Terrestrial Ecological Evaluations

A Terrestrial Ecological Evaluation (TEE) works to protect native plants, soil biota, and wildlife at contaminated sites cleaned up under the state's cleanup law, the Model Toxics Control Act (MTCA). You can help us accomplish this goal by completing a TEE at any cleanup site that does not qualify for an exclusion. This page helps you determine if your site qualifies for an exclusion, explains the types of TEEs, and provides resources to help you plan and understand the TEE process.

What is a Terrestrial Ecological Evaluation?

The TEE process allows us to determine what plants or animals might be harmed by contaminants at a site. It also allows us to calculate protective levels that will keep them living and healthy.

We use Washington's cleanup law, the Model Toxics Control Act (MTCA), to direct cleanups that protect you and your community from the threats of hazardous waste. MTCA also helps protect plants, soil biota, and wildlife (known as ecological receptors) that live in the environment. For example, sometimes cleanup levels for contaminants are calculated to protect people from hazardous chemicals, but aren't low enough to protect the plants and animals that live in close contact with the soil.  

When do I need to conduct this evaluation?

You must complete a TEE any time contaminants could harm ecological receptors, such as native plants, soil biota, or wildlife. But you don't need to complete a TEE if you have one of these four exclusions: 

  1. All of the contamination at the site is located deep in the soil and will not reach the ecological receptors (Exclusion 1); OR
  2. All of the contamination at the site is covered by physical barriers (Exclusion 2); OR
  3. There is insufficient habitat surrounding the site (depending on the type of contaminant) to endanger ecological receptors (Exclusion 3); OR
  4. The contaminant levels at the site are lower than natural background levels (Exclusion 4).

How do I know if my site qualifies for an exclusion?

The Exclusion Table helps you determine if your site qualifies, and whether it would require "institutional controls" such as deed restrictions on certain types of development. For more information read the draft guidance.

Exclusion Table: Does my site qualify for a TEE Exclusion?

What types of TEEs can be performed?

Conditions at your site will determine which TEE should be performed: 

  • A simplified TEE can be used at many urban sites. The simplified TEE process is intended to identify (and mitigate) those sites that do not have a substantial potential for posing a threat to terrestrial ecological receptors. Qualifying for a simplified TEE can speed up and reduce the cost of your cleanup. (See Chapter 173-340-7492 WAC)
  • A site-specific TEE is allowed at any site but is intended for rural settings, or cleanup sites surrounded by native vegetation. (See Chapter 173-340-7493.)  It involves:
    • a problem formulation step;
    • choosing an appropriate evaluation method; and
    • calculating protective contaminant concentrations for each terrestrial ecological receptor of concern (plants, soil biota, wildlife).

How do I perform a TEE or get more information?

Access MTCA's TEE procedures and read the draft guidance, Terrestrial Ecological Evaluations under the Model Toxics Control Act. A public comment period on this draft should be available in the spring or early summer of 2019. The draft guidance  help you determine if your site qualifies for an exclusion, which TEE should be performed, and how to implement both simple and site-specific TEEs.   

How can I provide comments on the TEE draft guidance?

Contact Toxicologist Arthur Buchan, 360-407-7146.