Fluid migration in the vadose zone from 3-D inversion of resistivity monitoring data

Geophysics ◽  
1998 ◽  
Vol 63 (1) ◽  
pp. 41-51 ◽  
Author(s):  
Stephen Park
Keyword(s):  
Vadose Zone ◽  
Fluid Migration ◽  
Inversion Process ◽  
Resistivity Tomography ◽  
Capillary Action ◽  
Fine Grained ◽  
Fluid Concentration ◽  
Resistivity Inversion ◽  
Systematic Development ◽  
Precipitation Events

The movement of a small plume of fresh water through the vadose zone was monitored using surface resistivity tomography and pole‐pole potential measurements. Sets of potential measurements on a square grid at several times throughout the experiment show gradual, progressive, and systematic development of low‐resistivity zones that are inferred to be loci of fluid concentration. A procedure for inverting percentage changes in potentials is developed here and used to map maximum potential changes of 13% into resistivity decreases of up to 40% through 3-D resistivity inversion. The resulting patterns are complex, with both resistivity increases and decreases needed to match the observed data. The resistivity reductions show a spatial connection to the plume’s source and are suggestive of the fluid migration. Resistivity increases generally appear to form rims surrounding the decreases and may be artifacts of the inversion process. However, some isolated increases in the surface layer may be caused by evaporation of fluid from previous precipitation events. Interpretation of the complex patterns may limit the usefulness of this method for monitoring fluid migration. Nonetheless, the resulting pattern of resistivity reductions may show details of fluid migration that are unavailable with more conventional monitoring techniques. In this experiment, comparison of the volume with reduced resistivity with the volume of injected water predicts only a 0.5% increase in saturated porosity, demonstrating that fluid flow in the vadose zone was most likely controlled by the distribution of fine‐grained clays and silts and occurred by capillary action.

Electrical resistivity tomography investigations in the ufita Valley (southern Italy).

2008 ◽  
Vol 51 (1) ◽  
Author(s):  
A. Giocoli ◽  
C. Magrì ◽  
P. Vannoli ◽  
S. Piscitelli ◽  
E. Rizzo ◽  
...  
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Southern Italy ◽  
Normal Fault ◽  
Fluvial Sediments ◽  
Resistivity Tomography ◽  
Fine Grained ◽  
Sedimentary Deposits ◽  
Lacustrine Deposits ◽  
Sedimentary Deposit

Several Electrical Resistivity Tomography (ERT) surveys have been carried out to study the subsurface structural and sedimentary settings of the upper Ufita River valley, and to evaluate their efficiency to distinguish the geological boundary between shallow Quaternary sedimentary deposits and clayey bedrock characterized by moderate resistivity contrast. Five shallow ERTs were carried out across a morphological scarp running at the foot of the northeastern slope of the valley. This valley shoulder is characterized by a set of triangular facets, that some authors associated to the presence of a SW-dipping normal fault. The geological studies allow us to interpret the shallow ERTs results obtaining a resistivity range for each Quaternary sedimentary deposit. The tomographies showed the geometrical relationships of alluvial and slope deposits, having a maximum thickness of 30-40 m, and the morphology of the bedrock. The resistivity range obtained for each sedimentary body has been used for calibrating the tomographic results of one 3560m-long deep ERT carried out across the deeper part of the intramountain depression with an investigation depth of about 170 m. The deep resistivity result highlighted the complex alluvial setting, characterized by alternating fine grained lacustrine deposits and coarser gravelly fluvial sediments.

scholarly journals Seasonal Groundwater Recharge Characterization Using Time-Lapse Electrical Resistivity Tomography in the Thepkasattri Watershed on Phuket Island, Thailand

