Oklahoma's Getting Even More Fracking Restrictions as Earthquakes Continue to Rattle the State

Trying to stem the dramatic increase in earthquakes that have rattled Oklahoma residents over the past few years, state regulators are asking the oil and gas industry to reduce the disposal of wastewater in wells that scientists suspect could be responsible.

About 125 well operators in Central Oklahoma received a letter from the state Corporation Commission on Monday directing them to bring the volume of wastewater pumped deep underground to 40 percent below what it was in 2014. About 400 wells in the Arbuckle formation, which spans most of the state, disposed of more than 433 million barrels that year. That was also the year Oklahoma experienced a sharp rise in the magnitude and number of earthquakes, said Matt Skinner, a spokesman for the commission.

The cutback has been scheduled in four phases, the first of which started Monday. Operators have until May 28 to fully comply with the request. Skinner said only two companies have formally challenged the commission's efforts to reduce disposal volumes over the past year but that both backed off. It has yet to be seen how operators will respond to this latest directive, and how it will affect oil and gas production in the state.

The Oklahoma Oil & Gas Association did not respond to VICE News questions about the plan.

Related: A Series of Strong Quakes in Oklahoma Triggers Republican Scrutiny of Oil Drilling

In February, the commission asked the operators of 245 wells injecting wastewater into the Arbuckle formation to cut back disposal by about 40 percent. Tim Baker, director of the commission's oil and gas conservation, said in a statement at the time that earthquake activity demanded a regional response. The commission characterized the effort as the largest volume reduction plan in western Oklahoma.

The Arbuckle formation is the state's deepest, Skinner said, and has long been a preferred wastewater disposal site because it's considered the best spot to protect underground sources of drinking water. But researchers have linked the formation with a high risk of earthquakes caused by wastewater injection. And well operators have come in the crosshairs of environmental organizations such as the Sierra Club. The group's Oklahoma chapter has urged the commission to reduce underground wastewater disposal in the state, and to stop it entirely in some areas.

Johnson Bridgwater, director of the Oklahoma chapter of the Sierra Club, said the commission is moving in the right direction, but the request doesn't go far enough.

Bridgwater said the commission's latest effort is the "biggest single order" it has issued, but excludes wells within some areas where earthquakes are occurring.

"We want to see an across-the-board reduction [in wastewater disposal]," he said.

Bridgwater said he's also concerned that the compliance process isn't transparent enough and will fail to hold well operators accountable.

Related: Environmentalists Sue the Oil Companies Allegedly Causing Oklahoma's Big Earthquakes

In February, the Sierra Club sued Oklahoma-based Devon Energy, New Dominion, and Chesapeake Operating, asking a federal judge to "immediately and substantially" reduce the amount of salty wastewater the companies inject thousands of feet underground. The litigation is pending.

The rate of increased seismic activity in Oklahoma is unprecedented and primarily concentrated in the central part of the state, according to the Oklahoma Geological Survey. In the past few years the one or two couple small but noticeable earthquakes the state experienced annually leapt to two or three daily. An early count of 907 tremors with a magnitude 3.0 or more were recorded in 2015.

The commission cautioned that an immediate decrease in the number and severity of earthquakes is unlikely, and that any changes in seismic activity must be evaluated over a period of several months.

Follow Ciara O'Rourke on Twitter: @ciaraorourke