Chapter 173-340 WAC

On August 23, 2023, the Department of Ecology (Ecology) adopted amendments to Chapter 173-340 WAC, the Model Toxics Control Act (MTCA) Cleanup Regulations.  The regulations govern the investigation and cleanup of sites in Washington state contaminated by the release of hazardous substances.  The adopted rule amendments:

  • Update the title of the chapter.
  • Update the general provisions and defined terms in Parts 1 and 2 of the chapter.
  • Update the requirements for release reporting, initial investigation, site hazard assessment and ranking, site listing, and program planning under Part 3 of the chapter.
  • Update the requirements for conducting a remedial investigation and selecting a cleanup action for a site in Part 3 of the chapter.
  • Update the requirements in WAC 173-340-450 for investigating and cleaning up underground storage tanks regulated under Chapter 173-360A WAC.
  • Update the requirements for public participation and tribal engagement in Part 6 of the chapter.
  • Incorporate requirements for cultural resource protection in new WAC 173-340-815 and update procedures for identifying appropriate sampling and analytical methods in WAC 173-340-830.
  • Make other conforming and selective changes to the administrative and procedural requirements in Parts 4, 5, and 8 of the chapter.
  • Make other changes in Parts 1 through 6 and Part 8 of the chapter to streamline and clarify requirements, make minor corrections, and improve consistency with other laws and rules.
  • Make changes in Parts 7 and 9 of the chapter to clarify language and make corrections without changing the effect of the rule.
  • Incorporate changes to the cleanup program specified in Chapter 70A.305 RCW, the Model Toxics Control Act.

Ecology did not change the cleanup standards in Parts 7 and 9 of the chapter as part of this rulemaking.

The rule amendments replace the outdated site hazard assessment and ranking process specified in the rule with an improved process developed outside the rule, called SHARP.  The Draft SHARP Tool and User Manual were available for public comment at the same time as the proposed rule amendments.

This rulemaking is the first of several rulemakings that Ecology plans to undertake to update the MTCA Cleanup Regulations.  Read more about our plans on our Exploratory Rulemaking page.

Rulemaking timeline


Announcement phase (CR-101)

Filing date:
Dec. 20, 2018

Announcement documents

Rule development phase

Dec. 20, 2018–Feb. 15, 2023

Public input & involvement

Rule proposal phase (CR-102)

Filing date:
Feb. 15, 2023

Rule proposal documents:

Additional documents:
The following additional documents are available to help in your review of the rule proposal:

Comment period

Comments were due on April 16, 2023

View comments received

We held two public hearings on the proposed rule amendments via webinar.  The public hearings were held March 23, 2023, and March 27, 2023.

The hearings began with a short presentation and question and answer session, followed by the opportunity to provide testimony.

No public hearings are scheduled at this time

Rule adoption phase (CR-103)

Adoption date:
Aug. 23, 2023

Rule effective date:
Jan. 1, 2024

Rule adoption documents:

Additional documents:
The following additional documents are available to aid your review of the adopted rule amendments:

These documents include only those sections amended in the rulemaking.

Additional languages

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To request ADA accommodation for disabilities, or printed materials in a format for the visually impaired, contact Ecology's ADA Coordinator by email at, or call 360-407-6831. People with impaired hearing may call Washington Relay Service at 711. People with speech disability may call TTY at 877-833-6341.