bluuebunny/crossref_metadata_2025 huggingface dataset:
Program to Calculate Hydraulic Conductivity Using Dugwell Recovery Data
Authors: Lalwani Anil , Kulkarni Himanshu , Deolankar S. B. , Thomas P. Paul
Published: August 2005

DUGREC is a computer program to estimate hydraulic conductivities for the Deccan basalts of India. Large‐diameter dugwells are still a very common source of water supply in the Deccan basaltic region of west‐central India. It is easier to conduct accurate recovery tests rather than conventional pumping tests on large‐diameter dugwells in the Deccan basalts of India. DUGREC is a program written in BASICA for IBM PC microcomputers and compatibles to calculate hydraulic conductivity values for the shallow unconfined Deccan basaltic aquifers using dugwell recovery data.
Geochemical Indicators of Intrinsic Bioremediation
Authors: Borden Robert C. , Gomez Carlos A. , Becker Mark T.
Published: August 2005

A detailed field investigation has been completed at a gasoline‐contaminated aquifer near Rocky Point, NC, to examine possible indicators of intrinsic bioremediation and identify factors that may significantly influence the rate and extent of bioremediation. The dissolved plume of benzene, toluene, ethylbenzene, and xylene (BTEX) in ground water is naturally degrading. Toluene and o‐xylene are most rapidly degraded followed by m‐, p‐xylene, and benzene. Ethylbenzene appears to degrade very slowly under anaerobic conditions present in the center of the plume. The rate and extent of biodegradation appears to be strongly influenced by the type and quantity of electron acceptors present in the aquifer. At the upgradient edge of the plume, nitrate, ferric iron, and oxygen are used as terminal electron acceptors during hydrocarbon biodegradation. The equivalent of 40 to 50 mg/I of hydrocarbon is degraded based on the increase in dissolved CO2 relative to background ground water. Immediately downgradient of the source area, sulfate and iron are the dominant electron acceptors. Toluene and o‐xylene are rapidly removed in this region. Once the available oxygen, nitrate, and sulfate are consumed, biodegradation is limited and appears to be controlled by mixing and aerobic biodegradation at the plume fringes.
The Correlation Between Bedrock Uranium and Dissolved Radon in Ground Water of a Fractured Carbonate Aquifer in Southwestern Ohio
Authors: Gall Ivan K. , Ritzi Robert W. , Baldwin A. Dwight , Pushkar Paul D. , Carney Cindy K. , Talnagi Joseph F.
Published: August 2005

Two hypotheses have previously been proposed for the source of elevated radon in ground water of southwestern Ohio: (1) penecontemporaneous uranium at the Silurian‐Ordovician unconformity, and/or (2) parent radionuclides transported from fragments of uranium‐rich Ohio Shale within the glacial drift above the aquifer. To further test the first hypothesis, vertical profiles of dissolved radon in ground water and uranium in rock cores were obtained at two locations immediately underlain by the Silurian/Ordovician unconformity. Radon concentrations exceeding 1000 pCi/l occurred in zones where the bedrock had uranium concentrations greater than 1.5 ppm. Radon concentrations of less than 500 pCi/l occurred in zones where the rock had uranium concentrations below 0.25 ppm. A log‐linear regression model between uranium and radon had a correlation coefficient of 0.82. Three aspects of the results support the hypothesis that the source is transported, although not necessarily from fragments of Ohio Shale. First, the high uranium‐radon zones did not occur consistently or exclusively at the Silurian/Ordovician unconformity. Second, the high uranium‐radon zones are correlated to fracture zones having a higher hydraulic conductivity and thus appear to be related to the zones of greater flow and transport. Third, the amount of uranium‐radon disequilibrium increases exponentially with increasing hydraulic conductivity. The hypothesis of a penecontemporaneous source, not supported by our study, arose when previous investigators conducted regional surveys of domestic wells and springs and found a correspondence between elevated radon and the location of the Silurian‐Ordovician unconformity. The observations of the previous investigators can be explained by the fact that the basal Silurian is in some places a horizon of higher hydraulic conductivity that facilitates transport. The two most probable external sources of uranium would be uranium‐containing detritus in the glacial drift or uranium‐containing phosphate fertilizers spread on the surface. Given that the uranium was transported into the aquifer during the Holocene, it could not have generated enough radium in the time elapsed since entering the aquifer to produce the radon levels that were measured. This observation indicates that radium was cotransported with uranium into the zones of high radon.
Analytical Solutions for Gas Flow Due to Gas Injection and Extraction from Horizontal Wells
Authors: Falta Ronald W.
Published: August 2005

