Formatted Title
Evaluation of Manufactured Gas Plant Waste as a Potential Source of Polychlorinated Dibenzodioxins/Furans
Background/Objectives
Polychlorinated dibenzodioxins and polychlorinated dibenzofurans (dioxins/furans) are a group of 210 individual structural congeners that are unintentionally produced as byproducts of numerous combustion, incineration, and industrial chemical manufacturing processes. Despite the similarities between historical manufactured gas plant (MGP) processes and other processes known to generate dioxins/furans, sparse data are available characterizing dioxins/furans at MGP sites. This is largely due to the lack of investigation of these chemical compounds at MGP sites not because these compounds have been eliminated by empirical demonstration. Despite the lack of data, available literature indicates that historical MGP operations produced the conditions necessary for dioxin/furan formation.
Dioxins/furans have been detected in soil, groundwater, and NAPL present at a former MGP facility adjacent to a major waterway in Portland, Oregon (the Site), as well as in sediments adjacent to the Site. The Site was historically used as a disposal area for MGP wastes. Other potential sources of dioxins/furans at the Site include historical placement of dredge spoils, and adjacent properties including a former pesticide manufacturing facility and a former chloralkali manufacturing facility.
Approach/Activities
MFA evaluated the chemical signatures of dioxins/furans in NAPL, soil, and groundwater from the Site and neighboring properties with available data, as well as sediment adjacent to the Site and neighboring properties. The relative proportions of dioxin/furan congeners were calculated in samples and compared to one another spatially and by media type to determine whether proportions indicated the same or dis-similar source(s). For these analyses the data were standardized by calculating the fractional composition of each compound. Figures were developed to show the fraction of each individual dioxin/furan congener as a proportion of the total dioxins/furans, establishing a chemical signature for the dioxins/furans that is independent of the overall mass of dioxins/furans present in a given area. Overall chemical mass was also evaluated to provide additional lines of evidence to distinguish multiple potential source areas. Both the chemical signature and overall chemical concentrations were evaluated to identify sources of dioxins/furans to soil, groundwater, and sediment.
Results/Lessons Learned
Dioxins/furans were observed in MGP waste NAPL at total concentrations that exceeded 500 µg/kg, which is comparable to concentrations observed in waste materials from a former pesticide manufacturing facility which is a known source of dioxins/furans. The dioxins/furans present in MGP waste NAPL had a chemical signature dominated by OCDD and 1,2,3,4,6,7,8-HpCDD, which was also observed in soil, groundwater, and sediment samples with elevated concentrations of dioxins/furans. The chemical signature of the dioxins/furans present in MGP waste DNAPL was distinct from the chemical signatures associated with other known sources of dioxins/furans in the vicinity of the site. Alternative sources of dioxins/furans with similar OCDD-dominant chemical signatures, including pentachlorophenol, trichloroethene, and urban background sources, were considered and eliminated as potential sources of the dioxins/furans observed in MGP waste DNAPL and associated soil, groundwater, and sediment samples. The findings of this evaluation indicate that MGP waste is a potential source of dioxins/furans and should be evaluated further at MGP sites.