bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lab and Field Measurements of the Hydraulic Conductivity of Clayey Silts
Authors: Döll Petra , Schneider Wilfried 
Published: August 2005

AbstractVarious lab and field experiments were conducted to determine the vertical hydraulic conductivity of two highly compressible, organic‐rich clayey silts (Holocene marsh sediments Klei and gyttja). Constant‐head permeameter tests in the lab show an increase in measured hydraulic conductivity with sample size by a factor of 5 (Klei) and 20 (gyttja). On a field scale, six different methods were tested: (1) evaluation of the propagation of the tidal wave from the aquifer into the silts; (2) aquitard reaction test; (3) evaluation of aquifer drawdown; (4) slug test; (5) evaluation of vertical profiles of measured organic contaminant concentrations in the silts; (6) evaluation of benzene concentrations measured in aquifer wells. Porous cup pressure cells instead of piezometers must be used to measure relatively fast changes of hydraulic head in these low‐permeability media. Comparison of the results is hampered by spatial heterogeneity.
A Method for Passive Release of Solutes from an Unpumped Well
Authors: Wilson Ryan D. , Mackay Douglas M. 
Published: August 2005

AbstractA new method was developed for releasing dissolved solutes into ground water which has application in both academic studies and practical efforts to stimulate in situ bioremediation, introduce chemical reactants, or understand flow and transport properties. The method involves the diffusion of solutes out of inexpensive, simple emitter devices which are installed in large diameter wells. Mass flux from an emitter depends on the geometry of the emitter, ground‐water flow rate, the imposed concentration gradient from the stock solution inside the emitter, and the diffusion coefficient of the solute through the emitter material. Diffusion coefficients are constants of a solute/tubing pair, and are established in simple experiments. If ground‐water flow rates and diffusion coefficients are known, emitter geometry and stock solution concentration can be tailored for a wide range of performance requirements.In laboratory experiments, benzene was released at or near 1.3 mg/1 for a total of 31 days, TCE for 17 days at approximately 4.5 mg/1, and bromide for 23 days at 667 mg/1. The emitted concentration of a wide range of solutes can be stabilized for much longer periods of time once the mass flux in the flow‐through system reaches steady‐state, provided the concentration gradient is maintained.A simple computer model was written to aid in the design of source emitters. The model was used to match diffusion coefficients to data for three solute‐tubing combinations. Once the diffusion coefficient of a given solute in a given type of tubing is determined from experimental data by curve‐matching, the model can be used in a predictive capacity. A second TCE release test showed that the diffusion coefficient calibrated from the model can be used to predict the steady‐state release concentration of TCE under different conditions.Simple two‐dimensional transport modeling suggests that a relatively uniform plume of solutes may be generated by emitters placed in wells spaced close together. The uniform introduction of nutrients and oxygen by this passive method may encourage more efficient in situ remediation, and in some situations, save time and money.
Relation of Ground‐Water Quality to Land Use on Long Island, New York
Authors: Eckhardt David A. V. , Stackelberg Paul E. 
Published: August 2005

AbstractWater‐quality data from 90 monitoring wells screened within 50 feet of the water table in the unconfined upper glacial aquifer beneath five areas of differing land use in Nassau and Suffolk Counties, Long Island, were compared to assess the effects of land use on ground‐water quality. The areas, which range from 22 to 44 square miles, represent suburban land sewered more than 22 years at the time of the study (long‐term sewered), suburban land sewered less than 8 years (recently sewered), suburban land without a regional sewer system, agricultural land, and undeveloped (forested) land. Comparison of water‐quality data from the 90 wells indicated that samples from the undeveloped area had the lowest and smallest range in concentrations of several human‐derived constituents, such as nitrate, alkalinity, boron, synthetic solvents, and pesticides. Concentrations of these constituents in samples from the three suburban areas and the agricultural area generally were intermediate to high and had the widest variation.Maximum‐likelihood logistic regression analysis of explanatory variables that characterize the type of land use and population density within a 1/2‐mile radius of each of the 90 wells was used to develop predictive equations for contaminant occurrence in ground water within 50 feet of the water table. Two logistic regression equations for the 90 monitoring wells were compared with equations developed independently from ground‐water quality data at more than 240 other wells throughout Nassau and Suffolk Counties to evaluate the predictive value of the land‐use variables at the larger two‐county scale. The results demonstrate that the population density and amount of agricultural, commercial, and high‐ and medium‐density residential land within specified areas around wells can be reliable predictors of contaminant presence. The strength of the correlations supports the premise that land use affects the quality of water in water‐table aquifers overlain by highly permeable material because land use commonly determines the types and amounts of chemicals introduced at land surface. When coupled with GIS technology and accurate, detailed land‐use and water‐quality information, the methods and results of this study can be useful to local planning boards in evaluation of potential effects of development on ground‐water quality. The methods can also be useful to hydrologists in the analysis and design of ground‐water‐monitoring networks.
An Iterative Cokriging‐Like Technique for Ground‐Water Flow Modeling
Authors: Yeh T.‐C. Jim , Gutjahr Allan L. , Jin Minghui 
Published: August 2005

