Monitoring stations (Nitrates Directive) deep filters

The National Groundwater Quality Measurement Network (LMG) was built between 1979 and 1984 and consists of approximately 350 measurement locations spread throughout the Netherlands. Sampling shall be carried out in permanent wells specially constructed for monitoring purposes. These observation wells have been constructed just outside the fields to be easily sampled and not to interfere with the work in the field. The sites were selected on the basis of soil type, land use and hydrological condition. At each site, groundwater samples are taken at depths of 5-15 m (shallow filters) and 15-30 m below ground level (deep filters). On sandy soil, samples are taken from shallow observation wells every year, while samples are taken from shallow wells on the other soils (clay and peat) every two years. A sample is taken from deep wells every four years, as well as from shallow filters at measuring points with marine influences. The wells that are not sampled every year shall be interpolated for the absent years.