Resistivity Tomography Profiles Research Articles

Assessment of Environmental Pollution using Electrical Resistivity and Logging Techniques over A Municipal Dumpsite of Ijagun Ijebu Ode

The present study aims to assess environmental pollution using the resistivity method and geological logging technique over a municipal dumpsite of Ijagun Ijebu Ode, underlain by the Afowo Formation within the Dahomey Basin southwestern Nigeria. Forty vertical electrical resistivity soundings stations and six 2D electrical resistivity imaging profiles using Schlumberger and Wenner array respectively with maximum spread-length of 40m at each sounding and profile length of 60 m and 120 m and one borehole log were carried out. Three geoelectrical layers were obtained in the control area, their resistivity values with their corresponding depth of sediment materials is 126 Ωm – 724 Ωm at depth range 0.9 m – 1.1 m (topsoil), 608 Ωm – 2517 Ωm at depth range 3.5 m – 17.7 m (sandy layer), and 800 Ωm – 6046 Ωm (dry sandy layer). Along with the 2D resistivity imaging profiles over the control (1 and 2), four geo-electric layers characterized by Resistivity values range of 40 Ωm – 126 Ωm (loam), 135 Ωm – 418 Ωm (loamy sand), 500 Ωm – 1500 Ωm (sandy), and >3000 Ωm (dry sand) were revealed. The lithology recovery from the logging techniques shows the subsurface is underlined chiefly with sand, which shows a significant correlation with the geophysical method. The lower values of resistivity at the dumpsite are clear evidence of the subsurface contamination of the sandy layer. The 2D images revealed the contaminated zone thickness ranges from 2 m in the northwest to 25 m in the southeastern part. The protective capacity map derived from the VES showed that the dumpsite is underlain by poorly protected sandy lithology, prone to leachate infiltration. Relocation of the dumpsite to a better protected environment or underlining the present area with an impermeable geotextile layer would halt further leachate invasion into the subsurface.

Integrated Geoelectrical Resistivity Method for Environmental Assessment of Landfill Leachate Pollution and Aquifer Vulnerability Studies

Leachate plumes from landfills are a major source of pollution in Nigeria, especially in urban areas. Assessing leachate contamination in the subsoil is considered a complex process that needs detailed field measurement to accurately define the extent of contamination. To ascertain the extent of pollution of the subsoil and groundwater sources which were reportedly contaminated by leachate plumes from an old dumpsite located in Osubi town, an integrated geo-electrical method involving 1-D vertical electrical sounding (VES) and 2-D, 3-D ERT techniques were employed. Orthogonal set of 2-D apparent resistivity data was collected in a 100 × 50 m2 rectangular grid around the dumpsite, using the Wenner array. Two years later, three (3) 2-D resistivity imaging profiles were also recorded in time-lapse mode at the dumpsite to monitor the possible effects of attenuation on the leachate over time. Ten (10) VES data were also acquired and used along with the 2-D imaging data. 2-D apparent resistivity data were inverted with Dipprowin software program. The orthogonal set of 2-D lines of apparent resistivity was merged into 3-D data and inverted with RES3DINV program to create a 3-D subsurface resistivity model. Geological models observed from 2-D and 3-D resistivity inversion revealed low resistivity values in the order ρ Ω·m which is indicative of leachate plumes in the saturation zone (pore water). The 2-D resistivity-depth sections imaged low resistivity leachate plumes at the near surface (ant within the first, second and third layers at depth ranging from 0.00 - 2.50 m, 2.50 - 5.38 m and 5.38 - 8.68 m respectively. Thus, leachate contamination clearly increased with depth beyond the depth of first and second aquifers in the area which implies that available groundwater for domestic use is already contaminated with leachate from the dumpsite. Leachate contaminant-depth map estimated for the second geoelectric layers for VES 2, 3, 4, 7, 8, 9, and 10 shows that the second layer has been invaded completely by leachate contamination up to 6.5 m depth. 2-D apparent resistivity data acquired two years after show lower resistivity anomalies of the leachate plume caused by time-lapse attenuation effect on the observed resistivity of the leachate. This indicates that the leachate plume has become more conductive and toxic to the environment. The Longitudinal conductance map of the area shows that the aquifer protective capacity of this area is weak (0.1 - 0.19 Mho) thus, aquifers in the area are prone to pollution from the dumpsite. The three techniques used in this study (2-D, 3-D ERT and 1-D VES) fitly provided crucial information on the degree of contamination caused by the landfill leachate plume. Therefore, it is advisable to implement an environmental remediation and leachate management program.

