GROUNDWATER AND HUMAN DEVELOPMENT
Bocanegra, E - Martínez, D - Massone, H (Eds.) 2002 - ISBN 987-544-063-9
GROUNDWATER QUALITY MONITORING NETWORKS
Jaroslav Vrba
Chairman of IAH Commission on Groundwater Protection
Prague, The Czech Republic
e-mail : javr@mymail.cz
1 INTRODUCTION
Groundwater quality monitoring supports sustainable management of groundwater protection and
quality conservation and strengthents anti-pollution policy on national, regional or local level.
Groundwater quality monitoring provides valuable data about groundwater chemical composition
for assessment of the current state and forecasting trends in groundwater quality.
A holistic approach should be implemented in the policy and management of groundwater
resources protection, considering the close connection between groundwater and surface water and
giving the same attention to both quantitative and qualitative aspects. The holistic concept appears
in co-ordination or even the integration of national groundwater monitoring programmes with
surface water, precipitation, climatic and soil monitoring networks. Establishment of pilot
monitoring stations with observation of all components of the hydrological cycle and soil helps to
reduce the costs of operation of monitoring networks.
2 DEFINITION OF GROUNDWATER QUALITY MONITORING
In general terms monitoring is defined as the continuous, standardised measurement and
observation of the environment (UNESCO/ WHO 1978). Groundwater quality monitoring can be
understood (Vrba, 2000) as a methodologically and technically standardised programme of
observations, measurements and analysis of selected physical, chemical and biological variables of
groundwater with the objectives:
1. To collect, process and analyse the data on groundwater quality as a baseline for assessing the
current state and forecasting trends in groundwater quality due to natural processes and human
impacts in time and space;
2. To provide information for improvements in the planning, policy and management of
groundwater protection and quality conservation.
3 OBJECTIVES AND STRATEGY OF GROUNDWATER QUALITY MONITORING
PROGRAMMES
Groundwater quality monitoring programmes support the data to analyse the chemical composition
and evolution of natural groundwater, to address groundwater quality problems, risks and conflicts
in relation to the existing or potential pollution sources, as well as to define the priorities in
groundwater resources protection with respect to land use.
Groundwater quality monitoring programmes operate at the international, national, regional and
local levels. The objectives of each of the above programmes govern the extent of monitoring
activities, such as design of monitoring networks, construction of monitoring wells, frequency and
methods of sampling and measurements and number of variables to be analysed.
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GROUNDWATER QUALITY MONITORING NETWORKS
International and national groundwater quality monitoring programmes are typically background
monitoring activities, whereas provincial and local monitoring programmes are oriented to the
specific monitoring purposes (van Lanen et al. 1998). Both background and specific monitoring
activities should also include early warning groundwater quality monitoring.
Groundwater quality monitoring programme is composed by monitoring, information and
management systems (Table 1).
Clearly defined objectives of monitoring are essential to achieve the expected results. The
requested output information by the users (planners, policy and decision makers, scientists, public)
cannot be defined precisely when monitoring objectives are not stated clearly. Only rarely a
monitoring system can cover more than one objective. The design of monitoring network, well
construction and sampling methods differ particularly in local monitoring programmes concern
mostly on particular pollution problem.
Definition of objectives and requested output information is the first critical point of
groundwater monitoring programme and have to be defined before the first monitoring station is
located and the first sample of water is taken. Prior to outlining the strategy for the monitoring
system, initial inventory of accessible data is made to gain a basic knowledge about groundwater
chemical composition and contemporary state of its quality and to define the extent of the required
complementary hydrogeological investigation.
Groundwater quality monitoring system includes the following activities:
 Delimitation of the monitoring area;
 Analysis of the geological framework, the groundwater flow system and groundwater
quality;
 Identification and inventory of existing and potential pollution sources;
 Design of monitoring network;
 Designation of field and laboratory monitoring methods;
 Determination of sampling frequency and selection of variables to be analysed, including
field and trip blanks samples as part of quality assurance (QA) and quality control (QC)
process;
 Database management, especially methods of data handling, processing and evaluation.
Data analysis and transformation of analysed monitoring data into a user tailored information
product is an other critical point of groundwater quality monitoring programme (Table 1). It is
being emphasized that however high the quality of monitoring data, is as long they are not
transmitted in an intelligible information to the user, the outputs of the groundwater quality
monitoring programme are not effectively utilised and the expenditures on its operation are not
vindicated. The output information on groundwater quality can be used for technical, socioeconomic, ecological, scientific or public purposes. Simple, easy to understand information is
required for the public and non-professionals. Planners, decision and policy makers and managers
need broad-ranging, comprehensive but intelligible information concern on specific groundwater
quality problems.
