California regulators ordered oil drillers including Chevron Corp. and Linn Energy to halt operations at 12 injection wells in the state because of concerns they may taint groundwater.

The Division of Oil, Gas, and Geothermal Resources said 10 of the well operators shut down voluntarily, while two were issued cease-and-desist orders. All the wells are located in Kern County, northeast of Los Angeles, are within a mile of the surface and 500 vertical feet underground of a water supply, the agency said.

According to information provided by Don Drysdale, an information officer with California Department of Conservation, there are 14 wells in San Luis Obispo County, 11 wells in Santa Barbara County and 23 wells in Ventura County that also fail to comply with federal safe drinking water laws. The oversight process failed because of a widespread administrative mishap at the state’s Division of Oil, Gas, & Geothermal Resources, which state officials confirmed in mid-February.

In an email, Drysdale said wells can be proposed and permitted without ever being drilled or converted to an injection well. Even where a well has been drilled, it may already have been plugged and abandoned or issued other orders preventing injection. Determining the current status of the wells listed is part of DOGGR’s Feb. 6 response to the U.S. Enivornmental Protection Agency, he wrote.

“The Division [of Oil, Gas, and Geothermal Resources] acknowledges that in the past it has approved UIC projects in zones with aquifers lacking exemptions. The division has not kept up with the task of applying for the necessary aquifer exemptions in hydrocarbon-bearing zones required by statute, even though many of these zones possess attributes that would qualify them for exemption,” the letter states. “The division has thus been slow to reconcile the reality that industry has expanded the productive limits of oil fields established in the 1982 primacy agreement with SDWA requirements to obtain aquifer exemptions.”

Drysdale said in his email to the Business Times that while halting injection may be necessary in some circumstances, for the most part the solution involves gaining exemption for certain aquifers from the EPA under the provisions of the Safe Drinking Water Act. The water quality in these aquifers varies greatly, he added.

Oil and gas drillers have been using injection wells for more than 50 years to help push hydrocarbons out of the ground. More than 50,000 oil-field injection wells operate in the state, according to the oil and gas division. An extensive shutdown of the wells would threaten the operations of a $34 billion industry that employs more than 25,000 people in the state, based on agency estimates.

The agency said the orders were part of a “systematic statewide review” of injection wells. The state acknowledged that some well injections were taking place in zones that hadn’t been approved by the EPA, triggering the evaluation of all 50,000 injection wells.

The order includes three wells operated by Linn Operating, three by California Resources Corp., two each by E&B Natural Resources Management Corp. and Chevron Corp., and one well each operated by Modus and Western States International. Modus and Western States International will receive cease-and-desist orders while the rest voluntarily relinquished their permits to inject.

— Bloomberg News contributed to this report