The increasing use of ethanol as a gasoline additive has raised concerns over the potential impacts ethanol might have on groundwater contamination. In North America, 10% ethanol is commonly being added to gasoline (termed E10). Ethanol is usually denaturated with gasoline compounds before being transported; consequently E95 (95% ethanol) mixtures are also common. Therefore, spills with compositions ranging from E10 to E95 can be anticipated. The compounds of main concern associated with gasoline spills are benzene, toluene, ethylbenzene and xylenes (BTEX), trimethylbenzenes (TMBs) and naphthalene, due to their higher mobility and potential risks to human health. Ethanol is thought to increase mobility of the NAPL, create higher hydrocarbon concentrations in groundwater due to cosolvency, and decrease the rate of gasoline hydrocarbon biodegradation, with consequent increase in the length of the dissolved plumes. The objective of this research was to improve the knowledge about ethanol fate in the subsurface and the impacts it might have on the fate of gasoline compounds. To investigate that, laboratory experiments and controlled field tests supported by numerical modeling were conducted. To evaluate the impact of ethanol on dissolved hydrocarbon plumes, data from a controlled field test were evaluated using a numerical model. The mass discharge of BTEX, TMB and naphthalene from three sources (E0, E10 and E95) emplaced below the water table was compared to simulation results obtained in the numerical model BIONAPL/3D. It was shown that if ethanol fuel mixtures get below the water table, ethanol is dissolved and travels downgradient fast, in a short slug. Mass discharge from the E0 and E10 sources had similar hydrocarbon decay rates, indicating that ethanol from E10 had no impact on hydrocarbon degradation. In contrast, the estimated hydrocarbon decay rates were significantly lower when the source was E95. The aquifer did not have enough oxygen to support the mass loss observed assuming complete mineralization. Assuming a heterogeneous distribution of hydraulic conductivity did little to overcome this discrepancy. A better match between the numerical model and the field data was obtained assuming partial degradation of hydrocarbons to intermediate compounds, with consequent less demand for oxygen. Besides depending on the concentration of ethanol in the groundwater, the impact of ethanol on hydrocarbon degradation appears to be highly dependent on the aquifer conditions, such as availability of electron acceptors and adaptation of the microbial community. Another concern related to ethanol biodegradation is formation of explosive levels of methane. In this study, methane δ13C from toluene and ethanol as substrates was evaluated in microcosm tests. It was shown that methane is enriched in δ13C when ethanol is the substrate. Ethanol derived methane δ13C is in the range of -20‰ to 30‰, while methane from gasoline is around -55‰. The different ranges of δ13C allow it to be used as a tool to identify methane’s origin. This tool was applied to seven ethanol-gasoline contaminated sites. Methane origin could be clearly distinguished in five of the seven sites, while in the other two sites methane appears to have been produced from both ethanol and gasoline. Both ethanol and gasoline were identified as the source of methane in hazardous concentrations. The behaviour of ethanol fuels in the unsaturated zone was evaluated in 2-dimensional (2-D) lab tests and in a controlled field test. In the 2-D lab tests, dyed gasoline and ethanol were injected in the unsaturated zone simulated in a transparent plexiglass box packed with glass beads. Tests were performed under both static conditions and with horizontal groundwater flow. It was confirmed that some ethanol can be retained in the unsaturated zone pore water. However, most of the ethanol went through the unsaturated zone and reached the pre-existing gasoline pool. Ethanol displaced the NAPL to deeper positions, and it was shown that for large ethanol releases much of the gasoline can be displaced to below the water table. The ethanol that reaches the capillary fringe was shown to travel downgradient rapidly at the top of the capillary fringe, while ethanol was also retained in the unsaturated zone. The behaviour of ethanol fuel spills was further evaluated in a controlled field test. 200L of E10 containing around 5% MTBE was released into the unsaturated zone. Groundwater concentrations of ethanol, MTBE, BTEX, TMB and naphthalene above and below the water table were monitored downgradient of the source in multilevel wells. Lab tests were performed to evaluate the applicability of these samplers for volatile organic compounds. It was shown that volatilization losses might be significant when bubbles formation in the sampling line could not be avoided. A method for losses estimation and correction of the concentrations was developed. Concentrations in the source zone were measured in soil samples. Despite the thin (35 cm) unsaturated zone at the site, most of the ethanol was retained in the unsaturated zone pore water, above the capillary fringe. Being in zones of low effective hydraulic conductivity, ethanol was not transported downgradient, and remained in the unsaturated zone for more than 100 days. Ethanol mass discharge was much lower than would be anticipated based solely on the ethanol fraction in the gasoline and on its solubility. Oscillations in the water table, particularly when a shallow position was maintained for prolonged periods, flushed some ethanol to zones with high water saturation, where horizontal transport occurred. The ethanol that reaches the saturated zone appears in the downgradient wells as a slug, with relatively low concentrations. No effect of ethanol on gasoline hydrocarbons was observed, a consequence of most of the ethanol being retained in the unsaturated zone. In summary, spills of ethanol fuels might have two different outcomes, depending on whether most of the ethanol is retained in the unsaturated zone or if most reaches the capillary fringe and the saturated zone. The relation between the ethanol volume spilled and the retention capacity of the unsaturated zone will control the spill behaviour. The volume of ethanol that can be retained in the unsaturated zone is a function of the volume of water that is contacted by the infiltrating NAPL. Therefore, the type of soil, heterogeneities, depth to the water table and area of the spill will be determinant factors. If a relatively large volume of ethanol reaches the capillary fringe, ethanol will travel rapidly in the groundwater possibly in high concentrations, potentially enhancing dissolved hydrocarbon plumes. However, when most of the ethanol is retained in the unsaturated zone, it will likely be detected downgradient only in low concentration, and in pulses spread in time. In this scenario, impact on hydrocarbon plumes will be minor.

