ABSTRACT Macropores are important preferential pathways for the migration of water and contaminants through the vadose zone. The objective of this study was to examine small-scale preferential flow processes during infiltration in... more
ABSTRACT Macropores are important preferential pathways for the migration of water and contaminants through the vadose zone. The objective of this study was to examine small-scale preferential flow processes during infiltration in macroporous, low permeability soils. A series of tension infiltration tests were conducted using Brilliant Blue dye tracer at two field sites in southwestern Ontario, Canada. The maximum applied pressure head was varied for each test and the resulting dye stain patterns and macropore networks were characterized by excavation, mapping, photography, and image analysis. Worm burrows were the dominant macropore type, with average macropore densities exceeding 400 m−2 and peak densities of more than 750 m−2 at 30 cm depth at both sites. Flow in macropores became significant at infiltration pressures > − 3 cm, with corresponding increases in infiltration rate, soil water content variability (spatially and temporally), and depth of dye staining. The results demonstrated clear evidence for partially saturated macropore flow under porewater tension conditions and the associated importance of macropore–matrix interaction in controlling this flow. Field observations of transient infiltration showed that film and rivulet flow along macropores yielded vertical flow velocities exceeding 40 m d−1. Simple calculations showed that film flow along the walls and corners of irregularly shaped macropores could explain the observed results. Copyright © 2009 John Wiley & Sons, Ltd.
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Semiconfined aquifers used as the principal water supply within the Basin of Mexico are overlain by lacustrine deposits that provide a degree of protection from contamination associated with metropolitan Mexico City. Solute transport... more
Semiconfined aquifers used as the principal water supply within the Basin of Mexico are overlain by lacustrine deposits that provide a degree of protection from contamination associated with metropolitan Mexico City. Solute transport behavior and the nature of chemical interactions with mineral components in these sediments is poorly understood. The objectives of this paper were to identify the clay mineral
Research Interests: Trace Metals, Clay Minerals, Multidisciplinary, Contaminant Transport, Contaminant hydrology, and 10 moreWater Supply, Mexico City, Solute transport, Specific surface area, X ray diffraction, Fourier transform infrared spectroscopy, Cation Exchange Capacity, Water Content, Cation Exchange, and Pore Water
ABSTRACT On the basis of an analysis of the weighting of the bulk electrical conductivity along time domain reflectivity (TDR) probes we show theoretical limitations to the measurement of solute concentrations with TDR. Simple example... more
ABSTRACT On the basis of an analysis of the weighting of the bulk electrical conductivity along time domain reflectivity (TDR) probes we show theoretical limitations to the measurement of solute concentrations with TDR. Simple example calculations demonstrate that there will only be a unique relationship between the TDR-measured electrical conductivity and the average solute concentration in the pore water under one of two conditions. First, if the water content is spatially uniform throughout the sample volume of the probe, TDR may be used to determine solute concentrations. Second, if the water content is spatially variable but the spatial distribution is temporally constant and the solute concentration is spatially uniform throughout the probe's sample volume, solute concentrations can be inferred from the electrical conductivity response. Further complications arise in soils with spatially variable porosities or surface electrical conductivities, making TDR unsuited to determining solute concentrations even if one of these conditions is met.
