ABSTRACT
ABSTRACT: Leakage from defective sewer systems has been the subject of several investigations during the last two decades. This paper compares the published results at the laboratory scale and investigates the possibilities of applying this small scale process knowledge to the city scale. All laboratory experiments show the importance of a colmation layer and its strongly varying hydraulic conductivity. Upscaling the small scale models to a real sewer system requires the knowledge of several parameters with high spatial and temporal variability which results in a significant uncertainty. A Monte Carlo simulation was applied to the data set of a real sewer network and resulted in most probable exfiltration rates of 10 l/day/detected leak, equal to 4 mm/a artificial groundwater recharge from sewers. However, the uncertainty involved is very significant. With a probability of 95% the resulting groundwater recharge will be below 65 mm/a. This large range of possible exfiltration rates underscores the necessity for groundwater quality monitoring and the use of marker species approaches.
