AN EVALUATION OF THE USE OF INDIGENOUS BACTERIA AS A GROUNDWATER TRACER IN FRACTURED BEDROCK

In this study the use of indigenous bacteria as a tracer for characterizing groundwater flow in fractured rock was evaluated. Advancements in the field of microbiology readily allow for the characterization of bacterial communities found in groundwater using DNA gene sequencing. Bacterial populations in groundwater systems respond to a myriad of environmental conditions which can vary between recharge zones and along flow paths. Additionally, the introduction of contaminants from anthropogenic sources has been shown to have a substantial impact on these bacterial communities in various hydrogeologic settings. As part of an ongoing investigation into sodium chloride and nitrate contamination in Sherman, Connecticut, samples from seven residential bedrock drinking water wells were collected for DNA gene sequencing analyses. The bedrock aquifer in Sherman is composed of fractured schists and marbles beneath varying thicknesses of flood plain alluvium, thin till deposits, or undifferentiated meltwater deposits. In these wells the bacterial population size and diversity increased systematically along a groundwater flow path inferred from the topography and varied across local drainage divides. The bacterial communities also appeared to be influenced by local residential septic sources as suggested by elevated nitrate levels. The results from Sherman demonstrate this is a promising approach to decipher bedrock flow conditions.