The chemical fate of wastes put into disposal wells can be determined using standard chemical engineering techniques. The concentration of hazardous constituents is typically reduced by reactions within the waste itself or by reactions with the injection zone material, thus reducing any potential impact on the environment. Such reactions include neutralization, hydrolysis, ion exchange, adsorption, precipitation, co‐precipitation and microbial degradation. Extensive research was done to quantify these phenomena, so they could be used in a predictive model. Neutralization, hydrolysis and precipitation were modeled using data from the open literature: reaction rates and equilibrium constants for the dominant reactions were incorporated into a sophisticated computer simulation that calculates solid‐liquid equilibria of aqueous electrolyte solutions. The model predicted the fate of two waste streams: (1) high‐pH, cyanide‐containing waste injected into sandstone is made less hazardous by hydrolysis and sand dissolution, and (2) FeCl3‐FeCl2 HCl‐H2 O waste is made non‐hazardous by reaction with dolomite. Experiments are planned to confirm certain model predictions. Further development and public access of the model are planned.