NRA Water Resources 28 Ig UIDE TO GROUNDWATER VULNERABILITY MAPPING IN ENGLAND AND WALES National Rivers Authority GUIDE TO GROUNDWATER VULNERABILITY MAPPING IN ENGLAND AND WALES R C Palmer, I P Holman (Soil Survey and Land Research Centre, Cranfield University) N S Robins, M A Lewis (British Geological Survey) The Information Centre National Rivers Authority Waterside Drive © National Rivers Authority, 1995. Applications for reproduction should be to HMSO Copyright Unit, St Crispins, Norwich NR3 1PD First edition 1995 ISBN 0 11 310103 1 ISSN 1358-328X This Guide was produced for the NRA by the Soil Survey and Land Research Centre (SSLRC) and The British Geological Survey (BGS) under a contract constituting part of the NRA’s Research and Development programme. Designed by HMSO Graphic Design Cover and text printed on recycled materials (HMSO Recycled Register — Score 60.0) FOREWORD In 1992 the National Rivers Authority published its Policy and Practice for the Protection of Groundwater. The implementation of the policy depends upon the definition of groundwater source protection zones and on the preparation of vulnerability maps. This guide is one of two volumes which provide the background to the production and use of these two policy tools and complement the original policy document. The companion volume to this Guide is the Guide to Groundwater Protection Zones in England and Wales. GUIDE TO GROUNDWATER VULNERABILITY MAPPING IH ENGLAND AND WALES CONTENTS 1 INTRODUCTION 1 1.1 Aims of the guide 1 1.2 Background 1 1.3 Groundwater vulnerability 3 2 PRINCIPLES USED IN GROUNDWATER VULNERABILITY MAPPING 6 2.1 Water cycle 6 2.2 Hydrogeology 6 2.3 Soil 9 2.4 Factors affecting pollutant movement in soil 12 3 MAP PRODUCTION METHODOLOGY AND DATA SOURCES 15 3.1 Overview 15 3.2 Geology 15 3.3 Soil 18 3.4 Low permeability drift deposits 22 4 USE AND INTERPRETATION OF THE MAPS 23 4.1 Overview of information provided by the maps 23 4.2 Example interpretations 25 4.3 Regional differences in low permeability drift interpretation 27 5 LIMITATIONS OF THE GROUNDWATER VULNERABILITY MAPS 29 5.1 Introduction 29 5.2 Geological data limitations 29 5.3 Soil data limitations 31 5.4 Drift data limitations 32 5.5 Site specific limitations 34 6 REFERENCES 37 APPENDICES 1 Stratigraphic column and strata in aquifer classes 38 2 Commonly occurring soil series within soil leaching potential classes 44 3 Key sheet for understanding the NRA Groundwater Vulnerability Maps 45 4 Glossary of Terms 46 IV 1 INTRODUCTION 1.1 AIMS OF THE GUIDE This guide is designed to be used with the series of 1:100 000 scale maps which form part of the National Rivers Authority (NRA) Policy and Practice for the Protection of Groundwater (abbreviated in this document to Groundwater Protection Policy - GPP), published in 1992. The maps depict groundwater vulnerability, a concept based on interpretations of geology and soil, and the series is being progressively published over a 4'/2 year period with full coverage of England and Wales expected by 1998. The programme is being carried out by the Soil Survey and Land Research Centre (SSLRC) and the British Geological Survey (BGS) to take advantage of the existing soil and geological databases of the two organizations. The aims of this guide are to: different ways by the various users of the Groundwater Vulnerability • give the background to the Maps. groundwater vulnerability Those who only require sufficient mapping programme guidance to use and interpret the • describe the groundwater, maps are advised to consult: geology, soils and contaminant transport principles used in the • Chapter 1 - Introduction classifications forming the basis • Chapter 3 - Map production of the maps methodology and data sources • describe the methodology and • Chapter 4 - Use and data sources used in the interpretation of the maps. production of the maps Those users requiring specialist • provide an overview of how to technical information on the use the maps through example principles used in the compilation of interpretations the maps and on the conceptual • discuss some limitations of limitations of the maps should also groundwater vulnerability consult: mapping in general and at 1:100 000 scale in particular. • Chapter 2 - Principles used in groundwater vulnerability This guide, together with the Source mapping Protection Zone Guide, provides a • Chapter 5 - Limitations of the complement and update to the GPP Groundwater Vulnerability and is directed towards the Maps following readership: • NRA officers, and particularly 1.2 BACKGROUND non-specialists in groundwater L2.1 The importance of groundwater protection Groundwater is contained naturally • developers and their agents within underground water-bearing • planning, central government strata (aquifers') of various types and other statutory authorities across the country. It is present • interest groups within all rocks but some contain • consultants. more than others and are therefore Because of the likely different levels more important for water resources. of technical knowledge between the