More than half of all liquid hazardous waste is disposed by deep well injection. Little is known about the chemical compositions of these wastes or about the subsurface reactions that could degrade hazardous compounds within them. Texas waste streams, which constitute 80 percent of the industrial waste disposed of annually by deep well injection in the United States, are probably representative of such injection. Phenols, chlorinated organic, cyanide, nickel, nitriles, and ketones-aldehydes compose 92 to 95 percent of the toxic wastes disposed of annually in Texas.

Biodegration, if it occurs in deep injection aquifers, is probably the most effective degradation process because it results in nearly complete removal of a wide range of hazardous organic compounds. Degradation in the deep subsurface probably changes with distance from the well bore. Abiotic oxidation and hydrolysis are likely near the well bore, where solutions may be oxidized and have extremely low or high pH values, whereas anaerobic microbial activity probably dominates in an outer zone where toxic compounds are more dilute.

All compounds in the waste solution must be considered when waste degradation processes are predicted. For example, generally nonhazardous carboxylic acids which are present in 24 percent of the organic waste streams studied, are highly reactive, and their presence in solution significantly affects microbial, hydrolysis, and sorption reactions of hazardous compounds. By considering predicted subsurface reactions, waste-stream compositions can be altered to enhance degradation and discourage unfavorable reactions.

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