The quality of natural waters is defined by concentrations of various natural chemical constituents as well as contaminants introduced by human activity. The value of a water source, for ecosystem services, as well as for various human uses, is dependent on the quality of the water, which is governed through numerous state and federal regulations. In support of these regulations, Tetra Tech has been involved in a wide range of water-related monitoring and modeling studies in the United States and around the world. The water resources studied have included lakes, streams and rivers, wetlands, and coastal and ocean waters. Constituents of concern have included trace elements such as arsenic, selenium, and mercury; nutrients such as nitrogen and phosphorus; organic compounds such as pesticides and polyaromatic hydrocarbons; and pathogenic indicators such as coliform bacteria and viruses. Typically, our analyses include field data collection of one or more chemical parameters of interest, followed by development or application of computer models of chemical fate and transport. These models are usually needed to help predict contaminant behavior under different scenarios and across different time scales.

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