Saline and hydrocarbon-bearing fluids detected in shallow aquifers of southern New Brunswick, Canada: Natural occurrence, or deep migration along faults and industrial wellbores?

Unconventional hydrocarbon production has sparked public concerns for several years, especially regarding potential potable groundwater contamination by hydrocarbons, brines, and various chemicals related to hydraulic fracturing operations. One possible contamination mechanism is upward migration of deep-seated contaminants over large vertical distances, through preferential pathways such as leaky well casings or permeable geological faults. In New Brunswick (Canada), thermogenic hydrocarbons and brackish water were previously reported in shallow water wells, some of them located close to unconventional gas wells or to major faults, but the exact origin of these fluids remained uncertain. The objective of this paper is to determine whether the presence of these fluids is the result of migration from the deep (>1 km) hydrocarbon bearing units (via natural or anthropogenic migration pathways), or whether they rather originate within the shallow aquifer (<100 m) or from intermediate zone. Tracking fluid origin was achieved by fingerprinting compositional and isotopic values of three indicators: 1) water isotopic signature (including tritium (3H), radiocarbon (14CDIC), δ18OH2O, δ2HH2O), 2) salinity (including Na, Ca, K, SO4, Cl, Br, 87Sr/86Sr), and 3) hydrocarbons (compositional data and δ13CCH4). These various analyses were conducted, when relevant, on samples of different matrices composing the hydrogeological system, namely shallow groundwater (12-90 m depth), shallow bedrock gas (8-131 m), and intermediate zone evaporitic rocks (173-332 m); they were compared with previously published values for deep basin brines and gases (1940-3168 m) from the hydrocarbon bearing Carboniferous Albert Formation. This unique suite of indicators, analytes and matrices allowed drawing the conclusion that thermogenic gas and high salinities present in the sampled wells were naturally occurring and originating from shallow and intermediate-zone bedrock units. Results obtained through this approach did not provide any evidence that hydrocarbon wells in this area have acted as preferential migration pathways for deep-seated fluids towards shallow aquifers.

Core-multi-shell design: unlocking multimodal capabilities in lanthanide-based nanoparticles as upconverting, T2-weighted MRI and CT probes.

Multimodal bioimaging probes merging optical imaging, magnetic resonance imaging (MRI), and X-ray computed tomography (CT) capabilities have attracted considerable attention due to their potential biomedical applications. Lanthanide-based nanoparticles are promising candidates for multimodal imaging because of their optical, magnetic and X-ray attenuation properties. We prepared a set of hexagonal-phase (ß)-NaGdF4:Yb,Er/NaGdF4/NaDyF4 core/shell/shell nanoparticles (Dy-CSS NPs) and demonstrated their optical/T2-weighted MRI/CT multimodal capabilities. A known drawback of multimodal probes that merge the upconverting Er3+/Yb3+ ion pair with magnetic Dy3+ ions for T2-weighted MRI is the loss of upconversion (UC) emission due to Dy3+ poisoning. Particular attention was paid to controlled nanoparticle architectures with tuned inner shell thicknesses separating Dy3+ and Er3+/Yb3+ to shed light on the distance-dependent loss of UC due to Yb3+ → Dy3+ energy transfer. Based on the Er3+ UC spectra and the excited state lifetime of Yb3+, a 4 nm thick NaGdF4 inner shell did not only restore but enhanced the UC emission. We further investigated the effect of the outer NaDyF4 shell thickness on the particles' magnetic and CT performance. MRI T2 relaxivity measurements in vitro at a magnetic field of 7 T performed on citrate-capped Dy-CSS NPs revealed that NPs with the thickest outer shell thickness (4 nm) exhibited the highest r2 value, with a superior T2 contrast effect compared to commercial iron oxide and other Dy-based T2 contrast agents. In addition, the citrate-capped Dy-CSS NPs were demonstrated suitable for CT in in vitro imaging phantoms at X-ray energies of 110 keV, rendering them interesting alternatives to clinically used iodine-based agents that operate at lower energies.

Geochemical and mineralogical investigation of cemented crusts in the tailings cover at Long Lake Gold Mine, Sudbury, Canada.

