The need for the control of volatile organic contaminants (VOCs) has led to the development of a computer-based suite of mechanistic models collectively known as TOXCHEM, which predicts the fate of VOCs in wastewater treatment plants. TOXCHEM includes both steady-state and dynamic models, and will predict the location and mass of VOC emissions from several locations within a wastewater treatment installation. Derivations are shown for expressions describing important removal rate coefficients and VOC mass balances for each unit process of a secondary treatment plant. Calibration of the model at pilot scale was conducted, and data from other full-scale investigations were used to verify the model. It was found that the TOXCHEM models predicted reasonably well and would improve as the true rate coefficients are established. This model has the potential to be an extremely useful tool for wastewater treatment plant engineers and administrators of sewer use regulations.