Subsurface Investigation Using Electrical Resistivity Imaging for Proposed Industrial Site near Erbil-Kirkuk Borders, Northern Iraq

The friendly-environment geophysical methods are commonly used in various engineering and near-surface environmental investigations. Electrical Resistivity Imaging technique was used to investigate the subsurface rocks, sediments properties of a proposed industrial site to characterize the lateral and vertical lithological changes. via the electrical resistivity, to give an overview about the karst, weak and robust subsoil zones. Nineteen 2D ERI profiles using Wenner array with 2 m electrode spacing have been applied to investigate the specific industry area. One of these profiles has been conducted with one-meter electrode spacing. The surveyed profiles are divided into a number of blocks, each block consists of several parallel profiles in a specific direction. The positions of Electrical Resistivity Imaging profiles in the project area have been determined according to a preliminary subject plan from the civil engineers for factory foundation constructions and proposed locations of heavy machines. The inversion results of profiles showed that areas of blocks A, B, C, and D consist mainly of clastic rocks and sediments, e.g., claystone, siltstone and sandstone. The Electrical Resistivity Imaging inversion sections of blocks A, B, C, and D do not show any indication of cavitation or weak zones of sizes more than 2.0 meters, and no signs of gypsum bodies are found in these areas in general. Gypsum bodies are probably detected at block E, the southern part of the study area. The researchers recommended to keep these rocks in block E away from the continuous running water to avoid cavitation. Furthermore, the construction of heavy machines should keep away from this part of the study area to avoid to some extent, subsoil failure and subsidence in the future. Middle and Northern parts are more consistent to the constructions and factory foundations.

Preserving Holocaust history: Geophysical investigations at the Ponary (Paneriai) extermination site

Holocaust mass grave sites in eastern Europe can be difficult to investigate due to a paucity of historical documentation relating to the events and because the use of traditional invasive archaeology methods raises concerns around the disturbance of the remains of Jewish people. When combined with other lines of evidence, including historic photos and eyewitness testimony, noninvasive geophysical methods help to effectively identify and demarcate buried features at Holocaust sites, limiting unnecessary excavations. Between 1941 and 1944, as many as 100,000 people were murdered at the Ponary (Paneriai) extermination site in Lithuania, but many critical details of the site layout during this period are still to be resolved, including the location of some of the mass graves and confirmation of an escape tunnel that was used by slave laborers to escape captivity and certain death at the site. At Ponary, a combination of electrical resistivity tomography (ERT) profiling, limited ground-penetrating radar data, and bare-earth elevation data (from a light and distance ranging data set) was used to confirm the location of a large unmarked mass grave with a diameter of approximately 25 m and depth of approximately 4 m. Additional ERT profiling at a second location imaged the entrance to an escape tunnel previously uncovered by an archaeological excavation in 2004, and it detected an approximately 5 m section of the continuation of the tunnel, approximately 33 m away from the tunnel entrance. The geophysical results are supported by evidence from limited archaeological excavations, historical photographs, eyewitness descriptions of the site layout, and testimonies from the few survivors who managed to escape Ponary.

