The Michigan Department of Transportation and the Michigan Electric Transmission Co. of Ann Arbor want to learn more about the land that a recent geological survey predicted will progressively sink and possibly even cave in over the coming decades.
A portion of I-196, roughly from Market Avenue to Fulton Street, runs alongside the land’s eastern edge and the expressway’s support pillars are on the property. The survey, conducted by local civil engineering firm Williams & Works Inc., rates that section of the property as free of sinkholes and relatively stable for now.
But the report adds that an outdated method of using long rectangular pillars to support the roof of a mine usually leads to sinkhole development, and that was the method used by Domtar Industries to support its gypsum mine on the property. The report then questions whether the pillars are adequate enough to support the roof over the long term.
In addition, the survey warned that the pillars could dissolve over time, as the gypsum will, and noted that the roof rock for this zone was the thinnest at its eastern edge, where I-196 sits, only 7 feet thick compared to 35 feet thick in the western side of the zone.
“We don’t know of any problems at this time with I-196 in regard to this issue. But obviously we will be looking at the freeway to ensure that there aren’t any problems now or in the future,” said Stephanie Litaker, regional communications representative for the Grand Region of MDOT.
“What that will entail is yet to be seen,” she added.
Litaker said that MDOT hadn’t seen the survey when the Business Journal spoke with her last Wednesday, but said the agency was anxious to review a copy of the report.
“Right now, we’re just basically focusing on what is going on now and what could happen in the future,” she said.
The situation for that stretch of I-196 is similar to a condition that once plagued the U.S. 131 S-Curve. Before MDOT rebuilt that highway stretch two years ago, the agency had to pour concrete into the bridge’s footings to prevent the highway from sinking further into the Grand River.
Litaker said that the mining operation on the property was taken into consideration when MDOT designed and built I-196 in the 1960s.
“But right now that’s not the main point. The big point for us right now is to look at the report, review it, and go from there based on what needs to take place in the future,” she said.
The Michigan Electric Transmission Co. (METC) owns the high-voltage electric transmission lines strung on support towers that cut through the middle of the parcel. The eastern two-thirds of the power lines are in the same geological zone as the highway, while the western third is in a more stable zone where the roof rock appears to be thick and the stability of the floor rock seems good.
The report added, however, that the mine pillars in the western section could also dissolve over time, likely decades, and decrease the stability of that property.
Like MDOT officials, METC executives hadn’t seen the survey when the Business Journal contacted the firm last week.
“These poles could be in the ground 10 to 12 feet, depending on the voltage and the size of the poles. And sometimes if it’s in unstable condition, we’ll concrete it in. But I don’t know if this is, in fact, the case,” said Jim Smith of METC from the Ann Arbor office.
Smith said he hoped to get a copy of the survey soon and have his engineers review it before visiting the property. He added that METC owns some of the electric towers and lines here, but not all of them.
METC bought its electric transmission system from Consumers Energy, the principal subsidiary of Dearborn-based CMS Energy Corp., in May. The sale was worth about $290 million and was the first U.S. transaction that involved a utility company selling its electric transmission system to an independent transmission company.
METC is a subsidiary of Trans-Elect Inc., a Canadian company. Deregulation of the state’s electric power industry prompted Trans-Elect to enter the Michigan market this year.
Kent County announced last week that it would not consider expanding John Ball Zoo on the property, which is just west of the zoo’s current location at John Ball Park. The geological survey determined that the property wasn’t stable enough to hold permanent structures, and that further erosion of the property’s stability would occur over the coming decades.