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Thames Water WRMP19 Resource Options
Fine Screening Report Update
September 2016
Thames Water Utilities Ltd
356236 WCD WAM 40 A
PiMS/356236/Documents
30 August 2016
Thames Water WRMP19 Resource Options
Fine Screening Report Update
Thames Water WRMP19 Resource Options
Fine Screening Report Update
September 2016
Thames Water Utilities Ltd
Clearwater Court, Vastern Rd, Reading, West Berkshire, RG1 8DB
Mott MacDonald, 22 Station Road, Cambridge CB1 2JD, United Kingdom
T +44 (0)1223 463500 F +44 (0)1223 461007 W www.mottmac.com
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Revision Date Originator Checker Approver Description
02 30 September 2016 Ania Bujnowicz Bill Hume Smith
Wendy Kilmurray Bill Hume Smith Draft for stakeholder comment
Issue and revision record
Information class: Secure
This report has been prepared solely for use by the party which commissioned it (the ‘Client’) in connection with the captioned project. It should not be used for any other purpose. No person other than the Client or any party who has expressly agreed terms of reliance with us (the ‘Recipient(s)’) may rely on the content, information or any views expressed in the report. We accept no duty of care, responsibility or liability to any other recipient of this document. This report is confidential and contains proprietary intellectual property.
No representation, warranty or undertaking, express or implied, is made and no responsibility or liability is accepted by us to any party other than the Client or any Recipient(s), as to the accuracy or completeness of the information contained in this report. For the avoidance of doubt this report does not in any way purport to include any legal, insurance or financial advice or opinion.
We disclaim all and any liability whether arising in tort or contract or otherwise which it might otherwise have to any party other than the Client or the Recipient(s), in respect of this report, or any information attributed to it.
We accept no responsibility for any error or omission in the report which is due to an error or omission in data, information or statements supplied to us by other parties including the client (‘Data’). We have not independently verified such Data and have assumed it to be accurate, complete, reliable and current as of the date of such information.
Forecasts presented in this document were prepared using Data and the report is dependent or based on Data. Inevitably, some of the assumptions used to develop the forecasts will not be realised and unanticipated events and circumstances may occur. Consequently Mott MacDonald does not guarantee or warrant the conclusions contained in the report as there are likely to be differences between the forecasts and the actual results and those differences may be material. While we consider that the information and opinions given in this report are sound all parties must rely on their own skill and judgement when making use of it.
Under no circumstances may this report or any extract or summary thereof be used in connection with any public or private securities offering including any related memorandum or prospectus for any securities offering or stock exchange listing or announcement.
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Chapter Title Page
Executive Summary i
1 Introduction 1
1.1 Background _______________________________________________________________________ 1 1.2 Structure of report___________________________________________________________________ 1 1.3 Stakeholder engagement _____________________________________________________________ 2
2 The water resources context 3
2.1 The TWUL Water Resource Zones _____________________________________________________ 3 2.2 The supply-demand balance situation ___________________________________________________ 3 2.3 London Water Resources Zone ________________________________________________________ 4
3 Approach to screening and appraisal 7
3.1 Overview of four-phased approach _____________________________________________________ 7 3.2 Changes in approach between Phase 1 and Phase 2 _______________________________________ 9 3.3 Generic list of options ________________________________________________________________ 9 3.4 Feasibility assessments ______________________________________________________________ 9 3.5 Cross-option studies ________________________________________________________________ 10 3.5.1 Water treatment cross option study ____________________________________________________ 10 3.5.2 Treatment technology _______________________________________________________________ 10 3.5.3 Network reinforcement cross option study _______________________________________________ 12 3.5.4 Raw water system cross option study __________________________________________________ 12 3.5.5 Operational philosophy ______________________________________________________________ 12 3.5.6 System Strategy ___________________________________________________________________ 13 3.6 Fine screening ____________________________________________________________________ 14 3.6.1 Environment & social dimension ______________________________________________________ 15 3.6.2 Cost dimension ____________________________________________________________________ 18 3.6.3 Promotability dimension _____________________________________________________________ 24 3.6.4 Flexibility dimension ________________________________________________________________ 26 3.6.5 Deliverability dimension _____________________________________________________________ 29 3.6.6 Resilience dimension _______________________________________________________________ 30 3.6.7 Screening decisions ________________________________________________________________ 34
4 Generic screening of resource management options 35
4.1 Generic option screening ____________________________________________________________ 35
5 London WRZ resource options 37
5.1 Resource option types ______________________________________________________________ 37 5.2 Feasibility report findings ____________________________________________________________ 37 5.2.1 Water reuse ______________________________________________________________________ 37 5.2.2 New reservoirs ____________________________________________________________________ 40 5.2.3 Raw water transfers ________________________________________________________________ 45 5.2.4 Desalination ______________________________________________________________________ 49 5.2.5 Direct river abstraction ______________________________________________________________ 50
Contents
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
5.2.6 Aquifer recharge ___________________________________________________________________ 51 5.2.7 Aquifer storage and recovery _________________________________________________________ 52 5.2.8 Groundwater development ___________________________________________________________ 53 5.2.9 Removal of Deployable Output constraints ______________________________________________ 54 5.3 Exclusivities/Interdependencies _______________________________________________________ 55 5.4 Fine screening assessment __________________________________________________________ 55 5.4.1 Scenario analysis __________________________________________________________________ 57 5.4.2 Rejection reasoning ________________________________________________________________ 59 5.5 Next steps for options passing fine screening ____________________________________________ 61 5.5.1 Deephams reuse __________________________________________________________________ 61 5.5.2 Beckton reuse ____________________________________________________________________ 61 5.5.3 Severn-Thames Transfer ____________________________________________________________ 61 5.5.4 Abingdon reservoir _________________________________________________________________ 62 5.5.5 Teddington direct river abstraction _____________________________________________________ 62 5.5.6 Beckton desalination _______________________________________________________________ 62 5.5.7 Thamesmead desalination ___________________________________________________________ 63 5.6 Next steps required to inform fine screening _____________________________________________ 63
6 SWOX WRZ resource options 64
6.1 Resource option types ______________________________________________________________ 64 6.2 Feasibility report findings ____________________________________________________________ 64 6.2.1 New reservoirs ____________________________________________________________________ 64 6.2.2 Raw water transfers ________________________________________________________________ 64 6.2.3 Direct river abstraction ______________________________________________________________ 64 6.2.4 Aquifer recharge ___________________________________________________________________ 65 6.2.5 Groundwater development ___________________________________________________________ 65 6.2.6 Removal of Deployable Output constraints ______________________________________________ 66 6.2.7 Internal inter-zonal transfers __________________________________________________________ 66 6.3 Exclusivities/Interdependencies _______________________________________________________ 67 6.4 Fine screening assessment __________________________________________________________ 67
7 SWA WRZ resource options 68
7.1 Resource option types ______________________________________________________________ 68 7.2 Feasibility report findings ____________________________________________________________ 68 7.2.1 Aquifer storage and recovery _________________________________________________________ 68 7.2.2 Groundwater development ___________________________________________________________ 68 7.2.3 Release of Deployable Output constraints _______________________________________________ 69 7.3 Exclusivities/Interdependencies _______________________________________________________ 70 7.4 Fine screening assessment __________________________________________________________ 70
8 Henley WRZ resource options 71
8.1 Resource option types ______________________________________________________________ 71 8.2 Feasibility report findings ____________________________________________________________ 71 8.2.1 Groundwater development options _____________________________________________________ 71
9 Guildford WRZ resource options 72
9.1 Resource option types ______________________________________________________________ 72 9.2 Feasibility report findings ____________________________________________________________ 72 9.2.1 Aquifer storage and recovery _________________________________________________________ 72 9.2.2 Groundwater development ___________________________________________________________ 72 9.2.3 Removal of Deployable Output constraints ______________________________________________ 73
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
9.3 Exclusivities/Interdependencies _______________________________________________________ 74 9.4 Fine screening assessment __________________________________________________________ 74
10 Kennet Valley WRZ resource options 75
10.1 Resource option types ______________________________________________________________ 75 10.2 Feasibility report findings ____________________________________________________________ 75 10.2.1 Groundwater development ___________________________________________________________ 75 10.2.2 Removal of Deployable Output constraints ______________________________________________ 76 10.3 Exclusivities/Interdependencies _______________________________________________________ 76 10.4 Fine screening assessment __________________________________________________________ 77
11 Conclusions 78
11.1 Screening summary ________________________________________________________________ 78 11.2 Constrained list ____________________________________________________________________ 79 11.3 Next steps _______________________________________________________________________ 81
Appendices 82
Appendix A. Summary of water quality modelling ____________________________________________________ 83 A.1 Beckton Re-use ___________________________________________________________________ 83 A.2 Deephams Re-use _________________________________________________________________ 84 A.3 Mogden Re-use ___________________________________________________________________ 84 A.4 Teddington Direct River Abstraction ____________________________________________________ 85 Appendix B. London WRZ fine screening tables ____________________________________________________ 86 Appendix C. Optimism bias & uncertainty __________________________________________________________ 92
i 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Introduction
This report describes the updated fine screening for resource options that has
been conducted. The report builds on the fine screening methodology and initial
fine screening assessment undertaken in Phase 1. The Phase 1 work also
identified a number of investigations required to inform the decision making
process. In many cases these Phase 2 investigations have been incorporated
into a set of feasibility assessments for each resource option type and into a
number of cross-option studies. The feasibility methodology is consistent with
other similar recent feasibility studies carried out by Thames Water for the
Thames Tideway scheme and for the Deephams sewage treatment works
upgrade. The approach also aligns to methods of site selection and feasibility
assessments that are now widely applied by other organisations for major
infrastructure schemes.
Figure S.1: Overview of reporting and documentation
Dra
ft
WR
MP
Fin
e sc
ree
nin
g
rep
ort
up
dat
e
Fin
e sc
ree
nin
g
rep
ort
up
dat
e
Resilience assessments
Environmental performance
Bottom up risk and updated cost
WRMP19 rejection register
Pro
gra
mm
e
ap
pra
isa
lMethodology reports
Option feasibility
reports
Cross option investment
needs
Year 1 Sept 2015 -
June 2016Year 2 July 2016 -
March 2017
Pre
ferr
ed
pro
gra
mm
e
From Phase 1:
Co
nc
ep
tua
l d
es
ign
rep
ort
fo
r
co
nstr
ain
ed
lis
t
Co
nstr
ain
ed
list o
f
optio
ns
Sc
ree
nin
g r
ep
ort
March 2017 –
Dec 2017
Ad
va
nc
ed
pro
gra
mm
e
inve
sti
gati
on
s
WRMP14
options
Screening
methodology
Option
investigation
needs
New options
3rd party
options
Executive Summary
ii 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
The information from these studies feeds into the updating of the fine screening
report which generates the Constrained List of options that feeds into the
WRMP19 programme appraisal. Figure S.1 illustrates these different stages.
Fine screening summary
This report, provides an update on the current fine screening position, focusing in
particular on the London Water Resource Zone (WRZ). A summary of the fine
screening status of those options identified on the Feasible List from the feasibility
reports can be found in Table S.1.
Table S.1: Fine screening summary for specific options
Fine screening for the Thames Valley Water Resource Zones has not been
updated at this stage pending:
Completion of the groundwater feasibility report
Completion of the inter-zonal transfers feasibility report
Finalisation of the raw water transfers feasibility report, particularly in
relation to the Canal & River Trust (CRT) canal transfer options
The fine screening report will be finalised once all of the feasibility reports have
been completed.
Size Band (Ml/d)
Option Comment
LondonReuse - Beckton Develop conceptual design for 100, 200 and 300Ml/d options
Reuse - Mogden Mutually exclusive w ith DRA Teddington
Reuse - Deephams Develop conceptual design for option to prove reuse technology concept
Reuse - Crossness Screened out on cost and not expected to be needed in planning period
Reuse - Mogden South Sew er Mutually exclusive w ith DRA Teddington
RWT - STT Deerhurst Develop 300 Ml/d transfer option at conceptual design
New Reservoir - Abingdon Develop conceptual design for 2 phase and single phase options (excl. 30 and 50Mm3)
New Reservoir - Chinnor Excessively costly compared to reuse, desalination and Abingdon reservoir
New Reservoir - Marsh Gibbon Excessively costly compared to reuse, desalination and Abingdon reservoir
DRA - River Lee Screened out due to uncertainty around w ater quality and yield
DRA - Teddington Develop concept design for 300Ml/d option. Assessment of navigational impact needed.
Desalination - Beckton Develop conceptual design for 150Ml/d option
Desalination - Crossness Screened out due to resilience and operability concerns
Desalination - Thamesmead Develop phased option connecting into Beckton desalination conveyance
Key
Screened out at f ine screening
Passes fine screening onto Constrained List
Fine screening TBC
0 25 75 125 175 225 275
iii 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Preliminary Constrained List
A preliminary view of the constrained list for the resource options is provided in
Table S.2 for the London Water Resources Zone (WRZ). The list only includes
options that have passed the fine screening and not those where decisions have
still to be confirmed.
For the large scale options the constrained list breaks the options into system
elements (see examples in Figure S.2). The reason for doing this is that the
information is not currently available to choose the optimal phasing of the different
system elements now.
Figure S.2: Separating options into system elements
The key data on the projected deficits and the drivers for the deficits (whether
growth, sustainability reductions or resilience) will not be available until 2017.
Once this information is available it will be possible to identify the optimal
combination of the different system elements.
Treated water
system
Water
Reuse
Desalination
New
Reservoir
Severn-
Thames
Transfer
Reuse
plant
WTW London
Ring Main
Desal
plant London
Ring Main
Resource Conveyance Raw water
system
Treatment
WTW London
Ring Main
WTW London
Ring Main
River regulation
London raw
water storage
London raw
water storage
London raw
water storage
iv 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Next steps
Further work is required in a number of areas to finalise the WRMP19 Constrained
List including:
Complete groundwater and catchment management feasibility reports and
incorporate into fine screening
Complete inter-zonal transfers feasibility report once WRMP19 demand
forecasts are available and incorporate findings into fine screening (includes
inter-company treated water transfers)
Incorporate findings from raw water transfers feasibility report for options whose
status has still to be confirmed (including CRT canal transfer options)
Complete investigation into reinforcements required to the raw water system in
the Rivers Thames and Lee
Complete investigation into an alternative site to the existing Coppermills water
treatment works for a new water treatment works in east London
For options included on the Constrained List the following next steps are planned:
1. Complete conceptual design reports, building on and updating WRMP14
dossiers where these exist
2. Undertake Strategic Environmental Assessment, Habitats Directive and Water
Framework Directive assessments of the Constrained List options
3. Update cost estimates for conceptual design
4. Undertake bottom-up assessment of risk
5. Use the above information to inform cost, deliverability and environmental
metrics to feed into programme appraisal
In addition to the general next steps associated with options on the Constrained
List, there are also a number of key next steps to address uncertainties
associated with specific options:
a. Progress negotiations and reach agreement in principle on terms for bulk
supply agreements (particularly for Severn-Thames Transfer resources)
b. Confirm process, timescales and nature of changes needed to the existing
River Severn regulation for the supported Severn-Thames Transfer options
c. Undertake hydro-dynamic modelling for Teddington DRA option to confirm
discharge location and extent of navigational impacts to inform engagement
with Port of London Authority and Environment Agency.
v 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Table S.2: Preliminary Constrained List for London WRZ
Option Resource Element Conveyance Element Raw Treatment Element Network Element
Type Location Nominal Nominal Location Nominal Location Nominal
Capacity
Ml/d
Capacity
Ml/d
Capacity
Ml/d
Capacity
Ml/d
Indirect water
reuse
Deephams 60 Deephams to
King George V
Intake
60 TBC East London
Treatment
60
100*3
See network reinforcement matrix
Beckton 100
200
300
Beckton to King
George V Intake
300
Raw Vyrnwy 180 Deerhurst to 300 TBC Kempton 100*3 See network reinforcement matrix
Water Minworth 88 Radcot
Transfer Draycote 25
Mythe 15
Desalination Beckton 150 N/A N/A N/A See network reinforcement matrix, plus
Thamesmead 300 Beckton to Coppermills 450
New Abingdon 75Mm3 153 N/A TBC Kempton 300 See network reinforcement matrix
Reservoir Abingdon 100Mm3 204 150
Abingdon 125Mm3 247 100
Abingdon 150Mm3 287
Abingdon 30+ approx 90Mm3 59+179
Abingdon 70+ approx 50Mm3 145+93
Direct River
Abstraction
Teddington Weir (Mogden effluent transfer) 300 Teddington to
Thames-Lee
tunnel shaft
300 Kempton /
East London
TBC See network reinforcement matrix
Water
System
Location
Thames Water WRMP19 Resource Options Fine Screening Report Update
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
1
Chapter 1 provides an introduction to the purpose of this report and its structure.
1.1 Background
Thames Water (TWUL) published its last Water Resources Management Plan (WRMP) in August 2014
(WRMP14) following approval from Defra. The plan sets out the need for development of new resources.
Since then TWUL has been carrying out detailed work to review and identify the best value resource
options to ensure a secure supply of water in the future.
A four phase programme has been developed to reduce uncertainties and update options for the next
WRMP in 2019 (WRMP19). Mott MacDonald, working in partnership with Cascade Consulting, completed
Phase 1 of the work programme; the investigations and findings were described in two reports published in
May 20151 and November 2015
2 covering the screening of large
3 and small resource options respectively.
The objective of Phase 1 was to reduce the number of resource options carried forward from the WRMP14
constrained list, including reviewing any rejected options, and to better target Phase 2 investigations by
focusing on uncertainties and risks that are material to option selection.
This report updates the Phase 1 screening reports to take account of progress with the Phase 2
programme of investigations. It is intended that the Fine Screening Report will cover all resource option
sizes, combining the two separate reports that were issued in Phase 1. However, the groundwater, inter-
zonal transfer and catchment management feasibility studies are ongoing and these reports are needed to
complete the fine screening for the Thames Valley Water Resources Zones. A further update is therefore
now planned for December 2016 once the remaining feasibility studies have been completed.
The scope of the report includes resource options to increase supplies. Demand management options
(e.g. metering and water efficiency) are covered in a separate screening report.
1.2 Structure of report
The report is structured as follows:
Chapter 1: sets out the purpose of the report and background;
Chapter 2: provides an introduction to the water resources situation;
Chapter 3: sets out the approach to screening and appraisal being followed, including any changes
in approach from the Phase 1 work;
Chapter 4: describes the review of generic option types that has fed into the specific option
development;
Chapters 5 to 10: describe the feasibility assessment and fine screening assessment for each
Water Resources Zone (WRZ) in turn;
1 Development of large scale water resource options. Option screening report. May 2015.
2 Development of small scale water resource options. Option screening report. November 2015.
3 Large options were defined as those with a Deployable Output above 50Ml/d
1 Introduction
Thames Water WRMP19 Resource Options Fine Screening Report Update
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
2
1.3 Stakeholder engagement
The Phase 1 resource option screening reports on small and large options were shared with stakeholders
and published on Thames Water’s website. The reports were presented to the water resources
Stakeholder Technical Group on 26 March 2015 (for large options) and on 13 July 2015 for small options.
Comments received from stakeholders were either directly addressed in revised reports or incorporated
into the Phase 2 investigation programme.
Feedback is invited on this report in writing to [email protected] by the end of October 2016.
Key findings from the report will also be presented to stakeholders at the forthcoming Technical
Stakeholder Meeting on 6 October 2016.
Thames Water WRMP19 Resource Options Fine Screening Report Update
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
3
Chapter 2 provides a brief introduction to the TWUL water resources situation.
2.1 The TWUL Water Resource Zones
The TWUL water supply area is divided into six WRZs: London, Swindon and Oxfordshire (SWOX),
Henley, Kennet Valley (KV), Slough, Wycombe and Aylesbury (SWA), and Guildford. A geographic
overview of these WRZs can be found below in Figure 2.1.
Figure 2.1: TWUL Water Resource Zones
Source: Thames Water (Figure A1, Appendix A, Final Draft Drought Plan March 2013)
2.2 The supply-demand balance situation
TWUL’s WRMP14 for the period 2015 to 2040 identified a large and increasing baseline supply demand
deficit in the London WRZ and baseline deficits in the mid-long term in the Swindon and Oxfordshire
(SWOX), Slough, Wycombe and Aylesbury (SWA) and Guildford zones. The Henley and Kennet Valley
zones remained in surplus throughout the 25 year planning period. The forecast deficit in London was
2 The water resources context
Thames Water WRMP19 Resource Options Fine Screening Report Update
356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
4
driven by a combination of population growth and climate change impacts. These also drove the SWOX
deficit with the addition of sustainability reductions4, which are reductions in licensed abstraction for
environmental benefit. Deficits for SWOX, SWA and Guildford were forecast in the Average Day Peak
Week scenario (ADPW)5. For SWOX deficits were also forecast in the Dry Year Annual Average scenario
(DYAA)6, but of smaller magnitude than the ADPW deficit. For London the deficit was forecast in the Dry
Year Annual Average scenario only.
For the 2019 WRMP the planning guidelines require that the planning period should be appropriate to the
risks of the company, but should cover at least the statutory minimum period of 25 years. Thames Water
has applied the problem characterisation step of the UKWIR decision making process guidance and
concluded that the scale and complexity of the problem for the London and SWOX WRZs justifies
developing the plan using a longer planning period of potentially up to 80 years to 2100, but that for the
other Thames Valley WRZs planning over a 25 year planning horizon will be sufficient.
Thames Water has work ongoing to develop updated demand forecasts for WRMP19. For the purposes of
fine screening a nominal deficit of 800Ml/d in the London WRZ has been agreed with Thames water. This
is to ensure that sufficient options are available at the programme appraisal stage under a range of future
scenarios. As well as allowing for the examination of a longer planning period of up to 80 years, this will
also facilitate the potential provision of water resource options to other WRSE companies (Affinity Water,
South East Water and Sutton & East Surrey Water). Affinity Water has requested Thames Water to
include for up to 100Ml/d of raw water supply from the River Thames as part of its planning process. South
East Water has also identified a potential requirement for additional raw water from the River Thames at
Bray.
Work is ongoing reviewing the future supply-demand position in the Thames Valley. Over the 80 year
planning horizon for SWOX a substantial deficit is anticipated over and above the 2040 ADPW baseline
deficit of 32Ml/d envisaged at WRMP14.
2.3 London Water Resources Zone
A geographic overview of the London WRZ can be found in Figure 2.2 below. The London WRZ is supplied
primarily (80%) from the River Thames and River Lee via storage reservoirs. The quantities that can be
abstracted from the River Thames depend on the relationship between the quantities stored in the
reservoirs, the need to ensure a residual freshwater flow in the River Thames over Teddington weir, and
the time of year. This is governed by the formal operating agreement between Thames Water and the
Environment Agency (EA) under Section 20 of the Water Resources Act 1991, called the Lower Thames
Operating Agreement (LTOA).
The remainder of supply is made up of groundwater abstractions, particularly from the chalk aquifer. In
addition, the Thames Gateway desalination plant at Beckton can abstract and treat brackish estuarine
water from the Thames Estuary.
4 Thames Water (2014) Chapter 6: Final Water Resources Management Plan.
5 Average Day Peak Week (ADPW) is one seventh of total demand or deployable output in the peak week in any 12 month
accounting period (ADPW).
6 Dry Year Annual Average (DYAA) is the annual average value of demand, deployable output or some other quantity over the course
of a dry year.
Thames Water WRMP19 Resource Options Fine Screening Report Update
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5
Treated water is conveyed to an integrated distribution system, a key feature of which is the Thames Water
London Ring Main which runs underneath central London and provides flexibility by connecting the
Thames and Lee systems. The Thames–Lee tunnel also connects the two systems on the raw water side.
There are various bulk supply imports and exports to the London WRZ, with the principal exports relating
to bulk supplies to Essex and Suffolk Water and Affinity Water.
6 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Figure 2.2: Principle features of the Thames Water London Water Resources Zone
Source: Thames Water/Mott MacDonald/Cascade
Thames Water Intakes
Thames Water Pumping Stations
Gauging Stations
Affinity Intakes
Datchet
Intake
Wraysbury
King
George
VI
Staines
Nth
Island
BarnSurbiton
intake
Ashford
Common
WTW Hampton
WTW
River Ash
River Wey
River Mole
Hogsmill
River
Laleham
Intake
Wraysbury
Intake
Teddington
Weir
Wraysbury River,
River Colne &
Colne Brook
Queen
Mary
Staines
South
BessboroughKnight
Littleton
PS
Datchet
PS
Staines PS
Old
Windsor
Weir
Bell
Weir
Penton Hook
Weir
Chertsey
Weir
Shepperton
Weirs
Molesey
Weirs
Windsor
Park GS
Staines
GS Kingston GS
Egham
Intake
Sunnymeads
Intake
Chertsey
Intake
Walton
Intake
River Brent
Beverley
Brook
River
Wandle
River Lee
Ravensbourne
River
Abbey Mills PS
Hogsmill
STW
Beckton
STW
Thames Barrier
River
Roding
Richmond
Half-Tide
Sluice
Hampton
Intake
London Ring Main
Lee Valley
Reservoirs
London Ring Main Shaft
Mogden
STW
Kempton
Park
WTW
Honor OakBrixton
Barrow Hill
Stoke
Newington
New
River
Head
Kew
Raynes
Park
Merton
Streatham
Holland Park
Avenue
Barnes
Queen
Mother
Map: Existing sources
William
Girling
King
George’s
Banbury
Coppermills
WTW
Deephams
STW
Queen
Elizabeth II
Sunbury
Weirs
Walton
GS
Walton Intake,
PS & WTW
Battersea
Park
Lane Crossness
STW
Riverside
STW
Longreach
STW
Beddington
STW
Chingford South
WTW
Sewage treatment works
Water treatment works
Raw water storage
Hornsey
WTW
Thames Water WRMP19 Resource Options Fine Screening Report Update
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7
3 Approach to screening and appraisal
Chapter 3 provides an overview of the four phase approach to development of
new resources for Thames Water. It then focuses in more detail on the fine
screening stage, which is the focus of Phase 2.
3.1 Overview of four-phased approach
An overview of the four-phase approach to reviewing and assessing options in the run up to WRMP19 is
shown in Figure 3.1. The four phases comprise:
Phase 1 – Option review and screening: The objective of Phase 1 was to reduce the number of
options carried forward and to better target Phase 2 investigations by focusing on uncertainties and
risks that are material to option selection.
Phase 2 – Detailed investigations: In Phase 2, targeted detailed investigations are being
undertaken to reduce uncertainties around identification of the best value options. The
investigations identified in Phase 1 have been grouped into a series of feasibility reports and cross-
option studies including:
– Raw water transfer feasibility report
– Groundwater feasibility report
– New reservoirs feasibility report
– Water reuse feasibility report
– Desalination feasibility report
– Direct river abstraction feasibility report
– Catchment management feasibility report
– Water treatment cross-option study
– Network reinforcement cross-option study
– Raw water system cross-option study
– Inter-zonal transfer study
– 3rd
party options report
As these investigations are completed the fine screening process will be re-applied to continually
improve understanding and reduce, as far as possible, uncertainties associated with the options.
The output of the fine screening report is the Constrained List of options that will continue to
conceptual design and programme appraisal in Phase 3.
Phase 3 – Programme appraisal: In Phase 3, the state of knowledge will improve again as new
supply/demand forecasts will become available. Conceptual design reports will be prepared for
options on the Constrained List, costs will be updated and bottom-up risk assessment will be
developed. Options on the Constrained List will be subject to economic, social and environmental
appraisal to determine the best value solutions, taking account of future scenarios.
