2.11. The Netherlands

2.11.1. Characteristics of Groundwater

The Netherlands is a densely populated country covering an area of 38,000 km². It is heavily industrialised whereas the agricultural use of soils is one of the most intense in the world. Because of the wide use of fertiliser (average use of e.g. nitrogen fertiliser 260 kg/ha/year) there are great problems of groundwater pollution in wide areas, especially sandy regions, about 42 % of the whole country. Consequently the nitrate concentration is often higher than the drinking water standard of 50 mg/l. In urbanised regions hundreds of thousands local pollution sources can be found, thereupon the groundwater quality is often endangered.

In more than 90% the country groundwater level is less than 4 m below the surface level. Only in the central glacial formed hills a deeper level can be measured. Several national environmental institutions gather national environmental data such as groundwater data. These networks -with exception of the surface monitoring one- are managed by the National Institute of Public Health and Environmental Protection. In addition smaller network units at regional and local level exist. The general goals of the networks are:

  • description and diagnosis of the environmental quality for the benefit of environmental policy

  • evaluation of the effects of corrective actions

  • increase of environmental knowledge

  • observation of changes in the quality of the environment

  • enforcement of regulations

  • facilitation of responses to emergency situations

Potential water resources can be divided in 30,000 mio m³/year precipitation, 80,000 mio.m³/year inflow from neighbouring countries minus 20,000 mio. m³/year evapo-transpiration. Most of the water, 4,000 mio m³/year is needed for the industrial sector, 600 mio. m³ for households. No detailed information is available for the agricultural sector.

2.11.2. Structure of the Administrative Organisations Concerning Groundwater Quality

The Netherlands are divided in 12 provinces. Although the national network provides sufficient national groundwater quality data there was also a need for the establishment networks of a provincial level (PMG-networks). Since 1993 the provincial monitoring networks has provided information needed for the special aspects of political measurements at provincial and regional levels. All these networks were designed in close co-operation with the National Institute for Public Health and Environmental Protection (RIVM). The RIVM co-ordinates the national groundwater quality monitoring activities (LMG-network) as well as sampling and analysing activities. The RIVM manages the groundwater database on both national and provincial level. The central government is the national authority which makes the laws and ordinances that are the legal basis for the networks. Sub regional and/or local level municipalities and water boards are the main responsible authorities for the water management.

2.11.3. Monitoring of Groundwater Quality

The Dutch groundwater network was established in the early 1980s. The objectives of the network are:

  • inventory and diagnosis of groundwater quality in relation to soil use, soil type and hydrogeological conditions

  • indication of human influence on groundwater quality

  • identification of long-term changes in groundwater quality

  • provision of data for groundwater quality control and groundwater management

The structure and operation modus of the network takes account of the objectives listed above. At present the network consists of approximately 380 monitoring wells i.e. an average density of 1 well/100 km². The majority of wells are spread in areas with fresh groundwater that can be used for drinking water. The monitoring sites are each closely associated with the soil type and the land use in their operation area. The wells used as sampling sites were drilled specially for the network. Taking into account the very low groundwater velocity in the Netherlands the sampling frequency is once per year. All samples are collected under standardised operating procedures. With the help of special instruments samples are collected under nitrogen gas directly before filtration. Quality assurance procedures (ISO 9000, EN 4500) are provided for all important steps in the course of monitoring from drilling of wells up to data presentation. There are two main programmes in the Netherlands, the „basic" and the „ad-hoc" programmes. The ad hoc programme is a kind of special monitoring programme in selected wells due to type and use of pollutants such as heavy metals, industrial organic pollutants or several groups of pesticides. The earliest record was taken in 1979, the average record length is 10 years.

The data are loaded onto a special database developed in 1991. In this INGRES database data of different networks in the Netherlands are included, thus simplifying mutative use of data. The hardware is HPUX and the software tools are INGRES/SHELL SCRIPT. The presentation of data occurs at different levels firstly individual data presentation, secondly annual data presentation on a provincial level and finally annual description and diagnosis of groundwater quality in the Netherlands through statistical characterisation and mapping of groundwater quality. In addition, all data are also collected in MONITOR, a user friendly GIS system developed by order of the RIVM. MONITOR is a tool for researchers and policy makers and can be easily installed at PCs. Data are free of charge but there are restrictions for the availability.

