bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Behavior of Dense, Nonaqueous Phase Liquids in Fractured Clay and Rock
Authors: Kueper Bernard H. , McWhorter David B. 
Published: August 2005

AbstractThis paper examines the behavior of dense, nonaqueous phase liquids (DNAPLs) in fractured clay and rock. The conditions under which a DNAPL will enter an initially water‐saturated, rough‐walled fracture are outlined and expressed in a number of ways, including the height to which a DNAPL pool can accumulate above a fracture prior to initial entry. To study the behavior of DNAPL in a rough‐walled fracture following initial entry, numerical simulations are carried out both in the plane of a fracture using a discrete representation of fracture roughness, and at a larger scale of averaging using an equivalent homogeneous porous media approach. The simulations illustrate that DNAPL will migrate through the larger aperture regions of a fracture plane, and that the DNAPL has the potential to enter progressively smaller aperture fractures with depth as it migrates. Additional numerical simulations indicate that the time taken for a nonaqueous phase liquid to traverse a fractured aquitard is inversely proportional to the fracture aperture, the fracture dip from the horizontal, and the height of the pool collected above the aquitard. It is also demonstrated that upward hydraulic gradients across a fractured aquitard can significantly slow the downward rate of DNAPL migration while downward water gradients enhance the rate of DNAPL migration across the aquitard.
Assessment of Uncertainty in Time‐Related Capture Zones Using Conditional Simulation of Hydraulic Conductivity
Authors: Varljen M. D. , Shafer J. M. 
Published: August 2005

AbstractA stochastic approach to steady‐state time‐related capture zone determination that is based on the conditional simulation of hydraulic conductivity is presented. Conditional simulation of hydraulic conductivity preserves the spatial correlation structure of the real hydraulic conductivity field as well as the measured, or known, values of hydraulic conductivity at sampling locations, thereby optimizing the use of available data and providing the most representative results possible. The stochastic analysis methodology utilizing conditional simulation is applied to a hypothetical ground‐water system with a water supply well to estimate uncertainty in the 1‐year and 10‐year capture zones of the well. The results demonstrate the influence of known hydraulic conductivity values on the estimates of uncertainty, as well as the behavior of the “zone of uncertainty” of the capture zone as a function of travel time and orientation of regional flow. The results have significant implications regarding strategies for sampling aquifer properties (e.g., hydraulic conductivity) for capture zone delineation and for interpretation of the effects of hydraulic conductivity uncertainty on capture zones.
Analysis of Ground‐Water Remedial Alternatives at a Superfund Site
Authors: Zheng C. , Bennett G. D. , Andrews C. B. 
Published: August 2005

AbstractThis paper presents a simple yet effective approach and methodology for the problem of evaluating ground‐water remedial alternatives at a waste disposal site, and discusses the application of this approach in a case study. The attainment areas, which represent the areas (outside the contaminant source itself) in which remediation is required, are first identified. Simulation of ground‐water flow in three dimensions, augmented by fluid particle tracking, is utilized to evaluate the travel times of ground water through the attainment areas. The mixed linear reservoir or “batch flush” model is then used to estimate the number of pore volumes which must be flushed through each attainment area in order to achieve remediation. The travel times are used in conjunction with this pore volume figure to estimate the time required for cleanup under each alternative. By comparing the cleanup time, the costs, and other features of each alternative, a cost‐effective remedy for the study site can be determined. While the development of remedial alternatives and the choice of the most cost‐effective remedy are highly site‐specific, the approach and methodology outlined in this paper have general applicability. The results presented herein also provide insight into the difficulties and special considerations associated with modeling and analyzing remedial alternatives.
A Monte Carlo‐Based Approach for Determining Traveltime‐Related Capture Zones of Wells Using Convex Hulls as Confidence Regions
Authors: Bair E. Scott , Safreed Connie M. , Stasny Elizabeth A. 
Published: August 2005

