ABSTRACT
This chapter explores microbiological pathways to natural attenuation. Isotopes of carbon have received the most attention as potential tools for fingerprinting natural attenuation of organic contaminants. In order to roughly classify the fate and transport characteristics of contaminants in groundwaters it is necessary to define a number of terms and outline the basic chemical controls on dissolved contaminant levels. The bulk of contaminant reactivity can be treated as one of a combination of seven types of chemical reactions: ion pairing, gas phase dissolution, mineral growth, mineral dissolution, electron transfer, adsorption, and radioactive decay. The water that moves between soil minerals and in pores at depth is delicately balanced in a chemical sense. In all but the saltiest of brines, soil and groundwaters contain far less dissolved material than the minerals they are intermingled with. A wealth of evidence indicates that the chemical composition of most groundwaters is, in effect, defined by reactions with the aquifer solids.
