groundwater early warning - unescounesdoc.unesco.org/images/0016/001622/162223e.pdf · groundwater...

Edited byJaroslav VrbaBrian Adams

A Methodological Guide

Groundwater Early WarningMonitoring Strategy

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United Nations Educational, Scientific and

Cultural Organization

InternationalHydrologicalProgramme

GroundwaterEarly Warning Monitoring Strategy


Edited byJaroslav VrbaBrian Adams

United NationsEducational, Scientific and


InternationalHydrologicalProgramme

GEWMSnwnw:Mise en page 1 16/04/2008 11:13 Page 1

The designations employed and the presentation of materialthroughout the publication do not imply the expression of anyopinion whatsoever on the part of UNESCO, in particularconcerning the legal status of any country, territory, city or of its authorities or concerning the delimitation of its frontieror boundaries.

Published in 2008 by the United Nations Educational, Scientific and Cultural Organization7, place de Fontenoy, 75352 Paris 07 SP

Composed by Marina Rubio 93200 Saint-Denis

SC-2008/WS/13

© UNESCO 2008

Printed in France


Printed by UNESCO

Prepared for the International Hydrological Programme

By the Project Working Group:

Jaroslav Vrba (The Czech Republic)

Chairman of the Working Group

Brian Adams(United Kingdom)

Editor of the report

Edmund Gosk (Denmark)

Daniel Ronen (Israel)

‘Prevention is Better than Cure’

GroundwaterEarly Warning Monitoring Strategy



This book is dedicated to the memory ofEdmund Gosk,

a long time member of theInternational Association of Hydrogeologists

and its Commission for Groundwater protectionwho died before this book was published


Preface

International Hydrological Programme (IHP) is basically a scientific and educational programme,however, UNESCO has been aware from the beginning of a need to direct its activities toward the practical solutions of the world’s very real water resources problems. Accordingly, and in linewith the recommendations of the 1997 United Nations Water Conference, the objectives of the IHPhave been gradually expanded in order to cover not only hydrological processes considered in inter -relationship with the environment and human activities, but also the scientific aspects of multi-purpose utilization and conservation of water resources to meet the needs of economic and socialdevelopment. Thus, while maintaining IHP‘s scientific concept, the objectives have shifted percep -tibly towards a multi-disciplinary approach to the assessment, planning, and sustainable mana-gement of water resources.

Since its very beginning, groundwater has always been important issue within all phases of the IHP.In nature groundwater is a key element in many geological processes, a geotechnical factor con di-tioning soil and rock behaviour and an ecological component which sustains spring discharge, riverbase-flow and many lakes and wetlands. Groundwater is the most valuable and safe source of drink-ing water in rural areas of developing countries, in arid and semi-arid regions and on islands. In some countries, such as Denmark and Austria, water supplies depend almost entirely on ground-water. Irrigation systems in many parts of the world depend on groundwater. The use of ground-water has increased significantly in recent decades due to its widespread occurrence, mostly goodquality, high reliability during drought seasons and generally modest development costs.

The idea that the geological environment protects groundwater from pollution and thereforegroundwater is not vulnerable to human impacts prevailed for a long time and had serious conse-quences on groundwater quality. That is why the risk aspect became an important element ingroundwater protection policy and management on international and national levels.

UNESCO then considered to contribute to the preparation of a methodological guide on ‘Ground-water Early Warning Monitoringg Strategy’.

Alice AureliResponsible for Groundwater Resources Activities

Secretariat of the International Hydrological ProgrammeDivision of Water Sciences, UNESCO, Paris

Jaroslav VrbaChairman of Groundwater Protection

Commission of the International Association of Hydrogeologists


Acknowledgements

This publication is the outcome of the International Hydrological Programme (IHP). Besides thelisted authors, who contributed the implementation of the report, many other colleagues and members of the Groundwater Protection Commission of International Association of Hydro-geologists (IAH) provided valuable suggestions and remarks during the preparation of this report.

Thanks are expressed also to the institutions, particularly to UNESCO for organization and budget-ary support of the project, to the Ministry of Science, Culture and Sport of Israel and Israel WaterCommission and to the Geological Survey of Denmark for hosting the meetings of Editorial Boardof this report in Israel (2000) and Denmark (2001).

GEWMSnwnw:Mise en page 1 16/04/2008 11:13

Contents

PrefaceAcknowledgementContents

CHAPTER 1. Introduction 13Jaroslav Vrba and Daniel Ronen

CHAPTER 2. Groundwater environments and their vulnerability 17Brian Adams

2.1 Introduction 17

2.2 Vulnerability to groundwater pollution 17

2.3 The soil zone 18

2.4 The unsaturated zone 18

2.5 The saturated zone 19

CHAPTER 3. Human impact on groundwater quality 20Jaroslav Vrba

3.1 Introduction 20

3.2 Point pollution sources 223.2.1 Impact of industrial effluents on groundwater quality 223.2.2 Impact of mining on groundwater quality 253.2.3 Impact of uncontrolled waste disposal site on groundwater quality 253.2.4 Impact of radioactive wastes on groundwater 26

3.3 Multipoint pollution sources 273.3.1 Groundwater pollution in urban areas 273.3.2 Groundwater pollution in rural areas 28

3.4 Diffuse pollution sources 283.4.1 Impact of nitrogen fertilizers on groundwater quality 293.4.2 Irrigation return flow 303.4.3 Impact of pesticides on groundwater quality 30

3.5 Line pollution sources 31

3.6 Areal pollution sources 32

3.7 Groundwater salinisation in coastal areas 32


CHAPTER 4. Early warning groundwater quality monitoring programmes 34Jaroslav Vrba

4.1 Introduction 34

4.2 National groundwater quality monitoring programmes 36

4.3 Regional groundwater quality monitoring programmes 37

4.4 Site specific groundwater quality monitoring programmes 41

CHAPTER 5. Some techniques used for early warning groundwater monitoring 43

5.1 Surface methods 43

Stanislav Mareš, Jan Švoma and Jaroslav Vrba

5.1.1 Introduction 435.1.2 Geobotanical methods 445.1.3 Photographic methods 455.1.4 Geophysical methods 47

5.2 On-site methods 51

Daniel Ronen and Edmund Gosk

5.2.1 Introduction 515.2.2 Suction cups 515.2.3 Direct push 535.2.4 Horizontal monitoring wells 565.2.5 The separation pumping techniques 575.2.6 The Multi Layer Sampler (MLS) 58

CHAPTER 6. Data handling 64Edmund Gosk

6.1 Introduction 64

6.2 Data collection strategy 65

6.3 Data analysis 67

6.4 Modelling 67

6.5 Forecasting 69


CHAPTER 7. Early warning groundwater quality monitoring strategy 70Jaroslav Vrba and Daniel Ronen

CHAPTER 8. References 74

CHAPTER 9. Case studies 78

9.1 Monitoring of groundwater quality problems 78

Petr Rasmussen and Edmund Gosk

9.1.1 Introduction 789.1.2 Monitoring concept 799.1.3 Instrumentation 819.1.4 Groundwater sampling and chemical analysis 839.1.5 Nitrate monitoring 849.1.6 Pesticide monitoring 869.1.7 Conclusion and recommendations 879.1.8 References 87

9.2 Application of a multi layer sampler (MLS) for managerial decision-making regarding utilization of effluents for agricultural irrigation in the coastal plain in Israel 89

Daniel Ronen

9.2.1 Introduction 899.2.2 The unsaturated - saturated interface 909.2.3 Application of a MLS technique in an agricultural area

irrigated with municipal sewage effluents 929.2.4 Conclusions 979.2.5 References 98

APPENDICESAbbreviations and acronyms 100

Glossary 101


FIGURES

1.1 Schematic representation of pollutants (bold arrows)approaching a pumping well 16

3.1 Typical movement of LNAPLs (top) and DNAPLs (below) into the groundwater system 24

4.1 Comparison of pore-water profiles from unconfined and confinedTriasic sandstones, south Yorkshire UK 38

4.2 Changes in hydrochemical profile of shallow fluvial aquifer in the period 1984–1989, Monitoring well HP-65, Middle Elbe region in Central Bohemia, the Czech Republic 39

4.3 N-NO3 distribution in the vertical profile of unsaturated zone.Experimental station Samšín, The Czech Republic 390

4.4 Vertical distribution of N-NO3- concentrations following application of potassium nitrate with limestone in the non-vegetational (left) and vegetational (right) season. Experimental station Samšin, The Czech Republic 40

5.1 Scheme of the unsaturated zone and the uppermost part of the saturated zone with depth variation of the moisture content W and the water saturation Sw 48

5.2 Energy gamma-ray spectrum measured on the Earth’s surface in Prague, the Czech Republic, (1) after the Chernobyl accident on May 4, 1986, (2) compared with the natural gamma-ray spectrum of rocks 50

5.3 A) Location of suction cups, B) Cross section showing the installation of the section cups 52

5.4 Gravimetric water content (θ) in the capillary fringe of continuous-core boreholes CF6 to CF13, in the Coastal Plain aquifer of Israel 54

5.5 Chloride concentration in pore water of continuous-core boreholes CF2, CF3, CF4 and CF5 55

5.6 Installation of horizontal monitoring wells and section of the horizontal screen 56

5.7 Principle of separation pumping 57

5.8 Segment of a multi layer sampler (MLS) showing the dialysis cells spaced at 3 cm intervals and separated by flexible seals (left) and schematic representation of a segment of the MLS inside of a monitoring well (right) 59

5.9 Equilibration test of dialysis cells conducted at 22°C 60

5.10 Schematic representation of a research well for monitoring the water table region 61

5.11 Chemical profiles obtained in the water table region of research well 7 in the Veluve region, the Netherlands, in the forested area subjected to the input of acid rain and ammonia volatized from cultivated land and feed-lots 62

11


5.12 Profiles of xylene, xylidine (dimethyl aniline) and toluene obtained with the MLS in the water table region of Brook Haven National Laboratory, N.Y. 63

6.1 Principles of groundwater monitoring aimed at detecting groundwater problems 66

9.1 Location of the six experimental agricultural watersheds (LOOP1-LOOP6) 80

9.2 Schematic layout of groundwater nests and soil water station 81

9.3 Soil water sampler, construction details 82

9.4 Groundwater nests, construction details 83

9.5 Median annual nitrate concentration in shallow groundwater for 3 sandy and 3 clay till watersheds in the period 1990–1996 85

9.6 Nitrogen load and nitrate in shallow groundwater in the sandy watershed Barslund Bek 85

9.7 Findings of atrazine and two metabolites 5 m bellow surface in the Lillebek watershed 87

9.8 Electrical conductivity and CL-, NO3- and SO42- concentrations found

in the water table region of two monitoring wells, WT-2 and WT-3 and three production wells pumping from the depth (37–55m) bellow the water table 90

9.9 A comparison between dissolved oxygen and dissolved organic carbon profiles obtained in the water table region of the study area (Glil Yam) and the profiles calculated in a simulation model by Molz et al. (1986b) 92

9.10 Production of N2O in the water table region of wells WT-2 and WT-3 93

9.11 Schematic representation of porous media with biochemically produced gas bubbles and antrapped air bubbles 94

9.12 Dramatic decrease in the horizontal component of the specific discharge (q) in the water table region of well WT-3 95

9.13 Example of discrete water layers of varying CL- content as detected in the unsaturated zone of the monitoring wells WT-2 and WT-3 95

9.14 Schematic representation showing two alternative possibilitiesfor the vertical build-up of micro scale water parcels of different salinity 96

9.15 Vertical cross-sections through micro scale isothermal water parcels of CL-, NO3-, SO4

2- and HCO3- in the water table region of well WT-3 96

9.16 Eulerian changes of chloride in consecutive profiles obtained in well WT-2 97


Groundwater, a renewable and finite natural resource, vital for the life of man, economic and socialdevelopment and a valuable component of the ecosystem, is vulnerable to natural and humanimpacts (e.g. pollution by agriculture and industry). The use of groundwater has increased signi -ficantly in the last decades as a result of its widespread occurrence, high reliability during droughtseasons, mostly good quality, advances in drilling and pumping technology and generally modestdevelopment costs. According to available data (UNESCO, 1998) half of the world’s drinking watercomes from groundwater. Historically, little attention was given to the protection of groundwaterquality, mainly because people were unaware of the threats to this hidden resource. The idea that thegeological environment protects groundwater from the impact of surface pollution and that there-fore groundwater is not vulnerable to human activities, prevailed for a very long time. This approachhad serious and long-term consequences on the groundwater quality in many countries.

During the sixties and seventies , there developed a growing interest in the need to protect ground-water. This lead to the establishment of conceptual approaches to groundwater protection and quality conservation based on monitoring, mapping, modelling and vulnerability assessment. Theconcept of groundwater protection and quality conservation has become an important element innational water planning, policy making and management in the course of eighties.

The holistic concept for water resources policy and management, as emphasized at the InternationalConference of Water and the Environment in Dublin (1992), significantly influenced the holisticapproach to development and protection of water resources. This concept stresses the social, econ -omic and ecological value of groundwater, the close connection between groundwater and surfacewater and the need to maintain the integrity of aquatic and terrestrial ecosystems. Moreover, it givesthe same attention to both groundwater quantity and quality and is based on a participatoryapproach involving planners, policy and decision makers, managers, stakeholders and the generalpublic.

Groundwater quality monitoring plays an important role in groundwater protection and effectivelysupports sustainable management of groundwater quality. It provides a valuable base for assessingthe current state of and trends in groundwater quality, helps to clarify and analyse the extent of natural processes and human impacts on groundwater systems in space and time, as well as addressgroundwater problems in relation to the economic development and social and economic needs.Credible, accurate and consistent groundwater quality monitoring data should be available and readily accessible to planners, regulators, decision and policy makers and managers through data management systems. The data should also helps to increase active public participation in the process of groundwater protection and quality conservation. However, at the present level of

1 INTRODUCTION

Groundwater Early Warning Monitoring Strategy 13


knowledge the relationship between the amount of a pollutant released at the soil and rock environ-ment by various human activities and its concentration in groundwater is highly uncertain. This is particularly owing to both the lack of knowledge and the scarcity of data concerning the physical,chemical biological and transport and transformation processes undergone by pollutants in theunsaturated zone, the capillary fringe and the aquifer. Groundwater quality monitoring networkshave to be developed and monitoring of the recharge-soil-unsaturated-saturated groundwater system applied to demonstrate our ability 1/ to study and forecast processes which influence thequality and chemical composition of groundwater, and 2/ to implement relevant measures ingroundwater quality management strategy and groundwater quality conservation policy.

Groundwater quality monitoring programmes operate at the international, national, regional/provincial and local levels. The objective of each of the above programmes governs the extent of themonitoring activities, such as the design of monitoring networks, construction of monitoring wells,frequency and methods of groundwater sampling and number of analysed variables. Internationaland national groundwater quality monitoring programmes are typically background-monitoringactivities, whereas regional and local monitoring programmes are directed towards solving specificproblems. Both background and site-specific monitoring activities should also include an earlywarning monitoring systems.

Background monitoring is usually a long-term activity focusing on systematic observation ofgroundwater quality of large transboundary and national groundwater basins and aquifers.Early warning monitoring systems are not yet a common part of background groundwaterquality monitoring programmes.

Site-specific monitoring of groundwater quality is a suitable tool for the identification of theimpacts of pollution sources on groundwater quality, observation of groundwater qualitychanges due to excessive aquifer abstraction, protection of public groundwater supplies and thedetection of the response of aquifers to remediation. In these activities various methods ofearly warning monitoring may be used. They help in the early identification and control of themovement of pollutants in both the unsaturated and saturated zones.

Early warning monitoring of groundwater quality is an activity or a sequence of activities thatmakes it possible to identify and to foresee the outcome of a process leading to groundwaterpollution with enough anticipation for measures to be taken in order to change or reduce themagnitude of the impact of the said process. Design of an early warning monitoring systemdepends on the time needed to take appropriate action with respect to the specific groundwaterpollution problem.

The penetration of a pollutant into the groundwater system may be either from land surface, froman adjacent area due to lateral movement of a pollution plume or through the bottom of the aquifer(Fig. 1.1). Therefore, different approaches, techniques and methods must be applied for early warn-ing groundwater monitoring according to the specific characteristics of the studied groundwatersystem and pollution impact. The target zone for early warning groundwater monitoring may be avulnerable region of the aquifer or selected extraction zones where pumping wells are located.

The early detection of changes in groundwater quality requires application of various monitoringmethods, which may facilitate the observation of pollutant migration, in the gaseous or liquidphases, through the unsaturated and saturated zone of the aquifer. These methods include mainly

14 Groundwater Early Warning Monitoring Strategy


photographic imaging, geobotanical and geophysical surveying, soil gas surveys, installation oflysimeters and retrieval of sediment, gas and water samples through specially located and designedmonitoring wells, the separation pumping techniques, suction cups, direct push, the multi layersamplers.

Existing monitoring strategies tends to focus attention primarily on the transport and transfor -mation of pollutants within the saturated zone and, in many cases, monitoring the impact ongroundwater quality depends primarily on the analysis of water samples from production wells. Thisstrategy reflects a fatalistic approach which can lead to a series of ex post facto sequential managerialactivities: a) the pollution of production wells is recognized; b) studies are conducted to find thesources of groundwater pollution and design possible (usually lengthy and costly) remedies; c) pro-duction wells have to be closed because groundwater pollution is found to be irreversible, and d) water quality standards are changed to accommodate the need for continued use of the ground-water source.

Production wells are mostly designed to pump water from deep below the water table. Therefore,evidence of pollution build-up in a production well reflects the mixing process in the aquifer, whichoften took place several months or even years after the pollutant had arrived at the groundwatertable.

Generally, existing groundwater quality monitoring programmes are mostly concerned with theidentification and control of the consequences of groundwater pollution and therefore do notaddress the preventive protection of groundwater quality. Clearly, an early warning monitoringstrategy is needed that detects pollutants before they are diluted in the aquifer and significant dete-rioration of groundwater quality occurs. This strategy supports groundwater management and pro-tection policy and helps in identifying human impacts on groundwater quality in the unsaturatedzone and uppermost part of the aquifer while they are still controllable and manageable.

This report is addressed particularly to policy and decision makers in the field of groundwater quality protection. The objective is to convey the message that, in relation to groundwater quality,‘prevention is better than cure’. This is particularly the case when considering time constraints andavailable experience regarding the cost-effectiveness of groundwater quality restoration pro-grammes.




(A) vertical downward influx from the unsaturated zone (e.g., nitrates); (B) lateral movement ofa pollution plume (e.g., trichloroethylene); (C) vertical upward influx through the bottom of theaquifer (e.g. chlorides), and (D) lateral movement of a polluted water body (e.g., seawater intru-sion). For all pollutants concentrations will decrease along the pathway of the small arrowswhere bold dots denote the position of early warning monitoring devices (e.g., multi layer samplers in a monitoring well for A and C and a series of monitoring wells for B and D).

Figure 1.1 Schematic representation of pollutants (bold arrows) approaching a pumping well


2.1 Introduction

In order to plan the installation of effective early warning systems for the detection of groundwaterquality problems, it is necessary to have a basic understanding of the hydrogeological environmentwithin which the groundwater is found, particularly regarding groundwater vulnerability to pollution. Generally, confined aquifers are much less vulnerable than unconfined aquifers due to thepresence of an overlying impermeable stratum. However, as pointed out by some authors (USNational Research Council, 1993), all groundwater is to some extent vulnerable. Thus early warninggroundwater quality monitoring systems are primarily designed for unconfined aquifers.

2.2 Vulnerability to groundwater pollution

As stated in Chapter 1, the focus of this book is the qualitative aspects of groundwater. Thus we areinterested primarily in the vulnerability of aquifers to pollution. Vrba and Zaporozec (eds. 1994)defined groundwater vulnerability to pollution as an intrinsic property of a groundwater system thatdepends on the sensitivity of that system to human and/or natural impacts. Adams and Foster(1992) defined vulnerability as a function of a) the hydraulic inaccessibility of the saturated zone tothe penetration of pollutants, and b) the attenuation capacity of the strata overlying the saturatedzone as a result of physicochemical retention or reaction of pollutants; this definition is particularlyrelevant to the objective of this manual to provide a basis for an early warning monitoring system.

The concept of groundwater vulnerability is based on the assumption that the physical environmentmay provide some degree of protection to groundwater against natural and human impacts. Theextent of the attenuation capacity (the decrease in the concentration of a pollutant as it penetratesthe aquifer system) depends on physical, chemical and biological processes in the soil, and in theunsaturated and saturated aquifer system. Pollutant attenuation is also affected by the transportmechanism in the groundwater system and the class and properties of the pollutant involved.

2 GROUNDWATER ENVIRONMENTS


AND THEIR VULNERABILITY


Two approaches to groundwater vulnerability should be considered: a) specific vulnerability that isrelated to a specific pollutant and/or human activity, and b) intrinsic vulnerability that solely con-siders the natural situation (e.g. net recharge, land slope, soil composition, and the nature of thegroundwater system). Vulnerability of groundwater is a relative, non-measurable, dimensionlessproperty. The accuracy of vulnerability assessment depends above all on the quantity, quality andreliability of available data.

2.3 The soil zone

Soil is commonly regarded as one of the principal natural attributes in the assessment of ground-water vulnerability. Most of the processes causing elimination and/or attenuation of pollutantsoccur in the biologically active soil zone as a result of its higher clay mineral and organic matter con-tent and large bacteriological populations. Texture, structure, composition and thickness of soil varyaccording to a number of factors including climate, topography and underlying geology. However, itis important to stress that the attenuation capacity of soils may be finite.

Many point pollution sources (pits, trenches, lagoons, underground tanks etc.) release their pollu-tants below the soil zone. Thus soil attenuation capacity is generally more important in connectionwith diffuse pollution sources such as the leaching of nutrients and pesticides from agriculturalland. However, the soil’s function as a natural protective filter for the retardation and degradation ofpollutants can be significantly decreased when the dynamic stability of the soil organic matter andthe carbon/nitrogen ratio are disturbed. Thus in the context of early warning systems, sensors orsampling devices should generally be placed below the soil zone to monitor those pollutants thathave not been retained by it.

2.4 The unsaturated zone

The unsaturated zone represents the first line of natural defense of unconfined aquifers againstgroundwater pollution due both to its strategic position between the land surface and the saturatedzone and its potential for pollutant attenuation. However, it must be noted that the role of the un -saturated zone can be complex and its ability to attenuate pollutants difficult to predict. The degreeof attenuation will depend upon the chemical nature of the pollutant, the release mechanism on theland surface (e.g. small spill vs. rupture of a big container), and the lithological and geochemicalcomposition of the unsaturated zone, its thickness and the flow regime through it. In effect, for persistent, mobile pollutants the unsaturated zone will merely introduce a time lag before arrival atthe water table, without significant attenuation. In many other cases the degree of attenuation willbe highly dependent upon the flow regime and residence time which are both largely dependent onannual recharge. Under conditions of natural rainfall infiltration it is reasonable to assume thattransit times in the unsaturated zone will be a function of the annual infiltration rate and a moisturecontent approaching the specific retention capacity following prolonged drainage. Since the lattervaries little among soil and rock types compared with the climatic variations of the former, undernatural conditions the transit time is essentially controlled by annual average infiltration rate.

