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1.
A wellhead protection study for the city of Sturgeon Bay, Wisconsin, USA, demonstrates the necessity of combining detailed hydrostratigraphic analysis with groundwater modeling to delineate zones of contribution for municipal wells in a fractured dolomite aquifer. A numerical model (MODFLOW) was combined with a particle tracking code (MODPATH) to simulate the regional groundwater system and to delineate capture zones for municipal wells. The hydrostratigraphic model included vertical and horizontal fractures and high-permeability zones. Correlating stratigraphic interpretations with field data such as geophysical logs, packer tests, and fracture mapping resulted in the construction of a numerical model with five high-permeability zones related to bedding planes or facies changes. These zones serve as major conduits for horizontal groundwater flow. Dipping fracture zones were simulated as thin high-permeability layers. The locations of exposed bedrock and surficial karst features were used to identify areas of enhanced recharge. Model results show the vulnerability of the municipal wells to pollution. Capture zones for the wells extend several kilometers north and south from the city. Travel times from recharge areas to all wells were generally less than one year. The high seasonal variability of recharge in the study area made the use of a transient model necessary. Electronic Publication  相似文献   

2.
Geophysical and hydrogeological investigations have been carried out around Sawmills in Zimbabwe, Africa. The investigations are components of a larger investigation to assess the groundwater potential of the Karoo sedimentary basin with regards to supplying water to Bulawayo City. The Sawmills area was selected due to the availability of borehole logs indicating favourable stratigraphy for groundwater availability and due to the high yields from the aquifers measured from these boreholes. Data collected using two geophysical methods are presented here: transient electromagnetic (TEM) and continuous vertical electrical sounding (CVES) data. The data have also been processed using laterally constrained inversion (LCI). Because the CVES provides greater detail in the shallow subsurface, whereas TEM is more effective at depth, a more accurate image of the entire subsurface profile is provided based on using both methods. The results suggest that LCI of CVES and TEM data, in the subsurface at the required depths at Sawmills, is able to provide a substantially more accurate image of the subsurface than either method alone. The hydrogeological interpretation of the geophysical data is valuable for determining the depth to and thickness of the potential aquifer horizon(s) and for identifying the position of potential recharge zones.  相似文献   

3.
Tracer data can serve to derive parameters related to groundwater systems or can be used in the calibration of transport and flow models. Temperature, 3H/3He (age dating) and hydrochemical data, together with head measurements, borehole logs and an aquifer test, were used to obtain insight into the flow and transport of a Quaternary aquifer system located in the Belgian polder area. Flow and transport model code SEAWAT acted as the integration medium for the different data. Each type of data has its own interpretation technique and adds components to the model. Additionally, different types of data aid in verification of the results. For instance, fluxes from temperature logs (used with the SEAWAT model), and water quality and age dating all provide information on flow to and velocities in the vicinity of drainage ditches. Different data also provide information on different scales. Temperature logs and aquifer tests act on a small scale, groundwater age is influenced by larger-scale flow, and water quality is determined by the general flow of the area. Integration of different kinds of geological, hydrological, geophysical and geochemical data is shown to be an important way forward in the efforts to model real-world cases.  相似文献   

4.
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5.
Different methods of lithology predictions from geophysical data have been developed in the last 15 years, among which the conventional logs are as follows: sonic, neutron–neutron, natural gamma, and density (backscattered gamma–gamma). This article concentrates on the nuclear geophysical suite, in particular, gamma and gamma–gamma logging, which, to date, provide the most accurate geophysical means of identifying coal seams and estimating their thickness. From the gamma and gamma–gamma logs of boreholes AEN 002, 007, 044, 045, 063, 085, and 105, which were carried out at the Phulbari Coal Basin of Bangladesh, two coal seams—upper and main with two lower seams of limited occurrence and of varying thickness—were identified, together with their regional occurrence.  相似文献   

