WSJ article:
https://www.wsj.com/articles/residents-of-village-near-ohio-train-derailment-begin-to-return-home-11675965939?page=1
If you are behind a paywall, here is the quote:
James Justice, an official with the U.S. EPA, said the decision to allow people to return home was based on “hundreds and hundreds of data points” showing the region’s air is safe.
“All of the readings we’ve been recording in the community have been at normal concentrations, normal backgrounds, which you find in almost any community,” he said.
An official with the state EPA said that some chemicals had reached local waterways and were immediately toxic to fish. He said that local drinking water hadn’t been affected, and that there would be ongoing monitoring, including along the Ohio River, which provides drinking water to many communities downriver.