Groundwater quality management system as a final stage of groundwater quality monitoring
programme (Table 1) is based on monitoring results and aspires to implement groundwater quality
protective measures in the frame of existing legal basis and institutional structure.
3.1 International Groundwater Quality Monitoring Programme
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Jaroslav Vrba
An international groundwater quality monitoring programme was initiated by the United Nations
Environment Programme and operates over the world within the Global Environment Monitoring
System (GEMS) since 1974.
3.2 National Groundwater Quality Monitoring Programme
National groundwater quality monitoring programmes are concerned with data collection of the
natural background level and current state of groundwater quality of main country aquifers. These
can support national policy of groundwater protection and quality conservation. Monitoring of
groundwater quality on a national level is an organisationally and technically demanding and
expensive process in terms of both, the capital and operation costs. The benefits derived from
expended financial means are therefore always compared with the value of the information
obtained.
Groundwater quality monitoring programme
Objective
Groundwater
quality
monitoring
system
Critical point
Definition of requested output information
Strategy
Delimitation of monitoring area
Determination of groundwater
system geometry and parameters,
evaluation of relevant data of
groundwater quality
Identification and inventory
of potential and existing
pollution sources
Data acquisition
Sample collection
Transmission
Laboratory analysis
Data handling
Processing
Database management system
Data analysis
Groundwater
quality
information
system
Groundwater
quality
management
system
Critical point
Information products
Information communication
Information utilization
Legislative and institutional
implementation of protective measures
TABLE 1 Groundwater quality monitoring
1955 programme
Storage
Feedback
Design and establishment
of monitoring network and
designation of monitoring methods
GROUNDWATER QUALITY MONITORING NETWORKS
Baseline and trend stations, according to the classification of Maybeck (1985), play dominant
roles in national groundwater monitoring networks (Table2). They have to represent natural
hydrogeological conditions and are located outside the influence of pollution sources and
groundwater abstraction sites. Using of existing wells drilled for other purposes without casing and
screening adequate to the objective of national monitoring programme is not considered suitable.
Groundwater quality monitoring stations are mostly identical with monitoring stations measuring
groundwater quantitative parameters.
National groundwater quality monitoring networks are in operation in a few countries only.
However, monitoring methods and procedures are not standardized and vary in each country. This
causes difficulties in mutual comparison of monitoring data particularly in internationally shared
groundwaters.
Importance of groundwater as a drinking water source and ecological phenomena and
vulnerability of aquifers control the design of national groundwater quality monitoring network.
3.3 Regional Groundwater Quality Monitoring Programmes
Regional groundwater quality monitoring programmes are concern on specific purposes and
complement the national monitoring programme.
The main objective of regional programmes is to acquire statistically significant sets of data as a
basis for creating the regional policy of groundwater resources protection, management of their
quality and for supporting groundwater quality data for decision making in land use planning.
Monitoring activities are concerned with the specific potential or existing diffuse pollution
problems (particularly the impact of agriculture on groundwater quality) and on protection of
catchment areas of groundwater supply sources.
The trend stations dominate in the design of regional groundwater quality monitoring networks
(Table 2). However through selected baseline stations of national monitoring network, both
monitoring programmes are interconnected.
Frequency of sampling in regional monitoring programmes is higher compared with national
monitoring programme (up to 12 times per annum); variables analysed are selected according to the
specific groundwater quality problems. Design of monitoring wells should permit vertical
hydrochemical profiling of particular aquifers of groundwater system. Monitoring of vertical
movement of pollutants in the unsaturated zone (lysimeters, centrifugal extraction of interstitial
water from core samples, sampling by means of compressed gas injection or other methods) should
be recommended especially in areas with a high potential for aquifer pollution (e.g. shallow aquifers
bellow arable sandy soil).
Regional groundwater quality monitoring programmes are often established in catchment areas
of groundwater supply sources. Water supply companies in many countries are legally obliged to
operate groundwater monitoring programme as part of protection policy of water supply systems.
The objects of monitoring are water supply wells or springs and monitoring wells located in
designating protection areas (wellhead protection areas in US terminology) of the groundwater
supply source. By reason of preventive protection of groundwater resource quality, monitoring
networks are established in outer or second degree protection areas encompassing usually the whole
catchment area. However, several water supply companies carry out groundwater quality
monitoring of water supply wells or springs only.
The number of monitoring stations and frequency of monitoring strongly depends on aquifer
vulnerability and related risk to pollution. Drinking water standards valid in individual countries
control the extent of variables analysed. Sampling frequency is high; some variables from water
supply wells sensitive to human impacts are analysed daily. Monitoring of organic chemicals is less
frequent (as little as once per year).