The volume of water stored in the many map user-groups this guide is pores and fractures of aquifers vastly aimed at the informed non-specialist exceeds the volumes of fresh water lay person. However, as the guide in lakes and rivers in England and provides both general and detailed background information, it is 1 Words shown in italics are defined in the envisaged that it will be used in glossary GUIDE TO GROUNDWATER VULNERABILITY MAPPING IN ENGLAND AND WALES Wales. Many of the most productive to the inaccessibility of the aquifers, such as the Chalk or strata, the slow rates of Triassic sandstones, occur in the groundwater movement and the densely populated relatively dry low levels of microbiological eastern and central parts of England activity. Processes which take and consequently, groundwater has a place in days or weeks in surface strategic significance in providing water systems are likely to take high quality water for public supply. decades in groundwater systems. It provides approximately 35 per cent of present national demand but It is better to prevent or reduce the in some southern and eastern risk of groundwater contamination regions more than 80 per cent. than to deal with its consequences. Groundwater is also an important source for industry and agriculture 1.2.2 Groundwater vulnerability within as well as sustaining the baseflow of the legislative framework rivers. Rivers can dry up without In 1980 the European Commission sufficient volumes of groundwater introduced a Groundwater Directive inflow as occurred in Chalk streams (80/68/EEC) aimed largely at the during the drought of the early control of discharges of a wide 1990’s. Baseflow often provides the range of potentially toxic bulk of a river’s flow in summer so substances. These are grouped by that groundwater quality is crucial the Directive into List I and List II in maintaining surface water quality substances (NRA 1992). The to the benefit of aquatic ecology, Directive did not address either wetland habitats and recreational diffuse pollution arising from the uses. use of agricultural fertilizers or the Groundwater is increasingly essential links to the management of under threat. Pollution can arise abstraction. from many activities carried out on, At a Seminar on Groundwater or near, the land surface. This may held in the Hague in November be at a particular place (a point 1991, EC Environment Ministers source) or be widespread over large recognized the limitations of areas (a diffuse source). Examples of existing community-wide point source pollution include regulations and adopted an action spillages of chemicals from programme for the future industrial sites which give rise to protection of groundwater. intense but localised effects. In Groundwater is recognized as a contrast, nitrate pollution from finite, natural resource of great value agriculture is a diffuse source which which should be managed and can build up over many years and protected on a sustainable basis. The affect significantly larger volumes of subsequent declaration stressed that groundwater. The protection of the objective of sustainability should groundwater quality is of critical be implemented through an importance for the following integrated approach, which means reasons: that surface water and groundwater should be managed as a whole, • The degradation of a widespread paying equal attention to both high quality water resource, quality and quantity aspects and through contamination of an taking into account all interactions aquifer, might necessitate the with the soil and atmosphere. development of more expensive The NRA (and the Environment water resources, if available, or Agency after April 1996) has a duty expensive water treatment to monitor, maintain and protect before use. groundwater resources from • Once polluted, groundwater is pollution with the aid of various costly and difficult, if not legislative provisions. These impossible, to rehabilitate due provisions implement EC Directives 2 including the 80/68/EEC Directive contamination from surface or near­ on the Protection of Groundwater surface derived pollutants, Against Pollution Caused by recognizes that the risk of pollution Certain Dangerous Substances, the from a given activity is greater in Control of Pollution Act 1974, the certain soil and hydrogeological Environment Protection Act 1990 situations than in others. and the Water Resources Act 1991. Groundwater vulnerability Together they control the storage depends on the natural and discharge of dangerous characteristics of a site and relates chemicals to groundwater, control to the ease of vertical movement of the disposal of wastes, and control pollutants. It is assessed on the the handling of potential pollutants physical, chemical and biological used in the agricultural industry. properties of the soils and rocks At its time of creation in 1989, beneath the site as these control the the NRA inherited various ease with which a pollutant can Groundwater Protection Policies migrate to the water table. The from the former Water Authorities.