bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytical Model for Aquifer Response Incorporating Distributed Stream Leakage
Authors: Fox Garey A. , DuChateau Paul , Dumford Deanna S. 
Published: December 2005

AbstractAn analytical model of stream/aquifer interaction is proposed that predicts drawdown in an aquifer with leakage from a finite‐width stream induced by pumping from a well. The model is formulated based on the assumptions of stream partial penetration, a semipervious streambed, and distributed recharge across a finite‐width stream. Advantages of the analytical solution include its simple structure, consisting of the Theis well function with integral modifications. The solution is derived for the semi‐infinite domain between the stream and pumping well, which is of primary interest to hydrogeologists. Previous stream/aquifer analytical models are compared to the analytical solution based on dimensionless drawdown profiles. Drawdown in the aquifer near a wide stream was found to be less than that predicted by a solution that ignored stream width. Deviations between the proposed analytical solutions and previous solutions increase as stream width increases. For a hypothetical stream/aquifer system, the proposed analytical solution was equivalent to prior solutions when the ratio of the distance between the stream and aquifer to the stream width was greater than 25. This analytical solution may provide improved estimates of aquifer and streambed leakage parameters by curve fitting experimental field drawdown data.
The Role of Capillary Forces in Steady‐State and Transient Seepage Flows
Authors: Naba Bassem , Boufadel Michel C. , Weaver James 
Published: December 2005

AbstractSteady and transient seepage problems were investigated numerically using a dimensionless formulation for water flow in variably saturated, two‐dimensional anisotropic and homogenous porous media. The dimensionless formulation combines the aspect ratio and the anisotropy ratio in one dimensionless parameter, M, and accounts for capillarity effects using the ratio of the domain height to the height of capillary fringe as another dimensionless parameter, a. Two domain geometries were considered: rectangular and trapezoidal. It was found that M and a play major roles in the development and the height of the seepage face. The height of the steady‐state seepage face increased with the decreasing value of a.The effects of capillarity on the development of the transient seepage face were investigated by lowering the open water level on one side of the domain at various uniform velocities while the other side was kept at a constant value. It was found for most scenarios that decoupling between the water table and the open water level first occurred for domains with large a. In other words, the seepage face heights of these systems were larger than those with a small a. These results are the opposite of the steady‐state results and are due to the fact that drainage of the pores was the major mechanism controlling the drop of the transient water table, especially at earlier times.A criterion for the decoupling of the water table from the falling open water level (i.e., the formation of the transient seepage face) was developed by Dracos (1965). It states that decoupling does not occur as long as the falling speed, VF, of the open water level is less than Vd= Ko sin2 B/φ where Ko is the saturated hydraulic conductivity of the soil, φ is the porosity, and β is the angle of the exit face with the horizontal (i.e., β=π/2 implies a vertical face). Our investigation revealed that decoupling occurs for smaller falling velocities than Vd, and is caused by, among others, the fact that the water table is not tangent to the exit face but rather intersects it at a nonzero angle.
Asymmetric Dipole‐Flow Test in a Fractured Carbonate Aquifer
Authors: Halihan Todd , Zlotnik Vitaly A. 
Published: December 2005

AbstractIn this study, a new method‐the asymmetric dipole‐flow test—is proposed and tested for characterization of conductive properties and structure of fractured aquifers. Analytical solutions were developed and then used for interpretation of a modification of the dipole‐flow test with a single packer at the Bissen Quarry test site (Wisconsin, USA). The asymmetric dipole‐flow tests were conducted by packing a well at various elevations, and fluids were pumped from the upper section (chamber) of the well to the lower section (chamber). The head was then monitored at 11 observation points and in both sections of the well, and the conductivities of the well segments were determined. The tests at seven packer elevations in the well were rapid (less than one hour to reach steady state). The asymmetric dipole‐flow test demonstrates the potential to quantify heterogeneities of a fractured aquifer and delineate the applicability of the continuum and discrete approaches for conceptualization of ground water flow.
Analysis of a Vertical Dipole Tracer Test in Highly Fractured Rock
Authors: Sanford William E. , Cook Peter G. , Dighton John C. 
Published: December 2005

