bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulating Ground Water‐Lake Interactions: Approaches and Insights
Authors: Hunt Randall J. , Haitjema Henk M. , Krohelski James T. , Feinstein Daniel T. 
Published: December 2005

AbstractApproaches for modeling lake‐ground water interactions have evolved significantly from early simulations that used fixed lake stages specified as constant head to sophisticated LAK packages for MODFLOW. Although model input can be complex, the LAK package capabilities and output are superior to methods that rely on a fixed lake stage and compare well to other simple methods where lake stage can be calculated. Regardless of the approach, guidelines presented here for model grid size, location of three‐dimensional flow, and extent of vertical capture can facilitate the construction of appropriately detailed models that simulate important lake‐ground water interactions without adding unnecessary complexity. In addition to MODFLOW approaches, lake simulation has been formulated in terms of analytic elements. The analytic element lake package had acceptable agreement with a published LAK1 problem, even though there were differences in the total lake conductance and number of layers used in the two models. The grid size used in the original LAK1 problem, however, violated a grid size guideline presented in this paper. Grid sensitivity analyses demonstrated that an appreciable discrepancy in the distribution of stream and lake flux was related to the large grid size used in the original LAK1 problem. This artifact is expected regardless of MODFLOW LAK package used. When the grid size was reduced, a finite‐difference formulation approached the analytic element results. These insights and guidelines can help ensure that the proper lake simulation tool is being selected and applied.
A Finite‐Volume ELLAM for Three‐Dimensional Solute‐Transport Modeling
Authors: Russell Thomas F. , Heberton Caroline I. , Konikow Leonard F. , Hornberger George Z. 
Published: December 2005

AbstractA three‐dimensional finite‐volume ELLAM method has been developed, tested, and successfully implemented as part of the U.S. Geological Survey (USGS) MODFLOW‐2000 ground water modeling package. It is included as a solver option for the Ground Water Transport process. The FVELLAM uses space‐time finite volumes oriented along the streamlines of the flow field to solve an integral form of the solute‐transport equation, thus combining local and global mass conservation with the advantages of Eulerian‐Lagrangian characteristic methods. The USGS FVELLAM code simulates solute transport in flowing ground water for a single dissolved solute constituent and represents the processes of advective transport, hydrodynamic dispersion, mixing from fluid sources, retardation, and decay. Implicit time discretization of the dispersive and source/sink terms is combined with a Lagrangian treatment of advection, in which forward tracking moves mass to the new time level, distributing mass among destination cells using approximate indicator functions. This allows the use of large transport time increments (large Courant numbers) with accurate results, even for advection‐dominated systems (large Peclet numbers). Four test cases, including comparisons with analytical solutions and benchmarking against other numerical codes, are presented that indicate that the FVELLAM can usually yield excellent results, even if relatively few transport time steps are used, although the quality of the results is problem‐dependent.
MAROS: A Decision Support System for Optimizing Monitoring Plans
Authors: Aziz Julia J. , Ling Meng , Rifai Hanadi S. , Newell Charles J. , Gonzales James R. 
Published: December 2005

AbstractThe Monitoring and Remediation Optimization System (MAROS), a decision‐support software, was developed to assist in formulating cost‐effective ground water long‐term monitoring plans. MAROS optimizes an existing ground water monitoring program using both temporal and spatial data analyses to determine the general monitoring system category and the locations and frequency of sampling for future compliance monitoring at the site. The objective of the MAROS optimization is to minimize monitoring locations in the sampling network and reduce sampling frequency without significant loss of information, ensuring adequate future characterization of the contaminant plume. The interpretive trend analysis approach recommends the general monitoring system category for a site based on plume stability and site‐specific hydrogeologic information. Plume stability is characterized using primary lines of evidence (i.e., Mann‐Kendall analysis and linear regression analysis) based on concentration trends, and secondary lines of evidence based on modeling results and empirical data. The sampling optimization approach, consisting of a two‐dimensional spatial sampling reduction method (Delaunay method) and a temporal sampling analysis method (Modified CES method), provides detailed sampling location and frequency results. The Delaunay method is designed to identify and eliminate redundant sampling locations without causing significant information loss in characterizing the plume. The Modified CES method determines the optimal sampling frequency for a sampling location based on the direction, magnitude, and uncertainty in its concentration trend. MAROS addresses a variety of ground water contaminants (fuels, solvents, and metals), allows import of various data formats, and is designed for continual modification of long‐term monitoring plans as the plume or site conditions change over time.
Modeling the Buildup of Iron Oxide Encrustations in Wells
Authors: Houben Georg J. 
Published: December 2005

