Making lemonade

A new form of storm water treatment, reported by Philly.com

Among its goals, the plan calls for the city to convert 3,200 acres of asphalt into fully pervious (that's the favored term) land by 2015. It may sound like a big number, but not when you consider that 67 percent of pre-World War II Philadelphia is covered with buildings and pavement. Rain simply rolls across all that surface to the nearest drain.

There are other ways to prevent a storm-water rush from overwhelming the sewers and polluting the Delaware River. The Water Department could construct huge underground cisterns, or catch basins, that would temporarily hold the water generated by a big storm.

But not only are such underground cisterns expensive, they need to be "the size of ball fields" to make a difference, says Howard Neukrug at the department's Office of Watersheds. Tearing up asphalt lots can be done cheaper and faster, and the new green acres have the side benefit of helping to cool the city's air temperature.

So why doesn't the Water Department start with a really big expanse of asphalt, such as the city-owned South Philly sports complex, where fields of parking spread out virtually to the horizon? A half-acre schoolyard hardly seems like an obvious choice for such a groundbreaking effort.

"We're looking at every square foot of surface area in Philadelphia and asking, 'What if?'," explains Neukrug.

That includes streets and sidewalks, too. But he argues that schoolyards are a good place to start because the greening does double duty, providing kids with shadier, healthier play areas while capturing runoff.

Actually, the Water Department is about to add another big incentive: a storm-water tax. In 2010, the agency will charge its nonresidential customers for the runoff their sites generate. The tax will be based on the amount of impervious surface, using GIS satellite technology to determine what's paved and what's green. [emphasis added]