Management of the London Basin Chalk Aquifer

Status Report 2009

We are the Environment Agency. It's our job to look after your environment and make it a better place - for you, and for future generations.

Your environment is the air you breathe, the water you drink and the ground you walk on. Working with business, Government and society as a whole, we are making your environment cleaner and healthier.

The Environment Agency. Out there, making your environment a better place.

Environment Agency Rio House

Waterside Drive, Aztec West Almondsbury, Bristol BS32 4UD Tel: 0870 8506506 Email: [email protected] www.environment-agency.gov.uk

© Environment Agency

All rights reserved. This document may be reproduced with prior permission of the Environment Agency.

Environment Agency Management of the London Basin Chalk Aquifer Status Report 2009 Contents

1 Introduction ...... 2 2 Geology beneath London...... 3 3 Groundwater beneath London ...... 5 4 Why we need to manage groundwater levels...... 7 5 How we manage groundwater levels...... 9 6 Recent Abstraction trends...... 10 7 Groundwater levels for January 2009...... 11 Recent Changes in Groundwater Levels...... 11 Long Term Changes in Groundwater Levels...... 11 8 Current licensing strategy ...... 13 9 Recent and developing management issues...... 15 Open Loop Ground source heat pump (GSHP) systems ...... 15 Thames Tideway Tunnel...... 16 Crossrail...... 16 Source Protection Zones ...... 16 10 Conclusions ...... 18 Figures...... 19 Appendix A London Basin Hydrographs List of abbreviations

Environment Agency Management of the London Basin Chalk Aquifer 1 Status Report 2009 1 Introduction

Thames Region of the Environment Agency produces an annual report on the state of groundwater levels in the Chalk aquifer beneath London. This is the eighteenth such report (previously called ‘Groundwater Levels in the Chalk-Basal Sands Aquifer of the London Basin’).

The reports were started in the 1990s to record the rise in groundwater levels, resulting from a significant reduction in groundwater abstraction from the Chalk aquifer beneath London, which started during the mid-1960s.

The rising groundwater and the re-saturation of the Chalk and overlying deposits can potentially affect the stability of buildings and tunnels. However, falling groundwater levels and de-saturation of the Chalk can impact local abstractors ability to abstract groundwater.

This report aims to describe the current condition of groundwater levels and abstraction within the Chalk and understand any changes seen in recent years. The area looked at within this report is shown in Figure 1. In order to manage groundwater levels to protect infrastructure and water resources, this monitoring data is used to see if changes to the local licensing policy need to be made to manage groundwater levels further. The current licensing policy is described as well as new and developing issues for groundwater management in the London Basin.

Environment Agency Management of the London Basin Chalk Aquifer 2 Status Report 2009 2 Geology beneath London

The geology of the London Basin is shown in Figure 2. Table 1 shows the geological formations found within the London Basin, the geological age that they were formed and their typical thickness.

Table 1 Geology of the London Basin

Era Group Formation Thickness (m) Palaeogene Thames Bagshot Formation 10 – 25 Claygate Member 30-90 London Clay Harwich Formation 0-10 Lambeth Woolwich and Reading Beds 10-20 Upnor Formation 5-7 Thanet Sands 0-30 Cretaceous Chalk 180-245 From the British Geological Survey Memoir Geology of London, 2004

As Table 1 shows, the Cretaceous sediments comprise of Chalk, and are overlain by Tertiary deposits of Thanet Sands, which consists of a fine sand, the Lambeth Group, comprising of sands, silts and clays, and Harwich Formation, comprising of sands and gravels. Overlying the Lambeth Group is London Clay, a dense blue/grey fissured clay. The Bagshot Formation, Bracklesham Formation and Claygate Member overlie the London Clay. Approximately half of the surface geology of the London Basin is formed by these younger deposits.

These deposits form the London Basin Syncline, which is asymmetric in shape. The northern limb of the syncline dips shallowly at around 1 degree to the south east, from its high point in the Chilterns. The southern limb in places dips steeply at up to 55 degrees at the Hogsback near Guildford in Surrey, decreasing in an easterly direction to 18 degrees at Gomshall and then to 1 degree at Dorking.

The London Clay is up to 80 metres thick at Hammersmith in the west, and Rainham in the east, and confines the Chalk aquifer over most of London. The depth to chalk increases to the southwest of the central basin area, with the greatest depth to Chalk in the basin at Chertsey, encountered at over 160 m below surface.

Two major faults are present in the south side of the London Basin. The Wimbledon Fault extends from Chessington through Malden, Wimbledon to Deptford. The downthrown block is the north west side of the fault, and has caused movements of beds as high as the London Clay, which is in contact with the Lambeth Group at East Dulwich. The Greenwich Fault runs parallel to the Wimbledon Fault from Mitcham, through West Norwood, Lewisham, Greenwich to Beckton. The downthrown side is also to the north, bringing the chalk into horizontal contact with the Thanet Sand, which contacts Lambeth Group at Lewisham. The maximum displacement is approximately 30 m.

