This paper summarizes international state-of-the-art applications and opportunities for employing and deploying hydrological, geochemical, and isotopic tools in an integrated manner for ...investigations of mining operations. It is intended to aid formulation of more integrated approaches for evaluating the overall sustainability of mining projects. The focus is particularly on mine waters, including: environmental water sources, mine water dynamics, and as a source and vector for pollution in the wider environment. The guidance is generic to mining projects and not just reflective of a particular extraction (e.g. coal, metalliferous, uranium) industry. A mine life cycle perspective has been adopted to highlight the potential for more integrated investigations at each stage of a mining operation. Three types of mines have been considered: new (i.e. those in the planning stage), active (i.e. working mines), and historical mines (i.e. inactive and abandoned mines). The practical usage of geochemical analyses and isotopic studies described here emphasise characterisation, dynamics, and process understanding for water quality considerations in tandem with water resource and environmental impact implications. Both environmental (i.e. ambient) and applied (i.e. injected) tracers are considered. This guide is written for scientists (including isotope specialists) who have limited or no mine water experience, environmental managers, planners, consultants, and regulators with key interests in planned, active, and legacy mining projects.
The expansion of petroleum resource development has led to growing concern regarding greenhouse gas emissions from fugitive gas migration, which occurs at some wells due to well integrity failure. In ...this study, we quantify methane surface expression and emissions resulting from gas migration using a number of complementary techniques, and thereby evaluate surface expression processes as well as the strengths and limitations of the monitoring techniques. Methane emissions were found to be highly localized and variable over time. Injected gas reached the surface via preferential pathways through the soils and also along an installed groundwater monitoring well. Cumulative emissions were estimated from flux chamber measurements to be 3.8–6.5% of the injected gas; whereas eddy covariance (EC) data inferred approximately 26% of the injected gas was released to the atmosphere. Together these methods provide enhanced interpretation of surface expression at the site, advance our understanding on fugitive gas migration from integrity compromised energy wells and provide insights to improve monitoring and detection strategies with a view to reducing future greenhouse gas emissions. Moreover that, up to 75% of fugitive gas released at the site remained in the subsurface, shows that capillary barriers will mitigate greenhouse gas emissions from leaky wells; however, may infer greater potential for impacts on groundwater resources, if present.
•Surface expression of a synthetic natural gas injection experiment was measured.•Soil gas wells, flux chambers and eddy covariance used to measure methane emissions.•Methane migrated through preferential pathways and emissions were heterogeneous.•Approximately 75% of injected methane remained in the subsurface.•Insight gained to improve monitoring strategies to reduce future GHG emissions.
Waste rock piles are an outcome of open pit and underground mining operations. Unprocessed low‐grade rock is disposed of in piles from several meters high to 100 m+ high. Waste rock piles may still ...contain sufficient concentrations of metals to be a potential source of pollution. The evaluation of the potential risk involves properly characterizing flow through these piles under unsaturated conditions. The main flow characteristic of the piles is the presence of a large range of grain and pore sizes. Based on data from an instrumented rock pile located in Saskatchewan Canada, unsaturated flow through the pile is modeled as a linear system after separating a fast and a slow component. Water reaching the base of the pile is monitored by 16 contiguous zero‐tension lysimeters. The fast component, flowing through macropores, is assumed to be released instantaneously, while the slow component is simulated using a linear‐reservoir model that assumes the presence of an interconnected porous matrix. An empirical transfer function (TF) is computed as the ratio of the spectra of signals between the output (basal outflow) and the input (rainfall time series). Determination of a parametric transfer function model provides information on the characteristic time of water storage in the matrix and on the fraction of the water within each subsection of the experimental pile that is channeled through the macropores. An analysis of the output signal at different support scales is performed, indicating the nonlinearity of the macropore fraction scaling processes.