6.
This study integrated surface and subsurface stratigraphic data with geophysical logs and hydrogeologic data in order to characterize the hydraulic properties of the Silurian dolomite in northeastern Wisconsin. Silurian stratigraphy consists of predictable alternations of characteristic facies associations. A vertical profile of hydraulic conductivity, obtained from short-interval packer tests in a core hole that penetrates a majority of the Silurian section, indicates that hydraulic conductivity ranges over five orders of magnitude (10–1 to 10–6 cm/s). Matrix conductivity is generally low and varies with texture; the finer-grained restricted-marine and transitional facies being less permeable than the coarser-grained open-marine facies. High-conductivity values are generally associated with bedding-plane fractures, and fracture frequency is greater in the restricted-marine facies. High-flow features in 16 wells were identified using fluid-temperature/resistivity and heat-pulse flowmeter logs. Natural-gamma logs were used to identify the stratigraphic position of flow features in each well and to correlate flow features to specific stratigraphic horizons. By combining stratigraphic, geophysical, and hydrogeologic data, 14 high-permeability zones within the Silurian aquifer have been identified and correlated in wells more than 16 km apart. These zones parallel bedding, appear most pronounced at contacts between contrasting lithologies, and are most abundant in restricted-marine lithologies. Electronic Publication  相似文献   

7.
Two geophysical techniques were integrated to map the groundwater aquifers on complex geological settings, in the crystalline basement terrain in northeast Nuba Mountains. The water flow is structurally controlled by the northwest–southeast extensional faults as one of several in-situ deformational patterns that are attributed to the collision of the Pan-African oceanic assemblage of the Nubian shield against the pre-Pan African continental crust to the west. The structural lineaments and drainage systems have been enhanced by the remote sensing technique. The geophysical techniques used are: vertical electrical soundings (VES) and electrical resistivity tomography (ERT), in addition to hydraulic conductivity measurements. These measurements were designed to overlap in order to improve the producibility of the geophysical data and to provide a better interpretation of the hydrogeological setting of the aquifer complex structure. Smooth and Block inversion schemes were attempted for the observed ERT data to study their reliability in mapping the different geometries in the complex subsurface. The VES data was conducted where ERT survey was not accessible, and inverted smoothly and merged with the ERT in the 3D resistivity grid. The hydraulic conductivity was measured for 42 water samples collected from the distributed dug wells in the study area; where extremely high saline zones were recorded and have been compared to the resistivity values in the 3D model.  相似文献   

8.
Southern Tunisia is an arid area where socio-economic activities are dependent on groundwater resources. The presented study aims to better characterize the Jurassic aquifer based on geological and geophysical data, with a view to develop a rational exploitation program. Well logs are used to precisely determine the position and composition of the known Jurassic aquifer layers and to identify others able to produce good quality water. The logs show that limestones, sandstones and dolomites of the Krachoua, Techout and Foum Tataouine formations are the main Jurassic aquifers. Sixty-eight seismic-reflection sections are integrated within this study. The interpolation between the interpreted sections leads to the construction of isochronous isopach maps and geoseismic sections, and their analysis finds that compressive and extensive tectonic deformations have influenced the Jurassic aquifer geometry. The Hercynian orogeny phase manifestation is remarkable in that there are several stratigraphic gaps in the Jurassic sequence. The E–W, NW–SE, and NNW–SSE accidents, reactivated in normal faults since the Permian to Lower Cretaceous epochs, have generated the structures found in the Jurassic series, such as subsided and raised blocks. Their syn-sedimentary activity has controlled the thickness and facies of these series. The Cretaceous, Tortonian and Post-Villafranchian compressions are responsible for the Jurassic-deposits folding in some localities. The highlighted tectonic and sedimentary events have an important impact on the Jurassic aquifer function by favoring the Jurassic aquifer interconnections and their connections with the Triassic and Cretaceous permeable series.  相似文献   

9.
Geoelectric and hydrochemical approaches are employed to delineate the ground-water potential zones in District Okara, a part of Bari Doab, Punjab, Pakistan. Sixty-seven VES surveys are conducted with the Electrical Resistivity Meter. The resultant resistivity verses depth model for each site is estimated using computer-based software IX1D. Aquifer thickness maps and interpreted resistivity maps were generated from interpreted VES results. Dar-Zarrouk parameters, transverse resistance (TR), longitudinal conductance (SL) and anisotropy (λ) were also calculated from resistivity data to delineate the potential zones of aquifer. 70% of SL value is ≤3S, 30% of SL value is > 3S. According to SL and TR values, the whole area is divided into three potential zones, high, medium and low potential zones. The spatial distribution maps show that north, south and central parts of study area are marked as good potential aquifer zones. Longitudinal conductance values are further utilized to determine aquifer protective capacity of area. The whole area is characterized by moderate to good and up to some extent very good aquifer protective area on the basis of SL values. The groundwater samples from sixty-seven installed tube wells are collected for hydro-chemical analysis. The electrical conductivity values are determined. Correlation is then developed between the EC (μS/cm) of groundwater samples vs. interpreted aquifer resistivity showing R2 value 0.90.  相似文献   