Numerous minor faults cross-cut the syncline and have led to the formation of domes, and cause the depth to chalk to vary significantly across the London Basin. The structures have resulted in high ground such as Hampstead-Highgate, Wimbledon and Blackheath, and has brought the chalk to shallow depth below ground and even to outcrop within the basin in the Lee Valley, Deptford, Lewisham, and around the River Thames from Greenwich to Woolwich.

In 2008 the British Geological Survey (BGS) completed a geological study of the London Basin for the Environment Agency. Their key findings regarding the basin structure were:

Environment Agency Management of the London Basin Chalk Aquifer 3 Status Report 2009 o In the northern part of the basin structural contours indicate gentle, low amplitude and long wavelength folding. This is in contrast to that observed in the southern part, where folding is more numerous, higher in amplitude and shorter in wavelength. o In the northern part, the Chalk dips to the south east at up to 0.7 degrees and the dip is not observed to steepen against structures. However, in the southern part, the dip is generally between 0.7 and 2 degrees to the north west and the dips steepen against structures up to a maximum of 14 degrees. o No evidence for faulting was found in the borehole logs in the northern part. However, numerous small-scale faults were recognised within the southern part. o In the central basin area new faults orientations are proposed (Figure 2), which are supported by the distribution of Lambeth Group deposits. o the known area of complexity within the Lambeth Group of London coincides with the proposed fault pattern. The faults appear to have had a persistent control on the extent of marine transgression and regression during Lambeth Group time, and presumably throughout the Palaeogene, and may control amount and type of sedimentation.

Environment Agency Management of the London Basin Chalk Aquifer 4 Status Report 2009 3 Groundwater beneath London

The Chalk aquifer is the major aquifer of the London Basin. The Chalk is confined in the basin by the overlying Tertiary formations, which means recharge largely occurs in the Chalk outcrops of the Chilterns to the north and the North Downs to the south.

The outcrop to the north of the London Basin is extensive, extending from the outskirts of London at Uxbridge in the west, in a northeasterly direction to Borehamwood and north of Cheshunt in the north, and as far as the Stevenage area in Hertfordshire and High Wycombe area in Buckinghamshire. In the south however the outcrop recharge area is more limited, with the chalk outcrop at the Hogsback being only hundreds of metres in width.

In the southern part of the London Basin at the point where the Chalk dips under the Tertiary formations, numerous springs are found where Chalk groundwater discharges to surface and contributes baseflow to the rivers Wandle, Hogsmill and Pool in South London. These rivers may also derive baseflow from the Harwich Formation over its outcrop in south London before it dips below the London Clay.

The rivers Ravensbourne and Quaggy derive all of their baseflow from the Harwich Formation and Lambeth Group with the exception of small windows to the Thanet Sand and Chalk in the Beckenham-Bromley-Chislehurst area where the rivers may lose to the aquifer. Recent spot flow gauging shows that across these windows the rivers continue to gain flow, indicating that the river beds may be partially in hydraulic discontinuity with the Chalk and Thanet Sands. To the East of Chislehurst there is extensive Thanet Sand and Chalk outcrop where London Clay is not present, and in this area the River Cray derives much flow from Chalk groundwater.

The Chalk is a low storage, high transmissivity aquifer comprising dual porosity, with flow and storage occurring both in the fractures and in the matrix. Most flow occurs in the fractures with storage in the matrix, released to the fractures as the groundwater level falls. In the south west part of the London Basin, the Chalk has much lower transmissivity, while under the river valleys of the rivers Thames and Lee, there are corridors of high transmissivity Chalk present.

Groundwater flows into the central London Basin from the areas of recharge in the north west and south west. The natural flow path for groundwater would be to discharge in areas of chalk outcrop such as in the River Thames area from Greenwich to Woolwich, and where chalk groundwater can discharge through Lambeth Group sediments to surface, such as in Hackney and the Lee Valley, and. As a result of historic and current abstraction, groundwater flow from the west does not flow beyond central London, and groundwater flow from the east, from Blackheath and East London and Essex, is drawn west into central London. Groundwater from south east London interacts with the River Thames from Greenwich to Woolwich as it flows north west to Stratford and then west to central London. In this area there is potential for saline tidal river water to enter the aquifer.

The Chalk group combined with the sands of the Thanet Sand Formation and the Lambeth Group (where less clayey and more sandy), make up the water-bearing Chalk-Basal Sands aquifer of the London Basin. There is hydraulic continuity between the Chalk and Thanet Sands, although this may be limited in places, and some continuity with the Lambeth Group depending on the clay and sand content. Although there can be limited flow between Chalk -Thanet Sands and Lambeth Group, they are of different depositional origins and hence have different chemistry, and therefore Chalk -Thanet Sands and Lambeth Group are regarded as separate aquifers for resource management.

The low permeability nature of the London Clay overlying these aquifer units prevents the water table reaching the surface and causes artesian pressure to build up underneath the London Clay. As groundwater pressure increases on the London Clay, it is increasingly saturated, albeit slowly. The London Clay is extensively fissured locally, and therefore rapid ingress of groundwater at

Environment Agency Management of the London Basin Chalk Aquifer 5 Status Report 2009 higher elevations is possible on a small scale. It is this re-saturation that could affect the stability of certain foundations and cause ingress of water into tunnels in the London Clay.

