bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ground Water Flow in a Fractured Carbonate Aquifer Inferred from Combined Hydrogeological and Geochemical Measurements
Authors: Zanini L. , Novakowski K.S. , Lapcevie P. , Bickerton G.S. , Voralek J. , Talbot C. 
Published: August 2005

AbstractA conceptual model for ground water flow is presented for a fractured Silurian dolomite in the Niagara Escarpment area of southern Ontario. Such a model is necessary to facilitate remedial efforts of a PCB‐contaminated site located in Smithville, Ontario. Both physical and chemical hydrogeological observations obtained from field investigations were used to deduce the structure of the ground water flow system in the fracture network. The field study was conducted using observations obtained from six bore‐holes drilled in the vicinity of the town of Smithville. The boreholes were diamond cored through the entire thickness of the dolomite formation (approximately 45 m), hydraulically tested using a 2 m packer spacing and then completed using multipacker casing strings. Measurements of hydraulic head were obtained on a weekly basis over a period of two years, and ground water from each borehole interval was collected for geochemical analyses for inorganic and isotopic composition. Transmissivity measurements indicate that the dolomite is divided into two ground water flow systems separated by an extensive unit of low transmissivity that is pervasive throughout the region. The upper flow system is characterized by water enriched in Mg2+ and SO42‐. Below the low transmissivity zone, ground water increases in salinity and is enriched in Ca2+ and SO42‐. Based on the geochemistry, the rate of ground water migration in the lower flow system is surmised to be much less than that in the upper system. Measurements of hydraulic head in conjunction with the results of the analyses of the environmental isotopes (δ18O and δ2H) suggest that ground water flow is mainly horizontal and likely governed by enlarged bedding plane fractures. The isotope geochemistry and topographical features further suggest that ground water recharge is occurring approximately 2 km to the north of Smithville.
Effect of Intra‐Population Variability on the Long‐Distance Transport of Bacteria
Authors: Bolster Carl H. , Mills Aaron L. , Hornberger George , Herman Janet 
Published: August 2005

AbstractRecent experimental work has suggested that within a single bacterial strain there may exist two distinet subpopulations, each with its own sticking efficiency. We performed a sensitivity analysis using an advection‐dispersion model to elucidate the effects of an influent suspension of bacteria composed of two subpopulations, each with distinet sticking efficiencies (dual‐alpha population), on the removal and transport of bacteria over distances of tens of meters. In the simulations, we assumed idealized conditions (i.e., one‐dimensional transport through physically and geochemically homogeneous porous media). Results demonstrate that in cases where a small fraction of the influent bacteria have surface characteristics favorable for transport, the prediction of field‐scale transport based on laboratory‐derived parameters from short column experiments will tend to overestimate substantially the amount of bacterial removal. Results demonstrate the importance of a priori knowledge of the presence of intra‐population variability when predicting the field‐scale transport of bacteria.
Analysis of Transient Data from Infiltrometer Tests in Fine‐Grained Soils
Authors: Guyonnet Dominique , Amraoui Nadia , Kara Reda 
Published: August 2005

AbstractData collected during ring infiltrometer tests are often analyzed while assuming either that the effect of gravity is negligible (early‐time, transient data) or that it is dominant (late‐time, steady‐state data). In this paper, an equation is proposed for inter‐preting both early‐time and late‐time data measured during infiltration tests under falling head conditions. It is shown that the method used by previous authors for interpreting both early‐time data is a special case of the proposed equation. The equation is applied to data collected during tests performed in fine‐grained soils, and results are discussed. The analysis suggests that to assume a priori values of the soil sorptive number, as indicated in the literature for various soils, may in some cases lead to severely underes‐timated values of the saturated hydraulic conductivity. Conversely, in low permeability soils, to assume steady‐state gravity drainage may lead to order of magnitude overestimates of the saturated hydraulic conductivity. A dimensionless analysis provides characteristic times that correspond either to the duration of the log‐log half slope displayed by early‐time data or to the log‐log unit slope characteristic of late‐time data.
Degradation of TCE with Iron: The Role of Competing Chromate and Nitrate Reduction
Authors: Schlicker Oliver , Ebert Markus , Fruth Margit , Weidner Markus , Wüst Wolfgang , Dahmke Andreas 
Published: August 2005

