Needs Report. Application for Development Consent. Thames Tideway Tunnel Thames Water Utilities Limited. Application Reference Number: WWO10001

Transcription

1 Thames Tideway Tunnel Thames Water Utilities Limited Application for Development Consent Application Reference Number: WWO10001 Needs Report Doc Ref: 8.3 Main Report APFP Regulations 2009: Regulation 5(2)(q) Hard copy available in Box 60 Folder A January 2013

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3 THAMES TUNNEL NEEDS REPORT LIST OF CONTENTS Page Number 1 EXECUTIVE SUMMARY Introduction Historical context The modern River Thames Legal requirements TTSS report, recommendation and EA view Regulatory Impact Assessment and Minister s 2007 request Work since the 2007 Ministerial request Investigation of solutions used elsewhere in Europe Written ministerial statements in Conclusions 5 2 INTRODUCTION Background Purpose of this report Report structure 8 3 THE LEGAL AND REGULATORY CONTEXT Introduction Sewer systems and governing legislation Overview of regulatory framework within which the water and sewerage undertakers operate Urban Waste Water Treatment Directive and related UK Regulations Statutory duties of the water and sewerage undertakers The Water Framework Directive and associated requirements Powers of the European Commission to bring infraction proceedings 17 4 THE NEED London s sewerage The Thames Tideway Strategic Study and further work by Thames Water Baseline conditions Model development work undertaken since the TTSS CSO performance The legal need - UWWTD, WFD and other statutory duties Water quality impacts Further considerations The long term effect of doing nothing Summary of the need 46 5 ACHIEVING COMPLIANCE London Tideway Tunnels Design and Performance Criteria Tunnel options Alternative approaches to the tunnel options Further considerations Other European schemes to meet UWWTD requirements 70

4 5.7 Related work 74 6 OVERVIEW AND CONCLUSIONS Legislation and European Commission Actions Background and the TTSS Government response to the TTSS studies in Tunnel options and alternatives Conclusion 77 ABBREVIATIONS 79 GLOSSARY 81 REFERENCES 84 APPENDICES (in separate volume) 86 APPENDIX A: MINISTERIAL CORRESPONDENCE, REGULATORY IMPACT ASSESSMENT APPENDIX B: REPORT ON APPROACHES TO UWWTD COMPLIANCE IN RELATION TO CSOs IN MAJOR CITIES ACROSS THE EU APPENDIX C: POPULATION STATISTICS APPENDIX D: SEWER SEPARATION FEASIBILITY STUDY APPENDIX E: POTENTIAL SOURCE CONTROL AND SUDS APPLICATIONS APPENDIX F: TIDEWAY FISHERIES REVIEW

5 LIST OF FIGURES Page Number Figure 4.1 Catchment areas draining to Mogden, Beckton and Crossness STWs Figure 4.2 Locations of discharges on the Thames Tideway Figure 4.3 TTSS Option 1c Figure 5.1 London Tideway Tunnels: Alignment Options Figure 5.2 Comparison of Dissolved Oxygen Standard Compliance (a) No improvements, (b) STW improvements and Lee Tunnel, (c) River Thames/ Rotherhithe route and (d) Abbey Mills route LIST OF TABLES Page Number Table 4.1 Comparison of annual spills at existing, intermediate and projected baseline conditions Table 4.2 Comparison of projected CSO performance during a typical year, before and after commissioning of Lee Tunnel and STW Improvements Table 4.3 Revised interim EQS for DO on the Tideway, derived by the TTSS Steering Group and the Environment Agency Table 4.4 Comparisons of WFD Standards (shaded rows) and Tideway EQS for DO Table 4.5 Summary of UK climate change predictions UKCIP02 and UKCP Table 5.1 Comparison of overflow volume and number of spills for tunnel route options Table 5.2 Comparison of tunnel alignments Table 5.3 Cost estimates 1 ( millions) for each tunnel alignment Table 5.4 TW asset data: Sewers categorised as combined Table 5.5 Allowances for non-construction costs Table 5.6 Total costs for each sewer separation study area Table 5.7 Summary of CSO discharge volume (m 3 ) for December event of the typical year during the 1-year 120m-min storm event for the expanded STWs and the 2021 population Table 5.8 Total costs for each source control/suds study area Table 5.9 Advantages and Disadvantages of options Table 5.10 Summary of main options and estimated costs Table 5.11 Percentage reduction in annual spill volumes and frequencies Table 5.12 Estimated quantities of sewage litter entering the Thames Tideway (tonnes) Table 5.13 Approaches to UWWTD compliance in relation to CSOs in major cities across the EU... 72

6 1 Executive Summary 1 EXECUTIVE SUMMARY 1.1 Introduction The Thames Tunnel is a full-length storage and transfer tunnel proposed to intercept discharges from overflows into the tidal Thames from West to East London and to pass them for treatment at Beckton Sewage Treatment Works. The primary objective of the Thames Tunnel is to capture discharges from Combined Sewer Overflows (CSOs) into the River Thames in order to meet the requirements of the EU Urban Waste Water Treatment Directive and the related UK Urban Waste Water Treatment Regulations. The Needs Report considers the need for the Thames Tunnel taking into account the Lee Tunnel and the other London Tideway Improvements (LTI), namely the sewage treatment works upgrades. It builds upon work undertaken for the purpose of the Thames Tideway Strategic Study (TTSS), as reported in February and November 2005, and the further report Tackling London s Sewer Overflows, as issued in December Historical context London s sewer system was designed in the 1800s to handle waste water and run-off rainwater through a combined collecting system. CSOs were incorporated into the sewer system as relief structures to prevent flooding caused by sewer overloading, especially during periods of heavy rainfall. Much of London s sewerage infrastructure consists of combined systems, whereby a single set of sewers convey both foul sewage and rainwater runoff to a sewage treatment works for treatment. The current sewer system is subject to significant flows from surface drainage and so generates large volumes of storm sewage (sewage and rainwater mixed). This is in part due to historic watercourses having been used for sewage disposal and subsequently culverted as the density of development intensified. Rainfall causes combined sewer systems to surcharge quickly. For this reason, it is normal practice to incorporate overflows that allow excess flows to discharge directly to a watercourse to reduce flood risk to properties and prevent overloading the sewerage system. The capacities originally allowed for in the interceptor sewer systems originally designed by Sir Joseph Bazalgette in the 1850s and subsequently extended have now been substantially exceeded. Despite improvements over the years there is little spare capacity in the sewerage network as a whole. This is largely due to the increases in population, water usage and increased hardstanding areas served. This greater proportion of hard surfacing has reduced the capability of the land to absorb rainwater which instead now enters the sewerage network such that it now only takes as little as a few millimetres of rainfall to cause some CSOs to discharge storm sewage into the River Thames. 1.3 The modern River Thames Currently, spillages to the tidal Thames occur more than 50 times per year at the most frequently overflowing CSOs in the Beckton and Crossness catchments, north and south of the river respectively. An estimated total of some 39 million cubic metres of storm sewage enters the river in a typical year from these catchments. In a wet year this volume can be much greater, but will otherwise reduce to some 18 million cubic metres by 2015 on completion of the sewage treatment works upgrades and the Lee Tunnel. The Beckton and Crossness drainage catchments are the principal source of storm sewage discharges to the tideway, and there are no significant CSOs discharging to the tidal River Thames west of Acton, As reported by the Minister for Climate Change and the Environment (Ian Pearson) in the Written Ministerial Statement (Hansard 22 Mar 2007: Column 53WS): These overflows are having an adverse effect on the environmental quality of the Thames. It has been found that the frequent overflows (on average once a week) and the large quantities of untreated discharges are causing: Adverse environmental impacts on fish species; Unacceptable aesthetic issues; and Page 1

7 1 Executive Summary Elevated health risks for recreational users of the Thames. The situation in London is exacerbated by the characteristics of the Thames river basin and the estuarine reach of the river Thames. Water moves up and down the river, with the incoming and outgoing tides, with the net seaward movement taking up to three months to travel along the estuary from Teddington to Southend. Summer storms in particular have the potential to cause greatest impact, due to (a) low natural flows in the river meaning less dilution of the overflows, and (b) higher water temperatures meaning the river contains less dissolved oxygen to sustain aquatic life and what dissolved oxygen is present is consumed more quickly. Should nothing be done to address the current situation, continuing population growth and incremental increases to impermeable areas are expected to increase the volume and frequency of discharges to the river. Such increased discharges will have associated increased adverse environmental impacts. 1.4 Legal requirements The Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors. The objective of the Directive is to protect the environment from the adverse effects of the above mentioned waste water discharges. The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI1994/2841) transpose the UWWTD into English law. Annex 1 of the UWWTD (and repeated in the Regulations) includes the following requirements for collecting systems: The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding: volume and characteristics of urban waste water, prevention of leaks, limitation of pollution of receiving waters due to storm water overflows. Infraction proceedings are being pursued by the European Commission against the United Kingdom for breach of the UWWTD. On 8 October 2009 the European Commission announced its decision to take the United Kingdom to the European Court of Justice on the grounds that urban waste water collecting systems and treatment facilities in London (and Whitburn) do not comply with EU legislation. Other EU and UK legislation also forms part of the legal framework within which the Thames Tunnel is to be designed and delivered. The Water Framework Directive (WFD), and the regulations which transpose it within the UK, set out various environmental objectives relating to surface water quality to be achieved by 2015, 2021 and In order to achieve these objectives in the UK, the Environment Agency has responsibility for the production of river basin management plans. The River Basin Management Plan for the River Thames, published in December 2009, states that the London Tideway Tunnels (the Thames and Lee Tunnels); represent the primary measures to address point source pollution from the sewer system and are fundamental to the achievement of good status in this catchment (Estuaries and Coastal Waters Catchment). The Thames Tunnel is therefore required to help to achieve compliance with the WFD as well as with the UWWTD. 1.5 TTSS report, recommendation and EA view The Thames Tideway Strategic Study (TTSS) was set up in 2001 and reported in February and November This Steering Group was established under the independent chairmanship of Professor Chris Binnie. Its members included representatives from Thames Water, the EA, DEFRA, the GLA and Ofwat, the latter with observer status. Its purpose was to assess the environmental impact of intermittent discharges of storm sewage on the Thames Tideway, to identify objectives for improvement and to propose potential solutions, having regard to costs and benefits. Page 2

8 1 Executive Summary As part of the TTSS the Environment Agency (EA) assessed the CSO discharges from the Beckton and Crossness catchments. The EA considered the volume and frequency of the different discharges, as well as assessing their impact on river water quality and ecology. These were then categorised on the basis of criteria including frequency and volume of discharge. A total of 36 CSOs were identified as being unsatisfactory and therefore requiring attention, of which 34 discharge to the Tidal Thames and two into the River Lee. Specific environmental objectives were developed by the TTSS which needed to be addressed by the project, namely to reduce: the adverse environmental impacts on the river ecosystems and on fish species in particular; the unacceptable aesthetic issues; and the elevated health risks for recreational users of the tidal Thames. The TTSS established that the environmental objectives can only be met at least cost by completing both quality improvements to the treatment works discharges and by the provision of a storage and transfer tunnel to intercept unsatisfactory CSOs. Ofwat commissioned Jacobs Babtie to review the TTSS. The principal output of this work was an alternative solution, based on two shorter tunnels (one in West London and one in East London), along with further recommendations. DEFRA considered the various reports and asked Thames Water to provide cost information on the identified tunnel solutions. 1.6 Regulatory Impact Assessment and Minister s 2007 request The TTSS and subsequent studies, including the Jacobs Babtie report, were considered by Defra and a Regulatory Impact Assessment was issued in March The Regulatory Impact Assessment specifically rejected the solution identified by Jacobs Babtie as it did not meet the required regulatory or TTSS environmental objectives. Ian Pearson, the then Minister of State for Climate Change and the Environment, in a letter to the Chief Executive Officer of Thames Water dated 17 April 2007, stated that his view was that: a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works is needed. This is both to provide London with a river fit for the 21 st century, and for the UK to comply with the requirements of the Urban Waste Water Treatment Directive concerning provision of collecting systems and, in particular, limitation of pollution from storm water overflows. Furthermore, Ian Pearson subsequently requested that Thames Water make provision for the design, construction, and maintenance of a scheme for the collecting systems connected to Beckton and Crossness sewage treatment works which involves a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works. (Letter reproduced in full at Appendix A, Item A1.1) 1.7 Work since the 2007 Ministerial request Since the Ministerial request in 2007, Thames Water has responded to the request. Its work has included the following activities: Modelling Thames Water maintains a numerical hydraulic model that represents the sewer system for the Beckton and Crossness catchments. This model has continued to be developed since As part of the model development work, a programme of flow monitoring of the system has been implemented, including monitoring at CSO locations. In parallel with the hydraulic model, a water quality model of the Thames Estuary from Teddington weir to Southend was developed for the Environment Agency (EA) to understand the impacts on water quality of discharges from sewage treatment works (STWs) and CSOs. Page 3

9 1 Executive Summary The catchment and water quality models were used to test the impacts of various proposed options. Climate change projections have been taken into account. The models have demonstrated that the do nothing option is unacceptable. The modelling has also confirmed that the addition of the full-length storage tunnel is necessary to achieve the required reduction in the frequency and volume of CSO discharges. Such a reduction is the key outcome to enable compliance with the UWWTD. The tunnel will also contribute towards achieving the WFD objective to attain good ecological potential in the Thames Tideway Refinement of the Scheme Considerable development work has been undertaken since 2007 to refine the full-length storage tunnel scheme. Three alternative tunnel alignments have been studied, namely the River Thames route (very similar to the original concept), the Rotherhithe route and the Abbey Mills route. All three alignments will contribute towards achieving the EA water quality standards and the TTSS environmental objectives whilst achieving the requirements of the UWWTD. However, the shorter Abbey Mills route offers the lowest cost and least adverse environmental and community impacts when compared to the other two routes. It is therefore recommended as the preferred route Investigations into sewer flooding Flooding of basements, gardens and roads occurs in parts of London during or following major rainfall events, caused by surcharging of combined sewers. A number of projects are planned to alleviate this sewer flooding. Once the storage tunnel has been developed and is in operation it will be a strategic component of London s infrastructure and will provide flexibility to adapt the network for future conditions, including opportunities for the flows from new sewerage infrastructure to be diverted to the tunnel Consideration of alternative options Alternative technologies have been explored such as source control (methods of managing and reducing storm water runoff at site level), sewer separation (separate storm water and foul networks), partial separation, dispersed storage units (capturing storm water and controlling the outflow), CSO screening and sustainable drainage systems (SUDS) (techniques employing ponds, swales, green roofs, detention ponds and permeable surfaces). None of these options have been found to be suitable cost effective solutions when compared to the full-length storage tunnel solution or capable of meeting the requirement to achieve compliance with the UWWTD by the target date of 2020 (the date provided by the UK Government to the European Commission) and meet the TTSS environmental objectives. Also these alternative options will not assist in meeting the WFD objective to attain good ecological potential in the tidal Thames. 1.8 Investigation of solutions used elsewhere in Europe Most major cities in the European Union have had or are having to address the issue of CSO discharges from their sewer networks. A review of the approaches to UWWTD compliance in relation to CSOs by certain major and many smaller cities across the EU has demonstrated that the most common approach to resolving CSO issues was the addition of extra capacity by the construction of detention tanks and/or trunk or interceptor sewers. Cities such as Helsinki, Naples, Stockholm and Vienna already use tunnels to resolve their CSO issues. Paris, like London, is developing a tunnelled storage and conveyance system to meet the requirements of the UWWTD. 1.9 Written ministerial statements in 2010 In a written statement to Parliament on 1 March 2010 the then Secretary of State for Environment, Food and Rural Affairs (Hilary Benn) announced that he was minded to direct planning applications for the tunnel to the Infrastructure Planning Commission. In doing so he set out the case for the Thames Tunnel as a project of national significance which, if not implemented, could cause reputational risk to the UK. The Secretary of State commented that the urgency of the works is Page 4

10 1 Executive Summary increased by the infraction proceedings being pursued against the UK by the European Commission for an alleged breach of the UWWTD. The succeeding Environment Secretary, Caroline Spelman, issued a written ministerial statement on 7 September 2010 confirming the coalition government s support for the construction of the tunnel from West London to Beckton and declaring that a Thames Tunnel continues to offer (by far) the lowest cost solution to the problem and I believe Thames Water should continue to press forward with this project working with Ofwat, the Environment Agency and Defra on the regulatory, commercial and planning processes. The Environment Secretary s statement added that I am also minded that development consent for the project should be dealt with under the regime for nationally significant infrastructure projects established by the Planning Act I consider that this project, with its unique scale and complexity, is of national significance, and therefore appropriate for this regime. (Written ministerial statement reproduced in full at Appendix A, Item A1.2) 1.10 Conclusions Thames Water has been requested by successive UK Governments to make provision for the design, construction, and maintenance of a scheme for the collecting systems connected to Beckton and Crossness sewage treatment works which includes a full-length storage tunnel with additional secondary treatment at the Beckton STW. The Thames Tunnel would meet these Ministerial requests. Delivery of such a scheme also provides benefits in improved water quality, aesthetics, health of recreational users and the sustainability of the aquatic environment in the Thames Tideway. It will also contribute towards achieving the UK s WFD objective to attain good ecological potential in the tidal Thames. The recommended full-length storage tunnel (Abbey Mills route) achieves compliance with the UWWTD and environmental objectives. At an estimated cost of 3,588 million it is the most cost effective scheme, involving the least disruption to residents, businesses and transportation when compared to alternatives. It also has the shortest implementation time which will facilitate the target date of The UWWTD provides that The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs. It is concluded that the full-length storage tunnel approach on the Abbey Mills route is the most cost effective solution which meets the requirements of the UWWTD and the environmental objectives. Page 5

11 2 Introduction 2 INTRODUCTION The primary objective of the Thames Tunnel is to capture flows discharging from CSOs into the River Thames to meet the requirements of the EU Urban Waste Water Treatment Directive. The quality of the Tidal Thames has been the subject of studies over a considerable period of time. These have been driven by increasing environmental expectations and obligations arising from the interpretation of successive European Directives. Mitigation of poor river water quality has been provided in several ways. In 2001 the Thames Tideway Strategic Study (TTSS) was set up to assess the impacts of intermittent discharges of combined storm and foul sewage on the Thames Tideway. The TTSS was co-ordinated by a Steering Group chaired by the independent Professor Chris Binnie with representatives from EA, Defra, GLA and Thames Water. The TTSS reports, published in 2005, recommended improvements to both collecting systems and treatment works, and proposed targets for water quality. These reports have formed the basis of all subsequent work. For the TTSS the EA categorised the 57 CSOs relating to the Beckton and Crossness sewer catchments (collecting systems) and identified 36 as unsatisfactory and requiring improvement. Of these, 34 discharge directly to the River Thames. There are no CSOs requiring improvement situated west of Acton. Subsequent work, presented in Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report (December 2006), developed a preferred solution, referred to as Option 1c, to intercept 36 unsatisfactory CSOs into a full length storage and transfer tunnel to convey flow to treatment at Beckton STW. Aside from the Thames Tunnel, other related improvements, including the Lee Tunnel and improvements to the STWs at Mogden, Beckton, Crossness, Riverside and Long Reach are now under construction. This report focuses on the need for the Thames Tunnel as part of the above suite of measures required to comply with European legislation and achieve environmental objectives. It is intended to assist the consultation process. 2.1 Background Substantial proportions of London s sewerage network were built on the combined principle, whereby a single set of sewers convey foul sewage, groundwater infiltration and rainwater runoff to sewage treatment works (STWs) for treatment, prior to discharge to the Thames Tideway. It is normal practice for combined sewer systems to incorporate overflows in the system, known as combined sewer overflows (CSOs). CSOs allow excess storm flows following rainfall to discharge directly to a water body to reduce flood risk to land and properties. This is the case with much of the London sewer system which has been extended over the years and now incorporates 57 CSOs in the Beckton and Crossness catchments which discharge to the Thames Tideway and lower River Lee. The impact of these discharges only began to be appreciated in the late 1970s when general improvements to sewage treatment improved the background water quality to the point where fish populations were able to re-establish. Operation of these overflows under certain conditions, particularly summer conditions of low natural river flows and high temperatures, could result in localised deoxygenation and fish deaths. Mitigation measures have been adopted to help maintain oxygen concentrations and these have been largely successful in avoiding major or frequent fish mortalities but these have always been recognised as ameliorating the impact. Recognising the causes and impacts of these episodes of poor water quality the Tidal Thames has been the subject of the many studies over a considerable period of time. These have been driven by increasing environmental expectations as well as obligations arising from the interpretation of successive European Directives. Nonetheless, it was clear that a major study would be required Page 6

12 2 Introduction and this was endorsed in 2000, leading to the establishment of the Thames Tideway Strategic Study (TTSS). The Steering Group of the TTSS was assembled in early 2001 to co-ordinate the study, to assess the environmental impact of intermittent discharges of combined storm and foul sewage on the Thames Tideway, to identify objectives for improvement and to propose potential solutions, having regard to benefits and costs. Thames Water (TW), the Environment Agency (EA), Department of Food and Rural Affairs (Defra) and the Greater London Authority (GLA) were represented on the Steering Group under the independent chairmanship of Professor Chris Binnie. The Water Services Regulation Authority (Ofwat) maintained an observer status. The Steering Group was supported by three working groups focussed respectively on Objectives, Cost-benefits and Solutions. As part of the TTSS the EA evaluated 57 CSOs in the Beckton and Crossness catchments by considering the volume and frequency of the discharges, as well as assessing their impact on river water quality and ecology. These were then categorised and a total of 36 CSOs were identified as being unsatisfactory and therefore requiring control. Of these, 34 discharge directly into the tidal River Thames and the other two into the tidal River Lee. The remaining 21 CSOs were assessed by the EA as not requiring any action to be taken. Of the two unsatisfactory CSOs discharging into the River Lee one is being addressed by the provision under a related, but separate, scheme of a 7km long, 7.2m diameter storage tunnel from Abbey Mills Pumping Stations to Beckton Sewage Treatment Works (STW). This is referred to as the Lee Tunnel. A local improvement solution is adequate for the other CSO. West of Acton there are no significant CSOs discharging to the tidal River Thames from the Beckton and Crossness catchments. Much of the pollution in the Richmond area of the River Thames originates from the CSOs downstream and reaches the area on the incoming tide. While the catchments served by Beckton and Crossness sewage treatment works to the east have a substantial proportion of combined sewers, the area in the west of London that drains to Mogden STW contains mostly separate sewers for rainwater and sewage. The Mogden sewerage network is, therefore, less responsive to rainfall and the volume of discharges in the area is small in comparison to those downstream. As part of the London Tideway Improvements significant works are under way at the Mogden STW to increase the secondary treatment capacity of the works and so reduce the frequency of overflow from the storm water settlement tanks that already exist as part of the treatment plant. Consequently there is no water quality justification, nor legislative driver, to extend the proposed tunnel west of Acton. Following on from the TTSS and an independent review by Jacobs Babtie, further study by Thames Water recommended that, in conjunction with the London Tideway Improvements and Lee Tunnel schemes, a single tunnel option, described as the Thames Tunnel Option 1c 1, was the optimal solution satisfying both policy frameworks and statutory requirements, including European requirements, in a phased programme of works. The study culminated with a policy decision by the responsible Minister, in support of a full-length storage tunnel. The Thames Tideway Sewer Tunnel Project is supported in the London Plan (2008) (Policy 4A.18), the draft Replacement London Plan, December 2009 (Policy 5.14), the Mayor s draft water strategy, 2009 (Proposal 10), and some local development framework core strategies produced by London Boroughs. 2.2 Purpose of this report This report sets out the latest position on the need for the Thames Tunnel in the light of further work since the publication of the Thames Tideway Tunnel and Treatment Summary Report in December 2006, including the improvements to the hydraulic modelling of the contributing catchments. It also takes account of the Lee Tunnel Project and the London Tideway Improvements schemes currently being implemented. The Thames Tunnel Needs Report will also assist in the consultation process for the Thames Tunnel. 1 Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report (December 2006) Page 7

13 2 Introduction 2.3 Report structure The document has been structured as follows: Section 3 provides the legal and regulatory context. Section 4 documents the need for a solution to meet the regulatory drivers and outlines the risks of doing nothing. Section 5 establishes a solution to achieve compliance examines other alternatives and outlines the benefits of the solution including its flexibility for facing future climatic conditions, population growth, water demands and changes in environmental requirements. It also provides information on the solutions being promoted to comply with the EU Directives elsewhere in Europe. Each of the above chapters is headed by a summary box which sets out the key issues covered within that chapter. These chapter summaries are intended to assist the reader in their understanding of the Needs Report. Section 6 provides an overview of the key issues and conclusions. Lists of the abbreviations, a glossary of terms and the references used are located at the end of the report. The Appendices are located in a separate accompanying document. Page 8

