New Delhi, March 31 -- About 100 of the nation's most contaminated toxic waste sites are in areas prone to flooding and wildfires, a potential public health threat to millions of Americans in surrounding communities, the internal watchdog at the U.S. Environmental Protection Agency has found.

The EPA's Office of Inspector General issued two new reports last week that are part of a series assessing the weather-related vulnerabilities of the 157 federal Superfund sites prioritized for cleanup due to the serious risk they pose to public health and the environment. About 3 million Americans live within a mile of a Superfund site, while 13 million people live within 3 miles (4.8 kilometers).

Some of the Superfund sites were found to be at ri...