Crews in Pennsylvania gained control Friday of a natural gas well that blew out and spilled thousands of gallons of chemical-laden drilling fluid into the environment over two days.
But the incident has drawn attention to concerns over a controversial drilling process of hydraulic fracturing or "fracking," which is seen as having enormous potential for capturing natural gas but has environmental risks.
The operator of the well, Chesapeake Energy, has suspended operations at its wells in Pennsylvania pending its investigation into the causes of the spill.
The environmental damage from the spill is unclear. The exact amount of fluid that spilled from the well was not disclosed, and it was not clear exactly what the fluid contains.
State environmental officials were taking samples to determine the extent of the damage, said Paul Spadoni, spokesman for the Pennsylvania Department of Environmental Protection.
Some of the fluid spilled into a nearby creek. Company officials asserted in a statement that "initial testing from Towanda Creek indicates little, if any, significant effect to local waterways."
The well is located near Canton, Pennsylvania, in Bradford County. Canton is about 280 kilometers (175 miles) northwest of Philadelphia, near the border of New York state, which has imposed a moratorium on fracking.
Hydraulic fracturing involves forcing chemicals deep into a well to dislodge natural gas from shale thousands of feet below the surface.
However, the method risks poisoning the water wells that many rural landowners in Pennsylvania rely on. The high pressure chemicals could dislodge other underground chemicals that might find their way into the water wells of homeowners.
Despite the controversy, the method is on the rise in Pennsylvania and across the country. The high price of natural gas has encouraged drilling, and new technology has made it possible to reach gas never before considered viable.
Proponents of such drilling say it provides much needed jobs in rural areas with depressed economies.
But opponents say the risks are high. The state's Department of Environmental Protection recently issued a list of all of the chemicals found in the drilling fluid. A newly released Congressional report listed far more chemicals used in drilling operations, many of them carcinogenic.
Amy Mall of the Natural Resources Defense Council said the latest accident highlights the dangers of fracking.
"Pennsylvania has become a national sacrifice zone for natural gas development. It has seen more than its share of drinking water contamination, houses exploding, and destroyed landscapes and communities," she said.
"These incidents, and many other spills, leaks, and explosions, reveal that accidents are not being prevented."
The spill came at a sensitive time for the oil and gas industry. The blowout occurred on the eve of the one-year anniversary of the BP oil disaster in the Gulf of Mexico.
On the day before the blowout, state environmental officials asked gas drillers to stop delivering waste water to public wastewater treatment facilities. The spill itself occurred on the day that state environmental officials decided to allow natural gas drilling in state game lands, areas reserved for hunting.
Fueling interest in gas is what is believed to be a massive reserve in the so-called Marcellus Shale over a wide area of the eastern United States.
Pennsylvania State University's Terry Engelder estimates the Marcellus shale holds between 168 trillion and 516 trillion cubic feet of gas that can be "easily produced."
Explore further: Hundreds attend EPA hearing on Pa. gas drilling