bluuebunny/crossref_metadata_2025 huggingface dataset:
An Image‐Well Method for Predicting Drawdown Distribution in Aquifers with Irregularly Shaped Boundaries
Authors: Kuo M.C.T. , Wang W. L. , Lin D. S. , Lin C. C. , Chiang C. J.
Published: August 2005

Many analytical methods use radial and rectangular systems to interpret unsteady‐state reservoir flow problems. However, there is no information currently available for irregularly shaped aquifers. For many practical cases the aquifer drainage shape is too complicated to be approximated by a circular or rectangular shape. This paper develops an image‐well method for predicting drawdown transient in an aquifer with irregularly shaped boundaries. Previously, the use of the image‐well method to predict drawdown transient was only possible for aquifer boundaries of regular shape.

In this paper, the well function is obtained by superposing the Theis solution of image wells in time. The image‐well method is first applied to regularly shaped aquifers. The validity of the approach is then proved by comparison of the calculated well functions with literature values for various regular drainage shapes. The proven method was applied to interpret a field pumping test and to characterize the reservoir boundaries with irregular shape.
Testing the Limits of ICP‐MS: Determination of Trace Elements in Ground Water at the Part‐Per‐Trillion Level
Authors: Stetzenbach Klaus J. , Amano Megumi , Kreamer David K. , Hodge Vernon F.
Published: August 2005

An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.
Hydraulic Connections Among Subaquifers of the Coastal Plain Aquifer, Israel
Authors: Nativ Ronit , Weisbrod Noam
Published: August 2005

The intensive use of the Coastal Plain aquifer, Israel, as well as its ongoing contamination by domestic and industrial waste and agrichemicals has resulted in the deterioration of its water quality. The Coastal Plain aquifer is divided into a number of calcareous sandstone units, separated by silt and shale lenses. Whereas the shallow, uppermost units are unconfined, the lowermost aquifers are partly confined. Although the presence of hydrological subunits is geologically well‐documented, the aquifer has been traditionally managed by the Israel Water Authority as a single water system. This study focused on the deeper units of the Coastal Plain aquifer where contamination may be less significant. The hydraulic connections between the overlying shallow units and the deep units were examined along two regions parallel to the main ground‐water flow direction, from east‐southeast to west‐northwest. The working hypothesis was that if hydraulic separation by the silt and shale lenses is effective, chemical and isotopic variations can be traced, and ground‐water‐level variations in each unit are likely to be different. The observed difference in hydraulic heads, distinct patterns of temporal water‐level variations, different C‐14 and tritium activities, and diverse chemical compositions suggest that the silt and shale lenses form an effective hydraulic partition between the shallow and deep sand units, both in the western and eastern parts of the aquifer. Our limited observations indicate that although the nature of the hydraulic separation and its effects are spatially variable, the prevailing conceptualization of the aquifer as one water body lacking vertical separation is incorrect.
Use of Tension Infiltrometer Data with Unsaturated Hydraulic Conductivity Models
Authors: Nachabe Mahmood H. , Illangasekare Tissa
Published: August 2005

A new method is presented to estimate the relationship between unsaturated hydraulic conductivity and soil‐water pressure using tension infiltrometer data. In this method, both the early transient and the subsequent quasi‐steady stages of the infiltration process underneath a tension infiltrometer disc are analyzed. Our investigation indicates that the infiltration rate at early times closely follows the aquare‐root‐of‐time relationship (Philip, 1969). This behavior permits the evaluation of the sorptivity, which is an integrated measure of soil diffusivity. At later times, three‐dimensional quasi‐steady flow beneath the infiltrometer disc develops, and the Wooding equation for flow from a circular pond is used to evaluate the sorptive number and the saturated hydraulic conductivity. Simple algebraic expressions are introduced to relate the sorptivity and sorptive number to the parameters of the Brooks and Corey model of unsaturated hydraulic conductivity. The method described here extends the utility of tension infiltrometer data to a large class of hydraulic conductivity models and provides an in situ technique to determine suitable parameters values for these models.

