Mine subsidence in region a constant problem for DEP
Shelva Corna wasn't too happy to spend part of her retirement on $30,000-plus in repairs for her Hyde Park basement that shifted in 2011 due to mine subsidence.
More than any other part of the state, Southwestern Pennsylvania is honeycombed with abandoned coal mines.
And they can collapse at any time.
Recently, 10 homes in Mt. Oliver Borough, which is next to Pittsburgh's Mt. Washington neighborhood, sustained damage from mine subsidence. The state Department of Environmental Protection is starting work on a $1.35 million project there to fill in the mine voids. It is expected to take eight to 10 weeks.
And in Hyde Park, the DEP is a few weeks away from completing a nearly $3.7 million, nine-month project that is injecting 48,000 tons of cement and fly ash grout into the underground mine voids beneath 69 homes in the borough.
Where will subsidence hit next?
Anywhere there are underground mines, which are most places in this corner of the state.
“We feel there are communities where residents possibly aren't aware that there are homes built over mines — based on the number of mine subsidence policies we have there,” said John Poister, DEP spokesman.
The state is responsible for shoring up mine subsidence from abandoned underground coal mines.
However, the state is not responsible for damage caused to private property.
Plum, Penn Hills, Mt. Lebanon, Upper St. Clair and Belle Vernon are among communities where DEP would like to see morehomeowners with mine insurance.
“As good as our guys are at doing this,” Poister said, “they cannot predict where it's going to happen and when it's going to happen.”
After Corna paid to fix her Hyde Park home, she bought the subsidence insurance “just in case,” she said.
Corna said that she considered buying the insurance earlier when she heard of mine subsidence years ago in nearby West Leechburg, Leechburg and North Apollo.
It's all too common for residents to not be prepared for mine subsidence: Only about 6 percent of the more than 1 million at-risk homeowners sitting on top of abandoned mines in the state — most of whom are in Southwestern Pennsylvania — have the insurance, according to Poister.
Standard homeowner's policies don't cover damage caused by subsidence.
The insurance is relatively cheap through the state program at $57 annually per $100,000 worth of coverage up to $500,000.
DEP administers the program, which is funded by insurance premium payments and no taxpayer money, according to Poister.
Trying to get the word out, DEP most recently sent 1,700 insurance brochures tohomeowners within a 5-mile radius of Mt. Oliver, according to Poister. In the coming weeks, DEP will target Munhall, Pleasant Hills and West Mifflin with mailings.
Not going away
After more than two centuries of coal mining, the room-and-pillar mines have been deteriorating and will continue to do so.
The rate of decay in mines is dependent on the location of the mines and type of surrounding rock, according to Paul Ziemkiewicz, director of the West Virginia University Water Research Institute.
“In some cases, the mine roof is still intact even if the pillars are gone,” he said. “Other times, you have a weak, shale rock, and those start falling down as soon as you pull out mining equipment.”
While the construction and condition of the mines differ, the depth of the mine is predictive of subsidence: The more shallow the mine — in the 50-foot deep range — the more likely that subsidence will make its way to the surface, Ziemkiewicz said.
The deeper mines will often fill in when they collapse and subsidence will never make it to the surface, he said.
According to DEP, the incidences of mine subsidence are constant, not increasing nor decreasing.
However, according to Ziemkiewicz and Poister, there could be more subsidence in years to come as the old coal mines continue to age and collapse underground.
DEP pumps in cement and grout into the mines that threaten to collapse.
Subsidence usually is discovered at one or several homes. The agency then drills holes throughout the area to assess the size and extent of the underground void caused by the mine collapse.
Some type of an event usually triggers the agency to check subsidence damage in a particular area, according to Gene Trio, a longtime DEP mining engineer.
Filling the void
The DEP projects have been successful in preventing future subsidence, according to Poister.
In the last two decades, there have been only four cases of subsidence reoccurrence out of 2,500 properties that DEP had to go in and fill in the underground mines, Trio said.
“Although we have not eliminated the chance of subsidence from occurring in these areas,” Trio said, “we greatly reduced the chance.”
Mary Ann Thomas is a staff writer for Trib Total Media. She can be reached at 724-226-4691 or email@example.com.
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