London’s super sewer to handle CSOs

Thames Water, the United Kingdom’s largest water and wastewater services agency, appointed CH2M HILL as program manager for the Thames Tideway Tunnel to help deliver what’s being called the "super-sewer," which is expected to prevent combined sewer overflows (CSOs) in London from entering the River Thames. The project involves construction of London’s deepest-ever tunnel—the Thames Tunnel—as deep as 260 feet beneath ground level and spanning about 20 miles beneath the River Thames from Hammersmith in West London, to Beckton, in East London. An additional tunnel—the 4.3-mile-long Lee Tunnel—will run from Abbey Mills in Stratford to Beckton.

The tunnels will capture and transfer wastewater discharges for treatment, which would otherwise enter the River Thames and its tributaries during heavy rainfalls. London has a combined sewer system, built during the Victorian era, to carry both stormwater and wastewater. Overflow points were constructed along the river banks as part of the system to prevent flooding during heavy rainfall by directing sewage into the River Thames and its tributaries.

"The Tideway Tunnel scheme is Thames Water’s biggest single investment project by far," said Steve Walker, major projects director for Thames Water. "These exceptional tunnels will have enough capacity to store millions of litres of diluted sewage and transfer it to our Beckton sewage treatment works. This scheme is essential if we are to improve the quality of the river and reduce the environmental impact of sewage overflows."

Both tunnels will be more than 23 feet wide, running beneath a vast network of existing tunnels, including six Tube (subway) lines and utilities. The overall program includes constructing numerous collection and diversion facilities; a large, high-head underground pumping station; and a major upgrade at Beckton sewage treatment works.

The Thames Tideway Tunnel project was approved by the U.K. government in March 2007. Construction of the Lee Tunnel, which will capture half of all Thames’ Tideway discharges from a single overflow point at Abbey Mills pumping station, is expected to start in 2009, once regulatory and planning approvals are obtained. The tunnel is expected to be completed by 2014. Construction of the Thames Tunnel, which will prevent discharges from 35 overflow points along the Thames Tideway, is not expected to start until 2012, with completion in 2020.

As program manager, CH2M HILL will help Thames Water implement the Tideway Tunnel Program through all phases, including planning consents, preliminary and final design, construction oversight, stakeholder communication, commissioning, and start-up of new facilities. The firm has been working in the United Kingdom for more than 17 years and has 255 professionals in seven offices throughout the country.

CH2M HILL has managed similar projects in Singapore, where the firm provided program management for one of the world’s largest wastewater reclamation projects; and in Milwaukee for the first successful, city-wide deep-tunnel CSO system implemented in the United States. The Milwaukee tunnel system has reduced CSO events from more than 60 per year to an average of two per year, enhancing the water quality in Lake Michigan.