AbstractThe results of a vertical dipole tracer experiment performed in highly fractured rocks of the Clare Valley, South Australia, are presented. The injection and withdrawal piezometers were both screened over 3 m and were separated by 6 m (midpoint to midpoint). Due to the long screen length, several fracture sets were intersected, some of which do not connect the two piezometers. Dissolved helium and bromide were injected into the dipole flow field for 75 minutes, followed by an additional 510 minutes of flushing. The breakthrough of helium was retarded relative to bromide, as was expected due to the greater aqueous diffusion coefficient of helium. Also, only 25% of the total mass injected of both tracers was recovered. Modeling of the tracer transport was accomplished using an analytical one‐dimensional flow and transport model for flow through a fracture with diffusion into the matrix. The assumptions made include: streamlines connecting the injection and withdrawal point can be modeled as a dipole of equal strength, flow along each streamline is one dimensional, and there is a constant Peclet number for each streamline. In contrast to many other field tracer studies performed in fractured rock, the actual travel length between piezometers was not known. Modeling was accomplished by fitting the characteristics of the tracer breakthrough curves (BTCs), such as arrival times of the peak concentration and the center of mass. The important steps were to determine the fracture aperture (240 μm) based on the parameters that influence the rate of matrix diffusion (this controls the arrival time of the peak concentration); estimating the travel distance (11 m) by fitting the time of arrival of the centers of mass of the tracers; and estimating fracture dispersivity (0.5 m) by fitting the times that the inflection points occurred on the front and back limbs of the BTCs. This method works even though there was dilution in the withdrawal well, the amount of which can be estimated by determining the value that the modeled concentrations need to be reduced to fit the data (∼50%). The use of two tracers with different diffusion coefficients was not necessary, but it provides important checks in the modeling process because the apparent retardation between the two tracers is evidence of matrix diffusion and the BTCs of both tracers need to be accurately modeled by the best fit parameters.
The Capture Efficiency Map: The Capture Zone Under Time‐Varying Flow
Authors: Festger Adam D. , Walter Gary R. 
Published: December 2005

AbstractThe capture zone or contributing area of a ground water extraction well can be defined as that portion of the aquifer from which the well draws its water. Accurate delineation of capture zones is important in many ground water remediation applications and in the definition of wellhead protection areas. Their mathematical delineation is often simplified by using quasi‐steady‐state models based on time‐weighted average pumping rates and background hydraulic gradients. We present a new semianalytic approach for the definition of capture zones under transient‐flow conditions. We then use this approach to evaluate the effects of time variations in the direction of the background hydraulic gradient on capture. Results are presented in the form of capture efficiency maps (CEMs). Although the area contributing to a given well is found to generally expand relative to the steady‐state average capture zone when the gradient direction varies, the zone of 100% capture may expand or contract depending on site‐specific conditions. We illustrate our CEM approach by applying it to the design of a plume containment system.
Recharge Estimation for Transient Ground Water Modeling
Authors: Jyrkama Mikko I. , Sykes Jon F. , Normani Stefano D. 
Published: December 2005

AbstractReliable ground water models require both an accurate physical representation of the system and appropriate boundary conditions. While physical attributes are generally considered static, boundary conditions, such as ground water recharge rates, can be highly variable in both space and time.A practical methodology incorporating the hydrologic model HELP3 in conjunction with a geographic information system was developed to generate a physically based and highly detailed recharge boundary condition for ground water modeling. The approach uses daily precipitation and temperature records in addition to land use/land cover and soils data. The importance of the method in transient ground water modeling is demonstrated by applying it to a MODFLOW modeling study in New Jersey.In addition to improved model calibration, the results from the study clearly indicate the importance of using a physically based and highly detailed recharge boundary condition in ground water quality modeling, where the detailed knowledge of the evolution of the ground water flowpaths is imperative. The simulated water table is within 0.5 m of the observed values using the method, while the water levels can differ by as much as 2 m using uniform recharge conditions. The results also show that the combination of temperature and precipitation plays an important role in the amount and timing of recharge in cooler climates. A sensitivity analysis further reveals that increasing the leaf area index, the evaporative zone depth, or the curve number in the model will result in decreased recharge rates over time, with the curve number having the greatest impact.
Remediation of the Wells G & H Superfund Site, Woburn, Massachusetts
Authors: Bair E. Scott , Metheny Maura A. 
Published: December 2005