In the 12 Dutch provinces networks on a provincial level are in operation. They have quite the same goals as the national network e.g.:

  • description of present quality situation

  • identification of temporal trends

  • source of basic data for research and management

  • evaluation of policy measures

  • signalling of quality developments in vulnerable areas (early warning).

Most attention is paid to the quality assurance procedures and standardised regulations for the whole monitoring procedures to make data comparable between provincial and national networks. The provincial authorities run the networks and are responsible for sampling and analysing. All data gathered are stored in the database of RIVM and are there accessible for the provincial authorities.

Other Dutch groundwater networks are:

  1. Drinking water networks. Water supply companies abstract groundwater at about 240 pumping stations. Before and after the treatment groundwater is sampled and analysed.

  2. Monitoring networks near local pollution sources like waste disposal sites (for every new site a network is obligatory), baseline stations, sites with polluted soil/groundwater.

  3. Forest monitoring programme: In 150 forest sites the effects of soil acidification in forests and heathland sites are focused. The programme is related to shallow groundwater in the Dutch sand regions.

  4. Eutrophication monitoring of groundwater in agricultural areas. The programme is related to the use of fertiliser and manure in agriculture as well as policy measurements to reduce environmental impacts of nutrient losses.


2.11.4. Structure of the Administrative Organisations Concerning Groundwater Quantity

As the Netherlands are a low-lying country, piezometric heads of groundwater are found at shallow depths. Slight changes of groundwater level can highly influence the situations for households, industry and agriculture. With regard to this vulnerable status the level monitoring is very important. There are approximately 30,000 groundwater observation wells. Monitoring networks can be divided in 3 groups: networks for water management, networks for exploration and exploitation of groundwater and networks for scientific research. The networks for water management can be found at three different levels:

  • on a national level; on behalf of the Ministry of Transport Public Works and Water Management

  • on a regional level; on behalf of the provincial authorities

  • on the local level; on behalf of water boards, municipalities and nature conservancies.

The national monitoring network is maintained by the TNO Institute of Applied Geo-science and provincial authorities. The other networks are maintained by their owners and the TNO Institute of Applied Geo-science. All data are stored in a national database maintained by the TNO Institute of Applied Geo-science. To ensure the quality of data a quality control programme has been developed which is also co-ordinated by the TNO Institute of Applied Geo-science. The most important legal basis for the monitoring activities is the Water Management Act. This act requires the water manager to design and implement water management plans, in which the water manager indicate how the water in a certain area will be used and protected.

2.11.5. Monitoring of Groundwater Quantity

The „Dutch Primary Monitoring Network for Groundwater Levels" was established in the 1980s. The number of observation wells expanded considerably as a result of an increase in groundwater investigations related to agricultural and public water supply. The main purposes for groundwater quantity monitoring are:

  • identify potential uses

  • design target scenarios

  • design management measures

  • evaluate water management

The responsible organisation for the co-ordination of the networks is the Ministry for Transports, Public Works and Water Management. It is supported by the RIZA, the Institute for Inland Water Management and Waste Water Treatment. The local sampling is carried out by provincial authorities. The TNO Institute of Applied Geo-science co-operates closely with all of them. It manages the database and is responsible for the design and the optimisation of the monitoring network, in some regions for the maintenance of the network and research on monitoring topics. In an area of 36,000 km² of porous media 4,000 sampling sites are distributed. They are bored wells measuring water level (2 times a month/basic programme and daily/special programmes); water temperature (every 15 minute/basic programme) and density -EC, TDS or Cl- (once a year/basic programmes). There are no standardised procedures with respect to the measurement methods and maintenance of observation wells. The quality assurance procedures for the groundwater level can be schematised in three phases, phase I -automatic plausibility check, phase II - detection of extremes in one time series and phase III - detection of spatial extremes. There are standardised methods for data handling. The earliest record was taken in 1870, the average length of record is 20 years.

The following data are stored in a DBMS:ORACLE and/or a GIS : ARC/INFO and SMALLWORLD database using UNIX hardware:

Point data

Spatial data

groundwater heads

dimension and properties of layers

chemical analyses

surface water system

well logs

infiltration/seepage areas

geophysical measurements

surface level

geo-electrical soundings

fresh/saline interfaces

pumping tests

groundwater head contours

groundwater abstractions

polluted areas

Data are available on floppy disks, paper sheets and hard disks of central-on-line-database. Data have to be paid for and are not accessible to everyone. Reporting is not a regular activity but it is carried out on an ad hoc basis normally (but not always) by the TNO Institute of Applied Geo-science.

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