The “Desarrollo Sustentable de la Cuenca Matanza-Riachuelo - Lot 3” project includes a gravity outfall system to discharge treated wastewater into the River Plate, in Buenos Aires (Argentina). It consists of: 50 m deep upstream shafts; 10.5 km long sub-fluvial outfall tunnel; 1.5 km long diffuser tapered tunnel; 34 risers to discharge the effluent from the diffuser tunnel up to the river bed diffuser heads. An innovative method has been developed, as know the “Riser Concept”, to install vertical risers by jacking pipe segments from inside the tunnel upward to the river bed and through soil formations. The Riser Concept is a bottom-up system to install vertical risers, by thrusting pipe segments using a jacking equipment, upward from inside an outfall tunnel, through soil materials in under water conditions and up to breakthrough into a waterbody. The Riachuelo project is a worldwide satisfaction, cleaning up the Rio de la Plata, one of the most polluted rivers in the world. It also allowed treatment and safe disposal of sewage effluents, improving the flexibility and quality of Riachuelo Sewage System. It improved the service for more than 4,3Million inhabitants, incorporating new 1,5 Million inhabitants into the sewer network. The project could also provide social benefits in terms of public health and safety, environmental sustainability, social development and responsibility, and jobs for the public.