Surface Resistivity Surveys Research Articles

An Effective Method for Quantitative Interpretation of Seawater Intrusion in Shallow Aquifers from Electrical Resistivity Data

Groundwater in coastal areas is vulnerable to saltwater intrusion. Electrical resistivity is commonly used in order to detect saltwater intrusion due to its ability to distinguish the occurrence of saltwater in the pore water. In this research, a correlational approach was used to estimate percentage seawater content that was mixed with fresh water in a shallow aquifer. The study area was located in Dumai City, which was covered mainly by peat soil, but some areas were covered by sand and silt. A ground surface resistivity survey and direct soil resistivity measurements were used in the study. For both experiments, the Wenner configuration of electrical resistivity was employed. In order to determine the direct soil resistivity values, measurements of the soil's fluid content and character were made. The findings indicate that the resistivity value in the aquifer increased to 5–10 Wm at a 25% seawater content, from roughly 2–5 Wm at a 50% seawater content. The pore soil's rising salt content was the primary source of the sharp decline in resistivity values. By measuring the electrical resistivity on the surface, it is possible to accurately forecast the percentage of seawater mixture in the pore soil fluid.

A valuable approach in a quantitative seawater intrusion interpretation from the geoelectrical resistivity data for groundwater investigation in Dumai area, Indonesia

An improvement of geoelectrical resistivity interpretation has been done through this research. Up to now, the geoelectrical resistivity data was interpreted qualitatively especially in the case of the aquifer intruded by seawater, and the percentage of seawater mixture content in the aquifer cannot be predicted. In this research, a valuable approach was used in the prediction of percentage seawater mixture in the shallow aquifer that is intruded by seawater. The study was conducted in the coastal area which is mainly covered by peat soil. The research employed the direct soil resistivity measurement and the ground surface resistivity survey. Geoelectrical resistivity with the Wenner configuration was used for both measurements. The soil character and the fluid content in the soil were measured to obtain their correlation to the direct soil resistivity value. The results show that resistivity value is about 2-5 ohm.m for 50% seawater content mixture in aquifer and it increase to be 5-10 ohm.m for 25% seawater mix to freshwater in the aquifer. The increasing seawater content in the pore soil caused the decreases in resistivity value drastically. The percentage of seawater mixture in the fluid pore soil has been successfully predicted through the geoelectrical resistivity measurement on the surface.

Evolution of a stratigraphic model in a fluvial deltaic wedge: implications for groundwater resource protection in an oil and gas-bearing region in the Upper Cretaceous Dunvegan Formation, Northwest Territories, Canada

The Liard Basin, in northwestern Canada, contains one of Canada’s largest natural gas reserves. There are concerns about degradation of Dunvegan Formation groundwater quality, which is the basin's main shallow freshwater aquifer, as a consequence of oil and gas development. Previous lithostratigraphic studies interpreted the Dunvegan as conglomeratic alluvial fans. In this study, newly collected cores and surface resistivity surveys are integrated with legacy hydrocarbon well data and measured sections for improved sedimentary bedrock characterization. Rather than alluvial fans, we interpret the upper Dunvegan as a coarse-sand to gravel bed fluvial system that was likely tributive to incised valleys associated with linked Alberta Basin base-level falls. Correlation of well logs and measured sections suggest the lower Dunvegan comprises a prograding delta complex with off-lapping clinoforms fed by smaller sand-bed rivers that grade into the upper Dunvegan conglomeratic system, which built southeast towards the Cretaceous Western Interior Seaway. This sequence stratigraphic and facies architectural approach is employed to inform the aquifer–aquitard flow system and aid in understanding the 3D groundwater flow system, once hydrogeologic characterisation confirms position and thickness of important hydrogeologic units. Resistivity surveys suggest upper Dunvegan channel-belt facies may be well-connected and laterally extensive, potentially acting as interconnected aquifer units; whereas lower Dunvegan channel belts may be discontinuous, indicating smaller-scale flow units separated by floodplain and marine shale. This revised geologic understanding provides opportunities for determining impacts or resilience from shallow and deep sources of contamination associated with human activities, including oil and gas development, land-use, and (or) climate change.

