Butler County — like most of Western Pennsylvania — has a rich history of coal mining dating to the late 18th century.

Since 1945, most of the coal produced in the county was recovered through strip-mining methods. Before 1945, underground mining was more prevalent.

It is this method of coal mining that has some Western Pennsylvanian residents concerned after a 64-year-old Westmoreland County woman fell into a sinkhole caused by subsidence from an abandoned underground mine. Police believe Elizabeth Pollard was searching for her missing cat when she fell into the void. Rescue and recovery teams found her body after an intensive four-day search hampered by unsafe conditions.

Sinkholes are circular depressions or holes in the ground that form when surface material collapses into underground voids. They can pose significant dangers to public safety, property and infrastructure, potentially causing substantial economic damage.

Butler County’s 2021 Hazard Mitigation Plan Update acknowledges sinkholes as a natural hazard based on geological risk.

In mid-April, a sinkhole in Evans City Road prompted a road closure while state Department of Transportation crews evaluated and then repaired the problem. A cause was not immediately identified and PennDOT verified that drainage in the area was working as intended.

Christina Gibbs, community relations director for PennDOT District 10, said county maintenance crews regularly ride roads to check conditions. For reports from an outside source, a crew can be on the site soon after being notified of cracks or holes on a state road to assess and respond to the situation.

“Typically, the roadway will exhibit some sign of distress such as cracks or visible dips before a hole forms,” Gibbs said. “The public or our county maintenance crews will notice this, and it will be brought to the attention of the District 10 geotechnical unit for further investigation.”

When a sinkhole happens on a state road, PennDOT follows a specific protocol. First, it examines the area and determines the severity of the situation.

“If there is an actual hole on the road surface, they will close the road immediately,” Gibbs said. “If there’s a dip in the road, they may close a lane or add a ‘bump’ sign and contact utility companies if underground utilities may be adversely affected due to the movement.”

Within 24 hours, a geotechnical unit worker investigates the site and makes recommendations. Core borings may be drilled to determine the size and depth of an underground void. Coal mine maps are researched to determine the depth of possible coal seams, with down-hole cameras sometimes used to take video of the void under the surface.

Repairs vary, Gibbs said, depending on the cause of the void.

“The district researches the site to determine if there are records of underground mining in the area and may drill core borings to determine the extent of the void,” she said. “Once the limits of the void are established, a plan is put into place to fill the void, typically with some kind of concrete or flowable cement grout.”

Sinkholes aren’t always caused by mine subsidence. Gibbs said shallow sinkholes may occur due to underground utilities.

“For example, a broken waterline can cause an underground stream to occur that carries material away with the water and creates a void that could collapse,” she said. “If the void is determined to be the result of a broken or deteriorated utility line, the utility company would be notified immediately.”

Iuri Santos, an assistant professor of civil engineering at Slippery Rock University, is an expert in geotechnical laboratory testing, geotextiles and finite element modeling. He said one of the most influential geologic factors that make a landscape more prone to sinkholes and other hazards is karst.

It’s formed by the dissolution of soluble rocks, mainly limestone and dolomite. Karst landscapes weaken subsurface structures, creating underground voids that can collapse under pressure. However, most karst regions of Pennsylvania are in the middle of the state, according to information from the state Department of Environmental Protection (DEP). Santos said Butler County’s geologic makeup consists mostly of sedimentary rocks like sandstone and shale.

Santos said it’s difficult to predict if someone will experience subsidence in Butler County based solely on the geologic structure and any evidence of previous underground mining.

Property owners worried about the possibility should seek a thorough analysis from a professional geologist or engineer, he advised.

“It’s important to note that not all ground movement is subsidence and not all ground movement means that your house is going to collapse,” he said.

He said Butler County residents shouldn’t worry that what happened in Westmoreland County could happen here.

“It’s not a natural phenomenon here. If you’re in an area that you know you have an old abandoned mine, you may want to get in contact with the DEP to chat about if your area is prone to subsidence or if you want to investigate anything that’s happened before.”

Thomas Decker, Regional Communications Manager for the DEP said county residents or businesses concerned about possible abandoned mines under their property can use special maps that show known or suspected underground mining throughout the region. The digital tool is available on the agency’s website at gis.dep.pa.gov/msiRisk.

Underground mining areas are denoted in gray. The DEP recommends mine subsidence insurance for properties located in these regions. The pink areas are sites where the DEP knows coal exists but has no concrete records of underground mining activity. Mine subsidence insurance is available for these areas if desired.

“If someone notices a sinkhole on their property or any environmental emergency, they should report it to DEP or call 911,” Decker advised. “Any environmental issue reported to DEP is routed to the appropriate environmental program area.”

DEP’s bureau of abandoned mine reclamation is responsible for dealing with hazards from coal mining before 1977. If the hazard is related to abandoned mining, DEP designs subsidence control projects in-house because it possesses the expertise and can move quickly in emergency situations, he said.

To report an issue to the DEP, call 866-255-5158 or visit dep.pa.gov and use the complaint form to file a request for assistance.