An ICP‐MS, equipped with an ultrasonic nebulizer and active‐film multiplier detector, is used to attempt to determine 54 trace elements directly in ground water. Lithium, arsenic, rubidium, strontium, barium, and antimony are found in the microgram‐per‐liter (part‐per‐billion = ppb) range. Most of the other elements are present at nanogram‐per‐liter (part‐per‐trillion = ppt) concentrations. Ion exchange preconcentration is utilized in order to improve the sensitivity for measuring the rare earth elements that exist at concentrations as low as 0.05 ppt for lutetium, thulium, and terbium. The formation of molecular species in the plasma produces false positive results for some of the elements. The presence of silicon or carbon dioxide interferes with the measurement of scandium, strontium interferes with rhodium and palladium, and barium interferes with europium. Correction procedures for these interferences are discussed. All together, the concentrations of the 54 elements in water from four Nevada springs span almost seven orders of magnitude.
Location Analysis in Ground‐Water Remediation Using Neural Networks
Authors: Johnson Virginia M. , Rogers Leah L.
Published: August 2005

Formal optimization techniques, of the kind developed in operations research to aid business decision‐making, show promise as tools for controlling the high costs of ground‐water remediation. A major barrier to the adoption of these tools in the industry, however, is the burden they place on the computational resources of an organization. Whenever a new pumping strategy is considered, a flow and transport model must be called to evaluate its effectiveness. Since it is common for optimization techniques to examine hundreds of strategies, at the very least, the bottleneck caused by the modeling step quickly becomes prohibitive. A method has been developed which uses artificial neural networks to substitute for the full model, permitting millions of strategies to be evaluated within reasonable time‐frames on conventional computer equipment. This method was applied to a 28‐location pump‐and‐treat problem at a western Superfund site. Networks were first trained to predict mass‐extraction and containment information normally generated by the 2‐D model SUTRA. They were then used in an optimization procedure to identify 250 (out of over 4 million) pumping patterns which met restoration goals at minimum cost. Analyses of the winning patterns classified individual locations as popular vs. unpopular. Sensitivity analyses on each location further distinguished: (1) locations which were strong performers under most circumstances from those which depended on other locations, and (2) locations which didnt aid the cleanup from those which were actually detrimental to it. All these analyses were made possible by the rapid evaluation of patterns provided by the neural networks.
Scale Dependency of Hydraulic Conductivity Measurements
Authors: Rovey Charles W. , Cherkauer Douglas S.
Published: August 2005

The hydraulic conductivity of five stratigraphic units in a carbonate aquifer has been measured with slug, pressure, and pumping tests, and with two calibrated digital models. The effective test radii range from less than one to greater than 10,000 meters. On log‐log plots hydraulic conductivity increases approximately linearly with test radius to a range between 20 and 220 meters, but thereafter, it is constant with scale.

The increase in magnitude of hydraulic conductivity is similar to scaling effects reported at seven additional sites in a variety of geologic media. Moreover, the increase in magnitude correlates with an increase in variance of log‐hydraulic conductivity measured at successively greater separation distances.

The rate of increase in both parameters, and particularly the range, have characteristic values for different pore systems. The larger ranges are consistently present in units with greater secondary porosity. Therefore, scaling effects provide a qualitative measure of the relative importance of secondary and primary permeability, and they can potentially be used to distinguish the dominant type of pore system.
A Model for Estimating the Hydraulic Conductivity of Granular Material Based on Grain Shape, Grain Size, and Porosity
Authors: Sperry James M. , Peirce J. Jeffrey
Published: August 2005

A model for delineating the relative importance of particle size, particle shape, and porosity, (and their interactions), in explaining the variability of hydraulic conductivity of a granular porous medium is developed and tested. Three types of porous media are considered in this work: spherical glass beads; granular sand; and irregularly shaped, shredded glass particles. A reliable method for quantifying the three‐dimensional shape and packing of large samples of irregular particles based on their angle of repose is presented. The results of column experiments indicate that in the size range examined (i.e., 149 μm to 2380 μm), the single most important predictor of hydraulic conductivity is seen to be particle size, explaining 69% of the variability. Porous media comprising irregular particles exhibit lower hydraulic conductivity only for the larger (707 to 841 μm) particles. For the smaller (149 to 177 μm) particles, particle shape has no observable influence on hydraulic conductivity. The results of the regression analysis reveal the importance of the interaction between particle size and porosity, indicating that similar pore configurations for a given type of particle are not achieved at different sizes. This empirical model seems to provide better estimates of the hydraulic conductivity of granular porous media comprising irregular particles than selected models based solely on grain size, including Hazen, Kozeny‐Carman, and more recently Alyamani and Sen.
Design Factors for Improving the Efficiency of Free‐Product Recovery Systems in Unconfined Aquifers
Authors: Kaluarachchi Jagath J. , Elliott Robert T.
Published: August 2005

