bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elucidating Ground‐Water Flow Paths in a Desert Terrane by Geochemical Methods
Authors: Fritz Steven J. , Lopez Hector J. , Wilson Michael P. 
Published: August 2005

AbstractDelineating ground‐water flow paths is difficult to accomplish in desert terranes because paucity of wells and boreholes yields little data to construct hydrologic interpretations based upon physical parameters. This is especially true in the Big Bend National Park where, in a study area encompassing over 500 km2, there are only four wells and six perennial springs. These wells and springs were sampled and analyzed for major‐element chemistry as well as for stable and naturally occurring radioactive isotopes to identify sources of recharge for the springs which discharge along banks of arroyos incised in alluvial pediment lying about 900 meters below the uplands of the Chisos Mountains.The springs recharge could be from three sources: (1) infiltration of precipitation falling on the desert floor to discharge at nearby arroyos; (2) infiltration of water at the onlap of the alluvial fan with the crystalline rock of the Chisos uplands and subsequent flow within the fan toward lowland springs; and (3) upward migration of deep‐seated water. Of these, the third scenario is least compatible with respect to temperature, dissolved oxygen, and isotopic data.The waters total dissolved solids and calcite saturation indices increase with decreasing altitude, suggesting recharge from the Chisos uplands. However, temperature, dissolved oxygen, δ18O, tritium, and Carbon‐14 data indicate a significant recharge component to springs occurs by infiltration of infrequent precipitation falling on the arid alluvial lowlands. This water percolates through the soil zone to aquitards (essentially calcitic hardpans) which function as horizons which channel the water laterally toward discharge in springs. The springs recharge‐to‐discharge paths are short with flow being slow enough to reflect seasonal temperature differences of greater than 12°, yet recent enough to contain post‐bomb spikes of tritium and Carbon‐14.
A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part I, Methodology and Field Site Characterization
Authors: Roberts Paul V. , Hopkins Gary D. , Mackay Douglas M. , Semprini Lewis 
Published: August 2005

AbstractCareful site characterization and implementation of quantitative monitoring methods are prerequisites for a convincing evaluation of enhanced biostimulation for aquifer restoration. This paper describes the characterization of a site at Moffett Naval Air Station, Mountain View, California, and the implementation of a data acquisition system suitable for real‐time monitoring of subsequent aquifer restoration experiments. A shallow, confined aquifer was chosen for the enhanced biodegradation demonstration, and was shown to have suitable hydraulic and geochemical characteristics. Injection and extraction wells were installed at a distance of 6 m, with intermediate monitoring wells at distances of 1, 2.2, and 4 meters from the injection well. Bromide tracer tests revealed travel times of S to 27 hours from the injection well to the various monitoring wells, and 20 to 42 hours from the injection well to the extraction well. Complete breakthrough of the tracer at the monitoring wells was facilitated by choosing a line of wells aligned with the regional flow, and selecting injection and extraction flow rates of approximately 1.5 and 10 liters/min. Transport studies were conducted with selected halogenated organic compounds. The retardation factors were found to range from approximately 2 to 12. The breakthrough responses for the more strongly sorbing compounds, e.g. TCE, exhibited pronounced tailing, such that a minimum period of several weeks was required to achieve complete saturation of the aquifer. The microcomputer‐driven sampling, analysis and data management system provided automated data acquisition at sample intervals of 40 minutes, with coefficients of variation smaller than 20%, and allowed for real‐time surveillance of the dynamic responses. Overall, the conditions were favorable for a quantitative evaluation of in‐situ aquifer restoration by enhanced biodegradation.
A Device for In Situ Determination of Geochemical Transport Parameters 2. Biochemical Reactions
Authors: Gillham R. W. , Starr R. C. , Miller D. J. 
Published: August 2005

