Mark Nechodom, the director of the California Department of Conservation, which oversees the embattled agency that regulates the state's oil and gas industry, resigned Thursday.
Gov. Jerry Brown appointed Nechodom to the post three years ago. He took over an agency that has generated significant controversy.
California's oil regulator, the Division of Oil, Gas and Geothermal Resources, has been facing scrutiny from the U.S. Environmental Protection Agency after allowing oil producers to drill thousands of oilfield wastewater disposal wells into federally protected aquifers.
Nechodom was named this week in a federal lawsuit filed on behalf of a group of Kern County farmers who allege that Brown, the oil and gas division and others conspired with oil companies to allow the illegal injections and to create a more lax regulatory environment for energy firms.
The lawsuit was filed under federal racketeering statutes and claims the conspiracy deprived Kern County farmers of access to clean water.
Nechodom, who could not be reached for comment, sent a brief letter Thursday to Resources Secretary John Laird. The one-paragraph letter did not give a reason for his departure.
Laird announced the resignation to state staff on Friday. The resources agency declined to comment, citing personnel issues.
Attorney Rex Parris, whose firm filed the lawsuit, said in a written statement Friday that the case alleges a broad and complex conspiracy involving other officials.
"We are not surprised that Nechodom resigned a day after the filing of this lawsuit," Parris said. "We are confident he is just one of many resignations to come."
Nechodom's resignation was unexpected, although he had increasingly been called upon by state officials to explain problems in the oil and gas division's oversight of the oil industry and a parade of embarrassing blunders.
The Department of Conservation failed to meet an April 30 deadline for making public a broad range of information regarding the source, volume and disposal of water used in oil and gas production.
The agency said the law, which legislators approved last year, vastly increased the data that the state is required to collect from oil companies. Regulators are now required to track 200 billion data elements, a task that oil division officials said exceeded the capacity of its antiquated data management system.
Nechodom blamed the reporting failure on "unforeseeable personnel and technical challenges."
The law is meant to allow state officials to track the water used in oil and gas production more closely. Up to 19 gallons of water may be pumped out of the ground for every gallon of oil.
Nechodom and other officials defended the agency's response to the discovery that oil wastewater was being injected into protected aquifers. The agency said it would review the location and operations of more than 2,500 wells. But environmental groups and state lawmakers have challenged the oil division's timeline. The agency has said it will take until 2017 to finish the review.
In one tense hearing before lawmakers in March, Nechodom received a barrage of criticism from elected officials who recited one oversight failure after another.
Nechodom sat stone-faced during the hearing, but eventually agreed, saying, "We all fell down."