AbstractRemediation of ground water and soil contamination at the Wells G & H Superfund Site, Woburn, Massachusetts, uses technologies that reflect differences in hydrogeologic settings, concentrations of volatile organic compounds (VOCs), and costs of treatment. The poorly permeable glacial materials that overlie fractured bedrock at the W.R. Grace property necessitate use of closely spaced recovery wells. Contaminated ground water is treated with hydrogen peroxide and ultraviolet (UV) oxidation. At UniFirst, a deep well completed in fractured bedrock removes contaminated ground water, which is treated by hydrogen peroxide, UV oxidation, and granular activated carbon (GAC). The remediation system at Wildwood integrates air sparging, soil‐vapor extraction, and ground water pumping. Air stripping and GAC are used to treat contaminated water; GAC is used to treat contaminated air. New England Plastics (NEP) uses air sparging and soil‐vapor extraction to remove VOCs from the unsaturated zone and shallow ground water. Contaminated air and water are treated using separate GAC systems. After nine years of operation at W.R. Grace and UniFirst, 30 and 786 kg, respectively, of VOCs have been removed. In three years of operation, 866 kg of VOCs have been removed at Wildwood. In 15 months of operation, 36 kg of VOCs were removed at NEP. Characterization work continues at the Olympia Nominee Trust, Whitney Barrel, Murphy Waste Oil, and Aberjona Auto Parts properties. Risk assessments are being finalized that address heavy metals in the floodplain sediments along the Aberjona River that are mobilized from the Industri–Plex Superfund Site located a few miles upstream.
Geostatistics and Bayesian Updating for Transmissivity Estimation in a Multiaquifer System in Manitoba, Canada
Authors: Kennedy Paula L. , Woodbury Allan D. 
Published: December 2005

AbstractIn ground water flow and transport modeling, the heterogeneous nature of porous media has a considerable effect on the resulting flow and solute transport. Some method of generating the heterogeneous field from a limited dataset of uncertain measurements is required. Bayesian updating is one method that interpolates from an uncertain dataset using the statistics of the underlying probability distribution function. In this paper, Bayesian updating was used to determine the heterogeneous natural log transmissivity field for a carbonate and a sandstone aquifer in southern Manitoba. It was determined that the transmissivity in m2/sec followed a natural log normal distribution for both aquifers with a mean of ‐7.2 and ‐ 8.0 for the carbonate and sandstone aquifers, respectively. The variograms were calculated using an estimator developed by Li and Lake (1994). Fractal nature was not evident in the variogram from either aquifer. The Bayesian updating heterogeneous field provided good results even in cases where little data was available. A large transmissivity zone in the sandstone aquifer was created by the Bayesian procedure, which is not a reflection of any deterministic consideration, but is a natural outcome of updating a prior probability distribution function with observations. The statistical model returns a result that is very reasonable; that is homogeneous in regions where little or no information is available to alter an initial state. No long range correlation trends or fractal behavior of the log‐transmissivity field was observed in either aquifer over a distance of about 300 km.
Stream‐Aquifer Interactions: Evaluation of Depletion Volume and Residual Effects from Ground Water Pumping
Authors: Chen Xunhong , Shu Longcang 
Published: December 2005

AbstractNumerical modeling techniques were used to simulate stream‐aquifer interactions from seasonal ground water pumping. We used stream‐aquifer models in which a shallow stream penetrates the top of an aquifer that discharges ground water to the stream as base flow. Because of the pumping, the volume of base flow discharged to the stream was reduced, and as the pumping continued, infiltration from the stream to the aquifer was induced. Both base‐flow reduction and stream infiltration contributed to total stream depletion. We analyzed the depletion rates and volumes of the reduced base flow and induced stream infiltration during pumping and postpumping periods. Our results suggested that for a shallow penetrating stream with a low streambed conductance, base‐flow reduction accounts for a significant percentage of the total stream depletion. Its residual effects in postpumping can last very long and may continue into the next pumping season for areas where recharge is nominal. In contrast, the contribution of the induced stream infiltration to the total stream depletion is much smaller, and its effects often become negligible shortly after pumping was stopped. For areas where surface recharge replenishes the aquifer, the residual effects of base‐flow reduction and thus its depletion volume will be significantly reduced. A stream of large conductance has a high hydraulic connection to the aquifer, but the relationship between stream conductance and stream depletion is not linear.
Retardation of Organic Contaminants in Natural Fractures in Chalk
Authors: Wefer‐Roehl A. , Graber E.R. , Adar E. , Yakirevich A. , Ronen Z. 
Published: December 2005

