I documented NA of dichloromethane (DCM) at sites in Oregon and California (Lehmicke et. al. 1996, Lehmicke and Mukherjee 1999). At a 3rd site in California, DCM concentrations exceeded 10,000 mg/l; the plume was undergoing NA and seemed to be at steady state. Biodegradation of DCM appeared to be generating electron donor for biodegradation of TCE where DCM/TCE plumes overlapped. It is known that acetate is produced during anaerobic degradation of DCM. This appeared to be occurring at the Oregon site as well.
A lab study using site soil and ground water demonstrated that anaerobic degradation of DCM could supply electron donor for TCE degradation and that DCM degradation is self-limiting at high concentrations due to a large pH drop (Freedman et. al. 2005b). Enhanced bioremediation was implemented on the TCE plume where it did not overlap with the DCM plume in late 2009 after a 2nd study showed DCM concentrations > 20 mg/l inhibited 2 commercial bioaugmentation cultures at different stages of the TCE degradation pathway (Bone et. al. 2009).