Ineffective natural attenuation of degradable organic compounds in a phenol-contaminated aquifer

Two detailed vertical profiles through a complex plume of phenolic contamin ants in a Triassic sandstone aquifer show that natural attenuation by biode gradation and dispersion is active but very slow. The plume has a microbial ly active aerobic and NO3 reducing fringe that is less than 2 m thick at bo th 150 and 350 m downstream of the source. The anaerobic core has evidence of active bacterial populations and degradation at total organic carbon (TO C) concentrations up to at least 1400 mg/L (1800 mg/L total phenolics), alt hough gross half-lives are more than 50 years. There is evidence from the s ame locations of Mn, Fe, and SO, reduction, with the latter inhibited by th e pollutant matrix and not significant at concentrations more than 1000 mg/ L TOC. Degradation of these contaminants in this aquifer is influenced by a range of environmental factors, including the chemical toxicity and pH of the contaminant matrix, and inputs of electron accepters into the plume by dispersion. The results show that the plume is likely to grow under the pre sent conditions, despite the biodegradable nature of the organic pollutants and availability of suitable electron accepters. Vertical profiles have pr oved a cost-effective method of understanding the evolution of the plume.