PHT3D – A MODFLOW/MT3DMS-based reactive multi-component transport model

PHT3D, a three-dimensional, MODFLOW/MT3DMS-based reactive multicomponent transport model is presented. The model couples, via an operator-splitting method, the transport simulator MT3DMS (Zheng and Wang, 1998) and the geochemical package PHREEQC-2 (Parkhurst and Appelo, 1999). Through the flexible, generic nature of PHREEQC-2, PHT3D can handle a broad range of equilibrium and kinetic reactive processes, including aqueous complexation, mineral precipitation/dissolution and ion exchange. The diversity of potential applications is demonstrated via simulation of literature benchmarks and new problems. The latter include applications involving natural and enhanced remediation of organic (e.g., BTEX, CHCs) and inorganic (e.g., metals) contaminants and the geochemical changes occurring during their degradation. Processes/reactions not included in the standard PHREEQC database but are typical for this type of application (e.g., NAPL dissolution, microbial growth/decay) can be defined and included via the PHREEQC database file. PHT3D has been integrated into the PMWIN pre/postprocessing package (Chiang and Kinzelbach, 2001). There, users can select from existing reaction packages/database-files or develop and integrate newly developed packages.