Chemical and bacterial pollution of stormwater urban runoff in Stang Alar Basin

Abstract

Characterization study of urban runoff pollution was conducted in Brest (France). Traditional parameters were analyzed, T.S.S, TKN, COD, TOC,... metals, hydrocarbons and bacteria ( total coliforms and Escherichia coli ). In general, on a mass basis, heavy metals,oxygen-demanding, suspended solids and bacteria in urban stormwater are significant. Water pollution comes from urban stormwater discharges and combined sewer overflows. Chemical pollutants are mainly related to total suspended solids excepted for low concentrations. Concentrations and flow varied considerably for different storm events. Intensity of rain as well as inter-events dry periods between two successive rainfall events are the main factors for explanation of mass pollution discharge. Most of separate stormwater drainage systems fonction as combined systems because of cross sanitary sewers and it seems to be the major cause of identified coliforms in urban stormater discharges. Chemical pollution only appears during storm events but bacteria are still present for several days in the river after those events.