A fixed link (tunnel and bridge, in total 16 km) was constructed between Sweden and Denmarkduring 1995--2000. As part of the work, approximately 16 million tonnes of seabed materials (lime--stone and clay till) were dredged, and about 0.6 million tonnes of these were spilled in the water.Modelling of the spreading and sedimentation of the spilled sediments took place as part of the envi--ronmental monitoring of the construction activities. In order to verify the results of the numericalmodelling of sediment spreading and sedimentation, a new method with the purpose of distinguishingbetween the spilled sediments and the naturally occurring sediments was developed. Because thespilled sedimellts tend to accumulate at the seabed in areas with natural sedimenis of the same size, itis difficult to separate these based purely on the physical properties. The new method is based on thegeo--chemical differences between the natural sediment in the area and the spill. The basic propertiesused are the higher content As part of the work, approximately 16 million tonnes of seabed materials (lime - stone and clay till) were dredged, and about 0.6 million tonnes of these were spilled in the water. Modeling of the spreading and sedimentation of the spilled sediments took place as part of the envi- ronmental monitoring of the construction activities. In order to verify the results of the numerical modeling of sediment spreading and sedimentation, a new method with the purpose of distinguishingbetween the spilled sediments and the natural occurring sediments was developed. The new method is based on the geo - chemical differences between the natural sediment in the area and the spill. The basic propertiesused are the higher content