An Evaluation of Risk Drivers from a Sample of Risk Assessments Conducted for the U.S. Army

We evaluate risk drivers at selected U.S. Army installations by developing a database containing contaminant-pathway-receptor combinations that exceed regulatory thresholds for ecological (toxicity quotient greater than one), human health cancer risk (predicted incremental lifetime cancer risk greater than one in ten thousand), and noncancer human health (hazard index greater than one). We compare the risk drivers from the database to reported corrective action objectives from available decision documents. For noncancer hazards, explosives (particularly in ground water) dominate the reported exceedances of regulatory thresholds in the database. PAHs in home-grown produce show the highest number of exceedances of regulatory thresholds for cancer risk. For ecological risks, PAHs in both terrestrial and aquatic environments dominate the exceedances of regulatory thresholds. All available cleanup levels were derived based on human health exposures rather than ecological exposures, except for one site. In general, ecological risks were considered to be “more uncertain,” and that was used as a basis for not relying on backcalculated target levels on the basis of ecological risk. The reverse was true for human health risks: the “conservative” assumptions incorporated into the modeling provided the justification for backcalculating health-protective target levels.