Evaluation of unit risk factors in support of the Hanford Remedial Action Environmental Impact Statement

Abstract

This report describes the generation of unit risk factors for use with the Graphical Information System (GIS) being developed by Advanced Sciences, Inc. for the Hanford Remedial Action Environmental Impact Statement. The GIS couples information on source inventory and environmental transport with unit risk factors to estimate the potential risk from contamination at all locations on the Hanford Site. The major components of the effort to generate the unit risk factors were: determination of pollutants to include in the study, definition of media of concern, and definition of exposure assessment scenarios, methods, and parameters. The selection of pollutants was based on inventory lists which indicated the pollutants likely to be encountered at the known waste sites. The final pollutants selected included 47 chemical pollutants and 101 radionuclides. Unit risk factors have been generated for all 148 pollutants per unit initial concentration in five media: soil (per unit mass), soil (per unit area), air, groundwater, and surface water. The exposure scenarios were selected as the basis for the unit risk factor generation. The endpoint in the exposure assessment analysis is expressed as risk of developing cancer for radionuclides and carcinogenic chemicals. For noncarcinogenic chemicals, the risk endpoint is the hazard quotient. The cancer incidence and hazard quotient values are evaluated for all exposure pathways, pollutants, and scenarios. The hazard index values and unit risk values are used by the GIS to produce maps of risk for the Hanford Site.