14 3 The Legal and Regulatory Context 3 THE LEGAL AND REGULATORY CONTEXT This section sets out the major driver for the Thames Tunnel, this being compliance with the legislation summarised below. The objective of the Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) is to protect the environment from the adverse impacts of insufficiently treated waste water discharges. Subject to a caveat that not all flows can be treated under situations such as unusually heavy rainfall, there is a presumption in UWWTD that all sewage collected will be treated to secondary standard prior to discharge, and that pollution due to stormwater overflows will be limited. In the event that the UK is found by the European Court of Justice to have failed to fully implement Directives (including UWWTD), then substantial financial penalties may be imposed on the UK. The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI 1994/2841) transpose the UWWTD into UK law. Failure to address identified obligations would expose water and sewerage undertakers to the risk of enforcement action from the UK Government and/or Regulators. The Water Framework Directive (WFD) (2000/60/EC) aims at maintaining and improving the aquatic environment in the Community. The Directive was transposed into UK law by the Water Environment (Water Framework Directive) (England and Wales) Regulations 2003 (SI 2003/3242). The WFD requires that Member States aim to achieve, subject to caveats, Good Ecological Status (GES) or, in the case of heavily modified waterbodies such as the tidal Thames, Good Ecological Potential (GEP) by Legislation therefore requires action to be taken to address CSO discharges which are found to cause adverse effects on the receiving watercourse and/or operate outside of adopted criteria. The legal framework for the required action is complemented by the economic framework regulated by the Water Services Regulation Authority (WSRA), known as Ofwat, and the environmental standards set and monitored by the Environment Agency (EA). 3.1 Introduction This section provides an overview of the law as it generally relates to sewerage and sewage disposal. Water and sewerage undertakers have a statutory duty to comply with the law and their activities are regulated, monitored and overviewed by various government established bodies to protect the environment and the interests of consumers. Specific details relating to Thames Water, the Thames Tideway and the Thames Tunnel in particular are covered in later sections. 3.2 Sewer systems and governing legislation Sewer systems are necessary in urban environments to remove both waste water and storm water from areas of habitation. Waste water may be defined as the flow originating from water closets and other domestic and industrial sources, while storm water is derived from rainfall falling on the catchment. Urban sewer systems are designed to handle waste water and storm water, while minimising their risk to human life and the environment. Two basic types of conventional sewer systems exist: combined systems, where waste water and storm water flow together, and separate systems where waste water and storm water are kept apart. Insufficient provision for drainage can lead to disease, inconvenience, damage, flooding and pollution. Consequently, regulations have been set in place, with the aim of providing measures that prevent and reduce the risk, and/or extent, of these undesirable consequences. Page 9

15 3 The Legal and Regulatory Context Three pieces of legislation are specifically related to sewers and their discharges: The Water Industry Act to provide, improve and extend a system of public sewers and dealing with their contents. The EU Urban Waste Water Treatment Directive 1991 (transposed into UK regulations) sets out more specific standards on the discharge requirements from waste water treatment plants and the general requirements for collecting systems. The UK Water Resources Act regulating discharges to controlled waters to avoid pollution. Controlled waters include rivers, estuaries, coastal waters, lakes and groundwaters. Discharge to controlled waters is only permitted with the consent of the Environment Agency. 3.3 Overview of regulatory framework within which the water and sewerage undertakers operate Water and sewerage undertakers are private companies, answerable to shareholders, which operate within a regulatory framework under the auspices of the UK Government s Department for Environment, Food and Rural Affairs (Defra). The regulators are the Water Services Regulation Authority (WRSA), the Drinking Water Inspectorate (DWI) and the Environment Agency (EA), each covering differing aspects of the statutory services and activities. The water consumers are represented by the Consumer Council for Water (CCW) The Water Services Regulation Authority (Ofwat) The Water Services Regulation Authority, referred to as Ofwat throughout this report, is the economic regulator of the water and sewerage undertakers in England and Wales. It ensures that the water and sewerage undertakers provide household and business customers with a good quality service and value for money. Ofwat regulates the 21 regional monopoly water and sewerage undertakers in England and Wales. This involves, inter alia: making sure that the water and sewerage undertakers provide customers with a good quality, efficient service at a fair price. establishing challenging efficiency targets for each water and sewerage undertaker, as part of setting a final price determination (establishing how much can be charged to customers), and including an investment and expenditure programme known as an Asset Management Plan (AMP). Each plan is for a five year period. AMP5 is the plan for the period 2010 to monitoring the companies performance and taking action, including enforcement, to protect consumers interests Requiring each company to plan forward and establish 25-year investment strategies and to put each AMP plan within this context. The 25-year plans should take into account, among other considerations, changes in legislation, household consumption, population, river water quality and environmental enhancements. Ofwat uses a network of independent reporters to assist them in monitoring the performance of the water and sewerage undertakers, assessing their efficiency and checking the quality of data provided Drinking Water Inspectorate (DWI) The main job of the DWI is to check that the water and sewerage undertakers in England and Wales supply water that is safe to drink and meets the standards set in the Water Quality Regulations. Inspectors carry out technical audits of each water company. The DWI is not involved in sewerage and waste water treatment regulation. Page 10

16 3 The Legal and Regulatory Context Environment Agency (EA) The Environment Agency is an executive non-departmental public body responsible to the Secretary of State for Environment, Food and Rural Affairs (Defra) in England and an Assembly-sponsored public body responsible to the National Assembly for Wales. The EA was established to bring together previously disparate responsibilities for protecting the environment and to contribute to sustainable development. The EA plays a central role in delivering the environmental priorities of Central Government and the Welsh Assembly Government through its functions and roles. This integrated approach means all elements of the environment are considered when any works are planned. It allows the EA to identify the best environmental options and solutions, taking into account the different impacts on water, land and air. The responsibilities include, for example, co-ordinating plans for whole river basins for water and land quality. More specifically, the Environment Agency is responsible for determining the acceptability of discharges associated with the treatment of waste water (including storm sewage) and will set environmentally protective conditions to any permits granted by them Consumer Council for Water (CCW) The Consumer Council for Water (CCW) is a non-departmental public body established under the Water Act 2003 to represent consumers of water and sewerage services in England and Wales. The CCW is a national body with an English regional and Welsh structure to reflect the significant geographic variations in water and sewerage provision, and to keep in touch with consumers in their local communities. The CCW functions and duties include the following: having regard to the interests of all consumers of water and sewerage services in England and Wales obtaining and keeping under review information about consumer matters and the views of consumers on such matters making proposals, providing advice and information and representing the views of consumers to public authorities, water and sewerage companies and others. 3.4 Urban Waste Water Treatment Directive and related UK Regulations The Urban Waste Water Treatment Directive The Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) concerns the collection, treatment and discharge of urban waste water and the treatment and discharge of waste water from certain industrial sectors (Article 1). It is made clear in Article 1 that The objective of the Directive is to protect the environment from the adverse effects of the above mentioned waste water discharges. Article 2 sets out the definitions of various terms. The term urban waste water is defined to mean domestic waste water or a mixture of domestic waste water with industrial waste and/or runoff rain water ; a collecting system means a system of conduits which collects and conducts urban waste water and secondary treatment means treatment of urban waste water by a process generally involving biological treatment with a secondary settlement or other process in which the requirements established in Table 1 of Annex 1 are respected. Article 3(1) provides that: Member States shall ensure that all agglomerations are provided with collecting systems for urban waste water. For an agglomeration over 15,000 such a system is to be in place by 31 December 2000, although the earlier date of 31 December 1998 applies where the discharge is into sensitive areas as so defined. Article 3(2) makes it clear that collecting systems described in Article 3(1) have to satisfy the requirements of Annex 1(A) to the Directive. Annex 1(A) provides that: Collecting systems shall take into account waste water treatment requirements. Page 11

17 3 The Legal and Regulatory Context The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding volume and characteristics of urban waste water, prevention of leaks, limitation of pollution of receiving waters due to storm water overflows. The footnote to Annex 1(A) provides as follows: Given that it is not possible in practice to construct collecting systems and treatment plants in a way such that all waste water can be treated during situations such as unusually heavy rainfall, Member States shall decide on measures to limit pollution from storm water overflows. Such measures could be based on dilution rates or capacity in relation to dry weather flow, or could specify a certain acceptable number of overflows per year. Article 4(1) provides that: Member States shall ensure that urban waste water entering collecting systems shall before discharge be subject to secondary treatment or an equivalent treatment This is to be achieved by the dates specified, depending on the size of the agglomeration. Article 4(3) then relates this to the requirements of Annex 1 as follows: Discharges from urban waste water treatment plants described in paragraphs 1 and 2 shall satisfy the relevant requirements of section B of Annex 1I. The requirements of Annex 1(B) include that: 2. Discharges from urban waste water treatment plants subject to treatment in accordance with Articles 4 and 5 shall meet the requirements shown in Table 1. Table 1 sets out certain technical requirements for discharges from waste water treatment plants. Annex 1(B) paragraph 3 makes provision for discharges to sensitive areas by reference to Table 2. Article 10 of the Directive states that: Member States shall ensure that the urban waste water treatment plants built to comply with the requirements of Articles 4, 5, 6, and 7 are designed, constructed, operated and maintained to ensure sufficient performance under all normal local climatic conditions. When designing the plants, seasonal variations of the load shall be taken into account The Urban Waste Water Treatment Regulations The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI 1994/2841) transpose the UWWTD into UK law. Regulation 2 gives many of the same (or very similar) definitions as were found in the UWWTD including those for urban waste water, collecting systems and secondary treatment. Regulation 4 sets out the duty to provide and maintain collecting systems and treatment plants. This is stated to supplement the duties on sewerage undertakers under Section 94 of the Water Industry Act Regulation 4(2) provides that the duty imposed by subsection (1)(a) of Section 94 shall include a duty to ensure that collecting systems are provided which satisfy Schedule 2 of the regulations. Schedule 2 provides that: Collecting systems shall take into account waste water treatment requirements. The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs, notably regarding volume and characteristics of urban waste water, Page 12

18 3 The Legal and Regulatory Context prevention of leaks, limitation of pollution of receiving waters due to storm water overflows. These are the same requirements as imposed under Annex 1(A) of the Directive. Regulation 4(3) provides that the duty imposed by subsection (1)(a) of Section 94 shall include a duty to ensure that urban waste water entering collecting systems is, before discharge, subject to treatment in accordance with Regulation 5. Regulation 5 imposes time limits for the provision of treatment plants which provide secondary treatment and Regulation 6 and Schedule 3 then impose technical requirements on the standard of discharge, etc. These requirements are in essence the same as those in Annex 1(B) and Tables 1 and 2 to the Directive. 3.5 Statutory duties of the water and sewerage undertakers The water and sewerage undertakers are also subject to various statutory duties under domestic legislation. This section draws particular attention to those duties contained in the Water Industry Act 1991 (WIA) and the Water Resources Act 1991 (WRA) Water Industry Act 1991 (WIA) Section 94 (1) of the WIA provides that: It shall be the duty of every sewerage undertaker - (a) (b) to provide, improve and extend such a system of public sewers (whether inside its area or elsewhere) and so to cleanse and maintain those sewers as to ensure that that area is and continues to be effectually drained; and to make provision for the emptying of those sewers and such further provision (whether inside its area or elsewhere) as is necessary from time to time for effectually dealing, by means of sewage disposal works or otherwise, with the contents of those sewers. Thus a sewerage undertaker has a duty to provide public sewers to effectually drain its area and to make provision for the emptying of those sewers and effectually dealing with the contents of those sewers. This duty is now supplemented by the requirements of Regulation 4 of the UWWTR. Section 94(3) of the WIA provides that the duties of a sewerage undertaker under section 94(1) shall be enforceable under section18 by the Secretary of State or, in certain circumstances, by the Chairman or Chief Executive of Ofwat. Section 18 provides for the making of an enforcement notice where there is contravention of any statutory or other requirement enforceable under the section Water Resources Act 1991 (WRA) Section 85 of the WRA creates the offence of pollution of controlled waters. In particular, section 85(3) provides that: A person contravenes this section if he causes or knowingly permits any trade effluent or sewage effluent to be discharged (a) into any controlled waters The tidal Thames is a controlled water for the purposes of section 85. Section 88(1), however, provides that a person shall not be guilty of an offence under section 85 in respect of any discharge, if that discharge is made under and in accordance with (a) a consent given under this Chapter. Section 88(2) gives effect to Schedule 10 to the WRA with respect to the making of applications for consent for the purposes of section 88(1)(a). Schedule 10 sets out the procedural requirements under the WRA relating to the grant of discharge consent by the Environment Agency. Regulation 6(2)(c) of the Urban Waste Water Treatment Regulations requires the Environment Agency, in exercising its functions under Chapter II of Part II of the WRA (which includes sections Page 13

19 3 The Legal and Regulatory Context 85 and 88), to secure the limitation of pollution of receiving waters due to storm water overflows with respect to any discharge from a collecting system described in regulation 4 (see above). 3.6 The Water Framework Directive and associated requirements The Water Framework Directive The Water Framework Directive (WFD) (2000/60/EC) establishes a framework for community action in the field of water policy. The Preamble sets out the objectives, including: This Directive aims at maintaining and improving the aquatic environment in the Community. (Paragraph 19); Member States should aim to achieve the objective of at least good water status by defining and implementing the necessary measures within integrated programmes of measures, taking into account existing Community requirements. Where good water already exists it should be maintained. (Paragraph 26); and Member States should adopt measures to eliminate pollution of surface water by priority substances and progressively to reduce pollution by other substances which would otherwise prevent Member States from achieving the objectives for the bodies of surface water. (Paragraph 45). Its stated purposes in Article 1 include the establishment of a framework for the protection of inland surface waters which prevents further deterioration and protects and enhances the status of aquatic ecosystems and aims at enhanced protection and improvement of the aquatic environment, inter alia, through specific measures for the progressive reduction of discharges. Article 2 sets out various definitions including environmental objectives which means the objectives in Article 4. Article 2 also defines the terms river basin and river basin district. A heavily modified water body means a body of surface water which as a result of physical alterations by human activity is substantially changed in character, as designated by the Member State in accordance with the provisions of Annex II. The Thames Tideway has been designated as a candidate heavily modified water body (HMWB) due to flood defence and ports/navigation uses. The term, good surface water status, is defined as meaning the status achieved by a surface water body when both its ecological status and its chemical status are at least good. The term good ecological potential is the status of a heavily modified body of water, so classified in accordance with the provisions of Annex V and good surface water chemical status means the chemical status required to meet the environmental objectives for surface waters established in Article 4(1)(a), that is the chemical status achieved by a body of surface water in which concentrations of pollutants do not exceed the environmental quality standards established in Annex IX and under Article 16(7), and under other relevant Community legislation setting environmental quality standards at Community level. Article 4 sets out environmental objectives and provides (Article 4(1)) that in making operational the programmes of measures specified in the river basin management plans for surface waters Member States shall: (i) implement the necessary measures to prevent deterioration of the status of all bodies of surface water (ii) protect, enhance and restore all bodies of surface water, subject to the application of subparagraph (iii) for heavily modified bodies of water, with the aim of achieving good surface water status at the latest 15 years after the date of entry into force of this Directive [2000], (iii) protect and enhance all heavily modified bodies of water, with the aim of achieving good ecological potential and good surface water chemical status at the latest 15 years from the date of entry into force of this Directive [2000], in accordance with the provisions laid down in Annex V Article 4 (4) allows the deadline for compliance to be extended, subject to various conditions Article 4(5) allows the adoption of less stringent environmental objectives, where achievement would be infeasible or disproportionately expensive, subject to conditions Page 14

20 3 The Legal and Regulatory Context Article 5 sets out various duties imposed on Member States in relation to analysis of the characteristics of river basin districts, review of the impact of human activity on the status of surface waters and economic analysis of water use. Article 11(1) provides that: Each Member State shall ensure the establishment for each river basin district of a programme of measures, taking account of the analysis required under Article 5, in order to achieve the objectives established under Article 4. Such measures are to include basic measures and, where necessary, supplementary measures. These are set out in Article 11 and Annex VI. (Note: Basic measures include full implementation of existing directives such as the UWWTD). Article 2 (18) defines Good surface water status as the status achieved by the body of surface water when both its ecological and chemical status are at least good. Article 2(22) and Annex V, Table 1.2 give the normative definition of good status as where the values of the biological quality elements for the surface water type show low levels of distortion resulting from human activity but deviate only slightly from those normally associated with the surface water body type under undisturbed conditions. Article 2(24) defines Good surface water chemical status as that required to achieve the objectives in Article 4(1)(a) as set out above by not exceeding the standards in Annex IX and under Article 16(7). Article 13(1) provides that Member States shall ensure that a river basin management plan is produced for each river basin district lying entirely within their territory. A river basin management plan has to include the information detailed in Annex VII (Article VII). This annex sets out the detailed requirements for the production of river basin management plans Water Framework Directive Regulations The WFD was transposed into UK law by the Water Environment (Water Framework Directive) (England and Wales) Regulations 2003 (SI 2003/3242) Implementation of the WFD In England and Wales the Environment Agency is the competent authority to implement the WFD. The key objectives of the WFD are summarised as follows: prevent deterioration in the classification status of aquatic ecosystems, protect them and improve the ecological condition of waters aim to achieve at least good status for all waters by Where this is not possible, good status should be achieved by 2021 or 2027 promote sustainable use of water as a natural resource conserve habitats and species that depend directly on water progressively reduce or phase out releases of individual pollutants or groups of pollutants that present a significant threat to the aquatic environment progressively reduce the pollution of groundwater and prevent or limit the entry of pollutants contribute to mitigating the effects of floods and droughts No deterioration The first principle of the WFD is to prevent deterioration in aquatic ecosystems. No deterioration must be met in all but very exceptional circumstances. Exceptional circumstances apply when the deterioration is caused by physical modifications or is the result of sustainable new human development activities. Even in such cases, it is necessary to demonstrate that there was no better way to achieve the desired development. No deterioration requires that a water body does not deteriorate from its current ecological or chemical classification, and is assessed on the quality achieved by individual pollutants within a water body. For example, if dissolved oxygen was currently classified as meeting the standards for moderate status, then the first principle of the WFD would be to ensure no deterioration from the moderate class. Page 15

21 3 The Legal and Regulatory Context Good status Under the WFD the objective is for all water bodies to meet good ecological status by For surface waters (rivers, lakes, transitional waters), good ecological status can be defined as: good chemical status for the relevant substances (with a series of daughter directives) good physico-chemical status on the scale high, good, moderate, poor and bad good biological class good hydro-morphological class. The status of a water body is measured through a series of specific standards and targets that have been developed by the UK administrations, supported by the WFD UK Technical Advisory Group ( This includes standards and targets for surface water, transitional waters, coastal waters, and lakes. The manner in which overall status is assessed is by using a one out, all out approach. That is, the status is determined by the lowest common denominator. As an illustration, if ammonia was classified as satisfying the standards for high status but dissolved oxygen was classified as moderate, then the water body would be considered to be in the moderate class Alternative objective Although the WFD specifies that good status should be met by 2015, there are circumstances where it is possible to delay meeting good status until 2021 or 2027, or where a lesser objective will be required. These circumstances include technical feasibility of the required measures, disproportionate costs or natural conditions (recovery times). For the first river basin plans an extended deadline (i.e., 2021 or 2027) to meet good status has been adopted, rather than setting a less stringent objective. Under Article 4 (3) of the WFD, it is possible to designate water bodies as artificial or heavily modified water bodies. The WFD recognises that some water bodies have been modified to provide valuable social or economic benefits, and it is recognised these water bodies are not able to achieve natural conditions, and hence should not be required to achieve good ecological status. Artificial or heavily modified water bodies therefore have an alternative objective of meeting good ecological potential and these are identified in the River Basin Management Plans. It should be noted that the chemical standards to meet good ecological potential for artificial or heavily modified water bodies are identical to the chemical standards to meet good ecological status. It is the hydro morphological requirements of a water body which differ depending on the designation of a water body River Basin Management Plans (RBMP) As part of their implementation role in England and Wales, the Environment Agency has prepared River Basin Management Plans (RBMP) 2, which set out: the current status for each water body (including confidence limits) the objectives and targets for each water body the main pressures for each water body an action plan outlining what will be required, by whom, and when to meet good ecological status (or potential). justification for setting an alternative objective by The first RBMPs were adopted in December 2009, and will be reviewed and updated every six years (i.e., 2021, 2027). 2 Further information on RBMP can be found at aspx Page 16

22 3 The Legal and Regulatory Context 3.7 Powers of the European Commission to bring infraction proceedings Article 258 of the Treaty of Lisbon gives the European Commission powers to take legal action against a member state that it considers is not respecting its obligations under EU Directives. The first stage is the issue of a Reasoned Opinion which serves as a formal warning. The next step in the Article 258 proceedings is for the Commission to refer the matter to the European Court of Justice seeking a judgement that the member state concerned has failed to meet its obligations. Were the court to make such a ruling, the Commission could then bring proceedings under Article 260 seeking fines (a lump sum and periodic penalty payments) due to a failure to take the necessary steps to comply with the judgement. Periodic penalty payments would continue to be due until the judgement had been fully complied with. Page 17

23 4 The Need 4 THE NEED The objective of the EU Urban Waste Water Treatment Directive relates to the protection of the environment from the adverse effects of insufficiently treated waste water discharges. Waste water collecting systems in London, in the opinion of the European Commission, are being allowed to spill untreated waste waters from combined sewer overflows too frequently and in excessive quantities. The Directive, and related UK legislation, accepts that collecting systems and treatment plants may spill water in certain situations, such as unusually heavy rainfall, but the Commission considers that spills in the case of London are excessive and go beyond what the legislation provides for. Infraction proceedings are being pursued by the European Commission against the UK for breach of the UWWTD. On 8 October 2009 the European Commission announced its decision to take the UK to the European Court of Justice because it considers that the waste water collection systems in London are being allowed to spill untreated waste water from CSOs too frequently and in excessive quantities. London s sewerage system (the Beckton and Crossness sewer catchments) has been progressively extended to accommodate development and population growth since it was designed by Sir Joseph Bazalgette in the 1850s. Despite this, there is now little spare capacity in the sewerage network. Currently, spillages to the Thames Tideway occur more than 50 times per year at the most frequently overflowing CSOs. An estimated total of some 39 million cubic metres of storm sewage enter the river from the Beckton and Crossness sewerage catchments in a typical year. Waste water discharges affect the environment in three main ways, which have been considered in developing the specific objectives for the project, namely by: o adverse environmental impacts on the river ecosystems and on fish species in particular; o unacceptable aesthetic issues; and o elevated health risks for recreational users of the Thames. The then Minister of State for Climate Change & Environment wrote to Thames Water on 17th April 2007: a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works is needed for the UK to comply with the requirements of the Urban Waste Water Treatment Directive concerning provision of collecting systems and, in particular, limitation of pollution from storm water overflows. The succeeding Environment Secretary, Caroline Spelman, issued a written ministerial statement on 07 September 2010 confirming the coalition government s support for the construction of the tunnel from Hammersmith to Beckton. As defined by the EA, there are 34 unsatisfactory CSOs in the Beckton and Crossness catchments discharging directly into the River Thames. Modelling has indicated that, after construction of the Lee Tunnel and the extensions to the STWs at Beckton and Crossness, in a typical year 18 million cubic metres of storm sewage will enter the river from these CSOs. The River Basin Management Plan for the River Thames (December 2009) states that in the Estuaries and Coastal Waters Catchment, the London Tideway Tunnels (the Thames and Lee Tunnels); represent the primary measures to address point source pollution from the sewer system and are fundamental to the achievement of good status in this catchment Thames Water is progressing improvement projects, including the construction of the Lee Tunnel and the upgrades to the STWs at Mogden, Beckton, Crossness, Riverside and Long Reach. The provision of a full-length storage tunnel under the river (the Thames Tunnel), as required by Government, will be the final step in reaching compliance with European legislation. Page 18

24 4 The Need 4.1 London s sewerage Introduction The Thames Tunnel catchment comprises the catchments served by the Beckton and Crossness STWs as illustrated in Figure 4.1. The Beckton and Crossness catchments are combined sewer systems (foul sewage and storm water runoff) whilst the Mogden catchment to the west is predominantly served by separate sewage and rainfall systems. Sewer capacity is currently sufficient for dry weather flows but it is normal practice for discharges to water courses via sewer overflows during rainfall events to avoid the sewers backing up and causing flooding. The location of the overflows in the Beckton and Crossness catchments are shown below in Figure 4.2. Figure 4.1 Catchment areas draining to Mogden, Beckton and Crossness STWs Figure 4.2 Locations of discharges on the Thames Tideway Page 19

25 4 The Need Over the years, urbanisation (the reduction in permeable areas in the catchment leading to increases in the flows and flow rates in the sewers) has increased the quantity of storm sewage and, as a consequence increased the frequency and volume of combined sewage discharged to the river. Currently, some CSOs spill more than 50 times per year, with a number activated by rainfall of only a few millimetres General characteristics of the catchments The Thames Tunnel sewer catchment consists of the area north of the River Thames (Beckton catchment) that drains to the Beckton STW, and the South London area (Crossness catchment) that drains to the Crossness STW. The catchments cover an area of about 326km 2 in the north and 230km 2 in the south, stretching approximately 25km north to south and approximately 30km west to east. Ground levels fall towards the River Thames in the direction from west to east hence the location of Beckton and Crossness in the east of the catchment (although waste water disposal at outgoing tides was also a consideration in works location). The River Thames has meandered through the valley over time but today is generally confined by river walls and other flood defences. The Thames Tunnel sewer catchment includes all or part of the London Boroughs, north of the River Thames, of Barking, Brent, Camden, the City of London, Ealing, Hackney, Hammersmith & Fulham, Haringey, Islington, Kensington & Chelsea, Newham, Redbridge, Tower Hamlets, Waltham, and Westminster, and, south of the river, the London Boroughs of Bexley, Bromley, Croydon, Greenwich, Lambeth, Lewisham, Merton, Southwark, Sutton and Wandsworth. In the north part of the area of Epping District Council also drains to the Beckton catchment. Since sewerage was provided in the 19 th century, London s population has continued to grow and expand. The peak in population total and density occurred in the 1930s to 1950s, with a steady decline following the Second World War into the late 1980s, after which saw an increase in the London population (population statistics are included in Appendix C). Population has therefore been steadily increasing since the 1990s, and the projection is for continued growth of the London population into 2021, when the Thames Tunnel is scheduled for completion, and beyond Description of a sewer system London s sewerage is fundamentally based on the London Main Drainage system constructed in the 19th century by the Victorian civil engineer, Sir Joseph Bazalgette. Many of the original tributary watercourses in London were incorporated into the sewer system, which means the massive volume of storm water runoff generated from the land area is drained to the combined sewer system. Flows into the combined sewer system are made up of dry weather flow, comprising domestic effluent, trade discharges, groundwater infiltration, and storm water runoff from the catchment. The amount of each is defined by the land use in the area and the type of sewer system serving the area. The sewer system is fully combined in the older parts of London, i.e. the inner boroughs, whereas in the outer boroughs there is a mixture of partially or fully separated collection systems. Generally, the amount of storm flow separation is dependent on the age of the development in the borough. The oldest parts of London are largely within the Beckton catchment, within which 53% of the area is served by a combined sewer system. The average impermeability of the land surface within the Beckton catchment is 54% with some sub-catchments almost fully impermeable. In comparison, 18% of the Crossness catchment is served by a combined system, with the remainder either partially or fully separated. The average impermeability is considerably lower, at 24%, which is indicative of the smaller area of combined sub-catchments and the slower development of the Crossness catchment historically Current level of service The capacities allowed for in Bazalgette s project have now been exceeded. Despite the numerous improvements and extensions over the years, there is little spare capacity in the sewer system. The existing collection system that normally conveys flow to Crossness and Beckton STWs has become progressively more overloaded as the population of London has increased. In addition, an Page 20