Hydrology ◽  
2019 ◽  
Vol 6 (2) ◽  
pp. 36 ◽  
Author(s):  
Yacob T. Tesfaldet ◽  
Avirut Puttiwongrak
Keyword(s):  
Electrical Resistivity ◽  
Groundwater Recharge ◽  
Vadose Zone ◽  
Rainy Season ◽  
Electrical Resistivity Tomography ◽  
Time Lapse ◽  
Dry Season ◽  
Discharge Zone ◽  
Hydrogeological Model ◽  
Resistivity Tomography

Understanding the recharge mechanisms in the vadose zone is crucial to groundwater management and artificial recharge development. In this study, a systematic characterization of seasonal groundwater recharge was done using time-lapse electrical resistivity tomography (time-lapse ERT). The objective of this study was to characterize the seasonal groundwater recharge through the vadose zone and streams. A total of six electrical resistivity surveys in two locations were taken during the dry and rainy seasons using an advanced geosciences incorporated (AGI) SuperSting R2 resistivity meter in 2018. Then, time-lapse inversion was calculated using the dry season ERT as the base model and the rainy season ERTs as the monitoring datasets. The results showed a significant decrease in inverted resistivity from the dry season to the rainy season, which suggests rainwater infiltration through the vadose zone. Similarly, significant water level rise was observed in wells monitored during the survey indicating groundwater recharge. The time-lapse ERT showed, in one case, the Nang Dak stream and the unsaturated zones are the preferential groundwater recharge zones throughout the year; in another case, the Rieng stream is the groundwater discharge zone and the vadose zone is the preferential recharge zone. Finally, a simplified conceptual hydrogeological model representing the study area is presented to visualize the recharge mechanisms in the study area.

What part of no do children not understand? A usage-based account of multiword negation

2007 ◽  
Vol 34 (2) ◽  
pp. 251-282 ◽  
Author(s):  
THEA CAMERON-FAULKNER ◽  
ELENA LIEVEN ◽  
ANNA THEAKSTON
Keyword(s):  
Frequency Effects ◽  
Fine Grained ◽  
Initial Analysis ◽  
Creative Learning ◽  
English Speaking ◽  
Systematic Development ◽  
Selection For

The study investigates the development of English multiword negation, in particular the negation of zero marked verbs (e.g. no sleep, not see, can't reach) from a usage-based perspective. The data was taken from a dense database consisting of the speech of an English-speaking child (Brian) aged 2;3–3;4 (MLU 2·05–3·1) and his mother. The focus of the study was the emergence and usage of negators in the child's and mother's speech (e.g. no, not, can't, won't, don't). Two analyses were conducted: firstly, the emergence and usage of all negators in Brian's speech and in the input were calculated in order to present an overall picture of negator usage across the sample. The findings indicate a gradual and systematic development of negator selection in Brian's speech which follows the trajectory no–not–'nt. The pattern of negator emergence was found to follow the frequency of negators in the input; that is negators used frequently in the input were the first to emerge in the child's speech. Secondly, a more fine-grained analysis of utterances containing negated zero marked verbs (neg V utterances) was conducted on both the child's and mother's speech. In the first instance the development of negator selection for all neg V utterances was calculated. The results indicated the same no–not–'nt cline as attested in the initial analysis. A function-based analysis of neg V utterances was also conducted which indicated that the speed of movement across the no–not–'nt cline varied from one function to the next. A function-based analysis of the input suggested that the speed at which Brian moved across the cline within a particular function could be traced to function-based frequency effects in the input. Thus the findings of the study indicate function-based, input-driven learning which is consistent with the usage-based approach. However the findings also indicate creative learning on the part of the child from the earliest stages of multiword negation.

scholarly journals A Geophysical-Geochemical Approach to the Study of the Paleogene Julian—Slovenian Basin “Megabeds” (Southern Alps—Northwestern Dinarides, Italy/Slovenia)