AbstractTransport of a conservative compound and two sorbing compounds through fractured chalk was studied using flow‐through columns consisting of chalk cores with a single subvertical fracture. Two types of chalk matrix were compared, an oxidized white chalk with low organic carbon content (0.2%), and a gray chalk with a higher organic carbon content (1.3%). Initial rapid breakthrough followed by a delayed approach to a relative concentration of unity for the conservative compound (2,6–difluorobenzoic acid [DFBA]) was clear evidence for diffusion into the porous chalk matrix. Matrix diffusion of DFBA was apparently much greater in the gray chalk columns than in the white chalk columns. Breakthrough curves (BTCs) of the sorbing compounds (2,4,6–tri‐bromophenol [TBP] and ametryn [AME]) were retarded in all cases as compared to the conservative compound. Sorption retardation was far greater in the gray chalk as compared with the white chalk, in good agreement with results from batch sorption experiments. BTCs for the conservative compound were relatively nonhysteretic for both white and gray chalk columns. In contrast, BTCs for the sorbing compounds were hysteretic in all cases, demonstrating that sorption was not at equilibrium before desorp‐tion began. These experiments suggest that on a field scale, transport of contaminants through fractures in chalk and other fractured porous media will be attenuated by diffusion and sorption into the matrix.
Static and Push‐Pull Methods Using Radon‐222 to Characterize Dense Nonaqueous Phase Liquid Saturations
Authors: Davis B.M. , Istok J.D. , Semprini L 
Published: December 2005

AbstractNaturally occurring radon in ground water can potentially be used as an in situ partitioning tracer to characterize dense nonaqueous phase liquid (DNAPL) saturations. The static method involves comparing radon concentrations in water samples from DNAPL‐contaminated and noncontaminated portions of an aquifer, while the push‐pull method involves the injection (push) and extraction (pull) of a radon‐free test solution from a single well. In the presence of DNAPL, radon concentrations during the pull phase are retarded, with retardation manifested in greater dispersion of radon concentrations relative to a conservative tracer. The utility of these methods was investigated in the laboratory using a physical aquifer model (PAM). Static and push‐pull tests were performed before and after contamination of the PAM sediment pack with trichloroethene (TCE), and after alcohol cosolvent flushing and pump‐and‐treat remediation. Numerical simulations were used to estimate the retardation factor for radon in push‐pull tests. Radon partitioning was observed in static and push‐pull tests conducted after TCE contamination. Calculated TCE saturations ranged up to 1.4% (static test) and 14.1% (push‐pull test). Post‐remediation tests showed decreases in TCE saturations. The results show that radon is sensitive to changes in DNAPL saturation in space and time. However, the methods are sensitive to DNAPL saturation heterogeneity, test location, sample size, and test design. The influence of these factors on test results, as well as the apparent overestimation of the retardation factor in push‐pull tests, warrant further investigation.
Regional Estimation of Base Recharge to Ground Water Using Water Balance and a Base‐Flow Index
Authors: Szilagyi Jozsef , Harvey F. Edwin , Ayers Jerry F. 
Published: December 2005

AbstractNaturally 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.
Application of Harmonic Analysis of Water Levels to Determine Vertical Hydraulic Conductivities in Clay‐Rich Aquitards
Authors: Boldt‐Leppin Brigitte E.J. , Jim Hendry M. 
Published: December 2005

AbstractA harmonic analysis method was used to determine vertical hydraulic conductivities (Kv) in geologic media between vertically separated piezometers using water level measurements. In this method, each water level time series was filtered and then decomposed using harmonic analysis into a sum of trigonometric components. The phase and amplitude of each harmonic function were calculated. These data were used to estimate Kv values between vertically separated data sets assuming one‐dimensional transient flow. The method was applied to water level data collected from nested piezometers at two thick clay‐rich till aquitards in Saskatchewan, Canada. At one site, routine water levels were measured in 12 piezometers (installed between 1 and 29 m below ground surface) since installation (1995). At the other site, water levels were measured in seven piezometers (installed between 4 and 53 m below ground surface) since installation (1998–1999). The Kv calculated using harmonic analysis decreased with depth below the water table at both sites, approaching matrix estimates of hydraulic conductivity between 10 and 11 m and between 21 and 43 m below ground surface. These depths reflected the depth of extensive vertical fracturing at the sites and showed that the depth of fracturing may be site specific.