TRANSPORT MODELING IN HETEROGENEOUS AQUIFERS .2. 3-DIMENSIONAL TRANSPORT MODEL AND STOCHASTIC NUMERICAL TRACER EXPERIMENTS

Statistical information on the coherent sedimentary structures of highly heterogeneous gravel deposits (Jussel et al., this issue) is used to investigate numerically the transport of conservative tracers. The data are the basis for a numerical generation of synthetic aquifer models, whose statistical distributions of the sedimentary structures and their hydraulic conductivity and porosity correspond to the findings in the investigated deposits. A three-dimensional finite element flow model and a corresponding random-walk transport model were developed for this purpose. Because of the large number of finite elements needed, the solution algorithm is optimized for applications on vector-type computers. In order to minimize the discretization errors a special interpolation technique is applied to the determination of the local velocity vector. Ten stochastic, numerical transport experiments over a transport distance of 100 m were carried out with synthetic gravel aquifer models. They allow the mean tracer velocity, the effective hydraulic conductivity, and the dispersion parameters to be estimated. These estimates are compared with estimates of these parameters from current theories for the flow and the tracer transport in random, correlated, anisotropic hydraulic conductivity fields.