After a 2014 chemical spill polluted drinking water for more than 300,000 people in West Virginia, lawmakers there quickly mandated tighter surveillance of the state's chemical storage tanks. It revealed dozens of tanks that shouldn't have been in service still posed a potential threat to drinking water for more than 134,000 people downstream.
Some were corroded and a few were filled with hazardous chemicals.
But under pressure from industry, lawmakers have already exempted thousands of tanks from the law.
Industry groups said the original law would stifle business.
Environmental and watchdogs groups say the law is working, despite officials' urgency to scale it back.
Regulators say the problem tanks are now mostly drained, and owners are monitoring others until they're taken out of service for repairs.