Longest sewage tunnel

The longest wastewater tunnel is the Túnel Emisor Oriente (Eastern Discharge Tunnel) located in Mexico City, which was completed on 27 November 2019. The Tύnel Emisor Oriente – intended to carry a mixture of sewage and rainwater – measures 7 metres (22 ft 11.3 in) in diameter and is 62.1 km (38.58 miles) long. During periods of heavy rainfall, the tunnel is designed to handle a flow rate of 150 cubic metres per second.

Mexico City is located in a closed drainage basin with no natural water outlet. Much of the land covered by the present-day city was once wetlands or lakes, meaning that the city has a tendency to flood during periods of heavy rainfall. This has been exacerbated over the last century by the drainage of the aquifer below the city, which has caused the entire region to sink by around 12 metres.

Beginning in 1789, authorities have tried to mitigate this tendency towards flooding by constructing artificial outflows that divert water north into the Moctezuma-Pánuco river basin. At the time that work began on the Túnel Emisor Oriente (or TEO), the combined capacity of these works was 195 m3/sec. The construction of the TEO increased the maximum outflow rate to 345 m3/sec.

The tunnel was excavated by six 8.93-m diameter (29 ft 3 in) Earth-Pressure Balance tunnel boring machines, three made by Robbins (USA) and another three made by Herrenknecht (DEU). The project was technically challenging, complicated by a wide range of soil conditions that damaged equiment and slowed progress. As a consequence, the tunnel, which started in 2008 with a planned completion date in 2012, took 11 years and cost five times more than was originally planned.