AbstractThis study evaluates the potential of using granular iron metal for the abiotic removal of the organic ground water pollutant trichloroethene (TCE) in the presence of the common inorganic co‐contaminants chromate and nitrate, respectively. Our long‐term column experiments indicate a competitive process between TCE dechlorination and reductive transformation of chromate and nitrate, which is reflected in a significantly delayed onset of TCE dechlorination. Delay times and therefore the ranges of the nonreactive flowpaths increased with increasing experimental duration, resulting in a migration of the contaminants through the iron metal treatment zone. The present investigation also indicates that the calculated migration rates of TCE and the added cocontaminants chromate and nitrate are linearly related to the initial content of the cocontaminants. With an average pore water velocity of 0.6 m/d and a surface area concentration of 0.55 m2/mL in the column, the calculated migration rates varled between 0.10 cm/d and 5.86 cm/d. The particular similarity between the values of TCE migration and the migration of the strong oxidants chromate and nitrate and the long‐term steady state of the TCE dechlorination in the absence of the chromate and nitrate indicates that these competitive transformations are the driving force for the gradual passivation of the granular iron due to the buildup of an electrically insulating Fe(III)‐oxyhydroxide. Based on these passivation processes, general formulae were developed that allow a simplified approximation of breakthrough times for the contaminants TCE, chromate, and nitrate.
How the Kd Approach Undermines Ground Water Cleanup
Authors: Bethke Craig M. , Brady Pathick V. 
Published: August 2005

AbstractEnvironmental scientists have long appreciated that the distribution coefficient (the “Kd” or “constant Kd”) approach predicts the partitioning of heavy metals between sediment and ground water inaccurately; nonetheless, transport models applied to problems of environmental protection and ground water remediation almost invariably employ this technique. To examine the consequences of this practice, we consider transport in one dimension of Pb and other heavy metals through an aquifer containing hydrous ferric oxide, into which many heavy metals sorb strongly. We compare the predictions of models calculated using the Kd approach to those given by surface complexation theory, which is more realistic physically and chemically. The two modeling techniques give qualitatively differing results that lead to divergent cleanup Strategies. The results for surface complexation theory show that water flushing is ineffective at displacing Pb from the sorbing surface. The effluent from such treatment contains a persistent “tall” of small but significant levels of contamination. Subsurface zones of Pb contamination, furthermore, do not migrate rapidly or far in flowing ground water. These results stand in sharp contrast to the predictions of models constructed using the Kd approach, yet are consistent with experience in the laboratory and field.
On Capture Width and Capture Zone Gaps in Multiple‐Well Systems
Authors: Erdmann John B. 
Published: August 2005

AbstractA barrier well line's capture width along its alignment is shown to depend only on total system flow rate QT, and aquifer back‐ground flow rate per unit width Qo (prepumping gradient times transmissivity) under idealized horizontal flow: Irrespective of number of wells, the capture width is QT/2Q0, as for a hypothetical single well with flow rate QT. This result applies even to barrier lines with irregular well spacings and flow rates–and, in fact, to the capture width through the center of any pumping configuration that is symmetrical respecting a line perpendicular to uniform background flow. A flow‐perpendicular line of regularly spaced, equal wells (“regular barrier line”) has the same capture width along its alignment as an identical well line parallel to background flow has through its center. In the general symmetrical case, the center capture width remains QT/2Q0 whether transverse well spacings are large (allowing contaminated ground water to escape through capture zone gaps), critical (with incipient gaps), or safely small. For design reference, critical spacings derived for regular barrier lines of N wells with N through 100 and N→∞ vary from Q/πQ0 (N = 2, previously known) to Q/2Q0 (N→∞), where Q is each well's flow rate. Incipient gaps at critical spacing occur always between the two center wells, or the center well and two adjacent wells. Spacings substantially smaller than critical are recommended for contaminant capture. Designs are illustrated that preclude capture zone gaps.
A Field Technique for Estimating Aquifer Parameters Using Flow Log Data
Authors: Paillet Frederick L. 
Published: August 2005

AbstractA numerical model is used to predict flow along intervals between producing zones in open boreholes for comparison with measurements of borehole flow. The model gives flow under quasi‐steady conditions as a function of the transmissivity and hydraulic head in an arbitrary number of zones communicating with each other along open boreholes. The theory shows that the amount of inflow to or outflow from the borehole under any one flow condition may not indicate relative zone transmissivity. A unique inversion for both hydraulic‐head and transmissivity values is possible if flow is measured under two different conditions such as ambient and quasi‐steady pumping, and if the difference in open‐borehole water level between the two flow conditions is measured. The technique is shown to give useful estimates of water levels and transmissivities of two or more water‐producing zones intersecting a single interval of open borehole under typical field conditions. Although the modeling technique involves some approximation, the principle limit on the accuracy of the method under field conditions is the measurement error in the flow log data. Flow measurements and pumping conditions are usually adjusted so that transmissivity estimates are most accurate for the most transmissive zones, and relative measurement error is proportionately larger for less transmissive zones. The most effective general application of the borehole‐flow model results when the data are fit to models that systematically include more production zones of progressively smaller transmissivity values until model results show that all accuracy in the data set is exhausted.
A Probabilistic Method for Estimating Monitoring Point Density for Containment System Leak Detection
Authors: Ross Randall R. , Vieux Baxter E. 
Published: August 2005

