Tracer studies using Br⁻ and bacteriophage PRD1 in both surface and subsurface flow constructed wetlands were conducted to analyze their hydrodynamic behavior and efficiencies in removing viruses from wastewater. A survival test in situ was also conducted to analyze the persistency of PRD1 in wetland environments. Concurrently, a sampling program for microbial and chemical indicators in the surface flow wetland for a period of 16 months was conducted. The tracer studies revealed a reduction of 99 and 84 percent in the subsurface and surface flow wetland, respectively. Bromide recovery at the outlet of both wetland systems was about 75 percent. The Convective-Dispersion Equation was able to predict the observed PRD1 and Br⁻ breakthrough curves obtained during the tracer study in the surface flow wetland. The monitoring program of pollution indicators showed that biochemical oxygen demand and total suspended solids can be reduced efficiently, reaching the tertiary effluent standard of 10 mg L⁻¹ required by The Arizona Department of Environmental Quality. This sampling program suggested that coliphages may be a better indicator of fecal contamination than total and fecal coliforms in surface flow wetlands.

Eleven series of replicated tests were conducted using 38.1 mm, 15.9 mm, and 9.5 mm gravel to determine the most effective soil surface cover to prevent soil erosion from rainfall. A sediment tray one meter square in size with an integrated rainfall simulator was used to generate data after initial trial runs had established test procedures. Various size gravels and a control with no cover were tested in a laboratory using simulated rainfall to evaluate their effectiveness in preventing erosion. Through thirty-three experiments, signature traits of specific rock sizes were identified. Experiments on 38.1 mm gravel indicated the usefulness of rock mulches in soil erosion prevention. Evaluations with 9.5 mm material indicated that erosion prevention varies inversely with particle size. Experiments with 15.9 mm gravel suggested that this material could increase erosion. This study reflects the ambivalence in the literature and points to the complexity of micro-interactions and erosion potential as influenced by gravel size. Six mechanisms governing rock mulch erosion were proposed.

A number of factors have contributed to the interest in reclaimed wastewater irrigation of vegetables. However safety of water as related to fresh cut vegetables has been a paramount concern of responsible agencies, growers and consumers. The objective of this study was to evaluate the risk mitigation potential of subsurface drip irrigation during reclaimed wastewater irrigation. Virus detection methodologies on produce were first optimized. Beef extract (3%) +0.04M sodium pyrophosphate was found to be the most efficient eluent to recover viruses from soil and plant material. The recovery efficiency of poliovirus type l and adenovirus type 40 from Pima clay loam soil ranged from 12--16%, and recoveries from Brazito sandy loam ranged from 58--81%. The recovery efficiencies of poliovirus type 1, adenovirus type 40, MS2 and PRD1 from lettuce ranged from 45 to 70%. The recovery efficiencies of MS2 and PRD1 from tomato fruit were in the range of 90%. Poliovirus type 1, adenovirus type 40, MS2 and PRD1 survived longer in Pima clay loam than in Brazito sandy loam. All enteric viruses remained stable at 4°C suggesting that little virus inactivation occurs during transportation and marketing. Poliovirus type 1 and adenovirus type 40 lost 1 log₁₀ in 11 and 17 days respectively on lettuce at room temperature. Hepatitis A virus lost 2.5 log₁₀ in 50 days on a lettuce head in a greenhouse during the winter season. Tomato, lettuce and cucumber crops were irrigated with virus-seeded water by subsurface and surface drippers. Subsurface drip irrigation resulted in 99% less viral contamination of vegetable leaves as compared to surface drip irrigation. The greatest risk of infection occurs from the outer leaves of lettuce. The risk of infection from consumption of reclaimed wastewater irrigated tomatoes and cucumber was 32% and 72% less than lettuce. The risk of infection from rotavirus by ingestion of vegetables is greater than poliovirus type 1. The risk of infection from subsurface drip irrigated vegetables did not approach the United States Environmental Protection Agency's acceptable annual risk (1:10,000) until the concentration of viruses in the irrigation water reached 100/l. No internal contamination by viruses of the vegetables was observed during their growth. The coliphages PRD1 survived longer than poliovirus type I, adenovirus type 40, and MS2. It would thus appear to be a good model for studying the persistence of those viruses on produce and in irrigated agricultural systems.