AbstractThe importance of field heterogeneities in ground‐water pollution problems has been widely recognized during the last few decades. To address the impact of field heterogeneities on ground‐water flow and solute transport, many different stochastic methods have been developed. Among all these stochastic methods kriging is the most popular one used by many practitioners to interpolate and extrapolate measured transmissivity data. However, hydraulic head measurements are generally more abundant than transmissivity data. Therefore, the cokriging technique which utilizes both the head and transmissivity measurements to estimate transmissivity and/or hydraulic head distributions has also received much attention in recent years.Classical cokriging relies on a linear predictor approach and uses covariance and cross covariance functions derived from a first‐order approximation. Consequently, it often results in head and transmissivity fields that can produce unacceptable velocity distributions. In this paper, we develop an iterative method which combines classical cokriging and a numerical flow model to obtain optimum estimates of transmissivity and head distributions and to alleviate the limitations of classical cokriging. Through several numerical examples, we demonstrate that this method is superior to the classical cokriging method in terms of producing mass conservative velocity fields. In addition, results of the study also indicate that hydraulic head measurements can improve for our prediction of ground‐water flow directions and paths in aquifers significantly.
Wellhead Protection Area Delineation Using the Analytic Element Method of Ground‐Water Modeling
Authors: Wuolo Ray W. , Dahlstrom David J. , Fairbrother Mark D. 
Published: August 2005

AbstractThe Analytic Element Method (AEM) of ground‐water modeling was used to delineate wellhead protection areas (WHPAs) for existing and proposed wells in Brooklyn Park, Minnesota by simulating steady‐state flow in two aquifers: the water‐table aquifer (in glacial outwash) and the Franconia‐Ironton‐Galesville bedrock aquifer. Ground‐water time‐of‐travel was used as the delineation criterion. Ground‐water flow is significantly affected by a buried bedrock valley underneath the City. Transmissivity values for the water‐table aquifer are much higher in the buried bedrock valley and the hydraulic connection between the water‐table and the Franconia‐Ironton‐Galesville aquifers is more pronounced. The Analytic Element Method does not utilize a grid mesh and incorporates both regional‐scale and more detailed, local‐scale features in the same solution. This feature of AEM provided for the simulation of the city wells in the context of the regional flow field. Separate models, encompassing an area of approximately 500 square miles, were developed and calibrated for each aquifer using the Single Layer Analytic Element Model (SLAEM) and then linked together using the Multi‐Layer Analytic Element Model (MLAEM). Ground‐water travel‐time zones and WHPAs were delineated for the existing wells using reverse particle tracking.
In Situ Denitrification of Septic‐System Nitrate Using Reactive Porous Media Barriers: Field Trials
Authors: Robertson W. D. , Cherry J. A. 
Published: August 2005

