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Este trabalho apresenta os resultados obtidos no processo de remediação de uma área impactada pelo composto tetracloroeteno através do emprego da tecnologia de oxidação química in situ (ISCO). O teste de bancada realizado em uma amostra de água subterrânea da área de estudo tratada com uma solução de 5% de permanganato de potássio resultou em um percentual de remoção da massa de tetracloroeteno e seus produtos de degradação natural (tricloroeteno, dicloroeteno e cloreto de vinila) superior a 99%. Ao todo, foram injetados em subsuperfície 2950 kg de permanganato de potássio a uma concentração de 6% para o tratamento de 20000 m³ de um aqüífero impactado pelo composto tetracloroeteno e os seus produtos de degradação natural. A injeção de permanganato potássio resultou na destruição de aproximadamente 70% das concentrações de tetracloroeteno e seus produtos de degradação natural na área alvo de remediação dentro de um período de 30 dias após o término da aplicação do oxidante em subsuperfície, comprovando a eficiência do processo de oxidação química in situ para o tratamento de águas subterrâneas impactadas pelo composto tetracloroeteno. / This work presents the results obtained during the remediation process of an area impacted by the compound tetrachloroethene applying the technology of in situ chemical oxidation (ISCO). The bench test performed in a groundwater sample from the study area treated with a 5% potassium permanganate solution resulted in a percentage removal of tetrachloroethene mass and its natural degradation products (trichloroethene, dichloroethene and vinyl chloride) superior than 99%. In total, it was injected in the subsurface 2950 kg of potassium permanganate with a concentration of 6% in order to treat 20000 m³ of an aquifer impacted by the compound tetrachloroethene and its natural degradation products. The potassium permanganate injection resulted in the destruction of approximately 70% of the tetrachloroethene concentration and its natural degradation products in the target area within a period of 30 days after finishing the oxidant application in the subsurface, confirming the efficiency of the in situ chemical oxidation process for treating groundwater impacted by tetrachloroethene.

A study was undertaken to examine the desorption/ iffusion of benzene after simulated ground water remediation in aquifer material of differing carbon content using column experiments and comparing the results to batch experiments and adsorption empirical relationships. It was hypothesized that the organic carbon of the aquifer material will affect desorption/diffusion. Results from the column experiment indicated no significant difference in the increase benzene concentrations after remediation between aquifer materials of differing carbon content, however, a significant increase in benzene concentration was observed for all aquifer material. Fair agreement of retardation factors was observed between empirical relationships and batch and column experiments. However, the desorption phase of the batch experiment showed hysteresis and seemed to differ from the column experiment.

No description available.

A series of bench-scale experiments was carried out to determine the rate and efficiency with which benzene and p-xylene, components of gasoline, could be removed from an unsaturated soil by air stripping. Glass columns, 30 cm in length, were packed with soil and wetted to volumetric moisture contents of 10 and 18 percent. Air saturated with one of the volatile organic compounds (VOCs) was used to load the column. Clean air was used to strip the contaminant from the soil. Benzene and p-xylene concentrations in the soil water and air were reduced four orders of magnitude after a few hours (2-8) of stripping. Benzene was removed faster than p-xylene. Air flow was the rate-limiting step early in the stripping, however slow desorption from the soil became rate-limiting as the stripping progressed. As moisture content increased the rate of removal of both contaminants decreased.

The impact of fire retardant waste on the aquatic environment was investigated at Abbotsford Airport located in the Lower Fraser Valley, in Southwestern British Columbia. The cleaning of fire fighting aircraft results in significant quantities of fire retardant waste being washed into the airport drainage system with subsequent transport to a drainage ditch located in the southwest corner of the Airport Chemical components of the fire retardant likely to be of environmental concern were identified as ammonia, phosphate, and a corrosion inhibitor. Glacial and outwash deposits consisting of sands and gravels comprise the surficial geology of the study area. Hence, the fire retardant waste would have the potential to impact both surface water and groundwater resources. Therefore there was concern due to the extensive use of groundwater in the local area for both drinking and irrigational purposes. The major components of the research design were 1) assessment of the spatial and temporal distribution of fire retardant introduced into the aquatic environment, and 2) overall impact of fire retardant contamination on surface water and groundwater quality. A long term and two short term monitoring programs were designed to determine the rate of transport and distribution of the fire retardant in the aquatic environment Results showed that although the fire retardant was observed to wash through the drainage system into the stream, no measurable impact on surface water quality was recorded during the study period. Fire retardant components which would cause surface water contamination are ammonia, phosphorus, iron and chromium. A significant rise in nitrate-nitrogen concentration was detected in groundwater samples less than a day after fire retardant waste was recorded in measurable quantities in the ditch water. Temporal distribution of fire retardant in the aquatic environment was correlated with the high hydraulic conductivity of the subsurface and specific hydrological events involving heavy precipitation. Results from the laboratory column experiments indicated that components of the Fire retardant were not retained in the soil and would therefore be rapidly leached into groundwater. Surface water quality and groundwater quality results were compared with established water quality standards for drinking water and protection of freshwater aquatic life. On the basis of these standards the fire retardant waste was not found to contribute to degradation of the surface and groundwaters at Abbotsford Airport Overall impact of the fire retardant waste on the aquatic environment at Abbotsford Airport during the study period was not found to be significant The low fire season combined with a change in washing policy resulted in a fewer number of planes being cleaned at Abbotsford Airport during 1983-84. Therefore, the impact on the aquatic environment recorded during this period cannot be considered typical. / Graduate and Postdoctoral Studies / Graduate

