Benld Elementary creaked and groaned as it slowly pulled apart. The sounds echoed through the halls as we walked through the condemned school building. Three inch thick cracks lined the walls and floor prompting our guide, state geologist Bob Gibson to say that the gym could eventually collapse.
Outside the building a sidewalk has buckled into a V shape that sticks up about two feet in the air. It appears likely that the school will keep moving for months, perhaps years. The property has already sunk more than two feet in some areas. The source of the problem lies hundreds of feet below the surface in a mine that is collapsing. The movement is called subsidence.
In recent years hundreds of people have filed claims for subsidence damage in the metro-east. Gibson showed us a collection of maps and tools that can help determine your risk.
The picture at the right shows a home (the green spot) superimposed over the pillar of an underground mine. Eventually that pillar will collapse. It could be tomorrow, it could be 200 years from now, according to Gibson. In general, Gibson told me there is minimal risk that current homeowners in the metro-east will have subsidence damage during their lifetime, or the lifetime of the people who may buy their home.
Gibson showed us how he's able to project the degree of damage that will be caused by a subsidence "event." The red in the image to the left represents the most severe damage that is closest to the center of the underground collapse. The damage will be less serious the farther you get from there.
Subsidence can create huge craters that swallow houses, but in most cases they shift buildings a foot or two. Experts monitor the movement of buildings by inserting screws in them, then they'll take measurements frequently enough to determine if there's any movement. If they determine your damage was caused by subsidence you will get a settlement that will pay for damages. If they determine it's settling, then you'll have to pay for it yourself. The Illinois DNR website can answer many of your questions about subsidence.
You can see if you live above an underground mine by using visiting the website of the Illinois State Geological Survey.
The Gillespie School District, which includes Benld, closed the damaged elementary school and considers it a "total loss." The students were moved to another school where the dramatically increased student population attended classes on morning or afternoon shifts. Superintendent Paul Skeans told me he's hoping to get state funding for modular classrooms that would allow students to attend classes on a regular schedule in the fall.
Skeans says it will cost $22 million to replace Benld Elementary. The cost includes tests to determine if the new location is above a mine and if the mine needs to be filled with material that would prevent subsidence. It could cost several million dollars just to stabilize a site that large. Skeans hopes the district can get federal stimulus money to build the school. It seems unlikely that district voters would approve a bond to pay for it. Skeans says the bond would double the local tax rate.
It's a big challenge for the Gillespie District, one that became clear as we walked down the halls of Benld Elementary listening to to the sound of a condemned school still on the move.