The “Costa do Estoril” is a large coastal zone located near the end of the Tagus estuary, that has became an urban extension, very densely populated, of the city of Lisbon.
The Costa do Estoril Wastewater System, nowadays under construction, is planned in order to free the marine waters of the beaches from any wastewater discharge. At the final phase (second stage) that system is prepared to serve more than one million inhabitants, from a tributary area of 22 000 ha, and consists, principally, of a large circular interceptor, a preliminary treatment plant and a long sea outfall with submerged multiport diffusere.
In this paper some important aspects concerning the geographical peculiarities of the region, the hydrodynamics of the marine environment near the coast and the general layout of the system are outlined. Special emphasis is given to the particular conditions that ruled out the sewerage facilities design, and to the characterization of the sanitary and hydraulic design of the long sea outfall.