State officials say a civil engineer deemed a portion of the site safe last week, so contractors could begin hauling away contaminated soil from the 1-acre spill site.

A second section of the site has not yet been declared safe, Laughlin said.

Chevron had hired two Bakersfield contractors to work on the cleanup job, Advanced Industrial Services and Sturgeon Services, according to Morgan Crinklaw, a spokesman for the oil company.

State regulators recently brought in nine experts from the Sandia, Lawrence Berkeley and Lawrence Livermore national laboratories to help evaluate the causes of the protracted release.

Chevron has said the probable cause was related to its efforts to seal off a damaged and abandoned oil well. The firm says its attempts to confirm the source of the original leak and shut it down unleashed even higher flows in the weeks after the initial problem was discovered.

DOGGR has issued two notices of violation to Chevron and ordered the oil company to "take all measures" to stop the flow and prevent a recurrence of the releases. Chevron is appealing the state's order, which it says lacks specifics.

"Despite the appeal, Chevron continues to do work required in the order to ensure the seepage ceases and clean up the surface expression," Drysdale said.

The spill has added fuel to arguments by environmental groups who want California to shift more aggressively away from oil and gas and believe state regulators are too soft on the industry.

"It's shocking that it's taken this long for the company and state officials to stop this dangerous pollution," said Clare Lakewood, a staff attorney at the Center for Biological Diversity, in an emailed statement Wednesday.

The incident is also expected to be the focus of legislative hearings. The chairs of the state Senate and Assembly committees overseeing much of California's oil industry say they plan to scrutinize the cause and response to the spill.