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HRS Guidance Manual, Section 5.1, Page 55

This section provides guidance on establishing an observed release in the ground water, surface water, and air migration pathways and on establishing observed contamination in the soil exposure pathway. Establishing an observed release (or observed contamination) is an important determinant of an HRS pathway score. If an observed release is established for a migration pathway (i.e., ground water, surface water, and air pathways), likelihood of release for that pathway is automatically assigned its maximum value of 550 points. Establishing observed contamination is a necessary condition for evaluating the soil exposure pathway; the pathway score is automatically assigned a 0 if observed contamination is not established. Establishing an observed release (or observed contamination) also is necessary for establishing actual contamination for targets.

An observed release can be established either by direct observation or by chemical analysis. Observed contamination (in the soil exposure pathway) can be established only by chemical analysis. Establishing an observed release by direct observation generally requires information on material containing a hazardous substance that has been placed into or has been seen entering the medium of concern and attribution of that substance to the site. Establishing an observed release (or observed contamination) by chemical analysis generally requires attributing the hazardous substance to the site, and also requires determining background, demonstrating that the concentration of the hazardous substance in a release sample is significantly increased above background, and attributing some portion of the significant increase to the site.


RELEVANT HRS SECTIONS
  Section 2.3   Likelihood of release
  Section 3.1.1   Observed release (ground water)
  Section 4.1.2.1.1   Observed release (surface water)
  Section 5.0.1   General considerations (soil exposure)
  Section 6.1.1   Observed release (air)

DEFINITIONS

Attribution: The determination that a hazardous substance in a release is likely to have originated in one of the sources at a site. Attribution usually requires documenting that at least one hazardous substance found in a release at a concentration significantly above background (or directly observed in the release) was produced, stored, deposited, handled, or treated at the site; and at least a portion of the significant increase could have come from a source at the site.

Background Level: The concentration of a hazardous substance that provides a defensible reference point that can be used to evaluate whether or not a release from the site has occurred. The background level should reflect the concentration of the hazardous substance in the medium of concern for the environmental setting on or near a site. Background level does not necessarily represent pre-release conditions, nor conditions in the absence of influence from source(s) at the site. A background level may or may not be less than the detection limit (DL), but if it is greater than the DL, it should account for variability in local concentrations. A background level need not be established by chemical analysis.

Background Sample: A sample used in establishing a background level.

Contract Laboratory Program (CLP): The analytical program developed for CERCLA waste site samples to fulfill the need for legally defensible analytical results supported by a high level of quality assurance and documentation.

Contract-required Detection Limit (CRDL): A term equivalent to the contract-required quantitation limit (CRQL), but used primarily for inorganic substances.

Contract-required Quantitation Limit (CRQL): The substance-specific level that a CLP laboratory must be able to routinely and reliably detect in specific sample matrices. The CRQL is not the lowest detectable level achievable, but rather the level that a CLP laboratory must reliably quantify. The CRQL may or may not be equal to the quantitation limit of a given substance in a given sample. For HRS purposes, the term CRQL also refers to the CRDL.

Detection Limit (DL): The smallest quantity of a hazardous substance that can be distinguished from the normal random "noise" of an analytical instrument or method. For HRS purposes, DL is the method detection limit (MDL) or, for real-time field instruments, the instrument detection limit (IDL) as used in the field.

Method Detection Limit (MDL): The lowest concentration of a hazardous substance that a method can detect reliably in either a sample or blank.

Observed Contamination: Surficial contamination related to a site. It must be established by chemical analysis. Observed contamination is present at sampling locations where analytic evidence indicates that:

  1. A hazardous substance attributable to the site is present at a concentration significantly above background levels for the site (i.e., meets the observed release criteria in HRS Table 2-3).

  2. The hazardous substance is present at the surface or covered by two feet or less of cover material (e.g., soil).

Observed Release: An observed release is established for the ground water, surface water, or air migration pathway either by chemical analysis or by direct observation. Observed release is not relevant to the HRS soil exposure pathway. The minimum requirements for establishing an observed release by chemical analysis are analytical data demonstrating the presence of a hazardous substance in the medium significantly above background level, and information that some portion of that increase is attributable to the site. The minimum criterion for establishing an observed release by direct observation is evidence that the hazardous substance was placed into or has been seen entering the medium.