26 4 The Need increasing proportion of hard surfacing has reduced the capability of the land to absorb rainwater before it enters the sewerage network. Local flooding remains a recurring problem in both the Beckton and Crossness catchments. During each Asset Management Plan (AMP) cycle, Thames Water has been set regulatory requirements that include reductions in flooding and flooding risk in the catchment, primarily achieved through local flood relief programmes using either local storage or sewer upsizing. The AMP cycle also sets out the improvements at the STWs. Between the 1990s to the present time, numerous local flood relief projects in the Beckton and Crossness catchments have been completed as part of the AMP3 and AMP4 capex programmes and more are proposed in AMP5. Nonetheless, sewage flooding remains a major concern and schemes will be developed in parallel with work on the Thames Tunnel as the tunnel alone cannot generally alleviate local catchment flooding issues without further local work. 4.2 The Thames Tideway Strategic Study and further work by Thames Water The Thames Tideway Strategic Study was set up in , initially as a three-year project, to: assess the environmental impact of intermittent discharges of storm sewage on the Thames Tideway; identify objectives for improvement; and propose potential solutions, having regard to costs and benefits. Specific environmental objectives were developed by the TTSS which were to be addressed by the project, namely to reduce: the adverse environmental impacts on the river ecosystems and on fish species in particular; the unacceptable aesthetic issues; and the elevated health risks for recreational users of the tidal Thames. The study established that the environmental objectives can only be met at least cost by completing both quality improvements to the treatment works discharges and by the provision of a storage and transfer tunnel to intercept unsatisfactory CSOs. Source control (methods of managing and reducing storm water runoff at site level), separation (separate storm water and foul networks), partial separation, dispersed storage units (capturing storm water and controlling the release), CSO screening and SUDS (techniques employing ponds, swales, green roofs, detention ponds and permeable surfaces) were among other options explored. None of these options were found to be suitable and cost-effective solutions. The main report of this study was published in February 2005, with a supplementary report published in November Ofwat commissioned a report by Jacobs Babtie to review the work and reports of the TTSS. This was published in February 2006 and proposed another option for dealing with the CSO discharges. This involved two short tunnels (west and east tunnels), a new treatment facility near Heathwall Pumping Station in central London, screening plant and enhanced primary treatment plant at Abbey Mills in east London. These measures were in addition to the STW upgrades, litter skimmer boats and re-oxygenation measures. It was also suggested that sustainable drainage systems (SUDS) to retain surface water runoff, either in open tanks and ponds or in covered storage which allows slow drainage, should be implemented over the medium to long term, where appropriate, in London s suburban fringes. In summary, Jacobs Babtie did not fully agree with the objectives derived as part of the TTSS (including the dissolved oxygen targets) and considered that their proposal would provide lesser but still adequate benefits at lower cost. 5 3 Regulatory Impact Assessment, 2007; Section Adapted from TTSS Executive Summary 5 Regulatory Impact Assessment, 2007; Section 2.12 Page 21

27 4 The Need The reports and options were considered by a working group set up by Defra in December The work of this group was initially to consider whether a partial solution, coherent with the approach to the wider Thames Tideway problem, could be delivered in time to protect the 2012 Olympic and Paralympic Games against the risk of significant aesthetic pollution from CSOs. This work led to the then Minister of State for Climate Change and the Environment writing on 27 July 2006 to ask Thames Water to provide (by 31 December 2006) a detailed assessment of and cost information for two identified options, defined below. These both involved large scale tunnels that intercept overflow discharges and take them for treatment in East London. As part of this assessment, the Minister also asked TW to consider whether a partial solution, to protect the Olympic Park, could be delivered by The Environment Agency, Ofwat and other stakeholders were involved in the development of the two options by way of the, Defra led, Thames Tideway Advisory Group (TTAG). This, together with a separate Olympic Measures Group, replaced the Working Group on Thames Tideway and the 2012 Olympic Games. The TTAG provided a focal point for progress reports, input to and comment on the work being carried out by Thames Water. Thames Water submitted the results of this detailed assessment to Ministers on 29 December The results of the assessment are detailed in the Thames Tideway Tunnel and Treatment Summary Report Tackling London s Sewer Overflows. The two options considered were: Option 1, comprising a full-length and continuous tunnel controlling all unsatisfactory CSOs in the Beckton and Crossness catchments, with the following sub-options assessed: Option 1a Full-length storage tunnel (30km) 7.2m diameter Option 1b Full-length storage tunnel (30km) 6.0m diameter Option 1c Full-length storage tunnel (30km) 7.2m diameter, tunnels from Abbey Mills and West London joining at Beckton. Option 2, comprising two separate tunnels, as proposed in the Jacobs Babtie report, with the following sub-options assessed: Option 2a West tunnel 7.6m diameter; East tunnel -13m diameter Option 2b West tunnel 7.6m diameter; East tunnel -10m diameter; supplementary additional treatment capacity Option 2c West tunnel 7.6m diameter; East tunnel (via Charlton) -10m diameter The variants of each option are mainly differing tunnel diameters, phasing details and routes. It was concluded that the Option 1 variants achieve a higher proportion of the objectives defined by the TTSS, and score more highly in the cost benefit ranking. Options 1a and 1c were broadly equal, but Option 1c (shown in Figure 4.3) was the only option realistically offering any potential for an early phased delivery. 8 This report, together with further information provided by various parties was used to inform the Regulatory Impact Assessment, 2007 for sewage collection and treatment for London, published by Defra in March The Regulatory Impact Assessment specifically rejected the solution identified by Jacobs Babtie as it did not meet the objectives set. Paragraph 4.29 explains that Options 2a 2c are considered not to meet the requirements of the Urban Waste Water Treatment Regulations: the proposal does not show how to deal with overflows from 18 or so unsatisfactory CSOs and the proposed reduction in the target DO does not meet future considerations. The RIA is included in Appendix A of this report. The preferred tunnel option arising from the TTSS, Option 1c, became the baseline tunnel option considered by the London Tideway Tunnels programme. This has been refined further as a result 6 Regulatory Impact Assessment, 2007; Sections Regulatory Impact Assessment, 2007; Sections Thames Tideway Tunnel and Treatment Summary Report Tackling London s Sewer Overflows, Executive Summary Page 22

28 4 The Need of continuing development work, as detailed in Section 5. The performance of the latest preferred tunnel option has been compared with baseline conditions representing the projected existing conditions at the start of the Thames Tunnel project. Figure 4.3 TTSS Option 1c 4.3 Baseline conditions The baseline conditions are the conditions projected to be current at the start of the operation of the Thames Tunnel. The need for the project is related to those aspects of the baseline conditions that are considered unacceptable by reference to the requirements of the UWWTD and the adopted TTSS environmental objectives. Benefits of proposed solutions are assessed against maintaining the baseline conditions. For the Thames Tunnel Project, the baseline conditions are defined as: completion of the currently planned upgrades to the Mogden, Beckton, Crossness, Riverside and Long Reach sewage treatment works discharging to the Thames Tideway (referred to as the London Tideway Improvements). conditions following the Sewer Flooding Alleviation schemes included in Asset Management Plan 5 (AMP5) (and relevant to the Tideway Tunnels projects) which will be completed before commissioning of the Tideway Tunnels projects. completion and commissioning of the Lee Tunnel Project components. projected 2021 population, being the proposed commissioning date for the Thames Tunnel. 4.4 Model development work undertaken since the TTSS Hydraulic modelling and system monitoring Thames Water maintains a numerical hydraulic model that represents the sewer system for the Beckton and Crossness STW catchments. In parallel with the hydraulic model, a water quality model of the Thames Estuary from Teddington weir to Southend was developed for the Environment Agency (EA) by WRc plc to understand the impacts on water quality of discharges from the sewage treatment works (STWs) and the 57 CSOs in the Beckton and Crossness catchments discharging to the Tideway. The hydraulic (InfoWorks) model representing the sewer system has continued to be developed in order to improve the level of confidence in the results. As part of the model development work, the Network and Process Modelling Group and the London Tideway Tunnels Development Team have instigated a programme of additional system monitoring. This involves the installation of long-term depth monitors at representative and critical locations throughout the system and specifically targets actual overflows at all 57 CSO locations. The monitoring programme also includes enhancements to data collection and telemetry at the major pumping stations. The CSO monitoring programme has increased confidence in the InfoWorks model predictions of overflows (flow and quality). Page 23

29 4 The Need Flood alleviation schemes like West Ham and Greyhound Rd Storage Tank have now been included into the sewer model. Proposed major flood relief sewers are not included at this time. These solutions will be included in the future models as the projects will affect the flow regime in the collection system, particularly the timing of peak flows arriving into the tunnel Water quality modelling and monitoring Associated with the CSO monitoring programme is the collection of water quality data at sites representative of the range of sub-catchment conditions. The sites are primarily near pumping stations and include Beckton and Crossness STWs influent flows. Samples are being collected at 15 locations throughout the sewer systems for a period of at least 12 months. The samples collected are tested for a variety of parameters including TSS, BOD 5, COD, total nitrogen, ammonia, chloride, phosphates, sulphides and sulphates and various metals including iron. Following on from the water quality modelling undertaken to support the TTSS, the water quality model was refined and rerun to assess the then latest options for the Thames Tunnel: Thames Tideway Tunnel and Treatment (TTTT) model update the water quality model was refined and rerun to assess the effectiveness of Options 1a-1c (Full length tunnel options) and Options 2a-2c (Two-tunnel options) Lee Tunnel and Beckton model update the water quality model was used to support the Environmental Impact Assessment (EIA) for the Lee Tunnel and Beckton STW improvements. In 2006, the water quality modelling undertaken as part of the TTTT study assessed the compliance of Options 1a-1c and Options 2a-2c against WFD standards and interim dissolved oxygen (DO) standards which were derived as part of the TTSS. The model was refined to reflect the latest understanding of the Tideway. A full description of the changes can be found in the December 2006 modelling and compliance report. 9 The key refinements to the model are highlighted below: population growth to 2021 was included the impact of climate change to the 2020s and 2080s epoch based on the UKCIP02 predictions (previously this had only been completed for the 2080s) inclusion of preceding events that accounted for background conditions in the Tideway prior to each of the discrete 154 summer rainfall events revised STW consents based on the proposed London Tideway Improvements (LTI) programme. Further water quality modelling has been undertaken to evaluate the subsequent developments to the Option 1c using the above refinements. 4.5 CSO performance Hydraulic analysis of the sewerage in the Thames Tunnel catchment, which includes the catchment of the River Lee, continues to be undertaken for a wide range of storm events, allowing for changes to the system, population growth to 2021, operational changes and increases in STW capacities. This has included an analysis of the entire rainfall over a typical year ( ) 10 representing how the system can be expected to perform in normal circumstances. A summary of the total spill volumes modelled to discharge from the Beckton and Crossness catchments to the Tideway is given in Table 4.1. This shows the current existing conditions, the intermediate conditions once the Mogden, Beckton, Crossness, Riverside and Long Reach STW upgrades are in place and finally the projected performance at the baseline conditions for the 9 TTT Objectives and Compliance Working Group Report Volume 2 Modelling and Compliance (2006) 10 Selection of Typical Year for CSO Spill Frequency Assessment (WRc, August 2006) Page 24

30 4 The Need Thames Tunnel, that is including the provision of the Lee Tunnel but without the Thames Tunnel being operational. Table 4.1 Comparison of annual spills at existing, intermediate and projected baseline conditions Conditions Modelled discharge to the Tidal Thames (total per typical year)* Modelled annual number of spills at any one CSO* Existing conditions 2006 population, no improvements Intermediate conditions 2021 population, upgrades of STWs, no Lee Tunnel. 39 million m million m 3 59 Baseline Conditions 2021 population, upgrades of STWs plus Lee Tunnel. 18 million m 3 59 Notes: * Based on typical year (Oct 1979 Sep 1980) rainfall, represented from data gathered Increase in spills due to population increase between 2006 and It has been assumed throughout the hydraulic analyses of the catchment and sewer systems that the London Tideway Improvements will proceed with the planned improvements to the flow and treatment capacities at the works. The London Tideway Improvements involves extensions and upgrades to the five main treatment plants along the tidal reach of the river (Mogden, Beckton, Crossness, Riverside and Long Reach). The capacity extensions at Beckton STW will enable the CSO discharges diverted into the Tideway Tunnels to be pumped out of the tunnels and, in the most part, forwarded to Beckton STW for full secondary treatment. Expansion of the treatment capacity at the remaining sewage treatment works has little effect on other overflows to the River Thames (except for Greenwich PS overflow which will be greatly reduced following the Crossness enhancement). Even after expansion of the works and the Lee Tunnel, there will be 18 million m 3 of sewage per year overflowing to the river in the typical year. The frequency of discharge from combined sewer overflows will remain location-specific with the CSO at Hammersmith PS operating most frequently (59 times per year) and discharging an annual volume of 2.5 million m 3. The largest annual total overflow volumes occur at Greenwich PS CSO (3.9 million m 3 ) and at Western PS CSO (2.5 million m 3 ). Pumping stations as a group discharge 67% of the total overflow volume (about 12 million m 3 of the 18 million m 3 remaining after the Lee Tunnel and STW expansions). The remaining 6 million m 3 of overflow is from gravity CSO outfalls. (Figures at Baseline Conditions) As part of the initial investigation carried out by EA in May 2004, the CSOs were grouped into four categories, based on the environmental impact and frequency of operation: Category 1: Discharges that have an adverse environmental effect and occur frequently during periods of rainfall, which cannot be defined as unusually heavy. Category 2: Discharges that have an adverse environmental effect but only operate infrequently, during periods of heavy rainfall. Category 3: Discharges that do not have any significant environmental effect. Category 4: Discharges that occur at a similar frequency to Category 1, but have been assessed as not causing a significant adverse environmental impact. Page 25

31 4 The Need Defra and the Environment Agency deemed that action should be taken to control the CSOs in Categories 1 and 2 to limit their frequency of operation and consequently their polluting potential. 11 This will not necessarily involve connection to the Thames Tunnel in all cases. A breakdown of the modelled operation of each CSO in terms of overflow volumes and number of spill events during the defined typical year is given in Table 4.2. This Table is organised in the order of the EA Category, starting with those CSOs adjudged to be causing the greatest adverse environmental effect and occurring most frequently during periods of rainfall after the completion of the extensions at Beckton and Crossness STWs and the commissioning of the Lee Tunnel (but no Thames Tunnel). Thus the CSO spilling most frequently in Category 1 is listed first and so on in declining spill frequency, then Category 2 CSOs etc. For completeness information on the CSOs controlled by the Lee Tunnel project and the storm tanks overflows at the STWs are provided at the end of the table. This demonstrates that even after the provision of the Lee Tunnel and the commissioning of the Mogden, Beckton, Crossness, Riverside and Long Reach STW upgrades the UK will still fail to comply with the requirements of the legislation. Only the completion of the Thames Tunnel will provide the infrastructure necessary for compliance with the UWWTD by limiting the pollution due to storm water overflows, by achieving agreed DO standards in the river and by reducing spill frequency.. 11 Thames Tideway Tunnel & Treatment, Solutions Working Group Report, Volume 1 Tunnels and Shafts (Section 2.2) (December 2006) Page 26

32 4 The Need Table 4.2 Comparison of projected CSO performance during a typical year, before and after commissioning of Lee Tunnel and STW upgrades LTT CSO Ref. CSO name Local Authority EA Category Type of CSO Receiving Waters Annual overflow volume (m 3 ) Number of spill events Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population CS04X Hammersmith PS H & F 1 Pumped Thames 2,303,700 2,458, CS30X Holloway SR Tower Hamlets 1 Gravity Thames 557, , CS09X Falconbrook PS Wandsworth 1 Pumped Thames 706, , CS10X Lots Road PS K & C 1 Pumped Thames 1,108,900 1,231, CS15X Western PS City of Westminster 1 Pumped Thames 2,175,900 2,469, CS16X Heathwall PS Wandsworth 1 Pumped Thames 658, , CS07A Frogmore SR - Bell Lane Creek Wandsworth 1 Gravity Thames via Wandle 17,400 18, CS32X Deptford SR Greenwich 1 Gravity Thames 1,518,500 1,975, CS05X West Putney SR Richmond 1 Gravity Thames 34,800 36, CS06X Putney Bridge Wandsworth 1 Gravity Thames 68,200 70, CS29X North East SR Tower Hamlets 1 Gravity Thames 784, , CS20X Brixton SR Lambeth 1 Gravity Thames 265, , CS14X Ranelagh K & C 1 Gravity Thames 284, , CS31X Earl PS Lewisham 1 Pumped Thames 556, , CS07B Frogmore SR - Buckhold Road Wandsworth 1 Gravity Thames via Wandle 91,700 94, CS33X Greenwich PS Greenwich 1 Pumped Thames 8,239,100 3,923, CS01X Acton Storm Relief Hounslow 1 Gravity Thames 245, , CS27X Fleet Main City of London 1 Gravity Thames 508, , CS28X Shad Thames PS Southwark 1 Pumped Thames 93, , CS17X South West SR Wandsworth 1 Gravity Thames 230, , Page 27

33 4 The Need LTT CSO Ref. CSO name Local Authority EA Category Type of CSO Receiving Waters Annual overflow volume (m 3 ) Number of spill events Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population CS23X Northumberland Street City of Westminster 1 Gravity Thames 47,700 58, CS19X Clapham SR Lambeth 1 Gravity Thames 13,400 14, CS22X Regent Street City of Westminster 1 Gravity Thames 10,200 11, CS34X Charlton SR Greenwich 1 Gravity Thames 600 1, CS08A Jews Row - Wandle Valley SR Wandsworth 1 Gravity Thames 2, CS08B Jews Row - Falconbrook SR Wandsworth 1 Gravity Thames 7,400 7, CS24X Savoy Street CS13A Smith Street Main Line CS21X Grosvenor Ditch City of Westminster 2 Gravity Thames 100, , K & C 2 Gravity Thames 1,400 1, City of Westminster 2 Gravity Thames 1,000 1, CS02X Stamford Brook SR H & F 2 Gravity Thames 1,100 1, King's Scholars' City of CS18X 2 Gravity Thames Pond SR Westminster City of CS26X Essex Street 2 Gravity Thames 1,400 1, Westminster CS03X North West SR H & F 2 Gravity Thames < CS11X Church Street K & C 2 Gravity Thames CS12X Queen Street K & C 2 Gravity Thames Page 28

34 4 The Need LTT CSO Ref. CSO name Local Authority EA Category Type of CSO Receiving Waters Annual overflow volume (m 3 ) Number of spill events Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population CS13B Smith Street SR K & C 2 Gravity Thames CS25X Norfolk Street City of Westminster 2 Gravity Thames CS39X Horseferry Road K & C 3 Gravity Thames 1,400 1, CS45X Iron Gate Tower Hamlets 3 Gravity Thames CS37X LL1 Brook Green H & F 3 Gravity Thames CS40X Wood Street K & C 3 Gravity Thames CS41X Goswell Street 2 City of London 3 Gravity Thames CS42X Paul's Pier Wharf City of London 3 Gravity Thames CS43X Battle Bridge Southwark 3 Gravity Thames CS44X Beer Lane City of London 3 Gravity Thames CS46X Nightingale Lane Tower Hamlets 3 Gravity Thames CS47X Union Wharf 2 Tower Hamlets 3 Gravity Thames CS48X Wapping Dock 2 Tower Hamlets 3 Gravity Thames CS49X Cole Stairs Tower Hamlets 3 Gravity Thames CS50X Bell Wharf Tower Hamlets 3 Gravity Thames CS51X Ratcliffe Cross Tower Hamlets 3 Gravity Thames CS52X Blackwall Sewer Tower Hamlets 3 Gravity Thames CS53X Henley Road Newham 3 Gravity Thames CS54X Store Road 2 Newham 3 Gravity Thames CS55X London Bridge Lewisham 4 Gravity Thames 8,200 8, CS56X Isle of Dogs PS Tower Hamlets 4 Pumped Thames 12,900 13, Page 29

35 4 The Need LTT CSO Ref. CSO name Local Authority EA Category Type of CSO Receiving Waters Annual overflow volume (m 3 ) Number of spill events Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population Existing system 2006 population and existing STWs Thames Tunnel baseline conditions Lee Tunnel, upgraded STWs and 2021 population CS35A CS35B Abbey Mills Pumping Station (Station F) Abbey Mills Pumping Station (Station A) Newham 1 Pumped Lee 14,986, Newham 1 Pumped Lee 3,819, CS36X Wick Lane Newham 2 Gravity Lee CS57X Canning Town PS Newham 4 Pumped Lee SUB-TOTAL, CSOs only 39,466,300 17,847, N/A N/A Crossness STW Storm Tanks Bexley N/A Gravity Thames 308,200 70, Tunnel Relief overflow at Newham N/A Pumped Thames N/A 521,100 N/A 3 Beckton STW TOTAL 39,774,500 18,439, The values reported for the existing system 2006 are from the system hydraulic models of June The Thames Tunnel Baseline Conditions (Lee Tunnel) values are based on the December 2009 model. Further enhancements to the model may alter the numbers in this table. Events are counted by considering the inter-event time: if no spill occurs for 24 hours a new event starts. 2. Four CSOs have no values attributed. This is because they are believed sealed or otherwise and no longer able to spill. 3. Consistent processes are applied when reducing modelling results to produce the summary tables. As the model inherently contains approximations there will be minor discrepancies particularly when very low flow conditions are encountered. This is illustrated by the values shown for the LL1 Brook Green CSO, where a single event of 100m 3 is shown for some conditions and not in others. Page 30

36 4 The Need 4. This value is the sum for all CSOs, including simultaneous discharges at individual CSOs. Page 31

37 4 The Need For the sewer modelling a spill event has been defined by the time between discharges, or the inter-event duration. If the time between discharges is greater than 24 hours, then a new event starts. Modelling demonstrates that with the Thames Tunnel in place all residual spill events will be less than 24 hours duration To improve confidence in the findings of the hydraulic modelling undertaken, Thames Water started installation of CSO monitors in The Thames Water programme includes short term flow monitoring to determine a relationship between flow and sewer flow depth followed by permanent depth monitoring. This monitoring was extended in The legal need - UWWTD, WFD and other statutory duties Section 3 outlined the legal framework. This section considers its specific application to the Tidal Thames Allegation of infringement of the UWWTD The European Commission has given formal notice that it believes the UK is in breach of the UWWTD and has announced its intention, by press release of 8 October 2009, to refer cases concerning the Thames (and Whitburn, NE England) to the European Court of Justice for a ruling that the UK is in breach UK Government Response and Action In July 2006, the Minister requested Thames Water to carry out an assessment of the two principal options for tackling the combined sewer overflows into the Thames Tideway. In December 2006, the Study Group issued the Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report recommending a variant of the TTSS Option 1 for the Thames Tunnel. In setting out the objectives for the project, Section 3 of the report adopted a similar package of objectives to TTSS, namely compliance with the UWWTD, protection of ecosystems and reducing aesthetic pollution and the health risk to river users by reducing the frequency of CSO discharges into the Thames. In March 2007, Defra published a Regulatory Impact Assessment (RIA) in connection with the collection and treatment of sewage in London. The RIA set out the objectives of the proposed Tunnel at Paragraph 2 as: 2.1 To reduce the number of overflows and their environmental impact from the sewers and treatment systems serving London,. The measures are to improve the environmental quality of the tidal reaches of the River Thames by limiting the volume, frequency and adverse environmental pollution of discharges from the sewer system (sewers and treatment works) of untreated sewage following wet weather by overflows. 2.2 To ensure that the London agglomeration and the Beckton and Crossness sewer systems comply with (the UWWTD) 2.3 The objective of the UWWTD is to protect the environment from the adverse effects of insufficiently treated waste water discharges. The RIA, 2007, concluded at Paragraph 11.7 by saying that: Having considered the recent report by TW, and a range of issues including legal obligations, compliance risks, timetables, cost benefit analysis, affordability and feasibility, it is recommended that a phased, single tunnel approach, which addresses all the unsatisfactory overflows, is the minimum required to meet our obligations. It is therefore proposed that TW are asked to proceed urgently with the development and implementation of a scheme which reduces and limits pollution from storm water overflows (starting with Abbey mills pumping station) of the Beckton and Crossness sewer system in the most cost effective way. Such an approach, which may be based on option 1c, offers the quickest prospect of making a significant impact on the volume of the discharges, and it would convey a sense of urgency and commitment to take measures to comply as soon as possible. Page 32