AbstractChemical and biological reaction rates are required in estimating migration rates of many reactive contaminants in ground water, and as input data for mathematical models. Reaction rates must be measured, and depend on environmental conditions that are often difficult to duplicate in the laboratory. In situ rate measurement minimizes the difficulties of controlling environmental variables such as temperature, pH, Eh, DO, solution and solid phase composition, and bacterial population.The instrument described in this paper isolates a 1.9 liter portion of an aquifer for in situ biochemical rate measurement. The device has been used successfully to measure the rate of reactions involving inorganic and organic contaminants in sandy aquifers. Two applications of the device, measurement of denitrification rates and rates of biodegradation of benzene, are presented.
Column Studies on Methanotrophic Degradation of Trichloroethene and 1,2‐Dichloroethane
Authors: Lanzarone Nancy A. , McCarty Perry L. 
Published: August 2005

AbstractThe potential for and variables affecting enhanced aerobic biodegradation of 14C‐labeled trichloroethene (TCE) and 1,2‐dichloroethane (1,2‐DC A) were evaluated using laboratory columns packed with fully saturated sandy aquifer material. The column fluids were exchanged weekly to simulate the growth of native microorganisms capable of biotransforming halogenated aliphatics. The exchange solutions for seven columns, one of which served as a control, contained dissolved oxygen as the electron acceptor. The electron donor, or primary substrate, for another column was dissolved propane, and the remaining five columns were fed varying concentrations of dissolved methane.Propane was not consumed, and TCE degradation did not occur in this column. However, methane was utilized in other columns, and the resulting stimulated populations mineralized both TCE and 1,2‐DCA to CO2. Little or no TCE degradation occurred when the methane concentration was 4.5 mg/1, but when the methane was reduced to 1.5 mg/1, degradation occurred. TCE degradation was greatest when either a low methane concentration (1.5 mg/1) or an alternating pulse of methane (4.5 mg/1 or 1.5 mg/1) with oxygen one week followed by oxygen only the next was used. Nutrient supplements (NH4+ and PO42‐) did not conclusively enhance TCE degradation.When TCE addition was stopped and methanotrophic bacteria stimulation was continued, half of the 14C from previously sorbed TCE that was subsequently eluted by exchange was present as nonvolatile compounds and CO2, and the other half as TCE. With a caution that the results obtained are site‐specific, they do suggest that the addition of methane and oxygen to water circulated through a ground‐water system to remove TCE by aboveground treatment can, in some cases at least, result in a doubling of the rate of removal and affect mineralization of about one‐half of the TCE removed.
Effect of Sensor Error on Interpretation of Long‐Term Water‐Level Data
Authors: Rosenberry Donald O. 
Published: August 2005

AbstractSubmersible strain‐gage pressure transducers and potentiometer‐float systems were used to monitor water‐level fluctuations in wells. Use of uncorrected data from six pressure transducers at a site in New Hampshire would have caused an incorrect interpretation of the vertical hydraulic‐head distribution. Seven potentiometer‐float systems at a site in Nebraska provided data that indicated a slight attenuation of water‐level fluctuations, which likely caused some small fluctuations to go unobserved.Digital data loggers were used at both sites to scan the sensors and calculate hourly and daily average values of water levels in the wells. Check measurements using a chalked steel tape were made weekly at the New Hampshire site and monthly at the Nebraska site. Comparisons of recorded data with check measurements indicated values measured by pressure transducers over periods of weeks to months were irregularly larger or smaller than the check measurement. This error was attributed to a drift of the zero reference point of the sensor, and was unpredictable. Values obtained by potentiometer‐float systems lagged the water‐level change indicated by the check measurements. The lag was attributed to the sum of the mechanical friction of the moving parts of the monitoring system. This error was somewhat constant and predictable. The average absolute error of six submersible pressure transducers that were in operation for 15 months was 0.098 foot. The average absolute error of seven potentiometer‐float systems that were operated for 17 months was 0.027 foot.
The Lognormal Distribution of Radon Concentration in Ground Water
Authors: Zikovsky L. , Chah B. 
Published: August 2005

