LONDON — Nov. 5, 2015 — London’s planned “super sewer” could bring environmental benefits worth almost £13 billion ($19.7 billion), according to U.K. Environment Minister Rory Stewart in a press release.

The Thames Tideway Tunnel will update the capital’s 150-year-old sewerage system which is now operating close to capacity, resulting in sewage overflowing into the River Thames on average once a week, noted the release.

Despite recent upgrades to the main sewage treatment works for London, and the Lee Tunnel opening by 2016, an estimated 18 million tons of untreated wastewater will still flow into the river in a typical year.

Figures show that the whole life cost of the new 25 km tunnel will amount to approximately £4.1 billion ($6.2 billion) but it will deliver a two- or threefold return, stated the release. Whole-life benefits are estimated at between £7.4 billion ($11.2 billion) and £12.7 billion ($19.2 billion).

Commenting on the new estimates, Stewart said in the release: “London is one of the most dynamic cities in the world and it is vital we have a river that is not filled with sewage every time there is heavy rainfall.

“This new research reveals the tunnel will bring up to £13 billion worth of benefits to the capital’s natural environment. It will prevent millions of tonnes of sewage flowing into the river every year and it will mean we will have cleaner water for all to enjoy and improved water quality to better protect the Thames’ precious marine wildlife.”

Construction of the tunnel is planned to begin next summer, reported the release.

You can find the entire release here.