Water movement through the unsaturated zone of sedimentary deposits is relatively slow and



restricted to small pores. The chemical condition is mostly aerobic and frequently alkaline. Thusthere is considerable potential for a) interception, sorption and elimination of pathogenic bacteriaand viruses, b) attenuation of heavy metals through precipitation, sorption or cation exchange, c) sorption and biodegradation of many natural and synthetic hydrocarbon compounds. In con -solidated fractured rocks having secondary porosity, the potential for rapid by-pass flow will rendergroundwater highly vulnerable to pollution. Rapid transmission of water and pollutants in some-times unexpected directions and over large distances is typical of karstic environments, where thefractures can become enlarged by solution. Thus the geochemical and lithological composition,especially the grade of consolidation and degree of fissuring of the unsaturated zone and ground-water table below surface are key elements in the assessment of aquifer vulnerability to pollution.

Sampling and measurement of solid, liquid and gaseous phases of pollutants throughout the unsat-urated zone (see chapters 4 and 5), is an important factor in the development of early warninggroundwater quality monitoring strategies.

2.5 The saturated zone

The definition of unconfined, semi-confined and confined conditions of the saturated aquifer isvery important in the process of assessment of groundwater vulnerability. Unconfined aquifersbounded above by an unsaturated zone formed by permeable layers, containing both air and water,are considered highly vulnerable. Confined aquifers bounded above and below by impermeable lay-ers, containing water under pressure, are considered to have low or very low vulnerability. In generalterms recharge to unconfined aquifers is from the land surface immediately above it whereas forconfined regions recharge is laterally from generally higher areas where the aquifer is unconfined.

Rock texture and permeability, groundwater flow direction, hydraulic gradient, hydraulic conduc-tivity, the contaminant class in terms of its mobility and persistence and biological, physical andchemical reactions all control pollutant attenuation and transport in the saturated groundwater sys-tem. Therefore, construction and screen location of monitoring wells for early warning monitoringof groundwater and dedicated sampling techniques should take in to consideration both thegroundwater system and the pollutant properties.



3.1 Introduction

This chapter is primarily concerned with adverse human effects on groundwater quality. However,certain natural constituents in groundwater can also reach undesirable concentrations with conse-quent potential impact on human health and ecosystems. The composition of groundwater is pri-marily controlled by: the properties of the soil and rock in which groundwater moves, the contacttime an contact surface of groundwater with geological materials along flow paths, the rate of geo-chemical, microbiological and physical processes within the soil-rock-groundwater system and thepresence of dissolved gasses.

Differences in chemical composition between lateral (recharge and discharge areas) and vertical(shallow oxidation zones and deep reduction zones) profiles in groundwater systems are recognised.Generally, shallow groundwater in recharge areas has a lower dissolved solids content than ground-water in discharge areas from deeper aquifers. An increasing content of total dissolved solids and ananion evolution sequence HCO3

- -SO42- - Cl-, expressing the change from oxidising to reducing

conditions, are usually observed in the vertical profile of groundwater systems. However, suchhydrochemical profile can not be applied to shallow coastal aquifers where groundwater compo -sition is under the influence of saline water.

Biological processes enhance the extent and rate of geochemical processes. They are particularlyintensive in the soil/root zone, where oxygen is available for both organism respiration and thebreakdown of organic matter.

Examples of the influence of natural constituents on groundwater quality include particularly highiron and manganese content, the presence of zinc, arsenic and other trace metals released intogroundwater from ore-bearing deposits, excessive concentration of fluoride and arsenic, elevatedconcentration of chloride in coastal aquifers and the presence of organic compounds from peatdeposits. The natural chemical composition of groundwater (natural background) needs to beknown, when assessing the extent of human impacts on groundwater.

Groundwater quality deterioration and pollution as a consequence of human activities are recog-nized as a serious worldwide environmental and socio-economic problems. Groundwater pollution

3 HUMAN IMPACT ON

GROUNDWATER QUALITY



is a process whereby water gradually or suddenly changes its natural physical, chemical or biologicalcomposition and quality and ceases to meet the criteria and standards set for drinking water, irriga-tion and other purposes (Vrba, 2000).

Various criteria have been used to classify groundwater pollution. The commonly used classificationsystems are based on the extent of pollution (point, multipoint, diffuse, line, regional), the source ororigin of pollution (industrial, mining and military activities, waste disposal sites, urban and ruralsettlements, agriculture, transport networks, oil lines, streams, sewerage systems and acid depo -sitions) and the types of pollutants (physical, chemical, biological, radioactive). Pollution classifi -cation criteria are given in Table 3.1. This chapter describes the impact of the most frequentpollution sources on groundwater quality and related monitoring activities.

pollution sources on groundwater quality and related monitoring activities.

Table 3.1 Classification criteria of groundwater pollution sources

Extent of pollution Source of pollution Main pollutants

Point Industry Heavy metals (Pb, Zn, Cd, Cr), arsenic, phenols, petroleum productsand additives, high BOD, suspended solids, chloride, sulphide, alkaline effluents, low pH, chlorinated hydrocarbons, PAHs, synthetic organic and organometalic compounds

Mining Heavy metals, salts (chloride, sulphate), low pH, high TDS, cyanide,PAHs, petroleum products

Waste disposal sitesincluding deep disposal wells

Heavy metals, ammonium, sulphate, chloride, phenols, variousbiodegradable and non-biodegradable organics, feacal pathogens

Radioactive wastes 3H - Tritium, 90Sr, 137Cs, 239Pu, 129I, 226Ra, toxic metals

Cattle – breading lots High suspended solids, BOD, total nitrogen, chloride, feacal pathogens

Multipoint Urban areas Heavy metals (Pb, Zn), ammonia, chloride, sulphate, petroleum products, chlorinated hydrocarbons, surfactants

Rural settlements Ammonia, nitrate, chloride, sulphate, surfactants, iron, manganese,feacal pathogens

Military areas Petroleum products, heavy metals

Non-point (diffuse)

AgricultureCrop and root-cropfarming, irrigation

Fertilizers (organic and inorganic): nitrate, ammonia, chloride, phosphate, natrium, potassium, feacal pathogens, salinityPesticides: organochlorine compounds (aldrine, hepta chlore), carba-mate insecticides (atrazine), polyphosphate, organometalic com-pounds (fungicides)

Line Roads High suspended solids, salts, petroleum products, solvents

Railways Petroleum products, organic chemicals

Oil pipelines Petroleum products

Sewerage systems High suspended solids, nutrients, chloride, high BOD, feacal pathogens

Streams Nitrate, ammonia, iron, manganese, phenols

Areal Acid depositions Aluminium, low pH, nitrate, sulphate

Coastal areas Salinisation Sodium, magnesium, chloride, sulphate, high salinity and TDS



3.2 Point pollution sources

The immediate impact of point pollution sources on groundwater quality is either local or site- specific in extent. However, if a pollution source is not soon identified, groundwater pollution couldbe detected a considerable distance (several hundreds metres or even kilometres) from it. Pollutionof public groundwater supply wells located a long distance from pollution sources have beenreported from several countries (Van Dam, 1967, Csanády, 1968, Williams and Wilder, 1971, Jackson, 1980, Elek, 1980, Ku, 1980, and many others). The most common point pollution sourcesare those relating to industrial, mining and waste disposal activities. Special attention is given hereto hydrocarbons, the most prominent pollutants of groundwater.

3.2.1 Impact of industrial effluents on groundwater quality

Groundwater pollution by industrial waste has been reported from many areas of the world. Sourcesof pollution include uncontrolled leaks and spills from poorly designed and improperly locatedponds, lagoons, pits, basins or ditches, used for the disposal of various kind of industrial liquid andsolid wastes, many of them hazardous. Deep injection wells are also used in some countries for thedisposal of liquid and semi-liquid industrial waste. Groundwater pollution problems related towaste disposal in deep wells described e.g. Aust and Kreysing (1985) and LaMoreaux and Vrba(1990). Disposal of hot water from cooling processes into aquifers is also widely practised.

Remediation of polluted water supply wells, particularly where organic substances are involved, isgenerally a long term, technological demanding and costly process. Wells have to be temporarilyclosed or even abandoned where groundwater pollution is irreversible. Groundwater quality moni-toring systems around industrial pollution sources are often missing. The design of monitoring networks and construction of monitoring wells require considerable expertise and experience incontaminant hydrogeology. The establishment of an early warning monitoring system focuses onthe identification of pollution in the unsaturated zone and on the control of the lateral movementof pollutants in the aquifer outside of the industrial area should be emphasized as a significant toolof groundwater protection policy.

In the following overview the main industrial pollutants (often toxic) of groundwater are identified.Metal plating technologies and surface finishing of metals produce mostly acid waste containinghexavalent chromium, cadmium, lead, zinc and other heavy metals, cyanides bound with heavy metals of different stabilities, phenols, abrasive salts, oils, benzene and thiosulphates. Wastes pro-duced by tannery factories are rich in dissolved chlorides, sulfides and chromium. Textile industrywaste contains heavy metals, dyes and orgnaochlorine compounds. The electrical industry produceswaste with high mercury content. Groundwater pollution by lead and fluorine originating fromenamelling processes in ceramic factories has been also identified (Pellergrini and Zavatti, 1982).Sugar refineries, breweries and other food and drink facilities produce effluents with high suspendedsolids and colloidal and dissolved organic substances.

Wastes from the production of gas by the distillation of coal, contain high concentration of variouskinds of aromatic hydrocarbons, phenols, thiofene and cyanide complexes. Several sites where gashas been produced but have been abandoned for several years still show high levels of pollution inboth the unsaturated and saturated zones.




The petrochemical, metal (cutting and cooling emulsions) and the fat processing industries producevarious kinds of oil wastes. Tenzides are bound with wastes from the textile, leather-tanning andfood industry. The paper and pulp industries produce waste containing organic matter and chlori-nated organic substances. The chemical and pharmaceutical industries generate a wide range oforganic often toxic pollutants, (including chlorinated and aliphatic hydrocarbons, polychlorinatedbiphenyls, phenols, pesticides – organochlorine and organophosphate compounds, surfactants) andinorganic pollutants (heavy metals, cyanide).

Groundwater pollution by oil hydrocarbons

Refined petroleum products (gasoline, petroleum, kerosene, diesel fuel, oil, lubricants and emul-sions) form the largest class of point pollution sources of groundwater. Spillages and leaks occurduring the production and handling (oil refineries, oil processing plants, filling stations), the storage(fuel storage facilities, underground fuel tanks) and the transport (tanker trucks, railway tankers,petroleum pipelines) of petroleum products. Accidental spillages are usually visible, occur suddenly,and the location and amount of the spilled product are generally known. On the other hand, petro-leum leaks due to corrosion or weld failures of underground storage tanks or petroleum pipelinesare latent, and the volume of leakage involved will be usually long term unknown. Because earlywarning monitoring systems are generally not installed, a long period may pass before such leaks areidentified. However, oil hydrocarbons in gaseous or liquid stage are generally easily detectable byearly warning monitoring systems located in the unsaturated zone.

Subsurface lateral and vertical movement of petroleum products depends on the nature of thegroundwater system (particularly its vulnerability) as well as on the quantity and physical andchemical properties of the petroleum products discharged. Their vertical migration will be stemmedon reaching impermeable strata or when the threshold of residual saturation is attained. In suchcases a petroleum plume is immobilised in the unsaturated zone above the water table. This gene -rally occurs when the volume of the discharge is small relative to the surface area of spill, or theunsaturated zone is thick and the permeability low. However, discharged petroleum products willoften reach the capillary fringe and then form a thin film on the groundwater table while emulsionsor the main body of petroleum will sink to different levels within the aquifer. Hydrodynamic disper-sion will cause lateral pollution migration in the direction of the groundwater gradient.

Viscosity and density affect contaminant penetration and migration in the subsurface and signifi-cantly influence the design (particularly well screen installation) and location of monitoring wells.Generally, light nonaqueous phase liquids (LNAPLs), such as gasoline, kerosene and light oils, havea lower density and higher viscosity than water. LNAPLs entering the unsaturated zone are partlyvolatilised (and move as a soil gas by molecular diffusion) and when they attain residual saturationare gradually dissolved by infiltrating water. When LNAPLs reach the saturated zone they float inthe immiscible phase on the groundwater table surface over long distance depends on the hydraulicgradient (Fig. 3.1). On the other hand, dense nonaqueous phase liquids (DNAPLs e.g. asphalt, heavyoils, lubricants and also chlorinated sotvents) have low solubility and are markedly denser and lessviscous than water. Large spills of DNAPL will quickly penetrate the full depth of the aquifer andaccumulate on its bottom. Whilst lateral migration of LNAPLs is controlled by the groundwater flowdirection, DNAPL movement follows the slope of the impermeable strata underlying the aquifer andcan move in the opposite direction to the groundwater gradient (Fig. 3.1b). The viscosity and den-sity of oil hydrocarbons therefore, significantly affect monitoring wells construction particularlywith regard to screen location.


The solubility of petroleum products in water is generally low. However, some light hydrocarboncompounds are very soluble, particularly during the first 24 hours of contact with water. The solu-bility of hydrocarbons in water increases with decreasing carbon number in the molecule.

The sorption capacity of petroleum products depends on product properties, capillary forces, mois-ture content and the physical (grain size) and geochemical composition of the rock material. Thosepolar components most readily sorped are naphtenic acids, resins and asphaltens. Selective sorptionof non polar components occurs in the sequence olefines → aromatics→ cyclanes→ alkanes.According to Schwille (1969) the values of petroleum products sorption by the rocks range from 5 to 40 l.m3.

Evaporation of petroleum products is an important early warning indicator of the undergroundextent of pollution. Petroleum products in the gaseous phase spread within the unsaturated zone bymolecular diffusion and are easily detectable by early warning monitoring of the soil air. The degreeof volatility of the petroleum products depends on their boiling point and decreases from gasolineto aviation fuel, diesel oil and oil. Therefore, soil gas monitoring for the delineation of pollution bydifferent volatile organic compounds and water quality monitoring within the unsaturated zone areimportant part of early warning groundwater quality programme (see chapters 4 and 5).

Figure 3.1Typical movement of LNAPLs (top) and DNAPLs (below) into the groundwatersystem (modified after Lawrence and Foster, 1987)



Emulsification of petroleum products is a typical property of heavier fractions of oil hydrocarbons.Various microorganisms act as emulsifiers (Schwille 1969).

Petroleum products in both gaseous and liquid phases retained in the groundwater system areaffected by oxidation and reduction processes. Products of oxidation processes include phenols, car-bonic acids, resins, alcohols, and ketones. Oxidation of petroleum products also occurs when thereis oxygen deficiency in the rock-groundwater system (Schwille and Vorreyer 1969).

Microbial processes are controlled by free oxygen, nutrients, carbon and temperature and have a sig-nificant influence on the rate of degradation of petroleum products. Biodegradation processes areintensive in aerobic environments, however they also occur in anaerobic conditions. Microbialdecomposition particularly occurs on the petroleum product/groundwater interface.

3.2.2 Impact of mining on groundwater quality

Mining activities which can impact on groundwater quality include the extraction of ore, coal, oil,salt and non-metallic deposits, ore washing and dressing, coal preparation and other post extractionprocessing of mining material and uncontrolled leakages from tailings, piles, evaporation ponds, pitsand other disposal sites of extracted mine material. Groundwater monitoring around mines andprocessing plants is often missing. However, monitoring of discharged acid mine effluents is neededto control their impact on groundwater and surface water quality.

Discharged mine effluents are mostly acidic (pH 4 and less). They contain various kinds of mobilesoluble anion complexes of heavy metals released by the oxidation process of metal sulphides, par-ticularly present in ore bearing deposits. Iron sulphide (pyrite) is frequently present in coal-measureunits, and, in an air-water environment, oxidises to form ferrous sulphate and sulphuric acid. Secondary reaction of sulphuric acid produces high concentrations of aluminium, manganese, cal-cium, sodium, which along with iron and sulphate are sources of groundwater pollution. Brines dis-charged from salt and potash mines are also potential pollutants of groundwater. Groundwaterpollution by oil brines is frequent in oil fields; such pollution is considered a serious environmentalproblem in the USA (Everet, 1980).

3.2.3 Impact of uncontrolled waste disposal sites on groundwater quality

Landfills, particularly abandoned disposal sites with unknown composition of disposed waste, formsignificant potential sources of groundwater pollution. Large numbers of landfills have been poorlylocated (in permeable sediments above shallow water table aquifers, close to surface water bodies),poorly constructed (without liners and other techniques to prevent uncontrolled leaks) and do nothave groundwater quality monitoring systems. However, in many European countries and in theUSA early warning groundwater quality monitoring along and beneath landfills is now obligatoryunder the relevant legislation. Monitoring wells should be designated during the construction ofwaste disposal facilities.

In studying the impact of landfills on groundwater quality, Knoll (1969) demonstrated significant



long-term increase of organic substances (560%), sulphate (310%) and chlorine (520%) in theaquifer bellow the landfill after 40 years of refuse disposal. According to Freeze and Cherry (1979)landfills from the Roman epoch are still generating leachate. Leachate migration contaminategroundwater over areas much more larger than the landfill, extended particularly in the direction ofgroundwater flow. Groundwater pollution due to uncontrolled leakages from landfills has beendescribed by many authors.

The extent and intensity of chemical and biological processes in the waste mass depend primarilyon climatic conditions (amount and infiltration rate of precipitation and temperature) and on thenature and age of the waste. Jackson (1980) pointed out that changes of leachate composition aredependent on the age of the waste (e.g. volatile fatty acids change to higher molecular weight sub-stances such as carbohydrates).

Household waste contains a wide spectrum of organic and inorganic material, of which a significantpart is soluble and biodegradable. However, disposed household waste also contains hazardousitems such as batteries, medicines, paints and oils. A high content of sulphate, chlorine, ammonia,total organic carbon, biodegradable and persistent organics and xenobiotics, emissions of methaneand carbon dioxide and high biological oxygen demand are typical for leakages from disposedhousehold wastes. However, elevated concentrations of organochlorine compounds and otherorganic solvents and residues, heavy metals, pigments, oil hydrocarbons and other hazardous compounds are also recorded. The content of soluble metals in waste leakage is reduced by theiradsorption on organic matter and by precipitation in immobilised form as metal sulphides (UK DoE, 1992). Gas production due to biochemical decomposition of disposed organic matter is atypical process occurring in sanitary landfill. Methane (CH4) and CO2 among other gases are themost abundant. Gas ventilation and monitoring systems operate in recent landfills, to observe bothgas production and its migration outside of disposal site.

3.2.4 Impact of radioactive wastes on groundwater

Uranium mining, the nuclear power industry and some medical and military facilities and activitiesproduce a wide range of radionuclides, which may enter the aquatic system by a variety of routes.However, the normal operation of nuclear facilities does not present a serious threat to groundwaterquality. Uranium mining, milling, refining, enrichment and reprocessing and land disposal ofradioactive waste are those activities which pose the greatest potential risk to groundwater quality.

In situ leach-mining of uranium-rich sedimentary deposits, which depends upon the introductionof a leaching solution into the uranium-rich formation via injection wells and the removal of theenriched solution by production wells, poses a high risk to groundwater quality and groundwaterpollution by the chemicals present in the leaching solution. In situ restoration techniques, surfacetreatment and forward and reverse recirculation of treated water, are implemented to remediate polluted groundwater. Serious impacts on groundwater quality occur when polluted groundwaterbreaches the hydraulic barrier formed by production wells bounding the area being mined. Anexample of such groundwater pollution by acid-leach solutions in a large sedimentary aquifer hasbeen recorded in the Czech Republic. Early warning groundwater monitoring systems establishedaround the hydraulic barrier of production wells play important role in groundwater protectionagainst the impact of uranium leach-mining.



Uranium mining produce large amounts of rock-waste and tailings from milling, both containingnatural isotopes of uranium, thorium, radium and radon gas. 226Ra poses the greatest risk to theaquatic system because of its long time of half life (1600 years) and high £ and γ radiation. In suchareas concentrations in groundwater are frequently greater than the permissible concentration of226Ra (10 -9 mg.l-1) for drinking water. The process of uranium refining and enrichment generateslow-level radioactive wastes containing 226Ra, 230 Th and 238U. The most significant potential riskto groundwater quality is posed by the subsurface burial of radioactive reactor wastes which containacid water having high concentrations of nitrate and aluminum and a wide range of radionuclidesof different half-life, solubility, persistence, and type of emitted radiation. According to Matthess(1982) the mobility of radionuclides in the rock-groundwater system is controlled by the concen -tration of radionuclides and their isotopes, the pH of the groundwater, the kind and concentrationof other dissolved solids and the physical and chemical properties of the rock environment. Gene -rally, tritium which serves as a tracer for groundwater dating is more mobile than strontium and caesium, the long half-life insoluble plutonium isotopes showing particularly low mobility.

Pollution of groundwater by radionuclides may also occur as a consequence of nuclear accidents.The release of radionuclides into the environment from the Chernobyl power plant disaster (1986)produced groundwater pollution by 137Cs and 90Sr up to a radius of a few kilometres from Chernobyl power plant (UNESCO, 1992).

3.3 Multipoint pollution sources

Urban and rural areas contain numerous point sources of groundwater pollution. Inadequate handling, treatment and management of household wastes and waste waters, industrial effluents,uncontrolled waste disposal sites, rain and melt waters, salt water intrusion in coastal aquifers, are the main sources of groundwater multipoint pollution. Design and operation of groundwaterquality monitoring systems is not yet usual in urban and particularly in rural areas.

3.3.1 Groundwater pollution in urban areas

More than half of the current world’s population is living now in urban settlements. The resultingenormous concentration of human activities generates a wide range of impacts on the urban envi-ronment including groundwater.

Untreated or poorly treated municipal wastewater is the main source of groundwater pollution inurban areas. Discharge of wastewater to infiltration ponds, lagoons, wells or even the surface waterbodies is still practiced in some countries and has serious consequences for groundwater quality.Cracks and breaks in urban sewerage systems are frequent sources of uncontrolled leaks of untreatedwastewater into shallow aquifers. The greatest potential threats to groundwater quality from house-hold wastes include dissolved organic compounds (chloride, sulphate, ammonium, nutrients – nitrogen and phosphorus), pathogenic micro organisms (bacteria and viruses), trace elements,high BOD and TOC, and various types of household surfactants. Uncontrolled leaks from industrialand commercial activities located in urban areas also provide a significant source of groundwaterpollution by heavy metals, oil hydrocarbons, phenols and others.



