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Electrical Resistivity Tomography (ERT) can be a key tool for aiding in characterization of karst geohazard risks at proposed landfill sites. This study is proximal to the south-central Kentucky karst and Mammoth Cave National Park and possesses siliciclastic cap rock upland areas that pose relatively high groundwater-contamination risks due to adjacent ravines floored by carbonates. Complex stratigraphy associated with the Mississippian-Pennsylvanian unconformity and juxtaposition of heterolithic sedimentary rocks in general presents further challenges for demarcating hydrogeological characterization of the base of engineered landfills. A conceptual site model integrates ERT surveying and field geology that both satisfactorily characterize the site and risks to groundwater resources without conducting multiple borings. The proposed landfill site is compared to well-known and mapped caves at a landfill near Bowling Green, Crumps Cave near Smiths Grove, and River Styx Spring at Mammoth Cave. Our work entails review of ERT datasets at known cave sites and compares these to two ERT profiles that traversed the proposed landfill site, which are integrated with study of outcrops, and an excavated pit and trench. ERT data range from several low 10 s to about 400 Ω-meter values for mud rock units whereas sandy units possess ERT values from approximately 500 to several tens of thousands of Ω meters. The greatest values are indicative of basal Pennsylvanian Caseyville Sandstone, and these exceed 32,000Ω meters. In comparison, ERT values at known cave sites range from one to 100,000 Ω meters, with elevated, dry rock or possibly dry (air filled) caves interpreted from the greatest values and low values reflective of conductive underground cave streams and moist caves. An unexpected challenge specific to the Hart County landfill study includes occurrence of well-drained and highly weathered Caseyville at the highest elevations of the site causing increased electrical contact resistance during ERT surveying. The overall ERT contrast however, between quartz-rich and clay poor strata (high-resistivity rocks and regolith) and clay-rich strata (low-resistivity rocks) provides independent data consistent with the observed stratigraphy exposed in site exposures. Nonuniqueness of conductive intervals at the Hart County site contrasts with other conductive areas at depth associated with moist or wet cave passages as documented at Crumps Cave and Mammoth Cave. [ABSTRACT FROM AUTHOR]

The diagnosis and monitoring of contaminated sites have become progressively critical. The effectiveness of electrical resistivity tomography (ERT) has been demonstrated in the assessment of contaminated sites, and its resolution can be significantly improved by array optimization. Gradient array involves the deployment of multiple electrodes in an array configuration to measure the variation in electrical potential across the subsurface, whereas there are some improved arrays which can often provide more accurate measurements. This study investigates the conventional gradient and improved Compare Resolution protocol to identify an abandoned quarry pit where pharmaceutical wastes were dumped. The acquired results were subsequently validated with borehole sampling. The results obtained from the gradient protocol revealed the presence of low-resistivity area. Nevertheless, it is difficult to define the range of the contamination plume area. The results from the optimized array illustrated that the maximum lateral contamination range in the vertical direction appears at a depth of 9 m. A portion of the contaminated area shown in the profile is confined by bedrock. Considering the high cost, only four locations are chosen for drilling to collect samples. The findings revealed that low resistivity corresponds to contamination of inorganic substances. The resistivity and drilling results further clarify that the site has a three-layer structure. The spatial variability of the contaminated site has been ascertained by the high-resolution ERT, and further identify four contaminant sources. This study proves the effectiveness of the ERT method to avoid the drawbacks of costly drilling in bedrock and accomplishes an efficient assessment of contamination. [ABSTRACT FROM AUTHOR]

This paper presents the design, implementation, and evaluation of VR-EX, a combination of a virtual field trip and a serious game in immersive virtual reality. The application's purpose is the communication of research conducted in the Mont Terri underground research laboratory in Switzerland. VR-EX enables users to actively attend electrical resistivity tomography measurements within a geological experiment, from planning to execution to analysis of the results, and in this way implements an active and playful learning approach. The work conducted in underground research laboratories has a high relevance for society as it contributes to research on the final disposal of nuclear waste. Therefore, the active communication of research methodology and results is crucial to increase understanding of scientific processes and boost interest. VR-EX was evaluated in a user study with 35 participants to measure its overall quality and its effectiveness of the knowledge transfer. Taking the evaluation's qualitative results into account, the application was improved in an iterative process. Overall, the results prove the good quality of the application and its high effectiveness in terms of knowledge transfer. The reported high engagement, joy, and immersion indicate the benefits of employing immersive virtual reality for vivid science communication. [ABSTRACT FROM AUTHOR]

