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Terrestrial Ecological Evaluation Process- The Site-Specific Evaluation

The information provided in this section about site-specific ecological assessments is intended only as an introduction.  It will not provide you all the information you need to complete a site-specific ecological assessment. If you must conduct a site-specific evaluation, you will need assistance from a habitat biologist and an experienced risk assessor, and you must obtain the department's approval.  You need to refer to the Model Toxics Control Act  Cleanup Regulation for the complete language regarding site-specific ecological evaluations - WAC 173-340-7493.  The information in this section is paraphrased and/or shortened for brevity, but provides links to the actual rule language for your convenience.  


The site-specific evaluation is intended to facilitate selection of a cleanup action by developing information needed to evaluate cleanup action alternatives in the feasibility study.

There are two elements in planning a site-specific ecological evaluation.  Both must be done in consultation with, and approved by the department.  

The two elements of the site-specific evaluation are:

  Problem formulation; and

  Selection of methods  - to address issues identified during problem formulation.

After reviewing information developed in the problem formulation step, the department may, at its discretion, determine that continuation of the site-specific evaluation is not required for either of the following reasons:

  The cleanup action plan developed for the protection of human health will eliminate exposure pathways of concern to all soil contamination; or 

  A simplified evaluation may be conducted because it will adequately identify and address any existing or potential threats to ecological receptors.

The Problem Formulation Step

The problem formulation step establishes the goals and scope of the site-specific assessment.  It identifies issues to be addressed, specifically: the identity and distribution of the chemicals of ecological concern; exposure pathways; terrestrial ecological receptors of concern; and a toxicological assessment.  

Selection of Appropriate Terrestrial Ecological Evaluation Methods

If, during the problem formation step, it is determined that further evaluation is needed, the soil concentrations listed in Table 749-3 may be used as the cleanup level at the discretion of the person conducting the evaluation.  Otherwise, one of the following 7 methods listed below, that are specifically relevant to the issues identified in the problem formulation step, shall be conducted. 

The purpose of employing the method is to ensure that the goals of the ecological evaluation are fulfilled, those being (from WAC 173-340-7489(1)(a)):

 Determining whether a release of hazardous substances to soil may pose a threat to the terrestrial environment;  Characterizing existing or potential threats to terrestrial plants or animals exposed to hazardous substances in soil;  and  Establishing site-specific cleanup standards for the protection of terrestrial plants and animals.

The Seven Site-Specific TEE Methods

  1. Literature Survey:

    An analysis based on a literature survey that helps set soil concentrations for chemicals not listed in Table 749-3; for the protection of plants or soil biota more relevant to site-specific conditions than the value listed in Table 749-3; or obtaining a value for any of the wildlife exposure model variables listed in Table 749-5 to calculate a soil concentration for the protection of wildlife more relevant to site-specific conditions than the values listed in Table 749-3.

  2. Soil Bioassays:

    Where Plants are a concern: you may use the test described in Early Seedling Growth Protocol for Soil Toxicity Screening; Ecology Publication No. 96-324.

Where risks to soil biota are a concern: you may use the test described in Earthworm Bioassay Protocol for Soil Toxicity Screening; Ecology Publication No.96-327.    

  Other bioassay tests approved by the department may be used, and bioassays may use sensitive surrogate organisms not found at the site if the test adequately addresses the issues raised during the problem formulation step.

  Soil concentrations protective of soil biota or plants may also be established with soil bioassays that use species ecologically relevant to the site rather than standard test species.  Species that do, or could, occur at a site are considered ecologically relevant.

  1. Wildlife Exposure Model: 
    Equations and exposure parameters to be used in calculating soil concentrations protective of terrestrial wildlife are provided in Tables 749-4 and 749-5.  Based on site-specific considerations, the department may approve changes to the wildlife model. The department may grant changes under the following conditions:

  Alternative values to Table 749-5 can be demonstrated to be more relevant to site-specific conditions; Alternative values obtained from literature need to be supported by a literature survey conducted in accordance with the section on Literature Surveys below.

  Receptor species of concern or exposure pathways identified in the problem formulation step may be added to the model;  

  A substitution may be made for one or more of the receptor species listed in Table 749-4. (See the section on Substitute Receptor Species below.

  1. Biomarkers:
    Biomarkers are physical or biological responses to environmental stressors (e.g. exposure to hazardous substances.)  Biomarker methods may be used in the site-specific evaluation if the measurements have clear relevance to the issues identified during the problem formulation and the approach has a high probability of detecting a significant adverse effect if it is occurring at the site.  Criteria such as biomarker effects may be used that serve as a sensitive surrogate for significant adverse effects.

