CHARACTERIZATION OF INDIGENOUS BACTERIA AS A GROUNDWATER TRACER IN FRACTURED BEDROCK

This study evaluates the use of indigenous bacteria as a tracer to gain insight into groundwater flow in fractured, crystalline bedrock. 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 impact these bacterial communities in various hydrogeologic settings. As part of an ongoing investigation into sodium chloride contamination of bedrock wells in Sherman Connecticut, samples from seven wells were collected for DNA gene sequencing analyses. The sampled wells are included in a groundwater monitoring program conducted by the local health department and provide drinking water to local residents, businesses, and municipal buildings. The classification of the bacterial communities indicates that population size and diversity increased systematically along the groundwater flow path. An understanding of the local flow pathways is deciphered through hydrologic modeling of the local topography, analysis of the distribution of major cations and anions, and detailed well log analysis. Due to these promising results, additional samples were collected from all twenty-four wells included in the towns monitoring program in March of 2018. These additional samples are currently in the process of being analyzed to determine if the results are consistent over a broader spatial extent and across drainage divides. However, the results to date from Sherman demonstrate the viability of using this method to increase understanding of fractured flow conditions.