Geosciences ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 155 ◽  
Author(s):  
Kei Ogata ◽  
Željko Pogačnik ◽  
Giorgio Tunis ◽  
Gian Pini ◽  
Andrea Festa ◽  
...  
Keyword(s):  
Carbonate Platform ◽  
Open Pit ◽  
Resistivity Tomography ◽  
Fine Grained ◽  
Deformation Structures ◽  
Slide Mass ◽  
Sediment Deformation ◽  
Depositional Units ◽  
Slovenian Basin ◽  
Depositional Setting

The Paleogene “megabeds” of the Julian-Slovenian Basin are regional, basin-wide deposits, produced by catastrophic carbonate platform collapses. They record the emplacement of a bipartite slide mass behaving as a cohesive blocky/debris flow in the lower part, and as a grain to turbulent flow in the upper part. Several types of primary (sedimentary) soft sediment deformation structures testify fluid overpressure conditions during emplacement. Such structures are identified within a brecciated, fine grained matrix that encloses and intrudes slide blocks and clasts, characterized by NE-, NW- and SW-directed paleo-transport directions, indicating a depositional setting close to the basin margins. Here we present an updated review of some representative megabeds, exposed in the open-pit quarry outcrops of Anhovo (SW Slovenia). In particular, we here discuss new interpretations based on X-ray fluorescence spectrometry (XRF), thermo-gravimetry (TG) and electric resistivity tomography (ERT). Our results indicate that basal marly clasts of the megabeds are markedly different from the uppermost draping marls, suggesting two different coeval sources. The relationships with the underlying successions are strongly erosive, with deep localized scouring of the substrate and amalgamations between different megabeds, and the depositional units inside individual megabeds, supporting the geochemical differences.

scholarly journals 2D Electrical Resistivity Imaging of Bedrock Fissures in Ogbomoso, Southwestern Nigeria

2021 ◽  
Vol 7 (2) ◽  
Author(s):  
I. A. Akinlabi ◽  
O. G. Bayowa
Keyword(s):  
Electrical Resistivity ◽  
Electrical Resistivity Tomography ◽  
Electrical Resistivity Imaging ◽  
Expansion Factor ◽  
Southwestern Nigeria ◽  
Resistivity Tomography ◽  
Resistivity Inversion ◽  
Potential Failure ◽  
2D Resistivity ◽  
Tomography Data

2D electrical resistivity surveys were conducted around the site of the failed proposed Ogbomoso North Secretariat building with a view to examining the trend of suspected bedrock fissures and assessing the vulnerability of structures in the vicinity to potential failure. Electrical Resistivity Tomography data were acquired along ten traverses 80-200 m long each, using the dipole-dipole electrode configuration with station interval of 5 m and expansion factor, n, varied from 1 to 6. The data were processed by using 2D resistivity inversion technique in the DipproTM software package to generate 2D resistivity sections beneath the traverses. The 2D resistivity sections delineated 2-19 m thick typically clay overburden underlain by bedrock with resistivity ranging from 103 to 59767 Ωm, and anomalously low resistivity zones suspected to be fissures within the bedrock. The bedrock fissures are generally 5-20 m wide and occur at depths ranging from 5 m to ˃25 m beneath the traverses. The fissures trend southward toward the roundabout and front of the College of Health Sciences premises. The incessant road failures and groundwater seepages observed within the study area are attributable to the network of bedrock fissure.

Transport of hexavalent chromium in the vadose zone by capillary and evaporative transport from chromium ore processing residue

2016 ◽  
Vol 53 (4) ◽  
pp. 619-633 ◽  
Author(s):  
Katrina Rhoades ◽  
Jongwan Eun ◽  
James M. Tinjum
Keyword(s):  
Vadose Zone ◽  
Capillary Rise ◽  
Small Diameter ◽  
Silty Sand ◽  
Column Tests ◽  
Chromium Ore ◽  
Ore Processing ◽  
Containment Strategy ◽  
Precipitation Events ◽  
Surface Background