Release Sample: A sample taken to determine whether the concentration of a hazardous substance is significantly above its background level in order to determine whether an observed release (or observed contamination) has occurred.

Sample Quantitation Limit (SQL): The quantity of a substance that can be reasonably quantified given the limits of detection for the methods of analysis and sample characteristics that may affect quantitation (e.g., dilution, concentration).

Similar Samples: Samples from the same environmental medium that are identical or similar in every way (e.g. field collection procedure, analytical technique) except the degree to which they are affected by a site.


ESTABLISHING AN OBSERVED RELEASE BY CHEMICAL ANALYSIS

Establishing an observed release (or observed contamination) by chemical analysis generally requires documenting that the concentration of at least one hazardous substance in a release sample is significantly increased above its background level, and that the substance in the release can be attributed to the site. Note that some additional rules apply for observed contamination (see Section 9.1). General guidance for establishing an observed release by chemical analysis is presented below. An observed release is established at most sites by comparing analytical data derived from samples reflective of site-specific background with analytical data derived from site-related samples. Sample data used to establish an observed release should be of known and documented quality. Analytical data may come from the SI or from studies done by other EPA offices, states, other Federal agencies, or PRPs.

Considerations for Background

All relevant data should be evaluated to determine representativeness of the background samples and attribution. In certain circumstances, background samples are not required to establish an observed release by chemical analysis. Additional guidance used for selecting background samples is provided in Section 5.2. See subsection below, Using Published Data for Background Levels, for a discussion on establishing background levels. The general guidelines below introduce the main concepts.

Background and release samples must be from the same medium (e.g., soil, water, tissue) and should be as similar as possible. Similar sampling methods should be used to obtain background and release samples. Ideally, background samples also should be outside the influence of contamination from the site, but background levels may be determined from samples which contain measurable levels of contamination.

Many hazardous substances may be widespread in the environment in the vicinity of a site. Widespread substances may originate naturally, from non-point sources, or from large point sources. The background level for widespread substances should account for local variability. Several background samples may be required to establish variability in background concentrations (see Section 5.2).

Significance Above Background

The concentration in the release sample must be equal to or greater than the release sample SQL. Continue with the steps below only after determining that the release sample is above its SQL. The criteria used for determining significance above background depend on whether the background level is above or below the background DL.

  • If the background level is greater than or equal to its DL, the minimum requirement for an observed release is that the concentration in the release sample is at least three times greater than the background level.
  • If the background level is below its DL, the minimum requirement for establishing an observed release is that the concentration in the release sample is greater than or equal to the background SQL.

    —  If the SQL for the hazardous substance cannot be established and the sample analysis was performed under the CLP, use the CRQL in place of the SQL.

    —  If the SQL for the hazardous substance cannot be established and the sample analysis was not performed under the CLP, use the DL in place of the SQL.

The considerations detailed in the bullets above are presented in flowchart form in Highlight 5-2. Highlight 5-3 presents several examples of how to decide whether or not significance above background is established.

Attribution

Attribution generally involves demonstrating that the hazardous substance used to establish an observed release can be associated with the site, and the site contributed at least in part to the significant increase in the concentration of the hazardous substance. Attribution can be established based on sampling or non-sampling data.

  • The following information generally is sufficient to associate the hazardous substance to the site:
    • —  Manifests, labels, records, oral or written statements, or other information about site operations exist that demonstrates that the hazardous substance was deposited or is present in a source (or somewhere at the site). Note that if confirmed by manifests, labels, or oral or written statements, attribution generally can be established even if the specific source(s) where the substance was deposited cannot be documented.
    • —  Analytical sampling data that demonstrate the presence of the hazardous substance in a source at a concentration greater than background.
  • The data required to attribute a portion of the significant increase in the concentration of the hazardous substance to the site generally depend on whether or not the site being evaluated is located in an area where other sources may have contributed to the significant increase.
    • —  When no other nearby sources are likely to have contributed to the release, or when the site-specific background concentration is less than the DL, it generally will be sufficient to document that the hazardous substance is associated with a source at the site that could have released to the environmental medium of concern.
    • —  When other sources are present in the vicinity of the site being evaluated and may have contributed to the significant increase (e.g., in highly industrialized areas), it generally is necessary to obtain sufficient samples between the site being evaluated and other known potential sources (or between the site and adjacent sites) in order to demonstrate an increase in concentration attributable to the site. Additional information may be required if other sites are known to release substances intermittently, such that "pulses" of hazardous substances are created in environmental media. Types of information that will strengthen such attribution include:
      • ­­  Data on concentration gradients (e.g., established based on samples from multiple wells or a series of samples between the site and the alternative source);
      • ­­  Data on flow gradients or other information about the movement of hazardous substances in the environmental medium of concern; or
      • ­­  Analytical "fingerprinting" data that establish an association between the site and a unique form of the substance or unique ratios of different substances.

