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EPA-Expo-Box (A Toolbox for Exposure Assessors)

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Water and Sediment


Contamination of water and sediment can occur from anthropogenic (manmade) sources or natural sources. Examples of anthropogenic sources include point and nonpoint sources. Natural sources that may contaminate water and sediment include volcanic activity, hurricanes and other storms, forest fires, and earthquakes.

  • Point sources involve releases of pollutants to surface water and sediment from a specific source, such as an outfall pipe or ditch. Examples of common point sources of water pollution include sewage treatment plants, industrial facilities, mining operations, construction sites, and storm drains. Contaminants in the surface water column have the potential to settle and contaminate sediments.
  • Nonpoint sources of water contamination are area-wide releases of pollutants to surface water and sediment, including nutrient runoff from agricultural sites or storm water runoff from urban or suburban sites. Storm water runoff can become contaminated when rain water comes into contact with contaminated soil and either dissolves the contamination or carries contaminated soil particles. Surface water can also be contaminated when contaminated groundwater migrates to surface water or when contaminants in the air are deposited on the surface water. Pollutants in the surface water column have the potential to settle and contaminate sediments.

Drinking Water Treatment—Quick Facts

There are a variety of treatment techniques used by public water systems to remove contaminants from drinking water and make it safe for consumers. The type of treatment depends on the size of the system, the source of water (i.e., surface water or groundwater), and the quality of water that enters the treatment plant.

The National Primary Drinking Water Regulations are legally enforceable standards that apply to public water systems. These standards protect public health by limiting the levels of contaminants in drinking water. Private, individual household wells are not regulated by EPA; however, state and local governments set rules to protect the users of these wells.

Contamination of groundwater is not classified as resulting from point or nonpoint sources. Contaminants may leach from soil into the groundwater causing contamination of the aquifer.

Contamination of drinking water can occur at the source (surface water or groundwater), during treatment (e.g., byproducts of chlorination), or after treatment (e.g., lead contamination from corrosion of plumbing materials). For more information on drinking water contaminants, public water treatment systems, primary drinking water regulations, and private drinking water wells, see the text box on the right and the list of resources provided under Guidance in this module.

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