Infiltration of wastes containing creosote and pentachlorophenol from surface impoundments at an abandoned wood-treatment facility near Pensacola, Florida, resulted in contamination of the underlying sand and gravel aquifer. Pond sludges and sediments near the source were contaminated with 2- to 5-ring azaarenes having log Kow values of from 2.0 to 5.6. However, the ground water contained only azaarenes and their oxygenated and methylated derivatives having log Kow values of less than 3.5. These compounds also were present in coal tar-contaminated ground water at a site near St. Louis Park, Minnesota. Laboratory anaerobic degradation studies and on-site observations indicated that oxygenated azaarenes probably were biotransformation products of reactions mediated by indigenous microbial populations. Microbial N-methylation, C-methylation and O-methylation reactions are reported here for the first time. In the presence of nutrients and carbon sources such as acetate and propionate, all azaarenes studied were either partially or completely degraded. Evidence for the microbial degradation of azaarenes in ground water from anaerobic zones is presented. Oxygenated azaarenes were relatively more water-soluble, mobile and persistent in hydrogeologic environments. ?? 1987.