bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factors Influencing Methane Distribution in Texas Ground Water
Authors: Zhang Chuanlun , Grossman Ethan L. , Ammerman James W. 
Published: August 2005

AbstractTo determine the factors that influence the distribution of methane in Texas ground water, water samples were collected from 40 wells in east‐central and central Texas aquifers. Among the chemical parameters examined, sulfate is most important in controlling methane distribution. Methane occurs in high concentration (>10 μM) in east‐central Texas only where sulfate concentration is low (<1 μM), supporting the hypothesis that abundant microbial methane production does not begin until sulfate is depleted. Because water samples from central Texas are high in either oxygen (up to 172 μM) or sulfate (up to 28.7 μM), methane concentrations are low (<5 μM) in these waters. A positive correlation between methane and sulfate in these waters indicates a different, perhaps thermogenic, origin for the trace methane.The 13C/12C ratios of dissolved methane ranged from ‐80%o to ‐21%o in east‐central Texas and from ‐41.2%e to ‐8.5%e in central Texas. Low values of < −50%e in the east‐central Texas ground water indicate a microbial origin for methane and are consistent with the observed sulfate‐methane relationship; high 13C/12C ratios of > −31%e likely result from bacterial methane oxidation. Similarly, methane with high 13C/12C ratios in central Texas may reflect partial oxidation of the methane pool. Overall, water samples from both regions show a positive correlation between sulfate concentration and the 13C/12C ratio of methane, suggesting that methane oxidation may be associated with sulfate reduction in Texas ground water.
Simulated Effects of Irrigation on Salinity in the Arkansas River Valley in Colorado
Authors: Goff Karin , Lewis Michael E. , Person Mark A. , Konikowd Leonard F. 
Published: August 2005

AbstractAgricultural irrigation has a substantial impact on water quantity and quality in the lower Arkansas River valley of southeastern Colorado. A two‐dimensional flow and solute transport model was used to evaluate the potential effects of changes in irrigation on the quantity and quality of water in the alluvial aquifer and in the Arkansas River along an 17.7 km reach of the river. The model was calibrated to aquifer water level and dissolved solids concentration data collected throughout the 24 year study period (1971–95). Two categories of irrigation management were simulated with the calibrated model: (1) a decrease in ground water withdrawals for irrigation; and (2) cessation of all irrigation from ground water and surface water sources. In the modeled category of decreased irrigation from ground water pumping, there was a resulting 6.9% decrease in the average monthly ground water salinity, a 0.6% decrease in average monthly river salinity, and an 11.1% increase in ground water return flows to the river. In the modeled category of the cessation of all irrigation, average monthly ground water salinity decreased by 25 %; average monthly river salinity decreased by 4.4 %; and ground water return flows to the river decreased by an average of 64 %. In all scenarios, simulated ground water salinity decreased relative to historical conditions for about 12 years before reaching a new dynamic equilibrium condition. Aquifer water levels were not sensitive to any of the modeled scenarios. These potential changes in salinity could result in improved water quality for irrigation purposes downstream from the affected area.
Absolute Hydraulic Conductivity Estimates from Aquifer Pumping and Tracer Tests in a Stratified Aquifer
Authors: Thorbjarnarson K.W. , Huntley D. , McCarty J.J. 
Published: August 2005

AbstractIndependent estimates of absolute hydraulic conductivity were obtained by a “standard” aquifer pumping test and a forced‐gradient tracer test in a highly heterogeneous aquifer. An aquifer hydraulic test was conducted to evaluate the average hydraulic conductivity (K), and to establish steady‐state flow for the tracer test. An average K of 48 m/day was interpreted from the drawdown data in a fully screened well. Type‐curve matching and simulation with MODFLOW of the hydraulic response in partially screened wells indicates K of 10 to 15 m/day for the upper section and 71 to 73 m/day for the deeper section. Iodide and fluorescent dye tracers were injected at low rates in wells located approximately 8 m upgradient of the production well. Tracer breakthrough was monitored in the production well and at ten depth intervals within the fully screened monitoring well. Interpretation of tracer response in the production well reveals tracer transport is limited to a 3.9 m thick section of the 20 m thick aquifer, with a hydraulic conductivity of 248 m/day. However, the depth distribution of these permeable strata cannot be determined from the production well tracer response. When sampled at 1.5 m depth intervals in the monitoring well, breakthrough was observed in only three intervals along the entire 18.2 m screened well. K estimates from tracer travel time within discrete high‐permeability strata range from 31 to 317 m/day. Inclusion of permeameter K estimates for the lower permeability aquifer sands (4–10 m/day) result in a range in relative K of 0.01 to 1.0. This field site has the highest absolute K estimate for a discrete stratum and the widest range in relative hydraulic conductivity amongst research field sites with K estimates for discrete strata. Within such a highly stratified aquifer, the use of an average K from an aquifer pumping test to predict solute transport results in great underestimation of transport distances for a given time period.
Development of Three‐Dimensional Hydrostratigraphical Architecture of the Unsaturated Zone Based on Soft and Hard Data
Authors: Langsholt Elin , Kitterød Nils‐Otto , Gottschalk Lars 
Published: August 2005

