Stormwater ingress threatens urban health

Abstract

STORMWATER INGRESS Infiltration of stormwater and groundwater (known as extraneous flow) into sewerage systems is not a new phenomenon. In fact, it is a problem for municipalities worldwide. Systems are usually designed to handle some of this ingress (a norm of 15% of the dry weather flow allowance for extraneous flows is the generally acceptable standard). However, excessive flows can have detrimental effects on a sewerage system. Research, undertaken by the Water Systems Research Group of the University of the Witwatersrand and captured in the new WRC report, has found that extraneous flow can reduce the originally designed capacity of a sewage collection system and negatively affect operation of the entire waterborne sanitation system, including the wastewater treatment component. This increases the potential of higher pollution loads leaving the wastewater treatment plant and disposing partially treated sewage into rivers, increasing the risk for waterborne diseases such as cholera.

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