Water quality degradation is the foremost environmental issue faced by the mining industry. Negative impacts on water quality are commonly associated with unmitigated drainage emanating from sulfide-bearing mine waste deposits. These impacts stem from the liberation of acidity, sulfate, metals (e.g. Fe, Ni, Cu, Zn and Pb), and trace elements (e.g. Co, As, Cd, Sb and Tl) during the oxidation of sulfide minerals. Drainage at operational mines is commonly treated using techniques such as chemical oxidation and acid neutralization, which can succeed in achieving regulatory discharge guidelines. However, active treatment techniques are commonly burdened by high capital and operating costs. The development of passive technologies for treatment of mine drainage, which promote sulfate reduction, metal-sulfide precipitation and alkalinity production, therefore present a cost-effective alternative for managing mine drainage quality. This thesis describes laboratory and field evaluations of techniques for passive in situ treatment of acidic and neutral mine waters. Laboratory batch experiments evaluated the treatment of acid mine drainage (AMD) with mixtures of organic carbon and zero-valent iron (ZVI) for use in permeable reactive barriers (PRBs). Modest increases in sulfate-reduction rates up to 15 % were achieved by amending organic carbon mixtures with 5 to 10 % (dry wt.) ZVI. Reactive mixtures containing organic carbon supported growth of sulfate-reducing bacteria (SRB) and facilitated removal of Fe, Zn, Cd, Ni, Co and Pb. However, organic carbon was necessary to support SRB growth and sulfate reduction. Removal of Zn, Cd, Ni, Co and Pb in the absence of organic carbon is attributed to sorption and (co)precipitation reactions at the ZVI surface. Scanning electron microscopy (SEM) and X-ray absorption near-edge structure (XANES) spectroscopy confirmed the presence of secondary Fe-sulfides in mixtures containing organic carbon. The dominant reaction product in these mixtures was identified as disordered mackinawite [Fe1+xS]. The addition of ZVI to organic carbon enhanced AMD treatment over the duration of this experiment; however, long-term evaluation is required to identify optimal reactive mixtures. Field-based investigations into passive management of near-neutral pH tailings pore-water were carried out at the Greens Creek mine, located near Juneau, Alaska, USA. These studies focused on delineation of mechanisms controlling tailings pore-water chemistry, and a evaluation of the effectiveness of organic carbon amendment of tailings for passive in situ management of pore-water quality. Results demonstrate that sulfide-mineral oxidation and carbonate dissolution are the primary influences on tailings pore-water composition. Pyrite [FeS2] accounted for < 20 to > 35 wt. % of the tailings mineral assemblage, whereas dolomite [CaMg(CO3)2] and calcite [CaCO3] were present at ≤ 30 and 3 wt. %, respectively. The sulfide-mineral assemblage was dominated by pyrite; however, sphalerite [(Zn,Fe)S] and galena [PbS] were commonly observed, and tetrahedrite [(Fe,Zn,Cu,Ag)12Sb4S13], arsenopyrite [FeAsS], and chalcopyrite [CuFeS2] were present in lesser amounts. Geochemical analysis of tailings core samples generally agreed with mineralogical data. The occurrence of Cd, Cr, Co, Mo, Ni, Se, and Tl is attributed to their occurrence as impurities in primary sulfide phases. Most probable number (MPN) populations of neutrophilic sulfur-oxidizing bacteria (nSOB) and SRB were elevated at several locations within the tailings deposit. Near-neutral pH conditions dominated; however, elevated concentrations of dissolved SO4, S2O3, Fe, Zn, As, Sb, and Tl were observed within and below the oxidation zone. Field-scale experiments conducted over four years evaluated passive in situ treatment of pore-water by amending unoxidized tailings with 5 and 10 vol. % organic carbon. Field-scale cells were constructed to evaluate amendments containing differing mixtures of peat, dried spent brewing grain (SBG), and municipal biosolids (MB). Organic carbon amendment of the tailings supported the development of conditions favorable to sulfate reduction. Decreases in aqueous SO4 concentrations were observed in three cells amended with mixtures of peat, SBG, and MB. Removal of SO4 was generally accompanied by H2S production, enrichment in 34S-SO4, and increased SRB populations. Undersaturation of pore-water with respect to gypsum was observed. Sulfate reduction was sustained for the duration of the experiment in cells amended with 5 vol. % peat + SBG and 10 vol. % peat + SBG + MB. The addition of organic carbon also supported reductive dissolution of Fe(III) (oxy)hydroxides and mobilization of Fe and As. The largest increases in aqueous Fe and As concentrations were observed in cells amended with MB. Subsequent decreases in Fe and As concentrations were observed under sulfate-reducing conditions. Attenuation of Zn, Sb, and Tl accompanied SO4 removal. Mineralogical examination by SEM revealed the presence of secondary Zn-S and Fe-S precipitates on surfaces of organic carbon particles, and carbonate and aluminosilicate grains. This study demonstrates that amendment of tailings with a small and dispersed mass of organic carbon has potential to improve the quality of tailings pore water.