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Athabasca Oil Sand Reserve: - Oil sands are contained within the Cretaceous McMurray Formation. (149,000 km2) - 2.5 trillion barrels of extractable oil (~ 25 % of Canada Crude Oil Production) - Surface mineable deposits cover 2,800 km2 -... more
Athabasca Oil Sand Reserve: - Oil sands are contained within the Cretaceous McMurray Formation. (149,000 km2) - 2.5 trillion barrels of extractable oil (~ 25 % of Canada Crude Oil Production) - Surface mineable deposits cover 2,800 km2 - 450 billion L of process water used annually - Currently over 130 km2 of tailings ponds (largest man-made structures in the world)
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Recent field studies have shown that both the application method and application rate influence the likelihood of liquid manure breakthrough to tile drains. Although a substantial amount of observational evidence exists to support the... more
Recent field studies have shown that both the application method and application rate influence the likelihood of liquid manure breakthrough to tile drains. Although a substantial amount of observational evidence exists to support the intuitive concept that higher application rates and pressures promote rapid liquid manure breakthrough to tiles, there is a scarcity of information regarding how physical processes govern the movement of manure constituents through macroporous soils in tile drained fields. Here we employ a dual permeability, flow and transport model to simulate liquid swine manure application experiments conducted in Sebringville, Ontario between 2000 and 2002. During the Sebringville experiments, ammonium and phosphate were detected in tile effluent soon after application. Using nutrient breakthrough data from the field experiment as a benchmark, the model was employed to predict how ammonium and phosphate are transported and ultimately distributed between tile drains...
Panel Discussion: U.S.-Canada Transboundary Perspectives Longest international border in the world: 8,890km, over 3,000km are water! - Major transboundary river systems (Columbia, Red River) - 1997 Red River Flood - Strategies for future... more
Panel Discussion: U.S.-Canada Transboundary Perspectives Longest international border in the world: 8,890km, over 3,000km are water! - Major transboundary river systems (Columbia, Red River) - 1997 Red River Flood - Strategies for future power and water needs - Canadian resource-based economy
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... Received 2 April 1997; accepted 8 June 1997; . Citation: Harvey, FE, DR Lee, DL Rudolph, and SK Frape (1997), Locating Groundwater Discharge in Large Lakes Using Bottom Sediment Electrical Conductivity Mapping, Water Resour. ...
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ABSTRACT This study investigated post-harvest temporal changes in macroporosity and hydraulic properties, relative to subsurface drain position, at three different locations within a single field. Tension and double-ring infiltrometer... more
ABSTRACT This study investigated post-harvest temporal changes in macroporosity and hydraulic properties, relative to subsurface drain position, at three different locations within a single field. Tension and double-ring infiltrometer tests were conducted on the field surface at distances between 0 and 4 m from drains to determine hydraulic conductivity and a soil structural parameter as a function of pressure head [K(psi) and alpha'(psi), respectively], and field-saturated hydraulic conductivity (K-fs). At two of the locations, duplicate sets of infiltration tests were conducted on significantly drier soils about 1 mo after the initial tests. Macroporosity values at each location were determined visually and with capillary theory (i.e., hydraulically effective macroporosity, (epsilon) over bar (m)), and results from the two methods were compared. At the two field locations with relatively low B horizon permeability, surface soil K-fs was greatest above the drains; however, at the location with the greatest B horizon permeability, surface soil K-fs increased away from the drain. The K-fs was also significantly (P < 0.1) greater under drier soil conditions. Although alpha'(psi) and K(psi) relationships were not influenced by drain position, they did exhibit temporal variability. For psi < -2 cm, both alpha'(psi) and K(psi) were less in dry soil, whereas for psi > -1 cm, both alpha'(psi) and K(psi) tended to be greater in dry soil. The (epsilon) over bar (m)) was not influenced by drain position but tended to be greater in wetter soil, although (epsilon) over bar (m)) attributable to pores with equivalent diameter > 0.3 cm tended to be greater in dry soil. The (epsilon) over bar (m)) m was approximately 100 times less than visible macroporosity.
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A new approach, named the Homogeneous Tectonic Domain method (HTD) is developed to correlate structural lineaments recognised through air-photo interpretation with subsurface fracture features that are associated with zones of high... more
A new approach, named the Homogeneous Tectonic Domain method (HTD) is developed to correlate structural lineaments recognised through air-photo interpretation with subsurface fracture features that are associated with zones of high groundwater production in frac- tured-rock environments. The analysis approach involves correlating the lineament features of a given area with the orientation of the pri- mary stress fields and fracture
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The Mexico City region has several flat plains formed on exceptionally porous (60–90%) lacustrine deposits overlying a highly productive regional aquifer. Severe land subsidence due to consolidation of the lacustrine aquitard caused by... more
The Mexico City region has several flat plains formed on exceptionally porous (60–90%) lacustrine deposits overlying a highly productive regional aquifer. Severe land subsidence due to consolidation of the lacustrine aquitard caused by aquifer exploitation has resulted ...
