High-Resolution Timeseries Analysis of Dynamic Geochemistry: A 27-Well Survey of Contaminated Groundwater Downstream of the former S-3 Ponds, Oak Ridge, Tennessee

Spatiotemporal variability of geochemistry of contaminated groundwater has large implications on overall water quality and ability to respond to remedial applications. Gaining knowledge of how geochemistry changes over time in an area can help establish response trends to changing external conditions like weather and level of contamination. In this study, a spatiotemporal survey was performed on 27 wells at the Y-12 Complex in Oak Ridge, Tennessee. This was completed to measure diurnal fluxes in geochemistry from seasonal changes and extreme weather conditions in three areas of historically different contamination levels from a single point contamination source. Measurements were gathered over 27 previously established groundwater wells, four days a week, for the span of 17 weeks (70 days total) to build a time series of geochemistry. In-field geochemical measurements were obtained using In-Situ Aqua TROLL 600s including dissolved oxygen (DO), pH, conductivity, oxidation-reduction potential (ORP), and salinity. Groundwater samples were taken for laboratory analysis and include metals, anions and organic acids, total organic carbon, and stable water isotopes. Here, the field measured geochemistry results are presented. Findings show that time and weather play critical roles in groundwater geochemistry but in varied ways for certain parameters. DO and conductivity values showed large effects due to changing weather conditions, but with extreme rainfall DO showed lasting changes, while conductivity levels quickly rebounded to baseline levels. However, this phenomenon was seen to a much lesser extent in wells with historically high amounts of contamination. PCA analysis showed that all parameters in areas of high contamination were more stable throughout the timeseries even under extreme weather conditions. Conclusions suggest time and weather play important roles in controlling overall geochemistry in groundwater and measuring geochemical response throughout time can also aid in determining redox conditions and extent of contamination. Therefore, it is necessary to have weather and water levels as parameters when establishing baseline geochemistry for any given area.