Climatic effects on near surface contaminant transport routes in fine-grained soils

2022 ◽  
Author(s):  
Christine M. Fiori
Keyword(s):  
Contaminant Transport ◽  
Climatic Effects ◽  
Near Surface ◽  
Fine Grained

Spatial Variability of Contaminant Transport in a Fractured Till, Avedøre Denmark

1999 ◽  
Vol 30 (4-5) ◽  
pp. 333-360 ◽  
Author(s):  
Larry McKay ◽  
Johnny Fredericia ◽  
Melissa Lenczewski ◽  
Jørn Morthorst ◽  
Knud Erik S. Klint
Keyword(s):  
Hydraulic Conductivity ◽  
Spatial Variability ◽  
Field Experiment ◽  
Contaminant Transport ◽  
Tracer Test ◽  
Conductivity Measurements ◽  
Fine Grained ◽  
Downward Migration ◽  
Rapid Transport ◽  
High Degree

A field experiment shows that rapid downward migration of solutes and microorganisms can occur in a fractured till. A solute tracer, chloride, and a bacteriophage tracer, PRD-1, were added to groundwater and allowed to infiltrate downwards over a 4 × 4 m area. Chloride was detected in horizontal filters at 2.0 m depth within 3-40 days of the start of the tracer test, and PRD-1 was detected in the same filters within 0.27 - 27 days. At 2.8 m depth chloride appeared in all the filters, but PRD-1 appeared in only about one-third of the filters. At 4.0 m depth chloride appeared in about one-third of the filters and trace amounts of PRD-1 were detected in only 2 of the 36 filters. Transport rates and peak tracer concentrations decreased with depth, but at each depth there was a high degree of variability. The transport data is generally consistent with expectations based on hydraulic conductivity measurements and on the observed density of fractures and biopores, both of which decrease with depth. Transport of chloride was apparently retarded by diffusion into the fine-grained matrix between fractures, but the rapid transport of PRD-1, with little dispersion, indicates that it was transported mainly through the fractures.

scholarly journals Characterization and formation of melt layers in polar snow: observations and experiments from West Antarctica

2005 ◽  
Vol 51 (173) ◽  
pp. 307-312 ◽  
Author(s):  
Sarah B. Das ◽  
Richard B. Alley
Keyword(s):  
Field Experiments ◽  
Preferential Flow ◽  
Ice Core ◽  
Ice Cores ◽  
West Antarctica ◽  
Near Surface ◽  
Fine Grained ◽  
Ice Core Record ◽  
Temperature Records ◽  
Polar Snow

AbstractSurface melting rarely occurs across most of the Antarctic ice sheet, away from the warmer coastal regions. Nonetheless, isolated melt features are preserved in the firn and ice in response to infrequent and short-lived melting events. An understanding of the formation and occurrence of these melt layers will help us to interpret records of past melt occurrences from polar ice cores such as the Siple Dome ice-core record from West Antarctica. A search in the near-surface firn in West Antarctica found that melt features are extremely rare, and consist of horizontal, laterally continuous, one to a few millimeter thick, ice layers with few air bubbles. The melt layers found date from the 1992/93 and 1991/92 summers. Field experiments to investigate changes in stratigraphy taking place during melt events reproduced melt features as seen in the natural stratigraphy. Melting conditions of varying intensity were created by passively heating the near-surface air for varying lengths of time inside a clear plastic hotbox. Melt layers formed due entirely to preferential flow and subsequent refreezing of meltwater from the surface into near-surface, fine-grained, crust layers. Continuous melt layers were formed experimentally when positive-degree-day values exceeded 1ºC-day, a value corresponding well with air-temperature records from automatic weather station sites where melt layers formed in the recent past.

scholarly journals Ice Fabrics and Petrography, Meserve Glacier, Antarctica

1974 ◽  
Vol 13 (68) ◽  
pp. 285-306 ◽  
Author(s):  
P.W. Anderton
Keyword(s):  
Steady State ◽  
Stress Level ◽  
Optic Axis ◽  
Near Surface ◽  
Fine Grained ◽  
Basal Ice ◽  
Single Maximum ◽  
Fabric Analysis ◽  
Rock Interface ◽  
Ice Fabrics

Results of petrographic and fabric analysis of fine-grained cold ice from the tongue of Meserve Glacier, Antarctica, are described. Most of the basal ice is remarkably uniform in texture and shows an optic-axis fabric with a single strong maximum, which is consistent with the steady-state conditions of flow. Within 0.5 m of the ice–rock interface, irregularities in the bed cause flow perturbations which are correlated with recrystallization and changes in fabric of the ice. Optic-axis fabrics in the basal ice show close symmetry relationships with dimensional fabric and deformation symmetry. Grain-size of the ice increases towards the surface of the glacier and the single maximum of the optic-axis fabric undergoes a rotation about the flow vector. In the near surface, where strain-rates are relatively much lower, the optic-axis fabric symmetry is not closely related to either deformation symmetry or the dimensional fabric. Syntectonic recrystallization of ice throughout the glacier tongue characteristically produces a strong single-maximum fabric, the orientation of which in relation to the stress field is apparently determined by stress level. Under steady-state conditions of flow, the strength of the maximum also appears to be a function of stress level.