This dissertation puts in place a risk-cost-benefit analysis for waste management facilities that explicitly recognizes the adversarial relationship that exists in a regulated market economy between the owner-operator of the facility and the government regulatory agency under whose terms the facility must be licensed. The risk-cost-benefit analysis is set up from the perspective of the owner-operator. It can be used directly by the owner-operator to assess alternative design strategies. It can also be used by the regulatory agency to assess alternative regulatory policies, but only in an indirect manner, by examining the response of an owner-operator to the stimuli of various policies. The objective function is written in terms of a discounted stream of benefits, costs, and risks over an engineering time horizon. Benefits are in terms of revenues for services provided; costs are those of construction and operation of the facility. Risk is defined as the expected cost associated with failure, with failure defined as a groundwater contamination event that violates the licensing requirements set forth by the regulatory agency. Failure requires a breach of the containment structure and contaminant migration through the hydrogeological environment to a compliance surface. Reliability theory is used to estimate the probability of breaching and Monte Carlo finite-element simulations are used to simulate advective contaminant transport. The hydraulic conductivity values in the hydrogeological environment are defined stochastically. The probability of failure is reduced by the presence of a monitoring network established by the owner-operator. The level of reduction in the probability of failure can be calculated from the stochastic contaminant transport simulations. While the framework is quite general, the development in this dissertation is specifically suited for a landfill in which the primary design feature is one or more synthetic liners and in which contamination is brought about by the release of a single, nonreactive species in an advective, steady-state, horizontal flow field. The risk cost benefit analysis is applied to 1) an assessment of the relative worth of alternative containment-construction activities, site-investigation activities, and monitoring activities available to the owner-operator, 2) an assessment of alternative policy options available to the regulatory agency, and 3) two case histories. Sensitivity analyses designed to address the first issue show that the allocation of resources by the owner-operator is sensitive to the stochastic parameters that describe the hydraulic conductivity field at a site. For the cases analyzed, the installation of a dense monitoring network is of less value to the owner-operator than a more conservative containment design. Sensitivity analyses designed to address the second issue suggest that from a regulatory perspective, design standards should be more effective than performance standards in reducing risk, and design specifications on the containment structure should be more effective than those on the monitoring network. Performance bonds posted before construction have a greater potential to influence design than prospective penalties to be imposed at the time of failure. Sitting on low-conductivity deposits is a more effective method of risk reduction than any form of regulatory influence. Results of the case histories indicate that the methodology can be successfully applied at field sites, and that the risks associated with groundwater contamination may be small when compared to the owner-operators' benefits and costs. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Critical water resources, such as groundwater, are undergoing a period of intense and global environmental change, driven by climate change, anthropogenic impacts and exploitation, and perturbations to interactions of fundamental processes that are affected by hydrological, mineralogical and biogeochemical factors. Arsenic contamination is a significant threat to these water resources and the populations who depend on them, yet there are few studies directly linking water quality with changes in hydrology and geochemistry in sediments on varying scales. My research explores environmental variability in hydrology and redox processes that regulate soluble arsenic concentrations at the pore scale (µm to mm), and develops methods of upscaling these mechanistic studies to understand heterogeneity in groundwater arsenic levels and their impacts on public health at larger scales (a couple of meters to hundreds of kilometers). Specifically, my research examines the interaction of redox processes in the Earth’s subsurface that drive the release of arsenic into groundwater. Naturally-occurring, or geogenic, arsenic contamination is the main source of arsenic release into groundwater that affects human health, with possible anthropogenic exacerbation of this natural contamination. Throughout this dissertation, I have developed a suite of data-driven approaches to understand and quantify the highly variable factors that underlie the mechanisms of geogenic arsenic release into groundwater and its migration in the environment. In Chapter 1, I investigate the effects of hydrologic perturbations on formerly uncontaminated aquifers that release arsenic due to increased groundwater pumping in the Red River Delta, Vietnam. To compare the effect of hydrologic processes to measured groundwater arsenic concentrations, I used Monte Carlo simulations in an end-member mixing model and quantified fraction of different recharge sources into an aquifer based on stable water isotopes. I find that changing flow patterns due to groundwater abstraction have increased the extent of arsenic release into groundwater and also changed the location of where arsenic contamination originates. In Chapter 2, I characterize iron mineralogy associated with arsenic release through sampling of sediment cores across a lateral redox gradient in Vietnam with extensive spectroscopy measurements. Through hierarchical cluster analysis on this data set of X-ray absorption spectroscopy (XAS) measurements of borehole cuttings paired with dissolved groundwater measurements, I reveal signatures of iron mineral reduction that could cause or exacerbate arsenic release. This was upscaled to other deltaic aquifers in South and Southeast Asia based on groundwater data to identify aquifers at risk of arsenic release. I showed that the extent of older and previously pristine aquifers that have been contaminated may have been misclassified and thus underrepresented in deltaic aquifers throughout South and Southeast Asia, disrupting the assumption that older and deeper aquifers are oxidized and thus guarded against arsenic release. In Chapter 3, I use process-based reactive transport modeling of a laboratory-scale experiment to mechanistically explain the infiltration of contaminated water into uncontaminated aquifers and find that arsenic contamination cannot be explained by the commonly invoked mechanism of iron reducing bacteria only, but instead relies on sulfate reduction and complexation of aqueous arsenic in solution. The role of sulfate reduction in mobilizing arsenic in groundwater is in stark contrast to and undermines the previous use of sulfate reduction as strategy for arsenic remediation. Finally, in Chapter 4, I quantitatively examine the processes that release arsenic across different arsenic-impacted aquifers, based on the relationships between redox status of iron and arsenic mineralogy and groundwater concentrations. Synthesis of X-ray absorption spectra of the deltaic aquifers of Southeast Asia and the glacial aquifer system in the Northern United States shows that arsenic release occurs in similar geochemical environments in both systems, and is highly generalizable via statistical and unsupervised machine learning approaches. This dissertation demonstrates that common assumptions behind geogenic arsenic release must be tested: from which aquifers are low in arsenic to the commonly assumed mechanism of arsenic release by iron reducing bacteria. These findings also reveal that the extent of anthropogenic impact on geogenic arsenic contamination is detectable: from changes in recharge sources to changes in mineralogy that affect arsenic concentrations and human health. The next step is to use these data driven and machine learning approaches to quantify the vulnerability of affected aquifers, to mitigate the risk of those currently reliant on contaminated groundwater, to reduce the risks of future contamination and, ultimately, to protect human health.

