Did test hole drilled 4 decades ago cause Mich. sinkhole?
Officials investigating a sinkhole in suburban Detroit are examining whether a hole drilled into a sewer line caused the pipe to collapse. (Jan. 4) AP
FRASER, Mich. — A hole bored into a sewer line nearly 40 years ago may be the cause of a sinkhole here that surfaced Christmas Eve, resulting in the condemnation of three houses and forcing 19 other families from their homes.
A similar hole bored at the same time was found to be close to the site of a 2004 sinkhole, also on 15 Mile Road but in neighboring Sterling Heights, that cost $53 million to repair, Candice Miller, Macomb County public works commissioner, said Wednesday. The holes had been bored at either end of a 1978 sewer line collapse to test how far the damage extended.
"We know we have a big problem," she said. "We know we have an expensive fix."
She said she doesn't know how much the repair will cost, but it, too, likely will be tens of millions of dollars. She said Michigan Gov. Rick Snyder's team is looking at every possibility to help the suburban Detroit county of about 850,000 people, including an emergency declaration, which could help bring in state and federal money. Miller's office is looking for money — right now public works customers would have to pay to fix the problem through a rate increase — and county officials said a bond sale is possible.
Two other houses near the sinkhole at the corner of 15 Mile Road and Eberlein Drive have been condemned, but the county's chief public works engineer, Keith Graboske, said the decision to condemn those two houses — deeming them uninhabitable — could be reversed.
Other displaced families in the neighborhood should be able to return home by Monday. A temporary road is built, gas services have been restored and results from a second water test are pending, Miller said.
Businesses remain open in the area, but only local traffic is getting around the barricades and construction equipment on 15 Mile Road. A temporary bypass line for sewage is being constructed and is expected to be up in three to four weeks. Once the damaged sewer line dries out, officials can get inside the 11-foot pipe to determine what caused the sinkhole.
Miller continued to urge 300,000 residents in 11 communities in the drainage district to restrict water usage so raw sewage does not have to be discharged into the Clinton River and basements don't back up, especially a problem during heavy rains.
Miller and Jason Edberg, vice president of NTH Consultants Ltd. of Detroit, which was contracted to investigate the sinkhole and did the same for the 2004 sinkhole, said the cause of both sinkholes might be connected to holes bored in 1979 when the Detroit Water and Sewerage Department owned the line.
Macomb County's public works department bought the line in 2009 and it was inspected in 2010, Miller said.
In 1978, a sewer line collapsed on 15 Mile between the two sinkhole sites when the city of Fraser tried to hook in, Miller and Edberg said. Eleven holes were bored in a segment of the line not used after the collapse, and a bypass line was created around the collapsed area.
However, in 1979 during the follow-up investigation of that collapse, the contractor also bored two other holes in the sewer line outside the collapse area to determine how far the collapse spread.
The 2004 and 2016 sinkholes are located at the sites of those two holes, both of which are on a segment of the line that has been in service to carry sewage since the 1970s, Edberg said.
All of the holes were believed to be patched with grout, but the patches may have failed, allowing groundwater to get into the pipe, carry soil out and erode the soil under the sewer pipe, Edberg said. The holes may not have been visible to the naked eye because the line always contains about 3 feet of water.
If this collapse turns out to be similar to the one in 2004, officials will know how to fix the problem, Miller said. But it's possible they may never know for sure what caused the sinkhole.
Macomb County Executive Mark Hackel said he is talking with other officials to determine how to help the affected families, including the possibility of buying the condemned homes.
Bills already are coming in, Miller said. Supervisors at the scene are keeping an electronic field book with time, material and equipment used.
The former GOP congresswoman was elected in November to the public works commissioner post — which covers Huron, Lapeer, Sanilac and St. Clair counties; northern Macomb County; and eastern Tuscola County — defeating a Democrat who had been in the position for 24 years. She officially took office Sunday and said she plans to contract with a company this month to do a forensic audit of the public works office accounts.
Contributing: Robert Allen, Detroit Free Press. Follow Christina Hall on Twitter: @challreporter