Using Time-Lapse Resistivity Imaging Methods to Quantitatively Evaluate the Potential of Groundwater Reservoirs

In this study, we attempt to establish an alternative method for estimating the groundwater levels and the specific yields of an unconfined aquifer for the evaluation of potential groundwater reservoirs. We first converted the inverted resistivity into the normalized water content. Then, we inverted the parameters of the Brooks-Corey model from the vertical profiles of the water content by assuming that the suction head was in proportion to the elevation regarding a predefined base level. Lastly, we estimated the groundwater level, the theoretical specific yield, and the specific yield capacity from the Brooks-Corey parameters at every survey site in the study area. The contour maps of the time-lapse groundwater levels show that the groundwater flows downstream, with a higher hydraulic gradient near the river channel than in the area away from the main channel. We conclude that the estimated maximum specific yield capacities are consistent with that derived from the pumping tests in the nearby observation well. Additionally, the specific yield capacities are only three quarters to two thirds of the theoretical specific yields derived from the difference between the residual and saturated water contents in the Brooks-Corey model. We conclude that the distribution pattern of the specific yields had been subjected to the distribution of natural river sediments in the Minzu Basin, since the modern channel was artificially modified. Although we had to make some simple assumptions for the estimations, the results show that the surface resistivity surveys provide reasonable estimations of the hydraulic parameters for a preliminary assessment in an area with few available wells.

Time-lapse electrical resistivity tomography mapping of DNAPL remediation at a STAR field site

Time-lapse Electrical Resistivity Tomography (ERT), a surface geophysical technique, was applied for the first time to directly map in-situ DNAPL destruction at a field site. Time-lapse ERT was used to map remediation of coal tar at a site undergoing full-scale application of Self-sustaining Treatment for Active Remediation (STAR). STAR is an in situ thermal treatment based on smoldering combustion that destroys dense non-aqueous phase liquids (DNAPLs) while generating heat, water, and combustion gases. ERT was used to provide spatially and temporally resolved data to complement the conventional discrete and overview data normally collected during STAR operations. A STAR treatment cell targeting coal tar at 2.4 mbgs and below the water table was monitored with 2D surface resistivity surveys conducted before, during and after treatment. Two 36-electrode lines, each 21 m long, were employed. Relative resistivity ratio maps and discrete (nodal) resistivity signal analysis both proved useful in numerous ways. For example, ERT was demonstrated to map likely treated coal-tar zones. This was accomplished by identifying a characteristic, local, temporal resistivity signal pattern corresponding to STAR-induced subsurface temperature and liquid saturation changes. In addition, ERT identified the subsurface areas (i) effectively captured by the vapor extraction system, (ii) possibly missed by the vapor capture system where gases built-up, and (iii) where and when re-infiltration of groundwater occurred post-treatment. In addition, the overall average subsurface resistivity provided a useful metric to correlate with traditional site measures of treatment such as the cumulative amount of DNAPL mass treated. This study provides a successful proof of concept however the maximum potential of the approach is expected with a full 3D survey. Overall, the resistivity surveys provided valuable continuous mapping of the subsurface, including the locations of DNAPL mass destruction, and showed that ERT is promising for supporting evaluations of in situ remediation programs.

Constructing the Apparent Geological Model by Fusing Surface Resistivity Survey and Borehole Records.

We constructed an apparent geological model with resistivity data from surface resistivity surveys. We developed a data fusion approach by integrating dense electrical resistivity measurements collected with Schlumberger arrays and wellbore logs. This approach includes an optimization algorithm and a geostatistic interpolation method. We first generated an apparent formation factor model from the surface resistivity measurements and groundwater resistivity records with an inverse distance method. We then converted the model into a geology model with the optimized judgment criteria from the algorithms relating the apparent formation factors to the borehole geology. We also employed a non-parametric bootstrap method to analyze the uncertainty of the predicted sediment types, and the predictive uncertainties of clay, gravel, and sand were less than 5%. Overall, our model is capable of capturing the spatial features of the sediment types. More importantly, this approach can be arranged in a self-updated sequence to enable adjustments to the model to accommodate newly collected core records or geophysical data. This approach yields a more detailed apparent geological model for use in future groundwater simulations, which is of benefit to multi-discipline studies.

