Comparison of Stainless Steel vs. PTFE Miniwells for Monitoring Halogenated Organic Solute Transport     

Gino C. Bianchi-Mosquera  Douglas M. Mackay 《Ground Water Monitoring & Remediation》1992,12(4):126-131

Field tests of organic solute transport behavior have often been monitored using small-diameter wells (miniwells). To determine if experimental results could be significantly biased by sorption to, desorption from, or diffusion through sampling lines, dissolved concentrations of tetrachloroethene and carbon tetrachloride were measured in ground water samples collected simultaneously from the same spatial location during a forced-gradient test in the Borden aquifer using polytetrafluoroethene (PTFE) and stainless steel miniwells (1/8-inch O.D.).
A semiautomated organic analytical system was used on-site to obtain real-time results, which avoided sample holding problems and permitted optimizing sampling times. The breakthrough curves (plots of concentration vs. time) for both organic compounds indicate that under the conditions of this experiment (low organic solute concentrations, short exposure time of sampling lines to the plume, adequate flushing of sampling lines) there is no significant difference between concentration histories (breakthrough curves) collected using a polytetrafluoroethene sampling line and those collected using a stainless steel sampling line. This suggests that organic solute tailing seen in this and also in a similar transport experiment previously conducted at the site is the result of transport processes in the aquifer rather than an artifact introduced by the PTFE miniwells.  相似文献   

Influence of Changing Atmospheric Circulation on Precipitation δO–Temperature Relations in Canada during the Holocene     

Thomas W.D. Edwards  Brent B. Wolfe  Glen M. Macdonald 《Quaternary Research》1996,46(3):211-218

Postglacial precipitation δ¹⁸O history has been reconstructed for two regions of Canada. Long-term shifts in the oxygen-isotope composition of annual precipitation (δ¹⁸O_p) in southern Ontario appear to have occurred with a consistent isotope–temperature relation throughout the past 11,500¹⁴C yr. The modern isotope–temperature relation in central Canada near present boreal treeline evidently became established between 5000 and 4000 years ago, although the relation during the last glacial maximum and deglaciation may also have been similar to present. In the early Holocene, however, unusually high δ¹⁸O_papparently persisted, in spite of low temperature locally, probably associated with high zonal index. A rudimentary sensitivity analysis suggests that a small reduction in distillation of moisture in Pacific air masses traversing the western Cordillera, perhaps accompanied by a higher summer:winter precipitation ratio, could have been responsible for the observed effect. Equivalent isotope–temperature “anomalies” apparently occurred elsewhere in western North America in response to changing early-Holocene atmospheric circulation patterns, suggesting that a time-slice map of δ¹⁸O_pfor North America during this period might provide a useful target for testing and validation of atmospheric general circulation model simulations using isotopic water tracers.  相似文献   

Large-Scale Aquitard Consolidation Near Mexico City   总被引：5，自引：0，他引：5  

Adrian Ortega-Guerrero  John A. Cherry  David L. Rudolph 《Ground water》1993,31(5):708-718

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The Use of Sulphur Hexafluoride as a Conservative Tracer in Saturated Sandy Media     

Ryan D. Wilson  Douglas M. Mackay 《Ground water》1993,31(5):719-724

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A Field Experiment to Study the Behavior of Tetrachloroethylene Below the Water Table: Spatial Distribution of Residual and Pooled DNAPL   总被引：6，自引：0，他引：6  

Bernard H. Kueper  David Redman  Robert C. Starr  Stanley Reitsma  May Mah 《Ground water》1993,31(5):756-766

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Sedimentological and stratigraphic investigations of a sequence of 106 varves from glacial Lake Assiniboine,Saskatchewan   总被引：1，自引：0，他引：1  