  2. Site-specific field studies:
    Site-specific empirical studies that involve hypothesis testing should use a conventional "no difference" null hypothesis (e.g. H0: Earthworm densities are the same in the contaminated area and the reference (control) area.  HA: Earthworm densities are higher in the reference area than in the contaminated area). In preparing a work plan, consideration shall be give to the adequacy of the proposed study to detect an ongoing adverse effect and this issue shall be addressed in reporting results from the study.

  3. Weight of evidence: 
    A weight of evidence approach is used when multiple data types need to be integrated to provide the basis for decision making.  The approach must balance the application of data obtained from literature, field, and laboratory, because each has certain strengths and weaknesses.  Information specific to the site will be given greater weight than default values or assumptions as appropriate.

  4. Other methods approved by the department:
    This may include a qualitative evaluation if relevant toxicological data are not available and cannot be otherwise developed (e.g. through soil bioassay testing.)

Literature Surveys

Toxicity reference values or soil concentrations established from a literature survey shall represent the lowest relevant LOAEL found in the literature.  Bioaccumulation factor values shall represent a reasonable maximum value from relevant information found in the literature.

In assessing relevance, the following principles shall be considered:

  Literature benchmark values should be obtained from studies that have test conditions as similar as possible to site conditions;

  The literature benchmark values or toxicity reference values should correspond to the exposure route being assessed; 

  The toxicity reference value or bioaccumulation factor value needs to be geared for the receptor being assessed and should be based on a significant endpoint as described in the problem formulation step; 

  The literature benchmark value or toxicity reference value should be based on chronic exposure. 

  The literature benchmark value, toxicity reference value, bioaccumulation factor should correspond to the chemical from being assessed.  Exceptions may apply for toxicity reference values where documented biological transformations occur following uptake of the chemical or where chemical transformations are known to occur in the environment under conditions appropriate to the site.

Documentation needed by the department if you use a literature survey:

A list of relevant journals and other literature used in the survey must be provided to the department.  Also provide a table summarizing information from all relevant studies in the report and identify the specific studies used to select a proposed value.  Provide the department copies of all literature cited in the table if the department is not already in possession of the study.  

Note: The department may identify relevant articles, books or other documents that must be included in the literature survey.

Uncertainty Analysis

If a site-specific evaluation includes an uncertainty analysis, the discussion of uncertainty needs to identify and differentiate between uncertainties that can and cannot be quantified, and natural variability.  The discussion shall describe the range of potential ecological risks from the hazardous substances at the site, and the uncertainty regarding the risks.

Potential methods for minimizing uncertainty must also be discussed, such as additional studies or post-remediation monitoring.

If multiple lines of independent evidence have been developed, a weight of evidence approach may be used in characterizing uncertainty.

New Scientific Information

The department shall consider proposals for modifications to default values based on new scientific information in accordance with WAC 173-340-702(14), (15), and (16).

Substitute Receptor Species

Substitutions of receptor species and the associated values in the wildlife exposure model described in Table 749-4 may be made subject to the following conditions:

  There is scientifically supportable evidence that a receptor  identified in Table 749-4 is not characteristic or a reasonable surrogate for a receptor that is characteristic of the ecoregion where the site is located.

    The proposed substitute receptor is characteristic of the ecoregion where the site is located and will serve as a surrogate for wildlife species that are, or may become exposed to soil contaminants at the site. It shall be a species that is expected to be vulnerable to the effects of high exposure or known sensitivity to the  contamination  present on-site, relative to the current default species. 

  Scientific studies are available in literature to select reasonable maximum exposure estimates for variables listed in Table 749-4

  In choosing among potential substitute receptor species, preference shall be given to the species most ecologically similar to the default receptor being replaced. 

  The following groups of animals will generally be included in the wildlife exposure model: a small mammalian predator on soil-associated invertebrates, a small avian predator on soil-associated invertebrates, and a small mammalian herbivore.

  The department may impose additional requirements to account for uncertainties in the level of protection provided to substitute receptor species and toxicologically sensitive species, such as: 

Use of toxicity reference values based on NOAEL;

  Use of uncertainty factors to account for extrapolations between species in toxicity or exposure parameter values; or

  Use of a hazard index approach for multiple contaminants to account for additive toxic effects.


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