Impacts of sewer leakage on urban groundwater -: Review of a case study in Germany

Leaky sewers have to be considered as potential sources for groundwater contamination in urban areas. The medium-sized city of Rastatt in SW-Germany with 50,000 inhabitants was subject of a series of investigations on sewer leakage which are summarized and discussed in this paper. Amongst others factors, the degree of pollution depends on the chemical composition of the wastewater and the amount of exfiltration. The groundwater underneath the city area showed anthropogenic influence resulting in elevated concentrations especially of boron, potassium and sodium as well as a generally increased electrical conductivity. Groundwater in the close vicinity of broken sewers showed typical sewage indicators such as iodated X-ray contrast media and microbiological parameters. Contamination with pharmaceutical residues and gadolinium could not be found in groundwater, despite significant concentrations of pharmaceuticals in wastewater. In autumn, the contents of boron and microbiological pollution were higher than in spring, indicating a higher ratio of wastewater in groundwater during times of less natural recharge. Groundwater monitoring wells near prominent leaks showed short-time fluctuations of EC and groundwater levels which could be correlated to changes of the wastewater composition and the flow regime in the pipe.