The direction of drilling wells in the plateau slope area is toward finding local favorable water-rich blocks, which are relative groundwater accumulation areas under the control of structure, lithology, and landform. These areas often have obvious geological boundary conditions (such as the presence of a water resisting layer in the vertical direction, the development of a fault fracture zone in the plane), and their corresponding physical boundary often has a relatively low or high resistivity to the surrounding rock. In this paper, the comprehensive geophysical method is used to study the application of water prospecting in the plateau slope of Shuangnuo village, Fuyuan, Yunnan Province. First, according to the hydrogeological conditions (the development of a fault fracture zone and clastic rock is unknown), the plane distribution range and vertical development of the low-resistivity abnormal fault fracture zone are determined using the electrical resistivity tomography (less than 100 m) and audio magnetotelluric methods (100–500 m). Vertically, the development depth and thickness of the clastic rock aquifuge (P1l) are determined using the audio frequency magnetotelluric method, which provides a basis for the maximum depth of the borehole layout. The combination of the electrical resistivity tomography and audio frequency magnetotelluric methods can delineate the favorable water-rich block in the study area well and verify that the study area has the prerequisite to become a water prospecting target. To determine the best location of the borehole layout, a combination of the composite profiling, microtremor horizontal-to-vertical spectral ratio (HVSR), apparent resistivity sounding, and K-reflection coefficient methods are carried out in the favorable water-rich block, which delineated by the electrical resistivity tomography and audio frequency magnetotelluric methods. The optimal borehole layout location is determined through the synchronous low resistivity anomaly of the composite profiling method, and the synchronous low resistivity anomaly is determined as a karst fracture zone (qualitative determination) in combination with the HVSR high-value anomaly of the microtremor method. The development depth of the karst fracture zone is finally determined by using the apparent resistivity sounding and K curves. This study reveals that the depth of the drilled hole is 243.5 m, and the water inflow is 144.3 m3/ day, successfully solving the serious water shortage problem in the local area. The case study results show that the combination of geophysical prospecting methods, namely, the electrical resistivity tomography, audio frequency magnetotelluric, composite profiling, microtremor, apparent resistivity sounding, and k-reflection coefficient methods, is effective for water exploration in the plateau slope zone. [ABSTRACT FROM AUTHOR]

Open dumping is one of the most common solid waste disposal methods in developing countries. As they lack planning and basic environmental protection engineering measures, dumpsites represent environmental and health risks that should be investigated. However, several dumpsites are abandoned without appropriate land-use management, difficulting their proper environmental assessment. The use of non-invasive methods for waste mass delimitation and preliminary screening of contamination plumes, such as geophysical methods, is an interesting alternative for the study of the environmental impacts caused by dumpsites. The aim of the present study is to apply electrical resistivity tomography (ERT) for the delimitation of the waste mass and the identification of anomalies related to the presence of alterations in the physical and chemical properties of soils and groundwater in an inactive dumpsite in the municipality of Miracatu, State of São Paulo, Brazil. The study was based on the use of the python software ResIPy, which uses an R family of ERT inversion codes. The 3D inversion of data showed a good correlation between the most electrically conductive anomalies and the delimitation of the waste mass. The behavior of these anomalies, associated with the presence of waste, was confirmed by the physical characterization of the geological materials obtained from drillings and installation of monitoring wells. The present study shows that the ERT inversion code for electrical data can be an interesting open-source alternative for data processing in complex scenarios: environments that present considerable anthropic interference, such as dumpsites. [ABSTRACT FROM AUTHOR]

Deciphering the internal composition of large-scale fault zone is a prerequisite for constructing conceptual models of fault zone architecture and is essential for a proper understanding of the seismological, mechanical and hydrological properties of fault zones. To this end, we conducted fine detection and interpretation of a large-scale fault (F31 fault) in the first Chinese underground research laboratory (URL) construction site for high-level radioactive waste geological disposal repository to elucidate the fault zone architecture. The fault, located in the west of the URL site, is an approximately 5.5-km scale steeply dipping normal fault extending continuously in a straight line. In this study, geophysical prospecting techniques including high-density electrical resistivity tomography (ERT) and reflection seismic tomography (RST) were employed to investigate and interpret the subsurface architecture of the fault zone along the strike of fault core and perpendicular to fault core, respectively. In addition, a 4-m long three-dimensional prospecting trench was excavated manually to observe the geological structure characteristics of the fault zone. Geophysical exploration results suggested that the shallow surface within the fault zone, which is mainly characterized by low conductivity and low wave velocity transmission medium, shows complex geological characteristics due to severe weathering, while the relatively complete bedrock lies beneath the overburden layer. Along the fault strike, the bedrock is buried shallowly at the south of the fault zone. In contrast, at the north, it is mainly characterized by a thick weathering layer overlying the bedrock. For the detection results of vertical fault core, both geophysical methods have deciphered the location of the fault core and the spatial distribution characteristics of F31 fault zone. However, compared with RST results, ERT also clearly diagnosed that there is another secondary fault zone with a certain scale at the hanging wall of F31 fault. In terms of the F31 fault core, ERT suggested that the fault dips about 70° NW and the width of the fault core is 2 – 5 m, which is consistent with the results of the 280° ∠ 75° discontinuities and the approximately 2.6-m long fault core revealed by the prospecting trench. These results provide an important basis for further understanding the internal structure of faults in this site and the avoidance design of the fault-affected range for the underground engineering layout. [ABSTRACT FROM AUTHOR]

Yingcheng (Hubei Province, China) has been a famous salt mining area since the Qing Dynasty. The underground salt mines are of high quality and high yield and have made great contributions to local economic development. However, due to the influence of mining technology and management, geological disasters related to mining have affected the local government and residents. Since the 1970s, the ground in Yingcheng has collapsed numerous times, which has seriously affected the property and safety of residents. In April 2019, another ground collapse event occurred in the Dongmafang salt mine, resulting in a sinkhole covering an area of approximately 960 m2. Although no one was killed or injured during the event, the impact of the sinkhole prompted local authorities to investigate potential collapse threats in the area. The formation mechanism and characteristics of such collapses constitute the basis of regional collapse assessments. Regional geological data, collapse site investigation, borehole sampling analyses, and electrical resistivity tomography surveys can be applied to analyze the formation mechanisms of these collapses. The results of field tests show that electrical resistivity tomography has great advantages in the identification of potential threat areas, thereby providing a theoretical basis and effective means for the exploration of potential subsidence areas. [ABSTRACT FROM AUTHOR]

