When an American Airlines jetliner caught fire on an O’Hare Airport runway in October 2016, firefighters rushed to the scene. Within three minutes, they’d blanketed the flames with a suffocating foam, a product used at airports for half a century. Known as AFFF, it has been used by Chicago and military firefighters because it can extinguish intense jet fuel fires.

The foam, now being phased out, also contains toxic substances known as forever chemicals that have been linked to cancers, liver damage, low birth weights, high cholesterol and other health threats.

Those chemicals contaminated groundwater beneath city of Chicago-run O’Hare and Midway airports, military investigators have found. As part of a U.S. Defense Department-initiated cleanup nationwide, another round of testing is planned as soon as next year. The department estimates that national cleanup costs will come to $39 billion.

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