GROUNDWATER AGES IN RICE COUNTY, MN INDICATE VULNERABILITY TO POLLUTION

Agricultural runoff in southeastern Minnesota has contaminated shallow aquifers with nitrates, a pollutant that reduces to nitrite with serious health consequences. Seeking to limit contaminates in drinking water, a new ordinance in Rice County requires private landowners to drill wells into the Jordan Aquifer, a sandstone unit that is confined by ~100 meters of glacial sediment to the west of the Cannon River, and by several strata of shaley limestones to the east. Although hydrologic models indicate groundwater in the Jordan Aquifer should be hundreds to thousands of years old, chlorofluorocarbon (CFC) concentration data shows recharge on a decadal scale. Previous tests of other aquifers in Rice County found groundwater age to negatively correlate with anthropogenic pollutant concentrations, including nitrate and chloride. Although this research found no nitrates within the Jordan Aquifer, these results show that the Jordan Aquifer could be more susceptible to pollution than previously thought. Atomic absorption data show greater concentrations of calcium, chloride, and potassium ions in the groundwater surrounding the Cannon River. The tested ions are not themselves pollutants, but they do suggest that agricultural runoff is polluting local surface waters. This study should inform concerned professionals as well as the general public about the importance of keeping pollutants from entering rivers and other surface water reservoirs.