Waste wells implicated in Ohio quake.

Waste wells implicated in Ohio quake

By injecting industrial waste into the ground, a chemical company in Ohio may have generated enough subsurface pressure to trigger the magnitude 4.9 earthquake that shook northeastern Ohio and a nearby nuclear power plant in early 1986, two Ohio geologists report. Although their conclusions differ from the findings of federal geologists, they highlight the questions some scientists are raising concerning the relationship between earthquakes and injection wells, which are used heavily in waste disposal and in the oil and gas industry.

Since 1974, the Calhio Division of Stauffer Chemical Co. has pumped liquid waste into a porous sandstone formation through two 1,800-meter-deep wells near Lake Erie. On Jan 31, 1986, an earthquake struck 12 kilometers from the wells. After studying the quake and constructing a computer model of the underground flow patterns, two U.S. Geological Survey researchers concluded that natural forces -- not waste injection -- generated the quake.

Moid Ahmad and Jeffrey A. Smith from Ohio University in Athens report in the August GEOLOGY that their computer simulations suggest otherwise.

By pumping waste into the sandstone, the Calhio wells are increasing fluid pressure within the pores of this rock, which lies directly above the crystalline bedrock. Geologists suspect the 1986 earthquake occurred along a fault in the bedrock, although they cannot be sure because it is covered by several kilometers of sedimentary rock.

Ahmad and Smith found that during computer simulations, the increased fluid pressure from the well spreads 12 km away into the proposed fault--to an extent that the pressure could have triggered the 1986 quake by reducing friction along the fault. Ahmad told SCIENCE NEWS that continuing waste injection could set off a larger earthquake that might threaten the proximal Perry Nuclear Power Plant.

Experts say they have little information about the subsurface rocks in the area, and for that reason they cannot rule out the possibility of a triggered quake. "I think it's possible that the earthquake was triggered and it's possible that more earthquakes could be triggered," says John Armbruster of the Lamont-Doherty Geological Observatory in Palisades, N.Y.

However, the lack of detailed information undermines the reliability of any computer model, and most Ohio earth scientists reject alarmist statements about future hazard. "Ahmad seems to be out on his own on this one," says Larry Wickstrom of the Ohio Geological Survey in Columbus. Still, geologists believe they need to monitor seismicity in the area and study the actual subsurface flow patterns.

Last year a magnitude 3.6 quake hit 700 meters from an injection well in Ashtabula, Ohio. On the basis of information from seismic monitoring stations set up after the 1986 quake, Armbruster has linked the later quake to the Ashtabula well -- a conclusion shared by the Ohio Geological Survey. There are only a handful of other instances for which geologists have found a clear connection between injection wells and quakes.