However, increased public awareness, coupled with the more stringent regulations, could be leading to higher disposal costs, according to a recent report from ClearView Energy Partners, a Washington, D.C.-based energy research firm. The report was released in January, after the Ohio quakes but before the state's new injection guidelines were announced. It said the average cost for injection disposal is $10-$15 per 1,000 gallons and identified the potential for higher disposal costs, in reaction to the earthquakes, as one of several emerging risks for drilling companies.

The Ohio Oil and Gas Association, an industry group, did not respond to requests for comment.

Travis Windle, a spokesman for the Marcellus Shale Coalition, which represents drillers across the region, said the group is confident that injection will continue to be a "workable option," for disposal. But he added that drillers are turning more and more to reusing their wastewater, reducing costs and lessening environmental impact.

State data show that drillers in Pennsylvania, which hosts the most extensive Marcellus Shale drilling, reused about half of their wastewater in the first half of 2011, before the state prohibited drillers from discharging to streams.

Meanwhile, Ohio officials say their injection guidelines, some of which can be implemented through administrative changes and some of which require legislation, will make the state's oversight program among the best in country. The federal EPA oversees wastewater injection, but states can regulate the practice if their rules are at least as stringent as federal guidelines, a status Ohio has enjoyed since 1983.

But the rules haven't placated anti-fracking activists, who have added Ohio's earthquakes to their list of reasons why fracking should be halted. Other environmental groups are lobbying for even tougher rules in Ohio, and, perhaps more important, for tougher enforcement.

"Our concern more so is whether or not the Ohio Department of Natural Resources has adequate resources to monitor and inspect and follow up on violations," said Jed Thorp, of the Sierra Club's Ohio chapter. Thorp is concerned that more injection could lead to more quakes. "They are relying on the industry to self report any violations they may have."

The Department of Natural Resources currently has 30 oil and gas inspector positions, though a few are vacant. But Hetzel-Evans said the agency expects to have between 80 and 90 inspectors by next spring. She said the inspectors are able to visit each injection well at least once every 12 weeks, far more often than the once-a-year visits required by the EPA.

All sides agree that while higher costs or logistical bottlenecks could present energy companies with new challenges, the drilling industry and state regulators are likely to find solutions to these significant hurdles.

"I don't think they're going to allow anything to really slow down the process," Thorp said.