GROUND AND AIRBORNE RESISTIVITY SURVEYS OF PERMAFROST NEAR FAIRBANKS, ALASKA

Geophysics ◽  
1975 ◽  
Vol 40 (4) ◽  
pp. 641-656 ◽  
Author(s):  
P. Hoekstra ◽  
P. V. Sellmann ◽  
A. Delaney
Keyword(s):  
Surface Impedance ◽  
Apparent Resistivity ◽  
Surface Sediments ◽  
Impedance Measurement ◽  
Impedance Method ◽  
Frozen Ground ◽  
Near Surface ◽  
Fine Grained ◽  
Ground Conditions ◽  
Geotechnical Information

In permafrost regions investigations for such geotechnical endeavors as route selection for roads and pipelines and site investigations for buildings and dam construction often require that a careful assessment be made of the presence or absence of frozen ground, of the ice content of frozen ground, and of the depth of frozen ground. In the vicinity of Fairbanks, Alaska, where the permafrost is discontinuous, ground and airborne methods of mapping electrical resistivity using radiowaves were tested as means of delineating permafrost. When the resistivity maps are compared with surficial geological data, the following conclusions are reached: (1) In areas of fine‐grained sediments, where the near surface sediments are relatively uniform, VLF resistivity delineates permafrost. (2) In areas where surface sediments vary widely (flood plains), VLF resistivity shows little information on permafrost conditions but can provide other important geotechnical information, such as, depth to bedrock, surface soil type, and layering. Comparison of the apparent resistivity derived from a surface impedance measurement at VLF on the ground with the apparent resistivity derived from an airborne measurement of wavetilt shows that the regional trends in the data agree, but the surface impedance measurements show much more local detail in ground conditions. When the surface layers are also frozen, the surface impedance method of measuring ground resistivity was found to have distinct advantages over conventional galvanic methods in terms of production and problems associated with probe contact resistance.

Mineralogy of the near-surface expression of Au-As-Cu mineralization in an arid environment

1994 ◽  
Vol 58 (391) ◽  
pp. 315-323
Author(s):  
R. Bogoch ◽  
M. Shirav ◽  
A. Gilat ◽  
L. Halicz
Keyword(s):  
Iron Oxide ◽  
Surface Expression ◽  
Arid Environment ◽  
Solid Solution Phase ◽  
Near Surface ◽  
Amorphous Phases ◽  
Fine Grained ◽  
Precambrian Terrain ◽  
Spherical Droplets ◽  
Neutral Conditions

AbstractIn the arid, Late Precambrian terrain of southern Israel, a complex suite of minerals and amorphous species were deposited in host gneiss from fluids under near-neutral conditions within 1 m of the surface. The morphology of secondary gold appears to relate to its host mineral (skeletal-dendritic with quartz; multi-faceted crystals with arsenates; spherical droplets with iron oxide). The gold is very fine-grained, and was most likely complexed as a thiosulphate.Three amorphous phases are present (iron oxide, chrysocolla, Cu-Mn-(Fe-As) silicate). At least in part, gold and baryte appear to have crystallized out of a metal-Fe-oxide gel. Other minerals, including apatite, anglesite, and conichalcite, may have grown from appropriate crystallites present in the gel.The conichalcite occurs mainly as bladed to acicular radial spherulites. In the presence of lead, a solid solution phase between duftite and conichalcite (‘Pb-conichalcite’) was formed.

The thermal regime of a retrogressive thaw slump near Mayo, Yukon Territory

2000 ◽  
Vol 37 (7) ◽  
pp. 967-981 ◽  
Author(s):  
C R Burn
Keyword(s):  
Dominant Mode ◽  
Yukon Territory ◽  
Permafrost Degradation ◽  
Near Surface ◽  
Ground Temperatures ◽  
Fine Grained ◽  
Data Loggers ◽  
Development Data ◽  
Retrogressive Thaw Slump ◽  
Frost Penetration

The development of a retrogressive thaw slump near Mayo, Yukon Territory, has been traced from initiation by bank erosion (~1949) of the Stewart River to stabilization in 1993-1994. The stabilized headwall of the slump is 450 m from the river, and the slope of the slump floor is 3°. A transect of the slump from the river to the stabilized headwall was drilled in July 1995, to determine the extent and rate of permafrost degradation in the slump floor. Thermistors were placed in access tubes to 12 m depth at five sites, four near the transect and one in undisturbed terrain, to determine the magnitude of thermal disturbance due to slump development. Data loggers at the sites recorded the ground temperature at 1 m depth for two years from August 1995. The annual mean ground temperatures measured by the data loggers varied between 1.2° and 1.8°C in the slump, compared with -2.4°C in undisturbed ground, indicating a disturbance of about 4°C due to slumping. The depth of thaw in the slump floor is consistent with the Stefan solution for thawing of permafrost. Conduction is the dominant mode of heat transfer in the slump, where the soil is fine grained and there is almost no organic horizon. Winter ground temperatures at 1 m depth were nearly 6°C warmer in the slump than in the surrounding forest, even though snow depths were similar, due to the release of latent heat during prolonged frost penetration. These data demonstrate the importance of subsurface conditions on near-surface ground temperatures in winter.