Environment Agency Management of the London Basin Chalk Aquifer 6 Status Report 2009 4 Why we need to manage groundwater levels

During the 19th century and first part of the 20th century, the Chalk-Basal Sands aquifer had been increasingly exploited, as a result of increased industrialisation and the associated development of groundwater sources. At the peak of abstraction in the 1960s, groundwater levels beneath central London had dropped to 88 metres below sea level, creating a large depression in the water table. A smaller cone of depression also developed to the east beneath the River Roding in Essex.

Since the mid-1960s industries in central London relocated or were closed down and business turned more to commerce than heavy industry. The subsequent reduction in abstraction resulted in groundwater levels recovering by as much as 3 metres per year in places by the early 1990s, leading to a gradual rebound of the water table.

Due to the threat to structures in the London Basin posed by rising groundwater levels, including tunnels such as London Underground and building foundations, the General Aquifer Research, Development and Investigation Team (GARDIT) strategy to control water levels was implemented in 1992. The objective of the strategy was “to control groundwater level in the Chalk aquifer under central London in order to maintain the integrity of underground structures and foundations in the London Clay”.

Implementation of the strategy was achieved by abstraction licensing and groundwater monitoring. Numerous large public water supply abstractions were licensed to Thames Water under the strategy, in order to slow the rise in groundwater levels and eventually stabilise them. These abstractions came into operation in the late 1990s with further abstractions developed through until 2004. Groundwater levels were monitored so adjustments could be made to abstraction volumes through the abstraction licensing process. Ongoing monitoring has enabled the effectiveness of the strategy to be ascertained and acted upon. Since the development of new sources significant volumes of additional abstraction has been granted through the GARDIT strategy. As the response times in the aquifer are measured in years, we have observed that since 2000 groundwater levels have stabilised. As the deep cone of depression from historic abstraction recovers then the gradient across the London basin shallows, and the rate of groundwater rise in key well hydrographs slows. In some places water levels can be seen to be falling again.

Consequently, we have felt it necessary to restrict further abstraction in certain parts of London. Our licensing strategy for London is set out in our London Catchment Abstraction Management Strategy (CAMS). The licensing policy is reviewed regularly so that further changes to the abstraction regime and its influence on groundwater levels can be incorporated.

The situation will change from year to year depending on the actual amount of abstraction rather than the licensed volumes. The aim of the management of the abstractions is to maintain groundwater levels below an upper level needed to protect underground structures and above a lower level, which is the point where the Chalk aquifer starts to be dewatered to an unacceptable level. This is considered to be the point beyond which the abstraction rate is unsustainable, yields would fall and protected rights to abstract would be derogated. These levels are not fixed elevations but are more conceptual. The London Chalk 3D map the Environment Agency commissioned from the BGS in 2007-8 provides a tool for visualising the interpreted lithological elevations with water levels.

As a result of the GARDIT strategy and since water levels in most areas have stabilised, the general water level management imposed on central London, the whole of the London Basin Chalk aquifer is becoming a highly managed entity, like many other natural systems in the UK. The great advantage of controlling this confined aquifer is that there is no negative environmental implications. No ecosystems depend on a specific groundwater level under London, and therefore,

Environment Agency Management of the London Basin Chalk Aquifer 7 Status Report 2009 provided levels are kept below that required to protect structures, the aquifer presents a very secure, stable and sustainable water resource. Our role is to continue to monitor levels and advise the major abstractors on the current situation so that abstraction can slowly be adjusted to achieve the required balance.

Environment Agency Management of the London Basin Chalk Aquifer 8 Status Report 2009 5 How we manage groundwater levels

The Environment Agency has a long-term commitment to monitor and report on the state of groundwater levels beneath London. We collect data from a network of nearly 200 observation boreholes in London to monitor absolute groundwater levels and rates of change of levels in the aquifer.

We also obtain data from other organisations, particularly water companies, and the availability of the data could be compromised in the future by modifications to these monitoring networks and by previously monitored boreholes becoming unavailable. Several longstanding observation boreholes have been lost in central London in recent years and any knowledge of, or data from, alternative boreholes would be very helpful to the Environment Agency. Similarly, where redevelopment and ground investigations offer the opportunity of obtaining one-off or short-term groundwater data, these data will be utilised wherever possible.

Figure 3 shows the location of the observation boreholes used in this analysis. The boreholes are located within the groundwater of the Chalk-Basal Sands aquifer and, as the figure shows, are widespread throughout the London Basin.

Observation boreholes are chosen on the basis of achieving a good spatial distribution across London and ensuring key areas of groundwater resources are included. Over time some observations are no longer monitored and new observations need to be chosen for a given area. Figure 3 shows observation boreholes that we used to monitor in the past and have since had to close or have had recent access issues. For this reason over time the ‘key wells’ used in this report may change. Figure 4 shows the key wells used in the previous report and those which can still be used in this analysis, as well as additional wells selected to improve the spatial distribution and analysis of areas under pressures of new abstractions or proposed development

The Water Information Management System Kisters (WISKI) database is the Environment Agency’s hydrometric archiving, analysis and reporting system. Groundwater level data for all boreholes within the London Basin is stored within this system. We use this database to extract groundwater levels for our review.

