BIODEGRADATION REACTIONS IN A MULTIPLE CONTAMINATED AQUIFER — BITTERFELD CASE STUDY

摘要

To evaluate the feasibility of using monitored and enhanced natural attenuation as a complimentary measure at the large-scale Bitterfeld contaminated site in Germany, the ongoing natural attenuation (NA) processes are investigated in relevant subunits. Three large, mostly non-coincident plumes of chlorinated aliphatic compounds, chlorobenzenes and BTEX were observed in the southeasterly Tertiary aquifer. Despite the high sulfate levels, direct evidence of reductive dechlorination of the chlorinated aliphatics and chlorobenzenes was observed due to the appearance of intermediates and a decrease in the degree of dechlorination along the flow path. The BTEX plume showed a relatively rapid disappearance of toluene, while benzene was the most recalcitrant compound. Increased methane concentrations, whose biogenic origin could be confirmed by their isotopic signature, were measured in the plume directly downstream from the source area, suggesting that methanogenesis in addition to sulfate reduction constituted a relevant process. A preliminary quantification of the NA processes was obtained via a modified centerline approach using chloride as conservative tracer, yielding relatively long half lives of 8 (for chlorinated aliphatics) to 17 years (for benzene). This approximation will consequently be refined in the future through a more detailed investigation including the modeling of contaminant transport.