Analytical solutions are developed for modeling the transient and steady‐state gas pressure and the steady‐state streamfunction fields resulting from gas injection and extraction from a pair of parallel horizontal wells. These solutions apply to cases in which the ground surface is open to the atmosphere, and in which the porous media is anisotropic but homogeneous. By neglecting end effects due to the finite length of the wells, the three‐dimensional gas flow field is approximated as a two‐dimensional cross section perpendicular to the wells. These solutions may be used to develop estimates of the horizontal well system behavior and to analyze horizontal well gas pump tests, and are useful for numerical model verification.
Modeling of Contaminant Movement Near Pumping Wells: Saturated‐Unsaturated Flow with Particle Tracking
Authors: Akindunni Festus F. , Gillham Robert W. , Conant Brewster , Franz Thomas
Published: August 2005

A transient axisymmetric saturated‐unsaturated numerical flow model was coupled with a particle tracking model to investigate the movement of contaminants when a shallow unconfined aquifer is pumped at a constant rate. The particle tracking model keeps track of locations and masses of solutes in the aquifer, and the time of capture by the well. At the end of each time‐step the flow model solves the Richard's equation for the hydraulic head distribution from which elemental velocities are calculated. Solutes are then displaced for a period equivalent to the time‐step using both the magnitude and direction of the elemental velocities. Numerical experiments were performed to investigate effluent concentrations in wells with screens of different length and in different positions relative to zones of stratified contamination. At early times of pumping the effluent concentrations were similar to the concentrations adjacent to the well screen, but at late times, the concentrations approached the vertically averaged concentration in the aquifer. Time to attain the vertically averaged concentration was determined by the well geometry, initial location of the contaminant plume in relation to the well screen, and hydraulic properties of the aquifer. The results are consistent with the hydraulics of flow to a pumping well and of particular importance, they demonstrate that short‐term pump tests could give erroneous design concentrations for pump‐and‐treat systems. The model provides a means of quantifying arrival times and mixing ratios. It could therefore provide a useful means of designing production wells in aquifers with stratified contamination and more efficient recovery systems for aquifer remediation.
Characterization of High‐K Pathways by Borehole Flowmeter and Tracer Tests
Authors: Young Steven C.
Published: August 2005

This paper reviews different borehole flowmeter analysis methods and evaluates their applicability to a test site composed of fluvial deposits. Results from tracer and aquifer tests indicate that the aquifer is highly heterogeneous and that low‐K skin effects exist at the wells. Borehole flowmeter tests were performed at 37 wells. An appropriate method for calculating borehole flowmeter K values was developed based on results from multiwell pumping tests, single‐well pumping tests, and slug tests. The flowmeter data produced 881 K values. The trends and the magnitude of the K values are consistent with results from geologic investigations, recirculating tracer tests, and large‐scale multiwell pumping tests. The field tests illustrate that high‐K deposits can significantly affect ground‐water flows in some heterogeneous fluvial aquifers.
Evaluation of Ground‐Water Contamination from Nonpoint Sources: A Case Study
Authors: van den Brink Cors , Zaadnoordijk Willem J.
Published: August 2005

In many countries a substantial part of the drinking‐water supply comes from subsurface‐water resources. During the last several decades an increasing extent of diffuse pollution has endangered these water resources. Knowledge of the changes in ground‐water quality is necessary in order to know if, and to what extent, ground‐water quality is endangered.

Changes in ground‐water quality can be predicted by means of models describing both the ground‐water flow and the transport of contaminants. A Geographic Information System is an efficient tool to handle the storage and manipulation of the large amount of data needed for the description of diffuse pollution. A methodology to predict changes in ground‐water quality, which is called FLUNIT, has been built around the programs FLUZO, NITRON, ARC/INFO, dBASE, and WELCON, and the ground‐water flow package TRIWACO. The method runs on a PC (with 386 processor).

The system has been applied to a well field on Csepel Sziget (near Budapest, Hungary). The purpose was not so much the prediction of the ground‐water quality, but much more the evaluation of ground‐water protection strategies based on risk analysis and effectivity of possible measures. The system has been designed in such a way that the important information can be used with the available resolution, and that new and more detailed data can be added efficiently.

