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Hydrogeology Journal, 2013
An integrated approach for monitoring the vertical transport of a solute into the subsurface by using a geophysical method and a simulation model is proposed and evaluated. A medium-scale (1m 3 ) laboratory tank experiment was constructed to represent a real subsurface system, where an olive-oil mill wastewater (OOMW) spill might occur. High-resolution cross-hole electrical resistivity tomography (ERT) was performed to monitor the OOMW transport. Time-lapse ERT images defined the spatial geometry of the interface between the contaminated and uncontaminated soil into the unsaturated and saturated zones. Knowing the subsurface characteristics, the finite element flow and transport model FEFLOW was used for simulating the contaminant movement, utilizing the ERT results as a surrogate for concentration measurements for the calibration process. A statistical analysis of the ERT measurements and the corresponding transport model results for various time steps showed a good agreement between them. In addition, a sensitivity analysis of the most important parameters of the simulation model (unsaturated flow, saturated flow and transport) was performed. This laboratory-scale study emphasizes that the combined use of geophysical and transportmodeling approaches can be useful for small-scale field applications where contaminant concentration measurements are scarce, provided that its transferability from laboratory to field conditions is investigated thoroughly.
An integrated approach for monitoring the vertical transport of a solute into the subsurface by using a geophysical method and a simulation model is proposed and evaluated. A medium-scale (1m 3 ) laboratory tank experiment was constructed to represent a real subsurface system, where an olive-oil mill wastewater (OOMW) spill might occur. High-resolution cross-hole electrical resistivity tomography (ERT) was performed to monitor the OOMW transport. Time-lapse ERT images defined the spatial geometry of the interface between the contaminated and uncontaminated soil into the unsaturated and saturated zones. Knowing the subsurface characteristics, the finite element flow and transport model FEFLOW was used for simulating the contaminant movement, utilizing the ERT results as a surrogate for concentration measurements for the calibration process. A statistical analysis of the ERT measurements and the corresponding transport model results for various time steps showed a good agreement between them. In addition, a sensitivity analysis of the most important parameters of the simulation model (unsaturated flow, saturated flow and transport) was performed. This laboratory-scale study emphasizes that the combined use of geophysical and transportmodeling approaches can be useful for small-scale field applications where contaminant concentration measurements are scarce, provided that its transferability from laboratory to field conditions is investigated thoroughly.
Aktarakçi Monitoring of contaminant transport by using geoelectrical resistivity tomography
Every human activity (industry, agriculture, and others) produces wastes that contaminate and cause continuous devastation of the environment through depletion of resources such as air, water and soil. The recent environmental management trends give emphasis to the control of the wastes' pollution and their deposition. Moreover, the characterization of pollution in public and/or private lands is facilitating the planning of rehabilitation investments in urban and agricultural environments, helping to minimize their consequences in public health. Thus, a robust characterization and monitoring of any released contaminant in the environment is essential for designing effective remediation strategies and for securing reliable water supplies especially in areas where water is scarce. This paper deals with a simulation study of soil pollution using an integrated approach for monitoring a solute transport downward to the subsurface by using modern geophysical methods. Specifically, a medium scale (1m 3 ) experimental tank was constructed and the contaminant flow into porous materials was monitored through cross-hole electrical resistivity tomography.
Editor: Frederic Coulon This work describes the efficiency and ability of Electrical Resistivity Tomography (ERT) to map and monitor the subsurface contamination caused by the wastes created during the production of olive oil. The spatial distribution and temporal variation of these wastes are investigated through an integrated methodological flowchart composed of numerical modeling tests and field data collected from an active waste disposal site. An Olive Oil Mills' Wastes (OOMW) real site was chosen to monitor the subsurface flow of the wastes that are disposed of in an artificial pond for 1.5 years. Synthetic modeling was used to simulate and reconstruct the movement of the OOMW as a conductive target within a layered resistive medium. The results of the ERT data show a high degree of correlation between published ERT, geochemical, and IP geophysical results. This indicates that ERT can be a powerful tool for mapping and monitoring the byproducts of the olive oil industry, in the form of subsurface contamination, as demonstrated by the synthetic modeling. The electrical signature of the OOMW was also verified through the identification of in situ wastes within an excavation trench along the monitoring ERT line. The results show that ERT can be used as a stand-alone tool to characterize the subsurface pollution in OOMW sites.