scholarly journals Frequency dependent amplification of weak ground motions in Porirua and Lower Hutt, New Zealand

1992 ◽  
Vol 25 (4) ◽  
pp. 303-331 ◽  
Author(s):  
J. John Taber ◽  
Euan G. C. Smith
Keyword(s):  
New Zealand ◽  
Frequency Band ◽  
Spectral Ratio ◽  
Silty Sand ◽  
Peak Ground Velocity ◽  
Soft Sediment ◽  
Spectral Ratios ◽  
Near Surface ◽  
Fine Grained ◽  
Water Saturated

The relative ground response due to microearthquakes has been examined at a total of 36 sites in the Porirua and Lower Hutt regions of New Zealand, as part of a multi-disciplinary microzoning project conducted with the Wellington Regional Council. The sites were studied in two separate experiments and were chosen to sample a variety of soil types and depths ranging from strong rock to thick sections of alluvial gravels and sands to soft water-saturated fine-grained deposits. The amplitude response of each site relative to a bedrock reference site has been determined as a function of frequency. Fourier spectral ratios (Fsr) were calculated for each earthquake and then between three and twenty-six earthquakes were averaged together at each of the sites. Spectral ratios of individual earthquakes varied significantly from the average spectral ratio. In the Hutt Valley there is a gradual down-valley increase in shaking in a similar pattern to the down-valley increase of the depth to bedrock and thickness of near-surface soft sediment. The response at the upper-most valley sites, underlain by less than 50 m of alluvial gravel and silty sand, is similar to the response at the rock sites on the side of the valley (Fsr = 2.4) while the Fourier spectral ratios reach 14 at the lower-most valley sites, which are underlain by greater than 20 m of soft sediment. The highest amplifications were recorded at two sites on soft flexible sediments (10 to 35 m thick) in an enclosed valley (Fsr = 16 to 18) and a site on an apparently drained and filled swamp (Fsr = 15). A spectral ratio of 18 corresponds to an increase in peak ground velocity by a factor of 5. The amplification at most Lower Hutt sites occurred over a broad frequency band from 0.5 Hz to up to 5 Hz, with the high frequency limit of the band decreasing as the spectral ratio in the band increased. Two of the flexible sediment sites exhibited a very narrow frequency response with a peak in the 1-2 Hz range, similar to three flexible sediment sites in the Porirua basin where the amplification was in the 1-3 Hz frequency band. These flexible sediment sites had Fourier spectral ratios of up to 18 relative to a hard rock site. Three other Porirua sites had spectral ratios greater than 5 at some frequency. Two of these sites were on fan alluvium and fine grained sediment, while the third was on siltly sand on a topographic ridge. The remaining five sites were on weathered gravels and showed little amplification.

scholarly journals Aerodynamic Characteristics Over Fine-Grained Gravel Surfaces in a Wind Tunnel

2021 ◽  
Vol 9 ◽  
Author(s):  
Jiaqi Liu ◽  
Reiji Kimura ◽  
Jing Wu
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Lower Layer ◽  
Aerodynamic Characteristics ◽  
Gobi Desert ◽  
Near Surface ◽  
Fine Grained ◽  
Wind Speeds ◽  
Speed Fluctuations

Gravels can protect soil from wind erosion, however, there is little known about the effects of fine-grained gravel on aerodynamic characteristics of the near-surface airflow. Drag coefficient, wind-speed gradient, and turbulent transfer coefficient over different coverages of gravel surfaces were investigated in a compact boundary-layer wind tunnel. The drag coefficient of the fine-grained gravel surface reached the maximum value at 15% coverage and then tended to stabilize at gravel coverage 20% and greater. At a height of 4 cm, near-surface airflow on gravel surfaces can be divided clearly into upper and lower sublayers, defined as the inertial and roughness sublayers, respectively. The coefficient of variation of wind speed over gravel surfaces in the roughness sublayer was 8.6 times that in the inertial sublayer, indicating a greater effect of gravel coverage on wind-speed fluctuations in the lower layer. At a height of 4 cm, wind-speed fluctuations under the observed wind speeds were independent of changes in gravel coverage. In addition, an energy-exchange region, where sand particles can absorb more energy from the surrounding airflow, was found between the roughness and inertial sublayers, enhancing the erosional state of wind-blown sand. This finding can be applied to evaluate the aerodynamic stability of the gravel surface in the Gobi Desert and provide a theoretical basis for elucidation of the vertical distributions of wind-blown sand flux.

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