Infiltration and inflow (I/I) into sanitary sewers causes numerous negative effects on the whole wastewater management system and ultimately, on the receiving waters. Consequently, a number of methods have been developed to analyse the performance of sewer systems with respect to I/I, including: distributed temperature sensing (DTS), closed-circuit television (CCTV) inspections, flow and conductivity measurements, automatic or grab sampling of ammonium, smoke testing, and visual inspection of manholes. Such methods were compared in an application to sanitary sewers in a small community and assessed with respect to their accuracy and ability to identify locations of sources of I/I, as well as temporal and spatial resolutions of the obtained results. Furthermore, different approaches to ammonium sampling during I/I monitoring campaigns were discussed. It was concluded that among the methods tested in this study, DTS had the highest temporal and spatial resolution, while ammonium grab sampling showed promise for initial screening of large catchments.

Infiltration and inflow (I/I) into sewers cause negative effects on the sewer system, wastewater treatment plant and environment. Identifying the causes and locating the inflows is necessary in order to address the I/I problem. This paper focuses on using distributed temperature sensing (DTS) for identifying, locating and characterising I/I into a sewer system during the end of winter-beginning of summer transition period under dry and wet weather conditions. During snowmelt, several locations with I/I were identified, while these locations did not show I/I during storm events after the snowmelt. In addition, during a very heavy storm after the snowmelt period, I/I was found at other locations. Therefore, DTS was demonstrated to be effective in identifying the type of I/I and in locating I/I. Finally, I/I monitoring campaigns in cold climates should take into account the variety of pathways of I/I during snowmelt and during rainfall.