Possible Geological-Geochemical Sources of Ammonium in Groundwater: Preliminary Results

Abstract

Ammonium has been detected in water wells in relatively large (>2 mg/L) concentrations in east-central Illinois and in central Iowa. Ammonium can interfere with drinking-water disinfection, and can be converted into nitrate and nitrite. The possible sources of ammonium in groundwater include fertilizers, landfill leachate, and wastewater disposal. However, the hypothesis of this study is that ammonium in groundwater can occur naturally from subsurface organic zones such as buried soils. Historical data indicated that ammonium has been detected in groundwater samples in relatively large concentrations before the current, voluminous use of nitrogen-containing fertilizers. The approach being used in this study is to conduct laboratory and field work to provide data on the possible link between buried organic material in Quaternary-age deposits and ammonium in water-wells. The results of the first year of this project indicate that the Robein silt is a potential source of ammonium in groundwater via dissolution, ion exchange, and mineralization reactions. The Robein silt can also retain ammonium via sorption. Enhanced (>2 mg/L) concentrations of ammonium were detected in water samples collected from wells located in two study areas (Champaign and Piatt Counties). However, there was insufficient evidence to link the ammonium in the well samples specifically with the Robein silt. On-going research will include the collection of additional groundwater samples, and the soil physical chemical characterization of recently collected soil samples.