bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hydraulic Tests with Direct‐Push Equipment
Authors: Butler James J. , Healey John M. , McCall G. Wesley , Garnett Elizabeth J. , Loheide Steven P. 
Published: December 2005

AbstractThe potential of direct‐push technology for hydraulic characterization of saturated flow systems was investigated at a field site with a considerable degree of subsurface control. Direct‐push installations were emplaced by attaching short lengths of screen (shielded and unshielded) to the bottom end of a tool string that was then advanced into the unconsolidated sediments. A series of constant‐rate pumping tests were performed in a coarse sand and gravel aquifer using direct‐push tool strings as observation wells. Very good agreement (within 4%) was found between hydraulic conductivity (K) estimates from direct‐push installations and those from conventional wells. A program of slug tests was performed in direct‐push installations using small‐diameter adaptations of solid‐slug and pneumatic methods. In a sandy silt interval of moderate hydraulic conductivity, K values from tests in a shielded screen tool were in excellent agreement (within 2%) with those from tests in a nearby well. In the coarse sand and gravel aquifer, K values were within 12% of those from multilevel slug tests at a nearby well. However, in the more permeable portions of the aquifer (K > 70 m/day), the smaller‐diameter direct‐push rods (0.016 m inner diameter [I.D.]) attenuated test responses, leading to an underprediction of K. In those conditions, use of larger‐diameter rods (e.g., 0.038 m I.D.) is necessary to obtain K values representative of the formation. This investigation demonstrates that much valuable information can be obtained from hydraulic tests in direct‐push installations. As with any type of hydraulic test, K estimates are critically dependent on use of appropriate emplacement and development procedures. In particular, driving an unshielded screen through a heterogeneous sequence will often lead to a buildup of low‐K material that can be difficult to remove with standard development procedures.
Probabilistic Capture Zone Delineation Based on an Analytic Solution
Authors: Jacobson Elizabeth , Andricevic Roko , Morrice Joseph 
Published: December 2005

AbstractA major tool used in the design of wellhead protection areas is the delineation of a capture zone for a pumping well by use of a simple, steady‐state analytic solution. This simple approach has been useful for many small municipalities because of the high costs associated with obtaining the hydrogeologic information needed for detailed numerical modeling. This analytic solution, however, is deterministic, and uncertainty in the mean value estimates of the hydraulic parameters used in this model can be a major source of error in predicting capture zones. To address this problem, a statistical theory was developed for including the uncertainty in the transmissivity and the magnitude and direction of the hydraulic head gradient in the analytic solution for both the ultimate and time‐dependent capture zone for an arbitrary reliability level. To demonstrate the method and investigate the effect of varying magnitudes of uncertainty on time‐dependent capture zones, the method is applied to three synthetic data sets based on data from the Borden Aquifer in Ontario, Canada. In general, the results show that uncertainty in the length of the time‐dependent capture zone at a given reliability level is dependent on the uncertainty in the magnitude of the mean regional flow, which is equal to the transmissivity multiplied by the hydraulic head gradient; uncertainty in the maximum width of the capture zone is dependent primarily on the uncertainty in the mean direction of the regional flow.
Using High Hydraulic Conductivity Nodes to Simulate Seepage Lakes
Authors: Anderson Mary P. , Hunt Randall J. , Krohelski James T. , Chung Kuopo 
Published: December 2005

AbstractIn a typical ground water flow model, lakes are represented by specified head nodes requiring that lake levels be known a priori. To remove this limitation, previous researchers assigned high hydraulic conductivity (K) values to nodes that represent a lake, under the assumption that the simulated head at the nodes in the high‐K zone accurately reflects lake level. The solution should also produce a constant water level across the lake. We developed a model of a simple hypothetical ground water/lake system to test whether solutions using high‐K lake nodes are sensitive to the value of K selected to represent the lake. Results show that the larger the contrast between the K of the aquifer and the K of the lake nodes, the smaller the error tolerance required for the solution to converge. For our test problem, a contrast of three orders of magnitude produced a head difference across the lake of 0.005 m under a regional gradient of the order of 10−3 m/m, while a contrast of four orders of magnitude produced a head difference of 0.001 m. The high‐K method was then used to simulate lake levels in Pretty Lake, Wisconsin. Results for both the hypothetical system and the application to Pretty Lake compared favorably with results using a lake package developed for MODFLOW (Merritt and Konikow 2000). While our results demonstrate that the high‐K method accurately simulates lake levels, this method has more cumbersome postprocessing and longer run times than the same problem simulated using the lake package.
Improving a Regional Model Using Reduced Complexity and Parameter Estimation
Authors: Kelson Victor A. , Hunt Randall J. , Haitjema Henk M. 
Published: December 2005