Free‐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

Seven 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

An 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

From 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

Five 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

Ground‐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

The 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

Four 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

Beginning 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

Periodic 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

The 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

Arrhenius 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. Abstract

A 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

The 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.
A Ground‐Water Tracer Test with Deuterated Compounds for Monitoring In Situ Biodegradation and Retardation of Aromatic Hydrocarbons
Authors: Thierrin Joseph , Davis Gregory B. , Barber Chris
Published: August 2005

Fully deuterated benzene, toluene, p‐xylene, and naphthalene were used with bromide (inert reference) as ground‐water and pollutant tracers inside a BTEX contaminated plume of anoxic ground water in the Swan coastal plain, Western Australia. Besides the determination of local aquifer parameters and retardation coefficients for several organic pollutants within the contaminated site, this natural gradient ground‐water tracer test shows that deuterated organic compounds can be successfully used for in situ determination of natural biodegradation rates of organic pollutants. It suggests that toluene, p‐xylene, and naphthalene, but not benzene, degrade under sulfate‐reducing conditions.
An Adaptive Finite‐Element Model for Calculating Subsurface Transport of Contaminant
Authors: Pepper D. W. , Stephenson D. E.
Published: August 2005

A finite‐element method which incorporates mesh adaptation is used to calculate ground‐water flow and pollutant transport. The formulation is based on the equations for conservation of mass, Darcy's law for an anisotropic medium, and the time‐dependent species transport equation. Modifications have been implemented to the finite‐element formulation to enhance computational speed and reduce storage; Petrov‐Galerkin weighting of the advection terms provides numerical stability. An explicit time marching scheme is used to solve the transient equations. By utilizing unstructured adaptive meshing, species concentration and location of steep fronts are accurately resolved, even though one begins with a coarse mesh. The algorithm currently runs on PC and workstation class computers.
Practical Probabilistic Ground‐Water Modeling
Authors: Woodbury Allan , Render Frank , Ulrych Tad
Published: August 2005

The major obstruction to the effective use of probabilistic models is the determination of the statistical properties of unknown model parameters. In this paper we use the principle of minimum relative entropy (MRE) to determine the prior pdf, p(m) of a set of model parameters, (m) based on limited information. The pdf is of the form of a multivariate truncated exponential distribution. In this paper we use p(m) in Monte Carlo simulations to provide expected values in field variables such as drawdowns, pumping rates, and confidence limits. The examples presented illustrate some dangers associated with the practice in probabilistic modeling of assigning Gaussian pdf's as priors. First, such an assumption for the input parameters actually injects more information into the problem than may actually exist, whether consciously or unconsciously. This fact is born out by comparison with minimum relative entropy theory. Second, the output parameters as suggested from the Monte Carlo analysis cannot be assumed to be Gaussian distributed even when the prior pdf is in Gaussian form. In a practical setting, the significance of this result and the approximation of Gaussian form would depend on the cost, risk, and consequences of the decision being made.
Use of Electric Logs to Estimate Water Quality of Pre‐Tertiary Aquifers
Authors: Lindner‐Lunsford J. B. , Bruce Breton W.
Published: August 2005

