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  • Final Report Project WFD28

    Development of a groundwater vulnerability screening methodology for the Water Framework Directive

    September 2004

  • © SNIFFER 2004

    All rights reserved. No part of this document may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without the prior permission of SNIFFER.

    The views expressed in this document are not necessarily those of SNIFFER. Its members, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance upon views contained herein.

    Dissemination status Unrestricted

    Research contractor This document was produced by:

    Derek Ball, British Geological Survey Alan MacDonald, British Geological Survey Brighid Ó Dochartaigh, British Geological Survey Maria del Rio, British Geological Survey Vincent Fitzsimons, SEPA Clive Auton, British Geological Survey Allan Lilly, Macaulay Land Use Research Institute

    SNIFFER’s project manager SNIFFER’s project manager for this contract is: Vincent Fitzsimons, SEPA

    SNIFFER First Floor, Greenside House 25 Greenside Place EDINBURGH EH1 3AA www.sniffer.org.uk

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  • Foreword

    This report was commissioned by the Scotland and Northern Ireland Forum for Environmental research (SNIFFER) on behalf of the Scottish Environment Protection Agency (SEPA). The groundwater vulnerability methodology developed under this project is intended not only to reflect the geological and hydrogeological conditions present in Scotland, but also that in Northern Ireland, England and Wales. The GIS map produced using the methodology is intended to assist SEPA to determine the risk of groundwater contamination within groundwater bodies in Scotland, as required by the EC Water Framework Directive (2000/60/EC).

    Acknowledgements

    The authors would like to thank the following for useful discussions and assistance with deriving the vulnerability methodology. N. S. Robins: British Geological Survey. H. Barron: British Geological Survey. Peter McConvey: British Geological Survey Rob Ward: Environment Agency, England and Wales. Donal Daly: Geological Survey of Ireland. Jean Alexander: British Geological Survey. Keith Holmes: British Geological Survey. Martin Smith: British Geological Survey. Nikki Smith: British Geological Survey.

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  • CONTENTS Foreword..................................................................................................................... iii Acknowledgements ..................................................................................................... iii Executive Summary ................................................................................................... vii 1 Introduction ....................................................................................................... 1 2 The Need For Groundwater Vulnerability Mapping........................................ 3 3 Basic Concepts Of Groundwater Vulnerability .............................................. 5

    3.1 Definitions.................................................................................................... 5 3.2 Key concepts............................................................................................... 6 3.3 Attenuation .................................................................................................. 8 3.4 Data Availability in Scotland ........................................................................ 9

    4 Methodology .................................................................................................... 12 4.1 Developing the key datasets ..................................................................... 12 4.2 Permeability of Superficial Deposits.......................................................... 12 4.3 Porosity type in bedrock receptor aquifers ................................................ 17 4.4 Permeability of intergranular and intergranular-dominant bedrock aquifers.. .................................................................................................................. 18 4.5 Superficial deposits thickness ................................................................... 18 4.6 Depth to Water .......................................................................................... 19

    5 The Vulnerability classification system ........................................................ 21 5.1 The seven vulnerability scenarios ............................................................. 22 5.2 Procedure for creating the vulnerability map............................................. 24

    6 Conclusions..................................................................................................... 26 Appendix 1 ............................................................................................................ 29 Appendix 2 ............................................................................................................ 39 Appendix 3 ............................................................................................................ 41 Appendix 4 ............................................................................................................ 43

    List of Figures

    Figure 3-1 The effective part of the pathway for governing the attenuation capacity and travel time for different porosity regimes within the receptor........................ 8

    Figure 4-1 Data sources for groundwater vulnerability derivation............................ 13 Figure 4-2 Cumulative frequency of clay content for the two soil parent material

    groups ............................................................................................................... 16 Figure 5-1 The seven vulnerability scenarios.......................................................... 23 Figure 5-2 Procedure for the creation of the vulnerability classification.................. 25 Figure 6-1 Groundwater vulnerability map of Scotland ........................................... 27

    List of Tables

    Table 1 Vulnerability definitions for potentially polluting surface activities (adapted from Foster, 1998)............................................................................................... 6

    Table 2 Attenuation mechanisms and contaminants ..................................................... 10 Table 3 Permeability categories for superficial deposits………………………………14 Table 4 Summary statistics for the clay contents of the parent materials of Scottish soils…………………………………………………………………………………………..15

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  • EXECUTIVE SUMMARY

    Development of a groundwater vulnerability screening methodology for the Water Framework Directive

    WFD 28 British Geological Survey Macaulay Land Use Research Institute December 2003 KEY WORDS: Water Framework Directive, groundwater, vulnerability, aquifers, geology, pollution A requirement of the EU Water Framework Directive is the assessment of the risk of groundwater contamination within those groundwater bodies identified in each Member State. In order to carry out the risk assessments, knowledge of the vulnerability of groundwater is necessary. The current project is in two parts: first, a groundwater screening methodology was developed that was suitable for use in Scotland, but allowance has been made in the design framework for its adaptation in Northern Ireland, England and Wales. Second, the creation of a GIS-based groundwater vulnerability map of Scotland at a working scale of 1: 100,000. Groundwater vulnerability is defined as the tendency and likelihood for general contaminants to reach the water table after introduction at the ground surface. All groundwater is to some degree vulnerable and the screening tool produced for the current project is designed to reflect the ability of contaminants to reach the water table surface across Scotland. It is not intended as a complete solution to risk assessment and should be used as a regional guide to the degree of specific site investigation required at any locality. The screening methodology applies to the situation where contamination from the land surface leaches vertically downwards to the water table within the uppermost aquifer at a particular locality. The groundwater vulnerability assessment is, therefore, influenced by several factors that relate to the pathway element of a typical hazard – pathway – receptor risk assessment. In this case, the pathway is characterised by the geological and hydrogeological characteristics of the soil layer, the underlying superficial deposits and bedrock. The pathway between the ground surface and the water table can affect the degree of attenuation of contaminants:

    The permeability and clay content of the superficial deposits. The thickness of the superficial deposits. The mode of groundwater flow in bedrock aquifers (fracture or intergranular

    flow). The permeability and clay content of intergranular bedrock aquifers. The depth to the water table in both superficial and intergranular bedrock

    aquifers.

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  • It is the above factors that determine the vulnerability classification. Vul