NATURAL ATTENUATION OF MTBE AS PART OF AN INTEGRATED REMEDIATION DESIGN

摘要

At a former industrial landfill site in southeastern Brazil, phenol and MTBE infiltrated into the soil until 1989. Significant concentrations of both pollutants have reached the local groundwater, and the contamination plume, currently over 400 meters long, is moving towards surface waters, thus putting at risk external receptors. The aquifer is shallow, has low hydraulic conductivity and a flow velocity of less than 20 meters per year. Water temperature is 25 - 30℃. The remediation concept for the contaminated groundwater has been designed to ensure the protection of the surface water receptors, and consists of two hydraulic barriers that intercept the front end of the plume. Monitoring data available from a period of more than 10 years for phenol in groundwater show clear evidence for the existence of significant natural attenuation processes which are responsible for a dynamic equilibrium of this contaminant in the groundwater. As for the MTBE concentrations, monitoring data have only been collected over the last two years and indicate a slower plume movement than predicted from the mathematical modeling with no decay factor. Detailed studies of groundwater chemistry along the contaminant flow path supplied further evidence of the existence of considerable degradation of MTBE, presence of aerobic bacteria, depletion of dissolved oxygen in the source zone of the plume and slightly increasing concentrations towards the fringe zone, increasing concentrations of specific MTBE degradation products such as TBA over the flow path, and reduction of total contained MTBE mass in the groundwater over time. A half-life of approximately 2.5 years for the decay of MTBE was obtained. This value is consistent with the values obtained in laboratory and pilot tests as reported in the literature. The reactions responsible for the MTBE degradation required presence of oxygen. In order to maintain and enhance the rates of intrinsic bio-degradation observed at this site, complementary remediation technologies, such as advanced oxidation, were considered as promising tools to speed up the operational time for achieving the established remediation and clean-up goals.