AbstractThe availability of powerful desktop computers and graphical user interfaces for ground water flow models makes possible the construction of ever more complex models. A proposed copper‐zinc sulfide mine in northern Wisconsin offers a unique case in which the same hydrologic system has been modeled using a variety of techniques covering a wide range of sophistication and complexity. Early in the permitting process, simple numerical models were used to evaluate the necessary amount of water to be pumped from the mine, reductions in streamflow, and the drawdowns in the regional aquifer. More complex models have subsequently been used in an attempt to refine the predictions. Even after so much modeling effort, questions regarding the accuracy and reliability of the predictions remain.We have performed a new analysis of the proposed mine using the two‐dimensional analytic element code GFLOW coupled with the nonlinear parameter estimation code UCODE. The new model is parsimonious, containing fewer than 10 parameters, and covers a region several times larger in areal extent than any of the previous models. The model demonstrates the suitability of analytic element codes for use with parameter estimation codes. The simplified model results are similar to the more complex models; predicted mine inflows and UCODE‐derived 95% confidence intervals are consistent with the previous predictions. More important, the large areal extent of the model allowed us to examine hydrological features not included in the previous models, resulting in new insights about the effects that far‐field boundary conditions can have on near‐field model calibration and parameterization. In this case, the addition of surface water runoff into a lake in the headwaters of a stream while holding recharge constant moved a regional ground watershed divide and resulted in some of the added water being captured by the adjoining basin. Finally, a simple analytical solution was used to clarify the GFLOW model's prediction that, for a model that is properly calibrated for heads, regional drawdowns are relatively unaffected by the choice of aquifer properties, but that mine inflows are strongly affected. Paradoxically, by reducing model complexity, we have increased the understanding gained from the modeling effort.
More Realistic Soil Cleanup Standards with Dual‐Equilibrium Desorption
Authors: Chen W. , Kan A.T. , Newell C.J. , Moore E. , Tomson M.B. 
Published: December 2005

AbstractThe desorption of contaminants from soils/sediments is one of the most important processes controlling contaminant transport and environmental risks. None of the currently adopted desorption models can accurately quantify desorption at relatively low concentrations; these models often overestimate the desorption and thus the risks of hydrophobic organic chemicals, such as benzene and chlorinated solvents. In reality, desorption is generally found to be biphasic, with two soil‐phase compartments. A new dual‐equilibrium desorption (DED) model has been developed to account for the biphasic desorption. This model has been tested using a wide range of laboratory and field data and has been used to explain key observations related to underground storage tank plumes. The DED model relates the amount of a chemical sorbed to the aqueous concentration, with simple parameters including octanol‐water partition coefficient, solubility, and fractional organic carbon; thus, it is the only biphasic model, to date, that is based on readily available parameters. The DED model can be easily incorporated into standard risk and transport models. According to this model, many regulatory standards of soils and sediments could be increased without increasing the risks.
Using Direct Current Resistivity Sounding and Geostatistics to Aid in Hydrogeological Studies in the Choshuichi Alluvial Fan, Taiwan
Authors: Yang Chieh‐Hou , Lee Wei‐Feng 
Published: December 2005

AbstractGround water reservoirs in the Choshuichi alluvial fan, central western Taiwan, were investigated using direct‐current (DC) resistivity soundings at 190 locations, combined with hydrogeological measurements from 37 wells. In addition, attempts were made to calculate aquifer transmissivity from both surface DC resistivity measurements and geostatistically derived predictions of aquifer properties.DC resistivity sounding data are highly correlated to the hydraulic parameters in the Choshuichi alluvial fan. By estimating the spatial distribution of hydraulic conductivity from the kriged well data and the cokriged thickness of the correlative aquifer from both resistivity sounding data and well information, the transmissivity of the aquifer at each location can be obtained from the product of kriged hydraulic conductivity and computed thickness of the geoelectric layer. Thus, the spatial variation of the transmissivities in the study area is obtained.Our work is more comparable to Ahmed et al. (1988) than to the work of Niwas and Singhal (1981). The first “constraint” from Niwas and Singhal's work is a result of their use of linear regression. The geostatistical approach taken here (and by Ahmed et al. [1988]) is a natural improvement on the linear regression approach.
Determination of Confined Phreatic Aquifer Anisotropy
Authors: Fallico Carmine , Mazzuca Rosa , Troisi Salvatore 
Published: December 2005

AbstractThe determination of anisotropy in a phreatic aquifer by means of a pumping test can be carried out, under given conditions, with common analysis methods. This paper develops and applies an amended method based on a technique proposed by Boulton (1970). This new method enables a quick, simple determination of vertical hydraulic conductivity, given drawdown data from a pumping well and at least one observation well, that is applicable to confined phreatic aquifers.
Influence of the Amount of Available K Data on Uncertainty About Contaminant Transport Prediction
Authors: Bright John , Wang Fuli , Close Murray 
Published: December 2005