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ABSTRACT Estimates of groundwater seepage flux in lake bottom sediments require knowledge of the hydraulic gradient at the sediment-surface water interface and the hydraulic conductivity of the lake-bottom materials. In deep waters, in... more
ABSTRACT Estimates of groundwater seepage flux in lake bottom sediments require knowledge of the hydraulic gradient at the sediment-surface water interface and the hydraulic conductivity of the lake-bottom materials. In deep waters, in situ measurement of these parameters can be accomplished through the use of piezometer probes lowered and monitored remotely from a surface vessel. In this research work a new tethered piezometer probe was developed and tested for use in collecting hydraulic property data in deep-lake bottom sediments. The probe uses a variable-reluctance transducer to measure the differential sediment pore pressure between two ports spaced 100 cm apart. The dissipation of pore pressure transients that develop during rapid emplacement of the probe were extrapolated in time to estimate equilibrium hydraulic gradients. In addition, various data analysis techniques were evaluated for determining sediment hydraulic conductivity and specific storage through interpretation of the pore-pressure dissipation data. The probe was used to estimate groundwater seepage in the bottom sediments of the Hamilton Harbour, at the western end of Lake Ontario. Upward gradients were measured at nine locations within the harbor ranging from 0.010 to 0.425 and a downward gradient of −0.015 was recorded at one site along the harbor's eastern boundary. Hydraulic conductivities determined from pore-pressure dissipation over time ranged from 6.9 × 10−9to 4.8 × 10−7 m/s. Specific storage values ranged from 0.08 to 0.19 m−1. Calculated average linear seepage velocities ranged from 4.3 × 10−8 to −8.5 × 10−9 m/s. The groundwater contribution to the harbor through the deeper, fine-grained sediments was estimated to be 9.1 × 10−2 m3/s, or 2.9 × 106 m3/yr. This represents approximately 1.0% of the harbor basin's total volume, 15% of precipitation's contribution, 1.2% of the contribution of surface inflows (excluding the Burlington ship canal) and 0.22% of the total surface outflow passing through the Burlington shipping canal, which connects the harbor to Lake Ontario.
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... weaknesses. The most basic of the methods involves manually identifying macropores on exposed soil surfaces and has been used extensively (eg, Ehlers, 1975; Lauren et al., 1988; Logsdon et al., 1990). ... As an example, Lauren et al.... more
... weaknesses. The most basic of the methods involves manually identifying macropores on exposed soil surfaces and has been used extensively (eg, Ehlers, 1975; Lauren et al., 1988; Logsdon et al., 1990). ... As an example, Lauren et al. (1988 ...
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Polystyrene latex microspheres are widely used as surrogates for biocolloid transport in porous media; however, relatively few studies directly compare microsphere transport with that of the microorganism it is intended to represent,... more
Polystyrene latex microspheres are widely used as surrogates for biocolloid transport in porous media; however, relatively few studies directly compare microsphere transport with that of the microorganism it is intended to represent, particularly at the field scale. Here, we compared the transport behaviour of a bacterium (Escherichia coli RS2g; 1.2 microm in diameter) and three different sized microspheres (1.1, 3.9, and 4.8 microm in diameter) within undisturbed agricultural field soil following infiltration under partially saturated conditions. The soil contained significant macroporosity. A tension infiltrometer was used to control the application of a transport solution containing Brilliant Blue FCF dye to two plots. A >2 log reduction in the concentration of all colloids was observed from the soil surface to 5 cm depth in both plots. The concentration of colloids in the soil was generally proportional to the intensity of soil dye staining; however, both the E. coli RS2g bac...
