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1.
The use of covers with capillary barrier effects (CCBEs) for reducing acid mine drainage (AMD) from sulphidic mine tailings is simulated using the MIN3P finite volume model for coupled groundwater flow, O2 diffusion and multi-component reactive transport. The model is applied to simulate five pilot-scale in situ test cells containing reactive tailings from the Manitou mine site, Val d’Or, Que., Canada. Four of the cells were constructed with CCBEs over the tailings, while the fifth tailings cell was left uncovered. Observed and simulated discharge from the base of each cell showed that the capillary barrier covers significantly reduced sulphide oxidation and AMD. Compared to acidic discharge from the uncovered cell, discharge from the four CCBE-covered cells had neutral pH levels and 1–7 orders of magnitude lower concentrations of SO4, Fe, Zn, Cu and Al. The simulations showed that the moisture retaining layer of the CCBEs reduced AMD by inhibiting O2 diffusion into the underlying reactive wastes. Provided the moisture-retention layer of the CCBE remains close to saturation, its thickness had a relatively minor effect. Under such near-saturated conditions, O2 availability is limited by its diffusion rate through the bulk porous medium and not by the diffusion rate through the oxidized grain shells. The model is providing important new insights for comparing design alternatives for reducing or controlling AMD. 相似文献
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Reactive barriers are passive and in situ ground water treatment systems. Heterogeneities in hydraulic conductivity (K) within the aquifer-reactive barrier system will result in higher flux rates, and reduced residence times, through portions of the barrier. These spatial variations in residence time will affect the treatment capacity of the barrier. A numerical flow model was used to evaluate the effects of spatial variations in K on preferential flow through barriers. The simulations indicate that the impact of heterogeneities in K will be a function of their location and distribution; the more localized the high K zone, the greater the preferential flow. The geometry of the reactive barrier will also strongly influence flow distribution. Aquifer heterogeneities will produce greater preferential flow in thinner barriers compared to thicker barriers. If the barrier K is heterogeneous, greater preferential flow will occur in thicker barriers. The K of the barrier will affect the flow distribution; decreasing the K of the barrier can result in more even distribution of flow. Results indicate that less variable flow will be attained utilizing thicker, homogeneous barriers. The addition of homogeneous zones to thinner barriers will be effective at redistributing flow only if installed immediately adjacent to both the up- and downgradient faces of the barrier. 相似文献
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The impact of road salt on a wellfield in a complex glacial moraine aquifer system is studied by numerical simulation. The moraine underlies an extensive urban and industrial landscape, which draws its water supply from >20 wellfields, several of which are approaching or have exceeded the drinking water limit for chloride. The study investigates the mechanisms of road salt infiltration, storage, and transport in the subsurface and assesses the effectiveness of mitigation measures designed to reduce the impact. The three-dimensional transport model accounts for increases in salt loading, as well as growth of the urbanized area and road network over the past 50 years. The simulations, which focus on one impacted wellfield, show chloride plumes originating mainly at arterial roads and migrating through aquitard windows into the water supply aquifers. The results suggest that the aquifer system contains a large and heterogeneously distributed mass of chloride and that concentrations in the aquifer can be substantially higher than the concentrations in the well water. Future impact scenarios indicate that although the system responds rapidly to reductions in salt loading, the residual chloride mass may take decades to flush out, even if road salting were discontinued. The implications with respect to urban wellfields in typical snow-belt areas are discussed. 相似文献
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Shojae Ghias Masoumeh Therrien René Molson John Lemieux Jean-Michel 《Hydrogeology Journal》2017,25(3):657-673
Numerical simulations of groundwater flow and heat transport are used to provide insight into the interaction between shallow groundwater flow and thermal dynamics related to permafrost thaw and thaw settlement at the Iqaluit Airport taxiway, Nunavut, Canada. A conceptual model is first developed for the site and a corresponding two-dimensional numerical model is calibrated to the observed ground temperatures. Future climate-warming impacts on the thermal regime and flow system are then simulated based on climate scenarios proposed by the Intergovernmental Panel on Climate Change (IPCC). Under climate warming, surface snow cover is identified as the leading factor affecting permafrost degradation, including its role in increasing the sensitivity of permafrost degradation to changes in various hydrogeological factors. In this case, advective heat transport plays a relatively minor, but non-negligible, role compared to conductive heat transport, due to the significant extent of low-permeability soil close to surface. Conductive heat transport, which is strongly affected by the surface snow layer, controls the release of unfrozen water and the depth of the active layer as well as the magnitude of thaw settlement and frost heave. Under the warmest climate-warming scenario with an average annual temperature increase of 3.23 °C for the period of 2011–2100, the simulations suggest that the maximum depth of the active layer will increase from 2 m in 2012 to 8.8 m in 2100 and, over the same time period, thaw settlement along the airport taxiway will increase from 0.11 m to at least 0.17 m.
