By Pete Stidman
News Editor

It is an unlikely place for a wetland, but in the shadows of the new Carruth condominium complex and the rising I-beam skeleton of the Ashmont T station in Peabody Square, a few water-loving plants may soon take root.

The Charles River Watershed Association has received a $25,000 grant to add hardy plants living in specially-engineered soils to the Boston Transportation Department's re-design of the square. The soil and plants would filter the runoff rushing through the square in rain, sleet and snowstorms and beautify two large plazas created by redirected traffic. The effort is unique in Boston and rare in the U.S., and it may indicate a fledgling trend for Main Street programs nationwide.

The storm water-filtering plan comes not a moment too soon. Planning has been underway for at least a year, but the presentation of the beginnings of a plan to neighbors last Wednesday came only two days before the release of an Environmental Protection Agency report on a state study of the Charles River confirming that phosphorus pollution needs to be cut by 54 percent.

Phosphorus, which is thrown into the river with storm run-off and other sources, is food for algae, including the toxic blue-green variety that causes the health department to warn swimmers out of the water.

Phosphorus is also food for plants and microbes in living soil, particularly the kind that will be used at Peabody in the storm drains. Peabody's drains feed into the Neponset, but environmental advocates conjecture it and many other similar urban watersheds across the country are filling up with the same type of pollution.

As far back as 2004, the St. Mark's Area Main Streets (SMAMS) group had defined one of its priorities as becoming a "green destination."

"A major one was the re-routing of the streets, another was to develop a green main streets district," said Dan Larner, the director of SMAMS. "There are some other Main Streets around the country that are doing that but it's fairly new. We want to show people that we're a thriving business district, but also that we're concerned about our environment."

It was the city's chief of Energy and Environment, James Hunt III, who made the connection between SMAMS and storm water, however.

"I had worked for years with the Charles River Watershed Association," said Hunt. "We were talking about ways that we can do a better storm water drainage strategy for the city, not only for building and development but also looking at public infrastructure."

As a way to demonstrate to the rest of the city's agencies that Low-Impact Development (LID) and green infrastructure can be cheap, good for the environment and low-maintenance, Hunt and CRWA started looking at street design projects already in the pipeline. They narrowed it down to three, including Peabody Square. The square's design already included pedestrian-friendly features such as two large plazas on either side of Dorchester Avenue, one in front of the Ashmont Grill and the other fronting Store 24.

That week, Hunt just happened to speak at a SMAMS meeting.

"It was in somebody's house I think," recalled Hunt. "They were asking how they could green not only Peabody Square but the whole St. Mark's area. It was kind of a meeting of the minds."

CRWA is basing their designs on elements of a "Green Street" project on SW 12th Avenue in Portland, OR. The Green Street's impetus there, in the land of continuous rain, came out of a cross-agency initiative of Portland's Bureau of Environmental Services and Office of Transportation. Maintaining and improving Portland's underground warren of big water pipes has always been a costly affair, and green streets seemed an affordable answer.

"With more development, we have more runoff going into the system," said Henry Stevens from Portland's Bureau of Environmental Services. "This technology will help us not to have to dig up the street and replace pipes."

Under Peabody Square, Boston's Water and Sewer Commission recently replaced the drain system. So the motivation here comes more from keeping the Neponset clean than lowering the water volume, said Kate Bowditch, a hydrologist at CRWA.

"The conventional urban landscape design is you build a mound of soil and mulch and put plants in it," said Bowditch. "The idea of these is you excavate them six to 12 inches and the water pours into them off streets, sidewalks and rooftops."

The soil is engineered dirt with a good amount of absorbent compost carefully selected, she said. Contractors will have to take special care not to compact the soil underneath so that some water can naturally soak back into the ground. Pipes under the organic material will also carry excess back into the Neponset.

"The soils are very microbe-active," said Bowditch. "So you have microbes absorbing and dissolving pollutants and plants taking in nutrients like phosphorous. Research shows them to be remarkably effective in cleansing water."

Trash would be cleared from the planters on a regular basis, instead of flowing into the river or clogging up catch basins in the current drainage system.

CRWA is considering recommending three features for the street. Water-permeable concrete or paving stones, tree planters that collect rainwater from the gutter and larger planting beds that do the same. Much of the design for Peabody has been completed, and according to Bowditch, the city is conservative about what can go in there.

"They've been pretty clear with us that we'll have to be pretty careful about what we recommend," said Bowditch. "It's pretty much going to look like a normal street."

Hunt said that interpretive signage aimed at passersby is part of his vision at Peabody, but this first project is aimed more at convincing city agencies that green storm water features can work to the city's advantage.

Nationally, Main Street programs may be on the road to becoming a more powerful catalyst for environmental change.

"My sense is that it's a fledgling trend &emdash;but yes, it's a trend," wrote former National Main Street director Kennedy Smith in an e-mail. "Main Street programs around the country have been instrumental in promoting pedestrianism, bike paths, etc. for a long time, but other aspects of environmentalism are just getting started. Storm water run-off and green roofs are still pretty scarce."