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How do they turn the Chicago River green? ‘It’s a secret’

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It’s St. Patrick’s weekend in Chicago. Andrea Darlas talks with Kevin Sherlock, with the Chicago Journeymen Plumbers Local Union 130, who oversees the dying of the Chicago River and the parade Saturday morning. Sherlock talks about the record crowds they’re expecting. But he won’t divulge the biggest secret: what is in the dye that makes the river emerald green.

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Manuel Banuerlos, left, and Charbel Kuri, second from left, pose as a boat leaves a trail of lime green dye in the Chicago River behind them on March 16, 2013. (Brian Cassella / Chicago Tribune)

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