38 4 The Need On 22 March 2007 the Minister for Climate Change and the Environment, Ian Pearson, announced the government s decision on the Thames Tunnel Project in a written answer (Hansard Col 53WS), including as follows: These overflows are having an adverse effect on the environmental quality of the Thames. It has been found that the frequent overflows (on average once a week) and the large quantities of untreated discharges are causing: adverse environmental impacts on fish species; unacceptable aesthetic issues; and elevated health risks for recreational users of the Thames. I have carefully considered the reports Thames Water submitted to me at the end of 2006 and met with stakeholders who were involved in this work to hear their views. A Regulatory Impact Assessment has been completed and is available on the Defra website. Today I am announcing the Government decision for an Option 1 type solution. This approach is needed to provide a River Thames fit for London in the 21st century and to meet the statutory requirements of the (UWWTR 1994).Thames Water, the Environment Agency, the Water Services Regulation Authority and others will be taking this forward for planning and funding applications. Government will be closely following this detailed work as it develops. The related Defra News Release confirmed that: In addition to improving the environmental quality of the Thames, the scheme will also help meet European obligations on sewage treatment. On 17 April 2007 Ian Pearson wrote to the Chief Executive Officer of Thames Water in the following terms: I have now considered the additional information you supplied, the Summary Report on Tackling London s Sewer Overflows you sent me on 29 December 2006, and Regulatory Impact Assessment published on 22 March On the basis of that information, my view is that an Option 1 type approach a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works is needed. This is both to provide London with a river fit for the 21 st century, and for the UK to comply with the requirements of the Urban Waste Water Treatment Directive concerning provision of collecting systems and, in particular, limitation of pollution from storm water overflows. My view is that early phasing of the Abbey Mills to Beckton tunnel, as well as work on the rest of the scheme, will be needed in order to make progress towards compliance with the Directive (and associated duties under the Water Industry Act and the Urban Waste Water Treatment (England and Wales) Regulations 1994 ( the 1994 Regulations )) as quickly as possible. This is because early phasing of this tunnel would enable 50% of the total volume of collecting system overflow discharges (those to the River Lee from Abbey Mills Pumping Station) to be addressed well before completion of the long tunnel. I am writing to request that Thames Water makes provision for the design, construction, and maintenance of a scheme for the collecting systems connected to Beckton and Crossness sewage treatment works which: involves a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works; meets the requirements of the 1994 Regulations, including for sewerage undertakers to ensure that the design, construction and maintenance of collecting systems is undertaken in accordance with best technical knowledge not entailing excessive cost (BTKNEEC); complies with discharge consent conditions as will be set by the Environment Agency, in exercise of its duty under regulation 6(2) of the 1994 Regulations, to secure the limitation of pollution of the tidal Thames and River Lee due to storm water overflows; limits overflow discharges at Abbey Mills Pumping Station as soon as possible. Page 33

39 4 The Need I am aware there is further detailed work to be done to design and deliver an appropriate scheme, which from your report may be option 1c, as quickly as possible. As this will involve major planning, regeneration, funding and financing considerations and applications, I encourage you to continue to work proactively with the relevant parties to identify issues and risks, and how to resolve them. I would be grateful for an Action Plan on these and other key points by Friday 20 April In the plan I would like to see your outline programme for delivery of a final design, planning and funding applications, and construction of the whole scheme. We plan to share this information with the Commission by the end of April. From a Government point of view much of the detailed work will fall to Thames Water, the Environment Agency (EA), and the Water Services Regulation Authority (Ofwat) as the environmental and economic regulators. I would be grateful for six monthly progress reports from you on this work. In addition, when important milestones are reached or critical issues arise, such as significant revisions to costs and bill impacts, or concerning the development of plans for Beckton sewage treatment works, I want to be kept informed. This letter does not amount to enforcement action which would require a precise enforcement order or set of undertakings under sections 18 or 19 of the Water Industry Act At this stage we do not consider such action to be appropriate, given the further design and feasibility work that needs to be done, or necessary for Thames Water to be able to take matters forward with Ofwat and the Environment Agency. In pursuance of the objectives of this letter, Thames Water has progressed both the Lee Tunnel Project and the Thames Tunnel Project. On 1 March 2010 the Secretary of State for Environment, Food and Rural Affairs (Hilary Benn), in a written statement to Parliament 12, set out the case for the Thames Tunnel as follows: I believe the project (Thames Tunnel) to be of national significance.. for the following reasons: It is essential to meet the ecological water quality objectives of a major river; It is essential to reduce the risk to human health and prevent negative aesthetic impacts; The unsatisfactory intermittent discharges cause reputational risk to the UK, detracting from the appeal of the river in the nation s capital, which is otherwise a great asset to residents and visitors alike;.. These improvement works are needed to enable us to continue to meet our obligations under the UWWTD. The urgency of the works is increased by the infraction proceedings being pursued against the UK by the European Commission for an alleged breach of the directive; The European Commission s position The European Commission has however, reinforced its view that the UK is still in breach of the requirements of the UWWTD through a press release issued on 8 October 2009, as follows: The European Commission has decided to take the United Kingdom to the European Court of Justice on the grounds that urban waste water collecting systems and treatment facilities in London and Whitburn in north east England do not comply with EU legislation. European Environment Commissioner Stavros Dimas said: More attention needs to be paid to upgrading collecting systems to ensure full compliance with EU legislation on waste water treatment. Such investment will bring enormous benefits in terms of improving the quality of the environment. 12 Hansard; House of Commons Ministerial Statements for 01 March 2010 (Hansard 1 Mar 2010:Column 94WS); Page 34

40 4 The Need The Commission is taking action because it considers that the waste water collecting systems in London and Whitburn are being allowed to spill untreated waste waters from storm water overflows (known as 'combined sewer overflows' in the UK) too frequently and in excessive quantities. The Commission is also concerned that treatment capacity for the waste waters collected in London is in need of improvement. These shortcomings represent an infringement of the 1991 EU directive on urban waste water treatment. The directive required Member States to put in place adequate waste water collecting systems and treatment facilities for large towns and cities by the end of The waste waters collected are required to undergo appropriate treatment before they are released. The directive provides that collecting systems and treatment plants may be allowed to spill waste water in certain situations such as emergency shutdowns or unusually heavy rainfall, but the spills being authorised in these two cases are excessive and go beyond what the legislation provides for. Untreated waste-water can be a serious threat to human health, since untreated waste water can carry harmful bacteria and viruses into waters used for bathing or other related forms of recreation. Untreated waste water also contains nutrients such as nitrogen and phosphorous which can damage the marine environment by promoting excessive growth of algae that chokes off other life The Government s water strategy for England Future Water:, the Government s water strategy for England published in February 2008, states at Chapter 4, Water Quality in the natural environment, Paragraph 12 (page 48) that: As water quality problems are caused by a wide range of activities, we must consider improvements in a joined-up way, looking at the whole water catchment, from groundwater, upland streams, rivers and flood plains, through to estuaries and coasts. The Water Framework Directive (WFD) is an important instrument in achieving this. Paragraph 17 (page 50) then goes on to say: The Thames Tideway scheme, consisting of large scale infrastructure improvements to London s combined sewer system and treatment works, will address pollution from sewage, which affects the tidal river Thames and the River Lee. It is expected to be completed by 2020, and will make significant improvements to water quality and the natural environment in London, where there are currently between 50 and 60 overflows per year. The National Policy Statement on water and waste water treatment infrastructure will include major infrastructure projects such as the Thames Tideway scheme WFD (River Basin Management Plans) The WFD is a secondary driver for the Thames Tunnel project. This requires surface waters to achieve and maintain good status. Under Article 13(1) of the WFD, EU Member States are required to ensure that a river basin management plan is produced for each river basin lying entirely in their territory. In the UK, the Environment Agency has responsibility for the production of river basin management plans. The River Basin Management Plan (RBMP) for the Thames River Basin District was published in December 2009 after a period of consultation from December 2008 to June Section 4 of the RBMP, The State of the Water Environment Now, identifies, in table 3, the main reasons for not achieving good ecological status or potential in rivers. Section 6, The state of the water environment in 2015 notes that one of the objectives of the Water Framework Directive is to aim to achieve good status in water bodies by However, for 75% of surface water bodies this target cannot be met by this date. The Plan sets out where good status cannot be achieved by In these cases an alternative objective of good status or potential by 2021 or 2027 is set. Section 7 explains the three river basin management cycles, , and Achieving good status in all water bodies by 2027 is a significant challenge. 13 EUROPA Press releases, Reference IP/09/1488 (8 October 2009) Page 35

41 4 The Need The Thames River Basin Catchments are discussed individually in Section 8 of the RBMP. The Tidal Thames is included within the Estuaries and Coastal Waters Catchment and on page 79 it is stated that: The water quality concerns for the Thames estuary centre around the impacts of storm discharges from the five major sewage works which serve London and from the combined sewer network. These discharge to the estuary frequently, resulting in drops in dissolved oxygen, and increases in aesthetic pollution, risk to health and fish kills. Improvements to the sewage treatment works along the tidal River Thames and the construction of the London Tideway Tunnels are planned to be delivered by Thames Water over the next two river basin cycles. These major projects represent the primary measures to address point source pollution from the sewer system and are fundamental to the achievement of good status in this catchment Key actions for the catchment are itemised on page 80. These include: Improvements to the London sewerage network to reduce the impact of storm sewage on water quality in the Thames Tideway - Thames and Lee Tunnels. Annex B of the RBMP is a large compendium of objectives for our waters. Section B23 Estuaries sets out various proposed actions for estuaries and details the ecological potential and chemical status of estuaries within the Thames water basin. Schedules setting out ecological potential and chemical status of Thames Lower, Thames Middle and Thames Upper estuary make it clear that the status of those stretches of the river are currently moderate and that they will not achieve good status by They do, however, indicate Good potential by Water quality impacts Introduction Discharges from CSOs contain a mixture of foul sewage, groundwater infiltration and storm water runoff, and contain pollutants such as suspended and colloidal solids and volatile organic matter that contribute significantly to the organic and chemical oxygen demand in the river, which, in turn, result in oxygen depletion and nutrient enrichment of the river through London. These conditions are most prevalent during summer months when temperatures are higher and oxygen in the river is more subject to depletion. Water quality is influenced by physical, chemical and biological conditions and is commonly compared to a set of standards against which compliance is assessed. In England and Wales, the Environment Agency is the competent authority for quality monitoring. The following parameters are among the most useful and important in assessing quality: Biochemical oxygen demand (BOD) - a measure of the amount of biodegradable organic matter in water. It is expressed as the number of milligrams of oxygen required by micro-organisms to oxidise biodegradable organic matter in one litre of water. As the BOD of a water body increases, so does the demand for oxygen, which causes a subsequent depletion in the dissolved oxygen (DO) concentration to the detriment of water quality. Total ammonia a compound of nitrogen and hydrogen which, at high concentrations, is toxic to freshwater organisms. It is also oxidised by certain bacteria in water causing a depletion of dissolved oxygen. The measurement of ammonia and other inorganic nitrogen compounds is usually referenced to the nitrogen and hence ammonia is often referred to as ammoniacal nitrogen. Un-ionised ammonia - a form of ammonia that arises under conditions of high temperature and/or ph (alkaline conditions). This form of ammonia is more toxic to freshwater organisms than other forms of ammonia. Dissolved oxygen (DO) the amount of oxygen dissolved in water expressed as milligrams of oxygen dissolved in one litre of water. It is influenced by temperature, atmospheric pressure, re-aeration, photosynthesis and the decay of pollutants (as indicated inter alia by ammonia and BOD levels). DO concentration decreases with rising temperature and low DO concentrations can result in fish kills. Page 36

42 4 The Need Nitrogen and phosphorus these are commonly referred to as nutrients. High concentrations can give rise to eutrophication, the condition where nutrient enrichment supports dense plant populations the decomposition of which kills aquatic life by reducing DO concentrations. In England and Wales, there are water quality standards that should be met in order to maintain water quality. Whilst those for freshwaters are well-established, and were in many instances statutory, those for estuaries were historically less well-developed. For this reason the TTSS developed a suite of water quality standards applicable to the Thames Estuary. Water quality is influenced by a number of sources, which are outlined in further detail below: Continuous discharges typically continuous discharges come from treated effluent from sewage treatment works, and the quality of the final effluent depends on the nature of the sewage treatment works. Specifically the BOD, ammonia and phosphate in final effluent are considered to assess the impact on water quality in the receiving watercourse. Intermittent discharges this is the discharge of untreated sewage into a watercourse during times of high flow in the sewer system, typically from CSOs or storm tanks at STWs. As the discharges are untreated (although perhaps screened), they may discharge high levels of pollutants into a watercourse which can cause detrimental impacts on water quality, in particular a depletion of DO. Diffuse pollution pollution from diffuse sources can include, for example, agricultural runoff, highway runoff, or runoff from contaminated land. Frequently diffuse runoff enters a watercourse without being treated and can add significant pollutant to a watercourse Influences on water quality in the Thames Tideway Prior to any improvements affecting water quality in the Thames Tideway, modelling indicated significant water quality impacts on the Thames Tideway due to a combination of continuous and intermittent discharges. Continuous discharges from the five STWs in the Tideway have been shown to have a significant impact on water quality in the Tideway 14 and resulted in the development of the London Tideway Improvements programme. There are significant intermittent discharges into the Tideway from storm tanks at the STWs and CSO spills. Water quality modelling of the Tideway clearly demonstrated that the pollutant load from both continuous and intermittent discharges caused a fall in DO concentrations in the Tideway that could result in fish mortality. Summer storms in particular have the capacity for an even greater impact, due to low flows meaning less dilution of the overflows. Furthermore, the Thames river basin does not generate large natural river flows and these are further reduced by abstractions from the Thames upstream of Teddington for use as a potable water supply for London. The tidal River Thames does not therefore receive large flows of freshwater from upstream to provide dilution and protection from pollution. As a consequence, there is a very slow net seaward movement of flow causing water to take up to three months to travel along the estuary from Teddington to Southend. The slow seaward movement of freshwater makes the upper and middle reaches of the tidal River Thames particularly vulnerable to pollution. The tidal effect moves water up to 15km up and down the River Thames on each flood and ebb tide, but on aggregate as little as half a kilometre per day towards the sea with very little mixing. During larger rainfall events, this can create discrete slicks of polluted water that move with the tide. Furthermore, solid material (known as sewage derived litter) will tend to be washed onto the foreshore during the ebb tide Water quality modelling As the Environmental Regulator the EA sets the discharge standards which Thames Water has to comply with. To understand the impacts of continuous and intermittent discharges and the effectiveness of solutions on water quality in the Tideway, a modelling group was established and a 14 TTSS Objectives Working Group Report Volume 2, Modelling Study (2004) Page 37

43 4 The Need water quality model developed for the EA. The water quality model used for the analysis was WRc s Quests, which is an estuary model comprising hydrodynamic and water quality components. The model is a one-dimensional (1D) time-series model of the Thames Estuary from Teddington Weir to Southend. The Quests model divides the river reach into cells and predicts water quality conditions within each cell. A 1D model assumes width and depth averaged conditions, where discharges to a cell are fully mixed over the contents of that cell. This is justified by the view that the Thames Tideway is reasonably well mixed and that width and depth gradients in concentrations tend to be of second order importance. The Quests water quality model has inputs from a number of sources, including dry weather inputs (flow and quality), extra over effluent flows (additional flow through the STW during rainfall), storm tank spills, and CSO spills. Further information on the inputs to Quests can be obtained from the Quests water quality modelling results report 15. A Compliance Testing Procedure (CTP) was developed where the model was run for 154 rainfall events, which were selected by the modelling group as the most significant summer rainfall events over a 34-year period. The most recent water quality modelling assessment included an allowance for antecedent conditions (referred to as preceding events) in the Thames Estuary. This was achieved by running a simplified hydraulic model of the catchment (SIMPOL3) over a continuous 34-year period, which provided estimates of water quality in the estuary in the six weeks prior to each of the 154 selected rainfall events. Although this approach was necessarily simplified, it provided a better representation of baseline conditions in the estuary prior to each of the events than previously, where it had been assumed that the background quality in the estuary was good prior to each event. The modelling indicated that the inclusion of preceding events did have a significant effect on the impact of the 154 rainfall events because background quality was poorer at the start of an event. To assess the compliance of proposed solutions, dissolved oxygen (DO) was selected to be the principal indicator of water quality and solutions would need to be compliant with the DO standard to be considered to provide adequate protection for the aquatic ecosystem. Interim environmental quality standards (EQS) for DO were derived as part of the TTSS as follows: Table 4.3 Revised interim EQS for DO on the Tideway, derived by the TTSS Steering Group and the Environment Agency Dissolved Oxygen (mg/l) Return period (years) Duration (no. of 6 hour tides) Note: The objectives apply to any continuous length of river >=3km. Duration means that the DO must not fall below the limit for more than the stated number of tides. A tide is a single ebb or flood. Compliance will be assessed using the network of Automatic Quality Monitoring stations. The December 2006 modelling and compliance report 16 provided the results from the modelling studies which led to the decision in March 2007 to build the Lee and Thames Tunnels. The TTSS standards have been compared with proposed dissolved oxygen standards to meet the requirements of the Water Framework Directive. The WFD standards have been developed for the whole of the UK and the TTSS standards have been developed particularly for the Thames 15 Thames Tideway Tunnel and Treatment, Option development: Quests water quality modelling results report (2007) 16 Thames Tideway Tunnel and Development, objectives and compliance working group report, Volume 2 - modelling and compliance (2006) Page 38

44 4 The Need Tideway. The validity of the TTSS standards are discussed in the Tideway Fisheries Review 17 and summarised in Table 4.4 below: 17 Thames Tunnel Project, Tideway Fisheries Review, (Jacobs, October 2009) Page 39

45 4 The Need Table 4.4 Comparisons of WFD Standards (shaded rows) and Tideway EQS for DO Dissolved Oxygen (mg/l) Return period (years) Duration (no. of 6 hour tides) 4 (M) to 5 (FW) 1 73 (as 5 th percentile) (M) to 2 (FW) *WFD Standards vary with salinity from marine (M) to freshwater (FW) The main conclusion is that the two sets of standards sit harmoniously together, but are expressed slightly differently, and confidence can be placed in the bespoke dissolved oxygen standards developed for the Tideway. Further illustration of this is given in Figure 5.2 and accompanying text Fish studies Fish are considered to be good indicators of ecological quality and that setting of standards on the basis of reducing impacts on fish is consistent with the aims of the Water Framework Directive. The principal cause of fish mortality in the Thames Tideway arises from low DO levels, especially associated with the operation of CSOs. The TTSS criteria for DO were developed to minimise adverse impacts on fish, and especially to avoid fish kills. These criteria have been based on research on lethal and sub-lethal effects on representative fish species present, or likely to be present, in the Thames. Impacts of the various options on DO have been considered as part of the consideration of water quality impacts. This section is concerned with the impacts of current and predicted future DO concentrations on fish overall and on specific fish species. An assessment of the impacts on Tideway fish of various levels of DO was developed over a two year riverside and laboratory study undertaken and reported on by Fawley Aquatic Research Limited (FARL, Jacobs Babtie and now Jacobs) (Thames Tideway Strategy: Experimental Studies on the Dissolved Oxygen Requirements of Fish (April 2004)). This study provided a body of hypoxia response data which were then used to evaluate and underpin new environmental quality standards (EQSs) for DO on the Tideway. The final aim of the study was to ensure that the EQSs would protect the sustainability of the Tideway fish populations. This was evaluated through the Tideway Fish Risk Model (TFRM), developed specially for the purpose. The study report suggests that the TTSS standards appear to be adequately protective of all of the test species from hypoxia-related lethality. An independent expert review of the FARL fisheries study by Prof. Mike Elliott of Hull University provided strong support for the technical approaches adopted and interpretation of the results. Prof Mike Elliot was of the opinion that the TFRM appears to remain the most suitable framework for the protection of the sustainability of the Tideway fish populations. Following publication of the Thames Tideway Strategic Study in 2004, Ofwat commissioned Jacobs Babtie (see also Section 4.2) to undertake an independent study to consider whether a cheaper engineering solution could be found. An area that the Jacobs Babtie report focussed on was the large measure of improvement that the WRc s QUEST water quality model predicted would occur as a result of AMP4/AMP5 sewage treatment work (STW) upgrades without a tunnel solution. It was also proposed that allowable water quality (dissolved oxygen) standards might be set at a less protective level if the ecological criterion were to be changed from no visible fishkills to maintaining sustainable fish populations. This was put forward on the basis that a degree of fishkill is sustainable (though not necessarily acceptable to the public). Page 40

46 4 The Need CCWater, in their representations relating to the Lee Tunnel planning application 18, pursued this line and considered that sustainability with or without the tunnel solution was finely balanced and therefore concluded that the tunnel solution might not deliver the required improvements identified by the Thames Tideway Strategy Group. Subsequent reruns of the QUEST model for the STW upgrades, carried out after the TTSS and Jacobs Babtie reports, have produced different outcomes to the previous analysis. Taking account of refined water quality data and updated fish survey data used within the Tideway Fish Risk Model, the revised assessments indicate relatively high numbers of not sustainable cases and no longer suggest that the STW upgrades alone would ensure sustainable fish populations in the Tideway. Another review of the FARL study was commissioned (Tideway Fisheries Review: Jacobs, October 2009) to update and evaluate the robustness of the findings in view of scientific data gathered since A number of points were questioned: Should the TFRM have included the effects on fish of ammonia toxicity? Was the set of seven common Tideway fish species tested representative of the full suite of fish found in the Tideway (>120 species recorded to date)? Were the fish mortality rate criteria used in the TFRM an appropriate measure of sustainability, or should this now be judged against WFD Ecological Status metrics? The question of potential ammonia toxicity to fish in the Tideway was examined by comparing levels of un-ionised ammonia recorded in the Tideway over a 33-year period ( ) against the 200μg/L acute toxicity threshold for salmonids. The 95th percentile values for this period were <10μg/L and even the maximum recorded value (152 μg/l) was below the lethal threshold. The exclusion of ammonia toxicity from the TFRM therefore remained valid. The set of seven common Tideway fish species tested, including salmonids, were still considered representative, all being more sensitive to toxicity and temperature than many of the other species found in the Tideway. A detailed assessment in the review took account of new WFD water quality standards but concluded that WFD Ecological Status metrics for transitional water fish cannot readily be applied to assess the outcome of improvements in water quality. The DO standards developed by the TTSS are regarded by the EA as more appropriate design standards for the Thames Tunnel to address the issue of combined sewer overflows as they have been empirically derived using lethal and sublethal response data from local fisheries and tested against historical and predicted water quality data United Kingdom climate projections (UKCP09) In June 2009, the latest set of UK climate projections (UKCP09) was released, and provides the latest understanding and assessment of the likely effects of climate change. The UKCP09 scenarios provide an update of the 2002 UK climate impact predictions (UKCIP02). However, the two projections are not directly comparable so it is necessary to understand the implications of the UKCP09 scenarios in relation to UKCIP02 because the modelling (hydraulic and water quality) for the TTSS used the UKCIP02 scenarios to identify the likely impacts of climate change. The UKCP09 scenarios include probabilistic projections. The climate change at the 50% probability level is that which is as likely as not to be exceeded. The 90% probability indicates that there is a 90% chance that the change will be less than this figure. In the south-east, the UKCP09 50% probability predicts, for the 2080s, a similar increase in both summer and winter temperatures for the high emissions scenario as in UKCIP02. Summer and winter temperature increases are predicted to be 4-5 C and 3-4 C, respectively. However, at the 90% probability levels summer temperatures in the 2080s are predicted to rise by 8-9 C, and winter temperatures by 5-6 C, which 18 Lee Tunnel and Beckton Sewage Treatment, Works Extension Scheme: ODA Consultation Application Reference 08/01158/ODA. Comments by CC Water London and South East Committee, 13 August Page 41

47 4 The Need is noticeably higher than the UKCIP02 scenarios. Increases in air temperature would cause a subsequent increase in water temperature, which would affect the water quality processes in the Tideway, and would cause more rapid depletion of DO. It was observed in the 2006 modelling report that increases in water temperature (a combination of increases in air temperature and solar radiation) would have the most significant impact on water quality, compared to other environmental changes due to climate change. Therefore, worst case temperature increases will be included as part of future water quality assessments, to understand the worst case impacts of climate change on DO, and hence on ecosystems. UKCIP02 indicated that sea level could rise by between 9cm and 69cm by the 2080s. In comparison, UKCP09 outlines a potential sea level rise of between 12cm and 75cm by 2095 (based on the medium emissions scenario). Increased river water levels at the outfalls will have an impact on the capacity of the STWs by restricting the free discharge of treated effluent to the river at high tides and the provision of outfall pumping stations will need to be considered. With respect to total rainfall, UKCIP02 indicated that winter rainfall could increase by up to 20-40%, and summer rainfall could decrease by more than 50%. In addition, the UKCIP02 indicated that the most intense summer rainfall could increase in their intensity, and this ethos was adopted to determine the adjustments to intense summer rainfall for the Compliance Testing Procedure (CTP). In the UKCP09 projections, the central (50% probability) estimate provides a similar overall increase in rainfall, compared to the UKCIP02 scenario. The 90% probability level indicates that at the worst case winter rainfall could increase by 50-70%. For summer rainfall, UKCP09 indicates that the predicted reduction in summer rainfall is not as significant as in the UKCIP02 scenarios. The central estimate predicts only a 20-30% reduction in summer rainfall, compared to a predicted 50% reduction in UKCIP02. Furthermore, the UKCP09 scenarios indicate that the frequency, duration or intensity of precipitation and storms in the UK is unlikely to significantly change due to climate change. Such changes as are seen (by the Met Office) as relatively modest, and the potential for substantial changes appears to be small. The major differences between the UKCIP02 and UKCP09 predictions are summarised in Table 4.5 below: Table 4.5 Summary of UK climate change predictions UKCIP02 and UKCP09 UKCIP02 UKCP09 Temperature: 1 Summer & winter temperatures due to climate change at 50% probability level 2 Summer & winter temperatures due to climate change at 90% probability level Sea Level Change: Similar to UKCP09 Lower than UKCP C & 3-4 C increase respectively 8-9 C & 5-6 C increase respectively 1 Rise by 2080s 9-69 cm cm Rainfall: 1 Winter total rainfall 20-40% increase Similar to UKCIP02 (50% probability case) 50-70% increase (90% probability case) 2 Summer total rainfall 50% decrease 20-30% reduction (50% probability case) 3 Rainfall intensity & duration Most intense summer rainfall events could increase in their Little evidence suggesting that the duration and intensity will Page 42