This study employed geographic information systems (GIS) technology to evaluate the vulnerability of groundwater to pesticide pollution. The study area included three provinces (namely, Kanchana Buri, Ratcha Buri, and Suphan Buri) located in the western part of central Thailand. Factors used for this purpose were soil texture, percent slope, primary land use, well depth, and monthly variance of rainfall. These factors were reclassified to a common scale showing potential to cause groundwater contamination by pesticides. This scale ranged from 5 to 1 which means high to low pollution potential. Also, each factor was assigned a weight indicating its influence on the movement of pesticides to groundwater. Well depth, the most important factor in this study, had the highest weight of 0.60 while each of the remaining factors had an equal weight of 0.10. These factors were superimposed by a method called “arithmetic overlay” to yield a composite vulnerability map of the study area. Maps showing relative vulnerability of groundwater to contamination by pesticides were produced. Each of them represented the degree of susceptibility of groundwater to be polluted by the following pesticides: 2,4-D, atrazine, carbofuran, dicofol, endosulfan, dieldrin & aldrin, endrin, heptachlor & heptachlor epoxide, total BHC, and total DDT. These maps were compared to groundwater quality data derived from actual observations. However, only the vulnerability maps of atrazine, endosulfan, total BHC, and heptachlor & heptachlor epoxide showed the best approximation to actual data. It was found that about 7 to 8%, 83 to 88% and 4.9 to 8.7% of the study area were highly, moderately, and lowly susceptible to pesticide pollution in groundwater, respectively. In this study a vulnerability model was developed, which is expressed as follow: V = 0.60CW + 0.10CS + 0.10CR + 0.10CL + 0.10CSL. Its function is to calculate a vulnerability score for a certain area. The factor “V” in the model represents the vulnerability score of a certain area, whereas CW, CS, CR, CL, and CSL represent the values or classes assigned to well depth, soil texture, monthly variance of rainfall, primary land use, and percent slope in that area.