An Interactive Tool for Comparing Sorption Conceptual Models (Surface Complexation Modeling versus KD)

Within reactive geochemical transport, several conceptual models exist for simulating sorption processes in the subsurface. Historically, the KD approach has been the method of choice due to ease of implementation within a reactive transport model and straightforward comparison with experimental data. However, for modeling complex sorption phenomenon (e.g. sorption of radionuclides onto mineral surfaces), this approach does not systematically account for variations in location, time, or chemical conditions, and more sophisticated methods such as a surface complexation model (SCM) must be utilized. It is critical to determine which conceptual model to use; that is, when the material variation becomes important to regulatory decisions. The geochemical transport tool GEOQUÌMICO has been developed to assist in this decisionmaking process. GEOQUÌMICO provides a user-friendly framework for comparing the accuracy and performance of sorption conceptual models. The model currently supports the KD and SCM conceptual models. The code is written in the object-oriented Java programming language to facilitate model development and improve code portability. The basic theory underlying geochemical transport and the sorption conceptual models noted above is presented in this report. Explanations are provided of how these physicochemical processes are instrumented in GEOQUÌMICO and a brief verification study comparing GEOQUÌMICO results to data found in the literature is given.