Trickle-Down Effect

A new program greens Chicago’s alleyways

By David Sokol

Chicago is often hailed as the most eco city in America. From its green roofs to its pristine parks, many argue that Chicago is the country’s true “emerald city.” But one aspect isn’t so pretty—its alleys, which often flood when it rains.

Located behind buildings and away from the streets, the majority of Chicago’s 3,500 acres of alleyways aren’t connected to sewers, meaning that rain tends to flood basements rather than gutters. Beginning in 2005, the city began researching how it could drain as many as 30 problem alleys each year without emptying into sewers, which already flow into the Chicago River nearly every time it rains, polluting the water with waste.

“There’s a reason our river is not considered swimmable,” Janet Attarian, a project director for the Chicago Department of Transportation’s streetscape and sustainable design program, says of the sludge and attendant E. coli that then flows into the Mississippi River.

As an alternative to burdening the sewer system with even more wastewater, the city is starting a program to green its alleys and minimize the yuck. In many ways, the Green Alleys Program (GAP), administered by the city’s department of transportation, mimics the benefits of Chicago’s much-acclaimed green roofs, which retain stormwater and prevent it from flowing through the sewers. As alleyways are repaired and remade into green alleys over the coming decades, organizers predict that this large network of spaces will allow rain to trickle into the earth rather than flood basements and sewers.

Accomplishing GAP’s goal meant finding an environmentally friendly yet absorbent material. Attarian would have substituted impermeable pavement for a penetrable road surface, but the Midwest had no such material. Lake Michigan sand, for example, doesn’t behave like sand used in permeable materials that are mixed in other states, and it would be prohibitively expensive to truck these components in.

GAP also faced a shortage of the synthetic fibers used to make permeable asphalt. The fibers are usually in short supply, and most of the stuff has been channeled into runways for O’Hare Airport’s ongoing modernization project. With no feasible solution at hand, GAP team members sought to create their own. One year and $175,000 later, GAP unveiled locally manufactured, permeable asphalt using ground, recycled tire rubber for fibers and concrete.

“That’s the part we’re most excited about,” says Attarian. “Now that we have a mix, and have gotten plants to produce them, the goal now is to get the market up and running.” Folks can simply call Attarian for the formula to make the asphalt. The department of transportation encourages private developers in particular to create permeable parking lots as a more affordable and eco-friendly alternative to installing underground water-storage tanks.

And like green roofs, which help reduce elevated temperatures in the city and insulate buildings, green alleys have multiple benefits. Neighbors have found that permeable alleys don’t produce dangerous black ice. In alleys that cannot be covered with a permeable surface—like where there’s hard-packed clay underneath, or where basements are too close to the moisture—GAP specifies a less permeable surface with a high albedo, or ability to reflect sunlight rather than absorb it. David Leopold, the project manager for GAP, measured a 23-degree temperature drop in the high-albedo alleys, which helps keep the city cool.

Perhaps most importantly, city officials estimate that green alleys are soaking up approximately 80 percent of storm runoff from adjacent properties. “The program has a more immediate local benefit in preventing basement backup,” says Pete Mulvaney, the assistant commissioner for Chicago’s Department of Water Management.

GAP is still testing its first six trial alleys, which are located throughout Chicago, but Leopold says that the city is going ahead with 28 more green alleys this year. “The response from aldermen and communities is really positive,” he says.

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