10.
本文叙述了在辽宁阜新煤盆地艾友矿区,利用视电阻率、自然伽玛、伽玛—伽玛测井曲线分析沉积环境的成果,着重总结了冲积扇、扇三角洲、湖泊以及河流等环境的测井曲线特征。在此基础上,根据该区100多个钻孔的测井曲线,作出了艾友矿区沙三段地层的含砂率等值线图和煤层等厚图。通过分析这些成果图件得出了该矿区聚煤带和富煤带的分布规律。这些研究成果对于煤田的预测和勘探具有普遍意义。  相似文献   

11.
This paper discusses a geostatistical approach to model a groundwater aquifer in 3-D. The study aims at utilizing geostatistics as a tool for characterizing zones of better-water quality in a brackish-saline aquifer. In particular, the geostatistical model was constructed to characterize the aquifer’s salinity, represented by total dissolved solids (TDS), using logs of porosity and resistivity. Quality-checked estimated TDS vertical profiles were employed to construct and model horizontal and vertical semivariograms. Parameters of semivariogram models were used to develop both the kriging plan and the generated model. Results of this modeling process are shown in the form of horizontal salinity distribution maps. The aquifer was sliced into 20 layers, each 20 m thick, to represent its overall thickness. Salinity layers maps reflect vertical stratification of TDS concentrations in the aquifer and show that water quality deteriorates with depth and toward the northern part of the aquifer. Relatively better-quality water (TDS ≤10,000 mg/l) can be found at depths between 100 and 250 m below the aquifer’s top in both eastern and southeastern parts. Water in the same interval to the western and southwestern parts reflects the presence of higher TDS concentration. From a planning point of view, it is more feasible to target the eastern part of the aquifer for pumping and desalination purposes. In addition, the generated model could be utilized as an initial condition for flow simulation.  相似文献   

12.
During a search for unpolluted resources, new wells have been drilled to a deep confined aquifer in central Jutland. Since little is known about the extent and vulnerability of the deep reservoir, geophysical logging was used to supplement hydraulic well-testing. Gamma-ray, SP and resistivity logs were recorded in the boreholes. Gamma-logs were also recorded in two cased wells. Analysis of the logs, combined with information from samples, shows an unconfined aquifer of quartz and mica sand to a depth of about 55 m at Grindsted. Below this level there is a 40 m thick aquitard with an apparent southerly dip. The aquitard is composed of interbedded sand, silt and clay. The deep confined aquifer extends from 95 to 110 m below the surface at Grindsted. Both the aquitard and the deep aquifer are provisionally dated as Early/Middle Miocene. The electrical logs discriminate well between sand, silt and clay beds. If a suitable mud is used in the well it is possible to calculate the formation water resistivities in good agreement with water samples obtained after completion. From the resistivity logs formation factors were calculated in the range 3–5 using no-invasion departure curves. The high content of heavy mineralsin the Tertiary deposits makes it impossible to obtain precise lithological information from the gamma-ray log. On the other hand this log provides clear markers for identifying the hydrogeological units in the well-bores.  相似文献   

13.
An integrated survey program involving geological, hydrogeological and geophysical techniques has been employed to characterize the aquifer geometry, recharge and circulation dynamics of thermal springs within a shallow aquifer system in Ethiopia. The selected springs for the case study are Sodere and Gergedi, which are situated within the tectonically active Main Ethiopian Rift (MER). Geologically, the studied springs are located on Plio-Quaternary volcanic rocks. The geophysical results indicate the presence of subsurface weak zones represented by extensional tectonics and weathering zones which are responsible for thermal water circulation and facilitate recharge from the adjacent surface-water bodies. The structures inferred by the resistivity survey, both sounding and electrical tomography, present contrasts in rock resistivity response. The anomalous zones in the magnetic data are in good agreement with the zones that are revealed by geological mapping and surface manifestation of the thermal water discharge zones. The shallow aquifer of the central MER is under the influence of thermal water, which increases the groundwater temperature and mineral content.  相似文献   

