Enhanced natural attenuation of organic chemical contaminants in groundwater.

This thesis presents an investigation into the enhanced natural attenuation of organic chemicals in groundwater. The focus of the research was directed towards the organic chemicals benzene, ethylbenzene, styrene, 1,2- dichloroethane and vinyl chloride, which were found to exist at a contaminated site located in the United Kingdom. A conceptual model was developed for the study site, based on the findings of previous consultant studies and investigations which were carried out solely for the purposes of this research. Sample collection and analytical procedures were designed to yield results, which could further define contamination issues at the study site, so that remedial measures could be appropriately developed. Lab-based microcosm treatability studies were carried out in order to determine the degradation potential of DCA, benzene and ethylbenzene under various enhanced conditions. The enhancements were selected in order to facilitate different degradation mechanisms for the organic contaminants, including aerobic respiration and reductive dechlorination. The microcosms were monitored for chemical and microbiological changes. A hydrogen release compound (HRC ) treatment was found to effectively degrade DCA and benzene under anaerobic conditions. A microorganism containing genetic sequence similarities with Desulfitobacterium dichloroeliminans bacteria was detected within the HRC -enhanced microcosms, indicating that reductive dechlorination was the likely degradation mechanism for DCA. The use of HRC is recommended as an enhancement for the natural attenuation of organic contaminants at the study site