Operation: Neighborhood Sinkhole
R. SCOTT RAPPOLD
January 14, 2009 – 10:13PM
Closing a street, drilling a hole in the pavement, spewing out water that turns to a sheet of ice and shattering the quiet with blasts of air might annoy residents in some neighborhoods. Folks on Country Club Circle are thrilled.
That’s because the old coal mines that run under their homes, relics of Colorado Springs’ forgotten days as a mining town, sometimes cause sinkholes, which sometimes cause houses and yards to collapse. The Colorado Division of Mining, Reclamation and Safety is nearing the end of a geophysical study on the subterranean chambers, and the agency will soon begin filling them with grout or a sand slurry. It marks the first time either has been done in Colorado on a mine tunnel that has not already collapsed.
“That would be awesome, absolutely awesome, and it certainly can’t hurt our (property) values if we get a clean bill of health,” said resident Dawson Davis.
A large chunk of Colorado Springs, roughly from the area around Colorado Springs Country Club northwest to Rockrimmon, was mined from the late 1800s to the 1950s.
Since there were no mining reclamation laws on the books, the snaking underground chambers were simply left open and abandoned, and houses were built above as Colorado Springs expanded.
The last major collapse was in 2005, when five houses on Country Club Circle, near Union Boulevard and North Circle Drive, were threatened. Thousands of residents buy mine insurance to cover damage if there’s a collapse.
In the past, the state responded to individual collapses by filling chambers, but officials had to rely on the “shotgun approach,” blind drilling, to find the underground chamber.
The mining agency, thanks to funding from coal mine taxes, last year commissioned a study of Country Club Circle with geophysics, by sending signals underground and recording them with a device that measures their reflections, to detect gaps that signify mining tunnels. The area was chosen as the first in the state for this technique because it has the most problems of underground
mine collapses affecting residents.
“The state is more proactive,” said Kanaan Hanna, of engineering firm Zapata Inc., which is doing the study. “Instead of waiting for a sinkhole to occur, they determine where they are and how they can ensure they don’t come back.”
Wednesday, Hanna’s crew was wrapping up testing for the project on Country Club Circle. The next step is to determine which mine chambers are most at risk of collapse – generally, those that are 65 feet or fewer below the surface – and to fill them, beginning this spring.
The whole project will cost up to $1 million, funded by the mining tax. This fall, the agency will conduct similar tests of nearby Fairway Drive. State officials have not announced plans for the rest of the mining area, where collapses have been less frequent.
Some residents could be inconvenienced by the work, which could involve drilling holes and moving heavy equipment in their yards.
“We try to minimize how much effect we have on a lawn by having the contractor drive on there through plywood and drill through plywood,” said division engineer Al Amundson. “When they get done, they’re responsible for cleaning up any damage or fixing any damage.”
Few residents seem to mind.
Davis called such an inconvenience “incidental.”
“I’m pretty happy about it,” resident Mike Provenzano said of the project. He grew up near here and remembers being told it was unsafe to play in the area because of sinkholes. Then they built houses there.
“I hope they don’t have to come drilling in my yard, but if they have to, they have to,” Provenzano said.