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ABSTRACT It is of great importance to be able to properly simulate flow mechanisms within the vadose zone as they are controlling factors for solute transport to groundwater bodies. The highly detailed pumping test data set collected by... more
ABSTRACT It is of great importance to be able to properly simulate flow mechanisms within the vadose zone as they are controlling factors for solute transport to groundwater bodies. The highly detailed pumping test data set collected by Bevan et al. (2005) at the Borden aquifer provides a unique opportunity to investigate the controlling factors for fluid flow and moisture distribution in the vadose zone in response to pumping. The field results show capillary fringe thicknesses that increased with duration of pumping, and decreased with distance from the well. This increased thickness was persistent for the duration of the 7 day test. Previous numerical analysis of the pumping test has been able to replicate the observed moisture contents at discrete time intervals (Moench, 2008), but the physical mechanisms controlling the moisture content observations are poorly understood.Hydraulic conductivity heterogeneity has been proposed as a potential mechanism for the capillary fringe extension observed in the field. Using stochastic hydraulic conductivity fields, moisture content distributions observed during the Bevan et al. (2005) pumping test were simulated using a variably saturated numerical model. A Monte Carlo analysis was performed and ensemble results are presented. The ensemble mean hydraulic head drawdown was an adequate match to the field data, although there was a small but consistent over prediction of drawdown. The ensemble mean thickness of the capillary fringe was not significantly different from the result of a homogeneous simulation, and did not replicate the increasing thickness observed in the field. The ensemble mean capillary fringe extension was not found to be dependent upon distance from the pumping well or duration of pumping. Zones of perched water were formed in many of the heterogeneous realizations; however, neutron probe data collected during the field experiment does not support the presence of these perched zones.
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ABSTRACT A 24-h pumping test was conducted in the shallow water table portion of an unconfined aquifer located at Canadian Forces Base Borden near Alliston, Ontario, Canada. This test was designed to monitor the dynamic nature of the... more
ABSTRACT A 24-h pumping test was conducted in the shallow water table portion of an unconfined aquifer located at Canadian Forces Base Borden near Alliston, Ontario, Canada. This test was designed to monitor the dynamic nature of the vertical gradients that form within the zone of tension saturation above the water table during pumping and recovery. During the test, pressure head was monitored throughout the saturated zone, both above (tensiometers) and below (piezometers) the water table; soil water content was monitored using both neutron moisture probes and time domain reflectometry (TDR). Following pumping, recovery was monitored in the same manner as the pumping portion of the test. The hydraulic head drawdown observed above the water table in the tension saturated zone during pumping and recovery was very similar to the drawdown observed below the water table. Vertical gradients throughout the saturated zone appeared to be uniform and low, and did not change significantly in the transition across the water table. The magnitude of the vertical gradients peaked early in the test, and subsequently decreased, with the reduction being more significant at greater radial distances from the pumping well. Neutron measurements indicate that only a minor degree of drainage occurred within the measurement interval for the duration of the test, a result of the low magnitude of drawdown generated during pumping and influence of hysteresis on the moisture profile. Although drainage was negligible from within the tension saturated zone during pumping, the hydraulic head drawdown below the water table displayed reduced rates of drawdown during the intermediate period of the test. TDR data was only collected during recovery; however, the data set displays hysteretic behavior in the pressure–saturation profiles, with all profiles plotting on scanning curves. Based on these observations it appears that a conceptual model in which vertical gradients below the water table are of the same order of magnitude as those within the capillary fringe is appropriate for the analysis of vadose zone response to pumping.Highlights► Data from a 24-hour pumping test including observations above the water table. ► Uniform vertical gradients observed through saturated zone including capillary fringe. ► Water table drawdown accurately predicted using piezometric drawdowns. ► Time-drawdown curve shows inflection yet no drawdown of top of saturated zone.
