scholarly journals Multidimensional simulation of PFAS transport and leaching in the vadose zone: impact of surfactant-induced flow and soil heterogeneities

2021 ◽  
Author(s):  
Jicai Zeng ◽  
Bo Guo
Keyword(s):  
Vadose Zone ◽  
Preferential Flow ◽  
Ground Surface ◽  
High Water Content ◽  
Three Dimensional Model ◽  
Minimal Impact ◽  
Early Arrival ◽  
Soil Heterogeneities ◽  
Induced Flow ◽  
Long Chain

PFAS are emergent contaminants of which fate and transport in the environment remain poorly understood. As surfactants, adsorption at air-water interfaces and solid surfaces in soils complicates the retention and leaching of PFAS in the vadose zone. Recent modeling studies accounting for the PFAS-specific nonlinear adsorption processes predicted that the majority of long-chain PFAS remain in the shallow vadose zone decades after contamination ceases—in agreement with many field measurements. However, some field investigations show that long-chain PFAS have migrated to tens to a hundred meters below ground surface. These discrepancies may be attributed to model simplifications such as a one-dimensional (1D) representation of the homogeneous vadose zone. Another potentially critical process that has not been fully examined by the 1D models is how surfactant-induced flow (SIF) influences PFAS leaching in multidimensions. We develop a new three-dimensional model for PFAS transport in the subsurface to investigate the multidimensional effects of SIF and soil heterogeneities. Our simulations and analyses conclude that 1) SIF has a minimal impact on the long-term leaching of PFAS in the vadose zone, 2) preferential flow pathways generated by soil heterogeneities lead to early arrival and accelerated leaching of (especially long-chain) PFAS, 3) the acceleration of PFAS leaching in high water-content preferential pathways or perched water above capillary barriers is more prominent than conventional contaminants due to the destruction of air-water interfaces, and 4) soil heterogeneities are among primary sources of uncertainty for predicting PFAS leaching and retention in the vadose zone.

scholarly journals Assessment of vadose zone sampling methods for detection of preferential herbicide transport

2009 ◽  
Vol 6 (6) ◽  
pp. 7247-7285 ◽  
Author(s):  
N. P. Peranginangin ◽  
B. K. Richards ◽  
T. S. Steenhuis
Keyword(s):  
Vadose Zone ◽  
Preferential Flow ◽  
Sampling Methods ◽  
Sandy Loam ◽  
Silty Clay ◽  
Water Sampling ◽  
Herbicide Transport ◽  
Flow Mechanisms ◽  
Ceramic Cups ◽  
Zone Sampling

Abstract. Accurate soil water sampling is needed for monitoring of pesticide leaching through the vadose zone, especially in soils with significant preferential flowpaths. We assessed the effectiveness of wick and gravity pan lysimeters as well as ceramic cups (installed 45–60 cm deep) in strongly-structured silty clay loam (Hudson series) and weakly-structured fine sandy loam (Arkport series) soils. Simulated rainfall (10–14 cm in 4 d, approximately equal to a 10-yr, 24 h storm) was applied following concurrent application of agronomic rates (0.2 g m−2) of atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and 2,4-D (2,4-dichloro-phenoxy-acetic acid) immediately following application of a chloride tracer (22–44 g m−2). Preferential flow mechanisms were observed in both soils, with herbicide and tracer mobility greater than would be predicted by uniform flow. Preferential flow was more dominant in the Hudson soil, with earlier breakthroughs observed. Mean wick and gravity pan sampler percolate concentrations at 60 cm depth ranged from 96 to 223 μg L−1 for atrazine and 54 to 78 μg L−1 for 2,4-D at the Hudson site, and from 7 to 22 μg L−1 for atrazine and 0.5 to 2.8 μg L−1 for 2,4-D at the Arkport site. Gravity and wick pan lysimeters had comparably good collection efficiencies at elevated soil moisture levels, whereas wick pan samplers performed better at lower moisture contents. Cup samplers performed poorly with wide variations in collections and solute concentrations.

