ABSTRACT
This chapter reviews important and recent findings involving the distribution, activities, and transport of subsurface microorganisms, particularly in contaminated zones and describes conceptual and mathematical models being used to describe subsurface microbial processes. Accurate delineation of the distribution and community structure of microorganisms have historically been hampered by lack of funding, suitable asepticsampling technology, and methodology for detecting and characterizing sparse microbial populations in the presence of aquifer solids. Delineation of numbers and types of microbes in the groundwater environment has been greatly facilitated by the development of aseptic procedures for obtaining cores of aquifer material. A number of studies involving subsurface bacterial communities have attempted to differentiate between total numbers and so-called “viable” counts. The term “viable” has often been used to describe the numbers of bacteria that form colonies on solid nutrient media within the time frame of the incubation.