Phase 4 – Scheme selection, outline design and planning: Depending upon the supply/demand
forecast in WRMP19 Phase 4 would then entail selection of the preferred options and progression
through to outline design and planning.
It is important that by the time Phase 4 is being progressed in 2018/19 that all screening decisions are
justified, based on the state of knowledge of the options at that time (not the earlier date when the
screening decision was first made).
8 356236/WCD/WAM/40/02 30 September 2016 Phase 1a Option Screening Report RevF.docx
Thames Water WRMP19 Resource Options Fine Screening Report Update
Figure 3.1: Phase 2 in relation to the proposed wider appraisal process
Phase 4 – TW
Outline design of 1/2 options
for planning application
Generic
options
list
OJEU
Others
Detailed costs &
benefits
June
2014May
2015
Sept
2016
December
2017March
2019
Scheme selection
(potentially including
Leading edge decision
making methodologies)EBSD Modelling
Confirm planning
problem
Supply and demand
forecasts
WRMP19 test run Draft WRMP19 Final WRMP19
Planning
Outline design
Timeline:
Large supply
options (50Ml/d+):
Other supply
options (0-50Ml/d):
Phase 2 – MM/Cascade
Detailed investigations to improve
confidence in scope, delivery,
environmental impacts and benefitsPhase 3 – TW
Refresh data on options
and conduct programme
appraisal
Phase 1 – MM/Cascade
• Review PR14 methodology
• Develop screening process
• Refine options with recommendations for
further investigations
Phase 2 – MM/Cascade
Detailed investigations to
improve confidence of
options for WRMP19
AMP7 Early work
TBC following phase 2
work
Engage on appraisal criteria and Phase 1
option screening
Stakeholder
engagementEngage on detailed studies &
impact on option set
Engage on WRMP19 &
preferred programme
Government
Review & Decision
WRMP19 Constrained List
WRMP19 Fine Screening
WRMP19 Rejection Register
Investigation
Requirements
WRMP14
Options
Phase 1 Phase 2 Phase 3 Phase 4
WRSE/EA
Phase 1A – TW & MM/Cascade
• Review PR14 constrained list
• Refine options with recommendations
for further investigations
Generic
screening
Feasibility assessments for
each option type to reduce
uncertainty and inform
decisions
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The focus of this report is on Phase 2. The following sections describe each of the stages of Phase 2 in
more detail.
3.2 Changes in approach between Phase 1 and Phase 2
There have been several changes in the fine screening approach since publication of the Phase 1 fine
screening report. These changes are summarised below:
The Phase 1 report included a coarse screening stage for options based upon the screening
criteria used at WRMP14. During Phase 2 a set of feasibility reports have been prepared to
identify specific options for each generic option type carried forward from the initial generic
screening of option types. The feasibility reports include specific options identified at WRMP14,
options proposed by third parties and new options identified. These specific options are then all
subject to a three stage screening process to identify the best specific options of each type to be
carried forward to this fine screening report which compares options between types. The feasibility
reports therefore supersede the coarse screening stage that was included in the Phase 1 screening
report.
The potential change in the planning horizon from 25 to 80 years for London and SWOX, and the
accompanying increase in the size of the planning problem, has necessitated a change in
approach to screening for cost. In Phase 1 the cost benchmark was set based upon the least cost
large scale option, but this is no longer appropriate with a larger planning problem and so an
alternative approach has been developed that is set out in Section 3.6.2.
In Phase 1 small and large options were assessed separately but the intention is that small and
large options will be assessed together in the fine screening report in Phase 2.
3.3 Generic list of options
The starting point for option development is the Generic List of option types (e.g. Reservoirs, Transfers)
referenced in the Water Resources Planning Tools report7. The list has been reviewed to identify option
types that have potential for providing feasible specific options for the Thames Water supply area. This is
discussed further in Section 4 of this report.
3.4 Feasibility assessments
For option types that pass the generic screening, feasibility assessments have been conducted. We have
carried out feasibility assessments for seven generic option types as listed in Section 3.1, that feed into this
report. The feasibility assessments identify specific options for each of the option types carried forward
from the generic list. There are then three stages to the feasibility report screening for the specific options:
Stage 1: options are screened against absolute constraints (pass/fail).
Stage 2: the performance of the options is compared qualitatively against a number of criteria that
differentiate between options of that type.
Stage 3: the performance of the options is assessed in further detail (e.g. including costing).
Further investigations associated with specific options are incorporated into the feasibility assessments,
where applicable.
7 UKWIR (2012), Water Resources Planning Tools 2012, Economics of Balancing Supply and Demand Report (Ref 12/WR/27/6), pp
10-12.
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Options are carried forward from stage 3 of the feasibility assessment into the Feasible List for further fine
screening where:
the option is not compromised by any absolute or key constraints; and
if there is mutual exclusivity between options then only the best performing option will be carried
forward, provided that this assessment can reasonably be made based upon the information
available during the feasibility stage; and
if the total estimated deployable output of resources for a given type in a WRZ exceeds the
indicative deficit for the WRZ over the planning horizon8 then only the best performing options are
carried forward to the Feasible List, provided that this assessment can reasonably be made based
upon the information available at the feasibility stage.
Feasibility reports will be updated where there is material change in assumptions that has potential to
impact on decisions.
3.5 Cross-option studies
The Phase 1 report identified the need to take account of network reinforcement and water treatment costs
when comparing options. Subsequently it has been identified that further work is needed to consider
reinforcement requirements on the raw water system and support has been provided to Thames Water on
the treatment of water for discharge back into the environment (for reuse and transfer options).
3.5.1 Water treatment cross option study
Work is ongoing by Thames Water reviewing the resilience of treatment capability in the London WRZ, but
following preliminary findings, it has been assumed that new resource options for London will require
additional treatment capacity (except in the case of desalination which produces potable water). A cross-
option study has been undertaken considering sites for additional treatment. Two sites have been
identified in London:
Kempton WTW for additional resources from the west (e.g. Upper Thames Reservoir, Severn-
Thames Transfer, Mogden reuse)
Coppermills WTW for additional resources from the East (e.g. Beckton and Deephams reuse) –
this would entail redevelopment of the existing works as there is no further space on the existing
site. Alternative sites to Coppermills in east London are also being investigated.
These additional treatment requirements have been included in the costings in this report for options that
augment raw water resources for the London WRZ.
3.5.2 Treatment technology
A key question to be addressed is the level of treatment required for water reuse. For the feasibility reports
a provisional assumption was made that planned water re-use would be indirect (i.e. that sewage would be
subject to advanced treatment, conveyed upstream and discharged into the environment before being re-
abstracted through existing intakes for further water treatment and supply). The technologies provisionally
assumed in the feasibility report were those selected at WRMP14:
For untreated “black water” options: advanced primary + aeration + membrane bio-reactor +
granular activated carbon
8 Planning horizon of 80 years for London and SWOX has been assumed and 25 years for other Water Resource Zones
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For sewage treatment works final effluent water options: microfiltration + reverse osmosis +
advanced oxidation process
The WRMP14 technologies were used for the feasibility report pending further work on technology
selection in two areas:
1. Modelling of water quality required to prevent material deterioration in the receiving water;
2. A review of risk from parameters of emerging concern to ensure provision of wholesome water.
3.5.2.1 Water quality modelling
The water quality modelling exercise has used available water quality data, to assess the required product
water quality based on the requirements of the receiving waters that discharges are being made to. Two
alternative treatment schemes have been considered for treatment of sewage treatment works effluent:
Scheme 1: Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process
Scheme 2: Ferric + Nitrifying Sand Filter + Ozone / GAC + Ion exchange
Scheme 1 is comprehensive and addresses all parameters considered, across all prioritisations and flows.
A variant of Scheme 1 that is under consideration is a Membrane Bio-Reactor (MBR) process (that
combines the activated sludge process with the ultrafiltration membrane process into a single process
treating settled sewage) instead of the Ultrafiltration membrane process (that would treat final effluent).
Scheme 2 is more selective, treating just those parameters that are considered to be high priority. The
analysis suggests that for reuse at Beckton Scheme 2 is also only effective up to discharge flows of
150 Ml/d: above this flow this treatment scheme would not be effective and Scheme 1 would be required.
A more detailed summary of the findings to date from this work can be found in Appendix A.
3.5.2.2 Review of risk from parameters of emerging concern
Thames Water manages risks to drinking water through the Drinking Water Safety Plan process (DWSP)
which is continually evolving. Of particular concern are the increased risk to water wholesomeness from
human transmitted disease (e.g. viruses and pathogens) and chemicals of emerging concern (e.g.
pharmaceuticals and personal care products). These risks cannot be controlled by source control
measures such as those used for industrial discharges. Thames Water is also cognisant that the means of
quantifying virus and pathogens risks is an emerging science and one that it is supporting through its reuse
research programme, that is expected to feed into changes to Thames Water’s future approaches and
enhancements to the Drinking Water Safety Plan process. Thames Water is committed to increasing the
resources available to its DWSP team to implement improved monitoring based on the insights obtained
from its research. This will no doubt in turn drive innovation in the field of cost effective control measures.
Thames Water proposes a precautionary, but adaptive, approach to implementing planned water reuse
that will also provide information on effectiveness of control measures for parameters of emerging concern.
The precautionary-adaptive approach involves initially implementing an intensive process (including
Reverse Osmosis) that can subsequently be adapted to follow any of three future pathways:
1. The plant is effective and water quality results demonstrate that the processes is suitable for direct
potable reuse plant through the addition of a chemical conditioning system
2. The plant is effective and water quality results demonstrate that the processes are all needed, but
concerns remain around direct reuse and so the plant continues as an indirect reuse scheme
3. The plant is effective and water quality results and associated pilot trials demonstrate that a lower
energy indirect reuse system is feasible (e.g. excluding Reverse Osmosis).
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Building upon previous and ongoing pilot trials, there would be benefit from applying this precautionary-
adaptive approach initially on a small-medium scale reuse plant so that the learning can be maximised
before deploying large scale water reuse.
3.5.3 Network reinforcement cross option study
A cross-option study has also been undertaken to identify network reinforcement requirements for London.
The report has found that reinforcements to the Thames Water Ring Main are required, but that the timing
is dependent on the options chosen whether they are entering the network in East or West London. Two
extensions have been identified:
1. West London: TWRM Hampton to Battersea Extension
2. East London: TWRM Coppermills to Honor Oak Extension
The matrix in Figure 3.2 shows whether one, other or both of these reinforcements are required for
different combinations of new resources – depending upon whether the new resources are brought in to
the west or the east of the existing TWRM. It can be seen that initially no new reinforcement is required.
For the purpose of costing options in this fine screening report, ring main costs have been proportionally
allocated to resource options assuming a notional ring main extension capacity of 800Ml/d.
Figure 3.2: Matrix showing TWRM reinforcement requirements for additional resource in East or West
3.5.4 Raw water system cross option study
A further study is being prepared considering what reinforcements to the raw water system (between the
point of abstraction and the WTW inlet) are required for the different resource options. This study is
dependent upon ongoing work developing models of the raw water system for the River Thames
abstractions and River Lee abstractions. This is of particular relevance for options that augment resources
in the River Thames or the River Lee (including new reservoir options, raw water transfers and effluent
reuse).
3.5.5 Operational philosophy
A cross-option study has also been undertaken to provide an operational philosophy for new water
resource options, to support minimum and maximum utilisation scenarios and contribute to developing
We
st
East
0 100 200 300 400 500 600 700 800
0 - - 2 2 2 2 2 2 2
100 - - 1, 2 1, 2 1, 2 1, 2 2 2
200 1 1 1 1, 2 1, 2 1, 2 1, 2
300 1 1 1 1, 2 1, 2 1, 2
400 1 1 1, 2 1, 2 1, 2
500 1, 2 1, 2 1, 2 1, 2
600 1, 2 1, 2 1, 2
700 1, 2 1, 2
800 1, 2
1. TWRM Hampton to Battersea Extension 2. TWRM Coppermills to Honor Oak Extension
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robust operating cost estimates for all major option types (desalination, wastewater reuse, raw water
transfers and reservoirs).
The working paper has considered the impacts of different operational modes on the different options
being considered under the WRMP19 programme. This work has identified that there are essentially four
possible operational modes for the options under consideration (although not all modes are applicable to
all options). These operational modes are:
Full Operation – Normal scheme operation between the minimum operational condition and full
operation.
Hot Standby – Under this mode the facility would be held at (typically) the minimum operational
condition with most / all facilities available. The scheme could be returned to full operation in a very
short time (such as a day)
Cold Standby - Under this mode the facility would be in a partial shutdown condition with only some
facilities available. The scheme could be returned to normal operation in a moderate time (say a few
days / weeks)
Mothballed – Under this mode the facilities are essentially shutdown, with only a minimal amount of
equipment operational (heating, lighting, etc.). Returning the scheme to service could be an extended
and complex process similar to commissioning the scheme from new, though it may be simpler.
This paper has developed a description of each option and the operational modes that are applicable.
Based on this description the estimates of the potential operating costs have been developed and a high
level qualitative risk assessment has been prepared.
3.5.6 System Strategy
The cross option studies consider the investment requirements and operating philosophy of individual
system elements. Figure 3.3 illustrates how these system elements combine to provide an individual water
resources option.
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Figure 3.3: Seperation options into system elements
Consideration is needed as to how the new resource options would operate in conjunction with the existing
supply system (from resource to water distribution) and with other new options. This may identify new
dependencies that need to be taken into account in programme appraisal.
It is therefore proposed that a system strategy will be developed that draws together the cross option
studies and considers alternative combinations of resource options and their implications for system design
and operation.
3.6 Fine screening
The options that pass Stage 3 of the feasibility assessments form the “Feasible List”. These options are
then subjected to a further ‘fine screening’ stage which will lead to the production of the “Constrained List”
of options which will be further developed before programme appraisal. The fine screening brings together
all resource option types and compares them using a consistent set of criteria. Where options are rejected
an explanation is provided in the report and they will also be compiled in a Rejection Register.
The fine screening process will compare options within each WRZ. The proposed fine screening approach
combines quantitative analysis of costs with qualitative analysis of other dimensions. A set of six
dimensions were developed for fine screening during Phase 1 of the project – these are shown in Figure
3.4 which illustrates the different stages in the project lifecycle that the dimensions relate to.
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Figure 3.4: Mapping of six fine screening dimensions to project lifecycle
Time
Option Development Construction Operation
Environment & Social
Pla
nn
ing
pe
rmis
sio
n g
ran
ted
✔
Co
mm
iss
ion
ing
✔
Cost ✔ ✔
Promotability ✔
Deliverability ✔
Flexibility ✔ ✔
Resilience ✔
All options that pass the generic screening have been assessed against these dimensions to identify
potential benefits/opportunities as well as the dis-benefits/risks for each option. The assessment against
each dimension is categorised and visualised in a summary matrix using the categories shown in Table
3.1. For any one dimension more than one symbol may be needed to capture the nature of the risks and
benefits. For example, under the environmental and social dimension some options (e.g. Cotswold Canals
transfer) may include material dis-benefits during the construction stage, but material benefits during the
operational phase.
Table 3.1: Dimension category definitions
Symbol Meaning Definition
◉ Substantial benefit/opportunity The option has substantial benefits/opportunities either individually or cumulatively.
◎ Material benefit/opportunity The option has some material benefits/opportunities.
- No benefit No benefit identified
○ Neutral The option does not have significant residual effects.
◑(r) Material disbenefit/risk The option has some material residual disbenefits/risks, either individually or cumulatively
●(r) Substantial disbenefit/risk The option has substantial residual disbenefits/risks, either individually or cumulatively
A superscript ‘(r)
’ next to the symbol would highlight that a disbenefit/risk could potentially be reduced to
‘neutral’ by additional development of mitigation measures during detailed design.
Definitions for each of the six fine screening dimensions were developed in Phase 1 and these are set out
below.
3.6.1 Environment & social dimension
3.6.1.1 Dimension description
Environment & Social: The WRMP falls within scope of the Strategic Environmental Assessment (SEA)
Directive. Evidence from the SEA, Habitats Regulations Assessment (HRA), and Water Framework
Directive (WFD) Assessment is reviewed into a single indicator of likely environmental effects.
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The SEA process promotes consideration of a wide range of environmental and social effects, requires
full assessment of options making up the WRMP and helps identify potential cumulative effects with
other plans and programmes. The SEA is informed by the HRA and WFD Assessment.
The WRMP is also subject to HRA to assess for likely significant effects on one or more European
sites.
The assessment of option effects on water body status is also undertaken as required by the WFD and
the EA Water Resources Planning Guideline (WRPG).
3.6.1.2 Discussion
For the Environmental and Social fine screening assessment of options on the WRMP14 constrained list,
the process largely involved the consideration of the existing set of comprehensive information and
assessment held within the SEA. This includes the HRA and WFD assessments which the SEA draws on.
For new options, screening of key issues in relation to SEA, HRA and WFD was carried out using the
same criteria as applied for WRMP14 options.
Strategic Environmental Assessment
The SEA took an objectives-led approach (as recommended in the revised UKWIR Guidance on SEA of
WRMPs and supported by the Environment Agency). A suite of SEA objectives were developed, informed
by key policy messages and environmental protection objectives, as well as the current and future state of
the environment in the study area and key environmental issues identified by the baseline review. The 13
objectives established were as follows:
– Objective 1. To protect and enhance biodiversity, ecological functions, capacity, and habitat
connectivity within Thames Water's supply and source area
– Objective 2. To strengthen the connections between people and nature and realise the value of
biodiversity
– Objective 3. To improve human health and well-being of the area, improve access to recreation
and the environment, and reduce inequalities
– Objective 4. To reduce, and make more efficient, the domestic, industrial and commercial
consumption of resources, minimise the generation of waste, encourage its re-use and eliminate
waste sent to landfill
– Objective 5. To maintain or improve the quality of rivers, lakes, groundwater, estuarine and coastal
waterbodies
– Objective 6. To ensure appropriate and sustainable management of abstractions
– Objective 7. To reduce and manage flood risk
– Objective 8. To increase awareness of water sustainability, its efficient use and the ecosystem
functions which rely on water resources
– Objective 9. To protect and enhance geology, the quality and quantity of soils and promote a
catchment-wide approach to land management
– Objective 10. To reduce air pollutant and greenhouse gas emissions
– Objective 11. To adapt and improve resilience to the threats of climate change
– Objective 12. To conserve and enhance the historic environment, the heritage assets therein and
their setting
– Objective 13. To protect, enhance the quality of, and improve access to designated and
undesignated landscapes, townscapes and the countryside.
Information drawn on for the assessment included engineering designs, outline operating philosophy and
an initial environmental appraisal for each scheme, including a strategic hydrological assessment and
WFD assessment (these are documented in the Thames Water full scheme dossiers (Appendix R of the
WRMP14). In addition, the assessment considered a range of environmental data and constraints
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including designated sites, heritage assets, flood risk zones and planning designations (e.g. green belt and
conservation areas).
An assessment framework was used to record and document the assessment of schemes against the SEA
objectives aided by a set of indicator questions to guide the assessments as illustrated in the two examples
below. The framework was designed to provide a basis for consistent and transparent effects assessment.
The range of objectives and the indicator questions developed resulted in comprehensive assessment of
each option.
Example indicator questions:
Objective 7: To reduce and manage flood risk, which included the indicator question:
Will it avoid reducing flood plain storage, or provide opportunities to improve flood risk management?'
This included hydrological assessment as to the change in flood risk likely to arise from the option, with
reference to the Environment Agency's flood risk zones and consideration of the volumes of
abstraction involved relative to the flood flows in the watercourses concerned.
Objective 4: To reduce, and make more efficient, the domestic, industrial and commercial consumption of
resources, minimise the generation of waste, encourage its re-use and eliminate waste sent to landfill,
which included the following indicator questions:
Will it help to minimise the demand for resources and promote their efficient use (including water e.g.
leakage or large scale inter-company transfers)?
Will it minimise the use of energy and promote energy efficiency or support the use of
sustainable/renewable energy?
Will it make use of existing infrastructure?
Will it help to encourage sustainable design or use of sustainable materials (e.g. supplied from local
resources)?
Will it reduce the amount of waste generated and increase the proportion sent to reuse or recycling?
In this example therefore, in addition to the physical use of material resources and energy, there was also
consideration of the effects of an option on other, potentially less sustainable sources of water.
Completed assessment frameworks for each scheme on the Constrained List were provided in Appendix D
of the SEA (which forms Appendix B of the Final WRMP14). An assessment commentary was provided for
each scheme and the assessment tables concluded by identifying the significance of the residual effect.
Effect significance was assigned according to a seven point scale (Major adverse to Major Beneficial), with
additional categories for 'Uncertain' and 'Mixed' effects.
Habitats Regulations Assessment
The Habitats Regulations implement the Habitats Directive (Council Directive 92/43/EEC) in England and
Wales. As a competent authority, Thames Water must ensure that its WRMP meets the requirements of
the Habitats Regulations prior to implementation. If the WRMP (i.e. one or more schemes within it) may
cause a likely significant effect (LSE) on one or more European sites, either alone or in-combination with
other schemes, plans or projects, the WRMP must be subject to Appropriate Assessment. In accordance
with the Habitats Regulations, Thames Water undertook an HRA of its WRMP.
The HRA process comprises four stages:
Screening, which identifies likely effects, alone or in-combination with other projects or plans, and
considers whether these effects are likely to be significant.
Appropriate assessment.
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Assessment of alternative solutions.
Assessment where no alternatives exist and adverse effects remain.
Screening of the constrained list of options was undertaken and outcomes discussed with Natural England
and Natural Resources Wales via preliminary consultation. Outcomes of the HRA process informed
assessment of the WRMP14 against the SEA objectives.
Water Framework Directive Assessment
In order to fulfil the requirements of Appendix 14 of the WRPG, it was necessary to consider the impact of
the WRMP14 on WFD waterbody status. The WRPG explains that this should include assessment of the
impact of both changes in operation of existing sources (i.e. schemes which enable increased abstractions
under current licences), and new abstractions (requiring new or changed licences). The WRPG
recommends that companies should asses the net impact of changes at a catchment and WRZ level and
demonstrate 'no deterioration' against waterbody status.
The WFD assessment methodology can be found in full in Appendix F of the SEA. The methodology
identifies four objectives to test for the assessment, plus another objective (5) to indicate if the scheme
actually assists with attaining WFD waterbody objectives (listed below). There is no obligation for objective
5 to be met; a 'no' answer to testing of Objective 5 does not indicate that the scheme has an adverse WFD
assessment.
– Objective 1: To prevent deterioration in the ecological status of the waterbody
– Objective 2: To prevent the introduction of impediments to the attainment of Good WFD status or
potential for the waterbody
– Objective 3: To ensure that the attainment of the WFD objectives for the waterbody are not
compromised
– Objective 4: To ensure the achievement of the WFD objectives in other waterbodies within the
same catchment are not permanently excluded or compromised
– Objective 5: To assist the attainment of the WFD objectives for the waterbody.
Following stakeholder feedback on the draft screening report, the WFD assessment has been broadened
to also consider whether an option could support achievement of GES/GEP in another waterbody by
means of offsetting or reducing abstraction from an existing Thames Water source. Additionally,
consideration of the role of catchment management in development of options has been mostly included
within the WFD assessment. However, recognising that catchment management is broader than WFD
delivery, benefits of catchment management to biodiversity and flood risk are considered under their
respective topics.
3.6.2 Cost dimension
3.6.2.1 Dimension description
Cost: Comparison of option Average Incremental Cost + carbon against a benchmark value. The
comparison will consider uncertainty ranges as well as the relative magnitude of point estimates.
3.6.2.2 Approach to costing
Calculation of AIC+carbon has been undertaken using option cost data extracted from Thames Water’s
Asset Planning System (APS). APS generates profiles of fixed and variable capital, operating, and carbon
costs.
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The APS inputs include:
Capital cost estimates using either Thames Water’s Engineering Estimating System (EES) or bottom-
up cost estimates where EES models are not available
Operating costs based upon estimates of the impact of the option on power, chemicals and labour
costs
Estimates of embedded and operational carbon monetised using the traded price of carbon (for
embodied carbon and for grid electricity) and the non-traded price of carbon (for non-grid operational
carbon)
Assumed splits between fixed and variable costs by option type
The outputs from APS have been used to generate the AIC+carbon. Key assumptions made in calculating
the AIC+carbon include:
1. When calculating variable costs, assumptions on utilisation need to be made. Currently zero and
100% utilisation scenarios have been used, except for the Crossness desalination option where a
minimum utilisation of 75% has been applied as it is assumed that the plant would operate
continuously9.
2. The scaling factor used for the denominator in the AIC calculation is the estimated Deployable Output
(DO). There is a risk that this approach could unfairly favour large options, but this has been mitigated
by increasing the screening threshold for small options.
3. Costs and benefits have been discounted using the Treasury declining long term discount rate:
a. 3.5% for years 0-30 of the appraisal period,
b. 3.0% for years 31-75, and
c. 2.5% for years 76-125
4. Financing costs have been calculated as a stream of annual costs over the life of the option, using an
assumed 3.6% average cost of capital.
5. A contingency has been added to option capital costs to cover optimism bias (see Appendix C)
6. A range of uncertainty has been applied to the capital costs for each option (see Appendix C)
7. A range of uncertainty can be entered for operating costs on the costing spreadsheets, with a default
figure of ±10% applied
For the purpose of comparing options using AICs it has been necessary to make assumptions around how
individual option elements (i.e. resource, conveyance, treatment and network reinforcement) combine to
provide overall supply options. The assumptions made for London are shown in Table 3.2. At this stage
information is not available on reinforcements to the raw water system that would be required. Once this
information becomes available from the ongoing raw water system cross-option study then this will be
incorporated into a subsequent update of the fine screening report.
Only a proportion of the Thames Water Ring Main extension network reinforcements costs have been
included in the AICs. The costs have been pro-rated based upon the ratio of option Deployable Output to
800 Ml/d. This approach is a simplification for screening purposes, and dependencies with TWRM
extensions will be modelled more rigorously as part of programme appraisal.
9 Unlike other desalination options identified, the Crossness desalination option is not blended with water from other sources and so
cannot be operated intermittently without causing changes in water quality that are likely to result in customer acceptability issues.
