By Victoria Colliver

Gov. Jerry Brown on Monday accepted the resignation of Steven Bohlen, who has supervised California's troubled Division of Oil, Gas and Geothermal Resources for the last 18 months.

Brown named Ken Harris to run the division, which has been under fire for a long-standing practice of letting oil companies dump wastewater into aquifers protected by federal law. Harris is now executive officer of the Central Coast Regional Water Quality Control Board.

Bohlen plans to return to Lawrence Livermore National Laboratory, where he was program director until Brown appointed him to head the resources division in May 2014.

"Steve brought strong leadership and valuable scientific expertise to the job of improving oil and gas oversight," Brown said in a statement.

A Chronicle investigation this year found that for more than three decades, the division has allowed petroleum companies to pump wastewater from their operations into aquifers that could one day be used for drinking or irrigation. A handful were already being used by water customers.

Bohlen could not be reach for comment Monday. The Division of Oil, Gas and Geothermal Resources referred calls to the Department of Conservation, which referred calls to Brown's press office.

Catherine Reheis-Boyd, president of the Western States Petroleum Association, said Bohlen had greatly expanded the agency's regulatory role and undertaken a sweeping review of the division's regulations.

"As a result, oil and gas production in California is today conducted under some of the most stringent regulations and oversight in the world," she said.

Hollin Kretzmann, staff attorney for the Center for Biological Diversity, said Bohlen's resignation won't fix the agency's fundamental problems.

"California regulators have prioritized oil company profits and the governor's personal requests at the expense of our air, water and health," Kretzmann said in a statement for the environmental group.

Kretzmann described the state agency as "far too close" to the oil industry it's supposed to regulate. "The next supervisor must address Californians' concerns about water contamination and safety risks from drilling and fracking," he said.

Harris has led the Central Coast Regional Water Quality Control Board since 2012 and has held positions at the state Water Resources Control Board since 1987. He will be paid $198,500 a year, and his appointment does not require the Legislature's confirmation.

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