AbstractFerric iron encrustations are a common problem that seriously affects the performance of wells and drains. Their formation is induced by the mixing of reduced ground water containing ferrous iron with oxic shallow ground water and exposure to air. The process of ferrous iron oxidation is a kinetically controlled reaction. The reaction rate has a quadratic dependency on pH. The precipitating oxides have an autocatalytic effect that further enhances reaction progress. This paper describes the application of kinetic models to the problem of encrustation formation. Influences of pH, residence time, and autocatalysis were modeled. The overall influence of the autocatalytic reaction path is particularly strong when initial amounts of iron oxides are present. Autocatalysis provides a good explanation on the development of well yield commonly measured in the field. Encrustation precipitation is slow at first, but speeds up after a sufficient amount of iron oxide has built up. An incomplete removal of iron oxide encrustations during rehabilitation leads to a renewed increase in catalytic efficiency and encrustation precipitation.
Use of Temperature Profiles and Stable Isotopes to Trace Flow Lines: Nagaoka Area, Japan
Authors: Salem Zenhom El‐said , Taniguchi Makoto , Sakura Yasua 
Published: December 2005

AbstractIn this study, we use borehole temperature data and stable isotopes to delineate the flow system and estimate the effect of urbanization in the Nagaoka area of Japan. Temperature profiles were measured four times in observation wells during the period 2000–2001 and compared with those measured in the same wells during the period 1977–1983 (Taniguchi 1986). Water was sampled in both observation and pumping wells during the same period. The temporal and spatial variability in temperature indicate clearly the effect of urban warming and heavy pumping on the ground water system. Urban warming caused higher temperatures recently as compared to the older values, and pumping caused induced recharge from the river to the ground water. The stable isotope data show the ground water flow system is divided into shallow, intermediate, and deep systems, and that land use and infiltration rate are affecting the shallow flow system.
Small‐Scale Electrical Resistivity Tomography of Wet Fractured Rocks
Authors: LaBrecque Douglas J. , Sharpe Roger , Wood Thomas , Heath Gail 
Published: December 2005

AbstractThis paper describes a series of experiments that tested the ability of the electrical resistivity tomography (ERT) method to locate correctly wet and dry fractures in a meso‐scale model. The goal was to develop a method of monitoring the flow of water through a fractured rock matrix.The model was a four by six array of limestone blocks equipped with 28 stainless steel electrodes. Dry fractures were created by placing pieces of vinyl between one or more blocks. Wet fractures were created by injecting tap water into a joint between blocks. In electrical terms, the dry fractures are resistive and the wet fractures are conductive. The quantities measured by the ERT system are current and voltage around the outside edge of the model. The raw ERT data were translated to resistivity values inside the model using a three‐dimensional Occam's inversion routine. This routine was one of the key components of ERT being tested.The model presented several challenges. First, the resistivity of both the blocks and the joints was highly variable. Second, the resistive targets introduced extreme changes the software could not precisely quantify. Third, the abrupt changes inherent in a fracture system were contrary to the smoothly varying changes expected by the Occam's inversion routine. Fourth, the response of the conductive fractures was small compared to the background variability.In general, ERT was able to locate correctly resistive fractures. Problems occurred, however, when the resistive fracture was near the edges of the model or when multiple fractures were close together. In particular, ERT tended to position the fracture closer to the model center than its true location. Conductive fractures yielded much smaller responses than the resistive case. A difference‐inversion method was able to correctly locate these targets.
Determining the Permeability of Fractured Rocks Based on Joint Mapping
Authors: Zhang Faming , Zhou Zhifang , Huang Yongqing , Chen Zuyu 
Published: December 2005