The eastern part of the Peshawar basin in Khyber Pakhtunkhwa (KPK) experiences the highest economic development, increasingly efficient agriculture, and rapid urbanization that embark on the growing demand for quality water. Peshawar Vale has bountiful water resources lying in shallow Quaternary sedimentary fill. The study aims to integrate non-invasive geoelectrical tools with hydrogeochemical and geospatial tools to analyse the effects of the Gadoon Amazai Industrial Estate (GAIE) on water resources in the eastern Peshawar basin. The hydrogeochemical data acquisition included a total of 110 water samples from the pre-monsoon and post-monsoon periods along with 30 soil samples from agricultural lands. Both the samples were analysed using an atomic absorption spectrophotometer. Geophysical acquisition comprised 40 1D vertical electrical sounding (VES) points and 28 2D electrical resistivity tomography (ERT) profiles at various locations in the area. The GIS interpolation tool was used to obtain the spatial and temporal distribution of surface and groundwater quality parameters in the area. The hydrochemical results indicated higher concentrations of heavy metals exceeding the permissible limits (WHO 2017). It was further observed that the contamination concentration in the surface water is more than in groundwater. Furthermore, post-monsoon concentrations of heavy metals are diluted indicated by decreasing values as compared to pre-monsoon concentrations. The cross sections derived from VES revealed four geoelectrical layers (clay with gravels, saturated gravels and boulders, dry gravel and boulders, and bedrock). The aquifers identified were unconfined owing to the top layer that consists of coarser sediments. ERT identified the contaminated mixed clays (resistivity ≤ 10 Ω-m), contaminated aquifer (resistivity 10–60 Ω-m), and the freshwater aquifer zone (resistivity 60–100 Ω-m). The resistivity data integrated well with hydrogeochemical data showing low values towards Gandaf, Sogandy, and Maini. The study will be of great help to local government, policymakers, and water resource experts. [ABSTRACT FROM AUTHOR]

Tidal forcing influences groundwater flow and salt distribution in shallow coastal aquifers, with the interaction between sea level variations and geology proving fundamental for assessing the risk of seawater intrusion (SI). Constraining the relative importance of each is often confounded by the influences of groundwater abstraction and geological heterogeneity, with understanding of the latter often restricted by sampling point availability and poor spatial resolution. This paper describes the application of geophysical and geotechnical methods to better characterize groundwater salinity patterns in a tidally dominated ~ 20 m thick sequence of beach sand, unaffected by groundwater abstraction. Electrical resistivity tomography (ERT) revealed the deposit to consist of an upper wedge of low resistivity (< 3 Ωm), reaching over 8 m thick in the vicinity of the low water mark, overlying a higher resistivity unit. Cone penetrometer testing (CPT), and associated high-resolution hydraulic profiling tool system (HPT), coupled with water quality sampling, revealed the wedge to reflect an intertidal recirculation cell (IRC), which restricts freshwater discharge from a relatively homogeneous sand unit to a zone of seepage within the IRC. The application of CPT and HPT techniques underscored the value of geotechnical methods in distinguishing between geological and water quality contributions to geophysical responses. Survey results have permitted a clear characterization of the groundwater flow regime in a coastal aquifer with an IRC, highlighting the benefit of combining geophysical and geotechnical methods to better characterize shallow SI mechanisms and groundwater flow in coastal hydrogeological environments. [ABSTRACT FROM AUTHOR]

Electrical resistivity tomography and induced polarization studies were conducted for groundwater exploration in eight selected agricultural sites in Brunei Darussalam. The study was undertaken to meet the growing demands for water supply in the agricultural sector, particularly for paddy field irrigation purposes. This study conducted nineteen surveys with lengths of up to 800 m and a depth of investigation of up to 150 m below ground level. 2D inverted resistivity and chargeability models delineated subsurface geological formations and aquifer zones in the study area. Aquifer zones were detected in all the investigated sites, with resistivity values ranging from 1 to 100 Ω m and chargeability values ranging from 0 to 10 ms. Based on the resistivity and chargeability interpretations, two new groundwater wells were drilled and constructed in two of the investigated sites. Borehole drilling encountered aquifer zones primarily in sand and sandstone layers. Hydraulic tests of the newly drilled boreholes revealed groundwater yields of 4.3 and 288 m3/day. Transmissivity values of the aquifer units estimated using the Cooper–Jacob time-drawdown solutions are 0.53 and 109 m2/day, while their hydraulic conductivity values are 0.05 and 2.75 m/day, respectively. Our findings suggest weak to moderate groundwater yield for withdrawal and distribution for irrigation purposes in the investigated sites. The present study helped decision-makers take suitable measures for placing future groundwater irrigation wells and achieve significant groundwater exploration results in the study area and other areas with similar geological settings. [ABSTRACT FROM AUTHOR]

