The Oregon Department of Environmental Quality (DEQ) has established guidance for completion of risk-based assessments. This guidance was first presented in the Risk-Based Decision Making for Remediation of Petroleum-Contaminated Sites (RBDM Guidance) dated September 22, 2003. Risk-based concentration (RBCs) or cleanup standards presented in the RBDM Guidance have periodically been updated with the most recent version issued September 15, 2009.

In summary, risk-based assessment requires answering the following questions:

What is risk? Risk = Toxicity x Exposure

To assess risk at a contaminated site, you must have information about the following:

• The nature of the release (what kinds of contaminants are there?)
• The magnitude of the release (what are the contaminant concentrations?)
• The extent of the contamination (soil, groundwater, on-site, off-site?)
• The toxicity of the identified contaminants (carcinogens, non-carcinogens?)
• The possible ways that exposure might occur (inhalation, ingestion, dermal contact?)

What information will be required to develop a conceptual site model (CSM)?

• Contaminant Sources (known or suspected)
• Exposure Pathways (all reasonably likely ways people might come into contact with contaminant sources)
• Receptors Scenarios (who is likely to be affected)

What are applicable exposure pathways?

• Direct contact with contaminated soil resulting in exposure due to a combination of dermal contact, soil ingestion, vapor inhalation, and particulate inhalation
• Leaching from soils to underlying groundwater with subsequent groundwater ingestion
• Volatilization from soils to outdoor air and subsequent inhalation
• Volatilization from soils to indoor air and subsequent inhalation
• Ingestion or other exposure to contaminated groundwater
• Volatilization from groundwater to outdoor air and subsequent inhalation
• Volatilization from groundwater to indoor air and subsequent inhalation

What are applicable receptor scenarios?

• Adults and children in a residential scenario (single family housing)
• Adults and children in an urban residential setting (apartment, condominium)
• Adults in an occupational scenario
• Adults in a construction worker scenario
• Adults in an excavation worker scenario

Having determined applicable exposure pathways and receptor scenarios, actual contaminants of concern (COC) can be compared to established RBCs or cleanup standards. Where it can be demonstrated that COC are below RBCs for all applicable exposure pathways and receptor scenarios, no further investigative or cleanup will be required.