Predicting preferential flow and water table fluctuations in karst systems using film-flow theory and source-responsive models

2021 ◽  
Author(s):  
Torsten Noffz ◽  
Jannes Kordilla ◽  
Alireza Kavousi ◽  
Thomas Reimann ◽  
Martin Sauter ◽  
...  
Keyword(s):  
Water Table ◽  
Vadose Zone ◽  
Water Resource Management ◽  
Preferential Flow ◽  
Film Flow ◽  
Dry Valleys ◽  
Diffuse Infiltration ◽  
Water Table Fluctuations ◽  
Aquifer Systems ◽  
Karst Systems

<p>The locally focused dissolution of the rock material (e.g., below dolines and dry valleys) in karst systems and in general percolating clusters of fractures in consolidated aquifer systems trigger the development of preferential flow paths in the vadose zone. Rainfall events may initiate rapid mass fluxes via macropores and fractures (e.g., as gravitationally-driven films) that lead to source-responsive water table fluctuations and comparably short residence times within the vadose zone. The degree of partitioning into a slow diffuse infiltration component and a rapid localized part depends, amongst others, on the hydraulic interaction of porous matrix and fracture domain as well as the geometrical characteristics of the fracture systems (e.g., persistence, connectivity) that are often difficult to obtain or unknown under most field conditions. Given their importance in water-resource management, specifically in arid and semi-arid regions (e.g., Mediterranean), it is desirable to recover such infiltration dynamics in porous-fractured systems with physically-based yet not overparameterized models. Here, we simulate water table fluctuations in a karst catchment in southwest Germany (Gallusquelle) using a source-responsive film flow model based on borehole and precipitation data. The model takes into account interfacial connectivity between slow and fast domain as well as phreatic zone discharge via classical recession analysis. This case study shows the potential importance of preferential flows while modeling water table responses in karst systems and recognizes the need for formulations other than those applied for a diffuse bulk fractured domain where infiltration patterns are assumed to be homogeneous without formation of infiltration instabilities along preferential pathways.</p>

scholarly journals Hydrological Cycle and Lake Water Source Indicated by Microrelief-Evaporite-Vegetation-Runoff Assemblage of Badain Jaran Desert

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1350
Author(s):  
Yandong Ma ◽  
Jingbo Zhao ◽  
Tianjie Shao ◽  
Zhifeng Jia ◽  
Zhiqiang Zhao ◽  
...  
Keyword(s):  
Vadose Zone ◽  
Lake Water ◽  
Preferential Flow ◽  
Hydrological Cycle ◽  
Fine Sand ◽  
Badain Jaran Desert ◽  
Sand Layer ◽  
Sandy Desert ◽  
Phreatic Water ◽  
Evaporite Minerals