The ability of supersaturated water injection (SWI) to recover non-aqueous phase liquids (NAPLs) was studied at the field scale as part of an ongoing program to evaluate its applicability to groundwater remediation. SWI uses Gas inFusionTM technology to efficiently dissolve gases into liquids at elevated pressures. SWI has been shown to both volatilize and mobilize residual NAPL ganglia (Li, 2004). During SWI pressurized water containing high concentrations of CO2 is injected into the subsurface below the zone of contamination. Once the injected water is in the aquifer the pressure drops substantially and the concentration of CO2 is no longer in equilibrium with the water and as a result CO2 bubbles nucleate. These bubbles then migrate upwards through the contaminated zone towards the water table. As they move they come into contact with residual NAPL ganglia and they either volatilize this NAPL, resulting in a bubble comprised of CO2 and gaseous NAPL, or mobilize this NAPL, resulting in a film of NAPL surrounding the bubble. In either case the bubbles continue to rise until they reach the water table at which point they are removed by a dual phase extraction system. In this work, a known amount of NAPL was emplaced below the water table at residual concentrations to represent a residual source of weathered gasoline. The source was created in a hydraulically isolated cell in an unconfined sand aquifer at CFB Borden, Ontario. After the source was emplaced SWI was used to remove as much of the contaminant mass as possible in 22.25 days of operation over three months. The goal of this project was to determine if SWI was capable of removing residual NAPL at a field site. It was successful in removing volatile NAPL but not non-volatile NAPL. 64% of the volatile compounds were removed but contaminant mass was still being removed when the system was shut down so with continued operation more mass would have been removed. There is no way of knowing how much more would have been removed had the project continued. These results indicate that continued development of the technology is warranted.

Groundwater flow in the capillary fringe is rarely measured during hydrogeological studies because of the difficulties associated with investigating this region. Previous research using a point velocity probe (PVP) to investigate groundwater velocity below the water table suggested that the PVP may also be capable of measuring groundwater velocity within the capillary fringe. The earlier PVP was redesigned for this study to allow for groundwater velocity data to be collected remotely. Using this system, groundwater velocity in the capillary fringe was investigated under field and laboratory conditions. Field experiments to investigate horizontal flow in the capillary fringe were conducted either by collecting vertical velocity profiles across the water table, or by holding the probe stationary and allowing seasonal recharge to move the capillary fringe and water table past the probe. Laboratory experiments were conducted in a controlled flow tank that simulated regions of an aquifer up to 85 cm above the water table. The redesigned PVP performed well as a remote system and provided velocity measurements up to 12 cm above the water table under field conditions. These values were consistent with those measured below the water table. In the laboratory, under conditions of drainage, groundwater velocity measurements in the capillary fringe consistent with values below the water table were measured up to 44 cm above the water table. The ability to measure horizontal flow of groundwater in the capillary fringe may open up new avenues for research in the study of contaminant transport in phreatic aquifers.