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Research Interests: Hydrology, Multidisciplinary, Quaternary, Holocene, Evapotranspiration, and 15 moreGround Water, Hydraulic conductivity, Deuterium, Cenozoic, Hydrodynamics, Phanerozoic, Groundwater flow, Coastal Plain, Lac, Coastal Wetlands, Sedimentary Rocks, Plains, ground water recharge, hydrographs, and Halides
Research Interests: Mass Transfer, Wetlands, Hydrology, Water quality, Multidisciplinary, and 15 moreAtmospheric deposition, Salinity, Evapotranspiration, Ground Water, Water balance, Solute transport, Groundwater flow, Runoff, Water Quality, Water Flow, Subsurface Flow, Vadose Zone Modeling, Recharge, Soil Water, and Surface Runoff
ABSTRACT Not Available.
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Fertilizer use in coffee plantations is a suspected cause of rising ground water nitrate concentrations in the ground water-dependent Central Valley of Costa Rica. Nitrate adsorption was evaluated beneath two coffee (Coffea arabica L.)... more
Fertilizer use in coffee plantations is a suspected cause of rising ground water nitrate concentrations in the ground water-dependent Central Valley of Costa Rica. Nitrate adsorption was evaluated beneath two coffee (Coffea arabica L.) plantations in the Central Valley. Previous work at one site had identified unsaturated zone nitrate retardation relative to a tritium tracer. Differences in nitrate adsorption were assessed in cores to 4 m depth in Andisols at this and one other plantation using differences in KCl- and water-extractable nitrate as an index. Significant adsorption was confirmed at the site of the previous tracer test, but not at the second site. Anion exchange capacity, X-ray diffraction data, extractable Al and Si, and soil pH in NaF corroborated that differences in adsorption characteristics were related to subtle differences in clay mineralogy. Soils at the site with significant nitrate adsorption showed an Al-rich allophane clay content compared with a more weathered, Si-rich allophane and halloysite clay mineral content at the site with negligible adsorption. At the site with significant nitrate adsorption, nitrate occupied less than 10% of the total anion adsorption capacity, suggesting that adsorption may provide long-term potential for mitigation or delay of nitrate leaching. Evaluation of nitrate sorption potential of soil at local and landscape scales would be useful in development of nitrogen management practices to reduce nitrate leaching to ground water.
Research Interests: Earth Sciences, Mineralogy, Coffee, Long Term Potentiation, Environmental Management, and 15 moreAgriculture, Clay Minerals, Environmental Pollution, Adsorption, Biological Sciences, Environmental Sciences, Ground Water, Nitrates, Nitrogen, Environmental quality, Clay mineralogy, Fertilizers, Mineral content, Environment Quality, and nitrate leaching
Organic carbon bioreactors provide low-cost, passive treatment of a variety of environmental contaminants but can have undesirable side effects in some cases. This study examines the production of methyl mercury (MeHg) in a streambed... more
Organic carbon bioreactors provide low-cost, passive treatment of a variety of environmental contaminants but can have undesirable side effects in some cases. This study examines the production of methyl mercury (MeHg) in a streambed bioreactor consisting of 40 m³ of wood chips and designed to treat nitrate (NO₃) in an agricultural drainage ditch in southern Ontario (Avon site). The reactor provides 30 to 100% removal of NO₃-N concentrations of 0.6 to 4.4 mg L(-1), but sulfate (SO₄(2-)) reducing conditions develop when NO₃ removal is complete. Sulfate reducing conditions are known to stimulation the production of MeHg in natural wetlands. Over one seasonal cycle, effluent MeHg ranged from 0.01 to 0.76 ng L(-1) and total Hg ranged from 1.3 to 3.4 ng L(-1). During all sampling events when reducing conditions were only sufficient to promote NO₃(-) reduction (or denitrification) ( = 5, late fall 2009, winter 2010), MeHg concentrations decreased in the reactor and it was a net sink for MeHg (mean flux of -5.1 μg m(-2) yr(-1)). During all sampling events when SO₄(2-) reducing conditions were present ( = 6, early fall 2009, spring 2010), MeHg concentrations increased in the reactor and it was a strong source of MeHg to the stream (mean flux of 15.2 μg m(-2) yr(-1)). Total Hg was consistently removed in the reactor (10 of 11 sampling events) and was correlated to the total suspended sediment load ( r² = 0.69), which was removed in the reactor by physical filtration. This study shows that organic carbon bioreactors can be a strong source of MeHg production when SO₄(2-) reducing conditions develop; however, maintaining NO₃-N concentrations > 0.5 mg L suppresses the production of MeHg.