Column tests were conducted to evaluate the transport of Cr from underlying chromium ore processing residue (COPR) through the vadose zone in capped and uncapped scenarios and to determine if an asphalt cover system is a viable containment strategy. Four large (140 mm diameter) columns and one small (50 mm diameter) column were filled with COPR underlying a silty sand. Wet–dry cycling (representing precipitation events) induced suction gradients in the uncapped columns. At termination, the uncapped columns contained 10–120 mg/kg Cr on the surface (background Cr level, 8.3 mg/kg), and the capped columns had Cr concentrations equal to background levels, indicating that the capped surface limited Cr migration to the surface. The smaller column was constructed to study the evaporative transport of Cr by simulating a heat source (i.e., sunshine) to increase suction. Soil specimens from the surface of the small-diameter, uncapped column were as high as 410 mg/kg Cr(VI) after 4 weeks. A series of numerical analyses was conducted to interpret and validate the experimental results and to quantify Cr(VI) transport through composite asphalt caps. Through column testing and numerical analysis, in a controlled condition, Cr was found to migrate from COPR in the vadose zone by evaporation and capillary rise, but a controlled, capped condition effectively limited Cr migration.

scholarly journals Hydrostratigraphic Characterisation of Shallow Coastal Aquifers of Eastern Dahomey Basin, S/W Nigeria, Using Integrated Hydrogeophysical Approach; Implication for Saltwater Intrusion

Geosciences ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 65 ◽  
Author(s):  
Jamiu A. Aladejana ◽  
Robert M. Kalin ◽  
Philippe Sentenac ◽  
Ibrahim Hassan
Keyword(s):  
Electrical Resistivity ◽  
Cross Sections ◽  
Electrical Resistivity Tomography ◽  
Saline Water ◽  
Silty Clay ◽  
Resistivity Tomography ◽  
Fine Grained ◽  
Dahomey Basin ◽  
Clay Lenses ◽  
Fine Grained Sand

This study employed electrical resistivity tomography (ERT) in characterising the shallow groundwater aquifers of Eastern Dahomey basin in southwestern Nigeria to assess the possible occurrence and distribution of saltwater within the aquifers. Electrical resistivity tomography (ERT), induced polarization (IP) and borehole logging were carried in locations with relatively enhanced electrical conductivity (EC) within the coastal zone of the basin through 97 groundwater samples from shallow wells and boreholes; 500 m-length ERT and IP sections were carried out along three traverses A–B, C–D and E–F in directions perpendicular and parallel to the coastline. Three geoelectrical layers were identified along traverse line A–B which comprises cross-sections 1, 2, 3 and 4 located around Ugbonla, Aboto and Igbokoda with layers’ resistivity and chargeability values ranging from (1–1000, 33–200 and 1–1700 Ωm), and (−50–200 Ωm, −30–200 Ωm and −50–120 Ωm, respectively, from the top to the bottom layer. These values indicated unconsolidated sand/lateritic silty clay, underlain by a sandy/silty clay layer with underlying fine-grained sand with disseminated clay lenses. The average thickness of the first two layers was 16 and 53 m while that of the third layer was undetermined. Resistivity and chargeability results from ERT and IP cross-sections along profile C–D exhibited characteristics similar to that of profile A–B with unconsolidated sands which were underlain by intercalation of sandy/silty clay and fine-grained sands with suspected clay lenses saturated with saline water. Profile E–F revealed a geoelectrical layer with low resistivity which ranged from 1–30 Ωm with the corresponding chargeability between −150–400 ms. This indicated a saline water-saturated layer of fine-grained sand and silty clay which is overlaid by the unconsolidated unconfined freshwater aquifer. Correlation of selected ERT results with borehole logs further affirmed the suspected lithology from the sections. Two scenarios of saltwater intrusions into coastal freshwater aquifer were suggested which include the presence of trapped salt-saturated clay lenses within aquifer lithology and seawater incursion induced by over-drafting of groundwater in this basin.Therefore, it identified the need for further investigation which will involve a combination of hydrochemical and isotopes to further understand the paleowater hypothesis.

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