Natural attenuation of phenolic compounds under different redox conditions in a deep sandstone aquifer

The natural attenuation of phenolic compounds in a deep UK Triassic Sandstone aquifer is discussed. Vertical profiles at two locations show that the plume has a 2m thick aerobic and NO3-reducing fringe, that there is simultaneous Mn, Fe and SO4-reduction, and methanogenesis in the anaerobic core, and that degradation is occurring at TOC concentrations up to 6500 mg l−1. Microbiological and mass balance studies show that biodegradation is greatest at the plume fringe where contaminant concentrations are diluted by transverse mixing. Stable isotope studies show that SO4-reduction is sensitive to contaminant concentration. Active bacterial populations exist throughout the plume but biodegradation is inhibited in the core by high contaminant concentrations. Less than 20% mass loss has occurred and gross half-lives exceed 150 years. Natural attenuation of these phenolic compounds will increase only by increased dilution of the plume.