13 L ot 3 of the Program for the Sustainable Development of the Matanza Riachuelo Basin envisages an outfall tunnel as main component of the works. With an excavation diameter of 5.20m and an inner diameter of 4.30m, the tunnel runs for its entire 12km length underneath the bed of the River Plate, at a depth of 40m and with a SW–NE horizontal orientation. The tunnel begins onshore from Dock Sud, in Buenos Aires Province, nearby the discharge point of the Riachuelo River into the River Plate. More than 70 years ago, the Argentinean Government conceived the idea of a new sewage system for the City of Buenos Aires and part of its southern metropolitan area. The project was designed for the first time in the late 80s to deliver a solution to the sanitary problems arising from the rapid demographic growth and the contemporary pollution of the Riachuelo river basin. Even though the idea dated from previous decades, it was only in 2008 that the project began to take shape. Residents of the area called Villa Inflamable – or Flammable – located in Dock Sud, The aim of this book is to put together the technical legacy that has been achieved through the execution of this magnificent engineering project, while also taking a look at tunnels and culture. Steel segments.