scholarly journals Development of Predictive Tools for Contaminant Transport through Variably-Saturated Heterogeneous Composite Porous Formations

2012 ◽  
Author(s):  
David Russo ◽  
Daniel M. Tartakovsky ◽  
Shlomo P. Neuman
Keyword(s):  
Contaminant Transport ◽  
Water Flow ◽  
Vadose Zone ◽  
Practical Importance ◽  
Computational Method ◽  
Computational Framework ◽  
Near Surface ◽  
Flow And Transport ◽  
Subsurface Environments ◽  
Heterogeneous Formations

The vadose (unsaturated) zone forms a major hydrologic link between the ground surface and underlying aquifers. To understand properly its role in protecting groundwater from near surface sources of contamination, one must be able to analyze quantitatively water flow and contaminant transport in variably saturated subsurface environments that are highly heterogeneous, often consisting of multiple geologic units and/or high and/or low permeability inclusions. The specific objectives of this research were: (i) to develop efficient and accurate tools for probabilistic delineation of dominant geologic features comprising the vadose zone; (ii) to develop a complementary set of data analysis tools for discerning the fractal properties of hydraulic and transport parameters of highly heterogeneous vadose zone; (iii) to develop and test the associated computational methods for probabilistic analysis of flow and transport in highly heterogeneous subsurface environments; and (iv) to apply the computational framework to design an “optimal” observation network for monitoring and forecasting the fate and migration of contaminant plumes originating from agricultural activities. During the course of the project, we modified the third objective to include additional computational method, based on the notion that the heterogeneous formation can be considered as a mixture of populations of differing spatial structures. Regarding uncertainly analysis, going beyond approaches based on mean and variance of system states, we succeeded to develop probability density function (PDF) solutions enabling one to evaluate probabilities of rare events, required for probabilistic risk assessment. In addition, we developed reduced complexity models for the probabilistic forecasting of infiltration rates in heterogeneous soils during surface runoff and/or flooding events Regarding flow and transport in variably saturated, spatially heterogeneous formations associated with fine- and coarse-textured embedded soils (FTES- and CTES-formations, respectively).We succeeded to develop first-order and numerical frameworks for flow and transport in three-dimensional (3-D), variably saturated, bimodal, heterogeneous formations, with single and dual porosity, respectively. Regarding the sampling problem defined as, how many sampling points are needed, and where to locate them spatially in the horizontal x₂x₃ plane of the field. Based on our computational framework, we succeeded to develop and demonstrate a methdology that might improve considerably our ability to describe quntitaively the response of complicated 3-D flow systems. The results of the project are of theoretical and practical importance; they provided a rigorous framework to modeling water flow and solute transport in a realistic, highly heterogeneous, composite flow system with uncertain properties under-specified by data. Specifically, they: (i) enhanced fundamental understanding of the basic mechanisms of field-scale flow and transport in near-surface geological formations under realistic flow scenarios, (ii) provided a means to assess the ability of existing flow and transport models to handle realistic flow conditions, and (iii) provided a means to assess quantitatively the threats posed to groundwater by contamination from agricultural sources.

Characterization of hydraulic properties in the upper vadose zone for two aquifers in Slovenia

2021 ◽  
Author(s):  
Vesna Zupanc ◽  
Matjaž Glavan ◽  
Miha Curk ◽  
Urša Pečan ◽  
Michael Stockinger ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Soil Water ◽  
Water Flow ◽  
Vadose Zone ◽  
Hydraulic Properties ◽  
Isotope Composition ◽  
Transport Processes ◽  
Precipitation Event ◽  
Water Fluxes ◽  
Flow And Transport

<p>Environmental tracers, present in the environment and provided by nature, provide integrative information about both water flow and transport. For studying water flow and solute transport, the hydrogen and oxygen isotopes are of special interest, as their ratios provide a tracer signal with every precipitation event and are seasonally distributed. In order to follow the seasonal distribution of stable isotopes in the soil water and use this information for identifying hydrological processes and hydraulic properties, soil was sampled three times in three profiles, two on Krško polje aquifer in SE Slovenia and one on Ljubljansko polje in central Slovenia. Isotope composition of soil water was measured with the water-vapor-equilibration method. Based on the isotope composition of soil water integrative information about water flow and transport processes with time and depth below ground were assessed. Porewater isotopes were in similar range as precipitation for all three profiles.  Variable isotope ratios in the upper 60 cm for the different sampling times indicated dynamic water fluxes in this upper part of the vadose zone. Results also showed more evaporation at one sampling location, Brege. The information from stable isotopes will be of importance for further analyzing the water fluxes in the vadose zone of the study sties. <br>This research was financed by the ARRS BIAT 20-21-32 and IAEA CRP 1.50.18 Multiple isotope fingerprints to identify sources and transport of agro-contaminants.  </p>