AbstractData on the concentration of radon in ground water were compiled from the literature. From this compilation and data collected for this study, the means, medians, modes, standard deviations, coefficients of skewness and histograms have been calculated. The histograms were compared with the normal and lognormal distribution functions using chi‐square test values for goodness of fit. Based on this, the concentrations were found to be lognormally distributed in all cases studied but one. The measured medians and modes were compared with their theoretical counterparts assuming either normality or lognormality, and lognormality was found once more.
Use of Tree‐Ring Chemistry to Document Historical Ground‐Water Contamination Events
Authors: Vroblesky Don A. , Yanosky Thomas M. 
Published: August 2005

AbstractThe annual growth rings of tulip trees (Liriodendron tulipifera L.) appear to preserve a chemical record of ground‐water contamination at a landfill in Maryland. Zones of elevated iron and chlorine concentrations in growth rings from trees immediately downgradient from the landfill are closely correlated temporally with activities in the landfill expected to generate iron and chloride contamination in the ground water. Successively later iron peaks in trees increasingly distant from the landfill along the general direction of ground‐water flow imply movement of iron‐contaminated ground water away from the landfill. The historical velocity of iron movement (2 to 9 m/yr) and chloride movement (at least 40 m/yr) in ground water at the site was estimated from element‐concentration trends of trees at successive distances from the landfill. The tree‐ring‐derived chloride‐transport velocity approximates the known ground‐water velocity (30 to 80 m/yr). A minimum horizontal hydraulic conductivity (0.01 to .02 cm/s) calculated from chloride velocity agrees well with values derived from aquifer tests (about 0.07 cm/s) and from ground‐water modeling results (0.009 to 0.04 cm/s).
A Field Evaluation of In‐Situ Biodegradation of Chlorinated Ethenes: Part 2, Results of Biostimulation and Biotransformation Experiments
Authors: Semprini Lewis , Roberts Paul V. , Hopkins Gary D. , McCarty Perry L. 
Published: August 2005

AbstractResults are presented from a field study that document the in‐situ biotransformation of trichloroethylene (TCE), cis‐dichLoroethylene (cis‐DCE), trans‐dichloroethylene (trans‐DCE), and vinyl chloride (VC) in a saturated, semiconfined aquifer. The enhanced biotransformation was accomplished by stimulating the growth of indigenous methane‐oxidizing bacteria (methanotrophs), which transform chlorinated aliphatic compounds by a cometabolic process to stable, nontoxic end products. Experiments were performed in the presence and absence of biostimulation by means of controlled chemical addition, frequent sampling, and quantitative analysis. The degree of biotransformation was assessed using mass balances and comparisons with bromide as a conservative tracer. Biostimulation of the test zone was successfully achieved by injecting methane‐ and oxygen‐containing ground water in alternating pulses under induced gradient conditions. After a few weeks of stimulation, methane concentrations gradually decreased below the detection limit within two meters of travel. Under active biostimulation conditions, 20 to 30% of the TCE was biotransformed during the first season of testing. Direct evidence for biotransformation of VC, trans‐DCE, cis‐DCE, and TCE was obtained in the second and third seasons of field testing. In the absence of biostimulation, the organic compounds concentrations at observation wells reached 95% of the injection concentration, demonstrating negligible losses due to abiotic processes. Biostimulation of the test zone resulted in a concurrent decrease in concentration of methane and the halogenated aliphatic compounds. The organic compounds were transformed within two meters of travel as follows: TCE, 20–30%; cis‐DCE, 45–55%; trans‐DCE, 80–90%; and VC, 90–95%. These results are in qualitative agreement with methane‐utilizing, mixed‐culture laboratory studies which indicate that the rate of biotransformation is more rapid when the molecules are less halogenated.A biotransformation intermediate was observed which was identified by GC‐MS analysis as trans‐dichloroethylene oxide (trans‐DCE epoxide), an expected intermediate based on laboratory studies. When methane addition was stopped, the concentration of the intermediate rapidly decreased, while halogenated compound concentrations slowly increased, indicating that active methane utilization was required for biotransformation to occur.
pH and Redox Buffering Mechanisms in a Glacial Drift Aquifer Contaminated by Landfill Leachate
Authors: Kehew Alan E. , Passero Richard N. 
Published: August 2005

