DEP goes from gray to green

The city Department of Environmental Protection plans to unveil a $130 million water-holding tank today in Queens. The facility is less important than what DEP hopes it will represent: a thing of the past.

The tank will catch water that floods the sewer system during storms. When 3.5 inches of rain fell in Central Park last week, the city's 14 wastewater plants treated 8.5 billion gallons of water during the five-day period. But 1.9 billion gallons of rain and raw sewage were dumped into city waterways.

Controlling sewer overflows is DEP's largest water-quality challenge. Overflows are a major source of water pollution and must be limited, in order to comply with the federal Clean Water Act.

Until now, the solution has been to build costly tanks to catch overflows. On May 12, for example, the department opened a $404 million facility in Brooklyn to prevent up to 50 million gallons of overflow from entering Jamaica Bay during storms. Because of environmental and land-use concerns, the Paerdegat Basin facility took 17 years to build.

The DEP wants to change course. The agency now plans to build so-called gray-water infrastructure only when “cost-effective and more efficient than green infrastructure,” a spokesman said. The department's green infrastructure plan, released last fall, would make the city more water-absorbent.

Yesterday, DEP Commissioner Cas Holloway and Deputy Mayor Stephen Goldsmith posed for photographs on the roof of 1 Union Square East, which was teeming with plant life. The 14,000-square-foot, $330,000 green roof, planted last year, can absorb about 250,000 gallons of rainwater at any one time. That water would otherwise go into the sewer system. The building's unit owners offset $63,000 of the cost with a city tax credit of $4.50 per square foot.

The idea, said Goldsmith, is to “unlock the value of city assets.” A green roof doesn't just soak up rainwater, but also filters it, so the city doesn't have to. “Green infrastructure costs less,” he said. “It allows aesthetics instead of ugly pipes. It reduces costs to ratepayers by a couple billion dollars.”