Hydrogeological characteristics of the Albertine Graben, Uganda: Evidence from surface geophysics and hydraulic testing

Current understanding of the hydrogeological characteristics of riftmargin environments is limited and not well reconciled to large-scale conceptual models of rift evolution. In East Africa where there is substantial dependence on groundwater for rural water supplies, it is unclear how global change including localised development of oil impacts the quality and quantity of available groundwater resources. Hydrogeological characteristics of the Albertine Graben (Uganda) were explored primarily using surface resistivity surveys and hydraulic testing and supported by evidence from lithological logs, structural data and drainage maps. Interpretation of the vertical electrical soundings and lithological data reveal a heterogeneous subsurface with three to five (geo-electric) layers in areas spatially underlain by the Precambrian basement and sedimentary formations. A hydrogeological conceptual model is developed that details the influence of the morphology and geological structures on the hydrogeology of the studied area. It is revealed that the two aquifer environments: (1) transmissive, unconsolidated sediments (Sedimentary formation with mean T = 45 m2.day-1 averaging 27 m thick) of predominantly Miocene to Pleistocene age within the trough below the escarpment and, (2) deeply weathered Precambrian basement rocks (Bunyoro formation with mean T of 6 m2.day-1 averaging 13 m thick and Karuma formation with mean T of 28 m2.day-1 averaging 38 m thick) of lower transmissivity within the Lake Albert basin above the escarpment occur. The results suggest, localised groundwater flow in the metamorphic aquifers towards surface drainage that exhibit a dendritic drainage pattern, and also have a regional flow system that is greatly influenced by NE-SW trending regional structural lineaments. In the Sedimentary formation, a dendritic drainage pattern is also exhibited and groundwater flow is dominantly westwards to Lake Albert that forms the main constant head boundary.

Comparison Study to the Use of Geophysical Methods at Archaeological Sites Observed by Various Remote Sensing Techniques in the Czech Republic

A combination of geophysical methods could be very a useful and a practical way of verifying the origin and precise localisation of archaeological situations identified by different remote sensing techniques. The results of different methods (and scales) of monitoring these fully non-destructive methods provide distinct data and often complement each other. The presented examples of combinations of these methods/techniques in this study (aerial survey, LIDAR-ALS and surface magnetometer or resistivity survey) could provide information on some specifics and may also be limitations in surveying different archaeological terrains, types of archaeological situations and activities. The archaeological site in this contribution is considered to be a material of this study. In case of Neolithic ditch enclosure near Kolín were compared aerial prospection data, magnetometer survey and aerial photo-documentation of excavated site. In the case of hillforts near Levousy we compared LIDAR data with aerial photography and large-scale magnetometer survey. In the case of the medieval castle Liběhrad we compared LIDAR data with geoelectric resistivity measurement. In case of a burial mound cemetery we combined LIDAR data with magnetometer survey. In the case of the production area near Rynartice we combined LIDAR data with magnetometer and resistivity measurements and result of archaeological excavation. Fortunately for successful combination of geophysical and remote sensing results, their conditions and factors for efficient use in archaeology are not the same. On the other hand, the quality and state of many prehistoric, early medieval, medieval and also modern archaeological sites is rapidly changing over time and both groups of techniques represent important support for their comprehensive and precise documentation and protection.