Change of the nitrogen concentrations in the extracted water can be predicted. The resolution is sufficient for the evaluation of alternative ground‐water protection strategies. Moreover, detailed insight into changes in ground‐water quality can be obtained quickly.
Location of Water Table by FEM and Verification by Electrical Analogy Experiments
Authors: Rao H. Suresh , Sankaranarayanan S.
Published: August 2005

Sheet piles are used to lower the water table that exists downstream of a sheet pile. Under certain conditions of the upstream water heads and sheet pile embedment depths, a free boundary in the form of the water table may occur on the downstream. This free boundary is not known a priori and must be determined as a part of the solution; to make this possible, additional boundary conditions need to be satisfied on the free boundary. Analytical solutions are readily available for the location of such water tables, but with the impervious bottom located at infinite depth and for rectilinear boundary geometry. In the present study, the location of the water table downstream of a sheet pile with the impervious bottom located at finite depth is obtained using Finite‐Element Method (FEM). An experimental solution using electrical analogy is attempted to validate the solution obtained using FEM. Parametric studies are also carried out to study the various parameters affecting the location of the water table.
Combining the Neuman and Boulton Models for Flow to a Well in an Unconfined Aquifer
Authors: Moench Allen F.
Published: August 2005

A Laplace transform solution is presented for flow to a well in a homogeneous, water‐table aquifer with noninstanta‐neous drainage of water from the zone above the water table. The Boulton convolution integral is combined with Darcy's law and used as an upper boundary condition to replace the condition used by Neuman. Boulton's integral derives from the assumption that water drained from the unsaturated zone is released gradually in a manner that varies exponentially with time in response to a unit decline in hydraulic head, whereas the condition used by Newman assumes that the water is released instantaneously. The result is a solution that reduces to the solution obtained by Neuman as the rate of release of water from the zone above the water table increases. A dimensionless fitting parameter, γ, is introduced that incorporates vertical hydraulic conductivity, saturated thickness, specific yield, and an empirical constant α1, similar to Boulton's α. Results show that theoretical drawdown in water‐table piezometers is amplified by noninstantaneous drainage from the unsaturated zone to a greater extent than drawdown in piezometers located at depth in the saturated zone. This difference provides a basis for evaluating γ by type‐curve matching in addition to the other dimensionless parameters. Analysis of drawdown in selected piezometers from the published results of two aquifer tests conducted in relatively homogeneous glacial outwash deposits but with significantly different hydraulic conductivities reveals improved comparison between the theoretical type curves and the hydraulic head measured in water‐table piezometers.
Effect of Well‐Screen Placement on Recovery of Vertically Stratified Contaminants
Authors: Conant Brewster , Akindunni Festus F. , Gillham Robert W.
Published: August 2005

Field experiments and numerical modeling showed that vertical placement of a pumping‐well screen in an appropriate location could enhance the recovery of dissolved contaminants from a distinct depth interval of an unconfined aquifer. Two single‐well contaminant recovery tests were performed for 72 hours each at Borden, Ontario in a thin, fine‐grained sand aquifer. A zone 1.5 m thick at the bottom of the aquifer was contaminated by landfill leachate. One screen was located entirely within the contaminated zone and the other had only half its length placed in the zone of contamination. In both tests, concentrations in the effluent were initially high, but asymptotically declined and approached the vertically averaged concentration of the aquifer. The decline in concentration occurred because converging flow in the vertical plane caused a reduction in the thickness of the plume near the well; that in turn decreased the ratio of contaminated to clean waters entering the well screen. The field results were simulated using SUNFLOWPT, a saturated‐unsaturated flow model with particle tracking. Predictions of the model successfully matched the observed drawdown and effluent concentration data. Propagation of simulated capture zones into the overlying uncontaminated aquifer waters are consistent with the observed declines in effluent concentrations. Two‐dimensional plan‐view modeling is unable to accurately simulate observed data at early times of pumping. In aquifers having stratified contamination, only models that incorporate vertical flow should be used to interpret or predict effluent concentrations from short‐duration tests conducted for the purpose of designing pump‐and‐treat remediation schemes. The results suggest that in some cases of long‐term cleanup, two screens that separately capture the clean and contaminated waters of the aquifer could significantly reduce the volume of water requiring treatment.
Interpretation of Prematurely Terminated Air‐Pressurized Slug Tests
Authors: Shapiro Allen M. , Greene Earl A.
Published: August 2005

