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Timothy R Ginn

Publications and source records attributed to Timothy R Ginn.

8 recordsLinked to original sources
PubMed2006

Upscaling heterogeneity in aquifer reactivity via exposure-time concept: forward model.

Reactive properties of aquifer solid phase materials play an important role in solute fate and transport in the natural subsurface on time scales ranging from years in contaminant remediation to millennia in dynamics of aqueous geochemistry. Quantitative tools for dealing with the impact of natural heterogeneity in solid phase reactivity on solute fate and transport are limited. Here we describe the use of a structural variable to keep track of solute flux exposure to reactive surfaces. With this approach, we develop a non-reactive tracer model that is useful for determining the signature of multi-scale reactive solid heterogeneity in terms of solute flux distributions at the field scale, given realizations of three-dimensional reactive site density fields. First, a governing Eulerian equation for the non-reactive tracer model is determined by an upscaling technique in which it is found that the exposure time of solution to reactive surface areas evolves via both a macroscopic velocity and a macroscopic dispersion in the artificial dimension of exposure time. Second, we focus on the Lagrangian approach in the context of a streamtube ensemble and demonstrate the use of the distribution of solute flux over the exposure time dimension in modeling two-dimensional transport of a solute undergoing simplified linear reversible reactions, in hypothetical conditions following prior laboratory experiments. The distribution of solute flux over exposure time in a given case is a signature of the impact of heterogeneous aquifer reactivity coupled with a particular physical heterogeneity, boundary conditions, and hydraulic gradient. Rigorous application of this approach in a simulation sense is limited here to linear kinetically controlled reactions.

Adsorption↗
PubMed2006

Upscaling heterogeneity in aquifer reactivity via the exposure-time concept: inverse model.

A novel inverse technique is proposed to quantitatively characterize macroscopic variability in aquifer reactivity in a Lagrangian representation. Reactivity heterogeneity is expressed in terms of distributions of flux over cumulative time of exposure of the solution to reactive surface area, termed here 'cumulative reactivity'. In cases involving single aqueous species the combined effects of physical and reactivity heterogeneity on reactive solute transport can often be established and further investigated through joint distributions of flux over travel time and cumulative reactivity. The inverse technique requires the breakthrough curve of a passive tracer to determine the distribution of flux over travel time, and additional breakthrough curves of reactive tracers provide additional moments of the distribution of flux over cumulative reactivity given travel time. Thus breakthroughs of one passive and two reactive tracers can provide the mean and variance of the distribution of flux over cumulative reactivity. This Lagrangian characterization is achieved with knowledge of the types of reactive surfaces present, but not their spatial locations. The distributions can subsequently be applied via forward modeling using the same technique to predict breakthrough curves of other solutes undergoing first-order reactions in similar physically and chemically heterogeneous configurations.

Adsorption↗
PubMed2005

Impact of environmental stressors on the dynamics of disease transmission.

Infectious disease within outmigrant juvenile salmon in the Columbia River Basin is modulated, in part, by abiotic stressors that influence host-susceptibility. Through the application of a dose-structured population dynamic model, we show that chemical (both in the river and in the estuary) and in-river (e.g., dams and/or predation) stressors influence host-susceptibility, increasing the mean force of infection (defined as the per capita acquisition rate of infection) by a factor of 2.2 and 1.6, respectively. Using Listonella anguillarum as a model pathogen, nonchemical in-river and chemical stressors contribute equally to a cumulative incidence of delayed disease-induced mortalities in Chinook salmon that range from 3% to 18% for estuary residence times of 30-120 days, respectively. Mitigation of environmental stressors that increase host-susceptibility could represent a significant component in future management strategies to recover listed stocks.

Animals↗
PubMed2005

Occurrence and fate of pharmaceutically active compounds in the environment, a case study: Höje River in Sweden.

Pharmaceutically active compounds (PhACs) in the environment lately have been acknowledged to constitute a health risk for humans and terrestrial and aquatic ecosystems. Human and veterinary applications are the main sources of PhACs in the environment and the major pathways are excretion and discharge to the environment through sewage treatment plants (STPs). In this study, the occurrence and fate of selected human PhACs belonging to different therapeutic classes (non-steroidal anti-inflammatory drugs, lipid regulators, anti-epileptics, antibiotics and beta-blockers) were investigated in a small river in the very south of Sweden. The objectives of the study were to evaluate the impact of a high and rather constant load in sewage influent on downstream concentrations and whether substances that are metabolized to a high degree in humans also show a low persistency in a natural aquatic environment. Water samples were collected from the influent and effluent of the STP, in a series of dammed reservoirs leading to discharge into the Höje River in Sweden, and at several locations in the river downstream of the outfall. After enrichment by solid-phase extraction, the compounds were analyzed using GC-MS (methylated derivatives) or LC-MS/MS. In addition to the targeted pharmaceuticals, GC-MS analysis of the samples revealed the presence of other sewage-related pollutants (triclosan, caffeine, flame-retardants, antioxidants) and these results where included for comparison. Removal efficiencies were calculated in the STP and found to display a wide range with numerous species surviving treatment at greater than half their influent concentrations, including diclofenac, the anti-epileptic carbamazepine, a beta-blocker (propanolol), and antibiotics trimetoprim and sulfamethoxazole. Low removals were also observed for Tris(2-chloroisopropyl)phosphate (flame retardant), BHT-aldehyde (oxidation product of BHT) and synthetic musk (HHCB). The concentrations of chloride (Cl(-)) and boron (B) were used as natural inert tracers to estimate the relative extent of dilution of PhACs measured in the effluent of the STP on concentrations measured further downstream. Based on spatial trends of concentrations (recalculated to reflect a hypothetical scenario with no dilution), ibuprofen, ketoprofen, naproxen and dicofenac were shown to be subject to significant abiotic or biotic transformations or physical sequestration in the river. The beta-blockers atenolol, metoprolol and propanolol, the antibiotics trimetoprim and sulfametoxazole, and carbamazepine demonstrated a high degree of persistence. Fluctuations in the concentration of carbamazepine and gemfibrozil were observed along the series of reservoirs and within the river and are hypothesized to be due to release of parent compound from glucuronides. Several of the investigated substances (metaprolol, propanolol and carbamazepin) that exhibit low excretion rates as parent compounds demonstrate a surprising persistence in the aquatic environment. It is concluded that pharmaceutical substances with a high metabolic rate in humans (low excretion rate) do not necessarily induce a short lifetime in aquatic environments. Results from this study emphasize the need for a broader view on the concept of persistence that accounts for loading rates, in addition to removal mechanisms (e.g., transformation, volatility and physical sequestration by solids), under a variety of spatial and temporal scales.