Vadose Zone, Part I : Characterization and Flow Processes

2003 ◽  
Author(s):  
Yoram Rubin
Keyword(s):  
Porous Media ◽  
Water Flow ◽  
Governing Equation ◽  
Vadose Zone ◽  
Stochastic Analysis ◽  
Transport Processes ◽  
Richards Equation ◽  
Saturated Porous Media ◽  
Flow And Transport ◽  
Flow Processes

Many of the principles guiding stochastic analysis of flow and transport processes in the vadose zone are those which we also employ in the saturated zone, and which we have explored in earlier chapters. However, there are important considerations and simplifications to be made, given the nature of the flow and of the governing equations, which we explore here and in chapter 12. The governing equation for water flow in variably saturated porous media at the smallest scale where Darcy’s law is applicable (i.e., no need for upscaling of parameters) is Richards’ equation (cf. Yeh, 1998)

Emerging Measurement Techniques for Vadose Zone Characterization

1999 ◽  
Author(s):  
Jan W. Hopmans ◽  
Jan M. H. Hendrickx
Keyword(s):  
Solute Transport ◽  
Water Flow ◽  
Vadose Zone ◽  
Measurement Techniques ◽  
Soil Physics ◽  
Flow And Transport ◽  
Regional Project ◽  
The Difference ◽  
Magnetic Resonance Imaging Mri ◽  
Western Regional

Variables and parameters required to characterize soil water flow and solute transport are often measured at different spatial scales from those for which they are needed. This poses a problem since results from field and laboratory measurements at one spatial scale are not necessarily valid for application at another. Herein lies a challenge that vadose zone hydrologists are faced with. For example, vadose zone studies can include flow at the groundwater-unsaturated zone as well as at the soil surface-atmosphere interface at either one specific location or representing an entire field or landscape unit. Therefore, vadose zone measurements should include techniques that can monitor at large depths and that characterize landsurface processes. On the other end of the space spectrum, microscopic laboratory measurement techniques are needed to better understand fundamental flow and transport mechanisms through observations of pore-scale geometry and fluid flow. The Vadose Zone Hydrology (VZH) Conference made very clear that there is an immediate need for such microscopic information at fluid-fluid and solid-fluid interfaces, as well as for methodologies that yield information at the field/landscape scale. The need for improved instrumentation was discussed at the ASA-sponsored symposium on “Future Directions in Soil Physics” by Hendrickx (1994) and Hopmans (1994). Soil physicists participating in the 1994-1999 Western Regional Research Project W-188 (1994) focused on “improved characterization and quantification of flow and transport processes in soils,” and prioritized the need for development and evaluation of new instrumentation and methods of data anlysis to further improve characterization of water and solute transport. The regional project documents the critical need for quantification of water flow and solute transport in heterogeneous, spatially variable field soils, specifically to address preferential and accelerated contaminant transport. Cassel and Nielsen (1994) describe the contributions in computed tomography (CT) using x-rays or magnetic resonance imaging (MRI) as “an awakening,” and they envision these methodologies to become an integral part of vadose zone research programs. The difference in size between measurement and application scales poses a dilemma for the vadose zone hydrologist.

scholarly journals Combining cross-hole geophysical and vadose zone monitoring systems for vadose zone characterization at industrial contaminated sites

2016 ◽  
Author(s):  
Natalia Fernández de Vera ◽  
Jean Beaujean ◽  
Pierre Jamin ◽  
David Caterina ◽  
Marnik Vanclooster ◽  
...  
Keyword(s):  
Water Flow ◽  
Vadose Zone ◽  
Preferential Flow ◽  
Pyrite Oxidation ◽  
Contaminated Site ◽  
Heterogeneous Distribution ◽  
Borehole Geophysics ◽  
Flow And Transport ◽  
Flow Mechanisms ◽  
Intermediate Part