AbstractDetermination of traveltime‐related capture zones of wells in instances where there is a lack of adequate or reliable site‐specific values of hydraulic parameters and/or the heterogeneous character of the geologic materials may lead to designation and management of wellhead‐protection areas of dubious function. In these instances, Monte Carlo simulation can be used to determine traveltime‐related capture zones that account for the uncertainty in values of hydraulic and geologic parameters that cannot be accounted for by deterministically based flow models.Monte Carlo simulations using 100 randomly generated values of hydraulic conductivity and effective porosity were used to determine one‐year capture zones based on determination of percentile confidence regions from reverse‐tracked flowpaths emanating from a well completed in a leaky‐confined aquifer. The mean of the lognormal distribution used to generate the hydraulic‐conductivity values was taken to be 3.89 ft/d, the log of the average value from an aquifer test, and a standard deviation of 1.0 ft/d was used. The normal distribution used to generate the effective porosity values had a mean of 25 percent and a standard deviation of 3.5 percent. The values of hydraulic conductivity and effective porosity were ordered and then paired to induce correlation. Other relevant hydraulic and geologic parameters were fixed at average or observed values from the available data.Simulations were made using an analytical flow model in conjunction with a particle‐tracking program to obtain 100 sets of endpoint coordinates for 36 reverse‐tracked, one‐year flowpaths emanating from the well. Wellhead‐protection areas based on the 90th‐ and 75th‐percentile confidence regions of the distribution of 3,600 endpoints were determined by deleting the 10 and 25 most‐extreme (distant) endpoints, respectively, from the 100 sets of flowpath endpoints of the 36 flowpaths. Delineation of the wellhead‐protection areas was based on determination of the convex hull of the remaining endpoints. The distribution of remaining endpoints around the well also was used to determine optimum locations for construction of sentinel wells to detect contaminants moving toward the well along the most probable flowpaths.
Multilevel Slug Tests with Comparisons to Tracer Data
Authors: Melville Joel G. , Molz Fred J. , Güven Oktay , Widdowson Mark A. 
Published: August 2005

AbstractMultilevel slug tests were conducted in a confined, granular aquifer near Mobile, Alabama. Tracer injection and travel time experiments, more direct measurements of transport in the aquifer, were also conducted at the same location. The objective was to compare results of the two field investigations to ascertain the accuracy and utility of slug testing to measure transport properties of the aquifer. Nondimensional hydraulic conductivity profiles inferred from the slug tests and the tracer experiments were similar. The similarity of the profiles supported the utility of multilevel slug testing to characterize the hydraulic conductivity profile in the aquifer.The slug test data collected in three wells were interpreted using a radial flow model (Cooper et al., 1967) and a finite element model which considered both radial and vertical flow (Widdowson et al., 1989, 1990). Hydraulic conductivity values inferred from the measured data considering both radial and vertical flow were approximately two‐thirds of the values inferred assuming radial flow.
A Comparison of Sorption Coefficients Determined by Batch, Column, and Box Methods on a Low Organic Carbon Aquifer Material
Authors: Maclntyre William G. , Stauffer Thomas B. , Antworth Christopher P. 
Published: August 2005

AbstractResults of three independent experimental methods for determination of sorption coefficients were compared on sieved aquifer material samples from Columbus AFB, Columbus, Mississippi. These aquifer materials contained <0.1% organiccarbon, and sorption coefficients for naphthalene ranged from 0.06 to 0.20 I/kg. There was low correlation between organic carbon contents and sorption coefficients. Good agreement was found among sorption coefficients measured by batch, dynamic column, and dynamic box methods. Similarity of the coefficients was attributed to measured fast sorption kinetics and to linearity of isotherms observed for naphthalene sorption on Columbus aquifer material. Results indicate that channeling, wall and end effects, and particle loss were insignificant in the dynamic systems. Since laboratory sorption coefficient measurements were found impractical on whole sand‐gravel aquifer samples, an equation is proposed to convert laboratory measured sorption coefficients on the separated sand (<2 mm) fraction to sorption coefficients on wholesand‐gravel aquifer materials.
Comparative Hydrogeology of Fresh‐Water Lenses of Bermuda and Great Exuma Island, Bahamas
Authors: Vacher H. L. , Wallis T. N. 
Published: August 2005