AbstractA new alternative septic‐system design is presented utilizing reactive porous media barriers for passive in situ attenuation of NO3−. The reactive material consists of solid organic carbon (sawdust) which promotes NO3‐ attenuation by heterotrophic denitrification. Four field trials are discussed demonstrating two barrier configurations: as a horizontal layer positioned in the vadose zone below a conventional septic‐system infiltration bed and as a vertical wall intercepting a horizontally flowing downgradient plume. During one year of operation both barrier configurations have been successful in substantial attenuation (60 to 100%) of input NO3‐ levels of up to 125 mg/1 as N. The horizontal layer configuration can be readily installed during the construction of new infiltration beds, whereas the vertical wall configuration may be more appropriate for retrofitting existing septic systems where NO3‐ contamination has already occurred. The layer configuration allows the flexibility of constructing the barrier in the vadose zone by using coarse silt or fine sand matrix material that has the ability to remain tension‐saturated, and thus anaerobic, even when positioned above the water table.Advantages of the barrier system are that it is simple to construct, no surface structures or additional plumbing are necessary, and treatment is passive requiring no energy consumption and little or no maintenance. Mass balance calculations and preliminary results suggest that conveniently sized barriers have the potential to last for decades without replenishment of the reactive material.
Evidence for Enhanced Mineral Dissolution in Organic Acid‐Rich Shallow Ground Water
Authors: McMahon Peter B. , Vroblesky Don A. , Bradley Paul M. , Chapelle Francis H. , Gullett Cheryl D. 
Published: August 2005

AbstractTotal concentrations of formate, acetate, and isobutyrate varied from less than 5 to greater than 9,000 μmol/l over distances of < 3 m in ground water from a shallow hydrocarbon contaminated aquifer. Laboratory incubations of aquifer material indicate that organic acid concentrations were dependent on the amount of hydrocarbon loading in the sediment and the relative rates of microbial organic acid production and consumption. In heavily contaminated sediments, production greatly exceeded consumption and organic acid concentrations increased. In lightly contaminated sediments rates were essentially equal and organic acid concentrations remained low. Concentrations of dissolved calcium, magnesium, and iron generally were one to two orders of magnitude higher in organic acid‐rich ground water than in ground water having low organic acid concentrations. Carbonate and Fe(III)‐oxyhydroxide minerals were the likely sources of these elements. Similarly, concentrations of dissolved silica, derived from quartz and k‐feldspar, were higher in organic acid‐rich ground water than in other waters. The positive relation (r = 0.60, p < .05, n = 16) between concentrations of silica and organic acids suggests that the microbially mediated buildup of organic acids in ground water enhanced quartz/k‐feldspar dissolution in the aquifer, although it was not the only factor influencing their dissolution. A model that included organic acid microequivalents normalized by cation microequivalents significantly strengthened the correlation (r = 0.79, p < .001, n = 16) between dissolved silica and organic acid concentrations, indicating that competition between silica and cations for complexation sites on organic acids also influenced quartz/k‐feldspar dissolution. Physical evidence for enhanced mineral dissolution in organic acid‐rich waters included scanning electron microscopy images of highly corroded quartz and k‐feldspar grains from portions of the aquifer containing organic acid‐rich ground water. Microporosity generated in hydrocarbon contaminated sediments may adversely affect remediation efforts that depend on the efficient injection of electron acceptors into an aquifer or on the recovery of solutes from an aquifer.
Effects of Agriculture on Ground‐Water Quality in Five Regions of the United States
Authors: Hamilton Pixie A. , Helsel Dennis R. 
Published: August 2005

AbstractWater‐quality conditions in surficial unconsolidated aquifers were assessed in five agricultural regions in the United States. The assessment covers the Delmarva Peninsula, and parts of Long Island, Connecticut, Kansas, and Nebraska, and is based on water‐quality and ancillary data collected during the 1980s. Concentrations of nitrate in ground water in these areas have increased because of applications of commercial fertilizers and manure. Nitrate concentrations exceed the maximum contaminant level (MCL) for drinking water of 10 milligrams per liter as nitrogen established by the U.S. Environmental Protection Agency in 12 to 46 percent of the wells sampled in the agricultural regions. Concentrations of nitrate are elevated within the upper 100 to 200 feet of the surficial aquifers. Permeable and sandy deposits that generally underlie the agricultural areas provide favorable conditions for vertical leaching of nitrate to relatively deep parts of the aquifers. The persistence of nitrate at such depths is attributed to aerobic conditions along ground‐water‐flow paths. Concentrations of nitrate are greatest in areas that are heavily irrigated or areas that are underlain by well‐drained sediments; more fertilizer is typically applied on land with well‐drained sediments than on poorly drained sediments because well‐drained sediments have a low organic‐matter content and low moisture capacity. Concentrations of other inorganic constituents related to agriculture, such as potassium and chloride from potash fertilizers, and calcium and magnesium from liming, also are significantly elevated in ground water beneath the agricultural areas. These constituents together impart a distinctive agricultural‐chemical trademark to the ground water, different from natural water.
Applying Higher Order DIRK Time Steps to the “Modified Picard” Method
Authors: Baker Donald L. 
Published: August 2005

