Study of 25-year-old Nipisi oil spill: Persistence of oil residues and comparisons between surface and subsurface sediments

Three oil spills that occurred in the Nipisi and surrounding area of Alberta between 1970 and 1972 were surveyed in 1995 to determine which of the cleanup methods used were the most successful. The survey also provided information about changes in residual oil and vegetative recovery 25 years after the spills took place. Chemical analysis results showed that the Nipisi site was still recovering but the process is very slow and more time is needed for the process to be complete. In fact, there have been no significant changes in the character of the residual oils between cleanup-treated sites and untreated sites. Subsurface biodegradation has been acidic and water-saturated. Subsurface oil levels are expected to decline over the years as increases in rainfall bring the oil to the surface where conditions are more favorable to aerobic microbial action and weathering processes. Significant differences in vegetation levels have been found which do not correlate with the level of oil contamination. These differences are believed to be due to the extreme physical disturbance after the cleanup, water saturation of the soil and periodic re-oiling of the low-lying areas by oil brought to the surface by heavy rainfalls. 34 refs., 8 figs