To provide the scientific understanding required to allow DOE sites to incorporate relevant biological, chemical, and physical processes into decisions concerning environmental remediation, a fundamental understanding of the controls on micro-organism growth in the subsurface is necessary. Specifically, mobility of metals in the environment, including chromium, technetium and uranium, is greatly affected by the process of dissimilatory metal reduction (DMR), which has been shown to be an important biological activity controlling contaminant mobility in the subsurface at many DOE sites. Long-term maintenance of DMR at constant rates must rely upon steady fluxes of electron donors to provide the maintenance energy needed by organisms such as Geobacter sulfurreducens to maintain steady state populations in the subsurface.