Environmental conditions determine in large part the chemical reactions that will occur when waste is injected. For example, precipitation-dissolution reactions are strongly controlled by pH. Thus, iron oxides, which may be dissolved in acidic wastes, may precipitate when injection-zone mixing increases the pH of the waste. Similarly, redox potential (Eh) exerts a strong control on the type of microbiological degradation of wastes.
The most variable and site-specific factor is the reservoir rock matrix. Geologic formations vary greatly in chemical and physical properties depending on the conditions under which they formed and the geologic processes to which they have been subjected.
20.4.1 Major Environmental Factors Influencing Geochemical-Fate Processes
The previous chapter examined the geochemical processes that can occur in the deep-well environment. The type and outcome of reactions that will actually occur when a waste is injected, however, depend on its chemical characteristics and on injection-zone conditions. This chapter examines six major environmental factors that must be taken into consideration.
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