Brent Wolfe  James T. Teller 《Journal of Paleolimnology》1993,9(3):257-273

Sediments retrieved from a long core on the floor of glacial Lake Assiniboine, Saskatchewan, expose 106 couplets, consisting of thick, light coloured, silt-rich beds and thin, dark, clay-rich beds. The couplets contain sharp lower and upper contacts of the silt bed, silty and clayey laminations within both the silt and clay beds, and ice-rafted debris in the silt beds, which are features characteristic of glacial varves.Seasonal variations in runoff are reflected in grain size profiles of individual silt beds in the varves. Mean grain size maxima in the lower portion of the silt bed suggest that snow accumulation during the previous winter had been substantial and that a warm spring combined with a rapid melting rate generated significant volumes of nival meltwater runoff. Coarse laminae higher in the silty part of the couplet imply that substantial meltwater inflow was produced by summer melting of glacier ice.Vertical trends in clay bed thicknesses, silt bed thicknesses, and total couplet thicknesses were strongly influenced by the proximity of meltwater inflow channels and lake depth. These interpretations, and correlation of the core to varve exposures at the surface, formed the framework for a paleohydrological reconstruction. Close to 11,000 BP, ice dammed the outlet of glacial Lake Assiniboine and the water depth rose about 2 m yr^–1. Eventually the lake became deep enough for couplets to form. Varve years 1–40 contain thick clay beds, silt beds, and couplets as a result of the proximal inflow of meltwater. A decline in silt bed and couplet thicknesses from varve years 41–85 occurred in response to ice retreat and more distal inflow. Varve deposition ceased in the shallow part of the basin probably because underflow currents from the distal source were redirected. Varve years 86–106 are distinguished by an increase in silt bed and couplet thicknesses and a decrease in clay bed thickness caused by a reduction in water depth and a return to proximal inflow. Varved sedimentation terminated when Lake Assiniboine drained through the Assiniboine valley to Lake Agassiz.  相似文献   

Enhanced Degradation of Halogenated Aliphatics by Zero-Valent Iron   总被引：89，自引：0，他引：89  

Robert W. Gillham  Stephanie F. O'Hannesin 《Ground water》1994,32(6):958-967

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Enhanced Degradation of Dissolved Benzene and Toluene Using a Solid Oxygen-Releasing Compound   总被引：6，自引：0，他引：6  

Gino C. Bianchi-Mosquera  Richelle M. Allen-King  Douglas M. Mackay 《Ground Water Monitoring & Remediation》1994,14(1):120-128

A field lest to evaluate the applicability of an oxygon-releasing compound (ORC) to the rernediation of ground water contaminated with benzone and toluene was conducted in the Borden Aquifer in Ontario. Canada. Benzene and toluene were injected as organic substrates to represent BTEX compounds, bromide was used as a tracer, and nitrate was added to avoid nitrate-limited conditions.
The fate of the solutes was monitored along four lines of monitoring points and wells. Two lines studied the behavior of the solutes upgradient and downgradient of two large-diameter well screens filled with briquets containing ORC and briquets without ORC. One line was used to study the solute behavior upgradient and downgradient of columns of ORC powder placed directly in the saturated zone. The remaining line was a control.
The results indicate that ORC in both briquet and powder form can release significant amounts of oxygen to conlaminated ground water passing by it. In the formulation used in this work, oxygen release persisted for at least 10 weeks. Furthemiore, the study indicates that the enhancement of the available dissolved oxygen content of at least 4 mg/L each of the ground water by ORC can support biodegradation of benzene and toluene dissolved in ground water. Such concentrations are typical of those encountered at sites contaminated with petroleum hydrocarbons; therefore, these results suggest that there is promise for ORC to enhance in situ biodegradation of BTKX contaminants at such sites using passive (nonpumping) systems to contact the contaminated ground water with the oxygen source.  相似文献   

Resistivity structure of the underconsolidated sediments of the Cascadia Basin     

Hong Lei  David C. Nobes 《Geophysical Journal International》1994,118(3):717-729

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A scaling parameter for turbulence in baroclinic convective boundary layers     

S. K. Pedersen  G. D. Stubley 《Boundary-Layer Meteorology》1994,68(3):319-325

The influence of baroclinicity on the structure and levels of turbulence in the convective boundary layer depends on both the magnitude and orientation of geostrophic wind shear and the level of convection. The geostrophic Richardson number, a Richardson number defined in the present work and based on the geostrophic wind shear, is shown to be a single non-dimensional parameter which determines the influence of baroclinicity on convective turbulence structure.  相似文献