Air‐pressurized slug tests offer a means of estimating formation transmissivity and storativity without extensive downhole equipment and in situations where contact with formation fluids may pose a health concern. An air‐pressurized slug test, as discussed in this paper, consists of applying a constant pressure to the column of air in a well, monitoring the declining water level, and then releasing the air pressure and monitoring the recovering water level. If the maximum declining (or new equilibrium) water level is achieved for a constant applied air pressure, the slug‐test solution of Cooper et al. (1967) can be used to interpret the water‐level recovery data and estimate the formation properties. In low‐permeability terranes, the time required to achieve the equilibrium water level during the pressurized part of the test may be too long for practical purposes, and it may be necessary to terminate the applied air pressure prior to establishing a new equilibrium. To analyze data from such tests, a solution to the boundary‐value problem for the declining and recovering water level during an air‐pressurized slug test is developed for an arbitrary time‐dependent air pressure applied to the well. For the special case of applying a constant air pressure and then reducing it instantaneously to atmospheric pressure at a prescribed time, the general solution reduces to the superposition of the solution of Cooper et al. (1967) at two displaced times. Type curves are generated to estimate formation transmissivity and storativity from the recovering water level associated with prematurely terminated air‐pressurized slug tests. The application of the type curves is illustrated in tests conducted in wells completed in the Minnelusa and Madison aquifers near Rapid City and Spearfish, South Dakota.
Roberts Rift, Canyonlands, Utah, A Natural Hydraulic Fracture Caused by Comet or Asteroid Impact
Authors: Huntoon Peter W. , Shoemaker Eugene M.
Published: August 2005

The impact that created Upheaval crater in Canyonlands National Park, Utah, is invoked here as the source for energy that simultaneously caused Roberts rift. However, no temporal linkage has been proven between the impact and rifting events.

Roberts rift lies between 22 and 32 km northeast of the Upheaval impact crater on a subradial trend. The fissure contains clasts that were carried as much as 1,000 m upward from Paleozoic sources into the Mesozoic section.

A plausible model for both the rifting and clast movement involves incremental loading of overpressured fluid compartments in the Pennsylvanian Paradox section and attendant hydraulic fracturing of the overlying confining strata during the impact event. The clasts were proppants entrained in upward moving fluids that originated from overpressured aquifers in the Pennsylvanian section or materials eroded from the fissure walls.

Alteration halos and mineralization along the fissure reveal that there was upward leakage of reducing fluids from the overpressured zones following opening of the fissure. The fissure infillings became cemented with time, thus reducing fissure permeabilities to negligible.
Evaluation of Simplified Stream‐Aquifer Depletion Models for Water Rights Administration
Authors: Sophocleous Marios , Koussis Antonis , Martin J. L. , Perkins S. P.
Published: August 2005

We assess the predictive accuracy of Glover's (1974) stream‐aquifer analytical solutions, which are commonly used in administering water rights, and evaluate the impact of the assumed idealizations on administrative and management decisions. To achieve these objectives, we evaluate the predictive capabilities of the Glover stream‐aquifer depletion model against the MODFLOW numerical standard, which, unlike the analytical model, can handle increasing hydrogeologic complexity. We rank‐order and quantify the relative importance of the various assumptions on which the analytical model is based, the three most important being: (1) streambed clogging as quantified by streambed‐aquifer hydraulic conductivity contrast; (2) degree of stream partial penetration; and (3) aquifer heterogeneity. These three factors relate directly to the multidimensional nature of the aquifer flow conditions. From these considerations, future efforts to reduce the uncertainty in stream depletion‐related administrative decisions should primarily address these three factors in characterizing the stream‐aquifer process. We also investigate the impact of progressively coarser model grid size on numerically estimating stream leakage and conclude that grid size effects are relatively minor. Therefore, when modeling is required, coarser model grids could be used thus minimizing the input data requirements.
Surface Geophysical Surveys of the Freshwater‐Saltwater Interface in a Coastal Area of Long Island, New York
Authors: McNew Elizabeth R. , Arav Sara
Published: August 2005

The North Fork of Long Island is a peninsula whose freshwater supply consists of several lenses of fresh ground water that are surrounded by saline ground water. A study to determine the thickness of one freshwater lens near the Village of Greenport used two surface‐geophysical techniques at several sites to provide ground‐conductivity data that were, in turn, used to estimate the depth to the freshwater‐saltwater interface. Surveys were made during the spring and fall of 1989. Wells drilled during 1989 provided some verification of geophysical interpretations.

Geophysical‐data interpretations were based on conceptual models with two, three, and four conductivity layers; the three‐layer concept produced interpretations that best matched geophysical measurements at all sites. The surface geophysical techniques were successful in interpreting depth to saline ground water. Interpreted depths to the freshwater‐saltwater interface were compared to assess seasonal changes; the interpreted differences were small and within the range of error of the survey techniques.
Estimation of Free‐Hydrocarbon Recovery from Dual‐Pump Systems
Authors: Charbeneau Randall J. , Chiang Chen Y.
Published: August 2005

