MARQUETTE, Mich. (AP) — Two concrete vaults used to store tar residue and other impurities from a manufactured gas plant more than 100 years ago were recently found buried underground just north of the Shiras Steam Plant in south Marquette.
Steve Harrington of the Michigan Department of Environmental Quality said the vaults and surrounding soil were tested for hazardous material and determined safe.
The plant's manufacturing process involved heating up coal in a vacuum to create a gaseous fuel.
"Typically, these coal gas sites are not hazardous," Harrington told The Mining Journal ( http://bit.ly/1B9IEWy ). "These were not uncommon operations back in that era, back before they had natural gas."
The process involved heating up coal in a vacuum and spraying the coal with a fuel-oil product to increase combustion. The process produced a type of coal gas, which was sucked out and kept in above-ground storage tanks. The tanks could be 60-75 feet across and as tall as two- or three-story buildings, Harrington said.
The gas manufacturing process also required below-ground concrete vaults, such as the two found near the Shiras plant, that would capture residue and impurities.
Harrington said most towns made their own gas that was distributed through a system of underground pipes to light street lamps and other light sources.
"In that process they did create a fair amount of residue," Harrington said, which would have been stored in the below-ground vaults.
The property where the vaults were found is owned by Indiana Michigan Power Company, a unit of American Electric Power.
IMPC contracted with Haley & Aldrich construction services to replace culverts in the area when the crews came across the vaults. Harrington said IMPC has entered into a "self-implemented cleanup."
"The property owner is allowed to conduct their own cleanups, which we encourage actually," Harrington said.
He estimated IMPC was spending about $1 million on the project already, which could have been coming out of taxpayers' pockets. Harrington said hazardous waste cleanup projects often involve "orphaned" property, leaving the state to pick up the tab.
"It's not unusual to be cleaned up with taxpayer dollars, so in this case it's fortunate," Harrington said.
He said the DEQ called IMPC's cleanup measure an interim response, meaning the company is trying to get most of the contaminants removed.
"They're probably removing 98 percent of it, but you'd have to really remove every speck of soil," Harrington said.
To do that complete of a cleanup, he said it would cost tens of millions of dollars.
About 12,000 tons of soil were tested by the DEQ and allowed to be transferred to the Marquette County Landfill.
Material in the vaults, which contained about 57,000 gallons of liquid, was also tested and permitted to be transferred to K.I. Sawyer's wastewater treatment plant.
Condensation occurred in the vaults leaving a fair amount of water and some oily substances that could be treated at the plant, Harrington said.
The construction crews were in the process of restoring soil to the area and replacing an old box culvert for Orianna Brook, which runs through the area.