What’s Polluting the Air? Not Even the EPA Can Say.

For decades, a factory on the outskirts of Portland, Oregon, has churned out hulking metal parts for Boeing’s commercial airplanes. Despite the steady pulse of its machinery, the plant maintains a low profile; Oregonians more readily associate Boeing with its historic headquarters up north in Seattle. Perhaps, I reasoned last spring, this helped explain why no one had noticed that the company’s satellite campus seemed to have unleashed an environmental catastrophe.

In 2016, Boeing reported to the Environmental Protection Agency that it had massively ramped up the amount of chromium...