Technical Report NTB 03-13

Prediction modelling of groundwater flow and solute transport is an indispensable prerequisite for any long-term safety analysis concerning radioactive waste disposal in deep geological formations. This requires extensive geological and hydraulic information, a powerful numerical model, and the definition of effective parameter sets for the model.

The objectives of the EFP-project (Effective Field Parameter) are to examine methods for characterising the rock mass and for developing a structural model, to check the numerical model for calculation of the temporal and spatial distribution of tracer concentration on a large-scale, and to validate the developed model using in-situ data from large-scale tracer experiments at the Grimsel Test Site (GTS).

The main working programs of EFP include:

1. geological and geophysical seismic investigation of two new boreholes EFP19 and EFP20,
2. geostatistical re-evaluation of fracture data and structural model building,
3. geophysical tomographic measurement combined with tracer experiment,
4. large-scale ‘up-scaling’ tracer experiment, and
5. numerical modelling.

Generally, the investigation results indicate that only a combined modelling strategy under consideration of deterministic and stochastic distribution of effective parameters and a correspondingly numerical code will allow to perform large-scale predictive modelling. However, the effective parameters, which were evaluated from the small and intermediate scale, should be up-scaled on the spatial variance and correlation length for the large-scale modelling. Non-linear adsorption and desorption dynamics combined with chemical reaction may become important in the near field, whereas, in the far field the matrix diffusion and the K_D concept will ensure, due to generally low concentration levels, a sufficient prediction capability.