Discharge of industrial wastewaters into waste disposal wells located in urban or suburban areas ispracticed in several countries. Here, corrosion of well casing and/or incorrect placing of well screenscan result in uncontrolled pollution of groundwater (La Moreaux and Vrba, 1990). Waste disposalwells are also used for the injection of treated wastewater as artificial recharge to the aquifers or forthe formation of hydraulic barriers to counter salt-water intrusion in coastal areas.

Rain and melt waters are further potential source of groundwater pollution in urban areas. They cantransport different pollutants (oil hydrocarbons, organic chemicals and seasonally salts in someregions) from road and street networks, parking lots, gasoline station areas and industrial zones togroundwater bodies.

Cases of groundwater pollution in urban areas are described by Balke at al. (1973), Jackson at al.(1980), Everett (1980), Mathess (1982), Vrba (1985), Foster at al. (1987), RIMV (1992) and manyothers.

3.3.2 Groundwater pollution in rural areas

IIn rural areas the most frequent sources of groundwater pollution are uncontrolled leaks from septic tanks, cesspools or latrines. Unsewered rural sanitation can affect groundwater quality in bothdomestic and public water supply wells. Chlorides, sulphates, nitrates, phosphorous, ammonia,household detergents and disinfectants and pathogenic micro organisms are the main pollutants ofgroundwater from such sources. High concentration of nitrates and pathogenic bacteria in drinkingwater in developing countries are a major cause of infections, illnesses and mortality of rural popu-lation, particularly infants.

Industrial and agricultural activities are other sources of groundwater pollution in rural areas. Localindustry generates similar pollutants as described above in urban areas, but to a lesser extent.Uncontrolled spillages of liquid wastes from manure and silage liquors and slurry and manure disposal sites are the most frequent point sources of groundwater pollution by farming activities inrural areas.

3.4 Diffuse pollution sources

Diffuse or non-point pollution of groundwater is mostly related to agricultural activities, above all to the massive application of fertilizer and pesticide on arable land and irrigation return flow. Historically, agriculture formed closed, environmentally sound and sustainable systems with insignificant impact on the environment. However, methods of contemporary agriculture have changed from crop rotation to monoculture and from single to mass-scale animal breeding.The intensification of agricultural production has created serious impacts on the quality of ground-water.



3.4.1 Impact of nitrogen fertilizers on groundwater quality

A big difference exists between continents and individual countries in the amount of fertilizersapplied. The average application rate of nitrogen fertilizers on arable land per year in Western andCentral Europe, North America and Eastern Asia is in the order of hundreds kg N/ha and in manycountries in Africa it may be as low as a single kg N/ha.

The most widely occurring class of groundwater pollutants with respect to the impact of agricultureare nitrates originating from organic and inorganic fertilizers applied to arable land. Potassium andphosphorous compounds derived from fertilizers accumulate in the soil and the unsaturated zonedue to their lower solubility and mobility, and their potential threat to groundwater is generally low.Conditions for groundwater phosphate pollution may arise in regions with large livestock concen-trations and a resultant high production of manure. Metals (cadmium, copper, and others) derivedfrom certain inorganic fertilizers, accumulate in soils with a negative effect on their fertility, but theirimpact on groundwater quality is recorded only exceptionally.

Research into the crop-soil-unsaturated zone-saturated zone system indicates that nitrate increasein groundwater is not a random, locally limited phenomenon, but a serious environmental, socialand economic problem that affects aquifers of many countries. A statistical relationship has beenfound between the amount of nitrogen fertilizer applied to the land surface and the nitrate contentin groundwater. Agriculture contributes particularly to nitrate pollution of shallow water tableaquifers, with economically accessible groundwater resources used for water supplies.

The Netherlands National Institute of Public Health and Environmental Protection (RIVM, 1992)calculated nitrate concentrations in the leachate from agricultural soils (at 1 metre depth) in Europe.Model computations indicate that over 85 % of the agricultural area in Europe has nitrate concen-trations above 25 mg/l and that drinking water standard (50 mg/l) is exceeded bellow approximately20% of the agricultural soils. Many European countries (mainly north-western and central European countries) indicated that they had serious nitrate groundwater pollution problem.

In the USA, particularly in the Corn Belt states, nitrate pollution of groundwater can be found inseveral regions of Iowa, Illinois, and Ohio. Occurrence of nitrate concentration in groundwatergreater than drinking water standards (10 mg/l NO3–N) was documented in several regions ofNebraska (Exner and Spalding, 1990). Man-induced mineralization of natural soil nitrogen hasresulted in nitrate pollution of groundwater in large semiarid areas of Texas and Montana (150 mg/lNO3 –N), however, such concentrations decreased after several years of cropping (Miller et al.,1981). A rapid increase of nitrate content in alluvial aquifers with shallow depths to groundwaterunder irrigated soils is observed in California, Florida and other US States (Spalding and Exner,1991). Vertical nitrate zonality of shallow aquifers is observed in many parts of USA (Hallberg,1989). The extremely high content of nitrate in shallow rural wells identified in Florida and Indianais a consequence of their location close to point pollution sources such as animal corrals, cattle feed-ing areas or domestic sewage disposal sites (Spalding and Exner, 1991).

In the developing economies of Asia and Africa, nitrate pollution of groundwater is mostly a resultof the effects of point pollution sources. The quality of water in many shallow public and domesticwells is affected by their poor construction, inappropriate sitting close to pollution sources (septictanks, latrines, dumps of animal slurry) or resulting from animals using the well head as a watering



point. Nitrate in groundwater in many rural wells in Asia and Africa reaches several hundreds mg/land can be a serious health hazard. The risk of methaemoglobianemia, also referred to as Blue-BabySyndrome, is considerable in many rural settlements in developing countries.

Sustainable management of groundwater quality beneath agricultural lands requires maintenanceof the dynamic stability of soil organic matter and restriction of the processes that lead to mineral-ization of organic nitrogen. Monitoring of the carbon / nitrogen ratio as an important indicator ofthe soil organic matter’s state should therefore be part of an early warning groundwater monitoringstrategy in regions where shallow water table aquifers underlay areas of intensive farming activities.

Monitoring of groundwater quality in many agricultural regions has proved nitrate vertical zonalityand movement of a nitrate plume through the unsaturated and saturated zones of the aquifer (see chapter 4). An overview of the threats of agriculture to groundwater quality in various countries is presented in the Proceedings of the International Workshop organized byUNESCO/CIHEAM/UPC in Spain (Candela and Aureli, 1998). However, non-point pollution ofgroundwater due to agriculture has been studied by many scientists and several international conferences, reports and books have been devoted to this topic.

3.4.2 Irrigation return flow

Soil and groundwater pollution as a consequence of irrigation return flow has been reported frommany countries. Increase of dissolved solids in groundwater occurs in agricultural areas with over-irrigated soil not having adequate drainage. Leached salts from the soil are transported by irrigatedwater and degrade the quality of the underlying aquifers. Soil-groundwater degradation processesaccelerate when groundwater with high content of salts from aquifers beneath an irrigated area isrecirculated. Groundwater salinisation in arid regions is described e.g. by Bouwer (1987) andChilton (1995). Desert soils contain natural salts, which are leached by irrigated water and penetrateinto the aquifer and degrade its quality.

3.4.3 Impact of pesticides on groundwater quality

The aquatic system has been exposed to an increasing number of types and quantity of agriculturalpesticides throughout the world for several decades. Different types of pesticides (the term of pesticides is used in broad sense for insecticides, herbicides and fungicides) are transformed todegradable residuals (owing to biodegradation or chemical hydrolysis), many of them break downto toxic derivatives.

In Europe, based on the model calculation (RIVM, 1992), the pesticides drinking water standard isexceeded in the leachate under 75 % and 60 % of the total arable and crop land in north-westernand central-eastern countries, respectively. The application of pesticides reflects in pesticide pollution of groundwater in many shallow aquifers bellow arable land in Europe. In the USA, systematic monitoring of pesticides in groundwater commenced at the beginning of the 1980s. As aresult of the application of pesticides on agricultural land in many American states, aldicarb,atrazine, DBCP, ethylene diobromide and other kinds of pesticides have been found in many wells



(Spalding and Exner, 1991). The US EPA prepared a background document on the strategy of groundwater protection against agricultural chemicals in 1986.

Groundwater vulnerability to pesticides is high in shallow water table aquifers below coarse or sandysoils having a high moisture and low organic matter and clay content, low adsorption and cationexchange capacity and low-level bioactivity and biodegradability. There are differences in the per-sistence of various groups of pesticides in soil. In general, the ionic pesticides are more soluble thannon-ionic groups. The most resistant organo-chlorine insecticides can persist in soil for years. Onthe other hand, organophosphate insecticides and aliphatic acid-herbicides degrade relatively rapidly in less than three months. The occurrence of toxic organochlorines in groundwater and theirpotential carcinogenic effects led many countries during the sixties to ban their use. Sustainablemanagement of pesticide application and groundwater quality monitoring are particularly desirablein agricultural areas used for the cultivation of vegetables, fruits, vines and potatoes.

Systematic monitoring of pesticides is particularly missing in both developed and less developedcountries. In less developed countries the appropriate laboratory equipments are often not available.

3.5 Line pollution sources

Road and railway transport, municipal and rural sewerage networks, oil and gas pipelines and sur-face streams are the main potential line pollution sources of groundwater.

Polluted runoff water from roads, soil and groundwater acidification by transport emissions andspills of various substances due to road and railway accidents can all have a serious influence ongroundwater quality. Runoff from roads contains oil hydrocarbons, various salts (NaCl, KCl, CaCl2)and solvents. Transport emissions contain fuel additives like lead (particularly in the past) and VOC(benzene). Highly soluble and mobile salts, applied in large amounts on the roads in winter, are asource of pollution for shallow aquifers, particularly where roads cross their recharge or vulnerableareas. The most dangerous risk for groundwater pollution is from traffic accidents involving trucktankers which can result in spills of several tonnes of various hazardous substances including flammable or even explosive ones. Downward penetration of such liquids through permeable soilsinto the groundwater body can have major effects on groundwater quality. However, a more impor-tant source of groundwater pollution is that of spills of large quantities of hazardous chemicalsreleased from cisterns in train accidents. The consequences on groundwater quality are often veryserious because one train usually transports a variety of chemicals having various properties andcompositions.

Uncontrolled leaks of wastewater and ballast water from defective sewerage networks form a majorhazard for shallow aquifers in urban areas. Microbiological pathogens and synthetic surfactants arethe most frequent pollutants. Seepage losses of wastewater from surface canals discharging house-hold liquid wastes from rural settlements in less developed countries have similar impacts ongroundwater quality.

Accidental spills and uncontrolled leaks of petroleum products and liquid natural gas from buriedpipelines are potential sources of soil and groundwater pollution by oil hydrocarbons and otherpetrochemicals. Spills of petroleum products due to the failure of welds in petroleum pipelines have



been recorded in many countries. Different monitoring systems are established along pipelines and different remote sensing monitoring methods are applied to control spills from pipelines (seechapter 5).

The hydraulic gradient between a surface stream and a groundwater level controls the possibility ofbank infiltration of polluted surface water into an underlying aquifer. Groundwater pollution mayoccur far from the pollution source, at locations where the river is a losing stream and the con ditionsof surface water infiltration exist.

3.6 Areal pollution sources

Acid atmospheric emissions (sulphur dioxide-SO2, nitrogen oxides-NOX) transported hundreds of kilometres over continents and their chemically converted products (sulphuric and nitric acids)are major sources of regional transboundary pollution of soil and surface water. However, theirinfluence on groundwater quality has also been recognised (Holmberg, 1987, Stanners and Bour-deau, 1995).

The sources of such pollution include: 1/ sulphur dioxide emissions produced by the burning of fossil fuels (oil and particularly coal with content of sulphur), 2/ nitrogen oxides mostly generatedby combustion engines, and 3/ ammonia emissions (originating from manure and sludge producedby mass scale animal breeding) converted by nitrification processes to nitric acids.

The capability of soil to neutralise acid deposition depends on its chemical composition (which controls cation exchange and attenuation capacity), its physical condition and the land use. Gener-ally, thin sandy soils with a coarse granular texture, lacking in nutrients and developed on acid crystalline rocks have a low neutralising capacity. Shallow aquifers beneath such soils are badlybuffered and thus highly vulnerable to acidification. Leaching of sulphur (as sulphate), nitrogen (asnitrate), aluminium and heavy metals into groundwater as a consequence of soil acidification isobserved in several regions in Europe. Rocks with a high content of calcium carbonate such as lime-stone, dolomite, marlite and calcareous marl, have great neutralising capability and therefore lowvulnerability to the adverse effects of acid deposition is registered in groundwater within these rockenvironments. However, exhaustion of the neutralising attenuation capacity of the unsaturated zoneleads to a lowering of pH values and subsequent gradual groundwater quality degradation.

3.7 Groundwater salinisation in coastal areas

Groundwater salinisation in coastal areas is a specific category of groundwater pollution. Coastalaquifer salinisation occurs particularly when the rate of groundwater exploitation exceeds meanannual recharge, the interface between saline and fresh water is disturbed and thus conditions for the invasion of saline water into the groundwater body are created. However, the risk of salineintrusion also depends on location and density of abstraction wells and wells construction anddepths.

An interface between fresh and salt groundwater occurs naturally due to the high difference in



density between fresh water (0.99 g.cm-3) and sea water (1.026 g.cm-3). The best method for theidentification of the interface is electrical logging carried out in monitoring wells. The interfacebetween salt and fresh groundwater is in fact marked by a zone of mixed water (transition zone), thethickness of which is controlled mainly by the intensity of the ocean tides, the stream flow changes,the volume of flow towards the seashore and the aquifer’s physical and chemical properties. Salinewater intrusion results in serious degradation of groundwater quality. High chloride, sodium, magnesium, and sulphate content and high salinity and TDS are typical for brackish water. Recu-peration of groundwater quality is a long-term process and water supply wells have to be often temporarily or even permanently abandoned. The design and operation of an early warning moni-toring network is a very effective tool for the prevention of groundwater quality deterioration incoastal and small islands areas.



4.1 Introduction

The main objective of an early warning groundwater quality monitoring strategy is to identify andto foresee the threats on groundwater quality still in the unsaturated zone and thus to timely definemeasures leading to protection of the aquifers until large volume of groundwater become polluted.However, early warning monitoring should also incorporate saturated aquifers, particularly theiruppermost part. The study of the soil-rock-groundwater environment and pollutant movementbetween the ground surface and the water table has been mostly ignored in the past. At present, particularly when pollutant hydrogeology issues are investigated, monitoring and assessment ofunsaturated zone properties (matric, osmotic and gravitational potential and hydraulic features)with respect to its ability to store, retain, remove and attenuate pollutants and delay their migrationto the saturated aquifer, are crucial tools for groundwater quality management. Early warning monitoring of both the unsaturated and saturated zones generates data about groundwater qualityand the movement and fate of pollutants and is an important element for groundwater pollutionrisk assessment and designation of groundwater protection policy. Institutional and technical capa -cities for the efficient development and implementation of early warning monitoring strategy needto be developed.

Institutional capacity building includes: 1) the establishment of governmental institutions onnational and local levels to formulate effective water policy, provide sustainable management of water resources and carry out the required administrative operations, 2) the establishment of atransparent and coherent legal framework, regulatory statutes and standards, 3) the creation of governmental water quality-control mechanism based on the polluter pays principle and on theimplementation of repressive and stimulating instruments, 4) the recruitment of qualified and expe-rienced human resources and 5) public awareness and information about groundwater protectionand pollution issues.

Technical capacity mainly includes: 1) groundwater system investigation and evaluation of the areato be monitored, 2) assessment of groundwater system vulnerability and pollution risk, 3) identi -fication and inventory of potential and existing threats to which the groundwater system is exposedand evaluation of their nature, extent and impact on groundwater quality, 4) setting-up of field andlaboratory monitoring equipments and procedures.

4 EARLY WARNINGGROUNDWATER

QUALITY MONITORING PROGRAMMES



Early warning groundwater quality monitoring is technically demanding and also a financiallyexpensive process in terms of capital, installation, operation and maintenance costs. However, theimplementation of a groundwater early warning monitoring strategy is many times less expensivethan the costs related to aquifer remediation and the investments required to overcome social andecological impacts of groundwater pollution. It is worthwhile noting that, in spite of huge budget-ary investments and long periods of aquifer remediation there are only few cases known when per-manent restoration of aquifer conditions to acceptable groundwater quality levels has been achieved.Many times groundwater quality conditions in the aquifer improve for a short period of time, but pollution levels increase again after changes in the mode of aquifer management and /or rainingseasons.

Early warning monitoring is particularly important in the soil-root-unsaturated zone and theuppermost part of the aquifer. However, early warning monitoring is also effective when lateralmovement of a pollution plume through the aquifer or upward penetration of pollutants throughthe bottom of an aquifer are observed and before they reach and affect the quality of groundwatersupplies. At the same time, early monitoring is an appropriate method for the identification of pollution leaks from landfills, waste pits, lagoons and other point pollution sources. Changes in vegetation cover detected by geobotanical and photographic methods are also important indicatorsof threats to groundwater systems and supplement regional and particularly site-specific early warning monitoring systems.

The important initial aspect in considering a early warning groundwater monitoring is the defi -nition of objectives and information needs. Clearly defined objectives are essential to achieve theexpected results and they have to be stated before the monitoring system is established and the firstsample of groundwater is taken. Objectives control the extent and variety of monitoring technicalactivities (monitoring networks design, wells construction, sampling frequency, variables analyzedand others). Transformation of collected, processed and evaluated data (see chapter 6) into a user-tailored information product is a second important step of early warning groundwater monitoring.It should be emphasized that the cost of the monitoring system design and operation will only beacceptable if the relevant information is transmitted on time and in an intelligible form to the users(planners, regulators, managers, decision makers, stakeholders, scientists, public) and effectively uti-lized. Simple, easy to understand information that can be translated into practical instructions isnecessary for potential polluters (usually not professionals) and the general public. These same datashould be transformed into more sophisticated information supported by GIS techniques to be pre-sented to professionals, governmental authorities, planners and water managers.

Integration and coordination of early warning groundwater quality monitoring activities withgroundwater, surface water, meteorological and soil monitoring networks is recommended, becauseof the close relations between them.

Different approaches are applied to national, regional and site-specific early warning monitoringprogrammes (Vrba, 2000):

(a) National groundwater monitoring programmes are mainly related to data collection of naturalbackground levels and the current state and trends of groundwater quality in time and spaceacross the entire country. An elaboration of a conceptual model of the main country aquifersand assessment of their quality and vulnerability is essential before the design of a nationalmonitoring network is proposed.



(b) Early warning monitoring systems on a regional level are focused on specific groundwater quality problems of selected country areas. The objective of regional monitoring system is toacquire statistically significant data sets which support regional management of groundwaterresources quality, groundwater protection policy and decision making in regional integratedland use planning and agricultural practices.

(c) For site specific problems, monitoring systems are established around potential point pollutionsources to give an early warning of groundwater quality changes and deterioration. They arealso located near existing point pollution sources to observe and control vertical and lateralmovement of pollution plumes, and to detect the effectiveness of applied protection measuresor the results of pollution remediation.

Different methodological approaches for each of the above monitoring systems are desirable. How-ever, comprehensive groundwater system analyses based on evaluation of the properties of aquifersand their vulnerability, identification of the threats to which groundwater is exposed and risk assess-ment of groundwater pollution are a basic premise of the design and effective operation of all earlywarning groundwater quality monitoring programmes.

4.2 National groundwater quality monitoring programmes

The monitoring network of a national early warning monitoring programme would be composedof baseline and trend monitoring stations as classified by Maybeck (1985). Monitoring stations arepreferably located outside of the influence of pollution sources or groundwater abstraction sites.The design of monitoring networks should permit separate measurement and testing of individualaquifers and their vertical hydrochemical profiling. Permeability and porosity of a rock mediuminvolve significantly on design of monitoring wells. Design of monitoring wells in rocks having fissure permeability and secondary porosity is more complicated than monitoring of groundwaterin a rock medium having primary porosity and diffuse groundwater flow system. In karst regionswhere groundwater flow is in conduits or in large open fissures, monitoring of springs and otherdischarge phenomena of the groundwater system (base flows of streams), allows more represen tativeobservation of groundwater quality than monitoring wells. The importance of groundwater as adrinking water source and the vulnerability of aquifers control the density of monitoring stations(e.g. wells, springs) and frequency of monitoring. However, monitoring methods are not yet stan-dardized and vary in each country. Groundwater basin or aquifer system are the basic monitoringunits of national groundwater monitoring programmes. Sampling frequency is generally low, inEuropean countries mostly 2–4 times per year or less; in fractured and fissured consolidated rocksand particularly in karst areas, with secondary permeability features, sampling is often more frequent. However, automatic in situ measurements of pH, temperature, electrical conductivity oxygen demand and other substances at daily or weekly intervals, along with groundwater levelmeasurements, are carried out on many monitoring wells within national monitoring networks ofseveral countries and give early warning of changes in chemical composition of groundwater.

Until now, the early warning monitoring approach has had limited application in national monitor-ing networks, and monitoring is mainly related to the saturated zone. One such example is the



National Monitoring Network of the Netherlands (Duijvenbooden, 1987). In the shallow aquifers ofthe Netherlands monitoring wells were installed having three screened segments at different depths.The wells are used to monitor the chemical composition of groundwater and nitrate vertical movement in highly vulnerable aquifers that extend over large areas under intensively cultivatedarable land.

4.3 Regional groundwater quality monitoring programmes

Regional early warning programmes are in operation in several countries and they are generallydesigned to monitor both the unsaturated and saturated zone. The trend and impact stations domi-nate in regional monitoring networks. Monitoring of vertical movement of water and pollutants inthe unsaturated zone (by lysimeters, extraction of interstitial water from core samples, suction caps,direct push sediment sampling or other methods, see chapter 5) and saturated zone (nested moni-toring wells with single screened segment placed at different depths, small diameter piezometrs nestplaced at different depths of a monitoring well, implementation of multilevel samplers in a singlemonitoring well, use of packers in monitoring wells in anisotropic aquifers, horizontal monitoringwells, separation pumping techniques, sampling under unaerobic conditions using a vaccuum tech-nique and others, see chapter 5) is implemented particularly in areas affected by diffuse pollution ofphreatic aquifers, in the catchment areas of public groundwater supply systems, in coastal aquifersand in wetlands regions. The extent and risk of human impacts on vulnerable groundwater systemscontrol the design of early warning groundwater quality monitoring networks, monitoring wellsconstruction and the range of variables analyzed for. Sampling frequency is higher than in nationalmonitoring programmes. Sensors for automatic in situ measurements of selected substances inmonitoring wells are often applied. Statistical techniques help to define an optimal sampling fre-quency (monthly, weekly or even daily).

