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HRS Guidance Manual, Section 4.1

This section provides guidance to assist the scorer in characterizing sources and areas of observed contamination by assigning factor values based on source type. Because source information is used throughout the HRS and deficiencies in that information or in its interpretation may have a significant impact on the site score, it is critical to correctly classify and characterize each source. This section defines sources (and areas of observed contamination), provides pathway-specific guidance for identifying and documenting sources and their hazardous substances, and discusses special cases where characterizing sources (or areas of observed contamination) is especially complex. This section does not discuss multiple-source sites.


Section 2.1.3 Common evaluations
Section 2.2 Characterize sources
Section 2.2.1 Identify sources
Section 2.2.2 Identify hazardous substances associated with a source
Section 2.2.3 Identify hazardous substances available to a pathway
Section 5.0.1 General considerations (soil exposure)


Area of Observed Contamination: Evaluated only in the soil exposure pathway and established based on sampling locations as follows:

:    Generally, for contaminated soil, consider the sampling locations that indicate observed contamination and the area lying between such locations to be an area of observed contamination, unless information indicates otherwise.

:    For sources other than contaminated soil, if any sample taken from the source indicates observed contamination, consider the entire source to be an area of observed contamination.
If an area of observed contamination (or a portion of such an area) is covered by a permanent, or otherwise maintained, essentially impenetrable material (e.g., asphalt), exclude the covered area from the area of observed contamination. However, asphalt or other impenetrable materials contaminated by site-related hazardous substances may be considered areas of observed contamination.

Hazardous Substances: CERCLA hazardous substances and pollutants or contaminants as defined in CERCLA sections 101(14) and 101(33), except as otherwise specifically noted in the HRS.

Source: Any area where a hazardous substance has been deposited, stored, disposed, or placed, plus those soils that may have become contaminated from hazardous substance migration. In general, however, the volumes of air, ground water, surface water, and surface water sediments that may have become contaminated through migration are not considered sources.

Unallocated Source: Not an HRS source type, rather a means of including within the hazardous waste quantity factor those hazardous substances or hazardous waste streams that are known to be at the site but that cannot be allocated to any specific source. Thus, the term only applies for hazardous waste quantity.

The following definitions are for specific source types evaluated in the HRS.

Above-ground Tank: Any tank that does not meet the definition of a below-ground tank (including any tank that is only partially below the surface).

Active Fire Area: Area presently burning or smoldering.

Below-ground Tank: A tank with its entire surface area below the surface and not visible; however, a fraction of its associated piping may be above the surface.

Buried/Backfilled Surface Impoundment: A surface impoundment that has been completely covered with soil or other cover material after the final deposition of waste materials.

Burn Pit: An uncovered area on the land surface that is not presently burning but that was at one time used to burn hazardous substances or was otherwise significantly inflamed.

Container or Tank: A stationary device constructed primarily of nonearthen materials (such as wood, concrete, steel, or plastic) used to contain an accumulation of a hazardous substance; or a portable device in which a hazardous substance is stored or otherwise handled.

Contaminated Soil (excluding land treatment): Soil onto which available evidence indicates a hazardous substance was spilled, spread, disposed, or deposited.

Drum: A type of container used to hold hazardous substances. For HRS purposes, drums are standard 55-gallon cylindrical containers.

Landfarm/Land Treatment: A method of waste management in which either liquid wastes or sludges are spread over land and tilled or liquids are injected at shallow depths into soils.

Landfill: An engineered (by excavation or construction) or natural hole in the ground into which wastes have been disposed of by backfilling or by contemporaneous deposition of soil and wastes.

Other: A source type used when defined source types do not apply. Examples include: contaminated buildings, storm drains, dry wells, injection wells, and French drains. "Other" also can be used for ground water plumes and sediments with no identified source.


Chemical Waste Pile: A pile consisting primarily of discarded chemical products (whether marketable or not), by-products, radioactive wastes, or used or unused feedstocks.

Other: A term reserved for a pile of indeterminate origin that contains hazardous substances.

Scrap Metal or Junk Pile: A pile consisting primarily of scrap metal or discarded durable goods such as appliances, automobiles, auto parts, or batteries, that contain or have contained hazardous substances.

Tailings Pile: A pile consisting primarily of any combination of overburden from a mining operation and tailings from a mineral mining, beneficiation, or processing operation.

Trash Pile: A pile consisting primarily of paper, garbage, or discarded nondurable goods that contain or have contained hazardous substances.

Surface Impoundment: A topographic depression, excavation, or diked area, primarily formed from earthen materials (lined or unlined) and designed to hold accumulated liquid wastes, wastes containing free liquids, or sludges that were not backfilled or otherwise covered during periods of deposition; depression may be dry if deposited liquid has evaporated, volatilized or leached; structures that may be more specifically described as lagoon, pond, aeration pit, settling pond, tailings pond, sludge pit, etc.; also a surface impoundment that has been covered with soil after the final deposition of waste materials (i.e., buried or backfilled).


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