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Sinkhole no longer poses danger, engineering study says

August 6, 2020 GMT

BLACK HAWK, S.D. (AP) — A sinkhole near an interstate in Black Hawk that forced some residents to evacuate their homes no longer poses danger based on an engineering study that did not find any voids under the road, the South Dakota Department of Transportation says.

DOT hired Rapid City-based FMG Engineering to look for underground abnormalities after the sinkhole on April 27 exposed that part of the Hideaway Hills community was built over an abandoned gypsum mine.

The study examined 1,500 feet (457.2 meters) of Interstate 90 adjacent to the mine and 60 feet (18.28 meters) under ground, according to a report from Geo-Vision, a California-based geophysical company that assisted FMG Engineering conduct the study.

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The groups used electrical resistivity tomography to look for any voids.

“The test results of the borings revealed none of the areas identified as anomalies were a void or anything else that would cause concern for the integrity of the interstate,” DOT spokeswoman Kristi Sandal said in an email to the Rapid City Journal. The Department and the state “are confident there is no threat to I-90 because of the mine discovery.”

The sinkhole forced about 40 residents in the area to evacuate. Hideaway Hill residents are suing the state, real estate agents, county officials and developers after public records revealed the Meade County Planning Board knew about the mine when it approved the Black Hawk housing development.

Meade County is investigating how the Meade County Planning Board approved the subdivision in 2002.