Chemical Wastes Disposed of by Deep Well Injection and Their Subsurface Reactions

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Capuano, Regina M.
Kreitler, Charles W.

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More than 8.6 billion gallons of liquid industrial waste are disposed of by deep-well injection each year (Mankin and Moffett, 1987). This constitutes more than half of the approximately 15 billion gallons of liquid hazardous waste that must be disposed. About 90 percent of these wastes are injected into deep aquifers in the Gulf Coast Region (Gordon and Bloom, 1986). In recent years, the proportion of waste managed by deep well injection has increased because of the limitations on other methods of disposal such as landfills, surface impoundments, and mixing with surface soil. Therefore, until methods of waste minimization adequately limit the production of liquid hazardous waste, deep well injection is a much-needed method for disposal.

Recent legislation limits deep well injection unless the injector demonstrates that there will be no migration of hazardous constituents from the injection zone for as long as the waste remains hazardous (Federal Register 40 FR 146). To prove that injected waste does not migrate from the vicinity of the wellbore, it must be shown that the fluid or chemical constituents in the fluid are immobile or that the hazardous material degrades to a nonhazardous form before the fluid migrates from the area. It is unlikely that fluids are immobile in deep Texas aquifers, as indicated by the large gradients in fluid potential produced around injection zones (Kreitler et al., 1988). In addition, improperly sealed abandoned wells and deep growth faults, which are both common in the Gulf Coast area, can provide unexpected pathways to the surface. Instead, it needs to be shown that the hazardous chemicals are immobilized through reactions with the sediments or are transformed into nonhazardous substances.


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