Groundwater has long been a reliable source of water for domestic, agricultural, and industrial use in the Eastern Haouz and upstream Tassaout, but the establishment of management program that integrates groundwater and surface water uses has been hampered by the lack of detailed informations. A geophysical study using the electrical resistivity tomography (ERT) has been established to get a better knowledge of both the geometry of the formations and the physical characteristics of the aquifer. The results of the ERT validated the authors hypotheses on the surface and groundwater divide line, the high salinity zone and the cause of Tassaout river's direction change. The ERT study has shown that the rise of the basement, east of the village of Tamelalet on the North of the plain, gave a surface and groundwater divide line. The zone of high mineralization is explained by the dissolution of the minerals present in the Triassic clayey formations, which later traps in shale fractures. The change in direction of the Tassaout river is due to a thick layer of conglomerate highly resistant to erosion by the water river. [ABSTRACT FROM AUTHOR]

A sudden water inrush will inundate the foundation pit and bring great difficulty to construction. Subway construction near a river is more complicated since the river water is usually closely related to the groundwater, providing a continuous water supply for the water gushing inside the foundation pit. This study took the Nanjing Shangyuanmen station water inrush accident as a case study. We proposed a comprehensive detection system that combined different geophysical methods for delineating the water inrush hazards around the foundation pit. Considering that the foundation pit was only 400 m away from the Yangtze River in the north, the combination of transient electromagnetic (TEM) and surface electrical resistivity tomography (ERT) was used to realize the rough exploration of the water supply outside the foundation pit. Since the hydrogeological conditions were complex in the foundation pit, the cross-hole ERT and surface ERT were adopted to determine the distribution range of the water-rich areas and the connection to the water-inrush channel. To provide a plane position for the grouting treatment, we integrated the detection results of the different methods with drilling information and divided the water-rich area into three parts, through which we determined the main water gathering area. The integrated detection system provides guidance for the later treatment of the water inrush hazards of a subway foundation pit near a river. [ABSTRACT FROM AUTHOR]

Opalinus Clay is considered a potential host rock for radioactive waste disposal. The Jurassic claystone formation is composed of several facies and subfacies types, which are characterized by varying amounts of quartz, carbonates (cements and fossils) and clay minerals. To provide samples for ongoing experimental and numerical studies, a complete core section was drilled in the Mont Terri rock laboratory. The lithological and structural variability (including tectonic fault structures) from borehole BAD-2 was investigated using a multidisciplinary approach including high-resolution geoelectric in situ borehole measurements, mineralogical/geochemical and (micro)structural analyses. The lithological–compositional variability was captured by successfully applying a modified subfacies approach, which is independently confirmed by the geochemical data and ERT (Electrical Resistivity Tomography) measurements. The variability on the cm to dm scale perpendicular to bedding can be determined based on the mean resistivity and variation of amplitude. In particular, the facies transitions could be precisely located. The new results suggest that both shaly facies types form the homogenous part of the investigated section, whereas the sandy facies and especially the carbonate-rich sandy facies represent the more heterogeneous lithofacies types of the Opalinus Clay. The varying resistivity can be attributed to differences in clay mineral and carbonate content. Regarding the structural variability, brittle faults were observed with varying frequency throughout the investigated section. Most fault planes occur in the shaly facies types, some of them concentrate along heterogeneities on the subfacies scale. The striking reproducibility of the measurements and observations was confirmed by a comparison with boreholes drilled in parallel, indicating a rather low compositional–structural variability parallel to bedding. The applied multidisciplinary approach is well suited to depict the vertical and lateral variability of a claystone formation, allowing an assessment of the degree of homogeneity/heterogeneity based on the subfacies concept. [ABSTRACT FROM AUTHOR]

High altitude, Andean wetlands, or bofedales as they are locally known, are important regulators of the local water balance and also play a key role in sustaining biodiversity. Nevertheless, there is almost no information regarding their hydrogeological structure and functioning. This paper aims to characterize the thickness of the alluvial filling of one peat-accumulating wetland in North-Central Chile using Electrical Resistivity Tomography (ERT) to assess its role as a water reservoir. To develop a quasi-3D understanding of the peatland’s structure, four ERT profiles were conducted. Results highlight a conductive basin shape of the peatland, with a thicker interface downstream than upstream between alluvial materials and the underlying bedrock or rock screes. Those results allow the estimate of the water column (1000–3400 mm) within the peatland alluvial filling. The second objective is to better understand the water exchanges between the peatland and the streamflow using discharge measurements and water stable isotopes. Water and isotopes budgets highlight a streamflow loss towards the peatland groundwater reservoir at the end of spring season. In addition, ten δ18O and δ2H surveys were used to characterize the distinct wetland water sources and their temporal variations. A peatland conceptual model is proposed to connect groundwater, rock glaciers, snowmelt, and hillslope flows. Andean peatlands provide a pivotal control on water delivery downstream, and therefore, understanding their structure and function is important, because they are unique structures providing ecological services at high elevations. [ABSTRACT FROM AUTHOR]

