No new hydrogen sulfide problems at sinkhole site

BAYOU CORNE, La. (AP) - Authorities report no new problems with poisonous hydrogen sulfide gas near a large sinkhole in Assumption Parish. A relief well near the sinkhole was shut down after hydrogen sulfide emissions were detected.

However, The Advocate reports that no similar problems have been found in testing of four other wells. That word came from a scientist for Shaw Environmental. Gary Hecox said in a blog post Thursday that researchers found no detectable hydrogen sulfide concentrations in gas being flared from two relief wells.

The other two relief wells had low concentrations of the gas, consistent with a swamp environment. The sinkhole led to evacuation in August of about 150 homes in the Bayou Corne and Grand Bayou areas. Scientists believe a salt cavern from which a company had been extracting brine failed, causing a chain of events that led to the sinkhole and the release of methane gas and crude oil.

Hydrogen sulfide is a colorless gas that is flammable and poisonous at high concentrations. The naturally occurring gas has a foul rotten-egg odor, can occur in natural gas deposits and is a known risk with oil and gas exploration.

Hecox said decaying trees and vegetation in swamps produce hydrogen sulfide. "While low concentrations of hydrogen sulfide have been detected at some of the bubble sites, the concentrations are well below those that would pose a human health risk," Hecox said in the blog. Bubble sites are where natural gas travels through the water to the surface.