The Matrix Diffusion Toolkit provides a valuable tool for developing site conceptual models, supporting site characterization efforts, planning remedial designs, and determining if matrix diffusion will affect remediation goals for groundwater sites. The software can assist site personnel in updating or creating a more accurate conceptual site model, which will enable them to determine if matrix diffusion processes are significant enough to cause “rebounding” of downgradient plume concentrations above remediation goals after plume remediation or isolation is complete. Having this information available before a remedy is implemented could assist site stakeholders in selecting more appropriate remedies and effectively and efficiently addressing the potential issues of matrix diffusion with regulators. Furthermore, addressing extended remediation time frames caused by matrix diffusion would lead to savings in project costs.