Abstraction data, both licensed and actual volumes, is stored in the Environment Agency’s National Abstraction Licensing Database (NALD), and includes returns data from all large abstractions such as from water companies. Abstraction and recharge data for the North London Artificial Recharge Scheme (NLARS), run by Thames Water, are also stored and compared to data from previous years.

The status of groundwater levels in the London Basin is assessed using trends in groundwater level hydrographs, temporally and spatially, as well as contouring groundwater levels and comparing changes in patterns year on year. Groundwater level changes are then compared to trends in abstraction. It is through this comparison we can identify areas of change that may need further groundwater level management or changes in licensing policy.

Environment Agency Management of the London Basin Chalk Aquifer 9 Status Report 2009 6 Recent Abstraction trends

Over the past year new abstraction licence applications or changes to existing licences have been handled by the National Permitting Service (NPS). The NPS is also charged with collating licence returns data. In line with other permitting arrangements it was decided that abstraction licence returns would now be made on a financial year basis rather than calendar year. As a result this report is delayed this year as a result of changes to the abstraction reporting period. As water company returns make up the bulk of consumptive abstraction this report describes the recent abstraction trends for water company abstractions only, which form around 80% of abstraction in the study area.

Figure 5 shows the distribution of total actual water company annual abstraction over the course of 2008 in the London Basin. There are some very large public supply sources in south east London at Deptford and Bell Green, as well as the Brixton, Catford and Shortlands pumping stations (PS) in south London. The East London Resource Development (ELRED) abstractions in east London are also significant abstractions. There are very few abstractions in the area of west London.

Licensed abstraction quantities have been gradually increasing over recent years, with a 1% increase on licensed quantities from 2005 to 2006, and a 0.4% increase from 2006 to 2007. Similarly, in 2008 water company licensed quantities increased by 0.5% on 2007, largely related to the Wandle Artificial Recharge Scheme (WARS).

Actual abstraction from water company licences fell by 26% over 2008 compared to the previous year, continuing the trend since a peak in 2005. The reduction is largely from Thames Water sources in south London as well as the reduction in NLARS abstraction. Nearly twice the volume of water was abstracted by WARS associated with the additional source at Goatbridge now aggregated to the Hackbridge licence. Figure 6 shows how actual abstraction increased during drought years, in 2003 and 2005-6, and how the recent wet years has lead to reduced actual abstraction. Figure 7 shows the spatial change in actual abstraction between 2007 and 2008.

Abstraction from NLARS in 2008 was 61% of the abstraction volume in 2007, totalling 557 ML compared to 903 ML in 2007, as shown in Figure 8. Significantly less water was reinjected, with 179 ML in 2008 compared to 2007. As described above with general abstraction trends, drought years have had a significant impact on the operation of NLARS. The large volume of artificial recharge in 2007 compared to abstraction reflects large, drought-related abstractions in the preceding years, rather than the lower abstraction in 2007.

Environment Agency Management of the London Basin Chalk Aquifer 10 Status Report 2009 7 Groundwater levels for January 2009

Recent Changes in Groundwater Levels

Figure 9 to Figure 11 show the recorded groundwater levels and associated groundwater contours within the London Basin for January 2000, January 2008 and January 2009. Each figure shows a similar pattern of low groundwater levels in central London with groundwater levels increasing to the north west and south east towards the Chilterns and North Downs outcrops.

By mapping the difference in groundwater levels, it is possible to contour the rise and fall of groundwater levels in the London Basin. Figure 12 shows the change in groundwater levels between January 2008 and January 2009. From Figure 12 the following changes can be seen:

• The central London groundwater depression has increased in size marginally with the -40 mAOD, -30 mAOD and -20 mAOD increasing in size toward the south and west. • Groundwater levels have risen in the order of 2-3 m in south east London. • Groundwater levels in east London have fallen between 1 m and 2 m between Stratford and Barking, however the orientation of the predicted contours indicate this has not increased the risk of saline intrusion, with the 0 mAOD contour moving south. In previous years these have been related to the CTRL dewatering works that were later converted into the public water supply scheme of East London Water Resource Development Scheme (ELRED). In 2008 however total abstraction from ELRED sources fell 22% and is therefore related to local activities. • Increases in groundwater levels of the order of 2-3 m are observed in south west and south east London, relating to reduction in abstraction from PS sources. • On the southern margin of the study area a mound of up to 16 m has developed related to the Wandle Artificial Recharge Scheme. Water levels tend to build up in the winter to be drawn down in the summer. • In 2000, there were two isolated depressions shown by the -10mAOD groundwater contour, one near central London and one in east London. By January 2007, these contours had combined to form one depression with groundwater level falls in the Lee Valley area. This depression has extended slightly further northward up the Lee Valley over the past year. • There is little change over much of the study area.