The first coal mining in India was started in the seventeenth century with an unplanned way in Raniganj coalfield, the coal capital of India. The coalfield was possessed by several small private companies which were nationalized in 1973. A part plan of Chanch/Victoria Area, Victoria West Colliery, BCCL, Raniganj Coalfield, India, indicates an underground coal mine gallery/goaf in the Begunia Coal-seam that connects to a Light Casting Factory. It was established as "Barakar Iron Works" in the year 1881 by the government at that time. It is understood that the approaching gallery was used for coal supply to the "Light Casting Factory" by the mining of "Begunia Coal-Seam". Mostly, these are uncharted and very poorly documented with scarce mine plans. So, the present study attempts to explore the location, depth, extension, and condition of the old working gallery through time-lapse monitoring using a combined study comprising of Self-Potential (SP) and Electrical Resistivity Tomography (ERT) techniques. Four SP profiles data along a line and thirteen ERT profiles data in four different lines were collected across the expected site with different station/electrode spacing covering different profile length in four seasons, viz., Summer (May 2016), Monsoon (August 2016), Post-Monsoon (October 2016) and Summer (April 2017). SP data were analysed using simulated annealing (SA) optimization technique for the evaluation of model parameters. The ERT data were acquired using Wenner, Dipole–Dipole and Schlumberger arrays and inversion of the combined data set was performed using the 2.5D ZZRESINV inversion software. Prominent negative SP signature with equivalent low resistivity anomaly have been delineated that possibly indicate the presence of the old mine working/mine gallery. However, the overall results of time-lapse study inferred that the ground is stable. All results are corroborated with available lithology and field photographs. [ABSTRACT FROM AUTHOR]

Landfill site is an intensely heterogeneous medium, in which application of 2-D geophysical techniques frequently does not enable its accurate examination due to the lack of correlation between different geophysical profiles. The study was aimed to eliminate such difficulty. Hereafter, the leachate detection methodology is presented including 2-D smoothness-constrained inversion of geoelectrical raw data collected in situ, the inverted data normalization and statistical examination. To eradicate influence of high heterogeneity of the landfill body, the generalized statistical model of the entire site was created including the likelihood analysis of the entire normalized data set. Three geoelectrical parameters were involved in the analysis: inversed electrical resistivity, inversed chargeability (IP) and the ratio of inversed chargeability-to-inversed electrical resistivity (IP/Res). The study was combined with the synthetic modeling, the analysis of bulk versus fluid electrical resistivity relationship and test borehole drillings. Such generalized analysis ensures independency of the results from the locality of sampling/measurements. It was shown that leachate detection can be correctly performed utilizing the IP/Res ratio while the anomaly's likelihood is higher than 90%. [ABSTRACT FROM AUTHOR]

In continental margin basins, the hydrogeological setting is complex due to transgression/regression events that removed old sediments in the basin and formed new geologic units. Due to the geological complexity, the use of vertical electrical sounding has proven to be insufficient for groundwater explorations. The lack of understanding the geological underground has resulted in many boreholes with low yield or poor water quality. By performing electrical resistivity tomography (ERT) and induced polarization (IP) measurements in 11 villages in Mongicual district, three different layers covering the basement were identified: a weathered autochthon layer, a weathered allochthon layer (paleo-coastal dune) and eolian white sand layer. The drilling at successful boreholes penetrates formations where the resistivity value is between 220 and 770 Ωm, whereas at unsuccessful boreholes the lower parts of the drilled range have resistivity values higher than 770 Ωm. Also, the thickness ratio of the weathered and semi-weathered layer in the unsuccessful boreholes is less than 1/3, whereas in all successful boreholes the ration is higher than 1/2. The difference between autochthon and allochthon layers was detected by heavy minerals content in the red eolian sand layer (Tupuito formation) that increased the chargeability value. The groundwater with a conductivity higher than 2000 µS/cm is linked to the white eolian sand. The surface extension of white eolian sand layer is small to be mapped; therefore, by mapping the eolian white sand formation and the use of ERT and enhanced with IP method would lower the failure rate. [ABSTRACT FROM AUTHOR]

Renewable energy resources are intermittent and need buffer storage to bridge the time-gap between production and demand peaks. The North German Basin has a very large capacity for compressed air/gas energy storage (CAES) in porous saltwater reservoirs and salt cavities. Even though these geological storage systems are constructed with high caution, accidental gas leakages occurred in the past. Stored gases migrated from deep reservoirs along permeable zones upwards into shallow potable aquifers. These CAES leakages cause changes in the electro-elastic properties, and density of the aquifers, and therefore justify investigations with the application of different geophysical techniques. A multiphase flow simulation has been performed to create a realistic virtual CAES leakage scenario into a shallow aquifer in Northern Germany. This scenario is used to demonstrate the detecting resolution capability of a combined geophysical monitoring approach, consisting of acoustic joint waveform inversion (FWI) of surface and borehole data, electrical resistivity tomography (ERT) and gravity. This combined approach of geophysical multi-techniques was able to successfully map the shape and determine the physical properties of the simulated gas phase body at a very early stage after leakage began. Techniques of FWI and ERT start to resolve CAES leakage anomalies only a few years and gravity even a few months after leakage began. Geophysical monitoring of vast areas may start by conducting time-effective aero-surveys (e.g. electromagnetic induction or gravity gradient methods) to isolate anomalous subareas of potential leakage risks. These subareas are then studied in detail using our combined high-resolution approach. In conclusion, our approach is sensitive to CAES leakages and can be used for monitoring. [ABSTRACT FROM AUTHOR]

