Report from the Sub-comittee on the environment and health

Database
Groundwater monitoring
programme GRUMO
4.1 Pesticides in groundwater
Denmark’s water supply system is based on pure groundwater, which can
be supplied to <strong>the</strong> consumers without treatment. In <strong>the</strong> last few decades,
groundwater has been found to be contaminated with industrial
chemicals, leachate <strong>from</strong> landfills, nitrate, heavy metals and, lately,
pesticides. In 1994, contamination of <strong>the</strong> groundwater in Ejstrupholm
with <strong>the</strong> herbicide atrazine led to splash headlines in <strong>the</strong> media. At <strong>the</strong>
same time, countrywide analyses showed that pesticides were commonly
found in <strong>the</strong> groundwater. New research results also show that even in
clayey soil, fissures and cracks <strong>from</strong> <strong>the</strong> Ice Age enable pesticides to
leach down to <strong>the</strong> groundwater relatively quickly.
Groundwater quality is one of <strong>the</strong> main elements of Denmark’s
environmental legislation. For pesticides, Denmark uses <strong>the</strong> EU’s limit
values of 0.1 microgramme per litre water for every substance and 0.5
microgramme per litre water for <strong>the</strong> sum of pesticides, irrespective of <strong>the</strong>
nature of <strong>the</strong> substance. Since groundwater is regarded as a basic
resource that must be kept free of pollution, <strong>the</strong>se limit values have been
set as ”hygienic limit values”. This is fur<strong>the</strong>r supported by <strong>the</strong> fact that
<strong>the</strong> groundwater used as drinking water forms over long periods of time.
This means that by <strong>the</strong> time pollution can be measured in <strong>the</strong> aquifer
itself, it is too late to avert it or control <strong>the</strong> extent of it.
In Denmark, groundwater is analysed for pesticides and, in some cases,
for degradation products in different contexts:
• The Aquatic Environment Plan’s National Groundwater Monitoring
Programme, GRUMO
• The Aquatic Environment Plan’s Nationwide Monitoring Programme
for Agricultural Catchments, LOOP
• The water companies’ raw-water monitoring system
• Expanded analytical programmes carried out for example by county
authorities and water companies.
The groundwater monitoring programme (GRUMO) covers 67
monitoring areas spread around <strong>the</strong> country. The areas have been chosen
with a view to providing a representative picture of Denmark’s aquifers.
In most cases, <strong>the</strong> monitoring areas are situated in regions in which land
is predominantly used for farming. Most of <strong>the</strong> areas include an
extraction well to a waterworks and 10-20 specially established
monitoring wells that characterise <strong>the</strong> main flow pattern of <strong>the</strong>
groundwater (Figure 4.1).
The samples of water are extracted <strong>from</strong> well screens. A ”well screen”
should be understood to mean a closed pipe placed at <strong>the</strong> lower end of
<strong>the</strong> groundwater well shaft. The well screen is equipped with slots or
similar openings, which, in interaction with a screen pack of filter gravel
around <strong>the</strong> well screen, are intended to retain <strong>the</strong> fine particles in <strong>the</strong> soil.
The length of <strong>the</strong> well screen can vary so that <strong>the</strong> pumped up water
comes <strong>from</strong> <strong>the</strong> depth interval in which <strong>the</strong> well screen is placed. Three
types of well screen are used in <strong>the</strong> groundwater monitoring programme:
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