Measurement of bacterial transport and immobilization in variably saturated geologic materials of WI

The occurrence of bacteria and other microbial agents in private wells across the state of Wisconsin poses significant risks to human health. Discrepancies between bacteria measurements in drinking water wells compared with the expected near-surface immobilization from laboratory experiments in homogeneous geologic materials indicate an incomplete understanding of bacterial transport and immobilization in heterogeneous geologic systems under environmental conditions. The objective of this proposal is to systematically quantify preferential bacterial breakthrough and immobilization through heterogenous saturated and unsaturated geologic materials relevant to Wisconsin. To achieve this objective, we will use positron emission tomography (PET), an imaging modality capable of quantifying the migration of radiolabeled bacteria (E. coli) through columns of geologic materials. Imaging data will provide three-dimensional time-lapse observations of the role of geologic heterogeneity and fluid saturation conditions on the advection, dispersion, and immobilization of radiolabeled bacteria. Our preliminary bacteria radiolabeling studies and previous work using PET imaging to quantify solute transport in variably saturated laboratory column experiments illustrate the feasibility of this approach. The expected outcomes will be unprecedented experimental measurements and uniquely constrained analytical and numerical models of bacterial transport and immobilization in soils and aquifer material specific to Wisconsin. These measurements and models will provide more accurate and geologically specific information about how bacteria and microbial agents contaminate groundwater sources. This information will complement existing contamination risk parameters such as depth-to-bedrock measurements, soil type, and climate and weather conditions to improve guidance, regulations, and risk assessments of bacterial contamination of drinking water wells in Wisconsin.