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Table 3.2: London WRZ - summary of options elements included in AIC calculation
Master Solution Name WRZ
WRMP19
Source
Yield
(Ml/d)
Indicativ
e DO
(Ml/d) Resource elements Conveyance elements Water treatment elements Raw water system elements Network reinforcement elementsReuse: Beckton 380Ml/d London 336 Reuse Beckton 380 MLD Beckton to KGV Intake 380 MLD Coppermills WTW 100 MLD + 100 MLD + 100 MLD + 100 MLD TBC (KGV to Coppermills) TWRM - Coppermills to Honor Oak
Reuse: Beckton 300Ml/d London 268 Reuse Beckton 300 MLD Beckton to KGV Intake 300 MLD Coppermills WTW 100 MLD + 100 MLD + 100 MLD
Reuse: Beckton 200Ml/d London 183 Reuse Beckton 200 MLD Beckton to KGV Intake 200 MLD Coppermills WTW 100 MLD + 100 MLD
Reuse: Beckton 150Ml/d London 138 Reuse Beckton 150 MLD Beckton to KGV Intake 200 MLD Coppermills WTW 100 MLD + 50 MLD
Reuse: Beckton 100Ml/d London 95 Reuse Beckton 100 MLD Beckton to KGV Intake 100 MLD Coppermills WTW 100 MLD
Reuse: Beckton 50Ml/d London 49 Reuse Beckton 50 MLD Beckton to KGV Intake 100 MLD Coppermills WTW 50 MLD
Reuse: Mogden 200Ml/d London 180 Reuse Mogden 200 MLD Mogden to Walton 200 MLD Kempton WTW new 100 MLD + 100 MLD TBC (Walton to Kempton) TWRM - Hampton to Battersea link
Reuse: Mogden 150Ml/d London 137 Reuse Mogden 150 MLD Mogden to Walton 200 MLD Kempton WTW new 150 MLD TWRM - Coppermills to Honor Oak
Reuse: Mogden 100Ml/d London 94 Reuse Mogden 100 MLD Mogden to Walton 100 MLD Kempton WTW new 100 MLD
Reuse: Mogden 50Ml/d London 49 Reuse Mogden 50 MLD Mogden to Walton 100 MLD Kempton WTW new 50 MLD
Reuse: Deephams 60Ml/d London 58 Reuse Deephams 60 MLD Deephams to KGV Intake 60 MLD Coppermills WTW 50 MLD TBC (KGV to Coppermills) TWRM - Coppermills to Honor Oak
Reuse: Crossness 190Ml/d London 174 Reuse Crossness 190 MLD Crossness to KGV Intake 200 MLD Coppermills WTW 100 MLD + 100 MLD TBC (KGV to Coppermills) TWRM - Hampton to Battersea link
Reuse: Crossness 150Ml/d London 138 Reuse Crossness 150 MLD Crossness to KGV Intake 200 MLD Coppermills WTW 100 MLD + 50 MLD TWRM - Coppermills to Honor Oak
Reuse: Crossness 100Ml/d London 95 Reuse Crossness 100 MLD Crossness to KGV Intake 100 MLD Coppermills WTW 100 MLD
Reuse: Crossness 50Ml/d London 49 Reuse Crossness 50 MLD Crossness to KGV Intake 100 MLD Coppermills WTW 50 MLD
Reuse: Mogden South Sewer 50Ml/d London 49 Reuse Mogden South Sewer 50 MLD Kempton to Walton Black Water 50 MLD Kempton WTW new 50 MLD TBC (Walton to Kempton) TWRM - Hampton to Battersea link
TWRM - Coppermills to Honor Oak
RWT: STT Deerhurst 300Ml/d (Lon only) London 262 Vyrnwy 180 MLD (Lon only)
Minworth 88MLD (Lon only)
Mythe 15 MLD (Lon only)
Draycote 25 MLD (Lon only)
RWT Deerhurst to Radcot 300 MLD (Lon only) Kempton WTW new 150 MLD + 150 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
TWRM - Coppermills to Honor Oak
RWT: STT Deerhurst 100Ml/d (Lon only) London 92 Vyrnwy 60 MLD (Lon only)
Mythe 15 MLD (Lon only)
Draycote 25 MLD (Lon only)
RWT Deerhurst to Radcot 100 MLD (Lon only) Kempton WTW new 100 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
TWRM - Coppermills to Honor Oak
RWT- STT Deerhurst 300Ml/d (2 zone Lon) London 252 Vyrnwy 180 MLD (2 zone Lon 170MLD)
Minworth 88 MLD (2 zone Lon 78MLD)
Mythe 15 MLD (Lon only)
Draycote 25 MLD (Lon only)
RWT Deerhurst to Radcot 300 MLD (2 zone Lon 290MLD) Kempton WTW new 150 MLD + 150 MLD TBC (Thames to Kempton)
RWT: STT Deerhurst 100Ml/d (2 zone Lon) London 82 Vyrnwy 60 MLD (Lon only)
Mythe 15 MLD (Lon only)
Draycote 25 MLD (Lon only)
RWT Deerhurst to Radcot 100 MLD (2 zone Lon 90MLD) Kempton WTW new 100 MLD TBC (Thames to Kempton)
Abingdon 150Mm3 (Lon only) London 287 Abingdon 150 Mm3 - 283 MLD (Lon only) N/A Kempton WTW new 150 MLD + 150 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
Abingdon 150Mm3 (2 Zone Lon) London 281 Abingdon 150 Mm3 - 274 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD + 150 MLD TWRM - Coppermills to Honor Oak
Abingdon 125Mm3 (Lon only) London 247 Abingdon 125 Mm3 - 252 MLD (Lon only) N/A Kempton WTW new 150 MLD + 100 MLD TBC (Thames to Kempton)
Abingdon 125Mm3 (2 Zone Lon) London 239 Abingdon 125 Mm3 - 242 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD + 100 MLD
Abingdon 100Mm3 (Lon only) London 204 Abingdon 100 Mm3 - 201 MLD (Lon only) N/A Kempton WTW new 150 MLD + 50 MLD TBC (Thames to Kempton)
Abingdon 100Mm3 (2 Zone Lon) London 196 Abingdon 100 Mm3 - 191 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD
Abingdon 75Mm3 (Lon only) London 153 Abingdon 75 Mm3 - 151 MLD (Lon only) N/A Kempton WTW new 150 MLD TBC (Thames to Kempton)
Abingdon 75Mm3 (2 Zone Lon) London 144 Abingdon 75 Mm3 - 141 MLD (2 zone Lon) N/A Kempton WTW new 150 MLD
Abingdon 50Mm3 (Lon only) London 103 Abingdon 50 Mm3 - 101 MLD (Lon only) N/A Kempton WTW new 100 MLD TBC (Thames to Kempton)
Abingdon 50Mm3 (2 Zone Lon) London 93 Abingdon 50 Mm3 - 91 MLD (2 zone Lon) N/A Kempton WTW new 100 MLD
Abingdon 30Mm3 (Lon only) London 59 Abingdon 30 Mm3 - 63 MLD (Lon only) N/A Kempton WTW new 100 MLD TBC (Thames to Kempton)
Abingdon 30Mm3 (2 Zone Lon) London 51 Abingdon 30 Mm3 - 53 MLD (2 zone Lon) N/A Kempton WTW new 100 MLD
Chinnor 50Mm3 (Lon only) London 103 Chinnor 50Mm3 - 100MLD (Lon only) N/A Kempton WTW new 100 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
Chinnor 50Mm3 (2 Zone Lon) London 93 Chinnor 50Mm3 - 80MLD (2 zone Lon) N/A Kempton WTW new 100 MLD TWRM - Coppermills to Honor Oak
Chinnor 30Mm3 (Lon only) London 59 Chinnor 30Mm3 - 60MLD (Lon only) N/A Kempton WTW new 100 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
Chinnor 30Mm3 (2 Zone Lon) London 51 Chinnor 30Mm3 - 50MLD (2 zone Lon) N/A Kempton WTW new 100 MLD TWRM - Coppermills to Honor Oak
Marsh Gibbon 75Mm3 (Lon only) London 153 Marsh Gibbon 75Mm3 - 150MLD (Lon only) N/A Kempton WTW new 150 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
Marsh Gibbon 75Mm3 (2 Zone Lon) London 144 Marsh Gibbon 75Mm3 - 135MLD (2 zone Lon) N/A Kempton WTW new 150 MLD TWRM - Coppermills to Honor Oak
Marsh Gibbon 50Mm3 (Lon only) London 103 Marsh Gibbon 50Mm3 - 100MLD (Lon only) N/A Kempton WTW new 100 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
Marsh Gibbon 50Mm3 (2 Zone Lon) London 93 Marsh Gibbon 50Mm3 - 80MLD (2 zone Lon) N/A Kempton WTW new 100 MLD TWRM - Coppermills to Honor Oak
Marsh Gibbon 30Mm3 (Lon only) London 59 Marsh Gibbon 30Mm3 - 60MLD (Lon only) N/A Kempton WTW new 100 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
Marsh Gibbon 30Mm3 (2 Zone Lon) London 51 Marsh Gibbon 30Mm3 - 50MLD (2 zone Lon) N/A Kempton WTW new 100 MLD TWRM - Coppermills to Honor Oak
DRA: River Lee 150 Ml/d London 150 River Lee (Potable) - 150 MLD N/A Treatment included in resource element N/A 3 Mills Lock Potable to Network 150 MLD
DRA: Mogden Effluent Transfer 300 Ml/d London 268 Teddington Weir (Mogden Effluent Transfer) - 300
MLD
Teddington to Thames Lee Tunnel Shaft 300 MLD Kempton WTW new 150 MLD + 150 MLD TBC (Thames to Kempton) TWRM - Hampton to Battersea link
TWRM - Coppermills to Honor Oak
Desalination: Beckton 150 Ml/d London 142 North Beckton RO 150 MLD N/A N/A (Desal provides treated water) N/A Desalination North Beckton to Coppermills 150 MLD
TWRM - Coppermills to Honor Oak
Desalination: Crossness 75 Ml/d London 75 South Crossness RO 75 MLD N/A N/A (Desal provides treated water) N/A Included in resource element
Desalination: Thamesmead 150 Ml/d London 138 South Thamesmead RO 150 MLD N/A N/A (Desal provides treated water) N/A Desalination South Thamesmead to Coppermills150 MLD
TWRM - Coppermills to Honor Oak
Desalination: Thamesmead 300 Ml/d London 268 South Thamesmead RO 300 MLD N/A N/A (Desal provides treated water) N/A Desalination South Thamesmead to Coppermills 300 MLD
TWRM - Coppermills to Honor Oak
Raw
Wate
r T
ran
sfe
rsW
ate
r R
eu
se
New
Reserv
oir
Dir
ect
Riv
er
Desali
nati
on
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21
The resulting AIC ranges within capacity bands are shown in Figure 3.6 and an explanation of the chart is
provided in Figure 3.5. For each option the red marker shows the ‘most likely’ estimate based upon
maximum utilisation while the green marker shows the ‘most likely’ estimate based upon minimum
utilisation. The whiskers above and below these markers indicate the extent of capex and opex
uncertainty assumed. The sensitivity of each option to utilisation assumptions can be seen by the distance
between the red and green ‘most likely’ cost markers. Where the markers are wide apart then a significant
proportion of the AIC comprises variable costs (varying by volume of water used) and where the markers
are close together then most costs are fixed.
For each water resource zone a benchmark option has been selected. The benchmark option for the
London WRZ has been identified by ranking options in order of increasing AIC at full utilisation and
selecting as the benchmark the option that would be the least cost option remaining at the end of the
planning horizon. The AIC threshold is then set at the most likely cost for the benchmark option at
maximum utilisation. For the London WRZ up to 800Ml/d of resource is estimated to be needed by the end
of the century. This includes potentially allowing for water supply to other water companies in the south
east region. This has led to the Thamesmead Desalination 150Ml/d option being selected as the
benchmark option for London, which results in a cost screening threshold for the 125-175 Ml/d band of
125p/m3.
Figure 3.5: Explanation for AIC chart and category definitions
The thresholds for other size bands have been adjusted to correct for two issues that arise when using
AICs (at full utilisation) to compare between options of very different sizes for addressing a gradually
increasing deficit profile:
Cost threshold
Symbol: ● ◐ ○ ◎ ◉
Meaning:Substantial
disbenefit
Material
disbenefitNeutral
Material
benefit
Substantial
benefit
Upper estimate (max utilisation)
Lower estimate (min utilisation)
Most likely cost (min utilisation)
Most likely cost (max utilisation)
Be
nch
mar
ko
pti
on
●
●
●
●
●
●
●
●
●
●
●
●
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22
1. If the full capacity of the option is not required upon commissioning then a capacity based AIC will over
estimate the resource benefit (denominator in the AIC calculation). This over estimate will be greater
for large options that for a series of smaller options. A higher threshold therefore needs to be applied
to smaller options to correct for this.
2. By more closely matching the deficit profile smaller options also allow expenditure to be deferred which
then reduces the discounted cost of a programme. Again, the benefits of being able to defer
expenditure for smaller options are not captured in the AIC calculations which consider each option on
an individual basis, with implementation starting in the first year of the planning period. A higher
threshold therefore also needs to be applied to small options to ensure that the advantage they offer in
deferment of expenditure is captured.
The screening threshold adjustment factors to correct for these two issues have been calculated using a
notional linear deficit profile increasing from zero to an indicative 800Ml/d over 80 years.
For Water Resource Zones outside London a simpler approach to setting the screening threshold is
proposed due to the smaller size of most options. The screening threshold for the Thames Valley will be
set at the most likely cost (at maximum utilisation) of the least cost, large scale resource for the Thames
Valley (i.e. the lower of the Abingdon Reservoir or Severn Thames Transfer options).
23 356236/WCD/WAM/40/02 30 September 2016 PiMS/356236/Documents
Thames Water WRMP19 Resource Options Fine Screening Report Update
Figure 3.6: AIC+carbon for options in the London WRZ
Benchm
ark
option
D
RA
: Riv
er L
ee 1
50
Ml/
d
DR
A: T
edd
ingt
on
30
0 M
l/d
Des
alin
atio
n:
Tham
esm
ead
30
0 M
l/d
Reu
se:
Mo
gden
20
0M
l/d
Reu
se:
Mo
gden
15
0M
l/d
Ab
ingd
on
75
Mm
3 (
2 Z
on
e Lo
n)
Des
alin
atio
n:
Cro
ssn
ess
65
Ml/
d
Des
alin
atio
n:
Tham
esm
ead
15
0 M
l/d
Des
alin
atio
n:
Bec
kto
n 1
50
Ml/
d
Reu
se:
Mo
gden
10
0M
l/d
Reu
se:
Bec
kto
n 2
00
Ml/
d
Ab
ingd
on
75
Mm
3 (
Lon
on
ly)
Reu
se:
Bec
kto
n 3
00
Ml/
dA
bin
gdo
n 1
25
Mm
3 (
2 Z
on
e Lo
n)
Ab
ingd
on
50
Mm
3 (
2 Z
on
e Lo
n)
Ab
ingd
on
12
5M
m3
(Lo
n o
nly
)
Ab
ingd
on
15
0M
m3
(2
Zo
ne
Lon
)
Ab
ingd
on
50
Mm
3 (
Lon
on
ly)
Ab
ingd
on
15
0M
m3
(Lo
n o
nly
)
RW
T: S
TT D
eerh
urs
t-R
adco
t 3
00
Ml/
d (
Lon
on
ly)
Reu
se:
Bec
kto
n 1
50
Ml/
d
Reu
se:
Mo
gden
So
uth
Sew
er 5
0M
l/d
Ab
ingd
on
10
0M
m3
(Lo
n o
nly
)
Reu
se:
Bec
kto
n 3
80
Ml/
d
RW
T: S
TT D
eerh
urs
t-R
adco
t 1
00
Ml/
d (
Lon
on
ly)
Reu
se:
Cro
ssn
ess
15
0M
l/d
Reu
se:
Mo
gden
50
Ml/
dA
bin
gdo
n 3
0M
m3
(2
Zo
ne
Lon
)
Reu
se:
Cro
ssn
ess
10
0M
l/d
Reu
se:
Bec
kto
n 1
00
Ml/
d
Mar
sh G
ibb
on
75
Mm
3 (
2 Z
on
e Lo
n)
Ab
ingd
on
10
0M
m3
(2
Zo
ne
Lon
)
Ch
inn
or
50
Mm
3 (
2 Z
on
e Lo
n)
Reu
se:
Cro
ssn
ess
19
0M
l/d
Mar
sh G
ibb
on
50
Mm
3 (
2 Z
on
e Lo
n)
Mar
sh G
ibb
on
75
Mm
3 (
Lon
on
ly)
Ch
inn
or
50
Mm
3 (
Lon
on
ly)
Mar
sh G
ibb
on
50
Mm
3 (
Lon
on
ly)
Reu
se:
Dee
ph
ams
60
Ml/
dA
bin
gdo
n 3
0M
m3
(Lo
n o
nly
)M
arsh
Gib
bo
n 3
0M
m3
(2
Zo
ne
Lon
)C
hin
no
r 3
0M
m3
(2
Zo
ne
Lon
)M
arsh
Gib
bo
n 3
0M
m3
(Lo
n o
nly
)R
euse
: C
ross
nes
s 5
0M
l/d
Reu
se:
Bec
kto
n 5
0M
l/d
Ch
inn
or
30
Mm
3 (
Lon
on
ly)
25-75 75-125 125-175 175-225 225-275 >275
0
100
200
300
400
500
600
700
AIC
(p
/m3
)
WAFU (Ml/d) Band
Max Utilisation Min Utilisation BenchmarkCost threshold
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Thames Water WRMP19 Resource Options Fine Screening Report Update
3.6.3 Promotability dimension
3.6.3.1 Dimension description
Promotability: The Promotability dimension considers the scheme up to the point of planning permission
being granted and includes professional judgement of:
Synergies (e.g. synergies with water resource needs of other water resource zones in the South East
and synergies with third party developments)
Customer acceptability (e.g. in relation to wastewater reuse, including views of Customer Challenge
Group);
Local acceptability (e.g. in relation to planning challenges);
Regulatory acceptability (including DWI, EA, Ofwat); and
Wider stakeholder acceptability.
3.6.3.2 Discussion
The Promotability dimension considers a range of potential issues and risks that could either singularly or
cumulatively result in the option type being rejected before it even reached the planning permission stage.
Each of the six sub-dimensions is described further below.
Synergies
Assessment of synergies with other water resources zones involves consideration of the extent that an
option will provide resources that could supply either other Thames Water WRZs or those of neighbouring
companies. Where an option has the potential to directly support another company’s new resource
requirements then this has been categorised as substantial benefit. Where an option could directly support
or indirectly free up water for export to other WRZs then this has been considered as a material benefit. All
other options have been categorised as neutral in terms of synergies.
Those option types where a benefit has been noted include all reservoir options. The level of benefit would
ultimately be dependent upon the geographical location of the site and known reservoir capacity range.
Options involving the canal network have been assigned a ‘material benefit’ based on synergies with the
navigational needs of other canal users. Wastewater reuse options could also potentially indirectly address
the needs of other water companies in the South East; but again dependent upon the capacity range for
the specific scheme.
Customer acceptability
Customer acceptability considers the long-term view of the consumer on a water resources option.
Customers’ perceptions on direct impacts such as customer bills and drinking water quality are considered,
alongside their perceptions on the indirect impacts, such as environmental effects. This question is
concerned with perceived rather than actual impacts. Actual impacts on such issues are covered by other
dimensions (Cost, Environmental & Social and ‘Regulatory Acceptability’ within Promotability etc.).
Research reported by the Customer Challenge Group for Thames Water10
highlighted the following
customer preferences, which, in turn, would develop and promote acceptability. Customers want their
water and sewerage suppliers to:
10
Customer Challenge Group for Thames Water: Report to Ofwat on Thames Water Business Plan. 2 December 2013.
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– conserve water;
– reduce the impact of their operations on the environment, particularly on local rivers;
– adopt energy-conserving technologies; and
– be more active in educating consumers on the preservation of water supplies and the wider
environment.
These views have been used as evidence for assigning categories to the Customer Acceptability sub-
dimension, alongside appreciation of customer engagement and consultation as a tool for managing and
developing customer acceptability. As such, high energy option types such as those involving intensive
treatment processes have been allocated a material disbenefit; reducible with the inclusion of renewable
energy sources, such as has been actively applied at the existing Thames Gateway desalination plant.
Wastewater reuse, however, has been allocated a neutral benefit/disbenefit, as The Customer Challenge
Group specifically highlighted the customer preference that “water that has already been captured into
supply should fully be used. Reuse of wastewater is preferred to massive capital expenditure on new
resources such as reservoirs”.
As such, option types potentially involving the construction of a new reservoir have been assigned a
material disbenefit.
Local acceptability
Local acceptability and planning risks associated with the option types are categorised in terms of their
severity and whether there is scope for them to be reduced through e.g. stakeholder engagement. This
sub-dimension highlights schemes that might give rise to strong local opposition. The views of
organisations such as the Group Against Reservoir Development (GARD) and local Councils are
considered and where pressure groups actively oppose a scheme this is noted.
Schemes involving reservoir development have been assigned as having substantial disbenefits. There
was significant opposition to the WRMP14 reservoir scheme and whilst regulatory support for such a
scheme could mitigate and reduce the opposition, this has high uncertainty as regulatory backing has not
at the present time been obtained.
For the option type involving a reservoir being constructed outside of the TWUL supply area (Longdon
Marsh reservoir in the supported raw water transfer options), there would also be a substantial local
acceptability disbenefit. This would be exacerbated by the specific flood risk concerns at the Longdon
Marsh site.
A further component of local acceptability is an awareness of potential issues surrounding perceived
increased flood risk from those options supporting river flow in the Thames. A discharge of additional water
into the Thames catchment could be perceived as augmenting flood risk to downstream areas. In these
cases, suitable public awareness and education would be required to mitigate against misplaced local
community concerns.
Regulatory acceptability
Regulatory acceptability includes the positions of the Environment Agency (EA), Drinking Water
Inspectorate (DWI), Ofwat, Natural England and English Heritage. Approval of abstraction licences,
http://www.thameswater.co.uk/pr14/CCG-for-Thames-Water-report-to-Ofwat.pdf
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potential challenges to achieving regulatory water quality standards and the views of the industry economic
regulator are all considered.
Where further research is required in order to mitigate any opposition to an option type, a reducible
material risk/disbenefit has been applied.
Wider stakeholder acceptability
Other bodies (who are not water industry regulators) may have a particular interest in an option type and
could offer either support or challenge to the realisation of an option. Such organisations might include the
Royal Society for the Protection of Birds and the Campaign for Rural England (CPRE).
Experience gained in WRMP14 has been used to assign categories to the wider stakeholder acceptability
sub-dimension. It is assumed, for example, that those organisations that made representations at the
Abingdon Reservoir WRMP09 public inquiry would continue to object to reservoir development and so a
material irreducible disbenefit has been ascribed to those option types potentially involving reservoir
development.
Where is it considered that wider stakeholder objections could be reduced through the provision of
evidence and/or engagement, the sub-dimension has been assessed to have a material, but reducible,
disbenefit. Depending on the results on the on-going inter-basin transfer investigations, the concerns of
environmental representative groups on water quality and ecology impacts could be an example of such a
material reducible disbenefit.
Risks of objections from media sources, however, are considered to be irreducible disbenefits, due to the
public platform on which any objections may be raised and difficulties in managing and challenging public
dissemination of misinformation.
3.6.4 Flexibility dimension
3.6.4.1 Dimension description
Flexibility: Assessment of how flexible an option is to changes in requirements including in relation to:
Lead time: WRMP14 lead times will be used to inform this assessment;
Phasing: Potential for the scheme to be incrementally built and/or commissioned;
Adaptability: Whether the scheme is extendable once built; and
Ramp-up: How quickly the system can respond to changes in demand over its operational life.
3.6.4.2 Discussion
The flexibility dimension considers potential issues and risks that could either singularly or cumulatively
result in a material benefit or disbenefit in the delivery or operational flexibility on an option. Each of the six
sub-dimensions is described further below.
Lead times
Information on the general lead times of option types has been used to assess the options, taken from the
WRMP14 WRP3a tables:
– Desalination and wastewater reuse have the shortest lead times, with a predicted lead time of 6
years;
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– Unsupported transfers and Lower Lee abstractions are predicted to have a lead time of 7 years;
and
– Supported raw water transfers (depending on the support option) and the Upper Thames Reservoir
options are predicted to have the longest lead times of up 12 years.
Wastewater reuse was reported as having a lead time of only 4 years at WRMP14; in practice, however, it
is now considered at that this would be at least 6 years due to the likely need for these schemes to involve
a tunnel to either Honor Oak or Coppermills.
An option that has a short lead time offers benefits in terms of its influence on the supply-demand balance.
Options’ lead times have been assessed as being a material benefit where they are less than 5 years,
neutral where they are 5 to 7 years, a material disbenefit when 8 to 10 years and substantial disbenefit
where over 10 years. For options with long lead times, another option may be needed to address short to
medium term deficits.
There are uncertainties regarding the development of an option type where significant planning challenges
would need to be overcome, such as all new reservoir and Lower River Lee options, with potential knock-
on effects on lead time.
Phasing
Phasing offers benefits in terms of spreading and/or deferring the capital expenditure of an option. Types
of assets lend themselves to phasing more than others. Options have been reviewed in light of the
potential for the scheme to be incrementally built and/or commissioned. For those where economies of
scale are strongest (e.g. pipeline construction at larger diameters), the benefits of phasing would be the
least as phasing could involve significant additional cost; however, these need to be weighed against the
benefit of deferred expenditure.
The following option type assessment can be made:
– Long distance pipelines: The phasing disbenefits of the raw water transfer options have been
assessed as being material but reducible, due to the influence of economies of scale but their
setting in a predominantly rural area. Desalination and wastewater reuse options include long
distance pipelines and have been assessed as having a material but irreducible disbenefit for
phasing, as these options have the added difficulty of being located in a heavily urban area.
– River intakes: Rather than being constructed and operated at the maximum available deployable
output from the outset, river intakes could be built in phases up to the maximum deployable output.
Phasing could therefore be possible by, for example, building the first 50% of the deployable output
in one AMP and then the remaining capacity in a later AMP. This could be a material benefit.
– Treatment options: Treatment plants would offer a material benefit in terms of phasing
opportunities, as treatment streams could be built and commissioned individually.
– Reservoirs: Reservoirs have been assessed as having a material benefit for phasing as provision
can be made in the design for subsequent reservoir extensions. The potential for this is, however,
highly dependent upon site-specific factors.
Adaptability
Adaptability is distinct from phasing in that it considers the ways in which an option might be adapted in
future to unexpected future requirements e.g. in terms of source availability and capacity; whereas phasing
relates to the potential for an option to be expanded in future to meet expected future requirements.
To this degree, the following option type assessment can be made:
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– Raw water transfers: These could potentially be linked up and connected to new sources and
demand centres in future (e.g. as part of a national grid) and so do offer some material adaptability
benefits. These are however highly uncertain.
– River intakes: River intakes have limited adaptability once built as they are constrained by the
hydrological yield of the Lower River Lee. As such, the option is considered to be neutral in terms
of adaptability.
– Treatment options: There may be opportunities to adapt treatment works to increase capacity,
depending on space constraints. However, the potential for adaptation of works for the treatment of
water from different sources will be dependent on raw water quality and the suitability of installed
treatment processes. Increasing the capacity of wastewater reuse options would be constrained by
the availability of effluent. As such, these options are considered to be neutral in terms of
adaptability. Desalination options would be the most adaptable of the options types and offer a
material benefit.
– Reservoirs: Once built, there is the potential for the reservoir to hold water from alternative sources,
thereby offering flexibility. For the purposes of assessment at the option type level, adaptability has
been categorised to be a material benefit.
Ramp-up
Ramp-up assesses operational flexibility. The time from which a scheme can be activated to the time that
potable water is available to go into the supply network has been estimated based on an understanding of
potential water quality constraints and discussions with process engineers and hydraulic engineers. A
scenario of a dry year has been employed, when a short ramp-up time offers a clear benefit. The operating
philosophy11
has been used to inform this assessment. The following categorisations have been made:
Material benefit: A scheme is able to provide potable water within a week;
Neutral: A scheme is able to provide potable water within two weeks;
Material disbenefit: A scheme is able to provide potable water within four weeks; and
Substantial disbenefit: A scheme would not be able to provide potable water within four weeks.
For those option types involving complex treatment processes, the stated minimum ramp-up times assume
that the plants are basically maintained in an operational condition i.e. UF/MF/RO membranes
stored/preserved according to manufacturers’ guidelines. The ramp-up times for these options have
consequentially been estimated as shown below in Table 3.3.
