Impacts of Sewer Leaks on Surrounding Groundwater and Surface Water Quality in Singapore

Underground sewers deteriorate over time resulting in cracks and joint defects. Sewage thus leaks out of the sewers and contaminates the surrounding groundwater. Singapore does not directly use groundwater as a water supply. However, contaminated groundwater flows into the drains nearby through weep holes, and subsequently enters water supply reservoirs. This study examines the impacts of sewage leaks on surrounding groundwater and surface water quality by modeling the interactions between leaky sewers, groundwater and drains. It first explores the representations of important yet challenging boundary conditions, namely weep holes and leaky sewers, so that their fluxes vary realistically with water pressure throughout a simulation. It then simulates groundwater flow and contaminant transport from leaky sewers to nearby drains over a period of ten years. It further rehabilitates the sewers and models the attenuation of contamination plume for another ten years. The results of this project contribute to the modeling and understanding of the potential impacts of sewer leaks on surrounding groundwater and surface water quality. For example, groundwater quality changes with hydrologic conditions, and it is highest during heavy rainfall and times of high water table because of the low leakage and high dilution rates. Water quality fluctuates daily or even hourly in the vicinity of the sewers, but is more stable in the flow through the weep holes into the drains. Overall, this study benefits the sewer leak monitoring and sewer rehabilitation in many urban areas worldwide.