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Fracking for oil and natural gas in California could slam to a halt, at least temporarily, under legislation circulating in Sacramento.

One bill calls for a moratorium on the practice until the state conducts a sweeping study of fracking’s benefits and risks, including the potential for groundwater contamination.

Another piece of legislation would allow fracking while the state conducts such a study. But the same bill, from Sen. Fran Pavley, would slap a moratorium on fracking if the study isn’t finished by 2015.

“What I’m trying to do is say to the oil companies, ‘Look, if there’s never been a problem with fracking, if it’s safe, you need to prove that to the public,’ ” said Pavley, D-Agoura Hills (Los Angeles County).

The proposals come as the use of hydraulic fracturing, or fracking, spreads across California. The process – which pumps pressurized water, sand and chemicals underground to crack rocks – has touched off a boom in U.S. oil and natural gas production. But environmentalists blame it for tainting water supplies, worsening air pollution and turning farms into oil fields.

Vast geologic formation

In California, a growing list of companies use fracking to wrest oil from the Monterey Shale, a vast geologic formation estimated to hold 15 billion barrels of petroleum.

The practice hasn’t taken off here the way it has in North Dakota or Texas. But at least 759 wells in the state have been fracked in recent years, according to a national website that compiles fracking data from oil companies. A study last week from the University of Southern California estimated that developing the Monterey Shale could add $24.6 billion in state and local tax revenue by 2020.