Benchmarking of two human health risk assessment methods : description, evaluation, and comparison of the streamlined programmatic environmental impact statement risk assessment method and the conventional risk assessment method

To accelerate the clean-up of the Department of Energy’s hazardous waste sites, a new method for expediting the risk assessment process has been developed and proposed as a potential replacement for the current system. The new method uses simplifying assumptions to streamline the risk assessment process. Because it is designed to be applied simultaneously to multiple waste sites, the new method yields risk assessment results in a fraction of the time previously required. However, the method is acceptable only if it yields results comparable to those of the conventional method. This study evaluates the comparability of the new method by applying it to a site that has previously been evaluated with the conventional method and comparing the results of the two assessments. Because both methods identify that the case study site poses risks above the threshold that warrants clean-up, the overall results of the two methods are comparable. Furthermore, both methods identify nitrate in groundwater as a principal risk concern. However, unlike the conventional method, the new method identifies additional contaminants and pathways of concern. This finding of the new method stems primarily from the use of inappropriately high contaminant surface soil concentrations and inappropriate toxicity values. Modifying the new method and implementing additional recommendations outlined in this report will improve the technical defensibility of the new method and thus facilitate its acceptance as a potential replacement for the current risk assessment system.