AbstractA typical fractured rock mass is intersected by several sets of discontinuities, which provide the main flowpath for ground water. Due to the limitations of data obtained by conventional field measurements, it is often difficult to estimate the anisotropic permeability tensor associated with the joints existing in the rock mass. For that reason, determining permeability tensors for fractured rocks is an important topic in rock mass hydraulics. Based on field surveys, joint parameters can be analyzed by using probabilistic and statistical tools, and three‐dimensional mapping of the jointed rock mass. Through analysis of a single joint's hydraulic characteristics, the principal value of the permeability tensor for the jointed rock mass can be determined by using Monte Carlo methods and the searching percolation trace method, which is developed in this paper. The study reports on practical examples demonstrating that results from the methods discussed in this paper are in agreement with those from field hydrogeological surveys and measurements.
Colonization by Aerobic Bacteria in Karst: Laboratory and In Situ Experiments
Authors: Personné J.‐C. , Poty F. , Mahler B.J. , Drogue C. 
Published: December 2005

AbstractExperiments were carried out to investigate the potential for bacterial colonization of different substrates in karst aquifers and the nature of the colonizing bacteria. Laboratory batch experiments were performed using limestone and PVC as substrates, a natural bacterial isolate and a known laboratory strain (Escherichia coli [E. coli]) as inocula, and karst ground water and a synthetic formula as growth media. In parallel, fragments of limestone and granite were submerged in boreholes penetrating two karst aquifers for more than one year; the boreholes are periodically contaminated by enteric bacteria from waste water. Once a month, rock samples were removed and the colonizing bacteria quantified and identified. The batch experiments demonstrated that the natural isolate and E. coli both readily colonized limestone surfaces using karst ground water as the growth medium. In contrast, bacterial colonization of both the limestone and granite substrates, when submerged in the karst, was less intense. More than 300 bacterial strains were isolated over the period sampled, but no temporal pattern in colonization was seen as far as strain, and colonization by E. coli was notably absent, although strains of Salmonella and Citrobacter were each observed once. Samples suspended in boreholes penetrating highly fractured zones were less densely colonized than those in the borehole penetrating a less fractured zone. The results suggest that contamination of karst aquifers by enteric bacteria is unlikely to be persistent. We hypothesize that this may be a result of the high flow velocities found in karst conduits, and of predation of colonizing bacteria by autochthonous zooplankton.
Radon (222Rn) in Ground Water of Fractured Rocks: A Diffusion/Ion Exchange Model
Authors: Wood Warren W. , Kraemer Thomas F. , Shapiro Allen 
Published: December 2005

AbstractGround waters from fractured igneous and high‐grade sialic metamorphic rocks frequently have elevated activity of dissolved radon (222Rn). A chemically based model is proposed whereby radium (226Ra) from the decay of uranium (238U) diffuses through the primary porosity of the rock to the water‐transmitting fracture where it is sorbed on weathering products. Sorption of 226Ra on the fracture surface maintains an activity gradient in the rock matrix, ensuring a continuous supply of 226Ra to fracture surfaces. As a result of the relatively long half‐life of 226Ra (1601 years), significant activity can accumulate on fracture surfaces. The proximity of this sorbed 226Ra to the active ground water flow system allows its decay progeny 222Rn to enter directly into the water. Laboratory analyses of primary porosity and diffusion coefficients of the rock matrix, radon emanation, and ion exchange at fracture surfaces are consistent with the requirements of a diffusion/ion‐exchange model. A dipole‐brine injection/withdrawal experiment conducted between bedrock boreholes in the high‐grade metamorphic and granite rocks at the Hubbard Brook Experimental Forest, Grafton County, New Hampshire, United States (42°56′N, 71°43′W) shows a large activity of 226Ra exchanged from fracture surfaces by a magnesium brine. The 226Ra activity removed by the exchange process is 34 times greater than that of 238U activity. These observations are consistent with the diffusion/ion‐exchange model. Elutriate isotopic ratios of 223Ra/226Ra and 238U/226Ra are also consistent with the proposed chemically based diffusion/ion‐exchange model.
Effects of Water Use on Arsenic Release to Well Water in a Confined Aquifer
Authors: Gotkowitz Madeline B. , Schreiber Madeline E. , (Toni) Simo J.A. 
Published: December 2005

