Formatted Title:

Approaches for Identifying and Applying PAH Source Diagnostic Ratios

Background/Objectives:

Polycyclic aromatic hydrocarbons (PAHs) are frequently commingled contaminant sources at remediation sites, and a wide range of techniques has therefore been developed to distinguish PAH sources. Many of these tools rely on forensic-quality PAH data, and other forensic hydrocarbon analysis methods, but frequently PAH source assessment faces the challenge of a lack of forensic-quality data. Data collected for remedial purposes are frequently limited to priority pollutant (PP) PAHs with no option to obtain better quality data. In such cases PP PAH source diagnostic ratios commonly relied upon use isomers as the numerator and denominator to negate environmental weathering effects on ratio values, but the utility of this approach can be limited. These ratios can separate petrogenic versus pyrogenic sources but overlaps occur and they don’t separate sources within the petrogenic and pyrogenic categories or consistently separate out background PAHs. Presented here are two approaches to overcome these limitations and develop PP PAH diagnostic ratios to better distinguish PAH sources.

Approach/Activities:

Using literature-derived data, the first approach evaluates the use of non-isomer ratios in combination with each other or with isomer ratios, to distinguish PAH sources under a wide range of source weathering stages. Ratio combinations were evaluated with the goal of separating petrogenic from pyrogenic PAH sources and further separating low, intermediate and high molecular weight PAH sources within the pyrogenic and petrogenic groups.

The second approach was applied at a New York State MGP sediment site where data were limited to PP PAHs. Isomer PP PAH diagnostic ratios and additional non-isomer ratios identified herein were unable to distinguish PAHs from background versus site-impacted sediments due to the mixed nature of the sources at this site. This work presents the development and use of a ratio search model to overcome the apparent lack of useful diagnostic PP PAH ratios. The model statistically compared all possible PP PAH ratios in upstream background samples versus site material and identified statistically significant ratios specific to the site.

Results/Lessons Learned:

The two approaches presented here overcame limitations of PP PAH results for successful PAH source assessment. In the first approach, use of a non-isomer/non-isomer and non-isomer/isomer multiple double ratio system with PP PAHs successfully distinguished common pyrogenic and petrogenic PAH sources including coal tar, carbureted water gas tar, creosote, pitch, diesel, heavy petroleum and crude oil. The system relied on differential molecular weight skew among petrogenic and pyrogenic sources that withstood a wide range of source weathering for high molecular weight non-isomer ratios. The method employs multiple ratio pairs, providing added assurance against false positive identification of sources and can be customized with site-specific source ratios.

In the second approach, use of a statistical ratio search model to identify novel site-specific PP PAH ratios was effective when commonly used isomer ratios and non-isomer ratios established herein failed. The ratio search model identified ratios that consistently distinguished site MGP impacts from background and downstream facility PAH sources, leading to an approximately 30% reduction in the site remedial footprint. A statistical ratio search, used here to overcome PP PAH data limitations, can also be applied to the full suite of forensic PAHs and other contaminant groups such as dioxins/furans or PCBs.

Deborah Chiavelli

Affiliation

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(Group 1, Poster Board #13) Approaches for Identifying and Applying PAH Source Diagnostic Ratios