3D spatial distribution of old landfills and groundwater pollution from electrical resistivity tomography with fuzzy set theory

Landfill leakage is a concerning source of soil and groundwater pollution. Geophysical methods have been widely used in the exploration of landfill structure and leakage. However, a disadvantage of this method is its inability to delineate the landfill and the leakage area finely. By employing the membership function of fuzzy mathematics, this paper presents a quantitative index of groundwater pollution, which can clearly show the groundwater pollution status of landfills. In this manuscript, a specific landfill in Beijing was used as an example. A total of 11 electrical resistivity tomography (ERT) profiles were gathered to obtain the geoelectrical structure of the landfill. Then, we convert ERT inversion results into a quantitative index for groundwater pollution using the fuzzy set theory. Some drill samples, collected from landfill boreholes, are analysed for ammonia-nitrogen concentration to determine the parameters of the membership function. Through the comprehensive analysis of drilling, sample testing, and ERT results, we have established an indicator system that can be genuinely applied in the field for the identification and determination of leachate contaminated soil. We obtained the 3D spatial distribution of groundwater pollution, which can provide accurate and reliable data for treating landfill leakage.

Geophysical Characterization of Oil Spill Sites in Parts of Niger Delta Using Electrical Resistivity Tomography, Southern Nigeria

Geophysical survey using 2D resistivity tomography was acquired to characterize two hydrocarbon impacted sites of Ikarama and Kalaba. In the impacted sites six (6) 2D resistivity imaging profiles were carried out to understand the resistivity distribution as basis for interpreting the depth and lateral extent of contamination. Additionally, two (2) 2D resistivity imaging profiles were also carried out in the un-impacted sites to serve as control. Surface geophysical survey was acquired using ABEM SAS 1000 terammeter set with electrode constant separation of 6 step array system with a maximum electrode separation of five metres in a traverse of 100 meters. The 2D resistivity imaging data was interpreted using Res2Div. The results indicated the distribution of electrical resistivity within the subsurface. The resistivity sections were displayed in shades of rainbow colours. The values for the models range from 1.05 the resistivity models show a general increase of resistivity with depth relative to the control points. The 2D resistivity models correlate well with the borehole logs as top soil, clay, sandy clay and sand. Also, some of the 2D models indicate increases in resistivity with depth. They also show interaction of water interplaying with the contaminant plume. The resistivity range of 0.005 to 11.3 which occurred from the surface is interpreted as top soil. Immediately underlying this layer is a region of high resistivity with range of 9.4 to 78.1 which indicate petroleum contamination that may have seeped through the clay horizon to the sandy layer. This may be due to the fact that the invading crude oil may have exceeded the retention capacity of the porous medium hence allowing crude oil to spread to other zones of high hydraulic conductivity materials. In addition, it is also possible that the clay bodies were not localized. Superimposition of the main profile generated to monitor petroleum contaminant and the control profiles established a remarkably difference showing the main profiles increases of resistivity with depth, while the resistivity of the control profiles decreases with depth and possibly with materials highly resistive at the top. The study established that biodegradation increases as the depth decreases. The characterization of high resistivity with decrease in depth of the impacted sites were due to oil spill contamination whereas, decrease in resistivity with respect to depth is agreeable to non-petroleum site having materials that were restive at the top. The study pointed out hydrocarbon contamination of the both sites between shallow depths of 3m to 7m which may infiltrate to change the composition of near surface aquifers in the locality. Therefore, more geophysical studies is recommended in this area. Keywords: Electrical Resistivity Tomography, Oil spill, Geophysical Characterization DOI: 10.7176/JEES/11-2-08 Publication date: February 28 th 2021

Surface Exposure Dating and Geophysical Tomography of the Royal Arches Meadow Rock Avalanche, Yosemite Valley, California

