Modelling of sewer exfiltration to groundwater in urban wastewater systems: A critical review

Increasing evidence from studies in urban wastewater systems proves that sewer exfiltration may present a profound threat for rising levels of toxic substances and microbial pollution in groundwater. New and innovative methods for monitoring sewage exfiltration are continuously developed, which provide a solicit ground for a better understanding of key processes and influencing characteristics of sewer exfiltration to support the development of mathematical equations and models worldwide. However, modelling of sewer exfiltration and its associated impacts on groundwater are still constrained and not fully understood in large urban systems. This paper reviews the knowledge advancements and challenges of sewer exfiltration modelling. Based on the present review, we define five key research domains for developing more generic framework of large-scale models. These domains inquire to advance the representation of hydraulic modelling (e.g. testing exfiltration models coupled with biofilm growth models), modelling of solutes originating from sewer leakages (e.g. heavy metals), define the practical values of key model parameters of main model components and sub-processes for calibration and uncertainty evaluations, develop upscaling approaches for integrated multi-dimensional sewer exfiltration models, and incorporation of sewer exfiltration from private sewers.