AbstractThe use of physical and hydraulic containment systems for the isolation of contaminated ground water and aquifer materials associated with hazardous waste sites has increased during the last decade. The existing methodologies for monitoring and evaluating leakage from hazardous waste containment systems rely primarily on limited hydraulic head data. The number of hydraulic head monitoring points available at most sites employing physical containment systems may be insufficient to identify significant leaks from the systems. A probabilistic approach for evaluating the performance of containment systems, based on estimations of apparent leakage rates, is used to introduce a methodology for determining the minimum number of monitoring points necessary to identify the hydraulic signature of leakage from a containment system. The probabilistic method is based on the principles of geometric probability. The method is demonstrated using three‐dimensional ground water flow modeling results of leakage through a vertical barrier. The results indicate that the monitoring point spacing used at many hazardous waste sites likely is inadequate to detect the hydraulic signatures of all but the largest leaks.
Regulation of Injected Ground Water Tracers
Authors: Holmbeck‐Pelham Skelly A. , Rasmussen Todd C. , Fowler Laurie A. 
Published: August 2005

AbstractGround water tracer tests are routinely performed to estimate aquifer flow and transport properties, including the determination of well capture zones, hydrogeologic parameters, and contaminant travel times. Investigators may be unaware of tracer test reporting requirements and may fail to notify their regulatory agency prior to conducting tracer tests. The injection of tracers falls under the jurisdiction of the federal Underground Injection Control (UIC) program, which regulates the introduction of substances into underground sources of drinking water as part of the Safe Drinking Water Act. The UIC program is administered by the U.S. Environmental Protection Agency (EPA) and by states with EPA‐approved programs. The federal UIC program requires that tracer tests must not endanger underground sources of drinking water, and all tracer tests must be reported prior to injection. We contacted the UIC program administrator for every state in early 1997. Some states report having more stringent requirements, while some states do not meet minimum federal requirements. Although the primary responsibility for ground water tracer selection and use rests on the investigator, national guidance is required to assure compliance with the UIC program. To assist investigators, we present acceptable tracers that have been identified by two states, Nevada and South Carolina, that require no further regulatory review.
Bimodal Transport of a Waste Water Plume Injected into Saline Ground Water of the Florida Keys
Authors: Dillon Kevin S. , Corbett D. Reide , Chanton Jeffrey P. , Burnett William C. , Kump Lee 
Published: August 2005

AbstractTwo experiments were conducted on Long Key, Florida, United States, to examine the fate of waste water following sewage disposal in 10 to 30 m deep injection wells. This waste disposal practice introduces extraordinary amounts of nutrients into the ground water of the Florida Keys. In these experiments, artificial ground water tracers, sulfur hexafluoride (SF6) and radioiodine (131I) were used to determine transport rates and directions of soluble nonreactive substances injected into the saline ground water underlying the Keys. Two types of transport were observed: (1) rapid flow (0.20 to 2.20 m/hr) presumably due to the many conduits present in the limestone; and (2) slower flow (less than 0.003 to 0.14 m/hr) associated with the limestone's primary porosity. Vertical flow was comparable to horizontal flow due to either the density‐driven buoyancy of the waste water plume or to preferential flowpaths that allow upward advection or combination of both. These experiments showed that conservative artificial tracers injected into the subsurface reach surface water in a matter of days and can remain in the immediate vicinity of the injection well for several months.
In Situ Ground Water Remediation Using the Trench and Gate System
Authors: Bowles Marc W. , Bentley L. R. , Hoyne B. , Thomas D.A. 
Published: August 2005

AbstractThe trench and gate remediation system is a funnel and gate design modified for installation in tills and other low permeability sediments. Modifications include the addition of high hydraulic conductivity trenches along the upgradient side of the funnel walls and a discharge reinfiltration gallery downgradient from the treatment gate. Preferential ground water flow through the high permeability trenches and reinfiltration gallery prevents mounding, which otherwise forces flow beneath and around funnel walls. The resultant capture zone is larger, both horizontally and vertically, than the cross‐sectional funnel area and is significantly larger than the capture zone of a similar funnel and gate system. The system constitutes an economical, in situ, long‐term contaminant plume capture and treatment method. In effectiveness and cost, the trench and gate system compares favorably with, or outper‐forms, other remediation systems in near‐surface, low permeability dissolved contaminant scenarios. A prototype trench and gate system was installed at the East Garrington Gas Plant, Alberta, Canada, in 1995. The installation demonstrated the effectiveness of the concept, and the system has successfully prevented off‐site migration of dissolved hydrocarbon contaminants.
Design of Soil Vapor Extraction Systems Under Conditions of Uncertainty
Authors: Barnes David L. , McWhorter David B. 
Published: August 2005

