Illinois lawmakers signed off Thursday on long-awaited rules regulating high-volume oil and gas drilling, clearing the way for companies to get "fracking" permits and unleash what they hope will be an energy boom in the southern part of the state.

But a number of key details were not disclosed including how the state plans to fund the hiring of new workers to oversee the practice, which uses high-pressure mixtures to crack open rocks and release trapped oil and gas.

The delay in the fracking rules — which took more than a year for the state Department of Natural Resources to write and which were revised by a legislative committee — prompted complaints from industry that energy development would suffer.

The final rules must be submitted to the Secretary of State to be published by Nov. 15.

The secretive approval process set off alarm bells with environmental activists, who say they have no idea what changes were made to the draft of regulations released by the department in late August.

"We are sure many changes benefiting industry have been made behind closed doors without scientific review," said Annette McMichael, spokeswoman for Southern Illinoisans Against Fracturing our Environment.

Lawmakers who approved the rules unanimously and without discussion, expressed confidence that concerns raised in 30,000 public comments had been addressed.

"All of the changes that were made were because the earlier proposed rules were inconsistent with the statute," said Democratic state Sen. Don Harmon, the committee chair.

The Illinois fracking law passed by the Legislature last year drew national attention as a model of compromise between environmental and industry groups. But cooperation broke down when a first draft of rules was criticized by environmentalists and a second draft was faulted by industry.

"It's a pendulum," Harmon said. "This is a return to the center."

Illinois Department of Natural Resources Director Marc Miller said key changes to the rules requested by environmentalists remain in place. They include clarification that wastewater would not be stored in open pits for more than a week at a time, which environmentalists had said would lead to contamination. Public hearings for fracking permits must not be held further than 30 miles from where a well site would be located. In addition, Miller said, fines were increased for violations of the rules.

Hydraulic fracturing uses a mixture of water, chemicals and sand to open rock formations thousands of feet underground and harness oil and gas. Opponents fear it will pollute and deplete groundwater or cause health problems. Industry officials insist the method is safe and will prompt the same economic boom seen in other states such as North Dakota

Mark Denzler, chief operating officer of the Illinois Manufacturers' Association, said he was "thrilled" with the new set of rules.

"We look forward to companies getting permits and starting fracturing in the state of Illinois," Denzler said.

Now that the committee has signed off on the plan, drillers can begin applying for permits 30 days after registering. Permits must then be approved or rejected by the department within 60 days.

Miller said the department has hired 32 of 53 people needed to oversee the process. But the department is quickly running out of money to add and keep staff, after the General Assembly eliminated more than $2.5 million for agency salaries in the current fiscal year.