<P> 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 has the ability to overflow into the Thames via 57 combined sewer overflows (CSO) along the banks of the river . </P> <P> 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 does not serve all of these eight million people, as areas in outer London, built later, were provided with separate sewerage and rainwater infrastructure . Overflows have become increasingly common and now occur on average 50 times a year . These discharges, of combined raw sewage and rainwater, need to be reduced to comply with the EU's Waste Water Treatment Directive (UWWTD) and to improve the ecology of the river . An estimated total of some 39,000,000 m (3.9 × 10 l), or 39 million tonnes, of storm sewage enters the river in a typical year . </P> <P> Instigated in 2001, the Thames Tideway Strategic Study, conducted by a group comprising Thames Water, the Environment Agency, DEFRA and the Greater London Authority, was intended to assess the impact of the CSO discharges into the Thames and to identify objectives and propose potential solutions, while keeping costs and benefits in mind . </P> <P> After four years, the Thames Tideway Strategic Study report was published in 2005, and outlined the following objectives: </P>

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