Table 3.3: Estimated option type ramp-up times of treatment options
Option type or Option element Minimum ramp-up time
Conventional water treatment 6 weeks
Desalination 8 weeks
Water reuse (MBR/GAC) 6 weeks
Water reuse (RO/AOP) 7 weeks
Direct River abstraction & partial treatment (abstraction & treatment elements)
6 weeks
Direct River abstraction & partial treatment (conveyance element)12 <1 day
Direct River abstraction and full treatment 6 weeks
11
Described in Options operating philosophy (Utilisation) Report prepared for TWUL by Mott MacDonald/Cascade for issue in September 2016.
12 Excludes Option 4 which discharges into the Walton WTW intake and for which standby modes would apply.
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Option type or Option element Minimum ramp-up time
Raw water transfer (Deerhurst Pipeline) 1 week
Raw water transfer (Cotswold Canal) 2 weeks
Treated water conveyance13
Raw water reservoirs (abstraction element) <1 day
Raw water reservoirs (conveyance element) <1 day
Groundwater abstraction (excluding treatment) 2 weeks
3.6.5 Deliverability dimension
3.6.5.1 Dimension description
Deliverability: The Deliverability criterion considers the option from the planning permission stage to
commissioning and operation. It includes assessment of construction, technology and other
implementation risks. Both the WRMP14 Delivery and Solution Confidence Scores will be used as part of
this assessment.
Constructability: Uncertainties surrounding construction e.g. unknown technologies, land availability, or
contamination risks;
Operability: Whether there is a track record of successfully using the technology and if it is a
dependable and proven technology;
Dependencies: Dependencies on other assets, activities or third parties; and
Data confidence: Reliability and uncertainty of design data and DO assessment methodologies, etc.
3.6.5.2 Discussion
The Deliverability dimension considers a range of potential issues or risks that could either singularly or
cumulatively result in the option type failing to deliver.
Constructability
Constructability embraces and assesses uncertainties surrounding construction, such as unknown
technologies, land availability, or contamination risks. The level of risk is determined based on the historic
experience of TWUL or, in the absence of any such experience, other known challenges.
The development of a new technology type is not a substantial risk, but should be highlighted as an area
requiring consideration. Where no recent experience or knowledge is available, this would constitute a
material irreducible risk; conversely where there is some experience, this would be a material reducible
risk.
Other examples of material constructability challenges include reservoir construction, construction
constraints within designated areas, and the availability of land for development.
13
Hot standby relates to the provision of a sweetening flow to avoid de- and re-commissioning.
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Operability
Operability includes an assessment of whether there is a track record of successfully using the technology
and if it is dependable. Where it is not, this can constitute a risk. As with constructability, this can be either
reducible or irreducible depending on the particular issue.
Where extensive experience has been had, an option type has been considered to be neutral (e.g.
reservoir and direct intake operation). Conversely, a material irreducible risk has been assigned where
TWUL has no experience of an option type (e.g. wastewater reuse or highly complex treatment
technologies or processes).
Limited experience has been categorised as a material reducible disbenefit when either greater experience
will be gained from time (e.g. desalination), or where learning could be had from analogous schemes either
nationally (e.g. Ely Ouse to Essex Transfer Scheme) or overseas (e.g. desalination).
Dependencies
An option type may be dependent upon other assets, activities or third parties. Internal dependencies
(such as on an upstream STW or downstream WTW) have also been excluded from the Dependencies
categorisation.
The dependencies sub-dimension has consequentially been assessed based upon third-party asset
delivery alone as it is considered that this poses the most risk to option type delivery. Where no such
dependency would occur, the option type has been categorised as having a neutral benefit/disbenefit in
terms of dependencies. Where a dependency on third parties exists in the day-to-day operation of an
option type, an irreducible disbenefit has been allocated.
Data confidence
Whilst not a reason to reject an option at the option type level, an understanding of the reliability and
uncertainty of the design data and deployable output assessment is important. For instance, yield certainty
surrounding a desalination plant or wastewater reuse scheme is considerably higher than for a surface
water source, where uncertainties are material due to being based on complex modelling and
assumptions. Such assessment methodologies are, however, in keeping with industry standards. As such,
where options offer a greater confidence in Deployable Output delivery that would normally be expected, a
material benefit has been assigned.
3.6.6 Resilience dimension
3.6.6.1 Dimension description
Resilience: The Resilience criterion considers the option from the operation stage continuing into the
future. It will be an assessment of confidence that the option at the given cost will provide the stated
deployable output, with the required water quality in the future, and include:
Vulnerability to climate change and severe drought;
Resource predictability;
Contribution to the wider system’s resilience to outage;
Vulnerability to other ‘failure modes’ (e.g. pollution events, power outages, chemicals commodity
chains and terrorism); and
Vulnerability to regulatory changes (e.g. abstraction reform).
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3.6.6.2 Discussion
The protection of London’s water supply system from failures is something that the Customer Challenge
Group specifically noted in consultation as being of paramount importance14
. The drought of 2010-12 with
its two dry winters highlighted the vulnerability of the water supply system to drought and Defra realised
that the potential for water supply shortages is higher than previously appreciated. The Water White
Paper15
set an action for Defra and the Environment Agency to assess options to increase future water
supply resilience across all water-reliant sectors and to evaluate the social and economic impacts of
enhanced levels of resilience to mitigate the effects of water supply shortage. Key questions considered in
the Phase 1 assessment of resilience include vulnerability of each proposed option type to climate change
and severe drought, predictability, net contribution to system outage resilience, vulnerability to other ‘failure
modes’ and regulatory change. For each option type, these sub-dimensions have been assessed and a
single category assigned.
It should be noted that the resilience dimension deals with events outside of normal operation.
Vulnerability of option type to climate change
A climate change vulnerability assessment of all of Thames Water’s WRZs was undertaken as part of
WRMP14 and showed London to be highly vulnerable16
. The UK Climate Projections show a clear trend of
wetter winters and drier summers by 2050 for the Thames catchment, under low, medium and high
emissions scenarios17
.
The use of the raw water transfers and Upper Thames Reservoir options would be driven by a requirement
for water in London, which in turn depends upon flows in the River Thames and reservoir water levels in
London.
With the projected wetter winters, any need for winter refill support would likely reduce. Whilst water would
be available in the winter to transfer from the River Severn, Thames Water would be unable to capture it
due to its limited reservoir capacity (currently 90 days of demand although this will reduce as demand
grows) and as a result a transfer might not be required. As such, the unsupported raw water transfers
would not offer any water resource benefit.
Climate change projections suggest that summer support would be of increasing importance. Options such
as wastewater reuse, desalination, reservoir storage or supported transfers would offer substantial
benefits, as they would all be able to contribute to addressing summer shortages either because they are
essentially unaffected by climate change (e.g. reuse and desalination) or because they provide additional
storage that would allow surplus winter rainfall to be utilised (e.g. reservoirs or transfers supported by
reservoirs). Unsupported raw water transfers would not, and as such this would be a substantial disbenefit
of that option type.
14
From Introduction to part A of the draft Water Resources Management Plan, citing ‘A Non-Essential Use Drought Order for London: Economic Impact Assessment’ (NERA, commissioned by Thames Water, April 2012)
15 Water for Life, Defra, HM Government, December 2011.
16 Thames Water Revised Draft Water Resources Management Plan 2014, Appendix U: Climate Change.
17 UK Climate Projections (2009). Mean winter and mean summer precipitation trends for the Thames basin. Downloaded from http://ukclimateprojections-ui.metoffice.gov.uk/ui/admin/login.php, accessed on 09/03/2015.
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Vulnerability of option type to severe drought
All water resource sources are assessed against the worst historic drought and an option’s yield is the
calculated output that could be achieved during that event. This is particularly pertinent for surface water
dependent options as, whilst yield is calculated based on estimations of water resources and there are
inherent uncertainties associated with this, standard industry methodologies are followed and the yield
calculated must be considered absolute. It is only under assessment of conditions outside of the historic
record that options can be differentiated on the basis of their wider reliability and vulnerabilities. This sub-
dimension investigates such events.
Sensitivity analysis undertaken by Thames Water as a part of WRMP14 showed that there could be more
extreme drought events and an increased probability of drought events in the future18
. If droughts are more
severe than the historical record it would reduce the forecast likelihood of the supply system meeting its
level of service.
The analysis of ‘failure modes’ has highlighted the predominance of sources vulnerable to severe drought
within the London WRZ. Those which can be considered to offer a substantial benefit to the wider
resilience of the London WRZ during droughts worse than the historic record are sources that are non-
reliant on natural hydrology, such as desalination. Options that are reliant on effluent (such as wastewater
reuse and, to a lesser extent, Lower Lee abstraction) are considered marginally more vulnerable than
desalination as it is unclear how the option would perform in an extreme drought (e.g. with severe
restrictions in place) and the option relies on existing sources to provide water for blending. Those option
types reliant on natural groundwater and surface water catchment flows are most vulnerable to droughts
outside of the historic record, although for options with reservoir storage there remains the possibility of
partially mitigating the risk by sizing storage to reflect the future uncertainty of severe droughts.
Future resource predictability
The predictability of the resource is also a key consideration in relation to drought planning and outage
response planning. An option type with storage would provide material benefits in terms of operational
predictability, which would again be a significant advantage over an unsupported option type. Desalination
and wastewater reuse options would offer the greatest benefit in terms of predictability.
Net contribution to system outage resilience
The provision of additional storage in the London supply system would provide extra operational flexibility
and security to deal with outages. This would be a substantial benefit of a supported option type over an
unsupported option type, as the availability of an unsupported supply would be highly uncertain; strictly
controlled by other factors such as seasonal timing and river flows etc.
Desalination would contribute towards resilience against outage but there would be no alternative
treatment route in the event of an on-site outage. In addition, those options types being transferred to the
Lee Valley reservoir and/or treated at Coppermills WTW would pose a material disbenefit to the wider
system outage resilience, due to the existing heavy London WRZ dependence on these assets.
Vulnerability of option type to other failure modes
As a part of work undertaken for Thames Water in 2013 on resilience gap analysis, a list of hazards was
compiled based upon that provided for the UKWIR resilience project “RG06 Resilience – Making a
18
Thames Water Revised Draft Water Resources Management Plan 2014, Section 4: Current and Future Water Supply.
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Business Case for PR14”. These hazards were then grouped together into ‘failure modes’ for the purpose
of the gap analysis so as to make the process more manageable as shown in the table below.
Figure 3.7: List of failure modes and associated hazards
Source: Thames Water Resilience Gap Analysis Rev B, Mott MacDonald, June 2013.
These ‘failure modes’ (excluding drought, communication and staffing) have been used as the basis of a
resilience review of the options type, in order to understand the range of vulnerabilities and what potential
future large scale resource options may add (or not) to overall resilience:
Flooding
– The review has been made on the assumption that key water resource assets are protected to a
certain level of fluvial and coastal flood risk.
– Fluvial flooding could halt river abstraction and reservoir refill due to water quality issues;
Pollution incidents
– Pollution outages would have the greatest impact on river abstractions that were not supported by
reservoir storage but this would likely be only for short periods;
Physical damage
– Options that require a large number of complex assets to be operational (e.g. desalination, or
reuse), and those where assets are geographically dispersed (e.g. canal transfers) tend to be more
vulnerable to physical damage than assets that have low operational complexity (e.g. reservoirs);
Power supply loss and supply chain loss
– Option types with high energy or chemical requirements would be most vulnerable to power supply
loss and increasing commodity prices.
An Upper Thames Reservoir has been assessed as being resilient to the most ‘failure modes’ of all the
option types. As reservoir storage already provides a considerable proportion of London’s supply, this
option type is in line with the majority of the existing London WRZ sources and therefore has been
assessed as having a neutral benefit/disbenefit. The other option types are all vulnerable to a number of
‘failure types’ and are therefore considered to have a material disbenefit in terms of resilience.
Flooding Physical damage: societal Communications loss
Coastal flooding Malicious damage Cyber attack
Fluvial Flooding Sabotage Solar flare/Space weather
Surface water flooding Security related Telecoms failures
Groundwater flooding Third party interventions National strike
Tsumani Civil unrest
Sea level rise War Supply chain loss
Aircraft Crash Chlorine - supply chain
Drought Nuclear incident Materials shortages
Drought Comodity prices and economic change
Supply chain failure
Pollution incidents Physical damage: geological Major fuel crisis
Catchment / site contamination Earthquake National strike
Contamination incident Landslides / subsidence
Extreme reservoir pollution Reservoir or dam breach Shortage of staff
Extreme river pollution Epidemic/Pandemic
Physical damage: internal Civil unrest
Physical damage: weather Fire / major fire Skills crisis
Excessive cold & ice/snow Asset deterioration / failure National strike
Prolonged hot/dry weather
Lighting strike Power supply loss Denial of access to sites
Storms and gales Power failure Transport disaster
Power loss (extended period) Civil unrest
National strike
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Vulnerability of option type to regulatory changes
The options have been reviewed against the above questions in order to determine their vulnerability to
potential future regulatory changes.
There is a level of uncertainty surrounding future regulatory changes but abstraction reform is a key
concern for the water industry. Those options that are dependent upon a water resources abstraction
licence therefore have a material risk attached to them as a direct result of this, potentially reducible
through regulatory engagement.
In addition to changes to abstraction regulation, changes to water quality standards would also impact
upon the resilience of an option type. This could impact any of the option types although some treatment
processes such as RO will provide a barrier against more parameters and so are potentially more resilient
to changes in water quality standards. This needs to be balanced against the potential for such
technologies to be less reliable.
There are uncertainties surrounding the nature of the regulatory changes that may occur, with the
exception of those not dependent upon fresh water resources. All option types have been categorised as
having a material (but reducible) disbenefit/risk associated with regulatory change, either from an
abstraction or water quality standards aspect (see Table 3.4). A summary of the results has been provided
below instead:
Table 3.4: Vulnerability to regulatory change
Option type Vulnerable to future abstraction
regulatory change? Vulnerable to future water quality
regulatory change?
Raw water transfer Yes Yes
Desalination - Yes
Reservoir Yes Yes
Direct river abstraction Yes Yes
Wastewater reuse - Yes
Effluent support Yes Yes
3.6.7 Screening decisions
Screening decisions have been made by looking across all six dimensions. Rather than imposing rigid
rules to make screening decisions, the focus is on ensuring that there is a clear and robust reasoning for
each screening decision which will then be reflected in the rejection register for WRMP19. It is expected
that the nature of fine screening may include:
Rejection of options with substantial irreducible dis-benefit/risk unless this may be offset by a
substantial benefit/opportunity
Where there are mutually exclusive options and some are clearly less favourable than others then
this would provide grounds for rejection
Where there are more options than could reasonably be required over the planning horizon under
future scenarios, then there may be a case for rejecting the least favourable options. For this
purpose the scenarios include: water reuse being unfeasible (e.g. due to customer acceptability);
and raw water transfers being unfeasible (e.g. due to environmental acceptability)
The reasons for screening decisions will be recorded in the WRMP19 rejection register. Stakeholder views
will be sought on the screening decisions and these decisions will be reviewed and updated in the light of
stakeholder observations where necessary.
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Chapter 4 reports the findings of the review of generic option types and provides a
summary of the reasoning for option type rejections.
4.1 Generic option screening
The option types considered in the generic screening are those listed in the UKWIR Water Resources
Planning Tools report19
. The generic options list and a summary of the results are shown in Figure 4.1.
Commentary on the reasoning behind the rejection is provided in Table 4.1. In some cases (marked TBC;
To Be Confirmed) further work was deemed needed to obtain the information needed to inform the
screening decision.
Figure 4.1: Summary of generic option type review
19
UKWIR, Water Resources Planning Tools, EBSD Report, Ref. 12/WR/27/6. 2012.
Generic resource management options† Gen
eri
c
scre
en
ing
Specific option identification
1 Direct river abstraction ✔ Direct river abstraction feasibility report
2 New reservoir ✔ New reservoirs feasibility report
3 Groundwater sources ✔ Groundwater feasibility report
4 Infiltration galleries ✔ Included in DRA/Desal as possible intake
5 Aquifer storage and recovery ✔ Groundwater feasibility report
6 Aquifer recharge ✔ Groundwater feasibility report
7 Desalination ✔ Desalination feasibility report
8a Bulk transfers of raw water ✔ Raw water transfer feasibility report
8b Bulk inter/intra company transfers of treated water ✔ Inter-zonal transfers study
9 Tankering of water ✖
10 Redevelopment of existing resources TBC
11 Reuse of existing private supplies ✔ Groundwater feasibility report
12 Water re-use ✔ Water reuse feasibility report
13 Imports (icebergs) ✖
14 Rain cloud seeding ✖
15 Tidal barrage ✖
16 Rainwater harvesting ✖
17 Abstraction licence trading ✔ Third party options report
18 Water quality schemes that increase DO ✔ Catchment management feasibility report
19 Catchment management schemes ✔ Catchment management feasibility report
20 Conjunctive use operation of sources ✔ Built into DOs through WARMS
21 Joint ("shared asset") resource ✔ Included in feasibility reports where applicable
22 Asset transfers ✔ Third party options report
23 Options to trade other (infrastructure) assets ✔ Third party options report
† Taken from UKWIR 2012, Water Resources Planning Tools, EBSD Report, Ref 12/WR/27/6
4 Generic screening of resource management options
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Table 4.1: Summary of options generic screening rejection
Scheme Key elements Screening decision
Comments
9 Tankering of water
Tankering by sea
Tankering requires the development of new infrastructure, including pipelines and deep water facilities for loading / unloading. The logistical, environmental and planning constraints at the Thames Estuary are considerable as the estuary is relatively shallow and access would be restricted.
✖
A proposal by Albion Water for tankering from sources in Norway and the Netherlands has been considered. This concluded that while technically feasible at full utilisation (one tanker per day) it would be excessively costly; and at low utilisation (one tanker per week) the option remains uncompetitive with other options of a similar size. Tankering has therefore not been developed as a water resources option, but is being considered by Thames Water as a potential drought plan option.
13 Imports (icebergs)
Icebergs
This option would require the development of a system for towing of icebergs over long distances e.g. from the Norwegian Sea to the Thames Estuary.
✖
Rejected on the basis that the techniques involved are not sufficiently advanced for commercial use and because of the high level of uncertainty around scheme yield. Also, as the Thames Estuary is designated under the EA Habitats Directive, an Appropriate Assessment is likely to be required. As part of this, the company will be required to demonstrate that there are no feasible alternative options; which is not the case.
14 Rain cloud seeding
Rain cloud seeding This option would require the development of a system for wide commercial implementation. ✖
Rejected on the basis that the techniques involved are not sufficiently advanced for commercial use and because of the high level of uncertainty that the scheme would provide significant yield.
15 Tidal barrage
The Thames Barrage The option for the use of the Thames Barrage to impound fresh water. ✖
Rejected as this option would limit the navigation of the river Thames to both private and commercial traffic resulting in disproportionate social and economic costs. It would also limit the passage of aquatic life which would cause significant ecological damage. The option could also result in raising the groundwater levels in the surrounding areas which could increase the incidence of flooding and cause damage to services and historic buildings in London.
16 Rainwater harvesting
Rainwater harvesting Direct collection and storage of rainwater. ✖ Rejected on the basis of limited drought resilience.
10 Redevelopment of existing resources
Redevelopment of existing resources (e.g. Staines Reservoir)
Changes to current system operation that may result in relatively cheap and simple operational changes that could yield benefits to the supply /demand balance.
TBC
TBC because redevelopment of reservoir storage is not possible unless sufficient surplus resources are available to compensate for the temporary loss of storage and the consequent risks to security of supply that would therefore result whilst the reservoir is being redeveloped. The provision of the surplus resources would be likely to be required for several years to allow the redevelopment of existing sources.
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Chapter 5 provides a summary of the feasibility reports and undertakes the fine
screening assessment for London Water Resource Zone grouped by option type.
Options are assessed qualitatively against the six dimensions: Cost,
Environmental and Social, Promotability, Flexibility, Deliverability and Resilience.
The assessment is presented for each option type together with the screening
decisions.
5.1 Resource option types
Section 5.2 summarises the feasibility report findings for each option type identified for the London WRZ,
which includes:
Water reuse
New reservoirs
Raw water transfers;
Desalination;
Direct river abstraction;
Groundwater development - Aquifer recharge;
Groundwater development - Aquifer storage and recovery;
Groundwater development; and
Removal of Deployable Output constraints.
Section 5.3 summarises exclusivities and interdependencies between options. Section 5.4 summarises the
fine screening assessment, identifying those options being screened out together with the reasons for
rejection. In section 5.5 next steps for options progressing onto the Constrained List are set out. Next steps
required to finalise the fine screening are described in section 5.6.
5.2 Feasibility report findings
5.2.1 Water reuse
The options identified in the feasibility report for water reuse are listed in the table below together with a
summary of the status of the options.
Table 5.1: London options identified in the feasibility report for water reuse
Source Location
Treatment Location
Discharge location
DO (Ml/d)
Stage*
Comment 1 2 3
Beckton STW - final effluent
Site within
Beckton STW
(initially assessed
River Lee Diversion - upstream of King George V Reservoir
380 ✔ ✔ ✔ Treatment site land - Armada Way initially considered however discounted due to proposed housing development. Area in the north of Beckton STW site to be used instead, although noted that TW have other schemes which demand land on the
300 ✔ ✔ ✔
200 ✔ ✔ ✔
150 ✔ ✔ ✔
5 London WRZ resource options
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Source Location
Treatment Location
Discharge location
DO (Ml/d)
Stage*
Comment 1 2 3
on Armada Way)
intake 100 ✔ ✔ ✔ STW site (desalination option, AMP7 growth).
50 ✔ ✔ ✔
Abbey Mills PS - sewer mining
Luxborough Lane
River Lee Diversion - upstream of King George V Reservoir intake
300 ✔ ✔ ✖ These options have been screened out in preference to the Beckton STW site options for the following reasons: the options are mutually exclusive - DO option
combinations are possible planning designations, consents and
requirements are more onerous at the Abbey Mills PS site
the land area available at Luxborough Lane offers less scope for expansion / additional treatment processes if required
less opportunities for biodiversity enhancement at the abstraction location
effects on heritage assets particularly at the PS site
restricted land opportunity for expansion at the Abbey Mills PS abstraction location
there is less potential to mitigate non-traffic impacts upon local properties
200 ✔ ✔ ✖
150 ✔ ✔ ✖
100 ✔ ✔ ✖
50 ✔ ✔ ✖
Abbey Mills PS - sewer mining
Lower Hall River Lee Diversion - upstream of King George V Reservoir intake
300 ✔ ✖ Options are screened out in preference to Luxborough Lane as follows: the Beckton catchment options are mutually
exclusive greater flood plain encroachment additional major crossing and conveyance
route complexity nature conservation and biodiversity
importance affected Lower Hall site is allocated for use as flood
compensation storage
200 ✔ ✖
150 ✔ ✖
100 ✔ ✖
50 ✔ ✖
Crossness STW - final effluent
Site adjacent to Crossness STW (Crossness Southern Marshes)
River Lee Diversion - upstream of King George V Reservoir intake
190 ✔ ✔ ✔ Best performing of the Crossness catchment options. Treated raw water to be discharged into the River Lee Diversion for treatment at Coppermills.
150 ✔ ✔ ✔
100 ✔ ✔ ✔
50 ✔ ✔ ✔
Greenwich PS - sewer mining
Lower Hall River Lee Diversion - upstream of King George V Reservoir intake
150 ✔ ✖ The two Greenwich PS options have been rejected at Stage 2 over retaining the better performing Millbrook Road and Wandle Valley options. The main / differentiating reasons being: the assumed limit for reuse in the Crossness
catchment is 190Ml/d
the Crossness catchment options are mutually
exclusive
other options available with shorter
conveyance
visually sensitive viewpoints affected
heritage assets affected
Lower Hall site is allocated for use as flood
compensation storage
100 ✔ ✖
50 ✔ ✖
Greenwich PS - sewer mining
Hogsmill STW
River Thames - upstream of the Walton WTW intake
150 ✔ ✖ The two Greenwich PS options have been rejected at Stage 2 over retaining the better performing Millbrook Road and Wandle Valley options. The main / differentiating reasons being: the assumed limit for reuse in the Crossness
catchment is 190Ml/d
other options available with shorter
conveyance
visually sensitive viewpoints affected
100 ✔ ✖
50 ✔ ✖
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Source Location
Treatment Location
Discharge location
DO (Ml/d)
Stage*
Comment 1 2 3
heritage assets affected Millbrook Road PS (Brixton) - sewer mining
Hogsmill STW
River Thames - upstream of the Walton WTW intake
100 ✔ ✔ ✖ These Crossness catchment options have been screened out in preference to the Crossness STW site options for the following reasons: the options are mutually exclusive - DO option
combinations are possible the AIC (average incremental cost) £/m3 for
corresponding DO options is higher than Crossness STW
more impacts on visual sensitivity particularly at the PS location
less opportunities for biodiversity enhancement at the abstraction site
potential of restricted land opportunity for expansion at the Millbrook Road PS abstraction location
less potential to mitigate non-traffic impacts upon local properties
50 ✔ ✔ ✖
Wandle Valley PS - sewer mining
Hogsmill STW
River Thames - upstream of the Walton WTW intake
17 ✔ ✔ ✖ The Crossness Wandle Valley PS option is screened out in preference to the Crossness STW site options for the following reasons: the options are mutually exclusive - DO option
combinations are possible the option has similar conveyance length as
Crossness STW but for lower DO availability there is no potential to expand the option AIC (average incremental cost) £/m3 is higher
than similar comparable options
Mogden STW - treated effluent
Kempton Park - Hydes Field
River Thames - upstream of the Walton WTW intake
200 ✔ ✔ ✔ Due to lack of available land at Mogden STW, treatment is located on at Hydes Field (TW owned land). Discharge of the treated raw water is into the River Thames upstream of the Walton intake with treatment at Kempton.
150 ✔ ✔ ✔
100 ✔ ✔ ✔
50 ✔ ✔ ✔
Mogden South Sewer - sewer mining
Kempton Park - Hydes Field
River Thames - upstream of the Walton WTW intake
50 ✔ ✔ ✔ This option takes untreated sewage from the southern sewer into Mogden STW located along the A316, near to Hydes Field. This option is mutually exclusive with the Mogden STW option at 200 Ml/d DO.
Deephams - treated effluent / post screening treatment stream
Lower Hall River Lee Diversion - upstream of King George V Reservoir intake
60 ✔ ✔ ✔ Explanatory
25 ✔ ✔ ✖ The 60 Ml/d option provides better value
Long Reach - treated effluent
Site adjacent to STW
River Lee Diversion - upstream of King George V Reservoir intake
80 ✔ ✖ The reasons for rejecting these options are: significant conveyance lengths conveyance complexity due to length and
number / type of pipeline crossings options 50 ✔ ✖
Riverside - treated effluent
Riverside STW
River Lee Diversion - upstream of King George V Reservoir intake
38 ✔ ✖ The reasons for rejecting this are: significant conveyance lengths conveyance complexity due to length and
number / type of pipeline crossings options
The post Stage 3 assessment feasible list is as follows:
Beckton STW reuse:
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– Development of a water reuse plant using effluent from Beckton Sewage Treatment Works (STW)
on land either on the Beckton STW site, or in the vicinity. The capacity of the plant could range
from 50 to 380Ml/d
– Transfer of reuse water to River Lee flood channel upstream of the King George V intake, or direct
to the Lee Valley reservoirs.
Crossness STW reuse:
– Development of a water reuse plant using effluent from Crossness STW, on land on or adjacent to
the STW. The capacity of the plant could range from 50 to 190Ml/d.
– Transfer of reuse water to River Lee flood channel upstream of the King George V intake, or direct
to the Lee Valley reservoirs.
