A multi-tracer study in the unsaturated zone of a heterogeneous formation

A multi-tracer experiment has been carried out in the unsaturated zone of a highly heterogeneous glaciofluvial sand deposit. Tritiated water, chloride and propylene glycol were injected at the surface of a lysimeter wall and the transport due to natural water fluxes was followed down to 2.5 m. A comparison of the mobility of chloride relative to tritium revealed a retardation factor of approximately 1.15. Longitudinal and transverse dispersivities were estimated by the methods of spatial moments and based on the spatial distribution of solute concentrations at discrete instances of time. The observed flow pattern shows characteristics of random effects due to the pronounced soil physical heterogeneity of the formation, and dispersivity values calculated vary within an order of magnitude. Transverse dispersivity is estimated to a few centimeters, whereas longitudinal dispersivity is found up to one order of magnitude larger. The transverse dispersivity tends to depend on the distance travelled. (author). 30 refs, 9 figs, 1 tab