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Jaroslav Vrba
3.4 Site Specific Groundwater Quality Monitoring Programmes
Site specific groundwater quality monitoring programmes are established around:
1. Potential point pollution sources, with the objective to give an early warning about
groundwater quality deterioration;
2. Existing point pollution sources with the purpose to observe and control movement of
pollution plume or effects of pollution remediation.
Good knowledge of the hydrogeological properties of the unsaturated zone and aquifer,
groundwater flow nets and pollutant source and behaviour is desirable before designing a local
monitoring programme.
Local monitoring programmes operate independently of national or regional programmes. A site
specific extent of monitoring networks, great density of monitoring stations, high sampling
frequency and field and laboratory analyses of variables selected according to the type and
properties of pollutants are typical for local monitoring programmes. Design of monitoring wells,
particularly well casing and screen material, setting of well screen with respect to pollutants
physical and chemical properties, type and placement of annular seal material, all affect the quality
and reliability of groundwater sample.
The impact monitoring stations dominate in local monitoring networks (Table 2). Monitoring of
unsaturated zone and remote sensing methods applied with respect to pollutant properties
supplement groundwater monitoring activities. Some of monitoring wells are located close to the
point pollution source and should be used as a remediation wells when pollution occurs.
Monitoring
programme
International
Category and importance of
monitoring station
Baseline
Trend
D
C
Station
density
Sampling
frequency
Variables
analysed
VL
L
B+
Impact
LS
ONational
D
C
LS
D
LS
L
L
C
M
M
B+
O+
Local
LS
LS
Station’s significance:
Station density:
Sampling frequency:
List of variables analysed:
D
H
H
Baseline station: natural
background groundwater quality
B+
O-
Privincial
Monitoring stations
characteristics
O+
Trend station: trends in
groundwater quality due to
natural processes and human
impacts
Impact station: changes of
groundwater quality due to
various human impacts
D Dominant, C Complementary, LS Low significance
Station per km2: H High – m2 to 10, M Medium – 10 to 100, L Low – 100 to 1
000, VL Very low – 1 000 and more
H High – more than 12 times a year, M Medium – 2 to 12 times a year, L Low
– 1 to 4 times a year
B Basic – physical, chemical and biological variables included into the
drinking water standards
O Optional – heavy metals, organochlorine compounds, oil hydrocarbons and
other variables depending on monitoring program objectives
+ Regular analysis
- Occasional analysis
TABLE 2 Categories of groundwater monitoring stations operating in groundwater quality
monitoring programmes
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GROUNDWATER QUALITY MONITORING NETWORKS
A refinement of the local groundwater quality monitoring networks based on pollution control
and the effect of remediation procedures is frequent. Fast and simple methods of data recording and
retrieval should be used to submit the monitoring results and information to the individual users in
time and in a intelligible form. Operational costs of local monitoring programmes are high, however
they are covered by the polluters (polluter pays principal). Operation of site specific monitoring
networks is mostly limited for a certain period only.
3.5 Early Warning Groundwater QualityMonitoring
Existing monitoring strategies tends to focus attention primarily on the movement of pollutants
within the saturated zone. Monitoring programmes are mostly concern on identification and control
of the concequences of groundwater pollution and not for preventive protection of groundwater
quality. An early warning monitoring strategy is needed that detects contaminant before massive
pollution of groundwater system occurs and solution of pollution problem is still at a controllable
and manageable stage.
The early detection of changes in groundwater quality requires application of various
monitoring methods which may facilitate the observation of contaminant migration, in the gaseous
and liquid phases, through the unsaturated zone and the uppermost part of the aquifer. These
methods include mainly retrieval of sediment, gas and water samples through specially located and
designated monitoring wells, installation of lysimeters, soil gas surveys, photographic imaging and
geobotanical and geophysical prospecting.
Early warning groundwater quality monitoring should be implemented within regional and local
monitoring programmes oriented on specific pollution impacts on groundwater system.
4 ESTABLISHEMENT OF NATIONAL GROUNDWATER QUALITY MONITORING
NETWORKS
Several experiences have been acquired about groundwater quality monitoring in countries
where national groundwater quality monitoring programme were designated and carried out. Even
though natural, social and economic conditions and land use vary from country to country it is
possible to give some generalization about national monitoring programmes.
An elaboration of conceptual models of main country aquifers, determination of groundwater
flow systems, assessment of groundwater vulnerability, inventory of groundwater supplies
protection zones and identification of pollution sources are essential, before the works on
groundwater quality monitoring programme are initiated. Existing land–use practices and land-use
planning should also be considered.
