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Human Health Risk Assessments

Oregon's state superfund law emphasizes risk-based decision making. For human health risk assessments, both statute and rules provide the option of performing either a deterministic risk assessment or a probabilistic risk assessment. The Department of Environmental Quality has developed a guidance document for each of these options.

Copies of the Department's Human Health Risk Assessment Guidance Documents can be downloaded below.

November 2015 Update to Human Health Risk Assessment Guidance

DEQ has clarified the definition of chemical classes to include such chemicals as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans (dioxins/furans), chlordanes and total petroleum hydrocarbons (TPH). These chemical classes should be evaluated as a single hazardous substance for determining risk and potential hot spots. The acceptable cancer risk level for individual hazardous substances of one-in-one-million and non-cancer hazard quotient of one applies to each chemical class, and potential hot spot determinations will be made accordingly.

Carcinogenic PAHs should be evaluated as summed benzo[a]pyrene equivalents. Dioxins/furans should be evaluated as the sum of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents. PCBs should be evaluated as total PCBs, either derived from congeners or Aroclors. Similarly, total petroleum hydrocarbons and chlordanes should be evaluated as totals. This approach for evaluating chemical classes replaces Section 3.3.5 of DEQ’s October 2010 Human Health Risk Assessment Guidance.

Screening Values

Risk-Based Decision Making Screening Values

DEQ originally developed the guidance document, “Risk-Based Decision Making for the Remediation of Petroleum-Contaminated Sites” in September 1999 and has updated it periodically. Significant updates expanded the original guidance document in 2003 to cover hazardous substance cleanups as well as petroleum-contaminated sites. Since then, DEQ made other revisions to the risk-based concentrations spreadsheet to bring it up to date with current risk assessment practices. These revisions are summarized in the revision history.

The 2003 guidance document and subsequent revised spreadsheets found on the Risk-Based Decision Making web page can be used for both:

  • Cleanup of petroleum releases from regulated underground storage tanks under Oregon cleanup rules for Leaking Petroleum Underground Storage Tank Systems (Oregon Administrative Rules 340-122-0205 through 340-122-0260)
  • Releases of hazardous substances including petroleum under the state’s hazardous substance remedial action rules (OAR 340-122-0100 through 340-122-0115).

This guidance provides a consistent, streamlined decision-making process for evaluating risk posed to human health and the environment. Use of the guidance is optional. Responsible parties and DEQ may use other models or approaches to evaluate site risk; these options may be more appropriate for individual sites. Alternative approaches must also meet risk-based cleanup standards specified in Oregon statute 465.315.

EPA Regional Screening Values

For chemicals where RBCs are not available, DEQ uses EPA screening values. Prior to 2007, DEQ human health risk assessment guidance allowed the use of EPA Region 9 preliminary remediation goals (PRGs) as screening values for site investigations. In 2007, DEQ began using screening values developed by EPA Region 6. DEQ now uses the comprehensive table of regional screening levels developed in mid-2008 by EPA Regions 3, 6, and 9. The EPA regional screening values are available at:

Screening values are tools for evaluating and cleaning up contaminated sites. They are risk-based concentrations that are intended to assist risk assessors and others in initial screening-level evaluations of environmental measurements. The screening values developed by EPA are generic; they are calculated without site specific information.

Screening values should be viewed as guidelines, not legally enforceable standards. They are used for site screening and as initial cleanup goals if applicable. Screening values are not de facto cleanup standards and should not be applied as such. However, they are helpful in providing long-term targets to use during the analysis of different remedial alternatives.

Implementation Schedule

The revised DEQ and EPA RBCs should be implemented according the following guidelines:

  1. For all newly initiated screening evaluations at a site, the recently revised RBCs and EPA regional screening values will be used from this point forward;
  2. For screening evaluations currently being performed, the revised RBCs and EPA regional screening values will be used on a case-by-case basis; and
  3. For completed screening evaluations submitted before October 9, 2008, reassessments may be performed on a case-by-case basis when a new decision is required that needs to be supported by a screening evaluation or updated risk assessment. Until that time, the current completed and approved screening evaluation will continue to be considered valid based on the guidance used when the assessment was completed.

EPA intends to update their screening table biannually. DEQ will evaluate updates to EPA screening values, and update RBCs in January of each year. Under special circumstances, DEQ may at any time require a revised screening value for a chemical based on new toxicity information.

Other Important Risk-Related Web Sites

Comments regarding the implementation or technical content of Deterministic Human Health Risk Assessments and Guidance for Use of Probabilistic Analysis in Human Health Risk Assessments should be directed to:

Mike Poulsen
Oregon Department of Environmental Quality
700 NE Multnomah St., Suite 600
Portland, OR 97232
In Oregon, call toll-free 1-800-452-4011

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For more information about DEQ's Land Quality programs, visit the DEQ contact page.

Oregon Department of Environmental Quality
Headquarters: 700 NE Multnomah Street, Suite 600, Portland, OR 97232
Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

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