Since the advent of the industrial era atmospheric concentrations of greenhouse gases have been on the rise leading to increasing global mean temperatures. Through increasing temperatures and changes to distributions of precipitation, climate change will intensify the hydrologic cycle which will directly impact surface water sources while the impacts to groundwater are reflected through changes in recharge to the water table. The IPCC (2001) reports that limited investigations have been conducted regarding the impacts of climate change to groundwater resources. The complexity of evaluating the hydrologic impacts of climate change requires the use of a numerical model. This thesis investigates the state of the science of conjunctive surface-subsurface water modeling with the aim of determining a suitable approach for conducting long-term transient simulations at the watershed scale. As a result of this investigation, a coupled modeling approach is adopted using HELP3 to simulate surface and vadose zone processes and HydroSphere to simulate saturated flow of groundwater. This approach is applied to the Alder Creek Watershed, which is a subwatershed of the Grand River Watershed and located near Kitchener-Waterloo, Ontario. The Alder Creek Watershed is a suitable case study for the evaluation of climate change scenarios as it has been well characterized from previous studies and it is relatively small in size. Two contrasting scenarios of climate change (i.e., drier and wetter futures) are evaluated relative to a reference scenario that is based on the historical climatic record of the region. The simulation results show a strong impact upon the timing of hydrologic processes, shifting the spring snow melt to earlier in the year leading to an overall decrease in runoff and increase in infiltration for both drier and wetter future climate scenarios. Both climate change scenarios showed a marked increase to overall evapotranspiration which is most pronounced in the summer months. The impacts to groundwater are more subdued relative to surface water. This is attributed to the climate forcing perturbations being attenuated by the shift of the spring snow melt and the transient storage effects of the vadose zone, which can be significant given the hummocky terrain of the region. The simulation results show a small overall rise of groundwater elevations resulting from the simulated increase in infiltration for both climate change scenarios.

To improve capabilities for understanding and predicting contaminant migration in fractured rock there is need for better field methods to identify the fractures that have active groundwater flow. Current methods have limitations, for example, borehole geophysical imaging, such as acoustic and optical televiewing, identifies fractures appearing on borehole walls but cannot sense groundwater flow. Borehole hydraulic tests determine the transmissivity of fractured zones under conditions altered by the presence of the borehole and its testing and not under natural flow conditions. The natural flow conditions are important because they govern contaminant transport in the whole flow system. Furthermore, conventional tracer tests are used to identify flow in fractures, but these too are typically done under imposed rather than ambient (natural) hydraulic conditions. High resolution fluid temperature logging in lined boreholes can identify some of the hydraulically active fractures, but this method lacks the sensitivity needed to indicate ambient flow in each individual fracture. This thesis presents a new method aimed at determining whether or not any particular fracture targeted for borehole measurement has substantial ambient flow. This method involves a device lowered into an open hole to a target zone where a packer is inflated. This packer has a water-flow-sensitive dyed cotton fabric wrapped around its exterior so that when the packer is inflated, it not only seals the borehole but presses the cotton fabric against the borehole wall. This set-up causes the exact location of hydraulically active fractures at the borehole wall to show up as imprints marked on the fabric. When viewed under black light, individual fracture markings can be seen, and the distribution of the hydraulically active fractures is identified. For this new method, a prototype system was developed for use in 10cm diameter wells and was tested first in a conventional slotted well screen in the laboratory and then in a simulated fracture (slotted) PVC pipe installed in a sandy aquifer where groundwater flow rates are well understood. From a large number of fabric/dye combinations tested in the laboratory, it was found that cotton dyed with a particular food grade additive provides the best fracture markings by far. The prototype system uses the double-acting packer system originally developed by Solinst Canada, and this novel packer design provides ease of use and flexibility for configuring multiple packers on a single pipe. This prototype system is now ready for the first field trials in a fractured dolostone borehole in Guelph, ON. While the ability of the device to identify active fractures as effectively as it has in the slotted casing trials may be reduced by the interaction of the dye with the porous rock matrix, it is anticipated that this new system for identifying hydraulically active fractures under resealed borehole flow conditions (resealing brings flow back to ambient conditions) will be useful in its own right in fractured rock investigations. This device also represents the first step in the creation of a more elaborate device to measure both the groundwater flux and the contaminant flux within plumes in fractured rock.

