Case Study
A refined ecological risk assessment yields less conservative risk estimates
By Todd Martin, P.E., Principal, Engineering
Stan Pauwels, Ph.D., Senior Consultant
OUR CHALLENGE
Integral performed a terrestrial ecological risk assessment at a former wood treatment facility using soils contaminated with polycyclic aromatic hydrocarbons (PAHs). Our goal was to evaluate the potential for ecological risk to the American robin foraging at several target areas to determine the need for a future cleanup. We initially used an exposure calculation approach favored by the regulator which identified high risks due to the conservative assumptions employed. Integral applied a site-specific method to achieve a more accurate assessment. This approach substantially reduced the potential for ecological risks and decreased the area of soil potentially needing remediation.
OUR APPROACH
Based on the requested guidance, we first calculated daily doses for the American robin using 95% upper confidence limits (95UCL) for soil PAH concentrations together with generic soil-to-invertebrate uptake equations required to estimate invertebrate tissue levels. This conservative approach identified high potential ecological impact across all the terrestrial target areas, indicating a need for extensive soil remediation. We refined the original exposure calculations by collecting terrestrial invertebrate samples from the target areas and analyzing them for PAHs. This approach bypassed the need for applying generic uptake equations. We introduced another refinement by estimating more realistic soil PAH levels based on surface-weighted average concentrations (SWACs) instead of 95UCLs. By integrating direct measurements of PAHs in invertebrate tissues with SWAC-based soil PAH levels, Integral recalculated a more realistic daily dose for the American robin, thereby reducing the risk estimates by a factor of 3 to 10.
OUR IMPACT
Integral’s adoption of a flexible, site-specific approach led to less conservative risk estimates for the American robin, which the regulator considered in its remedial decision making. This adjustment optimized the risk evaluation and substantially reduced the soil area identified for remediation.
