ORTI3D stands for Open Reactive Transport Interface. It is a general interface for reactive transport modelling that can handle several models, mainly from the modflow series (Modflow Mt3dms and Pht3d) and more recently Modflow-USG (with transport and chemistry capability) with unstructured grids. It also includes writing/viewing capacity for Min3p.
It is based on an equivalent GIS approach where parameters are defined through zones and then transferred to files. As developed for reactions, ORTI3D reads phreeqc database files to offer easy handling of spatial distribution of solutions.
Written in python, the models can both be used within the interface but also in standalone from a python interpreter, which has access to all commands. There is also a version designed as a QGIS plugin.