Fate and Transport of Microbial Contaminants in Groundwater

Abstract

Microbial contamination of groundwater by viruses, bacteria, and parasitic protozoa is a significant human health problem when drinking water supplies are untreated or inadequately treated. The decision to treat groundwater supplies, if sufficient resources are available, often depends on the adequacy of pathogen and indicator organism attenuation in the subsurface. Microbial fate and transport processes govern attenuation in the subsurface. Hence, a thorough understanding of the mechanisms and factors affecting the fate and transport of microbial contaminants in the subsurface environment is essential for the protection of public health from waterborne disease. First, the various sources and types of microbial contaminants found in the subsurface are presented. Sources of microbial contaminants may be zoogenic (e.g., wildlife) or anthropogenic (e.g., septic systems). Second, the surrogates and indicators most commonly used to assess microbial transport and fate in groundwater are discussed. These include pathogenic and nonpathogenic bacteria, bacteriophage, and microbe-sized microspheres. Next, the key processes governing microbial fate and transport are described. Microbial transport is mainly controlled by advection, whereas the key processes governing the fate of microorganisms are retention onto aquifer solid surfaces and inactivation (or survival) of the microbes. Groundwater chemistry and moisture content are identified as two of the main physicochemical factors that influence the retention and survival of microorganisms in the subsurface. Finally, the importance of linking this fundamental science to the development of appropriate public policy and land use strategy is highlighted.