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Decentralized water management requires innovative technical solutions due to restricted operational and economic resources. In this study, a combined, decentralized infiltration system in the form of closely-spaced sub-systems for precipitation water and treated wastewater has been numerically analyzed. Flow and transport simulation shows that a closely-spaced system, by arranging the infiltration pipes closely in a longitudinal manner, is feasible under the consideration of German national guidelines for both infiltration methods. Precipitation events up to a recurrence interval of five years can be infiltrated alongside with treated wastewater of a one-family house without significant reduction of the wastewaters’ residence time. Scenario analyses highlight that harmless wastewater infiltration remains mainly undisturbed for a broad bandwidth of hydrological, subsurface, and technical conditions.

The closely-spaced infiltration of treated waste water and precipitation water may have advantages when compared to the single infiltration, such as reduction of construction costs and space requirements. Recent numerical works showed the theoretical applicability of this approach. A physical tank experiment has been set-up to study the processes in more detail and provide real data on the water flow as well as the purification potential during infiltration. Various scenarios of treated waste water infiltration with and without precipitation events have been technically realized. These data have then been used to implement a numerical model that supported the review of criteria for a proof of the principal applicability. A joint infiltration set-up is proposed and analyzed after successful evaluation of the closely-spaced, but separated infiltration of treated waste water and precipitation water. Again, both the laboratory and numerical works show the principal applicability of the proposed technique.

Earth dam is always a safety issue, as it can experience catastrophic destruction due to the slope failure caused by various factors, such as water content increasing in earth slopes, vegetation root decay and so on. This study is to investigate the variation of hydrological processes in the saturated and partially saturated slopes with a new simulation program PCSiWaPro ® (a computer aided leachate forecast tool) under transient boundary conditions. The integration of a weather generator inside the PCSiWaPro ® allows a transient water flow calculation with respect to atmospheric conditions (precipitation, daily mean temperature and sunshine duration) and removal of water by plant roots and leaves. The simulation results of one scenario in a Chinese earth dam clearly demonstrate a good applicability of the program PCSiWaPro ® .