The above general guidelines apply to all HRS pathways and threats. Additional pathway-specific considerations are presented below.

Pathway­Specific Considerations

Ground Water Pathway

  • Background and release samples must be from the same aquifer because background levels, water chemistry, and other parameters may vary among aquifers.

  • In some cases a contaminated well can serve as its own background (e.g., if similar samples at different points in time establish background levels and levels significantly above background).

  • When evaluating a ground water plume with no identified source, background samples are required, but the release need not be attributed to a specific site.

Surface Water Pathway

  • Background samples and release samples must be the same type of sample (e.g., aqueous samples must be compared to aqueous samples, sediment samples must be compared to sediment samples).

  • For tissue samples, only samples from essentially sessile, benthic organisms (e.g., mussels, oysters) can be used to establish an observed release.

  • When evaluating contaminated sediments with no identified source, background samples are required, but no separate attribution is required.

Soil Exposure Pathway

  • Observed contamination can be established only when the hazardous substance is present at the surface or covered by two feet or less of cover material (e.g., soil). However, any area covered by a permanent or otherwise maintained, essentially impenetrable material (e.g., asphalt) cannot be considered an area of observed contamination.

  • For contaminated soil, areas of observed contamination can be inferred for the area lying between sampling locations at which observed contamination is established unless available information (e.g., topography, site operations, impenetrable cover, drainage patterns) indicates otherwise.

  • For sources other than contaminated soil, the entire source is considered an area of observed contamination if observed contamination is established at any point on the source and within two feet of the surface.

Air Pathway

  • Indoor air samples cannot be used to establish an observed release.

USING PUBLISHED DATA FOR BACKGROUND LEVELS

At some sites, it may not be possible to collect sample(s) to determine a background level. Certain circumstances may preclude background sampling (or use of available background sampling data) for the site. Several such circumstances are outlined below.

  • No appropriate background sampling locations for the site were found. This circumstance generally applies only to the surface water pathway (e.g., a release to an isolated pond or wetland; surface water originates from a spring on the site).

  • Resource constraints precluded background sampling.

Under such circumstances, it may be necessary to establish the background level based on published data relevant to the site. Existing data from published reports should be evaluated to determine if background levels can be developed. Documentation should focus on establishing what the concentration of the hazardous substance of concern should be for the medium of concern in the absence of contamination attributable to the site.

The appropriateness of published data for establishing background levels must be determined on a case-by-case basis. No a priori set of criteria regarding use of published data can be established for every hazardous substance and type of site. The guidelines presented below, while helpful in evaluating the appropriateness of such data, are not intended as definitive criteria for accepting or rejecting such data. Published values may not be site-specific enough to be appropriate for determining background levels.

  • Potential background levels should be obtained from multiple data sources. Sources of data should include regional and local studies. Ideally, only primary sources should be used. Examples of primary data sources include regional soil lead studies, surveys of sediment contamination in harbors and bays, and national tissue residue surveys such as NOAA's mussel watch program.

  • The variability of background concentrations for the substance on a national, regional, and local scale should be described as fully as possible. Variability will depend, in part, on the nature of the hazardous substance. Naturally occurring substances such as heavy metals, for example, are expected to be distributed more widely in the environment than are organic substances used in a limited number of manufacturing practices. Variability will also depend on the local environment. Information on other sources near the site will help determine whether unusually high background concentrations are expected (e.g., soil lead levels are expected to be higher near major highways).

