Risk Assessment Standards

Risk assessment is a process that evaluates the risk of a hazard, estimates the population exposed to the hazard, and then determines the relative importance of the public health risk. To determine the health problems caused by pollutants at a contaminated site, scientists must calculate the exposure to the pollutants multiplied by the toxicity of the pollutants. A risk assessment is usually presented as a range of probabilities. For instance, the risk of cancer from exposure to a particular chemical might be 5-10 additional illnesses per 10,000 people. As a result of this exposure, ten more people in every 10,000 people are likely to get cancer.

One model to help predict risk is the Risk-Based Corrective Action (RBCA). RBCA is a framework to develop a corrective action plan based on risk and exposure assessment. Members of American Society for Testing and Materials (ASTM) have developed the ASTM W 1739-95 and ASTM PS 104-98 guides for RBCA. The RBCA approach to corrective action is intended to be flexible and to meet the needs of individual states. These guides may be purchased from ASTM by calling 610-832-9585.

The steps of the RBCA approach are as follows:

  1. Involve stakeholders in determining what the acceptable cancer risk will be.
  2. Conduct an initial site assessment. This assessment includes reviewing the records associated with the site, conducting a visual site inspection, and developing a conceptual model of the site.
  3. Classify the site in terms of the urgency of an initial response needed. The site can be reclassified as more information is obtained.
  4. A Tier I evaluation is conducted to determine the Risk-Based Screening Levels (RBSL). These RBSLs provide an estimate of the risks from the type of chemicals found and their concentrations, but is not site-specific. Rather the RBSL uses a standard exposure level for a given contaminant to make an assumption about the site. If needed, a Tier II evaluation can be conducted. This evaluation uses additional data for fate and transport models to help replace assumptions with site-specific information. Site Specific Target Levels (SSTL) replace the RBSL. SSTLs are based on site-specific values of chemicals and exposure points. A Tier III evaluation goes beyond the analytical models and develops numerical models. This effort requires substantial effort and cost.
  5. Remedial Action is then initiated to reduce the contaminant concentration to an acceptable level. The contaminant may be removed, treated and contained, or engineered or controlled to eliminate the exposure pathway.
  6. The site is then monitored to ensure the remedial action is effective over time.

Risk assessments can be somewhat uncertain and guided by assumptions. One of the reasons for the uncertainty is that there are varying levels of exposure to a wide variety of chemicals over widely varying environmental circumstances. With so many variables, identifying a single "cause" of illness is extremely difficult. An example of the differences between individuals in a risk assessment is the increased risk of asbestos workers that smoke cigarettes. In other words, although all who work with asbestos are at risk, those who smoke have a significantly greater risk

For the other risk-related pages, please see:

  • Steps of Assessment. This page describes detailed descriptions of the steps in risk assessment, with emphasis on human health risk assessment.
  • Ecological Risk Assessment This page focuses on the unique aspects of ecological risk assessment.
  • Risk Management This page provides information about plans for managing and/or preventing risk.
  • Risk Communication This page provides information about communicating with communities facing contaminated sites.
<< Steps of Assessment Ecological Risk Assessment >>

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