A fracking operation at the eastern border of Ohio remained closed Wednesday, two days after a string of earthquakes stirred some people from their sleep and prompted state regulators to investigate whether the shale-drilling may have been a cause.
Areas in the central and southern U.S. have seen a 20-fold increase in small earthquakes during the past few years, and federal scientists have said the boom in drilling for oil and natural gas has been a contributing factor.
Primarily, part of the dramatic rise has been attributed by the scientists to injection wells, where waste water from fracking is gushed back deep into the earth for storage. The fracking process of firing a mix of water and chemicals at underground rocks -- in hopes of freeing oil and gas stored inside them -- has not been a major cause for earthquakes, according to the U.S. Geological Survey.
But none of the seven wells near the Ohio temblors are for waste disposal, leading local officials and environmentalists to question whether fracking that began last month on one of the wells might have been enough to trigger the human-felt earthquakes.
"The epicenters are right where they are doing the work," Ray Beiersdorfer, a Youngstown State University geology professor whose wife co-founded Frackfree America, told the Los Angeles Times. "There had never been any earthquakes in this county until these wells starting coming in, so it seems suspect."
Hilcorp Energy Co. said one of its 7,900-foot-deep wells at Carbon Limestone Landfill in Poland, Ohio, had already been fracked without incident.
"It is far too early in the process to know exactly what happened, and we are not aware of any evidence to connect our operations to these events," the Houston-based company said in a statement.
The Ohio Department of Natural Resources said Monday that its halt-work order reflected "an abundance of caution." The department "is using all available resources to determine the exact circumstances surrounding this event and will take the appropriate actions necessary to protect public health and safety," it said.
Hilcorp added that it agreed with the agency's rationale and was fully cooperating. The oil and gas industry has held that the link between drilling and earthquakes is weak, noting that tens of thousands of wells have been drilled over several decades without causing any trouble. Industry leaders have urged that strong scientific evidence be shown before any restrictions are imposed.
During the span of about nine hours on Monday, four earthquakes ranging from magnitude 2.23 to magnitude 3.0 were recorded below Hilcorp's drilling site. Another one struck on Tuesday, magnitude 2.1, in the same spot.
Ohio has been in this situation before.
A couple of large earthquakes in 2011 were linked to the opening of a waste-water injection drill in Youngstown, according to seismologists at Columbia University's Lamont-Doherty Earth Observatory. The state ordered the operation and ones close to it shut down indefinitely.
The effects of fracking remain hotly contested. Advocates see it as a reliable source of energy, but critics charge that the injections pollute groundwater supplies. State and federal authorities are keeping a watchful eye as the practice grows.
Among the areas hardest hit by the alleged earthquake side effect since 2009 has been Oklahoma. It's recently surged past Nevada and a dozen other states to become the second most seismically active state in the lower 48, behind only California.
The majority of the activity, which is 40% higher than the average during the past 30 years, "appear to be the result of natural stresses," the Oklahoma Geological Survey said last month. Still, the agency said waste-water drilling was likely a factor for some of the shaking.
Texas, Arkansas and Kansas have seen increases in shaking, too. Some geology experts have suggested that waste water be treated and then reused, avoiding the waste-water injection altogether. But such a reclamation effort would be expensive, according to the drilling companies. Scientists and environmentalists have also called for more monitoring of how much pressure companies use in fracking and storage efforts.
Beiersdorfer, the geology professor, has advocated for keeping wells at least 10 miles away from population centers. But at the least, he wants to see Ohio officials deploy seismographs close to the wells in this case, ensure their integrity and see if cracks have opened up at the landfill.
"To jump ahead with this technique just because they can do it, without proving its safe, is just irresponsible," Beiersdorfer said of what has transpired.
The estimated amount of oil production in Ohio nearly doubled in 2013 from 2012 while natural gas drilling soared nearly 2.5 times, the Ohio Oil & Gas Assn. reported at its winter meeting last week. The organization noted that 580 wells were completed in 2013, a 5% increase from the year earlier. The group hearlded that the natural gas increase, saying energy bills for Ohio residents have plunged.