In mine tailings, precipitation of secondary minerals may cement the tailings material and form cemented crusts or hardpans. Hardpans typically form beneath the surface of reactive tailings. However, at the former Long Lake Gold Mine near Sudbury, Ontario, cemented crusts formed in a clean sand cover above the tailings. We applied mineralogical and geochemical techniques to investigate the formation of these cemented crusts. Representative samples were collected from the sand cover and vertical cores from the underlying tailings. Elevated concentrations of arsenic (As), iron (Fe), and sulfur (S) in the sand cover indicate the upward transport of sulfide-mineral oxidation products. The shallow porewater of the tailings is acidic (pH 4 - 6) and contains elevated concentrations of As (up to 346 mg/L), Fe (up to 1844 mg/L), and SO4 (up to 12,000 mg/L). Mineralogical observations indicate that primary sulfide minerals in the near-surface tailings display moderate to strong oxidation, and secondary Fe-arsenate and jarosite minerals are formed both in the near-surface tailings and the sand cover. Upward migration of sulfide-mineral oxidation products leads to the formation of cemented crusts, which with continuing erosion, represent a long-term source of pollution to the surrounding environment.

Growth rates for freshwater ferromanganese concretions indicate regional climate change in eastern Canada at the Northgrippian-Meghalayan boundary.

The existence of freshwater ferromanganese concretions has been known for decades, but we are not aware of a generally accepted explanation for their formation, and there has been little research into their potential use as records of Holocene climate and paleohydrology. A conceptual model is presented to describe the environmental and geochemical processes which result in the formation and growth of freshwater ferromanganese concretions. In order to evaluate their potential as historical geochemical records, a concretion from Magaguadavic Lake, New Brunswick, Canada is the focus of a detailed geochronological and geochemical investigation. The radiocarbon data provide a coherent growth curve and a maximum age for the concretion of 8448 ± 43 years, consistent with the establishment of Magaguadavic Lake as a stable post-glacial lacustrine system. The data suggest accretion rates of 1.5 and 3.4 mm per 1000 years during the Northgrippian and Meghalayan stages of the Holocene, respectively. The abrupt change in growth rate observed at the stage boundary may be an indicator of Holocene climate change. These features are consistent with inferences from previous research that warmer climate in the Northgrippian led to eutrophication in some lakes in eastern North America. The results confirm that freshwater Fe-Mn concretions may yield important information about past climatic and environmental conditions.

A cross scale investigation of galena oxidation and controls on mobilization of lead in mine waste rock.

Galena and Pb-bearing secondary phases are the main sources of Pb in the terrestrial environment. Oxidative dissolution of galena releases aqueous Pb and SO4 to the surficial environment and commonly causes the formation of anglesite (in acidic environments) or cerussite (in alkaline environments). However, conditions prevalent in weathering environments are diverse and different reaction mechanisms reflect this variability at various scales. Here we applied complementary techniques across a range of scales, from nanometers to 10 s of meters, to study the oxidation of galena and accumulation of secondary phases that influence the release and mobilization of Pb within a sulfide-bearing waste-rock pile. Within the neutral-pH pore-water environment, the oxidation of galena releases Pb ions resulting in the formation of secondary Pb-bearing carbonate precipitates. Cerussite is the dominant phase and shannonite is a possible minor phase. Dissolved Cu from the pore water reacts at the surface of galena, forming covellite at the interface. Nanometer scale characterization suggests that secondary covellite is intergrown with secondary Pb-bearing carbonates at the interface. A small amount of the S derived from galena is sequestered with the secondary covellite, but the majority of the S is oxidized to sulfate and released to the pore water.

Field, Laboratory and Modeling Evidence for Strong Attenuation of a Cr(VI) Plume in a Mudstone Aquifer Due to Matrix Diffusion and Reaction Processes.

This study uses a combination of conventional and high resolution field and laboratory methods to investigate processes causing attenuation of a hexavalent chromium (Cr(VI)) plume in sedimentary bedrock at a former industrial facility. Groundwater plume Cr(VI) concentrations decline by more than three orders of magnitude over a 900 m distance down gradient from the site. Internal plume concentrations generally exhibit stable to declining trends due to diffusive and reactive transport in the low permeability matrix as fluxes from the contamination source dissipate due to natural depletion processes and active remediation efforts. The strong attenuation is attributed to diffusion from mobile groundwater in fractures to immobile porewater in the rock matrix, and reactions causing transformation of aqueous Cr(VI) to low-solubility Cr(III) precipitates, confirmed by high spatial resolution rock matrix contaminant concentrations and comparisons with groundwater concentrations from multi-level sampling within the plume. Field characterization data for the fracture network and matrix properties were used to inform 2-D discrete-fracture matrix (DFM) numerical model simulations that quantify attenuation due to diffusion and reaction processes, which show consistency with field datasets, and provide insights regarding future plume conditions. The combination of field, laboratory and modeling evidence demonstrates effects of matrix diffusion and reaction processes causing strong attenuation of a Cr(VI) plume in a sedimentary bedrock aquifer. This approach has important implications for characterization of sites with Cr(VI) contamination for improved site conceptual models and remediation decision-making.