Inversion of capacitively coupled resistivity (line-antenna) measurements

The capacitively coupled resistivity method using line antennas (or electrodes) has been widely applied for various kinds of applications. To solve the associated inversion problem, the general practice (i.e., the indirect inversion method) for 2D surface resistivity surveys is to approximate the line-electrode array by an equivalent point-electrode array, so that the existing direct current resistivity inversion programs can still be used. Based on the experimental evidence from this study that two resistivity arrays with a similar sensitivity (1D) curve offers comparable measurement, we optimized the equivalent point-electrode array by minimizing the sensitivity (1D) difference between the line- and point-electrode arrays in terms of the depth of investigation difference (DID). The dipole length of the optimal equivalent point-electrode array can be determined by considering only the array with the shortest dipole distance. For the line-electrode arrays with the dipole lengths of 2.5, 5, and 10 m, the suggested optimal dipole lengths are 74%, 73%, and 73% of the respective dipole lengths. The numerical examples carried out in this study prove the effectiveness of the indirect inversion method for 2D surface resistivity surveys when the appropriate equivalent point-electrode array with a low DID value is chosen, and vice versa. The direct inversion of the line electrode resistivity measurements from 3D resistivity surveys is achieved with a MATLAB-based, open-source resistivity inversion package called RESINVM3D incorporating line electrodes. The usefulness of this modified code was demonstrated with a numerical example that considered cross-borehole resistivity tomography using line electrode measurements. The location of the assigned resistivity anomaly and the boundary between two soil layers were well captured by the direction inversion.

Surface Resistivity Survey for Siting Shallow Boreholes within The 1000 Housing Estate, Maiduguri, Northeast Nigeria.

Surface Resistivity Survey for Siting Shallow Boreholes within The 1000 Housing Estate, Maiduguri, Northeast Nigeria.

Assessment of aggregate resources: an integrated geophysical approach

ABSTRACTFluvio‐glacial sand and gravel provide an important resource for the construction industry. The efficient and economic extraction of such geologically complex deposits requires a detailed understanding of their grade distribution. This is typically undertaken as point observations over the resource using a borehole drilling programme. We investigate the viability of using measurements of the elastic and electrical properties of the subsurface, derived from geophysical profiles, to determine the spatial variability of aggregate quality.A refraction seismic, surface wave seismic and resistivity survey was carried out over a fluvioglacial sand and gravel deposit at Scorton, Yorkshire, UK, on agricultural land adjacent to an active quarry. Two 190 m profiles, with borehole control at their extremes, were acquired with a 2 m source and receiver spacing. The P‐ and S‐wave velocities ( and ), together with resistivity and depth distributions were determined down to c. 20 m. The subsurface was divided into four layers: uncon‐solidated sand and gravel; dry consolidated sand and gravel; saturated sand and gravel; and basal clay.The work flow initially involved processing and interpreting the three geophysical techniques independently. Crossplots of the elastic and electrical parameters were used to distinguish unconsolidated from consolidated material; the water table; increased silt content; and recognize the basal clay. The Vp/Vs ratio proved very powerful at discriminating fine material () from coarse material (Vp/Vs ~ 1.5). Regression analysis of crossplots produced P‐ and S‐wave relationships for the material, while electro‐acoustic relationships were less successful, especially below the water table. The results of the petrophysical analysis were used to set up guided inversions for the resistivity survey. Careful use of the refraction results as an a priori model for the resistivity survey was found to improve the resistivity inversion, though use of a sharp boundary introduced edge effects at the water table.The results from the integrated analysis were combined with the guided inversions into a final interpretation that enabled silt content, particle size and clay lenses to be mapped, which were not identified in the separately processed data.

Correlation of Geoelectric Data with Aquifer Parameters to Delineate the Groundwater Potential of Hard rock Terrain in Central Uganda

