Homeowners in the metro-east who are concerned about mine subsidence can use an interactive mapping tool provided by the Illinois State Geological Survey to see if there's a coal mine under their property.
The online map has been used thousands of times since mine subsidence damage forced the recent closing of Wolf Branch Middle School in Swansea, said Scott Elrick, a geologist with the survey, which is part of the Prairie Research Institute of the University of Illinois.
The map has been available for several years, but people often don't find out about it until there is a mine subsidence incident that makes the news.
“The more we can spread this around and the more people who are aware of it and can utilize it, I think the better. People can make more informed decisions,’’ Elrick said.
Those decisions could include buying mine subsidence insurance — or even whether to build or purchase property, he said.
More than 800,000 acres of Illinois land has been undermined for coal and minerals, according to the geological survey, and about one-fourth of that acreage is residential or “built-up” land. An estimated 330,000 homes in the state are built above coal mines. Much of St. Clair and Madison counties are undermined.
Elrick said the tool, which uses a Google map interface, is limited to 2,500 inquiries a day, but they are working to increase that number. He encourages people who are having trouble using the map to try again later in the week.
Here are a few things to know:
What is mine subsidence?
Here’s a simple explanation, courtesy of the Illinois Mine Subsidence Insurance Fund: In most coal mines, workers created underground rooms, leaving pillars of un-mined coal to support the mine roof and ground surface. Over time, the roof can sink or shift, causing the ground above to sink or subside.
What does the interactive map show?
The interactive map is on the website of the Illinois State Geological Survey. People can type in their addresses to see whether their homes are located above an underground coal mine or close to an underground mine.
Elrick said the digital tool was compiled using a variety of data, including old maps of mines. The geological survey has maps for about half of the estimated 5,500 coal mines in the state. Most of these mines have been abandoned for decades.
Even if property is not directly above a mine, it can be impacted by subsidence.
“If a collapse in a mine occurs, the subsidence doesn't travel up to the surface in a straight line. It works its way out at an angle,’’ Elrick said.
Mine subsidence insurance
Illinois requires all insurance companies that insure property in the state to provide coverage for mine subsidence, according to Kathleen Moran of the Illinois Mine Subsidence Insurance Fund.
In the 34 counties where most underground mines are located, the state requires the insurance to be included in residential and commercial policies, unless the insured rejects the coverage in writing.
The insurance fund is a private enterprise that was established in 1979 by an act of the Illinois General Assembly to re-insure insurance companies for mine subsidence claims.
Moran encourages homeowners to check the geological survey’s map, and to also make sure they’ve purchased enough insurace coverage, based on the value of their property.
“It's a good time to check your insurance policy to see where you are in terms of this map and at least make sure that you're taking full advantage of this program,’’ she said.
Signs of mine subsidence
Moran says homeowners should watch for signs of subsidence and contact their insurance company if they suspect damage.
“It can be very subtle and you might not notice, but over time you might see cracks in the walls or the pavement or your foundations or sidewalks pulled apart,’’ she said.
Some signs include:
Cracks or breaks in the foundation
Cracks in basement walls, driveways or garage floors
Popping or snapping sounds, as if the structureis shifting
Unlevel walls or floors
Doors that swing open or closed on their own
Ruptured utility lines
Follow Mary Delach Leonard on Twitter: @marydleonard
Note: The map with this story has been corrected to include the correct address for Wolf Branch Middle School.