ABSTRACT
For the investigation of reactive transport processes within a physically and chemically heterogeneous porous aquifer, forced gradient tracer tests were conducted at the ‘Horkheimer Insel’ test site in Germany. In each of the experiments, two tracers, one practically non-sorbing and the other one sorbing, were injected simultaneously across the entire aquifer thickness at the same location. In order to examine the scale dependence of the effective retardation factor, different transport distances of up to about 30 m were chosen for the experiments. The results show, that at the scales investigated the effective retardation factor increases with the transport distance. The measurements suggest that a complex numerical flow and transport modelling approach within a stochastic framework is needed to adequately describe the transport behaviour observed. Therefore, a three-dimensional Monte Carlo type non-parametric numerical stochastic transport simulation model, accounting for parameter uncertainty and variability, is applied for the evaluation of the experiments. Based on laboratory investigations on core sample aquifer material from the field site, the sorption process is treated spatially variable in the model, not needing a predefined correlation law of hydraulic conductivity and sorption parameters. According to the first results, the transport simulation technique proved to be suitable for highly heterogeneous aquifer conditions such as at the ‘Horkheimer Insel’ test site.
