Minutes 10 July 2001 Appendix 2 Slide 1 London’s Rising Groundwater Archie Galloway Chair, GARDIT Slide 2 The problem l Hydrogeology l History of abstraction l Groundwater quality l Effects and possible damage The part of the presentation will review these four issues associated with the problem of rising groundwater in London. 1 Slide 3 Plan of basin - Geology Anglian Severn - Trent Water Water Banbury Luton Oxford Cirencester Swindon Central London Wessex Water Reading Basingstoke Guildford Southern LEGEND Water Clay Chalk River Gravels Limestones This plan indicates the geology of the London basin. London is a saucer shaped basin. Chalk overlain by sands form the water bearing strata. Impervious London Clay overlays these rocks. Aquifer is confined – water that fell as rain on the Chiltern and North Downs 1000s of years ago is now running through the centre of the London basin. 2 Slide 4 Section of basin North South ft OD Welwyn Potters Hornsey Westminster North Downs m OD 500 Garden Bar 150 Stevenage City Enfield Lambeth Croydon 400 100 300 200 50 Thames Fault Original (Vauxhall Bridge) Fault 100 water level 0 0 Water level in -100 aquifer (1997) Water level in -50 -200 aquifer (1965) -300 -100 Chalk Woolwich and Reading Beds Basal Sands London Clay This is a section through the basin. First water level is the natural or historical water level – boreholes sunk in central area would have been artesian. Second water level shows the situation c1965. From the 1850s, increased industrial activity led to greater water demand. As the water levels receded, ever deeper boreholes were sunk and the use of steam driven pumps allowed exploitation beyond any previous level leaving the aquifer depleted. The third water level is from c1997. Industries in central London, eg. Breweries, paper mills, have closed down or relocated. London has turned more to commerce than heavy industry and reduced abstraction leads to a water level recovery. 3 Slide 5 History of abstraction l Development of deep boreholes l Over-abstraction until 1940’s l Period of relative stability until 1970’s l Period of rising levels To sum up. Slide 6 Variation in groundwater levels -30 -40 -50 Period of increasing abstraction -60 Period of stable abstraction -70 Period of decreasing -80 abstraction Water level, metres below sea level below sea metres level, Water Ground level, 12.6 metres above sea level -90 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 4 Slide 7 Groundwater quality l Confined aquifer l Age of water l Ion exchange and softening l Anaerobic conditions - iron l Fluoride, sulphate, and manganese l Saline intrusion The water is very old. Emphasis from this slide is that there is a long time for chemical reactions to occur and hence some water quality can be very poor. This makes potable water use difficult. To the east, saline intrusion is present – from R. Thames Estuary . Slide 8 Effects and possible damage l Seepage into tunnels and deep basements l Saturation of the clay l Changes in clay bearing capacity l Movement in deep structures l Movement of inclined tunnels l Differential movement of adjacent foundations Most high-rise buildings and deep tunnels constructed in the last 100 years with little thought given to changes in water levels. LUL pumps around 30000m3 from their network every day – 4500m3 from Victoria per day alone! 5 Water rises through the sand and effects the clay. This is especially prevalent with inclined tunnels – eg. Escalator shafts. Interesting fact – 1m3/day is equivalent to the ave. daily water consumption of 7 people. Slide 9 Progress Towards a Solution l Raising Awareness l The creation of the strategy l The five-phase strategy l Programme l Progress to date This part of the presentation will discuss these issues concerning the delivery of solutions. 