Pyrene, a four-ring polycyclic aromatic hydrocarbon (PAH), was identified as the chemical that requires the largest land area for soil bioremediation due to the slow rate of biodegradation at the Libby, Montana Superfund site. Prepared bed land treatment is the specific bioremediation technology that is currently employed at this site. Although bioremediation has been widely accepted for treatment of contaminated soil due to its low cost, the effective application of bioremediation is often hindered by the lack of information related to: 1) biochemical pathways, 2) enzymatic mechanisms, and 3) effects of amendments. Mycobacterium sp. KMS is a new strain isolated from the land treatment units of the Libby site and has been found to utilize pyrene as a carbon and energy source. The genome of Mycobacterium sp. KMS was sequenced by Joint Genome Institute (JGI) and is publically available in the NCBI database. This dissertation is comprised of seven chapters. Chapter I provides information concerning PAH characteristics, the Libby Superfund site, accelerated bioremediation approaches, and the hypotheses for this dissertation. Chapter 2 addresses the pyrene degradation pathway used by Mycobacterium sp. KMS based on isolating and identifying pyrene degradation intermediates. Chapter 3 describes the enzymatic mechanism of pyrene degradation by Mycobacterium sp. KMS. Chapter 4 presents the effect of Elliott soil HA (ESHA) amendment on pyrene solubility in soil slurry systems and pyrene mineralization in unsaturated soil microcosms. Chapter 5 describes the overall effect of ESHA amendment on pyrene distribution in a soil slurry system. Chapter 6 addresses the engineering significance of this study and future research recommendations. Chapter 7 summarizes the dissertation. The main theme of this dissertation is to provide the basic scientific information and knowledge for better understanding, better control, and improvement of the bioremediation process at PAH-contaminated sites.