AbstractThe islands of Bermuda and Great Exuma are similar in that they are both composed of Quaternary marginal‐marine, calcarenitic limestones. These limestones are predominantly eolianite. Topographic depressions between eolian ridges are locally lower than present sea level; consequently, the ground water is coupled to inland marshes and ponds. The islands differ climatically. Rainfall in Bermuda exceeds potential evapotranspiration by about 0.1 m/yr, while in Great Exuma, potential evapotranspiration exceeds rainfall by some 0.5 m/yr. As a result, the inland ponds of Great Exuma are brackish to hypersaline, and fresh‐water lenses are localized beneath the topographic highs between the ponds and the shoreline. In contrast, the marshes of Bermuda are not strong discharge sites, and the surrounding fresh‐water lenses are geologically rather than topographically controlled. Dupuit‐Ghyben‐Herzberg modeling indicates that if the climates of Bermuda and Great Exuma were reversed, the characteristics of their fresh‐water lenses would be reversed as well. This comparison indicates that climate, as reflected in the water budget, is one of the important controlling variables in the occurrence and geometry of fresh‐water lenses in low‐lying subtropical islands.
Hydraulic Barriers in Pleistocene Buried‐Valley Aquifers
Authors: Shaver Robert B. , Pusc Steve W. 
Published: August 2005

AbstractAquifer‐test analysis, evaluation of potentiometric data, and numerical simulation of ground‐water flow are useful techniques for detecting hydraulic barriers in Pleistocene buried‐valley aquifers. Using these techniques, hydraulic barriers were identified in both the Spiritwood and Sundre‐New Rockford buried‐valley aquifers in North Dakota. The existence of hydraulic barriers in these two aquifers was confirmed by geologic data obtained from test drilling.Two types of hydraulic barriers have been distinguished based on orientation with respect to the principal axes of buried valleys. Longitudinal hydraulic barriers are relatively narrow, linearly discontinuous ridges comprised of shale bedrock or till that are aligned roughly parallel to the long axes of buried valleys. Transverse hydraulic barriers are narrow, continuous barriers comprised of silt and clay aligned roughly perpendicular to the long axes of buried valleys.The principal directions of ground‐water flow in buried‐valley aquifers commonly are parallel to longitudinal hydraulic barriers and perpendicular to transverse hydraulic barriers. As a result, under natural conditions, transverse hydraulic barriers generally are manifested by larger potentiometric surface discontinuities.Pleistocene drainageways explain the occurrence and formation of hydraulic barriers in buried‐valley aquifers. Longitudinal hydraulic barriers are erosional features that appear to be formed by stream‐valley bifurcation in melt‐water channels or glacial‐lake spillways. Transverse hydraulic barriers appear to be formed by catastrophic flooding along spillways from the rapid drainage of glacial lakes and subsequent deposition of silt and clay deposits by sluggish, underfit streams.
Estimating Aquifer Properties by Nonlinear Least‐Squares Analysis of Pump Test Response
Authors: Johns R. A. , Semprini L. , Roberts P. V. 
Published: August 2005

AbstractIn this study, nonlinear least‐squares analysis of pump test data is used as a method for estimating aquifer parameters and choosing a conceptual model of the aquifer. The goal of this study is to investigate the potential advantages and disadvantages of using statistical algorithms for pump test analyses. Four different aquifer models were fitted to an extensive set of pump test data to characterize the aquifer at a single aquifer test site. These models were the Theis model, the equipotential boundary model, the confined leaky aquifer model, and the water‐table aquitard model. For several of the data sets, more than one aquifer model was found to match the pump test response with the same residual least‐squares error, and a review of the local hydrogeology was required to choose the leaky aquifer model as the most appropriate aquifer model. A few data sets, however, did not agree well with the leaky aquifer model. Using the fitting routine, the water‐table aquitard model was found to significantly improve the fit to these data sets. Further analysis of hydrogeologic features at the site indicated that the duration of the pump tests which matched the leaky aquifer model was probably insufficient to exhibit deviation from the leaky aquifer model. The water‐table aquitard model is, therefore, chosen as the most suitable model for this site, and parameters for the aquifer are estimated using the results from the fitting procedure. In comparison, an earlier graphical interpretation of these pump tests did not distinguish the improved fit which could be obtained with the water‐table aquitard model. However, the graphical analyses were valuable as they did provide preliminary estimates of the aquifer transmissivity, aiding in accepting or rejecting the results of the fitting analysis. Thus, we found that nonlinear least‐squares analysis can complement, but does not replace, graphical interpretation methods. The nonlinear least‐squares analysis can provide a means for analyzing pump tests which may not have been easily interpreted using traditional techniques, as the nonlinear least‐squares analysis attempts to match all the test data at both large and small values of time. However, this analysis also illustrates that fitting methods cannot be totally automated, but rather must be interpreted in light of other hydrogeologic data in order to arrive at a reasonable model for the aquifer.
The Topographic Approach to Locating High‐Yield Wells in Crystalline Rocks: Does It Work?
Authors: Yin Zhi‐Yong , Brook George A. 
Published: August 2005

