Thames Tideway Scheme  The Thames Tideway Tunnel will be a tunnel running mostly under the tidal section of the River Thames through central London to capture, store and convey almost all the raw sewage and rainwater that currently overflows into the river. Bazalgette Tunnel Limited (BTL) is the licensed 'Infrastructure Provider' set up to finance, build, maintain and operate the Thames Tideway Tunnel. BTL is a consortium of investors that comprises Allianz, Amber Infrastructure, Dalmore Capital and DIF. From the licence award, BTL trades and is known to the public as 'Tideway'. On 3 November 2015, BTL received its operating licence from Ofwat, ensuring the start of the project. Started in 2016, construction of the Thames Tideway Tunnel aimed to take seven to eight years with all work completed by 2024. Once constructed, the main tunnel will have an internal diameter of and will run from at Acton in the west of London for over under central London finally reaching at Abbey Mills in the east. It will connect 34 of the most polluting combined sewer overflows (CSOs), via transfer tunnels, and was expected to reduce the number of overflow events to a maximum of four per CSO per year at time of commissioning, although increasing gradually due to effects of climate change and population growth. The tunnel will transfer the captured sewage to the Stratford to East Ham part for onward delivery to Beckton Sewage Treatment Works for treatment. The recycled clean water will then be released into the River Thames. The estimated capital cost – excluding unknown financing costs and ongoing operations and maintenance costs – is £3.8bn to complete, with an additional £1.1bn for preparatory works. Built between 1859 and 1865, Sir Joseph Bazalgette's original London sewerage system was designed to capture both rainwater runoff and the sewage produced by four million people. As a failsafe, to prevent sewage backing up and flooding people's homes, Bazalgette's system had the ability to overflow into the Thames via 57 combined sewer overflows (CSO) along the banks of the river. By 2012, the population of Greater London had grown to an estimated eight million and Thames Water said that the current system lacked the necessary capacity. Bazalgette's original system did not serve all the population, since as London continued to grow in the 19th- and 20th- centuries, outer suburbs were provided with separate sewerage and rainwater infrastructure. Overflows became increasingly common and by the beginning of the 21st-century occurred on average 50 times a year.