Key Points
Preferential flow through an unsaturated waste rock pile
Use of parametric transfer functions to model unsaturated flow
Dependence of preferential flow on the spatial arrangement of the matrix
Coal-seam methane reservoirs have a number of unique feature compared to conventional porous or fractured gas reservoirs. We propose a simplified mathematical model of methane movement in a coal seam ...taking into account the following features: a relatively regular cleat system, adsorptive methane storage, an extremely slow mechanism of methane release from the coal matrix into cleats and a significant change of permeability due to desorption.Parameters of the model have been combined into a few dimensionless complexes which are estimated to an order of magnitude. The simplicity of the model allows us to fully investigate the influence of each parameter on the production characteristics of the coal seam. We show that the reference time of methane release from the coal matrix into cleats – the parameter which is most poorly investigated – may have a critical influence on the overall methane production.
A three dimensional flow and transport modeling using FRAC3DVS was undertaken to examine factors which influence plume detection in a performance monitoring network for a site where an unconfined ...aquifer composed of uniform unconsolidated sediments overlies fractured bedrock. The bedrock is assumed to contain a fracture system with three orthogonal fracture sets embedded in a low permeable homogeneous rock matrix. A dissolved phase, non-reactive contaminant is released from a source zone located at the ground surface. The processes which influence plume geometry, and probabilities of plume detection for a performance monitoring network located between the contaminant source and a downstream compliance boundary, are evaluated. Factors considered include the hydraulic conductivity of the unconfined aquifer, the geometric properties of the fracture network and the matrix permeability of the bedrock, and the contaminant detection threshold concentration. The simulations demonstrate that the character of the fracture network not only controls contaminant transport and plume detection in the bedrock but also influences plume detection in the overlying unconfined aquifer. The ratio of the hydraulic conductivity of the unconfined aquifer to the effective hydraulic conductivity of the fractured bedrock, and the contaminant detection threshold concentration, are principal factors influencing detection probability in the performance monitoring network. Results suggest that in many instances encountered in field practice, the unconfined aquifer and fractured bedrock should be viewed as an integrated hydrogeologic system from a monitoring perspective.
► Conceptual design basis for a performance monitoring network at a contaminated site. ► Plume detection probabilities for an unconfined aquifer overlying fractured bedrock. ► Unconfined aquifer and fractured bedrock should be viewed as integrated system. ► Role of fracture network relative to unconfined aquifer on plume detection.
The relationships between factors that control subsurface flow and the timing, duration, and intensity of acidity generation and leaching of metals from waste-rock dumps are investigated. A 12
m high ...waste-rock pile that had been constructed in 1994 at Key Lake, Saskatchewan, Canada was disassembled, sampled and characterized in 2000. Physical properties that control water flow were characterized by measuring soil–water suction, volumetric water content, and the grain-size distribution at 60 randomized sites within the pile. Grain-size distribution was also measured at an additional 20 grid locations within the pile. Paste pH, pore-water geochemistry, mineralogy, and water-soluble extractions were used to investigate geochemical processes and sulfide oxidation at each of the 20 grid locations. A field-based soil–water characteristic curve could not be developed from the spatially variable and hysteretic field data; consequently, the grain-size distribution was used as a relative measure of subsurface flow and of the tendency to contain water under unsaturated conditions. The geochemical characterization demonstrated that marcasite underwent preferential weathering relative to pyrite and chalcopyrite, that dolomite was the main buffering carbonate mineral, and that gypsum, jarosite, and Fe oxyhydroxides were the main secondary (supergene) minerals. The pore waters contained up to 78,000
mg
L
−1 SO
4, 690
mg
L
−1 Ni and 1400
mg
L
−1 U (800, 11.7 and 6
mM, respectively), suggesting that significant weathering had occurred. The pore water chemistry varied considerably between sampling sites. However, neither a correlation of pore-water chemistry with grain-size distribution nor a spatial relationship within the sampled grid was discernible.
The cover image is based on the In the Field article Advancing knowledge of gas migration and fugitive gas from energy wells in northeast British Columbia, Canada by Aaron G. Cahill et al., DOI: ...10.1002/ghg.1856. Image Credit: Dr. Aaron Graham Cahill, University of British Columbia.
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