Atkins and Arup have won roles on London’s £4bn super sewer.
The pair, working as a joint venture, were appointed as a consultant to the team delivering the western section of the Thames Tideway Tunnel.
The project is designed to ensure the capital’s waste water system is fit to support its projected population for the next 100 years.
Bam Nuttall, Morgan Sindall and Balfour Beatty (BMB) was last summer awarded the £416M main contract for the 6km stretch of the sewer from Acton to Wandsworth.
Atkins chief executive Nick Roberts said: “The Thames Tideway Tunnel will help transform the river and we are very pleased that BMB chose the valuable experience, expertise and approach we’ve developed with Arup from projects such as Crossrail.
“We look forward to playing our part in promoting a positive change in the relationship that Londoners and visitors have with the Thames.”
Arup UK chairman Alan Belfield added: “We have already made great strides in creating a cleaner and safer River Thames but there is a clear need to modernise our essential infrastructure.
“Partnerships such as ours with Atkins will play a pivotal role in driving forward these major feats of engineering and we look forward to working together on this unique project to see the benefits it will provide to the city.”
Mobilisation work for the western section begun in September 2015 with completion scheduled for 2022.