The hydrologic process of the sandy desert remains a focus in research in arid areas. Three major natural phenomena that can indicate the hydrological cycle in the extremely dry Badain Jaran Desert were found, namely the assemblage of megadune microrelief and evaporite, megadune vegetation and microrelief, as well as lakeside runoff and vegetation. The microrelief sand layer water, evaporite minerals, and lakeside hydrogeological features were analyzed by the drying and weighing method, environmental scanning electron microscopy with energy spectrum analysis functions, and a hydrogeological borehole survey. The water content of the microrelief 0–0.5 m sand layer is between 4.7% and 9.3%. The evaporite minerals are mainly composed of calcite (CaCO3) and gypsum (CaSO4). The shallow groundwater system in the off-shore area of lakes consists of an aeolian sand layer, a peat layer, and a lacustrine sedimentary layer, and the phreatic water with a thickness of 20 cm to 40 cm is reserved in the bottom of aeolian sand layer with a peat layer as a waterproof baseboard. Based on these results, the above three natural phenomena can be explained as follows: (1) The assemblage of megadune microrelief and evaporite was caused by the outcropping of water from megadune vadose zone in the form of preferential flow for a long time. Its leading edge differential wind erosion and calcium cemented fine sand layer indicate that water from the megadune vadose zone moves to and recharges the microrelief water along the micro-scale fine sand layer, during which, it features a multiple layer as it is controlled by a vertical dune bedding structure. (2) The small-scale assemblage of megadune vegetation and microrelief indicates that the water from the megadune vadose zone moved laterally and led to vegetation development, and the assemblage of microrelief and vegetation at a slope scale indicates that the vadose zone water presented multilayer enrichment and runoff producing due, to a great extent, to the bedding structures of different spacial locations. (3) The assemblage of lakeside runoff and vegetation is related to the phreatic water recharged by precipitation surrounding the lake, which indicates that the megadune water recharged by precipitation moved to the bottom of the megadune and constituted supply to the lake water. The three assemblages fully demonstrate that the megadune water recharged by precipitation in this desert could recharge the groundwater water and even lake water in the form of preferential flow due to the control of the bedding structure of different scales within the megadune. The results of lake water balance and the occurrence conditions of phreatic water surrounding the lake imply that the precipitation in this desert plays an important role in sustaining the lake. This study provides reliable evidence for revealing the essence of the hydrological cycle and the source of lake water in the Badain Jaran Desert, which indicates that although precipitation is small, it cannot be ignored in arid sandy desert areas.

Preferential Flow and Transport of Cryptosporidium parvum Oocysts through the Vadose Zone: Experiments and Modeling

2004 ◽  
Vol 3 (2) ◽  
pp. 736-736 ◽  
Author(s):  
Christophe J.G. Darnault ◽  
Tammo S. Steenhuis ◽  
Patricia Garnier ◽  
Young-Jin Kim ◽  
Michael Jenkins ◽  
...  
Keyword(s):  
Cryptosporidium Parvum ◽  
Vadose Zone ◽  
Preferential Flow ◽  
Flow And Transport ◽  
Cryptosporidium Parvum Oocysts

scholarly journals UNDERGROUND AIR DUCT TO CONTROL RISING MOISTURE IN HISTORIC BUILDINGS: IMPROVED DESIGN AND ITS DRYING EFFICIENCY

2017 ◽  
Vol 57 (5) ◽  
pp. 331 ◽  
Author(s):  
Jiří Pazderka ◽  
Eva Hájková ◽  
Martin Jiránek
Keyword(s):  
Experimental Study ◽  
Reference Sample ◽  
Ground Surface ◽  
High Water ◽  
Laboratory Model ◽  
High Water Content ◽  
Technical Solution ◽  
Historic Buildings ◽  
Concrete Blocks ◽  
Drying Efficiency

The underground air ducts along peripheral walls of a building are a remediation method, which principle is to enable an air flow along the moist building structure’s surface to allow a sufficient evaporation of moisture from the structure. This measure reduces the water transport (rising moisture) into the higher parts of the wall where the high water content in masonry is undesirable. Presently, underground air ducts are designed as masonry structures, which durability in contact with ground moisture is limited. The article describes a new design of an underground air duct, which is based on specially shaped concrete blocks (without wet processes, because the blocks are completely precast). The air duct from concrete blocks is situated completely below the ground surface (exterior) or below the floor (interior). Thanks to this, the system is invisible and does not disturb the authentic look of rehabilitated historic buildings. The efficiency of the air duct technical solution was verified by the results of tests (based on the measured moisture values) conducted on a laboratory model. The experimental study showed that the moisture in the masonry equipped with the presented underground air duct had decreased considerably compared to the reference sample, namely by 43 % on average. The experimental study was numerically validated through numerical simulations performed with the program WUFI 2D.