AbstractField‐based experiments were designed to investigate the release of naturally occurring, low to moderate (< 50 ug/L) arsenic concentrations to well water in a confined sandstone aquifer in northeastern Wisconsin. Geologic, geochemical, and hydrogeologic data collected from a 115 m2 site demonstrate that arsenic concentrations in ground water are heterogeneous at the scale of the field site, and that the distribution of arsenic in ground water correlates to solid‐phase arsenic in aquifer materials. Arsenic concentrations in a test well varied from 1.8 to 22 ug/L during experiments conducted under no, low, and high pumping rates. The quality of ground water consumed from wells under typical domestic water use patterns differs from that of ground water in the aquifer because of reactions that occur within the well. Redox conditions in the well can change rapidly in response to ground water withdrawals. The well borehole is an environment conducive to microbiological growth, and biogeochemical reactions also affect borehole chemistry. While oxidation of sulfide minerals appears to release arsenic to ground water in zones within the aquifer, reduction of arsenic‐bearing iron (hydr)oxides is a likely mechanism of arsenic release to water having a long residence time in the well borehole.
SEEPAGE, a New MODFLOW DRAIN Package
Authors: Batelaan O. , De Smedt F. 
Published: December 2005

AbstractThe prediction of the location of ground water discharge areas is a key aspect for the protection and (re)development of ground water‐dependent wetlands. Ground water discharge areas can be simulated with MODFLOW using the DRAIN package by setting the drain level equal to the topography, while the conductance is mostly set to an arbitrary high value. However, conceptual and practical problems arise in the calculation of the ground water discharge by the DRAIN package as calculated water tables above the land surface, difficult parameterization of the conductance, and large water balance errors. To overcome these problems, a new SEEPAGE package for MODFLOW is proposed. The basic idea of this package is an adaptable constant head cell. It has a variable head, unless the ground water rises above the seepage level, in which case it has a constant head cell. The estimation of the ground water discharge location along a homogeneous, isotropic, linear sloping profile is used to verify the model and to compare it to the DRAIN solution. In an application to three basins in Belgium, it is shown that the SEEPAGE package can be used in combination with the DRAIN package in situations where an upper boundary for a free water table and additional resistance for drainage is required. It is clearly demonstrated that the identification and delineation of regional ground water discharge areas is more accurate using the SEEPAGE package.
Degradates Provide Insight to Spatial and Temporal Trends of Herbicides in Ground Water
Authors: Kolpin Dana W. , Schnoebelen Douglas J. , Thurman E. Michael 
Published: December 2005

AbstractSince 1995, a network of municipal wells in Iowa, representing all major aquifer types (alluvial, bedrock/karst region, glacial drift, bedrock/nonkarst region), has been repeatedly sampled for a broad suite of herbicide compounds yielding one of the most comprehensive statewide databases of such compounds currently available in the United States. This dataset is ideal for documenting the insight that herbicide degradates provide to the spatial and temporal distribution of herbicides in ground water.During 2001, 86 municipal wells in Iowa were sampled and analyzed for 21 herbicide parent compounds and 24 herbicide degradates. The frequency of detection increased from 17% when only herbicide parent compounds were considered to 53% when both herbicide parents and degradates were considered. Thus, the transport of herbicide compounds to ground water is substantially underestimated when herbicide degradates are not considered. A significant difference in the results among the major aquifer types was apparent only when both herbicide parent compounds and their degradates were considered. In addition, including herbicide degradates greatly improved the statistical relation to the age of the water being sampled. When herbicide parent compounds are considered, only 40% of the wells lacking a herbicide detection could be explained by the age of the water predating herbicide use. However, when herbicide degradates were also considered, 80% of the ground water samples lacking a detection could be explained by the age of the water predating herbicide use. Finally, a temporal pattern in alachlor concentrations in ground water could only be identified when alachlor degradates were considered.
A Program for Evaluating Dual‐Equilibrium Desorption Effects on Remediation
Authors: Chen Wei , Lakshmanan Kalyan , Kan Amy T. , Tomson Mason B. 
Published: December 2005

