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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of Nitrate-Nitrogen Movement Near High-Capacity Irrigation Wells (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 18 (1998), S. 0 
    Details
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: AGalerkin finite-element model coupled with a particle tracking routine was developed to analyze the flow and transport dynamics near a high-capacity irrigation well. The model was used to compute the head distribution around the pumping well, to determine the area of influence, and to define ground water flowlines during short-term pumping periods typical of those used to collect water quality samples from high-capacity wells. In addition to hypothetical example results, the model was used to qualitatively analyze data obtained from pump-and-sample experiments conducted in an unconfined alluvial aquifer within the Platte River valley of south-central Nebraska where nitrate-nitrogen (NO3-N) contamination is prevalent.Simulation results of both the hypothetical and field cases suggest that short-term pumping events, impact a limited volume of aquifer. The area of influence and flowlines are affected by aquifer anisotropy, pumping rate, and well construction characteristics). Ground water above or below the screened intervals does not enter a partially penetrating well in anisotropic aquifers. In aquifers where NO3-N concentration varies vertically and horizontally, waler quality samples from an irrigation, or other high-capacity, well provide only limited information about ground water contamination. A numerical model is thus recommended for calculating the area of influence and determining flowlines around high-capacity wells so that information derived from water quality samples collected at the wellhead can be better interpreted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6592.1998.tb00174.x
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  • 2
    Electronic Resource
    Electronic Resource
    Regional Estimation of Total Recharge to Ground Water in Nebraska (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 43 (2005), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Naturally occurring long-term mean annual recharge to ground water in Nebraska was estimated by a novel water-balance approach. This approach uses geographic information systems (GIS) layers of land cover, elevation of land and ground water surfaces, base recharge, and the recharge potential in combination with monthly climatic data. Long-term mean recharge 〉 140 mm per year was estimated in eastern Nebraska, having the highest annual precipitation rates within the state, along the Elkhorn, Platte, Missouri, and Big Nemaha River valleys where ground water is very close to the surface. Similarly high recharge values were obtained for the Sand Hills sections of the North and Middle Loup, as well as Cedar River and Beaver Creek valleys due to high infiltration rates of the sandy soil in the area. The westernmost and southwesternmost parts of the state were estimated to typically receive 〈 30 mm of recharge a year.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2005.tb02286.x
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  • 3
    Electronic Resource
    Electronic Resource
    Design of a Multi-Level Monitoring Well for Continuous Sample Collection (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 15 (1995), S. 0 
    Details
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: As part of a study of the flow dynamics and sampling environment around a high-capacity irrigation well, it was necessary to design and install a multi-level monitoring well network close to the production well. A requirement of the monitoring well network was the capability of continuous pumping over periods typical of those used during water sample collection. This was accomplished through the use of a control valve and air manifold system connected 10 a common gasoline engine-operated air compressor. The system provided adequate air pressure to operate 24 half-size bladder pumps to depths between 21 feet (6.4 m) and 56 feet (17.1 m) below the surface. Preliminary data collected from the monitoring well network indicate that the system will meet the requirements of the high-capacity well study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6592.1995.tb00559.x
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  • 4
    Electronic Resource
    Electronic Resource
    Regional Estimation of Base Recharge to Ground Water Using Water Balance and a Base-Flow Index (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Naturally occurring long-term mean annual base recharge to ground water in Nebraska was estimated with the help of a water-balance approach and an objective automated technique for base-flow separation involving minimal parameter-optimization requirements. Base recharge is equal to total recharge minus the amount of evapotranspiration coming directly from ground water. The estimation of evapotranspiration in the water-balance equation avoids the need to specify a contributing drainage area for ground water, which in certain cases may be considerably different from the drainage area for surface runoff. Evapotranspiration was calculated by the WREVAP model at the Solar and Meteorological Surface Observation Network (SAMSON) sites. Long-term mean annual base recharge was derived by determining the product of estimated long-term mean annual runoff (the difference between precipitation and evapotranspiration) and the base-flow index (BFI). The BFI was calculated from discharge data obtained from the U.S. Geological Survey's gauging stations in Nebraska. Mapping was achieved by using geographic information systems (GIS) and geostatistics. This approach is best suited for regional-scale applications. It does not require complex hydrogeologic modeling nor detailed knowledge of soil characteristics, vegetation cover, or land-use practices. Long-term mean annual base recharge rates in excess of 110 mm/year resulted in the extreme eastern part of Nebraska. The western portion of the state expressed rates of only 15 to 20 mm annually, while the Sandhills region of north-central Nebraska was estimated to receive twice as much base recharge (40 to 50 mm/year) as areas south of it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.2003.tb02384.x
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  • 5
    Electronic Resource
    Electronic Resource
    MODELING CONCENTRATION VARIATIONS IN HIGH-CAPACITY WELLS: IMPLICATIONS FOR GROUNDWATER SAMPLING (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Water Resources Association 30 (1994), S. 0 
    Details
    ISSN: 1752-1688
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Notes: : High-capacity wells are used as a convenient and economical means of sampling groundwater quality. Although the inherent limitations of using these wells are generally recognized, little has been done to investigate how these wells actually sample groundwater. A semi-analytical particle tracking model is used to illustrate the influence of variable vertical contaminant distributions and aquifer heterogeneity on the composition of water samples from these wells during short pumping periods. The hypothetical pumping well used in the simulations is located in an unconfined, alluvial aquifer with a shallow water table and concentration gradients of nitrate-nitrogen contamination. This is a typical setting for many irrigated areas in the United States. The main conclusions are: (1) high-capacity wells underestimate the average amount of contamination within an aquifer; (2) shapes of concentration-time curves for high-capacity wells appear to be governed by the distribution of the contaminant and travel times to the well; (3) variables such as well construction, pumping rate, and hydrogeologic properties contribute to the magnitude of the concentration-time curves at individual high-capacity wells; and (4) a sampling strategy using concentration-time curves based on the behavioral characteristics of the well rather than individual samples will provide a much better framework for interpreting spatial contaminant distributions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1752-1688.1994.tb03316.x
