Assessing the Risks Posed by Refinery Releases

To better evaluate pollution prevention options, the project attempted to assess the risks posed to individuals and populations exposed to chemical contaminants released from the refinery. An initial risk assessment analysis was performed to identify chemicals requiring further study, and to establish a baseline by which to judge potential risk reduction opportunities. Since change in exposure to benzene was used as a proxy for evaluating relative risk reductions associated with alternative pollution prevention options, the usual uncertainty associated with risk assessments was not a factor in the option analysis. The uncertainty in absolute risk assessments can arise from multiple sources the use of animal study results, difficulties with human studies, variation in individual responses to chemical exposures, the impact of differing dose rates, multiple simultaneous exposme to chem- 

Risk assessment typically begins with a characterization of the risks associated with baseline or current releases. The baseline assessment gives an indication of the potential for human health or ecological risk problems. The predicted changes in emissions and sources are then estimated and the expected risk from the option scenarios is evaluated. The risk evaluation is based on both risk reduction to the most highly exposed individuals and to the exposed population as a whole. Cumulative benefits of risk reduction are estimated by adding the benefits for each risk reduction option. 

The project s risk assessment effort followed ERA methods and established agency policy as outlined by the National Academy of Sciences (NAS, 1983) and established in final risk assessment guidelines (ERA, 1986). It involved four steps (1) hazard identification, (2) determination of dose-response relations, (3) evaluation of human exposme and, finally, (4) characterization of risks. 

Boundary conditions for this risk assessment were established so that the risk assessment did not attempt to analyze secondary environmental effects associated with refinery releases such as their contribution to formation of ozone, acid rain, risks associated with occupational exposure, transportation of products or wastes, or the potential for accidental releases. 

Screening analysis was conducted for different exposure pathways and chemicals of concern. Using a screening level cutoff of a one-in-a-million excess risk for a 70-year lifetime exposure for the maximally exposed individual (MEI), a set of carcinogenic chemicals was identified for further analysis. For noncarcinogens, MEI exposure levels were compared to health thresholds. If the MEI exposure exceeded the established health threshold, further analysis was done. 

---