Subsurface Behavior of Spilled Fuel in a Permafrost Environment.

摘要

This dissertation focuses on the subsurface behavior of spilled fuel consisting of diesel and gasoline, which are subsets of light nonaqueous phase liquids (LNAPLs), in a permafrost environment. Particular emphasis is laid on mobile LNAPL in fractured bedrock. The site chosen for this study is the abandoned Colomac gold mine, 220 kilometers northwest of Yellowknife in the Northwest Territories, where over 50,000 liters of spilled fuel occurred between 1990 and 2003. The site is underlain by fractured bedrock with 0 to 4.6 m of overburden soil. The broad objectives of this work involve determination of contamination extent and LNAPL behavior at the site. Other specific objectives include determination of the major geochemical processes and identification of mechanisms influencing LNAPL movement and accumulation at the site.;Analyses of the groundwater suggested ongoing anaerobic biodegradation of the dissolved LNAPL components. Furthermore, the analyses showed that the water was Ca-SO4 type and the main geochemical processes were gypsum dissolution and carbonate weathering. The analyses underscored the importance of bedrock mineralogical composition on groundwater constituents and geochemical processes.;The laboratory test results involving entrapment of diesel fuel below the water column and admixture of soluble oils with water in the freezing cell showed upward mobility of LNAPL under cyclic freezing, and downward progressive expulsion of the soluble oils ahead of the advancing freezing front. The results corroborated literature findings on cryogenic expulsion ahead of freezing front, and provided new insight into the behavior of trapped LNAPL below the water table when subjected to cyclic freezing.;Both field and laboratory studies were performed to achieve the above-stated objectives. The field study involved site characterization, and the laboratory study involved a top-down freezing experiment using a freezing cell, consisting of parallel glass plates, to evaluate the impact of cyclic freeze-thaw on LNAPL movement The site characterization efforts showed that the LNAPL contamination is limited to the upper section (∼7 m) of the fractured bedrock. The field study showed that water table fluctuations and freezing-induced displacements were active but discontinuous mechanisms contributing to LNAPL migration and accumulation in the formation and monitoring wells at the site.