48 4 The Need intensity significantly change Water quality impacts at the baseline conditions As part of the Lee Tunnel and Beckton improvements EIA, the Quests model of the Tideway was rerun for the EA, to assess the effectiveness of the Lee Tunnel and STW improvements on water quality in the Tideway (i.e. without the Thames Tunnel). This is subsequently referred to as the baseline conditions assessment and was based on: 2021 population 2020s climate change from UKCIP02 (temperature changes, but rainfall as current) inclusion of preceding events. The baseline conditions (2021 population, Beckton and Crossness STW upgrades plus the Lee Tunnel) model results indicate that these schemes would result in improvements in predicted DO in the Tideway. This is due to the capacity improvements to the STWs and a reduction in overflows from the STWs and Abbey Mills Pumping Station. As shown in Table 4.1, the existing (2006 population) spill volume with no improvements is modelled to be 39 million m 3 /year. This is reduced to 18 million m 3 /year at the baseline conditions. Approximately 6 million m 3 /year of the reduction in spill volume is attributable to the provision of the Lee Tunnel. However, the results clearly indicate that the baseline conditions would still result in noncompliance with the current and future environmental conditions with respect to spill volumes and frequencies. The baseline conditions do not capture approximately 50% of the current discharge volumes and none of the CSOs which discharge directly to the Thames would be intercepted. These overflows have a noticeable impact on DO concentrations in the Tideway. Forecast population growth beyond 2021 will place further stress on the sewer system assuming the baseline conditions remain as has been indicated in Table 4.2. Additional load being discharged would have an impact on DO, and would cause further breaches of the interim standards. Although beneficial, the installation of water meters and other water conservation measures will not reduce foul sewage flows to a sufficient extent to counteract the impacts of population growth. Overall, the evidence confirms that improvements in water quality will arise after the baseline conditions are in place. There will be significantly fewer breaches of the DO interim standards (TTSS), and the annual DO 5%ile indicates that there would be a shift from bad to moderate/poor under the WFD as a result of the provision of the STW upgrades and the Lee Tunnel. However, the modelling clearly indicates that the baseline conditions cannot achieve either the interim DO standards or the WFD good ecological potential, and that the overflows which discharge to the Thames will continue to have a noticeable and unacceptable impact on water quality in the Tideway. 4.8 Further considerations Health impacts on recreational users With each rainfall event that causes an overflow, it is typical for the discharge to contain - in addition to human pathogens and bacteria - large quantities of waste water solids (eg, condoms, human faeces, syringes, tampons and other foul flow products), industrial and commercial waste water constituents (eg, chemicals, solvents, kitchen grease, rags), resuspended sediment, street litter and other debris. Such discharged materials are typically either floating on the water surface or deposited on the foreshore of the river. Direct access to the river foreshore for a large variety of recreational and commercial uses is practised and encouraged in virtually every reach of the river. Therefore, the aesthetic and recreational impairments can be substantial. Where there is river usage for contact recreation combined sewer overflows produce a potential threat to human health from viruses, bacteria and other pathogens. The general perception of the suitability of the rivers and foreshores for recreational uses is greatly diminished once they are subject to the impacts of sewage overflows. Page 43

49 4 The Need An assessment of health impacts upon recreational users of the River Thames was conducted and reported by the Health Protection Agency in This report, which quoted an EA estimate of between 3,000 and 5,000 recreational users of the tidal Thames, concluded that the background concentration of microbiological indicator organisms exceeded the WHO guidelines for recreational use at Kew, Barnes and Putney, but that water quality generally improved as one moved downstream between Kew and Putney. This would be reflective of the continuous discharge of treated, but not disinfected, sewage effluent and indicates that these standards are exceeded in the absence of CSO discharges. While there was evidence of an elevated health risk (gastric infection) to recreational users in the upper Tideway two to four days after a CSO spill event, the rate of gastric infection among recreational users was very low (12.8/1000/year) compared to the general population (190/1000/year). This may be due to the relative good health and fitness of recreational users, a greater awareness of hygiene and health and safety issues, and a developed immune response to infection from repeated exposure, which results in asymptomatic infection. However, incidence of infection appears to be elevated in the period following CSO spill events, with 77% of cases taking place within three days of a CSO spill event. Comparison with non-cso events indicates a six-fold increase in infections associated with CSO spills. The nature of tidal movement for waters receiving CSO spills is that plugs of CSO discharge containing elevated levels of micro-organisms stay intact and move upstream and downstream under influence of the tide for periods of up to four days before they disperse. The report suggests that it is contact with these plugs which accounts for the higher rates of infection among recreational users Aesthetics The operation of CSOs results in the discharge of sewage litter along with the discharge of effluent. It was estimated by the TTSS that overflows from the combined sewers introduce approximately 10,000 tonnes of sewage derived solid material annually. Due to the nature of the tidal system, water can take three months to travel to the sea. The upper and middle reaches of the Tideway through London are therefore especially vulnerable to pollution because of long residence times. Sewage derived litter creates offensive slicks of sewage in the water and deposits of solid material on the foreshore. The presence of this sewage litter in the river is aesthetically offensive. The majority of the river is accessible to the public through tourist and commuter boats, waterside housing, and recreational use; hence the value of having a clean river is evident. In particular, the upper tidal reaches of the river have greater public access, where there is less volume of water for mixing of untreated overflows. There have been public complaints especially concerning the conditions in the upper reaches above Vauxhall but also, after heavy rainfall, in the areas of the Embankment, Greenwich and the Thames Barrier. Currently, under an agreement between Thames Water and the Environment Agency, Thames Water has deployed, as interim mitigation measures, two skimmer boats, which collect floating debris after storm events, and two river oxygenation barges that provide direct oxygenation of river water. These barges are augmented by a land-based hydrogen peroxide dosing system that in combination help maintain minimum dissolved oxygen concentrations above that where fish would be harmed.. These measures provide a degree of mitigation of the impacts of the CSOs in the river, but do not prevent impairments to the river from occurring, or are able to meet applicable regulatory requirements in the longer term. In general, the largest proportion of sewage litter will be discharged when the CSO begins to discharge. This being the case, the discharge of sewage litter is more closely related to the number of CSO discharge events than the volume of the discharge. Furthermore, as the number of CSO spill events reduces so will the quantity of sewage litter discharged. Therefore the number of CSO events needs to be considered when assessing the aesthetic impact of CSO discharges and the need for a solution. 19 The Thames Recreational Users Study Final Report (2007), a collaborative partnership project between the City of London Port Health Authority and the Health Protection Agency Page 44

50 4 The Need While the commissioning of the Lee Tunnel and improvements at Beckton and Crossness STWs will remove more than half the volume of CSO effluent currently discharged to the Thames, the Lee Tunnel will only address a small proportion of the total number of spill events. At these baseline conditions, 34 Category 1 and 2 CSOs in the Beckton and Crossness catchment would still discharge to the Thames Tideway during a typical year. Therefore, the improvements over the existing system provided by the STW improvements projects and the commissioning of the Lee Tunnel can only be expected to have a minimal beneficial effect on the amount of sewage litter in the river,. In particular, the baseline conditions will not result in a reduction in the volume of sewage litter in the upper reaches where the issue is greatest. 4.9 The long term effect of doing nothing Table 4.2 gives the projected spill volumes and spill frequencies at the baseline conditions for the Thames Tunnel, which is with the improvements to the STWs and the Lee Tunnel in place and with population projected to In essence, these are the conditions that would remain if no further schemes are commissioned and possible adverse effects due to climate change do not materialise. However, with a total annual average CSO discharge to the Thames Tideway of 18 million m 3 and the annual number of spills from certain individual overflows still being up to 59 times in a typical year, this will not be sufficient to satisfy the Commission. The UK Government is still likely be subject to the imposition of financial penalties if suitable further action were not taken. It is not possible to make a reasonable estimate of the size of any fines that might be imposed in relation to the infraction proceedings against the UK government. However, previous cases suggest that fines levied by the Commission will be significant, as the sole purpose is to ensure that Member States comply. To this end, the level of the fine is usually scaled upwards, based on the Member State s ability to pay, to a point where it is no longer economically viable to do anything other than comply with the legislation. The European Commission argues that the UK is failing to fully implement the UWWTD. There are extant infraction proceedings in respect of insufficient collecting systems and treatment processes. The European Commission announced in a press release dated 8 October 2009, that it has decided to continue with the legal process and take the United Kingdom to the European Court of Justice on the grounds that urban waste water collecting systems and treatment facilities in London do not comply with EU legislation. This is because it considers that the waste water collecting system in London is currently being allowed to spill untreated waste waters from combined sewer overflows too frequently and in excessive quantities. With the effects of future population changes and climate change (as projected), even if modified by changing patterns in water usage, the doing nothing approach is likely to mean the increased risk of more frequent overflows, more frequent fish kills, continued increased health risks to recreational users, worse litter blight, and adverse impacts on the attractiveness of the water frontage. Climate change can be considered to have two principal impacts on the Tideway: On the operation of the sewer system although the predicted reduction in summer rainfall is now not as significant as originally thought, drier periods could cause an increase in pollutant build up which could increase the adverse impacts of the first flush in any overflow from the tunnel. Furthermore, wetter winters could lead to more overflows during winter events. On water quality processes in the Tideway water quality modelling demonstrated that increases in river water temperatures lead to DO depletion due to lower DO saturation and faster reaction rates. Warmer winter temperatures in conjunction with wetter winters could lead to higher overflows from the sewer system and an associated impact on water quality, although the impact of these may be moderated by higher flows. To support the Lee Tunnel and Beckton EIA, further water quality modelling was undertaken in March The water quality assessment aimed to assess the effectiveness of the Lee Tunnel and STW improvements in protecting DO levels in the Thames Tideway and the River Lee for the immediate and long term situations. The modelling illustrated that with preceding events included, the Lee Tunnel and the Mogden, Beckton, Crossness, Riverside and Long Reach STW upgrades Page 45

51 4 The Need (the baseline conditions) would result in improved DO levels in the Thames Tideway, but would not result in compliance against the interim DO standards derived as part of the TTSS. 20 Thus the conclusions of the water quality assessment are that the baseline conditions (STW upgrades and Lee Tunnel, without the Thames Tunnel) are insufficient to: a) meet water quality objectives, and b) adapt to the impacts of population growth and climate change Summary of the need The need for the Thames Tunnel arises from the objective of the EU Urban Waste Water Treatment Directive; to protect the environment from the adverse impacts of insufficiently treated waste water discharges. Waste water collecting systems in London, in the opinion of the EC, are being allowed to spill untreated waste waters from combined sewer overflows too frequently and in excessive quantities. The Directive, and related UK legislation, accepts that collecting systems and treatment plants may spill storm water in certain situations, such as unusually heavy rainfall, but in the case of London, the spills are considered by the Commission to be excessive and go beyond the intentions of the Directive. Hence the UK is currently considered non-compliant by the European Commission, although it is believed that the suite of schemes including the Thames Tunnel should demonstrate the UK s intent to achieve compliance of the UWWTD within the target timescale of The European Commission is taking infraction proceedings because it considers that the current situation of high spill frequencies and large discharge volumes into the tidal Thames is in breach of the EU UWWTD. The spills also stand to cause breach of the UK UWWTR and may cause the River Thames to be non-compliant with the objectives of the Water Framework Directive. The Thames Tunnel will, however, capture the majority of those spills and significantly reduce the volume and frequency of any residual spills to the Tideway in the future. Waste water discharges affect the environment in three main ways, which have been considered in developing the specific objectives for the project, namely: adverse environmental impacts on the river ecosystems and on fish species in particular; unacceptable aesthetic issues; and elevated health risks for recreational users of the Thames. Should nothing be done to address the current situation, with continuing population growth and incremental changes to impermeable areas, the risk will increase of greater spillage to the river, with associated adverse environmental impacts. 20 Lee Tunnel and Beckton STW extension water quality modelling assessment of Lee Tunnel (2008) Page 46

52 5 Achieving Compliance 5 ACHIEVING COMPLIANCE To meet the requirements of the UWWTD, the design, construction and maintenance of collecting systems must be undertaken in accordance with best technical knowledge not entailing excessive costs, notably regarding: volume and characteristics of urban waste water, prevention of leaks, limitation of pollution of receiving waters due to storm water overflows. The UK Government has accepted that more measures are needed to limit pollution from some of the storm water overflows that are part of the Beckton and Crossness sewerage systems. Thames Water had developed a proposed option consisting of two full-length storage tunnels intercepting 36 CSOs in the Beckton and Crossness catchments discharging into the Rivers Lee and Thames and transferring the flows to Beckton STW (Option 1c). Further work has developed the Lee Tunnel dealing with 2 CSOs (now under construction) and three route options for the Thames Tunnel dealing with 34 CSOs. The route options for the Thames Tunnel are the River Thames route, the Rotherhithe route and the Abbey Mills route. All three route options for the Thames Tunnel provide additional benefits for the sewer system, in terms of robustness and flexibility, by making provision for schemes to reduce sewer flooding, and the future impacts of population growth and climate change. Further consideration has been given to options involving source control, separation, partial separation, dispersed storage units and SUDS. None of these resulted in a suitable or cost-effective solution meeting the requirements of legislation. 5.1 London Tideway Tunnels Thames Water has actioned the Minister s request to make provision for the design, construction and maintenance of a scheme for the collecting systems connected to Beckton and Crossness involving a full length storage tunnel (see copy of the Minister s letter of 17 April 2007 at Appendix A). It has planned the strategy for implementation, and appointed a London Tideway Tunnels Delivery Team (LTTDT) to deliver the Lee Tunnel and the provision for the Thames Tunnel - the London Tideway Tunnels. The Lee Tunnel is under construction with target completion in Thames Water has separately commenced construction of the upgrades to the sewage treatment works discharging into the tidal reaches of the River Thames (at Mogden, Beckton, Crossness, Riverside and Long Reach) and these are due to be commissioned between 2012 and Design and Performance Criteria Objectives The overall goal of the London Tideway Tunnels and STW upgrades is to meet the regulatory requirements of the UWWTD and the WFD to provide a cleaner, healthier London Tideway, including reaches of the Rivers Thames and Lee. Associated separate projects under construction are: The 6.9 kilometre, 7.2 metre diameter, Lee Tunnel from Abbey Mills to Beckton STW. The improvements to Beckton STW increasing the treatment capacity to 27m3/s. This will significantly reduce CSO discharges at the Abbey Mills CSO, and also the discharges to the Lee Tunnel, by maximising the capacity of the Northern Outfall Sewer. The improvements to Crossness STW increasing the treatment capacity to 12.94m 3 /s. This will significantly reduce CSO discharges from the Southern Outfall Sewer. Page 47

53 5 Achieving Compliance The improvements at Mogden, Riverside and Longreach STWs (which improve Tideway river water quality but are not directly influencing the Thames Tunnel project). In general, the following overall environmental requirements to be met by the above improvements are: Protection of the ecology, assessed by reference to adopted dissolved oxygen standards; Reduction of sewage solids and litter in the Tideway; Reduction of health risk for water users attributable to intermittent sewage discharges from CSOs. To meet these requirements the specific objectives of the Thames Tunnels are: To reduce the frequency and volume of the CSO discharges and so limit pollution due to stormwater overflows in accordance with UWWTD; To improve the quality of the River Thames by diverting discharges from unsatisfactory CSOs in the Beckton and Crossness catchments and conveying collected overflows via the storage tunnel to sewage treatment works for secondary treatment prior to discharge. Previous work identified 34 unsatisfactory CSOs discharging to the River Thames. To provide adequate system capacity such that any residual discharges from the existing unsatisfactory CSOs to the river will only occur during unusually heavy rainfall or in emergency conditions, recognising that there will be occasional discharges occurring when the tunnel is full. The TTSS estimated a tunnel volume of 1.6million m 3 would provide sufficient storage to reduce spill frequency from these unsatisfactory overflows to a level consistent with the objectives established. It is accepted that it is not possible to design a system that will guarantee no spills. To limit the maximum retention time of captured CSO discharges in the tunnel to a duration which is consistent with reasonable treatment capability and effective odour management. Previous work identified a storage time of less than 48 hours. Attainment of the above objectives will also substantially reduce the elevated human health risks from anthropogenic bacteria and pathogens discharged to the River Thames which are attributable to the CSOs. This will result in a cleaner and healthier Tideway System capacity requirements The LTTDT sets out to provide a framework within which the project would achieve appropriate ecological status of the river, judged by compliance with defined and adopted dissolved oxygen standards, and control of discharges at the Category 1 and 2 CSOs to meet the requirements of the UWWTD by limiting the numbers of spills to the river (see Table 4.2). Criteria considered include the following: Planning horizon: Thames Water has developed a plan which, if implemented, should complete by the target date of System population growth to 2021, changes in the areas connected to the system and the design life of various components have all been taken into consideration. Future population: Overall, the system population growth rate is about 1.2% per annum between 2006 and 2021, which results in additional 1.23 million people being served. Sensitivity analysis for growth beyond 2021 has been undertaken to provide confidence that the proposed solution remains appropriate into the future. Storm water capacity requirements: capable of dealing with 1 in 30 year storm intensities hydraulically and with a storage volume sufficient to contain CSO discharges for all but 3 to 4 events per typical year when limited residual discharges may occur. Tunnel arrangements to minimise sediment deposition (ensuring self cleansing velocities are achieved) and mitigate against odour generation, providing odour treatment facilities as appropriate. Climate change: UKCP09 projections show little change in annual rainfall volume to 2088, but project changes to summer and winter rainfall volumes (22% less and 20% more respectively). Page 48

54 5 Achieving Compliance The change in rainfall over the next 80 years is therefore considered minimal and within the normal range expected between years (as reflected in the 34 years of records used in the system performance analysis). The normal variation in rainfall between years is addressed in the analysis of the project performance, by considering wet and dry years in addition to a typical year rainfall series and a series of the largest summer events. Climate change in the form of changes to seasonal temperatures does not directly affect how the project addresses CSO discharges, but does affect dissolved oxygen concentrations in the River Thames. Design life: the design life for an element of the works is defined as the first replacement of a major system component, given that adequate maintenance of facilities and equipment will occur during the design life. The design life for all major civil structures, that is the main tunnels, connecting tunnels, chambers and shafts, is 120 years. The interception structures and conduits and mechanical gates are to be designed for a life of 60 years. 5.3 Tunnel options TTSS Refinement The TTSS considered four alternative strategies; Source control, Within the sewer system, At the CSO outfall, and In-river treatment, and concluded that only Strategy 3, At the CSO Outfall would achieve all the TTSS objectives 21. Following an independent review 22 which added a fifth strategy; Integrated Stormwater Management, the then Minister of State for Climate Change and the Environment, Ian Pearson, requested in July 2006 further work to develop two principal options. These both involved large scale tunnels that intercept overflow discharges and take them for treatment in East London. This study 23 resulted in the development of a preferred option (Option 1c) which comprises a full-length storage tunnel/transfer system intercepting 36 CSOs in the Beckton and Crossness catchments and transferring the flows to Beckton STW. In his letter of 17 April 2007 (see Appendix A), the Minister endorsed an approach involving a full length storage tunnel with secondary treatment at Beckton STW in order to achieve compliance with the Urban Waste Water Treatment Directive (and associated duties under the Water Industry Act and the Urban Waste Water Treatment (England and Wales) Regulations 1994) as quickly as possible. The Minister requested that Thames Water makes provision for the design, construction and maintenance of such a scheme for the collecting systems connected to Beckton and Crossness sewage treatment works Further developments Subsequent studies and evaluation of tunnel options and CSO controls have been in accordance with the Ministerial request to Thames Water to make provision for the design, construction and maintenance of the Option1c scheme. There has been considerable development of solutions since 2007, leading to the development of a 7.2m diameter tunnel from Abbey Mills to Beckton STW, which is referred to as the Lee Tunnel, and subsequently to three alternative alignments for the 7.2m diameter Thames Tunnel, as shown in Figure 5.1. These alignments are described as follows: River Thames route, which largely follows the river from west London downstream to Beckton STW as previously proposed, though subject to numerous detailed improvements in terms of optimising performance of CSO controls and ensuring full utilisation of the extended treatment capacity of the Beckton and Crossness STWs. 21 Thames Tideway Strategic Study, Executive Summary, (February 2005) 22 Independent Review to assess whether there are Economic Partial Solutions to Problems caused by Intermittent Storm Discharges to the Thames Tideway Phase 1, (Jacobs Babtie, February 2006) 23 Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report Page 49

55 5 Achieving Compliance Rotherhithe route, which cuts across the Rotherhithe Peninsular reducing the tunnel length by 1.8km by avoiding a segment following a major bend in the river. The tunnel system otherwise intercepts CSO discharges from the Acton Storm Relief Sewer at the upstream end by connection tunnel to the main tunnel at Hammersmith, and connects to the overflow shaft at Beckton at the downstream end, exactly as for the River Thames route. Abbey Mills route, which is different from the other routes by connecting the Thames Tunnel to the head of the Lee Tunnel at Abbey Mills. The upstream tunnel system would stay the same as the River Thames or Rotherhithe tunnel alignments from the interception of Acton Storm Relief Sewer as far as Rotherhithe, but would then veer northeast to Abbey Mills. The Thames Tunnel length would reduce by 9.1km. CSOs to be intercepted downstream of Rotherhithe would connect back to the main tunnel by connection tunnels except for Charlton Storm Relief CSO which would be addressed by local modifications and an alternative means of control. Details of the approach to determining the tunnel alignments and the recommendations arising from the analysis of the three routes described above can be found in the Preferred Scheme Report, Summer This report shows how the outline design of the Thames Tunnel scheme was advanced in parallel with the site selection exercise and how various tunnelling drive strategies were evaluated in relation to each of these three routes. The design of the tunnel was originally based on providing the necessary storage capacity to capture overflows from identified CSOs, so as to limit the operation of the CSOs and meeting the derived dissolved oxygen criteria. This criterion was used to arrive at the full-length 7.2m diameter tunnel solution. Performance was assessed to be proportionally less with the reduced storage provided by an alternative 6m diameter full tunnel. Modelling of the sewer sub-catchments in the Beckton and Crossness catchments continued to update and calibrate the hydraulic models with information gained from existing and additional flow measurement monitors at every CSO. Improved assessments have been made of the spill frequencies and volumes discharged for a current typical year. The modelling also checked the projections for future years (2021, 2050) of the spill frequencies and discharge volumes when taking into account population increases, the do nothing approach and the effect of the completion of the Mogden, Beckton, Crossness, Riverside and Long Reach STW Upgrades and Lee Tunnel schemes. The modelling shows that, although discharge volumes reduce markedly, spill frequencies are not reduced with the commissioning of the STW Upgrades and Lee Tunnel schemes. Only the full-length storage tunnel is effective in reducing spills to a level deemed necessary by experts and regulators to meet compliance with the UWWTD. Page 50

56 5 Achieving Compliance Figure 5.1 London Tideway Tunnels: Alignment Options Page 51

57 5 Achieving Compliance The hydraulic model output in Table 5.1 indicates that the Abbey Mills option will capture about 93% of the reference typical year overflow volume and the River Thames and Rotherhithe options will capture about 97% of the total reference condition overflow volume. All options reduce the number of spills at connected CSOs to four or less. All options allow very infrequent residual spills to the River Lee at Abbey Mills to protect the tunnel system from high water levels during extreme rainfall events. The spills at Abbey Mills can be limited by a discharge arrangement that uses the Beckton Pumping Station to pump flow to the inlet works at Beckton STW. This will discharge either through the STW for treatment or to the storm bypass if capacity is not available. Table 5.1 shows the two alternative scenarios for the Abbey Mills route. (Baseline conditions from Table 4.2). Table 5.1 Comparison of overflow volume and number of spills for tunnel route options Lee Tunnel expanded STW population (Baseline conditions) River Thames route (with Abbey Mills spills) Rotherhithe route (with Abbey Mills spills) Abbey Mills route (with Abbey Mills spills) Abbey Mills route (with 12m 3 /s bypass at Beckton STW) Typical year Total spill volume at Abbey Mills (million m 3 ) Total Spill volume at Beckton (million m 3 ) Total spill volume to the rivers Lee and Thames (million m 3 ) Percent CSO Discharge Capture (2006 no improvements) Number of residual spill events from individual connected CSOs % 97% 97% 95% 93% Note: Percent CSO discharge capture (2006, no improvements) based on the proportion of the current estimate of 39,466,300m 3 overflow in a typical year (see Table 4.2) Extensive modelling work and supporting studies have been undertaken into the critical CSO performance for these tunnel options, and the consequence of the residual discharges on the four dissolved oxygen (DO) standards in the River Thames. Each of the tunnel alignments will reduce spill frequency at the unsatisfactory CSOs to no more than four events in the typical year. Several CSOs considered to be satisfactory by the EA following their categorisation process would discharge up to seven times in the typical year but remain as low volume overflows. The low frequency and volumes involved are believed to be consistent with UWWTD requirements and modelling simulations demonstrate compliance with water quality standards. Compliance with the specified dissolved oxygen (DO) standards (as derived for the TTSS and set out above in Table 4.3) in the river is the other measure for comparing performance of the Thames Tunnel alignment options. These DO standards have been adopted as appropriate by the EA as consistent with the aims of the WFD. Compliance is based on modelling of the Tidal Thames with simulation of 154 Compliance Test Procedure (CTP) summer events (as described in Section 4.7.3) that were selected to replicate stress to the river system through large CSO discharges. The results of the DO modelling show that all Thames tunnel options are compliant with all DO standards. Figure 5.2 shows that the DO results are not significantly different between the three options even with different discharge volumes. Page 52

