Geography and Geology
Encyclopedia of Geology, 2nd Ed
Chemicals come to be in groundwater as the result of natural interactions of water with the minerals of soils and bedrock and with gases of the atmosphere as well as by human-caused introduction of chemicals into the surficial environment. The degree to which a solute occurs in water is determined by the solubility of gases and minerals in contact with water, acid-base reactions in aqueous solution, dissolution and precipitation of minerals, sorption or ion-exchange reactions of solutes with the surfaces of minerals and particulate organic matter, oxidation or reduction of elements, and the biodegradation of organic compounds as mediated by bacteria. The human activities of farming, mining, manufacturing, transportation, and waste disposal have the potential to contaminate natural water with a huge variety of inorganic and organic compounds. Contaminants in water are undesirable constituents that may cause harm to human health or environmental ecosystems. In the hydrologic cycle, the migration of chemicals from one reservoir to another may occur by circulation of water through the atmosphere, surface water, and groundwater, so contamination of one site may lead to degradation of water quality at a distant location. Once a contaminant is introduced into groundwater, although some attenuation of the contaminant may occur, it is practically impossible to remove all contamination from an aquifer. Insights into the occurrence and distribution of natural and contaminant chemicals in groundwater depend upon an understanding of the fundamental physicochemical phenomena of biogeochemical reactions, the chemical character of the geologic setting, and the hydrogeological properties of the subsurface environment. Although the environmental properties of many chemicals are well understood, a far greater number of chemical compounds are poorly characterized and insufficiently studied. More knowledge is required for many identified groundwater contaminants in order to successfully describe their environmental fate in the hydrologic system.
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Herman, J. S., & Gellasch, C. A. (2021). Geohydrology: Hydrogeochemistry. In S. A. Elias & D. H. M. Alderton (Eds.), Encyclopedia of Geology (2nd ed., pp. 416–425). Elsevier. https://doi.org/10.1016/B978-0-12-409548-9.12504-7