The city of Philadelphia has finally won the federal Environmental Protection Agency's backing for its green stormwater-management plan.

The city's "Green City, Clean Waters" initiative was submitted to the EPA for approval back in 2009. It dedicates nearly $2 billion over the next 25 years to significantly reduce combined-sewer overflows through "green infrastructure" -- by increasing parks and open spaces, installing green roofs and rain gardens, and using porous pavement instead of just adding new pipes and treatment facilities.

"Our plan uses green technologies on top of Philadelphia's gray infrastructure to capture rainwater before it enters the city's 3,000-mile sewer network," Philadelphia Mayor Michael Nutter said Tuesday before signing the partnership agreement with the EPA. "We will transform a third of our paved surfaces like streets, parking lots and sidewalks with green areas."

Project partners at the Natural Resources Defense Council see the agreement as nationally significant because it provides upper-level support for the most comprehensive green infrastructure plan in America.

EPA administrator Lisa Jackson said she hopes Philadelphia can serve as a nationwide model.

"We want to see the benefits of green infrastructure taking hold in other large metropolitan areas, not just Philadelphia," Jackson said at the signing.

The EPA will help the city monitor water quality in surrounding rivers to measure the effectiveness of the new initiatives.

The green infrastructure plan must meet requirements for combined-sewer system improvements mandated by updates to the Clean Water Act more than a decade ago.

The city and EPA will sign a more formal consent decree in the upcoming months to finalize the plan.