Baseline Report Series: 14. The Corallian of Oxfordshire and Wiltshire Groundwater Systems and Water Quality Commissioned Report CR/04/262N Science Group: Air, Land & Water Technical Report NC/99/74/14 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/04/262N ENVIRONMENT AGENCY Science Group: Air, Land & Water Technical Report NC/99/74/14 This report is the result of a study jointly funded by the British Baseline Report Series: Geological Survey’s National Groundwater Survey and the 14. The Corallian of Oxfordshire and Environment Agency Science Group. No part of this work may be Wiltshire reproduced or transmitted in any form or by any means, or stored in a retrieval system of any nature, without the prior permission of the copyright proprietors. J Cobbing, M Moreau, P Shand, A Lancaster All rights are reserved by the copyright proprietors. Contributors Disclaimer The officers, servants or agents of both the British Geological Survey and the R Hargreaves (GIS) Environment Agency accept no liability 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 Internal: Release to Regions External: Public Domain ISBN: 978-1-84432-639-6 Product code: SCHO0207BLYL-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 Shelly, oolitic Corallian limestone near Baulking, Vale of White Horse. Key words Environment Agency Project Manager: Baseline, Corallian, water quality, hydrogeochemistry, UK aquifer. Dr Rob Ward / Jonathan Smith Science Group: Air, Land & Water Bibliographic Reference Cobbing, J, Moreau, M, Shand, P & British Geological Survey Project Manager: Lancaster, A. 2004. Baseline Report Series 14: The Corallian of Oxfordshire Dr Paul Shand and Wiltshire. British Geological Groundwater Systems & Water Quality Programme Survey Commissioned Report No. CR/04/262N Environment Agency Science Group, Solihull 2004 British Geological Survey, Keyworth, Nottingham 2004 ©Environment Agency 2004 ©NERC 2004 BRITISH GEOLOGICAL SURVEY ENVIRONMENT AGENCY 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. 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EXECUTIVE SUMMARY 1 2. PERSPECTIVE 2 3. BACKGROUND TO UNDERSTANDING BASELINE QUALITY 4 3.1 Introduction 4 3.2 Geology 4 3.3 Hydrogeology 7 3.4 Aquifer mineralogy 9 3.5 Rainfall chemistry 9 3.6 Land use 10 4. DATA AND INTERPRETATION 12 4.1 Project sampling programme 12 4.2 Previous data 12 4.3 Interpretation of pumped groundwater samples 12 4.4 Data handling 13 5. HYDROCHEMICAL CHARACTERISTICS 14 5.1 Introduction 14 5.2 Water types and physicochemical characteristics 16 5.3 Major elements 17 5.4 Minor and trace elements 19 5.5 Pollution indicators 21 6. GEOCHEMICAL CONTROLS AND REGIONAL CHARACTERISTICS 22 6.1 Introduction 22 6.2 Mineral Dissolution Reactions 22 6.3 Redox reactions 23 6.4 Ion exchange reactions 24 6.5 Mixing with connate waters 26 6.6 Chemical evolution along flowlines 28 6.7 Temporal variations 30 i 6.8 Depth variations 30 6.9 Age of the groundwater 32 6.10 Spatial variations 32 7. BASELINE CHEMISTRY OF THE AQUIFER 43 8. SUMMARY AND CONCLUSIONS 45 9. REFERENCES 46 ACKNOWLEDGEMENTS 48 ii List of Figures Figure 2.1 Topographic Map of the study area showing the main towns. .....................................2 Figure 2.2 A view north across the Corallian outcrop from the Chalk scarp at Whitehorse Hill (from approximately SU 297 865)................................................................................3 Figure 3.1 Solid geology of the study area.....................................................................................5 Figure 3.2 Drift geology of the study area. ....................................................................................7 Figure 3.3 Geophysical Logs at Kingston Hill Farm. ....................................................................7 Figure 3.4 Generalised land use map of the study area. Data from Land Cover Map 1990, supplied courtesy of the Centre for Ecology and Hydrology. ©NERC......................10 Figure 3.5 Sand and aggregate quarrying operations near Shellingford (SU 329 938)................11 Figure 3.6 Former Corallian limestone quarry near Stanford in the Vale (SU 326 943). ............11 Figure 5.1 PIPER plot showing the relative concentrations of major elements...........................16 Figure 5.2 Box plot showing the ranges of major element concentrations. .................................18 Figure 5.3 Cumulative probability plot of major elements. .........................................................18 Figure 5.4 Box plot showing the ranges of minor and trace element concentrations...................19 Figure 5.5 Cumulative probability plot of selected minor and trace elements.............................20 Figure 6.1 Plots of Sr/Ca ratio against HCO3 concentration, and Mg/Ca ratio against Na concentration...............................................................................................................23 Figure 6.2 Plots of selected element concentrations against Eh (mV). ........................................25 Figure 6.3 Ca concentration plotted against Na concentration for confined and unconfined groundwaters...............................................................................................................26 Figure 6.4 Selected parameters plotted in relation to a seawater dilution line.............................27