Separation of Infiltration and Inflow in Sanitary Sewers

Abstract

A novel method is developed and demonstrated for identifying the dominant component of rainfall-driven infiltration and inflow (I&I) in sanitary sewers. The method uses synoptic measurements of rainfall, sewer flow rates, and water-table elevations to extract the ratio of infiltration to total I&I as a function of rainfall amount. The method is based on three quantifiable relations: the incremental flow rates resulting from rainfall events of different magnitudes, the responses of the water-table elevations to rainfall events of various magnitudes, and the responses of dry-weather flow rates to changes in water-table elevations. Application of the method is demonstrated at 10 locations in South Florida. The results show that infiltration is the dominant mechanism for small rainfall events at five of the 10 locations, and inflow is the dominant mechanism for large rainfall events at nine of the 10 locations.