Altura, MN Waste Treatment Lagoon Failures: A Hydrogeologic Study

Abstract

In April 1976, a series of karat sinkholes opened in the holding lagoon of the Altura MN Waste Treatment Facility. Subsequent detailed field mapping of the region around the community revealed at least 22 sinkholes not shown on existing maps. The distribution of the sinkholes as well as post-failure investigations of the lagoon indicate that catastrophic collapse is related to the presence of a thin, poorly indurated, jointed sandstone overlying a thick carbonate unit. The sandstone served to collect solutionally aggressive vadose water and to concentrate that water onto specific areas of the underlying carbonate. The resulting differential solution produced voids into which the overlying materials collapsed. The disabled facility has been diverting partially treated effluent into a nearby dry run since the lagoon collapsed. A dye trace documented that the effluent after sinking underground reemerges from three local springs and then flows into a river which is a regional trout fishery. However, a second dye trace from the sinkhole in the lagoon failed to establish a connection to any local well or spring.