Free‐product hydrocarbon which floats on the water table may be recovered using single‐pump and dual‐pump systems. The factors that affect the long‐term free‐product recovery using dual‐pump systems include the free‐product thickness as measured in monitoring wells, the ground‐water pumping rate, hydrocarbon density and viscosity, and the soil permeability. This paper presents a simple model for prediction of free‐product recovery using dual‐pump systems. The model predicts the long‐term rather than short‐term recovery rates, and lends itself to spreadsheet calculations on microcomputers. A particularly simple form arises for cases where the drawdown is small. An application for estimating recovery from a dual‐pump system is presented, and limitations of the model are summarized.
Observed and Simulated Movement of Bank‐Storage Water
Authors: Squillace Paul J.
Published: August 2005

Detailed hydrologic and water‐chemistry data were collected that document the movement of bank‐storage water during March 7‐April 17, 1990, in an alluvial aquifer adjacent to the Cedar River, Iowa. Hydrologic data included 745 daily ground‐water‐level measurements from 27 observation wells. Water‐chemistry data indicate that bank‐storage water had smaller specific conductance and larger concentration of atrazine than ambient ground water. To quantify the movement of the bank‐storage water, a two‐dimensional ground‐water flow model was constructed, and the resulting calibrated model accurately simulated observed conditions. Analysis of water chemistry and model results indicate that a 2‐meter rise in the river stage caused bank‐storage water to move horizontally at least 30 meters into the aquifer and vertically about 4 meters below the river bottom, whereas the remaining 30 percent moved laterally through the riverbank. The model also showed that bank storage caused the ground‐water flux to the river to increase by a factor of five during the first three weeks of base flow after runoff and that it required about five weeks for bank‐storage water to discharge from the alluvial aquifer after the peak river stage. These results quantitatively demonstrate the importance of bank storage as a source of recharge to the alluvial aquifer and as a source of water to the river during early base‐flow conditions.
The Constant Displacement Scheme for Tracking Particles in Heterogeneous Aquifers
Authors: Wen Xian‐Huan , Gómez‐Hernández J. Jaime
Published: August 2005

Simulation of mass transport by particle tracking or random walk in highly heterogeneous media may be inefficient from a computational point of view if the traditional constant time step scheme is used. A new scheme which adjusts automatically the time step for each particle according to the local pore velocity, so that each particle always travels a constant distance, is shown to be computationally faster for the same degree of accuracy than the constant time step method. Using the constant displacement scheme, transport calculations in a 2‐D aquifer model, with nature log‐transmissivity variance of 4, can be 8.6 times faster than using the constant time step scheme.
Feasibility of Bioremediation of a Ground Water Polluted with Alkylpyridines
Authors: Ronen Zeev , Bollag Jean‐Marc , Hsu Cheng‐Hsiung , Young James C.
Published: August 2005

The potential for bioremediation of ground water polluted with various alkylpyridines was investigated. Aerobic bacteria, indigenous to the ground‐water aquifer, were utilized for biodegradation of the various contaminants. Laboratory experiments demonstrated that biodegradation occurred only under aerobic and not under anaerobic conditions. Analysis of the ground water in the site indicated that levels of oxygen were below 1 mg/l. Thus, it is suggested that oxygen limitation prevented the biodegradation of pollutants in the aquifer. Phosphate amendment (5 mg/1) into slurries of contaminated sediment and ground water resulted in enhanced degradation rates.

Columns filled with aquifer material and leached with contaminated ground water were used to simulate possible in situ bioremediation. Reduction in concentration of the different compounds in column effluents ranged between 40 and 80%, with 2,3‐, 2,6‐, and 3,5‐lutidine degrading at lower rates than other contaminants. In addition to in situ treatment, the potential of using aboveground systems for treatment was explored. A mixed culture capable of degrading 14 different alkylpyridines was isolated from the subsurface sediment. This culture was used to seed a two‐stage fixed film reactor. The reactor was fed with a mixture of organic acids and alkylpyridines that simulated the ground‐water composition. The reactors were very effective in removing the pollutants from the waste stream. The efficiency of alkylpyridine removal was between 98 and 100% and overall COD removal was 97%, when operating at a loading rate of 4.32 g COD/L‐h and hydraulic retention time of 3 h. These results imply that a combined approach which utilizes both in situ and aboveground treatments should be used for the bioremediation of polluted ground water.
Surface Application System for In Situ Ground‐Water Bioremediation: Site Characterization and Modeling
Authors: Sweed Howard G. , Bedient Philip B. , Hutchins Stephen R.
Published: August 2005