6 Slide 10 Raising Awareness & Gaining Commitment l CIRIA study 1989 l GARDIT 1993 l London Underground studies l GARDIT update 1996 l Meeting with the Minister Nov 1997 l The Creation of the GARDIT Strategy l The GARDIT Strategy launch Mar 1999 l 1st Committee Meeting July 2000 l 2nd Committee Meeting October 2001 CIRIA=Construction Industry Research & Information Association Special Publication 69. LUL studies were in 1995 and carried out by TW. 1997 meeting was with John Prescott. 1999 GARDIT strategy was endorsed by Nick Raynsford. 7 Slide 11 The original five-phase strategy l 70 Ml/d abstraction • Groundwater model • Phase 1 – Existing licensed sites 20Ml/d • Phase 2 – Proven unlicensed sites 12Ml/d • Phase 3 – Private commercial boreholes 20Ml/d • Phase 4 – New central area boreholes 15Ml/d • Phase 5 – New outer area boreholes 3Ml/d The strategy revolved around increasing abstraction from the central London area by 70Ml/d. This figure was agreed by the EA based on abstraction information during the period of stability. Phase 1 - computer model constructed of the lower aquifer. Commissioned by TW&EA, built by Mott McDonald. Idea is to use it as a predictive tool. Phase 1 – these were TW existing licenses at Streatham, Merton, Honor Oak and Wanstead. The sites had become disused or for emergency only. Phase 2 – Three sites are being worked on – New River Head nr Finsbury, Battersea and Brixton. Brixton is having a treatment plant installed, the other sources will be transferred raw to remote treatment plants. Phase 3 – This phase is to allow private individuals and new entrant water companies to exploit water for (mostly) non-potable use. Eg. Queens Gallery, Buckingham Palace. MWC boreholes in Hackney and Hammersmith. Also a GLA borehole (EA to comment). Phase 4 – Identifications and exploitation of new sources in central London. TW – Campden Hill-Kensington & Chelsea, Porchester Square-Westminster and Barrow Hill-Camden. Others being reviewed. Raw water transfers predominantly. Phase 5 – As yet unscoped. 8 Slide 12 Affected area Phase 3 boreholes Map showing area subject to fluctuations in water level – Outer level abstraction more influential in controlling water level. Sites also shown. Phase 3 boreholes are MWC sites in Hackney, Hammersmith and Dulwich, the Buckingham Palace borehole and the GLA borehole. Slide 13 WATER QUALITY GREEN CLUSTER A water supply needs to be wholesome, SUPPLY guaranteed and appropriate for the purpose for which is it required. Water for a green city Hospital Industrial Estate Industrial Use 20% potable School Office Use 80% non-potable Housing 37% potable Parks & Estate 63% non-potable Gardens Household Use 52% potable 48% non-potable London Clay Chalk Chalk This slide provided by MWC one of the new entrant water companies. It shows statistics related to water use and that there is more than one company involved. Prompt Mr. Shirley-Smith to comment further during presentation. 9 Slide 14 Affected area - Water quality Waltham Redbridge Barnet Forest Islington Brent Camden Hackney Barking & Dagenham K e To w e r H n a s Hamlets m in C Newham m g ITY t Ea l in g e o r n s We stminste r m & it C h h & e Hounslow ls F e Greenwich u a lh Southwark a m Richmond Le wish a m Wandsworth Area of high sodium levels (>150mg/l) 1996 water level <-40m Central Area boundary 1996 water level <-10m Outer Area boundary Shows area where sodium levels are above 150mg/l – this is above the Drinking Water Inspectorate max. limits. Treatment is difficult/expensive. Slide 15 Programme 1999 2000 2001 2002 2003 2004 2005 Set up model Phase 1 Operate Build & equip Phase 2 Control pumping Build treatment plant Treat water Identify potential sites Phase 3 Drill, test and equip Abstraction from sites Exploration/testing Equip for pumping Phase 4 Control Pumping Build treatment plant Treat water Exploration/testing Equip for pumping Phase 5 Control Pumping Build treatment plant Treat water Phase 3 progress reported by EA. 10 Slide 16 Progress to Date l Phase 1 complete l Groundwater model calibrated and running l Phase 2 drilling and initial testing complete l Phase 3 20Ml/d identified with 8Ml/d under construction l Phase 4 site identification progressing In words – the progress to date. 11.