The nation’s largest electric grid studied whether its reliance on natural gas could threaten the system. The answer: Not now, but a perfect storm of events could cause problems.

The groups say the Brunner Island plant is discharging toxic pollutants including arsenic, boron, sulfate, and lithium from its unlined coal ash waste ponds.

States may be able to stop monitoring at some sites, and power plants have more time to close leaking ash ponds.