Federal regulators believe “there is a significant possibility” that recent earthquakes in North Texas are linked to oil and gas activity, even if state regulators won’t say so.

That’s according to the U.S. Environmental Protection Agency’s annual evaluation of how the Texas Railroad Commission oversees thousands of injection and disposal wells that dot state oilfields — underground resting places for millions of gallons of toxic waste from fracking and other drilling activities.

“In light of findings from several researchers, its own analysis of some cases and the fact that earthquakes diminished in some areas following shut-in or reduced injection volume of targeted wells,” the Aug. 15 report states, “EPA believes there is a significant possibility that North Texas earthquake activity is associated with disposal wells.”

Scientists have known for decades that injecting fluid deep underground could trigger earthquakes, and a growing body of research has linked disposal wells to seismicity in Texas and other states, which has grown more frequent.

Jim Bradbury, a Fort Worth-based oil and gas attorney who has closely followed the earthquake saga, said he could not recall the EPA explicitly tying Texas earthquakes to industry activity.

“It’s a big deal they said that,” he said.

Texas, home to thousands of such wells, is the third-most at-risk state for man-made earthquakes, according to the U.S. Geological Survey — behind only Oklahoma and Kansas.

Several Texas drilling regions have recently felt more earthquakes, most of them small. But temblors in the Dallas-Fort Worth area have drawn the most attention, particularly those that struck in the past two years.

“EPA is concerned with the level of seismic activity during 2015 in the Dallas/Ft. Worth area because of the potential to impact public health and the environment, including underground sources of drinking water,” the agency wrote.

The shaking has created political challenges for the Texas Railroad Commission, which oversees the powerful oil and gas industry.

Since 2014, the agency has added a staff seismologist and approved regulations requiring disposal well operators to submit more geographical information. But the agency, which has conducted its own investigations, has not publicly tied any of the shaking to industry activity — even as regulators in other petroleum states acknowledge a connection. The Railroad Commission has pushed back against conclusions of some outside studies.

Responding to the EPA report Monday, the commission told The Texas Tribune that it “takes the issue of induced seismicity very seriously and has in place some of the most stringent rules on disposal wells.”

Since approving those 2014 rules, the commission has received 56 disposal well applications in historically seismic areas, spokeswoman Gaye McElwain said in an email. Of those, the agency has issued 28 permits with “special conditions” — those related to injection volumes and pressures, for instance. Eleven applications were withdrawn or returned, while three were protested and sent to hearings. “Ten permits were issued without special conditions, and four applications are pending,” McElwain said.

• Read More On Quakes, Regulator Sides with Energy Companies

In its assessment, the EPA “commended” the Railroad Commission for establishing new regulations on disposal wells and clarifying its authority to shut down certain operations it ties to earthquakes. But the federal agency recognized that its own findings about North Texas seismicity run counter to what the Railroad Commission has publicly stated.

Earthquakes are generated by slipping faults, or fractures. Experts say that injecting fluids at high pressures can relieve pressure in some faults, causing them to slip. And “naturally fractured injection formations may transmit pressure buildup from injection for miles,” the EPA assessment notes, highlighting one such formation in North Texas — the Ellenburger — which is a popular disposal zone.

Luke Metzger, director of the advocacy group Environment Texas, suggested the EPA was simply “stating the obvious” about the cause of the quakes.

“EPA should insist the [Railroad Commission] accept the scientific evidence and take action to protect Texans from earthquakes,” he said.

But Bradbury, the North Texas attorney, found something more remarkable in the federal agency’s message to the Railroad Commission — particularly because the EPA had previously said little publicly about quakes in Texas.

“It is obvious to everyone that [the Railroad Commission] is intentionally avoiding the reality that the larger scientific community has embraced and is working on,” Bradbury said in an email. “I think it reveals that EPA is troubled by that reality.”

In its report, the EPA recommended, “close monitoring of injection activity” going forward, coupled with “appropriate data analysis methods, in a coordinated effort to detect possible correspondence with seismic activity.”

Bradbury noted that the EPA has the power to revoke the commission’s authority over disposal wells.

“It’s the EPA’s program, and they can cause the [commission] a lot of grief,” he said.

Read more on earthquakes and oil and gas activities in Texas

• University of Texas at Austin researchers call it “plausible” that underground injections of oil and gas waste triggered a series of temblors that rattled Timpson residents in 2012.
• State lawmakers are considering a nearly $2.5 million plan to help answer a pressing question in some Texas communities: Why does the ground keep shaking?
• A peripatetic seismologist and son of McCamey has been hired to figure out whether oil and gas drilling is causing earthquakes in Texas. No matter what he says, some people will not believe him.
• After wrapping up a round of testing, Texas regulators say they have found no evidence that injecting oilfield waste into five disposal wells triggered the largest recorded earthquake in North Texas’ history.
• After a contentious town hall meeting concerning the possible links between wastewater injection and a spate of North Texas earthquakes, locals say they cannot afford to wait for state regulators to address the issue.