USE OF BACTERIA COMMUNITY ANALYSIS AND DISCRETE GROUNDWATER SAMPLING TO IMPROVE HYDROGEOLOGIC CHARACTERIZATIONS

Groundwater bacteria are influenced by subtle changes in biogeochemical conditions. As such, comparing bacteria communities from different sampling locations can be used to better understand biogeochemical gradients in a study area. In this study, bacteria samples were collected from fractured bedrock wells as part of a hydrogeologic investigation of a drinking water aquifer impacted with road salt. Water quality and bacteria samples were collected from domestic wells throughout a two-year period. Downhole geophysics and other flow profiling methods were then used to characterize the geologic and flow conditions in the open borehole wells. In-situ bacteria samples were collected from discrete depths identified from the downhole testing. 16S rRNA sequencing was used to identify the present bacteria and compare community composition among the samples. In a productive well, bacteria community composition in the active flow interval was similar to the tap water samples collected from the same well in prior years. It was also found that community composition at various depths outside of active flow interval differed greatly from each other and the tap water samples despite having similar water quality. These findings were useful in confirming the results from the downhole flow profiling methods by identifying distinctly similar bacteria communities at productive well depths and in the tap water samples from the same borehole.