Some observation boreholes are located near to abstraction licences or are abstracted from. This can mean that the monthly recorded groundwater levels at that observation may show daily changes related to the abstraction rather than the regional groundwater level change. However, these observation wells have been included within the groundwater contour maps of Figure 9 to Figure 11, due to the limited coverage of the observation network.

Long Term Changes in Groundwater Levels

The rise in groundwater that the GARDIT strategy was designed to arrest had largely been achieved by 2000, so this year provides a useful baseline year for comparisons. By comparing the January 2009 groundwater levels it is possible to see long term changes in the groundwater levels. The difference in groundwater levels for January 2000 and January 2009 is shown in Figure 13, which shows that: • water levels continue to rise in the north west of the study area. This relates to water levels just outside the study area where increases of up to 2 m were measured while inside the basin rise of less than 1 m were measured. Environment Agency Management of the London Basin Chalk Aquifer 11 Status Report 2009 • Two small cones of depression in east London have now joined together based on the interpolated -4 mAOD contour • The cone of depression in south east London has shifted slightly to the west reflecting additional drawdown in the past year in central London and rising groundwater in south east London

In east London, where the Chalk outcrops around the River Thames from Greenwich to Woolwich, there is a risk of saline intrusion. When groundwater levels near the river are lower than the water level in the River Thames, saline river water can enter the Chalk aquifer. As groundwater flow is in a north westerly direction, as shown by the groundwater contours of Figure 11, abstractions could capture any saline waters that enter the aquifer. As a result of this risk there are conditions attached to abstraction licences in this area, requiring regular water quality sampling. To date sampling associated with Thames Water’s ELRED licence has indicated no change to groundwater salinity.

Environment Agency Management of the London Basin Chalk Aquifer 12 Status Report 2009 8 Current licensing strategy

As groundwater levels are now falling in some areas of London, we are now looking at how much abstraction from the Chalk beneath London is sustainable, rather than reducing rising groundwater levels. The quantity of groundwater abstraction that is sustainable in London will always be difficult to determine with any certainty as it takes time for the groundwater level to respond to changes in abstraction. That is, there is a lag between authorising changes and seeing their impact, and there will always be a difference between licensed and actual abstraction. As the abstraction regime is always changing, groundwater levels will never actually stabilise. Since 1999 there has been an increase in the licensed volume of abstraction of at least 30 Ml/d in central London and there are an increasing number of proposals for large abstractions.

In 2006, we put into practice a policy to restrict further abstraction in areas that may be approaching their sustainable limit. In order to manage groundwater resources, the groundwater level needs to be above the top of the Chalk. Licensing restrictions were based upon ‘headroom’ estimates of the groundwater level above the top of the Chalk and the current licensed abstraction volume over a 500m grid across central London. Areas where there is a large volume of current abstraction or groundwater levels near the top of the Chalk are unlikely to be able to support significant further abstraction.

From this methodology, three areas were defined where further abstraction needed to be restricted. The extent of these areas is shown in Figure 14. The restrictions for each area is detailed in Table 2. Full details of these areas is provided in our London CAMS Final Strategy document.

Table 2 London Licensing Zone Restrictions

Licensing Zone Restrictions

Central and South New Licences restricted to 73,200 m3/year and time limited to 2013. London No new licences in Battersea area or in the unconfined Chalk catchment

South East No new licences in the confined or unconfined Chalk catchment London

East London New licences restricted to 182,500 m3/yr and time limited to 2013.

Figure 14 shows a representative groundwater hydrographs for each licensing policy zone described below. It shows the variable trend in groundwater level across the London Basin, with levels falling in East London, South London and Central London, while levels are still rising in West London, where consequently there is no restrictive zone as further abstraction is required to stabilise groundwater levels in this area.

We are presently working towards improving our understanding of the London Basin with a conceptual study of the aquifer nearing completion. It will then be considered what improvements to the existing London Basin numerical groundwater model could be made. The new understanding should help us improve our quantification of the inflows to the London Basin from surrounding catchments to better manage abstraction within the basin, improve the conceptualisation of the London CAMS, and enable further reviews of the London licensing policy.

Licensing decisions are also subject to local assessments. The assessment will take into account the following:

Environment Agency Management of the London Basin Chalk Aquifer 13 Status Report 2009 • Has there been any long-term (several years) downward trend in the groundwater level in the vicinity of the application?

• The groundwater level in relation to the base of the London Clay. If the groundwater level is near the base of the London Clay, then we will be unlikely to grant the abstraction licence. We will use discretion if there is a significant thickness of the Lambeth Group below the London Clay, but the aim is to manage abstraction to keep groundwater levels above the Thanet Sands.

• Any recent abstraction development in the same area. If groundwater levels have not yet responded to a recent change in abstraction, we may not grant further licences in that area.

• Other proposals in the area that have been refused for water resource reasons in the last five years.

• Proximity of the proposal to an existing or proposed Artificial Recharge Scheme. Artificial Recharge scheme proposals will be treated as a special case as they involve the management of groundwater levels to provide additional resource to the scheme operator.

