Understanding the Evolution of Groundwater-Contaminant Plume Chemistry Emanating from Legacy Contaminant Sources: An Example from a Long-Term Crude Oil Spill

Understanding the evolution of plumes emanating from residual hydrocarbon contaminant sources requires evaluating how changes in source compositions over time cause changes in dissolved plume chemistry as residual sources age. This study investigates such changes at the site of a 1979 crude-oil pipeline spill and is the first comprehensive look at groundwater chemistry associated with a residual hydrocarbon source zones in different stages of aging. The data show a direct relationship between concentrations of benzene and naphthalene in the residual oil and those measured in water samples collected below the oil. Groundwater associated with oil near the spill site had different chemical composition compared with water associated with oil that had spread downgradient from the spill zone, indicating a shift in biodegradation reactions. These results emphasize that source zone processes are spatially and temporally heterogeneous and should be accounted for in natural attenuation studies where residual source zones persist.

Automated summary

This study provides a comprehensive investigation into the groundwater chemistry of residual hydrocarbon source zones in different stages of aging. The results show a direct relationship between benzene and naphthalene concentrations in residual oil and water samples collected below the oil. The chemical composition of groundwater associated with oil near the spill site differs from that associated with oil spread downgradient, indicating a shift in biodegradation reactions. These findings highlight the spatial and temporal heterogeneity of source zone processes.