Since the retreat of glaciers after the Last Glacial Maximum, rock avalanches have occurred intermittently in Yosemite Valley, California. We investigated the distal portion of the oldest of these, the Royal Arches Meadow rock avalanche, which has been partially buried by sediment aggradation. Cosmogenic 10 Be exposure ages of boulders within the deposit indicate that the rock avalanche occurred at 16.0 +/- 0.3 ka, immediately after deglaciation and thus prior to most aggradation. The interface between the rock avalanche deposit and the underlying glaciofluvial sediments therefore provides an elevation marker of the valley floor at the time of deposition. To identify the elevation of this interface, we collected eight Ground Penetrating Radar (GPR) and five Electrical Resistivity Tomography (ERT) profiles across the rock avalanche. Both methods are sensitive to contrasts between the granitic avalanche deposit and the underlying sediments. By constraining ERT inversions with GPR interfaces that are continuous across the profiles, we identified a single interface, interpreted as the basal contact of the rock avalanche, that separates resistive material from conductive material underneath. The elevation of this approximately horizontal interface is between 1,206 m and 1,209 m, roughly 10 m below the modern ground surface, indicating ≈10 m of sediment aggradation since deglaciation. Based on topographic expression and depth to this contact, we determined a minimum volume estimate of between 8.1*10^5 m^3 and 9.7*10^5 m^3 , nearly three times larger than what would be estimated from surface expression alone. Our findings allow reconstruction of the sedimentation history of Yosemite Valley, inform hazard and risk assessment, and confirm that geophysical methods are valuable tools for three-dimensional investigations of rock avalanches, particularly those buried by younger sediments.

Abandoned Mine Tailings Affecting Riverbed Sediments in the Cartagena–La Union District, Mediterranean Coastal Area (Spain)

This study presents the results of the geoenvironmental characterization of La Matildes riverbed, affected by mine tailings in the Cartagena–La Unión district, Murcia (southeast Spain). Soils and riverbeds in this area are highly polluted. Two Electrical Resistivity Imaging (ERI) profiles were carried out to obtain information about the thickness of the deposits and their internal structure. For the mine tailings deposits of La Murla, a tributary of the El Miedo riverbed, the geophysical method imaged two different units: the upper one characterized by low resistivity values and 5–8 m thickness, correlated with the mine tailings deposits; and the lower more resistive unit corresponding to the Paleozoic metasediments bedrock. The ERI profile transverse to the Las Matildes dry riverbed revealed the existence of three different units. The uppermost one has the lowest resistivity values and corresponds to the tailings deposits discharged to the riverbeds. An intermediate unit, with intermediate resistivity values, corresponds to the riverbed sediments before the mining operations. The lower unit is more resistive and corresponds to the bedrock. Significant amounts of pyrite, sphalerite, and galena were found both in tailings and riverbed sediments. The geochemical composition of borehole samples from the riverbed materials shows significantly high contents of As, Cd, Cu, Fe, Pb, and Zn being released to the environment. Mining works have modified the natural landscape near La Unión town. Surface extraction in three open-pit mines have changed the summits of Sierra de Cartagena–La Unión. Rock and metallurgical wastes have altered the drainage pattern and buried the headwaters of ephemeral channels. The environmental hazards require remediation to minimize the environmental impact on the Mar Menor coastal lagoon, one of the most touristic areas in SE Spain.

Illustrate mud-fluid conduits and their variety using resistivity image profiling method in Southwest Taiwan

Illustrate mud-fluid conduits and their variety using resistivity image profiling method in Southwest Taiwan

In-situ reductive degradation of chlorinated DNAPLs in contaminated groundwater using polyethyleneimine-modified zero-valent iron nanoparticles