AbstractThree‐dimensional geological maps that include the hydrostratigraphical heterogeneity and depositional architecture of the natural formation are needed in hydrogeology to understand flow and transport. This paper presents a practical procedure for the generation of such maps. The method includes multiple indicator kriging, where the estimation of the structural architecture is conditioned on ground penetrating radar data. Physical core samples are used as tie points. This study utilizes data obtained from the unsaturated zone of a highly heterogeneous, glaciofluvial delta formation in Norway.
Rhodamine WT and Bacillus subtilis Transport through an Alluvial Gravel Aquifer
Authors: Pang Liping , Close Murray , Noonan Mike 
Published: August 2005

AbstractA field study was conducted to characterize the transport of rhodamine WT dye and endospores of the bacterium Bacillus subtilis through preferential flowpaths in an alluvial gravel aquifer using natural gradient tracer experiments. Preliminary tracer experiments were conducted with rhodamine WT to determine preferential flowpaths using a resin bag method, because of spatial heterogeneity at the study site. Rhodamine WT, Cl, and B. subtilis endospores were then injected 0.1 to 1.6 m below the water table, and downgradient ground water was monitored.Rhodamine WT behaved like Cl in the field and was used as a nonreactive tracer in this study. The method of time moments (MTM) and a curve fitting method (CFM) using the AT123D model were applied to estimate transport parameters of rhodamine WT and B. subtilis endospores along preferential flowpaths within the aquifer, assuming each individual flowpath to be uniform. The results from CFM fit the observed data better than did MTM. Ground water velocities through preferential flowpaths ranged from 30 to 85 m/day with a median of 63 m/day, and longitudinal dispersivities ranged from 0.71 to 5.24 m with a median of 2.70 m. These values are within the range reported in the literature for similar hydrogeological conditions. B. subtilis endospores exhibited slightly faster velocities (median retardation factor 0.86) and lower longitudinal dispersivities (0.23 to 2.4 m, median 0.79 m) compared to rhodamine WT. When multiple concentration peaks were observed in the rhodamine WT breakthrough curves (BTCs), the bacteria always arrived with the first rhodamine WT peak, regardless of whether the first peak was small or large. For those wells with a single peak for both the dye and the bacteria, the bacteria tended to coincide with the front portion of the dye BTC. This suggests that convection is relatively more important for B. subtilis endospores than for the dye, probably due to pore size exclusion of the spores. For this reason, the use of non‐reactive solute tracers to reflect the movement of microorganisms may not be appropriate. The total removal rates of B. subtilis varied from 2.4 to 9.36 day−1 (median 3.36 day−1, probably resulting from filtration, sedimentation, and irreversible adsorption, as die‐off was not observed in the field during the 45 days of the study. The longevity of B. subtilis endospores in ground water makes it a good choice to use as a bacterial tracer in the study of transport processes in the absence of die‐off.
Radon in Quaternary Aquifers Related to Underlying Bedrock Geology
Authors: Morland G. , Strand T. , Furuhaug L. , Skarphagen H. , Banks D. 
Published: August 2005

AbstractA survey of radon concentrations in water abstracted from 31 of Norway's largest waterworks, using ground water from Quaternary fluvial and glaciofluvial sediments, returned values of between 0.4 Bq/L and 83 Bq/L, with a median of 23 Bq/L. Significantly higher Rn concentrations were present in ground water from Quaternary aquifers underlain by gneissic and granitic lithologies compared with those underlain by metasandstones, phyllites and mica schists. Compared to the recommended national action level of 500 Bq/L and concentrations of up to 19,900 Bq/L, which have been detected in boreholes in Norwegian granite aquifers, the concentrations measured in Quaternary aquifers are regarded as unproblematic for consumers, although a more detailed assessment may be required for workers spending a lot of time in wellhead areas.
A Nonlinear Time Series Model for Spring Flow: An Example from Shanxi Province, China
Authors: Jian Wen‐Bin , Yao Huan , Wen Xian‐Huan , Chen Bao‐Ren 
Published: August 2005

AbstractA nonlinear time series model is presented to describe the dynamics of ground water flow. The procedures for model‐establishing and parameter estimation are discussed. The proposed nonlinear model uses a threshold parameter that relates different precipitation processes, and a lag parameter that relates the time lag between precipitation events and observed increasing spring flow. This model is then applied to the prediction of time‐dependent flow of the Longzichi Spring, Shanxi Province, northwest China. The results in this analysis show that the proposed approach can accurately describe the complicated nonlinear time series and the discharge regime of the Longzichi Spring.
Efficient and Responsible Use of Prior Information in Inverse Methods
Authors: Weiss Richard , Smith Leslie 
Published: August 2005

