Sinkhole treatment to improve water quality and control erosion in southeastern Minnesota.

Abstract

Sinkholes in the karst region of southeastern Minnesota present a concern because of potential water quality degradation, erosion, and unsafe conditions. The State of Minnesota recently launched a program to provide costshare and technical assistance to several counties for developing measures to reduce these concerns. Sinkhole treatments such as surface water controls, sinkhole filling techniques, and other specialized treatments were evaluated for implementation under this program.

A review of available literature and our experience revealed that, although there were many methods of sinkhole treatment available, a design methodology or framework for selection of the proper treatment method was not available. A design methodology was developed to assist county Soil and Water Conservation District technicians in screening potential sinkhole treatment sites and evaluating possible sinkhole treatments. The methodology for sinkhole treatments was based on the treatment objective, physical conditions of the sinkhole or the sinkhole site, and economics.

Several projects were put in place to reduce pollution of groundwater from agricultural and residential sources and to prevent erosion of soil into sinkholes. A particularly interesting project involved diverting surface water away from a streamsink that had been shown by dye tracing to be connected to a spring supplying an important state fish hatchery. The sink was suspected of being a major contributor to elevated sediment, nitrate, and pesticide concentrations in the springs, particularly following runoff events. Preliminary results indicate the diversion was successful in improving water quality to the hatchery springs.