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  • 6
    Electronic Resource
    Electronic Resource
    Aquifer Properties Determined from Two Analytical Solutions (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: In the analysis of pumping test data, the quality of the determined aquifer parameters can be greatly improved by using a proper model of the aquifer system. Moench (1995) provided an analytical solution for flow to a well partially penetrating an unconfined aquifer. His solution, in contrast to the Neuman solution (1974), accounts for the noninstantaneous decline of the water table (delayed yield). Consequently, the calculated drawdown in these two solutions is different under certain circumstances, and this difference may therefore affect the computation of aquifer properties from pumping test data. This paper uses an inverse computational method to calculate four aquifer parameters as well as a delayed yield parameter, α1 from pumping test data using both the Neuman (1974) and Moench (1995) solutions. Time-drawdown data sets from a pumping test in an unconfined alluvial aquifer near Grand Island, Nebraska, were analyzed. In single-well analyses, horizontal hydraulic conductivity values derived from the Moench solution are lower, but vertical hydraulic conductivity values are higher than those calculated from the Neuman solution. However, the hydraulic conductivity values in composite-well analyses from both solutions become very close. Furthermore, the Neuman solution produces similar hydraulic conductivity values in the single-well and composite-well analyses, but the Moench solution does not. While variable α1, seems to play a role in affecting the computation of aquifer parameters in the single-well analysis, a much smaller effect was observed in the composite-well analysis. In general, specific yield determined using the Moench solution could be slightly higher than the values from the Neuman solution; however, they are still lower than the realistic values for sand and gravel aquifers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1998.tb02196.x
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  • 7
    Electronic Resource
    Electronic Resource
    Behavior of Nitrate-Nitrogen Movement Around a Pumping High-Capacity Well: A Field Example (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: This study examines the near-field flow regime influencing the chemical composition of water samples collected from an irrigation well during short pumping periods. Data on the radial and vertical distribution of nitrate-nitrogen (NO3-N) and on drawdown were collected from a closely spaced multi-level monitoring well network installed around an irrigation well. Aquifer properties were determined from grain-size analyses performed on samples collected from test holes drilled around the irrigation well and from drawdown data using the method of Neuman (1974). Grain-size characteristics were determined from cumulative distribution curves and used to construct vertical hydraulic conductivity (K) profiles based on frequently used empirical formulas applied to grain-size data for the determination of aquifer properties. Resultant vertical profiles show a general increase in K with depth. Results from the analysis of drawdown curves support the general trend of K determined from the grain-size data, drawdown-based K values, however, were 1.5 to 2 times greater than those determined from the empirical methods.Results from four pump-and-sample experiments at different times during the irrigation season indicate: (1) the distribution of NO3-N around the irrigation well is complex and variable over time and space; (2) shapes of concentration-time curves for individual sample points are governed by the initial contaminant distribution, and shapes of concentration-time curves for the pumping well are governed by variables such as well screen position and hydrogeologic properties; (3) irrigation well samples underestimate the highest, as well as the average NO3-N concentrations within the aquifer; and (4) a sampling strategy based on the behavioral characteristics of the well as reflected in concentration-time curves can improve the interpretation of water quality data collected from high-capacity wells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1998.tb01098.x
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  • 8
    Electronic Resource
    Electronic Resource
    Utilization of the Hantush Solution for the Simultaneous Determination of Aquifer Parameters (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 35 (1997), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A method is presented to determine aquifer parameters simultaneously and uniquely based on time-drawdown data collected from a single observation well in the vicinity of a pumping well partially penetrating a confined leaky aquifer. The Hantush solution is analyzed inversely for the identification of hydraulic properties using the Taylor series and a nonlinear least squares method. Aquifer parameters investigated include vertical and horizontal hydraulic conductivities, storage coefficient, and the leakage factor of the overlying aquitard. The developed method is verified using a hypothetical example and is applied to a field case. Error limits between the determined and true parameter values can be less than 0.1% depending on the quality of the field data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1997.tb00143.x
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  • 9
    Electronic Resource
    Electronic Resource
    REPLY TO the preceding Discussion by Robert W. Lankston of “Application and Comparison of Shallow Seismic Methods in the Study of an Alluvial Aquifer” (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 28 (1990), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1990.tb02240.x
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  • 10
    Electronic Resource
    Electronic Resource
    Conjunctive Use of Geophysical and Geological Data in the Study of an Alluvial Aquifer (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 27 (1989), S. 0 
    Details
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A geoelectric survey, composed of vertical electrical soundings, was conducted over part of the lower Platte Valley alluvial aquifer of east-central Nebraska. Survey results, in conjunction with seismic-survey data and test- hole-log information, provided the basis to map the areal extent and thickness of a near-surface, low-permeability clay unit. Because of the low hydraulic conductivity of the clay, the unit forms a confining layer over a significant part of the aquifer.Generally, the approach to evaluating the lower Platte Valley alluvial aquifer for sustained yield has been to assume that the entire flow system is under water-table conditions. However, numerical-model simulations with and without the clay unit indicate that this confining layer has a significant effect on the hydraulic behavior of the groundwater flow system under pumping stresses.An estimate of the bulk porosity of the aquifer was made by using geoelectric data and applying the Archie equation. Values of porosity ranged from 0·27 to 0·43; although reasonable for fluvial sand and gravel, the range is higher than previous estimates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1745-6584.1989.tb00475.x
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