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Netherlands standard - https://connect.nen.nl/ - full text freely visible on line after registration. In the Netherlands, before dredging first you have to conduct a preliminary investigation following: NEN5717 Soil - Sediment - Strategy for the preliminary investigation of the environmental quality One of the outputs of the preliminary investigation is a stratification of the area to be dredged into sublocations which are internally relatively homogeneous and typically between 10 and 30 hectares in size. then you follow: NEN5270 Soil - Sediments - Strategy for exploratory investigation or the environmental quality The Port of Rotterdam authority follow this procedure and take 6 samples from each of 300 different locations within the dredged area.