There follow some examples of regional early warning monitoring systems focused on the impact ofagricultural activities on groundwater quality, particularly diffuse nitrate pollution and on the pro-tection of catchment areas of groundwater supplies.

(1) In Great Britain, deep profiles of pore water in the unsaturated zone were obtained from theBritish Chalk by Foster and Young (1980). They used microanalytical techniques on pore-watersamples centrifuged from cores obtained by periodic destructive sampling. Many unsaturatedzone profiles were obtained beneath long-standing arable farmland, dryland pastures convertedto cereal cultivation and permanent dryland pastures. Unsaturated zone monitoring signi -ficantly improved the knowledge of complex processes and interactions between the quality ofvadose zone water, soil moisture conditions, rainfall regime and infiltration rate, agriculturecropping regime and nitrogen fertilizer management (e.g. Foster et. al., 1982; Lawrence and Foster, 1986; Geak and Foster, 1989; Whitmore et. al., 1992; Foster and Chilton, 1998). Monitor-ing confirmed generally slow average rates of unsaturated zone transport of contaminantsleached from cultivated soils; even for non reactive pollutants vertical fluxes did not exceeded 2 m/year beneath non irrigated land and 5 m/year under irrigated soils (Foster, 1976; Bouwer,1987). Vertical stratification of groundwater quality bellow the outcrop with peak concen -trations of major ions in the top of the saturated zone and N–NO3 progressive decrease withdepth may be seen on the Figure 4.1 (Foster at al., 1986).



(2) A regional monitoring system for shallow vulnerable aquifers has been operated in the CzechRepublic for the study of the areal distribution of nitrates in the soil-groundwater system(Pěkný, Skořepa and Vrba, 1989). The monitoring network was installed in a water table shal-low aquifer in the fluvial deposits of the Elbe river valley covering an area of 3,000 km2 devotedto long-term crop farming on arable land. Monitoring wells having screens at three differentdepth intervals (Figure. 4.2) confirmed movement of a nitrate front from the upper part to thebottom of the aquifer within a five year period (Vrba and Pěkný, 1991).

The transport and transformation processes of nitrogen compounds in the soil-groundwatersystem have been also studied. The intensity of the processes that take place in the nitrogenmobilization/immobilization cycle has been determined using the nitrification constants of soilsamples. The analysis has proved the considerable importance of these processes for the totalbalance of nitrate nitrogen. The intensity of denitrification processes over the unsaturatedzone’s profile was determined on the basis of the NO3-N and Cl ion content and their ratio insamples taken from the soil, deposits of the unsaturated zone and in groundwater (Figure 4.3).In the non-vegetational season in the recharge period, the NO3-N /Cl ratio was 1.5–3.5 over the0.0–0.3 m soil profile. Higher nitrate contents were indicated in the upper, more aerated soil

Figure 4.1

Comparison of pore-water profilesfrom unconfined and confinedTriasic sandstones, south YorkshireUK (Foster et al., 1986)



layers. Over the unsaturated zone profile, due to the decreasing permeability and porosity, theconcentration of nitrate nitrogen and chlorine declined with increasing depth. At the ground-water table level, 2,5 m under the surface, their content was about 60% lower than their relativeaverage content in the soil layer (Beneš at al., 1989). Assuming that 60 % of nitrogen based onthe NO3-N/Cl ratio in the unsaturated zone are largely accounted for by the denitrificationprocesses, the remaining 40 % of nitrogen flow away with the groundwater.

The dynamics of nitrogen uptake by vegetation was systematically being determined withrespect of vegetational and nonvegetational seasons. The Figure 4.4 indicate the time/spacedevelopment of N-NO3 concentrations in the soil profile, with fertilizers applied to the soil

Figure 4.3

N-NO3 distribution in the vertical profile of unsaturated zone.Experimental station Samšín, The Czech Republic

Figure 4.2

Changes in hydrochemical profile of shallow fluvial aquifer in the period 1984–1989. Monitoring well HP-65, Middle Elbe region in Central Bohemia, the Czech Republic



surface void of vegetation as well as at the time of the optimum growth of vegetation. Both fig-ures suggest that fertilizer application in the nonvegetational season is not effective. During thisperiod nitrates penetrate the soil profile to greater depths, thereby the risk of groundwater pollution is much more greater than if nitrogen uptake by vegetation and its root zone occurs.

Study of the soil organic matter state is essential for gaining insight into the processes whichcontrol the amount of nitrogen leached into the saturated zone. A significant indicator of thesoil organic matter state is the carbon/nitrogen ratio. When C:N is greater than 10, the freenitrate ions are immobilized by the microbial biomass; when C: N is less than 10 , the ammoniareleased during mineralization processes is utilized by heterotrophic microflora for protein syn-thesis, and its surplus is oxidized to NO3 by nitrification bacteria. The intensity of theseprocesses depends mainly on: the soil’s hydrothermal conditions (temperature, initial and incu-bation moister), the composition of the soil’s organic and inorganic components, the CO2 con-tent in the soil atmosphere, the amount of remineralized NH4 needed in nitrification processesas well as on the sowing procedures, the types and doses of organic and inorganic fertilizersapplied and techniques of soil cultivation. When the stability of soil organic matter is disturbed,inorganic nitrogen compounds and organic carbon-nitrogen compounds are washed out intothe unsaturated zone and groundwater. Perturbation of the organic carbon and nitrogen bal-ance in soil, with consequences for the groundwater quality, occurs parti cularly when tradition-ally crop rotation is replaced by monoculture (over a monitoring period of 4 years the nitratecontent increase in groundwater under monoculture was twice as high as for soil with croprotation), or when organic fertilizers are replaced by inorganic fertilizers or the doses of inor-ganic fertilizers suddenly increased (both are reflected in the degradation of soil organic matterwhich leads to an increased influence of stochastic processes and loss of control over ground-

Figure 4.4

Vertical distribution of N-NO3 - concentrations following application of potassium nitrate with limestone in the non-vegetational (left) and vegetational (right) season. Experimental station Samšin, The Czech Republic (Benes at al., 1989)



water quality). However, research has also revealed the significance of short-term changes forthe nitrogen balance due the immobi lization and denitrification processes in a year’s cycle. Generally, short –term cyclic changes in nitrate content occur in the aquifer upper parts,depending mainly on the climatic conditions. The long-term s and the upward trend in nitratecontent in groundwater reflect human impacts, especially farming effects.

Based on this early warning monitoring groundwater system, several changes of agriculturalpractices have been proposed to reduce conflict of interests between agricultural and water sec-tors. However, restoration of the soil-groundwater system’s quality is a complicated and long-term process requiring improvements in the management of nutrients and chemicals appliedon the farm land, control over the extent and intensity of agricultural activities particularly inregions having vulnerable and valuable aquifers and consistent attention to natural conditions.

(3) An early warning monitoring strategy on a regional scale is an important part of the protectionpolicy and management of public groundwater supplies. Monitoring networks are establishedin outer or second degree protection zones encompassing usually the whole source catchmentarea. Water supply wells or springs and monitoring wells located in designated protection areasform monitoring networks. Sampling frequency of water supply wells is high; some variableswhich are sensitive to human impacts are analyzed for daily. Monitoring wells located inrecharge and vulnerable areas of the supplies’ protection zones are observed less frequent.Groundwater early warning monitoring of water supply systems will alert managers to ground-water chemistry changes and/or quality degradation at an early stage, allowing them to protectand manage aquifer systems so that water is supplied according to available drinking waterquality standards. Monitoring recharge and vulnerable areas of groundwater supplies is of para-mount importance. In these regions land-use activities should be controlled and restrictedunder special guidelines or even prohibited under an established legal framework. Distributionof benefits and costs and related compensation measures must be implemented for the popu -lation, especially farmers, whose economic activity is affected by restrictions in groundwaterprotected areas.

(4) Natural ecosystems of regional extent, particularly wetlands, can also benefit from the imple-mentation of early warning regional groundwater quality monitoring. Wetlands are highly vulnerable to toxic pollutants however, they have a high microbiological capacity and an abilityto degrade many organic pollutants. Wetlands are closely connected with aquatic systems. Moni-toring and evaluation of the relation between wetland hydrological regime and adjacent ground-water system is therefore an important task. Early identification of pollution impacts ongroundwater in wetlands, natural reservations and parks, is an important monitoring activitythat may help maintaining the ecological sustainability of these delicate environments.

4.4 Site specific groundwater quality monitoring programmes

Site specific early warning groundwater quality monitoring networks established around potentialor existing point pollution sources (e.g. waste disposal sites, oil storage facilities, industrial and mining sites) operate independently of national or regional monitoring networks. Good knowledge



of groundwater system, aquifers boundaries and hydraulic conditions, groundwater flow nets andpollutant behaviour is desirable before early warning site specific monitoring is designated. Theimpact stations (Maybeck, 1985) are the core elements of site specific monitoring networks. A highdensity of monitoring wells (designated according to origin, magnitude and duration of pollutionand mobility and extent of pollution plume), designation of suitable in situ and on-site remote sens-ing monitoring methods (selected with respect to the specific properties of pollutants), high sam-pling frequency, and analyses of variables chosen with respect to the type of specific pollutants aretypical for site specific early warning monitoring programmes. Monitoring of the local climatic con-ditions is particularly important in regions repeatedly affected by catastrophic rains, storms andother catastrophic atmospheric phenomena.

Installation of well screens and monitoring device selection and their placement with respect to pol-lution source properties is critical, particularly when the unsaturated zone is highly stratified. Insuch a case, lateral pollution migration prevails and a combination of vertical and horizontal moni-toring facilities should be utilised both to avoid drilling through polluted soil-rock media and dis-semination of pollution into not yet polluted aquifer and to ensure placement of the pollutionsensors at the right depths. However, the design of monitoring wells of site specific early warningmonitoring system is mainly adapted on observation of water and pollutant vertical movement atdifferent depths of the unsaturated zone or on observation of the aquifer vertical hydrochemicalprofile.

Implementation of sophisticated remote sensing methods in combination with in-situ monitoringof soil gas, soil solute and ground water in the chapter 5 supports early detection of groundwaterquality problems, before the pollution reaches the groundwater level. Some of the monitoring wellsthat are located close to the potential pollution source can be used as recovery wells when ground-water pollution occurs. Reference monitoring wells should be also established as part of early warn-ing monitoring network to observe the natural groundwater quality. Operation of site specific earlywarning monitoring networks is usually limited to a specific period (e.g. until the industry, miningfacility or other potential pollution sources cease the operation, pollution plume is clean up, etc.).

Early monitoring of pollutants in the unsaturated zone and pollutant fluxes at maximum concen-tration in the water table before they are diluted in the aquifer, gives ample time for remedial actionto be undertaken before massive pollution of groundwater occurs. Such measures enable establish-ment of a quantitative relationship between the amount of a pollutant released on the ground andthe amount that reaches groundwater body. In some European countries and the USA, early warn-ing monitoring of the unsaturated zone and the saturated aquifer around and beneath potential pol-lution sources (e.g. municipal landfills or other facilities) is obligatory under the relevant legislation.Vertical and horizontal monitoring stations are designated during the construction of treatmentfacilities.



Remote sensing and on-site methods are both widely used for the early detection of pollution in thesoil, the unsaturated zone and the uppermost part of the saturated zone. Remote sensing techniques(geobotanical, airborne photographic and geophysical methods) are particularly helpful for thedetection of pollution in the soil and the unsaturated zone. A large variety of on-site methods (coresampling and groundwater sampling) are applied in hydrochemical profiling of the unsaturated andsaturated part of the groundwater system and for studying the vertical movement of a pollutionplume towards the water table and in the saturated aquifer. The following text describes the mostfrequently used methods, which provide a considerable time between pollutant detection and itsarrival into groundwater supply systems, recharge and vulnerable areas of aquifers, or as salineintrusion in coastal areas.

5.1 Surface methods

5.1.1 Introduction

Experience has proved that geobotanical and photographic methods are most effective for the earlydetection of soil and shallow groundwater pollution when implemented together. Both methods arebased on the response of vegetation cover to the presence of specific substances in the soil, surfacewater and groundwater. The detected substances causing pollution are not always harmful to vege-tation; sometimes they could even be beneficial for plants and the biosphere.

Therefore, 1) the state of plants health, shift of phenophases (i.e. blossoming and ripening), densityof vegetation cover, and 2) the presence or absence of certain plant species and communities and the change of successions, size, habitat and their abundance, both are helpful tools to reveal thepresence of pollutants in soil and rock environments and the hydrosphere.

Other photographic methods are rare, except for recording the state and changes of rooted plantswhich is limited to sites where polluted groundwater or acid mining water discharge into the riversor lakes. The detection of pollutants is then based on their physical and chemical properties which

5 SOME TECHNIQUES USED FOR

EARLY WARNING GROUNDWATER MONITORING



cause changes of reflectance of surface water both in the visible and the near infrared spectral range.Unfortunately ultraviolet bands, which are theoretically suitable for revealing oil slicks on the watertable, cannot be employed in photography because of the lack of special films; the use of necessarymultispectral scanners lies beyond the range of photographical methods.

Geophysical methods are successfully implemented if there is sufficient contrast between the measured parameters of the geological system, the groundwater body and the pollution plume. Generally, geophysical methods are more effective in detection of inorganic pollutants and less effec-tive in the case of organic pollutants, particularly in the case of Dense Nonaqueous Liquids(DNAPLs). Continuous electromagnetic profiling measurements with high lateral resolution andresistivity methods with high vertical resolution are those geophysical methods which are most frequently used for detecting the extent and flow direction of a pollution plume. However, severalothers geophysical techniques are often applied in pollutant hydrogeology, such as magnetometryand electromagnetic induction for the location of pollution spills from damaged undergroundpipelines or tanks, radioactive spectrometers for the identification of aerial and site-specific radio -active pollution, and borehole logging methods for the detection of a groundwater-saline waterinterface.

5.1.2 Geobotanical methods

Geobotanical detection of soil and shallow groundwater pollution depends on the site’s naturalcharacteristics, the chemical and physical composition of the pollutants and particularly the pro -perties of the vegetation cover. The principle of pollution detection is to compare the state of vege -tation at the pollution site with a botanically similar unaffected area. When there are pre-pollutionbotanical data available, comparison should be made with the present state of vegetation affected bypollution. The species of vegetation within the investigated area and their variability, particularly thepresence of those plants which are sensitive to and those plants which are tolerant to pollution, formthe basis of geobotanical methodologies. The resistance of certain species, however, depends on several natural factors such as soil organic and mineral matter and moisture content, groundwaterlevel and groundwater chemistry, and the local climate. The botanical indicative value is a usefulparameter in this context which rises with the number of species and their diversity and dependspositively on the presence of trees with deep roots systems (Pyšek et al., in press). The pollutantsmost easily detected by geobotanical methods are oil and oil products, natural gas, fertilizers, pesti-cides and heavy metals.

Oil and oil products affect vegetation in different ways according their composition and concen -tration. While a small amount of oil hydrocarbons in water or soil may have no or even a beneficialeffect on plants, strong concentrations can result in necrosis of leaves leading to the total death ofvegetation in the most drastic events. The most frequent symptoms of oil pollution are, in case ofindividual plants, growth (nanism, gigantism), leaf colour change (change of green colour and itsshades, yellowing, whitening), turgor (wilting), necrosis, defoliation, sterility and shift ofphenophases (blossoming, ripening). In the case of plant communities the typical symptoms arepresence, variety and diversity of species and the density of plants or canopy. The response of plantsto pollution should be carefully analysed. It depends both on the vegetation itself and also on complex environmental factors, such as water and nutrient content, temperature, air pollution, etc.Nevertheless the general division of plants into two basic groups, sensitive and tolerant, has provedto be suitable for pollution detection by geobotanical methods.



Sensitive vegetation includes Scots Pine (Pinus sylvestris), Silver Birch (Betula pendula), Mugwort(Artemisia vulgaris), Fat Hen (Chemopodium album) and Meadow Fescue (Festuca pratensis). Resis -tant plants include Common Elder (Sambucus nigra), Stinging Nettle (Urtica dioica), Wood SmallReed (Calamagrostis epigejos), False Acacia (Robinia pseudoacatia), Cow Parsley (Anthriscussylvestris) and others. These representative plants can be used as photoindicators of pollution due totheir common occurrence in anthropogenically affected areas (Pyšek at al., in press).

Pyšek A.(1983) formulated the following main geobotanical procedures for the detection of hydro-carbon pollution: 1/ gather information on all significant human activities in the studied area, 2/ evaluate the occurrence and vitality of the petroleo-sensitive species, 3/ observe the reaction ofpetroleo-tolerant species, 4/ record all growth abnormalities performed by species present in polluted area, 5/ observe the shift of flowering phenophases, 6/ try to detect the existence of the border zone of vigorous plant growth.

Natural gas generally impacts indirectly on vegetation. Biodegradation of gaseous hydrocarbonseventually leads to carbon dioxide production which causes a reducing environment and theabsence of oxygen needed for plant life. In the Czech Republic, field tests were carried out to findthose plants which were either sensitive or tolerant to natural gas with a view to their cultivation asindicators of leaks on land above natural gas pipelines. The most sensitive were found to be sugarbeet, feed cabbage, sunflower, barley, alfalfa, potatoes, maize and larch. The most resistive to leakingnatural gas were beans and onions (Pyšek P. et al., 1988). The indicative symptoms of the impact ofgas on vegetation are: deficiencies in growth (height reduction, lodging of straws), anomalies indevelopment (shift of phenophases), physiological changes (colouring of leaves) and death of highlystressed plants which make very striking soil circles above large leaks in pipelines.

Nitrates generally impact on vegetation in such a way as to be almost indistinguishable to the effectof other fertilizers. Nevertheless combined usage of nitrophyllic species which react with a loss ofvitality to a lack of nitrogen in soil and the negative response of nitrophobic species to an abundanceof nitrogenous matter, enable phytoindication. Generally, common species of corns show increasedgrowth, cover density and have deep dark green colours with higher nitrates concentrations. Theamount of some weeds declines with the rising doses of N-fertilizers: Persian Speedwell (Veronicapersica), Field Pansy (Viola arvensis), Black Medick (Medicago lupulina) etc. Diversity of species ishighest at plots having lowest nitrate content. (Pyšek P. et al., 1988).

Heavy metals are generally toxic on vegetation, even in low concentration (Ernst, 1974). Toxiceffects manifest in dwarf growth -Scots Pine (Pinus sylvestris), leaves necrosis-Silver Birch (Betulapendula), change of green colours- Norwegian Spruce (Picea abies).Strong pollution by heavy metals causes, at general, absence of trees and lower variety of herbs. Among resistant species againstthe impact of heavy metals may be mentioned Vernal Sandwort (Minuartia verna), Sea Pink (Armeria maritima), Bladder Campion (Silene vulgaris), (Pyšek A. et al., in press).

5.1.3 Photographic methods

Photographic pollution detection primarily makes use of the state of and changes in vegetationcaused by the presence of pollutants in the rhizosphere, which can be recorded on films at visibleand near infrared wavebands. Photographic detection employs two causally and temporally



connected phenomena: 1) the state of and changes in plant health, 2) the density of and changes invegetation cover (canopy) below ground.

Infrared (IR) photography detects vegetation stress, which is manifested by loss of reflectance,chiefly at wavebands greater than 700 nm. The lost of cells turgor, which is the reason for the declineof near photographic reflectance, generally appears sooner and more distinctly than changes ofcolour in visible light. Of cause there are more reasons which may lead to the loss of near IRreflectance and to the worsening of state of plant health (mechanical damage, pests, drought, air pollution). Therefore close cooperation between specialists evaluating photographs and geobotani-cal data is vital.

The optimal means for recording initial physiological changes is a combination of true colour andIR colour photography. The state of highly stressed dying vegetation is easily visible on bothpanchromatic and IR black and white film. Photographic detection of simulated escapes of naturalgas from a pipeline at an experimental site gave very good results (Svoma 1990). Distinctive symptoms of vegetation stress were found using colour IR photography 10 to 21 days after the startof the experiment. The main diacritical symptom was loss of vegetation cover (canopy). The affectedarea varied from 13 to 36 m2 according to the sensitivity of the plants. The agricultural plants mostsensitive to the gas proved to be winter wheat followed by alfalfa with regard to the time of theresponse and potatoes and sunflower with regard to the extent of the area affected. The plants werereacting to doses of 36 to 100 cubic metres of natural gas injected into subsurface holes.

Photographic detection of groundwater pollution depends on the pollutant class and concen-tration, the sensitivity of the plants and the relation between root systems of sensitive plants (mostly trees) and the level of the groundwater table (GWT). An investigation carried out at geologically different regions of former Czechoslovakia proved that at many contaminated sites the GWT was at a depth (up to 4 metres) which enabled contact between the rhizosphere of trees and ground-water. Thus favourable hydrogeological conditions for pollution detection by photographical methods existed. A study of 2,201 boreholes used for pollution remediation showed that in 5,3%bore-holes the GWT was from 0-1 m below ground; in 15,2% between 1 and 2 m below ground; in 48% 2 to 4 m below ground; in 21,9% 4 to 8 m and in 9,6% the GWT was more than 8 m below.

Diversity of plant species is not at all advantageous for pollution detection by photographic methods (in contrast to geobotanical methods). The difference in reflectance of species both in thevisible and near IR bands, makes evaluation of photographs more difficult and may even mask the changes of reflectance caused by vegetation stress. The most suitable vegetation for this approachis that provided by monocultures (agricultural or forest). Over-fertilized monocultures on arableland with potential leakages of nitrogen into the soil and groundwater system are easily detectableby both true colour and IR colour films.

Broad leaf trees enable better recognition of stress that needle-leaved trees because of the generallylow IR reflectance of conifers. The best time for surveying depends on the kind of vegetation. Springor early summer seems to be the most suitable. Autumn is not recommended because of the naturalseasonal changes in leaf colour. Simultaneous use of vertical true colour and false colour (colour IR)photography has proved to be the optimum combination of photographic techniques for the detec-tion of pollution impact on vegetation. The best results are given by Kodak Aerochrome IR film with a dark yellow Wratten filter 70. For the early detection of stress in conifers, additive colour



compensating magenta filters should be used. Aerial photography used for pollution detectionshould sometimes be replaced by more the practical and cheaper method of photographing fromradio-operated models or moveable platforms (Švoma, 1990). The use of video cameras does not provide any additional detail to still photography. Nevertheless, it can be very useful to haveimmediate information regarding the state of pollution recorded in real time.

Continuous (overlapping) aerial photographic surveys provide an extremely useful form of photo-graphic pollution detection as they allow a simultaneous comparison of polluted areas and adjacentunpolluted areas and also provide a record of changes in the state of the vegetation with time. Photographic records can also be used as legal evidence because they show the state and extent ofpollution at any given time.

