ABSTRACT
Natural attenuation (NA) of petroleum hydrocarbons (PHC) has become increasingly popular as a substitute for classical remediation approaches such as pump-and-treat. At PHC-contaminated sites, the NA processes are in operation when a sufficient supply of electron acceptors such as oxygen and nitrate is available (Wiedemeier et al., 1999). However, other processes than the PHC degradation can consume electron acceptors (Chapelle et al., 2002; Schreiber and Bahr, 1999). Ferric iron may play a key role in electron mass balance (Christensen et al., 2000), especially at sites like Bemidji in Minnesota, USA, where concentrations of other electron acceptors are limited (Cozzarelli et al., 2001).
