ABSTRACT
Once drilling is complete and the various data sets are integrated, then a revised geohydrologic model is developed that forms the framework for the interpretation of microbiological and geochemical results. Key geochemical parameters include the bulk chemistry and mineralogy of the solids. Useful information in geohydrologic and geochemical characterization include geologic age dating and paleotemperatures of the host rock and ground water. To evaluate the origins and transport of microorganisms in the subsurface, studies have been conducted in regions with demonstrated geohydrologic isolation to minimize the potential for contamination of the subsurface microbial community with those from the near surface. Most of the characterization methods are designed for measuring the properties of clastic sediments or sedimentary rocks and groundwater, but many of the methods apply to geohydrologic materials as well. Permeability controls the relative importance of advective and diffusive transport of nutrients within the sediments.
