Average Natural Groundwater Fluoride Concentration vs. Soil/Rock Type

Objective: To determine if there is a correlation between soil/rock type and Indiana's natural groundwater fluoride concentrations. Methods: A total of 8,519 water samples from private wells were collected by private citizens and sent to the Indiana State Department of Health for fluoride analysis. Laboratory analyses using a fluoride electrode were performed to determine the fluoride concentration in mg/liter (or parts per million-ppm). These data were then plotted on a Geographic Information System (GIS) map relative to the collection site by postal zip code within counties. Geological data showing Indiana bedrock geology and soil types were obtained from the Indiana Geological Survey at Indiana University. Results: The results of the survey showed that a wide range of fluoride concentrations exist in Indiana's groundwater and that wide variation of fluoride concenetrations can occur within an individual county. In comparing fluoride concentration with soil/rock types, the highest naturally occurring fluoride levels in private wells are found in soil consisting of discontinuous loess over weathered sandstone and shale soil overlying Pennsylvania age bedrock aquifers. Conclusion: The data indicate there is a positive correlation between soil/rock type and naturally occurring fluoride levels in Indiana groundwater. There appears to be a correlation between well depth and alkalinty, with higher fluoride concentrations.