Using permutational and multivariate statistics to understand inorganic well water chemistry and the occurrence of methane in groundwater, southeastern New Brunswick, Canada.

Concerns over possible impacts from the rapid expansion of unconventional oil and natural gas (ONG) resource development prompted a regional domestic well sampling program focusing on the Carboniferous Maritimes Basin bedrock in southeastern New Brunswick, Canada. This work applies recent developments in robust multivariate statistical methods to overcome issues with highly non-Gaussian data and support the development of a conceptual model for the regional groundwater chemistry and the occurrence of methane. Principal component analysis reveals that the redox-sensitive species, DO, NO3, Fe, Mn, methane, As and U are the most important parameters that differentiate the samples. Permutation-based MANOVA and ANOVA testing revealed that geology was more important than geographic location and topography in influencing groundwater composition. The statistical inferences are supported by chemistry trends observed in relation to road de-icing salt and other saline sources. However, source differentiation between Carboniferous brines, entrapped post-glacial marine water and modern seawater cannot be made. Furthermore, Cl:Br ratios lower than those of seawater or regional brines suggest an origin related to the diagenesis of organic-rich sediment and that the groundwater may be influenced by local low permeability units. Combined spatial, statistical and chemical analysis shows that, while trace or low levels of methane, <1 mg/L, are found ubiquitously throughout the Maritimes Basin, elevated concentrations, >1 mg/L, are associated with the Horton Group, consistent with it being the host and inferred source of ONG resources in the province. The highest methane concentrations (14-29 mg/L) were detected in the region with a complex history of cycles of uplift and erosion which, in some locations, resulted in the juxtaposition at the surface of the Horton Group with several other groups of the Maritimes Basin. It is thought that proximity to the Horton Group can lead to naturally high methane concentrations in non-ONG-bearing units.

Determination of Cr(III) solids formed by reduction of Cr(VI) in a contaminated fractured bedrock aquifer: Evidence for natural attenuation of Cr(VI).

Hexavalent chromium Cr(VI) is toxic and can be highly mobile in many aquifer systems. Redox reactions with naturally occurring minerals and organic compounds can reduce Cr(VI) to Cr(III), forming labile Cr(III) oxyhydroxide precipitates, which is a natural attenuation process. In fractured bedrock aquifers, reduction of Cr(VI) in the rock matrix can enhance attenuation beyond that from matrix diffusion only, and potentially reduce back diffusion if concentrations in fractures decline following source reduction via natural processes or engineered remediation. In this study, we develop an extraction method for labile Cr(III) precipitates from Cr(VI) reduction using 5% hydrogen peroxide (H2O2). Combining Cr(III) extractions with an established sodium hydroxide (NaOH) method for determination of Cr(VI) concentrations in rock porewater, a measure of the labile Cr(III) and Cr(VI) fractions in geologic samples is achieved. The methods were applied to cores from a contaminated groundwater system in fractured porous bedrock in order to assess the effectiveness of natural attenuation and whether Cr(VI) mass that diffused into the bedrock matrix was undergoing reduction. Detailed vertical distributions display two depth intervals with corresponding elevated concentrations of Cr(VI) in the porewater and extractable total Cr. The correspondence of Cr(VI) and labile Cr(III) provides evidence for reduction of Cr(VI) contamination in the bedrock matrix. Mineralogical analysis suggests that Fe(II)-bearing minerals, chlorite and biotite are the most likely candidates for natural reductants. This study provides evidence for the natural attenuation of anthropogenic Cr(VI) contamination in the porewater of a fractured bedrock aquifer, and it outlines a quantitative method for evaluating the effectiveness of natural attenuation in groundwater systems.

Calibration-free quantification of interior properties of porous media with x-ray computed tomography.