Photographic pollution detection for groundwater without the combined use of geobotanical methods is limited to sites where polluted water discharges into surface water bodies. The possibilityof direct photographic detection is limited by the physical properties of the dissolved or floating pollutants transported by the discharging groundwater after their dilution and/or interaction withthe surface water. The change of reflectance of the surface water affected by yellowish coloured mining water and landfill water with compounds of oxidized ferrous ions is mostly detectable in visible light and may be easily recorded on true colour films. However, the detection of oil slicks,films or layers in discharging polluted groundwater is the most common application of this method-ology. It is even possible to estimate the thickness of a floating oil layer by consideration of thecolour changes seen (Estes, 1972). Toxic substances discharged by groundwater into surface watersmay kill a large percentage of the fish population whose floating bodies are then detectable on blackand white and colour films. Such discharges may also result in a decline in algal growth which iseasily detectable by IR film which is generally more efficient than true colour film in this case. Onthe other hand a massive increase in algal growth in ponds or lakes owing to discharged ground-water polluted by phosphates may be distinctly detected in the green or near IR wave bands usingboth kinds of photography.

5.1.4 Geophysical methods

Geophysical methods provide relatively limited possibilities for the detection of polluting substancesin the unsaturated zone. This is particularly due to the inhomogeneity of the vadose zone (whichincludes the soil layer close to the ground, the capillary fringe above the water table and the properunsaturated zone in between – see Fig.5.1). The water content W of the rock medium and the watersaturation Sw of the pore space both change with depth below the surface and with time (due tochanges in precipitation, dry and wet seasons etc.). Therefore, the measurable physical properties(resistivity, electric permittivity, chargeability, density and the hydrogen index) of the unsaturatedzone are also subject to change with depth and with time.

Industrial fluids – the main sources of pollution of the soil and rock medium and consequently alsogroundwater – can be divided into three groups according to their chemical composition, physicalproperties and capacity for detection by geophysical techniques.



Inorganic compounds (acids, alkalis, salts) are usually easily soluble in water and dissociate to pos-itive and negative ions. The conductivity γwc of polluted water, is proportional to the total dissolvedchemicals and exceeds by one to two orders the conductivity of fresh water. It has a great influenceon the conductivity of the geological formation γt. The electric permittivity εr of inorganic solu-tions, however, is comparable to the permittivity of fresh water (εr = 80).

Inorganic chemicals drastically change the electrical properties of the rock medium. The electricconductivity (γt) of the upper part of the unsaturated zone (soil with suspended capillary water)will be particularly influenced. Under these conditions, inorganic chemical compounds can bedetected in the soil by electromagnetic conductivity meters (e.g. EM-31 product of Geonics Com.,Canada or CM-31 product of Geofyzika Com., Czech Republic), by standard resistivity arrays with short electrode spacing (0.5 m) or by multielectrode resistivity survey. This sophisticated geo-electrical method, if repeated over different time intervals, enables the estimation of the speed ofspill-penetration through the unsaturated zone. Inorganic chemicals also change the charge of the soil and the induced polarization method can be very helpful in deliminating the extent of the con-ta minated area. Seawater intrusion in coastal areas causes a similar geophysical effect to those ofinorganic compounds. However, it can also be recorded by repeated remote sensing images in the IRrange (3 to 20 um).

Organic compounds – typically hydrocarbons – are usually characterized by a very high resistivity(practically insulators) and very low electric permittivity (εr < 5), approaching the permittivity of the air (εr = 1). Hydrocarbons have generally low solubility in water and can be considered prac-tically immiscible with water. Their transport and accumulation in geological media is controlled bytheir density.

Figure 5.1Scheme of the unsaturated zone and the uppermost part of the saturated zone with depth variations of the moisture content W and the water saturation Sw



Direct detection of organic pollutants in the unsaturated zone by geophysical methods is extremelydifficult. The best way is to combine resistivity survey together with atmogeochemical methodsusing e.g. special equipments on detection of hydrocarbons in the soil-air, based on the photo -electric effect. Anomalies of hydrocarbon content in soil-air correlate with the areas of higher soilresistivities only if artificial or natural disturbing materials in the soil (stones, concrete pieces, PVCproducts etc.) are not present. Then the existence and thickness of a Light Nonaqueous Phase Liquid (LNAPL) layer on the ground water table (at the bottom of the unsaturated zone) can bedetermined in unconsolidated clastic sediments by means of cone penetration tests combined withgeophysical logging (gamma-ray, neutron-neutron, permittivity logging). The hydrogen index ofhydrocarbons is comparable to the hydrogen index of water. The top of an aquifer saturated by an LNAPL is indicated on the neutron-neutron log, the top of the 100% water saturated aquifer isindicated on the permittivity log. Under favorable conditions, the water saturation Sw and thehydrocarbon saturation Sh of the transition zone at the groundwater level can be calculated.

Both groups of pollutants, inorganic and organic, have characteristic electrical properties and sotheir detection will generally depend on geoelectrical methods.

Radioactive materials contaminate the soil as a result of incidents in their transportation and/orprocessing. The source of pollution can be uncontrolled spills of the transported radioactive material following a vehicle accident (resulting in a polluted area of small extent) or radioactiverains carrying radioactive elements to the ground after an accident at an atomic power plant (largeextent of contaminated area, such as the radioactive pollution of large regions of Eastern and Central Europe after the Chernobyl accident). These industrial radioactive elements usually havedifferent emitting spectra of gamma rays in comparison to natural radioactive elements and can bedetected by the use of radiospectrometric methods (Fig. 5.2).

The properties of the transported radioactive material spilled as a result of a vehicle accident are usually known and consequently the type of radiation and its parameters (energy and half-life)are as well. Therefore appropriate radiometric equipment can be used for detecting the extent of the contaminated area (e.g. radiometers measuring total gamma activity, or gamma spectrometersin the case of isotopes, which are sources of gamma radiation). After the Chernobyl accident, thecharacter of the distributed isotopes following the breakdown of the atomic power plant was alsoknown (see Fig. 5.2), gamma spectrometers were thus very useful in the delineation of the extent ofthe polluted area.

The first two groups of pollutants (inorganic and organic compounds) have characteristic electricalproperties and this is the reason for the predominant use of geoelectrical methods in their detec-tion.

Pollution identification by geophysical methods usually precedes drilling of investigation boreholesand monitoring wells and provides the first overview of the pollution problem (Mares et al., 1997;Iliceto and Mares, 2000). Delineation of a pollution plume by geophysical methods is faster and less expensive than identification of the extent of pollution by the drilling of a large number ofinvestigation boreholes. When the polluted area is defined by geophysical measurements, the number of monitoring wells needed to delineate the borders of the pollution plume is significantlyreduced.

To summarize, electromagnetic and resistivity methods are widely and successfully applied in con-



taminant hydrogeology, particularly for the delineation of the boundaries of a pollution plume.However, other geophysical methods should also be implemented, such as gravimetry, for site-specific studies of polluted sites, thermal measurements to identify the extent of higher tempe raturesaround landfills, or radiometric methods for delineation of polluted area by radio active material.For the determination of pollution type and intensity in the vertical profile of the saturated zone(e.g. hydrocarbons floating on groundwater table, fresh-salt water interface) various electrical, elec-tromagnetic and nuclear logging methods are often utilised in investigation or monitoring bore-holes.

Figure 5.2Energy gamma-ray spectrum measured on the Earth’s surface in Prague, The Czech Republic, (1) after the Chernobyl accident on May 4, 1986 (2) compared with the natural gamma-ray spectrum of rocks



5.2 On-site methods

5.2.1 Introduction

This work does not intend to give a comprehensive review of all available hydrological samplingmethods that can be employed for developing early warning monitoring systems in the unsaturatedand saturated zones. In reality many of the methods described in the literature can be used for sucha purpose provided that the scientists are willing to apply the groundwater early warning monitor-ing concept. Moreover, due to the wide range of possible scenarios where an early warning moni -toring method could be applied (e.g., unsaturated zone, water table region, contact between twooverlying aquifers, salt water-fresh water interface, Fig. 1.1); it is difficult to give a general method-ological approach. There is, however, a basic fundamental principle: in an early warning monitoringsystem the sampling and/or in-situ detection technique employed should allow a considerable timelag between pollutant detection in the sampling (detection) system and pollutant arrival into pro-tected target area (e.g., aquifer recharge area, pumping well, water supply region). The desired timelag should be established according to available response methods to overcome the problem. Forexample, the required time lag will be different if in response to a slug of organic pollutants it is necessary to build a water treatment unit or to operate an existing one.

5.2.2 Suction cups

Pore water in the unsaturated zone will not flow into a well as long as the rock volume considered isunder tension – which happens when the pores are partially filled with water and partially with air.In this situation the sampling is normally done using suction cups. The cups are made of porousmaterial for which capillary forces are higher than the tension in the partially filled pores in the soils.

Suction cups can be placed in the sampling location in several ways. The important principle shouldbe, that the procedure applied during placement of the cups in the soil does not alter the soil con-ditions along the pathway of infiltrating water from the land surface to the location of the cup. Anexample of a procedure applied for sitting of suction cups is shown in Fig. 5.3 (Lindhardt, 2001).Suction cups were installed in such a way, that the soil above them was not disturbed. The cups wereinstalled from excavation pits in two layers one meter apart. Suction cups, when installed at variousdepths, will support studies about the rate of transformation of potential pollutants during move-ment through the unsaturated zone.

However, great care has to be taken to avoid any boundary influence on the readings from the cups.This can be achieved by sitting the cups away from the edges of the field and away from places whereagricultural machines have to make specific manoeuvres such as turning; doses of fertilizers andpesticides in such places are different from doses applied at the remaining part of the field.

The holes for installation of the suction cups were drilled to the desired depth minus 20 cm; the last20 cm being completed using a steel rod with a diameter corresponding to the diameter of the suc-tion cup. A thick slurry of silica flour was poured to the bottom of the hole immediately before



inserting the suction cup. The hole was then sealed with 20 cm of clay pellets and back-filled withbentonite.

Each suction cup is connected to an individual sampling bottle, placed at the edge of the field beingobserved, via tubing running at a depth not accessible by ploughing. There is a large variety of suc-tion cups available and careful selection of this equipment is advisable. Compatibility of the grainsize of the monitored material and the pore size of the suction cups has to be assured. Use of silicaslurry is recommended for the initial phase of the measurements. Refrigeration or some other formof sample preservation should be considered if the monitored pollutant requires it.

Figure 5.3A) Location of suction cups, B) Cross section showing the installation of the suction cups (modified from Lindhardt, 2001)



5.2.3 Direct push

The chemical composition of pore water in the unsaturated zone is frequently a precursor ofchanges in the chemical composition of groundwater. Scarcity of programmes monitoring porewater in the unsaturated zone may be the result of the technical difficulty in sampling this region.Drilling methods to obtain sediment and water from the unsaturated zone are relatively expensiveand difficult to use. Continuous in-situ sampling techniques (e.g., porous cups) can only be used inregions of the profile where pore-water content is relatively abundant (e.g., the root zone after rainor irrigation; the capillary fringe – see for example, EPA, 1986).

A convenient sediment probing technique which is cost-effective and produces extensive samplingrates is based upon the ‘direct push’ of sampling tools into the ground without the use of drilling toremove sediment to provide a pathway for the tool. An example of such an instrument is the Geoprobe®. The Geoprobe® instrument relies upon a relatively small amount of static weight (theweight of the carrier vehicle) combined with percussion as the energy for advancing the tool string.The probing tools do not remove cuttings from the probe-hole but depend on compression of soilor rearrangement of soil particles to permit advancement of the tool string (Christy and Spradlin,Geoprobe® Systems; Geoprobe® Systems Catalogue 1998-1999). With the direct push technique it ispossible to obtain, for example, continuous sediment-cores or discrete core samples (Ronen et al.,1998), groundwater samples, and gas samples from the unsaturated zone (Affek et al., 1998). Soilprobing equipment is typically employed for site investigations to depths up to 20 m, but has beenused by the ‘direct push’ method up to depths of 30 m (Affek et al., 1998). Generally, direct pushmethods can not penetrate boulders or consolidated rock layers (e.g., limestone).

In a study conducted in the Coastal Plain aquifer of Israel a Geoprobe® was used to sample theunsaturated zone in two sampling studies. Over two days, 13 continuous-core boreholes were drilledto sample a sandy and sandy-loam unsaturated zone within a radius of 5 m, in a region where thewater table lay at a depth of 7 m. Three to five cores, each 1.2 m long, were collected from each bore-hole. The cores were collected within transparent plastic sleeves (having an internal diameter of5 cm), which were immediately capped and subdivided into 10 cm subsections. The sediment con-tent of each subsection was mixed inside a plastic bag and a sample was transferred into a glass vialfor the determination of water content and particle density. Core samples, 20 cm long, were cappedinside the plastic sleeve for the determination of bulk density and saturation percent. All sampleswere preserved in the field in iceboxes and were transferred to a refrigerator (5 °C) at the end of eachsampling day. While drilling, there was almost no compaction of the sediment inside the plasticsleeve, and recovery (ratio between penetration of the corer to the length of the core) was almost100%. To avoid the possibility of collecting displaced samples, the first 5 cm at both ends of eachcore were discarded.

In the course of this study, devoted to the analysis of transport phenomena in the capillary fringe ofgranular sediments, approximately 550 samples were obtained from the unsaturated zone. For eachsample, the gravimetric water content, the bulk density, the particle density and the saturation per-cent were calculated (Black, 1965). Figure 5.4 shows the gravimetric water content in the entireunsaturated profile and below the water table for 8 continuous-core boreholes obtained with theGeoprobe® (Ronen et al., 2000). Figure 5.5 depicts chloride concentration in pore water at the samestudy site. Pore water samples were obtained by the water addition-extraction method (Ronen et al.,1997).



Figure 5.4

Gravimetric water content (Θ) in the capillary fringe of continuous-core boreholes CF6 to CF13, in the Coastal Plain aquifer of Israel. The insert shows the gravimetric water content in the entire unsaturated profile andbelow the water table.



Figure 5.5

Chloride concentration in pore water of continuous – core boreholes CF2, CF3, CF4 and CF5. These boreholes were located in the same location as boreholes CF6 to CF13 (Figure 5.3), in the Coastal Plain aquifer of Israel. Note the heterogenity in the chloride concetration between profiles and within profiles. The study area is subjected to replenishment of rain in winter only. The gravimetric water content (Θ) is also shown.The shaded area in CF3 denotes the water content and chloride concentration in CF1 made solely below the water table (after Ronen at al., 1997).



5.2.4 Horizontal monitoring wells

Pollutant transport through clayey till, sandy clays and other sediments characterized by a large variation of hydrogeological properties within short distances, is primarily governed by preferentialflow pathways associated with fissures and occurrences of sandy lenses. It is obvious that samplingshould be done within the preferential flow rather than within an isolated, ‘dead’ volume of clay notparticipating in the transport of the pollutants. Interception of the preferential flow pathways ismuch easier with horizontal rather than vertical monitoring wells. Horizontal wells can be dividedinto separated screened sections providing samples from different parts of the monitored field. Anexample of installation of a horizontal monitoring well (Lindhardt, 2001) is shown on Fig. 5.6.

Figure 5.6

Installation of horizontal monitoring wells and a section of the horizontal screen(Lindhardt, 2001)



The installation of a horizontal monitoring well takes place in three stages: drilling of a horizontalopen hole is done by flushing with water (drawing A), reaming and placing of the outer casing(drawing B) and completion of the installation by placing of the screened intervals and removal ofthe outer casing (drawing C). The screened intervals, monitoring different parts of the well, are separated by bentonite seals preventing short-cuts between the various intervals.

Each screened interval is equipped with two tubes connected to a peristaltic pump on the surface.All the tubes from the screened intervals are placed inside the inner pipe going to the ground surface.

5.2.5 The separation pumping techniques

Sampling from wells will often provide samples consisting of a mixture of water with distinctly different concentrations of the pollutant considered. For an early warning system it is of paramountimportance to collect samples representing the most adverse conditions in the aquifer, i.e. the highest concentration of the pollutant. The separation pumping technique helps to delineatethe zones contributing the highest concentrations of the pollutant and allows the design of a reme-diation procedure aimed at these zones. The unpolluted groundwater zones are delineated as welland water from these zones can be discharged without treatment. Treatment cost can be reducedand efficiency increased significantly if the amount of polluted water requiring treatment is reduced.

The separation pumping technique is one of the methods used for taking level-determined ground-water samples. This technique allows the collection of samples from a required depth interval and/orthe definition of chemical profiles by analysis of a series of samples collected in either screened wellsor open boreholes. The principle of separation pumping, illustrated in Fig. 5.7 (Gosk et al., 1992), isbased on the creation of a water divide in the borehole by diverting flow to two pumps, one near the

Figure 5.7 Principle of separation pumping (Gosk et al., 1992)



water surface and one near the bottom of the sampling zone. By adjusting the rates of the two pumps, the position of the water divide can be adjusted to the required sampling level. If thediameter of the borehole is sufficiently large, a sampling set-up consisting of three pumps, and aheat-pulse-flow-meter can be applied, while for boreholes of smaller diameter an alternative systemconsisting of two pumps can be used. Two pumps, preferably with adjustable flow rate, are placed atthe top and at the bottom of the well while the third pump (typically with smaller flow rate) isplaced around the middle of the saturated (screened) depth with a heat-pulse-flow-meter, a deviceused to determine the direction of flow in the borehole, attached to it. Simultaneous pumping fromthe bottom and the top of the well creates a draw down in the well and inflow to the well from thesurrounding formation. One part of the in-flowing water will go to the upper pump and the otherpart to the lower pump. The share of water delivered by each pump will be determined by the valvescontrolling the flow rate of the top and bottom pumps. The intervals in the geological formationsupplying the upper and the lower pump respectively will be governed by permeability distributionat the face of the well screen or face of the open bore hole.

In a set-up like this a zone of (almost) stagnant water will develop between the interval with a down-ward flow going to the bottom pump and an upward flow going to the top pump. The location ofthis stagnant zone is then determined by means of the heat-pulse-flow-meter. The third, smallerpump connected to the heat-pulse-flow-meter is turned on as soon as it is positioned within thestagnation zone. After the sampling is completed the procedure may be repeated with a differentcombination of the flow taken by the upper and the lower pump. The new position of the stagnantzone for the different combination of flow rates then has to be determined. For the purpose of earlywarning the set-up providing the highest concentrations of pollutant in the samples provided by thesampling pump should be maintained.

The chemical profile obtained by this method will reflect the trends of pollutant concentration variation with depth rather than provide an exact chemical profile comparable to the profileobtained by analyses of pore water extracted from soil samples collected during drilling. In screenedwells completed with a sand and/or gravel filter there will be a tendency to smear-out the chemicalconcentration profile existing in the formation, particularly if the permeability of the filter materialis order(s) of magnitude higher than the permeability of the geological formation.

There are several advantages associated with the separation pumping technique: existing boreholescan be used, inflow zones for polluted water can be localised and remediation actions requiringtreatment of smaller amount of polluted water can be designed. The pumps do not need to bemoved between repeat sampling events. It is possible to carry out multi-step separation pumpingusing only two pumps: one placed on the top and the other at the bottom of the investigated interval.

5.2.6 The Multi Layer Sampler (MLS)

A major problem in hydrochemical studies is that of obtaining small-interval, representativegroundwater samples of the undisturbed system of flow. Generally, samples are collected by pump-ing or by samplers lowered to different depths in observation boreholes. These procedures disturbchemical gradients and can yield mixed water samples from different horizons of the aquifer.Devices to obtain profile samples reported in the literature have been used primarily for shallowaquifers. In most of these devices the water sample is pumped to the surface and the sampling



intervals are greater than 0.5 m (e.g., Hansen and Harris, 1974; Oberman, 1982; Pickens et al., 1978;Harrison and Osterkamp, 1981; Molz et al., 1986a). The challenge is to sample a flowing system withminimal perturbation due either to the introduction of the sampler or the retrieval of the sample.With respect to the water table region, fluctuations of the water table necessitate a variable samplingsystem (not fixed with regard to the aquifer) enabling the adjustment of sampling depth accordingto variations in the water table.

In order to sample the water table region without disturbing the chemical profile, a sampling systemwas developed composed of a Multi Layer Sampler (MLS) and a research well (Ronen et al., 1987a).The MLS enables water sampling at predetermined depth intervals by use of the dialysis cell tech-nique (Mayer, 1976; Hesslein, 1976). The sampler consists of a rod with crisscrossed holes, whichaccommodates dialysis cells filled with distilled water (Fig. 5.8 - right). Sampling intervals (distancebetween dialysis cells) may be as small as 3 cm. The cells are separated in the well by seals which pre-vent mixing by vertical currents and diffusion (Fig. 5.8 - left). The sampler is built in a modularfashion so that several rod segments may be connected to attain any desired length. The equili -bration time between the dialysis cell and a solution is determined empirically in the laboratory. Toobtain a sample for the analysis of major ions (e.g., Cl-, NO3- and SO4

2-) the equilibration time isabout 48 hours (Fig. 5.9). However, a minimum sampling period is established which enables re-equilibration of the well-aquifer system to ‘normal’ hydrochemical conditions following the lower-ing of the sampler into the well (e.g., about 7 days in a sandy aquifer). After retrieving the samplerfrom the well the sample is extracted from the dialysis cell for chemical analysis. The MLS has alsobeen used to obtain: (a) detailed vertical profiles of the horizontal component of the specific discharge, employing both a modified point-dilution technique under natural gradient flow con ditions, and a mathematical diffusion model (Ronen et al., 1986), (b) samples of dissolved gasesboth in the water table region and the capillary fringe (Ronen et al., 1988a), and (c) samples ofgroundwater colloids (Weisbrod et al., 1996).

Figure 5.8

Segment of a Multi Layer Sampler (MLS) showing the dialysiscells spaced at 3 cm intervals and separated by flexible seals (left) and, schematic representation of a segment of the MLS inside a monitoring well (right). V1, C and V2, S designate the volumesand solute concentrations in water contained in the dialysis celland sampling segment, respectively. For simplicity slots are onlyshown on the lower part of the PVC screen.



The sampler must be utilised in a screened well. It is recommended that the well is drilled withoutthe addition of water or drilling mud. The main requirement of the research well (Fig. 5.10) is thatscreens be installed both above and below the water table to enable long term observations consi -dering both short- and long-term fluctuations (monthly to yearly) of the water table.

Figure 5.9

Equilibration test of dialysis cells conducted at 22°C. To conduct this test pairs of dialysis cells (14 ml each) filled with distilled water were submerged in separated baths of a 800 ml solution (Cl - = 200 mg /l ; NO3- = 100 mg/l ; SO4 2- = 60 mg/l). The cells were overed with nylon membranes with a pore size of 0.2 μm (Versapor V-200, Gelman Sciences). The water was continuouslystirred at 126 RPM to eliminate spatial heterogeneities.



