pathways
of exposure.
It is emphasised that the consumption rates listed in Table 29 are for adults and are for
typical rate consumers. Rates for infants, children and adults, for both typical and
high rate consumers, are given in Table 5.3 of Thorne and Kane (2006), which should
be consulted for further details and justification of the rates adopted.
In practice, it is anticipated that most types of human intrusion will result in
contaminated areas substantially smaller than the 6.7 ha estimated above. This is
because the estimate of 6.7 ha is based on a relatively large volume of excavated
material and because that material is assumed to be uniformly dispersed into topsoil.
In practice, the material may be used for a variety of purposes, such as landscaping,
that do not require such dispersion. Thus, there will be many contexts in which it will
be appropriate to consider only Groups C and D (see also Thorne and Halcrow, 2003).
3.3
Smallholder PEGs located on the Cap
The smallholder PEGs described in Section 3.2.2 and with the characteristics set out
in Table 29 are also relevant in the context of the ‘bath-tubbing’ scenario and identical
characteristics may be assumed. Also, an identical PEG can be used to assess the
radiological impact of abstraction of contaminated groundwater from a well.
However, whereas, the smallholder PEG in the ‘bath-tubbing’ scenario may be
assumed to drink uncontaminated water, the smallholder PEG in the well scenario can
be expected to drink 1 litre of contaminated water per day (see Table 24), as well as
irrigating the crops on the smallholding with that water and using it as a drinking
water supply for any animals that are kept.
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4.
Conclusions
Based on previous work, a well-defined methodology for the identification and
characterisation of exposure groups and PEGs has been developed. This comprises
the following steps:
1) Define the context in which the exposure groups or PEGs are present and
provide outline descriptions of them;
2) Identify the pathways of exposure relevant to each exposure group or PEG;
3) Define the exposure groups or PEGs in terms of present-day population
groups;
4) Select point estimate reference parameter values and uncertainty ranges for
adult members of each exposure group or PEG to achieve relative
homogeneity of characteristics;
5) Select point estimate reference parameter values and uncertainty ranges for
children and infants associated with each exposure group or PEG;
6) Audit local resource use and range of uncertainty for each exposure group
or PEG.
Work on climate and landscape evolution provided much of the basis for step 1
(Section 2.3), so the analysis presented in Section 3.1 was based on steps 2 to 5 and
resulted in a set of nine groups relevant to the groundwater, gas and facility
degradation pathways from the present day through to the end of termination due to
the effects of coastal processes. An important aspect of the analysis was the audit of
exposure pathways that should be considered for each exposure group or PEG, as set
out in Table 13.
The nine groups of relevance were identified as:
• Occupational users of the storm beach and intertidal zone;
• Recreational users of the storm beach and intertidal zone;
• Casual and recreational users of the facility cap area;
• Agricultural smallholder making use of the cap area;
• Users of water abstracted from a well downstream of the facility;
• Users of the East-West and Drigg streams and of the Site South area;
• Users of the estuary and lagoon;
• Occupational users of Ravenglass Bay;
• Recreational users of Ravenglass Bay.
Smallholders making use of the cap area are identified as the most likely intensive
users of locally abstracted well waters. As the same group had to be considered in the
context of human intrusion, only seven groups were addressed in the specific context
of the groundwater, gas and facility degradation pathways.
For each of these seven groups, the following general pathways were considered:
• External exposures to contaminated soils, sediments and water bodies;
• Ingestion of contaminated soils and sediments, water, plant products and animal
products;
• Inhalation of contaminated soils and sediments and radioactive gases (including
radon, thoron and their progeny).
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The groups identified have some similarities with the Analogue PEGs adopted in the
2002 PCSC, but also some substantial differences. These differences reflect the
shorter timescale now considered and the greater emphasis that is placed on the
potential disruption of the facility by coastal processes.
A further difference from the 2002 PCSC arises in the specification of parameter
values for each exposure group or PEG. In the 2002 PCSC, point estimates only were
given. However, in this analysis both reference point estimates and reasonable ranges
are provided to facilitate the undertaking of sensitivity studies. Also, although the
principal assessment calculations are still to be undertaken for adults, reference
parameter values and ranges are also given for 10-year-old children and 1-year-old
infants in all appropriate cases to facilitate comparisons between age groups.
In defining ranges for exposure group or PEG characteristics, correlations between
those characteristics have been recognised. Therefore, rather than specifying ranges of
values for all of the parameters directly, in some cases, formulae have been developed
to represent the relationships between parameters and ranges have been specified for
secondary parameters used in those formulae.
In respect of inadvertent human intrusion, a stylised approach was adopted in the
2002 PCSC and no good reason was identified for adopting a different approach. The
stylised approach adopted is set out in Section 3.2.
In suitably generalised terms, three modes of intrusion are distinguished:
• Small: Representative of the type of disturbance that might be caused by the
drilling of boreholes during site investigation;
• Medium: Representative of the type of disturbance that might be caused by
impact from an aircraft crash, a trial pit excavated on the site of the disposal
facility, or a limited bulk excavation, e.g. associated with the construction of
an isolated dwelling;
• Large: Representative of large-scale excavations associated with major
construction projects or, potentially, archaeological investigations at the site.
PEGs have been identified for each of these modes of intrusion. In each case,
identification of the appropriate PEG had to take into account two main categories of
exposure:
• Type A: Individuals involved directly or indirectly in the activity giving rise to
the intrusion;
• Type B: Site inhabitants exposed to wastes dispersed on the site as a
consequence of the intrusion.
In principle, there will be only a single most-exposed PEG for each mode of intrusion.
However, in practice, without undertaking specific calculations, it is not always
possible to determine whether the most exposed PEG will be the intruder, an associate
or a site inhabitant. For this reason, potential PEGs for each type of exposure were
defined for generalised large intrusions. For generalised small and medium
intrusions, it was clear that Type A dominates so only this type of exposure has been
addressed. The characteristics of the site inhabitant PEG were also considered
appropriate to an agricultural smallholder making use of the cap area.
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5.
References
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Byrom, J, Robinson, C, Simmonds, J R, Walters, B and Taylor, R R, 1995, Food
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Clyne, F, McTaggart, K and Tipple, J, 2004, Radiological Habits Survey: Sellafield,
2003, CEFAS, Lowestoft, Suffolk, UK.
Defra, 2006, Drigg Review Decision Document.
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