Zero-valent iron nanoparticles (ZVIN) have found applications in many strategies for on-site soil and groundwater decontamination. A number of studies have reported the prospective utilization of ZVIN in the reduction of chlorinated organic compounds such as dense non-aqueous phase liquids (DNAPLs) in groundwater. Due to their bioaccumulation and carcinogenesis, DNAPLs in groundwater are a human health hazard and pose environmental risks. Therefore, decontamination of these contaminants is necessary. This study presents the in-situ remediation of trichloroethylene (TCE), perchloroethene (PCE), and 1,2-dichloroethene (1,2–DCE) DNAPLs through the direct injection of polyethylenimine (PEI)-coated ZVIN (PEI–ZVIN composite materials) to facilitate the reduction of contaminants in low-permeability media. A field test was conducted at the premises of a petrochemical company, situated in the Miaoli County of Northern Taiwan that discharged significant amounts of DNAPLs. After in-situ injection and one-day of reaction with groundwater contaminants, ZVIN was further characterized to examine its efficacy in the reduction of pollutants. After the direct injection of PEI–ZVIN, a notable reduction in the concentration of DNAPLs was recorded with conversion from toxic to non-toxic substances. Use of resistivity image profiling (RIP) technique suggested similar conductivity data for the PEI-coated ZVIN suspension and groundwater samples. X-ray absorption near edge structure (XANES) and X-ray absorption fine structure (EXAFS) studies depicted that the oxidation of ZVIN and PEI–ZVIN was occurring after the reductive reaction with contaminated groundwater. The reacted samples had bond distance values of 1.98, 2.00, 1.96, and 1.94 Å. Combining floating surface-coated ZVIN and RIP technique seems promising and environmentally attractive.

Geophysical Investigation for Post Foundation Studies at Ikekogbe Primary School, Ekpoma, Edo State, Nigeria

This research showed the significance of electrical resistivity method for foundation studies at Ikekogbe Primary School, Ekpoma, Edo State, Nigeria. The aim of the study is to assess the building in the area that was intensively affected by cracks resulting in structural instability. The Electrical Resistivity method involved three techniques; Vertical Electrical Sounding (VES), 2-D Electrical Resistivity Tomography (ERT) and Horizontal Profiling (HP) which covers a pilot test of 60 meters. Eight (8) VES were carried out using Schlumberger array with current electrode spacing varying from 1 to 40 m, with 2-D ERT using Dipole-Dipole electrode array with inter-station separation of 5 m and an expansion factor that varied from 1 to 5 and HP using Wenner array with an electrode spacing of 5 m interval. The results obtained from the VES delineated three geoelectric units which comprise of topsoil, clayey sand and sandstone formation. The 2 D imaging (Dipole-Dipole) gave information on the subsurface characteristic in the area with low apparent resistivity which indicates low competence material. The Wenner profile is characterised by low resistivity. All the results correlate well with one another showing that all the techniques used are complemented and also deduced that the failures of these buildings arise from incompetent clay materials and lateral inhomogeneity. Evidence has shown that a suspected weak zone cut across the study area and the weak zones contributed a great deal to the cracks observed on the classroom block. The presence of clay materials beneath the classroom also contributed to the cracks observed. It is therefore recommended that future engineering construction should consider possible weak zones before designing or imposed structure as such can instigate failure in the proposed structure.

Preferential groundwater seepage in karst terrane inferred from geoelectric measurements

ABSTRACTThe Ellenburger–San Saba aquifer discharges spring flows into the overlying Hamilton Creek bed in Burnet County, central Texas. The aquifer is susceptible to contamination from surface‐water reservoirs because of the presence of dissolution cavities that are hydraulically connected to the reservoirs in some locations. There is concern that preferential groundwater seepage from reservoirs into the aquifer in these locations might ultimately degrade the quality of the springwater that enters Hamilton Creek. To investigate preferential groundwater seepage patterns and hydraulic connectivity between surface‐water reservoirs and the Ellenburger–San Saba aquifer, geophysical reconnaissance surveys were completed between July 2017 and January 2018 to map dissolution cavities and locate preferential groundwater seepage within a specific region of the aquifer. Two‐dimensional electric resistivity tomography and self‐potential profiling were utilized, and a simplified, three‐dimensional finite‐element model of the field site was constructed to provide an interpretive aid. The self‐potential data indicated the occurrence of preferential groundwater seepage through a porous seepage conduit that was imaged by the electric resistivity tomography data but did not indicate the occurrence of groundwater seepage through two fluid‐filled dissolution cavities that were imaged by electric resistivity tomography data. Collectively, the surveying and modelling results demonstrate the efficacy of geoelectric methods for mapping the locations of dissolution cavities and preferential groundwater seepage in the electrically resistive karst terrane of the Ellenburger–San Saba aquifer.