The increased use of both organic and synthetic fertilizers on agricultural land has lead to rising groundwater nitrate concentrations in some areas of southern Ontario. This has occurred at the Thornton Well Field in Oxford County, likely as a result of impacts from legacy agricultural activities in the area. In an attempt to mitigate the impact on water quality within the well field, the County purchased some of the agricultural land in the vicinity of the well field in 2001 with plans to reduce nutrient loading through the implementation of Beneficial Management Practices (BMPs). Since the initiation of the BMPs, the nitrogen application rates within the study site were reduced by 20 to 100% relative to historical rates. The objectives of this study were to provide a unique, five year data set which can assist in BMP development and provide direction for regional scale agricultural policy; evaluate the nitrate mass flux at numerous locations through the unsaturated zone beneath a BMP-activated agricultural field within a complex moraine environment; develop and compare various methods to upscale point measurements of mass flux to mass loading (t N03-N/yr) at the field and regional scale; evaluate standardized methods of assessing aquifer vulnerability and compare results within the context of non-point source agricultural contaminants at the field and regional scale; and determine whether monitoring water levels and temperature within monitoring wells is able to aid in evaluating vulnerability to surface contaminants. Information collected over two years was combined with data gathered by former researchers at the field site to create a unique and extensive data set. Nineteen new monitoring wells, including two Continuous Multilevel Tubes (CMT), were installed to further develop the geological conceptual model and identify crucial discontinuities in the aquitard units. This network was devised and installed by a team of hydrogeologists. Eight geologically and topographically diverse monitoring locations or “stations” had been previously established and monitored by Bekeris (2007) to track changes in soil nitrate mass within the unsaturated zone through successive geologic coring. This study involved the selection of seven new locations that were predicted to behave similarly to one of the original eight stations in order to assess the predictive capability of scaling up point measurements. The upscaling criteria were based primarily on near surface geology, topography and field observations, with the former being determined as exerting the greatest influence on the results. Recharge rates estimates were combined with unsaturated zone soil nitrate data obtained from geologic coring events to produce nitrate mass flux estimates. Four methods of scaling up point estimates of mass flux made at fourteen of the stations to produce mass loading estimates across the whole field site were compared. The best method displayed nitrate mass loading having decreased within Parcel B from 6.77 t/yr in May 2006 to 2.55 t/yr in May 2008 resulting in a total mass reduction rate of 4.20 t/yr or 62 % which verifies the effectiveness of the BMPs. This corresponds well with the 46% decrease in applied nitrogen associated with the BMP. Groundwater quality measured using standard monitoring wells with long screens indicated that nitrate concentrations have ceased to increase, while groundwater taken from the discrete sampling ports of the CMT wells shows significantly lower concentrations of nitrate within the ports located closer to the water table. This further validates the success of the BMPs but suggests that there is a long lag time between BMP implementation and the flushing of deeper aquifer zones with cleaner, recharging water. Despite the decrease in applied nitrogen, crop yields have remained at or above historical values. Three commonly applied vulnerability assessment methods including the Aquifer Vulnerability Index (AVI), Intrinsic Susceptibility Index (ISI) and Surface to Aquifer Advection Time (SAAT) were utilized to rank the vulnerability of the Thornton Well Field to surface contaminants. The results highlighted how complex hydrogeology may result in inconsistent rankings of vulnerability by each of the methods. The results from analyzing temperature and pressure data collected from pressure transducers within wells across the site suggest that these data can verify and improve the results from standardized vulnerability assessment techniques, especially during highly vulnerable snow melt events.

The increasing use of ethanol as a gasoline additive has raised concerns over the potential impacts ethanol might have on groundwater contamination. In North America, 10% ethanol is commonly being added to gasoline (termed E10). Ethanol is usually denaturated with gasoline compounds before being transported; consequently E95 (95% ethanol) mixtures are also common. Therefore, spills with compositions ranging from E10 to E95 can be anticipated. The compounds of main concern associated with gasoline spills are benzene, toluene, ethylbenzene and xylenes (BTEX), trimethylbenzenes (TMBs) and naphthalene, due to their higher mobility and potential risks to human health. Ethanol is thought to increase mobility of the NAPL, create higher hydrocarbon concentrations in groundwater due to cosolvency, and decrease the rate of gasoline hydrocarbon biodegradation, with consequent increase in the length of the dissolved plumes. The objective of this research was to improve the knowledge about ethanol fate in the subsurface and the impacts it might have on the fate of gasoline compounds. To investigate that, laboratory experiments and controlled field tests supported by numerical modeling were conducted. To