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ABSTRACT Extraction of oil sands in the relatively dry Western Boreal Plains near Fort McMurray, Alberta, destroys the natural surface cover including fen peatlands that cover upto 65% of the landscape. Industry and environmental... more
ABSTRACT Extraction of oil sands in the relatively dry Western Boreal Plains near Fort McMurray, Alberta, destroys the natural surface cover including fen peatlands that cover upto 65% of the landscape. Industry and environmental monitoring agencies have questioned the ability to reclaim fen peatlands in the post-mine landscape. This study proposes a conceptual model to replace fen systems with fen peat materials supported by groundwater inflow from a constructed watershed. A numerical model is used to determine the optimum system geometry, including the ratio of upland to fen area, thickness and slope of sand materials, and thickness of peat and of the liner that would result in flows that sustain peat wetness to a critical threshold soil water pressure of −100 cm of water at a peat depth of 10 cm. We also test the sensitivity of the system to variations in the value and spatial configuration of the hydraulic conductivity (K) of locally available materials. The optimal conditions were achieved using an upland area at least twice that of the fen, underlain by a sloping (3%) layer of fine-grained material with hydraulic conductivity (K) of 10−10 m/s, that maintains lateral groundwater flow in a sand layer with K of 10−4 to 10−5 m/s. Using daily climate inputs that included 1998, the driest summer on record, the model suggests that adequate wetness can be sustained in the fen for the growing season, and that the extent of water table recession was similar to undisturbed systems during that period.
Research Interests: Hydrogeology, Hydrology, Environmental Monitoring, Spatial Configuration, Conceptual Design, and 11 moreHydrological modelling, Conceptual Model, Water Table, Groundwater flow, Numerical Model, Reclamation, Peatland, Optimality Condition, Soil Water, ENVIRONMENTAL SCIENCE AND MANAGEMENT, and Growing Season
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... To do so would also require the fundamental principals of Darcy's Law controlling groundwater flow to be ignored, which the responding authors ... on dry ground immediately adjacent to the Sistem Lerma wells and approximately 200... more
... To do so would also require the fundamental principals of Darcy's Law controlling groundwater flow to be ignored, which the responding authors ... on dry ground immediately adjacent to the Sistem Lerma wells and approximately 200 m from the edge of Laguna Almoloya, higher ...
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Oil sand mine tailings are primarily contained by dykes constructed of permeable sand tailings. The environmental impacts of process waters released from these tailings facilities are controlled by groundwater flow within the impoundment... more
Oil sand mine tailings are primarily contained by dykes constructed of permeable sand tailings. The environmental impacts of process waters released from these tailings facilities are controlled by groundwater flow within the impoundment structures. Transient groundwater flow characteristics were assessed within the Tar Island Dyke structure at the Suncor Inc. site near Fort McMurray, Alberta, to assist in quantifying potential long-term environmental impacts. A sequence of low-permeability fine tailings underlying the tailings water pond is supported by coarse sand tailings that are connected to and form the containment dyke structure. A clay unit separates the foundation from the underlying limestone that is hydraulically connected to the Athabasca River. The primary groundwater flow pathways are through the toe of the dyke and through the foundation. Field data and numerical simulations indicate that drainage of process water within the structure remains transient yet decreases o...