ABSTRACT
This work summarizes research on a diesel fuel-contaminated aquifer in Menziken, Switzerland, which has been treated by engineered in situ bioremediation, stimulating indigenous microbial populations. After terminating engineered measures, intrinsic in situ bioremediation of the remaining weathered diesel fuel took over. Field investigations during the transition period are reported which focused on changes of 1) redox parameters, 2) geochemical reactions, 3) mineralization rates of diesel fuel, and 4) stable carbon isotopes. Redox parameters and stable carbon isotopes reveal that the importance of methanogenic processes increased after the engineered treatment was terminated. The mineralization rates fell to about one forth after terminating the engineered treatment. The data suggest that mass balances for overall pollutant removal have to consider the engineered treatment with oxidants as well as the subsequent intrinsic processes.