Electric logs provide a means of estimating ground‐water quality in areas where water analyses are not available. Most of the methods for interpreting these logs have been developed for the petroleum industry and are most reliable in saline aquifers (concentration of dissolved solids as sodium chloride greater than about 50,000 mg/l). The resistivity‐porosity and spontaneous‐potential methods were evaluated to determine if they could be applied to identify zones of fresh water (concentration of dissolved solids as sodium chloride less than 1,000 mg/l) in three potential aquifers in central Wyoming. The potential aquifers have different lithologies–sandstone, clayey sandstone, and carbonate. The two methods generally were reliable predictors of water quality in the sandstone and carbonate potential aquifers. In the clayey sandstone potential aquifer, predictions of the dissolved‐solids concentration using the two methods differed by more than an order of magnitude in several cases. When the resistivity values are corrected for the presence of clay and shale as identified on a natural gamma log, the agreement between the results of the two methods improved by an average of 58 percent.
Virus and Bacteria Transport in a Sandy Aquifer, Cape Cod, MA
Authors: Bales Roger C. , Li Shimin , Maguire Kimberly M. , Yahya Moyasar T. , Gerba Charles P. , Harvey Ronald W.
Published: August 2005

Transport of the bacteriophage PRD‐1, bacteria, and latex microspheres was studied in a sandy aquifer under natural‐gradient conditions. The field injection was carried out at the U.S. Geological Survey's Toxic Substances Hydrology research site on Cape Cod. The three colloids and a salt tracer (Br−) moved along the same path. There was significant attenuation of the phage, with PRD‐1 peak concentrations less than 0.001 percent of Br− peaks 6 m from the source; but the low detection limit (one per ml) enabled tracking movement of the PRD‐1 plume for 12 m downgradient over the 25‐day experiment. Attenuation of phage was apparently due to retention on soil particles (adsorption). Attenuation of bacteria and microspheres was less, with peak concentrations 6 m from the source on the order of 10 and 0.4 percent of Br−, respectively. Injection of a high‐pH pulse of water 20 days into the experiment resulted in significant remobilization of retained phage, demonstrating that attached phage remained viable, and that PRD‐1 attachment to and detachment from the sandy soil particles was highly pH dependent. Phage behavior in this experiment, i.e. attenuation at pH 5.7 and rapid resuspension at pH 6–8, was consistent with that observed previously in laboratory column studies. Results illustrate that biocolloids travel in a fairly narrow plume in sandy (relatively homogeneous) media, with virus concentrations dropping below detection limit several meters away from the source; bacteria concentrations above detection limits can persist over longer distances.
Estimation of Unsteady, Three‐Dimensional Drawdown in Single, Vertically Heterogeneous Aquifers
Authors: Székely Ferenc
Published: August 2005

A quasi, a mixed, and a weighted three‐dimensional model are applied to approximate the three‐dimensional, unsteady drawdown in vertical pumping and observation wells, fully or partially penetrating a single, vertically heterogeneous, anisotropic aquifer. Cases of confined, semiconfined, and unconfined flow conditions are considered. Numerical examples are used to quantify the numerical error of the methods, introduced by the vertical heterogeneity of the aquifer. Results of pumping test data analysis in a three‐layer, anisotropic aquifer with multiple screens in the pumping well are presented.
Applicability of Slug Interference Tests for Hydraulic Characterization of Unconfined Aquifers: (1) Analytical Assessment
Authors: Spane F. A.
Published: August 2005

Slug interference responses within unconfined aquifers are characterized by an initial wave or “hump,” which is followed by a flat transitional plateau region and then by a declining, recessional limb segment. The shape and amplitude of the initial wave are primarily controlled by the elastic characteristics (i.e., S) and degree of anisotropy within the aquifer, while transmissivity is the principal parameter affecting the transmission (i.e., arrival time) of the slug interference response. Wellbore storage and delayed‐yield effects tend to attenuate the test response. The transitional and late‐time recessional segments are significantly influenced by the aquifer's specific yield. In addition, test well/aquifer relationships, e.g., observation well distance, aquifer thickness, and well depth/aquifer penetration, also strongly affect slug interference characteristics. The sensitivity of the propagated response to test well/aquifer relationships indicates that slug interference tests can be designed to maximize the expected response for aquifer property characterization.
Trace Element Geochemistry in Water from Selected Springs in Death Valley National Park, California
Authors: Kreamer David K. , Hodge Vernon F. , Rabinowitz Irving , Johannesson Kevin H. , Stetzenbach Klaus J.
Published: August 2005