Influence of the shape of inter-horizon boundary and size of soil tongues on preferential flow under shallow groundwater conditions: A simulation study

2011 ◽  
Vol 91 (2) ◽  
pp. 211-221 ◽  
Author(s):  
Priyantha B. Kulasekera ◽  
Gary W. Parkin
Keyword(s):  
Solute Transport ◽  
Vadose Zone ◽  
Simulation Study ◽  
Soil Profile ◽  
Preferential Flow ◽  
Shallow Groundwater ◽  
Soil Horizon ◽  
Tongue Length ◽  
The Impact ◽  
Water And Solute Transport

Kulasekera, P. B. and Parkin, G. W. 2011. Influence of the shape of inter-horizon boundary and size of soil tongues on preferential flow under shallow groundwater conditions: A simulation study. Can. J. Soil Sci. 91: 211–221. Detailed studies of the impact of soil tongues at soil horizon interfaces are very important in understanding preferential flow processes through layered soils and in improving the accuracy of models predicting water and solute transport through the vadose zone. The implication of having soil tongues of different shapes and sizes created at the soil horizon interface on solute transport through a layered soil horizon was studied by simulating water and solute transport using the VS2DI model. This 2-D simulation study reconfirmed that soil tongues facilitate preferential flow, and the level of activeness of tongues may depend on the number of soil tongues, their spacing and distribution. Also, the size of the soil tongues (length and diameter at the interface between the soil horizons) and their shape influence the rate of preferential flow. Increasing tongue length consistently resulted in an increase in solute velocity across the entire soil profile regardless of the tongue shape; for example, a soil tongue of 0.25 m length increased solute velocity by about 1.5 times over a soil profile without tongues, but this increase might be different for soil types and groundwater conditions other than those considered in this study. Narrowing of tongues increased solute velocity, whereas increasing the number of tongues in a wider soil profile decreased the solute-front's velocity. As tongue length increased, the area containing solutes at prescribed elapsed times decreased. An implication of this study is that soil horizon tongue shape and spacing reduce pollutant residence times, hence inter-horizon boundary morphology should be considered when modelling transport through the vadose zone. As well, since the solute velocity behaviours of a triangular- and a wider rectangular-shaped tongue were nearly identical, simply measuring solute velocity in the field will reveal little information on the shape of a soil tongue.

scholarly journals Technical Note: The use of an interrupted-flow centrifugation method to characterise preferential flow in low permeability media

2015 ◽  
Vol 12 (1) ◽  
pp. 67-92
Author(s):  
R. A. Crane ◽  
M. O. Cuthbert ◽  
W. Timms
Keyword(s):  
Preferential Flow ◽  
Molecular Diffusion ◽  
Breakthrough Curves ◽  
Technical Note ◽  
Dual Porosity ◽  
Low Permeability ◽  
Efficiency Coefficient ◽  
Transport Modelling ◽  
Induced Flow ◽  
Interrupted Flow

Abstract. We present an interrupted-flow centrifugation technique to characterise preferential flow in low permeability media. The method entails a minimum of three phases: centrifuge induced flow, no flow and centrifuge induced flow, which may be repeated several times in order to most effectively characterise multi-rate mass transfer behaviour. In addition, the method enables accurate simulation of relevant in situ total stress conditions during flow by selecting an appropriate centrifugal force level. We demonstrate the utility of the technique for characterising the hydraulic properties of smectite clay dominated core samples. All samples exhibited a non-Fickian tracer breakthrough (early tracer arrival), combined with a decrease in tracer concentration immediately after each period of interrupted-flow. This is indicative of dual (or multi) porosity behaviour, with solute migration predominately via advection during induced flow, and via molecular diffusion (between the preferential flow network(s) and the low hydraulic conductivity domain) during interrupted-flow. Tracer breakthrough curves were simulated using a bespoke dual porosity model with excellent agreement between the data and model output (Nash–Sutcliffe model efficiency coefficient was >0.97 for all samples). In combination interrupted-flow centrifuge experiments and dual porosity transport modelling are shown to be a powerful method to characterise preferential flow in low permeability media.

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