evaluate the impact of ethanol on dissolved hydrocarbon plumes, data from a controlled field test were evaluated using a numerical model. The mass discharge of BTEX, TMB and naphthalene from three sources (E0, E10 and E95) emplaced below the water table was compared to simulation results obtained in the numerical model BIONAPL/3D. It was shown that if ethanol fuel mixtures get below the water table, ethanol is dissolved and travels downgradient fast, in a short slug. Mass discharge from the E0 and E10 sources had similar hydrocarbon decay rates, indicating that ethanol from E10 had no impact on hydrocarbon degradation. In contrast, the estimated hydrocarbon decay rates were significantly lower when the source was E95. The aquifer did not have enough oxygen to support the mass loss observed assuming complete mineralization. Assuming a heterogeneous distribution of hydraulic conductivity did little to overcome this discrepancy. A better match between the numerical model and the field data was obtained assuming partial degradation of hydrocarbons to intermediate compounds, with consequent less demand for oxygen. Besides depending on the concentration of ethanol in the groundwater, the impact of ethanol on hydrocarbon degradation appears to be highly dependent on the aquifer conditions, such as availability of electron acceptors and adaptation of the microbial community. Another concern related to ethanol biodegradation is formation of explosive levels of methane. In this study, methane δ13C from toluene and ethanol as substrates was evaluated in microcosm tests. It was shown that methane is enriched in δ13C when ethanol is the substrate. Ethanol derived methane δ13C is in the range of -20‰ to 30‰, while methane from gasoline is around -55‰. The different ranges of δ13C allow it to be used as a tool to identify methane’s origin. This tool was applied to seven ethanol-gasoline contaminated sites. Methane origin could be clearly distinguished in five of the seven sites, while in the other two sites methane appears to have been produced from both ethanol and gasoline. Both ethanol and gasoline were identified as the source of methane in hazardous concentrations. The behaviour of ethanol fuels in the unsaturated zone was evaluated in 2-dimensional (2-D) lab tests and in a controlled field test. In the 2-D lab tests, dyed gasoline and ethanol were injected in the unsaturated zone simulated in a transparent plexiglass box packed with glass beads. Tests were performed under both static conditions and with horizontal groundwater flow. It was confirmed that some ethanol can be retained in the unsaturated zone pore water. However, most of the ethanol went through the unsaturated zone and reached the pre-existing gasoline pool. Ethanol displaced the NAPL to deeper positions, and it was shown that for large ethanol releases much of the gasoline can be displaced to below the water table. The ethanol that reaches the capillary fringe was shown to travel downgradient rapidly at the top of the capillary fringe, while ethanol was also retained in the unsaturated zone. The behaviour of ethanol fuel spills was further evaluated in a controlled field test. 200L of E10 containing around 5% MTBE was released into the unsaturated zone. Groundwater concentrations of ethanol, MTBE, BTEX, TMB and naphthalene above and below the water table were monitored downgradient of the source in multilevel wells. Lab tests were performed to evaluate the applicability of these samplers for volatile organic compounds. It was shown that volatilization losses might be significant when bubbles formation in the sampling line could not be avoided. A method for losses estimation and correction of the concentrations was developed. Concentrations in the source zone were measured in soil samples. Despite the thin (35 cm) unsaturated zone at the site, most of the ethanol was retained in the unsaturated zone pore water, above the capillary fringe. Being in zones of low effective hydraulic conductivity, ethanol was not transported downgradient, and remained in the unsaturated zone for more than 100 days. Ethanol mass discharge was much lower than would be anticipated based solely on the ethanol fraction in the gasoline and on its solubility. Oscillations in the water table, particularly when a shallow position was maintained for prolonged periods, flushed some ethanol to zones with high water saturation, where horizontal transport occurred. The ethanol that reaches the saturated zone appears in the downgradient wells as a slug, with relatively low concentrations. No effect of ethanol on gasoline hydrocarbons was observed, a consequence of most of the ethanol being retained in the unsaturated zone. In summary, spills of ethanol fuels might have two different outcomes, depending on whether most of the ethanol is retained in the unsaturated zone or if most reaches the capillary fringe and the saturated zone. The relation between the ethanol volume spilled and the retention capacity of the unsaturated zone will control the spill behaviour. The volume of ethanol that can be retained in the unsaturated zone is a function of the volume of water that is contacted by the infiltrating NAPL. Therefore, the type of soil, heterogeneities, depth to the water table and area of the spill will be determinant factors. If a relatively large volume of ethanol reaches the capillary fringe, ethanol will travel rapidly in the groundwater possibly in high concentrations, potentially enhancing dissolved hydrocarbon plumes. However, when most of the ethanol is retained in the unsaturated zone, it will likely be detected downgradient only in low concentration, and in pulses spread in time. In this scenario, impact on hydrocarbon plumes will be minor.