AbstractThe KL Landfill in Kalamazoo County, Michigan was closed in June 1979 because of ground‐water contamination. Study of water analyses from a monitoring‐well network has provided insight into a variety of pH and pe buffering reactions within the contaminant plume. The reactions occur when contaminated ground water containing dissolved organic acids from the landfill reacts with carbonate minerals and other solid phases in a glacial drift aquifer. Concentrations of Total Inorganic Carbon (TIC) in the plume, measured as the difference between Total Carbon (TC) and Total Organic Carbon (TOC), are lower than those obtained by alkalinity titrations. The difference results from the dissociation of organic acids in solution, producing organic anions that are included in the erroneously high titration alkalinity values.Organic acids cause dissolution of carbonate minerals in the drift and increased concentrations of calcium, magnesium, and bicarbonate in the plume. Geochemical modeling using WATEQF indicates that the plume is supersaturated with respect to calcite, dolomite, and siderite. The dissolution reactions buffer pH in the plume at near background levels.Redox potentials are below the level of sulfate reduction in the contaminant plume. Therefore, redox buffering mechanisms, reactions that inhibit changes in redox potential in the presence of a strong reducing agent, are much less effective than pH buffering in this system. Possible redox reactions occurring along the flow path include oxidation of organic compounds coupled with reduction of nitrate to ammonium and reduction of ferric iron in oxyhydroxide phases to ferrous iron.WATEQF simulations indicate that dissolved iron concentrations in the plume are well above saturation levels with respect to sulfide phases, moderately above saturation with respect to siderite, and below saturation with respect to iron hydroxide. It is likely that iron precipitates as sulfide phases until the dissolved sulfide is consumed. The concentration of dissolved iron is subsequently controlled by precipitation of siderite, which occurs when moderate levels of supersaturation are reached.These redox buffering reactions are insufficient to maintain high pe levels, and pe values drop to the level of sulfate reduction in the contaminant plume. Together, pH and redox buffering reactions control the concentrations of most major chemical species in the KL Landfill contaminant plume.
Hydrogeological Decision Analysis: 1. A Framework
Authors: Freeze R. Allan , Massmann Joel , Smith Leslie , Sperling Tony , James Bruce 
Published: August 2005

AbstractThis paper is the first in a four‐part series that describes the application of decision analysis to engineering design for projects in which the hydrogeological environment plays an important role. The methodology is well‐suited to the design of containment facilities at new waste‐management facilities, purge‐well networks in contaminant remediation applications, or drainage systems in geotechnical projects. It is based on a risk‐based philosophy of engineering design. It involves the coupling of three separate models: a decision model based on a risk‐cost‐benefit objective function, a simulation model for ground‐water flow and transport, and an uncertainty model that encompasses both geological uncertainty and parameter uncertainty. The approach can be used for the comparison of alternative engineered components of a system, for the design of monitoring systems, and for the assessment of data worth in the design of site investigation programs. This first paper lays the framework; the subsequent papers escribe how the methods can be applied in geotechnical and waste‐management applications.
Particle Tracking Analysis of Recharge Areas on Long Island, New York
Authors: Buxton Herbert T. , Reilly Thomas E. , Pollock David W. , Smolensky Douglas A. 
Published: August 2005

