BIODEGRADATION OF ORGANIC CONTAMINANTS IN THE SUBSURFACE OF HAZARDOUS WASTE SITES (GROUNDWATER, MICROBIOLOGY, AQUIFER)
LEE, MICHAEL DONALD
Doctor of Philosophy
The ability of the subsurface microbial population to degrade the major organic contaminants at three sites was assessed. The three sites included an abandoned wood creosoting facility in Conroe, Texas where the silty sand aquifer was contaminated primarily with polynuclear aromatic hydrocarbons; a sandy aquifer in Traverse City, Michigan where a spill of jet fuel polluted the ground water with benzene, toluene, and xylenes; and a site on the Texas Gulf Coast in which the fine sand aquifer was contaminated with benzene, toluene, naphthalene, and bis(2-chloroethyl) ether. Representative subsurface cores and ground water samples were collected for each site and used in the experiments to characterize the microbial population, to determine their ability to degrade the organic contaminants particular to the site, and to ascertain the factors limiting biodegradation of the contaminants at these sites. Laboratory experiments on the Conroe site revealed that the microbial population found in the contaminated zone could degrade the pollutants, but the microorganisms were not acclimated in the uncontaminated areas. The limiting factor at this site was the supply of dissolved oxygen. Field tests and modeling simulations confirmed these results. At the Traverse City site, few organisms were found that could degrade the test compounds in the uncontaminated zone. The microorganisms from the uncontaminated site could not respond as rapidly to a natural substrate as organisms in the contaminated zone which suggests their metabolic status was altered by the contamination. Oxygen, not inorganic nutrients, limited biodegradation at this site although anaerobic degradation of the contaminants may also occur. At the third site, the organisms in the uncontaminated zone were active against benzene, toluene, and to a lesser degree, naphthalene. In the contaminated zone, a toxicant may have reduced the amount of biodegradation occurring. This project demonstrated that microorganisms in the contaminated zones of two sites were active against the contaminants, but were limited in their ability to degrade these contaminants by the supply of dissolved oxygen. At the third site, a toxicant appeared to control biodegradation.