Workers block the road to a natural gas well Friday that had gotten out of control Thursday in Pennfield, Pa. The gas never caught fire and no injuries were reported, but state officials worried about an explosion before the well could be controlled. The well was brought under control just after noon Friday, about 16 hours after it started spewing gas and brine. Environmental officials are investigating to see what caused the accident.

HARRISBURG — Pennsylvania's environmental regulators worked Sunday to get to the bottom of what caused a natural gas well to spew explosive gas and polluted water for 16 hours last week before it could be brought under control.

Neil Weaver, spokesman for the Department of Environmental Protection, said the well's blowout preventer failed, but stressed the investigation is ongoing into whether the failed equipment was the accident's main cause.

Investigators are trying to figure out what caused the malfunction, he said. A blowout preventer is a series of valves that sit atop a well and allow workers to control the pressure inside.

The Thursday blowout is the latest in a string of accidents connected by regulators to the rapidly growing pursuit of the rich Marcellus Shale gas reserve that lies beneath much of Pennsylvania.

It seems likely the Pennsylvania blowout will enter the debate in the Capitol, where legislators are battling over the merits of approving a severance tax and tighter regulations on an industry that has spent several billion dollars and drilled more than 1,000 wells in Pennsylvania in just a couple years.

A leading environmental advocate, Rep. David Levdansky, D-Allegheny, said such problems could bring increased support for a moratorium on leasing public land for gas drilling and a tax to fund existing environmental protection and cleanup programs.

However, Senate President Joe Scarnati, whose house is two miles from the well blowout in rural north-central Pennsylvania, said the accident doesn't alarm him or make him feel differently about how the state should approach the industry.

The state is doing a good job policing the exploration industry, and a severance tax should return money to the communities where the impact is being felt on roads and other public resources, said Scarnati, R-Jefferson.

"Should we find that there needs to be greater safeguards in place, I don't have blinders on and neither does the industry," he said.

Weaver declined to discuss whether well driller EOG Resources of Houston committed any violations that could lead to fines or any other penalties.

An EOG spokeswoman said Sunday the investigation into the cause is ongoing, and the company had no light to shed on the blowout.

The crew of about eight workers evacuated the Clearfield County site Thursday night and accident specialists didn't regain control over it until just past noon Friday. No one was injured, the gas didn't explode and polluted water didn't reach a nearby waterway, officials said.

The blowout sent highly pressurized gas and polluted water 75 feet into the air. Huge tanks were required to cart off chemical- and mineral-laced water collected on the grounds of the private hunting club where the well had just been drilled. There are no homes within a mile of the heavily forested site.