Wearing blue hard hats, white hazmat suits and respirator masks, workers carted away bags of debris on a recent morning from a sprawling and now-defunct oil refinery once operated by Philadelphia Energy Solutions (PES).

Other laborers ripped asbestos from the guts of an old boiler house, part of a massive demolition and redevelopment of the plant, which closed in 2019 after a series of explosions at the facility.

Plans call for the nearly 1,400-acre site to be transformed into a new commercial hub with warehousing and offices. All it will take is a decade, hundreds of millions of dollars, and confronting 150 years’ worth of industrial pollution, including buried rail cars and a poisonous stew of waste fuels poured onto the ground. A U.S. refinery cleanup of this size and scope has no known precedent, remediation experts said.