The above criteria will be used to assess abstraction proposals and uses the monitoring data and interpretation described in previous sections. If the proposal is acceptable in principle once the assessment has been done, the area in which the licence is proposed will be considered. Potential applicants are advised to contact their local licensing officer at an early stage to discuss any proposal.

In east London, the Chalk aquifer and local abstractors are sensitive to saline intrusion. When a new licence application is being made, the risks of lowering groundwater levels in this area and the risk of encouraging saline waters in to the aquifer will need to be considered.

Environment Agency Management of the London Basin Chalk Aquifer 14 Status Report 2009 9 Recent and developing management issues

The Chalk-Basal Sands aquifer in the London Basin is a highly managed entity. It is under increasing pressure from several sources.

Open Loop Ground source heat pump (GSHP) systems

Guidance

A new report by the Environment Agency has reviewed the regulatory issues and evidence of ground source heat pumps (GSHPs). This review forms the initial stage in the work required which aims to update the Environment Agency’s evidence base and provide staff with the policy and operational guidance they need to deal with GSHP permit applications. This will help the Environment Agency to facilitate the deployment of sustainable ground source heating and cooling pumps and deal efficiently with the increase in operational workload expected as a result of the Government’s renewable energy target.

The Environment Agency wants to promote renewable energy while avoiding unacceptable environmental impacts. However, the potential environmental impacts and interference effects of GSHP systems, primarily associated with discharge of hotter or colder groundwater, are not well understood.

The Environment Agency needs to understand the sustainability of ground source heat resources so that it can target its regulation of the resource appropriately. Changes in legislation may be required to establish the regulation of heat, or it may be possible to adapt existing regulatory tools. This requires legal and policy consideration.

Either way, the Environment Agency needs a risk-based approach for the regulation of GSHP systems and research is needed to fill knowledge gaps and provide evidence to underpin decision making.

Longer term recommendations are divided into administrative, regulatory and guidance. Sustainability of ground source heat resources, heat propagation through rock and water, and the effect of temperature changes on chemistry are the three principal areas where there are gaps in knowledge and understanding. The priority research needs identified are: heat propagation in the major aquifers; impacts of thermal discharges on the Chalk; recharge mounds around injection wells in open loop systems and a development of a monitoring strategy for temperature, which includes identification a network and deriving technical standards for temperature monitoring.

New Development

There were 21 new proposals for open loop GSHP systems in the study area in 2008, while two existing proposed schemes were withdrawn. Four schemes that had been at the investigation stages in previous years are now active. These investigations took place between 2005 and 2007. There were 13 proposed schemes from previous years that undertook investigations in the study area in 2008.

It can be seen that from inception to operation a GSHP scheme can take several years to bring to fruition with the number of proposals and investigations significantly larger than the number of schemes that become active. Figure 16 shows the trends in applications, investigations and active schemes for the past few years, and the locations of schemes proposed in 2008 in relation to Environment Agency Management of the London Basin Chalk Aquifer 15 Status Report 2009 existing schemes (active, investigative, or proposed). It can be seen that in the past year the rate of increase in proposals, investigations and newly active schemes has slowed.

Thames Tideway Tunnel

Construction of the Lee Tunnel is provisionally scheduled to take place from 2009, starting at Beckton and is anticipated to take 5 years. Four shafts will link to the tunnel, these being a 25 m diameter shaft at Abbey Mills, a 25 m overflow shaft at the end of the tunnel at Beckton and a 38 m diameter pumping station linked to a 25 m connection shaft at Beckton.

The Environment Agency has asked Thames Water to monitor groundwater quality and groundwater levels for a period of six months, to establish baseline conditions along the eastern end of the tunnel construction prior to the commencement of the works. Monitoring commenced in February and the baseline study was completed in August 2009.

Baseline monitoring will allow any impacts on the Chalk aquifer from tunnel construction and future use to be identified and managed.

In view of the scale of the project and potential environmental impacts of the scheme, we are maintaining regular discussions with Thames Water. We have advised Thames Water that the provisions of the Water Act 2003 may be implemented in autumn 2009 whereby the previous exemption from groundwater licensing for dewatering will be withdrawn. As a result, the proposed dewatering for construction of the deep shafts would then require a transfer licence to be granted to permit the abstraction of groundwater and subsequent discharge without intervening use to take place. However, until such time the assessment of impact will still be required.

Crossrail

De-watering activities have been planned at various sites along the Crossrail alignment in the vicinity of stations, shafts and cross passages. Pumping commenced in August 2008 on the Isle of Dogs in preparation for the construction of the Isle of Dogs Station. The required drawdown was achieved in December 2008 and the rate of pumping is progressively being reduced. The programme for future de-watering sites is currently under review, pending confirmation of the adoption of cross passages in place of a number of shafts. The cone of depression generated by dewatering was shallower but of similar extent to that predicted by the London Basin Groundwater Model. A 26 m drawdown was measured within an approximate 200 m of the station location with no drawdown detected approximately 2.5 km distant.

Water quality data indicate that there has been some localised saline intrusion as indicated by drinking water standard exceedences of conductivity, sodium and chloride, since the commencement of pumping in August 2008.

