Geogenic chlorides anomalies in groundwater of useful aquifers in Central Poland

Zones of Cl anomalies in Mesozoic and Cenozoic aquifers, defined as groups of wells with concentration of the chloride ion in groundwater exceeding 60 mg/dm3, were mapped on the basis of 12 000 archival chemical analyses. These zones are predominantly developed in tectonic conditions enabling the inflow of Mesozoic salt waters into useful aquifers: 1) fault zones, 2) hydrogeological windows above salt anticlines and elevated tectonic blocks, and 3) salt diapirs. As a result, significant decline in groundwater quality has been reported from many intakes due to the elevated concentration of chlorides, sodium and the amonium ion