14.
The geophysical characterization of a previously unstudied endorheic karstic system is presented. The studied area, known as the Esta?a Lakes, is located in the Pyrenean Marginal Sierras, northern Spain. The Esta?a Lakes are a set of natural water ponds on a bedrock of Triassic evaporites, lutites and carbonates. This wetland is included in the Natura 2000 European network of nature protection areas as a “Site of Community Importance”. Two geophysical techniques were used, magnetic resonance sounding (MRS) and electrical resistivity tomography (ERT), to map the subsurface geology and characterize the aquifer layers and the hydraulic links between the aquifers and lakes. The geophysical data were integrated with the surface geology and data from six boreholes. Ten electrical profiles were performed to identify the thickness of the units and lithological changes, whereas the MRS was used to determine the top of the saturated zone. As result, the aquifer in the Esta?a Lakes system and surrounding area has been identified as Middle Triassic carbonates, which does not correspond with the regional aquifer in the area (Upper Cretaceous and Eocene). This work shows the power of geophysical methods in poorly understood and tectonically complex areas in addition to the standard aquifer tests to evaluate hydraulic properties.  相似文献   

15.
Numerical models encompassing source zones and receptors, based on representative conceptual models and accounting for aquifer heterogeneity, are needed to understand contaminant migration and fate; however, aquifer characterization seldom provides the necessary data. This study aimed to develop a workflow for field characterization and data integration, which could: (1) be adapted to the definition of subwatershed-scale aquifer heterogeneity (over 10 km2) and (2) adequately support mass transport model development. The study involved the field investigation of a shallow granular aquifer in a 12-km2 subwatershed in Saint-Lambert-de-Lauzon, Canada, in which a decommissioned landfill is emitting a leachate plume managed by natural attenuation. Using proven field methods, the characterization sequence was designed to optimize each method in terms of location, scale of acquisition, density and quality. The emphasis was on the acquisition of detailed indirect geophysical data that were integrated with direct hydraulic and geochemical data. This report focuses on the first qualitative and geostatistical data integration steps of the workflow leading to the development of a hydrogeological conceptual model. This is a prerequisite for further integration steps: prediction of hydrofacies and hydraulic conductivity (K), geostatistical simulations of K, studies of geochemical processes and numerical modeling.  相似文献   

16.
The increasing demand for freshwater has necessitated the exploration for new sources of groundwater, particularly in hard rock terrain, where groundwater is a vital source of freshwater. A fast, cost effective, and economical way of exploration is to study and analyze geophysical resistivity survey data. The present study area Omalur taluk, Salem District, Tamil Nadu, India, is overlain by Archaean crystalline metamorphic complex. The study area is a characteristic region of unconfined aquifer system. The potential for occurrence of groundwater in the study areas was classified as very good, good, moderate, and poor by interpreting the subsurface geophysical investigations, namely vertical electrical soundings, were carried out to delineate potential water-bearing zones. The studies reveal that the groundwater potential of shallow aquifers is due to weathered zone very low resistivity and very high thickness and the potential of deeper aquifers is determined by fracture zone very low resistivity and very high thickness area. By using conventional GIS method, the spatial distribution maps for different layer (top soil, weathered zone, first fracture zone, and second fracture zone) thicknesses were prepared. The geoelectrical approach was successfully applied in the study area and can be therefore easily adopted for similar environments.  相似文献   

17.
Detailed local geological, geophysical, and hydrogeological investigations were carried out for the alluvial aquifer in the Kangavar basin, West Iran to delineate the architecture of different subsurface geological horizons using lithologs and generated vertical electrical sounding (VES) data. An attempt has also been made to estimate aquifer transmissivity from resistivity data. Forty VESs were recorded with the Schlumberger electrode configuration in the study area; 28 of these were selected for evaluation. The maximum current electrode spacing was 400–500 m. The data obtained were interpreted by computer iterative modeling with curve matching for calibration purposes. In order to ascertain the subsurface geological framework, the general distribution of resistivity responses of the geological formations was obtained and geoelectrical sections along a number of lines were prepared. Probable aquifer horizons from these sections were identified. The transmissivity of the unconfined aquifer was computed by determining the Dar-Zarrouk parameters (longitudinal unit conductance and transverse unit resistance) and were compared with the actual field transmissivity. The results showed a direct relation between aquifer transmissivity and modified transverse resistance.  相似文献   

