The presence of substances in groundwater may be affected by naturally occurring processes as well as by actions directly associated with human activities. Naturally occurring processes such as decomposition of organic material in soils or leaching of mineral deposits can result in increased concentrations of several substances. Those of health concern include arsenic, fluoride, selenium, uranium, nitrate, metals, and radionuclides such as radon. Problems of aesthetic quality and acceptance may be caused by iron, manganese, sulphate, chloride and organic matter. .
