Effects of Environmental Conditions on MTBE Degradation in Model Column Aquifers

The current concern over point-source and non-point-source contamination of ground water by methyl tert-butyl ether (MTBE) has increased the need for a better understanding of the processes that control its environmental fate. As part of an ongoing study to characterize the potential for natural attenuation of MTBE, we have prepared a series of model column aquifers to investigate the pathways and kinetics of MTBE biodegradation under controlled conditions. The sediments used for these columns were collected aseptically from a variety of geographically and geologically distinct sites: (i) an urban site near Detroit, Michigan; (ii) an urban site in Turnersville, New Jersey; (iii) a controlled spill test site at Base Borden, Ontario, Canada; and (iv) a leaking underground storage tank site at the Laurel Bay Exchange, South Carolina. In all cases, autoclaved site ground water spiked with approximately 100 micrograms/liter MTBE was used as the column influent, and the column effluent was analyzed for MTBE and its potential degradation products. In aerobic column microcosms prepared with core materials from three sites, conversion of MTBE to TBA was observed after a lag period of approximately 35 days, but no evidence of subsequent TBA degradation was observed. This apparent MTBE to TBA conversion subsequently declined, as did measured dissolved oxygen. However, in similar columns with anaerobic influents, or with BTEX (gasoline constituents: benzene, toluene, ethyl benzene, and o-, m-, and p-xylene) contaminated aerobic influents, we have not seen any evidence of MTBE degradation up to 120 days. These results suggest that, if in situ biodegradation of MTBE occurs, it is most likely under aerobic conditions, and only in the absence of significant concentrations of more readily metabolized contaminants such as BTEX compounds.