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Superfund

Section 4: Source Characterization

Although the Hazard Ranking System (HRS) is designed to score releases and sites, sources and areas of observed contamination play a crucial role in determining HRS pathway scores. Sources and areas of observed contamination are central to the evaluation of the likelihood of release factor categories and the hazardous waste quantity factors. Source and area of observed contamination information is also frequently used in identifying the hazardous substances associated with a site and in determining where targets are located relative to the site. Thus, complete and accurate characterization and documentation of both sources and areas of observed contamination are essential in producing defensible site scores. Both "source" and "area of observed contamination" are specifically defined concepts in the HRS whose definitions do not exactly correspond to their common usage. Areas of observed contamination will be addressed in the soil exposure pathway sections.


4.1 What is a Source?

Examples of sources include:

  • Contaminated Soil
  • Landfills
  • Surface Impoundments
  • Drums
  • Piles
  • Tanks

The following emphasize certain aspects of the HRS definition of source. The following are NOT sources for purposes of HRS scoring.

  • Ground water plumes originating from known sources (such as a landfill);
  • Surface water plumes originating from known sources (such as discharge pipes or overland runoff discharge areas);
  • Areas of contaminated surface water sediments arising from discharges from known sources; and
  • Volumes of contaminated ambient air.

The following ARE considered sources for purposes of HRS scoring:

  • Ground water and surface water plumes of unknown origin;
  • Areas of contaminated surface water sediments arising from direct placement (other than discharge) of waste materials into surface water bodies when the origin is unknown;
  • Cylinders containing confined, gaseous hazardous substances; and
  • Soils contaminated as a result of overland runoff, volatilization of ground water contaminants, or atmospheric deposition (from non-vehicular sources).

Areas of observed soil contamination are sources. Sources need not contain waste materials. Materials that might not be considered a source if undisturbed, may become a source if excavated and moved (e.g., contaminated dredge disposal materials).


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