A method is presented for interpreting the values of x-ray attenuation coefficients reconstructed in computed tomography of porous media, while overcoming the ambiguity caused by the multichromatic nature of x-rays, dilution by void, and material heterogeneity. The method enables determination of porosity without relying on calibration or image segmentation or thresholding to discriminate pores from solid material. It distinguishes between solution-accessible and inaccessible pores, and provides the spatial and frequency distributions of solid-matrix material in a heterogeneous medium. This is accomplished by matching an image of a sample saturated with a contrast solution with that saturated with a transparent solution. Voxels occupied with solid-material and inaccessible pores are identified by the fact that they maintain the same location and image attributes in both images, with voxels containing inaccessible pores appearing empty in both images. Fully porous and accessible voxels exhibit the maximum contrast, while the rest are porous voxels containing mixtures of pore solutions and solid. This matching process is performed with an image registration computer code, and image processing software that requires only simple subtraction and multiplication (scaling) processes. The process is demonstrated in dolomite (non-uniform void distribution, homogeneous solid matrix) and sandstone (nearly uniform void distribution, heterogeneous solid matrix) samples, and its overall performance is shown to compare favorably with a method based on calibration and thresholding.

Effects of health education of diabetic patient's knowledge at Diabetic Health Centers, Khartoum State, Sudan: 2007-2010.

BACKGROUND: Educating and training diabetic patients is necessary for controlling and improving their health. METHODS: It was Quasi-experimental study design study. The study aimed to determine the effects of health education on the achievements of diabetic patients regarding control and improvement of their health status; at Diabetic Health Centers in Khartoum State, Sudan; 2007-2010. The target populations were diabetic patients, who attended the diabetic health centers to receive their treatment. Using simple random sampling 152 patients were selected (58 males and 94 females). Before and after comparison was done. Data was processed using SPSS and pair t-test was used to determine the effect of health education. P-value equal or less than 0.05 was considered statistically significant. FINDINGS: Test for before and after comparison was found to be statistically significant (p<0.05) for diabetic patients. They gained more knowledge after the implementation of the program; particularly in the areas of the nature and signs and symptoms of the disease, signs and symptoms of hypo & hyperglycemia, causes and warning signs of foot problems, foot care, and importance of exercises. CONCLUSIONS AND RECOMMENDATIONS: Health education of diabetic patients is crucial for control of diabetes. Capacity building of diabetic health centers, strengthening diabetic patients association, and more research to study the effect of health education on diabetic patients were needed.

Designing an educational and training program for diabetes health educators at Diabetic Health Centers, Khartoum State, Sudan; 2007-2010.

BACKGROUND: By the year 2030 the number of diabetic patients is expected to reach 366 million worldwide (World Health Organization [WHO], 2013). METHODS: It was an intervention-facility based. The study focused on designing and implementing an educational and training program for health educators and to assess its effects on achievements of diabetes health educators; at Diabetic Health Centers in Khartoum State, Sudan; 2007-2010. The study population composed of diabetes health educators working in Diabetic Health Centers. Their total number was (36) and all were included in the study. Pre and post tests were done. Data was entered using SPSS. Parametric methods including t-test to assess result of training program before and after intervention were used. P-value ? 0.05 was considered statistically significant. RESULTS: Thirty six diabetes health educators attended the program. There was a significant statistical difference (p=0.001) between mean of Pre and post test concerning knowledge of diabetes health educators. To my knowledge there were no studies done, before, in Sudan to evaluate knowledge of diabetes health educators after attending an educational program in order to compare results with. CONCLUSION AND RECOMMENDATIONS: The designed education program improved health educators' knowledge. Educating diabetes health educators is important in program of diabetes management. In-serving training of diabetes health educators, aiding diabetic health centers with educational materials, and more research on evaluation of impact of education on diabetes health educators; was recommended.

Three dimensional imaging of porosity and tracer concentration distributions in a dolostone sample during diffusion experiments using X-ray micro-CT.