Figure 5.10

Schematic representation of a research well for monitoring the water tableregion. Note that screens are installed both above and below the water table to enable long-term observations considering both short- and long-term fluctuations (monthly to yearly) of the water table. The PVC-coated stainless steel wire, mounted on one of the screens, was used to determine (with an ohmmeter) the exact position of the screen in relation to the water table. The well in this figure is located 15 km north of Tel Aviv (WT-2) and was used to monitorthe water table region under land irrigated with sewage effluents. The lithologicalprofile at the study site is also shown.



Figure 5.11 depicts typical chemical profiles obtained with the MLS in the water table region of the Veluwe region, of the Netherlands, in a forested area subjected to the input of acid rain and ammonia volatilised from cultivated land and feed-lots (Krajenbrink et al., 1988). The watertable is at a depth of 7 m and the aquifer is composed of gravels, coarse sand, and clay loam layers.Figure 5.12 shows profiles of xylene, xylidine (dimethyl aniline) and toluene obtained with the MLSin the water table region of Brookhaven National Laboratory, N.Y. (BNL, Kaplan et al., 1991). Thephreatic aquifer at BNL, composed of sand and gravel, has been polluted by a spill of mixed liquidfuels. Benzene, toluene and xylene have been identified in local wells at a low mg/l level. In samplestaken with a pump, from depths greater than 200 cm below the water table (from the same researchwell into which the MLS was subsequently lowered), the concentration of toluene and xylene was0.43 mg/l and 2.3 mg/l, respectively.

Figure 5.11

Chemical profiles obtained in the water table region of research well 7 in the Veluwe region, the Netherlands, in a forested area subjected to the input of acid rain and ammonia volatilized from cultivated land and feed-lots. Note that the oxygen concentration found in the dialysis cells located in the capillary fringe (empty circles just above the water table) reflects the expected concentration of atmospheric oxygen dissolved in water, at the prevailing temperature (9°C).



Figure 5.12

Profiles of xylene, xylidine (dimethyl aniline) and toluene obtained with the MLS in the water table region of Brookhaven National Laboratory, N.Y. (Kaplan et al., 1991). In samples taken with a pump, at depths greater than 200 cm below the water table, the concentration of toluene and xylene was 0.43 mg/l and 2.3 mg/l, respectively.



6.1 Introduction

An early warning monitoring system can be established to monitor different types of stress appliedto the groundwater system under consideration. There are few specific properties of an early warn-ing monitoring which make data handling for this system different from, for example, data handlingfor an ordinary groundwater monitoring network. While monitoring data are collected with a viewto analysis some time in the future, early warning monitoring data have to be used immediately toenable important management decisions to be made. When the warning arrives there is no time forevaluation, lengthy investigations and discussions of remedial strategies. All this should be donebefore the emergency situation occurs. Therefore, it is necessary to make realistic simulations of thevarious scenarios and strategies, preferably with the help of a computer model of the aquifer systemconcerned.

In principle all aquifer pollution cases can be regarded as irreversible within our time scale (tens tohundreds years) and so it is necessary to follow the pollutant long before its entry to the saturatedzone of the aquifer. Therefore the typical early warning monitoring systems will consist of samplingstations situated in the unsaturated as well as the saturated zone of the groundwater system.

Data requirements and data handling will vary for different types of monitoring systems and there-fore the various early warning systems should be designed specifically for an existing stress situationor for situations where an immediate threat to the aquifer (water supply) exists.

Data requirements for an early warning monitoring designed for a water supply system threatenedby a chemical pollutant will mainly depend on:

• Type of pollutant source and pollution scenario,• Type and importance of the considered water supply,• Complexity of the system and degree of knowledge of the hydrogeological situation.

Typically, an early warning monitoring system will be designed either for a point pollution or for anon-point (diffuse) and line pollution situation. Data requirements for these two types will be dif-ferent. While the design of the network of observation points for point pollution cases will depend

6 DATA HANDLING



heavily on the extent of the pollution plume, the network for surface pollution situations has to takeaccount of the variability of the system in its design. The network density and frequency of data col-lection will be proportional to the importance of the well field or other object for which the moni-toring system is established and to the complexity of the system.

6.2 Data collection strategy

A proper strategy for detecting groundwater quality problems should enable detection of problemsbefore groundwater pollution occurs. Therefore the data collected within a properly designed earlywarning monitoring system established for groundwater should:

• Provide a detailed coverage of those zones currently with high concentration of pollutants,• Assure that there are no undetected pollution zones,• Provide information about the transport and transformation of pollutants along flow path

from the ground surface to the water table and within the saturated zone.

In all cases it is necessary to make a compromise between the three objectives specified above. Therewill always be a trade off between the necessity to have detailed point information (necessary fordetermination of the health risks caused by the pollutant) and integrated volume informationwhich assures that the whole groundwater aquifer volume is being monitored.

Each of the objectives specified above require a specific approach with respect to the modelling.Therefore the concepts of point monitoring, line monitoring and volume monitoring techniqueshave been developed (Fig. 6.1). While point can be established both in saturated and unsaturatedzone the line and volume monitoring refer mostly to the saturated zone. All above monitoring tech-niques correspond to the category of regional monitoring programmes

Point monitoring technique consists of a network of sampling points collecting small water samples from the unsaturated and the saturated zones. Point monitoring sites provide informationfrom a very limited volume of rocks extending from ground surface to the sampling point. The sampling point for this type of monitoring can be situated within the unsaturated zone, within aperched aquifer or just below water table in an observation well. Information obtained from a network of point monitoring points is closely related to the conditions on the land surface imme di-ately above the point monitoring site.

Line monitoring technique consists of a network of sampling points situated within the saturatedzone along the groundwater flow path. Line monitoring sites provide information about the changesof groundwater chemistry occurring with time and the distance travelled. Line monitoring wellssample at rates which do not significantly disturb the existing natural flow field.

Volume monitoring technique consists of wells pumping at a rate sufficient to affect the naturalflow field. Volume monitoring sites provide information from a large surface area and a large aquifer volume. The information obtained from the volume monitoring sites will always be averaged bothin space and in time. If the purpose of our groundwater monitoring system is detection of futuregroundwater quality problems, we need to know the averaged trend in groundwater quality for theaquifer under consideration and also the extreme values of selected parameters occurring locally.



6.3 Data analysis

Handling of the data collected within early warning monitoring system can be done using:

• Isolated treatment (groundwater chemistry time series for a specific well or groundwaterchemistry situation at a specific time) or

• Comprehensive treatment utilising the existing relationship between the different componentsof the system.

For the isolated treatment approach no knowledge about the dynamic behaviour of the system isneeded and data handling may consist, for example, of a standard XY-plot of concentration versustime or a standard contouring of concentration distribution within the aquifer. The ease of data treatment is the main advantage in this approach. The main disadvantage of this approach isasso ciated with the inability to make predictions about the future development of the situation due

Figure 6.1Principles for groundwater monitoring aimed at detecting groundwater problems



to a lack of knowledge of the dynamics of the groundwater system. Most commonly, the amount of information gathered for the early warning system will be insufficient to make a meaningful pre-diction based on extrapolation of the existing data. Within this approach a lot of existing (and essen-tial) information will not be used in the assessment

Comprehensive treatment involves use of not only all the relevant information on the parameters(concentrations, heads) but also use of the relationship governing the dynamics of the aquifer sys-tem. To put it another way both the knowledge of parameter values and the governing equationssuch as flow and mass balance equations are incorporated in this approach. This approach makes itpossible to verify our understanding of the system during the calibration procedure and to use thecalibrated model for prediction of the future situation in the aquifer under different scenarios. Thecomprehensive treatment requires, as a rule, that computer modelling using monitoring data is car-ried out. Furthermore, several efficient GIS-software packages have been developed during the lastdecade which offer the opportunity of combining the various types of surface-related information(geology, hydrogeology, pollutant distribution etc.) in an efficient way.

6.4 Modelling

Model in this context is understood to refer to a set of consistent rules established for a specificgroundwater system regarding

• Composition of the system,• Geometry of the system,• Interactions within the system and between the systems and surroundings.

While the composition and geometry of a system are in general time independent the interaction ofthe system with the surroundings will normally depend on time.

Composition of the system

Properties of the various rocks, occurring within the considered groundwater system, such aslithology, permeability and groundwater chemistry should be described. Furthermore, propertiesrelevant for transport and attenuation of relevant pollutants should be addressed. Groundwaterchemistry: both background and anthropogenically influenced, should be described.

Geometry of the system

Spatial distribution of the different types of rocks should be defined. In cases where no head distri-bution within the aquifer system is defined, a flow field based on the measured head values shouldbe constructed.

Interactions within the system and between the systems and surroundings

Definition of the interactions within the system is typically made using the basic laws governinggroundwater flow and contaminant transport: such as Darcy’s law, Fick’s law etc. Definition of theinteractions between the system and the surroundings involves an evaluation of: infiltration,



exchange with surface water bodies and intensity and distribution of the pollutant source. Establish-ment of the proper boundary conditions for the groundwater system is the most important and fre-quently the most difficult task during construction of conceptual and digital modelss.

Types of models

Both the design of an early warning system and the subsequent data analysis should be done usingmodels. The basic model necessary in all cases is the so called conceptual model. In most cases inaddition to the conceptual model it will be feasible to develop a so called digital model.

A conceptual model consists of a description of the hydrogeology of the groundwater system anddefinition of the boundary conditions. Establishment of this model is the most important part ofthe analysis of a groundwater system. To prepare a useful conceptual model it is necessary to have anidea about: direction and magnitude of groundwater flow, exchange of water between the differentaquifers and between groundwater and surface water bodies, infiltration rate prevailing in the system and type and intensity of the existing pollution sources.

A digital model, which is an extension of the conceptual model, requires strong discipline from theuser because all points within the modelled system have to be defined as far as properties of the sys-tem are concerned. Depending on the amount and type of information available for the establish-ment of the digital model, it can either be of steady state or transient type. Input to the digital modelconsists of the definition of system properties within the solution domain and the definition ofboundaries and initial conditions of the system. The primary output from the models is in the formof head (water level) distribution for flow models and pollutant distribution for pollutant transportmodels. Some simple techniques exist which allow simplified calculations of pollutant distributionto be made using the flow model with an assumption requiring that the pollutant behaves as a con-servative tracer.

While it is absolutely necessary to establish a conceptual model for the system being considered,construction of a digital model is optional and will mainly depend on the amount of informationavailable and complexity of the system. It is a common misunderstanding, that sparse hydrogeolog-ical information excludes the use of digital models. Digital models should always be used for sys-tems characterised by complex geometry and in cases where complicated boundary conditions makeit impossible to apply analytical solutions.

A digital model can be used to prove the validity of a conceptual model by successful calibration ofthe model against the existing data or to analyse the system by geometry and interactions which aretoo complicated for treatment without the aid of the computer. It is recognised, that analytical solu-tions for groundwater flow can only be obtained for a very limited number of cases with unrealisticgeometry and highly idealised initial and boundary conditions.

Sensitivity of the system

One of the most important tasks which can be solved with models is an evaluation of the sensitivityof the system to changes of the different parameters within the limits specified by the user of themodel. Sensitivity analysis will provide information on which parameters are crucial for the per-formance of the system and will help to design the data collection campaign and field work in the



most effective manner. As a typical result of such analysis a prioritisation of the different parametersand conditions should be established and a cost-effective data-collection campaign launched.

6.5 Forecasting

Important function of an early warning system is the forecasting of the development of the pollution plume under different conditions. A well-calibrated digital model is an suitable tool forthe calculation of different scenarios covering a wide range of situations. Various remedial actionsincluding different pumping strategies within the existing well fields, establishment of hydraulic barriers with the help of remedial wells, re-circulation of the contaminated water etc. can easily beinvestigated using digital models. This ease of forecasting is the best argument for the developmentof digital models for aquifers observed by early warning monitoring system.



Early warning groundwater quality monitoring programmes can be regarded as a widely acceptedconcept of preventive care, helping to avoid serious outbreaks of groundwater pollution. In mostcountries, we are at best monitoring fully developed groundwater quality problems rather thanattempting to monitor earlier stages of aquifer deterioration process. This is the contradictory philo-sophical approach fluctuating between post mortem analysis and a diagnosis of an in status nacendiproblem by means of an early warning groundwater monitoring strategy.

The main objective of an early warning groundwater quality monitoring strategy is therefore, toidentify and to foresee the threats which may cause adverse effects on groundwater quality whilethey are still in the unsaturated zone and thus to timely define measures leading to protection of theaquifers. Early warning monitoring generates data about groundwater quality in space and time andmovement and the fate of pollutants and is an important element of groundwater protection andquality conservation programmes. However, institutional and technical capacities for the develop-ment and implementation of monitoring strategies have to be available or to be established.

Early warning, as an integral part of a groundwater quality monitoring programme, is broad innature, has different objectives, requires a progressive approach and supports both short-term (spe-cific monitoring) and long-term (background monitoring) groundwater protection policy and sus-tainable management of groundwater resources. Establishing a groundwater early warningmonitoring programme is a scaling process, that advances step by step and which has to be fundedand implemented within national and river or groundwater basin water management plans. Subtlechanges in groundwater chemical composition may be observed many times before groundwaterlevel decline or other hydraulic phenomena become evident. Therefore, early warning groundwaterquality monitoring, particularly on regional and site specific levels, should be implemented and tar-geted with respect to the specific groundwater quality problem caused by pollution impact, land usechanges, excessive aquifer exploitation or well failure.

Establishment of early warning groundwater monitoring programmes supports also data for pre-vention, preparedness and mitigation of natural disasters and management of groundwaterresources in emergency situations. The frequency and magnitude of disastrous events is increasing

7 EARLY WARNING GROUNDWATER

QUALITY MONITORING STRATEGY



worldwide. Therefore, the operation of integrated early warning monitoring programmes, inclusiveof groundwater is desirale for 1/ the timeous recognition and better understanding of risk andimpact of natural disasters on the population, 2/ identification, delineation and evaluation ofgroundwater resources resistant to natural hazards and suitable as a source of drinking water for emergency situations and 2/ formulation effective groundwater disastrous protection and miti-gation policy.

An early warning groundwater quality monitoring strategy supports:

• Evaluation of the chemical composition and chemical evolution of groundwater in space andtime.

• Identification of groundwater pollution risks and assessment of the threats to which thegroundwater system is exposed.

• Assessment of groundwater vulnerability to both human impacts and natural disasters. • Conservation of groundwater quality.• Solution of groundwater quality problems while there are still at a controllable and manageable

stage.• Groundwater preventive protection policy and sustainable management of groundwater

quality.• Decision making taking into account pollution risks, potential water conflicts and sustainability

between social and health requirements on groundwater sources, economic development andgood status and functionality of groundwater dependent ecosystems

A priori it could be envisaged that it should not be necessary to convince politicians, decision makers and professionals about the necessity of having groundwater early warning monitoring systems. Such an approach could be considered to be parallel to the well-known slogan suggestingthat ‘prevention is better than cure’.

However, there is an intrinsic and not always spelled out psychological problem related to theexploitation and protection of groundwater. Since groundwater cannot generally be seen (asopposed to the case for a lake or a river) people do not feel much responsibility for this hiddenresource and its quality. Moreover, since groundwater systems are known to have a delayed response,particularly with respect to quality changes, decision and policy makers know that reactions to impacts on the system will be felt years after they have resigned from their political and adminis-trative responsibilities (this is a ‘benefit’ resulting from the very large residence time of groundwateras compared to the political residence time of bureaucratic officers).

A possible reaction when phased with the ‘to-know-now’ possibility, offered by early warning moni-toring systems, could be the ‘what do I need this for now’ approach. In other words, early warninggroundwater monitoring systems need to overcome the inertia of systems that, in relation togroundwater, are accustomed to postponing action and investment of human and financialresources for its protection

All the above is related also to the necessity of thinking in a non-conventional way. A manager accus-tomed to long term planning may regard the knowledge that a groundwater supply source will bepolluted within a decade as information of great economical and social value. For another profes-sional worried by daily problems, this same information can be considered as an anachronistic andundesired noise.



The establishment of early warning groundwater monitoring systems requires, in many cases, extrabudgetary allowances. For example, for professionals to learn and get used to new field methods andnew analytical approaches, for acquiring field equipment (e.g., multi layer samplers, porous caps),for the installation of new specifically designed monitoring wells and for obtaining periodic fieldprofiles. These costs are generally not large when compared to the cost of developing an alternativewater source due to groundwater supply pollution, or the cost needed for groundwater qualityrestoration. However, the dilemma of a contemporary investment as compared to a possible futureone is always present.

A administrative, legislative, and political framework must also be developed to efficiently utilize the information gained from groundwater quality early warning monitoring. In general, the admin -istration and legislation will need to analyse and react to future scenarios on the basis of currentinformation supplied by the groundwater monitoring network for what may in some cases beremote parts of the system (e.g., results obtained in the water table region suggesting that pumpingwells downstream will be polluted within a five year period).

Early warning groundwater monitoring systems generate data that enable assessment of ground-water quality of transboundary aquifers too. Special regard must be given to the transboundaryaquifers whose recharge area is in one country and the discharge area is in neighbouring country orcountries. Transboundary aquifers boundary, aquifers geometry, groundwater flow conditions fromrecharge to discharge areas and groundwater quality have to be therefore studied and known beforetransboundary groundwater monitoring network is established. The UN Convention on the Protec-tion and Use of Transboundary Watercourses and International Lakes (Helsinki, 1992) endorsed theharmonization of rules and methods for establishment and operation of transboundary monitoringnetworks, correlation of monitoring programmes, standardization of monitoring procedures andanalytical laboratory techniques and methods of data processing, evaluation and transfer amongneighbouring countries. Monitoring of groundwater quality and establishment, operation of earlywarning groundwater monitoring systems around potential and existing pollution sources locatedin transboundary aquifers and data management, assessment and reporting will provide valuableinformation for a joint assessment and sustainable management of shared aquifers, coordination ofgroundwater protection policy and prevention of water related transboundary conflicts. However,internationally coordinated effort to collect, process and evaluate data in a standardized manner andthus support early detection of transboundary groundwater quality problems, is generally missingtill this time.

Establishing a conceptual model of the groundwater system is an important initial stage in the devel-opment of early warning monitoring network and programme. Monitoring of the unsaturated zonewith respect to its ability to store, retain, remove and attenuate pollutants and delay their migrationto the saturated aquifer, is a crucial tool for groundwater protection policy and strategy and ground-water quality management. Data collection by early warning groundwater quality monitoring is a technically demanding, time consuming and costly process. However, with growing industrial-ization, urbanization and intensification of agriculture, threats to groundwater quality are increas-ing and implementation of an early warning monitoring strategy is justified from social,environmental and economic points of view.

Governmental institutions, water supply organizations and other water stakeholders in many countries of the world may not yet be prepared to accept the need for an early warning groundwaterquality monitoring strategy. However, the reality in the field and the costs of restoration of polluted



aquifers suggest that early warning monitoring may be an important cost-benefit approach for pre-serving the quality of groundwater as a strategic source of drinking water and a valuable componentof environment.



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Balke, K.D. 1973. Chemische und Thermische Kontamination des Grundwassers durch Industrieab-wasser. Z. Ditsch, Geol. Ges., pp. 447-460.

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Bouwer, H. 1987. Effect of Irrigated Agriculture on Groundwater. J. Irrig. Drain. Eng., 113, pp. 4-15.Candela, L. and Aureli, A. 1998. Agricultural Threat to Groundwater Quality. Workshop Proceedings.

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440 pp.

8 REFERENCES



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9.1 Monitoring of groundwater quality problems caused by agriculture in Denmark

9.1.1 Introduction

Serious problems with groundwater quality are occurring all over the world. These problems willaccelerate with increasing demand for potable water and for irrigation water. Unlike pollutedstreams and rivers, where the proper efforts and removal of the source of pollution can restore goodwater quality within a few years, restoration of groundwater qualityis a long term process. Thereforeavoiding groundwater pollution is much wiser than aquifer remediation.

In order to avoid groundwater quality problems it is necessary to have a strategy that facilitatesdetection of possible future pollution problems long before these problems are encountered in watersupply wells. In most cases when the water supply wells show signs of pollution the affected volumeof aquifer is so large that no strategy can help to save the aquifer. This logic appeals to the Danishpoliticians and protection of groundwater resources is one issue that almost all of them can agreeupon.

This case study refers to selected aspects of the Danish Environments Monitoring Program in general and to the monitoring of agricultural pollution in particular. In this context no attempt hasbeen made to present the whole Danish program, rather just those aspects relevant to groundwatermonitoring strategies are emphasized

Denmark is situated in the Temperate Zone. The annual precipitation varies from less than 650 mmin the central and eastern part of the country to over 900 mm in western part. The annual net pre-cipitation amounts to 280 mm. The highest point in Denmark is less than 180 metres above sealevel. In Denmark about 65% of the total area is used for intensive agricultural production.

9 CASE STUDIES



In Denmark approximately 99% of the water supply comes from groundwater. Until 20 to 30 yearsago the groundwater was often withdrawn from quite shallow, phreatic aquifers. However, due tothe increasing pollution of these vulnerable aquifers by nitrates, pesticides and other organic micro-pollutants, an increasing number of supply networks are now getting their groundwater from deeperaquifers.

Practically all of Denmark is covered by Quaternary, glacial-influenced deposits such as tills andmelt-water sand and gravel. The central and eastern parts of Denmark are dominated by lime-richclayey till, whereas glacial sand and gravel dominate the northern part. The landscape is undulating.In the western part of Denmark ‘hill islands’ and alluvial ‘heath plains’ of glacial sand and graveldominate the upper sediments and landscape. In the central and western parts of Denmark shallowaquifers consist mainly of dilluvial sand, whereas in the eastern part shallow chalk aquifers arefound.

Growing problems with nitrate pollution of groundwater and surface water during the 1980sprompted the Danish government to initiate a nation wide Environment Monitoring Programme in1988. One of the elements of this programme was the implementation of an integrated, comprehen-sive monitoring system in 6 agricultural watersheds called LOOPs. For each LOOP nutrient input,nutrient transport through the different parts of the environment and nutrient removal from thearea as crops and leakage were either measured or calculated. The monitoring system was laterextended to include pesticides. One of the main objectives of the LOOPs was the development of amonitoring system allowing the determination and prediction of the magnitude and extent ofgroundwater pollution caused by agricultural production.

The monitoring of shallow and vulnerable groundwater aquifers in Denmark, carried out within the Agricultural Watershed Monitoring Programme, has has previously been described in the papersof Gosk (1988) and Rasmussen (1986, 1998). The following description is based upon those papers.

9.1.2 Monitoring concept

Monitoring of shallow groundwater is being carried out in 6 agricultural watersheds varying in sizefrom 5 to 15 km2 (Fig. 9.1). These watersheds are called LOOP1, LOOP2, ... LOOP6. These water-sheds represent the range of agricultural land use and drainage, the most important soil types, shallow groundwater, recharge areas, top of stream systems and climatic variation found in Den-mark (Rasmussen, 1996).

