Principal Component Analyses of Groundwater Chemistry Data During Enhanced Bioremediation

Abstract

A bioremediation project has been monitored for two years at a former sour gas plant site that had ethanolamine, glycol and their degradation products in the subsurface. The active enhanced bioremediation program consisted of dewatering and bioventing. An extensive groundwater monitoring program mapped the distribution of chemical species. Principal component analysis was used to help organize and interpret the chemical analysis. Three principal components accounted for 75% of the variability in the data. The first component separated contaminated waters from background. The second component indicated aerobic versus anaerobic conditions and the third component was indicative of the accumulation of nitrogen compounds. The site is extremely heterogeneous with preferential pathways due to fractures, sand lenses and a fractured horizontal well. In addition the source and contaminated areas are very heterogeneous. The PCA shows drastically different geochemical conditions residing within relatively small areas. The study site can be conceptualized as a series of small, meter-scale sized reactors that interact and mix due to preferential flow paths and diffusion. The evolution of the chemistry shows that the bioremediation process is successfully removing acetic acid, and it is becoming more aerobic. Enhanced infiltration in the process area is slowly removing the source and degradation products.