Studies have led to an understanding of how chlorate ion (ClO3-) formation in the pH 6-13 region from decomposing bleach is affected by pH, temperature, NaOCl concentration, chloride ion concentration (by means of an ionic strength effect), and transition metal ion impurities. The hypochlorite ion degradation model developed by Gordon and Adam predicts free available chlorine decomposition, ClO3- formation, and oxygen generation. Thus, a utility applying liquid bleach can use this newly developed model to predict the time dependent changes that occur in stored liquid bleach and to develop chemical specifications and control strategies to minimize the formation of ClO3- during the storage of sodium hypochlorite. The field studies reported here provide verification of the model showing a strong correlation between the model predictions and the measured data taken in the field. Includes 6 references, tables, figures.