New York City set a target to improve harbor water quality by reducing the amount of sewage that goes into it by 10 percent or 1.5 billion gallons by 2030, the New York State Department of Environmental Conservation announced Tuesday.

"It is good news all around," Joe Martens, DEC commissioner, said. "It's a huge win for New York's waterways, a huge win for New York City's real estate and I think it's a win for all New York City residents."

Rainwater drains into sewers, sometimes causing them to overflow and overload the city's 14 treatment plants, which must release the rain and untreated sewage into the harbor. This is a common problem in the nation's older cities that receive a significant amount of rainfall.

The new enforcement order mandates an investment of $2.4 billion of combined public and private funds to upgrade the city's water infrastructure with trees, gardens, new runoff tunnels, porous sidewalks and underground reservoirs. These will trap water and dampen sewer flooding while using it to grow plants that improve air quality. Of the total amount, $1.5 billion are public funds. In the next three years, $187 million will be spent.

"Our goal is to capture the first inch of rain on 10 percent of all of the city's impervious surfaces," said Carter Strickland Jr., the city's environmental protection commissioner, adding that the combined benefits "will add $400 million to the city's value every year."

The commissioners said they would be flexible with the process, developing and adjusting new ideas on the fly and staying open to what could be classified as an eligible green infrastructure project.

Environmental groups such as the U.S. Green Building Council of New York praised the plan, with the council's executive director Russell Unger calling it a "smarter approach to stormwater management" that will "make New York a better place to live."

The Brooklyn Navy Yards building where the decision was announced will be one of the first places to be transformed. Currently, it has a flat, silvery roof scuffed with dirty footprints. But in two months' time, Ben Flanner, a green rooftop developer, said that the roof would be transformed into a garden that would be able to capture 1 million gallons of water per year and produce vegetables.

"I can't wait to get my hands dirty," Flanner said.

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