Study: Abandoned S.D. Gypsum Mine May Extend Below Interstate

An abandoned gypsum mine in Black Hawk, S.D., that was exposed by a sinkhole in 2020 may extend farther than current mapped areas show, according to a geophysical study.

Mohammad Sadeghi, a professor of geological engineering at Montana Technical University who led the study, says there’s the possibility that the mine extends below Interstate 90. The group recommends that further research be done in the area.

More than 40 people from 15 homes in the Hideaway Hills neighborhood were forced to evacuate after the collapse in April 2020 in Black Hawk, which is located about eight miles northwest of Rapid City.

There are at least two lawsuits filed in relation to the collapse, one of which is one step closer to class-action status, the Rapid City Journal reported.

The Fitzgerald Law firm of Rapid City filed a lawsuit against developers and county and state entities. Fox Rothschild, a large national law firm, filed one against state government.

Hideaway Hills residents are also seeking answers to a potential loss of sewage service due to the mine.

Sadeghi has presented his team’s research methods to Hideaway Hills residents and said he believed the sinkhole opened due to surface water infiltrating the ground and seeping into the roof of the mine that dissolved gypsum.