ORIGINS AND CHARACTERISTICS OF URBAN WET WEATHER POLLUTION IN COMBINED SEWER SYSTEMS - THE EXPERIMENTAL URBAN CATCHMENT LE MARAIS IN PARIS

An experimental urban catchment has been created in the centre of Pari s, in order to obtain a description of the pollution of urban wet weat her flows at different levels of the combined sewer system, and to est imate the contribution of runoff, waste water and sewer sediments to t his pollution. Twenty-two rainfall events were studied from May to Oct ober 1996. Dry weather flow was monitored for one week. Roof, street a nd yard runoff, total flow at the catchment outlet and waste water wer e analysed for SS, VSS, COD and BOD5, on both total and dissolved frac tion. Results show an evolution in the characteristics of wet weather flow from up to downstream: concentrations increase from the catchment entry to the outlet, as well as the proportion of particle-bound poll utants and the part of organic matter. A first evaluation of the diffe rent sources of pollution establishes that a major part of wet weather flow pollution originates from inside the combined sewer, probably th rough erosion of sewer sediments. (C) 1998 IAWQ, Published by Elsevier Science Ltd.