Public housing authorities across the country have refused to find and remove radioactive gas from inside tenants’ homes, leaving children, senior citizens and other vulnerable people unnecessarily exposed, an investigation by The Oregonian/OregonLive found.

And the U.S. Department of Housing and Urban Development let them, shirking a 30-year-old legal mandate from Congress to fix the problem.

The news organization’s reporting on cancer-causing radon included contacts with 64 large public housing authorities, including records requests for test records that produced thousands of pages of documents. The Oregonian/OregonLive also worked with other Advance Local affiliates to test for radon in public housing, readily finding radon in buildings housing authorities failed to check out. Localized versions of the story ran in four other publications, from Denver to Portland, Maine.