Cleanup Levels and Risk Calculation (CLARC)

CLARC February 2024 updates are now online. 

Cleanup Levels and Risk Calculation (CLARC) is a compendium of technical information related to calculating cleanup levels under Washington's Cleanup Rule, the Model Toxics Control Act (MTCA) Regulation, Chapter 173-340 WAC. On these pages, you'll find information to help you establish cleanup levels for chemicals found at hazardous waste sites. Cleanup levels help determine what actions (if any) may be needed to protect the health of people, animals, and plants from chemical contamination at a hazardous waste site being cleaned up under MTCA. 


Before using CLARC, read its cautions and limitations. CLARC is not required by law. We provide it to help staff and the public. CLARC has a lot of information, but it isn’t exhaustive. You may need to get information from other sources for certain hazardous substances. Read the full disclaimer.

CLARC is always changing. We make minor updates and corrections as needed. Every six months in the spring and fall, we may make major updates to align with EPA’s regional screening levels (RSL).

Additional cleanup information

What are cleanup levels?

MTCA cleanup levels are the concentrations of hazardous substances in the environment that are considered sufficiently "protective of human health and the environment under specified exposure conditions" (WAC 173-340-200). Determining cleanup levels for hazardous substances is a crucial part of the MTCA cleanup process, since "cleanup levels must be established for every [contaminated] site" (WAC 173-340-355(2)).

What should you consider when determining cleanup levels?

Each contaminated site varies in size and complexity. Depending on the hazardous substance(s) and the potential for exposure at each site, you may need to consider one or more of the following options before determining a cleanup level. See Cleanup Rule sectionsWAC 173-340-700 through WAC 173-340-760, which specify how to select the appropriate cleanup level among those that are:

  • Listed in the MTCA Method A Table 720-1, Table 740-1, and Table 745-1 (WAC 173-340-900)
  • Calculated for groundwater (WAC 173-340-720), surface water (WAC 173-340-730), soil (WAC 173-340-740, WAC 173-340-745), and air (WAC 173-340-750) using equations and procedures identified under MTCA Method B unrestricted land use or Method C for qualifying site uses and conditions (e.g., industrial). 
  • Based on protection of cross-media contamination (i.e., concentrations that prevent violations of cleanup levels for other media)
  • Based on applicable state and federal laws
  • Based on ecological risk
  • Based on natural or area background concentrations
  • Based on practical quantitation limits of analytical methods
  • Based on additive cancer risk and noncancer effects from multiple hazardous substances, multiple exposure pathways, or both.


CLARC is not mandated by law, but rather is provided as a service to staff and the public. While the information provided in CLARC is extensive, it is not exhaustive and the user may need to obtain information from additional sources for certain hazardous substances. Although CLARC has undergone review to ensure the quality of the information provided, there is no assurance that CLARC is free from errors. If necessary, calculation results and values obtained from applicable state and federal laws and literature sources should be verified independently and confirmed by consulting Ecology's site managers. CLARC cannot be relied on to create rights, substantive or procedural, enforceable by any party in litigation with the state of Washington.