A direct current (DC) resistivity and time domaininduced polarization (TDIP) survey was undertaken at a decommissionedlandfill site situated in Hørløkke, Denmark,for the purpose of mapping the waste deposits and to discriminateimportant geological units that control the hydrology ofthe surrounding area. It is known that both waste deposits andclay have clear signatures in TDIP data, making it possibleto enhance the resolution of geological structures comparedto DC surveys alone.Four DC/TDIP profiles were carried out crossing the landfill,and another seven profiles in the surroundings providea sufficiently dense coverage of the entire area. The wholedataset was inverted using a 1-D laterally constrained inversionscheme, recently implemented for TDIP data, in orderto use the entire decay curves for reconstructing the electricalparameters of the soil in terms of the Cole-Cole polarizationmodel.Results show that it is possible to resolve both the geometryof the buried waste body and key geological structures.In particular, it was possible to find a silt/clay lens at depththat correlates with the flow direction of the pollution plumespreading out from the landfill and to map a shallow sandylayer rich in clay that likely has a strong influence on thehydrology of the site. This interpretation of the geophysicalfindings was constrained by borehole data, in terms of geologyand gamma ray logging. The results of this study are importantfor the impact of the resolved geological units on thehydrology of the area, making it possible to construct morerealistic scenarios of the variation of the pollution plume asa function of the climate change.