Deephams STW reuse:
– Development of a water reuse plant using effluent or convert one of the treatment streams into an
MBR plant at Deephams STW. The capacity of the plant being up to 60Ml/d.
– Transfer of reuse water to River Lee flood channel upstream of the King George V intake, or direct
to the Lee Valley reservoirs.
Mogden STW reuse:
– Development of a water reuse plant at Hydes field (located south east of Kempton) using effluent
transferred from Mogden STW. The capacity of the plant could range from 50 to 200Ml/d.
– Transfer of reuse water to River Thames upstream of Walton intake.
Kempton South Sewer (black water):
– Development of a water reuse plant at Hydes field (located south east of Kempton) using sewage
from the Mogden South Sewer at Kempton. The capacity of the plant is 50Ml/d.
– Transfer of reuse water to River Thames upstream of Walton intake.
Further explanation on reasons for rejection of options is set out in the relevant feasibility report and will be
summarised in the option Rejection Register.
5.2.2 New reservoirs
The options identified in the feasibility report for new reservoirs are listed in the tables below together with
a summary of the status of the options. The land areas covered by the potential sites ranged from
approximately 200 hectares to almost 1,500 hectares. Due to this wide range of land area, the feasibility
report defines land area “size bands”. This is to allow the comparison of similarly sized sites at the later
stages of the assessment. Following a review of the range of site sizes identified in previous studies it was
determined that the size bands would be:
Band A: 200 – 399 hectares;
Band B: 400 – 699 hectares;
Band C: 700 hectares or larger.
The potential reservoir sites are shown on a map in Figure 5.1.
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Figure 5.1: Potential reservoir sites
Table 5.2: London options identified in the feasibility report for new reservoirs
Element
Stage Comment
Size band
1 2 3
Site 1 – Minety
A ✔ ✖
Rejected due to poor performance across many criteria including statutory heritage designation and loss of residential dwellings
Site 2 - Leigh A ✔ ✖
Rejected due to poor performance across many criteria including presence of a Wiltshire Wildlife Trust nature reserve
Site 3 - Cricklade
C ✖ Rejected due to statutory heritage designation and birdstrike risk
Site 4 - Swindon
A ✖ Rejected due to built development (housing)
Site 5 – Broad Blunsdon
C ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 6 - Highworth
B ✔ ✖
Rejected due to poor performance across many criteria including distance from intake / outfall point and loss of agricultural land
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Element
Stage Comment
Size band
1 2 3
Site 7 - Wanborough
A ✔ ✔ ✖ Rejected due to poor performance in criteria including planning (housing) and flood risk
Site 8 - Bishopstone
C ✔ ✖
Rejected due to poor performance across many criteria including distance from intake / outfall point and proximity to an Area of Outstanding Natural Beauty
Site 9 - Lechlade
B ✖ Rejected due to statutory heritage designation
Site 10 - Shrivenham
B ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 11 – Clanfield
A ✔ ✖ Rejected due to poor performance across many criteria including access and loss of agricultural land
Site 12 - Faringdon
C ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 13 - Uffington
B ✖
Rejected due to insufficient clay thickness
Site 14 – Brize Norton
B ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 15 - Bampton
B ✔ ✖ Rejected due to poor performance across many criteria including flood risk and loss of agricultural land
Site 16 - Witney
B ✔ ✖ Rejected due to poor performance across many criteria including flood risk, loss of agricultural land and heritage
Site 17 – Stanford in the Vale
B ✔ ✖
Rejected due to poor performance across many criteria including access and loss of residential properties
Site 18 - Longworth
B ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 19 – South Leigh
A ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 20 – West Hanney
B ✖ Rejected due to insufficient clay thickness
Site 21 – Stanton Harcourt
A ✔ ✖
Rejected due to poor performance across many criteria including flood risk and recreation
Site 22 - Abingdon
C ✔ ✔ ✔ Best performing site for all storage capacities
Site 23 - Wantage
B ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 24 - Kidlington
B ✖ Rejected due to statutory nature conservation designations
Site 25 - Oxford
A ✔ ✖ Rejected due to poor performance across many criteria including of Ancient Woodland and recreation
Site 26 - Didcot
A ✔ ✖ Rejected due to poor performance across many criteria
including presence of Area of Outstanding Natural Beauty
Site 27 - Beckley
C ✖ Rejected due to statutory nature conservation and heritage designations
Site 28 – Brightwell cum Sotwell
B ✖
Rejected due to statutory heritage designation
Site 29 - Ambrosden
A ✖ Rejected due to insufficient clay thickness
Site 30 – Drayton St Leonard
A ✔ ✖
Rejected due to poor performance across many criteria including numbers of adjacent local residents and loss of agricultural land
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Element
Stage Comment
Size band
1 2 3
Site 31 - Wheatley
B ✖ Rejected due to statutory nature conservation designations
Site 32 – Benson
B ✖
Rejected due to statutory heritage designation and birdstrike risk
Site 33 – Chalgrove
B ✔ ✖ Rejected due to poor performance across many criteria including construction traffic and topographical variation
Site 34 - Bicester
B ✖ ✖ Rejected due to insufficient clay thickness
Site 35 – Chalgrove Airport
B ✔ ✖
Rejected due to poor performance across many criteria including construction traffic and heritage
Site 36 – Marsh Gibbon
C ✔ ✔ ✔
Next best performing site (along with Site 41 – Chinnor) at 30Mm3, 50Mm3 reservoir capacities. Next best performing site at 75Mm3
Site 37 - Ludgershall
B ✔ ✔ ✖ Rejected due to landscape, construction complexity and impact on the floodplain
Site 38 – Great Haseley
A ✔ ✖
Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 39 - Quainton
B ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
Site 40 - Postcombe
A ✔ ✔ ✖ Rejected due to insufficient storage capacity
Site 41 - Chinnor
B ✔ ✔ ✔ Next best performing site (along with Site 36 – Marsh Gibbon) at 30Mm3, 50Mm3 reservoir capacities
Site 42 – Haddenham
A ✔ ✔ ✖ Rejected due to construction complexity, landscape and views
Site 43 - Aylesbury
B ✔ ✔ ✖ Rejected due to planning, views and construction complexity
Site 44 - Stone
B ✖ Rejected due to statutory heritage designation
Site 45 - Whitchurch
A ✖ Rejected due to insufficient clay thickness
Site 46 - Stewkley
B ✖
Rejected due to statutory heritage designation and insufficient clay thickness
Site 47 - Bierton
B ✖ Rejected due to birdstrike risk and insufficient clay thickness
Site 48 - Wingrave
A ✖ Rejected due to insufficient clay thickness
Site 49 - Cheddington
A ✔ ✖ Rejected due to poor performance across many criteria including heritage and distance from intake / outfall point
Site 50 - Kintbury
B ✔ ✖
Rejected due to poor performance across many criteria including presence of Area of Outstanding Natural Beauty and Ancient Woodland
Site 51 - Burghfield
A ✖ Rejected due to built development (military establishment)
Site 52 – Beech Hill
B ✔ ✖ Rejected due to poor performance across many criteria including presence of Ancient Woodland
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Element
Stage Comment
Size band
1 2 3
Site 53 - Wokingham
A ✖ Rejected due to statutory heritage designation
Site 54 - Bracknell
A ✔ ✔ ✖ Rejected due to insufficient storage capacity
Site 55 - Maidenhead
A ✖ Rejected due to insufficient clay thickness
The assessment of the sites that passed through to Stage 3 considered a range of property, planning and
engineering criteria. The assessment identified Site 22 - Abingdon as the best performing site against
these criteria across all reservoir capacities from 30Mm3 – 150Mm
3.
Although the conclusion of the staged assessment approach was that Site 22 – Abingdon was the best
performing site, consideration was given to the next best performing site(s) and where appropriate these
were also identified to be taken through to the fine screening stage for further appraisal.
At the larger reservoir capacity options (125Mm3 and 150Mm
3), Abingdon was the only available site
option. Two potential options were considered at a 100Mm3 reservoir capacity; however, the difference
between the overall assessment performance of Site 22 - Abingdon and Site 36 - Marsh Gibbon at this
capacity was such that only Abingdon was considered suitable to be taken through to the fine screening
stage.
At some of the smaller reservoir capacity options, the difference in performance between Site 22 –
Abingdon, Site 36 – Marsh Gibbon and Site 41 – Chinnor was less. In consequence, at a reservoir capacity
of 75Mm3 the next best performing site, which was Site 36 – Marsh Gibbon, was also taken forward to the
fine screening stage.
The next best performing sites at both 30Mm3 and 50Mm
3 reservoir capacities were Site 36 – Marsh
Gibbon and Site 41 – Chinnor. As there was limited difference in the performance of these two sites at
these reservoir capacities, both these sites were taken forward to the fine screening stage for
consideration.
Consideration of different reservoir capacities ranging from 30 Mm3 to 150 Mm
3 provides flexibility in terms
of reservoir options that could potentially feed into the WRMP19 option appraisal process. To retain this
flexibility, an initial review as to the feasibility of a phased development of a reservoir at the Abingdon site
has also been undertaken. This exercise has identified the possibility of the Abingdon site being developed
in two phases, nominally including a 30Mm3 + 120Mm
3 option as well as a 75Mm
3 option + 75Mm
3 option,
but further review of the impact on deployable output and the phasing of reservoir volumes is required at
conceptual design phase to take account of more refined embankment profiles and borrow pit shapes as
constrained by site specific geological conditions. Consideration of both single and phased development at
the Abingdon site has therefore been taken forward to the fine screening stage.
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The preferred options taken forward to the fine screening stage are therefore:
30Mm3 – Site 22 Abingdon, Site 36 Marsh Gibbon, Site 41 Chinnor
50Mm3 – Site 22 Abingdon, Site 36 Marsh Gibbon, Site 41 Chinnor
75Mm3 – Site 22 Abingdon, Site 36 Marsh Gibbon
100Mm3 – Site 22 Abingdon
125Mm3 – Site 22 Abingdon
150Mm3 – Site 22 Abingdon
30Mm3 + 120Mm
3 – Site 22 Abingdon
75Mm3 + 75Mm
3 – Site 22 Abingdon
Further explanation on reasons for rejection of options is set out in the relevant feasibility report and will be
summarised in the option Rejection Register.
5.2.3 Raw water transfers
For raw water transfers the resource element and conveyance elements have been considered separately
in the feasibility reports. The elements considered are listed in the tables below together with a summary
of their status.
Table 5.3: London options identified in the feasibility report for raw water transfers (resource elements)
Element
Capacity
(Ml/d)
Stage
Comment 1 2 3
Kielder Reservoir Not defined ✔ ✖ Rejected because its associated conveyance elements fail
Stage 2 screening. These conveyance elements (existing
canals and a new pipeline) are considered the only realistic
ones.
South-East Wales Resource
(Including Great Spring)
TBC This option is on hold pending further information from Welsh
Water and confirmation of Natural Resources Wales and
Welsh Government view.
(The option replaces the historical Columbus options).
CRT Bradley groundwater
abstraction
15 ✔ ✔ TBC TBC pending further information from CRT on abstraction
yield and costs
Minworth STW effluent and
pipe to the River Avon
88 ✔ ✔ ✔ This resource element includes a pipeline conveyance to take
the water to the carrier watercourse as per the Water
Resource definition.
Minworth STW effluent 88 ✔ ✔ ✔p This resource element is without a pipeline conveyance, for
potential transfer via an adjacent canal.
Provisionally passed pending cost data from Severn Trent
Water
Expansion of Draycote
Reservoir and an abstraction
from the River Avon
25 ✔ ✔ ✔ This resource element as offered by Severn Trent Water
includes a new feed pipeline into the reservoir.
Mythe WTW unused part of
licence
15 ✔ ✔ ✔
Middle Severn 197.5 ✔ ✖ This resource element as offered by Severn Trent Water
comprises a number of components, including Draycote
Reservoir expansion with a new feed pipeline from the River
Severn, the Minworth STW effluent and a pipeline
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Element
Capacity
(Ml/d)
Stage
Comment 1 2 3
conveyance from Eathorpe to the River Thames.
Rejected because of comparatively poor performance against
other resources on several criteria, including associated
pipeline conveyance length, total pumping head, operational
complexity, construction complexity and water source and
availability.
Netheridge STW effluent 15 ✔ ✔ TBC Dependent on confirmation of Cotswold Canal conveyance
status. If pumped to another location would further increase
the cost and resource would fail assessment on normalised
cost.
Lake Vyrnwy 180 ✔ ✔ ✔
Craig Goch Reservoir
expansion
Not defined ✖ Failed on National/ International Nature Conservation
designations.
River Severn (unsupported) Not defined ✖ Failed on resilience to drought (Hands-off flow prevents
abstraction at times when water is needed by Thames Water)
Longdon Marsh reservoir to
support River Severn
abstraction
Reservoir
volume
50/89/125
Mm3
✔ ✖ Rejected because of comparatively poor performance against
other resource/ support elements on several criteria, including
estimated land acquisition cost, flood plain encroachment,
impact on residential dwellings and archaeology and the
historic environment.
Use of a new Thames
reservoir (as in reservoir
report, if successfully
promoted) to support River
Severn abstraction and
transfer
TBC ✔ ✔ ✔p Provisionally passed pending further investigation of
Deployable Output of a combined reservoir and Severn
Thames Transfer option.
Use of Farmoor Reservoir to
support River Severn
abstraction and transfer
n/a ✔ ✔ TBC Further assessment required to confirm capacity and benefit.
Expected to fail on normalised cost / lack of benefit when
deployable output is available.
Note: ✔p denotes options provisionally passed.
Table 5.4: London options identified in the feasibility report for raw water transfers (conveyance elements)
Element
Capacity
(Ml/d)
Stage
Comment 1 2 3
South-East Wales resource
conveyance (previously known as
Columbus)
TBC n/a TBC TBC This conveyance will be provided in conjunction
with any Welsh Water resource. On hold awaiting
confirmation on the Welsh Water resource.
Oxford Canal – Thames (for London
WRZ only)
15 n/a ✔ ✔p Provisionally passed pending further engineering
review
Oxford Canal - Grimsbury Reservoir
(SWOX)
15 n/a ✔ ✔p Provisionally passed pending further engineering
review
Canal transfer Minworth STW to Isis
Lock
100 n/a ✔ TBC To be confirmed pending review of more detailed
cost data from CRT / canal transfer report team
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Element
Capacity
(Ml/d)
Stage
Comment 1 2 3
Pipeline from Kielder Reservoir Up to 300 to
LON;
40 Ml/d to
SWOX
n/a ✖ Rejected because of comparatively poor
performance against other conveyances on several
criteria including total pipeline conveyance length,
pumping head, construction complexity and
operational complexity.
Canals from Kielder Reservoir 45 n/a ✖ Rejection reasons include: the Water UK study
concluded that the water from Kielder Reservoir is
likely to be required by neighbouring areas; and the
operational complexity associated with this
conveyance is disproportionate to the limited DO
benefit that could be achieved.
Pipeline Deerhurst to Culham for 100
Ml/d transfer
100 n/a ✖ Rejected because the Deerhurst to Radcot pipeline
route for the same capacity is significantly shorter
route and had similar performance for other criteria.
Pipeline Deerhurst to Culham for 300
Ml/d transfer
300 n/a ✔ ✖ Rejected as mutually exclusive with the Deerhurst
to Radcot element for the same capacity and the
latter is a significantly shorter route and performed
better on a number of criteria including normalised
cost.
Pipeline Deerhurst to Culham for 600
Ml/d transfer
600 n/a ✔ ✖ Rejected due to risk of adverse effects on the River
Thames environment
Pipeline Deerhurst to Cricklade for
100 Ml/d transfer
100 n/a ✔ ✖ Rejected as mutually exclusive with the Deerhurst
to Radcot element for the same capacity and the
latter performed better on water resources and
water quality.
Pipeline Deerhurst to Radcot for 100
Ml/d transfer
100 n/a ✔ ✔
Pipeline Deerhurst to Radcot for 300
Ml/d transfer
300 n/a ✔ ✔
Pipeline Deerhurst to Radcot for 600
Ml/d transfer
600 n/a ✔ ✖ Rejected due to risk of adverse effects on the River
Thames environment
Pipeline Deerhurst to Farmoor 100 n/a ✔ ✔p Pipeline passes assessment but Farmoor Reservoir
support option is TBC and this pipeline is specific to
that option.
Pipeline Deerhurst to a new TW
reservoir
300 n/a ✔ ✖ Rejected as transfer to Radcot and subsequent
abstraction at the new TW reservoir is feasible and
more cost effective.
Cotswold Canal 100 Ml/d 100 n/a ✔ ✖ Rejected as it is mutually exclusive with the
Deerhurst pipeline conveyances and was concluded
to be overall less feasible than the latter. Performed
worse on the key criteria of Water resources and
Water quality and on normalised cost.
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Element
Capacity
(Ml/d)
Stage
Comment 1 2 3
Cotswold Canal 300 Ml/d 300 n/a ✔ TBC This element is mutually exclusive with the
Deerhurst pipeline 300 Ml/d conveyances and was
concluded to perform less well on a number of
criteria and carry more risk than the latter. However,
the assessment is TBC pending further review of
cost and risks.
Note: ✔p denotes options provisionally passed.
During the Validation stage, the resource and conveyance elements assessed separately in stages 1 to 3
were considered in combination. The potential combinations are given in Table 5.5 below.
Table 5.5: Raw Water Transfer Combined Options
Resource(s)
/Support(s) Conveyance
Resource zones
Capacity (Ml/d)
Feasible List? Comments
South-East Wales resource (Incl. Great Spring)
South-East Wales conveyance
TBC TBC TBC Option to be defined and assessed when information received from Welsh Water
CRT Bradley groundwater abstraction
Oxford Canal – Grimsbury Reservoir
London and SWOX
15 TBC Abstraction costs TBC pending further discussion with CRT
CRT Bradley groundwater abstraction
Oxford Canal – River Thames
London 15 TBC Abstraction costs TBC pending further discussion with CRT
Minworth STW effluent, CRT Bradley groundwater abstraction
Canal transfer Minworth STW to Isis Lock
London, SWOX or both
88+15 TBC Further information required from CRT and Severn Trent Water to confirm costing
Minworth STW, Draycote Reservoir, Mythe WTW and Lake Vyrnwy resources
Deerhurst to Radcot Pipeline conveyance element
London, SWOX or both
308 from listed resources
✔
Minworth STW, Draycote Reservoir, Mythe WTW, Netheridge STW and Lake Vyrnwy resources
Costwold Canal conveyance element
London, SWOX or both
323 from listed sources
TBC Further review of operating costs and risks
As above, including use of a new Thames reservoir
Pipeline from Deerhurst to a new Thames reservoir
London, SWOX or both
300 TBC Further investigation to confirm the Deployable Output benefit and normalised cost
Use of Farmoor Reservoir Pipeline from Deerhurst to Farmoor Reservoir
London, SWOX or both
TBC TBC Further investigation to confirm the Deployable Output benefit and normalised cost
Work to finalise the feasibility report is ongoing and the above table will be updated once the work is
complete. Pending finalisation of the feasibility report only the Deerhurst pipeline option at 100Ml/d and
300Ml/d have been carried forward to fine screening. A brief description of this option is provided below.
Severn-Thames Transfer (Deerhurst to Radcot pipeline) 300 Ml/d
– Redeployment of Lake Vyrnwy from United Utilities to support flows in the River Severn
(180Ml/d) and development of replacement resource by United Utilities as required
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– Transfer of Minworth effluent to the River Avon (by Severn Trent Water) to support flows in the
River Severn catchment (88Ml/d)
– Transfer of 15Ml/d of Severn Trent Water Mythe licence to support flows in the River Severn
– Expansion of Draycote reservoir (by Severn Trent Water) to support flows in the River Severn
– A 300Ml/d transfer of raw water from the River Severn at Deerhurst, via a new pipeline, for
discharge at Radcot and reabstraction at existing TWUL intakes downstream.
Further explanation on reasons for rejection of options is set out in the relevant feasibility report and will be
summarised in the option Rejection Register.
5.2.4 Desalination
The options identified in the feasibility report for desalination are listed in the table below together with a
summary of the status of the options.
Table 5.6: London options identified in the feasibility report for desalination
Ref. Plant Location Distribution Location
DO (Ml/d)
Stage
Comment 1 2 3
1a Beckton STW
Coppermills WTW
(blended)
150 ✔ ✔ ✔
Treatment site land - Armada Way initially considered however discounted due to proposed housing development. Areas of Beckton STW site to be used instead, although noted that TW have other schemes which demand land on the STW site (water reuse, AMP7 growth).
1b River Lee
Coppermills WTW
(blended)
150 ✔ ✖
Source – Option considered abstraction from the River Thames and return of brine reject stream to River Lee.
Rejected at Stage 2 due to constraints on land availability.
2a Manor Rd, Erith Honor Oak
(blended) 150 ✔ ✖
Rejected at Stage 2 due to length of conveyance.
2b(i) Crossness
(Honor Oak) – Coppermills WTW
(blended)
150 ✔ ✔ ✖ Distribution location – Honor Oak considered, but Coppermills WTW preferable due to greater capacity for blending treated water.
Rejected at Stage 3 due to being located on greenfield land with longest conveyance.
2b(ii) 300 ✔ ✔ ✖
2c(i) Tripcock Ness, Thamesmead
(Honor Oak) – Coppermills WTW
(blended)
150 ✔ ✔ ✔ Distribution location – Honor Oak considered, but Coppermills WTW preferable due to greater capacity for blending treated water.
2c(ii) 300 ✔ ✔ ✔
3a Crossness
Northumberland Heath
(direct-supply)
65 ✔ ✔ ✔
Distribution location – Northumberland Heath service reservoir for direct-supply to Riverside WRZ
Following the Stage 3 assessment the following desalination options have been identified as being
feasible:
Desalination plant located at Beckton STW:
– Development of a 150 Ml/d desalination plant located on Beckton STW, using brackish estuarine
water from the River Thames as its feedwater.
– Transfer of treated water to Coppermills WTW for blending.
Desalination plant located at Tripcock Ness, Thamesmead:
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– Development of a desalination plant located at Tripcock Ness, Thamesmead, using brackish
estuarine water from the River Thames as its feedwater. The capacity of the plant could range
from 150 to 300 Ml/d.
– Transfer of treated water to Coppermills WTW for blending.
Desalination plant located south of Crossness STW:
– Development of a 75 Ml/d desalination plant located to the south of Crossness STW, using
brackish estuarine water from the River Thames as its feedwater.
– Transfer of treated water to Northumberland Heath service reservoir for direct-supply of Riverside
Zone.
Further explanation on reasons for rejection of options is set out in the relevant feasibility report and will be
summarised in the option Rejection Register.
5.2.5 Direct river abstraction
The options identified in the feasibility report for direct river abstraction are listed in the table below
together with a summary of the status of the options.
Table 5.7: London options identified in the feasibility report for direct river abstraction
Option Sub-option Capacity / DO
Stage Comment
1 2 3
Lower Lee Surface Water abstraction
1a) Abstraction at Three Mills Lock, transfer flow to King George V reservoir and treat at Coppermills WTW from where it is put into supply.
150 Ml/d
✔ ✔ ✖
Potential significant WQ issues-Pending Data.
Length of conveyance and cost compared to 1b.
Lower Lee Surface Water abstraction
1b) Abstraction at Three Mills Lock, treat flows and put into supply.
150 Ml/d
✔ ✔ ✔
Potential significant WQ issues-Pending Data*
Teddington Weir (Mogden effluent transfer)
3a) Transfer 300Ml/d from Mogden to Teddington. New intake upstream of Teddington Weir with direct transfer to Thames Lee Tunnel.
300 Ml/d
✔ ✔ ✔
Teddington Weir (Mogden effluent transfer incl. Storage)
3b) New intake and upstream of Teddington weir and transfer to Queen Mother reservoir for storage.
300 Ml/d
✔ ✔ ✖
High construction complexities. Cost
comparison higher when compared to 3a.
Teddington Weir (Mogden effluent transfer incl. treatment)
3c) New intake and treatment works upstream of Teddington Weir at Canbury Gardens for direct supply.
300 Ml/d
✔ ✖
Land available not sufficient for full treatment site. Ownership of land issues.
Mogden effluent transfer to Teddington Weir
4) Increase existing abstraction upstream at Surbiton.
300 Ml/d
✔ ✖
Area availability on site insufficient.
Beckton effluent transfer
5a) No treatment and transfer to Thames Lee Tunnel
300 Ml/d
✖
The proximity to abstraction means high length
of conveyance and associated cost.
Beckton effluent transfer
5d) Partial Treatment and transfer to reservoir
300 Ml/d ✖
Beckton effluent 5c) Full treatment transfer to 300 Ml/d ✖
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Option Sub-option Capacity / DO
Stage Comment
1 2 3
transfer supply network
Lower River Roding 6) Lower River Roding abstraction for direct supply to potable network or transfer to Lee Valley Reservoirs
17.3 Ml/d
✖
Not resilient during drought conditions.
River Mardyke 7) River Mardyke 3.7 Ml/d ✖
Not resilient during drought conditions.
River Rom/Beam 8) River Rom/Beam abstraction for direct supply to potable network
7.2 Ml/d
✖
Not resilient during drought conditions.
River Ingrebourne 9) River Ingrebourne abstraction for direct supply to potable network
4.2 Ml/d
✖
Not resilient during drought conditions.
*goes through to fine screening with an associated significant risk
Following the Stage 3 assessment the following direct river abstraction options have been identified as
being feasible for the London WRZ:
Option 1b - New Intake at Three Mills Lock on the Lower River Lee followed by treatment and direct
supply to distribution network.
Option 3a - Transfer of 300Ml/d from Mogden STW to downstream of Teddington Weir, enabling
additional abstraction upstream of Teddington Weir. New intake upstream of Teddington weir
connecting into the existing Thames Lee Tunnel.
Further explanation on reasons for rejection of options is set out in the relevant feasibility report and will be
summarised in the option Rejection Register.
5.2.6 Aquifer recharge
The aquifer recharge options identified in the groundwater feasibility report are listed in the table below
together with a summary of the status of the options.
Table 5.8: London options identified in the feasibility report for aquifer recharge
Option
DO (Ml/d)
Stage*
Comment 1 2 3
SLARS Kidbrooke (SLARS1)
5.1 ✔ ✔ TBC
Eltham Green site removed from the option (with consequential reduction in yield) to allow progression of scheme through Stage 2. EA approved as non- consumptive with recommendations for consented test pumping to assess the risk of sub-surface flooding.
Requires agreement with the EA on operating principal as part of SLARS.
AR – Kidbrooke 5.0 ✔ ✔ TBC
Network modelling is to be carried out by others to determine recharge capacity of the system. Requires agreement with the EA on operating principal as part of SLARS.
AR Merton (SLARS3) 6.0 ✔ ✔ TBC
Drilling and test pumping of a new abstraction borehole will be required at the Byegrove Road site to confirm yield and water quality.
Requires agreement with the EA on operating principal as part of SLARS.
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Option
DO (Ml/d)
Stage*
Comment 1 2 3
AR Streatham (SLARS2)
5.0 ✔ ✔ TBC
Definition of operating strategy required. Requires agreement with the EA on operating principal as part of SLARS.
It is expected that all the options will be to be carried forward from the feasibility report:
SLARS Kidbrooke:
– Component of the larger SLARS project based on the development of boreholes for
recharge/abstraction purposes in the confined Chalk. The scheme comprises the upgrade of
the existing borehole at the Rochester Way site and another at the Bromley Reservoir site.
– The scheme also includes construction of a new 5.1 Ml/d WTW located on the existing
Kidbrooke borehole site to serve the Rochester Way and Bromley Reservoir AR boreholes, and
associated pipelines.
