LOCAL COLOR/A city’s draining project

As businesses and residents moved out of Philadelphia over the past few decades, they left behind more than 700 acres of vacant lots that fed blighted conditions in city neighborhoods. Recently, many of those lots have received makeovers, changing them from litter-strewn black holes to green oases that are improving real estate values for adjacent properties, as well as helping the city divert stormwater from its combined sewer system.

For the past 30 years, the Philadelphia-based Pennsylvania Horticultural Society’s (PHS) Philadelphia Green program has been working with neighborhood groups to create community gardens, revitalize parks and spruce up public spaces with grass, flowers and trees. Despite their work, a growing number of neighborhoods began showing signs of neglect. “We were trying to improve the neighborhoods, but as more buildings were coming down, more and more vacant lots were becoming a significant problem,” says Mike Groman, senior director for Philadelphia Green. “Vacant land just facilitates the downward spiral of the city.”

So PHS started, in 1995, attacking the problem in one small neighborhood by cleaning vacant lots, planting grass and trees, building fences and organizing volunteers to maintain the open space. After seven years, conditions were steadily improving. In fact, a study by the Wharton School at the University of Pennsylvania found that property values in the neighborhood had increased by as much as 30 percent.

Success in the small neighborhood sparked similar projects across the city and eventually led to Mayor John Street’s Neighborhood Transformation Initiative that has devoted close to $9 million since 2003 to turn abandoned lots into green space. “The results that we’re finding are pretty amazing,” Groman says. “Residents say the sites look terrific. They feel like they want to stay in the neighborhood. Kids are going out to throw ball again and to play on the areas. People are getting married on these sites.”

The newly cleaned lots also attracted attention from Water Department officials who saw their potential for helping manage stormwater. Two years ago, PHS received a $200,000 grant from the state Environmental Protection Department to adapt some of the newly cleaned lots to capture stormwater more easily. By reducing the amount of runoff that enters the city’s combined sewer system, the Water Department also can reduce the number of sewer overflows that release untreated wastewater into rivers and streams. “You wouldn’t think that that much rain actually runs off of a grass lot, but in fact it does,” says Glen Abrams, urban watersheds planner for the city. “Because of the dense root structure and because the lots tend to have fairly compacted soil, the water doesn’t soak in that quickly.”

Local contractors excavated the lots and backfilled them with washed gravel to create a layer of sub-surface storage. Then, soil amendments were added to allow water to infiltrate the ground more quickly. The lots were re-graded to create berms, swales and shallow depressions that can hold shallow pools and drain within 48 hours. To finish the lots, grass and other plants that thrive in wet conditions were planted.

So far, more than 3,000 vacant lots — 10 percent of the city’s total — have been “cleaned and greened,” and five of them, totaling 86,499 square feet, are designed specifically for managing stormwater. The sites complement the Water Department’s other efforts to reduce combined sewer overflows. “In the end, we’re all holding in our heads a vision of a system of green spaces going through Philadelphia that will serve multiple purposes for open space and stormwater management,” Groman says.