摘要:

SummaryA ground‐water study carried out in the Serowe area of eastern Botswana between 1985–1988 has provided the opportunity to evaluate the role of a multiparameter low‐level airborne geophysical survey in a hydrogeological investigation. The survey included magnetic, VLF (very low frequency), and coaxial EM (electromagnetic) measurements. In total, 7,500 line kilometers were flown over an area of 3,300 km2 with a nominal ground clearance of 20 m and a line spacing of 400 m.The main aquifer, the Ntane Sandstone Formation (Karoo age), is confined between mudstones below and basalt above, and is broken into a series of graben and horst structures by numerous E‐W striking faults. All bedrock, however, is completely masked by a 20–60 m thick overburden of sands, calcretes, silcretes, and sandstones known collectively as the Kalahari beds.Airborne magnetic and VLF geophysical surveys have been used to penetrate this masking cover. Images and stacked profiles obtained from the survey revealed structural and geological features of major hydrogeological significance. This provided the information necessary for the formulation of a conceptual model.The results helped guide the subsequent exploration drilling program in an efficient and effective manner, cutting down the need for extensive ground surveys. The investigation confirmed the availability of a 35,000 m3/day resource, sustainable for a 25‐year period. Highest yields were obtained from fracture zones associated with VLF anomalies. Potential wellfields were identified in confined sections of the aquifer, with production boreholes to be sited, where possible, on fractures associated with VL

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00614.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00615.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractHelium has several characteristics that make it attractive for use as a tracer in hydrological studies. Two types of experiments were conducted to investigate applicability of helium as a tracer of ground‐water movement. The experiments included studies using laboratory sand and soil columns and field ground‐water tracing in a basaltic aquifer. A water helium analyzer comprised of a thin quartz glass membrane and diode ion pump (making use of the preferential permeation of helium through the quartz glass into an evacuated space) was developed and used for the experiments.Results of our studies demonstrated that breakthrough curves of specific conductance and helium were similar under saturated conditions. In the unsaturated sand/soil columns, breakthrough curves of helium were retarded relative to specific conductance reducing the usefulness of helium as a tra

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00616.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractA semianalytical transient expression was used to evaluate the performance of a finite‐length horizontal well as compared to a vertical well in a hypothetical recovery scenario. Recovery was simulated in two hypothetical confined aquifers to study the effect of aquifer thickness and well orientation on recovery performance. The results show that horizontal wells can initially mobilize larger volumes of ground water (and contaminants) but that vertical wells have the same ultimate recovery ability in a homogeneous, isotropic mediu

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00617.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractTwo nuclear methods were used to quantify hydrogeologic parameters in the unsaturated zone of a reclaimed and revegetated coal strip mine in Clarion, Pennsylvania. Am‐Be (neutron) and Cs‐137 (gamma‐gamma) geophysical logging tools were used to quantify volumetric moisture content, bulk density, total porosity, and unsaturated hydraulic conductivity. An additional study at the same site used postsampling neutron activation analysis to determine concentrations of a bromide tracer in unsaturated zone water samples. Those additional data were used to independently calculate unsaturated hydraulic conductivity.Geophysical logging of six boreholes at the site was conducted on seven different dates. Temporal variations in volumetric moisture content versus depth were observed to be short‐lived, with the general shape of the volumetric moisture content profiles remaining spatially stable over the eight month period of investigation. Bulk density values ranged from less than 1.14 to 1.86 g/cm3, corresponding to total porosities of greater than 57% to 30.1%. Large void spaces were encountered during past and present drilling and observed at a measurement point. Unsaturated hydraulic conductivities were calculated using draining profile volumetric moisture content data as input to an explicit numerical solution of the unsaturated flow equation. Calculated values ranged from 2.4 × 10−7to 1.5 × 10−3cm/s. Examination of all of the geophysical log data together showed sharp increases in volumetric moisture content spatially coincident with zones where bulk density increases (and porosity decreases). The bulk density contrast appears to be of more influence than the magnitude of the material property. Increased unsaturated hydraulic conductivity associated with increased volumetric moisture content was seen in several boreholes.Bromide tracer‐labeled waters were collected from pressure‐suction lysimeters installed at depths of up to 18.1 m for a period of 16 months. Unsaturated hydraulic conductivities, calculated by interpreting concentration peaks as average arrival times of steadily infiltrating water through a uniformly porous media, ranged from 2.8 × 10−6to 7.2 × 10−5cm/s. However, a dual‐permeability mechanism is suggested by the observed behavior of the tracer. Analysis of the data suggests that fluid flow in this hydrogeologic setting is dominantly transient. Ground‐water recharge occurs in short‐lived pulses. The periodicity of acid mine drainage formation and flushing to the water table is expected to correspond to inf

