Baseline Report Series: 16. The Granites of South-West England Groundwater Systems and Water Quality Commissioned Report CR/04/255 Environment Agency Science Group Technical Report NC/99/74/16 The Natural Quality of Groundwater in England and Wales A joint programme of research by the British Geological Survey and the Environment Agency BRITISH GEOLOGICAL SURVEY Commissioned Report CR/04/255 ENVIRONMENT AGENCY Science Group: Air, Land & Water Technical Report NC/99/74/16 This report is the result of a study jointly funded by the British Geological Baseline Report Series: Survey’s National Groundwater Survey and the Environment Agency’s Science 16. The Granites of South-West Group. No part of this work may be reproduced or transmitted in any form or England by any means, or stored in a retrieval system of any nature, without the prior permission of the copyright proprietors. All rights are reserved by the copyright P L Smedley and D Allen proprietors. Disclaimer Contributors The officers, servants or agents of both the British Geological Survey and the Environment Agency accept no liability *M Thornley, R Hargreaves, C J Milne whatsoever for loss or damage arising from the interpretation or use of the information, or reliance on the views contained herein. Environment Agency Dissemination status *Environment Agency Internal: Release to Regions External: Public Domain ISBN: 978-1-84432-641-9 Product code: SCHO0207BLYN-E-P ©Environment Agency, 2004 Statement of use This document forms one of a series of reports describing the baseline chemistry of selected reference aquifers in England and Wales. Cover illustration Cliffs of jointed granite at Pordenack Point, near Land’s End (photography: C J Jeffery). Environment Agency Project Manager: Key words Baseline, Granite, Cornwall, Devon, Dr Rob Ward / Jonathan Smith groundwater quality, hydrogeochemistry, Science Group: Air, Land & Water UK aquifer. British Geological Survey Project Manager: Bibliographic Reference Smedley, P.L. and Allen D. 2004 Dr Paul Shand Baseline Report Series 16: The Granites Groundwater Systems & Water Quality Programme of South-West England British Geological Survey Commissioned Report No. CR/04/255 ©Environment Agency 2004 Environment Agency Science Group, Solihull 2004 British Geological Survey, Keyworth, Nottingham 2004 ©NERC 2004 ENVIRONMENT AGENCY BRITISH GEOLOGICAL SURVEY The full range of Survey publications is available from BGS The Environment Agency is the leading public body protecting Sales Desk at the Survey headquarters, Keyworth, Nottingham. and improving the environment in England and Wales. The more popular maps and books may be purchased from BGS-approved stockists and agents and over the counter at the It's our job to make sure that air, land and water are looked after by Bookshop, Gallert 37, Natural History Museum, (Earth everyone in today’s society, so that tomorrow’s generations inherit Galleries), Cromwell Road, London. Sales. Sales Desks are a cleaner, healthier world. also located at the BGS London Information Office, and at Murchison House, Edinburgh. The London Information Office Our work includes tackling flooding and pollution incidents, reducing maintains a reference collection of the BGS publications industry’s impacts on the environment, cleaning up rivers, coastal including maps for consultation. Some BGS books and reports waters and contaminated land, and improving wildlife habitats. may also be obtained from the Stationery Office Publications Centre or from the Stationery Office bookshops and agents. Environment Agency, Rio House, Waterside Drive, Aztec West Almondsbury, Bristol, BS32 4UD The Survey publishes an annual catalogue of maps, which lists Tel: 01454 624400 Fax: 01454 624409 published material and contains index maps for several of the www.environment-agency.gov.uk BGS series. Further copies of this report are available from the Environment The British Geological Survey carries out the geological Agency's National Customer Contact Centre by emailing: survey of Great Britain and Northern Ireland (the latter as an [email protected] agency service for the government of Northern Ireland), and of or by telephoning 08708 506506. the surrounding continental shelf, as well as its basic research projects. It also undertakes programmes of British technical aid in geology in developing countries as arranged by the Department for International Development and other agencies. Environment Agency Regional Offices The British Geological Survey is a component body of the Anglian Natural Environment Research Council. Kingfisher House, Goldhay Way, Orton Goldhay, Peterborough PE2 5ZR Keyworth, Nottingham NG12 5GG Tel 01733 371811 Fax 01733 231840 0115-936 3241 Fax 0115-936 3488 e-mail: [email protected] Midlands