X-ray micro-computed tomography (micro-CT) techniques for measuring the three-dimensional (3-D) distributions of diffusion-accessible porosity (φ(d)) and temporal tracer-concentrations (C(t)) within a dolostone sample subjected to solute diffusion are developed and tested in this work. The φ(d) and C(t) measurements are based on spatially resolved changes in X-ray attenuation coefficients in sequentially acquired 3-D micro-CT datasets using two (calibration and relative) analytical approaches. The measured changes in X-ray attenuation coefficient values are a function of the mass of X-ray absorbing potassium-iodide tracer present in voxels. Mean φ(d) values of 3.8% and 6.5% were obtained with the calibration and the relative approaches, respectively. The detection limits for φ(d) measurements at individual voxel locations are 20% and 36% with the calibration and the relative methods, respectively. The detection limit for C(t) are 0.12 M and 0.22 M with the calibration and the relative approaches, respectively. Results from the calibration method are affected by a beam-hardening artifact and although results from the relative approach are not affected by the artifact, they are subject to high detection limits. This work presents a quantitative assessment of micro-CT data for studies of solute transport. Despite limitations in precision and accuracy, the method provides quantitative 3-D distributions of φ(d) and C(t) that reflect solute diffusion in heterogeneous porous geologic media.

Determination of spatially-resolved porosity, tracer distributions and diffusion coefficients in porous media using MRI measurements and numerical simulations.

This work is focused on measuring the concentration distribution of a conservative tracer in a homogeneous synthetic porous material and in heterogeneous natural sandstone using MRI techniques, and on the use of spatially resolved porosity data to define spatially variable diffusion coefficients in heterogeneous media. The measurements are made by employing SPRITE, a fast MRI method that yields quantitative, spatially-resolved tracer concentrations in porous media. Diffusion experiments involving the migration of H(2)O into D(2)O-saturated porous media are conducted. One-dimensional spatial distributions of H(2)O-tracer concentrations acquired from experiments with the homogeneous synthetic calcium silicate are fitted with the one-dimensional analytical solution of Fick's second law to confirm that the experimental method provides results that are consistent with expectations for Fickian diffusion in porous media. The MRI-measured concentration profiles match well with the solution for Fick's second law and provide a pore-water diffusion coefficient of 1.75×10(-9)m(2)s(-1). The experimental approach was then extended to evaluate diffusion in a heterogeneous natural sandstone in three dimensions. The relatively high hydraulic conductivity of the sandstone, and the contrast in fluid density between the H(2)O tracer and the D(2)O pore fluid, lead to solute transport by a combination of diffusion and density-driven advection. The MRI measurements of spatially distributed tracer concentration, combined with numerical simulations allow for the identification of the respective influences of advection and diffusion. The experimental data are interpreted with the aid of MIN3P-D - a multicomponent reactive transport code that includes the coupled processes of diffusion and density-driven advection. The model defines local diffusion coefficients as a function of spatially resolved porosity measurements. The D(e) values calculated for the heterogeneous sandstone and used to simulate diffusive and advective transport range from 5.4×10(-12) to 1.0×10(-10)m(2)s(-1). These methods have broad applicability to studies of contaminant migration in geological materials.

Manganese and trace-metal mobility under reducing conditions following in situ oxidation of TCE by KMnO4: a laboratory column experiment.

The stability of Mn oxides, and the potential for mobilization of associated trace metals, were assessed by simulating the onset of microbially-mediated reducing conditions in a continuous-flow column experiment. The column had previously been used for an in situ chemical oxidation (ISCO) experiment in which trichloroethylene was reacted with permanganate in the presence of aqueous trace metals, which produced Mn oxyhydroxides (MnO(x)) that sequestered the trace metals and coated the column sand. The column influent solution represented the incursion of ambient groundwater containing dissolved organic carbon (DOC) into an ISCO treatment zone. The influx of DOC-containing groundwater initiated a series of cation-exchange, surface-complexation and reductive-dissolution reactions that controlled the release of aqueous metals from the system. Peak concentrations in the effluent occurred in the order Na, Mo, Cr, Zn, K, Mn, Fe, Pb, Mg, Ni, Cu and Ca. Manganese release from the column was controlled by a combination of cation exchange, reductive dissolution and precipitation of rhodochrosite. The trend in Fe concentrations was similar to that of Mn, and also resulted from a combination of reductive dissolution and cation exchange. Cation exchange and/or surface-complexation were the primary mechanisms controlling Cu, Ni, Mo and Pb release to solution, while Zn and Cr concentrations did not display coherent trends. Although metal release from the treatment zone was evident in the data, concentrations of trace metals remained below 0.05 mg L(-1) with the exception of Mo which reached concentrations on the order of 1 mg L(-1). The establishment of anaerobic conditions in ISCO-treated aquifers may result in a prolonged flux of aqueous Mn(II), but with the exception of MoO(4)(2-), it is unlikely that trace metals sequestered with MnO(x) during ISCO will be released to the groundwater in elevated concentrations.

