UPDATED 3:26 p.m.
FARGO - The mystery gas may not be methane after all.
The source of a mysterious odor that made three workers ill this morning at a construction site in downtown Fargo was apparently discovered this afternoon after two of the workers - fresh from being treated and released from MeritCare Hospital - returned to the site and smelled the odor again, said Dave Asplin, owner of Asplin Excavating.
Crews found a network of old pipes running underground, he said.
"They were full of something stinky," but officials haven't been able to determine what the gas is, Asplin said.
Assistant Fire Chief Dean Meyer Meyer said at about 3:15 p.m. that the fire department was back on the scene and trying to find someone who can identify the gas.
Asplin Excavating was preparing the site to be resurfaced as a parking lot between NDSU's new Klai Hall and Barry Hall on Second Avenue North.
Two Asplin crew members became ill at 10:30 a.m. and drove together to MeritCare Hospital.
An electrician working inside and outside of Klai Hall also became ill, Assistant Fire Chief Steve Balstad said. He was decontaminated at the scene and taken to the hospital.
Firefighters and hazmat crews tested the air on the scene but found only trace amounts of methane before turning the site back over to North Dakota State University, Balstad said.
"The symptoms that these gentlemen were exhibiting was consistent with breathing methane - shortness of breath, burning of the throat and lungs - but it would have to be a sizeable (concentration)," Balstad said.
"It could have been just a pocket (of methane) down there coming out, that accumulated out of that old sewer line," he added.
Asplin said Zachary Hill, who is in his early 20s, was operating a backhoe while Robbie Whitten, who is in his late 40s, was on the ground before the two became sick. Hill is from Fargo and Whitten is from Moorhead.
Hill was digging with the backhoe when he jumped out of the machine and began gagging, coughing and dry heaving, according to Whitten, Asplin said.
Whitten told Asplin that he went over to check on Hill and caught a whiff of the mysterious odor, and that it smelled like mothballs and naphtha, an industrial fuel and solvent, mixed together, Asplin told The Forum.
"He got a little bit of a whiff, but it wasn't nearly the concentration the operator had, because he was downwind of it. It blew the cab full," Asplin said.
MeritCare spokeswoman Kirsten Jensen said the hospital saw five patients Friday related to the hazmat incident, and all were treated and released.
Work has been halted at the site so NDSU can take soil samples, Balstad said, adding the history of the lot wasn't immediately known. An NDSU official said crews uncovered and hauled away a concrete basement/foundation on Thursday, but that was west of where the backhoe was operating Friday.
Second Avenue North was blocked off between Seventh and 10th streets for about two hours during Friday's incident.
Asplin said it's not uncommon to uncover old petroleum spills during excavation, but he's never encountered anything like Friday's incident.