Decontamination of 1,2-Dichloroethane DNAPL in Contaminated Groundwater by Polymer-Modified Zero-Valent Iron Nanoparticles

Remediation of dense non-aqueous phase liquids (DNAPLs) contaminants in groundwater has received considerable attention in the environmental field. Generally, DNAPLs can flow with groundwater and further infiltrate down to deeper aquitard zone that is difficult to be removed by pumping. The DNAPLs may also contaminate the soil and groundwater concurrently in the duration of flowing with groundwater slowly. In this study, remediation of 1,2-dichloroethane (1,2-DCE) in DNAPL contaminated groundwater was studied by a reductive reaction with polyethylenimine (PEI) surface-modified zero-valent iron nanoparticles (PEI-nZVI). The prepared PEI-nZVI was injected into upstream wells and reach the plume of DNAPLs down with the flowing groundwater. Moreover, nZVI was further characterized after field injection and 1-day reaction with the contaminants to assess its effectiveness for the on-site reduction of 1,2-DCE. After direct injection of PEI-nZVI into the contaminated plume, the concentrations of 1,2-DCE was significantly reduced. Moreover, the plume was decontaminated to nontoxic species onto the highly active nZVI. By using resistivity image profiling (RIP), the conductivity data of modified nZVI solution and sampled groundwater were similar. In addition, RIP can reveal complex subsurface DNAPLs structures by dense sampling of resistivity variation at shallow depth. Additionally, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies indicated that after the reductive reaction, nZVI and PEI-nZVI were oxidized to Fe3O4. The interatomic distances for the reacted samples were 1.95 A and 1.93 A, respectively. The combined technique of floating surface-modified nZVI and RIP method would be economically and environmentally attractive.

Groundwater Assessment Using Geophysical Survey at Insat, Perlis, Malaysia

In this study, a 2D geo-electrical resistivity survey was conducted at Institute of Sustainable Agrotechnology (InSAT) Padang Besar, Perlis to locate potential groundwater zone. A set of ABEM Terrameter SAS 400 was used to measure resistivity and chargeability value of 400-meter survey line. Then, the measured data was analysed using RES2DINV software to produce resistivity and chargeability imaging profiles. It was found that, there is one groundwater reservoir detected at a distance of 180 m from left end at distance 0 m. The groundwater reservoir zone was located at 50 m depth below ground surface. The resistivity and chargeability values of this zone varied between 500 to 5000 Ωm and 0 to 2 ms, respectively.

Geophysical Assessment of Subsurface Conditions at Proposed Building Sites: Implications for Foundation Failure and Building Collapse

Abstract Building collapse has been a recurrent environmental hazard in Nigeria in the last two decades. This is a corollary of inadequate foundation investigation prior to construction, poor government policies, and general lack of awareness on the importance of geophysical and geotechnical investigations. In this study, geological mapping and detailed geophysical investigation using Electrical Resistivity Imaging (ERI) and Vertical Electrical Sounding (VES) were carried out to understand the suitability of proposed building sites at the main campus of the Olabisi Onabanjo University (OOU), Ago-Iwoye, Nigeria for construction. Both Wenner array and dipole-dipole were used for profiling and Schlumberger for sounding. Four transverses and VES were used in each of the three areas investigated. Our results show that the subsurface of the study areas is underlain by Precambrian basement rock of Nigeria. Rocks in the study area include banded gneiss, porphyroblastic gneiss, biotite-hornblende granite and quartzite schist. The sounding stations across the three areas and 2D resistivity imaging revealed three principal geoelectric layers, the topsoil, the weathered layer and the fractured/fresh basement with varied resistivity values for each layers. At the VES stations, the three geoelectric layers have resistivity values of 62 to 1182 Ωm, 3.2 to 1360Ωm and 87 to 4680 Ωm. On the 2D resistivity imaging profiles, the resistivity of the three layers varies from 2 to 1182 Ωm, 30to 1360 Ωm, and 40 to 2904 Ωm for the topsoil, the weathered basement, and fractured/fresh bedrock. Our work demonstrates that some of the proposed sites are structurally incompetent for engineering or foundation purposes. Excavation of the topsoil and reinforcement are required to sustain the proposed structures.