Source Protection Zones

In the past year several public water supply sources in London have had source protection zones (SPZs) delineated for their protection. These will appear on the Environment Agency website soon and are located particularly in east London. Further zones have been delineated for new NLARS sources in the Lee Valley and several other sources scattered across the London Basin.

Since the publication in 1996 of the first version of the manual, there have been advances in available techniques and in the use of geographical information systems (GIS), together with increased availability of spatial data in electronic formats and the development of national databases. The science team has worked on a revised SPZ methodology manual, drawing on Environment Agency Management of the London Basin Chalk Aquifer 16 Status Report 2009 advances in groundwater research over the period and takes account of changes in the Environment Agency’s groundwater protection policy.

The new manual updates the procedure for defining SPZs. The main changes to the previous manual are: • changes in the procedure for definition of the SPZ2 (i.e. dropping the 25 per cent rule) and use of a default minimum radius of 250 or 500 metres around the source; • merging of SPZ3s where these cover a significant part of the aquifer outcrop; • incorporating the fourth zone ‘Zone of Special Interest’ previously defined for some sources into one of the three zones, whichever is appropriate; • modifications in the shape of modelled SPZs to take account of other hydrogeological information that cannot be readily incorporated within many of the models; • changes in the procedure for assessment of the uncertainty in SPZ boundaries; • updating of the tools used to model hydraulic capture zones.

These changes have been introduced to provide a more pragmatic approach to determining source protection zones. They reflect an improved understanding of groundwater protection and its implementation.

Environment Agency Management of the London Basin Chalk Aquifer 17 Status Report 2009 10 Conclusions

• Between 2007 and 2008 licensed abstraction from water companies in the London Basin has increased by 0.5%, while actual abstraction has decreased by 26%.

• The central London groundwater depression has increased in size marginally and falls of up to 2 m have occurred in east London, while groundwater levels have risen in the order of 2-3 m in south east London.

• Dewatering on the Isle of Dogs for Crossrail has created a localised cone of depression not picked up by the regional monitoring network. Further dewatering activities for Crossrail and the Lee Tunnel in the coming year are likely to depress groundwater levels further adding to the risk of saline intrusion.

• The rate of growth in GSHP schemes has slowed in 2008. Four new schemes became active in the central London area.

• New source protection zones have been created, several of which are in the London Basin, particularly east London. These should be available on the Environment Agency website soon. A new methodology for SPZ delineation is available.

Environment Agency Management of the London Basin Chalk Aquifer 18 Status Report 2009 Figures

Figure 1 Area of the London Basin

Figure 2 Geology of the London Basin

Figure 3 London Observation Borehole Network

Figure 4 Location of Key Wells

Figure 5 Total Annual Abstraction for 2008

Figure 6 Licensed Abstraction from Chalk Aquifer beneath London

Figure 7 Difference between 2007 and 2008 Total Annual Abstraction

Figure 8 North London Recharge Scheme Operation

Figure 9 Monitored Groundwater Levels for January 2000

Figure 10 Monitored Groundwater Levels for January 2008

Figure 11 Monitored Groundwater Levels for January 2009

Figure 12 Difference between Jan 2008 and Jan 2009 Groundwater Levels

Figure 13 Difference between Jan 2000 and Jan 2009 Groundwater Levels

Figure 14 London Licensing Areas and Hydrographs

Figure 15 Location of Open Loop GSHP Schemes

Environment Agency Management of the London Basin Chalk Aquifer 19 Status Report 2009

Figure 6 Water Company Licensed Abstraction from Chalk Aquifer

120000 112506 111946 111946 111576 100000 110946 98436 111970 99033 98727 80000 97440 98726 100078 101216 98813 89162 81060 81516 81646 81415 60000 Abstraction (Ml/yr) 40000 45092 39139 36069

20000 30224 24229 23550 22318 20961 18402 18237 17361 15808 15274 14268 14229 14416 13699 13527 12425 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Licensed Abstraction Actual Abstraction

Figure 8 North London Recharge Scheme Operation

12000 10981 9946 10000 9920

8000

6000 5836 Abstraction (Ml/yr) Abstraction 4284 4256

4000 3946 3564 3516 2898 2878 2304 2000 1155 1113 903 557 531 333 295 246 206 179 125 86 62 32 19 0 0 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

NLARS Abstraction (Ml/yr) NLARS Recharge (Ml/yr)

Appendix A London Basin Hydrographs

Figure A1 TQ18/35 I.B.M Greenford

Figure A2 TQ18/44B Hoover Building

Figure A3 TQ26/143A Beddington Sewage Treatment Works

Figure A4 TQ27/159 Youngs Brewery

Figure A5 TQ27/163 Springfield Hospital

Figure A6 TQ27/285A Richmond Park Observation Borehole

Figure A7 TQ27/88 Ashley Gardens

Figure A8 TQ28/153 St Agnes Well

Figure A9 TQ36/105 Avenue Road

Figure A10 TQ38/241 Leith Ho. Gresham St

Figure A11 TQ38/263A Liverpool Victoria

Figure A12 TQ38/465 Oliver Rd Leyton

Figure A13 TQ38/466 Memorial Recreation

Figure A14 TQ38/515 Mile End Road Observation Borehole

Figure A15 TQ39/145 Friday Hill

Figure A16 TQ47/90 Charlton Observation Borehole

Figure A17 TQ48/2 Victoria Docks

Figure A1 Groundwater Hydrograph for TQ18/35 - I.B.M GREENFORD

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 20.0

15.0

10.0 evel (mAOD)

