Effect of Infiltration and Inflow in Dry Weather on Reducing the Pollution Loading of Combined Sewer Overflows

The objective of this study was to investigate the effect of infiltration and inflow (I/I) during dry weather on reducing pollution loads to discharged areas in combined sewer overflows (CSOs). Especially, we focused on effects of I/I on CSOs in high-density urban areas and after sewer rehabilitation. A stormwater management model was used to simulate the occurrence frequency of CSOs and the reductive effect of pollution loads. SWMM simulations demonstrated that a decrease in I/I to below 5% resulted in a reduction to five events of occurrence frequency and reductions in chemical oxygen demand (COD) and suspended solids (SS) loads of 14.9 and 20.4%, respectively. We found that I/I reduction during dry weather has the effects of (1) reducing the occurrence frequency of the pollution load of CSOs, (2) increasing the capacity of collection, and (3) decreasing the concentration of pollutants. In conclusion, controls on I/I and transport capacity are significantly useful tools in reducing the pollution loads.