Bioremediation in the vadose zone is unpredictable because of poor understanding of factors influencing microbial growth in this environment. A lab-scale experimental system was developed to examine, noninvasively, interactions between microbial growth, water flow, and solute transport in unsaturated porous media. Measurements of microbial colonization, and its impact on hydrology, were facilitated by using the luxCDABE-containing reporter bacterium Pseudomonas fluorescens HK44 and digital CCD imaging. Experiments were conducted in glass-walled two-dimensional flow cells (45 x 50 x 1 cm) packed with silica sand. Several bioengineering problems associated with chamber design and function required solution before microbial experiments were successful. These included: choice of materials for chamber components; development of sterilization, packing, and inoculation protocols; and development of procedures for data collection and chamber maintenance during experiments lasting several days. Bacterial growth was mapped daily by quantifying development of salicylate-induced bioluminescence. A model relating the rate of increase in light emission after induction successfully predicted microbial densities over four orders of magnitude (R��=0.95) provided that sufficient oxygen for the bioluminescence reaction was available. Total model-predicted growth during a one-week experiment agreed with potential growth calculated from the mass-balance of the system and previously established kinetic parameters (predicted, 1.2x10���� cells; calculated, 1.7x10���� cells). Although the rate of expansion of the colonized zone (and predicted populations in newly colonized regions) remained relatively constant, the proportion of the daily potential growth remaining within the chamber declined over time. Monitoring of bioluminescence revealed the development of an (hypothesized) anaerobic zone associated with microbial growth in the unsaturated porous media. Water content and flow streams were measured using light transmission. Accumulation of microbial growth modified the hydrologic properties of the sand causing up to 50% decrease in saturation within the colonized zone, diversion of flow around the colonized zone, and lowering (5 cm) of the capillary fringe height. Apparent solute velocity through the colonized region was reduced from 0.39 cm min����� (R��=0.99) to 0.25 cm min����� (R��=0.99). These experiments provide proof-of-concept for combining light transmission and bioluminescence technologies to study interactions between microbial growth and hydrology in unsaturated porous media. / Graduation date: 2002

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 336-344).

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 100-102).

Thesis (Ph.D. - Hydrology and Water Resources)--University of Arizona. / Includes bibliographical references (leaves 52-62).

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2008. / Title from title screen (site viewed Sept. 18, 2008). PDF text: ix, 228 p. : ill. (some col.) , maps (some col.) ; 4 Mb. UMI publication number: AAT 3297902. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (D.Eng.)--University of Delaware, 2008. / Principal faculty advisor: Paul T. Imhoff, Dept. of Civil and Environmental Engineering. Includes bibliographical references.

Thesis (M.S.)--Brigham Young University. Dept. of Civil and Environmental Engineering, 2007. / Includes bibliographical references (p. 45-47).

Thesis (doctoral)--Swiss Federal Institute of Technology, Zurich, 1997. / Vita. Includes bibliographical references (p. 121-128).

Natural enrichment of ²³⁴U with respect to ²³⁸U was investigated in perched water, vadose zone pore waters, and secondary minerals. The activity ratio (AR) for dissolved ²³⁴U increased from about 1.4 in runoff to >6 in perched water. The AR in the vadose zone increased sharply at a transition that correlated with increased magnetic susceptibility and decreasing hydraulic conductivity. This was evidently caused by auto—oxidative selective leaching controlled by matrix saturation. The direct recoil fractionation mechanism has been proposed for tuffs on the Nevada Test Site, and could imply enhanced retardation of U. Direct recoil was evaluated using a steady state isotopic mass balance formulated to represent matrix pore water, and including first order sorption and selective leaching. Matrix sorption parameters were estimated by selectively leaching intact core with hydroxylamine. Much U was recovered, fractionated similarly to pore water. Interpreting this as isotopic exchange limited by Fickian transport within a sorbent layer, the rate constant and distribution coefficient were estimated. Uranium—series analysis of fracture—lining MnO₂ indicated that isotopic exchange was operant. The isotopic mass balance showed that direct recoil is a minor contribution to fractionation, so the predominant mechanism is selective leaching. This result depends mainly on the sorption rate constant, and where direct recoil is likely such as in roll—front deposits, it implies that the rate constant is smaller than in typical oxidizing waters. Extrapolating matrix properties to formation scale transport, an upper bound on formation scale sorption was inferred from the isotopic mass balance. Formation scale sorption is greater where the perched water table lies in more porous, permeable tuff. The layer diffusion model predicts that the effective sorption rate constant decreases significantly for thicker sorbent layers. Thus although fracture lining MnO₂ minerals are common at Yucca Mountain, U retardation may be strongly rate limited. Elevated AR's (>5) generally signify conditions favorable to U retardation, based on hydraulic isolation from recharge. Elevated vadose zone AR's do not necessarily signify the former presence of perched water, but could be interpreted that way at Yucca Mountain if similar fractionation is not found where past perching is unlikely.

Thesis (M.S. in environmental science)--Washington State University, August 2007. / Includes bibliographical references (p. 19).