W11 PM Advances in Biorestoration Strategies for Contaminated Sediments
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 343-344

(SIM-1118-276961) Biodegradation and Sorption of TBA and MTBE in Near-Surface Sediments at a Full Scale Site in Wyoming.

Greenwood, M¹, Swank, A¹, McLean, J¹, Sims, R¹, ¹ Utah State University, College of Engineering, Logan, UT, USA

ABSTRACT- Natural recovery of TBA (tertiary butyl alcohol) and MTBE (methyltertiarybutyl ether) contaminated sediment was evaluated at a gasoline contaminated site located 60 miles north of Missoula, Montana in the town of Ronan along U.S. Highway 93. A LUFT at a refueling station released approximately 40,000L of gasoline from 1993 to 1994. A dissolved plume of MTBE and BTEX traveled underneath an alfalfa field and potentially discharges into Spring Creek located approximately 460 meters west of the spill site. Remediation activities began in 1995. Monitoring wells installed by the state of Montana DEQ showed MTBE concentrations from 8 mg/l at 200 meters west of the spill to 1 mg/l at 37 meters east of Spring Creek, to non-detectable levels at Spring Creek. The groundwater/surface water interface, or hyporheic zone, at this site provides an opportunity to evaluate the natural recovery of the sediments as ground water moves through this area. The purpose of this study was to evaluate biodegradation and sorption components for MTBE and TBA within the hyporheic zone sediments at the site. There is currently a lack of information concerning experimentally determined biodegradation rates and sediment sorption coefficients for these chemicals at full scale sites. Biodegradation rates and sorption coefficient are used in mathematical models of monitored natural attenuation for prediction of treatment times and for assessment of contaminants movement. Biodegradation rates currently available have been developed based on pure culture methods, and sorption coefficients have been primarily derived from prediction methods and have not been measured. This study also focused on the effects of specific environmental conditions, including dissolved oxygen status, temperature, and nutrient effects on biodegradation, and sediment organic matter content and effect of co-solutes on sorption. These factors were evaluated for the development of potential management strategies for enhancing the natural recovery of contaminated sediments at the Ronan site. Results indicated that both MTBE and TBA are biodegraded, and that the two compounds demonstrate different rates and different sorption patterns in the Ronan sediments. Both compounds were degraded under aerobic conditions. MTBE sorption isotherms developed showed a linear relationship for MTBE, and the value for the organic carbon distribution coefficient is an order of magnitude higher than those based on prediction methods that were identified in the literature and five times higher than predicted for TBA. Isotherms for TBA demonstrated a non-linear relationship of aqueous concentration to sorbed concentration at low TBA concentrations (ug/l levels). Results indicated that environmental variables have an effect on both biodegradation rate and extent of sorption, and therefore potential management strategies may be used to enhance the natural recovery of the contaminated sediments at the Ronan site.

Key words: biodegradation, TBA, MTBE