Karst Terrain and Sinkholes

Karst terrain is characterized by the presence of easily dissolved bedrock (limestone and dolomite) near the ground surface. Because carbonate rocks can be dissolved by groundwater, karst areas are often characterized by sinkholes, springs, and losing streams where some surface flow is lost to groundwater. Groundwaters and surface waters in these areas are highly vulnerable to contamination because contaminants can travel quickly from the surface through open fractures and caves to aquifers, springs, and streams and are not likely to be filtered by soils.

The DNR has developed a statewide map of karst terrain that producers can check to determine if a potential animal feeding operation site would be located near a sinkhole or in karst terrain. Instructions for using the karst maps are available on the DNR AFO Maps site. See karst requirements below for confinements.

Karst Requirements for Confinement Feeding Operations: The Iowa Administrative Code prohibits new, expanding and modified confinement operations from constructing unformed manure storage (earthen basins) in karst terrain.

The Iowa Administrative Code also prohibits new, expanding and modified confinement operations from constructing within 1,000 feet of a sinkhole unless secondary containment is provided. Any new confinements in karst terrain, with more than 500 animal units, must meet upgraded concrete standards, by providing the DNR with soil borings indicating the depth to bedrock below the proposed formed structures. If there is less than five feet to bedrock below the bottom of a proposed formed structure, the construction plans must be signed and sealed by a professional engineer, and a two-foot clay liner must be installed below the structure. Water monitoring for ammonia-nitrogen may also be required for new confinements in karst terrain.