Environmentally Acceptable Endpoints for PAHs at a Manufactured Gas Plant Site

Abstract

Samples from a former manufactured gas plant (MGP) site in Santa Barbara, CA, were tested to evaluate the environmentally acceptable endpoints (EAE) process for setting risk-based cleanup criteria. The research was part of an ongoing effort to develop and demonstrate a protocol for assessing risk-based criteria for MGP sites that incorporates the availability of polycyclic aromatic hydrocarbons (PAHs). Six samples were tested: source soil, treated source soil, aged soil, lampblack soil, background soil, and spiked soil. The samples were subjected to a battery of physical and biological tests that focused on determining the “availability” of the soil-bound contaminants to groundwater, ecological receptors, and human receptors. Different assays yielded similar qualitative results, but the magnitude of the effects differed significantly. Each assay has unique inherent limitations, but the earthworm uptake assay is preferred because it is reliable, inexpensive, and sensitive at meaningful soil concentrations. Results demonstrated that sorption to soil, matrix effects, aging, and treatment can significantly reduce chemical availability. Including these reduced availability results in risk assessment calculations yielded environmentally protective cleanup levels almost 3−10 times greater than levels derived using California default risk assessment assumptions. Using an EAE-based approach for MGP soils, especially those containing lampblack, could provide more realistic risk assessments.