AbstractPrior information on parameters such as hydraulic conductivity or ground water recharge rates is often used to stabilize the inverse problem in parameter estimation. A cautious use of prior information is advisable, however, because it may be biased or unrepresentative of the model parameters and/or it may not significantly stabilize the parameter estimates. Procedures are given: (1) to identify the model parameters for which prior information may best stabilize the parameter set; and (2) to identify the model parameters for which errors in the prior information lead to the smallest possible errors in the final set of parameter estimates. The first case is referred to as the efficient use of prior information; the second case is referred to as the responsible use of prior information. The procedures are based on an analysis of the model parameter space using response surfaces, multiparameter confidence regions, and eigenspace analysis. The guidelines lead to the selection of prior information on those parameters whose axes are most closely aligned with the longest axis of the parameter confidence region. Simple synthetic examples are used to explain the concepts. The advantages gained in screening the model parameters to identify those parameters for which prior information will be most efficient and responsible in determining the final values of the parameter estimates are demonstrated in the calibration of a ground water flow and solute transport model for the San Juan Basin, New Mexico.
A Numerical Model for Simulation of Bioremediation of Hydrocarbons in Aquifers
Authors: Muňoz José F. , Irarrázaval Manuel J. 
Published: August 2005

AbstractA numerical model was developed to describe the bioremediation of hydrocarbons in ground water aquifers considering aerobic degradation. The model solves the independent transport of three solutes (oxygen, hydrocarbons, and microorganisms) in ground water flow using the method of characteristics. Interactions between the three solutes, in which oxygen and hydrocarbons are consumed by microorganisms, are represented by Monod kinetics, solved using a Runge‐Kutta method. Model simulations showed good correlation as compared with results of soil column experiments. The model was used to estimate the time needed to remediate the columns, which varied from one to two years.
Anomalously High Nitrate Concentrations in Ground Water
Authors: Guimerà Jordi 
Published: August 2005

AbstractAnomalously high nitrate concentrations are found in aquifers with agricultural lands in their recharge area, with restricted water outflows and with partially penetrating wells which induce ground water recirculation. A comprehensive methodology is proposed, which characterizes the source term ‐ nitrate leaching ‐ in time and space and couples it to the hydrodynamic characterization of the aquifer. The methodology is applied to a heavily polluted aquifer. Results show that poor management of irrigation and fertilization practices cannot be separated from unfavorable hydrodynamic conditions to explain concentrations as high as 160 mg/L NO3−N in ground water.
Prediction of Regional Ground Water Flow to Streams
Authors: Christensen S. , Rasmussen K.R. , Moller K. 
Published: August 2005

AbstractDatabase information on geology, hydrology, and hydrometeorology may form an excellent basis for studying ground water flow and seepage to surface water in a catchment. In a field case study of a 114 km2catchment, geological database information was used to determine layer thicknesses and boundary conditions as well as to parameterize a ground water flow model. Hydraulic head and stream flow data were used to estimate the model parameters by nonlinear regression. The uncertainty of the estimated parameters and of the predicted stream flow gains was quantified by individual likelihood method confidence intervals. During four stages of calibration, ranging from using only head data to also using an extensive set of measured stream flow gains, no parameter estimates changed significantly, but the number of parameters was increased from 12 to 14 in order to fit local stream flow gains. This indicates that the geology‐based parameterization is firm.Adding stream flows to the calibration data reduced the uncertainty of the estimated parameters significantly. However, the uncertainty of some of the parameters was significant even when an extensive set of measured stream flow gains and hydraulic heads was used to calibrate the model. Parameter uncertainty is reflected in the uncertainty of the predicted stream flow gains. When an extensive set of stream flow data was used during calibration, the prediction uncertainty is up to ±25% in large streams, and up to ±60% in smaller streams. The confidence intervals in general are skewed, and they are very skewed in the case where no stream flow measurements were used to calibrate the model.The case study shows that even when relatively extensive geological information and calibration data are available, there may be significant uncertainty connected with the prediction of local discharge of ground water to streams. Reducing uncertainty in such cases will require extensive field investigations in order to improve the definition of recharge areas and to describe the local fluxes and flow patterns in the aquifers.
Use of Solute and Isotopic Composition of Ground Water to Constrain the Ground Water Flow System of the Azraq Area, Jordan
Authors: Abu‐Jaber Nizar S. , Ali Ali Jawad , Al Qudah Khaldoon 
Published: August 2005

