De kwaliteit van ondiep en middeldiep grond-water in Nederland in het jaar 2000 en verandering daarvan in de periode 1984-2000

This report documents the quality of shallow (about 10 m below surface level) and medium-deep (about 25 m below surface level) groundwater in the Netherlands in the 1984-2000 period. Observations were grouped according to groups of eco-district areas. The observed concentrations were compared with environmental quality objectives for groundwater. The percentage of the surface with groundwater at concentrations exceeding the environmental quality objectives (%OBS) was calculated and depicted in maps for 2000. Maps showing the change in %OBS in the 1984-2000 period are also presented. In the sandy and loess areas, high OBS percentages (at least > 10%) are shown for nitrate, potassium and aluminium that are the effect of a combination of over-fertilisation, acidification and aggravation of drought. The effects highly resemble each other and are therefore not discernible. The %OBS that is observed in the shallow groundwater is often found to be higher than the %OBS in the medium-deep groundwater. Specifically, increased concentrations for cadmium, nickel and zinc occurs in the sandy area of the southern Netherlands. It is most plausible that the elevated concentrations represents the effect of a combination of over-fertilisation, acidification, aggravation of drought and the properties of the subsoil (poor, pyrite-containing), and not the effect of transport due to the burdening of the subsoil (caused by direct burdening with trace elements from the metal industry or fertiliser/manure). In clay and peat areas, high %OBS's are found for chloride, sulphate, ammonium, phosphate and potassium as a result of marine deposits. Often the %OBS observed in medium-deep groundwater are higher than in shallow groundwater. The %OBS for arsenic is inherently high in the marine clay and peat areas. In general, the groundwater quality did not change much in the 1984-2000 period. Only the concentration of chloride shows a decrease. This corresponds with the observed decrease in the chloride load on the soil in the Netherlands.