Abstract Groundwater contamination at the Port of Rotterdam is studied using a regional scale model. Reactive transport is calculated along pathlines accounting for redox-dependent biodegradation. The contaminant flux is calculated on so-called planes of compliance. These are the main receptors where there is potential danger of receiving contaminant. In this case the receptors are surface water, the first main aquifer and the border of the port area. Due to the comparatively high degree of uncertainty in the input parameters, a Monte Carlo analysis is performed. The input parameters cause the highest degree of uncertainty in the model. An uncertainty distribution was derived based on all information available. These parameters are: contaminant concentration at the source, degradation rates, redox conditions, and sand-filled vertical drain parameters such as depth and permeability. The Monte Carlo analysis uses the combined uncertainty of the individual input parameters to obtain an uncertainty distribution for the entire megasite. A number of realizations of the pathline analysis obtain different modelling outcomes which can be interpreted as an uncertainty distribution itself. In this case, we have chosen to express the outcome as the chance of exceeding the intervention value on a plane of compliance.

Keywords groundwater contamination; Monte Carlo analysis; reactive transport; regional scale