Surface application offers an inexpensive, noninvasive alternative to injection wells and infiltration galleries for in situ ground‐water bioreniediation applications. The technology employs artificial recharge to create favorable hydraulic conditions for mixing and vertical transport of supplemental electron acceptor and nutrients. A test plot infdtration test and a conservative tracer test at Eglin Air Force Base, FL confirmed the potential for transporting solutes to the subsurface via recharging water. These experiments demonstrated both the mounding hydraulics and vertical solute transport that occurs in response to surface application. Modeling provided quantitative estimates of site‐specific hydrogeologic and transport parameters. Experimental results also indicated that dilution may be a dominant attenuation mechanism associated with high surface application rates. The tests also served as the basis for the design of a pilot scale surface application system for delivery of nitrate to bioremediate a JP‐4 contaminated aquifer at the Eglin site. Models calibrated to data from the infiltration experiment were scaled up for design of the pilot scale surface application system. Preliminary tracer results from the pilot scale experiment confirm that surface application can adequately deliver chemicals to the subsurface.
Controls on 222Rn Variations in a Fractured Crystalline Rock Aquifer Evaluated Using Aquifer Tests and Geophysical Logging
Authors: Folger P. F. , Poeter E. , Wanty R. B. , Frishman D. , Day W.
Published: August 2005

Concentrations of 222Rn in ground water may vary considerably within megascopically homogeneous rocks over relatively short distances. Calculations indicate that different hydraulic apertures of water‐bearing fractures may account for variations in dissolved 222Rn concentration measured in domestic water wells completed in fractured Pikes Peak Granite, assuming that all other factors influencing dissolved 222Rn concentrations are constant. Concentrations of dissolved 222Rn range from 124 to 840 kBq m‐3 [3,360 to 22,700 picocuries per liter (pCi L‐1)] within a 2.5 km2 well field. Aquifer tests show that transmissivities range from 0.072 to 160 m2 day‐1 within the well field. Acoustic televiewer and heat‐pulse flow meter logging of four wells reveals that, despite tens to hundreds of fractures that intersect each well, a single fracture supplies all the flow to three wells, and one fracture provides 65% of the flow to the fourth well. Aquifer tests indicate that two pairs of the four wells are hydraulically connected. Type‐curve interpretation of early‐time data from aquifer tests reveals classic half‐slope behavior on log‐log plots of drawdown versus time for two wells, suggesting linear flow to a single fracture. Drawdown versus time for the other two wells indicates radial or pseudo‐radial flow, which suggests a higher degree of fracture interconnectivity near those boreholes.

Hydraulic apertures calculated using the cubic law are 0.024 and 0.038 cm for producing fractures in the first hydraulically connected well pair and 0.011 and 0.020 cm for flowing fractures in the second well pair. Assuming uniform distribution of 226Ra along fracture walls and long residence time of water relative to 222Rn decay, the ratio of fracture apertures should equal the inverse ratio of 222Rn concentration in each well. Assuming 50% error in hydraulic aperture estimation and 10% analytical uncertainty in 222Rn measurement, differences in 222Rn concentration between wells in the hydraulically connected pairs can be attributed solely to differences in hydraulic aperture. Different hydraulic apertures, however, do not explain different 222Rn concentrations between well pairs. Allowing for measurement error, a cubic meter of rock transfers from 1.3 to 20 times more 222Rn to ground water in the first pair of wells than in the second pair. Nonuniform distribution of 226Ra along fracture walls, heterogeneous emanating power in the rock‐water system, or short ground‐water residence time along the transmissive fracture network may account for the difference between well pairs.
Bias in Ground‐Water Data Caused by Well‐Bore Flow in Long‐Screen Wells
Authors: Church Peter E. , Granato Gregory E.
Published: August 2005

The results of a field experiment comparing water‐quality constituents, specific conductance, geophysical measurements, and well‐bore hydraulics in two long‐screen wells and adjacent vertical clusters of short‐screen wells show bias in ground‐water data caused by well‐bore flow in long‐screen wells. The well screen acts as a conduit for vertical flow because it connects zones of different head and transmissivity, even in a relatively homogeneous, unconfined, sand and gravel aquifer where such zones are almost indistinguishable. Flow in the well bore redistributes water and solutes in the aquifer adjacent to the well, increasing the risk of bias in water‐quality samples, failure of plume detection, and cross‐contamination of the aquifer. At one site, downward flow from a contaminated zone redistributes solutes over the entire length of the long‐screen well. At another site, upward flow from an uncontaminated zone masks the presence of a road salt plume.