Manganese valence in oxides formed from in situ chemical oxidation of TCE by KMnO4.

Batch and column experiments designed to simulate in situ chemical oxidation (ISCO) in a sand aquifer were conducted to create Mn-oxides (MnOx) by oxidation of trichloroethylene (TCE) with permanganate (MnO4-). Electron energy-loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) were used to quantify Mn valence in the oxides. The valence of Mn in the MnOx generated in near-source ISCO conditions was 2.2 and 2.3 when formed at low (<3) and neutral (6-7) pH conditions, respectively. There is no significant difference between these values. Valence was found to be sensitive to the preparation method and to aging. When formed in the presence of excess MnO4-, or aged for 3 months, Mn valence ranged from 2.5 to 3.6. Aging in a lower pH environment inhibited Mn oxidation. The EELS and XPS methods provided similar results, but there was a slight bias to higher values for XPS. This work demonstrates that MnO2(s) may not be the main product of MnO4- reaction with chlorinated solvents as is commonly assumed and that the efficiency of ISCO treatment may be greater than previously known.

Measurement of spatial distribution of total and accessible porosity in sedimentary rocks using isotopic radiation transmission: device design and testing.

An isotopic radiation transmission technique for quantifying the spatial distribution of porosity in sedimentary rocks is presented. A device was designed and constructed to examine rock samples of volumes sufficiently large for studying solute migration in rocks, so that a one-millimeter spatial resolution is attained with measurement acquisition time of one point per second. The paper demonstrates how the device was optimized for these specifications, while abiding by the restrictions implicit in the utilization of the exponential law of radiation attenuation to quantify physical parameters. Total porosity was obtained from measurements of radiation attenuation in dry samples, while solute-accessible porosity was determined from measurements with samples saturated with either KNO(3) or KI solutions. Results are presented for three different rock types to demonstrate the capabilities and limitations of the technique.

Three-dimensional density-dependent flow and multicomponent reactive transport modeling of chlorinated solvent oxidation by potassium permanganate.

A popular method for the treatment of aquifers contaminated with chlorinated solvents is chemical oxidation based on the injection of potassium permanganate (KMnO(4)). Both the high density (1025 gL(-1)) and reactivity of the treatment solution influence the fate of permanganate (MnO(4)) in the subsurface and affect the degree of contaminant treatment. The MIN3P multicomponent reactive transport code was enhanced to simulate permanganate-based remediation, to evaluate the pathways of MnO(4) utilization, and to assess the role of density contrasts for the delivery of the treatment solution. The modified code (MIN3P-D) provides a direct coupling between density-dependent fluid flow, solute transport, contaminant treatment, and geochemical reactions. The model is used to simulate a field trial of TCE oxidation in a sandy aquifer that is underlain by an aquitard. Three-dimensional simulations are conducted for a coupled reactive system comprised of ten aqueous components, two mineral phases, TCE (dissolved, adsorbed, and NAPL), reactive organic matter, and including ion exchange reactions. Model parameters are constrained by literature data and a detailed data set from the field site under investigation. The general spatial and transient evolution in observed concentrations of the oxidant, dissolved TCE, and reaction products are adequately reproduced by the simulations. The model elucidates the important role of density-induced flow and transport on the distribution of the treatment solution into NAPL containing regions located at the aquifer-aquitard interface. Model results further suggest that reactions that do not directly affect the stability of MnO(4) have a negligible effect on solution density and MnO(4) delivery.

A technique for estimating one-dimensional diffusion coefficients in low-permeability sedimentary rock using X-ray radiography: comparison with through-diffusion measurements.