AbstractProtection of ground‐water resources from the effects of anthropogenic contamination requires definition of the source of water flowing in developed aquifers. Aquifer recharge areas for the confined Magothy and Lloyd aquifers of Long Island, New York, are estimated by using a three‐dimensional model of the Long Island ground‐water flow system and a particle‐tracking algorithm.Aquifer recharge areas under predevelopment conditions are consistent with an understanding of the ground‐water flow system operation. A budget comparison indicated that the recharge occurring in each area as calculated by particle tracking was within one percent of the flow entering that aquifer, according to the water budget computed from the flow model.Aquifer recharge areas for two stressed conditions, one at the present time and the other an estimate for the year 2020, are more difficult to define because of numerous pumped wells. Maximum and minimuitn recharge areas for each aquifer are presented for both present conditions and the year 2020 to bracket the actual aquifer recharge areas. These results also are consistent with the water budgets computed from the flow model.Results indicate that development causes large‐scale changes in flow patterns and the size and shape of aquifer recharge areas. The accuracy of defining recharge areas is limited by the model's representation of local‐scale characteristics of the flow system and the wells.
Ground‐Water Contamination from Two Small Septic Systems on Sand Aquifers
Authors: Robertson W. D. , Cherry J. A. , Sudicky E. A. 
Published: August 2005

AbstractDistinct plumes of septic system‐impacted ground water at two single‐family homes located on shallow unconfined sand aquifers in Ontario showed elevated levels of Cl−, NO3−, Na+, Ca2+, K+, alkalinity, and dissolved organic carbon and depressed levels of pH and dissolved oxygen. At the Cambridge site, in use 12 years, the plume had sharp lateral and vertical boundaries and was more than 130 m in length with a uniform width of about 10 m. As a result of low transverse dispersion in the aquifer, mobile plume solutes such as NO3− and Na+ occurred at more than 50 percent of the source concentrations 130 m downgradient from the septic system. At the Muskoka site, in use three years, the plume also had discrete boundaries reflecting low transverse dispersion. After 1.5 years of system operation, the Muskoka plume began discharging to a river located 20 m from the tile field. Almost complete NOs attenuation was observed within the last 2 m of the plume flowpath before discharge to the river. This was attributed to denitrification occurring within organic matter‐enriched riverbed sediments.The very weakly dispersive nature of the two aquifers was consistent with the results of recently reported natural‐gradient tracer tests in sands. Therefore, for many unconfined sand aquifers, the minimum distance‐to‐well regulations for permitting septic systems in most parts of North America should not be expected to be adequately protective of well‐water quality in situations where mobile contaminants such as NOs are not attenuated by chemical or microbiological processes.
Numerical Simulation of Subsurface‐Water Rise in Kuwait Citya
Authors: Hamdan L. , Mukhopadhyay A. 
Published: August 2005

AbstractThe residential areas of Kuwait City have been affected by a rise in the subsurface‐water level in recent years, causing waterlogging and flooding of the basements of buildings. To study this phenomenon, and to ascertain its causes, a numerical aquifer simulation model was developed. The aquifer model showed that, over the period 1961‐1985, the net yearly addition to the aquifer storage due to the contribution from man‐made sources like sewage systems, irrigation, and water distribution networks, ranged from 8,300 to 10,100 m3 d−1, causing a subsurface‐water‐level rise of about 5 m locally, resulting in high water‐table conditions. A maximum local rise in the water table of 2.5 m was predicted between the end of 1985 and 1990, if no remedial actions are undertaken. Preventive methods to reduce or eliminate recharge from man‐made activities would help control the water‐level rise and even lower the water table in affected areas. Remedial measures to lower and maintain the subsurface‐water level at acceptable depths would entail the withdrawal of significant quantities of ground water.
Estimation of Hydraulic Conductivity Values In a Coastal Aquifer
Authors: Pandit Ashok , EI‐Khazen Clovis C. , Sivaramapillai Sanjiv P. 
Published: August 2005

AbstractA method is presented to compute the ratio of the vertical to horizontal component of the hydraulic conductivity of a homogeneous aquifer using a finite‐element model. The method requires knowledge of: (1) the boundary conditions along a vertical cross section of the aquifer, and (2) the hydraulic head measurements of two vertically separated well screens (preferably at the top and bottom of the aquifer). The method was used to estimate the anisotropy ratio for the aquifer at Port St. Lucie, Florida. The value of the horizontal component of the hydraulic conductivity was also estimated for this region by comparing measured tidally influenced ground‐water elevations to calculated elevations.