Over the past century, woody plants and shrubs have increased in abundance at the expense of grasslands in many semiarid regions. The availability and concentrations of nutrients influence the relative success of plants, but the effects of fire frequency on soil nutrients is unknown for semiarid grasslands. On the gunnery ranges of Fort Huachuca in southeastern Arizona, study sites were established to examine the effects of fire frequency on soil biogeochemistry, plant biochemistry, and δ¹³C values in soil organic matter (SOM). The sites were on homogeneous granitic alluvium where wildfire frequency history is known from 1973 to present and no cattle grazing has occurred in recent decades. Subplots represent fire frequencies of no burns, 3 fires per decade, and 5 fires per decade. The "no burn" plot has abundant C3 Prosopis velentina (mesquite) trees, whereas the burned plots are open C4-dominated grasslands with scattered mesquite trees. Prosopis trees have altered SOM pools by the concentration of plant nutrients and the addition of isotopically light shrub litter. Frequent fires have altered the basic geochemistry and nutrient availabilities of the soil, and the changes appear to be significant enough to affect plant growth. Soil pH increases with burning frequency, and TOC, total nitrogen, and plant-available phosphorus show significant increases on the infrequently burned plot. Burning is advantageous for preservation or restoration of grasslands, as total living grass biomass is greater on the two burned plots. Root biomass 11 is significantly lower on the "frequently burned" plot. Concentrations of the key nutrients nitrogen and phosphorus are reduced in plants on the burned sites compared to plants on the unburned site. Fires help re-distribute nutrients but evidence of nutrient concentrations and δ¹³C values are retained in SOM for many decades. Estimates of bulk carbon turnover rates range from 112 to 504 years. Evidence for modern C3 shrub expansion is found in the shift of SOM δ¹³C values from values characteristic of C4 grasses to C3 shrubs in surface soil layers. δ¹³CSOM values indicate that the Holocene and Late Pleistocene were dominated by C4 grasslands, and the pre-Late Pleistocene vegetation was a C4-grass savanna with abundant C3 plants.

A numerical first order approach is proposed to conduct stochastic analyses of head and concentration under variably saturated conditions. The approach is based on a first-order Taylor series expansion and an adjoint state method. To implement the approach in different flow and transport regimes, numerical models are adopted to evaluate sensitivities of head and concentration with respect to hydrological parameters. This provides the possibility of conducting stochastic analyses of flow and transport problems with any kind of boundary and initial conditions. As a result, limitations of analytical approaches such as the spectral/perturbation approach can be avoided. In addition, the use of adjoint state method also alleviates the computational burden encountered in Monte Carlo simulation by allowing us to evaluate the sensitivities of head and concentration only at interesting/measurement locations. Several numerical simulations are performed to examine the sensitivities and moments of head and concentration under different flow conditions. The results show that the existence of water tables in the simulation domain can have a significant impact on the moment calculation of head and concentration. The calculated statistical moments are used to estimate log-conductivity by cokriging. The conditioning effect of head, concentration, and arrival time in estimating log-conductivity is investigated under different flow conditions. The results show steady state head is the best secondary information compared to solute concentration and arrival time in estimating conductivity by providing stable and consistent results. Estimates can be error prone when concentration measurements are used to estimate LnKs because of the nonlinear relationship between concentration and LnKs and the large variability in the simulated solute plumes. A sequential estimating technique is shown to be able to overcome some of these inadequacies of using concentration measurements. Arrival time, requiring a large amount of CPU time, does not show any advantage over concentration and head in estimating conductivity.