The measurement of diffusive properties of low-permeability rocks is of interest to the nuclear power industry, which is considering the option of deep geologic repositories for management of radioactive waste. We present a simple, non-destructive, constant source in-diffusion method for estimating one-dimensional pore diffusion coefficients (D(p)) in geologic materials based on X-ray radiography. Changes in X-ray absorption coefficient (Deltamicro) are used to quantify changes in relative concentration (C/C(0)) of an X-ray attenuating iodide tracer as the tracer solution diffuses through the rock pores. Estimated values of D(p) are then obtained by fitting an analytical solution to the measured concentration profiles over time. Measurements on samples before and after saturation with iodide can also be used to determine iodide-accessible porosity (phi(I)). To evaluate the radiography method, results were compared with traditional steady-state through-diffusion measurements on two rock types: shale and limestone. Values of D(p) of (4.8+/-2.5)x10(-11) m(2).s(-1) (mean+/-standard deviation) were measured for samples of Queenston Formation shale and (2.6+/-1.0)x10(-11) m(2).s(-1) for samples of Cobourg Formation limestone using the radiography method. The range of results for each rock type agree well with D(p) values of (4.6+/-2.0)x10(-11) m(2).s(-1) for shale and (3.5+/-1.8)x10(-11) m(2).s(-1) for limestone, calculated from through-diffusion experiments on adjacent rock samples. Low porosity (0.01 to 0.03) and heterogeneous distribution of porosity in the Cobourg Formation may be responsible for the slightly poorer agreement between radiography and through-diffusion results for limestones. Mean values of phi(I) for shales (0.060) and limestones (0.028) were close to mean porosity measurements made on bulk samples by the independent water loss technique (0.062 and 0.020 for shales and limestones, respectively). Radiography measurements offer the advantage of time-saving for diffusion experiments because the experiment does not require steady-state conditions and also allows for visualization of the small-scale heterogeneities in diffusive properties within rocks at the mm to cm scale.

Metal mobility during in situ chemical oxidation of TCE by KMnO4.

The potential for trace-metal contamination of aquifers as a side effect of In Situ Chemical Oxidation (ISCO) of chlorinated solvent contamination by KMnO(4) is investigated with column experiments. The experiments investigate metal mobility during in situ chemical oxidation of TCE by KMnO(4) under conditions where pH, flow rate, KMnO(4), TCE, and trace-metal concentrations were controlled. During ISCO, the injection of MnO(4) creates oxidizing conditions, and acidity released by the reactions causes a tendency toward low pH in aquifers. In order to evaluate the role of pH buffering on metal mobility, duplicate columns were constructed, one packed with pure silica sand, and one with a mixture of silica sand and calcite. Aqueous solutions of TCE and KMnO(4) (with 1 mg/L Cu, Pb, Zn, Mo, Ni, and Cr(VI)) were allowed to mix at the inlet to the columns. After the completion of the experiments, samples of Mn oxide were removed from the columns and analyzed by analytical scanning and transmission electron microscopy. In order to relate the results of the laboratory experiments to field settings, the analyses of Mn-oxide samples from the lab experiments were compared to samples of Mn oxide collected from a field-scale chemical-oxidation experiment that were also analyzed by analytical electron microscopy as well as time-of-flight secondary-ion mass spectroscopy. The pH ranged from 2.40 in the silica sand column to 6.25 in the calcite-containing column. The data indicate that aqueous Mo, Pb, Cu and Ni concentrations are attenuated almost completely within the columns. In contrast, Zn concentrations are not significantly attenuated and Cr(VI) is transported conservatively. The results indicate that within the range 2.40 to 6.25, metal mobility is not affected by pH. Comparison of analyses of Mn-oxide from the lab and field demonstrate that a variety of metals are sequestered from solution by Mn oxide.

A STEM/EELS method for mapping iron valence ratios in oxide minerals.

The valence state of iron in minerals has useful applications in the geosciences for estimating redox conditions during mineral formation or re-equilibration. STEM/EELS techniques offer the advantage over other methods of being able to measure Fe valence with very high spatial resolution across mineral grains and grain boundaries. We have modified an EELS method for point analyses of iron valence ratios (Fe(3+)/SigmaFe) making it possible to generate line scans and maps of Fe valence. We demonstrate this method with measurements at an interface between iron-bearing oxides in a finely intergrown sample of magnetite and ilmenite. The STEM/EELS method is based on a calibrated relationship between Fe(3+)/SigmaFe and the relative intensities of the Fe L(3) and L(2) white lines in core energy-loss spectra for oxide and silicate minerals. Our method overcomes problems of energy drift in spectrum images by aligning energy-loss edges at a fixed energy position prior to background removal. An automated routine for batch processing of core loss spectra, including additional background removal and calculation of Fe L(3)/L(2) intensity ratios, allows for rapid Fe(3+)/SigmaFe determinations of multiple point analyses or spectrum images and the preparation of Fe valence maps, with an analytical error of +/-0.05 to +/-0.09 in the Fe(3+)/SigmaFe measurements.