Diffuse pollution loading from urban stormwater runoff in Daejeon city, Korea

In this paper, stormwater runoff from an urban watershed with combined sewer systems located in Daejeon metropolitan city, Korea, was characterized to measure the stormwater runoff discharge rates and pollutant concentrations. The observed averaged event mean concentrations (EMCs) of combined sewer overflows (CSO) were 536.1 mg TSS/L, 467.7 mg TCODcr/L, 142.7 mg TBOD/L, 16.5 mg TN/L, and 13.5 mg TP/L. A detention basin was proposed to reduce CSO, and its essential design elements were discussed. The first flush significantly affected contaminant constituents in the descending order of suspended solid>organics>nutrients. Storage volumes for containing the first flush to improve water quality of the receiving stream can be estimated based on the total suspended solid loading. In this study, detention of the first flush equivalent to 5 mm of precipitation could reduce CSO-induced diffuse pollution loading to a receiving water body by up to 80% of the total suspended solid loading.