AbstractThe “modified Picard” iteration method, which offers global mass conservation, can also be described as a form of Newton's iteration with lagged nonlinear coefficients. It converges to a time step with first‐order discretization error. This paper applies second‐ and third‐order diagonally implicit Runge Kutta (DIRK) time steps to the modified Picard method in one example. It demonstrates improvements over the first‐order time step in rms error and error‐times‐effort model quality by factors ranging from two to over two orders of magnitude, showing that the “modified Picard” and DIRK methods are compatible.
Spreadsheet Modeling of Slug Tests Using the van der Kamp Method
Authors: Wylie Allan , Magnuson Swen 
Published: August 2005

AbstractSlug testing is frequently employed to calculate aquifer transmissivity and hydraulic conductivity. The van der Kamp technique for interpreting slug test data which experience force‐free water level oscillations is not routinely employed because it requires adjusting equations to match the observed well response data. This adjustment can be rapid and convenient when a commercial spreadsheet is employed.
Darcian Weighted Interblock Conductivity Means for Vertical Unsaturated Flow
Authors: Baker Donald L. 
Published: August 2005

AbstractThe true Darcian interblock conductivity mean for vertical unsaturated flow, Kv, is derived from Darcy's law, q/Ks = Kv (dH/dx), and the assumption that flow is constant between grid centers. It can be expressed as Kv = (Δx Kx −Δp Kh)/(Δx −Δp), where Kx is the gravity flow mean, Kh is the capillary flow mean, and H =×− p (total head = elevation ‐matric suction). Plotting contours of Kx, Kh, and Kv in the plane of adjacent grid center conductivities, (kr1, kr2), shows that a component of Kx behaves like a simple weighted mean, Kw = w kr2 + (1 − w) krl, where w is a nonlinear, monotonic function of the grid separation, Δx. Results from a mass‐conservative model of infiltration into dry sand are compared for substituting: (1) the arithmetic mean, Ka = (krl + kr2)/2, for Kv, (2) Kw for Kv, (3) Ka for Kx in Kv (called Km), and (4) Kw for Kx in Kv (called Kmw), over a range of the ratio of Δx to the conductivity displacement pressure, pk, from 0.01 to 1.6. The simulation for Δx/pk = 0.002 is taken to be the exact solution. Kw and Kmw reduce the gross cumulative net inflow error generated with Ka and Km from 3.84 to 8.84 times. Kmw performs consistently better in terms of gross water content distribution error by up to a factor of three.
Landfills in New York City: 1844–1994
Authors: Walsh Daniel C. , LaFleur Robert G. 
Published: August 2005

AbstractHistoric topographic maps are reviewed to locate landfills constructed within New York City during four time intervals between 1844 and 1994. A total of 184.75 km2 (45,650 acres) of landfill are identified (approximately 20% of the study area). Data are not available to determine the fill composition at most sites but literature sources indicate that municipal solid waste (MSW) has been an important source of fill since at least 1891. Qualitative temporal trends in the spatial distribution of landfills and the composition and thickness of MSW landfills are observed. The oldest landfills are clustered in the vicinity of the early urban center (southern New York County) but expand in spatial distribution after the turn of this century. Logs of borings through 10 MSW landfills show that waste landfills built prior to the mid‐1950s contain abundant ash (coal ash is common in the oldest landfills) and are relatively thin (3‐7 m) with no topographic mounding. In MSW landfills built since that time, uncombusted organic matter is abundant, thicknesses increase greatly (16–27 m), and pronounced topographic mounding is observed. Most landfills identified in this study were built on tidal wetlands. Fine‐grained wetland deposits underlying the landfills and close proximity to large surface‐water bodies favor lateral transport of leachate from MSW landfills in shallow ground water and local discharge to surface water. The wide distribution of historic landfills and common use of MSW for fill indicates that these sites should be considered in investigations of ground water, surface water, and sediment quality in New York City and other urban areas where extensive historic landfilling has occurred.
An Investigation of Saturation‐Capillary Pressure Relations in Two‐ and Three‐Fluid Systems for Several NAPLS in Different Porous Media
Authors: Busby Robert D. , Lenhard Robert J. , Rolston Dennis E. 
Published: August 2005