AbstractThe effect of increasing the amount of hydraulic conductivity (K) data on the level of uncertainty about contaminant concentration predictions was examined. Contaminant concentrations were predicted using Monte Carlo numerical simulations with progressively more K information, and were compared to reference data obtained from a physical experiment. Increasing the amount of K data used in generating the aquifer's K field improved the measure of confidence in the predicted contaminant concentration. The normalized concentration interval with 95% confidence decreased from 1.29 to 0.75 when the amount of K data increased from 20 to 71. However, the trade‐off is the increase in the costs of aquifer investigation. Conducting Monte Carlo numerical simulations may help design an optimal aquifer investigation scheme, so that it can provide enough input data to predict concentrations with the desired level of confidence and at the same time avoid the excessive costs of aquifer investigation.
Delineation of Three‐Dimensional Well Capture Zones for Complex Multi‐Aquifer Systems
Authors: Frind E.O. , Muhammad D.S. , Molson J.W. 
Published: December 2005

AbstractThe delineation of well capture zones is a basic component of ground water protection. The conventional methodology for capture zone delineation is backward advective particle tracking, often applied under the assumption of a two‐dimensional aquifer. The suitability of the conventional approach for complex heterogeneous multi‐aquifer systems was investigated, using the Waterloo Moraine aquifer system as an example. It was found that the conventional approach produces irregular particle tracks that require judgment to interpret in a meaningful way, and it can raise questions that may affect the credibility of the capture zone delineation. As an alternative, the potentially powerful but little‐used backward‐in‐time advective‐dispersive transport approach was investigated. A key advantage of this approach is its capability to represent local heterogeneities through the dispersion term. The dispersion process has a natural smoothing effect that results in unambiguous capture zones without the need for interpretation, thus enhancing credibility. The question of capture zone validation is also addressed. The meaning of a three‐dimensional capture zone is considered, and it is shown that a fully three‐dimensional representation of the system is crucial for valid results. The distinction between the maximum extent capture zone and the surface capture zone is also explained. In the case of complex heterogeneous systems, advective particle tracking can be used as an initial screening tool, whereas the more realistic backward‐transport modeling approach can be used for final capture‐zone delineation.
Optimized System to Improve Pumping Rate Stability During Aquifer Tests
Authors: Young Michael H. , Rasmussen Todd C. , Lyons F. Comer , Pennell Kurt D. 
Published: December 2005

AbstractAquifer hydraulic properties are commonly estimated using aquifer tests, which are based on an assumption of a uniform and constant pumping rate. Substantial uncertainties in the flow rate across the borehole‐formation interface can be induced by dynamic head losses, caused by rapid changes in borehole water levels early in an aquifer test. A system is presented that substantially reduces these sources of uncertainty by explicitly accounting for dynamic head losses. The system which employs commonly available components (including a datalogger, pressure transducers, a variable‐speed pump motor, a flow controller, and flowmeters), is inexpensive, highly mobile, and easily set up. It optimizes the flow rate at the borehole‐formation interface, making it suitable for any type of aquifer test, including constant, step, or ramped withdrawal and injection, as well as sinusoidal. The system was demonstrated for both withdrawal and injection tests in three aquifers at the Savannah River Site. No modifications to the control system were required, although a small number of characteristics of the pumping and monitoring system were added to the operating program. The pumping system provided a statistically significant, constant flow rate with time. The range in pumping variability (95% confidence interval) was from ±2.58 × l0−4 L/sec to ±9.07 × 10−4L/sec, across a wide range in field and aquifer conditions.
The Lisse Effect Revisited
Authors: Weeks Edwin P. 
Published: December 2005

AbstractThe Lisse effect is a rarely noted phenomenon occurring when infiltration caused by intense rain seals the surface soil layer to airflow, trapping air in the unsaturated zone. Compression of air by the advancing front results in a pressure increase that produces a water‐level rise in an observation well screened below the water table that is several times as large as the distance penetrated by the wetting front. The effect is triggered by intense rains and results in a very rapid water‐level rise, followed by a recession lasting a few days. The Lisse effect was first noted and explained by Thal Larsen in 1932 from water‐level observations obtained in a shallow well in the village of Lisse, Holland. The original explanation does not account for the increased air pressure pushing up on the bottom of the wetting front. Analysis of the effect of this upward pressure indicates that a negative pressure head at the base of the wetting front, Ψf, analogous to that postulated by Green and Ampt (1911) to explain initially rapid infiltration rates into unsaturated soils, is involved in producing the Lisse effect. Analysis of recorded observations of the Lisse effect by Larsen and others indicates that the water‐level rise, which typically ranges from 0.10 to 0.55 m, should be only slightly larger than |Ψf| and that the depth of penetration of the wetting front is no more than several millimeters.
Hydrogeological Research: Just Getting Started
Authors: Miller Cass T. , Gray William G. 
Published: December 2005

