RT3D is a Fortran-based software for simulating three-dimensional, multi-species, reactive transport of chemical compounds (solutes) in groundwater. RT3D is a MODFLOW-based solute transport code derived from MT3DMS, but with greatly expanded reaction capabilities. Although RT3D is often discussed in the context of accelerated in situ bioremediation (ISB) and natural/enhanced attenuation scenarios, RT3D is a general-purpose reactive transport code suitable for simulating a multitude of scenarios. Potential capabilities include simulation of inorganic reactions, geochemistry reactions, NAPL dissolution, mobile/immobile dual porosity, colloid transport, virus transport, heat transport, and risk analysis. With some degree of effort, RT3D can be linked to other codes to include time-varying porosity, interaction with the unsaturated zone, or full geochemistry. Commercial thirdparty graphical user interface software is typically used to define RT3D simulation model configurations and to visualize contours or isosurfaces of results. Results consist of whole-grid data sets at points in time and location-specific time series data sets. Multiple examples of RT3D application in the published literature are discussed, with a more in depth look at case studies for a monitored natural attenuation application and the design of an active remediation system.
Keywords: User-defined reactions, natural attenuation, bioremediation, reactive transport groundwater modeling, solute transport, three-dimensional, multi-species, finite difference, operator split, MODFLOWbased.