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Many large-diameter brick sewers were built in central Calcutta (now Kolkata), India during the 1870s. However, over the past century they have deteriorated due to age, changed land-use patterns, lack of adequate maintenance and failure of limited past measures to upgrade them. In 2007, the Kolkata Municipal Corporation embarked on a major project of refurbishing the most critical stretches of these man-entry brick sewers with an estimated initial cost of £70 million. The first phase of this work is due for completion in 2014. A cost-benefit analysis shows an economic internal rate of return of over 15%, amply justifying the investment towards sustainable renewal of an indispensable infrastructure component. [ABSTRACT FROM AUTHOR]