Groundwater contamination risk from refinery-derived water-soluble fractions: A comprehensive assessment of organic carbon, hydrocarbons, and oxygenated organic compounds

Petroleum products can contaminate groundwater through dissolution of their Water-Soluble Fractions (WSFs), yet the composition and dissolution behavior of WSFs from different refined products remain insufficiently understood. In this study, oil-water equilibrium WSFs of 25 refined petroleum products from the same refinery were generated using a slow-stirring method and analyzed for Total Organic Carbon (TOC), Total Petroleum Hydrocarbons (TPH), Volatile Petroleum Hydrocarbons (VPH), Extractable Petroleum Hydrocarbons (EPH), and Ooxygen-Containing Organic Compounds (OCOCs). The results showed that the dissolved organic concentrations of WSFs varied by 1–2 orders of magnitude among different product types. Gasoline, naphtha, and atmospheric residues produced WSFs with relatively high TOC and TPH concentrations, dominated by C6-C9 aromatic hydrocarbons. In contrast, kerosene, diesel, and most gasoline blending components exhibited much lower dissolved hydrocarbon concentrations. In several gasoline-related products, oxygenated additives such as Methyl Tert-Butyl Ether (MTBE) and Tert-Amyl Methyl Ether (TAME) were detected at high levels and dominated the dissolved organic composition, resulting in elevated OCOCs/TPH ratios. In addition, butane was identified as a characteristic dissolved compound in the WSF of alkylated oil. These results demonstrate pronounced differences in the chemical composition and distribution patterns of dissolved constituents among refined petroleum products.