Contamination of soil and groundwater environments by toxic metals and organic compounds is of major concern because of the potential health hazard posed for humans. Remediation of such sites may require the addition of chemical agents that help in the mobilization of contaminants which are likely to be bound to solid surfaces. Surfactants are one of the agents proposed for addition to enhance the removal of soil-bound contaminants. In this dissertation, a series of laboratory experiments were conducted to investigate constraints to the potential application of a microbially produced surfactant (biosurfactant) for removal of metal contaminants from soil. The first part of the dissertation describes the measurement of stability constants and 13 metals including ten of the metals most frequently found in contaminated sites as well as three of the most common metal cations found in soil, Ca²⁺, Mg ²⁺, and K⁺. The second part of the dissertation describes a series of experiments designed to determine the interaction of the biosurfactant with soil matrix components including clays, metal oxides, and organic matter. The biosurfactant used in this research was monorhamnolipid produced by Pseudomonas aeruginosa ATCC 9027. A mixture of mono- and dirhamnolipid produced by P. aeruginosa UG2 was also used in some cases. Results showed that selectivity of the monorhamnolipid followed the order: Al³⁺ > Cu²⁺ > Pb²⁺ > Cd²⁺ > Zn²⁺ > Fe³⁺ > Hg ²⁺ > Ca²⁺ > Co²⁺ > Ni²⁺ > Mn²⁺ > Mg²⁺ > K⁺. These results suggest that monorhamnolipid binds common metal contaminants in preference over common soil cations such as Ca²⁺, Mg²⁺, and K⁺. Rhamnolipid was shown to bind to some soil constituents very strongly including hematite, illite, kaolinite, and montmorillonite. These results indicate that the effectiveness of rhamnolipid in soils with high amounts of iron oxide or clay may be limited due to extensive sorption. Finally, it was found that monorhamnolipid sorbed more strongly than a rhamnolipid mixture containing both monorhamnolipid and dirhamnolipid. This suggests that the use of a biosurfactant mixture may improve the effectiveness of rhamnolipid in the removal of organic and metal contaminants from soil.

In-situ bioremediation is a promising biotechnology for removing aqueous phase contaminants from groundwater. Utilizing indigenous bacteria to degrade organic contaminants into non-toxic components, bioremediation is relatively inexpensive, fast, and complete. Making predictions about its applicability and success is difficult because of the complexity and variability intrinsic to the subsurface environment. Analytical studies of models, independent of this detailed subsurface data, are essential to finding accurate quantitative results, yet few have been obtained. This dissertation is a collection of three mathematical reports on a one-dimensional model for bioremediation. Using degree theory, the elliptic maximum principle, and comparison theorems, existence of traveling wave solutions to the biodegradation model is proved, a formula for the speed of the traveling concentration front is derived, and bounds on the biomass concentration are obtained. In the second section, the model is shown to reduce to a single equation in the relaxation limit by using properties of systems of hyperbolic conservation laws. In the third section, a formula is found for the parameters at which an unstable traveling wave solution bifurcates to a stable limit cycle (oscillatory solution). These results provide practical information about the structure of concentration fronts for the contaminant, nutrient, and biomass. The fronts travel at speeds that are either constant or time-periodic, depending on the kinetic parameters of the bacteria and the sorption properties of the contaminant. When there is little growth in biomass, many critical properties of the concentrations are derived. For aquifers with low permeability, the model is reduced to a much simpler system, also allowing the derivation of many analytical properties. Though comparisons with experimental data have not yet been done, numerical simulations support these results.

Vegetation change, particularly from the grass to shrub lifeform, is a critical issue on the world's rangelands. The plant community present on a site is the primary determinant of the land's value for watershed protection, wildlife habitat, livestock production, and recreation. Studying past vegetation composition can help separate natural from anthropogenic sources of change and guide natural resource conservation and management decisions. Stable carbon isotope (δ¹³C) values and associated radiocarbon ages from soil organic matter (SOM) were used to evaluate vegetation change across five landscape positions at a small enclosed basin in southeastern Arizona. The utility of the carbon isotope method was verified for this site based on the clear and wide separation in δ¹³C values between grasses having the C₄ photosynthetic pathway and shrubs having the C₃ pathway. The direction and timing of vegetation dynamics differed with landscape position along a gentle elevation gradient from the basin outlet to a nearby volcanic ridge top. Warm-season C₄ perennial grasses have dominated the basin outlet, center, and toe slope landscape positions since at least 5000-6000 yr BP, except for a dramatic increase in C₃ plants at the bottom of the outlet excavation around 5000 yr BP. This isotopic change is associated with rounded cobbles that may have been a stream channel, suggesting the presence of C₃ herbaceous or woody riparian vegetation. On mid-slope and ridge top landscape positions, where semidesert shrubs now dominate, warm-season perennial grass, composition decreased from approximately 60% as recently as 400 yr BP to only 1.5% now. SOM density separates were also analyzed. The youngest SOM is represented by the <2 g/cm³ density fraction that turns over in a few years to several decades and has a post-bomb radiocarbon age. For the ridge top landscape position, this fraction yielded 39% C₄ vegetation, suggesting that the conversion from grass to shrub vegetation occurred recently.