58 5 Achieving Compliance Figure 5.2 Comparison of Dissolved Oxygen Standards Compliance (a) No improvements, (b) STW improvements and Lee Tunnel, (c) River Thames/ Rotherhithe routes and (d) Abbey Mills route (negative figures refer to distances upstream of London Bridge) Threshold 1 (4mg/l, 29 tides): No Improvements, STW Improvements/Lee Alone, River Thames / Rotherhithe and Abbey Mills Routes Threshold 2 (3mg/l, 3 tides): No Improvements, STW Improvements/Lee Alone, River Thames / Rotherhithe and Abbey Mills Routes Threshold 1: 34 breaches allowed Threshold 2: 11 breaches allowed No improvements 120 STW and Lee Alone No improvements 120 STW and Lee Alone Abbey Mills Route 100 River Thames / Rotherhithe Route Abbey Mills Route 100 River Thames / Rotherhithe Route Number of Br each es Number of Breaches Distance from London Bridge km Distance from London Bridge km Thresh old 3 (2mg/l, 1 tide): No Improvements, STW Improvements/Lee Alone, River Thames / Rotherhithe and Abbey Mills Routes Threshold 4 (1.5mg/l,1 tide): No Improvements, STW Improvements/Lee Alone, River Thames / Rotherhithe and Abbey Mills Routes Threshold 3: 7 breaches allowed Threshold 4: 3 breaches allowed No improvements 120 STW and Lee Alone No improvements 120 STW and Lee Alone Abbey Mills Route Abbey Mills Route River Thames / Rotherhithe Route River Thames / Rotherhithe Route Number of Breaches Number of Breaches Distance from London Bridge km Distance from London Bridge km Page 53

59 5 Achieving Compliance Consideration of spill frequencies The UWWTD refers to the adoption of spill frequencies as one of the criteria which Member States could apply when determining how to limit pollution due to storm overflows. However it is not defined further by the European Commission. The UK has adopted spill frequencies only where it has been necessary to manage risk from sewage-borne pathogens such as for CSO discharges to bathing waters or shellfish waters (as designated) 24. Otherwise, spill frequencies are used in combination with the amenity value of watercourses to establish the extent of any screening requirement. As this reach of the Tidal Thames is neither a designated Bathing nor a Shellfish Water, there are no applicable spill frequency limits, the requirement being solely that of UWWTD/UWWTR that discharges should occur only under unusual conditions such as heavy rainfall. Nonetheless, the use of spill frequency helps to give a simple indication of the effectiveness of alternative solutions as a comparator. The preferred solution of the TTSS achieved a spill frequency of some 3 events per annum for a typical year. This spill frequency has been reviewed following information received from other Member States regarding their interpretation of the UWWTD 25, where events of 7 to 10 times per year have been proposed, and is clearly at least as stringent. In developing alternative options to the original TTSS proposal, the spill frequency has been retained as a secondary assessment of comparability after achievement of DO standards. The retention of a low typical year figure means that spills should not be excessively frequent even in wet years, and the Thames Tunnel will also be able to cope with future increased populations. The modelling demonstrates that when including these changes the spill frequencies at any CSO remains within a notional 7 to 10 spills per annum to 2050 and beyond Consideration of tunnel alignment options Key aspects of the three tunnel alignment options are summarised in Table 5.2: Table 5.2 Comparison of tunnel alignments Category River Thames route Rotherhithe route Abbey Mills route Main Tunnel length (km) (7.2m diameter) Number of main shafts (diameters) Rider tunnel lengths (km) (diameters) Total storage volume 1 (million m 3 ) Nr of CSOs directly connected Nr of CSOs otherwise connected or locally addressed 10 (20m to 25m) 8.6 (2.2m to 4.5m) 8 (20m to 25m) 8.6 (2.2m to 4.5m) 5 (20m to 25m) 8.8 (2.2m to 4.5m) Max. number of spill events in a typical year per CSO Includes the Lee Tunnel volume 2 Number of spills from the Category 1 and 2 CSOs in the Beckton and Crossness catchments 24 DETR and Welsh Office: Working Document for Dischargers and Regulators: A Guidance Note, Appendix 8(ii), July EUREAU 1998 Stormwater pollution control in EU Member States ; Contract No B4-3040/96/000173/DI Page 54

60 5 Achieving Compliance As discussed in Section all three tunnel alignment options allow infrequent residual spills to the River Lee at Abbey Mills to protect the tunnel system from high water levels during extreme rainfall events. It is recommended that spills at Abbey Mills are limited by the discharge arrangement which uses the Beckton Pumping Station to pump flow to the STW inlet works and discharge through the STW for treatment, or to the storm bypass if capacity is not available in the STW. The options also include the use of a subsidiary connection from the Beckton Pumping Station to the bypass channel or outfall culverts. Furthermore: All three Thames Tunnel alignment options meet all four of the EA water quality standards. All options deliver low residual CSO spills during the typical year. For the accepted typical year, the number of CSO spills at controlled locations is no more than four at the largest CSO locations and generally less than three at most locations. The three options (with STW capacity improvements, the Lee Tunnel and 2021 conditions) capture between 97% and 98% of the estimated CSO discharge volumes in a typical year rainfall. None of the options demonstrate any benefit over the others regarding water quality, significant CSO event or volume captured. It has been concluded that all three tunnel routes have merits and demerits but the Abbey Mills route has several considerable advantages, and has therefore been selected as the preferred route. The substantial reduction in construction scope associated with the shortest tunnel length and fewest main construction sites, coupled with tunnelling through less difficult ground, results in the Abbey Mills route being the safest and least-cost construction choice with the environmental performance being within the criteria set by the EA for compliance with the requirements of the UWWTD. In cumulative terms, the detailed analysis of the three routes shows that the Abbey Mills route has the least adverse environmental impact, slightly fewer community impacts, fewest property issues and lower planning risks. (This analysis of the three routes can be found in the Preferred Scheme Report, Summer 2010) Details of the cost comparisons of the three tunnel routes are given in Table 5.3. Table 5.3 Cost estimates 1 ( millions) for each tunnel alignment Category River Thames route Rotherhithe route Abbey Mills route Budget estimate 2, 3 4, , , All costs at a December 2008 base date. 2 See Table 5.5 for details of contingency risks and Optimism Bias. 3 Accuracy of cost estimates in the range ± 10% and ± 25%. These costs have been independently reviewed for Ofwat and the UK Government and are considered to be reasonable estimates for the three tunnel alignments with non-construction costs (see Table 5.5), risks and contingencies properly evaluated and included. For all three tunnel alignments the year 2020 is the target completion date. Phasing the construction of the tunnel to be complete at various later dates was considered and shown to be more expensive (due to increases in contractor establishment costs, cost of interim measures and greater management and administration costs). Also a phased delivery schedule would not meet the requirements of the UWWTD until completed and thus would contravene undertakings made to the UK Government to the European Commission. Such contravention will attract the imposition of larger and significant penalties for failure to comply with the UWWTD. 5.4 Alternative approaches to the tunnel options In addition to the tunnel options detailed above further investigative work on alternative non-tunnel based approaches was commissioned to ensure the most cost-effective solution is chosen to comply with the requirements of the UWWTD and meet the environmental objectives of the Thames Tideway as required by Schedule 2 of the UWWTR. These options were examined in the TTSS but it was considered that more detailed analysis was needed on (a) the separation of foul and storm water collection networks and (b) the potential for retrofitting source control and SUDS. Other approaches such as hybrid solutions/partial separation, real time control, screening and Page 55

61 5 Achieving Compliance dispersed storage were re-examined to see how these techniques can contribute, if at all, to the cost-effectiveness of the scheme Sewer Separation As the root cause of the CSO pollution problem is surface water combined with foul sewage flows, separating the two is an obvious potential option for consideration. This could be achieved by either having the existing sewers deal only with surface water and installing a new foul system or by installing a new storm water collection system with foul flows only in the existing sewers. However, there would be significant disruption to nearly all communities in the Beckton and Crossness catchments as a result of construction work in potentially every road in London and the modification of the drainage system for virtually every property 26. The TTSS found that the construction of a separate system for the catchment served by the combined collecting system connected to Beckton and Crossness STWs would only be possible at very high cost, unlikely to be less than 12,000 million, and would entail construction over a very long timescale 27. An example, for instance, is the recent and ongoing disruption caused to Londoners by the Victorian Mains Replacement scheme. Lengths of sewer, split into use and size categories, are recorded in Thames Water s assets database. For the Beckton and Crossness catchments, the data for sewers classified as combined is given in Table 5.4. The TTSS figure of 12bn for sewer separation equated to a cost per metre of sewer length of 2,500 (at a December 2006 cost base), which is realistic given the nature of the area served. Table 5.4 TW asset data: Sewers categorised as combined Size <300 (Length in metres) Size (Length in metres) Size >600 (Length in metres) Total length of combined sewer in metres Beckton catchment Crossness catchment 985, ,000 1,203,000 2,705,000 1,190, , ,000 2,097,000 Total 2,175, ,000 1,696,000 4,801,000 NB: Based on figures and sewer categorisation provided by Thames Water, July Please note that the combined sewer lengths shown above and the catchment areas and percentage of combined sewer by area (as in Sections and 4.1.3) cannot be correlated. It was pertinent to update the TTSS work previously undertaken on sewer separation. Separation of the combined system could be achieved by establishing: a separate storm water collection network, or a separate foul network (involving smaller diameter pipework) with the existing combined network converted to a storm water only carrier, or a collection system for storm water from roads and hardstandings only. These various approaches were investigated in a Sewer Separation Feasibility Study undertaken by MWH; see Appendix D. This study developed hydraulic models, outline designs and cost estimates for five representative sub-catchments as follows (the LTT CSO reference in brackets): Frogmore (Buckhold Road) (LTT CSO ref. CS07B) sub-catchment (454 ha) in the Crossness catchment. This area is 40% - 70% combined and is largely residential with some light industrial premises. 26 TTSS Supplementary Report to Government (2006), Summary Section Regulatory Impact Assessment sewage collection and treatment for London (March 2007) Page 56

62 5 Achieving Compliance South West Storm Relief (LTT CSO ref. CS17X) sub-catchment, eastern branch (1,404 ha), in the Crossness catchment. This area is 40% - 70% combined and is largely residential with some commercial and light industrial premises. Lots Road Pumping Station (LTT CSO ref. CS10X) sub-catchment, southern area (3,276 ha), in the Beckton catchment. This area is 70% - 100% combined and is largely residential with some commercial properties. Regent Street (LTT CSO ref. CS22X) sub-catchment, southern area (1,015 ha), in the Beckton catchment. This area is 70% - 100% combined and is largely residential with significant areas of business and commercial premises. Northumberland Street (LTT CSO ref. CS23X) sub-catchment (93 ha) in the Beckton catchment. This area is 70% - 100% combined and is largely commercial and includes government premises. These sub-catchments were selected as they are located in the west of the Beckton and Crossness catchments where there is a broad spectrum of different land uses and sewer types. Additionally, these areas have fewer cross connections and interactions with the interceptor sewers and hence there is greater potential to find robust separation opportunities to achieve no more than four spills per typical year into the River Thames or its tributaries. The study established that the collection of storm water solely from roads and hardstandings would not achieve the required reduction in discharges to four spills per typical year. Consequently a significant proportion of roof drainage would also need to be captured. The study further established that if the required reduction in spills could be achieved by capturing the drainage from road-facing roofs only (up to 50% of the total roof area) then construction of a separate storm water system would be the appropriate less disruptive solution. However, where more than 50% of roof area drainage needed to be captured to meet the requisite spill target, then construction of a separate foul network would be more appropriate. This is because establishing a separate storm water system in these circumstances would require access to the rear of properties for further roof rainfall collection. A more comprehensive re-arrangement of all household and connection pipework would then be required meaning greater disruption to individual properties than would be necessary to establish a new foul water collection system. Outline design of the new separate foul and storm water systems was carried out to Thames Water specifications. These include minimum velocities for new foul sewers and 1 in 30 year design rainfall capacity for the new storm water networks. This resulted in the need for very large diameter storm water sewers and very large storm water pumping stations to discharge the peak flows into the River Thames at high tides. The pipe and pumping station sizes were much greater than in the existing, albeit under capacity, interceptor sewer networks. This apparent anomaly was investigated and the reason found to be the lack of attenuation in the numerous and discrete new networks. The Thames Tunnel, on the other hand, will have the capability to attenuate and store the inflows over a comparatively large geographical area, easily accommodating the 1 in 30 year storms until nearly full, after which one of the four spills per typical year would occur. Estimating the construction costs of the outline sewer separation designs followed a methodology consisting of: Property/premises costing for property type, land use, density, pipe size, typical depths and lengths, inspection chambers and buildability/difficulty assessments; Local and street level costing for pipe sizes, depths, lengths and manhole numbers; Spine system costing based on the hydraulic modelling including new pumping stations, new outfalls, appropriate construction methods (trenchless technology), existing foul and storm water system modifications and buildability/difficulty assessments. To establish the total costs for each of the study areas the uplift factors, risks and non-construction costs were taken into account. These indicative allowances, which are based on Thames Water s experience on similar types of contract (Victorian Mains Replacement, London Water Ring Main and extensions, West Ham Flood Alleviation Scheme) and are common to all the alternative options costed (tunnels, sewer separation and SUDS), are listed in Table 5.5 below. Page 57

63 5 Achieving Compliance Table 5.5 Allowances for non-construction costs Category Design and Planning consents Allowance applied to construction costs 10% Comments Higher than for Thames Tunnel (8.1%) due to complexity of multiple contracts Preliminaries 25% Higher than for Thames Tunnel (18.7%) due to complexity of multiple contracts Fees 8.5% As Thames Tunnel estimates Insurances 5% As Thames Tunnel estimates Price contingency 10% As Thames Tunnel estimates Risk allowance 35% As Thames Tunnel estimates Management and overhead costs 18% As Thames Tunnel estimates Contingency for external costs 11.5% As Thames Tunnel estimates Based on 80% probability using the industry standard analysis of assumed likelihood and three point cost estimates of each identified risk. As Thames Tunnel estimates Optimism bias 27% From HM Treasury optimism bias calculator for non-standard civil engineering projects (on civil and MEICA construction costs) Enabling works, including utilities diversions and investigations, were taken into account by establishing the degree of complexity of each sub-catchment studied and attributing an uplift bias. Similarly the social impacts and compensation costs were assessed for each sub-catchment. The sewer separation feasibility study took the non-construction costs into account and developed the following cost estimates for each of the study sub-catchments, as given in Table 5.6 below. Table 5.6 Total costs for each sewer separation study area Sub-catchment Area (ha) Total costs ( millions) 1 Frogmore (Buckhold Road) South West Storm Relief 1, Lots Road Pumping Station 3,276 1,494 Regent Street 1,015 1,175 Northumberland Street Sub-totals 6,242 3,588 1 December 2008 cost base This estimate is for the works required to reduce spills at the ten CSOs within the five subcatchments studied to four spills per typical year. The sewer separation proposals were then extrapolated to cover the whole of the Beckton and Crossness catchments served by the Thames Tunnel scheme to reduce spills at the 34 unsatisfactory CSOs. The upscaling exercise estimated the costs of foul sewer separation only (the lower cost separation option) by sub-catchment and then made adjustments for the double counting created by numerous interconnections across subcatchment boundaries. This resulted in a total estimated cost of 14,000 million, with a variance Page 58

64 5 Achieving Compliance range of +50% to -30% due to the estimate being based on a planning level of detail: See Appendix D, Annex 1, Sewer Separation Total Cost. This extrapolated cost estimate of sewer separation is significantly more than the preferred tunnel options. Furthermore such a foul sewer separation arrangement has the following limitations which should be noted: The capacity of the existing combined sewer network to convey storm water flows would only marginally increase with the removal of foul flows. This is due to the large volume of infiltration that enters the existing sewer network from the lost rivers of London. Thus the conversion of the existing combined sewers to convey the surface water flows will only provide marginal relief from sewer flooding. Full separation would not remove all pollution from entering the River Thames due to the build up of hydrocarbons and debris on the roads and pavements that would be flushed into the surface water system during times of rainfall. Misconnections, which occur when errors in domestic plumbing introduce connections between systems, will often mean a system will never be completely separate and there would always be the opportunity for foul flows to be in a separate surface water system. The desk-based qualitative study indicated that high negative social impacts could be expected during the construction of separate foul sewer systems in London. High levels of transport disruption could be anticipated with potential financial impacts as a consequence of the disruption. Social and economic impacts identified also included loss of amenity due to access limitation of parks, public and tourist facilities and attractions. In addition there is a limit to how much construction could be carried out in any given year both in terms of resource to carry out the work and also an acceptable level of funding from water bills. The annual spend for the Victorian water mains replacement project is approximately 200 million and if this spend rate were to be doubled the sewer separation project would still be estimated to take some 35 years to complete Hybrid solutions/partial separation Hybrid solutions which separate substantial volumes of surface water runoff from the combined sewer system, while not requiring the construction of new storm water sewers to serve every individual property, have been successfully applied in moderate to large size communities. Such solutions have therefore been included for consideration in this report. 28 A project at Evanston in the USA incorporated a means of limiting the inflows to existing road gullies and the provision of a new parallel surface water system to intercept the excess surface water runoff from the highway. A similar solution could be practical in the fully combined boroughs, i.e., those where there are no localised surface water or highway drainage systems. This could achieve a reduction in impermeable area draining to the existing system estimated to be around 15%, but this is likely to be at a significant construction cost. The option to solely provide new highway drainage was considered as part of the Sewer Separation Feasibility Study and found not to achieve the target CSO spill frequencies. Modelling of the effect of reducing the contributing areas in such a manner has also been carried out as part of the investigation into the feasibility of sustainable drainage systems (SUDS). This has shown that spill volume would be reduced if the impermeable area draining to the existing sewers could be reduced evenly across the catchment by 50%, but 18 CSOs would still discharge more frequently than ten times during a typical year. Consequently, a reduction of impermeable area, achieved through partial separation, would yield correspondingly less benefits Real time control Real time control (RTC) systems aim to maximise the use of available capacity in the sewer system. Thames Water operates the current networks to maximise the flows to the Beckton and Crossness STWs and by managing the operation of the pumping stations to fully utilise the 28 Binnie Black and Veatch, Thames Tideway Strategy, SUDS Study (2002), Para 2.7 Page 59

65 5 Achieving Compliance available storage in the system and limit possible sewer flooding. Consideration of extending RTC is not an option due to there being insufficient available storage capacity within the existing system Screening Provision of screening to CSO outfalls would serve to capture sewage derived litter and meet the aesthetic need. However, this is not considered as a complete solution since pathogens are carried in suspension and will not be reduced through screening. Frequency of overflow spills would be unaffected and water quality improved only marginally. Consequently, screening alone does not meet the need. Furthermore, provision of screening would require additional land, storage facilities, access for maintenance and cause potential adverse impacts such as odour. Construction of screens at a number of CSOs is not feasible. These practical difficulties were considered as insurmountable (at realistic cost) by the TTSS and screening individual CSOs was discounted. That conclusion remains valid Dispersed storage units Providing storage in a dispersed manner throughout the sewerage network has the advantage of staged implementation, providing some early targeted benefits. As a complete substitution for the tunnel, however, this is outweighed by a longer overall delivery timescale, considerably more disruption and greater cost. The operating regime of this option would also require implementation of RTC as described above. Compared to the tunnel options, a larger total of fragmented storage would be necessary to cater for the spatial distribution of rainfall and the response times of the system. A volume of approximately 2,914,500m 3 would be required for dispersed storage, nearly double the combined volume provided by the tunnel system options of 1,500,000m 3. This figure is derived from the sum of the overflow volumes for the worst case storm occurring in the typical year, or where this is zero, the spill volume for each CSO caused by the design one-year, 120-minute event, as in Table 5.7. Thus the overall cost of providing individual storage units is much higher than for the tunnel options. Furthermore, the implication of a dispersed and therefore fragmented solution is that it is inefficient, inflexible and a cause of disruption over a potential delivery period in excess of 30 years 29. Table 5.7 Summary of CSO discharge volume (m 3 ) for December event of the typical year during the 1-year 120m-min storm event for the expanded STWs and the 2021 population Description 1 Targeted for control December event of typical year 1-yr 120-min 4 Abbey Mills PS F Yes 641, ,000 3 Abbey Mills PS A 2 Yes 235, ,300 Acton SR Yes 45,000 21,000 Brixton SR Yes 29,100 32,200 Charlton SR Yes Church Street Yes - - Clapham SR Yes - 7,000 Deptford SR Yes 155, ,500 Earl PS Yes 88,200 51,900 Essex Street Yes - 1,400 Falconbrook PS Yes 75,800 66, Regulatory Impact Assessment (March 2007), Para 4.9 Page 60

66 5 Achieving Compliance Description 1 Targeted for control December event of typical year 1-yr 120-min 4 Fleet Main (Blackfriars Bridge) Yes 61,600 98,700 Frogmore SR - Bell Lane Creek Yes 1,500 3,100 Frogmore SR - Buckhold Road Yes 4,200 13,300 Greenwich PS Yes 538, ,100 Grosvenor Ditch Yes Hammersmith PS Yes 286, ,300 Heathwall PS Yes 95,600 58,400 Holloway SR Yes 48,500 31,000 Horseferry Rd No - 1,500 Iron Gate No Isle of Dogs PS (Foul Only) No - 4,200 Jews Row - Falconbrook SR Yes - - Jews Row - Wandle Valley SR Yes - 1,900 King's Scholars' Pond SR Yes London Bridge No - 3,900 Lots Road PS Yes 133,900 82,300 Norfolk Street Yes - - North East SR Yes 89,400 99,400 North West SR Yes - 7,100 Northumberland Street Yes - 13,000 Putney Bridge Yes 4,900 8,500 Queen Street Yes - - Ranelagh Yes 32,100 38,500 Regent Street Yes - 6,100 Savoy Street Yes 7,300 8,900 Shad Thames PS Yes 3,400 30,800 Smith Street Main Line Yes Smith Street SR Yes - - South West SR Yes 27,300 45,100 Stamford Brook SR Yes - 1,000 West Putney SR Yes 3,900 3,600 Western PS Yes 270,000 96,100 Wick Lane (separate project) Some Category 3 and 4 CSOs not targeted for control (Battle Bridge, Beer Lane, Bell Wharfe, Canning Town, Cole Stairs, Henley Road, LL1 Brook Green, Nightingale Lane, Pauls Pier, Ratcliffe and Wood Street) are omitted from the list as not discharging. 2 Model configuration splits Abbey Mills outfall to two connected discharge points. Discharge predominantly from Station A but can also receive flows from Station F. Page 61

67 5 Achieving Compliance 3 The difference in estimated overflow volume between the December event and design storm series is primarily due to the longer duration of the December event rainfall and subsequent longer duration of CSO overflows. 4 Numbers reported from the hydraulic modelling of December Sustainable drainage systems (SUDS) It had been concluded as part of the TTSS that, because London s catchments are densely urbanised, widespread retrofitting of SUDS techniques would be disruptive, costly and technically difficult as insufficient land is available. Due to system constraints, open storage features would not hold clean rainwater but combined storm sewage. The few installations of this type that do exist are already subject to public complaints. To prevent this would entail a large degree of sewer separation being carried out in conjunction with the installation of attenuation tanks. Implementing SUDS via redevelopment would take decades to have a significant impact on CSO discharges. The Thames Tunnel is being designed to significantly reduce the spill flows from CSOs and pumping stations into the River Thames. The planned intervention strategy to transfer the flow into the tunnel has, in many cases, resulted in the need for costly diversion structures. As discussed above, in some instances the volumes and magnitudes of the spilled flow are relatively small and this has raised the question as to whether other options could be viable. For example, the installation of sustainable drainage systems could see a potential benefit in the reduction of the spilled flow, and hence in a reduced cost of, or entire elimination of, some diversion or overflow structures. This cost saving would need to be balanced against the cost and practicability of the implementation of SUDS systems within urbanised areas. The latter not only include the selection and design costs, and the capital and construction costs, but also the social, economic and environmental costs. Impacts associated with the acceptance of SUDS and their implementation must be agreed with all stakeholders, particularly the public. Pennine Water Group was therefore commissioned to reassess the practicality of partial SUDS solutions. This project sought to address the potential to influence the performance of the storm water system, by reducing the frequency, volumes and flow rates of overflow at certain CSOs by use of source control and other SUDS techniques within the catchment. The study examined the performance and cost benefit potential associated with the application of source control and SUDS within three suitable sub-catchments (the LTT CSO reference in brackets), all in the Crossness catchment, namely: West Putney (LTT CSO ref. CS05X) sub-catchment (425ha), an urban area mainly residential with significant parkland and open spaces; Putney Bridge (LTT CSO ref. CS06X) sub-catchment (142ha), an inner urban area, mainly residential, with some institutional and commercial premises; and Frogmore (Buckhold Road) sub-catchment (LTT CSO ref. CS07B) (454ha), an urban area mainly residential with parkland, open spaces and significant light commercial premises in the lower north eastern corner. The report on potential source control and SUDS applications (see Appendix E) evaluated the implementation of SUDS on these three sub-catchments. Although all are at the upstream end of the Crossness catchment, these sub-catchments were chosen on the basis of the likelihood of a SUDS solution being feasible in these areas and also the degree of independence of the sewer system from that serving other sub-catchments. The latter means that it is possible to assess the benefits of SUDS within one sub-catchment by relating these to the performance of an individual CSO. The report provides an assessment of the potential of, and options for, retrofitting storm water disconnection measures in the three selected sub-catchments. The objective of the study was to determine whether or not there was scope for retrofitting storm water disconnection that would be effective in reducing the frequency of spills from the CSOs in the Crossness catchment, in order to achieve compliance with the UWWTD and enhance the water quality in the River Thames. The overall potential for reducing the corresponding CSO discharges was initially assessed, using the InfoWorksCS Crossness catchment sewerage simulation model, by uniformly reducing the modelled impermeable area by 25% and 50% respectively. It was found that reductions in contributing impervious areas of the order of 50% could result in significant improvements to the Page 62