AR – Kidbrooke:
– Development of two existing boreholes for recharge and abstraction in the confined chalk at
Kidbrooke
– The abstracted water would be treated at a new WTW on the site and returned to the local
distribution network.
AR – Merton (SLARS)
– The proposed works at Merton Abbey include redevelopment of the existing 1.5 m diameter
borehole and provision of a new abstraction pump. A new connection will provide recharge
water while abstracted raw water will be routed to the existing WTW which is currently limited to
a maximum flow of 5 Ml/d, though the full design capacity is 8 Ml/d;
– The proposed works at Byegrove Road include a new recharge borehole and two additional
observation boreholes, network connection to provide recharge water, equipping the borehole
with an abstraction pump rated at 4.5 Ml/d and pumping of the abstracted water to the new
Merton Abbey WTW via a new 1.1 km main.
AR Streatham (SLARS)
– Component of the larger SLARS project based on the upgrade of an existing borehole plus the
construction of a new AR borehole. Water for recharge will be abstracted from the River
Thames in west London during periods of low demand, treated to drinking water standards and
supplied through the existing mains network. The scheme also includes works on the WTW at
Streatham to service these two boreholes.
5.2.7 Aquifer storage and recovery
The aquifer storage and recovery options identified in the groundwater feasibility report are listed in the
table below together with a summary of the status of the options.
Table 5.9: London options identified in the feasibility report for aquifer storage and recovery
Option
DO (Ml/d) Stage*
Comment 1 2 3
ASR South East London (Addington)
1.5 ✔ ✔ TBC
Stage 1 & 2 passed. Assessment of hydrogeological suitability complete. Stage 3 assessment in progress
ASR Thames Valley/Thames Central
1.5 ✔ ✔ TBC
Stage 1 & 2 passed. Assessment of hydrogeological suitability complete. Stage 3 assessment in progress
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Both options are expected to be carried forward from the feasibility report.
ASR South East London Addington
– Scheme comprises the upgrade of one existing borehole and installation of four new
operational ASR boreholes in the confined Lower Greensand aquifer at the TWUL Addington
site.
– Recharge of up to 5Ml/d will take place using water from the treated water network during the
winter months.
– Abstraction from the ASR boreholes at up to 5Ml/d will be treated at a new Addington WTW
during the summer, as required.
ASR Thames Valley/Thames Central
– Scheme comprises the installation of five new operational ASR boreholes in the confined
Lower Greensand aquifer at the TWUL Ashford WTW site.
– Recharge of up to 5Ml/d will take place using water from Ashford WTW during the winter
months.
– Abstraction from the ASR boreholes at up to 5Ml/d will be treated at the existing Ashford WTW
during the summer, as required.
5.2.8 Groundwater development
The groundwater development options identified in the groundwater feasibility report are listed in the table
below together with a summary of the status of the options.
Table 5.10: London options identified in the feasibility report for groundwater development
Option
DO (Ml/d) Stage*
Comment 1 2 3
Arla Foods Licence Trading/Transfer
1.9 ✔ ✔ TBC
Requires agreement with Arla Foods over licence trading. TWUL to decide whether to progress this option.
GW – Epsom 3.3 ✖ Passed Phase 1 but modelling shows a severe impact on the River Hogsmill.
Shortlands 4.2 ✔ ✔ TBC
Modelling impact of the abstraction using the London Basin Aquifer Model required. Subject to agreement from the EA once modelled impacts are available.
GW - London confined Chalk (north)
1.5 ✔ ✔ TBC
Drilling and test pumping of a new abstraction borehole will ultimately be required at the site to confirm yield and water quality.
GW - Southfleet/Greenhithe (new WTW)
9.0 ✔ ✔ TBC
Further liaison with the EA to understand what they would require to grant this licence. Test pumping and monitoring may be required.
GW – Addington 1.5 ✔ ✔ TBC
Drilling and test pumping of a new abstraction borehole will ultimately be required at the site to confirm yield, water quality, impacts on third parties and impact on surface water features
It is expected that the following options are to be carried forward from the feasibility report:
GW – Arla Foods
– Arla Foods own and operate two boreholes at their dairy site in north London. TWUL are
interesting in utilising the available water within the existing licence.
– Contractual agreement between TWUL and Arla Foods is required.
– Buy in form the Environment Agency is also needed and currently under discussion.
Shortlands:
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– Increase in licence quantity to reflect available potential yield of existing boreholes.
GW – Addington
– The construction of new abstraction borehole located on the site of the existing WTW to be
operated within existing licence limits.
– Water abstracted from the borehole will be treated at the existing WTW.
GW – London confined Chalk (north)
– The scheme is a new unlicensed and unproven groundwater development scheme and will
require drilling of a new abstraction borehole and test pumping to support the application for a
new abstraction licence.
– The target most likely deployable output of the scheme is 2.3 Ml/d (average & peak); and
– Abstracted water will be treated at a new on site water treatment works (WTW), processes will
include superchlorination, dechlorination and reverse osmosis.
GW – Southfleet/Greenhithe (new WTW)
– This scheme is for the dissagregation of group licence to allow increased abstraction from the
chalk aquifer.
– Redevelopment of two boreholes (previously owned by Empire Paper Mills) for abstraction as
part of the scheme.
– Provision of a new WTW at the Southfleet EMP borehole
– Connection pipeline from the Greenhithe Borehole to the new WTW
– Treated water pipeline from the WTW to the existing network
5.2.9 Removal of Deployable Output constraints
The options for removal of Deployable Output constraints identified in the groundwater feasibility report are
listed in the table below together with a summary of the status of the options.
Table 5.11: London options identified in the feasibility report for aquifer storage and recovery
Option
DO (Ml/d)
Stage*
Comment 1 2 3
RC - Green St Green 0.62 ✖ In progress, TWUL delivering so removed
from options.
None of the options are expected to be carried forward from the feasibility report.
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5.3 Exclusivities/Interdependencies
Table 5.12: Exclusivities and interdependencies
Option type Exclusivities/Interdependencies
Water reuse The Deephams reuse option is mutually exclusive with the Lower Lee direct river abstraction option.
The Kempton black water options is mutually exclusive with Mogden reuse
Both Kempton black water and Mogden reuse are mutually exclusive with Teddington direct river abstraction (Mogden effluent transfer)
New reservoirs Reservoirs of different sizes are mutually exclusive on the same site. Phased options will be developed at Conceptual Design stage.
Raw water transfers None
Desalination There is a potential limiting factor on desalination capacities due to possible increased salinity levels in a given reach of the Tideway. A precautionary approach to the environmental assessment has been adopted that has resulted in a limit of 300 Ml/d of additional desalination capacity in any single reach of the River Thames, but subject to further analysis (i.e. estuarine modelling) it is expected that higher levels may be acceptable.
Direct river abstraction See water reuse
Aquifer recharge The AR options may all be delivered independently. However, they are all part of SLARS and, therefore, the proposed operating strategy reflects this interdependence. The Kidbrooke option, however, is seen as a pre-cursor to the SLARS Kidbrooke option in order to provide a fast-track development of AR capacity in London.
ASR The Thames Valley/Thames Central option is independent of all other options.
Groundwater development None
Removal of constraints to DO
None
5.4 Fine screening assessment
The previous sections identified the options that have been carried forward from the feasibility reports.
Each of these options has been assessed against the six dimensions and associated sub-dimensions set
out in Chapter 3 of this report. The assessment for each option type is set out, with commentary, in
Appendix B and summarised in the table below.
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Table 5.13: Sub-option screening at the sub-dimension level – London WRZ
Sub-dimension
Supported raw water
transfer Water reuse
Desalination
River Regulation Reservoir
Direct River
Abstraction
Aquifer recharge Aquifer
storage & recovery
Groundwater development
ST
T v
ia D
eerh
urs
t
to R
ad
co
t P
ipe
lin
e
ST
T v
ia D
eerh
urs
t to
Rad
co
t P
ipe
lin
e
Deep
ha
ms
Beckton Mogden
Kem
pto
n
Crossness
Beckto
n
Th
am
esm
ead
Cro
ssn
ess
Abingdon
Marsh Gibbon
Chinnor
Lo
wer
Le
e
Te
dd
ing
ton
SL
AR
S K
idb
roo
ke
Str
eath
am
Me
rto
n
Kid
bro
ok
e
HA
RS
SE
Lo
nd
on
A
dd
ing
ton
Th
am
es V
alley
Cen
tral
Ad
din
gto
n
Lo
nd
on
Co
nfi
ne
d
Ch
alk
So
uth
fleet/
G
reen
hit
he
Arl
a F
oo
ds
Sh
ort
lan
ds
100 Ml/d
300 Ml/d
60 Ml/d
50 Ml/d
100-150 Ml/d
200-380 Ml/d
50 Ml/d
100-150 Ml/d
200 Ml/d
50 Ml/d
50 Ml/d
100-150 Ml/d
190 Ml/d
150 Ml/d
150-300 Ml/d
75 Ml/d
<75 Ml/d
75-174 Ml/d
>175 Ml/d
<75 Ml/d
75-174 Ml/d
<75 Ml/d
75-174 Ml/d
150 Ml/d
300 Ml/d
5.1 Ml/d
5 Ml/d
6 Ml/d
5 Ml/d
2 Ml/d
1.5 Ml/d
1.5 Ml/d
1.5 Ml/d
1.5 Ml/d
9 Ml/d
1.9 Ml/d
4.2 Ml/d
Env & Social
SEA ○◑ ○◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◎◑ ◎◑
HRA ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
WFD ◑r ◑
r ◑
r ○ ○ ○ ◑
r ◑
r ◑
r ○ ○ ○ ○ ○ ○ ○ ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
Cumulative effects ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Cost
○ ○ ○ ◑ ○ ○● ◎ ◎ ○ ◎ ◑ ○◑ ◑ ○ ○ ◉ ◎ ◎○ ◑● ◑ ◑● ◑● ◑ ◉ ◉
Promotability
Synergies ◎ ◉ ○ ○ ◎ ◎ ○ ◎ ◎ ○ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◎
Customer acceptability ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r ◑
r ● ◑ ◑ ◑ ◑ ◑ ◑ ◑ ○ ○
Local acceptability ◑r ◑
r ○ ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑r ◑r ◑
r ◑
r ◑ ◑ ◑ ◑ ● ● ● ● ● ● ○ ◑
Regulatory acceptability ◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑r ◑r ◑
r ◑
r ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ●
r ◑
r
Wider stakeholder acceptability ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑ ◑ ◑ ◑ ◑ ◑ ○ ◑
Flexibility
Lead time ○ ○ ◎ ○ ○ ◑ ○ ○ ○ ○ ○ ○ ◑ ○ ○ ◎ ● ● ● ● ● ● ● ○ ◑r
Phasing ◑r ◑
r ○ ◑ ◑ ◑ ◑ ◑ ◑ ○ ◑ ◑ ◑ ◑ ◑ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◑
Adaptability ◎ ◉ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◎ ◎ ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ○
Ramp-up ◎ ◎ ● ● ● ● ● ● ● ● ● ● ● ● ● ○ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ● ●
Deliverability
Constructability ◑r ◑
r ○ ◑
r ◑
r ◑
r ○ ○ ○ ○ ◑
r ◑
r ◑
r ◑
r ◑
r ○ ◑ ◑ ◑ ● ● ● ● ◑
r ◑
r
Operability ◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ● ◎ ◎ ◎ ◎ ◎ ◎ ◎ ○ ○
Dependencies ◑ ◑ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◑r
Data confidence ◑r ◑
r ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ◉ ◉ ◉ ○ ○ ○ ◑
r ◑
r ◑
r ◑
r ●
r ○
Resilience
Climate change ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◎
Severe drought ○ ○ ◎ ◉ ◉ ◉ ◎ ◎ ◎ ◎ ◉ ◉ ◉ ◉ ◉ ◉ ● ◑ ◑ ◑ ◑ ◑ ◑ ○ ○
Resource predictability ◎ ◎ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎ ◎
System outage ◎ ◎ ◑ ◑ ◑ ◑ ○ ○ ○ ○ ◑ ◑ ◑ ◑ ◑ ● ◎ ◉ ◉ ◉ ◉ ◉ ◉ ◑ ◑
Other ‘failure modes’ ◑ ◑ ◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑ ◑ ◑ ○ ○ ○ ○ ○ ○ ○ ◑ ◑
Screening decision
✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖
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5.4.1 Scenario analysis
To support the fine screening a simple scenario analysis has been conducted that considers potential
combinations of options that could satisfy a nominal 800Ml/d deficit. The scenarios considered were:
Scenario 1: all options available
Scenario 2: Teddington Weir (Mogden effluent transfer) direct river abstraction option is
unavailable (e.g. because navigation impacts are found to be significant)
Scenario 3: Severn Thames Transfer is also unavailable (e.g. due to insurmountable concerns
around invasive species transfer)
Scenario 4: Water reuse is also unavailable (e.g. due to public acceptability)
Options have been selected broadly on the basis of least cost, taking account of the potential need for a
solution that can supply SWOX (either the STT or Abingdon reservoir) being needed early in the planning
period. Options that have been screened out for reasons other than cost (Lower Lee DRA and Crossness
Desalination) have been excluded from the scenario analysis. The results are presented in Figure 5.2.
The purpose of this “What If” analysis is to ensure that sufficient options are included on the Constrained
List to account for key future risks that could impact the programme. The analysis is not in any way
intended to pre-judge the programme appraisal work, for which sophisticated evaluation and visualisation
tools have been developed by Thames Water.
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Figure 5.2: “What If” analysis to support fine screening
Indicative order of option selection
Scenario
Ted
din
gto
n
DR
A
ST
T
Reu
se 1st 2nd 3rd 4th 5th 6th
Option Groundw ater Teddington DRA Abingdon 75 Mm3 Reuse Deephams STT 300 Desal Beckton 150
DO 31 268 152 58 262 138
Cumulative DO 31 299 451 509 771 909
Option Groundw ater Reuse Deephams Abingdon 75 Mm3 STT 300 Desal Beckton 150 Desal Thamesmead 300
DO 31 58 152 262 138 268
Cumulative DO 31 89 241 503 641 909
Option Groundw ater Reuse Deephams Abingdon 150 Mm3 Desal Beckton 150 Desal Thamesmead 300 Reuse Beckton 150
DO 31 58 287 138 268 138
Cumulative DO 31 89 376 514 782 920
Option Groundw ater Desal Beckton 150 Abingdon 150 Mm3 Desal Thamesmead 300
DO 31 138 287 268
Cumulative DO 31 169 456 724
✖ ✔ ✔
✔ ✔ ✔
✖ ✖ ✖
✖ ✖ ✔
1
2
3
4
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5.4.2 Rejection reasoning
The reasons for rejecting options at the fine screening stage are summarised below.
5.4.2.1 Crossness reuse
Deephams Sewage Treatment Works has been identified as the best potential site for a first water reuse
plant for London. The main reason for this is that the other options require substantial conveyance
infrastructure that would be a sunk cost if Thames Water were to decide at a later date either not to expand
water reuse further (for example because innovation in desalination technologies made desalination more
competitive) or if the Deephams plant were to demonstrate that direct reuse is acceptable.
The capacity of reuse at the Deephams site is limited to approximately 60Ml/d and Beckton has been
identified as the best site to follow on for subsequent large scale development of water reuse. It is
envisaged that indirect reuse at Beckton would require a tunnel from Beckton to King George V Reservoir,
while direct reuse would require a tunnel to Coppemills WTW for blending. The distance to both King
George V and to Coppermills WTW is greater from Crossness than it is from Beckton. In both cases,
Crossness reuse could potentially be added at a later stage by constructing a link tunnel from Crossness to
Beckton.
A scenario is not currently envisaged in the “What if” analysis above over the 80 year planning period
where both Crossness and Beckton reuse are both required. The Crossness reuse option has not
therefore been carried forward to the constrained list, however this decision should be revisited if other
large scale options are prevented from proceeding.
5.4.2.2 Mogden water reuse
Mogden reuse is screened out at the fine screening stage as it is mutually exclusive with the Teddington
Direct River Abstraction option that relies on Mogden effluent to substitute the flows abstracted at
Teddington. The Teddington DRA option performs significantly better than Mogden reuse against the cost
dimension. The Mogden reuse option perform better on constructability, but this material risk is considered
reducible with further option development. If issues arise that prevent Teddington DRA from proceeding,
then Mogden reuse should be reviewed. However, in relation to the question around impacts on
navigation on the Thames Tideway, this would impact both the DRA and reuse options equally.
5.4.2.3 Kempton reuse
The Kempton reuse option is a black water reuse option using sewage from the South Sewer into Mogden.
As with the Mogden reuse option it is also mutually exclusive with the Teddington DRA option.
5.4.2.4 Lower Lee Direct River Abstraction
This option, which involves abstraction of water from the Lower Lee and treatment locally, has been
rejected on the basis of deliverability associated with data uncertainty around water quality and deployable
output. This also impacts upon promotability of the option, and regulatory acceptability by the Drinking
Water Inspectorate in particular. It is recommended, however, that the scheme should be revisited at future
WRMPs as further information becomes available.
The main reason this option has been rejected is that in low flow conditions the source water is made up of
approximately 95% treated effluent from Sewage Treatment Works and there are concerns around the
presence of viruses, pathogens and contaminants of emerging concern, such as pharmaceutical, personal
care products, etc. in the source waters. The presence of viruses and pathogens has been raised as a
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concern by the Independent Expert Review Panel on reuse commissioned by Thames Water. TW
envisage that reuse technologies for addressing these concerns would first be trialled through an indirect
potable reuse plant at Deephams Sewage Treatment Works. Once the materiality of concerns and the
efficacy of potential controls, are better understood through the Deephams indirect potable reuse plant, it is
recommended that the feasibility of a Lower Lee option with direct supply should be reviewed.
In addition to concerns around emerging parameters, Arsenic has previously been identified to be present
in the catchment upstream of the intake for the Lower Lee DRA option. Data on arsenic concentrations
from studies commissioned by the Olympic Delivery Authority will be analysed to understand if there is a
risk, and the extent of the risk, to inform future consideration of this option.
There is also significant uncertainty around the Deployable Output from the Lower Lee option due to
limited information on the hydrology in the Lower Lee. Collection of further hydrological data would help
improve understanding, but it is important to note that if the Lower Lee DRA option were implemented after
the Deephams Reuse option then the Deployable Output of the Lower Lee option would be significantly
reduced as both options rely on the same resource.
5.4.2.5 New reservoirs at Chinnor and Marsh Gibbon
The new reservoir options at Chinnor and Marsh Gibbon have been screened out in comparison with the
Abingdon reservoir and reuse and desalination options, all of which perform significantly better against the
cost dimension. The main reason for the increased cost compared with the equivalent Abingdon option is
the requirement for substantially longer intake pipelines to the reservoir and treated water pipelines to
connect the treatment works into distribution. As well as impacting the cost dimension the pipelines would
have a significant additional construction impact.
5.4.2.6 Desalination at Crossness
A desalination option at Crossness was developed that would continuously supply Northumberland Heath
service reservoir with desalinated water. The option was developed as it requires only a relatively short
conveyance compared to the options for blending at Coppermills WTW, and by operating continuously it
would not lead to a change in water quality (and associated customer complaints) that would be associated
with an un-blended option that is operated intermittently (e.g. as a drought scheme). However, the option
has been screened out due to substantial disbenefits associated with the promotability, deliverability and
resilience dimensions. The key issues are summarised below:
A substantial dis-benefit has been identified associated with changes in water quality arising from
desalination plant outage events, during which the supply would need to revert to water supplied
from the ring main via Honor Oak. TW’s experience is that these changes in water quality would
lead to a significant increase in customer water quality complaints.
Operation of the Crossness plant without water for blending means that the full capacity of the plant
may not generally be utilised, as it is less suitable than conventional sources for supplying other
zones (due to the impact of changing water quality). The assumed Deployable Output is based
upon forecast annual average demand on Northumberland Heath in 2070 of 65Ml/d, but the current
average demand on Northumberland Heath is only 50Ml/d meaning that up to 15Ml/d may be
unutilised in the short-medium term.
Desalination resources contribute less to system resilience than surface water resources where
treatment can be provided at alternative works in the event of WTW outage. Furthermore, for the
un-blended Crossness option the works could not be used to support outage at another works
without a change in water quality and associated customer complaints.
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5.5 Next steps for options passing fine screening
5.5.1 Deephams reuse
Deephams Sewage Treatment Works has been identified as the preferred site for initial development of
water reuse for London. A plant capacity of 60Ml/d is assumed. Further work is required to confirm the
appropriate treatment processes for use on this experimental plant but Thames Water’s current proposal is
to use membrane bio-reactor, reverse osmosis and advanced oxidation processes for treatment of
Deephams settled sewage. At feasibility stage a discharge location at the intake of King George V was
proposed to maximise retention time, but given the relatively small size of the plant, consideration will be
given at the conceptual design stage to discharging at the northern end of William Girling reservoir.
5.5.2 Beckton reuse
Three future scenarios are envisaged for the Beckton reuse option:
1. Development as an indirect reuse option using treatment processes including Reverse Osmosis
2. Development as an indirect reuse option using a lower level of treatment
3. Development as a direct reuse option using treatment processes including Reverse Osmosis
It is envisaged that conceptual designs will be prepared for all three scenarios. Further work is needed to
confirm the exact treatment technologies to be assumed for each scenario. For the indirect reuse
scenarios it is assumed that conveyance of the raw water would be to the intake of King George V
reservoir where dilution and retention time would be maximised, but the capability to also discharge directly
into the King George V reservoir should also be provided. For the direct reuse scenario it is assumed that
the conveyance would be to Coppermills for blending of the reuse water with water from Coppermills
WTW.
5.5.3 Severn-Thames Transfer
It is proposed that only the 300Ml/d Severn-Thames Transfer option should be developed at the
conceptual design stage. While larger options could be feasible there are no currently confirmed support
options available above 300Ml/d, although additional options may become available in future (e.g. transfers
from Wales). A 600Ml/d option has been rejected due to adverse effects on the River Thames
environment. A 100Ml/d option is feasible but has been screened out in comparison with the 300Ml/d
option as the larger transfer has significant benefits in terms of:
Greater adaptability to transfer new sources of water in future and to facilitate a market for
transferring water between the Severn and Thames catchment
Greater synergies in terms of potential to supply other companies (e.g. Affinity Water).
It is therefore recommended that the 300 Ml/d Deerhurst to Radcot pipeline is carried forward to the
Constrained List supported by:
15 Ml/d of Mythe licence transfer;
180 Ml/d of Vyrnwy releases;
88 Ml/d effluent reuse Minworth STW transfer to Severn catchment; and
25 Ml/d Draycote expansion
Investigations also need to be completed to confirm the magnitude of natural environmental losses that are
likely to occur as part of the transfer process.
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5.5.4 Abingdon reservoir
The “What If” scenario analysis indicates that there are potential future scenarios where a large reservoir
option may be required, if other options are prevented from progressing. However, development of a small
reservoir on the site would potentially “sterilise” the site preventing a large reservoir from being constructed
at a later date. It is therefore recommended that if small reservoirs are required then they should be
designed so as to allow future expansion. The following reservoir options are proposed for development at
the conceptual design stage.
Abingdon Reservoir single phase 75Mm3
Abingdon Reservoir single phase 100Mm3
Abingdon Reservoir single phase 125Mm3
Abingdon Reservoir single phase 150Mm3
Abingdon Reservoir two phase: 30Mm3 first phase followed by approximately 90Mm
3 second phase
Abingdon Reservoir two phase: 70Mm3 first phase followed by approximately 50Mm
3 second phase
The sizes proposed for the two phase options differ from those assumed at feasibility stage (see section
5.2.2) as further work has since been done taking account of more refined embankment profiles, borrow pit
shapes and site specific geological conditions. The result of this work is that due to the dividing
embankment profile and geological conditions the maximum reservoir volume that can be achieved on the
Abingdon site for a phased option is approximately 120Mm3.
The following small single-phase reservoir sizes are screened out on the grounds that their development
would prevent a large reservoir from being developed on the site.
Abingdon Reservoir single phase 30Mm3
Abingdon Reservoir single phase 50Mm3
Should a small reservoir be required (e.g. to supply the SWOX WRZ) then the first 30 Mm3 phase of the
two phase 30Mm3 + 90 Mm
3 would be more appropriate as it would not preclude subsequent expansion to
supply London.
5.5.5 Teddington direct river abstraction
Direct river abstraction at Teddington, supported by the transfer of Mogden effluent, has passed the fine
screening. It is one of the best performing options against the cost dimension. A substantial disbenefit has
been identified due to the ramp up time of tertiary treatment at Mogden, but this disbenefit can be reduced
by setting an earlier trigger for ramp-up of the treatment. It is also necessary to conduct further work to
demonstrate the extent of any navigational impact on the Thames Tideway from reduced flows
downstream of the Mogden discharge at Isleworth Ait; hydraulic modelling to address this is currently being
scoped.
5.5.6 Beckton desalination
The option for development of a second 150Ml/d desalination plant at Beckton has passed the fine
screening. It is proposed that the plant would operate intermittently, and a substantial disbenefit that has
been identified relates to the ramp-up time from a mothballed state, however this dis-benefit can be
reduced by setting an earlier trigger for ramp-up. The option includes a tunnel conveyance from Beckton
to Coppermills for blending of desalinated water at Coppermills. A potential opportunity associated with the
option is that the tunnel could also be used to convey water from the existing Gateway desalination plant to
Coppermills which would improve blending and address concerns around change of water quality when the
Gateway plant is operated at full capacity.
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Whilst land has been identified for the desalination plant on the Beckton site further confirmation is needed
that this does not conflict with requirements for expansion of the sewage treatment works.
5.5.7 Thamesmead desalination
Land availability is expected to constain future development of desalination at Beckton. It is therefore
proposed to develop up to 300Ml/d of additional treatment at Thamesmead on the south bank of the
Thames estuary opposite the Beckton desalination plant. Part of the site is designated as Metropolitan
Open Land while another part of the site has outline planning permission for development. Further work is
therefore needed to confirm the best location on the site for the Thamesmead plant.
There is a potential limiting factor on desalination capacities due to possible increased salinity levels in a
given reach of the Tideway. A precautionary approach to the environmental assessment has been adopted
that has resulted in a limit of 300 Ml/d of additional desalination capacity in any single reach of the River
Thames, but subject to further analysis (i.e. estuarine modelling) it is expected that higher levels may be
acceptable.
5.6 Next steps required to inform fine screening
Further development and investigation is required for several options before the fine screening and
associated constrained list can be finalised. These include:
Lower Lee Direct River Abstraction: Further work is needed to assess the risks to water quality
from the presence of contaminated land in the Lower Lee valley.
Finalising the groundwater feasibility report and feeding the findings into the fine screening report
Finalising the raw water transfers report, and including any additional options that may be carried
forward to the fine screening
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6 SWOX WRZ resource options
Chapter 6 provides a summary of the feasibility reports and fine screening
assessment for the Swindon and Oxfordshire (SWOX) Water Resource Zone
grouped by option type. Options are assessed qualitatively against the six
dimensions: Cost, Environmental and Social, Promotability, Flexibility,
Deliverability and Resilience. The assessment is presented for each option type
together with the screening decisions.
6.1 Resource option types
The resource option types identified for the SWOX WRZ comprise:
Bulk raw water transfers;
Aquifer recharge;
Groundwater development;
Surface Water development;
Removal of Deployable Output constraints; and
Inter-zonal transfers.