相似文献5.
Mario Schirmer Frido Reinstorf Sebastian Leschik Andreas Musolff Ronald Krieg Gerhard Strauch John W. Molson Marion Martienssen Kristin Schirmer 《Environmental Earth Sciences》2011,64(3):607-617
Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany. 相似文献
6.
S. Harrison J. Molson H. Abercrombie J. Barker D. Rudolph R. Aravena 《Hydrogeology Journal》2000,8(6):608-622
Discovery of high contents of methane gas in coals of the Mist Mountain Formation in the Elk River valley, southeastern British
Columbia, Canada, has led to increased exploration activity for coal-seam gas (CSG). CSG production requires groundwater abstraction
to depressurize the coal beds and to facilitate methane flow to the production wells. Groundwater abstraction will have hydrodynamic
effects on the flow system, and an understanding of the groundwater flow system is needed to evaluate these effects. The purpose
of this paper is to describe the groundwater flow system in the area by means of a groundwater flow model and interpretation
of hydrochemical and isotopic analyses of groundwater and surface water.
Groundwater flow for the Weary Creek exploration area is modeled in two vertical sections. The model domains, based on classic
upland–lowland conceptual flow models, are approximately 10,000 m long and 4,000 m deep. Each consists of a fixed water-table
boundary and no-flow boundaries along the traces of major faults. Steady-state groundwater flow is calibrated to hydraulic-head,
streamflow, and groundwater-recharge data. Simulated steady-state velocity fields define regional and local flow components
consistent with the conceptual model.
The results are consistent with regional trends in δ2H, δ18O, tritium, and TDS, which define two distinct groundwater groups (A and B) and a third of intermediate composition. An active,
shallow, local flow component (group A) is recharged in beds cropping out along subdued ridges; this component discharges
as seeps along lower and mid-slope positions in the southern part of the study area. The waters are tritiated, relatively
enriched in δ2H and δ18O, and have low TDS. A deeper regional flow component (group B), which originates at a higher altitude and which discharges
to the Elk River valley bottom, is characterized by non-tritiated groundwater with relatively depleted δ2H and δ18O, and higher TDS.
Groundwater contributes less than 10% of the total direct flow to the Elk River, as indicated by flow measurements and by
the absence of group A and group B characteristics in the river water. Thus it is hypothesized that groundwater extraction
during CSG production will have little impact on the river. The groundwater flow model developed in this work is used in a
companion paper to further test this hypothesis.
Electronic Publication 相似文献
7.
The concept of vulnerability of drinking water sources is reviewed, and a quantitative approach for assessing well vulnerability for complex three-dimensional ground water systems is developed. The approach focuses on the relative expected impact of potential contaminant sources at unknown locations within a well capture zone, providing relative measures of intrinsic well vulnerability, including the expected times of arrival of a contaminant, the dispersion-related reduction in concentration, the time taken to breach a certain quality objective, and the corresponding exposure times. Thus, the result of the analysis includes the usual advective travel time information used in conventional wellhead protection analysis, plus a set of selected quantitative measures expressing the expected impact. The technique is based on adjoint theory and combines forward- and backward-in-time transport modeling using a standard numerical flow and transport code. The methodology is demonstrated using the case study of a complex glacial multiaquifer system in Ontario. The new approach will be useful in helping water managers develop more physically based and quantitative wellhead protection strategies. 相似文献
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A new approach has been developed to detect, characterize, and quantify hydraulic short-circuits in boreholes with faulty seals. The methodology, applicable to an aquifer-aquitard-aquifer system, involves a series of successive, constant-rate pumping tests in the lower aquifer while determining the leakage rate with a simultaneous nonreactive tracer test. During each pumping step, the tracer is injected under constant concentration and constant hydraulic head from a piezometer in the upper aquifer. If a seal defect exists, the tracer will follow the leak and will be recovered from the pumped water. The theoretical equations relate the leakage rate, the pumping rate, the concentration of the injected tracer, and the recovered concentration. Leakage rates can be determined for any pumping rate. The theory is tested using numerical analysis and a full-scale field test. 相似文献