SAN FRANCISCO (AP) - As oil companies move to access one of the largest shale oil deposits in the country, California regulators on Tuesday released draft rules that would more tightly govern the oil recovery method known as hydraulic fracturing, or "fracking."
The proposed rules were posted online by state oil regulators and marked California's first foray into regulating the contentious practice of fracking, which involves extracting hard-to-reach gas and oil by pummeling rocks deep underground with high-pressure water, sand and chemicals.
California currently oversees oil well construction generally but had not previously required disclosure of fracking.
Under the draft regulations, operators would usually have to name the chemicals they use and test wells to ensure the drilling process could be withstood without contaminating groundwater.
Fracking has been quietly going on for decades in several counties, including Los Angeles, Kern, Monterey and Sacramento. Other states use the technique to recover natural gas.
Environmentalists worry that fracking can contaminate groundwater and pollute the air. However, the industry has said the practice has been safely used for decades.
Jason Marshall, chief deputy director of the California's Department of Conservation, said decades of fracking in California have left no evidence that groundwater has been contaminated.
"I know the absence of evidence is not proof," Marshall said. "We pride ourselves on having very good well construction standards in place that are stronger than many other states."
The release of the draft was the first step in creating new regulations at a time when the state is poised for a possible oil boom. Last week, federal land managers auctioned off nearly 18,000 acres of oil leases on public lands in Central California.
That's where California's Monterey Shale formation is located. The formation contains more than 15 billion barrels of "technically recoverable shale oil," more than the amount contained in the Bakken oil fields of Montana and North Dakota, according to a U.S. Energy Information Administration estimate.
What's not known is whether fracking is the best method for recovering the energy resource, said Tupper Hull, a spokesman for the Western States Petroleum Association.
"There's quite a bit of exploration taking place and people trying to answer that question," Hull said. "We think the jury is still out on whether or not this resource can be developed, but there's no question there's a lot of energy locked in that shale."
The public will have a chance to comment on the proposed rules early in 2013 in a process that will take about a year to finalize.
"These regulations ... go well beyond disclosure requirements to require rigorous testing and evaluation before, during and after hydraulic fracturing operations to ensure that wells and geologic formations remain competent and that drinking water is not contaminated," the agency said in comments posted on its website.
"Some of the testing and evaluation requirements of the proposed regulations have not yet been implemented by any other state," it said.
While the chemical disclosure requirement was hailed by some fracking critics as an important step forward, California's draft rules also include a "trade secrets" exemption.
The trade secrets exemption would allow a company to bypass public reporting of the specific chemicals in "fracking fluid" if that information would reveal secrets that competitors could use to gain an advantage.
In lieu of specifics, companies would be required instead to post the "chemical family or similar descriptor" for the agents it is using.
Doctors and nurses treating anyone harmed by a chemical spill or groundwater contamination would be required to sign non-disclosure agreements before a trade-secret protected company would identify the chemicals it uses.
In addition, the privately-owned website on which operators would be required to report the chemicals - FracFocus.org - has been criticized as hard to use and not subject to freedom of information laws.
"These draft regulations would keep California's fracking shrouded in secrecy and do little to contain the many threats posed by fracking," Kassie Siegel of the Center for Biological Diversity said in a statement.
AP Science Writer Alicia Chang in Los Angeles contributed to this report.