AbstractThis paper comments on the current state of knowledge in the field of hydrogeology and claims that fundamental understandings must be developed if creative research is to have maximum impact. Problems of great importance to society include water development and quality, waste disposal, and global cycling of resources. These problems cannot be addressed effectively unless significant advances are made in understanding of a range of challenging scientific issues including fundamental physics, the importance of scale, modeling, and chemical and biological processes. Meaningful advances in hydrogeologic research will require an increased emphasis on fundamental understanding, interdisciplinary approaches, educational reforms, and the attraction of excellent researchers to the field.
New Combined Log and Tracer Test Interpretation Method for Identifying Transfers in Fissured Aquifers
Authors: Pistre Séverin , Marliac Séphane , Jourde Hervé , Bidaux Pascal 
Published: December 2005

AbstractTracer tests represent the most appropriate approach for assessing hydrodispersive parameters such as transversal and longitudinal dispersivities or kinematic porosity on an aquifer scale. They are generally carried out by injecting a tracer in a borehole and measuring its concentration over time in neighboring boreholes by extracted volume sampling or downhole measurements. Logging is one of the most suitable methods for evaluating fissured reservoirs. But short circuits between fractures with different hydraulic potential through boreholes induce mixing phenomena that cannot be avoided without packers. This mixing can shift the breakthrough curves deduced from the logs for each producing fracture and distort determination of their location.The method proposed in this paper aims at measuring the flow rate and the solute breakthrough for hydraulically active fractures, in open boreholes. It involves estimating a velocity profile along the borehole column by the analysis of two successive logs: a shift function according to depth is thus determined by comparison between log portions on each successive one. The velocity gradients reflect the inward or outward flow rates produced by each fracture. On the basis of these flow rates, it is possible to determine the mixing effects inside the borehole and then to plot unbiased breakthrough curves for each producing fracture.This method was applied at a granitic site in the eastern Pyrenees. In spite of some questionable limitations, the results showed that the method seems adapted to situations with many fractures. The precise hydraulic pattern which is obtained at the borehole scale is discussed in terms of a dual porosity model. Furthermore, interpretation of the breakthrough curves for fractures corrected for mixing effects revealed that Peclet numbers are strongly underestimated if this phenomenon is not considered.
Determining Extreme Parameter Correlation in Ground Water Models
Authors: Hill Mary C. , Østerby Ole 
Published: December 2005

AbstractIn ground water flow system models with hydraulic‐head observations but without significant imposed or observed flows, extreme parameter correlation generally exists. As a result, hydraulic conductivity and recharge parameters cannot be uniquely estimated. In complicated problems, such correlation can go undetected even by experienced modelers. Extreme parameter correlation can be detected using parameter correlation coefficients, but their utility depends on the presence of sufficient, but not excessive, numerical imprecision of the sensitivities, such as round‐off error. This work investigates the information that can be obtained from parameter correlation coefficients in the presence of different levels of numerical imprecision, and compares it to the information provided by an alternative method called the singular value decomposition (SVD). Results suggest that (1) calculated correlation coefficients with absolute values that round to 1.00 were good indicators of extreme parameter correlation, but smaller values were not necessarily good indicators of lack of correlation and resulting unique parameter estimates; (2) the SVD may be more difficult to interpret than parameter correlation coefficients, but it required sensitivities that were one to two significant digits less accurate than those that required using parameter correlation coefficients; and (3) both the SVD and parameter correlation coefficients identified extremely correlated parameters better when the parameters were more equally sensitive. When the statistical measures fail, parameter correlation can be identified only by the tedious process of executing regression using different sets of starting values, or, in some circumstances, through graphs of the objective function.
Interbasin Underflow Between Closed Altiplano Basins in Chile
Authors: Montgomery Errol L , Rosko Michael J. , Castro Santiago O. , Keller Barry R. , Bevacqua Paolo S. 
Published: December 2005

AbstractInterbasin ground water movement of 200 to 240 L/sec occurs as underflow beneath a mountainous surface water divide separating the topographically higher Salar de Michincha from the topographically lower Salar de Coposa internally drained basins in the Altiplano of northern Chile. Salt‐encrusted flats (salars) and saline lakes occur on the lowest parts of the basin floors and comprise the principal evaporative discharge areas for the basins. Because a surface water divide separates the basins, surface water drainage boundaries do not coincide with ground water drainage boundaries. In the region, interbasin ground water movement is usually not recognized, but occurs for selected basins, and at places is an important component of ground water budgets. With increasing development of water for mining industry and potential exportation of ground water from the Altiplano for use at coastal cities, demonstration and quantification of interbasin movement is important for assessment of sustainable ground water development in a region of extreme aridity. Recognition and quantification of interbasin ground water underflow will assist in management of ground water resources in the arid Chilean Altiplano environment.