68 5 Achieving Compliance CSO spill behaviour; for example, the number of spills from the Frogmore (Buckhold Rd) CSO was reduced from 29 to 10 per typical year. Improvements were also found for the use of SUDS systems that removed or attenuated the initial few millimetres of runoff from contributing surfaces. Estimation of a realistic potential reduction in contributing impervious areas, as opposed to the theoretical percentage reductions, was first made by considering the applicability of a retrofit SUDS technique by assessing physical, mapped characteristics of the underlying surface and local topography using GIS Multimap (mapping software). A method has been developed to automatically select areas of land that are suitable for each potential retrofit option. From this, an initial set of disconnection options was generated and found by modelling to be potentially viable for reducing CSO spills. The next stage was to investigate a number of subareas in detail. In these areas the retrofit options were designed at least to a feasibility stage so that these could be priced. The detailed investigation and development of revised potential options resulted in the view that it could be feasible to disconnect approximately 37% of the existing impermeable area from the existing sewer system. This is less than the initial estimate calculated by the automated method described above and the corresponding impact on the CSOs performance has not been modelled. However, based on the analysis of the effects of the 50% reductions in impermeable area, the spill event frequency will increase, ie, the number of predicted spills from the Frogmore (Buckhold Rd) CSO would be more than ten per typical year. This analysis indicated that the retrofit options applied would not provide sufficient reduction to achieve compliance with the UWWTD. A review of the potential intangible and other costs and benefits in non-monetary terms identified, where these benefits may be significant and add value to the application of retrofit storm water disconnections. This is particularly significant for mitigating and adapting to future climate change, for which SUDS are generally much more resilient than piped drainage systems. However the study areas selected, despite being among the most favourable sub-catchments for retrofit SUDS, did not have sufficient areas or scope available to use this flexibility to cope with future climate change effects and population growth. Estimated construction costs, at the December 2008 cost base, are given in Table 5.8. Table 5.8 Total costs for each source control/suds study area Sub-catchment Area (ha) Construction costs ( millions) Total costs 1 ( millions) West Putney Putney Bridge Frogmore (Buckhold Road) Totals 1, Indicative allowances, uplift factors, risks and non-construction costs as in Table 5.5 N.B.: The total area of the Beckton and Crossness catchments combined is 55,600 ha In parallel with the feasibility investigation, the whole life costs for the suggested disconnection options were determined based on the methodology and database originally developed by UKWIR/WERF in This showed the low operating costs of the SUDS installations. If the scheme cost for these three areas of 241m is simply extrapolated across the whole of the Beckton and Crossness catchments a cost of around 13,000 million is indicated (with a planning level variance of +50% to -30%). However this simple calculation is unreliable due to the complex nature of the sewer networks, the variable impermeabilities across the catchments and the numerous interconnections between sub-catchments. This extrapolated figure is likely to be an underestimate given the increasing difficulty of implementing SUDS towards the eastern ends of the Beckton and Crossness catchments. Furthermore, the implementation period for installing SUDS in these catchments would be many decades. Overall, it is concluded that, while it may be technically feasible to retrofit storm water disconnection using SUDS in some catchments, there are significant logistical, legal and regulatory impediments to their utilisation. Furthermore, the implementation of the SUDS retrofit option does not achieve compliance with the UWWTD and only partially meets the required environmental benefits. Consequently the SUDS option is not a cost-effective solution which meets the need. Page 63

69 5 Achieving Compliance Summary of alternative options and estimated costs None of the alternative options to the tunnel options are considered to constitute a suitable or cost effective alternative approach to the Thames Tunnel for the reasons set out above and summarised in Table 5.9 below. Table 5.9 Advantages and Disadvantages of options Option Advantages Disadvantages Full-length storage tunnel (Abbey Mills route) Full-length storage tunnel (Rotherhithe route) Full-length storage tunnel (River Thames route) Separation using new storm water sewers or new foul sewers (with storm water in existing combined network) Sustainable drainage systems (SUDS) Complies with UWWTD and environmental objectives Cheapest option Least disruption to businesses and residents Is capable of being delivered by target date of 2020 Use of river for materials transportation where practicable and economic Least amount of land needed Adaptable and flexible Complies with UWWTD and environmental objectives Is capable of being delivered by target date of 2020 Complies with UWWTD and environmental objectives Least spills (2) of tunnel options Is capable of being delivered by target date of 2020 Sewer flooding relief can be incorporated Desirable and mandatory for new build developments, but difficult to retrofit Enhances the environment Can manage surface water flooding Low whole life operating costs Low carbon footprint More spills (4) and greater volume discharged in typical year than other tunnel options High operating costs High carbon footprint High operating costs High carbon footprint High operating costs High carbon footprint Cannot comply with UWWTD or environmental objectives Very disruptive to business, residents and transportation Not possible to complete by 2020, with over 35 year implementation period Very expensive High whole life operating costs, affected by need for estimated 48 or more new pumping stations High carbon footprint Cannot comply with UWWTD or environmental objectives Very disruptive to business, residents and transportation Not possible to complete by 2020, with over 30 year implementation period Very expensive Complex logistical processes Page 64

70 5 Achieving Compliance Option Advantages Disadvantages for planning permission Legal and regulatory obstacles to implementation Combining the advantages and disadvantages with the cost estimates produced for each alternative approach is set out in Table Table 5.10 Summary of main options and estimated costs Option Response to need Estimated costs 1 ( millions) Comments Full-length storage tunnel (Abbey Mills route) Complies with UWWTD and environmental objectives 3,588 (accuracy range +/-10% to +/-25%) Most cost effective scheme. Spills at CSOs limited to 4 events in a typical year. Least disruption to residents, businesses and transportation. Is capable of being delivered by target date of Full-length storage tunnel (Rotherhithe route) Complies with UWWTD and environmental objectives 4,310 (accuracy range +/-10% to +/-25%) Spills at CSOs limited to 2 events in a typical year. Is capable of being delivered by target date of Full-length storage tunnel (River Thames route) Complies with UWWTD and environmental objectives 4,336 (accuracy range +/-10% to +/-25%) Spills at CSOs limited to 2 events in a typical year. Is capable of being delivered by target date of Separation using new storm water sewers or new foul sewers (with storm water in existing combined network) New sewerage designed for 1 in 30 storms. Will alleviate sewer flooding. Would eventually comply with UWWT and environmental objectives 14,000 (variance +50% to -30%) Cost significantly greater than tunnel option. Significant disruption to residents, businesses and transportation. Prolonged timescale for completion; e.g. 30 years at 400m spend per annum, so not capable of complying with UWWTD and environmental objectives by Sustainable drainage systems (SUDS) In certain catchments a 37% reduction in impermeable area potentially contributing to CSO discharges could be achieved. 13,000 (variance +50% to -30%) High cost and time to implement. Reduction in impermeable area still results in more than ten* CSO spills in a typical year. Not able to achieve compliance with requirements of UWWTD. Not applicable to inner city catchments and many practical limitations to implementation. 1 Cost base date of December * Maximum spill frequency allowed by other EU Member States regarding their interpretation of the requirements of the UWWTD. Page 65

71 5 Achieving Compliance Retrofit SUDS and sewer separation are considered not to be practical solutions for the Beckton and Crossness catchments to achieve compliance with the requirements of the UWWTD and the adopted TTSS environmental objectives. Both the sewer separation and SUDS studies were based on outline designs of sample areas considered most favourable to the respective alternative approaches and the subsequent extrapolations are considered to be biased in favour of those options. The effect of relaxing the spill events allowed from the 4 spills per typical year to, say, 10 spills would have only minor impacts on cost reduction and very little impact on reducing the time scales to implement. With respect to hybrid approaches, and apart from the practical difficulty of looking at an infinite number of possibilities, the very high comparative cost of all these alternative options to the tunnel approach and the prolonged timescales to implement meant that no combination of sewer separation, SUDS or additional surface storage could be cost effective or meet the requirement to be completed by year The UWWTD, Schedule 2, does provide that The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing excessive costs. Table 5.10 shows that the full-length storage tunnel approach, particularly the Abbey Mills route, is the cheapest and the most cost effective solution which meets the requirements of the UWWTD and the environmental objectives. 5.5 Further considerations Project flexibility A significant advantage of a single tunnel solution is that every connected CSO is potentially able to utilise the storage capacity provided by the whole tunnel. The total storage volume required is consequently less than the equivalent localised storage that would be necessary for each CSO to be independently protected to the same standard. This is due to the tendency of high intensity storms to be relatively localised; it is unlikely that an intense storm will occur simultaneously in each of the CSO catchment areas. By nature, the assessment of climate change includes inherent uncertainties, and the objective is to ensure that the final scheme is adaptable in light of this uncertainty. The evidence gathered and analysed indicates that the Thames Tunnel offers significantly more flexibility in an uncertain environment, compared to the baseline conditions. However, by the 2080s, even with the Thames Tunnel, there could be non-compliance with the adopted TTSS DO standards. This is due to a combination of sea level change, temperature increases and rainfall changes, although it appears that temperatures could be the dominant factor. Thus the projected number of breaches of the adopted TTSS DO standards by the 2080s with the Thames Tunnel in place is predicted to approach that of the existing situation. This is, however, a reflection of deteriorating background water quality due to higher river water temperatures, and it would take further improvements in the treatment at the major STWs for the impact on DO objective compliance to be reversed. This situation, which will also occur elsewhere, needs to be addressed in future AMPs and not as part of a CSO solution assessment. Without the Thames Tunnel the situation would be considerably worse and in any event the facility is needed to achieve existing UWWTD requirements. Although designed to cater for the excess flows currently discharging to the river, the Thames Tunnel will ultimately form part of the conveyance system. It will therefore become an extension to Bazalgette s network. By forming part of the conveyance system, the Thames Tunnel will be able to help prevent any potential for future dry weather spills to the River Thames and it therefore offers the flexibility to mitigate the effect of long-term population growth. Once the tunnel is in place, there will be opportunities to install real time control (RTC) systems to optimise the use of capacity within the extended sewer system, as has been done elsewhere in Europe. In addition, as part of the conveyance system, the Thames Tunnel may provide opportunities to close off sections of the existing network for maintenance, by enabling the flows to be diverted into the tunnel. Page 66

72 5 Achieving Compliance System benefits Flooding relief projects have been constructed in past AMP cycles and more are planned for AMP5. To date, the assessment of the Thames Tunnel scheme has not included the impact of potential scheme benefits, such as the incorporation of sewer flooding alleviation schemes or other capital improvements to the interceptor network. Two known large proposed flood alleviation projects which could interact with the Thames Tunnels are the solutions proposed in the Counters Creek Flood Alleviation Study in the Beckton catchment, and the Lambeth/Southwark Flood Alleviation Study in the Crossness catchment. The Counters Creek proposal is to provide new storm relief sewers which are planned to discharge directly into the River Thames. The project identified in the Lambeth/Southwark study may interact with the Deptford Storm Relief, where the new relief sewer would discharge. Large projects such as these are future critical components of the collection system and as such will be co-ordinated with the CSO programme, as both projects can be complementary in reducing facilities needed and programme costs. By co-ordinating the Thames Tunnel and sewer flooding relief projects a better overall system would be delivered, by for example, discharging Counters Creek storm water sewage overflows directly to the Thames Tunnel. The addition of the Thames Tunnel provides a strategic benefit to the sewer network in the form of additional storage capacity and many sewer flooding alleviation projects could potentially be connected to the Thames Tunnel as part of the solution. However, the connection of future sewer flooding alleviation projects does not mean that the tunnel would require more storage capacity to deal with these future possibilities. The volume of run-off generated by any particular rainfall event will be the same and therefore the volume of the tunnel will not need to be increased; neither will the frequency of residual overflows increase. An assessment into the interaction between such schemes and the Thames Tunnel will be made once the outcomes of AMP5 flooding studies become available. As designs progress and other programmes are developed, the schemes may be adapted to maximise the benefits which can be provided by the Thames Tunnel. A study has been carried out to investigate the potential for alleviation of sewer flooding to properties in the Battersea Bridge Road and Falcon Road areas within the Crossness catchment. These areas experience basement flooding and are believed to be typical of many other areas within London. The study found that because the area was low lying and centrally located within a large catchment, there was a hydraulic balancing effect across the surrounding area such that the benefit that could be gained by the elimination of significant local road runoff was minimal. Uprating a nearby storm relief pumping station, Falconbrook PS, was reviewed but this too was found to be ineffective as increasing the rate of pumping simply pulled the flow through the area more quickly. Other than providing yet more valves to prevent backflow into properties, the only solution found to be theoretically viable to reduce levels in storm conditions was to provide a number of new local flood relief sewers, fed either to an extremely large and impractical storage tank or to a new pumping station located adjacent to the Falconbrook PS. This example is felt to be typical of other locations along the river, where the basic difficulty in identifying flood alleviation solutions is the lack of capacity of the interceptor sewer system itself. It is therefore believed that a comprehensive review of flooding properties would find that there could be opportunities for other projects to alleviate sewer flooding, were it possible for overflows to be diverted to the tunnel Water quality benefits The water quality modelling carried out to date indicates that while the baseline conditions (Mogden, Beckton, Crossness, Riverside and Long Reach STW upgrades and Lee Tunnel) alone do result in an improvement of DO in the Tideway, this is not sufficient to meet the adopted TTSS DO requirements. This is largely because, with the baseline conditions in place, a significant number of overflows to the Tideway remain (34 CSOs discharging over 50 times a year on average) which are predicted to have a significant effect on DO in the Tideway. As a result, these overflows need to be intercepted or reduced to achieve water quality that would protect ecosystems from DO sags. Page 67

73 5 Achieving Compliance The provision of the Thames Tunnel, in combination with the baseline conditions (STW upgrades and Lee Tunnel), will result in compliance with all of the interim water quality thresholds up to As the DO standards have been developed to protect ecosystems in the Tideway, it is possible to infer from the evidence that the full Thames Tunnel solution would adequately protect the ecosystems of the Thames Tideway from intermittent discharges, and has the flexibility to account for population growth and climate change Ecological benefits As discussed in Section 4.8, it has been reasoned that fish are the most sensitive indicator of ecological quality. The benefits to fish arising from the provision of the Thames Tunnel can largely be attributed to the flexibility of the scheme in relation to maintaining standards which would otherwise be compromised by the effects of climate change. The Thames Tideway is not only an important habitat for a wide variety of fish species, but is also an important breeding ground for several species, especially sole. The sole nursery near Woolwich is probably the most economically significant in England and Wales. The benefit of appropriate management of water quality in the Thames is such to encourage the further improvement of the habitat for fish and especially to permit the upstream migration of species, most notably salmon, but including other species such as bass and flounder which use the tidal Thames as an important part of their lifecycle Aesthetic benefits The following Table 5.11 compare the overflow volumes and number of overflow events which allow a proportional comparison to be made of the improvements attributable to the Lee Tunnel and Thames Tunnel. The data for the existing network shown relates to a 2021 population to be consistent with the population basis used for the baseline conditions (see also Tables 4.2 and 5.1). Table 5.11 Percentage reduction in annual spill volumes and frequencies Existing network no improvements 1 Existing network expanded STWs 2021 population 1 Lee Tunnel added 2 (Baseline conditions) Thames Tunnel added 2 Total annual CSO spill volume (m 3 ) 39, 466,300 24,391,600 17,847,600 2,600,000 Percentage reduction in annual spill volume compared to existing situation Percentage reduction in spill volume compared to baseline conditions 38% 55% 93% Total number of individual CSO spills in a typical year Percentage reduction in annual number of CSO spills compared to existing situation 85% 2% 9% 89% Percentage reduction in spill events 88% compared to baseline conditions 1 The values reported are from the catchment modelling of December The Thames Tunnel Baseline Conditions (Lee Tunnel) and the Thames Tunnel (Abbey Mills route with a 12m 3 /s bypass at Beckton STW) values are based on the December 2009 model. 3 This value is the sum for all CSOs, including simultaneous discharges at individual CSOs. 4 Expanding Beckton STW reduces the frequency of discharge from Abbey Mills; however the frequency of discharge from the remaining CSOs actually increases as a result of higher dry weather flow due to growth Page 68

74 5 Achieving Compliance These results have been used to interpolate the estimates of sewage litter discharged into the tideway at the baseline conditions and subsequently with the provision of the Thames Tunnel. The TTSS estimated the quantity of sewage litter discharged from CSOs into the Tideway to be approximately 10,000 tonnes 30, based on limited information of litter quantities. The discharges from Abbey Mills are screened and therefore the quantity of sewage generated litter into the Tideway (via the River Lee) from this source was assumed to be small. Thus the reduction in sewage litter is interpolated on the basis of CSO overflow volumes from the Beckton and Crossness catchments into the Tideway. Hence Table 5.12 indicates that the reduction in the amount of sewage litter attributable to the Lee Tunnel and Mogden, Beckton, Crossness, Riverside and Long Reach STW upgrades (baseline conditions) is small compared to that achieved by the provision of the Thames Tunnel. Table 5.12 Estimated quantities of sewage litter entering the Thames Tideway (tonnes) Existing network no improvements Existing network + expanded STWs population With Lee Tunnel added (Baseline conditions) Thames Tunnel (Abbey Mills route + 12m 3 /s bypass) added Total annual discharge from Abbey Mills (m 3 ) Estimated sewage litter in the Tideway (tonnes) associated with Abbey Mills discharges assuming 80% efficiency for screening plant Total annual CSO spill volume (m 3 ) excluding Abbey Mills discharges Estimated sewage litter in the Tideway (tonnes) associated with CSO overflows (based on reduction in spill volume) 18,906,800 6,495, , , ,413,700 17,847,600 17,847,600 2,600,000 8,435 7,375 7, Estimated total sewage litter in the Tideway (tonnes) associated with CSO overflows and Abbey Mills 10, , Note: Abbey Mills CSO flows screened to 6mm. Assumed Abbey Mills screens would achieve approximately 80% capture. 1 The Thames Tunnel will capture all first flush flows not retained in the existing interceptor sewers and the residual overflows, when the tunnel is full, will only occur 4 times in an average year. This crude figure of 926 tonnes litter per annum is considered to be an over-estimate Human health benefits Although recreational users of the Tideway have a relatively low rate of gastric infection compared to the general population for reasons discussed in Section 4.9, incidence of infection does appear to be elevated in the period following a CSO spill event. Based on the predicted 96% reduction in spill events resulting from construction of both the Lee and Thames tunnels, construction of the Thames Tunnel can be expected to have a substantial positive impact on reducing health risks to recreational users. The large reduction in CSO spill events achieved by the Thames Tunnel, together with the hygiene and health and safety procedures in place at recreational clubs, should result in the already low rate of infections compared to the general population decreasing further. 30 TTSS, Objectives Working Group Report, Vol 1 (Section 6.3.1) (February 2005) Page 69

75 5 Achieving Compliance Climate Change The tunnel design is based on an analysis of the rainfall between the years 1970 and 2003, from which a typical year was generated. This simulated for modelling purposes the rainfall patterns, storm intensities and durations. The rainfall patterns for the seven years 2003 to 2009 were also analysed and when added to the 34 year storm series it was found that the typical year rainfall pattern did not change in terms of storm intensities and durations and therefore remained valid. This typical year rainfall data was used in hydraulic models of the Beckton and Crossness catchments to simulate the flows in these sewer networks under varying storm conditions. Thus the typical annual volumes of discharge and numbers of spill events were calculated for each of the 57 CSOs identified in these catchments discharging into the River Thames and River Lee between West London and Beckton STW. The Environment Agency (EA) used this data to identify 36 of these 57 CSOs as unsatisfactory and requiring control to deal with the discharges. These hydraulic models were calibrated using readings from rain gauges and actual sewer measurements and relating these to impermeable areas, population data from local authorities and the National Office of Statistics, infiltration assessments and other factors. These provided the basis for the design of the Thames Tunnel. The tunnel was originally sized, in length and diameter, to achieve a storage volume of about 1.6 million cubic metres. This capacity was shown to be necessary by the sewer hydraulic modelling to reduce spill frequencies from the 36 unsatisfactory CSOs to meet a guideline target of an average of three events per annum. Latest official projections indicate that the climate of the UK will continue to change over time in several ways, particularly in changes in rainfall volume and higher air temperatures in summer which will cause river water temperatures to be higher. The sensitivity of the tunnel scheme to such changes has been assessed to ensure that the design is robust, flexible enough to accommodate the projected changes in climate and remains valid and fit-for-purpose. The climate change sensitivity assessment for the project entailed projecting populations and rainfall trends forwards to 2050 from the 2021 basis. Population projections beyond 2050 become increasingly speculative but average rainfall patterns have been projected to 2080 with greater winter and lower summer precipitations. Applying the projected population increases to 2050 and the 2080 rainfall patterns to the hydraulic models indicated that by 2050: (a) the CSO spill volumes will increase, but still with some 94% of the combined sewer overflows captured by the Thames Tunnel, and (b) the CSO spill frequency will rise to 5 events per annum for the 36 controlled CSOs in the Beckton and Crossness catchments. Thus the tunnel will continue to protect the River Thames from harmful CSO discharges consistent with UWWTD requirements. An additional projected consequence of climate change is that the ambient river water temperature will rise over time which will mean that it will contain less dissolved oxygen during the summer months. This will make the river more susceptible to adverse environmental impacts from CSO operation in hot summers if no action is taken. 5.6 Other European schemes to meet UWWTD requirements A study was carried out to examine schemes that other European cities are planning or have implemented to comply with the UWWTD. The report (which is included in full in Appendix B) concentrates on specific schemes and major cities/rivers where CSOs are problematic. An overview of this report is summarised below: A thorough review of relevant publications from journals and conference proceedings was undertaken as well as contacting experts from across Europe in order to provide the most up to date information. The most common approach to resolving CSO issues was identified to be the addition of extra sewer capacity, whether by the construction of detention tanks and/or trunk or interceptor sewers, several implemented through tunnelling. Large storage tunnels in conjunction with one or several other storm water control techniques, such as Real Time Control (RTC), SUDS, new sewers, storage tanks and additional treatment, have been built or are planned by several cities, some details of which are noted below: Helsinki: The solution adopted involved deep tunnels, RTC, sewer separation where cost effective, and extra treatment capacity. Page 70

76 5 Achieving Compliance Naples: The main feature is a 12km long tunnel up to 80 metre depth RTC and a new STW with expanded screening and treatment facilities. Paris: Still in the planning stage but the solution being evaluated involves dispersed storage facilities, four tunnels conveying flows to different STWs, extensions and new treatment processes at the STWs. Stockholm: Large deep tunnel network and extensions to the STW. Vienna: A new 3km long 7m diameter tunnel 30m deep, 7 large drop shafts, RTC, new interceptor sewers, detention tanks (dispersed storage) and extra treatment capacity. More details of the schemes mentioned above are given in Appendix B. Within some cities the use of RTC was used to complement the sewerage design (Barcelona, Lisbon, Marseille, Vienna and Zagreb). Several cities also combined both of these approaches with STW expansion (Copenhagen, Lisbon, Paris and Prague). Two German cities (Berlin and North Rhine-Westphalia) were identified as using SUDS techniques alongside some of the more traditional approaches of new trunk sewers, storage tanks and extra treatment capacity. A summary of the approach to meeting the requirements of the UWWTW to control CSOs by many of the major cities across Europe is included in Table Page 71

77 5 Achieving Compliance Table 5.13 Approaches to UWWTD compliance in relation to CSOs in major cities across the EU Country City name Receiving water bodies City population Metropolitan population Driver for CSO abatement Approach(es) Status Austria Vienna River Danube 1,697,937 2,000,000 National guidelines Belgium (Flanders) Croatia (candidate EU member) RTC, additional detention tunnel/. Tunnel 3km long, 30m deep, 7.0m dia.; 7 shafts Mostly operational Bruxelles Zagreb River Sava 786,000 1,108,000 Water quality; Environment Czech Rep. Prague Rivers Vltava / Elbe 1,233,211 (E) Denmark Copenhagen Various waterways 613,603 1,390,000 Finland Helsinki Gulf of Finland 578,126 1,299,541 France Germany Lyon Marseille Rhône and Saône Rivers Mediterranean / Canal de Marseille - Flooding; Water quality Bathing water quality Bathing water quality; Environment 472,305 4,415,000 WFD; Flooding 839,043 1,500,000 Bathing water quality Paris River Seine 2,188,500 10,000,000 WFD Berlin Rivers Elbe / Spree / Havel 3,425,000 4,275,000 National guidelines (via UWWTD) Hamburg Rivers Elbe / Alster 1,773,218 2,575,000 National guidelines (+ flooding) Rhine-Ruhr area Rivers Ruhr to south, Rhine to west, Lippe to north - 11,800,000 Environment RTC, expand collectors Data collection/ Pre-treatment, expand interceptor, additional detention tanks, expand STW RTC, detention basins, STW expansion, sewer separation RTC, STW, sewer tunnels, separate sewers Part implemented, part planned Operational Operational RTC, data collection, modelling Operational RTC, trunk sewers Operational RTC, new/expanded STW, storage (reservoirs/) RTC (local), SUDS, heightening CSO crests, storm tanks Sewer separation, detention basins, interceptors, STW expansion Trunk sewer, disconnection of impervious areas, infiltration Mostly operational Operational Operational Part operational, part ongoing construction Greece Athens Saronikos Bay 745,514 3,750,000 Flood and pollution control Thessaloniki River Axios 360,000 1,200,000 Flood and pollution control Interceptor sewer diversion/ Planned Additional interceptor Under construction Ireland Italy Rome 2,718,768 3,500,000 (Scheme not developed) Page 72

