Risk assessment combines both toxicity assessment and exposure assessment to estimate a risk characterization. This risk characterization is then provided to the decision-maker along with the other inputs to determine the extent of the response. Elements of the risk assessment (identification of health effects associated with hazardous chemical contaminant, chemical persistence that may impact exposure duration, etc.) will guide the development of risk-based clearance goals.
See Section 4 for a discussion of the principles of conducting a risk assessment, in the context of hazardous chemicals.
A risk assessment (as described in Section 4) is a process that combines toxicity information, site-specific exposure estimates, and the concentration of the chemical in the environment to estimate the magnitude of cancer risk or noncancer hazard associated with the exposure. Developing risk-based clearance goals is a similar process. Rather than calculating risk or hazard, a target risk/hazard is defined by the IC/UC with appropriate stakeholder input. Information on the chemical toxicity as well as exposure magnitude and duration will guide the estimation of an environmental target concentration (risk-based goal) for the chemical contaminant. The resultant risk-based goal should be established at an environmental concentration that is without adverse health effects for the expected duration of exposure.
This is the process that various governmental and professional organizations use to derive risk-based exposure guidelines. A more detailed discussion of risk-based exposure guidelines is found in Appendix A. Risk-based exposure guidelines can be used during different phases of the response for a variety of purposes. For example, acute exposure guidelines (i.e., action levels) used to evaluate acute effects experienced following short-term exposures can be used during the initial response and can inform public health determinations and help in decision-making for activities such as evacuation/shelter-in-place or can provide information to modify the HASP as needed; for example, informing occupational risk decisions concerning appropriate worker protections. Chronic or long-term exposure guidelines derived for longer-term exposures and chronic health effects may be employed in developing risk-based, chemical-specific, site-specific clearance goals when making decisions concerning decontamination/remediation options. These exposure guidelines based on site- and incident-specific conditions and environmental contaminant concentrations without inequitable adverse health effects for protracted exposure durations can serve as clearance goals.
As discussed below, other factors will likely be needed to ensure a selected remediation/cleanup goal will be both feasible to achieve and acceptable to those affected. For example, given the potential significant extent of contamination or complexity of remediation options, striving for an extremely stringent goal may prove to be technically infeasible or may contribute to other adverse economic problems that will significantly decrease quality of life for the same population. Feasibility and acceptability decisions should be made as much as possible by those affected, taking into consideration all the available information.
However, it is of paramount importance that all potential health effects are evaluated when determining the preliminary clearance goal and the clearance criteria that will be used to make the final decision for ultimate resumed use/re-occupancy. Both acute health risks associated with the short-term exposures and potential chronic health effects associated with low levels of potential residual chemical concentration remaining after cleanup/remediation must be considered.