Trevor Hughes

USA TODAY

GREELEY, Colo. — A series of small but unusual earthquakes near a well being pumped full of liquid drilling waste north of Denver has reignited a debate about the impacts of oil and gas development near homes.

Colorado isn't normally earthquake territory, but aggressive drilling and pumping here and across the country may be changing that, contributing to the debate about what costs we're willing to bear to achieve energy independence.

"What we have seen since about 2009 has been a steady increase of the rate of earthquake activity in parts of the country that normally are seismically quiet," said Bill Ellsworth, a seismologist with the United States Geological Survey. "This is something very anomalous and we have no natural analogue of what's going on in the rest of the world."

The rise of small quakes, most too small to be felt, appears to mirror the country's booming petroleum production. Oklahoma and Texas have both seen unusual "swarms" of quakes that scientists say appear to be linked to oil production efforts, even though most experts are reluctant to draw direct connections.

The most recent attention is focused on what are known as injection wells, where drilling waste is pumped several miles below the Earth's surface, to be soaked up by rock formations. That waste, which is mostly water contaminated with drilling fluids and sand, comes from either fracking other wells to release oil and gas, or naturally occurring water brought to the surface along with petroleum products.

Fracked wells are pumped full of high-pressure water, chemicals and sand to crack deposits loose. The water is pumped back out, followed by the oil or natural gas, and the wastewater is then injected back underground into a different well for permanent disposal. Injection is cheaper than cleaning and recycling the contaminated water.

The quakes, and the booming oil and gas industry as a whole, have generated emotional debate across the country's heart.

Some residents unnerved by the Colorado quakes are demanding the state shut down all wells responsible for causing them.

"I don't want to end up like the Oklahoma City area with a cluster of these quakes because the oil and gas companies are too lazy to clean up their polluted water and just inject it into deep wells," said Greeley resident Carl Erickson, who launched a petition drive aimed at forcing state regulators to step in.

But longtime Greeley resident Byra Gillham said the quakes may just be the cost of helping secure American energy independence and boost the economy. Gillham said the oil and gas industry is pouring millions of much-needed dollars into the Greeley area while providing good jobs.

"I do feel like the environmental people get too concerned," she said. "They seem like they're more worried about a thing than the people."

The well's owner did not respond to phone messages seeking comment.

Ellsworth, in a paper published last summer, concluded that "some" of the nation's approximately 30,000 injection wells can be blamed for causing quakes but noted scientists don't have enough data to provide clear answers. While injection wells have been used for decades, Ellsworth said what may have changed is the volume and pressure of the water being pumped into them, or perhaps they're starting to have a cumulative effect that wasn't noticeable earlier. Existing injection well regulations are concerned more with protecting drinking-water aquifers than preventing quakes, he said.

In the dusty cornfields surrounding the Greeley injection well, geophysics professor Anne Sheehan hopes to provide some answers. Sheehan and her graduate students from the University of Colorado-Boulder have deployed a network of portable seismographs around the area to track any further quakes while charting the amount and pressure of water going down the injection well, which began accepting drilling waste in April 2013.

More than a year later, a 3.4-magnitude quake shook the area May 31, 2014, followed by a 2.6-magnitude quake June 23.

The preliminary data from Sheehan's team shows that the quakes subsided after the well's owners filled in the deepest part of the well and state regulators ordered them to reduce the amount of wastewater being pumped down it. That preliminary data also shows the well successfully stored millions of gallons of wastewater for months before any significant quakes began occurring.

"It's hard to prove definitively because it's not a laboratory setting," said Sheehan. "What we're trying to do is get good information out there and let people make their own decisions."

A new study released this week suggests that injection-related quakes feel weaker than they really are. Building off Ellsworth's studies, fellow USGS scientist Susan Hough analyzed injection-related quakes in Arkansas, Colorado, Ohio, Oklahoma and Texas and found they tended to feel less powerful to people living nearby. She theorized the quakes feel weaker because they tend to occur at shallower depths than naturally occurring seismic events. Hough compared seismograph data to reports submitted by residents to the government's "Did You Feel It?" quake-reporting system.

In Oklahoma, regulators are working closely with drillers to develop new standards for digging and filling the wastewater wells.

The Oklahoma Corporation Commission, which oversees the state's petroleum industry, now generally prohibits disposal wells from being bored into or close to bedrock, said spokesman Matt Skinner. "We've reached a level where the data shows us that's not a prudent thing to do," he said.

Gerry Baker understands the two sides. He's working with regulators, environmental groups and the oil industry through the Interstate Oil and Gas Compact Commission, a government body representing more than half the states as they work for responsible energy development.

Baker, who lives in Oklahoma, has felt more than a dozen quakes at his home in the last year, helping sharpen his focus as the commission's associate executive director. He said oil and gas production plays an important role in the country's economy, but acknowledges the earthquakes that have rattled his home are a cause for concern.

"I understand the science behind it, but still it's a little disconcerting."