Characterization of dispersion in an alluvial aquifer by tracing techniques and stochastic modelling

Dispersion in aquifers is dominated by the spatial structure of the hydraulic conductivity field. The aim of the study is to characterize the dispersive properties of a heterogeneous aquifer located near Grenoble, France, through two approaches both based on the use of experimental tracing data: a deterministic approach, interpretation of field scale natural gradient tracer tests; and a statistical approach, the geostatistical study of the spatial structure of the experimental hydraulic conductivity field, followed by the spatial moment analysis of stochastic particle trajectories. With the choice of exponential variograms, the simulated longitudinal dispersivity fits quite well to the experimental one, and reaches an asymptotic limit of 6 m after a 50 in travel distance, say about ten correlation lengths, which accords with the stochastic theories.