AbstractThis study shows that hydrological systems in arid areas where water level data are incomplete can be better understood and constrained by using chemical and isotopic data. These constraints significantly alter the conceptual hydrological model of the Azraq area.Previous studies, based on water level data, suggest that water in the Azraq oasis is derived from two major piezometric highs; the western basalt aquifer to the northwest and the Tulul el Ashaquif highlands to the northeast of the oasis. Water from the Tulul el Ashaquif aquifer is also considered to drain to a piezometric low at Ruwaishid to the east, and then into deeper aquifers.Chemical data from this study show that the northwest basalt aquifer provides most of the water (80‐85 %) to the Azraq oasis. Water from the Tulul el Ashaquif supplies a relatively small proportion, but due to its high solute content, imparts its chemical signature on the oasis water. This study has shown that water from Tulul el Ashaquif are not supplied to the Ruwaishid area, as previously thought.Stable isotopic data show that each piezometric high contains water which originated in a distinct climatic setting. Both water types are poor in tritium. Traces of tritium at the Azraq oasis and at Ruwaishid indicate some recent local recharge.
Solution of Ground Water Flow Problems with General Purpose and Special Purpose Computer Codes
Authors: Gribb Molly M. , Sewell Granville 
Published: August 2005

AbstractIncreasingly, ground water hydrologists and engineers must solve saturated/unsaturated flow and transport problems. The unsaturated component of flow is especially important when considering transport of contaminants that originate from surface or near‐surface sources such as waste spill sites, landfills, and hazardous waste storage sites. Numerical solution of such problems has been accomplished with special purpose computer programs developed for solution of unsaturated flow problems. However, general purpose partial differential equation (PDE) solvers also exist, which often provide greater model flexibility. In this paper, the performance of PDE2D, a general PDE solver, and SWMS_2D, a special purpose program, are compared for solution of unsaturated flow and transport problems. Both programs accurately calculated changes in water volume in the flow domain for four examples, but PDE2D did not calculate boundary fluxes as well as SWMS_2D, resulting in high mass balance errors. However, PDE2D yielded a smoother solution of the example solute transport problem, despite a large mass balance error. SWMS_2D offers ease of use and excellent mass balances while PDE2D offers the user greater flexibility in terms of the types of problems solved, and a grid generator that ensures that the element size and distribution of elements are appropriate for a given problem.
Dipole Probe: Design and Field Applications of a Single‐Borehole Device for Measurements of Vertical Variations of Hydraulic Conductivity
Authors: Zlotnik Vitaly A. , Zurbuchen Brian R. 
Published: August 2005

AbstractA dipole probe (DP) for measuring vertical variations of hydraulic conductivity has been designed, constructed, and tested in field conditions. The variable‐length device designed for the dipole flow test (DFT) consists of three packers separated by changeable spacer rods. The assembled DP is lowered into a well with a long screened interval. The packers are inflated, isolating two screened sections (chambers) between them. A small submersible pump, mounted on the central packer, transfers water from the upper (extraction) chamber into the lower (injection) chamber. This simultaneous injection and extraction creates a recirculatory flow within the aquifer. The chamber head responses are measured by two pressure transducers in the DP chambers. The DP can be used at discrete intervals along the entire well screen length. The DP has been successfully tested in a specially constructed well with a continuous screen in a highly conductive sand and gravel aquifer. During drilling, disturbed samples were collected using the split spoon method and the vertical profile of K was estimated from grain‐size analysis. A total of 153 DFTs were performed with various DP geometries. Results indicate that the chamber head changes are sensitive to aquifer properties, reach steady state rapidly, vary linearly with redrculation pumping rate, and can be controlled by changes in DP dimensions. Vertical profiles of K compare well with grain‐size analysis estimates.
Evaluation of Multi‐Well Test Data in a Faulted Aquifer Using Linear and Radial Flow Models
Authors: Allen Diana M. , Michel Frederick A. 
Published: August 2005

AbstractAn extensive drilling and testing program was undertaken at Carleton University, Ottawa, Canada, to characterize the aquifer for the design of an aquifer thermal energy storage (ATES) system. The substantial data base provides an excellent record of well yields and hydraulic responses to a series of aquifer tests in a faulted carbonate aquifer. Well yield variability is reflected in the wide range in specific capacity (1.4 to 75.8 L/s/m) and is dependent upon the proximity of a well to a major fault. Constant discharge data, available for nine pumping wells and several observation wells, reflect both the excellent hydraulic connection along major faults and the limited hydraulic connection between fault blocks. Three different flow models, including vertical fracture and vertical dyke (linear), and Theis (radial), are used to interpret constant discharge test data from nine pumping wells and several observation wells. In all tests, the duration of pumping is sufficient to identify early‐time linear flow along faults and late‐time pseudo‐radial flow between fault blocks. This paper demonstrates the influence of fault‐induced heterogeneity on the hydraulic response of a carbonate aquifer and demonstrates the application and limitation of simple radial continuum models to aquifers of this type.