The document discusses the application of blind source separation (BSS) techniques in hydrogeochemistry for contaminant source identification and the development of reduced-order models for contaminant transport, emphasizing machine learning methods like independent component analysis and non-negative matrix factorization. It highlights the challenges in sourcing signals from contaminated groundwater using neural networks and analytical solutions, and it presents findings from case studies at a chromium site. The conclusion summarizes the integration of BSS methods in groundwater transport modeling and informs ongoing decision analysis related to aquifer heterogeneity.