D.C. Mayor Vincent C. Gray (D) joined several council members on Tuesday morning to unveil the city’s new 20-year vision for creating an environmentally-friendly city, including 20-year goals to slash emissions and fossil fuel usage, plant new trees, clean up the Potomac and Anacostia rivers, and capture three-fourths of rainwater for reuse locally.

 Undoubtedly, plenty of skeptics will scrutinize the plan for being too pie-in-the-sky, unrealistic, and offering few specifics on how to fund what could be billions of dollars in future investments.

But, it turns out, some key components of the plan are well underway.

Four "gardening activists" work in D.C. (Sarah L. Voisin/THE WASHINGTON POST)

 Now, one major developer hopes to take the art of creating usable, green roofs to the next level.

 Sean C. Cahill, a vice president of Property Group Partners, has been in discussions with city planning officials about constructing entire mini-farms on the roofs of several buildings planned for the air rights above part of Interstate 395 near Mount Vernon Triangle. Called Capitol Crossing, Property Group Partners is in the final stages of winning approval to build a deck over the highway and then construct “five or six” buildings as high as 12-stories.

 Cahill said he hopes the roofs of the 2.2 million-square-foot project can be used as urban farms to supply fresh food to restaurants that operate below.

 To pull off the concept, Cahill said developers are working on ways to create a thick dirt bed that would be capable of supporting herbs and other vegetables.

 “Most green roofs are 3 or 4 inches deep, thick,” Cahill said. “To do an intensive roof, deeper plants, you need a thicker soil base…The idea is we would try to do that up on the buildings and create areas where stuff could be planted.”

 Cahill said the concept could be a strong selling point for restaurants that are increasingly looking to offer the freshest products.  He noted Founding Farmers has become one of the city’s most popular restaurants by offering “farm-to-table” meals.

In the winter, Cahill added, the preliminary plans for the project call for the inclusion of green houses to extend the growing season.

 “Anything they could harvest, we would be up for allowing to take place,” Cahill said.

 In an interview Monday, District Planning Director Harriet Tregoning cited the Capitol Crossing Project as a potential model for future growth in the city.

 “We got 30 acres of vegetative roofs in D.C. already,” Tregoning said. “Lets rethink this idea of the green roof and create the kind of environment where we can produce that.”

 Earlier this month, The New York Times reported on the proliferation of community and commercial gardens on rooftops in that city.  Christophe Tulou, director of the D.C. Department of the Environment, is also touting the success Berlin Germany has had in creating a network of community gardens in raised  beds.

 “We could have acres of land on top of buildings,” Tulou said.

As it relates to the Capitol Crossing project, planners may have to address concerns about whether pollution from thousands of cars traveling under the buildings each day could somehow diminish the quality of the produce grown on the roof.

But Cahill said the growing season would not be impacted.

“You are 130 feet up in the air,” Cahill said. “It’s no different than the victory gardens that are all over town. They would have higher levels of pollution than being that far up in the air.”

Cahill said he hopes to start construction of the deck over I-395 later next year.  The Washington Business Journal reported the first phase of the project could be completed in 2015.

Within two decades, according to Gray’s sustainability plan, the city envisions 25 percent of all food consumed in the District will be grown within a 100-mile radius.