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.

This report contains the results of the National Soil Monitoring Network of the Netherlands in 1994, the second year of sampling. The network represents a cooperative effort of the National Institute of Public Health and the Environment (RIVM), the Agriculture Economics Research Institute (LEI-DLO) and the Research Institute for Agrobiology and Soil Fertility (AB-DLO). The primary objective of the network is to identify changes in soil quality over time. The network's secondary objective is to identify the actual quality of soil and upper groundwater. Attention is focused primarily on rural areas. The monitoring program involves sampling 40 locations yearly over a period of five years. In 1993 the network started by sampling the soil and upper groundwater on 35 dairy-cattle farms in the sandy regions of the Netherlands. In 1994, 20 intensively managed cattle farms (i.e. farms with a high phosphate production) and 20 forest sites (deciduous, pine and mixed vegetation) on sandy soils were sampled. Concentrations of heavy metals, polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides and triazines in the topsoil (0-10 cm) and the litter layer of the forest sites have been reported. Concentrations of macroparameters, nutrients and heavy metals in the upper groundwater are also presented. The measured concentrations are compared with the Dutch objectives for soil and groundwater quality (target values).

The report documents the results of the four years of a monitoring programme started in 1992 to assess the quality of the upper groundwater in the sandy regions of the Netherlands affected by fertiliser and manure use in agriculture. This programme is a cooperative effort of the National Institute of Public Health and the Environment (RIVM) and the Agricultural Economics Research Institute (LEI-DLO). The upper 100 cm of groundwater occurring within five metres of the surface was sampled at 99 farms (80 cattle and 19 arable) situated in the central, northern, eastern and southern sandy regions of the Netherlands. The samples were analysed for chloride, nitrate, ammonium, potassium, dissolved organic carbon and phosphate (ortho and total). Taken on average, the nutrient load did not change in the study period. The groundwater characteristics, on the contrary, did change as a consequence of the increase in precipitation in the periode 1992-1995. Nitrate and chloride concentrations in the upper metre of the groundwater were halved in this period, while the phosphorus concentration doubled. The potassium and ammonium concentrations showed a slight decrease. The average nitrate concentration in the upper metre of the groundwater under farms in the sandy regions of the Netherlands in the period 1992 - 1995, corrected for precipitation deviation from average, was found to be 158 mg.l-1. This is over three times the limit value of 50 mg.l-1. More than 95% of the farms in the sandy regions have a (precipitation corrected) nitrate concentration higher than the limit value. A relationship was derived between groundwater quality on cattle farms (nitrate and potassium) and nutrient balance surplus, as well as between the percentage of silage maize and groundwater level. On arable farms no relationship could be derived because the number of farms was too small.