IRRIGATION PUMPING ASSOCIATED SINKHOLE DEVELOPMENT IN DAKOTA COUNTY, MINNESOTA

Water impoundments on Minnesota’s karst lands have led to multiple examples of sudden induced sinkhole failure: three Waste Water Treatment Lagoons, at least three major storm water retention lagoons, and many smaller ponds. In five of these six largest examples, the failures occurred when clusters of three to nine sinkholes formed more or less simultaneously. All of the six large failures have been at sites where thin sedimentary cover directly overlay Ordovician Prairie du Chien carbonates or St. Peter Sandstone over Prairie du Chien carbonates.

Between 11 Oct 2014 and 11 Aug 2015 a cluster of five new sinkholes developed within about 100 m of each other along a linear NW-SE trend in Dakota County. The largest sinkhole (MN19:D00044, 10 m diameter, 3 m deep, at: 504,539 m E; 4,935,345 m N, UTM Zone 15) is located near the center of the northern boundary of sec 26, Hampton Township. The site is within the broad glacial Cannon River Valley, and about four miles north of the currently active Cannon River Valley.

A Prairie du Chien aquifer irrigation well (Well # 779073, 105 m deep, installed 11 Apr 2012) is located about 100 m NW of D44 along the linear trend of the sinkhole cluster. In 2013 that well began supplying water to about 29 ha (72 acres) of row crop land via two center pivot irrigation systems. A second well (Well # 806080, 130 m deep, installed 6 Jul 2015) was completed in the Jordan aquifer and began supplying water to a third center pivot irrigation system on about 15 ha (38 acres) of land shortly after its completion , as seen on an air photo dated 11 Aug 2015. This second well is about 120 m NNE of D44. The first bedrock under both wells is the lower part of the St. Peter Sandstone.

The second largest sinkhole in the cluster (MN19:D00045, 4 m in diameter) is in an irrigated corn field. D45 clearly developed after that field was planted in spring 2015 but before the11 Aug 2015 air photo. None of the sinkholes in the cluster can be seen in an 11 Oct 2014 air photo. The nearest old sinkhole to this new cluster is 0.9 km to the NW and roughly along the trend of the cluster. The second closest old sinkhole is 2.3 km to the west.

To my knowledge the development of this sinkhole cluster is the first one in Minnesota that can be associated in time and space with irrigation pumping. As such it may represent a new form of human induced sinkhole development in Minnesota.