The present study deals with delineation and mapping of subsurface voids which are very common around the Patherdih colliery of Jharia coal field, India. These are caused by coal fire and old unplanned/illegal mining activity. Initially, a conceptual model of void formation associated with coal fire has been proposed. The burning of coal leads to the void formation due to volume reduction because of transformation of coal to ashes. It is supposed to have significant resistivity contrasts between bedrock i.e. mainly sandstone/clay stone/shale etc. and void space, which are filled with ashes generated from burned coal seam. Field situations have been simulated through forward modeling and the data generated by gradient and dipole–dipole arrays have been corrupted by 5 % noise. The simulations have been carried out for two voids with varied resistivity. The inversions of the data for both the arrays bring up the dimension of the void within reasonable accuracy unlike its resistivity. In fact, the considered resistive void seems to be a conducting void. In the present study, data have been collected by a state-of-the-art FlashRES-Universal electrical resistivity tomography (ERT) instrument, which have 61-channel and 64 electrode data acquisition capacity. ERT sections have been generated over two profiles using Wenner, Schlumberger, gradient, dipole–dipole and joint inversion of all combine arrays. Different resistive anomalous features with resistivity of about 300–200 Ωm have been delineated in both profiles. These are associated with voids at the depths of about 23–25 and 45–54 m generated by burning of coal seams XIVA and XIV, respectively. The obtained results are in broad agreement with the available litholog and surface manifestation of coal fire. The results prove the efficacy of the ERT technique for detection of voids associated with coal fire. [ABSTRACT FROM AUTHOR]

An electrical resistivity tomography survey has been conducted along the eastern coast of the Gulf of Aqaba in order to assess the salinity of the coastal shallow aquifer. The study area is extended from Ra's Shikh Humayd to the town of Maqnah, northwest of Saudi Arabia. Eight electrical profiles were conducted using the Wenner-Schlumberger configuration. The total length of each profile was 360 m providing an expected maximum depth of penetration of about 50 m. All electrical profiles were conducted perpendicular to the coast and directed in the west-east direction. The inversion of the electrical data provided a clear two-dimensional image of the subsurface in the area that reflected the variations in the resistivity of the shallow aquifer system. The subsurface is composed of three layers: the upper layer corresponds to the dry alluvial and gravel deposits that have resistivity values in the range between 40 and 1400 Ω m. The second layer is the saturated zone of the alluvial sediments which represents the coastal aquifer in the study area. The resistivity value of the saturated zone is in the range of 0.15 to 25 Ω m. The lower layer in the subsurface stratification is the resistive bedrock which has resistivity values of more than 100 Ω m. It is composed of Pleistocene-Miocene sediments. The extension of saline water body has been mapped along all electrical profiles. The interpretation of the resistivity models shows that the salinity of the groundwater in the area is strongly related to three main factors: (1) the closeness to the coast; (2) closeness to wadis and low areas which allow saline surface water to infiltrate into the shallow aquifer and; (3) the abundance of gypsum outcrop in the vicinity. This last factor emphasizes the important effect of the local geological setting on the salinity of groundwater; the abundant supply of leached gypsum contributes to the salinity of the shallow aquifer. [ABSTRACT FROM AUTHOR]

Groundwater resource investigations primarily involve inferring groundwater levels and recharge sources from factors such as the distributed location and range, subsurface geological structure, and flow paths of groundwater sources. This study conducted an investigation on the underground aquifer at the downstream of the Chih-Ben Creek basin, Taiwan. In addition, convenient, rapid, and accurate two-dimensional electrical resistivity tomography (ERT) was employed for evaluations. The cross-sectional ERT image indicates that the low-resistivity region in the stratum at survey line CB01 may be a groundwater deposit or fracture zone. This region can be divided into three major segments. The segment that is 0-50 m from the survey line exhibits a decreasing trend and is thus inferred to be a recharge source. Survey line CB02 can be generally divided into four layers, with the second layer containing a greater amount of groundwater. This layer is an aquifer with a depth of approximately 25-100 m below the ground surface and 75-100 m in thickness. The base of the aquifer slopes toward the east and primarily possesses a lithological composition of slate and sandstone with explicit and fractured joints. [ABSTRACT FROM AUTHOR]

This paper presents an approach to assess the methods of 2D elastic seismic full waveform inversion (FWI) and electrical resistivity tomography (ERT) for monitoring storage of CO in deep saline formations. As at a real site the subsurface is not fully known, this approach uses a synthetic field site. Densities and saturations are obtained from a numerical simulation of the injection process and are introduced into geophysical forward models which simulate the geophysical data acquisition from the surface (FWI) and boreholes (ERT). These synthetic geophysical data are then evaluated with respect to changes in CO saturation and are compared to the fully known CO saturation of the numerical process model to verify the geophysical monitoring methods. Results show that both methods are capable of detecting a thin CO phase body in about 2,200 m depth for a synthetic site in the North German Basin. Inverted CO saturations are in good agreement, however, both methods cannot resolve the CO phase edges of less than 4 m saturated thickness. The maximum error of estimated CO saturation is 10 % for the FWI method and 15 % for the ERT method, if accurate baseline models are available. The FWI method sensitivity on the baseline model is tested by a sensitivity analysis demonstrating high sensitivity on bulk density, but low sensitivity on fluid densities and porosity. ERT results are considerably improved using structural information from the FWI as constraint. [ABSTRACT FROM AUTHOR]

