Study of the effects of waste disposal in a selected rock-salt formation (SESAM). Simulation of the subrosion process with the METROPOL-3 code
[Studie betreffende de effecten van afvalopberging in een steenzoutformatie (SESAM). Simulatie van het subrosieproces met de METROPOL-3 code.]
Oostrom M , Leijnse A
RIVM Report 715205002
A number of two- and three-dimensional Galerkin finite element simulations have been carried out with the geohydrological model METROPOL-3 to evaluate flow and transport in the vicinity of a selected rock-salt diapir in the Netherlands. With METROPOL-3, variable density flow and solute transport can be modelled. In those studies, special emphasis was placed on the subrosion of the salt dome. Besides simulations reflecting the present conditions, attempts were made to investigate flow and transport for six Late Quaternary periods (Late Saalian, Eemian, Early Weichselian, Middle Weichselian, Atlanticum and Roman Time). A dissolving salt dome boundary condition was implemented into METROPOL-3 to simulate the subrosion process. Using realistic permeabilities, the calculated subrosion rates for two 2-D cross sections at y=568 km and x=258 km were about 0.08 and 0.12 mm/year. The subrosion rates during the Late Saalian glacial were considerably higher then for all other geological periods because during the Late Saalian the pressure gradients and groundwater velocities were much larger than for the other periods, including the Weichselian glacial. The 3-D local geohydrological model was used for two simulations, one with realistic heterogeneous permeabilities and the other with homogeneous permeabilities. After 50,000 years the subrosion rate of the realistic simulation was 0.119 mm/year, while the subrosion rate of the homogeneous case was almost twice as high. By using uniform permeabilities, the clay layer that covers the salt dome could not effectively restrict groundwater flow and transport of the dissolved salt, resulting in larger salt mass fraction gradients near the dome and higher subrosion rates.