AbstractDespite convincing evidence that fracture trace mapping can be extremely useful in locating sites for high‐yield wells, well drillers persist in using the “lay of the land” to select well sites. This paper examines: (1) the value of topographic variables in predicting the productivity of wells in crystalline rocks; and (2) whether topographic data for well sites can increase the accuracy of well yield predictions based on fracture trace data alone. Topographic and fracture trace data for 29 wells in the Georgia Piedmont and Blue Ridge area were studied. Regression analysis revealed that the LeGrand (1967) point value (TOPO) explained only 0.3% of the variation in the productivity of the 29 wells. More explanation was afforded by the less subjective topographic variables, distance from the well to the nearest valley or draw axis (DISTV), and the difference in elevation between the nearest valley or draw axis and the well site (ELEV). Together these variables still explained only 15.3% of the variation in well productivity.Brook (1988) showed that a single fracture trace variable, distance from the well to the nearest fracture trace intersection (DISTIN), explained 59% of the variation in the productivity of the 29 wells and that the two variables well depth and DISTIN explained 81% of the variation in well productivity. Addition of the topographic variables TOPO, DISTV, and ELEV to the models of well productivity developed by Brook (1988) did not greatly improve the explanation. None of the added variables were significant at the 0.05 confidence level. Results, therefore, indicate that well productivity is only poorly related to topographic characteristics, perhaps explaining why so many of the wells drilled in crystalline rocks using the “lay of the land” have a low yield or are dry regardless of their topographic locations.
Predicting Ground‐Water Nitrate‐Nitrogen Impacts
Authors: Hantzsche Norman N. , Finnemore E. John 
Published: August 2005

AbstractThe buildup of nitrates in upper ground‐water zones is a potential cumulative effect of on‐site sewage disposal practices which is not addressed by standard siting and design criteria. Literature concerning the contribution and fate of nitrogen beneath septic tank disposal fields is reviewed. From these findings, convenient, simplified methods are developed for estimating long‐term ground‐water nitrate increases on an area‐wide basis. The methods are presented in a manner useful to engineers, planners, and regulatory agencies for routine evaluation of existing and proposed land developments and for design of large, common disposal systems. Typical solutions are shown graphically to illustrate the relative importance of various factors, including development density, rainfall recharge, and soil denitrification. Predicted values are compared with actual monitoring data for three California communities to verify the reasonableness of the suggested methods. Several possible regulatory applications are suggested.
Parameter Estimation of the Coefficients in Soil Hydraulic Equations from Steady‐State Unsaturated Flow
Authors: Richie E. B. , Schnabel R. R. 
Published: August 2005

AbstractA parameter estimation procedure which determines the coefficients of soil hydraulic equations (soil‐water characteristic and hydraulic conductivity curves) is developed. The parameters are determined by nonlinear least‐squares regression of steady‐state water potential measured at several points along an unsaturated horizontal soil column to an equation, herein derived, which describes water potential continuously along the column. To estimate parameter values, total mass of water in the soil column at steady‐state, saturated water content, and steady‐state flow rate must also be measured.The parameter estimation procedure is verified using synthetic data and is applied in the laboratory. The coefficients appearing in the van Genuchten and Campbell soil hydraulic equations are estimated by the procedure. Alternative methodologies are proposed to augment this procedure and to provide user flexibility. The coefficients in the difficult‐to‐ measure wet range can be determined from measurements taken at steady‐state without independently measuring water retention.
Chlorine‐36 Releases from the Savanniah River Site Nuclear Fuel Reprocessing Facilities
Authors: Beasley T. M. , EImore D. , Kubik P. W. , Sharma P. 
Published: August 2005