The application of electrical resistivity tomography (ERT) techniques involving the Wenner and Schlumberger electrode configurations was conducted at the ancient site of Al-Berktain of Jerash, N-Jordan during June, 2011. It may be considered as the first archaeogeophysical survey at this site. The city lived by succession of ancient cultures and still has archaeological remains (e.g. water pools) which gave it historical value and boosted the archaeological interest to make this study. The objective of the work was to determine the layout, dimension, and the depth of expected buried structures (i.e. water channels related to the pool structure) within the site, and to provide recommendations for future excavation projects. The results showed high resistivity anomalies (red color) located within the site. These anomalies were interpreted as a part of a general infrastructure of ancient man-made buried channels or supporting basins draining out or feeding water to the two the water pools especially at the western and eastern sides. Inside the pool (the main structure in the site), results of the survey showed anomalous thin shallow zone interpreted as a layer limestone pavement of a thickness of 1 m. The ERT successfully determined the dimensions of the buried features and proved that this site was water reservoirs to serve the ancient city of Jerash or irrigations purposes beside its use for leisure (i.e. presence of the theatre, roman path and the pools). [ABSTRACT FROM AUTHOR]

Groundwater contamination is one of the most significant problems in arid countries. Al-Quwiy'yia region is an example of an area where the groundwater is contaminated as a result of infiltration of waste water in low-lying areas adjacent to inhabited zones. Such contamination poses significant environmental threats for the surrounding environment and groundwater. Surface observations and spatial distribution of contamination observed in the shallow aquifer indicate that the main contamination sources were from sewage as well as from waste water dumping. However, the main source of water supply for the whole area is groundwater abstracted from the relatively shallow aquifer. Therefore, the transient electromagnetic method (TEM) and 2D electrical resistivity tomography (2D ERT) have been applied close to the waste water dump site to characterize the response of pollution plumes. Both of these geoelectrical techniques are sensitive to electrical conductivity as well as to other physical properties, which are greatly influenced by the polluted groundwater. Therefore, it is possible to profile the contamination plumes, both vertically and horizontally, in the vicinity of the measured stations. The ERT profiles gave detailed information about the lateral distribution of the contaminated groundwater, whereas the TEM demonstrated the vertical extensions. [ABSTRACT FROM AUTHOR]

As part of a larger regional research program 'KarstEAU', the authors have applied electrical resistivity tomography (ERT) techniques to characterize heterogeneities in the Port-Miou coastal karst aquifer (Cassis, SE France). Field surveys were carried out on intensely fractured and karstified Urgonian carbonates. Extensive research has characterized macro- and micro-scale geology of the Port-Miou area and particularly underground water-filled conduits and fault/fracture and karst systems within a former quarry. The authors applied 2D ERT along two surface profiles of length 420 and 595 m to test capability for delineating subsurface conduits and possibly relationship between conduit and fault/fracture/karst orientation; and 3D ERT with a dense 120 electrode array at 1 m spacing (11 × 10 m) was applied over an area of the quarry that had been profiled using 3D georadar and which has had intensive nearby structural geological interpretation. The 2D profiling imaged several underground conduits at depths to >50 m below ground surface and below sea level, including possibly the main Port Miou submarine spring and smaller springs. The 2D profiling within the quarry provided a better understanding of the connectivity between major fractures and faults on the quarry walls and secondary springs along the coast supporting flow of the secondary springs along interpreted fracture orientations. In addition, 2D inversion-derived conductivity models indicate that high resistivity zones above sea-level are associated with non-saturated zones and low resistivity anomalies in the non-saturated zone are associated with residual clays in paleokarsts. A partitioned lower resistivity zone below sea-level can be associated with a higher porosity/permeability zone with fractures and karstic features. Inversion models of the dense 3D ERT data indicate a higher resistivity volume within the larger surveyed block. The survey characterized the non-saturated zone and the ERT resistivities are correlated with karst features interpreted by 3D georadar and visible in the inferior wall of the quarry. [ABSTRACT FROM AUTHOR]

Anthropogenic pressure influences the two-way interactions between shallow aquifers and coastal lagoons. Aquifer overexploitation may lead to seawater intrusion, and aquifer recharge from rainfall plus irrigation may, in turn, increase the groundwater discharge into the lagoon. We analyse the evolution, since the 1950s up to the present, of the interactions between the Campo de Cartagena Quaternary aquifer and the Mar Menor coastal lagoon (SE Spain). This is a very heterogeneous and anisotropic detrital aquifer, where aquifer-lagoon interface has a very irregular geometry. Using electrical resistivity tomography, we clearly identified the freshwater-saltwater transition zone and detected areas affected by seawater intrusion. Severity of the intrusion was spatially variable and significantly related to the density of irrigation wells in 1950s-1960s, suggesting the role of groundwater overexploitation. We distinguish two different mechanisms by which water from the sea invades the land: (a) horizontal advance of the interface due to a wide exploitation area and (b) vertical rise (upconing) caused by local intensive pumping. In general, shallow parts of the geophysical profiles show higher electrical resistivity associated with freshwater mainly coming from irrigation return flows, with water resources mostly from deep confined aquifers and imported from Tagus river, 400 km north. This indicates a likely reversal of the former seawater intrusion process. [ABSTRACT FROM AUTHOR]

