Abstract

Multiple monitoring networks in the Netherlands collect data on the quality of the groundwater and the concentrations of various substances, including nitrate. There is a national monitoring network and each province also has its own monitoring network. The provincial networks use some of the national wells for their sampling, the number varying according to the province in question. Roughly speaking, the nitrate concentrations measured by the national and the provincial monitoring networks are the same, but there are also variations, particularly when it comes to different regions.

Clear figures on concentrations are needed to be able to substantiate and evaluate national policy on groundwater quality. RIVM therefore recommends that the methods used be improved nationwide.

The monitoring networks have different objectives. The national monitoring network, the National Groundwater Quality Monitoring Network (LMG), is used for the statutory European report on nitrate, among other things. The provincial monitoring networks, on the other hand, yield data for regional objectives and for the statutory European report for the Water Framework Directive (KRW).

Datasets from the LMG are generally consistent but datasets from the provincial monitoring networks are less so, primarily because fewer samples are taken. Statistical research is necessary to be able to indicate how usable the provincial data is for the various national applications. RIVM makes recommendations for improving the quality and management of the data. Activities to this end are already ongoing.

These were the findings of a report by RIVM on the monitoring of the groundwater quality in the Netherlands. This report describes the differences and similarities between the ways in which the monitoring networks operate (who does what) and how they are implemented (where, what substances are monitored and when). Because of the country’s European obligations, the fertiliser ‘nitrate’ was mainly looked at for the report.