The aims specified for the LOOPs were:

• To evaluate the effects of measures taken by the Danish government to reduce the input ofnutrients and chemicals to the environment.

• To obtain fast and field related measurements of changes in agricultural practice (early warn-ing).

• To measure nutrient flow and pesticide leaching under ‘farming as usual’ conditions.

To fulfil the objectives specified above, water, nutrient and pesticide fluxes were measured in differ-ent parts of the hydrological cycle. A network of stations for monitoring climate, groundwater



levels, stream flow and nutrient content together with other water quality parameters in soil water, drainage water, groundwater and streams was established during 1988 and 1989. Samplingfrequencies for the different parameters varied from once per week to once every second month,depending on the type of monitoring station, water quality parameter and time of year.

In every LOOP annual surveys of agricultural practice were conducted for all the farms in order todetermine the magnitude of nutrient input and output associated with farming. The surveys werecarried out on a field scale and covered all the fields within the watershed. Detailed soil survey anddescription of the geological and hydrogeological conditions in the watersheds were included in themonitoring programme (Grant and Andersen 1996).

Each county, responsible for an individual LOOP, prepared yearly reports summarising the resultsof the sampling programme and sent all the data to the National Environmental Research Institute(NERI) and the Geological Survey of Denmark and Greenland (GEUS). NERI and GEUS made anevaluation of the results on a national scale. Administratively the Danish Environmental ProtectionAgency made an overall evaluation of the results from the whole monitoring programme. A uniquedata transport system, STANDAT, was developed for the transfer of monitoring data from the counties to NERI and GEUS.

Figure 9.1 Location of the six experimental agricultural watersheds LOOP1 - LOOP6



9.1.3 Instrumentation

A variety of monitoring stations is present in every LOOP. Two kinds of monitoring stations werespecially developed for the LOOPs: groundwater nests and soil water stations, while other stationslike drainage and stream flow stations were of standard type. Both the groundwater nests and thesoil water stations were constructed in such a way, that no change of agricultural practice was neces-sary in spite of large number of instruments present at varying depths in the field. The samples,originating at spots located far away from the edges of the fields, i.e. where the conditions are repre-sentative for the agricultural practice, were transported to the edge of the field using either a vac-uum or compressed nitrogen (or air) and a special tubing system (Fig. 9.2). This system permitsnormal cultivation of fields while allowing the collection of samples from the unsaturated zone andfrom the top of the saturated zone.

A typical LOOP contains:

• 6 to 8 soil water stations, each station containing 10 samplers,• 21 to 25 groundwater nests with a total of 50-72 screens, situated in 15-17 fields,• Piezometers for groundwater level measurement drilled down to 5 to 7 meters below surface

next to all fields with groundwater nests,• Several drain stations and stream gauges and• 1 to 2 rain gauges.

Soil water stations, collecting water from the unsaturated zone immediately below the root zone,can be regarded as a first stage of a system monitoring transport and transformation of con-taminants. Water samples from the soil water stations will give the first warning about possibleproblems with groundwater quality in the saturated zone. Due to a large spatial variation in the transport velocity within the unsaturated zone, each soil water station has to contain severalsampling points in order to give meaningful information.

Figure 9.2 Schematic layout of groundwater nests and soil water station



In the Danish LOOPs each soil water station consists of ten sampling points (samplers) arrangedas a letter ‘V’, see Fig. 9.2. The samplers, made of Teflon or ceramics, are placed about one metrebelow the soil surface in sandy areas and 1.2 metres in clayey areas. The cells were installed froma 0.4 m wide trench and the cells are inserted at an angle of 45° (Fig. 9.3). This procedure allowscollection of samples of water infiltrating through practically undisturbed soil. Each cell was connected to an individual bottle using two 1/8-inch polyethylene tubing. The bottles werestored in a thermo-box placed below the ground surface at the edge of the investigated field.

At the beginning of each one-week sampling period and after each sampling event the bottles weresubjected to a 0.7 bar vacuum. A tube system, extending from the sampling stations to the edge ofthe field, allows the sampling procedure to be carried out without interference with the usual agri-cultural routines. Sampling at the soil water stations is normally possible only during winter, whenthere is a surplus of infiltrating water.

Usually, samples of groundwater from groundwater nests (Fig. 9.4), if compared to samples of soilwater from the unsaturated zone, are characterised by significantly larger concentrations of the dif-ferent chemical compounds present in the infiltrating water when averaged over time and space.Normally such an averaging is advantageous but, when strategies for detecting groundwater qualityproblems are concerned, the extreme values of different pollutants in soil water and groundwaterare important. When we are looking for the future threats to our groundwater we do not want to unnecessarily dilute a potential pollutant before sampling. Therefore a special system of ground-water nests has been developed for the LOOPs where it is possible to collect the youngest groundwater from the very top of the unconfined aquifer or from the perched, small aquifers sepa-rated from the main unconfined aquifer by varying thickness of unsaturated zone.

In a similar way to the soil water stations, the groundwater nests, see Fig. 9.4, permit normal culti vation of fields, while allowing for collection of groundwater samples from the top of the satu-rated zone. Monitoring of nitrate and pesticides in shallow groundwater 2 to 5 meters below the surface for clayey areas and 1 to 3 metres below the water table for sandy areas provides an earlywarning for deeper regional aquifers. The nests are located 20-25 meters from the edge of the field

Figure 9.3 Soil water sampler, construction details



(Fig. 9.2). Tubes extend from the top of the wells, one metre below the ground surface, to the edgeof the fields, where the samples are collected by the montejus pump system (Andersen, 1990). Com-pressed air or nitrogen is used as a driving agent.

In the clayey till watershed it is often difficult and time consuming to determine water level in theupper layers. Therefore at these locations the wells are placed at fixed depths: 1½, 3 and 5 metresbelow surface.

Due to the more predictable groundwater level in the sandy watersheds it is easier to relate the filterlocation to the measured water level. In the LOOPs situated in sandy areas the screens are placed at1 and 2 metres below the measured groundwater table. The screens are 30 cm long and are made ofPVC.

9.1.4 Groundwater sampling and chemical analysis

As the frequency of sampling in groundwater nests is typically once per month, it is necessary toremove the old water prior to sampling. In clayey watersheds, where the hydraulic conductivity islow and water movement is slow, it is necessary to pre-empty the wells 1 to 3 days before sampling.In the sandy watersheds where the hydraulic conductivity is higher and re-filling of the nests is fast,the wells are pre-emptied at least three times immediately before sampling. The amount of ground-water obtained from the nests is typically 0.5 to 4 litres. During sampling, measurements of pH andconductiv ity are made. Samples are analysed by certified laboratories adhering to Danish Standards.

Figure 9.4 Groundwater nests, construction details



All farmers within the entire watershed participated in an annual interview carried out in order todetermine the input and output of nutrients at the field level. The survey includes among otherthings crop type, time of sowing and harvest, yield, amount and time of application of fertiliser andmanure, as well as type of manure. From 1993 the use of pesticides in selected fields was included inthe survey. Since 1998 all fields within the LOOPs are included in the survey.

Nitrate monitoring was carried out from the very beginning of the LOOP project (1989-90). Thegroundwater wells were sampled between 4 and 10 times per year and analysed, for 13 additionalparameters beside nitrate: Ammonium, Total Nitrogen, Ortho-phosphorus, pH, Conductivity,Potassium, Alkalinity (or Acidity), Sodium, Chloride, Sulphate, Calcium, Magnesium and Iron.

Since 1993 pesticide monitoring has been carried out in the six LOOP-areas. Groundwater sampleshave been taken from 1.5 to 5 metres below surface in clayey LOOPs and 0.5 to 4 metres belowgroundwater table in the sandy areas. Samples were analysed for up to 44 different pesticides andmetabolites 1 to 6 times a year.

Trend and seasonality analysis for nitrate content in groundwater samples were carried out for quar-terly averages of nitrate concentrations. The Kendall Tau Test was used for trend analysis and theKruskal-Wallis Test was used for seasonality analysis of the data. In order to get a better picture ofseasonality, the linear trend was removed using the Ordinary Least Squares method. Similarly, toimprove the estimation of trends it was necessary to remove the seasonal variations from the dataset by subtracting the mean of all observations in a given quarter from each observation in thatquarter (Phillips et al., 1988).

9.1.5 Nitrate monitoring

The nitrate content in the shallow groundwater is generally high and clearly influenced by agri cultural production. During the very dry spring/summer of 1992 the harvest was poor and alarge surplus of nitrogen was seen as increasing nitrate content in the shallow groundwater wells. A dry autumn/winter 1995-96 with low groundwater recharge may explain the decreasing nitratecontent in 1995-96 (Fig. 9.5).

Changes in groundwater nitrate content due to changes in agricultural practice should first bedetected in the shallow groundwater. A trend analysis has been carried out on 111 nitrate time seriesfrom wells located between 1.5 metres and 7 metres below surface in the 6 LOOPs (Phillips et al.,1988). Only time series containing not less than 20 quarters within the first six years of monitoringhave been evaluated. Out of the 111 time series analysed, 25 series showed a significant decrease ofnitrate concentration, 11 time series a significant increase of nitrate concentration and 75 time seriesshowed no significant trend in the nitrate concentration. ‘No trend’ was defined when the annualchange of nitrate concentration was less then ±1.0 mg NO3 / l. The trend test was made at a 10%level of significance.

Fig. 9.6 shows how large changes in the amount of nitrogen applied (graph A) influence the nitrateconcentrations in the shallow groundwater (graph B). The example shows that the response in twodown-gradient wells is fast and well correlated with the changing input.



Figure 9.6

Nitrogen load and nitrate in shallow groundwater in the sandy watershed Barslund Bæk; Graph A: annual net amount of nitrogen applied; Graph B: nitrate content in two down-gradient wells sampled 2 and 3 metres below surface

Figure 9.5Median annual nitrate concentrations in shallow groundwater for 3 sandy and 3 clayey till watersheds in the period 1990–1996



9.1.6 Pesticide monitoring

Investigation shows that out of 15 cases with pesticide (and metabolites) pollution of shallow groundwater in 1996, it was possible in 10 cases to determine that the discovered pesticideswere used up-gradient of the wells in the period 1993 to 1995. Due to the fact that from 1998 all fields are included in the annual interview of farmers, the possibility of relatingpesticide use and pesticide in groundwater has been improved. In one case the degradation productof atrazine, atrazine-desethyl, was found at a concentration of 0,12 μg/l, exceeding the drinkingwater limit of 0,1 μg/l (Fig. 9.7).

The result of repeated analysis and findings of atrazine and the 2 metabolites, atrazine-desethyl andatrazine-desisopropyl, in groundwater samples taken 5 metres below the surface in the clayey Lille-bæk watershed are shown in Fig. 9.7. 11 analysis for atrazine and 2 for atrazine-desethyl andatrazine-desisopropyl were taken in the period 1990-95. The last known use of atrazine on the sur-rounding fields was from 1990 to the Spring of 1993.

Fig. 9.7 illustrates that: (1) there is a time lag between the use of the pesticide in the field to theoccurrence of pesticides and metabolites in groundwater, (2) the concentration of pesticides at a given well may oscillate between values exceeding drinking water standards (0,12 μg/l) and the detection limit of 0,01 μg/l and (3) the concentration of a metabolite might be higher than the parent product.

Figure 9.7

Findings of atrazine and two metabolites 5 metres below surface in the Lillebæk watershed; the five measurements plotted on the horizontal dotted line (detection limit) correspond to cleansamples (no pesticide); the last known use of atrazine

on the surrounding fields was in the period 1990 to 1993



9.1.7 Conclusions and recommendations

Development of strategies for detecting groundwater quality problems for important aquifers is necessary in many industrialised and developing countries. Often a compromise between the inter-ests of the agricultural and water supply sectors will be needed. Such a compromise can be achievedif a reliable methodology and adequate monitoring equipment for tracking of the pollutant’s pathto the aquifer is available. The groundwater nests and soil water stations developed for nitrate andpesticide monitoring within the Danish Environment Monitoring Programme perform well underdifferent soil conditions and can be recommended as a part of a system designed for early detectionof the future groundwater quality problems.

Monitoring nitrate and pesticides in shallow groundwater nests provides a fast field related earlywarning system for deeper regional aquifers. The system of groundwater nests permits normal culti-vation of fields while allowing the collection of samples from the top of the saturated zone. Anannual survey of farming practice is carried out as part of the monitoring programme.

The nitrate concentration in the shallow groundwater is strongly affected by climatic variations during the year and from year to year. Based on Danish experience and conditions, 6 to 10 ground-water analyses a year are needed to describe the annual variation in nitrate concentration. The monitoring has shown that large, short-term changes in nitrogen load cause significant changes innitrate concentration within one to three years in shallow groundwater sampled down gradient.

But although a (small) overall improvement in the utilisation of fertiliser and manure was observedin the 6 watersheds, only 25 out of 111 shallow wells show a significant decrease in nitrate co n -centration during the 6 years of monitoring. Based on monitoring groundwater quality over severalyears it was concluded that short-term cyclic change in nitrate content is influenced by the climate,whereas long-term trends reflect man-made impacts (Vrba and Pekný, 1991).

The same system of groundwater nests has been used for analysing pesticide leaching. Water sam-ples were analysed for between 8 to 44 different pesticides and metabolites. It was found that, forregular use, both pesticides and metabolites cause concentrations exceeding the official sustainableleaching concentration of 0.1 μg/l. Of 15 findings in 1996 the survey showed the use of 10 of thesame pesticides up-gradient the wells. These were detected between 6 months and 5 years after theapplication of the pesticides.

9.1.8 References

Andersen, L.J. 1990. Botesam, Separation Pumping and Capillary Barrier. A Remedial-Action ConceptApplicable to Point Pollution. In: Proceedings, First USA/USSR Joint Con ference on Envi-ronmental Hydrology and Hydrology. Minneapolis: American Institute of Hydro-logy, pp.271-279.

Gosk, E. 1988. Monitoring Programme for the Agricultural Watersheds. In: Vækst 6/88 (in Danish).Grant, R., Jensen, P.G., Andersen, H.E., Laubel, A.R., Deibjerg, C., Rasmussen, H. and Ras -

mussen, P.1996. ‘Agricultural Watershed Monitoring. Nation-Wide Monitoring Programme’. Danish Environmental Research Institute, Technical Report No. 175 (in Danish).



Phillips, R.D., Hotto, H.P. and Loftis, J.C. 1988. ‘WQStat II. A Water Quality Statistics Program’.User’s Guide. Colorado State University. 42 pp.

Rasmussen, P. 1996. Monitoring Shallow Groundwater Quality in Agricultural Watersheds in Den-mark. In: Environmental Geology, Vol. 27, No. 4, pp. 309-319.

Rasmussen, P. 1998. Early Warning by Monitoring Shallow Groundwater. In: IAH InternationalGroundwater Conference. Proceedings. Groundwater: Sustainable Solutions. University ofMelbourne, Australia 8-13 February, 1998. pp 551-556.

Vrba, J. and Pekný, V. 1991. Groundwater-Quality Monitoring - Effective Method of HydrogeologicalSystem Pollution Prevention. In: Environ. Geol. Water Sci., Vol. 17 (1), pp. 9-16.



9.2 Application of a Multi Layer Sampler (MLS) for managerial decision making regarding utilization of effluents for agricultural irrigation in the coastal plain of Israel

9.2.1 Introduction

Management of groundwater resources quality requites an understanding of pollutant behaviourin subsurface environments. At the present level of knowledge the quantitative relationship betweenthe amount of pollutant released at the soil surface, e.g. by agricultural and industrial activity, andits concentration in groundwater is highly uncertain. This is primary due to both the lack of knowl-edge and the scarcity of data concerning the physical, chemical, biological and transport processesundergone by pollutants in the unsaturated zone, the capillary fringe and the uppermost saturatedpart of the aquifer – the water table region. Groundwater quality monitoring networks have been developed as a result of our inability to forecast the cause-effect processes which influence the chemical composition of groundwater. Groundwater pollution is usually a complex and long-termprocess which can be divided into four schematic stages:

A. Surface disposal of pollutantsB. Transport through the unsaturated zoneC. Arrival at the groundwater table surfaceD. Transport within the saturated zone

Existing monitoring techniques tend to focus attention primarily on events occurring at stage Dand, in many cases, monitoring of groundwater quality depends primarily on the analysis of sam-ples obtained from active pumping wells.

Generally, production wells are designed to pump water from deep below the water table. Therefore,evidence of pollution build-up in a production well reflects the mixing process in the aquifer whichoften took place years after the pollutant had arrived at the water table. An illustration of such delayis presented in Fig. 1.1 The study area depicted in Fig. 9.8 had been under irrigation with sewageeffluents for 22 years (Ronen and Magaritz, 1985) and the vertical flow rate of anions through the30 m thick unsaturated zone was determined to be about 1.4 m/yr (Gvirtzman et al., 1986). The veryhigh concentration of solutes in the water table region (monitoring wells WT-2 and WT-3; Fig. 9.8)is related to the influx of sewage effluents. However, the concentration of solutes in the deep pro-duction wells (e.g., Glil Yam B) is not yet affected by sewage irrigation. Since the residence time inthe active part of the aquifer (upper two thirds of the saturated thickness of the aquifer) is about25 years, the quality of groundwater in the pumping wells reflects the replenishment conditions


* The water table region is here defined as a water layer of about 3 m thick immediately below the surface along which the hydrostatic pressure is equal to the atmospheric pressure.


some 45 years earlier. Eventually, the pollutants detected in the water table region will be dispersedthrough the groundwater body, and their concentration in the production wells will increase. It isworth noting that a similar phenomenon will be observed in a monitoring well where the screen islocated deep below the water table.

Clearly a different monitoring approach is needed. Much as the Monitor (a lizard of the genusVaranus) gives warning of the approach of crocodiles (American College Dictionary, 1964) a moni-toring system is needed which will alert concerned parties before massive pollution of groundwateroccurs. A MLS technique introduced here, which monitors the arrival of pollutants at the watertable, was described in the paper of Ronen et al. (1987a). In this paper importance of MLS techniqueto the management of groundwater resources is discussed.

Figure 9.8

Electrical conductivity (E.C. μmho/cm) and Cl-, NO3- and SO4=

concentrations (mg /l) found in the water table region of two monitoring wells, WT-2 and WT-3 and three production wells pumping from deep (37-55 m) below the water table. The average water table depths in WT-2and WT-3 are 27 and 30 m, respectively. The vertical flow rate of anions

through the unsaturated zone was determined to be about 1.4 m/yr (Gvirtzman et al., 1986). The black arrow shows the regional direction of groundwater flow. The coordinates denote distance (km).



9.2.2 The unsaturated-saturated interface

The interface between the unsaturated and saturated zones of a phreatic aquifer is characterized by the change from a three phase (rock-water-gas) system to a two phase (rock-water) system. Satu-rated conditions already exist in the capillary fringe above the water table (Davis and DeWiest, 1966;Bear, 1972; Ronen et al., 1997). In this zone water is held by surface tension forces (at pressures lowerthan atmospheric) and the ‘real’ unsaturated-saturated interface has an irregular shape (Ronen etal., 1997). In the unsaturated zone, water is in close contact with the gaseous phase which fills thepore space. Moisture content increases in the capillary fringe, and at the water table (or more strictlywhen the pores are totally saturated with water), groundwater is isolated from the atmosphereabove.

If a solute (e.g., Cl-, NO3- or dissolved organic carbon [DOC]) originating in the top-soil, is trans-

ported downwards through the unsaturated zone, and the input concentration of the solute ishigher than the background concentration in the aquifer (the common situation in areas with a highsurface load of pollutants), it would be expected that its highest concentration in groundwaterwould occur in the water table region.

The variation with time in concentration of a conservative solute (e.g., Cl -), in the water tableregion, can be defined by the rate of transport controlling processes (in the capillary fringe and inthe water table region). The variation in concentration of a non-conservative component (like nitro-gen and DOC) may also be influenced by chemical and biological processes. Since the solubility ofoxygen in water is low (8.7 mg/l at 22°C) and because oxygen replenishment in subsurface environ-ments is limited, the biodegradation of only a small amount of organic matter can lead to anoxicconditions in the water table region (Ronen et al., 1987b). Therefore, processes such as denitri -fication (Ronen et al., 1987c) may control the influx of nitrate from the unsaturated to the saturatedzone.

From the above arguments it is reasonable to assume that large chemical variabilities can beexpected to be found in the water table region. Chemical heterogeneity in the water table region canalso result from recharge of varied chemical composition (e.g., rain water and irrigation water;Gvirtzman et al., 1986).

In the water table region the concentration of a chemical in the liquid phase is the result of a massbalance between:

I - (a) its rate of supply from the unsaturated zone, (b) the rate at which it is produced in situ(e.g., nitrification), and

II - (a) the rate at which it is dissipated into the bulk aquifer by transport processes, (b) the rate atwhich it is transformed into other chemical species by chemical and biological reactions (e.g.,denitrification).

All the above processes eventually determine the influx of solutes to the groundwater body. There-fore, the water table region should be monitored both to alert against initial arrival of a pollutant(‘early warning’ or ‘preventive monitoring’) and to measure its influx from the unsaturated zone(stage B).



9.2.3 Application of a MLS technique in an agricultural area irrigated with municipal sewage effluents

Sewage effluent is foreseen as the only economic water source for agricultural use in many arid tosemiarid countries around the world. When use of this ‘free’ new source of water is considered, theeventuality of groundwater pollution by sewage irrigation is often overlooked. In other cases, dis-cussions about the potential of pollution continue long after pollutants have arrived in the watertable region.

The MLS (see Section 5.2.6) has been used to study and monitor the water table region of a 30 mdeep sandy, phreatic aquifer in Israel in an agricultural area irrigated with municipal sewage effluents. The following are the major findings of this project.


Figure 9.9

A comparison between dissolved oxygen (O2) and dissolved organic carbon(DOC) profiles obtained in the water table region of the study area (Glil Yam)and the profiles calculated in a simulation model by Molz et al. (1986b).

Note the sharp decrease of DOC in the capillary fringe (shaded area) and the development of anoxic conditions in the water table region. The persis-tence of DOC under unsaturated conditions for very long time periods (about 20 years in the study area) indicates that moisture content may be a major controlling factor in biodegradation.


The study site (Glil Yam), located 15 km north of Tel Aviv, is devoted to the cultivation of citrus treesand cereals. Municipal sewage effluents from the city of Herzlia have been used for irrigation of75 ha during the summer season, May to November. In the early 1960s sewage was treated in an oxi-dation pond; in 1977 an extended aeration treatment plant replaced the old facility. The study areais under a high organic carbon load. About 140 kg Corg /ha are annually applied each summer, incontrast to the negligible amount added to fields irrigated with fresh water. DOC is not completelybiodegraded as it percolates from the topsoil to groundwater (Amiel et al., 1990). A DOC mass balance suggests that the unsaturated zone still contains about 50% of the total DOC input. DOCpersistence for more than 20 years under unsaturated conditions suggests that moisture content maybe a major controlling factor for biodegradation (Amiel et al., 1990).