Moisture content is considered to play an important role in the degradation of municipal solid waste (MSW). The present study was carried out to test the use of electrical resistivity tomography (ERT) to estimate the daily variations in the volumetric moisture content (VMC) during waste degradation. The degradation of MSW in a laboratory-scale reactor was monitored daily by ERT and time domain reflectometry (TDR) over a period of 55 days after the waste was landfilled. The bulk electrical resistivity, normalised to a standard temperature of 25 °C, was compared to the VMC obtained by TDR. The relationship between the bulk electrical resistivity and the VMC was not obvious in the upper unit, because there was a bias in the positions of the ERT and TDR measurements due to the settling of the waste. However, the bulk electrical resistivity depended on the VMC in the lower unit of the reactor. According to a power equation fitted in the lower unit, the 2-D distributions of the VMC are presented. Variations in the VMC reflected the processes of waste degradation and leachate transportation. Furthermore, the volume of water stored in the lower unit of the reactor was calculated and found to be consistent with that estimated from the gravimetric moisture content during waste sampling. The data showed that ERT could be used to estimate the variations in moisture content in the initial period following the landfilling of waste. [ABSTRACT FROM AUTHOR]

Excessive water usage together with limited capacity of local hydrogeological environment to dispose excess water or waste water has emerged as a problem of water level rise in many parts of ArRiyadh, the capital city of Saudi Arabia. In the past, groundwater rise to shallow horizons has caused considerable impact on public health, environment and infrastructure. In order to reduce and maintain groundwater to safe level, ArRiyadh Development Authority has constructed a gravity drainage system in the affected areas. During the initiation of the gravity drain project, water level in eastern ArRiyadh was >15 m; therefore, the area was not included in the project but was subjected to regular groundwater monitoring. During the recent decade, eastern ArRiyadh has witnessed quick water level rise, with an average rate of 0.55 m/year. This water level rising trend seems persistent with time which may impart serious damage to the environment and infrastructure. The study shows that the presence of thick clays within eastern alluvium retards hydrodynamic connectivity and inhibits vertical groundwater movement. [ABSTRACT FROM AUTHOR]

This paper deals with the integration of electrical resistivity tomography and geochemical methods for studying four different fire-prone landfills. Landfill gas composition (CH4, H2S, O2, CO, CO2) and subsurface temperature were measured with the constant net 50 × 50 m from the depth 10–60 cm. 28 electrical resistivity tomography lines were surveyed, while Wenner and Sclumberger electrode arrays were employed for all measurements. At the studied sites the landfill gas and temperature measurements mapped gas and temperature anomalies over underground fire sources. 2D electrical resistivity tomography lines, performed over these anomalies, showed these fire sources as high-resistivity zones. The joint employment of the electrical imaging and geochemical survey seems to be a useful tool in carrying out diagnostic investigations at fire-prone landfills. [ABSTRACT FROM AUTHOR]

The scope of the electrical resistivity survey has recently been extended to various fields beyond groundwater and underground resource exploration. Electrical resistivity techniques were evaluated in two case studies to substantiate their applicability to geotechnical and environmental problems. First, electrical resistivity imaging (ERI) was used to map the fractured zone ahead of the tunnel face during construction using the new Australian tunneling method (NATM). The ERI technique could adequately modify tunnel support patterns in quasi-real time, on the basis of the field test results, and could subsequently improve the stability of tunnel excavation. Second, electrical resistivity tomography (ERT) was used between two test boreholes in a research tunnel site to monitor the movement of brine after it was injected in one of the two boreholes. A pair of low-conductivity zones that were regarded as the pathway of groundwater flow between the two boreholes was clearly imaged because of enhancement of conductivity caused by diffusion of the brine. The applicability of electrical resistivity techniques to geotechnical and environmental problems was successfully substantiated. [ABSTRACT FROM AUTHOR]

Mining of massive (Cu, Pb and Zn) sulphide bodies in the Iberian Pyrite Belt (SW Spain) has generated a great number of abandoned waste deposits such as mine ponds. These represent large accumulations of reactive minerals and subsequently, emission sources of trace elements and formation of acid drainage. Even if they have been restored, monitoring studies are required to evaluate the corrective effects and how they may change over time. This work presents the results of a monitoring study carried out at Mine Concepción mine pond, based on mineralogical (XRD), geochemical (INAA, X-ray fluorescence, ICP-MS) and geophysical (electrical resistivity tomography) techniques. In it, a series of relevant parameters have been well delimited, such as the infilling thickness and its variation and, the position, geometry and absence of water leakages through the base of the mine pond. Additionally, the existence of an internal, remnant flow of acid waters that tends to come out through the pond dyke has been identified. Chemistry of these waters indicates that oxidation processes affecting the Mina Concepción mine tailings are generating acid drainage waters which could potentially release substantial amounts of trace elements to the river Odiel. Thus, giving that not complete sealing is accomplished by the restoration capping and rainfall water infiltrates into the pond materials, at least the sealing of the dyke through which leakages occur should be revised. [ABSTRACT FROM AUTHOR]