AbstractLack of constitutive data has impeded efforts to model the subsurface transport of organic‐liquid contaminants. To help fill this need, functional relationships between fluid saturations and capillary pressures were obtained using a unique fluid‐retention cell. The functional relationships between water saturations and NAPL‐water capillary pressures, and between total‐liquid saturations and air‐NAPL capillary presures in two‐ and three‐fluid phase systems were measured directly during monotonic drainage of a fine quartz sand and a nonswelling loam soil. Additionally, measurements were made between water saturations and air‐water capillary pressures for an air‐water fluid system in both porous media. The NAPLs investigated were Soltrol 170®, toluene, and trichloroethylene (TCE). Following the measurements, the two‐ and three‐fluid retention relations were compared to test the validity of extending two‐phase saturation‐pressure (S‐P) relations to three‐fluid systems. Good agreement was observed between the two‐ and three‐fluid data for Soltrol 170®, toluene, and TCE in both porous media. An S‐P scaling format for two‐ and three‐phase systems was also evaluated. Results indicate that a single multiphase retention function is suitable for describing two‐ and three‐phase S‐P relations in similar porous media; however, it is unclear whether the scaling factors can be predicted a priori from ratios of interfacial tensions.
Laboratory Investigation of Buoyancy‐Induced Flow (Plume Sinking) During Two‐Well Tracer Tests
Authors: Istok Jonathan D. , Humphrey Mark D. 
Published: August 2005

AbstractThe occurrence of buoyancy‐induced vertical flow (sinking) of a bromide (Br−) tracer plume at small injection concentrations is investigated in transport experiments conducted in a large‐scale physical aquifer model containing a homogeneous and isotropic sand pack. Two‐well tracer tests are conducted using Br− at concentrations ranging from 50 to 1000 mg/1, corresponding to relative densities between 7.5 × 10−5 and 1.5 × 10−3. Analysis of three‐dimensional solute concentration data indicates that the center of mass of the Br− plume was displaced downward as the denser tracer solution sank through the sand pack. Plume sinking occurred at all solute concentrations investigated; the magnitude of the vertical displacement increased with increasing Br− concentration of the injected tracer solution. The dynamic collapse of the Br−plume caused by buoyancy forces resulted in increased apparent transverse and longitudinal dispersivities. The results suggest that the possibility of buoyancy‐induced flow must be considered when interpreting tracer tests conducted with anion concentrations as low as 50 mg/1. The occurrence of buoyancy‐induced flows at such low relative densities also suggest that the phenomenon may be more widespread than is generally recognized.
A Modified Gauss‐Newton Method for Aquifer Parameter Identification
Authors: Li Jingsheng , Elsworth Derek 
Published: August 2005

AbstractThe accuracy of parameter estimation procedures is evaluated for a modified Gauss‐Newton method applied to transient ground‐water flow. Three different approaches of evaluating the sensitivity coefficient matrix are examined, including influence coefficient, sensitivity equation, and variational approaches. The performance of each of the techniques is evaluated by applying a common synthetic data set. The latter two techniques are shown to perform with least sensitivity to starting parameters and extraneous sampling noise. Where either random or systematic noise is added to the time‐series data set, the resulting predictions become increasingly more sensitive to the form of the starting transmissivity vector. It is concluded that the modified Gauss‐Newton method is attractive because of its simplicity, high rate of convergence, and modest computational demands, especially when the number of the parameters to be identified is not large.