This diploma thesis deals with the behavior of aqueous solutions in the vadose zone. The investigations are part of the principles necessary for the development of an in-situ decontamination-method, which will be applied at an abandoned industrial site contaminated with hexavalent chromium. The chromate in the vadose zone is converted into the less toxic trivalent chromium by using a reduction agent injected into soil. For developing an optimum in-situ decontamination-method it is necessary to know about the flow characteristics of the used aqueous reduction-agent and the interaction with chromium. To obtain these required data a series of laboratory scale irrigation experiments with underpressure soil column equipment were conducted. Additional simulation was carried out to evaluate flow characteristics of the reducing agent in the vadose zone. Literature research concerning influence of soil structure, dispersion of aqueous solutions in the vadose zone and simulation of the flow using appropriate mathematical models provides the theoretical background for irrigation experiments.