NATURAL ATTENUATION RATES OF ETHANOL AND BTEX COMPOUNDS IN GROUNDWATER CONTAMINATED WITH GASOHOL

Natural attenuation biodegradation rate is a key parameter to perform a risk assessment of hydrocarbon plumes. This study determines first-order kinetics for a gasohol controlled release experiment site in Brazil using data of BTEX and ethanol concentrations of eight sampling campaigns. The rates of individual BTEX compounds and ethanol were estimated using the methods of trimethylbenzene correction, Buscheck and Alcantar (1995), mass flux, and Bioscreen fate and transformation model. Results showed that the fate and transport model is the method that best fits transient state flow conditions of BTEX and ethanol plumes. Biodegradation first-order coefficients calculation with the model showed the following half- lives: ethanol = 0.60 year, toluene = 0.70 year, benzene = 1.00 year, ethylbenzene and total xylenes = 1.20 year. However, due to the interference of ethanol on BTEX degradation, neither Bioscreen nor any other model that do not incorporate multiple substrate interference are adequate to correctly predict the behavior of gasohol plumes.