Factors Influencing Microbial Contamination of Groundwater: A Systematic Review of Field-Scale Studies

Pathogenic microorganisms released onto the soil from point or diffuse sources represent a public health concern. They can be transported by rainwater that infiltrates into subsoil and reach the groundwater where they can survive for a long time and contaminate drinking water sources. As part of the SCA.Re.S. (Evaluation of Health Risk Related to the Discharge of Wastewater on the Soil) project, we reviewed a selection of field-scale studies that investigated the factors that influ- enced the fate of microorganisms that were transported from the ground surface to the groundwa- ter. A total of 24 studies published between 2003 and 2022 were included in the review. These stud- ies were selected from the PubMed and Web of Science databases. Microbial contamination of groundwater depends on complex interactions between human activities responsible for the release of contaminants onto the soil, and a range of environmental and biological factors, including the geological, hydraulic, and moisture characteristics of the media traversed by the water, and the characteristics and the viability of the microorganisms, which in turn depend on the environmental conditions and presence of predatory species. Enterococci appeared to be more resistant in the un- derground environment than thermotolerant coliforms and were suggested as a better indicator for detecting microbial contamination of groundwater.