Upon the filling of the Seine Centre sewage plant in May 1998, the SIAAP commissioned its first wastewater treatment plant adapted for handling part of the large amounts of rain period surplus water: its flow rate ranges from 2.8 m3/s during dry weather to 12 m3/s in wet weather conditions. Four operational configurations for treating 240,000 m3/day during dry weather, with different quality objectives, and three configurations for treating the rain period surplus water were designed. Immediately upon filling of the plant, however, the operators had to devise innovative configurations for meeting new discharge standards. This paper will aim at demonstrating (considering a major achievement the various aspects of which will be explained) the SIAAP's will to conform in real time, through a dynamic management of its facilities, to the variation of the priorities in the environmental demands, while preserving the quality of the adjacent owners' immediate environment.