Assessing the impact of infiltration and exfiltration in sewer systems using performance indicators: case studies of the APUSS project

The structural quality and functional efficiency of sewer systems are key parameters to guarantee the transfer of domestic, commercial and industrial wastewater to treatment plants without infiltration nor exfiltration. Infiltration of groundwater is particularly detrimental to treatment plant efficiency, while exfiltration of wastewater can lead to groundwater contamination. The APUSS project associating universities, SMEs and municipalities in 7 European countries, developed new methods and techniques to assess and quantify infiltration and exfiltration (I/E) in sewer systems. This paper describes the establishment of a set of performance indicators (PI) developed to assess the impact of I/E on sewer systems and their application to three project case studies, in Italy and France, focusing on sewer systems characteristics, I/E measurements campaigns and PI application results. The methodology for PI definition consists in the selection and development of a sewer network property or state variable, which is expressive of aspects being scrutinized (I/E); the PI values are then calculated; finally, a classification of the PI values is made in relation to good or bad performance. The use of PI allows a standardized and objective comparison of the performance of sewer systems and constitutes a means to technically support the establishment of priorities for rehabilitation and/or construction investments taking into account I/E impacts.