Impact of the geological structures on the groundwater potential using geophysical techniques in West Bani Mazar area, El Minia – Western Desert, Egypt

Establishment of the new agricultural projects in west Bani Mazar area, El Minia, Egypt needs a good knowledge about groundwater. Groundwater serves as the unique source of water supplies in the study area. Vertical Electrical Sounding technique is a convenient tool for groundwater exploration. This technique was utilized to illustrate the geoelectric succession, vertical and spatial extensions of the encountered layers, depth to water bearing layers and the structures affecting these layers. Profiling technique was carried out along a grid pattern using different half current electrode spacings (150 m, 300 m and 500 m) to clarify changes in resistivity values throughout the study area at different depths. Geoelectric layers B1 and B2 of the saturated zone are suitable for groundwater extraction in the study area. The resistivity values of the geoelectric layer B1 decrease towards the West direction, they decrease from 23.0 Ωm to 16.0 Ωm; and its thicknesses increase towards the SE direction from 12.0 m to 18.0 m. Whereas, the resistivity values of the geoelectric layer B2 decrease towards the NW direction from 40.0 Ωm to 26.5 Ωm; and its thicknesses vary from 34.0 m to 40.0 m. The depths to the upper surface of the water bearing layer B1 increase towards the NW direction from 44.0 m to 89.4 m. Based on the results obtained from the Vertical Electrical Soundings, four two-dimensional resistivity imaging profiles were measured at the selected sites. These 2-D resistivity profiles aim to determine depths to the water bearing layers, their thicknesses and the shallow structure. The inverted models of these profiles matched with the geoelectric sequence at these sites. In addition, a normal fault is detected at the northwestern part of the study area.According to the results obtained from this study it is clear that the groundwater in the area under consideration is occurred in the fractured limestone layers that belong to Eocene Age. Resistivity values of the water bearing layers increase with depth as a result of decreasing fracture density; and these values decreased towards the northwestern direction due to their proximity from the fault zone. The groundwater potential of these layers depends mainly on the lithologic composition and the geological structures affecting these layers. The secondary porosity of these limestone layers depends mainly on the degree of fracturing and fissuring. The proper sites to drill new productive wells were recommended, and the obtained data from drilling new well in the southeastern part of the study area coincide with the interpreted data of the different geophysical techniques.

Geophysical and Hydrochemical Characteristics of Groundwater at Kerian Irrigation Scheme

.A study was conducted to determine the potential of groundwater uses at the Kerian irrigation scheme, specifically the Selinsing irrigation area. Resistivity image profiling method was employed at four sampling locations within the study area to identify the depth and variation of aquifer layer and the possibility of hard layer presence. Investigations conducted revealed that the thickness of aquifer within the study area varies between 5 m and 10 m, which is located at a depth of 30 m to 70 m below the ground surface. The thickness of clay layer is between 1 m and 80 m which dominates the upper subsurface layer. Seven samples of groundwater were used in determining their hydrochemical and physicochemical characteristics, ionic composition, and the quality suitability for irrigation use. A preliminary characterisation based on the piper diagram provides the hydrofacies classification while Stiff diagram is used to exhibit the ionic relationship. The degree of correlation between cations and anions has been estimated in order to assess their mutual relationships. Strong positive correlation exists for Ca2+-Mg2+, Ca2+-Na+, Na+-Mg2+, Na+-K+, Ca2+-K+, Mg2+-K+, Mg2+-Cl-, K+-HCO3-, and Na+-Cl-. Profusion of elements also reflects the composition of aquifer and the climatic conditions, which possibly contribute to the genetic relationship.