18.
A large number of valleys and basin systems are present in the northwestern part of the Himalayas in Pakistan which form significant aquifers in the region. Hydrogeophysical investigations in the western part of Nowshera District, a part of the intermontane Peshawar basin, were undertaken to help to determine the availability of groundwater resources in the region. Thirty vertical electrical resistivity soundings (VES) were acquired using a Schlumberger expanding array configuration with a maximum current electrode spacing (AB/2) of 150 m in delineating the groundwater potential in the study area. The results of the interpreted VES data using a combination of curve matching technique and computer iterative modeling methods suggest that the area is underlain by 3 to 5 geo-electric layers. The interpretation results showed that the geo-electrical succession consists of alluvium comprising of alternating layers of clay, silty clay, fine to coarse sands, sand with gravels and gravels of variable thickness. High subsurface resistivity values are correlated with gravel–sand units and low resistivity values with the presence of clays and silts. The modeled VES results were correlated with the pumping tests results and lithological logs of the existing wells. The pumping test suggests the transmissivity of the aquifer sediments is variable corresponding to different sediments within the area. The gravel–sand intervals having high resistivity value show high transmissivity values, whereas clay–silt sediments show low transmissivities. It is concluded that majority of the high resistive gravel–sand sediments belong to an alluvial fan environment. These gravel–sand zones are promising zones for groundwater abstraction which are concentrated in the central part of the study area.  相似文献   

19.
An integrated approach using hydrogeochemical analysis, remote sensing, GIS, and field data was employed to characterize the groundwater resources in southern Wadi Qena, Egypt. Various thematic maps showing topography, lineaments, wadi deposits, slope, and stream networks were combined through GIS analysis to discriminate groundwater potential zones on the valley floor. The resulting map classifies the area into five groups of groundwater potentiality from very high to very low zones, supported by the groundwater level, well locations, and by the results of previous geophysical studies. Thirty-seven groundwater well data were tested from the Quaternary and Nubian Sandstone aquifers and analyzed for physio-chemical parameters. Results of hydrochemical analysis show that water quality varies widely through the aquifers, and groundwater in the Quaternary aquifer shows the highest salinity values and a predominance of Na and Cl in water chemical facies. Overlay GIS maps of alkalinity (SAR and RSC) and salinity hazards (EC and Cl) of the Quaternary aquifer were prepared. The resulting maps show that samples do not present an alkalinity hazard in most areas but are potentially salinity hazard. Therefore, the water is fit for agricultural use with certain restrictions, but is not suitable for direct human consumption because it is either very hard or too saline.  相似文献   

20.
Deltaic aquifers are complex due to the important heterogeneity of their structure and their hydrogeological functioning. Auger drilling provides localized, but very robust geological and hydrogeological information, while geophysical surveys can provide integrated subsurface information. An effective, easy-to-use and low-cost methodology combining geological/hydrogeological information from Auger drillings and the results from three geophysical techniques (Electromagnetic mapping, Electrical Sounding and Electrical Resistivity Tomography) is being developed to characterize the structure of a typical Mediterranean deltaic aquifer. A first hypothesis about hydrodynamic properties of the aquifer is also obtained. The study area is located in the Rhone delta (Middle Camargue/southern France). Integration of geophysical and geological techniques allowed identifying the presence and lateral extension of the Saint-Ferréol paleochannel, the vertical contact between lagoonal–fluvial deposits and the marine clayed silt that separate the superficial aquifer from the deeper aquifer. Likewise, high north–south heterogeneity and east–west homogeneity were highlighted in the study area. Presence of clay in sandy deposits in the low areas implies changes in lateral hydraulic permeability. This fact, jointed to the low hydraulic gradient, suggests a slow groundwater flow in the local system. The Rhone delta presents a typical configuration of a Mediterranean deltaic aquifer, thus this methodological approach can be used for similar deltaic Mediterranean systems.  相似文献   

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