Calibrating a Sanitary Sewer System for Low and High flows

Sanitary sewer normal flow is usually estimated using domestic average daily flows estimated from per capita consumption (McGhee 1991). This research work was conducted for the sanitary sewer system of the Town of Highland, Indiana. The sanitary and storm sewer systems were separated in 1980s. Sanitary sewer discharge from this town is delivered to a nearby town called Hammond, which operates the waste water treatment plant through two outlets. For this study 5th Street basin, which contributes 60% of the load, was considered. Normal loads are usually handled comfortably by this system. But during high rainfall events, the sanitary sewer flow to Hammond is regulated due to capacity constraints. The Town of Highland initiated a modeling process to plan and design suitable alternatives to avoid this issue. Using USEPA SWMM modeling software version 5, the Town of Highland sewer system was modeled in this study. Using Tiger Census data, the population statistics were extracted for the town. Using ARC GIS software, the land use and soil details were extracted and used in this modeling. The whole system was subdivided into 15 subwatersheds. At all 15 subwatershed outlets, flow meters were installed and observations were made by covering low and high flow events. Using EPA-recommended daily typical variations in daily usage (Das 2011), initial low flow calibration was performed. High flow calibration was conducted by fine-tuning the infiltration parameters.