The Ohlsbach Plume - Discharge of deep saline water from the crystalline basement of the Black Forest, Germany

Salt-water discharges from a fault system in the crystalline basement of th e Black Forest into the gravel aquifer of the Kinzig River valley near Ohls bach, upper Rhine River valley, southwestern Germany. The salt water (TDS, 16 g/kg) ascends from a reservoir at >3 km depth, Once discharged into the gravel aquifer, the saline deep water mixes with fresh groundwater and is c arried along the groundwater flow path to the middle of the Rhine River val ley. There, the natural geogene salt-water plume merges with a manmade chlo ride-rich infiltration zone along the Rhine River. The plume was mapped usi ng (1) chloride data from groundwater observation wells, and (2) resistivit y data from geoelectric sounding. Background chloride is about 7 mg/kg. In the central region of the plume, chloride concentration exceeds 200 mg/kg. A continuous area of Cl > 50 mg/kg is distinguished from the discharge faul t to the Rhine River over a distance of 12 km. Resistivities range from >50 Omega in uncontaminated regions to <7 Omega in the 700 m-long central regi on of the plume. A low resistivity plume (7-10 Omega) stretches for >7 km i nto the Rhine River valley. The two plume maps are in good agreement.