An overview of hydrogeological modeling for Permeable Reactive Barrier (PRBs) is given in Gupta and Fox. The most challenging component of PRB design and implementation is the site hydraulics, and several case studies of PRBs demonstrate this aspect of the technology. Subsurface hydrogeology modeling is implemented at various stages of the PRB technology. The general principles of PRB design and implementation have been discussed in detail by Gavaskar et al. This chapter provides a general overview of mathematical models used for implementing the PRB technologies. The presence of a PRB induces changes in subsurface heterogeneity, which influence the groundwater flow and contamination migration pathways. To demonstrate the modeling of a PRB, a case study demonstrating remediation of trichloroethene (TCE) at a long-term contaminated site in South Australia is summarized. From the groundwater monitoring investigations, a steady increase of TCE concentration at the site was observed, suggesting either direct disposal of TCE into the groundwater or significant leaching from contaminated soils.