Studies have found the projects help. In Milwaukee and Grand Rapids, Mich., for instance, green infrastructure reduced runoff by up to 3 percent in neighborhoods where public and private construction work included runoff-absorbing methods.

In Chicago, city and regional leaders say the problem starts with sewers built more than a century ago. Not only do some of them leak, the pipes were designed to combine waste from homes and factories with storm runoff. When the area is hit with heavy rains, the pipes quickly fill to capacity and a fetid mix of sewage and runoff is either forced back into basements or spilled into local waterways.

More intense storms, like the one in April when rain fell for several consecutive days, can force officials to open locks and gates to Lake Michigan.

The water reclamation district contends that Chicago and suburban Cook County will finally start seeing relief when a Deep Tunnel reservoir in south suburban Thornton is completed in 2015 and another in McCook is partially completed in 2017. The McCook reservoir won't be fully operational until 2029.

The two converted quarries will hold 18 billion gallons collected from 130 miles of tunnels, 9 to 35 feet in diameter, that are connected to smaller neighborhood sewers. Once a storm passes, the wastewater will be pumped back to sewage plants for treatment.

After years of delays, a pending legal settlement with federal and state authorities would impose court-enforced deadlines to finish the sprawling plumbing system. The deal also would require the district to start investing in green infrastructure projects that, over time, would divert at least 10 million gallons per storm, according to the U.S. Environmental Protection Agency.

Environmental groups that sued for changes contend the proposed deal doesn't go far enough. The Deep Tunnel service area encompasses 350 square miles, but the completed green projects would capture the equivalent of a half-inch of rain on just one square mile.

Meanwhile, some officials with the water district are starting to agree with other experts that the Deep Tunnel may not solve the problem even when it is finished. Officials fear that a system designed in the 1960s and '70s won't be able to handle a projected increase in big storms where rain falls hard and fast.

"It's hard to handle that amount of water," said David St. Pierre, the district's executive director. "Regardless of what (Deep Tunnel) is doing, it won't necessarily mitigate basement backups. If we don't get a cultural change about how we look at water, we aren't going to solve this problem."

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