Understanding the extent of microbial transport, distribution and activity in the subsurface is paramount for effective in-situ bioremediation. In one study, we investigated the impact a substrate pulse has on the movement of inoculated or indigenous bacteria through saturated porous media. In another study, we developed a method to visualize the distribution of bacteria on soil surfaces. The elution of either inoculated or indigenous bacteria was monitored from model (homogenous) sand or natural (heterogenous) soil column systems. Sand columns receiving salicylate resulted in enhanced elution of inoculated P. putida. However, the salicylate pulse did not result in enhanced elution of P. putida from a natural system. For natural heterogenous systems, the salicylate pulse significantly affected the elution of certain indigenous bacteria. Specifically, more heterotrophs were eluted from soil columns receiving salicylate than from those that did not for both loamy sand soils tested. On the other hand, there were consistently fewer salicylate-degrading cells eluted in the presence of salicylate from one of the two soils tested. These data suggest that bacterial transport is a function of both the porous medium and the microbial population(s) under investigation. In the second study, an agar lift-DNA/DNA hybridization technique was developed to visualize the distribution of eubacteria on soil surfaces. Briefly, a single layer of soil was lifted from the surface of soil microcosms onto agar slabs and allowed to incubate. Bacterial colonies were lifted from the agar slabs onto membranes. The location of individual colonies was detected on the membranes by hybridization with a probe complementary to a conserved region of the eubacterial genome. This method was able to detect active microorganisms on different soil surfaces. The probe signal correlated well with the number of metabolically active microorganisms found in soils amended with a carbon source. This technique also allowed for visualization of localized microbial activity. A combined approach utilizing both soil column studies and the agar-lift technique should allow researchers to better elucidate microbial transport, distribution and activity in subsurface environments.

Soil venting, which includes gas injection as well as gas extraction in subsurface media, has become the primary method used in the United States to remove volatile organic compounds (VOCs) from unsaturated subsurface media. The popularity and widespread use of venting is due to its simplicity of operation and proven ability to remove contaminant mass inexpensively compared to competing technologies. Despite the common use of venting in the Superfund program, there is little consistency in approach to assessment of performance and closure. Assessment of the technology's performance and eventual decisions on closure are based primarily on negotiations between responsible parties and regulators. In this process there is widespread use and reliance on empirical methods as opposed to an emphasis on understanding fundamental physical, chemical, and biological processes controlling mass removal during the venting operation. This results in the technology not being used to its fullest potential, nor its limitations being well understood. The overall purpose of the work described in this dissertation was to improve the "state of the art" and "state of the science" of soil venting application. This purpose was accomplished by attainment of three specific objectives. The first objective was to develop an overall regulatory approach to assess venting performance and closure including measures to ensure consistency in ground-water and vadose zone remediation. The second objective was to provide comprehensive and detailed literature reviews on gas flow and vapor transport. These reviews formed the basis of recommendations and methods to improve venting design and monitoring. The third objective was to perform research to improve various aspects of venting application. This research consisted of: (1) analysis of linearization of the gas flow equation, (2) one-dimensional steady-state analysis of gas slippage, (3) two-dimensional steady-state analysis of gas flow and permeability estimation in a domain open to the atmosphere, (4) two-dimensional steady-state analysis of gas flow and permeability estimation in a semi-confined domain, (5) two-dimensional transient gas flow analysis and permeability estimation, (6) analysis and comparison of radius of influence versus critical pore-gas velocity based venting design, (7) modification of a gas extraction well to minimize water-table upwelling, (8) simulation of rate-limited vapor transport with diffusion modeling, (9) assessment of respiration testing, (10) development of a one-dimensional, analytical, vadose zone transport code to simulate mass flux to and from the capillary fringe, and (11) analysis of water-table mounding during sparging.