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HRS Guidance Manual, Section 5.3

A hazardous substance exposed to other substances or to the environment is susceptible to transformation by physical, chemical, and biological processes. The products of these reactions are termed transformation products. Substances found in the environment (i.e., the transformation products) may be different than those found or otherwise documented in sources at the site (i.e., the parent substances). This section provides guidance for establishing an observed release (or observed contamination) based on transformation products.

  Section 2.3   Likelihood of release
  Section 3.1.1   Observed release (ground water)
  Section   Observed release (surface water)
  Section 5.0.1   General considerations (soil exposure)
  Section 6.1.1   Observed release (air)


Transformation Product: The substance(s) resulting from the transformation of a hazardous substance in the environment by physical, chemical, and/or biological processes. The original hazardous substance is referred to as the parent substance. When a transformation product is a simpler, less complex substance than the parent substance, it is referred to as a degradation product. When a more complex substance is produced, the product is often referred to as a formation product.


Most transformation products of environmental concern at waste sites are degradation products. Examples of physical degradation processes include spontaneous decay of radioactive substances (e.g., uranium to radium) and dechlorination of aromatic hydrocarbons due to photodegradation (e.g., heptachlorobiphenyl to hexachlorobiphenyl). Examples of chemical degradation processes include oxidation/reduction reaction of chromium VI to chromium III, acid/base reaction of sulfuric acid to sulfate salts, and dissolving of metals due to ground water acidification by landfill leachate (e.g., lead solid to lead ion under low pH conditions). Examples of biological degradation processes include transformation of trichloroethane to dichloroethane; hydroxylation of benzenes to phenolics by aerobic microorganisms (dichlorobenzene to dichlorophenol); and dehalogenation (i.e., removal of a halide) of aromatic pesticides by anaerobic microorganisms (e.g., pentachlorophenol to tetrachlorophenol). Highlight 5-9 provides some examples of common degradation products and their parent substances.

The same requirements for establishing an observed release by chemical analysis that apply to hazardous substances in general apply to transformation products (see Section 5.1). Transformation products must be hazardous substances in order to be used to establish an observed
release (or observed contamination). Also, an observed release based on transformation products cannot be established by direct observation.


The steps outlined below describe how to establish an observed release (or observed contamination) for transformation products.

  1. Document the presence of the transformation product(s) in the release sample at levels significantly greater than background. Analytical data used to demonstrate the presence of a transformation product must meet the same significance, attribution, and QA/QC requirements as for any other hazardous substance (see Section 5.1). The transformation products should be considered to be present in the media they have been found in, but this does not mean they necessarily are available to other pathways. For example, a transformation product detected in ground water is not necessarily available to the air pathway. Any hazardous substance documented to be in a source is considered available to all pathways for which the source has a non-zero containment factor value.

  2. Attribute the parent substance to the site. Establishing attribution of the parent substance to the site usually involves documenting that the parent substance was deposited or is present in a source, or that the parent substance was produced, stored, deposited, or treated at the site and/or originated in or resulted from activities at the site.

    The following types of information may be used to establish attribution of a parent substance to a site (in order of preference).

    • The most complete information is chemical analysis of samples from at least one source in the site and documentation that the substance was placed in the source. If the source is contaminated soil or contains soil used as cover or fill material, it generally also will be necessary to document that the concentration of the substance in the source is significantly above background.

    • If the above information cannot be obtained, documentation by chemical analysis that the parent substance is in a source can be used alone if the source does not contain soil or if the substance is not a naturally occurring substance.

    • If analytical data are not available, records or manifests indicating the parent material was placed in a source are preferred. Documentation that the parent substance was used, stored, or handled at the site is also acceptable.

    • In some situations, information indicating that a parent substance was most likely present at a site because of the nature of the site activity may also be considered adequate attribution (e.g., carbon tetrachloride or tetrachloroethene at a dry cleaning facility).

  3. Attribute the transformation product to the site. Attributing the transformation product to the site generally involves documenting that the hazardous substance detected in the receiving medium is the transformation product of a parent substance attributable to that site. Establishing attribution of a transformation product to the site usually involves documenting the following.

    • The substance detected in a medium is a transformation product of the parent material, as shown by:

      • Site-specific studies on the transformation process by qualified research organizations (e.g., universities, EPA research laboratories);

      • EPA technical reports discussing the transformation of the parent substance, such as from the Office of Research and Development, the Risk Reduction Engineering Laboratory (RREL), and/or the Center for Environmental Research Information (CERI);

      • Information in data bases containing EPA-reviewed information (e.g., the computerized RREL "Treatability Data Base");

      • Articles from peer reviewed journals; or
      • Textbooks on soil and environmental microbiology, biotechnology, and biotreatment processes and their effectiveness.

    • A significant increase of the transformation product relative to its background for the site has occurred.

    • At least some portion of the significant increase of the transformation product above background can be attributed to the site.

      Information that would further support attribution (but would not be sufficient by itself) includes:

    • Conditions at the site are such that it is possible that the parent material has transformed into these substances, or, at minimum, that the conditions at the site do not prevent the transformation from occurring (e.g., the transformation requires oxidizing conditions and these exist at the site); and

    • There is a non-zero containment factor value for at least one source at the site containing the parent material.


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