The method of electrically switched ion exchange (ESIX) involves the sequential application of reduction and oxidation potentials to an ion exchange film to induce the respective loading and unloading of Cs+. In this study, four films of nickel hexacyanoferrate were prepared on nickel electrodes with different preparation procedures. Films were characterized by SEM/EDX. Each film shows a different performance with regard to Cs+ separation. Scanning electron microscopy was used to characterize the modified film surfaces. Cyclic voltammetry was used to investigate the ion exchange capacity and stability. The four films show a better capacity for Cs+ separation compared to previous methods for the deposition of ESIX films. An optimal nickel hexacyanoferrate film was generated when using an applied potential of 0.2 V relative to a saturated calomel electrode (SCE) to generate the nucleation sites, followed by a 1.3 V vs. SCE potential during the growth stage of the film. This film demonstrated the highest film capacity for ion exchange initially (17.3 × 10−3 C cm−2) and again after 1000 cycles (11.1 × 10−3 C cm−2).

An increasing number of factors pose challenges to the development and management of water resources in rural, remote, or otherwise marginalized (RRM) communities. Indicators and indices have been developed for evaluation, prioritization, and decision-making at local and supra-local scales. Indicators and indices are useful assessment tools as they simplify the modeling process and provide results in an accessible format. The purpose of this paper is to consolidate a list of indicators (n = 176) from a review of community-and basin-level indices and a selection of other literature within a water security framework for RRM communities. A detailed discussion of each of the six dimensions within the framework is provided. This paper concludes with some general remarks on the standards used for evaluation, the reliance upon historical and field data, suggestions for improving the descriptive clarity where it is lacking, and the prospect of these indicators getting used by community members.

Electrically switched ion exchange (ESIX) can be used to separate ionic contaminants from industrial wastewater, including that generated by the nuclear industry. The ESIX method involves sequential application of reduction and oxidation potentials to an ion exchange film to induce the respective loading and unloading of cesium. This technology is superior to conventional methods (e.g electrodialysis reversal or reverse osmosis) as it requires very little energy for ionic separation. In previous studies, ESIX films have demonstrated relatively low ion exchange capacities and limited film stabilities over repeated potential applications. In this study, the methodology for the deposition of electroactive films (nickel hexacyanoferrate) on nickel electrodes was modified to improve the ion exchange capacity for cesium removal using ESIX Cyclic voltammetry was used to investigate the ion exchange capacity and stability. Scanning electron microscopy (SEM) was used to characterize the modified film surfaces. Additionally, the films were examined for the separation of cesium ions. This modified film preparation technique enhanced the ion exchange capacity and improves the film stability compared to previous methods for the deposition of ESIX films.

Groundwater from fractured rock aquifers serves as a source of drinking water around the world; however, wells in fractured rock can be susceptible to contamination. Aquifer vulnerability assessments are tools used for identifying the risk potential in groundwater sources, as well as efficiently allocating resources for source water protection. Existing methods include DRASTIC, GOD, EPIK, AVI, COP, and ISI. Some approaches do not consider risks posed by fractures, while others were developed for karstified regions; all are ill suited to fractured formations. This work proposes a new vulnerability assessment method incorporating quantitative portions of existing methods together with fractured rock characteristics. The proposed method is applied to a study area in Acton-Georgetown, Ontario; the DRASTIC and AVI methods are also applied for comparison. DRASTIC and AVI methods yield significantly different results from each other and from the proposed method. The proposed method demonstrates the heavy influence the fractured rock has on vulnerability, highlighting the need for its inclusion in vulnerability assessments.

Fractured aquifers are a relatively under-studied area of groundwater science particularly because of the heterogeneities present in fractures which make it difficult to understand and predict the transport and retention of contaminants. This research was designed to elucidate some of the factors that contribute to particle transport and retention in fractures using solute and particle tracers in a natural rock fracture and a transparent epoxy replica of that same fracture. Significantly less attachment was observed from the tracer experiments conducted in the replica fracture illustrating the large effect that matrix properties have on transport and retention of particles in fractures. The E. coli RS2-GFP tracer experiments conducted in the replica fracture show that increasing specific discharge results in increasing recovery; however, there is a critical specific discharge at which particle recovery seems to steady or slightly decrease. Images were collected of the E. coli RS2-GFP transport through the epoxy replica fracture, which capture for the first time the preferential pathways of E. coli in fractures, and also demonstrate a slight broadening of the dominant preferential pathway under increasing flow conditions. These results are instructive to the development and improvement of predictive models for particle transport in fractured aquifers.