Abstract. Water flow and solute transport through a fractured vadose zone underneath an industrial contaminated site in Belgium were studied with a new methodological concept. The Vadose Zone Experimental Setup (VZES) combines a vadose zone monitoring system (VMS) with cross-borehole geophysics. The VMS provides continuous chemical and hydraulic information at multiple depths in the vadose zone. When combining such information with multidirectional subsurface imaging from geophysical measurements, flow and transport can be characterized at a scale that covers the spatial variability of the subsurface. The setup was installed on site and monitoring was carried out under natural recharge conditions. Results reveal quick rises in water content as a response to rainfall events in the upper and intermediate part of the vadose zone (down to 3.65 m depth). Macropore, micropore, matrix and preferential flow mechanisms are identified at these depth ranges. At greater depths, flow dynamics is slower and dominated by matrix flow. The governance of water flow mechanisms at different directions is controlled by the heterogeneous distribution of geological materials. Results from sampled waters across the vadose zone reveal that the chemistry of water collected from matrix is different from that collected from fractures. In addition, analysis of heavy metals indicates that Ni is leaching across the vadose zone, and its release might be a consequence of pyrite oxidation from backfilled materials. Results obtained from VZES indicate that the combination of different techniques providing in situ quantitative and qualitative information improves conceptual models of flow and transport in a heterogeneous subsurface.

scholarly journals Separation and Lithological Mapping of PFAS Mixtures in the Vadose Zone at a Contaminated Site

2020 ◽  
Vol 2 ◽  
Author(s):  
Dawit N. Bekele ◽  
Yanju Liu ◽  
Mark Donaghey ◽  
Anthony Umeh ◽  
Chamila S. V. Arachchige ◽  
...  
Keyword(s):  
Vadose Zone ◽  
Organic Contaminants ◽  
Sulfonic Acid ◽  
Experimental Studies ◽  
Simulation Models ◽  
Contaminated Site ◽  
Transport Parameters ◽  
Near Surface ◽  
Lithological Mapping ◽  
Subsurface Environments

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are persistent organic contaminants of concern to human and environmental health. Several literature reviews and laboratory column experiments have been conducted to determine the transport parameters and to describe the fate of PFAS as they migrate in subsurface environments. However, there are very few case studies focusing on contaminated sites with high-resolution field data. Such studies are crucial for the validation of transport simulation models that have been developed from experimental studies, prior to their broader applications. The key purpose of this research was to evaluate lithological separations of PFAS fractions as they are transported in the vadose zone of a historically (1979) contaminated site where Aqueous Film Forming Foam (AFFF) formulations (3M Lightwater™ and Ansulite™) have been used for fire training exercises. Surface and subsurface soils, and groundwater samples were collected across the site and a total of 29 PFAS compounds were selected as target analytes. The results indicated a distinct profile of PFAS concentration with depth at most of the test bores, exhibiting separation of PFAS as transported in vadose zone soils. Perfluorooctanoic acid (PFOA), Perfluorooctane sulfonic acid (PFOS), and Perfluorohexane sulfonic acid (PFHxS) were the predominant compounds detected in the site samples and they have been found in near-surface soils (<3 m) with concentrations declining with depth. The concentration of the 6:2 fluorotelomer sulfonate showed little change with depth in most of the test bore wells. The percentage concentration of each compound relative to the sum of PFAS, and the ratio of PFHxS/PFOS with depth, suggested transformation processes. Despite the relatively high solubility of PFAS, and that the application of AFFF has been ceased for some years at the site, there were still significant concentrations of PFAS adsorbed to the vadose zone soils that acted as ongoing sources of contamination to groundwater.

Natural and Engineered Barriers in a Romanian Disposal Site for Low and Intermediate Level Waste

2003 ◽  
Author(s):  
Daniela Diaconu ◽  
Kay Birdsell ◽  
George Zyvoloski
Keyword(s):  
Contaminant Transport ◽  
Vadose Zone ◽  
Nuclear Power ◽  
Water Movement ◽  
Intermediate Level ◽  
Danube River ◽  
Disposal Site ◽  
Near Surface ◽  
River Level ◽  
Engineered Barriers

