Contrary to total sealing of soils by tar or concrete, partially sealing by semi-pervious pavements has some ecological advantages concerning water infiltration, aeration and evaporation. Because of this it is promoted among ecological motivated town-planning. Due to various inputs of urban dust, the original yellow sandy seam filling of such pavements turns dark and changes its properties by time. We observed such during only one year. We hypothesized that deposited organic carbon inputs do mostly not have natural characteristics but are man-made, e.g. diesel dust, fly ash etc. Thus, properties of the seam material are not predictable from experiences with forest or agricultural soils. Semi-pervious sealed urban areas are sites of contaminant deposition as well as groundwater recharge. For an assessment of the resulting groundwater contamination risk in these areas, the properties of the seam material, which influences transport processes, must be known. The aim of this study was to investigate the pore system build-up, which includes size distribution and fractal character in the seam material of urban sites. The investigated samples were taken from pavements adjacent to roads in Berlin and Warsaw. The micropore parameters (nanometer range) were characterized using water vapor desorption isotherms, mesopore parameters (micrometer range) were estimated from mercury intrusion porosimetry and macropore parameters (millimeter range) from water retention curves. Particle density, dry bulk density and particle size distribution were measured using standard methods. Volumes of micro- and mesopores as well as particle densities and dry bulk densities correlated with C_tot contents. However, no such relation was found for macropore volumes. Compared to the original sandy seam filling, the altered seam material shows significantly higher Corg contents and higher amounts of micro- and mesopores. Therefore, the available water capacity increases by 0.05 – 0.11 m³ m^-3, as compared to the original sandy seam filling. Compared to natural sandy soils having similar Corg contents, the seam material shows similar macropore volumes, but the volume of mesopores and micropores is a few times smaller. That is mainly because of the particulate character of the deposited organic matter.