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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





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.



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



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



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


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


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


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


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


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


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



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



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.

mailto:[email protected]



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



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.



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


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


356236/WCD/WAM/40/02 30 September 2016 Phase 1a Option Screening Report RevF.docx

356236/WCD/WAM/40/A 30 August 2016 PiMS/356236/Documents

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


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


• Review PR14 methodology

• Develop screening process

• Refine options with recommendations for

further investigations


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



9

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.



10

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



11

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).



12

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



13

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.



14

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.



15

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.



16

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



17

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.



18

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


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.



19

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.



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


RWT: STT Deerhurst 100Ml/d (Lon only) London 92 Vyrnwy 60 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


RWT- STT Deerhurst 300Ml/d (2 zone Lon) London 252 Vyrnwy 180 MLD (2 zone Lon 170MLD)

Minworth 88 MLD (2 zone Lon 78MLD)



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)



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)






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





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


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


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


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


Raw

Wate

r T

ran

sfe

rsW

ate

r R

eu

se

New

Reserv

oir

Dir

ect

Riv

er

Desali

nati

on



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

●

●

●

●

●

●

●

●

●

●

●

●



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).



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

24 356236/WCD/WAM/40/02 30 September 2016



3.6.3 Promotability dimension


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.




– 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

http://www.thameswater.co.uk/pr14/CCG-for-Thames-Water-report-to-Ofwat.pdf




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


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;




– 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:




– 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.




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


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.




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


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).




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.




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.




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




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.




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




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.




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




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)


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


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 ✔ ✖




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


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


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


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


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


60 ✔ ✔ ✔ Explanatory

25 ✔ ✔ ✖ The 60 Ml/d option provides better value

Long Reach - treated effluent

Site adjacent to STW


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


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:




– 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.



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.



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.




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




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


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


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


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




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


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


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


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





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


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.




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



30Mm3 + 120Mm

3 – Site 22 Abingdon

75Mm3 + 75Mm

3 – Site 22 Abingdon



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




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




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.


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.


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 ✔ ✔


Ml/d transfer

300 n/a ✔ ✔


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.




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


308 from listed resources

✔

Minworth STW, Draycote Reservoir, Mythe WTW, Netheridge STW and Lake Vyrnwy resources

Costwold Canal conveyance element


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


300 TBC Further investigation to confirm the Deployable Output benefit and normalised cost

Use of Farmoor Reservoir Pipeline from Deerhurst to Farmoor Reservoir


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




– 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.



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:




– 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.



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 ✖





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 ✖


River Rom/Beam 8) River Rom/Beam abstraction for direct supply to potable network

7.2 Ml/d

✖


River Ingrebourne 9) River Ingrebourne abstraction for direct supply to potable network

4.2 Ml/d

✖


*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.



5.2.6 Aquifer recharge

The aquifer recharge options identified in the groundwater feasibility report are listed in the table below


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.




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




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:




– 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.




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.



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

✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✖



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.



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



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



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.



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.



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 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.



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.



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



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.


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.


6.2.1 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


Table 6.1: SWOX options identified in the feasibility report for direct river abstraction


Stage

1 2 3 Comment

River Thames 2a) Abstraction at Culham 4.5 Ml/d ✔ ✖

Significant Pumping



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


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.




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



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.


The options for removal of DO constraints identified in the groundwater feasibility report are listed in the


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.


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.




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.


The fine screening assessment for SWOX will be updated once the Groundwater Feasibility Report has

been completed.



7 SWA WRZ resource options


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.


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.





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.







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.




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 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.



No exclusivities or interdependencies have been identified.


The fine screening assessment for SWA WRZ will be updated once the Groundwater Feasibility Report

has been completed.



8 Henley WRZ resource options


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.


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


8.2.1 Groundwater development options

The options identified in the feasibility report for groundwater development are listed in the table below


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.




9 Guildford WRZ resource options


assessment for the Guildford Water Resource Zone grouped by option type.

Options are assessed qualitatively against the six dimensions: Cost,



decisions.


The resource option types identified for the Guildford WRZ comprise:

Aquifer storage and recovery;


Removal of Deployable Output constraints;





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.





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.



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.




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.


The options for removal of DO constraints identified in the groundwater feasibility report are listed in the


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.




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



– 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.


Dapdune and Ladymead operate under an aggregate licence. Therefore changes in abstraction from one

must be considered in terms of operation of both sources.


The fine screening assessment for the Guildford will be updated once the Groundwater Feasibility Report

has been completed.

.



10 Kennet Valley WRZ resource options


assessment for the Kennet Valley (KV) Water Resource Zone grouped by option

type. Options are assessed qualitatively against the six dimensions: Cost,



decisions.


The resource option types identified for Kennet Valley WRZ comprise:


Removal of Deployable Output constraints.



The options identified in the feasibility report for groundwater development are listed in the table below


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.






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.


The options identified in the feasibility report for removal of deployable output constraints are listed in the


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.




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).


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.




The fine screening assessment for the Kennet Valley will be updated once the Groundwater Feasibility

Report has been completed.



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



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



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



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



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.



Appendices

Appendix A. Summary of water quality modelling ____________________________________________________ 83 Appendix B. London WRZ fine screening tables _____________________________________________________ 86 Appendix C. Optimism bias & uncertainty __________________________________________________________ 92



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



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


UF+RO+AOP

High

Medium

Low

Fe+NSF+O3/GAC+IX

High (1)

(1)

(1)

(1)

(1)

(1)

Medium

Low

Note:


Fe+NSF+O3/GAC+IX Ferric + Nitrifying Sand Filter + Ozone / GAC + Ion Exchange

(1) Except for Phosphate


UF+RO+AOP

High

Medium

Low

Fe+NSF+IX

High (1)

(1)

(1)

(1)

(1)

(1)

Medium

Low

Note:


Fe+NSF+IX Ferric + Nitrifying Sand Filter + Ion Exchange

(1) Except for Phosphate



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.


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.



Appendix B. London WRZ fine screening tables



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


◑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


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.


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’ ◑ ◑



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.


○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○

Local acceptability

○ ◑r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r


◑r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r ◑

r


◑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.


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



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’.


◑ ◑ ◑ ◑ ◑ ◑ ◑

Local 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 ● ◑ ◑ ◑ ◑ ◑ ◑


◎ ◎ ◎ ◎ ◎ ◎ ◎

System outage ◎ ◉ ◉ ◉ ◉ ◉ ◉

Other ‘failure modes’

○ ○ ○ ○ ○ ○ ○



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.


○ ○

Local acceptability ○ ◑


●r ◑

r


○ ◑

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


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 ○ ○


◎ ◎

System outage ◑ ◑

Other ‘failure modes’ ◑ ◑



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 ○ ○ ○


◑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


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.


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’ ◑ ◑ ◑



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



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