5.0 Groundwater L Groundwater

0.0

-5.0

Figure A2 Groundwater Hydrograph for TQ18/44B - HOOVER BUILDING

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 20.0

15.0

10.0 evel (mAOD)

5.0 Groundwater L Groundwater

0.0

-5.0

Figure A3 Groundwater Hydrograph for TQ26/143A - BEDDINGTON STW (Chalk)

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 35.0

30.0

25.0

20.0 evel (mAOD)

15.0 Groundwater L Groundwater 10.0

5.0

0.0

Figure A4 Groundwater Hydrograph for TQ27/159 - YOUNGS BREWERY

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-5.0

-10.0 evel (mAOD)

-15.0 Groundwater L Groundwater

-20.0

-25.0

Figure A5 Groundwater Hydrograph for TQ27/163 - SPRINGFIELD HOSPITAL

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 20.0

15.0

10.0

5.0 evel (mAOD) 0.0

-5.0 Groundwater L Groundwater

-10.0

-15.0

-20.0

Figure A6 Groundwater Hydrograph for TQ27/285A - RICHMOND PARK OBH

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 12.0

10.0

8.0

6.0

4.0

2.0 evel (mAOD)

0.0

-2.0 Groundwater L Groundwater -4.0

-6.0

-8.0

-10.0

Figure A7 Groundwater Hydrograph for TQ27/88 - ASHLEY GARDENS

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-10.0

-20.0

-30.0 evel (mAOD) -40.0

-50.0 Groundwater L Groundwater

-60.0

-70.0

-80.0

Figure A8 Groundwater Hydrograph for TQ28/153 - ST AGNES WELL

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-10.0

-20.0 evel (mAOD) -30.0

-40.0 Groundwater L Groundwater

-50.0

-60.0

Figure A9 Groundwater Hydrograph for TQ36/105 - AVENUE ROAD

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 40.0

35.0

30.0

25.0 evel (mAOD) 20.0

15.0 Groundwater L Groundwater

10.0

5.0

0.0

Figure A10 Groundwater Hydrograph for TQ38/241 - LEITH HO. GRESHAM ST

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-10.0

-20.0 evel (mAOD) -30.0

-40.0 Groundwater L Groundwater

-50.0

-60.0

Figure A11 Groundwater Hydrograph for TQ38/263A - LIVERPOOL VICTORIA

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-10.0

-20.0 evel (mAOD) -30.0

-40.0 Groundwater L Groundwater

-50.0

-60.0

Figure A12 Groundwater Hydrograph for TQ38/465 - OLIVER RD LEYTON

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-2.0

-4.0 evel (mAOD) -6.0

-8.0 Groundwater L Groundwater

-10.0

-12.0

Figure A13 Groundwater Hydrograph for TQ38/466 - MEMORIAL RECREATION

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-5.0

-10.0 evel (mAOD) -15.0

-20.0 Groundwater L Groundwater

-25.0

-30.0

Figure A14 Groundwater Hydrograph for TQ38/515 - MILE END ROAD OBH

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 -21.5

-22.0

-22.5

-23.0

-23.5

-24.0

-24.5

Groundwater Level (mAOD) -25.0

-25.5

-26.0

-26.5

Figure A15 Groundwater Hydrograph for TQ39/145 - FRIDAY HILL

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-5.0

-10.0 evel (mAOD)

-15.0 Groundwater L Groundwater

-20.0

-25.0

Figure A16 Groundwater Hydrograph for TQ47/90 - CHARLTON OBH

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-0.2

-0.4

-0.6

-0.8 evel (mAOD) -1.0

-1.2

Groundwater L Groundwater -1.4

-1.6

-1.8

-2.0

Figure A17 Groundwater Hydrograph for TQ48/2 - VICTORIA DOCKS

Date 01 Jan 1985 01 Jan 1990 01 Jan 1995 02 Jan 2000 01 Jan 2005 01 Jan 2010 0.0

-2.0

-4.0

-6.0

-8.0 evel (mAOD)

-10.0

-12.0 Groundwater L Groundwater

-14.0

-16.0

-18.0

List of abbreviations

GARDIT General Aquifer Research, Development and Investigation Team

CAMS Catchment Abstraction Management Strategy

WISKI Water Information Management System Kisters

NALD National Abstraction Licensing Database

NLARS North London Aquifer Recharge Scheme

CTRL Channel Tunnel Rail Link

PS Pumping Station

GSHP Ground Source Heat Pump

ELRED East London Water Resource Development Scheme

WARS Wandle Artificial Recharge Scheme

SLARS South London Artificial Recharge Scheme