It should be noted that for schemes resulting in a net increase in water available within the SWOX resource
zone, there is a potential deployable output benefit to London through increase in outflow to the River
Thames via sewage works effluent. A review will be carried out to check that options that could benefit
SWOX and London would not be screened out on cost grounds without a sensitivity test on the impact of
the combined water resource benefit.
6.2 Feasibility report findings
6.2.1 New reservoirs
The options identified in the feasibility report for new reservoirs are listed in section 0.
6.2.2 Raw water transfers
The options identified in the feasibility report for raw water transfers are listed in section 0.
6.2.3 Direct river abstraction
The options identified in the feasibility report for direct river abstraction are listed in the table below
together with a summary of the status of the options.
Table 6.1: SWOX options identified in the feasibility report for direct river abstraction
Option Sub-option Capacity / DO
Stage
1 2 3 Comment
River Thames 2a) Abstraction at Culham 4.5 Ml/d ✔ ✖
Significant Pumping
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Culham abstraction transfer to Farmoor Reservoir via a new pumping main
head on 13km transfer to Farmoor Reservoir.
River Thames Culham abstraction
2b) Abstraction at Culham,
treatment and direct supply to SWOX.
4.5 Ml/d
✔ ✔ ✔
Following the Stage 3 assessment the following direct river abstraction option has been identified as being
feasible:
Option 2b - New Intake at Culham on the site of disused intake followed by treatment and direct supply
to SWOX.
6.2.4 Aquifer recharge
The aquifer recharge options identified in the groundwater feasibility report are listed in the table below
together with a summary of the status of the options.
Table 6.2: SWOX options identified in the feasibility report for aquifer recharge
Option
DO (Ml/d)
Stage*
Comment 1 2 3
AR – Cricklade 9.5 ✔ ✖
Failed at stage 2 primarily for hydrogeological suitability reasons (the assessment suggests water does not stay in aquifer for sufficient time to provide a dry weather resource, or would require excessive injection pressures).
Work to finalise the feasibility reports is ongoing however no options are expected to be carried forward.
6.2.5 Groundwater development
The groundwater development options identified in the groundwater feasibility report are listed in the table
below together with a summary of the status of the options.
Table 6.3: SWOX options identified in the feasibility report for groundwater development
Option
DO (Ml/d) Stage*
Comment 1 2 3
Woods Farm licence increase 3.5 ✖ Removed from WRMP19 option list following comments from the EA.
GW - South Stoke 1 3.5 ✔ ✔ TBC
Confirmation of details of the option and completion conceptual design report required. Mutually exclusive with Moulsford 1.
GW - South Stoke 2 (with treatment)
10.0 ✖ Removed from WRMP19 option list following comments from the EA
GW - Moulsford 1 3.5 ✔ ✔ TBC
Confirmation of details of the option and completion conceptual design report required. Mutually exclusive with South Stoke 1.
GW - Moulsford 2 (with treatment)
10.0 ✖ Removed from WRMP19 option list following comments from the EA
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Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from the
feasibility report is provided below.
South Stoke 1 Groundwater Scheme
– Construction of two new abstraction boreholes on private land in the unconfined Chalk
north of Goring. Water abstracted from the boreholes will be treated at the existing Cleeve
water treatment works (WTW), with 1.8 km run to waste pipeline to the River Thames; and
2.2 km raw water pipeline between the boreholes and the WTW.
– This scheme would provide a likely DO benefit of 2 Ml/d average and 3.5 Ml/d peak and is
mutually exclusive to the Moulsford 1 groundwater scheme.
Moulsford 1 Groundwater Scheme
– Construction of one new abstraction boreholes on agricultural land in the unconfined Chalk
adjacent to the existing Moulsford (Cow Lane) operational reservoir site. Water abstracted
from the boreholes will be treated at the existing Cleeve water treatment works (WTW), with
0.6 km run to waste pipeline to the River Thames; and 1.5 km raw water pipeline between
the boreholes and the WTW, which will pass beneath the River Thames.
– This scheme would provide a likely DO benefit of 2 Ml/d average and 3.5 Ml/d peak and is
mutually exclusive to the South Stoke 1 groundwater scheme.
6.2.6 Removal of Deployable Output constraints
The options for removal of DO constraints identified in the groundwater feasibility report are listed in the
table below together with a summary of the status of the options.
Table 6.4: SWOX options identified in the feasibility report for removal of DO constraints
Option
DO (Ml/d)
Stage*
Comment 1 2 3
Ashton Keynes borehole pumps
0.9 ✔ ✔ TBC
Further investigation required to understand the maximum potential DO increase .
Witheridge Hill borehole pumps
0.63 ✔ ✖
This option has failed due to the low resilience of source, high cost to potential DO benefit ratio and a number of areas of uncertainty regarding what is required to deliver the option.
Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from
the feasibility report is provided below.
Ashton Keynes borehole pumps
– Installation of new borehole pumps at a lower level than the current pumps to increase both
average and peak source DO;
– This option would provide a likely DO benefit of 0.2 Ml/d average and 3.1 Ml/d peak.
6.2.7 Internal inter-zonal transfers
Work reviewing the potential for inter zonal transfers has now commenced and this will be reported on in
subsequent report updates.
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6.3 Exclusivities/Interdependencies
The Moulsford, South Stoke and Woods Farm schemes all carry some degree of interdependence and
cannot all be delivered together due to resource availability, though some combinations may be possible.
Only one of the two Culham options can be progressed.
6.4 Fine screening assessment
The fine screening assessment for SWOX will be updated once the Groundwater Feasibility Report has
been completed.
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7 SWA WRZ resource options
Chapter 7 provides a summary of the feasibility reports and fine screening
assessment for the Slough, Wycombe & Aylesbury (SWA) Water Resource Zone
grouped by option type. Options are assessed qualitatively against the six
dimensions: Cost, Environmental and Social, Promotability, Flexibility,
Deliverability and Resilience. The assessment is presented for each option type
together with the screening decisions.
7.1 Resource option types
The resource option types identified for the Swindon Wycombe Aylesbury WRZ comprise:
Aquifer storage and recovery;
Groundwater development;
Release of network/treatment constraints; and
Release of Deployable Output constraints.
7.2 Feasibility report findings
7.2.1 Aquifer storage and recovery
The aquifer storage and recovery options identified in the groundwater feasibility report are listed in the
table below together with a summary of the status of the options.
Table 7.1: SWA options identified in the feasibility report for aquifer storage and recovery
Option
DO (Ml/d)
Stage*
Comment 1 2 3
Hampden Bottom-Wendover
7.5 ✔ ✖
Option failed as investigations indicated that the Lower Greensand aquifer, which was proposed as the target aquifer for ASR, was thin or missing at the identified site.
Work to finalise the feasibility reports is ongoing however no options are expected to be carried forward.
7.2.2 Groundwater development
The groundwater development options identified in the groundwater feasibility report are listed in the table
below together with a summary of the status of the options.
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Table 7.2: SWA options identified in the feasibility report for groundwater development
Option
DO (Ml/d)
Stage*
Comment 1 2 3
GW – Datchet 4.3 ✔ ✔ TBC Assessment on impact of abstraction on river required.
Remenham 10.0 ✖
Further information required to review impact. Rejected by the EA for local use and up-catchment use
GW – West Marlow 15.0 ✖
Rejected by the EA due to environmental concerns for local and up-catchment use
Bourne End (Marlow East)
9.3 ✖ EA have clarified that the licence increase is not acceptable
Medmenham 2.73 ✖
Failed at stage 1 due to EA response that no water is available for licensing in the area.
Taplow 5.1 ✖ Lack of Environment Agency support for abstraction licence increase.
Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from the
feasibility report is provided below.
Groundwater Datchet
– Redevelopment of two existing boreholes. The scheme also includes upgrade of an existing
WTW. No licence change would be required.
– The DO benefit to SWA WRZ would be 4.3 Ml/d.
7.2.3 Release of Deployable Output constraints
The options for release of DO constraints identified in the groundwater feasibility report for are listed in the
table below together with a summary of the status of the options.
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Table 7.3: SWA options identified in the feasibility report for release of DO constraints
Option
DO (Ml/d)
Stage*
Comment 1 2 3
RC - Datchet Main Replacement
5.2 ✔ TBC
Additional constraints identified that means this option potentially no longer delivers the increase in yield proposed.
RC - Hampden Disinfection Upgrade
1.1 ✖
Option rejected as the restrictions to the licence mean that the DO benefit would be too small to justify upgrading the treatment capacity. The EA will not support a change to the licence conditions.
Work to finalise the feasibility reports is ongoing however no options are expected to be carried forward.
7.3 Exclusivities/Interdependencies
No exclusivities or interdependencies have been identified.
7.4 Fine screening assessment
The fine screening assessment for SWA WRZ will be updated once the Groundwater Feasibility Report
has been completed.
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8 Henley WRZ resource options
Chapter 7 provides a summary of the feasibility reports and fine screening
assessment for the Henley Water Resource Zone grouped by option type. Options
are assessed qualitatively against the six dimensions: Cost, Environmental and
Social, Promotability, Flexibility, Deliverability and Resilience. The assessment is
presented for each option type together with the screening decisions.
8.1 Resource option types
The resource option types identified for the Henley WRZ comprise:
Groundwater development.
It should be noted that the WRMP14 supply-demand review concluded that Henley would be in surplus
until 2040
8.2 Feasibility report findings
8.2.1 Groundwater development options
The options identified in the feasibility report for groundwater development are listed in the table below
together with a summary of the status of the options.
Table 8.1: Henley options identified in the feasibility report for groundwater development
Option
DO (Ml/d)
Stage*
Comment 1 2 3
Sheeplands licence disaggregation
8.5 ✖
Lack of Environment Agency support for abstraction licence disaggregation.
Work to finalise the feasibility reports is ongoing however no options are expected to be carried forward.
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9 Guildford WRZ resource options
Chapter 9 provides a summary of the feasibility reports and fine screening
assessment for the Guildford Water Resource Zone grouped by option type.
Options are assessed qualitatively against the six dimensions: Cost,
Environmental and Social, Promotability, Flexibility, Deliverability and Resilience.
The assessment is presented for each option type together with the screening
decisions.
9.1 Resource option types
The resource option types identified for the Guildford WRZ comprise:
Aquifer storage and recovery;
Groundwater development; and
Removal of Deployable Output constraints;
9.2 Feasibility report findings
9.2.1 Aquifer storage and recovery
The aquifer storage and recovery options identified in the groundwater feasibility report are listed in the
table below together with a summary of the status of the options.
Table 9.1: Guildford options identified in the feasibility report for aquifer storage and recovery
Option
DO (Ml/d) Stage*
Comment 1 2 3
ASR - Guildford (Abbotswood)
4.5 ✔ ✖
Option has failed due to the risks of flooding at the proposed site and due to the requirements for land acquisition.
Work to finalise the feasibility reports is ongoing however no options are expected to be carried forward.
9.2.2 Groundwater development
The groundwater development options identified in the groundwater feasibility report are listed in the table
below together with a summary of the status of the options.
Table 9.2: Guildford options identified in the feasibility report for groundwater development
Option
DO (Ml/d) Stage*
Comment 1 2 3
Mousehill & Rodborough Rehab
0.18 ✖
Failed at stage 1 due to EA response that a licence increase is not acceptable in the area.
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Option
DO (Ml/d) Stage*
Comment 1 2 3
Dapdune Licence Disaggregation
2.2 ✔ ✔ TBC
EA would support disaggregation of
licence for peak abstraction but would
expect the annual average to remain
the same as the current aggregated
volumes.
Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from the
feasibility report is provided below.
Dapdune licence disaggregation
– Disaggregation of the Dapdune, Ladymead and Millmead licence to increase DO.
– This scheme would provide a likely benefit of 2.2 Ml/d.
9.2.3 Removal of Deployable Output constraints
The options for removal of DO constraints identified in the groundwater feasibility report are listed in the
table below together with a summary of the status of the options.
Table 9.3: Guildford options identified in the feasibility report for removal of DO constraints
Option
DO (Ml/d) Stage*
Comment 1 2 3
RC - Ladymead borehole pumps 0.63 ✖
Investigations show that DO is constrained by the licence, not pump capacity so the resultant DO increase has been incorporated into the baseline.
RC - Sturt Road Spring Capture 0.25 ✔ ✔ TBC
EA approved as this spring capture is treated as a surface water discharge. Further assessment of uncaptured flows required to understand potential increase in DO.
Dapdune removal of constraints to DO
3.2 ✔ ✔ TBC
Additional investigation into treatment required in order to confirm the increase in yield.
Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from the
feasibility report is provided below.
Dapdune
– This scheme involves an increase in the GAC capacity at Ladymead WTW and/or providing
a robust treatment for periodic microbiological contamination of the raw water quality. The
option also includes increasing the pump capacity and/or modifying the operational control
of the borehole pumps at the source, to enable them to be operated as duty-assist.
– The scheme would increase only the peak source DO, by a most likely 3.2 Ml/d, and
provide additional resources to the Guilford WRZ.
Sturt Road Spring Capture
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– The Sturt Road spring source is an existing licensed, natural groundwater discharge from
the Lower Greensand aquifer, developed via several headings that transfer flow out of the
Hythe Beds into a raw water network that transfers the water to the treatment works. There
are several spring overflows that discharge into the River Wey that are neither captured nor
gauged. The proposed scheme involves capturing the currently uncaptured springflows.
– This scheme would provide a likely benefit of 0.25 Ml/d.
9.3 Exclusivities/Interdependencies
Dapdune and Ladymead operate under an aggregate licence. Therefore changes in abstraction from one
must be considered in terms of operation of both sources.
9.4 Fine screening assessment
The fine screening assessment for the Guildford will be updated once the Groundwater Feasibility Report
has been completed.
.
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10 Kennet Valley WRZ resource options
Chapter 10 provides a summary of the feasibility reports and fine screening
assessment for the Kennet Valley (KV) Water Resource Zone grouped by option
type. Options are assessed qualitatively against the six dimensions: Cost,
Environmental and Social, Promotability, Flexibility, Deliverability and Resilience.
The assessment is presented for each option type together with the screening
decisions.
10.1 Resource option types
The resource option types identified for Kennet Valley WRZ comprise:
Groundwater development; and
Removal of Deployable Output constraints.
10.2 Feasibility report findings
10.2.1 Groundwater development
The options identified in the feasibility report for groundwater development are listed in the table below
together with a summary of the status of the options.
Table 10.1: Kennet Valley options identified in the feasibility report for groundwater development
Option
DO (Ml/d) Stage* Comment
1 2 3
GW – Purley 15.0 ✖
Clarification sought from the EA regarding their comments
GW - Mapledurham 15.0 ✖ Clarification sought from the EA regarding their comments
GW - Mortimer disused source (recommission)
4.5 ✔ ✔ TBC
Awaiting EA confirmation of support for this option. Groundwater model/investigations to investigate the impacts of this option on the River Pang may be required.
GW - Mortimer (transfer peak licence from Arborfield)
6.8 ✔ ✔ TBC
Awaiting EA confirmation of support for this option. Use groundwater model/investigations to investigate the impacts of this option on the River Pang
GW – Hungerford 1.4 ✖ Not approved by the EA
GW - Playhatch (increased licence)
1.3 ✖
EA approved as long as this is within licence quantity and not an increase in licensed amount. Therefore, the increased licence option no longer exists.
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Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from the
feasibility report is provided below.
Mortimer disused source (recommission)
– Refurbishment of two disused confined chalk abstraction boreholes located on-site at the
existing, but disused Mortimer water treatment works (WTW). Water abstracted from the
boreholes will be treated at the disused WTW which will be upgraded for ammonia and iron
removal and recommissioned.
– This scheme would provide a likely benefit of 4.5 Ml/d and is mutually exclusive to the
Mortimer (transfer peak licence from Arborfield) option.
Mortimer (transfer peak licence from Arborfield)
– As for Mortimer recommissioning but also with transfer of the peak licence from the disused
Arborfield source to the existing Mortimer borehole source, as well as upgrading the
borehole pumps and WTW, and refurbishment of 1 km distribution pipeline.
– This scheme would provide a likely benefit of 6.8 Ml/d and is mutually exclusive to the
Mortimer disused source (recommission) option.
10.2.2 Removal of Deployable Output constraints
The options identified in the feasibility report for removal of deployable output constraints are listed in the
table below together with a summary of the status of the options.
Table 10.2: Kennet Valley options identified in the feasibility report for removal of DO constraints
Option
DO (Ml/d) Stage*
Comment 1 2 3
East Woodhay borehole pumps
2.1 ✔ ✔ TBC
Some uncertainties that still need to be clarified.
Work to finalise the feasibility reports is ongoing and the above table will be updated once the work is
complete. A brief description of the options that are currently expected to be carried forward from the
feasibility report is provided below.
East Woodhay
– This option describes upgrading the pumps and pump control in the existing licensed,
operational abstraction boreholes at East Woodhay, to allow the borehole pumps to be run
together. It includes a treatment upgrade at East Woodhay Water Treatment Works (WTW).
– This scheme would provide a likely benefit of 2.1 Ml/d (peak). No changes to average DO
are proposed (constrained by aggregate licence).
10.3 Exclusivities/Interdependencies
There may be limitations for the delivery of Purley in addition to the Mapledurham groundwater scheme
due to water resource availability constraints. The capacity of the pipeline to the Tilehurst service reservoir
and booster station would have to be revised if both schemes are progressed.
The Mortimer disused source (recommission) and Mortimer (transfer peak licence from Arborfield) options
are mutually exclusive: only one of these can be delivered due to licensing constraints.
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10.4 Fine screening assessment
The fine screening assessment for the Kennet Valley will be updated once the Groundwater Feasibility
Report has been completed.
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Chapter 11 provides a summary of the screening decisions that have been made
feeding into the constrained list, together with a summary of next steps.
11.1 Screening summary
A summary of the progression of option types through the screening stages is provided in Table 11.1. A
summary of the reasons for screening out of options will be set out in the Rejection Register. For those
options that progressed to fine screening from the feasibility stage a summary of option status is provided
in Table 11.2.
Table 11.1: Summary of option types considered at each stage of the screening process
11 Conclusions
Generic resource management options† Gen
eri
c
scre
en
ing
Specific option identification Feasib
ilit
y
rep
ort
Feasible list Fin
e
scre
en
ing
Constrained list
1 Direct river abstraction ✔ Direct river abstraction feasibility report ✔ ✔
2 New reservoir ✔ New reservoirs feasibility report ✔ ✔
3 Groundwater sources ✔ Groundwater feasibility report ✔ TBC
4 Infiltration galleries ✔ Included in DRA/Desal as possible intake n/a
5 Aquifer storage and recovery ✔ Groundwater feasibility report TBC
6 Aquifer recharge ✔ Groundwater feasibility report ✔ TBC
7 Desalination ✔ Desalination feasibility report ✔ ✔
8a Bulk transfers of raw water ✔ Raw water transfer feasibility report ✔ ✔
8b Bulk inter/intra company transfers of treated water ✔ Inter-zonal transfers study TBC
9 Tankering of water ✖
10 Redevelopment of existing resources TBC
11 Reuse of existing private supplies ✔ Groundwater feasibility report TBC
12 Water re-use ✔ Water reuse feasibility report ✔ ✔
13 Imports (icebergs) ✖
14 Rain cloud seeding ✖
15 Tidal barrage ✖
16 Rainwater harvesting ✖
17 Abstraction licence trading ✔ Third party options report TBC
18 Water quality schemes that increase DO ✔ Catchment management feasibility report TBC
19 Catchment management schemes ✔ Catchment management feasibility report TBC
20 Conjunctive use operation of sources ✔ Built into DOs through WARMS n/a
21 Joint ("shared asset") resource ✔ Included in feasibility reports where applicable n/a
22 Asset transfers ✔ Third party options report TBC
23 Options to trade other (infrastructure) assets ✔ Third party options report TBC
† Taken from UKWIR 2012, Water Resources Planning Tools, EBSD Report, Ref 12/WR/27/6
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Table 11.2: Fine screening summary for specific options
11.2 Constrained list
For the purpose of fine screening independent specific options of different sizes have been developed. For
programme appraisal it is proposed that elements of some options will be phased. A summary of the
options currently included on the Constrained List is provided in Table 11.3. It is important to note that
there are a number of options that remain TBC at the feasibility or fine screening stages and so once a
decision has been reached on these options it is expected that additional options will be added to the
constrained list.
The Constrained List for the Thames Valley WRZs will be developed once the groundwater and inter-zonal
transfer feasibility reports are complete.
Size Band (Ml/d)
Option Comment
LondonReuse - Beckton Develop conceptual design for 100, 200 and 300Ml/d options
Reuse - Mogden Mutually exclusive w ith DRA Teddington
Reuse - Deephams Develop conceptual design for option to prove reuse technology concept
Reuse - Crossness Screened out on cost and not expected to be needed in planning period
Reuse - Mogden South Sew er Mutually exclusive w ith DRA Teddington
RWT - STT Deerhurst Develop 300 Ml/d transfer option at conceptual design
New Reservoir - Abingdon Develop conceptual design for 2 phase and single phase options (excl. 30 and 50Mm3)
New Reservoir - Chinnor Excessively costly compared to reuse, desalination and Abingdon reservoir
New Reservoir - Marsh Gibbon Excessively costly compared to reuse, desalination and Abingdon reservoir
DRA - River Lee Screened out due to uncertainty around w ater quality and yield
DRA - Teddington Develop concept design for 300Ml/d option. Assessment of navigational impact needed.
Desalination - Beckton Develop conceptual design for 150Ml/d option
Desalination - Crossness Screened out due to resilience and operability concerns
Desalination - Thamesmead Develop phased option connecting into Beckton desalination conveyance
Key
Screened out at f ine screening
Passes fine screening onto Constrained List
Fine screening TBC
0 25 75 125 175 225 275
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Table 11.3: Preliminary Constrained List for London WRZ
Option Resource Element Conveyance Element Raw Treatment Element Network Element
Type Location Nominal Nominal Location Nominal Location Nominal
Capacity
Ml/d
Capacity
Ml/d
Capacity
Ml/d
Capacity
Ml/d
Indirect water
reuse
Deephams 60 Deephams to
King George V
Intake
60 TBC East London
Treatment
60
100*3
See network reinforcement matrix
Beckton 100
200
300
Beckton to King
George V Intake
300
Raw Vyrnwy 180 Deerhurst to 300 TBC Kempton 100*3 See network reinforcement matrix
Water Minworth 88 Radcot
Transfer Draycote 25
Mythe 15
Desalination Beckton 150 N/A N/A N/A See network reinforcement matrix, plus
Thamesmead 300 Beckton to Coppermills 450
New Abingdon 75Mm3 153 N/A TBC Kempton 300 See network reinforcement matrix
Reservoir Abingdon 100Mm3 204 150
Abingdon 125Mm3 247 100
Abingdon 150Mm3 287
Abingdon 30+ approx 90Mm3 59+179
Abingdon 70+ approx 50Mm3 145+93
Direct River
Abstraction
Teddington Weir (Mogden effluent transfer) 300 Teddington to
Thames-Lee
tunnel shaft
300 Kempton /
East London
TBC See network reinforcement matrix
Water
System
Location
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11.3 Next steps
Further work is required in a number of areas to finalise the WRMP19 Constrained List including:
Complete groundwater feasibility report and incorporate into fine screening
Complete catchment management feasibility report and incorporate into fine screening
Complete inter-zonal transfers feasibility report once WRMP19 demand forecasts available and
incorporate findings into fine screening (includes inter-company treated water transfers)
Incorporate findings from raw water transfers feasibility report for options whose status has still to be
confirmed (including CRT canal transfer options)
Undertake assessment of catchment water quality risks to inform Lower Lee DRA
Complete investigation into reinforcements required to the raw water system in the Rivers Thames and
Lee
Complete investigation into alternative site to Coppermills for new treatment in east London
For options included on the Constrained List the following next steps are planned:
1. Complete conceptual design reports, building on and updating WRMP14 dossiers where these exist
2. Undertake Strategic Environmental Assessment
3. Update cost estimates for conceptual design
4. Undertake bottom-up assessment of risk
5. Use the above information to inform cost, deliverability and environmental metrics to feed into
programme appraisal
In addition to the general next steps associated with options on the Constrained List, there are also a
number of key next steps to address uncertainties associated with specific options:
a. Progress negotiations and reach agreement in principle on terms for bulk supply agreements
(particularly for Severn-Thames Transfer resources)
b. Confirm process, timescales and nature of changes needed to River Severn regulation
c. Undertake hydro-dynamic modelling for Teddington DRA option to confirm discharge location and
extent of navigational impacts to inform engagement with Port of London Authority.
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Appendices
Appendix A. Summary of water quality modelling ____________________________________________________ 83 Appendix B. London WRZ fine screening tables _____________________________________________________ 86 Appendix C. Optimism bias & uncertainty __________________________________________________________ 92
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Several options include transfer and treatment of either raw water or sewage treatment works effluent and
in these cases consideration is needed of the appropriate treatment required before discharge into the
environment. To select the appropriate treatment technology and treatment scheme it is necessary to
understand the quality of the source water to be treated and the required product water quality to be
achieved. To this end a water quality modelling exercise has been undertaken, using the available water
quality data, to assess the required product water quality based on the requirements of the receiving
waters that discharges are being made to.
A.1 Beckton Re-use
Two treatment schemes have been considered for treatment at Beckton for transfer to the River Lee
Division Channel. The first scheme utilises Reverse Osmosis and advanced oxidation, while the second
scheme utilises sand filtration, ozone and GAC adsorption and nitrate removal. The following table
summarises the conclusion of the analysis for Beckton reuse, showing whether the treatment scheme
address water quality parameters at different flows. A distinction is made between High, Medium and Low
priority parameters based upon an assessment of materiality.
As can be seen from the table, the first treatment scheme is comprehensive and addresses all parameters,
across all prioritisations and flows. The second scheme is more selective, treating just those parameters
that are considered to be high priority. This is only effective up to discharge flows of 150 Ml/d. Above this
flow this treatment scheme would not be effective and Scheme 1 would be required.
It should be noted, that unlike other expansions, such as a water treatment works, where the product water
quality is constant and expansions can just duplicate existing treatment trains, in this application the
treatment standard becomes more stringent as the discharge flow increases. This effectively means that if
treatment Scheme 2 were adopted, to increase the capacity from 150 Ml/d to 200 Ml/d would mean that the
Scheme 2 treatment process would have to be abandoned and replaced with a 200 Ml/d treatment plant
based on the Scheme 1 technologies.
It is considered that treatment Scheme 1 provides more flexibility in terms of future treatment capacity and
is better able to treat a wide range of parameters, beyond the limited list identified as high priority
parameters treated by Scheme 2, and as such Scheme 1 has been adopted as the preferred technology
for the development of a re-use scheme utilising effluent from the Beckton STW.
50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 300 Ml/d 380 Ml/d
UF+RO+AOP
High
Medium
Low
Fe+NSF+O3/GAC+IX
High (1)
(1)
(1)
Medium
Low
Note:
UF+RO+AOP Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process
Fe+NSF+O3/GAC+IX Ferric + Nitrifying Sand Filter + Ozone / GAC + Ion Exchange
(1) Except for Phosphate and zinc
Appendix A. Summary of water quality modelling
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A.2 Deephams Re-use
The capacity of the Deephams Re-use scheme is limited by the impact the scheme could have on the
downstream water body, because of reduced flows. As such it is understood that the Environment Agency
would be unwilling to accept a scheme with a capacity greater than 60 Ml/d
The following table presents the anticipated performance of the two treatment schemes (same as
considered for Beckton re-use above) over a range of flows.
As can be seen both schemes would treat the high priority parameters, while Scheme 1 will treat the High,
Medium and Low parameters.
