The heavy rains that have doused the village of Oak Park the past two years have brought a problem other than the much-ballyhooed flooding: sinkholes.
This year, Oak Park has identified 32 sinkholes all over town — caused when rainwater dribbles down through the pavement and into a ruptured sewer pipe below, pulling the pavement downward. That number exceeds the 25 sinkholes formed in Oak Park streets all of last year and the 19 in 2009.
“It does seem like they’re happening more often with the heavy, frequent rains we’re having,” said Brian Jack, water and sewer superintendent for the village.
Most of the 32 sinkholes have been repaired already, save for a few that popped up just recently. On average, it costs about $2,500 to repair a sinkhole — including labor, materials and equipment — which involves patching up the busted pipe with plastic, filling in the hole with stones, and capping it with asphalt or concrete.
Most of the sinkholes have been relatively small in size, just 1 foot in diameter and a couple of feet deep. However, a giant crater, about 10 feet deep and 10 feet wide, did form on the 800 block of North Harvey during heavy rains last summer.
A man driving his SUV to work in Chicago plummeted into a 10- to 12-foot sinkhole on Saturday, according to the Chicago Tribune. Jack was unaware of any reported vehicular accidents or pedestrian injuries because of sinkholes, but at least one bicycle accident involving a sinkhole occurred earlier this summer, causing a thrown rider to dislocate both wrists.
The hardest hit area has been the 800 block of North Harvey, with five so far this year. That’s because the pipes running from the main sewer line below, up to the houses above, are made out of clay, rather than plastic, according to Village Engineer Jim Budrick. Plus, those lines run almost straight up because of how deeply the sewer line is buried, rather than at a less steep incline.
Budrick said the quick vertical incline of those sewer pipes puts more pressure on the joints connecting the pipes, causing them to rupture and sinkholes to form. To remedy the problem, Oak Park is sending cameras through the sewers to seek out problems and see if the sewer system needs a more complete reconstruction.
That’s unlikely, though, as the sewer pipes below 800 N. Harvey were last replaced in 1969, while pipes in other parts of Oak Park date back to the early 1900s, according to Jack.
Anyone who spots a sinkhole should call Public Works at 708-358-5700.