State officials allowed oil and gas companies to pump nearly three billion gallons of waste water into underground aquifers that could have been used for drinking water or irrigation.

Those aquifers are supposed to be off-limits to that kind of activity, protected by the EPA.

“It’s inexcusable,” said Hollin Kretzmann, at the Center for Biological Diversity in San Francisco. “At (a) time when California is experiencing one of the worst droughts in history, we’re allowing oil companies to contaminate what could otherwise be very useful ground water resources for irrigation and for drinking. It’s possible these aquifers are now contaminated irreparably.”

California’s Department of Conservation’s Chief Deputy Director, Jason Marshall, told NBC Bay Area, “In multiple different places of the permitting process an error could have been made.”