Proposed Amendments to the Model Toxics Control Act (MTCA) Cleanup Regulation

The Washington State Department of Ecology (Ecology) is proposing changes to the Model Toxics Control Act (MTCA) Cleanup Regulation (Chapter 173-340 WAC). The rule revisions will update the policies and procedures for establishing and evaluating compliance with cleanup levels and remediation levels for several types of chemicals.


The Model Toxics Control Act (MTCA) was passed by Washington voters in November 1988.  The law establishes the basic authorities and requirements for cleaning up contaminated sites.  Ecology originally adopted cleanup standards in February 1991.  The Department completed significant changes to the cleanup standards in February 2001.  Under the revised rule, a person undertaking a cleanup action may use the Environmental Protection Agency’s toxicity equivalency factor (TEF) values and methodology when assessing dioxin and furan mixtures.  Later that year, Ecology published a guidance document (Cleanup Levels and Risk Calculations (CLARC) that explains how to use the TEF methodology when establishing cleanup levels. 
In November 2005, the Rayonier Corporation filed a lawsuit challenging Ecology’s use of the guidance document at the Port Angeles mill site.  Rayonier argued that the MTCA rule requires Ecology to establish cleanup levels for each dioxin congener using a cancer risk level of one-in-one million (or 10-6 ) (as opposed to applying 10-6  risk level to the whole mixture).  In April 2006, Ecology settled the lawsuit and agreed that Rayonier's approach was also a plausible interpretation of the current MTCA rule. Ecology agreed to settle the lawsuit because neither the current MTCA rule nor the federal guidance referenced in the MTCA rule explicitly require the procedures in the CLARC guidance.

Concurrent with the settlement discussions, several environmental organizations submitted a rulemaking petition to Ecology in March 2006. These groups requested that Ecology amend the rule to clarify that the policies and procedures specified in the Ecology guidance should be used when establishing cleanup levels for dioxins/furans and other similar mixtures. Ecology reviewed the petition and decided to initiate a rulemaking process to address the issues raised in the lawsuit and rulemaking petition. Ecology decided that amending the MTCA rule to explicitly define key policy choices is preferable to repeatedly resolving those policies on a site-specific basis.

Ecology initiated the rulemaking process on June 7, 2006 by filing the CR-101 with the Office of the Code Reviser.  Later that month, Ecology prepared draft rule language that was distributed to interested parties for review and comment.   Ecology held several meetings to discuss the draft rule language and key rulemaking issues.   Ecology received numerous comments on the draft rule language.   After reviewing those comments, Ecology modified the draft rule language and incorporated additional revisions that establish a new default Gastrointestinal Absorption Fraction (AB1) for soil-bound dioxins and furans.  Ecology also held four meetings with the MTCA Science Advisory Board to discuss key rulemaking issues.   Based on the Board’s review, Ecology made further modifications to the proposed rule in early 2007.  

Summary of the Proposed Rule Changes

Ecology is proposing revisions to the policies and procedures for setting and evaluating compliance with cleanup levels and remediation levels for certain chemical mixtures.  The changes apply to mixtures of dioxins and furans, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). I have attached a copy of the proposed rule language to this E-mail message.  The proposed revisions include:

  • Risk Policies Applicable to Certain Mixtures, Ecology is proposing that:
    • Cleanup levels for dioxin and furan mixtures must be based on a cancer risk of one-in-a-million;
    • Cleanup levels for PAH mixtures must be based on a cancer risk of one-in-a-million;
    • Cleanup levels for PCB mixtures must be based on a cancer risk of one-in-a-million.

  • Toxic Equivalency Factors Used to Characterize Mixtures, Ecology is proposing to amend the rule to incorporate the most recent toxicity equivalency factors (TEFs) for dioxins/furans and PCBs recommended by the World Health Organization and updated potency equivalency factors (PEFs) for carcinogenic PAHs adopted by the California Environmental Protection Agency.

  • Default Parameters Used to Calculate Cleanup Levels, Ecology is proposing to revise the default Gastrointestinal Absorption Fraction used to establish soil cleanup levels for dioxins and furans.

  • Evaluating Cross-Media Impacts,Ecology is proposing to require that cleanup proponents consider the physical-chemical properties of individual PAH compounds or dioxin-congeners when evaluating cross-media impacts.

Opportunities for Public Review and Comment

Ecology will be filing the proposed rule with the Code Reviser on April 4, 2007.   The public comment period will run from April 4 to May 25, 2007.   If you have comments on the proposed rule, please send them to:

Mr. Pete Kmet
Department of Ecology,
Toxics Cleanup Program
PO Box 47600
Olympia, WA 98504-7600

Ecology has scheduled three public hearings to receive written or oral comments on the proposed changes to the rule.  At each public hearing, an overview presentation and question/answer period will be held prior to the start of the official public hearing. Following are the dates, times, and locations of the public hearings:

May 10, 2007 - 5:30 p.m.
St. Benedict School Auditorium

4811 Wallingford AVE N
Port Angeles
May 14, 2007 - 5:30 p.m.
County Commissioners Board Room
Clallam County Courthouse

223 E 4th ST
May 17, 2007 - 5:30 p.m.
Department of Ecology
Eastern Regional Office

N 4601 Monroe ST, STE 100
Second Floor Conference Room

For more information or questions, please call (360) 407-7187 or 1-800-826-7716 or view the website at:




Proposed  MTCA Rule Amendment


SEPA Determination of Non-Significance

Background Document for the Proposed Amendments to MTCA

Click here for a consolidation of all of the above documents.

Cost Benefit Analysis


Pete Kmet