The operation presented constitutes the second phase of a global project to transfer effluent from the mahogany treatment plant (STEP) near the Galléria — Autos GM motorway and commercial area to the Gaigneron STEP, located near the Place d’Armes subdivision and the eponymous industrial and commercial zone. This second phase of the project consists of the construction of 3 new outposts (PRs) in Mahjou, Mahault and Petit Manoir and the rehabilitation of the second line of treatment of Gaigneron’s STEP; the latter has never been put into operation due to a sufficient volume of effluent to be treated. With the transfer of an additional 5000 EH from Mahogany, there is therefore a need to upgrade this 2nd biological treatment line. In addition to assistance with construction management, the operation requires a land acquisition for the Petit-Manoir refoulement station (estimated by the Domaines) as well as work to create a new access route to the STEP and future Macajou PR. The 4.5 km of effluent collection and transfer between the 3 PRs have already been implemented and funded under the first phase of the project.