www.bgs.ac.uk Sapphire East, 550 Streetsbrook Road, Solihull, West Midlands Shop online at: www.geologyshop.com B91 1QT Tel 0121 711 2324 Fax 0121 711 5824 Murchison House, West Mains Road, Edinburgh EH9 3LA 0131-667 1000 Fax 0131-668 2683 North East e-mail: [email protected] Rivers House, 21 Park Square South, Leeds LS1 2QG Tel 0113 244 0191 Fax 0113 246 1889 London Information Office at the Natural History Museum (Earth Galleries), Exhibition Road, South Kensington, London North West SW7 2DE Richard Fairclough House, Knutsford Road, Warrington WA4 1HG 020-7589 4090 Fax 020-7584 8270 Tel 01925 653999 Fax 01925 415961 020-7942 5344/45 email: [email protected] South West Forde House, Park Five Business Centre, Harrier Way, Manley House, Kestrel Way, Exeter EX2 7LQ Sowton, Exeter, Devon EX2 7HU Tel 01392 444000 Fax 01392 444238 01392-445271 Fax 01392-445371 Southern Geological Survey of Northern Ireland, Colby House, Guildbourne House, Chatsworth Rd, Worthing, Sussex BN11 1LD Stranmillis Court, Belfast BT9 5BF Tel 01903 832000 Fax 01903 821832 028-9038 8462 Fax 028-9066 2835 e-mail: [email protected] Thames Kings Meadow House, Kings Meadow Road, Reading RG1 8DQ Maclean Building, Crowmarsh Gifford, Wallingford, Tel 0118 953 5000 Fax 0118 950 0388 Oxfordshire OX10 8BB 01491-838800 Fax 01491-692345 Environment Agency Wales e-mail: [email protected] 29 Newport Road, Cardiff CF24 0TP Tel 01222 770088 Fax 01222 798555 Sophia House, 28 Cathedral Road, Cardiff, CF11 9LJ 029–2066 0147 Fax 029–2066 0159 Parent Body Natural Environment Research Council, Polaris House, North Star Avenue, Swindon, Wiltshire SN2 1EU 01793-411500 Fax 01793-411501 www.nerc.ac.uk Contents FOREWORD v BACKGROUND TO THE BASELINE PROJECT vii 1. EXECUTIVE SUMMARY 1 2. PERSPECTIVE 2 2.1 Study area 2 2.2 Current issues in groundwater quality 4 3. BACKGROUND TO UNDERSTANDING BASELINE QUALITY 6 3.1 Introduction 6 3.2 Geology 8 3.3 Hydrogeology 12 3.4 Mineralogy and mineral chemistry 14 3.5 Rainfall chemistry 16 3.6 Land use 18 4. DATA AND INTERPRETATION 19 4.1 Data sources 19 4.2 Data quality and handling 19 5. HYDROCHEMICAL CHARACTERISTICS 21 5.1 Introduction 21 5.2 Major constituents 23 5.3 Trace elements 25 5.4 Organic compounds 26 6. GEOCHEMICAL CONTROLS AND REGIONAL CHARACTERISTICS 28 6.1 Introduction 28 6.2 Regional variations and controls 28 6.3 Temporal variations 38 6.4 Depth variations 38 6.5 Groundwater residence time 39 7. BASELINE CHEMISTRY OF THE AQUIFER 40 8. SUMMARY AND CONCLUSIONS 41 9. REFERENCES 43 ACKNOWLEDGEMENTS 47 i List of Figures Figure 2.1. Geographical setting of south-west England showing generalised topography, rivers, rainfall-gauging stations and the location of the Cornubian granites; these are from west to east: Land’s End, Godolphin, Carnmenellis, St Austell, Bodmin Moor and Dartmoor (smaller plutons are not marked)..................................................................2 Figure 2.2. Land’s End, Cornwall [SW 342 253] from the South West Coast Path. ......................3 Figure 2.3. Sandy beaches and tourism in St Ives, Land’s End granite [SW 520 403]...................3 Figure 2.4. Granite tor, Heltor Rock, Dartmoor [SX 7997 8703] (photography: T. Cullen). .........4 Figure 3.1. View of the East Dart River and granite landscape, Bellever, Dartmoor [SX 658 773]. ......................................................................................................................................6 Figure 3.2. Legacy of the Cornish tin-mining history, St Just, Land’s End granite [SW 388 312].7 Figure 3.3 Geological map of south-west England showing the locations of the Cornubian granite outcrops and locations of groundwater samples included in this study............8 Figure 3.4 Map of the distribution of drift deposits on the granites of south-west England........11 Figure 3.5. Kaolin extraction, Greensplat quarry in the St Austell granite [SX 000 555]. ...........11 Figure 3.6. Typical biotite granite, Trevone Quarry [SW 7473 3235], Carnmenellis granite (photography: J.M. Pulsford)......................................................................................14 Figure 3.7. Map of land use in the study area. Data from Land Cover Map 1990, supplied courtesy of the Centre for Ecology & Hydrology, ©NERC. ......................................17 Figure 5.1. Piper diagram for groundwater samples from the granites of south-west England investigated in this study.............................................................................................23 Figure 5.2. Box-and-whiskers plots showing the ranges of minor constituents in groundwaters from the granites of south-west England. Black line: concentrations of ‘diluted’ seawater (normalised to median Cl concentration); grey line: typical detection