MARION COUNTY, Iowa — Officials have determined the cause of a sinkhole that opened up in a farmer’s field south of Knoxville in April and now work is underway to fix it and part of a road affected by the sinkhole.

Marion County’s Public Information Officer Emily Feagins said the sinkhole at 135th PIace was the result of limestone mining in the area. Bruening Rock Products Inc., the company that does the mining in an area directly adjacent to the sinkhole, has submitted a mitigation plan to the county and it has been approved.

Work on the repairs began this week. Feagins tells WHO 13 the work will include first digging deeper into, and around, the sinkhole before it is filled in. Bruening Rock Products will also have to remove the section of the road damaged by the sinkhole and then replace it.

As part of the mitigation plan, the work will be done by Bruening Rock Products at no cost to the county.

Part of 135th Place remains closed as the repairs are being done. It will be several weeks before the work is complete.