California officials, responding to concerns about groundwater contamination, are closing 12 wells in the Central Valley used to dispose of chemical-laden water from oil and gas production, regulators announced Tuesday.
Steve Bohlen, who leads the state Division of Oil, Gas and Geothermal Resources, said the wells are being shut down "out of an abundance of caution for public health."
Ten of the wells, including some owned by Chevron, have been closed voluntarily and the companies have surrendered their permits. Two more are being ordered to cease operations.
Federal officials have expressed concerns about the state's oversight of injection wells. Some of the wells are used to dispose of wastewater produced during hydraulic fracturing, a method of oil and gas extraction better known as fracking.
California has about 50,000 underground injection wells, and 2,553 are in areas with aquifers that have been or could be a source of usable water. State regulators have been focusing their review on 176 wells and expect to complete their study in the next three months.
Jonathan Bishop, chief deputy director of the State Water Resources Control Board, said there's no evidence yet that drinking water has been affected.
"We are going to be continuing to look at the information," he said.
But Patrick Sullivan of the Center for Biological Diversity said the state's actions fall far short of what's needed.
"It's inadequate, it's ridiculous, it's unacceptable," Sullivan said. "They've allowed decades of injections into these aquifers that should have been protected. Even now, they're still dragging their feet."
The wells are clustered in Kern County, the heart of California's oil and gas industry.