ABSTRACT
This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The ubiquitous and dynamic nature of the intrinsic microbial activities in ground waters is becoming recognized as one of the inherent and essential factors. These are involved in such events as plugging, remediation of pollution events, hydrophobicity in soils and the bioaccumulation and degradation of potentially hazardous chemicals. In the ground water within the crust, there are number of physical and chemical factors that would begin to stress any incumbent microorganisms at deeper and deeper depths. These stressors would change the nature of dominant microbial species. In general, geothermal temperature gradients show average increase in ordinary formations of 2.13°C per 100 meters of depth. Ground water at a depth of 1,000 meters would therefore be expected to have a temperature elevation of 21.3°C. Hydraulic pressures be exerted to an increasing extent at greater depths particularly below the interface between the unsaturated zone and saturated.