Knowledge of aquifer parameters is essential for management of groundwater resources. Conventionally, these parameters are estimated through pumping tests carried out on water wells. This paper presents a study that was conducted in three villages (Tumba, Kabazi, and Ndaiga) of Nakasongola District, central Uganda to investigate the hydrogeological characteristics of the basement aquifers. Our objective was to correlate surface resistivity data with aquifer properties in order to reveal the groundwater potential in the district. Existing electrical resistivity and borehole data from 20 villages in Nakasongola District were used to correlate the aquifer apparent resistivity (ρ e) with its hydraulic conductivity (K e), and aquifer transverse resistance (TR) with its transmissivity (T e). K e was found to be related to ρ e by; \( {\text{Log }}(K_{\text{e}} ) = - 0.002\rho_{\text{e}} + 2.692 \). Similarly, TR was found to be related to T by; \( {\text{TR}} = - 0.07T_{\text{e}} + 2260 \). Using these expressions, aquifer parameters (T c and K c) were extrapolated from measurements obtained from surface resistivity surveys. Our results show very low resistivities for the presumed water-bearing aquifer zones, possibly because of deteriorating quality of the groundwater and their packing and grain size. Drilling at the preferred VES spots was conducted before the pumping tests to reveal the aquifer characteristics. Aquifer parameters (T o and K o) as obtained from pumping tests gave values (29,424.7 m2/day, 374.3 m/day), (9,801.1 m2/day, 437.0 m/day), (31,852.4 m2/day, 392.9 m/day). The estimated aquifer parameter (T c and K c) when extrapolated from surface geoelectrical data gave (7,142.9 m2/day, 381.9 m/day), (28,200.0 m2/day, 463.4 m/day), (19,428.6 m2/day, 459.2 m/day) for Tumba, Kabazi, and Ndaiga villages, respectively. Interestingly, the similarity between the K c and K o pairs was not significantly different. We observed no significant relationships between the T c and T o pairs. The root mean square errors were estimated to be 18,159 m2/day and 41.4 m/day.

Inorganic Plume Delineation Using Surface High‐Resolution Electrical Resistivity at the BC Cribs and Trenches Site, Hanford

A surface resistivity survey was conducted on the Hanford Site over a waste disposal trench that received a large volume of liquid inorganic waste. The objective of the survey was to map the extent of the plume that resulted from the disposal activities approximately 50 yr earlier. The survey included six resistivity transects of at least 200 m, where each transect provided two‐dimensional profile information of subsurface electrical properties. The results of the survey indicated that a low resistivity plume resides at a depth of approximately 25 to 44 m below ground surface. The target depth was calibrated with borehole data of pore‐water electrical conductivity. Due to the high correlation of the pore‐water electrical conductivity to nitrate concentration and the high correlation of measured apparent resistivity to pore‐water electrical conductivity, inferences were made that proposed the spatial distribution of the apparent resistivity was due to the distribution of nitrate. Therefore, apparent resistivities were related to nitrate, which was subsequently rendered in three dimensions to show that the nitrate likely did not reach the water table and the bounds of the highest concentrations are directly beneath the collection of waste sites.

RESINVM3D: A 3D resistivity inversion package

We have developed an open source 3D, MATLAB based, resistivity inversion package. The forward solution to the governing partial differential equation is efficiently computed using a second-order finite volume discretization coupled with a preconditioned, biconjugate, stabilized gradient algorithm. Using the analytical solution to a potential field in a homogeneous half space, we evaluate the accuracy of our numerical forward solution and, subsequently, develop a source correction factor that reduces forward modeling errors associated with boundary effects and source electrode singularities. For the inversion algorithm we have implemented an inexact Gauss-Newton solver, with the model update being calculated using a preconditioned conjugate gradient algorithm. The inversion uses a combination of zero and first order Tikhonov regularization. Two synthetic examples demonstrate the usefulness of this code. The first example considers a surface resistivity survey with 3813 measurements. The discretized model space contains 19,040 cells. For this example, the inversion package converges in approximately [Formula: see text] on a [Formula: see text] Pentium 4, with [Formula: see text] of RAM. The second example considers the case of borehole based data acquisition. For this example there were 4704 measurements and 13,200 model cells. The inversion for this example requires [Formula: see text] of computational time.

Complex extensional faulting of Triassic rocks north of York, North Yorkshire, UK

SUMMARY Borehole records, seismic reflection traverses and surface resistivity surveys have established the presence of previously unknown graben complexes north of York. A major NE–SW to E–W trending complex with vertical displacements of up to around 200 m is traceable for 22 km through Beningbrough and Strensall. A narrower NW-SE trending graben with similar displacements can be traced for at least 8 km through Lilling, south of Sheriff Hutton. A large part of the Beningbrough-Strensall Graben Zone is complexly faulted on both large and small scales. It is located at the southern edge of the Howardian-Flambor-ough Head Fault Zone and may have been within an area of maximum ‘sag’ deformation along the hinge between the subsiding Cleveland Basin to the north and the more rigid Market Weighton Block to the south. Major consequences of the faulting are: (i) a 10 km sinistral shift of the sub-drift crop of the Triassic Mercia Mudstone Group, (ii) substantial changes to ground water levels and flow, and (iii) the presence of small fault bounded blocks of Rhaetian Penarth Group rocks many kilometres from their main sub-drift crop.

