Biogeochemical reactions and vadose zone transport, in particular gas phasetransport, are inherently coupled processes. To explore feedback mechanisms between these processes in a quantitative manner, multicomponent gas diffusion and advection are implemented into an existing reactive transport model that includes a full suite of geochemical reactions. Multicomponent gas diffusion is described based on the Dusty Gas Model, which provides the most generally applicable description for gas diffusion.Gas advection is described by Darcy's Law, which in the current formulation, is directly substituted into the transport equations. The model is used to investigate the interactions between geochemical reactions and transport processes with an emphasis to quantify reaction-induced gas migration in the vadose zone. Simulations of pyrite oxidation in mine tailings, gas attenuation in partially saturated landfill soil covers, and methane production and oxidation in aquifers contaminated by organic compounds demonstrate how biogeochemical reactions drive diffusive and advective transport of reactive and non-reactive gases. Pyrite oxidation in mine tailings causes a pressure reduction in the reaction zone and drives advective gas flow into the sediment column, enhancing the oxidation process. Release of carbondioxide by carbonate mineral dissolution partly offsets pressure reduction, and illustrates the role of water-rock interaction on gas transport. Microbially mediated methane oxidation in landfill covers reduces the existing upward pressure gradient, there by decreasing the contribution of advective methane emissions to the atmosphere and enhancing the net flux of atmospheric oxygen into the soil column. At an oil spill site, both generation of CH⁴ in the methanogenic zone and oxidation of CH⁴ in the methanotrophic zone contribute to drive advective and diffusive fluxes. The model confirmed that non-reactive gases tend to accumulate in zones of gas consumption and become depleted in zones of gas production. In most cases, the model was able to quantify existing conceptual models, but also proved useful to identify data gaps, sensitivity, and inconsistencies in conceptual models. The formulation of the model is general and can be applied to other vadose zone systems in which reaction-induced gas transport is of importance.

Arsenic contamination of groundwater has been reported in over 20 countries worldwide where tens of millions of people are being exposed to excessive levels of arsenic in their drinking water, especially in countries of the Asian region, Bangladesh in particular. This study focusses on analytical techniques currently used for the estimation and speciation of arsenic in aqueous phase (soil and water) and in plant tissues; the uptake of arsenic by two commonly used vegetable crops (amaranth and silverbeet) using solution culture and pot culture studies; speciation-toxicity relationship of arsenic to plants; the nature of arsenic species in plant tissue and Bangladesh groundwater samples; and the effect of iron (Fe) on arsenic (As) uptake by plants and animals. / Thesis (PhD)--University of South Australia, 2006.

Thesis (MApSc(EnvironmentManagement))--University of South Australia, 2002.

No description available.

Arsenic contamination of groundwater has been reported in over 20 countries worldwide where tens of millions of people are being exposed to excessive levels of arsenic in their drinking water, especially in countries of the Asian region, Bangladesh in particular. This study focusses on analytical techniques currently used for the estimation and speciation of arsenic in aqueous phase (soil and water) and in plant tissues; the uptake of arsenic by two commonly used vegetable crops (amaranth and silverbeet) using solution culture and pot culture studies; speciation-toxicity relationship of arsenic to plants; the nature of arsenic species in plant tissue and Bangladesh groundwater samples; and the effect of iron (Fe) on arsenic (As) uptake by plants and animals. / Thesis (PhD)--University of South Australia, 2006.

In the Wairau Valley 40 km southwest of Blenheim, elevated salinities are present in the groundwater below a depth of approximately 15 m, to the north of the Wairau Fault. Saline water is present very close to the surface between the Southern Hills and the Wairau Fault. Highest concentrations are located in well O28/w/0219 with total dissolved solids concentrations approximately 31,000 mg/L. Only a few wells in the study area have intercepted the saline groundwater. A report by Taylor (2003) has identified the groundwater below the Holocene terrace surface is recharged from Southern Hills runoff, however the Wairau Fault has a significant impact on the groundwater flow on the south bank acting as a semi-permeable barrier to groundwater flow from the southern Hills streams identified by several spring which emerge on the fault trace. The scope of this investigation was to identify the extent of the saline groundwater in the Homelands area and to attempt to define the origin of the highly saline groundwater. Furthermore, to define the groundwater flow path below the upper terrace surface to recharge the Wairau Valley Aquifer. The Multi-Electrode Resistivity technique was used to define the extent of the saline groundwater. This shows the saline groundwater is ubiquitous at depth in the study area. The depth to the freshwater/saline water interface varies laterally in the resistivity profiles. A major control on the presence of the groundwater salinity is considered to be the permeability of the gravel. Gravels with a higher permeability are probably washed of any residual salinity that may have been present in the past. Investigations into the origins of the saline groundwater were completed using stable isotope analysis (¹⁸O, ²H, and ¹³C), hydrochemistry and age dating techniques (³H and ¹⁴C). Due to the complex chemistry a single source could not be identified, however two methods were identified as the most likely. This was evaporative concentration of fresh water in the Wairau Valley, or the upward migration from the Wairau Fault of formation water probably of seawater origin. The stable isotope data fits best with an evaporative concentration of freshwater within the Wairau Valley, however, ratios of chemical constituents are very similar to other formation waters found in other parts of the world. Stream gauging of streams on the south bank show no significant water loss in the reaches north of the Wairau Fault. Therefore, recharge must be crossing the Fault trace as groundwater. Boundary Creek looses all of its surface flow for most of the year upon reaching the valley floor. Bounday Creek has washed out sections of the Wairau Fault and Major terrace riser between Wr 1 and Wr 2 terrace surfaces. It is proposed that groundwater flowing in the gravels reworked by Boundary Creek is the major recharge source for the Wairau Valley Aquifer.

Australia has a widespread and significant incidence of land and water contamination, which can lead to economic, trade, ecosystem and human health impacts. Over the past 20 years the problem has been growing and there is also a growing realization of the extent of the problem. The installation of monitoring network is pivotal for understanding the groundwater hydraulics and subsurface contamination. At the same time the process is expensive. The systematic study of the subsurface system with the available scanty data regarding the groundwater flow and the subsurface contamination can help us to arrive at the optimum monitoring network design for effective site characterization.

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

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

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