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.

The new rule largely exempts coal plants that will retire or switch to burning natural gas by 2028. Coal plants are responsible for as much as 30% of all toxic water pollution from all industries in the U.S. The revised rule is expected to affect 75 out of 914 coal power plants nationwide, compared to more than 100 plants affected by the 2015 rule. Thats in part because coal power usage has dropped dramatically over the past decade and many plants have been shuttered. The other stream is water used to wash coal ash out of the bottom of power plant furnaces.