Freshwater reserves of mid-atlantic coast barrier Islands

A multiple regression model was constructed for the purpose of predicting barrier island hydrology from easily measureable island characteristics. The model was developed using data obtained from 17 sites on the Outer Banks of North Carolina. The accuracy of the model for predicting key hydrologic variables was evaluated by statistical and graphic procedures. In general, agreement between observed and predicted values of the hydrologic variables was very good, suggesting that the quantity of potable water at various island sites can be estimated without resorting to extensive field investigations. The model was then applied to Assateague Island, a barrier island located off the coasts of Maryland and Virginia. Results indicate that the original model developed for the Outer Banks may be applied to other barrier islands but that errors involved may necessitate corrections in detailed studies. Correction for bias in predictions for Assateague was shown to be possible with limited field data from surface resistivity surveys.

A geoelectrical investigation of the drift deposits in Northwest Lancashire

AbstractA surface resistivity survey around and to the south of Garstang has indicated a predominance of boulder clay, with some sands and gravels, in an overburden of markedly variable thickness and lithology. The survey techniques, data processing and interpretation are discussed. The data suggest that the Lower Boulder Clay may be represented northeast of Garstang, with the Middle Sands present over a much wider area. The major subdivision, the Upper Boulder Clay, seems to be overlain by patches of presumed Upper Sands. Possible isopachytes of these four suggested subdivisions are presented, and certain hydrogeological implications briefly mentioned.

Geothermal exploration in Mexico 1968–1969

The Federal Electricity Commission is developing a second geothermal field in the Cerro Prieto area, near Mexicali, Baja California, with twenty-two producing drill holles. Exploration is concentrated south-east of Cerro Prieto where hot water and steam at high temperature and pressure are present in the reservoir. To the north and south of Cerro Prieto there are three further areas of surface manifestations. During the period from the beginning of 1968 to August 1969, the Research Institute for the Electrical Industry, a branch of the Federal Electricity Commission, has carried out geological, geophysical, and geochemical studies in four geothermal fields in the central volcanic belt, located approximately between parallels 18 and 21 north latitude, and composed of volcanic rocks of ages ranging from Tertiary to Recent. All of them have very good contrast in their physiographic expression, intimately connected with active volcanic and tectonic zones of Mexico. The fields of Los Negritos and Ixtlán de los Hervores, State of Michoacán, (1535 metres a.m.s.l.) are at the intersection of the western Sierra Madre and the west-central part of the neovolcanic axis. They are about 27 km apart and separated by the Pajacuarán Ridge, on the eastern side of Lake Chapala, 130 km east of Guadalajara. The lake Chapala region is structurally a tectonic trench formed by the Chapala-Acambay system of E-W faults, partially covered by lacustrian sediments and pyroclastic materials. It is a very rich agricultural valley, and there are zones of intense surface thermal activity in areas of recent volcanic activity. The field of Los Humeros, State of Puebla, (2700 metres a.m.s.l.) is at the center of a caldera in the eastern part cf the neovolcanic axis, and the activity consists of dry steam manifestations distributed along three small N-S faults. In these three areas, geological mapping (photogeology and surface sampling) surface temperature, heat flux and resistivity surveys, and also chemical sampling, have been completed. Los Azufres (2800 metres a.m.s.l.) is the highest and most mountainous of these geothermal fields. Preliminary surveys have been made of some hot springs and fumaroles, including temperature measurements, chemical sampling, photogeology, and establishment of a network of benchmarks. The programme is well advanced in Ixtlán de los Hervores, where five exploration drill holes have been sited, and drilling has commenced on the first two sites.