Geochemistry Revisited: Selected Aspects -- Characterization of the Subsurface Environment -- Selected Geochemical Processes -- Properties of Potential Contaminants: Environmental and Health Hazards -- Inorganic and Organometallic Compounds -- Organic Compounds -- Contaminant Partitioning in the Subsurface -- Sorption, Retention, and Release of Contaminants -- Contaminant Partitioning in the Aqueous Phase -- Partitioning of Volatile Compounds -- Selected Research Findings: Contaminant Partitioning -- Contaminant Transport from Land Surface to Groundwater -- Water Flow in the Subsurface Environment -- Transport of Passive Contaminants -- Transport of Reactive Contaminants -- Selected Research Findings: Contaminant Transport -- Transformations and Reactions of Contaminants in the Subsurface -- Abiotic Contaminant Transformations in Subsurface Water -- Abiotic Transformation at the Solid-Liquid Interface -- Biologically Mediated Transformations -- Selected Research Findings: Transformations and Reactions. This book combines earth science, subsurface hydrology and environmental geochemistry, providing a comprehensive background for specialists interested in the protection and sustainable management of the subsurface environment. The reader is introduced to the chemistry of contaminants, which usually disturb the natural equilibrium in the subsurface as a result of human activity. The major focus of the book is on contaminant reactions in soil solutions, groundwater and porous media solid phases, accounting for their persistence and transformation in the subsurface, as they are transported from the land surface into groundwater. Discussions on selected case studies are provided.