Philadelphia officials had been hoping for a big announcement in time for Earth Day - the one that would say their 25-year, $2 billion plan for managing stormwater using trees, rain gardens, and other such "green infrastructure" had been approved.

They didn't get it. But on Thursday, visiting U.S. Environmental Protection Agency Administrator Lisa P. Jackson was plenty positive.

"It's a wonderful concept and a wonderful plan, so I am looking forward to a day in the near future when we can move forward on that approval," Jackson said at a tree-planting and ceremony in the courtyard of Kensington High School for the Creative and Performing Arts.

She met with Mayor Nutter and Water Commissioner Howard Neukrug several weeks ago to discuss the plan, proposed in 2009. It also needs state approval.

"It inspired me so much that when my staff said, 'What would you like to do for Earth Day?', I said I wanted to do a green infrastructure event, and I want to go to Philadelphia," Jackson said.

Traditional stormwater plans involve piping water away from where it falls as quickly as possible, and then treating it to remove contaminants.

In Philadelphia, as in some other cities with aging pipes, the system is frequently overwhelmed, and water that contains pollution from streets, and even raw sewage, overflows untreated into streams.

Some cities are spending billions of dollars on huge underground tunnels to collect and store stormwater until it can be treated and released. Philadelphia's plan calls for returning "as close as possible to the way nature intended the water cycle to be," said Neukrug.

The Kensington school and a broader effort on neighboring properties - the Big Green Block Initiative - is typical of what could happen throughout the city, he said.

It incorporates "tree trenches" and "rain gardens" to stall the water long enough to let it be absorbed into the ground. Porous pavement and retention basins do the same thing on a bigger scale.

Herbs and wildflowers are planted atop the school on green roofs that absorb stormwater and cool the building in the summer. Rainwater also is collected in a cistern and reused to flush toilets.

The school opened last fall, but finishing touches are still being added. On Thursday, workers were installing raised beds for a vegetable garden the students will tend.

The building has achieved a platinum rating - the highest - of the Leadership in Energy and Environment Design (LEED), a program of the U.S. Green Building Council.

Neukrug praised the project as incorporating "almost every possible technique you could for water. It's transformed. It's just what this program is all about." The building was designed by SMP-SRK Architects.