Sprawling over a manicured suburban landscape in Portsmouth, N.H., the Pease International Tradeport office park encompasses 250 companies, a golf course and a pair of day care centers. Nearly 10,000 people arrive here for work every day. But belowground lies a toxic legacy. Until 1988, the site was a U.S. Air Force base, where fire crews, during routine training exercises, would torch old planes in a field, then douse the flames with chemical foam. At the time, it did not seem to matter that the foam sank into the soil. But it contaminated groundwater Pease workers and their children have been drinking for decades.