Abstract

The National Groundwater Quality Monitoring Network (LMG) was established in the Netherlands around 1985. Since then, groundwater samples have been taken yearly at some 400 locations. Samples are taken at two depths (about 10 m and 25 m below soil surface) and analysed in the laboratory. The intention, expressed at the LMG start, was to optimalise the network after 10 years of measurements. The objective of the optimalisation, based on the RIVM strategy and worked out in several workshops, was to maintain the LMG as a stable monitoring network, in which the relevance for policy makers would be maximal, in combination with a 50% reduction in costs and capacity. The result of the optimalisation is a new LMG sampling scheme which meets both the objective and all the pre-defined conditions, shallow filters in sandy regions are sampled every year; shallow filters in other regions are sampled every two years; deep filters are sampled every four years; shallow filters with high chloride concentrations (marine influence) are measured every four years; filters dominated by local conditions (e.g. nearby rivers and, local sources of pollution) are eliminated. In this way, the number of filters to be sampled every year has been reduced from 756 to about 350.