AbstractThis paper proposes a risk‐cost approach for the design of soil vapor extraction (SVE) systems that takes into account uncertainties in the soil properties. The proposed design methodology consists of three separate models: a soil‐gas flow and vapor transport model, a parameter uncertainty model, and a decision model based on a risk‐cost objective function. A description of each of these models is provided and an example using a hypothetical scenario is given to illustrate the use of the methodology. Results from the example show that the methodology is suited for determining the number, location, and spacing of SVE extraction wells. The methodology can also be used to size the vacuum blower to be used and to predict when the SVE system should be shut off.
Simple Analytical Equations for Estimating Ground Water Inflow to a Mine Pit
Authors: Marinelli Fred , Niccoli Walter L. 
Published: August 2005

AbstractSteady‐state analytical solutions are presented for estimating the ground water inflow rate to a mine pit that may contain a pit lake of finite depth. The solutions consider (1) the effect of decreased saturated thickness near the pit walls; (2) distributed recharge to the water table; and (3) upward flow through the pit bottom. While the solutions are not appropriate for all hydrogeologic situations, they are relevant to conditions encountered at many mine sites. An example calculation is presented for an actual mine pit containing a pit lake. The analytical solutions provide an estimated ground water inflow rate that is similar to the rate determined independently from a detailed water balance study.
Hydraulic Gradient Comparison Method to Estimate Aquifer Hydraulic Parameters Under Steady‐State Conditions
Authors: Guo Xiaoniu , Zhang Chuan‐Mian 
Published: August 2005

AbstractThe hydraulic gradient comparison method is an inverse method for estimation of aquifer hydraulic conductivity (or trans‐missivity) and boundary conductance for a ground water flow model under steady‐state conditions. This method, following formal optimization techniques, defines its objective function to minimize differences between interpreted (observed) and simulated hydraulic gradients, which results in minimization of differences between observed and simulated hydraulic heads. The key features of this method are that (1) the derived optimality conditions have an explicit form with a clear hydrology concept that is con‐sistent with Darcy's law, and (2) the derived optimality conditions are spatially independent as they are a function of only local hydraulic conductivity and local hydraulic gradient. This second feature allows a multidimensional optimization problem to be solved by many one‐dimensional optimization procedures simultaneously, which results in a substantial reduction in computation time. The results of the numerical performance testing on a heterogeneous hypothetical case confirm that minimizing gradient residuals in the entire model domain leads to minimizing head residuals. Application of the method in real‐world projects requires rigorous conceptual model development, use of a global calibration target, and an iterative calibration proess. The conceptual model development includes interpretation of a potentiometric surface and estimation of other hydrologic parameters. This method has been applied to a wide range of real‐world modeling projects, including the Rocky Mountain Arsenal and Rocky Flats sites in Colorado, which demonstrates that the method is efficient and practical.
Gravel‐Corrected Kd Values
Authors: Kaplan Daniel I. , Kutnyakov Igor V. , Gamerdinger Amy P. , Serne R. Jeff , Parker Kent E. 
Published: August 2005

AbstractStandard measurements of solute sorption to sediments are typically made on the <2 mm sediment fraction. This fraction is used by researchers to standardize the method and to ease experimental protocol so that large labware is not required to accommodate the gravel fraction (>2 mm particles). Since sorption is a phenomenon directly related to surface area, sorption measurements based on the <2 mm fraction would be expected to overestimate actual whole‐sediment values for sediments containing gravel. This inaccuracy is a problem for ground water contaminant transport modelers who use laboratory‐derived sorption values, typically expressed as a distribution coefficients (Kd), to calculate the retardation factor (Rf), a parameter that accounts for solute‐sediment chemical interactions. The objectives of this laboratory study were to quantify the effect of gravel on strontium Kd and Rf values and to develop an empirical method to calculate gravel‐corrected Kdgcvalues for the study site (Hanford Site in Richland, Washington). Three gravel corrections, Kd values, were evaluated: a correction based on the assumption that the gravel simply diluted the Kd<2mmand had no sorption capacity (Kdgc,g=0), a correction based on the assumption that the Kd of the intact sediment (Kdtotwas a composite of the Kd<2mmand the Kd>2mm(Kdgc,g = x), and a correction based on surface area (Kdgc,surf). On average, Kd<2mmtended to overestimate Kdtotby 28% to 47%; Kdgc,g = xoverestimated Kdtotby only 3% to 5%; and Kdgc,g = 0and Kdgc,surfunderestimated Kdtotby 10% to 39%. Kdgc,g = xprovided the best estimate of actual values (Kdtot); however, Kdgc,g = 0was appreciably easier to acquire. Although other contaminants will likely have different gravel‐correction values, these results have important implications regarding the traditional approach to modeling contaminant transport which uses Kd<2mmvalues. Such calculations may overestimate the tendency of gravel‐containing sediments to retard contaminant migration.