AbstractDeterminations of 36CI (T½= 301,000 a) in waters on and near the U.S. Department of Energy's Savannah River Site (SRS) in South Carolina reveal that nuclear fuel reprocessing activities there have released measurable amounts of this radionuclide to the environment. The natural atmospheric flux of 36CI at the latitude of SRS is 20‐25 atoms m‐2 sec‐1. Atmospheric releases of 36CI from SRS, within the site boundaries, have increased this flux by a factor of at least 10 to 20. Approximately 3×109 Becquerels (Bq) [84 millicuries (mCi)] of site‐derived 36 CI have been deposited within 200 km of the plant boundaries. By comparison, fallout of 36CI from nuclear weapons testing in the 1950s deposited twice this amount of activity in the same area. Surface‐water 36CI concentrations in on‐site streams represent about 0.01 percent of the Environmental Protection Agency (EPA) drinking‐water standard and therefore pose no health concern. At SRS and similar facilities, this additional source of 36CI should prove useful for validating ground‐water and atmospheric transport models.
Apparent Relative Retardation of Tritium and Bromide in Dolomite
Authors: Leap Darrell I. 
Published: August 2005

AbstractIn order to determine the suitability of bromide as a surrogate for tritium for ground‐water tracing in fractured and fissured dolomite, apparent relative retardation coefficients of bromide with respect to tritium were computed by the cumulative relative mass‐time method from breakthrough curves of both substances, when used simultaneously as tracers in a two‐well recirculating tracer test. Throughout the 33.78‐day test, relative retardation differences of only a few hundredths were detected for most of the testing time.Tritium was less retarded in flow through highly transmissive openings than in more diffuse flow. Bromide was generally retarded relative to tritium except at the pumping well where the concentrations of both were diluted an order of magnitude below those in the monitoring wells, and tritium was retarded slightly more than bromide.Apparent relative retardation was found to change with transmissivity, concentration, flow‐path length and time, but not enough to rule out bromide as a suitable surrogate for, or even better than, tritium in dolomite if the limitations of each tracer are known.
Saturated Mound Development on Sloping Clay Layers Due to a Finite Source: An Analytical Solutiona
Authors: Filley T. H. 
Published: August 2005

AbstractSloping clay layers beneath percolation ponds can cause infiltrating waste water to pond and move in directions not predicted by vertical infiltration equations. This paper presents a method for estimating the potential of percolation sumps located over sloping clay layers to interact with nearby ground‐water resources. The analytical solution developed is for steady‐state conditions and includes a procedure to estimate the time needed to reach steady state. The fundamental assumption used in the mathematical development requires that elevation‐head gradients be much larger than pressure‐head gradients. A method for testing the validity of this assumption is also included. An example calculation was performed for percolation sumps on the Naval Petroleum Reserves No. 1 in Elk Hills, California. That analysis shows that under the assumptions used, a sump exclusion zone on the Elk Hills is required to protect ground‐water resources within the adjacent San Joaquin Valley.
Optimal Design of Ground‐Water Capture Systems Using Segmental Velocity‐Direction Constraints
Authors: Ratzlaff Steven A. , Aral Mustafa M. , Al‐Khayyal Faiz 
Published: August 2005

AbstractAn effective means of containing contaminant plumes in regional aquifers is to regulate the ground‐water flow through extraction wells that are strategically located. In this paper, the best well locations and flow rates are determined using numerical ground‐water simulation and optimization techniques. As a first step in the analysis, the methodology utilizes a novel idea of delineating the capture zone by imposing segmental implicit velocity‐direction constraints as opposed to explicit and unilateral velocity‐direction constraints which have been proposed by others. The optimization problem that arises is a mixed‐integer linear program which is solved by standard branch and bound techniques. The overall procedure is illustrated on representative example problems.