Scheme 1 is considered the preferred treatment scheme as it would treat all the parameters of concern
(High, medium and low priority) and would also treat many other parameters because of the more general
nature of the RO / AOP treatment processes. Further selection of Scheme 1 would allow a comparable
treatment scheme to be adopted at both Beckton and Deephams, rather than having different processes at
each site, and potentially would allow Deephams to be developed and operated, providing full-scale
operational experience in advance of the development of a larger Beckton re-use scheme.
A.3 Mogden Re-use
For the Mogden reuse option, unlike the effluent transfer option considered below, the effluent will
ultimately (following mixing and blending with river water) be abstracted for further treatment to produce
potable water. As such the full list of parameters is considered. The table below presents the assessment
of the treatment schemes.
As with the Beckton and Deepham’s Options, Scheme 2 is suitable for treatment of the high priority
parameters but not the Low and Medium Priority parameters, whereas Scheme 1 is suitable for all
25 Ml/d 35 Ml/d 50 Ml/d 60 Ml/d 80 Ml/d 100 Ml/d
UF+RO+AOP
High
Medium
Low
Fe+NSF+O3/GAC+IX
High (1)
(1)
(1)
(1)
(1)
(1)
Medium
Low
Note:
UF+RO+AOP Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process
Fe+NSF+O3/GAC+IX Ferric + Nitrifying Sand Filter + Ozone / GAC + Ion Exchange
(1) Except for Phosphate
50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 250 Ml/d 300 Ml/d
UF+RO+AOP
High
Medium
Low
Fe+NSF+IX
High (1)
(1)
(1)
(1)
(1)
(1)
Medium
Low
Note:
UF+RO+AOP Ultrafiltration membrane + Reverse Osmosis Membrane + Advanced Oxidation Process
Fe+NSF+IX Ferric + Nitrifying Sand Filter + Ion Exchange
(1) Except for Phosphate
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parameters considered, across all flows. As such Scheme 1 is considered the preferred treatment
scheme.
A.4 Teddington Direct River Abstraction
The Teddington Direct River Abstraction option is different from Mogden re-use in that the treated effluent
is not abstracted and subsequently used for potable water. As such the list of parameters considered in
the analysis has been reduced to include only those parameters that are of environmental concern. The
preferred treatment process is presented below and is considered to be ferric addition for phosphate
control and a nitrifying sand filter for ammonia and suspended solids and particulate material removal.
50 Ml/d 100 Ml/d 150 Ml/d 200 Ml/d 250 Ml/d 300 Ml/d
Fe+NSF
High (1)
(1)
(1)
(1)
(1)
(1)
Medium
Low
Note:
Fe+NSF Ferric + Nitrifying Sand Filter
(1) Further consideration is need as to the level of performance that could be relably achieved with respect to
phosphate and ammonia.
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Appendix B. London WRZ fine screening tables
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Table B.1: London WRZ – Supported raw water transfer options screening commentary:
ST
T v
ia D
ee
rhu
rst
to R
ad
co
t P
ipe
lin
e
ST
T v
ia D
ee
rhu
rst
to R
ad
co
t P
ipe
lin
e
Sub-dimension 100 Ml/d
300 Ml/d Comments
Env & Social
SEA ○◑ ○◑ The Severn-Thames transfers would have beneficial effects on flows in the River Thames, and transfers from the River Severn will be supported. No likely significant effects on Severn Estuary European Site due to supported flows and hands-off flow conditions.
Water treatment prior to discharge to the Thames will address risks associated with water quality and control of invasive, non-native species.
Adverse effects from the use of moderate to significant amounts of materials in construction and power and chemical use for conveyance and water treatment when in operation. Some temporary pipeline construction effects which will be mitigated through careful design of the pipeline route.
Risks to WFD objectives in River Thames will be addressed through water treatment of the River Severn transfers. Impacts on WFD objectives relating to the river support to River Severn to be further reviewed (once support options confirmed), but can be mitigated.
Cumulative effects assessed as neutral given supported abstraction and transfers will be treated prior to discharge to River Thames
HRA ○ ○
WFD ◑r ◑
r
Cumulative effects ○ ○
Cost
○ ○
Promotability
Synergies ◎ ◉ The large 300Ml/d supported transfer option offers the potential for synergies through ability to provide other WRZs besides London and other companies in the South East. The smaller transfer offers less potential for this.
In terms of local acceptability, the options would all have planning permission challenges, but these are likely to be reducible. There might also be the possible requirement to actively alleviate local flood risk concerns. These can be considered to be material but reducible disbenefits.
There would be regulatory support for transfers for reasons of allocative efficiency. However, there are EA concerns over water quality and ecology impacts of a basin to basin transfer which require further consultation. Environmental representative groups may also have concerns which would need to be managed through evidence and engagement.
New abstraction licences and discharge permits would also be required, as would changes to the regime for River Severn regulation.
Customer acceptability ○ ○
Local acceptability ◑r ◑
r
Regulatory acceptability ◑r ◑
r
Wider stakeholder acceptability
◑r ◑
r
Flexibility
Lead time ○ ○ The lead time of the STT options is estimated to be 7 years.
Bulk transfers could potentially be linked up and connected to new sources and demand centres in future, offering adaptability benefits. It is considered that the 300Ml/d transfer option provides a substantial adaptability benefit as it has the potential to open up more resource options in future (e.g. from Wales).
All the supported raw water transfer (via Deerhurst pipeline) option ramp-up times are estimated to be within one week.
Phasing ◑r ◑
r
Adaptability ◎ ◉
Ramp-up ◎ ◎
Deliverability
Constructability ◑r ◑
r Pipelines offer benefits in terms of operability and constructability, being a well-known and developed technology. All options,
however, have a material reducible risk associated to them in terms of operability, due to the complexities associated with national-scale water transfer schemes. Operational experience, however, could be drawn from existing schemes such as the Ely Ouse to Essex Transfer Scheme and the Trent Witham Ancholme Scheme.
The data confidence for all options is classified as a material reducible risk: There are significant modelling complexities and uncertainties associated with inter-basin transfer schemes such as the STT options. These uncertainties are all reducible with further research and investigation.
Operability ◑r ◑
r
Dependencies ◑ ◑
Data confidence ◑r ◑
r
Resilience
Climate change ◉ ◉ The resource benefits of these options would all be diminished as a result of increasingly wetter winters and drier summers. The need for winter support of London’s reservoirs would reduce and summer support would be of greater importance. Fully supported transfer would be resilient to these issues.
In terms of other ‘failure modes’, there would be a high impact of power outages and physical damage on long distance transfer operation as assets are ‘in series’. This particularly applies to options that require multiple pumps in series. The STT options would be vulnerable to pollution events in the River Severn and all the options would be vulnerable to pollution events in the River Thames.
Severe drought ○ ○
Resource predictability ◎ ◎
System outage ◎ ◎
Other ‘failure modes’ ◑ ◑
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Table B.2: London WRZ – Wastewater reuse options screening commentary
De
ep
ha
ms Beckton Mogden
Ke
mp
ton
Crossness
Sub-dimension
60 Ml/d
50 Ml/d
100-150 Ml/d
200-380 Ml/d
50 Ml/d
100-150 Ml/d
200 Ml/d
50 Ml/d
50 Ml/d
100-150 Ml/d
191 Ml/d
Comments
Env & Social
SEA ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ ◎◑ Reuse enables climate change resilience and avoids additional pressures on freshwater resources.
Adverse effects due to significant amounts of materials for construction and power and chemicals for operation. Tunnelling and/or pipeline routes will avoid conveyance impacts on sensitive terrestrial features, including likely significant effects on any European designated sites.
WFD effects of treated effluent on receiving waterbodies can be mitigated through robust treatment processes. WFD risks to Lower Lee (Deephams) and upper Thames Tideway (Mogden) due to reduced effluent flow returns – any effects would need to be mitigated.
HRA ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
WFD ◑r ○ ○ ○ ◑
r ◑
r ◑
r ○ ○ ○ ○
Cumulative effects
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Cost
○ ◑ ○ ○● ◎ ◎ ○ ◎ ◑ ○◑ ◑
Promotability
Synergies ○ ○ ◎ ◎ ○ ◎ ◎ ○ ○ ◎ ◎ Synergy opportunities would be reduced to neutral at the lower capacities. There is the potential to increase the synergy for the Mogden and Kempton options by extending the discharge further upstream (Staines) to allow direct supply to Affinity intakes.
Material environmental regulatory acceptability issues need to be addressed but these are considered reducible.
All options apart from Deephams, Kempton and to a degree Mogden involve pipelines of 19 + km. The potential to cause disruption could materially impact on local acceptability.
Customer acceptability
○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Local acceptability
○ ◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
Regulatory acceptability
◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
Wider stakeholder acceptability
◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
Flexibility
Lead time ◎ ○ ○ ◑ ○ ○ ○ ○ ○ ○ ◑ Deephams’ lead time is estimated to be only 4 years, due to the relatively low DO and the shorter
pipeline routes. Options with higher DO in the east of London have longer pipelines and would involve strengthening of the distribution network.
Phasing opportunities are greater for options with shorter pipelines, however these options offer limited maximum DO. Options with higher DO will require tunnelling and therefore reduced potential for phasing.
All RO options (treatment of final effluent) would be capable of being ramped-up within 7 weeks.
Phasing ○ ◑ ◑ ◑ ◑ ◑ ◑ ○ ◑ ◑ ◑
Adaptability ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Ramp-up ● ● ● ● ● ● ● ● ● ● ●
Deliverability
Constructability ○ ◑r ◑
r ◑
r ○ ○ ○ ○ ◑
r ◑
r ◑
r Options with longer pipes pose greater risk to constructability. Water reuse would be new use of
industry standard technology. Hence smaller capacity plants as a first option would be beneficial in terms of constructability and operability
TWUL have been operating Beckton Gateway for 6 years, which includes UF and RO. RO technology is complex and requires skilled operators, through operation of Gateway greater experience would be gained.
Yield certainty regarding data confidence pose limited uncertainty.
Operability ◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
Dependencies ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Data confidence ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○
Resilience
Climate change ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ Options with larger catchments (Beckton and Crossness) offer greater severe drought resilience regarding higher DWF in relation to the reuse quantity
Options that discharge to the Lee Valley are less resilient to outage as they are reliant on Coppermills.
Severe drought ◎ ◉ ◉ ◉ ◎ ◎ ◎ ◎ ◉ ◉ ◉
Resource predictability
◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉ ◉
System outage ◑ ◑ ◑ ◑ ○ ○ ○ ○ ◑ ◑ ◑
Other ‘failure modes’
◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
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Table B.3: London WRZ – New reservoir options screening commentary
Ab
ing
do
n
Re
se
rvo
ir
Ab
ing
do
n
Re
se
rvo
ir
Ab
ing
do
n
Re
se
rvo
ir
Ma
rsh
Gib
bo
n
Re
se
rvo
ir
Ma
rsh
Gib
bo
n
Re
se
rvo
ir
Ch
inn
or
Re
se
rvo
ir
Ch
inn
or
Re
se
rvo
ir
Sub-dimension <75 Ml/d
75-174 Ml/d
>175 Ml/d
<75 Ml/d
75-174 Ml/d
<75 Ml/d
75-174 Ml/d Comments
Env & Social
SEA ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ ◉◑ Beneficial effects include provision of additional storage for water resources resilience, opportunity for
recreational resource provision and opportunity for biodiversity enhancement, as well as beneficial effects on River Thames at low flows due to river regulation provision.
Adverse effects on landscape and visual amenity can be mitigated to an extent through landscaping.
Adverse effects include loss of a small number of properties and agricultural land.
Adverse effects from prolonged construction period will be mitigated as far as possible through best practice construction methods, traffic management controls and measures to mitigate temporary effects on recreational facilities.
Options will not lead to significant effects on any European designated sites.
Options involve some loss or diversion of watercourses and therefore risk to WFD objectives but these risks may be addressed through careful design and mitigation measures.
Cumulative effects are assessed as neutral with other options or projects.
HRA ○ ○ ○ ○ ○ ○ ○
WFD ◑r ◑
r ◑
r ◑
r ◑
r ◑
r ◑
r
Cumulative effects
○ ○ ○ ○ ○ ○ ○
Cost
◎ ◎○ ◑● ◑ ◑● ◑● ◑ AICs lower for two zone options
Promotability
Synergies ◎ ◉ ◉ ◉ ◉ ◉ ◉ The potential for synergies through supplying other WRZs (both belonging to TW and other companies) exists for all river regulation reservoir options but would be greater with larger capacity reservoirs as larger schemes provide greater potential for supplying other WRZs or water companies.
Local and wider stakeholders may prefer smaller reservoirs. Local stakeholders may also prefer dual purpose reservoirs as these offer a local water resource ‘benefit’.
Customer acceptability
◑ ◑ ◑ ◑ ◑ ◑ ◑
Local acceptability ◑ ● ● ● ● ● ●
Regulatory acceptability
○ ○ ○ ○ ○ ○ ○
Wider stakeholder acceptability
◑r ◑ ◑ ◑ ◑ ◑ ◑
Flexibility
Lead time ● ● ● ● ● ● ● There is no clear differentiation in flexibility at the sub-dimension level between the sub-options.
Phasing ◎ ◎ ◎ ◎ ◎ ◎ ◎
Adaptability ◎ ◎ ◎ ◎ ◎ ◎ ◎
Ramp-up ◎ ◎ ◎ ◎ ◎ ◎ ◎
Deliverability
Constructability ◑ ◑ ◑ ● ● ● ● Conveyance for the Abingdon reservoir is shorter because the distance to the river is much greater for both Marsh Gibbon and Chinnor.
Geological risk is greater for Marsh Gibbon and Chinnor reservoirs due to the lack of ground investigations, which are available for the Abingdon site.
Operability ◎ ◎ ◎ ◎ ◎ ◎ ◎
Dependencies ○ ○ ○ ○ ○ ○ ○
Data confidence ○ ○ ○ ◑r ◑
r ◑
r ◑
r
Resilience
Climate change ◉ ◉ ◉ ◉ ◉ ◉ ◉ Larger capacities provide greater resilience whilst the full DO is not required and would provide more support to the existing London supply system to outage events.
Smaller reservoirs would offer less protection against droughts worse that the historical record. They also contribute less to outage resilience.
Severe drought ● ◑ ◑ ◑ ◑ ◑ ◑
Resource predictability
◎ ◎ ◎ ◎ ◎ ◎ ◎
System outage ◎ ◉ ◉ ◉ ◉ ◉ ◉
Other ‘failure modes’
○ ○ ○ ○ ○ ○ ○
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Table B.4: London WRZ – Direct river abstraction options screening commentary
Lo
we
r R
iver
Le
e
Ab
str
acti
on
Te
dd
ing
ton
Sub-dimension 150 Ml/d 300 Ml/d Comments
Env & Social
SEA ◎◑ ◎◑ Lower Lee DRA enables climate change resilience and avoids additional pressures on freshwater resources by use of river flow support, as well as optimising the use of existing infrastructure.
Adverse effects from the use of materials in construction and power and chemicals for treatment of effluent or poor quality river water when in operation. Teddington option may have some adverse effects on navigation at low flows in upper Thames Tideway.
No likely significant effects on designated European sites, with tunnelling or careful pipeline routing to avoid any such sites.
Potential risk to WFD water quality objectives of Lower Lee reservoirs which should be mitigated through treatment design and discharge arrangements to the reservoirs.
Impact of Teddington option on WFD water quality objectives will need to be carefully managed through design of discharge location and extent of effluent treatment.
HRA ○ ○
WFD ◑r ◑
r
Cumulative effects ○ ○
Cost
◉ ◉ The Lower Lee DRA option performs well on cost as it is based upon conventional treatment and direct supply into distribution. However, concerns around emerging parameters and contamination in the catchment mean that further information is needed to confirm the appropriate treatment and whether direct supply is acceptable.
Promotability
Synergies ◎ ◎ Options could indirectly benefit other companies by freeing water from existing licences that could be traded.
No material customer acceptability concerns identified.
Planning permission challenges may be significant associated with a new outfall and new intake upstream of Teddington weir.
New abstraction licence required for both options. Change to discharge consent needed for Mogden effluent transfer needed for Teddington DRA.
At low river flows the lower lee is estimated to comprise approximately 95% sewage treatment works effluent and there are concerns around the presence of viruses, pathogens and contaminants of emerging concern, such as pharmaceutical, personal care products, etc in the source waters. TW envisage that reuse technologies for addressing these concerns would first be trialled through an indirect potable reuse plant at Deephams Sewage Treatment Works. Once the materiality of concerns around emerging parameters, and the efficacy of potential controls, are better understood then the potential treatment scheme for the Lower Lee should be revisited.
Tertiary treatment required for Mogden effluent to meet EA consent conditions to discharge to semi-tidal reach. EA may raise concerns over environmental impacts of reducing flow downstream of Isleworth Ait on SSSI.
Port of London Authority agreement needed in relation to Teddington DRA option. Local river users likely to raise concerns over reduced flows at Isleworth Ait.
Customer acceptability
○ ○
Local acceptability ○ ◑
Regulatory acceptability
●r ◑
r
Wider stakeholder acceptability
○ ◑
Flexibility
Lead time ○ ◑r The Lower Lee abstraction is predicted to have a lead time of 7 years, but there are uncertainties regarding planning, environmental and
construction timings for both options.
Both the river intakes and treatment components of the Teddington DRA option could be phased, however phasing likely to be less economic due to requirement for pipeline/tunnel infrastructure. The Lower Lee intake and treatment components could be phased.
River intakes considered to have limited adaptability as they are dependent constrained by the hydrological yield of the rivers.
Ramp up time for River Lee option TBC depending upon treatment requirements, however likely to be a minimum of 6 weeks. A minimum of 6 weeks is also assumed for the tertiary treatment for Mogden effluent.
Phasing ◎ ◑
Adaptability ○ ○
Ramp-up ● ●
Deliverability
Constructability ◑r ◑
r Land availability a particular concern for both options. There is an unconfirmed risk of arsenic contamination in the ground through which the Lower
Lee pipeline will pass to connect to the existing network.
Operability for Lower Lee option will depend upon treatment technology and whether arsenic removal and treatment for emerging parameters is required.
Teddington option is dependent on there being sufficient intake capacity upstream in the Thames-Lee tunnel to abstract the volumes that would be otherwise abstracted for conveyance in the Thames-Lee tunnel.
There is significant uncertainty around water quality both because of the high degree of sewage effluent in the raw water and because of concerns around contaminated groundwater in the catchment. Further information is needed both on the quality of the raw water and on the appropriate treatment processes for emerging parameters of cconcern.
There is significant uncertainty around the Deployable Output from the Lower Lee option due to limited information on the hydrology in the Lower Lee. The option is also partially mutually exclusive with Deephams reuse.
Operability ○ ○
Dependencies ○ ◑r
Data confidence ●r ○
Resilience
Climate change ◎ ◎ For River Lee raw water availability less vulnerable to climate change due to significant effluent baseflow. Teddington option dependent on transfer of effluent from Mogden treatment works, which has been estimated conservatively.
Teddington option could make process of applying for a drought permit to reduce Teddington target flows more straightforward as it would provide some of the mitigation. Additional intake at Teddington could improve ability to manage flows over Teddington to maximise abstractions during drought.
Both options provide good predictability as flow predominately determine by effluent discharges.
The water abstracted at Teddington is discharged into the Thames Lee tunnel and ultimately treated at Coppermills WTW. Outage at Coppermills would mean that there would be no alternative treatment route. The Lee River option is unsupported.
Complex treatment processes increase vulnerability to power supply loss. Neither river abstraction is supported by reservoir storage and thus would be vulnerable to impact by pollution incidents.
Severe drought ○ ○
Resource predictability
◎ ◎
System outage ◑ ◑
Other ‘failure modes’ ◑ ◑
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Thames Water WRMP19 Resource Options Fine Screening Report Update
Table B.5: London WRZ – Desalination option screening commentary
Be
ck
ton
Th
am
es
me
ad
Cro
ss
ne
ss
Sub-dimension 150 Ml/d
150-300 Ml/d
65 Ml/d Comments
Env & Social
SEA ◎◑ ◎◑ ◎◑ Enables climate change resilience and avoids additional pressures on freshwater resources
Adverse effects from the use of materials in construction and chemicals and power for treatment when in operation.
Tunnelling and/or pipeline routes will avoid conveyance impacts on sensitive terrestrial features, including likely significant effects on any European designated sites.
WFD water quality risks from brine discharges can be mitigated through design and location of the discharge.
Cumulative effects on Thames Tideway can be mitigated through careful design and location of brine discharges if two or more of these schemes are developed.
HRA ○ ○ ○
WFD ○ ○ ○
Cumulative effects ○ ○ ○
Cost
○ ○ ◉
Promotability
Synergies ◎ ◎ ◎ Could potentially also indirectly support other water companies in the South East, but with a reduced DO for London.
A substantial risk of customer complaints due to outages of the desalination plant is envisaged for the Crossness option (that would supply the Northumberland Heath Service Reservoir exclusively, without blending). This risk is considered to be significantly less for the Beckton and Thamesmead options where desalinated water would be blended with water from Coppemills Water Treatment Works.
All three options require tunnelling or directional drilling. This will require intermediate shafts with the potential to cause disruption and materially impact local acceptability, especially through heavily urbanised areas.
Opposition from customers to high energy schemes. Reducible with inclusion of renewable energy sources, such as at Gateway desal plant.
Possible objection from conservationists. Reducible with further evidence and engagement.
Customer acceptability ◑r ◑
r ●
Local acceptability ◑ ◑ ◑
Regulatory acceptability ○ ○ ○
Wider stakeholder acceptability
◑r ◑
r ◑
r
Flexibility
Lead time ○ ○ ◎ This desalination option has an estimated lead-time of 6 years, in-line with other WRMP19 options.
Crossness expected to have shorter lead time.
Treatment options can be implemented incrementally at low cost; however phasing is often less economic because of significant upfront cost for long distance pipelines.
Transfer pipeline provides opportunities to transfer water from the existing Beckton Gateway plant and/or form part of the future expansion of the London ringmain.
The ramp-up time for RO technology desalination is estimated at 8 weeks (if plant is mothballed), allowing for the commissioning of the UF/RO membranes, remineralisation and disinfection treatment streams. Crossness desalination plant assumed to be in service all the time and so ramp up time is less material.
Phasing ◑ ◑ ○
Adaptability ◎ ◎ ○
Ramp-up ● ● ○
Deliverability
Constructability ◑r ◑
r ○ TWUL have experience of constructing and operating a desalination plant. The Beckton and Thamesmead sites have
constraints; the Crossness site has fewer constraints. The majority of constructability challenges relate to conveyance.
TWUL has been operating the Beckton Gateway plant for 6 years. Desalination technology is complex and requires skilled operators. Through operation of the existing Gateway WTW greater experience would be gained by TWUL.
Operation of the Crossness plant without water for blending means that the full capacity of the plant may not generally be utilised, making it less flexible to supply other zones (due to the impact on changing water quality).
There would be limited dependencies on third parties. There are competing TWUL schemes for land available at Beckton.
There is high yield confidence for all the options.
Operability ◑r ◑
r ●
Dependencies ○ ○ ○
Data confidence ◉ ◉ ◉
Resilience
Climate change ◉ ◉ ◉ Raw water availability for the option would not be vulnerable to climate change or extreme drought and is highly predictable.
Desalination resources contribute less to system resilience than surface water resources where treatment can be provided at alternative works in the event of WTW outage. Furthermore for the un-blended Crossness option the works could not be used to support outage at another works without a change in water quality and associated customer complaints.
In terms of other ‘failure modes’, desalination involves complex treatment processes which increases its vulnerability to failure, is vulnerable to power outages (mitigated by own power generation), has a high dependency on the chemical supply chain and would be vulnerable to coastal flooding but mitigation is already provided from the existing flood defences. Pollution incident from shipping would impact water quality.
Severe drought ◉ ◉ ◉
Resource predictability ◉ ◉ ◉
System outage ◑ ◑ ●
Other ‘failure modes’ ◑ ◑ ◑
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There is a systematic tendency for project costs developed at the outline business case stage to
underestimate the actual outturn cost. As a result, HM Treasury Green Book20
guidance recommends that
adjustments be made to project costs to reflect ‘optimism bias’. For non-standard civil engineering projects
a factor of 66% is applied. The supplementary Green Book Guidance on Optimism Bias21
provides an
approach for reducing optimism bias based upon an assessment of the extent that the various contributing
factors have been mitigated. For WRMP14 Thames Water adopted an approach to mitigation of optimism
bias that took an assessment of the confidence grade for each option from its corporate Asset Planning
System (APS) and used this to mitigate optimism bias, splitting options into three categories: High Risk,
Medium Risk and Low Risk.
An assessment was also made of uncertainty which drew upon guidance from the Association for the
Advancement of Cost Engineering22
(AACE). The AACE guidance provides a range of uncertainties for
projects at different levels in the development process (see Table C.1 below).
Table C.1: AACE cost estimate classification matrix for process industries
Estimate class
Level of project definition End usage
Accuracy range low
Accuracy range high
Preparation effort
Class 5 0% to 2% Concept Screening -20% to -50% +30% to +100% 1
Class 4 1% to 15% Study or Feasibility -15% to -30%
+20% to +50% 2 to 4
Class 3 10% to 40% Budget Authorisation
-10% to -20%
+10% to +30% 3 to 10
Class 2 30% to 70% Bid or Tender -5% to -15%
+5% to +20% 4 to 20
Class 1 50% to 100% Check Estimate or Bid/Tender
-3% to -10%
+3% to +15% 5 to 100
Source: AACE Recommended Practice No. 18R-97
For WRMP14 Thames Water took the mid-point of the low and high accuracy ranges from Table C.1 to
provide a range of uncertainty. For options assessed as being Low Risk the Class 3 ranges were used as
TW’s view was that the cost estimates it had developed for those options were at a level that would not
change significantly before reaching Class 3 (Budget Authorisation). Similarly, for Medium Risk projects
the Class 4 uncertainty ranges were used and for High Risk projects the Class 5 uncertainty ranges were
used. This resulted in the combined optimism bias and uncertainty assumptions set out in Table C.2
below.
20
HM Treasury (2003), The Green Book, Appraisal and Evaluation in Central Government
21 HM Treasury, Supplementary Green Book Guidance – Optimism Bias
22 AACE, Cost Estimate Classification System – As Applied in Engineering, Procurement , and Construction for The Process Industries, 18R-97
Appendix C. Optimism bias & uncertainty
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Table C.2: Optimism bias and uncertainty assumptions used at WRMP14
Low Risk Medium Risk High Risk
Estimating Uncertainty -15% to +20% -22.5% to +35% -35% to +65%
Optimism Bias +5% +25% +66%
Estimating & Scope Uplift -10% to +25% +2.5% to +60% +31% to +131%
Most Likely Point +5% +25% +66%
Source: HFA, PR14 Option Development and Uncertainty Estimating
The WRMP14 approach to optimism bias and uncertainty has been taken as the basis for adjustments
made to costs in the fine screening process. However, rather than banding options into three risk bands a
continuous adjustment to the capital costs has been made linked directly to the APS confidence grade and
using the relationship set out in Figure C.1.
Figure C.1: Allowance for optimism bias and uncertainty used in fine screening
-20%
0%
20%
40%
60%
80%
100%
120%
140%
1 1.5 2 2.5 3 3.5 4 4.5 5
Pe
rce
nta
ge u
plif
t fo
r o
pti
mis
m b
ias
and
un
cert
ain
ty
Confidence Grade (5 = low confidence; 1 = High confidence)
Lower (linear)
Most likely (linear)
Upper (linear)
Min confidence grade = 2.05