A series of modelling studies were carried out as part of the GAM project.

Generic studies on synthetic media

This series of modelling experiments examined the effect of variable transmissivity on solute and gas transport.

There are two fundamental ways to represent the transmissivity field in a numerical model. These are:

1. with variable hydraulic conductivity (K) and a constant aperture size and
   
2. with a constant K and variable aperture size.

Solute tracer tests cannot discriminate between these two model concepts. However, by carrying out tests such as the GAM project, variations in the models be examined. It is clear that there are significant differences between the results and this is believed to be a result of gas bubbles becoming trapped in the bottle neck, represented in the variable aperture model (visco-capilliary flow is sensitive to aperture variations rather than K variations)

Interpretation of field experiments (hydrotests, solute tracer tests, particle tracer tests and gas tracer tests) using the method of geostatistical inversion.

The estimation of the transmissivity field was based on the joint inversion of:

• Crosshole responses for three hydraulic interface tests.
  
• Breakthrough curves for the two solute tracer tests.

The model used 2D hydraulic and transport models to estimate transmissivity and porosity via a simultaneous joint inversion of the results of both hydraulic testing and tracer breakthrough curves.