Quantifying Rainfall-Derived Inflow from Private Foundation Drains in Sanitary Sewers: Case Study in London, Ontario, Canada

Abstract

Rainfall-derived infiltration and inflow (RDII) is a major issue causing surcharge flows in many municipal sanitary sewer systems. This paper demonstrates a statistical method for characterizing the rainfall-derived inflow (RDI) originating from residential foundation drains (also referred to as weeping tiles), as well as the importance of having site-specific data. The results differentiating the contribution of RDI from residential weeping tiles (WT) to total RDII are demonstrated for a case study site in a residential subdivision in London, Ontario, Canada. This research used statistical linear regression analyses with bootstrapping methods to quantify the RDI and its flow duration. It was found that the RDI from WT contributed up to 85% of the total RDII in the sanitary sewer. By disconnecting WT at this site, the RDI generated as a result of rainfall events was reduced by a minimum of 78% in volume and 32% in flow duration. Thus, this paper presents a novel method to quantify RDI and its duration from statistical perspectives, which provides better supporting evidence and guidance for RDI projects.