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Toxics Cleanup Program

CLARC - Cleanup Levels and Risk Calculation

Ecology is updating the CLARC web application

What is CLARC?

CLARC stands for “Cleanup Level and Risk Calculations.”  CLARC is a web application tool developed by Ecology that uses the equations and default input parameters in the MTCA Cleanup Regulation to calculate cleanup levels.  CLARC is intended to help Ecology site managers and others gather the information needed to set cleanup standards and make decisions according to the requirements in the regulation.

Do I have to use CLARC or can I do my own calculations?

No, you do not have to use CLARC.  CLARC is simply a tool Ecology has developed to help you establish cleanup levels for a site.  You may do your own calculations according to the equations and parameters specified in the MTCA Cleanup Regulation.

What exactly is being updated in CLARC and why?

The equations in the MTCA Cleanup Regulation use toxicity values to calculate cleanup levels, including cancer-slope factors for carcinogens and reference doses for non-carcinogens.  The MTCA Cleanup Regulations specify a hierarchy of sources for those values: 

  • Values from EPA’s Integrated Risk Information System (IRIS) must be used if available.

  • If a value is not available in IRIS, then values from the Health Effects Assessment Summary Tables (HEAST) or, if more appropriate, the National Center for Environmental Assessment (NCEA) must be used.

See WAC 173-360-708(7) and (8).  The toxicity values for many chemicals have been updated.  To remain useful as a tool CLARC needs to reflect this.  Ecology has been working on this update for several months.  Ecology’s goal is to update the toxicity data at least on an annual basis. 

Must I use CLARC to identify toxicity values?

No, CLARC is just a convenient compilation of toxicity values. You may use the values in the databases authorized under WAC 173-340-708.

How can I determine which toxicity values have changed?

All changes are documented and summarized on the CLARC website. Here is a link: to the CLARC Tool.

For how many chemicals have toxicity values changed?

The updates to CLARC reflect 287 new toxicity values for 206 chemicals. While most of those chemicals have been determined to be more toxic, some of the chemicals have been determined to be less toxic.

The updates also reflect the removal of toxicity values for some chemicals previously included in the CLARC database. Specifically, Ecology removed several California EPA toxicity values from CLARC to avoid confusing them with the U.S. EPA values (that is, those from the hierarchy of sources in the MTCA rule). As discussed below, Ecology believes that many of the California EPA toxicity values provide a reliable basis for establishing MTCA cleanup levels. Ecology plans to begin reviewing individual California EPA values. Over time, Ecology intends to incorporate (as appropriate) those values into the CLARC database using the MTCA procedures specified in WAC 173-340-702 and -708.

If a toxicity value for a chemical does not exist in CLARC, then what may I do?

If a toxicity value for a chemical does not exist in CLARC (that is, a value is not available from the hierarchy of sources in the MTCA rule), then you may do one of the following:

  1. Use a toxicity value from Tier 3 of EPA’s hierarchy of sources in MTCA Method B and C Equations.
    EPA has developed its own hierarchy of sources of human health toxicity information for use in Superfund risk assessments (OSWER Directive 9285.7-53). Tier 3 sources of toxicity information include non-EPA sources, such as the California EPA (Cal EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR). Toxicity values from such non-EPA Tier 3 sources may only be used if approved by Ecology on a chemical-specific basis. Once approved, Ecology may include those values in CLARC for future use.

    Based on the OSWER Directive, EPA Region 9 has published within their Regional Screening Level (RSL) tables a comprehensive set of toxicity information that includes values from non-EPA Tier 3 sources when values from the EPA are not available. The RSL tables are available at Cal EPA’s toxicity values are available at NOTE: The EPA Preliminary Remediation Goals (PRG’s) in the RSL tables are not appropriate for use as MTCA cleanup levels. See WAC 173-340-708. All Cleanup Action Plans (CAP’s) should explicitly note when the MTCA cleanup levels and standards have been established using toxicity information or values not available from the hierarchy of toxicity information sources in the MTCA rule (i.e., when using sources other than IRIS, NCEA, or HEAST). MTCA cleanup levels and standards established for naphthalene and chromium VI should not use RSL table toxicity values for cancer shown as slope factors (SFOs) or inhalation unit risk factors (IURs).
  2. Establish your own toxicity value.
    You may also establish your own toxicity values in accordance with the requirements in the MTCA rule. See WAC 173-340-708(7)(f) and (8)(c).

Note that under the MTCA rule, non-EPA sources may not be used in place of EPA sources unless Ecology determines there is clear and convincing scientific data which demonstrates that the use of EPA sources is inappropriate. See WAC 173-340-708(7)(e) and (8)(b).

For more information about your alternatives, please contact Craig McCormack in Ecology’s Toxics Cleanup Program at, or (360) 407-7193.

How do the changes in toxicity values affect cleanup levels?

The answer to this question depends on the method used to establish cleanup levels.

  • Method A.  The changes DO NOT affect Method A cleanup levels.

  • Method B or C.  The changes DO affect Method B and C cleanup levels.  Higher toxicity results in lower cleanup levels; lower toxicity results in higher cleanup levels.

If no toxicity value is available for a chemical, and this chemical is an important chemical at a site, you should consult with the Toxics Cleanup Program’s Information and Policy Section at (360) 407-7205 for advice on how to proceed.

How do the changes in toxicity values affect my on-going investigations or cleanups?

The answer to this question depends on whether the remedial actions are being performed independently or under Ecology-supervision.

  • Ecology-conducted or Ecology-supervised remedial actions.  If remedial actions are being performed or supervised by Ecology, then the cleanup levels that apply must be based on the toxicity values  at the time Ecology issues a cleanup action plan for that release.

  • Independent remedial actions.  If remedial actions are being performed independently, then the cleanup levels that apply to a release must be based on the toxicity values (1) at the time the final cleanup action for that release began or (2) at the time Ecology reviews the cleanup action, whichever is less stringent.

See WAC 173-360-702(12).

How do the changes in toxicity values affect periodic reviews of completed cleanups?

Ecology staff performing periodic reviews should use the updated CLARC values when evaluating the protectiveness of cleanup actions.  Note however that lower cleanup levels do not automatically trigger the need for further cleanup.  As stated in WAC 173-340-702(12)(c), decisions on the need for further cleanup should be made on a case-by-case basis after considering whether the previous cleanup action is still sufficiently protective of human health and the environment.  In making this determination, it is important to consider whether actual exposure is occurring at the site.1 

When do these updates show up on the web application?

Ecology anticipates the updates will be visible on April 2011.

Will CLARC be updated again in the future?

Yes, the CLARC database will continue to be updated.  At this time Ecology anticipates CLARC will be updated on an annual basis.

I have some questions about CLARC; who should I talk to?

If you have questions about CLARC please contact toxicologist Craig McCormack in Ecology’s Toxics Cleanup Program at, or (360) 407-7193.


1For example, exceeding a new groundwater drinking water standard that is applied to groundwater produced by an active water supply well would likely trigger a concern of protectiveness.  Exceeding that same new standard in a monitoring well that no one is drinking from would likely still be protective, assuming there aren’t other exposure pathways of concern at the site needing to be assessed (such as vapor or surface water protection).