The continuous flow pore and surface diffusion model (CFPSDM) applies intraparticle and external mass transfer mechanisms to activated carbon adsorption in a completely mixed flow reactor (CMFR). The model was primarily developed to assess the removal of organic compounds from drinking water using powdered activated carbon (PAC) adsorption. PAC is commonly used to remove taste and odor compounds, low concentrations of pesticides as well as natural organic matter. The CFPSDM provides plant operators and engineers a rigorous tool for determining optimal PAC treatment techniques. It is the only available transient model that includes both intraparticle pore and surface diffusion mass transfer mechanisms and external mass transfer mechanisms in a CMFR. The CFPSDM was verified by comparing a special case using a very low flow rate to a batch pore surface diffusion model as well as an analytical solution. The model was successfully validated by predicting the removal of atrazine from drinking water. A sensitivity analysis identified external mass transfer as the controlling mass transfer mechanism. A graphical user interface (GUI) provides a user-friendly platform to operate the model and tools to determine model parameters. Includes 19 references, tables, figures.