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.
Unpublished manuscript outlining hydrogeologic investigation (including geology, hydrology, dye tracing, etc.) of the Altura WWTF lagoon failure in 1976 in Winona County, MN. Work was later published in the proceedings of the first multidisciplinary conference on sinkholes (see, "Sinkholes: Their Geology, Engineering and Environmental Impact").
Legislative Commission on Minnesota Resources of the State of Minnesota
Book, Paul R; Alexander Jr., E. Calvin.
Altura, MN Waste Treatment Lagoon Failures: A Hydrogeologic Study.
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