Abstract

A number of particle tracking simulations have been carried out for radionuclide particles which are hypothetically released from the Zuidwending diapir. The particle tracking code used was METROPART, a postprocessor of the METROPOL model. Two-dimensional METROPOL-3 simulations and subsequent METROPART particle tracking were done for a W-E and S-N cross-section through the Zuidwending salt diapir. In a sensitivity analysis, the two-dimensional model sensitivity was evaluated by varying the groundwater velocities at the site boundaries, the permeabilities, heterogeneous and homogeneous flow systems, and the anisotropy ratio. The METROPOL-3 code was also used to carry out two three-dimensional simulations, one for a heterogeneous and the other one for a homogeneous flow domain, for a period of 50.000 years. The flow fields obtained after this simulation period were also used for particle tracking purposes. The METROPART results show that for the two-and three-dimensional simulations alsmost all released particles in heterogeneous flow domains were transported out of the flow domain through either the Plio-Pleistocene aquifer or the aquifer-containing the Brussels Sand Member. None of the particles reached the top boundary of the model area. Totally different results were obtained when homogeneous flow field were used. In those cases, the particles moved to the top of the flow domain in both the two- and three-dimensional simulations. The particle tracking results obtained with flow fields from the sensitivity analysis showed that an increase of the side boundary velocities resulted in a decreased averaged travel time of the particles. The effects of changes in permeability values were also pronounced. An increase in the permeability values generally resulted in a decrease in the average travel times of the particles, while a decrease in the permeability values caused the average travel times to increase.