Borehole induction logs, conducted in a fully penetrating short‐screen well, can provide a profile of solutes in the aquifer that is not attainable in long‐screen wells. In this study, the induction‐log profiles show close correlation with data from analyses of water‐quality samples from the short‐screen wells; however, both of these data sets differ markedly from the biased water‐quality samples from the long‐screen wells. Therefore, use of induction logs in fully cased wells for plume detection and accurate placement of short‐screen wells is a viable alternative to use of long screen wells for water‐quality sampling.
Detection and Monitoring of Chlorinated Solvent Contamination by Thermal Neutron Logging
Authors: Endres Anthony L. , Greenhouse John P.
Published: August 2005

Thermal neutron logging is used to determine water content by measuring the elastic scattering due to hydrogen present in rocks and soils. The response of a thermal neutron device is also affected by the radiative capture of thermal neutrons by all elements. Chlorine has a large capture cross section in comparison to other elements usually found in aquifers; therefore, theory predicts that thermal neutron devices should respond to the presence of chlorinated solvents. Thermal neutron logging performed during a controlled release of perchloroethylene (PCE) confirmed that these methods can be used successfully to detect and monitor chlorinated solvents in the subsurface. To quantify the field results, a series of laboratory tests assessed the response of a neutron moisture probe used in the field experiments. These tests show that this device is very sensitive to the presence of chlorine and provide a basis for converting its response into an apparent PCE saturation. These saturation values compare favorably with PCE saturations obtained from core samples.
Modeling of Nitrogen Cycle and Nitrate Transfer in Regional Hydrogeologic Systems
Authors: Geng Q. Z. , Girard G. , Ledoux E.
Published: August 2005

A model of the nitrogen cycle and nitrate leaching in soil, called MORELN, was developed to calculate the nitrate flux percolating from soils into aquifers. It uses a “coupled model,” which simulates both surface and subsurface flows. A third model, NEWSAM, is linked to the above models to simulate nitrate migration in an aquifer system. This methodology gives a quantitative global description of nitrate transfer, taking into account both leaching in soils and migration in aquifers. Three examples of application tested this methodology (especially the nitrate leaching code, MORELN) at different scales and with different emphases: (1) in a soil plot of several square meters; (2) in a small experimental basin of several square kilometers; and (3) in a regional hydrogeologic system of several hundred square kilometers. Satisfactory results were obtained for the simulation of nitrate leaching at the small scale. Major differences between the measured and simulated nitrate concentrations were observed in a regional aquifer, where the measured concentration does not spatially correlate and the larger spatial variability of the input data were averaged in the model.
LNAPL Thickness in Monitoring Wells Considering Hysteresis and Entrapment
Authors: Marinelli Fred , Durnford Deanna S.
Published: August 2005

Case histories of LNAPL contaminated sites indicate that LNAPL thicknesses in monitoring wells exhibit certain characteristic behaviors when related to water‐table fluctuations. This paper investigates these behaviors using established theories for fluid saturataions in three‐phase (air‐LNAPL‐water) porous media systems. A semianalytical model is developed to predict the LNAPL thickness in a monitoring well considering the effects of saturation hysteresis and air/LNAPL entrapment. Given the total LNAPL volume in the soil profile and the historical sequence of water‐table elevations, the model predicts LNAPL thicknesses, based on the assumption of a succession of hydrostatic pressure distributions. For example simulations, the model indicates that the LNAPL thickness in a monitoring well can exhibit complex behaviors that are strongly dependent on the previous saturation history. While many of these predicted behaviors are consistent with field observations, some are not. This suggests that certain aspects of current theories pertaining to three‐phase fluid saturations warrant further technical evaluation.
A Structured Approach for Calibrating Steady‐State Ground‐Water Flow Models
Authors: Yeh T.‐C. Jim , Mock Peter A.
Published: August 2005

A structured approach for calibrating two‐dimensional, steady‐state ground‐water flow models is developed. The first step of the proposed approach is to replace the heterogeneous aquifer with an equivalent homogeneous one using the geometric mean of transmissivities. Then, boundary conditions are adjusted with the aid of a scatter gram to reduce bias of the simulated hydraulic head distribution of the equivalent homogeneous aquifer. After the bias is removed, the differences between the simulated mean hydraulic head and the observed hydraulic head, resulting from small‐scale heterogeneities, are then reduced by adjustment of local transmissivity values based on hydrological and geological information. The validity of the proposed procedure was tested for a hypothetical aquifer under idealized conditions and it was then applied to the Avra Valley in southern Arizona to demonstrate its utility in real world scenarios.
Multiphase Numerical Simulation of Air Sparging Performance
Authors: Lundegard Paul D. , Andersen Greg
Published: August 2005

The performance of air sparging systems, as measured by the predicted region of airflow, was investigated by conducting numerical simulations with a multiphase modeling program (TETRAD). The simulations employed standard two‐phase flow theory, and included pressure‐dependent calculations of the compressibility of water and air. Simulations tested the response of air sparging systems to variations in geological properties (intrinsic permeability and anisotropy of permeability) as well as different injection scenarios (depth, pressure, and rate of injection).