Journal of Hydrology, 2002
We assess the usefulness of electrical resistivity tomography (ERT) in imaging and characterising subsurface solute transport in heterogeneous unconfined aquifers. A field tracer experiment was conducted at the Krauthausen test site, Germany. The spatial and temporal evolution of the injected NaBr solute plume was monitored in a 2D ERT image plane located downstream of the injection well for 90 days. Since ERT maps changes in bulk electrical conductivity, the reconstructed images at selected time intervals are first converted to solute concentration maps by postulating a linear relation. The concentration maps are then analysed using an equivalent convection -dispersion model (CDM), which conceptualises the aquifer as a homogeneous medium with a uniform mean flow velocity. As demonstrated by associated synthetic model studies, ERT resolution in terms of recovered equivalent dispersivities is limited due to spatial smoothing inherent to the imaging algorithm. Since for heterogeneous media, local concentrations within the plume deviate from those predicted by the equivalent CDM, we also interpret the ERT-derived pixel breakthrough curves in terms of an equivalent stream-tube model (STM). The STM represents transport in the aquifer by a set of 1D convection -dispersion processes, allowing the degree of mixing and the heterogeneity of transport within the plume to be quantified. We believe that the observed tracer plume is satisfactorily described by the equivalent CDM, probably because the tracer plume was small relative to the heterogeneity scale of the aquifer. Even though application of the STM revealed some deviation from the ideal homogeneous case, the equivalent dispersivity in the STM matches the longitudinal dispersivity of the CDM closely, consistent with predominantly homogeneous mixing. However, the STM analysis illustrates how ERT results can be used to quantify the variability of parameters relevant to flow and transport in heterogeneous aquifers. q
ENVIRONMENTAL EARTH SCIENCES, 2010
A portion of an unconfined alluvial aquifer located in the Padana Plain (Italy) was characterized following an integrated hydro-geophysical approach. Initially an electrical resistivity tomography (ERT) survey was employed to localize the boundaries of a modest paleochannel body and to design the installation of a groundwater monitoring network. Multilevel slug-tests were performed to estimate the aquifer’s saturated hydraulic conductivities. Determined permeability values together with electrical resistivity data were correlated. The correlation resulted in a site specific bi-logarithmic linear relationship. Based on this relationship, punctually determined hydraulic conductivities were spatially extended over the studied flow domain. Finally, continuously measured piezometric heads were used to calibrate a 3D flow model. Sensitivity analysis was performed to confirm the reliability of the reconstructed permeability field, as well as, to assess the minimum number of direct measurements needed to safely characterize the selected aquifer portion. The integration of the ERT survey results with the classical hydrogeological tests can be conveniently applied to constrain the permeability field during flow model calibration. Although the applicability of the determined relationship is site specific, the followed procedure is useful especially when there is a need to optimize the available resources and in case of smallscale pilot studies.
Terrestrial, Atmospheric and Oceanic Sciences, 2020
Time-lapse methodology was applied to cross-hole electrical resistivity tomography (CHERT) to investigate two groundwater contamination sites. In the first case study, resistivity profiles were used to delineate the transport direction and spatial distribution of the contaminant, which can serve as a basis for adjusting the remediation treatment by the remediation team. In the second case study, changes in electrical conductivity were used to evaluate the remediation reagent's transport direction and area of effect, and this was used to indirectly verify the effectiveness of the remediation efforts. CHERT equipment was installed simultaneously at the monitoring wells, which enhanced the benefits of the boreholes, enabling them to be even more economical. In large-scale groundwater contamination sites or sites with complex hydrogeological environments, application of CHERT techniques can result in greater amounts of data, particularly in analyzing localized preferential flow paths. This data would be greatly beneficial to the remediation of groundwater contamination sites and long-term groundwater management.
