Infiltration and inflow to wastewater sewer systems - A literature review on risk management and decision support

Report, 2021

Wastewater sewer systems are one of our largest infrastructural assets. By transporting the sewage from our homes and other facilities to the wastewater treatment plants, the sewer systems protect public health, properties, and the environment. However, in addition to the sanitary sewage, there is an infiltration and inflow (I/I) of other water to the sewer system. This additional load can result in adverse effects such as basement flooding, combined sewer overflows, and larger pumping and treatment costs. I/I can originate from rainfall but also from sources such as groundwater, surface water or leaking drinking water pipes. Expected climate change effects include more intense rain events and periods of higher water levels which will increase the problem of I/I. Hence, it is important to manage I/I in a proper way by implementing efficient measures that provide the largest societal gain from a sustainability point of view.

This literature review was performed to form a basis for research on developing risk-based decision support models to evaluate I/I in wastewater sewer systems from a system perspective and with focus on sustainability. It reviews publications on I/I focusing on sources, impacts, quantification and mitigation measures, addresses risk definitions, and the risk management process. Further, common decision support methods are described and literature on decision support models to evaluate I/I are reviewed.

Important conclusions are that a vast amount of literature exists on finding and reducing I/I from a technical point of view and in several publications different decision support models are used to evaluate measures aiming at reducing I/I. However, existing models are focused on project internal and financial aspects and a need for future studies is identified, evaluating I/I from a broader societal and sustainability perspective, including project external, environmental, and social criteria.