Additional homes may be at risk where sinkhole exposed mine

BLACK HAWK, S.D. (AP) — A second phase of geophysical tests in a Rapid City area neighborhood where a sinkhole exposed an abandoned mine shows 30 additional homes may be affected.

The sinkhole that exposed the old gypsum mine opened in April 2020 in the Black Hawk neighborhood where it has already forced 40 people to evacuate from 15 homes.

Geoscientist Mohamed Khalil, with the University of Nebraska-Lincoln, said the second phase shows the seasonal fluctuation of the groundwater table over the past few decades has created conditions for a sinkhole in any weak spot, the Rapid City Journal reported.

The Fitzgerald Law Firm released the latest report on the geophysical testing in the neighborhood. It represents homeowners who have filed lawsuits in relation to the sinkhole.

One lawsuit says the state of South Dakota should compensate affected residents since it mined underneath the entire neighborhood up until 1993 but failed to reclaim and warn buyers about the now-collapsing mines.

Khalil said the tests also showed there are likely tunnels filled with water that extend to Interstate 90 and the southern area of Hideaway Hills subdivision. He said he would recommend structural analysis before drilling, excavation or construction is done.