The operational waste generated by the Cernavoda Nuclear Power Plant will be disposed in a near-surface facility. The low and intermediate level wastes, containing particularly large concentrations of C-14 and H-3, are treated and conditioned in steel drums, which will be placed in the disposal cells and then immobilized in concrete. The Saligny site has been proposed for LIL waste disposal. Geologically, the main components of this site are the quaternary loess, the Precambrian and pre-quaternary clays, and the Eocene and Barremian limestones. Hydrologically, the site can be divided into a vadose zone down to 45–50m and three distinct aquifers, two of them in the limestone beds and the third into the lenses of sand and limestone existing in the pre-quaternary clay layer. Preliminary performance assessments, presented in this paper, indicate that the geologic layers are efficient natural barriers against water flow and radionuclide migration from the vadose zone to the Barremian aquifer. The semi-arid climate and the low precipitation rate prevent contaminant transport from the disposal site to the Eocene aquifer. FEHM simulations of transient groundwater flow showed that seasonal variations influence the moisture content profile in the top of the vadose zone, but the influence over the long term is not significant for contaminant transport. The Danube River level variations control water movement in the Barremian aquifer, especially in the upper part where the limestone is highly fractured and water moves toward the river when its level is low and toward the site when the river level is high. The disposal concept tries to combine the natural and engineered barriers in order to ensure the safety of the environment and population. Therefore, the concrete filling the disposal cells surrounds the waste with a medium that facilitates C-14 retention by precipitation, thus reducing the C-14 releases in the atmosphere and geosphere.

scholarly journals Simulating nonequilibrium movement of water, solutes and particles using hydrus – a review of recent applications

2008 ◽  
Vol 3 (Special Issue No. 1) ◽  
pp. S42-S51 ◽  
Author(s):  
J. Šimůnek ◽  
M. Köhne ◽  
R. Kodešová ◽  
M. Šejna
Keyword(s):  
Water Flow ◽  
Vadose Zone ◽  
Preferential Flow ◽  
Chemical Nonequilibrium ◽  
Nonequilibrium Processes ◽  
Modeling Tools ◽  
Flow And Transport ◽  
Wide Range ◽  
Flow Pathways ◽  
Physical And Chemical

Water and contaminants moving through the vadose zone are often subject to a large number of simultaneous physical and chemical nonequilibrium processes. Traditional modeling tools for describing flow and transport in soils either do not consider nonequilibrium processes at all, or consider them only separately. By contrast, a wide range of nonequilibrium flow and transport modeling approaches are currently available in the latest versions of the HYDRUS software packages. The formulations range from classical models simulating uniform flow and transport, to relatively traditional mobile-immobile water physical and two-site chemical nonequilibrium models, to more complex dual-permeability models that consider both physical and chemical nonequilibrium. In this paper we briefly review recent applications of the HYDRUS models that used these nonequilibrium features to simulate nonequilibrium water flow (water storage in immobile domains and/or preferential water flow in structured soils with macropores and other preferential flow pathways), and transport of solutes (pesticides and other organic compounds) and particles (colloids, bacteria and viruses) in the vadose zone.

scholarly journals Modeling Flow and Transport in Unsaturated Porous Media: A Review

2000 ◽  
Vol 5 ◽  
pp. 265
Author(s):  
H.H. Al-Barwani ◽  
M. Al-Lawatia ◽  
E. Balakrishnan ◽  
A. Purnama
Keyword(s):  
Porous Media ◽  
Contaminant Transport ◽  
Water Flow ◽  
Unsaturated Zone ◽  
Unsaturated Flow ◽  
Numerical Solutions ◽  
Transport Processes ◽  
Field Conditions ◽  
Unsaturated Porous Media ◽  
Flow And Transport

Underground water is a vital natural resource and every effort should be made to understand ways and means of efficiently using and managing it. The unsaturated zone, bounded at its top by the land surface and below by the water table, is the region through which water, together with pollutant carried by the water, infiltrates to reach the groundwater. Therefore, various processes occurring within the unsaturated zone play a major role in determining both the quality and quantity of water recharging into the groundwater. Classical methods of predicting water flow and contaminant transport processes in unsaturated porous media are generally inadequate when applied to natural soils under field conditions, due to the occurrence of macropores, structured elements and spatial variability of soil properties. Contaminant transport models also require the simultaneous solution of the unsaturated flow and transport equations. For applications to field conditions, numerical solutions and computer simulations based on numerical models have been increasingly used. Advances and progress in modeling water flow and contaminant transport in the unsaturated zones are reviewed, and specific research areas in need of future investigation especially relevant to Oman are outlined.

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