AbstractDesorption is one of the most critical processes affecting the effectiveness of soil and ground water remediation. None of the currently adopted desorption models can accurately quantify desorption of low‐hydrophobicity organic chemicals, and thus could potentially mislead remediation design and decision‐making. A recently developed dual‐equilibrium desorption (DED) model was found to be much more accurate in quantifying desorption. A screening‐level transport model, DED‐Transport, was developed to simulate the DED effect on behaviors of organic contaminant plumes during remediation. DED‐Transport requires only simple parameters, but is applicable to many remediation scenarios. DED‐Transport can be used as a decision‐support tool in site remediation to more precisely predict the time required for cleanup.
Geochemical Imaging of Flow Near an Artificial Recharge Facility, Orange County, California
Authors: Clark Jordan F. , Hudson G. Bryant , Davisson M. Lee , Woodside Greg , Herndon Roy 
Published: December 2005

AbstractCritical for the management of artificial recharge operations is detailed knowledge of ground water dynamics near spreading areas. Geochemical tracer techniques including stable isotopes of water, tritium/helium–3 (T/3He) dating, and deliberate gas tracer experiments are ideally suited for these investigations. These tracers were used to evaluate flow near an artificial recharge site in northern Orange County, California, where ∼2.5 × 108 m3 (200,000 acre‐feet) of water are recharged annually. T/3He ages show that most of the relatively shallow ground water within 3 km of the recharge facilities have apparent ages < 2 years; further downgradient apparent ages increase, reaching > 20 years at ∼6 km. Gas tracer experiments using sulfur hexafluoride and xenon isotopes were conducted from the Santa Ana River and two spreading basins. These tracers were followed in the ground water for more than two years, allowing subsurface flow patterns and flow times to be quantified. Results demonstrate that mean horizontal ground water velocities range from < 1 to > 4 km/year. The leading edges of the tracer patch moved at velocities about twice as fast as the center of mass. Leading edge velocities are important when considering the potential transport of microbes and other “time sensitive” contaminants and cannot be determined easily with other methods. T/3He apparent ages and tracer travel times agreed within the analytical uncertainty at 16 of 19 narrow screened monitoring wells. By combining these techniques, ground water flow was imaged with time scales on the order of weeks to decades.
Spatial Interpolation Methods for Nonstationary Plume Data
Authors: Reed Patrick M. , Ellsworth Timothy R. , Minsker Barbara S. 
Published: December 2005

AbstractPlume interpolation consists of estimating contaminant concentrations at unsampled locations using the available contaminant data surrounding those locations. The goal of ground water plume interpolation is to maximize the accuracy in estimating the spatial distribution of the contaminant plume given the data limitations associated with sparse monitoring networks with irregular geometries. Beyond data limitations, contaminant plume interpolation is a difficult task because contaminant concentration fields are highly heterogeneous, anisotropic, and nonstationary phenomena. This study provides a comprehensive performance analysis of six interpolation methods for scatter‐point concentration data, ranging in complexity from intrinsic kriging based on intrinsic random function theory to a traditional implementation of inverse‐distance weighting. High resolution simulation data of perchloroethylene (PCE) contamination in a highly heterogeneous alluvial aquifer were used to generate three test cases, which vary in the size and complexity of their contaminant plumes as well as the number of data available to support interpolation. Overall, the variability of PCE samples and preferential sampling controlled how well each of the interpolation schemes performed. Quantile kriging was the most robust of the interpolation methods, showing the least bias from both of these factors. This study provides guidance to practitioners balancing opposing theoretical perspectives, ease‐of‐implementation, and effectiveness when choosing a plume interpolation method.