78 5 Achieving Compliance Country City name Receiving water bodies City population Metropolitan population Driver for CSO abatement Approach(es) Status Milan 1,299,633 3,550,000 (Scheme not developed) Naples Tyrrhenian Sea 966,209 3,075,000 UWWTD Tunnel 12km length up to 80m deep, vortex drop shafts; new STW; RTC; odour control Operational Luxemburg Netherlands Amsterdam 1,041,157 1,499,665 (Information awaited) Rotterdam - 986,557 1,831,496 Portugal Lisbon River Tagus 499,700 2,550,000 Spain Barcelona Rivers Llobregat / Besòs Flood and pollution control Water quality (pollution) 1,615,908 4,250,000 Flood and pollution control Madrid River Manzanares 3,213,271 6,100,000 (RTC, detention tanks and small scale SUDS RTC, on/line storage, interceptor sewer, STW upgrade Operational RTC, detention tanks Operational Part operational, part ongoing construction Sweden Stockholm Lake Malaren, Baltic Sea UK 814,418 1,989,422 Various Tunnels, STW Operational London Thames Tideway 8,278,251 12,300,000 UWWTD Tunnels, 29 km total length, 7.2 internal dia, 40-75m depth; approx 22 shafts; cascade and vortex drops; max 4 spills per annum (typical year); RTC; STW expansion and improvements Liverpool (MEPAS) Belfast River Lagan / Irish Sea Preston River Ribble / Irish Sea Mersey Estuary 477,600 - UWWTD 4.7km of 3.2m pipe. 14 shafts varying between 5 and 18m depth. 268, ,554 UWWTD 9.4km tunnel length, 30-40m depth, main tunnel 4m diameter. 5 shafts inc. 37m dia shaft for TPS. Also upgrade to STW. 131, ,200 UWWTD / Bathing Water Directive 3.5km pipe providing approx 30,000m 3 storage. Up to 26m below ground. Lee Tunnel construction started in 2010, target completion in Thames Tunnel planning ongoing; construction from 2014, target completion Operational Completed 2009 Construction to start Spring 2010, completion 2012 Brighton English Channel 461,181 - UWWTD Tunnel, 5.1 km length, 6m dia, 25-43m depth, vortex drop shafts; RTC Operational since 1998 Page 73

79 5 Achieving Compliance 5.7 Related work Thames Water vision and strategy Taking care of water 31, Thames Water s strategic direction statement covering the next 25 years notes in the section entitled How are we protecting rivers and managing surface waters? that: The last 10 years have seen a substantial improvement in sewage treatment and resulting improvements in water quality. However, further improvements are anticipated as a result of the Water Framework Directive. The Government has given the go-ahead for the Tideway Tunnel. This will capture overflows from London s sewer system following rainfall, helping to protect wildlife and users of the river Drain London The Drain London Forum was created in 2007 as a partnership project, bringing together representatives from organisations with the information and/or responsibility for managing surface water drainage in London. The rationale for the forum stemmed from the fact that no single organisation has overall responsibility for coordinating collaboration between relevant parties, and there is very little collation of information about the location, duration, cause and severity of surface water flooding events or the extent, location and condition of drainage infrastructure. The Drain London Forum was set up to meet six aims: To assess the quality and quantity of information on the location, ownership and capacity of surface water drainage in London To assess the location, frequency, severity and cause of surface water flooding in London, and the impact of surface water flows on the tributary river network To recommend appropriate data management measures (platforms, access, maintenance and compatibility with other systems, eg, hydrological model) To assess the capacity of the surface water drainage network and urban river networks to manage future increases in rainfall and the impact of new development and urban creep To identify current and future flood hot spots and their causes To identify and prioritise solutions and determine responsibility to deliver actions, including areas where sustainable drainage systems or strategic surface water flood management options may be needed. The forum has developed into a committed and effective partnership, which has delivered a scoping study report outlining the data holdings of all its members and recommended strategies for sharing the data among them. The Scoping Study made four key recommendations: That further analysis of surface water flood risk in London should use a hierarchical assessment approach employing a series of tiers of analysis, from strategic to local to identify and prioritise surface water flood risk. This approach avoids the need to intensively model all of London, allows work to progress with the best available information and enables the greatest emphasis to be placed upon the areas at greatest risk. That boroughs facing shared risks should work collaboratively on producing a common Surface Water Management Plan. 31 Taking care of water the next 25 years, (Thames Water, December 2007) Page 74

80 5 Achieving Compliance To create a Spatial Data Infrastructure Portal (SDIP) to provide access to the information required to undertake the tiers of hierarchical analysis. Data owners retain the responsibility for maintaining their own data and will be required to regularly update the SDIP. For all Drain London Forum member organisations to use a single agreed data capture form for flood incidents that balances the need for information with the ability of call centres (for example) to capture the information. Drain London s work preceded the Pitt Review and one of the partnership s earlier successes was to inform the Review, culminating in London being seen to be ahead of some of the proposals now being put forward in the Review recommendations and provisions in the Flood and Water Management Act. Following the publication of the Drain London report, Defra officials contacted the Forum for suggestions on how to deliver surface water management planning in London. In response, Drain London is now proposing to deliver a surface water management strategy for Greater London and establish an organisational framework that will support the implementation of the strategy at the local level. This will enable the Forum to implement the second edition of surface water management plans (SWMPs) across the Capital, in a more efficient, cost-effective and holistic manner than could be achieved if all 33 London authorities were to act independently. Although the Tideway is not included as part of the drainage network as defined by Drain London the Thames Tunnel project has implications on the drainage network which should be addressed by the Surface Water Management Plan in order to develop an integrated approach and maximise the benefits of the scheme. Hence Thames Water will continue to maintain an active role in the Forum. Page 75

81 6 Overview and Conclusions 6 OVERVIEW AND CONCLUSIONS 6.1 Legislation and European Commission Actions The objective of the Urban Waste Water Treatment Directive (UWWTD) (91/271/EEC) is to protect the environment from being adversely affected by disposal of insufficiently treated urban waste water. The Directive requires, among other things, the provision of collection systems for urban waste water, and that the design construction and maintenance of the collection system be undertaken in accordance with best technical knowledge not entailing excessive costs notably regarding the volume and characteristics of urban waste water, prevention of leaks and limitation of pollution of receiving waters due to storm water overflows. The Urban Waste Water Treatment Regulations 1994 (UWWTR) (SI 1994/2841) transpose the UWWTD into UK law. The Water Framework Directive (WFD) (2000/60/EC) aims at maintaining and improving the aquatic environment in the [European] Community. The Directive was transposed into UK law by the Water Environment (Water Framework Directive) (England and Wales) Regulations 2003 (SI 2003/3242). The WFD requires that Member States aim to achieve at least good status for all waters by Infraction proceedings are being pursued by the European Commission against the UK for alleged breach of the UWWTD. On 8 October 2009 the European Commission announced its decision to take the UK to the European Court of Justice because it considers that the waste water collection system in London (and Whitburn, NE England) is being allowed to spill untreated waste water from CSOs too frequently and in excessive quantities. In the event that the UK is found by the European Court of Justice to have failed to fully implement Directives (including UWWTD), then substantial financial penalties may be imposed on the UK. Legislation therefore requires action to be taken in relation to CSO discharges. 6.2 Background and the TTSS London s sewerage system (The Beckton and Crossness sewer catchments) has been progressively extended to accommodate development and population growth since it was designed by Sir Joseph Bazalgette in the 1850s. Despite this, there is now little spare capacity in the sewerage network. Currently, discharges to the Thames Tideway occur more than 50 times per year at the most frequently overflowing CSOs. An estimated total of some 39 million cubic metres of storm sewage enter the river from the Beckton and Crossness sewerage catchments in a typical year. The Thames Tideway Strategic Study (TTSS) was set up to assess the impacts of intermittent discharges of combined storm and foul sewage on the Thames Tideway. It was co-ordinated by a Steering Group chaired by the independent Professor Chris Binnie with representatives from EA, Defra, GLA and Thames Water. The Study reports published in 2005, recommended improvements to both treatment works and collecting systems and established targets for water quality. The findings of the TTSS form the basis of all subsequent work. As part of the TTSS the EA categorised the 57 CSOs relating to the Beckton and Crossness catchments and identified 36 as unsatisfactory and requiring improvement. Of these, 34 discharge directly to the River Thames. There are no significant CSOs in the Beckton and Crossness catchments requiring improvement that are situated west of Acton. Subsequent work, presented in; Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report (December 2006), developed a preferred solution, referred to as Option 1c, to intercept the unsatisfactory CSOs into a full length storage and transfer tunnel to convey flow to treatment at Beckton STW. 6.3 Government response to the TTSS studies in 2007 The then Minister for Climate Change and the Environment, Ian Pearson, reported to Parliament on 22 March 2007 that: Page 76

82 6 Overview and Conclusions These overflows are having an adverse effect on the environmental quality of the Thames. It has been found that the frequent overflows (on average once a week) and the large quantities of untreated discharges are causing: Adverse environmental impacts on fish species; Unacceptable aesthetic issues; and Elevated health risks for recreational users of the Thames. The Minister followed this by writing to Thames Water on 17th April 2007: a full-length storage tunnel with additional secondary treatment at Beckton sewage treatment works is needed for the UK to comply with the requirements of the Urban Waste Water Treatment Directive concerning provision of collecting systems and, in particular, limitation of pollution from storm water overflows. Thames Water developed a scheme based on Option 1c consisting of a full-length storage tunnel intercepting the 36 CSOs in the Beckton and Crossness catchments which discharge into the Rivers Lee and Thames and transferring the flows to Beckton STW (Option 1c). Further work has developed the Lee Tunnel (dealing with 2 CSOs) and three route options for the Thames Tunnel (dealing with 34 CSOs). The route options for the Thames Tunnel are the River Thames route, the Rotherhithe route and the Abbey Mills route. The Thames Tunnel, together with the STW improvement schemes and the Lee Tunnel, will facilitate UK compliance with the requirements of the UWWTD. 6.4 Tunnel options and alternatives Consideration has been given to alternative options involving separation, partial separation, dispersed storage units, screening and SUDS. This analysis concluded the following: The full-length storage tunnel (Abbey Mills route) achieves compliance with the UWWTD and contributes towards achieving the WFD objective of good ecological potential in the Thames Tideway. At an estimated cost of 3,588 million it is the most cost effective scheme, involving the least disruption to residents, businesses and transportation when compared to alternatives. It also has the shortest completion time facilitating the target completion date of Sewer separation using new storm water sewers or new foul sewers (with storm water conveyed by the existing combined network) would alleviate sewer flooding and would eventually comply with UWWTD and environmental objectives. However the estimated cost of 14,000 million is significantly greater than any of the tunnel options. The prolonged timescale for completion would entail significant disruption to residents, businesses and transportation. Sustainable drainage systems (SUDS) in certain western sub-catchments could achieve a 37% reduction in impermeable area drained, reducing CSO discharges and potentially achieving around ten spills in a typical year. However retrofit SUDS are not practicable in inner city sub-catchments and there are many other limitations to implementation. This option is not cost-effective due to the combination of the prolonged time to implement, the high cost at an estimated 13,000 million, and an inability to achieve compliance with the UWWTD. The Thames Tunnel option will address the water quality, ecological, aesthetic and health issues identified as supporting the need for the scheme. The Thames Tunnel will also provide additional benefits for the sewer system, in terms of improving the operation and maintenance of the sewer network, and providing greater robustness and flexibility for the future impacts of population growth and changes in the pattern of rainfall due to climate change. Schemes to alleviate sewer flooding caused by local deficiencies in the sewer network can, in many cases, be connected to the fulllength storage tunnel when it is in operation. 6.5 Conclusion The UWWTD, Annex 1(A), provides that The design, construction and maintenance of collecting systems shall be undertaken in accordance with the best technical knowledge not entailing Page 77

83 6 Overview and Conclusions excessive costs. It is concluded that the full-length storage tunnel approach is the most costeffective solution which meets the requirement of achieving compliance with the UWWTD and the environmental objectives. This view is confirmed by the Environment Secretary, Caroline Spelman, who issued a written ministerial statement on 07 September 2010 giving the coalition government s support for the construction of the tunnel from West London to Beckton and declaring that a Thames Tunnel continues to offer (by far) the lowest cost solution to the problem and I believe Thames Water should continue to press forward with this project working with Ofwat, the Environment Agency and Defra on the regulatory, commercial and planning processes. Page 78

84 Abbreviations ABBREVIATIONS AMP BOD CCW CEC COD CSO CTP Defra DO DWF DWI EA EC EEC EIA EQS ES EU FARL Asset Management Plan Biochemical Oxygen Demand Consumer Council for Water Council of European Communities Chemical Oxygen Demand Combined Sewer Overflow Compliance Testing Procedure Department for Environment Food and Rural Affairs Dissolved Oxygen Dry Weather Flow Drinking Water Inspectorate Environment Agency European Commission European Economic Community Environmental Impact Assessment Environmental Quality Standards Environmental Statement European Union Fawley Aquatic Research Ltd FFD Freshwater Fish Directive (1978) FST GEP GLA HMWB IPC LTI LTT M&E NERA Final Settlement Tank Good Ecological Potential Greater London Authority Heavily Modified Waterbody Infrastructure Planning Commission London Tideway Improvements London Tideway Tunnels Mechanical & Electrical National Economic Research Associates NERCA Natural Environment and Rural Communities Act 2006 NOS Ofwat Northern Outfall Sewer (Office of Water Services), the Water Services Regulation Authority PR09 Periodic Review of Water Price Limits 2009 PS QPE RBMP RIA Pumping Station Quarterly Population Estimates River Basin Management Plan Regulatory Impact Assessment Page 79

85 Abbreviations RQO RTC SDIP River Quality Objective Real Time Control Spatial Data Infrastructure Portal SUDS Sustainable Drainage Systems (as defined by CIRIA 2007) SMP SR STW SWMP TBM TFRM TTAG TTSS TTTT TW UKCIP UKCP UKTAG UK-WIR UPM UWWTD System Master Plan Storm Relief Sewage Treatment Works Surface Water Management Plan Tunnel Boring Machine Tideway Fish Risk Model Thames Tideway Advisory Group Thames Tideway Strategic Study Thames Tunnel Tideway & Treatment Thames Water UK Climate Impacts Programme UK Climate Projection United Kingdom Technical Advisory Group United Kingdom - Water Industry Research Urban Pollution Management Urban Waste Water Treatment Directive UWWTR Urban Waste Water Treatment Regulations 1994 WAG WERF WFD WHO Welsh Assembly Government Water & Environmental Research Foundation Water Framework Directive World Health Organisation WIA Water Industry Act 1991 WRc Water Research centre Page 80

86 Glossary GLOSSARY Term London Tideway Tunnels (LTT) Lee Tunnel London Tideway Improvements (LTI) Thames Tunnel Aesthetic Ammonia Asset Management Plan Background concentration Baseline Biochemical oxygen demand (BOD 5 ) Biodiversity Chemical oxygen demand (COD) Collecting system Combined sewer Description The LTT comprises two separate projects: the Lee Tunnel and the Thames Tunnel. The Lee Tunnel comprises a storage and transfer tunnel from Abbey Mills Pumping Station (PS) to Beckton STW and the interception of the Abbey Mills CSO. The LTI comprise five separate improvement projects at Thames Water s five Tideway sewage treatment works (STWs): Mogden, Beckton, Crossness, Riverside and Long Reach. The Thames Tunnel comprises a full-length storage and transfer tunnel from West London to Beckton STW in East London and the interception of CSOs along the Thames Tideway. The perception (visual appearance, smell, etc) of water quality, not including biological and chemical impacts. The initial product of the decay of nitrogenous organic wastes, and the breakdown of animal and vegetable wastes within the waste water entering the STW. Bacterial oxidation of ammonia rapidly depletes oxygen dissolved in water. The STW process removes the majority of ammonia prior to effluent discharge. The Thames Water Asset Management Plan (AMP) is the five-yearly funding agreement with the Environment Agency and Ofwat. AMP5 refers to the period 2010 to The contribution to the total measured or predicted concentration of a pollutant that does not originate directly from local sources of emissions. The situation against which the potential impacts due to the proposed development are assessed. BOD is a measure of the amount of biodegradable organic matter in water. It is frequently, but incorrectly, known as biological oxygen demand. It is expressed as the number of milligrams of oxygen required by micro-organisms to oxidise biodegradable organic matter in one litre of water. In the standard test, a sample is incubated at 20 oc for five days and the demand calculated from the difference in dissolved oxygen measured at the beginning and that at the end of the period. The correct designation is BOD 5 to indicate the five-day period but most often it is simply referred to as BOD. It has a number of important uses: It is used as a measure of sewage strength. It is one of the most important measures of effluent and river quality. It is used in both effluent and river quality standards. It is used in studies that model river quality. The variation of life forms within an ecosystem a high level of biodiversity is desirable. The amount of dissolved oxygen consumed in a set period by a chemical oxidising agent. It is an indirect measure of organic material in a water body. A system of conduits that collects and conducts urban waste water. A sewer conveying waste water of domestic or industrial origin and rain water. Page 81

87 Glossary Term Combined sewer overflow (CSO) Cyprinid Detention tank Dissolved oxygen level Domestic waste water Ecology Description A structure, or series of structures, designed to allow spillage of excess waste water from a combined sewer under high rainfall conditions. Flows may discharge by gravity or by pumping. Of or relating to the fish family Cyprinidae, including carp and minnows. A tank built to store runoff and release it at a controlled rate so that the peak flow is reduced and the flow is spread over a longer period. Indicator of water quality a higher level is preferable. Waste water from residential settlements and services which originates predominantly from the human metabolism and from household activities. The study of the relationships between living organisms and their surroundings including details of plants, animals and micro-organisms, their variations, scarcity, abundance, etc. Human ecology: the study of the interaction of people with their environment. Effluent Environmental Impact Assessment (EIA) Environmental Statement Eutrophication Final effluent Foul sewer Industrial waste water Impermeable surface Infiltration InfoWorks CS London Plan Optimism bias Pathogens Permeable surface Primary treatment The treated waste water discharged from the sewage treatment works. An assessment of the possible impact that a proposed project may have on the environment, considering natural, social and economic aspects. A document to be prepared following an EIA which provides a systematic and objective account of the EIA s findings. The enrichment of water by nutrients, especially compounds of nitrogen and/or phosphorus, causing an accelerated growth of algae and higher forms of plant life to produce an undesirable disturbance to the balance of organisms present in the water and to the quality of the water concerned. The treated liquid resulting from a treatment process, at the point of discharge to a watercourse. A sewer conveying waste water of domestic and/or industrial origin, but little or no rain water. Waste water which is discharged from premises used for carrying on any trade or industry, other than domestic waste water and run-off rain water. Surfaces or ground unable to absorb rainfall; e.g. concrete, most tarmac surfaces and hardstandings. The process whereby water seeps into a pipe via imperfections such as cracks, etc. Urban drainage network modelling software. Spatial Development Strategy for Greater London The Mayor of London (Feb 2008). The term used to describe the demonstrated, systematic tendency for project appraisers to be overly optimistic about project costs, duration and benefits. Disease-causing organisms. Surfaces or ground able to absorb rainfall; e.g. open textured ground, soil, grassed areas, open spaces. Treatment of urban waste water by a physical and/or chemical process involving settlement of suspended solids, or other processes in which the BOD 5 of the incoming waste water is reduced by at least 20% before discharge and the total suspended solids of the incoming waste water are reduced by at least 50%. Page 82

88 Glossary Term Public sewer QUESTS Model Real time control Receptors Recreational users Salmonid Secondary treatment Sewerage Sewerage undertaker SIMPOL3 Source control Spill event Storage and transfer tunnel Surface water runoff Suspended solids 24-hour mean concentration Tideway Trunk sewer Turbidity Urbanisation Urban waste water 90%ile Description A sewer that is owned and maintained by one of the UK water and sewerage undertakers. A WRc plc estuary water quality modelling package comprised of water quality and hydrodynamic components. The control or management of flow within a sewer system. People (both individually and communally) and the socio-economic systems they support. People who use the river for leisure, eg, rowers. Of or related to the fish family Salmonidae, including salmon, trout and char. Treatment of urban waste water by a process generally involving biological treatment with a secondary settlement or other process in which the requirements established in Table 1 of Annex 1 of the UWWTD are respected. A system of pipes and drains for the collection and transportation of domestic and industrial waste water. The statutory undertaker for sewerage responsible for sewerage maintenance. A WRc environmental modelling package, simulating flow and water quality in response to rainfall and temperature variations. Methods of managing and reducing storm water runoff at site level. A spill occurrence isolated by at least 24 hours of no spill either side of a spill. Sewer which captures spillages from the existing sewers and transports them to be properly treated. Water that travels across the ground and hard surfaces rather than seeping into the soil, e.g., from paved roads and buildings. The small solid particles that remain in suspension within a liquid. The average (mean) of the hourly concentrations measured for each pollutant over any 24 consecutive hours. The tidal area of River Thames (ie, from Teddington to the Thames Estuary). A sewer that receives many tributary sewers and serves a large area. The thickness or opaqueness as caused by the suspension of matter. Agglomerations of buildings and infrastructure for human accommodation and commercial, social and industrial activities leading to the reduction in permeable areas. Domestic waste water or the mixture of domestic waste water with industrial waste water with industrial waste water and/or run-off rain water. A figure that 90% of the data are less than. Page 83

89 References REFERENCES 1. Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report (December 2006) 2. Further information on RBMP can be found at aspx 3. Regulatory Impact Assessment, 2007; Section Adapted from TTSS Executive Summary 5. Regulatory Impact Assessment, 2007; Section Regulatory Impact Assessment, 2007; Sections Regulatory Impact Assessment, 2007; Sections Thames Tideway Tunnel and Treatment Summary Report Tackling London s Sewer Overflows, Executive Summary 9. TTT Objectives and Compliance Working Group Report Volume 2 Modelling and Compliance (2006) 10. Selection of Typical Year for CSO Spill Frequency Assessment (WRc, August 2006) 11. Thames Tideway Tunnel & Treatment, Solutions Working Group Report, Volume 1 Tunnels and Shafts (Section 2.2) (December 2006) 12. Hansard; House of Commons Ministerial Statements for 01 March 2010 (Hansard 1 Mar 2010:Column 94WS); EUROPA Press releases, Reference IP/09/1488 (8 October 2009) 14. TTSS Objectives Working Group Report Volume 2, Modelling Study (2004) 15. Thames Tideway Tunnel and Treatment, Option development: Quests water quality modelling results report (2007) 16. Thames Tideway Tunnel and Development, objectives and compliance working group report, Volume 2 - modelling and compliance (2006) 17. Thames Tunnel Project, Tideway Fisheries Review (Jacobs, October 2009) 18. Lee Tunnel and Beckton Sewage Treatment, Works Extension Scheme: ODA Consultation Application Reference 08/01158/ODA. Comments by CC Water London and South East Committee, 13 August The Thames Recreational Users Study Final Report (2007), a collaborative partnership project between the City of London Port Health Authority and the Health Protection Agency 20. Lee Tunnel and Beckton STW extension water quality modelling assessment of Lee Tunnel (2008) 21. Thames Tideway Strategic Study, Executive Summary, (February 2005) 22. Independent Review to assess whether there are Economic Partial Solutions to Problems caused by Intermittent Storm Discharges to the Thames Tideway Phase 1 (Jacobs Babtie, February 2006) 23. Tackling London s Sewer Overflows, Thames Tideway Tunnel and Treatment Option Development, Summary Report 24. DETR and Welsh Office: Working Document for Dischargers and Regulators: A Guidance Note, Appendix 8(ii) para 2.7, July EUREAU 1998 Stormwater pollution control in EU Member States; Contract No B4-3040/96/000173/DI Page 84

90 References 26. TTSS Supplementary Report to Government (2006), Summary Section Regulatory Impact Assessment sewage collection and treatment for London (March 2007) 28. Binnie Black and Veatch, Thames Tideway Strategy, SUDS Study (2002), Para Regulatory Impact Assessment (March 2007), Para TTSS, Objectives Working Group Report, Vol 1 (Section 6.3.1) (February 2005) 31. Taking care of water the next 25 years, (Thames Water, December 2007) Page 85

91 Appendices APPENDICES (in separate volume) APPENDIX A: APPENDIX B: APPENDIX C: APPENDIX D: APPENDIX E: APPENDIX F: MINISTERIAL CORRESPONDENCE AND REGULATORY IMPACT ASSESSMENT REPORT ON APPROACHES TO UWWTD COMPLIANCE IN RELATION TO CSOs IN MAJOR CITIES ACROSS THE EU POPULATION STATISTICS SEWER SEPARATION FEASIBILITY STUDY POTENTIAL SOURCE CONTROL AND SUDS APPLICATIONS TIDEWAY FISHERIES REVIEW Page 86

92 Copyright notice Copyright Thames Water Utilities Limited January All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities Limited Clearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are Thames Water Utilities Limited. All rights reserved. DCO-DT-000-ZZZZZ