Due to high nitrogen concentrations, two groundwater bodies in Northern Brandenburg were classified under the heading “poor (chemical) condition” according to the Water Framework Directive of the European Commission. These evaluations of the “Landesumweltamt Brandenburg” were based on several investigations that compared the hydrogeochemical data with the quality norm for nitrate and with the threshold value for ammonia from the European Groundwater Directive. By sampling with direct push techniques, we re-analysed the extent of contamination in order to decide whether the water quality could be improved in a cost-effective manner. Based on the newly established data set, the area of contamination could be more precisely delineated with geostatistical techniques. This helped to determine whether the previous evaluation of local groundwater quality was still valid.