Analysis of solute transport in a heterogeneous aquifer: the Krauthausen field experiment

A field-scale natural gradient tracer experiment with bromide, uranin and lithium was conducted in a heterogeneous aquifer at Krauthausen, Germany. The temporal and spatial evolution of the solute plumes was monitored over 398 days for bromide and 449 days for uranin and lithium. The spatial variability of basic aquifer parameters, hydraulic conductivity, and sorption parameters of the aquifer material was investigated in detail. Local Darcian velocities were measured using NH4Br82 as a radioactive tracer in 33 observation wells. Vertical and horizontal correlation lengths of hydraulic properties were determined using variogram analysis. The magnitude of the local Darcian velocities was found to be lognormally distributed. In addition, the groundwater flow direction showed a clear trend in the vertical direction. The horizontal correlation length of the magnitude of Darcian velocity agreed with the correlation length of K estimated from grain size data. Batch experiments on aquifer sediments showed that sorption of uranin and lithium could be described by a Freundlich isotherm. The Freundlich n parameter of uranin sorption showed little variation with depth. The time evolution of the bromide plume was quantified in terms of spatial moments. The longitudinal effective dispersivity estimated from spatial moment analysis was within the range of calculated effective dispersivities, taking into account the uncertainty of estimates of the lnK statistics.