Wastewater treatment by conventional methods as ion exchange, coagulation and precipitation is very important. A relatively new method for wastewater treatment is introduced; this method is known as electrically switched ion exchange (ESIX). ESIX can be used to separate metal ion contaminants from industrial wastewater. The ESIX method involves sequential application of reduction and oxidation potentials to an ion exchange film to induce the respective loading and unloading of Cs + . The metal ion separated from the wastewater and unloaded from the electrode by modulating the potential applied to the film. This technology is superior to conventional methods (e.g conventional ion exchange) as it requires very little energy for ionic separation. In this study, two films of nickel hexacyanoferrate were prepared on nickel electrodes with different preparation procedures. Each film shows different performance in Cs + separation. Scanning electron microscopy was used to characterize the modified film surfaces. Cyclic voltammetry was used to investigate the ion exchange capacity and stability. These two films show a high capacity and stability for Cs + separation.

The characterization of fractured aquifers is commonly limited to the methodologies developed for unconsolidated porous media aquifers, which results in many uncertainties. Recent work indicates that fractured rocks remove more particulates than they are conventionally credited for. This research was designed to quantify the number of Escherichia coli RS2-GFP retained in single, saturated, variable-aperture fractures extracted from the natural environment. Conservative solute and E. coli RS2-GFP tracer experiments were used to elucidate the relationships between dominant retention mechanisms, aperture field characteristics, and flow rate. A non-destructive method of determining a surrogate measure of a coefficient of variation (COVS) for each fracture was used to better understand the transport behaviour of E. coli RS2-GFP. The results from this research all point to the importance of aperture field characterization in understanding the fate and transport of contaminants in fractured aquifers. The mean aperture was a very important characteristic in determining particulate recovery, so were matrix properties, COVs, and flow rate. It was also determined that attachment is a much more significant retention mechanism than straining under the conditions employed in this research. Finally, it was demonstrated that the dominant retention mechanism in a fracture varies depending on the specific discharge. An improved understanding of the mechanisms that influence the fate and transport of contaminants through fractures will lead to the development of better tools and methodologies for the characterization of fractured aquifers, as well as the ability to manipulate the relevant mechanisms to increase or decrease retention, depending on the application.

This work employed numerical experiments simulating colloid and solute transport in single parallel-plate fractures, using the random walk particle tracking method, to demonstrate that (1) there exists an aspect ratio of the colloid radius to half the fracture aperture, delta(o), where the average velocities of colloids and solutes are similar. When delta>delta(o), the velocity distribution assumption is satisfied, and the fact that the ratio of the colloid transport velocity to the solute transport velocity, tau(p), decreases as delta increases is well documented in the literature. However, when delta<delta(o), the velocity distribution assumption is violated, and tau(p) increases as delta increases and (2) the Taylor dispersion coefficient and its extension by James and Chrysikopoulos [S.C. James, C. V. Chrysikopoulos, J. Colloid Interface Sci. 263 (2003) 288] will overestimate the colloid dispersion coefficient significantly. Additionally, numerical experiments simulating colloid and solute transport in variable-aperture fractures demonstrated that tau(p) and D(L,)(coll)/D(L,)(solute) decrease with increasing CoV, and the anisotropy ratio only plays a minor role compared to the CoV. These observations have important implications towards the interpretation of colloid transport in both porous and fractured media.

Acknowledgements Preface List of Tables List of Figures iii vi vii xiii xiv Chapter

Three distinct definitions of “equivalent aperture” have been used in the literature to describe variable‐aperture fractures; however, significant inconsistencies exist in the literature as to which “equivalent aperture” is appropriate for simulating solute transport. In this work, a systematic series of hydraulic and tracer tests was conducted on three laboratory‐scale fracture replicas, and the cubic law, mass balance, and frictional loss apertures were calculated. The analytical solution of the one‐dimensional advection‐dispersion equation was fit to the experimental breakthrough curves. Additionally, one of the experimental aperture fields was measured directly using a light transmission technique. The results clearly demonstrate that the mass balance aperture is the only appropriate “equivalent aperture” for describing solute transport in a single variable aperture fracture and that the mass balance aperture is an excellent approximation of the arithmetic mean aperture. Previously, these conclusions have been reached based only on theoretical and numerical analyses.