Water quality degradation is the foremost environmental issue faced by the mining industry. Negative impacts on water quality are commonly associated with unmitigated drainage emanating from sulfide-bearing mine waste deposits. These impacts stem from the liberation of acidity, sulfate, metals (e.g. Fe, Ni, Cu, Zn and Pb), and trace elements (e.g. Co, As, Cd, Sb and Tl) during the oxidation of sulfide minerals. Drainage at operational mines is commonly treated using techniques such as chemical oxidation and acid neutralization, which can succeed in achieving regulatory discharge guidelines. However, active treatment techniques are commonly burdened by high capital and operating costs. The development of passive technologies for treatment of mine drainage, which promote sulfate reduction, metal-sulfide precipitation and alkalinity production, therefore present a cost-effective alternative for managing mine drainage quality. This thesis describes laboratory and field evaluations of techniques for passive in situ treatment of acidic and neutral mine waters. Laboratory batch experiments evaluated the treatment of acid mine drainage (AMD) with mixtures of organic carbon and zero-valent iron (ZVI) for use in permeable reactive barriers (PRBs). Modest increases in sulfate-reduction rates up to 15 % were achieved by amending organic carbon mixtures with 5 to 10 % (dry wt.) ZVI. Reactive mixtures containing organic carbon supported growth of sulfate-reducing bacteria (SRB) and facilitated removal of Fe, Zn, Cd, Ni, Co and Pb. However, organic carbon was necessary to support SRB growth and sulfate reduction. Removal of Zn, Cd, Ni, Co and Pb in the absence of organic carbon is attributed to sorption and (co)precipitation reactions at the ZVI surface. Scanning electron microscopy (SEM) and X-ray absorption near-edge structure (XANES) spectroscopy confirmed the presence of secondary Fe-sulfides in mixtures containing organic carbon. The dominant reaction product in these mixtures was identified as disordered mackinawite [Fe1+xS]. The addition of ZVI to organic carbon enhanced AMD treatment over the duration of this experiment; however, long-term evaluation is required to identify optimal reactive mixtures. Field-based investigations into passive management of near-neutral pH tailings pore-water were carried out at the Greens Creek mine, located near Juneau, Alaska, USA. These studies focused on delineation of mechanisms controlling tailings pore-water chemistry, and a evaluation of the effectiveness of organic carbon amendment of tailings for passive in situ management of pore-water quality. Results demonstrate that sulfide-mineral oxidation and carbonate dissolution are the primary influences on tailings pore-water composition. Pyrite [FeS2] accounted for < 20 to > 35 wt. % of the tailings mineral assemblage, whereas dolomite [CaMg(CO3)2] and calcite [CaCO3] were present at ≤ 30 and 3 wt. %, respectively. The sulfide-mineral assemblage was dominated by pyrite; however, sphalerite [(Zn,Fe)S] and galena [PbS] were commonly observed, and tetrahedrite [(Fe,Zn,Cu,Ag)12Sb4S13], arsenopyrite [FeAsS], and chalcopyrite [CuFeS2] were present in lesser amounts. Geochemical analysis of tailings core samples generally agreed with mineralogical data. The occurrence of Cd, Cr, Co, Mo, Ni, Se, and Tl is attributed to their occurrence as impurities in primary sulfide phases. Most probable number (MPN) populations of neutrophilic sulfur-oxidizing bacteria (nSOB) and SRB were elevated at several locations within the tailings deposit. Near-neutral pH conditions dominated; however, elevated concentrations of dissolved SO4, S2O3, Fe, Zn, As, Sb, and Tl were observed within and below the oxidation zone. Field-scale experiments conducted over four years evaluated passive in situ treatment of pore-water by amending unoxidized tailings with 5 and 10 vol. % organic carbon. Field-scale cells were constructed to evaluate amendments containing differing mixtures of peat, dried spent brewing grain (SBG), and municipal biosolids (MB). Organic carbon amendment of the tailings supported the development of conditions favorable to sulfate reduction. Decreases in aqueous SO4 concentrations were observed in three cells amended with mixtures of peat, SBG, and MB. Removal of SO4 was generally accompanied by H2S production, enrichment in 34S-SO4, and increased SRB populations. Undersaturation of pore-water with respect to gypsum was observed. Sulfate reduction was sustained for the duration of the experiment in cells amended with 5 vol. % peat + SBG and 10 vol. % peat + SBG + MB. The addition of organic carbon also supported reductive dissolution of Fe(III) (oxy)hydroxides and mobilization of Fe and As. The largest increases in aqueous Fe and As concentrations were observed in cells amended with MB. Subsequent decreases in Fe and As concentrations were observed under sulfate-reducing conditions. Attenuation of Zn, Sb, and Tl accompanied SO4 removal. Mineralogical examination by SEM revealed the presence of secondary Zn-S and Fe-S precipitates on surfaces of organic carbon particles, and carbonate and aluminosilicate grains. This study demonstrates that amendment of tailings with a small and dispersed mass of organic carbon has potential to improve the quality of tailings pore water.

