The fracking industry’s latest environmental bugbear is earthquakes, which can be caused by injecting a briney cocktail of wastewater produced in the fracking process deep into disposal wells. And a paper making the rounds this week, by a researcher from Columbia University, clarifies just how drastically a single wastewater injection well can rattle its surroundings.

The study, by Won-Young Kim, found that in a single year, 167 distinct earthquakes occurred in and around the town of Youngstown, Ohio. All of these were caused by just one wastewater injection well. It stored, over its life, nearly half a million barrels of the wastewater cocktail—including thickeners, drilling lubricants, and saltwater—forced to the surface of the earth by the fracking process.

The 9,200 foot deep well, known as Northstar 1, opened in 2010, two weeks before Youngstown experienced its first quake—ever. From then until frackers stopped using the well at the end of 2011, about 12 tremors struck the area every month. And while Youngstown residents could not feel most of these, the very last injection into the well—the Ohio Department of Natural Resources had ordered the well be shut down—happened a day before an earthquake that registered a magnitude 3.9 struck the area. Michael Behar reported for Mother Jones this spring that there are roughly 40,000 of these disposal wells in the country.

Geologists are quickly forming a picture of how the millions of gallons of fracking waste stored underground have dangerously rearranged the earth. As Behar described, “Disposal wells are drilled into vast, permeable formations—think giant sponges—where there's plenty of space for water to spread out. But because water is heavy, the more of it that is sluiced into a well, the more it weighs on the rock below. … Too much wastewater in a disposal well forces liquid downward and outward. It can meander for months, creeping into unknown faults and prying the rock apart just enough to release pent-up energy.”

But although the damage potential for these wells is becoming more obvious, for the moment, they are almost never regulated. In 2011, the very quakes at the center of this study prompted Ohio Governor John Kasich, a Republican, to require operators to conduct seismic testing before obtaining a well permit. But while many states—especially Texas and Arkansas—are experiencing tremors from these wastewater sites, Ohio is the only state that regulates where frackers can place their wells. Oklahoma, for instance, where the state’s largest-ever earthquake, a 5.7, emanated from a dead fault line reawakened by wastewater injection, requires no seismic surveys around potential well sites. Seventeen states felt that quake, in late 2011, which ripped open a clefts in the road and was followed by a 4.7 aftershock.