Biodegradation of methanol and tertiary butyl alcohol in previously uncontaminated subsurface systems

The objective of this study was to determine the potential for biodegradation in subsurface soils and groundwater from sites in Williamsport, PA, Wayland, NY, and Dumfries, VA. These subsurface systems were characterized both physically, chemically and biologically. Bacterial populations were substantial in all systems and ranged from 10³ to 10⁸ colony forming units per gram. Soil sampling was done in a quality-controlled aseptic manner using conventional drilling end sampling equipment. A matrix of test-tube microcosms was used to determine biodegradation rates of methanol and t-butyl alcohol at concentrations ranging from 1 to 1000 mg/L. Methanol degraded readily at all sites ranging from 0.8 mg/L/day to 20.4 mg/L/day and rates were generally greater in the saturated zone. TBA biodegraded at all sites, but was refractory in nature. Biodegradation rates for TBA in anaerobic subsurface systems were found to increase directly with initial concentration from 10⁻⁴ mg/L/day for 1 mg/L to 10⁻¹ mg/L/day for 80 mg/L. TBA biodegradation in the aerobic system was essentially constant over all concentrations. Biokinetic coefficients were determined for methanol and TBA at each site based on plots of utilization rates versus substrate concentration and reciprocal plots of these values. The K values found suggest that aerobic subsurface systems can utilize alcohols at a greater rate than anoxic subsurface systems and can be used for comparative purposes. The K_s of anoxic subsurface systems were found to be large due to the low temperature (10°C) found in aquifers. The results indicate that methanol contamination in groundwater has much less associated risk to drinking water supplies due to the ease of biodegradation. However, TBA poses a much greater risk due to the very slow removal rates at low concentrations, which could result in a residual level for over a decade in some cases.