Monitoring wells of national monitoring networks should be located beyond the influence of
pollution sources or groundwater abstraction sites. In the monitoring network formed by monitoring
wells with standing water is not suitable to incorporate wells in dynamic stage (e.g. water supply
wells, irrigation wells). Groundwater samples taken within a different hydraulic and hydrochemical
conditions are not mutually comparable. Automatic data acquisition system is recommended to
install on pilot monitoring stations.
In case of a groundwater system formed by two or more aquifers, it is preferable to have separate
monitoring of each aquifer, both quantitative and qualitative, by individual small diameter wells.
Employment of the packer technique on the separation of sampling segments in deep monitoring
well is less suitable. When packers operate in the long term, the monitoring well should be affected
by natural and human impacts, aquifers should be interconnected and monitoring data depreciated.
However in shallow unconfined aquifers intercalated by low permeable sediments two or three
small diameter piezometers of different depths should be placed into a large diameter borehole.
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Jaroslav Vrba
Water samples are taken from the bottom part of the piezometer. Such a national groundwater
monitoring system successfully operates in the Netherlands (Duijvenbooden 1987).
When designing a monitoring network in area with fissured rock permeability the orientation and
geometry of the fracture system (preferred flow path) should be carefully studied. However, the
location of monitoring wells representing such complicated hydrogeological conditions is always
difficult. In karst regions where groundwater flow is in conduits or in large open fissures, springs
allow more representative observation of groundwater quality than monitoring wells. Sampling of
groundwater in karst regions must be frequent, because groundwater is moving through the karst
system quickly and water quality changes as a consequence of pollution are usually fast.
Selection of suitable methods of taking representative sample of groundwater is the most
problematic part of sampling procedure. The water is standing in the monitoring well several weeks
or even months in the column above the screen without direct contact with the groundwater flow
system and under the impact of atmosphere and casing material which all affect its chemical
composition. Purging the well is, therefore, desirable to take groundwater samples at a dynamic
stage.
The main sampling methods implemented according to the aquifer and groundwater flow
conditions are 1) sampling after removing the volume of water accumulated above the well screen,
2) in low yielding wells sampling by suction or sample collection after pumping the well dry and
the recuperation of water column, 3) purging the well until selected field measured parameters
(usually pH, Eh, temperature, electrical conductivity, oxygen demand) are stabilised.In case of
deeper unconfined high yielding aquifers with lateral groundwater flow, simple or special
multistage samplers combine with packer techniques should be used to take water sample from a
define depth. A mixed water sample from the entire profile of the aquifer is not considered
satisfactory.
Sampling collection and field and laboratory analysis are usually carried out by various
companies. The state agency responsible for the operation and management of groundwater
monitoring programmes has the responsibility to coordinate and control applied monitoring
methods and procedures.
Groundwater quality monitoring of internationally shared groundwater requires close
cooperation among neighbouring countries. Sampling collection methods have to be unified as
much as possible to minimise potential problems with data evaluation and implementation.
Feedback is an essential future of the monitoring process (Table 1). Modification of the
monitoring system (number and location of monitoring wells, sampling frequency, extent of
chemical analyses) is based on a long-term data sets evaluation.
5 CONCLUSIONS
The objective of groundwater protection policy is timely identification and evaluation of potential
conflicting issues, validation of competitive factors and their hierarchical screening with the aim to
find a balance between groundwater resources protection, sustainable economic development and
potential social and health implications with a view to both, the short term and long term prospects.
Groundwater quality monitoring programme is one of the effective methods supporting
groundwater protection policy and management. However establishment and operation of
groundwater quality monitoring programmes, especially on national level, is a technically and
financially demanding process in terms of capital, operational and maintenance costs. A cost-benefit
analysis is, therefore, required to compare the value of data and information with the cost involved.
Importance of early warning groundwater quality monitoring in preventive protection policy is
pointed out. Early warning monitoring is nearly every time less expensive than the cost related to
aquifer remediation and investments needed to overcome social and ecological damages of
groundwater pollution, in case, that early warning monitoring system was not in operation.
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GROUNDWATER QUALITY MONITORING NETWORKS
REFERENCES
European Commission – DG XI 1996. Evaluation of the Costs of Groundwater Inspection in the
Member States. Final report: 1-79
Maybeck, M. 1985. The Gems Water Programme 1978-1983. Water quality bull., volume 10, no.4,
Canada: 167-173
UNESCO and WHO 1978. Water Quality Surveys. Studies and reports in hydrology, 23. Paris
Van Lanen, H. et al. 1998. Monitoring for Groundwater Management in (Semi-) Arid Regions.
Studies and reports in hydrology 57, UNESCO
Vrba, J. 2000. The Role of Groundwater Quality Monitoring in the Strategy of Groundwater
Protection.Proceedings of the XXX IAH Congress, Balkema/Roterdam: 1057-1063
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