  • Regional geology may help determine where higher concentrations of naturally occurring substances are likely (e.g., ore veins, soil types with unusually high metals concentrations).

USING QUALIFIED DATA

For analytical results, particularly those developed within the CLP, various data qualifiers and codes (collectively termed "qualifiers") may be attached to certain data by the laboratory conducting the analysis. Data qualifiers also may be added, modified, or changed during data validation. The qualifiers pertain to QA and QC variations which result in uncertain confidence concerning the identity of the substance being analyzed, its concentration, or both. The QA and QC conditions that result in data qualification must be evaluated with respect to the decision being made (e.g., establishing an observed release) before using the data in HRS scoring. Because non-CLP laboratories may assign codes that differ from those of the CLP, it is important to ascertain the exact meaning of all data qualifiers. See Highlight 5-4 for some considerations that are usually applicable to data generated within CLP.


ESTABLISHING AN OBSERVED RELEASE BY DIRECT OBSERVATION

In contrast to establishing an observed release by chemical analysis, where significance above background and attribution are interrelated, establishing an observed release by direct observation generally only requires information that material containing a hazardous substance attributable to the site was placed into or has been seen entering the medium of concern. Attribution in this case generally involves documenting that the substance in the release is associated with the site, either with non-sampling or sampling data. Pathway-specific considerations are outlined below.

Ground Water Pathway

  • Establishing an observed release by direct observation generally requires information that material containing a hazardous substance has been deposited directly into or otherwise has come to be located (e.g., due to a rising water table) below the top of the aquifer being evaluated.

Surface Water Pathway

  • Establishing an observed release by direct observation generally requires information that:
    • —  Material containing a hazardous substance has been seen entering surface water through migration or direct deposition;
    • —  A source area has been flooded at a time that a hazardous substance was present in the source, and material containing a hazardous substance was in direct contact with the surface water; or
    • —  Information documenting adverse affects associated with a release of a hazardous substance to surface water (e.g., a fish kill incident) supports the inference of a release of material containing that hazardous substance from the site to surface water.
  • When basing an observed release on inference of a release by demonstrated adverse effects, it generally is necessary to provide a rationale for inferring the release from the site, to document that the substance was present on the site prior to or at the time the adverse effects occurred, and to document that the adverse effects were likely caused by the substance.

  • When the source area that has been flooded is contaminated soil, it is necessary to demonstrate that the hazardous substance was present at a concentration significantly above background level in order to document an observed release.

Soil Exposure Pathway

  • Observed contamination in the soil exposure pathway cannot be established by direct observation.

Air Pathway

  • Establishing an observed release by direct observation generally requires information that:
    • —  Material containing a hazardous substance has been seen entering the atmosphere directly (e.g., particulate material blowing off a pile);
    • —  Information supports the inference of a release from the site to the atmosphere of material that contains at least one hazardous substance; or
    • —  Information documenting adverse effects associated with the release of a hazardous substance to air (e.g., human health effects) supports the inference of a release of material containing that hazardous substance from the site to air.
  • When basing an observed release on inference of a release by demonstrated adverse effects, it generally is necessary to provide a rationale for inferring the release from the site, to document that the substance was present on the site prior to or at the time the adverse effects occurred, and to document that the adverse effects were likely caused by the substance.

  • If the source used to establish an observed release is contaminated soil, it is necessary to demonstrate that the hazardous substance was present at a concentration significantly above background level to document an observed release.

TIPS AND REMINDERS

  • Establishing an observed release by direct observation generally requires the following information: (1) material containing a hazardous substance was placed into or has been seen entering the medium of concern, and (2) the substance in the release is associated with the site. If the source is contaminated soil, the concentration of the hazardous substance in the contaminated soil must be significantly above background and some portion of the increase must be attributable to the site.

  • Establishing an observed release by chemical analysis generally requires the following information: (1) the concentration of at least one hazardous substance in a release sample is significantly increased above the background level, (2) the substance in the release is associated with the site, and (3) the site contributed at least in part to the significant increase.

  • Background level need not be established by chemical analysis.

  • The difficulties in attributing an increase in concentration to a site can be avoided if an observed release by direct observation can be established.

 

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