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California state regulators say they’re making new attempts to stop persistent oil spills in the oil-rich Central Valley, including one that has been flowing intermittently for 16 years and may have spilled more than 50 million gallons.

The problems stem from the production method used in the oil field about 35 miles west of Bakersfield, where steam is injected into the ground to soften the thick crude oil. It is a different process from fracking, which breaks up underground layers of rock.

It’s blamed for a surface flow of crude oil since May from near a Chevron well into a dry creek bed.

State regulators have now served Chevron with a notice of violation ordering it to halt surface flows at a second site, this one flowing off and on since 2003, KQED News reported Monday. The two sites are about 1,500 feet apart.

Officials at the state Division of Oil, Gas and Geothermal Resources, known as DOGGR, said it’s part of a broader effort to enforce a regulation that took effect in April and bans such surface flows.

“DOGGR is looking to put an end to their occurrence,” division spokeswoman Theresa Schilling told KQED in an email. The division “is exploring swift next steps to evaluate and investigate the oil field as a whole,” including bringing in independent experts.

Gov. Gavin Newsom fired the previous head of DOGGR in July over a recent increase in hydraulic fracturing permits and amid a conflict-of-interest investigation of other division employees.

Chevron spokeswoman Veronica Flores-Paniagua said in a statement that the company’s goal is “the prevention of all seeps” including the one flowing for more than a decade. But she said there has been no harm from that surface flow to people, groundwater, surface water, wildlife or agriculture.

The flow has been going on so long that Chevron built a collection facility in 2012. Spilled oil is pumped into a pipeline or sucked up by vacuum trucks. Chevron said about 84 million gallons have flowed since 2003, of which about 60% to 80% is crude. The rest is water from steam, but the company’s lower estimate means about 51 million gallons of oil has spilled.

State regulators said in an email Monday to The Associated Press that the flow “is fully confined to a concrete containment structure and the area is actively vacuumed out by Chevron. This expression is several miles from any community and does not pose a threat to drinking water. Additionally, appropriate actions have been taken to protect the health and safety of workers and the community, as well as the wildlife and the environment.”

Regulators ordered Chevron to stop injecting steam into the ground near the spills, among other steps.

The problem has been getting worse.

Releases grew from an average of about 250 to 1,100 barrels a day in recent years to a peak of 3,000 barrels a day this summer, spiking after the flow began near Chevron’s nearby well in May. Each barrel is 42 gallons.

The company reported a third, smaller surface spill this month, near the other two.