Concentrations of 40 trace elements and other constituents in ground water from springs in Death Valley National Park were measured to investigate whether trace element composition of the ground water can be related to the aquifer materials. Samples from these springs were analyzed by inductively coupled plasma‐mass spectrometry (ICP‐MS) for the trace elements and by ion chromatography (IC) for the major anions. A Principal Component Analysis was performed on the data set. Surprise and Scotty's Springs formed one group; Texas, Nevares, and Travertine Springs formed another group; and Mesquite Springs did not group with any of the others. Scotty's and Surprise Spring issued from volcanic rocks; Texas, Nevares, and Travertine discharge from carbonate rocks; and Mesquite Spring is located in alluvial basin‐fill deposits. The first three components in each Principal Component Analysis accounted for approximately 95% of the variance in the data set. The Principal Component Analysis suggests that ground water inherits its trace element composition from the rocks or aquifer material with which it has interacted and may be used for the purpose of identifying ground‐water movement and source.
Surfactant Solutions Developed for NAPL Recovery in Contaminated Aquifers
Authors: Martel Richard , Gélinas Pierre J.
Published: August 2005

Phase diagrams can be used to select surfactant solutions for diesel dissolution and extraction in contaminated aquifers. They indicate the active matter concentrations which can be injected into an aquifer. Due to surfactant precipitation or fine particles dispersion in sediments, surfactant solutions concentration greater than 5% and less than their solubility limit can be used for injections. Surfactant solution effects on interfacial tension (IFT) are consistent with predictions from phase diagrams. For similar active matter concentrations, IFT are lower for surfactant solutions that dissolve more diesel. IFT values between equilibrated diesel and surfactant solutions and observation of the oil‐in‐water microemulsions in column effluents confirm that solubilization of oil can occur in a Winsor type I system without oil mobilization. More than 50 sand column experiments were done for this study and a good agreement is observed between diesel dissolved in sand column experiments (with downward injection) and diesel dissolution predicted from phase diagrams. However, sand columns experiments showed significant decrease in efficiency with a drop in temperature from 25° C to 8° C (phase diagrams predict no change) and they are essential to check efficiencies of washing solution selected by phase diagrams. Optimal injection concentration of solutions decreases as the alcohols ratio (n‐AmOH:n‐BuOH) increases and as the temperature decreases. In columns, optimal concentration of surfactant solutions has a maximum efficiency of 0.4 (dissolved diesel/active matter). This limited performance is explained by: (1) the use of water to push a slug of washing solution creates dilution and thus demixing of the oil‐in‐water microemulsion in the column; (2) the limited interfacial area between diesel and washing solution in the porous media; (3) surface effects on the solid phase. Diesel extraction in sand columns is strongly influenced by the flow direction (up/down), the volume of the solution, and to a lesser extent by water salinity. Small modifications of flow velocity (three times faster) do not have a significant effect on diesel dissolution. Efficiency of diesel dissolution by surfactant solutions decreases as washing progresses because interfacial area (diesel/surfactant solution) decreases. The selection of a surfactant for diesel recovery is not based on efficiency alone but must also consider the costs of the ingredients.
Geophysics and Shallow Faults in Unconsolidated Sediments
Authors: Wyatt Douglass E. , Waddell Michael G. , Sexton G. Boyd
Published: August 2005

This paper presents a case study using various geophysical techniques in unconsolidated sediments where shallow faulting is probable and most likely affects ground‐water flow. Wenner and dipole‐dipole resistivity, ground penetrating radar (GPR), and high resolution reflection seismic data are compared with cone penetrometer (CPT) information, existing monitoring well data and models of anticipated fault styles. The results of this study suggest that (1) the CPT study, combined with monitoring well data may suggest that discontinuities in corrrelatable zones indicate that faulting is present; (2) the addition of Wenner and dipole‐dipole data may further suggest that offset zones exist in the shallow subsurface but make it difficult to map specific faults; (3) the high resolution seismic data will image faults to within a few meters of the surface but cannot identify faulting on the scale of our models; (4) offset 100 MHz and 200 MHz common mid‐point (CMP) GPR will image features that may be fault planes and strands similar to the models; and (5) the combination of all the tools in this study, particularly the GPR and seismic, may allow for the mapping of small‐scale, shallow faults in unconsolidated sediments that affect ground‐water flow.