In fractured geologic media, flow and contaminant transport are predominantly controlled by the fractures, their distribution and connectivity. The accurate characterization of fractured geologic medium, imaging of fracture patterns and their connectivity have been a challenge for decades. Given the complexities of fractured networks in the subsurface and Dense Non Aqueous Phase Liquid (DNAPL) contamination, in this thesis, transient hydraulic tomography (THT), a recently developed tool for characterizing aquifer heterogeneity is evaluated under laboratory conditions to delineate discrete fractures. Laboratory experiments and modeling studies are also conducted to understand TCE plume behavior. A dolomite rock sample, which is 91.5 cm in length, 60.5 cm in height and 5 cm thick, was fractured in the laboratory to perform the experiments. After the fractured block was enclosed in a flow cell, flow-through and pumping tests were conducted to characterize the fractured rock block. The data from the pumping tests were then analyzed using the SSLE code developed by Zhu and Yeh [2005] and transient hydraulic tomography (THT) was conducted to image the fracture pattern and their connectivity through the delineation of K and Ss distributions (the tomograms). Synthetic pumping tests, identical in configuration to the laboratory ones were also conducted using HydroGeoSphere (HGS) [Therrien et al, 2009] in a synthetic replica of the fractured block to compare the observed and simulated drawdowns. Then synthetic THT analysis was performed utilizing the synthetic pumping test data to compare the tomograms obtained from the THT analysis of synthetic and laboratory pumping tests. Results suggest that the THT analysis of multiple laboratory pumping tests captured the fracture pattern and their connectivity quite well and they became more vivid with the additional pumping tests. The estimated high hydraulic conductivity (K) and low specific storage (Ss) zones clearly show the fractures and their connectivity. The pattern of K and Ss tomograms obtained from the analyses of synthetic and laboratory pumping tests were similar. Estimated K and Ss values for the fractures and the matrix may not exactly replicate the actual K and Ss values for the fractured rock, but the model also provides uncertainty estimates associated with the resulting K and Ss tomograms. In this study, two cases of transient hydraulic tomography (THT) analysis of the laboratory pumping tests were performed by changing the location of 2nd and 3rd pumping tests among the three to examine if there is any significant impact of these pumped location on the pattern of resulting hydraulic conductivity (K) and specific storage (Ss). The initial pumping test was the same for two cases. Results show that the patterns of estimated K and Ss tomograms obtained from these two cases are similar, although the pumped locations (2nd and 3rd tests among the three) utilized for the inversion were different for two cases suggesting that the location of these later pumping tests does not significantly impact the estimates for this fractured rock block. However, the initial test should be selected carefully as that seems to set the pattern of the tomograms. The estimated K and Ss tomograms were validated by predicting five independent pumping tests conducted in the fractured rock block. These five pumping tests were not included during the construction of the K and Ss tomograms. For most of the independent pumping tests, good correspondence between the simulated and observed drawdown was achieved. The study indicates that, it is possible to delineate discrete fractures, their pattern and connectivity by carefully applying of THT analysis of multiple pumping tests based on the inverse code SSLE [Zhu and Yeh, 2005]. In addition, hydraulic tomography seems to be a cost effective tool for characterizing fractured rock since it does not require the detailed information on fracture geometry parameters such as aperture, trace length, orientation, spatial distribution, and connectivity, which are difficult to quantify. These parameters are usually unavailable between boreholes. Therefore, THT appears to be a promising approach in delineating fractures and their connectivity in subsurface. However, it is still at the early stage as the study was conducted in the laboratory under controlled conditions. Small scale field experiments need to be conducted to validate THT as a tool for the characterization of hydraulic parameters of fractured rocks. Upon completion of the hydraulic characterization, several conservative tracer tests were conducted using bromide (Br-) as a conservative tracer to aid in the design of TCE dissolution experiment. Once the tracer experiments were completed, a known volume of pure phase TCE was injected at a known location in the flow cell to create a well-defined source zone. A constant hydraulic gradient was maintained by fixing the hydraulic heads at the two head tanks to induce steady groundwater flow through the flow cell. Water samples were obtained at a down gradient monitoring port for 3 months to obtain a long-term breakthrough curve of TCE in the aqueous phase. The purpose of this experiment was to study TCE dissolution behaviour in the fractured rock sample. Then HydroGeoSphere (HGS) was used to model the aqueous phase TCE transport using two separate approaches: 1) the Discrete Fracture Network modeling approach and 2) the stochastic continuum approach, to investigate whether they can capture the dissolution behavior. Both approaches were able to capture the pattern of the breakthrough curve in the fractured rock. The discrete fracture approach captured the observed TCE plume and the dissolution behavior quite well. On the other hand, the stochastic continuum approach, in which the fractured rock block was treated as porous medium having a heterogeneous K field obtained from THT analysis, also appeared to be promising in capturing the aqueous phase transport of TCE. Despite some early time deviation, the simulated breakthrough curve captured the overall observed concentration profile. However, the stochastic continuum approach seems to be more cost effective as it does not require detailed information about fracture aperture and their spatial distribution which are difficult if not impossible to obtain between boreholes. Note that, the studies were conducted based on a laboratory experiment conducted in a controlled environment. The experimental block was well characterized and the geometry of the experimental block as well as the flow through the system was well understood from the hydraulic and tracer experiments. Thus small scale field experiment is required to support this conclusion.