Geophysical and geochemical studies to delineate seawater intrusion in Bagoush area, Northwestern coast, Egypt

Coastal aquifers are the main source for sustainable freshwater in many arid and semi-arid regions around the earth. In such regions, groundwater extraction far exceeds the natural replenishment rates due to additional demands on groundwater resources especially in the last few decades. The characterization of the seawater intrusion in the Baghoush area along the northwestern coast of Egypt assesses the risk of seawater intrusion for the purpose of managing the groundwater resources in coastal areas. The (SI) in the oolitic Pleistocene aquifer is affected by several natural factors, including the drainage patterns, geological structures, distance from the sea and the manipulation of groundwater. Electrical Resistivity Tomography (ERT) has been implemented to identify the geometry of the brackish/saline water interface and to map the distribution of brackish water zone floating over the denser saline water. Seven 2-D resistivity imaging profiles were conducted using a Wenner array with different electrode distance spacings. The inverse resistivity models of these profiles indicate that these profiles are composed of three zones: the upper dry zone, the middle brackish water zone, and the lower saline water zone. The thickness of the brackish groundwater zone decreases toward the sea and the resistivity decreases with depth due to increase in water salinity. Water table along these profiles decreases from south to north, which indicates that groundwater flow is from south (inland) to north (sea). Groundwater chemistry and stable isotopes were used to determine the fresh groundwater recharge source(s), to identify mixing of different groundwaters, to evaluate seawater intrusion zone along the coast, and to investigate the upwelling of deep saline groundwater underneath the brackish zone. The recharge of fresh groundwater originates from the mountain watershed located upstream as well as the annual rainfall; however, seawater is the main source of groundwater salinization. The estimated mixing ratios between the fresh groundwater recharge to seawater ranges between 32% and 75% groundwater to 68% and 25% seawater. The outcomes of this study emphasize the importance of closely monitoring groundwater management to limit upwelling of the underlying salt-water into the overlying groundwater along the coast to limit further seawater intrusion.

Site Characterization during Bridge Foundation Construction Using Electrical Resistivity Tomography

A shallow underground water-filled cavity was encountered in limestone bedrock during the construction of a new column footing for the Gasconade River Bridge over Interstate 44. Five electrical resistivity tomography (ERT) profiles and borehole control were acquired in immediate proximity to the existing and the new column footings in order to assess the integrity of the rock beneath the foundation columns and characterize the encountered cavity. Two parallel southwest- northeast trending fracture zones were identified on the acquired ERT profiles and competent rock was differentiated from more extensively fractured rock. The volumetric extent of the void was mapped based on the interpretation of the ERT, borehole and injected grout data. A conceptual model for the development of the water-filled cavity was proposed.

Characterization of Dredged Oyster Shell Deposits at Mobile Bay, Alabama Using Geophysical Methods

The need for disposing materials dredged from ship channels is a common problem in bays and lagoons. This study is aimed at investigating the suitability of scour features produced by dredging oyster shell deposits in Mobile Bay, Alabama, to dispose excavated channel material. A study area approximately 740 by 280 m lying about 5 km east of Gaillard Island was surveyed using underwater electrical resistivity tomography (UWERT) and continuous electrical resistivity profiling (CERP) tools. The geophysical survey was conducted with the intent to map scour features created by oyster shell dredging activities in the bay between 1947 and 1982. The geoelectrical surveys show that oyster beds are characterized by high resistivity values greater than 1.1 ohm.m while infilled dredge cuts show lower resistivity, generally from 0.6 to 1.1 ohm.m. The difference in resistivity mainly reflects the lithology and the consolidation of the shallow sediments: consolidated silty clay and sandy sediments rich in oyster shell deposits (with less clay content) overlying unconsolidated clayey materials infilling the scours. Results show that most of the infilled dredge cuts are mostly distributed in the north-south direction. Considering that the scours are generally up to 6 m deep across the survey location, it is estimated that about 0.8 million cubic meters of oyster shells and overlying strata were dredged from the survey location.