Natural attenuation of petroleum hydrocarbons in groundwater

A multidisciplinary field research experiment was conducted at Columbus AFB, Mississippi, in order to develop a better mechanistic understanding of the various processes involved in the natural attenuation of petroleum hydrocarbons. This experiment was termed the Natural Attenuation (NAT) Study. The NAT Study was conceived to evaluate the efficacy of linking microbiological evidence generated from laboratory assays of core samples obtained form the subsurface with measurements collected under field conditions. Initial studies were performed to evaluate the microbial potential for natural attenuation at Columbus AFB. Mineralization assays utilizing ¹⁴C-labeled substrates indicated indigenous organism possessed the capacity to biodegrade aromatic hydrocarbons without any nutrient augmentation or environmental manipulation. Molecular analysis using an array of DNA probes developed for this study further indicated the near ubiquitous distribution of aromatic degrading genotypes at the research site. Microbiological analyses performed after 278 days reflected the impact of hydrocarbons in the indigenous microbial community, with mineralization of naphthalene reaching levels of 60% in 24 hours and hydrocarbon degrading genotypes reaching levels of almost 50% of the total microbial community. After 462 days, microbial mineralization and hydrocarbon degrading populations were at lower levels. Groundwater measurements indicated that migration of the contaminant hydrocarbons had been retarded at the field scale by microbial processes. The NAT Study provided the ability to link field measurements of natural attenuation with laboratory evidence from examining the indigenous microbial community.