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Tar oils are nonaqueous phase liquids (NAPLs) byproducts formed during the manufacture of gas and coke. A variety of tar oil types were generated at manufactured gas plants and coke oven plants: some were refined into saleable products (e.g., creosote, Tarvia, and pitch) and others were discharged into the environment. Historical tar oil spills into shoreline soils and proximal sediments can cause sediment oiling and sheening in coastal and riverine environments. These impacts are often confused with petroleum spills based on visual properties, especially in shoreline environments with marinas, bulkheads, and industrial histories. Fortunately, tar and petroleum products exhibit many product specific chemical patterns. Tar oils contain higher concentrations priority pollutants, like polycyclic aromatic hydrocarbons (PAHs), relative to comparable petroleum oils. Petroleum oils contain high proportions of saturated hydrocarbons with lower viscosity and higher mobility compared to tar oils. The hydrocarbon fingerprinting methods herein provide many lines of evidence for distinguishing tar oil and petroleum products with metrics that can be customized for site specific conditions. Forensic signatures comprised of PAHs, saturated hydrocarbons, and geochemical biomarkers are provided for comparison of hydrocarbon product reference samples and sediment samples from four case studies with alleged tar and petroleum product impacts. Diagnostic ratios help demonstrate the compositional features that differentiate and allocate these products in the case-study samples.

Large-scale and long-term environmental investigations, like regional oil spills, typically employ multiple laboratories to prepare and analyze large numbers of samples within regulatory holding times and contractual specifications. These projects generate large quantities of quality control data for assessing method performance. In this study we compare intra- and interlaboratory variability among laboratories participating in the Deepwater Horizon Natural Resource Damage Assessment between 2010 and 2015. Results show that although interlaboratory measurements of EPA Priority Pollutant polycyclic aromatic hydrocarbons (PAHs) were consistent with environmental industry standards the concentrations of alkylated PAHs and geochemical biomarkers exhibited high variability. These observations serve as important benchmarks when designing sampling and analysis plans for source identification or other forensic purposes. As such, interlaboratory datasets generally lack the level of precision and accuracy needed to differentiate compositionally similar sources, low-level impacts from background, contaminant mobility, and natural recovery in multimedia samples.

Polycyclic aromatic hydrocarbons (PAHs) are measured extensively to determine the nature and extent of oil spill impacts. Conventional testing methods determine the concentrations of 16–34 PAH analytes for regulatory compliance and risk assessment. Recognizing the limited value of these data for source identification purposes, forensic investigators typically rely on a larger number of PAH analytes (n = 49) with potential source specific associations. However, even these PAH analytes represent only a small fraction of the chemical fingerprinting potential imbedded in the 19,303 individual PAHs thought to exist in the semivolatile range. The absence of authentic PAH standards is one of the primary limitations for improving the testing methods. However, chemists recently expanded the number of quantitative forensic PAH analytes to include 37 additional parent and alkylated PAH isomers. This method revision also provides qualitative chemical fingerprints from which the relative abundances of hundreds of additional PAH isomers are determined. In this chapter, the quantitative and qualitative fingerprints are presented for 12 reference samples that represent a wide range of hydrocarbon sources potentially encountered during oil spill investigations. The reference samples include crude oils, diesel, heavy gas oil, asphalt pavements, dielectric fluid, lube oil, tar, creosote, urban dust, and urban sediment. A review of PAH weathering and source ratios demonstrate many options for differentiating petrogenic and pyrogenic releases. The ratios herein reflect past investigations described in the literature and the derivation of new ratios from the expanded list of PAH analytes. The updated method provides increased signature richness for distinguishing spilled oil from hydrocarbons derived from numerous other anthropogenic sources.