2019
The Reklaw Formation is the upper bounding unit for the Carrizo-Wilcox Aquifer throughout the Gulf Coastal Plain of East Texas and consists of low permeability, glauconite-rich strata that isolate semi-confined portions of the aquifer system from potential contaminants. Electrical resistivity methods were employed within a forested watershed in Nacogdoches County, Texas to characterize solute transport. 2-D and 3-D temporal resistivity data collected with an AGI SuperSting (R8/IP) were processed with AGI Earthimager 2D/3D software for inversion modeling. Data were collected over 135 days within a 14 X 26 meter (46 X 85 feet) gridded survey at 15-day intervals after initiation of a NaCl solute plume; numerical modeling was developed from physical site characterizations. Resistivity analyses and numerical modeling demonstrated solute migration is extremely slow within the Reklaw Formation, confirming strata effectiveness for preventing contaminant migration into the Carrizo-Wilcox Aqu...
Water Resources Research, 2005
1] With time-lapse electrical resistivity tomography (ERT), transport processes in the subsurface can be imaged and monitored. The information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability. Difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ERT is generally underdetermined and that ERT data acquisition is often limited to two-dimensional (2-D) image planes. To address this problem, we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2-D image plane perpendicular to the mean flow direction using time-lapse ERT. The tracer breakthrough patterns in the image plane were interpreted using equivalent transport models: an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves. Equivalent parameters derived from simulated and from ERT inverted concentrations showed a good agreement, which demonstrates the potential of ERT to characterize subsurface transport. Using first-order approximate solutions of stochastic flow and transport equations, equivalent model parameters and their spatial variability were interpreted in terms of the local-scale dispersion and the spatial variability of the hydraulic conductivity. The spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related. Consequently, the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions, which can be observed with sufficiently high spatial resolution using ERT.
International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1991
A field experiment is reported which monitored the three-dimensional movement of cubic solute plumes through an unsaturated, loamy sand soil. The plumes were created with one of two methods, a two-dimensional flux application and an initial resident distribution. Soil coring was used to sample resident concentrations for the three solutes studied. The data were analyzed using the method of moments. In addition to the solute transport experiments, a detailed set of physical properties of the field was obtained by excavating three pits to a depth of 5.0 m and also by taking soil cores throughout the study area. This paper explains the experimental methodology, summarizes the relevant site characteristics, and describes the observed transport based on the zeroth and first order spatial moments. Mass balance varied between 78 and 138%. The field-averaged gravimetric water content and dry bulk density were used to accurately predict the mean vertical plume displacements. The plumes spread relatively little in the horizontal direction. INTRODUCTION Many chemicals enter and move through unsaturated soil as part of a compact plume. A solute plume may originate at the soil surface as a consequence of a spill or a leaking surface tank. It may also emanate from within the vadose zone by leaking through the bottom of a disposal pond or subsurface storage tank. The dissolution of solids, such as the leachate underneath a fly ash pit, may also create a chemical plume. In all of these scenarios, a contaminant plume is created which will likely migrate downward (depending on the soil moisture regime) toward an underlying water resource. There are numerous reasons for wanting to improve the understanding of how a chemical moves through unsaturated soil. First, in many contamination episodes such as waste spills, the only information available is the volume of fluid that enters the soil and the area over which it infiltrated. Without an understanding of the degree of lateral dispersion of the plume, it is not possible to estimate even roughly the downward penetration of the spill. In the absence of a preliminary means for making this assessment, expensive and time-consuming soil concentration measurements must be made over a dense grid in the soil to characterize the plume geometry. Furthermore, even when the initial volume