• artificial recharge using stormwater and treated wastewater;

  • water “banking” via injection or aquifer storage and recovery;

  • extraction of brackish groundwater for desalination;

  • introduction of imported or recycled irrigation water; and

  • changes in land use, vegetation, and irrigation practices that alter rates of infiltration, drainage water runoff, and evapotranspiration.

All of these have the potential to alter the major and minor ion composition of groundwater. For example, fresh surface water stored in a brackish aquifer during aquifer storage and recovery will experience an increase in total dissolved solids due to mixing with ambient brackish water and dissolution of minerals from the aquifer matrix. Many of these may also introduce contaminants such as microbial pathogens, organic contaminants such as pesticides or solvents, and inorganic contaminants such as nitrates or metals. Of particular interest with respect to surface water are changes in water quality induced by urban and agricultural runoff, discharge of waste effluents from municipal or industrial sources (including the extractive mineral and energy industries), construction and operation of dams and reservoirs, drainage of wetlands, and channel modifications for purposes of flood control, navigation, or environmental improvement.

  1. Identify and quantify the health risks posed by “emerging”contaminants, including newly discovered pathogens and pharmaceutical chemicals.The health effects of many naturally occurring substances at low concentrations and the health effects associated with interactions of multiple naturally occurring substances are poorly understood. Public health professionals and earth scientists will need to collaborate to identify emerging substances of potential concern and to improve understanding of the processes controlling the mobility of these substances in the environment, particularly in light of potential changes in concentrations induced by human activities that alter the land or the hydrological cycle. Of particular interest are “emerging” contaminants such as hormones, pharmaceuticals, personal care products, and newly identified microbial pathogens for which sources and transport processes are poorly understood. The synergistic and antagonistic interactions of mixtures of contaminants with naturally occurring substances in water also pose priority research questions. Examples of specific research priorities include an understanding of the:

    • fate and transport of prions from soil to groundwater and surface water and their relationship to disease incidence;

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