Sinkhole Whack-A-Mole - Lessons Learned Grouting a 25MGD Karstic Mine Leak-Paper

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A limestone mine near Big Stony Creek, Virginia, experienced a dramatic rise in groundwater inflow in March 2020. Following unusually heavy rainfall, water entering the mine increased from about 4,000 to 12,000 gallons per minute, eventually peaking at 17,000 GPM—far beyond the mine’s dewatering capacity. The site’s karstic limestone contains sediment-filled conduits that were rapidly enlarged by erosion, triggering multiple sinkholes in and beside the creek.<br /><br />Repairs had to protect the creek’s endangered Candy Darter population and meet transportation-agency requirements after a sinkhole affected a nearby bridge footing. Cement-based grout was rejected because of environmental risks. Instead, crews used potable-water-certified, hydrophobic polyurethane grout, which expands rapidly, cures into a rigid foam, fills voids, and compacts surrounding material. Modified driven anchors placed grout up to 35 feet deep; temporary barriers and bulk bags helped reduce water flow and grout washout.<br /><br />The work proceeded in several rounds as new sinkholes appeared. After grouting five sinkholes and placing additional material to stabilize the area near the bridge, mine inflow fell to approximately 4,000 GPM, and no visible sinkholes remained. The emergency treatment provided time to assess longer-term options but was not a permanent solution: karst features extended much deeper than the grout placements, and new sinkholes formed in 2021, ultimately contributing to the mine’s indefinite closure.<br /><br />The project demonstrated that polyurethane grouting can rapidly control leaks and fill cavities in a dynamic, environmentally sensitive setting. However, shallow emergency treatment may only provide temporary relief. Preventing recurrence would likely have required a deeper grout curtain across the creek and floodplain—an impractical option during the emergency because of the need for extensive drilling in the creek bed.

Keywords

limestone mine

groundwater inflow

karstic limestone

sinkholes

Big Stony Creek

polyurethane grout

emergency grouting

Candy Darter

bridge footing

dewatering capacity