The average DOC flux to the water table region has been calculated to be at least 3.1 x 10-2 mgCorg/cm2 per year. The high concentrations of DOC found in the water table region (up to 8 mg/l),the anoxification process (DO < 1 mg/l) resulting from the biodegradation of the DOC in this zone(Fig. 9.9; Ronen et al., 1987b), and the high concentrations of N2O (up to 400 μg/l; Fig. 9.10) andCO2 (2% to 5%; Magaritz et al., 1990) are evidence of both: (a) DOC mobility through the unsatu-rated zone and, (b) DOC biodegradability as the water content of the system changes in the capillary fringe/water table region. This observation seems to contradict commonly used modelswhich suggest a relatively large retardation factor for organic components in relation to water. More-over, the results obtained differ significantly from the findings on the removal of most of the DOCduring infiltration from effluent ponds (Rettinger et al., 1991). This difference is related to the


Figure 9.10

Production of N2 O in the water table region of wells WT-2 and WT-3 (Fig. 9.8). The N2 O molar fraction in the gaseous phase of the capillary fringe (empty squares and circles) can reach 12,000 μg/l. This is forty times higher than the atmospheric concentration. The inverted triangles denote the position of the water table.


conditions that exist during infiltration to groundwater. While saturated conditions prevail underthe infiltration ponds, unsaturated conditions exist under land irrigated with the sewage effluents.

The gases produced during the biodegradation of the DOC and/or air entrapped in the pore spaceduring groundwater recharge accumulate as a distinct gas phase – bubbles – down to a depth of less1 m below the water table (Ronen et al., 1989). Large bubbles (radius 200 μm) reduce volumetricwater content and, hence, hydraulic conductivity. Small bubbles (radius 50 μm) clog pores withoutsignificantly decreasing the volumetric water content (Fig. 9.11). In the studied area, and at a depthof less than one metre, the pressure at a point in the moving fluid (10-1 atm) is at least one order ofmagnitude smaller than that required to both initiate the movement of bubbles through a porespace and to overcome the resistance to flow offered by detached gas bubbles and liquid drops in capillary conduits. Thus, under natural gradient flow conditions, the presence of gas bubbles sig-nificantly reduces the flow, leading to the development of an almost stagnant water layer in the watertable region (Ronen et al., 1986, Fig. 9.12). It is expected that stagnant water layers which are theresult of biochemical activity will develop mainly in regions under high organic loads such as sani-tary landfills, feedlots, or areas where dissolved organic carbon has been mobilized from natural sources by anthropogenic activity. Air bubbles will preferentially develop in aquifers where:(a) the fluctuations of the water table are rapid, and (b) the rate of groundwater replenishment is large.


Figure 9.11

Schematic representation of porous media with biochemically produced gas bubbles and entrapped air bubbles. The bubbles are present below the water table as seen in the monitoring well (right hand side). Note the small bubbles clogging the pore conduits without significantly reducing the volumetric water content. For the studied area it was calculated that the critical depth at which bubbles are most likely to be found is of about 1 m (Ronen et al., 1989). This estimate coincides with the depth of 0.60 m of an almost stagnant water layer found at the study site under natural gradient flow conditions.


The intermittent input of rain and irrigation water of varying chemical composition (e.g., 20 mg/lCl- from rain and about 200 mg/l Cl- from sewage effluents) along with the periodic input of otherchemicals such as fertilizers creates a vertical profile composed of discrete water layers of varyingcomposition in the unsaturated zone (Fig. 9.13; Ronen et al., 1988b). Evapotranspiration reducesthe amount of water recharge mainly during summer, thus further increasing the difference betweenthe salinity input of sewage effluents and that of rain. The replenishment of groundwater by this


Figure 9.13

Example of discrete water layers of varying Cl- content as detected in the unsaturated zone of monitoring wells WT-2 and WT-3 (Fig. 9.8).Also shown is the calculated water density (σ0 = ρ0 [kg/m3] – 1,000, where ρ0 is density at 0 oC; Ronen et al., 1988b). The vertical axis denotes depth from the land surface. The inverted triangle denotes the water table.

Figure 9.12

Dramatic decrease in the horizontal component of the specific discharge (q) in the water table region of well WT-3 (Fig. 9.8). The decrease is attributed to (a) gas bubbles produced during biodegradation of organic matter (e.g. CO2, N2O),and (b) air bubbles entrapped during inhibition. The vertical axis denotes depth from the water table.


influx and the almost stagnant conditions prevailing in the water table region lead to the develop-ment of micro scale parcels of water having vertical and horizontal length dimensions of less than1metre (Fig. 9.14) and varying chemical composition (e.g., in some cases by more than 50% in theconcentration of Cl-, NO3

- and SO4=) and density (Fig. 9.15). Micro scale water parcels may also be

formed in situ in the water table region by chemical or biochemical processes (e.g., denitrification,Fig 9.15). These processes determine the influx of pollutants into the main groundwater body. Thesharp boundaries between overlaying water parcels, which may have in some cases persisted over long periods of time (months) and the calculated range of the Peclet number at the study site(6.25 x 10-2 to 6.25 x 10-3) implies that mechanical dispersion by advection is not an important


Figure 9.14

Schematic representation showing two alternative possibilities for the vertical build-up of micro scale water parcels of different salinity (S). In alternative ‘b’ groundwater velocity V2 is greater than V1.See vertical cross sections through such parcels in Fig. 9.15.

Figure 9.15

Vertical cross sections through micro scale isothermal water parcels (Fig. 9.12) of Cl-, NO3

-, SO4= and HCO3

- in the water table region of well WT-3 (Fig. 9.8). Profile 13 was obtained 30 days after profile 12. Note denitrification in the upper 50 cm of the profiles and concomitant increase of HCO3

-. The concentration of HCO3- was measured

in the laboratory and is given as the relative amount in relation to the HCO3

- content of the standard.


mixing mechanism in the water table region. The observed rapid destruction of the boundariesbetween the overlaying water parcels, which may occur within one month (Fig. 9.16), suggests halineconvection. The overlaying water parcels are at times gravitationally unstable due to destabilizingsalinity-density differences. The critical density difference which overcomes viscous drag forces atthe study site is in the range of 0.230 to 0.281 kg/m3. This value fits the estimated free convectionparameter or modified Rayleigh number for porous media (Bear, 1972). Haline convection shouldovercome stratification, which would develop under very slow laminar flow conditions, and there-fore greatly influence the influx of pollutants to bulk groundwater (Ronen et al., 1988b).

9.2.4 Conclusions and recommendations

The potential of the sampling methodology presented in this case study should be recognized forthe development of groundwater early warning systems in phreatic aquifers. Sampling and measur-ing the actual pollutant fluxes reaching the water table through the unsaturated zone, before theyare diluted in the groundwater body, has several advantages: (a) it increases the detection sensitivityof the monitoring system as pollutants arriving from the unsaturated zone will be found at maxi-mum concentration in the water table region; (b) it gives ample time (decades) for remedial actionto be undertaken before the onset of massive groundwater contamination, and (c) it enables theestablishment of a quantitative relationship between the amount of a pollutant released on the topsoil and the amount that actually reaches groundwater.


Figure 9.16

Eulerian changes of chloride in consecutive profiles obtained in well WT-2 (Fig. 9.8). Note the development of sharp interfaces between water parcels. Gravitational instability between the parcels (after the density difference between them increased up to 0.230 kg/m3 on September 20) triggers convective flow. Note that the Cl - profile on November 1 below a depth of 120 cm has an average concentration which can be ascribed to the convective mixing of both water parcels observed on September 20. Haline convection is suggested to be a mechanism that influences the influx of pollutants to bulk groundwater.


For the monitoring example presented above, available results suggest that long term and continu-ous irrigation with sewage effluents over the recharge area of a water table aquifer will lead togroundwater quality degradation. Three questions must be answered to quantify this phenomenon:(a) what is the net influx of pollutants to the saturated zone?; (b) what is the new steady-state con-centration of the pollutant in the aquifer?; (c) what is the time that will elapse before wells producewater in violation of standards?

The proposed monitoring system was designed especially to answer the first critical question. Forexample, if decision-makers utilize the proposed warning scheme as a real ‘Monitor’ they will be ableto take one of the following managerial decisions: (a) permit the irrigation with effluents until a pre-established concentration of pollutant is reached, (b) re-allocate the water pumped from the aquiferaccording to its predicted quality, (c) design a dual pumping system that uses the upper part of theaquifer (the polluted region) for agriculture and continue to pump water from deeper strata forgeneral use. The benefits of this last alternative are: (1) continued use of existing pumping wells(which pump deep below the water table), and (2) reduction in the quantity of required added fertilizers when taking advantage of effluent nutrient content in the upper water layer.

9.2.5 References

American College Dictionary, 1964. Random House, New York.Amiel, A.J., Magaritz, M., Ronen, D. and Lindstrand, O. 1990. On the Mobility of Dissolved Organic

Carbon in the Unsaturated Zone under Land Irrigated by Sewage-Effluents. Journal Water Pol-lution Control Federation, 62, pp. 861-866.

Bear, J. 1972. Dynamics of Fluids in Porous Media. American Elsevier Pub. Co. Inc., New York,764 pp.

Davis, S.N. and DeWiest R.J.M. 1966. Hydrogeology. John Wiley, New York, 463 pp.Gvirtzman, H., Ronen, D. and Magaritz, M. 1986. Anion Exclusion During Transport through the

Unsaturated Zone. Journal of Hydrology, 87, pp. 267-283.Kaplan, E., Banerjee, S., Ronen, D., Magaritz, M., Machlin, A., Sosnow, M. and Koglin, E. 1991. Multi-Level

Sampling in the Water Table Region of a Sandy Aquifer. Ground Water, 29, pp. 191-198.Magaritz, M., Brenner, I. and Ronen, D. 1990. Ba++ and Sr++ Distribution at the Water Table:

Implications for Monitoring Groundwater at Nuclear Waste Repository Sites. Applied Geochem-istry, 5, pp. 555-562.

Molz, F.J., Widdowson, M.A. and Benefield, L.D. 1986b. Simulation of Microbial Growth DynamicsCoupled to Nutrient and Oxygen Transportation in Porous Media. Water Resources Research, 22,pp. 1207-1216.

Rettinger, D., Ronen, D., Amiel, A.J., Magaritz, M. and Bischofsberger, W. 1991. Tracing Sewage Influxfrom a Leaky Sewer in a Very Tthin and Fast-Flowing Aquifer. Water Research, 25, pp. 75-82.

Ronen, D. and Magaritz, M. 1985. High Concentration of Solutes at the Upper Part of the SaturatedZone (Water Table) of a Deep Aquifer under Sewage-Irrigated Land. Journal of Hydrology, 80,pp. 311-323.

Ronen, D., Magaritz, M., Paldor, N. and Bachmat, Y. 1986. The Behavior of Ground-water in the Vicinity of the Water Table Evidenced by Specific Discharge Profiles. Water Resources Research, 22,pp. 1217-1224.

Ronen, D., Magaritz, M. and Levy, I. 1987a. An in situ Multilevel Sampler for Preventive Monitoringand Study of Hydrochemical Profiles in Aquifers. Ground Water Monitoring Review, 7, pp. 69-74.

Ronen, D., Magaritz, M., Almon, E. and Amiel, H. 1987b. Anthropogenic Anoxification (‘Eutrofica-



tion’) of the Water Table Region of a Deep Phreatic Aquifer. Water Resources Research, 23,pp. 1554-1560.

Ronen, D., Magaritz, M., Gvirtzman, M. and Garner, W. 1987c. Microscale Chemical Heterogeneityin Groundwater. Journal of Hydrology, 92, pp. 173-178.

Ronen, D., Magaritz, M. and Almon, E. (1988a). Contaminated Aquifers are a Forgotten Componentof the global N2O budget. Nature, 335, pp. 57-59.

Ronen, D., Magaritz, M. and Paldor N. (1988b). Microscale Haline Convection - A Proposed Mecha-nism for Transport and Mixing at the Water Table Region. Water Resources Research, 24,pp. 1111-1117.

Ronen, D., Berkowitz, B. and Magaritz, M. 1989. The Development and Influence of Gas Bubbles inPhreatic Aquifers under Natural Flow Conditions. Transport in Porous Media, 4, pp. 295-306.

Ronen, D., Scher, H. and Blunt, M. 1997. On the Structure and Flow Processes in the Capillary Fringeof Phreatic Aquifers. Transport in Porous Media, 28, pp. 159-180.



APPENDICES

Abbreviations and acronyms

BOD Biological Oxygen Demand

Bull. Bulletin

Conf. Conference

DNAPLs Dense Nonaqueous Phase liquids

ed(s). Editor(s); also: edition

e.g. for example (Latin exempli gratia)

EPA Environmental Protection Agency

IAH International Association of Hydrogeologists

IHP International Hydrological Programme

IHP-V Fifth phase of the IHP

Jour. Journal

LNAPLs Light Nonaqueous Phase Liquids

NAPLs Nonaqueous Phase Liquids

No. Number

pp. Pages

RIVM Rijksinstituut voor Volksgezondheid en Milieuhygien

TDS Total Dissolved Solids

UK United Kingdom

UNESCO United Nations Educational, Scientific and


Vol. Volume



Appendix 2: Glossary

A conscious effort has been made to write in clear language, keeping technical jargon to a minimum.Even so, some terms are in such common use that their inclusion is considered to be justified. How-ever, some terms are used with rather different meanings by individual authors and in differentcountries. For these terms a particular meaning has been utilized in this publication as is explainedin the glossary. The following terms and definitions were compiled from various sources (AmericanCollege Dictionary, 1964; Phannkuch, 1990; UNESCO/WMO, 1992).

Adsorption: The attraction and adhesion of ions from an aqueous solution to the solid soil or rocksurfaces with which they are in contact.

Advection: The process by which solutes are transported with and at the same rate as movinggroundwater.

Aeration: The process by which air becomes dissolved in water.Alkalinity: The ability of the salts contained in water to neutralize acids.Anaerobic: Describing a process conducted in the absence of oxygen.Aquifer: A geologic unit that is capable of yielding a significant amount of groundwater to a well or

spring. Aquifer, confined: An aquifer bounded above and below by confining beds of distinctly lower per-

meability than that of aquifer itself. Aquifer, unconfined: An aquifer in which there are no confining beds between the zone of satura-

tion and the ground surface.Attenuation: The intrinsic ability of earth materials and groundwater to reduce, remove, dilute or

retard contaminants by the complex of physical, chemical, and biological processes acting in thesoil–rock–groundwater system.

Base flow: That component of the flow of streams composed solely of groundwater discharge.Biodegradation: The breakdown of chemical constituents through the biological processes of natu-

rally occurring organisms.Capillary fringe: The zone immediately above the groundwater table in which water is drawn

upward by capillary attraction and the voids are filled with water under pressure less thanatmospheric.

Cation exchange capacity: A measure of the availability of cations that can be displaced from siteson solid surfaces and that can be exchanged for other cations.

Cone of depression: A depression in the groundwater table or potentiometric surface that developsaround a well from which water is being withdrawn.

Contaminant (Pollutant): A naturally–occurring or human-produced physical, chemical biological,or radiological substance that renders water unfit for a given use. In this publication pollutantis used as a synonym.

Contamination (Pollution): The introduction into water of any undesirable chemical, biological orradiological substances which render the water unfit for its intended use. In this publicationpollution is used as a synonym.



Contamination (Pollution) plume: The spreading of a contaminant (pollutant) in the direction ofgroundwater flow.

Density: The mass or quantity of a substance per unit volume.Detergent: Any material with cleaning powers, including soaps, synthetic detergents, alkaline mate-

rials, and solvents.Diffusion: The process by which both ionic and molecular constituents move under the influence of

their kinetic activity in the direction of their concentration gradient.Diffuse contamination (pollution) source: A source of contamination (pollution) in which a con-

taminant (pollutant) entering the receiving water can not be attributed to a single outlet. Dispersion: A process of contaminant (pollutant) transport that occurs as a result of mechanical

mixing and molecular diffusion.Dissolution: The process of dissolving.Dissolved solids: The weight of inorganic and organic matter in true solution in a stated volume of

water.DNAPL: Acronym for dense, nonaqueous phase liquid.Effective porosity: Ratio of the volume of interconnected pore space to the total volume of a porous

material.Eh – Redox potential: A measure of the electron balance in an water sample.Electrical earth resistivity: A surface geophysical method in which a direct or low frequency current

is applied to a pair of electrodes into the ground and the resulting voltage is measured at a sec-ond set of electrodes.

Electric logging: Methods oriented towards estimation of physical and/or chemical properties offormation, fluids filling the borehole or the formation voids and fractures, and the determina-tion of geometrical parameters of the borehole and encountered layers.

Flow net: A set of intersecting equipotential lines and flow lines representing a two- dimensionalsteady flow field in porous media.

Flow path: The direction of movement of groundwater (and contaminants) as governed principallyby the hydraulic gradient.

Fracture: A break in a rock formation due to mechanical failure by stress; includes cracks, joints (fis-sures), and faults.

Groundwater: Subsurface water in the saturated zone.Groundwater flow: The movement of water through openings in sediment and rock that occurs in

the saturated zone.Groundwater runoff: That portion of precipitation which is absorbed by soil to the groundwater

body and later discharged to surface streams. Groundwater protection zone: An area of land within which activities liable to contaminate (pol-

lute) groundwater are restricted or prohibited.Halogenated hydrocarbons: Organic compounds containing one or more halogens.Hazardous waste: Any waste that poses a substantial present or potential hazard to human health or

living organisms.Hydraulic conductivity: The quantity of water that will flow through a unit cross-sectional area of a

porous material per unit of time under a hydraulic gradient of 1.00. Hydrodynamic dispersion: The process by which groundwater containing a solute is diluted by

uncontaminated groundwater and spread out from the flow path because of mechanical mixingduring fluid advection and molecular diffusion due to the thermal- kinetic energy of the soluteparticles. Longitudinal dispersion is usually much stronger than lateral dispersion.

Hydrolysis: The chemical decomposition of a compound by reaction with water.



Imaging methods: Remote sensing methods in which data are displayed in the form of an image, asin a set of photographs along a flight path.

Immiscible: Fluids that are not significantly soluble in water.Infiltration: Passage of water downward from the land surface into and through the soil and rock

layers.Injection well: A well used for injecting fluids into an underground stratum.Ion exchange: A process by which an ion in a mineral lattice is replace by another ion that was

present in an aqueous solution.Karst (karst topography): A topographic area that has been formed by the dissolution of carbonate

rocks and that is characterized by sinkholes, caves, caverns, and lack of surface streams.Landfill: A disposal facility in which waste is placed in or on the land.Leachate: A solution produced by water or other liquid percolating through soil or solid waste and

the subsequent dissolution of certain constituents in the water.Line source: A linear source of contamination that can spread contaminants over large distances,

e.g. leaking pipelines or contaminated streams.Lithology: Description of rocks in terms of mineral composition and texture.Losing stream: A stream in which water flows and infiltrates from the streambed into the ground.Lysimeter: Unsaturated (vadose) zone sampling device used to collect soil pore water via suction or

gravity drainage; is capable of retaining the accumulated water within the sampling vessel.Magnetometry: A surface geophysical method for measuring the total intensity of the earth’s

magnetic field by means of high resolution proton magnetometers.Mobilize: To accelerate the movement of a contaminant in the groundwater system by changing the

prevailing chemical conditions.Molecular diffusion: The process whereby ionic or molecular constituents in solution move under

the influence of their kinetic activity in the direction of their concentration gradient.Monitoring well: A well that is designed for the purpose of extracting groundwater samples for test-

ing, or for measuring groundwater levels.Nested wells: A series of single-cased monitoring wells that are closely spaced, but with screens at

different depths.Neutralization: The inorganic reaction of an acid and a base to create a salt and water. Non-point contamination (pollution) source: See diffuse source.Oxidation: A chemical reaction in which there is an increase in valence resulting from a loss of elec-

trons.Percolation: Downward movement of water under gravity or hydrostatic pressure through earth

materials.Piezometer: A small-diameter well installed to measure the elevation of the groundwater table or

potentiometric surface, or to permit collection of groundwater samples from discrete horizons.Permeability: The ability of a soil or rock medium to transmit a fluid.Point contamination (pollution) source: Any discrete, well-defined source of contamination

(pollution).Pollutant: See contaminant.Porosity: The ratio of volume of void spaces in a rock or sediment to the total volume of the rock or

sediment.Potable water: Water that is suitable for human or animal consumption.Precipitation: The formation of solids out of constituents that were once dissolved.Recharge: The addition of water to the groundwater system by natural or artificial processes.Recharge area: An area in which there are downward components of hydraulic head in the aquifer.



Reduction: A chemical reaction in which there is a decrease in valence as a result of gaining electrons.

Remote sensing: The process of obtaining information about the surface of the upper layer of theearth’s crust from aircraft, satellites or by other above-ground techniques.

Retardation: Preferential retention of contaminants or slow down of their travel in the subsurfaceby physical, chemical, or biological processes.

Root zone: The zone from the land surface to the depth penetrated by plant roots.Saturated zone: The zone in which the voids in the rock or soil are filled with water at a pressure

greater than atmospheric.Soil moisture content: The amount of water in the soil expressed as a fraction of the total porous

volume of the soil.Solute transport: The net flux of solute through a hydrogeologic unit controlled by the flow of sub-

surface water and transport mechanism.Solution: A homogenous mixture of two or more components.Sorption: The combined effect of adsorption and absorption.Spring: A discrete place where groundwater flows naturally from a geologic formation onto the land

surface or into a body of surface water.Texture: The interrelationship between the size, shape, and arrangement of minerals or particles in a

rock or soil.Total dissolved solids (TDS): The total concentration of dissolved constituents in solution.Transmissivity: The rate at which water is transmitted through a unit width of an aquifer under unit

hydraulic gradient.Unconfined aquifer: An aquifer that has a water table forming a free upper surface.Unsaturated zone: The zone between land surface and the water table that contains both water and

air. It includes the root zone, intermediate zone and capillary fringe.Viscosity: The property of a fluid describing its resistance to flow.Volatile constituents: Solid or liquid compounds that are relatively unstable at standard tempera-

ture and pressure, and undergo spontaneous phase change to the gaseous state.Vulnerability (groundwater): An intrinsic property of a groundwater system that depends on the

sensitivity of that system to human and/or natural impacts. Water table: The surface in a groundwater body at which the pore water pressure is atmospheric.Water table region (defined for this report): a water layer of about 3 m thick immediately below the

surface along which the hydrostatic pressure is equal to the atmospheric pressure.Well screen: A filtering device, typically steel or plastic, that allows groundwater to flow freely into a

well from the adjacent formation.Zone of saturation: See saturated zone.

