Estimation of releases into rivers with the steady-state surface water model EXWAT using dichloromethane

The surface water model EXWAT is applied to monitoring studies of hazardous substances to estimate site-specific emissions from measured concentrations. The model includes the main processes which govern the fate of chemicals in rivers, namely, advection, volatility, degradation processes, sedimentation, resuspension, and protonic equilibria. The steady-state solution of the linear mass balance equations leads to proportionality between input and concentration of a chemical, which is used to assess input rates from measured concentrations. Subsequently, the model can be used for pollution control and identification of unknown releases. With measured concentrations in the Rhine near Koblenz (95 km downstream from the mouth of the river Main) the load of dichloromethane from the tributary Main was estimated. The comparison with measured concentrations in the tributary mouth has a good agreement in this case.