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Terrestrial Ecological Evaluation (TEE)

Information Updates:

11/28/12 – Additional clarification regarding MTCA requirements and how they pertain to the Terrestrial Ecological Evaluation can be found at:

05/31/2012 – A compendium to the Terrestrial Ecological Evaluation (TEE) document is now available.  This compendium document provides the references and resources that have been cited in the new TEE technical assistance document.  To see the Table of Contents and Sections, please click on this link.  The new TEE technical assistance document is still in development, however, it should go out for internal review soon.  Please check back with this website frequently for the most recent updates.

02/28/12 – From time to time Ecology gets questions regarding availability of qualified professionals to perform Terrestrial Ecological Evaluations (TEE’s).  Ecology does not make recommendations for professional services.  If you are an environmental consulting agency with experience  performing TEE’s, Ecology recommends attaching the keyword “MTCA TEE” to your website.   
If you would like to join an informal group with expertise in TEE’s in order to provide professional review to Ecology on the draft TEE guidance document, please contact:
Arthur Buchan at (360) 407-7146 (
Brendan Dowling at (509) 329-3611 (

02/07/12 - Ecology is currently working on a Terrestrial Ecological Evaluation guidance document.  For questions/concerns regarding this guidance document, please contact:

Arthur Buchan at (360) 407-7146 (
Brendan Dowling at (509) 329-3611 (

Terrestrial Ecological Evaluation (TEE) Process An Interactive User's Guide:


TEE Process Flow Diagram

Why Ecological Evaluations Are Needed

TEE Requirements

     Independent Remedial Actions

Evaluating Protectiveness for Commercial and  Industrial Sites, and Other Land Uses

Point of Compliance

     Conditional Point of Compliance

Documenting Decisions


The purpose of a Terrestrial Ecological Evaluation (TEE) is to protect land-based plants and animals from exposure to contaminated soil.  The purpose of this interactive guide is to help you understand the Washington State Department of Ecology's Terrestrial Ecological Evaluation process, and to help you in considering the potential effects to any ecological receptors at your site.

These procedures are not intended for the evaluation of plants or animals in water, wetlands, or sediments.  Procedures for evaluating sediments are described in section 760 of the Model Toxics Control Act Cleanup Regulation and surface water evaluations are described in section 730.  Wetland evaluations are determined on a case-by-case basis.

The TEE procedures also do not address impacts to livestock or domesticated animals or cultivated non-native plants.  If crop or livestock impacts or uptake are likely, impacts to human health should be considered.

The following introductory pages provide some basic information about terrestrial ecological evaluations.  If you want to see if you qualify for an exclusion from this evaluation process you can skip right to the Exclusions.  If contaminant concentrations in the soil do not exceed the ecological indicator concentrations described in Table 749-3, those hazardous substances may be eliminated from further consideration.  Your ecological evaluation is complete if you can eliminate all the chemicals of concern at your site in this manner.

TEE Process Flow Diagram

You can view a flow chart of the Terrestrial Ecological Risk Assessment Process (pdf version)
You can view the flow chart in MSWord format here.

Why Ecological Evaluations Are Needed 

There are three reasons Terrestrial Ecological Evaluations are necessary: 

  To determine if a release of hazardous substances may harm the plants and/or animals on your property;

  To identify and understand - to characterize - the existing or potential threats to the plants and/or animals that may be exposed to hazardous substances in the soil; and

To establish cleanup standards to protect not only human health, but the plants and animals, and ecologically important functions of the soil biota as well.

TEE Requirements 

When hazardous substances are released to the soil at a site, one of the following three actions must be taken:

Independent Remedial Actions:  

Any approvals or determinations by the department required as part of a terrestrial ecological evaluation under the Model Toxics Control Act Cleanup Regulation, are not necessary in order to conduct an independent remedial action.  However, independent remedial actions must still meet the substantive requirements of the cleanup regulation.  [WAC 173-340-515(3)(b)]

Evaluating Protectiveness for Commercial and  Industrial Sites, and Other Land Uses

In considering the potential impacts to ecological receptors, Ecology will evaluate protectiveness relative to the land use at a site: 

For Industrial or Commercial Properties - Protectiveness is evaluated relative to Wildlife receptors.  Current or future potential for exposure to soil contamination need be evaluated for terrestrial wildlife protection.

Plants and soil biota need not be considered unless:

  The species is protected under the Endangered Species Act; or

  The soil contamination is located on an area of an industrial or commercial property where vegetation must be maintained to comply with local government land use regulations.

For All Land Uses Other than Commercial or Industrial - Protectiveness is evaluated relative to terrestrial plants, wildlife, and ecologically important functions of soil biota that effect plants or wildlife.

NOTE: Any terrestrial remedy, including exclusions, based even in part on future land use assumptions shall include a completion date for such future development that is acceptable to the department.   If land-use assumptions used in the TEE are not accomplished by that completion date, the site must be reevaluated using existing land-use conditions.

Point of Compliance

"Point of Compliance" defines the point or points on a site where cleanup levels must be met.  The term includes both "standard" and "conditional" points of compliance.

For soil cleanup levels based on protection of terrestrial ecological receptors, the point of compliance is defined in WAC 173-340-7490(4).  See also WAC 173-340-740(6)(e).

Standard Point of Compliance  

The standard point of compliance is defined as throughout the site from the ground surface to fifteen feet below the ground surface.  Fifteen feet represents a reasonable estimate of the depth of soil that could be excavated and distributed at the soil surface as a result of site development activities, resulting in exposure by terrestrial ecological receptors. 

Institutional controls are not required for soil contamination that is at least fifteen feet below the ground surface.  

Unless a site qualifies for a conditional point of compliance (described below), soil cleanup levels must be met at the standard point of compliance.

Conditional point of compliance 

A conditional point of compliance may be established at the biologically active soil zone if institutional controls are used as part of the cleanup action to prevent excavation of deeper soils. 

Default  Depth for Conditional Point of Compliance

The regulation establishes a presumption that the biologically active soil zone extends to a depth of six feet.

Site-Specific Depth for Conditional Point of Compliance

Ecology may approve a depth other than the default depth for a conditional point of compliance based on a site-specific demonstration that this alternative depth is more appropriate for the site.  In making this demonstration, the following factors must be considered:

  1. Depth to which soil macro-invertebrates are likely to occur;
  2. Depth to which soil turnover (bioturbation) is likely to occur due to the activities of soil invertebrates;
  3. Depth to which animals likely to occur at the site are expected to burrow; and
  4. Depth to which plant roots are likely to extend.

Documenting Decisions

Documentation, including sampling and analysis data,  needs to be added to the site record in support of the decision-making regarding ecological evaluations.  You must provide sufficient detail to explain how your site  meets one of the primary exclusionary criteria or qualifies for a simplified evaluation, if applicable.  Information on the development of conditional points of compliance and institutional controls based on ecological evaluations should also be included.
If this information is already contained within a site investigation or cleanup report in the department's files, you may cite the specific locations  in the reports where the supporting data can be found.

We have created two forms to assist you in documenting your TEE decision-making. One for documenting primary exclusions,  and one for documenting the type of ecological evaluation required (either a simplified or a site-specific).

We recommend you go to Exclusions main page next

Please contact Arthur Buchan if you have any questions or comments about the TEE web pages.

[Exclusions Main] [TEE Definitions] [Simplified or Site-Specific?] [Simplified Ecological Evaluation] [Site-Specific Ecological Evaluation] [WAC 173-340-7493] [Index of Tables]