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00618.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe numerical model ARMOS, which simulates areal flow of water and light hydrocarbon in an unconiined aquifer, isdescribed. Based on the assumption of local vertical equilibrium, area! flow equations for water and hydrocarbon are derived which exhibit reduced dimensionality and nonlinearity. A finite‐element method is used to solve the water and oil equations using an efficient semidecoupled approach. Input required by the model includes area! boundaries, elevations of the aquifer lower boundary, and initial water and hydrocarbon levels in monitoring wells. Soil and fluid properties include hydrocarbon density, viscosity and surface tension, saturated hydraulic conductivity, van Genuchten air‐water capillary pressure curve parameters, and the maximum residual hydrocarbon saturations in the saturated and unsaturated zones. Fluid heads or fluxes may be specified on the domain perimeter and pumping rates are prescribed at recovery wells. The water pumping rate is automatically limited when drawdown reaches a pump‐off set point (or the screen bottom), and hydrocarbon recovery is limited when well hydrocarbon thickness becomes zero. Model output includes water and hydrocarbon levels in monitoring wells, cumulative product recovery, and free and residual hydrocarbon volumes in the soil. A hypothetical problem involving optimization of free product recovery and a field application of the model to a large pipeline leak are desc

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00619.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe Princeton Transport Code (PTC), a three‐dimensional finite‐element flow and transport model, was used to evaluate contaminant movement and recovery in the vicinity of a manufacturing facility in western Nebraska. The modeling was complicated by seasonal recharge from a nearby irrigation canal, a drainage ditch flowing across the site, municipal wells pumping at variable rates and screened at different levels in the underlying semiconfined aquifer, and the pumping of the three high‐capacity wells being used to recover contaminated ground water. The flow model was calibrated in several steps: steady‐state calibration using the unstressed (no pumping) conditions; steady‐state calibration using the prerecovery pumping conditions; and finally, transient calibration using results obtained for the early recovery pumping period–first for the nonirrigation season and then for the irrigation season. The calibrated flow model was further tested by simulating transport during the early stages of the recov

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00620.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe U.S. Geological Survey's MODFLOW finite‐difference ground‐water flow model has been coupled with three surface‐water packages–the MODBRANCH, River, and Stream packages–to simulate surface water and its interaction with ground water. Prior to the development of the coupling packages, the only interaction between these modeling packages was that leakage values could be passed between MODFLOW and the three surface‐water packages. To facilitate wider and more flexible uses of the models, a computer program was developed and added to MODFLOW to allow direct flows or stages to be passed between any of the packages and MODFLOW. The flows or stages calculated in one package can be set as boundary discharges or stages to be used in another package. Several modeling packages can be used in the same simulation depending upon the level of sophistication needed in the various reaches being modeled. This computer program is especially useful when any of the River, Stream, or MODBRANCH packages are used to model a river flowing directly into or out of wetlands in direct connection with the aquifer and represented in the model as an aquifer block. A field case study is shown to illustrate an

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00621.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00623.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

ISSN:0017-467X    

DOI:10.1111/j.1745-6584.1994.tb00624.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY