bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design Factors for Improving the Efficiency of Free‐Product Recovery Systems in Unconfined Aquifers
Authors: Kaluarachchi Jagath J. , Elliott Robert T. 
Published: August 2005

AbstractFree‐product recovery system designs for light hydrocarbon recovery were investigated to evaluate the effects of multiple‐stage pumping, delayed startup, and uncertainty of key residual oil saturation input data using a vertically integrated three‐phase flow model, ARMOS. The results obtained from a single well recovery system subjected to a given well location and uniform soil properties suggested that multiple‐stage water pumping can enhance the recovery and provide optimal design conditions if cost and recovery oil volume are the targets. However, if containment of the spill area with simultaneous recovery is the target, then single‐stage pumping still provides the optimal design. Delayed startup of the operation from the initial site characterization can cause substantial plume movement during the lag period making predictions made with zero time lag invalid. Allowance should be made in the design to account for this time delay. Uncertainty of maximum residual oil saturations in both saturated and unsaturated zones may cause considerable differences in predicted results. Careful attention should be paid to obtaining these data for accurate remediation design.
Observed Migration of a Controlled DNAPL Release by Geophysical Methods
Authors: Brewster M. L. , Annan A. P. , Greenhouse J. P. , Kueper B. H. , Olhoeft G. R. , Redman J. D. , Sander K. A. 
Published: August 2005

AbstractSeven hundred seventy liters of a dense nonaqueous phase liquid (DNAPL), tetrachloroethylene (PCE), were released into an isolated volume of a completely saturated natural sandy aquifer. The release was monitored over a period of 984 hours with a variety of geophysical methods including ground penetrating radar, time domain reflectometry, in situ resistivity, and a neutron soil moisture probe. The PCE formed a pool on a low permeability layer at approximately 1 m depth and spread over an area exceeding 32 m2. In its course of downward migration, the PCE subsequently formed eight smaller pools. At the end of the experiment an estimated 41 percent of the total PCE volume remained trapped in the upper pool.The PCE mass and its spatial moments were calculated from radar reflection amplitudes. Between 48 and 100 percent of the PCE mass was accounted for by radar measurements. The center of mass moved a total of 0.5 m south southeast and 1.3 m downward. Spatial variances showed that the greatest lateral spreading occurred in the east‐west direction. The results demonstrate that natural heterogeneities, even in a relatively homogeneous aquifer, can cause DNAPLs to spread laterally over large areas in the subsurface. This experiment also demonstrated that while the ability of geophysics to uniquely measure the presence of DNAPL is limited, certain techniques are well‐suited to monitoring changes in DNAPL saturation.
Automated Base Flow Separation and Recession Analysis Techniques
Authors: Arnold J. G. , Allen P. M. , Muttiah R. , Bernhardt G. 
Published: August 2005

AbstractAn automated base flow separation technique has been developed and tested. Base flow is considered to be the ground‐water contribution to stream flow. Estimates of the amount of base flow can be derived from stream flow records. Such estimates are critical in the assessment of low flow characteristics of streams for use in water supply, water management, and pollution assessment. An automated base flow separation technique using a digital filter has been tested against three other automated techniques and manual separation methods. The filter appears to be comparable to other automated techniques in its ability to reproduce the results produced from graphical separation techiques. The filter technique is easy to use and has the added advantage in that it can be adjusted by the user to take into account personnel preferences in separation of stream flow into surface flow and base flow.The slope of the base flow recession has been used to estimate the volume of water in storage in the basin above the level of the stream channel, the amount of recharge to the shallow aquifer, and as an input into water budget models. A second automated technique was developed to calculate the slope of the base flow recession curve from stream flow record. This technique is an adaptation of the Master Recession Curve procedure. The results of this method were compared to manual estimates with an efficiency of 74 percent.
Meaningful Interpretation of Step‐Drawdown Tests
Authors: Kawecki M. W. 
Published: August 2005

AbstractFrom a critical review of literature it is concluded that the available methods of analyzing step‐drawdown tests produce information which can be misleading, inaccurate, or meaningless. Calculation of the total well loss from step‐drawdown tests, on the other hand, provides a meaningful evaluation of well performance but is not explicitly described in literature. Therefore, a method is presented for determining the total well loss as a function of discharge with linear and nonlinear components. The method is restricted to confined aquifers, but an observation well is not required because any reasonable estimate of the storage coefficient is usually adequate. An advantage of the method is that it is valid for any stepped pumping pattern and any observed fluctuations in discharge during a step are simply accommodated as additional steps. Field examples show that the method can be very successful and useful. Other specific conclusions are that well efficiency should not be calculated because it is misleading, and that aquifer transmissivity should be determined in step‐drawdown tests from recovery data in the pumped well, not pumping data, to improve accuracy.
A Comparison of Methods to Determine K in a Shallow Coastal Aquifer
Authors: Millham Newton P. , Howes Brian L. 
Published: August 2005

AbstractFive methods (tidal damping, tracer, slug, permeameter, and grain‐size analysis) for the determination of hydraulic conductivity (K) were compared in both upland and shoreline regions of a sandy outwash aquifer adjacent to a shallow coastal embayment. The 7 m tracer test and tidal damping methods appeared to determine in situ K over sufficient horizontal scales to integrate the spatial variability of K within the aquifer, with the tracer test giving the most reproducible K estimates for the upland, 109 m/d. The tidal K measurements were similar to the tracer results, 106 m/d, integrating K over greater distances (30 to 85 m), but were highly variable due to the large aquifer storativity, small tidal amplitude, and irregular tides.The smaller scale methods yielded lower upland K estimates with the lowest value from permeameters, 29 m/d, only about one‐third of the other four methods. Estimates of upland K by both grain‐size and slug tests were comparable, 86 m/d and 71 m/d, respectively. However, the K derived from grain‐size methods was dependent not only upon the sediment but on the method selected, with consistently higher values of K generated by the Hazen equation than the Krumbein and Monk equation. Verification by in situ tests may be useful in removing this bias.Significant differences in K were found between shoreline and upland regions, though the relative magnitude of the difference was not constant: among the four methods where comparative measurements were possible, shoreline K ranged from 42% to 75% of upland values. Slug tests yielded the largest differences, 30 m/d and 71 m/d, with permeameter, 18 m/d and 24 m/d, the lowest. The lower K of shoreline sediments appears to be the result of processes associated with coastal embayments and should be addressed in the measurement and modeling of coastal ground‐water discharge.
Radiocarbon and δ13C Values Related to Ground‐Water Recharge and Mixing
Authors: Landmeyer James E. , Stone Peter A. 
Published: August 2005

AbstractGround‐water levels in the Upper Floridan aquifer beneath the southeastern coast of South Carolina have undergone pumpage‐induced declines approaching 20 ft below sea level at the southern end of Hilton Head Island. This scenario suggests the potential exists for the inducement of recharge to the Upper Floridan aquifer across the island, which could affect the quality of water being pumped by wells. However, low radiocarbon concentrations in ground‐water samples (0.5 to 1.4 ± 0.1 PMC) indicate that most of the water is relict ground water reflecting prepumpage ground‐water flow conditions in the Upper Floridan aquifer. The isotopic data indicate long residence times and water‐chemistry evolution more characteristic of ground‐water recharge occurring farther inland prior to the commencement of pumpage in the late 1800s.Radiocarbon concentrations (as Percent Modern Carbon) and stable carbon isotope ratios (as δ13C in dissolved inorganic carbon) determined during this study and reported in other studies on and around Hilton Head Island varied in a systematic manner. Heavier δ13C values (–2.8 to –1.6 per mil) in ground water beneath southern Hilton Head Island reflect ground‐water discharge from prepumpage flowpaths originating over 100 miles away, hence a depletion in radiocarbon concentration with corrected ground‐water ages no younger than 16,000 yrs BP. In contrast, lighter δ13C values (–13.9 to –8.67 per mil) beneath the northern part of the island indicate recent recharge as a result of water‐level declines, and recharge in areas off the island that have not changed as a result of pumpage (evidenced by enrichment in radiocarbon with corrected ground‐water ages no older than 4,000 yrs BP). This suggests that the δ13C composition of ground water in the Upper Floridan aquifer is a useful indicator of mixing between ground waters from different sources, and can be used to delineate recharge‐discharge patterns. This approach may be applicable to other aquifers of highly evolved ground‐water chemistry in regional carbonate aquifer systems that may be receiving recent recharge. Moreover, this approach could prove useful in delineating the contribution of recent water being captured by pumped wells as part of wellhead protection programs designed to assess aquifer vulnerability from surficial contaminant sources.
An Evaluation of Interpolation Methodologies for Generating Three‐Dimensional Hydraulic Property Distributions from Measured Data
Authors: Boman Gerald K. , Molz Fred J. , Güven Oktay 
Published: August 2005

AbstractThe process of attempting to model ground‐water systems requires a good understanding of the spatial variation of aquifer hydraulic properties. The capabilities of the more recent innovative flowmeters such as the electromagnetic and heat pulse flowmeters provide the sensitivity to measure ambient flows and pump‐induced flows. These flowmeters provide the measurements of pump‐induced vertical flows which are analyzed to obtain vertical variations in horizontal hydraulic conductivity, K(z). With discrete areal K‐values, K(x, y), and vertical profiles of K, provided by multiwell testing, the essential elements are present to produce a three‐dimensional hydraulic conductivity field. The advent of these new flow measuring devices has contributed much to the motivation behind this paper.This paper presents the results of applying deterministic and stochastic methodology to the three‐dimensional interpolation of hydraulic properties, specifically, hydraulic conductivity, K. Three of the approaches applied in this paper are deterministic in nature, inverse‐distance weighting, inverse‐distance‐squared weighting, and ordinary kriging, while the fourth is a stochastic approach based on self‐affine fractals. All of the methods are applied to measured data collected from 14 wells at a site in the United States near Mobile, Alabama. The three‐dimensional K‐distributions generated by each of the methods are used as inputs to an advective based transport model with the resulting model output compared to a two‐well tracer study run previously at the same site.
Major Ion and Trace Metal Geochemistry of an Acidic Septic‐System Plume in Silt
Authors: Robertson W. D. , Blowes D. W. 
Published: August 2005

AbstractFour years of detailed ground‐water monitoring at a newly installed, seasonal‐use, domestic septic system located on poorly buffered (CaCO3 equivalent content ≤ 1.6 wt.%) lacustrine silt, has revealed the development of an acidic ground‐water plume. Acid, generated by the partial oxidation of effluent NH4+ dissolved organic carbon (DOC), and possibly sulfide minerals present in the sediment, has resulted in a distal plume core zone with pH values in the range of 4.4 to 5.0. The acidic zone, where NH4+ does, however, persist (> 2 mg/1, as N) and where DOC remains elevated (6–13 mg/1), is associated with high average concentrations of the trace metals Fe (4.7 mg/1), Al (1.9 mg/1), and Mn (3.6 mg/1). Attenuation of nitrogen along the plume core flowpath is indicated by a decrease in the N/ Cl− ratio from an effluent value of 1.7, to a plume value of only 0.5 after 4 m of subsurface flow. Increased SO42− levels observed in the zone of N depletion suggest that attenuation can be at least partly attributed to reduction of plume NO3− by oxidation of reduced S present in the sediment. PO43− has not migrated significantly beyond the infiltration bed gravel layer, demonstrating that PO43− mobility is limited in these sediments (retardation factor > 10).
Survey of Nitrate Contamination in Shallow Domestic Drinking Water Wells of the Inner Coastal Plain of Georgia
Authors: Stuart Maureen A. , Rich Fredrick J. , Bishop Gale A. 
Published: August 2005

AbstractBeginning in 1990, 2,588 wells were sampled within the Inner Coastal Plain of Georgia in an effort to assess the quality of ground water in this major farm belt. The project was one aspect of an EPA‐sponsored program to assess ground‐water quality statewide. Several variables were measured, including pH, specific conductivity, dissolved oxygen, temperature, nitrate, nitrite, total hardness, calcium, magnesium, and bicarbonate. In some wells sulfate, chloride, potassium, iron, and manganese contents were also determined. Particular emphasis was placed, however, on pH, specific conductivity, temperature, and nitrite/nitrate content. Generally, pH was between 6 and 8, and temperatures were within a range of 18° and 24°Celsius. Measurements of specific conductivity varied, but averaged 250–275 microsiemens/cm. Nitrite contamination was negligible, and nitrate contamination of the ground water within the shallow aquifers did not appear to be significant. In fact, 56% of the wells sampled showed no detectable signs of nitrate or nitrite contamination. There were, however, a few isolated wells where nitrate as nitrogen measurements exceeded the EPA's Safe Drinking Water Standard of 10 ppm. The general lack of contamination may be the result of the nature of the agricultural practices used in this region and/or the effect of natural denitrification.
Estimating Local Ground‐Water Flow Conditions in a Granitoid: Preliminary Assessments in the Waldoboro Pluton Complex, Maine
Authors: Sidle W. C. , Lee P. Y. 
Published: August 2005

AbstractPeriodic dry wells are reported by some homeowners in Knox and Lincoln Counties, Maine. These wells pump from the migmatitic Bucksport Fm. which is intermixed with the granitoids of the Waldoboro Pluton Complex. Previous remote sensing and geologic mapping delineated marked northeast‐trending structures in the WPC which were initially suspected as influencing ground‐water flow for sustainable well yields. A sample area, Pemaquid Pond, in the WPC was studied in more detail including preliminary hydraulic testing of homeowner wells and ground‐waiter flow modeling.Wells with sustainable and greater yields appear to be associated instead with zones of northwest‐trending structures in granitoids not intermixed with the Bucksport Fm. Dry wells appear to be more prevalent amongst northeast‐trending structures in areas where the migmatitic metamorphic rocks outcrop. Hydraulic studies, including pumping, slug, pressure, and borehole dilution testing, resulted in a wide range of calculated hydraulic conductivities. Dual‐porosity flow modeling and geostatistical parameterization of the flow conditions suggest that the anisotropic hydraulic conductivity is near E‐9 m/d.
Optimal Estimation of Two‐Dimensional Contaminant Transport
Authors: Zou S. , Parr A. 
Published: August 2005

AbstractThe state‐space estimation technique presented herein provides a method for obtaining optimal estimates of concentrations for two‐dimensional plumes in ground water. The concentration of a plume was defined as the state variable. The technique uses the Kalman filter and involves combining two independent estimates of plume concentrations. One estimate is called the process modeling data and the other is called the “measurement” data. The process modeling data is obtained from a numerical model. The “measurement” data is obtained from field measurements; however, for illustration in this paper it was generated by a different numerical model than the one used to obtain the process modeling data. The state‐space technique produces a distribution of contaminant concentrations that is more accurate than either of the distributions generated by the process modeling or the “measurement” data. An example is presented to show that the technique produces significant improvements in the prediction of plume concentration distributions.
Hydrolysis Rates of Dissolved Volatile Organic Compounds: Principles, Temperature Effects and Literature Review
Authors: Washington John W. 
Published: August 2005

AbstractArrhenius parameters, 25° and 10°C rate constants for hydrolysis of most EPA 601/602 volatile organic compounds (VOCs), their hydrolytic progeny, and selected other VOCs are tabulated. Data include Arrhenius parameters for base‐mediated hydrolysis of bromodichloromethane, bromoform, dibromochloromethane, and the acid‐mediated hydrolysis of ethylene oxide which have not been published before. The average activation energy of the tabulated values, excepting epoxides, is 110,100 joules per mole, which exceeds values reported previously as typical for VOCs. As a result of this high activation energy, the half‐lives of VOCs typically are more than an order of magnitude longer at 10° than 25°C.These data are necessary for calculating hydrolysis rates accurately and, thus, for estimating remediation effectiveness when hydrolysis is being considered for remediation. Other things being equal, hydrolysis rates become much faster with increasing temperature and, for some VOCs, with increasing pH. The hydrolysis half‐lives at 25°C and pH = 7 of many haloalkanes and halogenated alcohols are less than 100 years (yr), many halomethanes (freon‐like compounds), and halogenated aldehydes are less than 1000 yr, and many haloalkenes and aromatic VOCs tend to exceed 1000 yr.These data can be used to select temperature and pH conditions to impose on water to favor fast hydrolysis or, for branching degradation schemes, select the shorter lived or less toxic progeny. Moreover, these data are necessary to calculate the major hydrolysis progeny for any conditions. Also, these data can be used in forensic geochemical applications such as estimating original contamination composition, time since contamination occurred, distance to source, and whether nonaqueous‐phase liquids persist.The main base‐mediated hydrolytic degradation route of haloalkanes is induced to be dehydrohalogenation and the main progeny of these reactions are ethenes. Another degradation phenomenon for chlorinated hydrocarbons in aquifers, chemical reductive dehalogenation by low concentrations of natural organic carbon, is proposed and shown to be consistent with published literature.
Application of a 2D Air Flow Model to Soil Vapor Extraction and Bioventing Case Studies
Authors: Mohr Donald H. , Merz Paul H. 
Published: August 2005

1. AbstractA two‐dimensional air flow model provides a practical tool to evaluate pilot test data and estimate remediation rates for soil vapor extraction systems. The model predictions of soil vacuum versus distance are statistically compared to pilot test data for 65 SVE wells at 44 sites. For 17 of 21 sites where there was asphalt paving, the best agreement was obtained for boundary conditions with no barrier to air flow at the surface. The model predictions of air flow rates and stream lines around the well allow an estimate of the gasoline removal rates by both evaporation and bioremediation. The model can be used to quickly estimate the effective radius of influence, defined here as the maximum distance from the well where there is enough air flow to remove the contaminant present within the allowable time. The effective radius of influence is smaller than a radius of influence defined by soil vacuum only. For a case study, in situ bioremediation rates were estimated using the air flow model and compared to independent estimates based on changes in soil temperature. These estimated bioremediation rates for heavy fuel oil ranged from 2.5 to 11 mg oil degraded per kg soil per day, in agreement with values in the literature.
Chemical and Isotopic Methods for Quantifying Ground‐Water Recharge in a Regional, Semiarid Environment
Authors: Wood Warren W. , Sanford Ward E. 
Published: August 2005

AbstractThe High Plains aquifer underlying the semiarid Southern High Plains of Texas and New Mexico, USA was used to illustrate solute and isotopic methods for evaluating recharge fluxes, runoff, and spatial and temporal distribution of recharge. The chloride mass‐balance method can provide, under certain conditions, a time‐integrated technique for evaluation of recharge flux to regional aquifers that is independent of physical parameters. Applying this method to the High Plains aquifer of the Southern High Plains suggests that recharge flux is approximately 2% of precipitation, or approximately 11 ± 2 mm/y, consistent with previous estimates based on a variety of physically based measurements. The method is useful because long‐term average precipitation and chloride concentrations in rain and ground water have less uncertainty and are generally less expensive to acquire than physically based parameters commonly used in analyzing recharge. Spatial and temporal distribution of recharge was evaluated by use of δ2H, δ18O, and tritium concentrations in both ground water and the unsaturated zone. Analyses suggest that nearly half of the recharge to the Southern High Plains occurs as piston flow through playa basin floors that occupy approximately 6% of the area, and that macropore recharge may be important in the remaining recharge. Tritium and chloride concentrations in the unsaturated zone were used in a new equation developed to quantify runoff. Using this equation and data from a representative basin, runoff was found to be 24 ± 3 mm/y; that is in close agreement with values obtained from water‐balance measurements on experimental watersheds in the area. Such geochemical estimates are possible because tritium is used to calculate a recharge flux that is independent of precipitation and runoff, whereas recharge flux based on chloride concentration in the unsaturated zone is dependent upon the amount of runoff. The difference between these two estimates yields the amount of runoff to the basin.