ABSTRACT
ABSTRACT: Severe deterioration in the sewer systems of many European cities as a result of age and structural deficiencies leads to groundwater ingress and wastewater exfiltration. Groundwater ingress is generally determined through measurements of night-time sewage flow. Exfiltration measurements in pipes provide estimates of the flow of exfiltrating water. Extrapolation of these data on the total defect areas determined by closed-circuit television (CCTV) inspection suggests that the amount of exfiltrating sewage is sufficient to account for a significant fraction of urban groundwater recharge. Laboratory tests have been conducted to investigate clogging (Dohmann et al., 1999; Vollertsen and HvitvedJacobsen, 2003) but detailed knowledge about the variability of the colmation layer is missing. In Rastatt, a medium-sized city in SW-Germany, detailed investigations have been undertaken to assess the impacts of sewage exfiltration on groundwater. A purpose-built exfiltration test site has enabled investigation of exfiltration from an active sewer under normal operating conditions in a qualitative and quantitative manner. Sewage seeps from a crack in the pipe into a steel tank underneath and the exfiltration rate is recorded by a pluviometer. Soil moisture is measured at different depths underneath a second identical trench. Depth specific soil water is sampled over intervals of 7 or 14 days. The waste water quality is monitored through regular and online measurements of major ions. Waste water discharge is permanently recorded by a flow meter accounting for the fill level, the velocity and the pipe geometry.