Adrenergic beta-Antagonists↗
PubMed2005

Colloid filtration theory and the Happel sphere-in-cell model revisited with direct numerical simulation of colloids.

The transport of colloids and bacterial cells through saturated porous media is a complex phenomenon involving many interrelated processes that are often treated via application of classical colloid filtration theory (CFT). This paper presents a numerical investigation of CFT from the Lagrangian perspective, to evaluate the role of some of the classical assumptions underlying the theory and to demonstrate a means to include processes relevant to bacterial transport that were inadequately characterized or neglected in the original formulation, including Brownian diffusion and potentially hysteretic potential functions. The methodology is based on conducting a Lagrangian trajectory analysis within Happel's sphere-in-cell porous media model to obtain the collection efficiency (eta), the frequency at which colloids or bacteria make contact with the solid phase of the porous medium. The Lagrangian framework of our model lends itself to mechanistic modeling of the biological processes that may be important in subsurface bacterial transport. The numerical study presented here focuses on the size range of bacterial colloids and smaller (down to 10 nm). Results of our model runs are in good agreement with the deterministic trajectory analysis of Rajagopalan and Tien (when diffusion is neglected) and in excellent agreement with the analytical solution to the Smoluchowski-Levich approximation of the convective-diffusion equation (when external forces and interception are neglected). Simple addition of our result for the deterministic eta to our result for the Smoluchowski-Levich eta matches the overall Rajagopalan and Tien eta to within 5% error or less for all cases studied. When we simulate diffusion and the deterministic forces together, our results diverge from the Rajagopalan and Tien eta as the particle size decreases, with discrepancies as large as 73%. These results suggest that accurate prediction of eta values for bacteria-sized (and all submicrometer) colloids requires simultaneous consideration of the primary transport mechanisms.

Journal Article↗
PubMed2003

Preliminary assessment of transport processes influencing the penetration of chlorine into wastewater particles and the subsequent inactivation of particle-associated organisms.

The diffusion of a chemical disinfectant into wastewater particles may be viewed as a serial two-step process involving transport through a macroporous network of pathways to micropores that lead into dense cellular regions. Previous research reveals that ultraviolet (UV) light penetration into wastewater particles is limited primarily to macropores, resulting in a residual concentration of targeted organisms in post-disinfected effluents that reflects the number of organisms embedded in the dense cellular regions of particles. Conversely, chlorine was demonstrated as part of this research to penetrate into both the macroporous and microporous network of pathways, implying that the application of chlorine may be designed feasibly to achieve a desired level of inactivation of particle-associated organisms. In the short term, a disinfection model previously developed for UV irradiation may be used to assess the inactivation of particle-associated organisms with chlorine. However, in the long-term, a more rigorous and complete understanding of the transport of chemical disinfectants into particles can be explored utilizing existing mathematical expressions commonly used to model mass transport into porous media. The parameters of interest in this modeling approach include the reaction rate of chlorine with particulate material, the diffusion rate of chlorine within a particle, the mass-transfer rate coefficient across the particle's boundary, and the particle porosity.

Chlorine↗
PubMed2002

Formulation of a soil-pesticide transport model based on a compartmental approach.

A semianalytical soil-pesticide transport model is formulated based on a compartmental approach to determine spatial and temporal variations of pesticide residues across a soil profile. The compartmental model is implemented by drawing an analogy between a series of continuous-flow stirred tank reactors and a soil horizon that consists of multiple perfectly mixed compartments. The analogy is strengthened by exploiting a relation between the compartment series and the conventional convective-dispersive equation (CDE) for vertical transport in the soil. Consequently, the number of compartments in the model formulation is not free, but dictated as a function of transport parameters. The model formulation allows consideration of arbitrary boundary value specifications and also, for some cases, spatially varying initial concentration profiles. Sorption kinetics is represented via a two-site model that involves a linear sorption isotherm and a first-order irreversible sorption or a radial diffusive penetrating model. For these three cases, analysis of the compartmental model allows the resultant concentration profiles to be expressed in terms of the Poisson distribution. When a nonlinear kinetic sorption model is used to simulate the sorption processes, an analytical solution is not found and a numerical approach is required.

Atrazine↗