By James R. Elliott and Scott Frickel

Philadelphia's hip Northern Liberties community is an old working-class neighborhood that has become a model of trendy urban-chic redevelopment. Crowded with renovated row houses, bistros and boutique shops, the area is knit together by a pedestrian mall and a 2-acre community garden, park and playground space called Liberty Lands.

First-time visitors are unlikely to realize they're standing atop a reclaimed Superfund site once occupied by Burk Brothers Tannery, a large plant that employed hundreds of workers between 1855 and 1962. And even longtime residents may not know that the 1.5 square miles of densely settled land around the park contains the highest density of former manufacturing sites in Philadelphia.