Three stages of flow behavior are predicted following initiation of air injection. These are: (1) an initial transient period of growth in the lateral and vertical limits of airflow (expansion stage); (2) a second transient period of reduction in the lateral limits of airflow (collapse stage); and (3) a steady‐state stage, during which the system remains static as long as injection parameters do not change. In homogeneous media the geometry of the region of airflow changes from a teardrop‐or bell‐shaped configuration to a shape that is roughly conical during the expansion stage. During the collapse stage, air is preferentially diverted to established regions of high effective air permeability, and ground water resaturates the remainder of the original region of influence. For pilot testing it is important to realize that measurements of the lateral extent of airflow expansion and collapse stages can be misleading because they will differ from the limits established at steady‐state. The time required for a particular system to progress through the transient stages and establish steady‐state behavior can vary from hours to years, and is dependent on the permeability structure of the aquifer, injection depth, and injection rate. Under homogeneous conditions the maximum width of the region of airflow attained during the transient expansion stage was substantially greater than the width attained at steady‐state.

The width of the steady‐state region of airflow is significantly affected by all the variables investigated, except injection depth, which appears to primarily influence the transient behavior. The simulations further show that the vertical permeability and anisotropy of the aquifer are very important variables, and warrant routine assessment during design of sparge systems. Simulation of heterogeneous media demonstrate that complex airflow patterns will occur as a result of air ponding beneath, and flow around, zones of low air permeability.
The Ratio Method of Estimating Water Resistivity and TDS from Resistivity Logs
Authors: Jorgensen Donald G.
Published: August 2005

It is a general belief that useful estimates of total dissolved solids concentrations of ground water cannot be made from borehole geophysical logs. A case study of estimating total dissolved solids concentration of ground water in the local area using the ratio method yielded estimates with an average error of less than 25 percent. The results do not support the hypothesis that useful estimates of total dissolved solids concentration cannot be made from borehole geophysical logs.

The case study included a comparison of estimates of total dissolved solids concentration utilizing a resistivity of the mud input versus using resistivity of the mud filtrate input. Estimates made using resistivity of mud had a correlation coefficient of 0.97 whereas estimates using resistivity of mud filtrate had a correlation coefficient of only 0.27. The results from the case study suggest that at least in some cases the resistivity of the mud (Rm) may produce a better estimate of the resistivity of water (Rw) in the fully flushed zone than an estimate using the resistivity of the mud filtrate Rmf.

The ratio method can be easily used to estimate ground‐water resistivity and total dissolved solids concentration of the formation water based only on data from resistivity logs. The advantage of the method is that data on porosity, cementation exponent, temperature, and volume of clay are not required. The method, which has been used by the oil industry to crudely estimate water resistivity, is based in part on the ratio of the resistivity of a fully water‐saturated formation to the resistivity of the fully flushed zone adjacent to the annulus in a mud‐filled borehole. The method, which is very robust, requires only an estimate of the resistivity of a fully water‐saturated formation from a deep looking induction or resistivity log, an estimate of the resistivity of the fully flushed zone from a microresistivity or short normal log, and a measurement of resistivity of the mud or mud filtrate and its temperature.
Application of Petroleum Geophysical Well Logging and Sampling Techniques for Evaluating Aquifer Characteristics
Authors: Temples Tom J. , Waddell Mike G.
Published: August 2005

The Hilton Head Island Test Well #1 was drilled to a depth of 3833 feet to evaluate the upper Cretaceous section as a potential ground‐water source for Hilton Head Island, South Carolina. The initial plan was to analyze continuous conventional cores. The interval to be analyzed extended from the top of the Eocene to the base of the Cretaceous (approximately 3500 feet). However, due to the high cost ($400,000), the decision was made to evaluate aquifer potential using advanced geophysical logs with sidewall cores for calibration.

The logging suite consisted of a dual induction resistivity, spontaneous potential, compensated neutron, density log, gamma ray, spectral gamma, multipole array acoustic log, caliper, high resolution dipmeter, and a circumferential borehole imaging log. In addition to the wireline logs, 239 sidewall cores and 12 Formation Multi‐Test samples were obtained.

The log, sidewall core, and FMT information were integrated into an interpretive package using computer generated logs and simple spreadsheets to calculate aquifer properties. Porosity, hydraulic conductivity, transmissivity, and lithologic data derived from this integrated analysis were then used to select screen zones. Water quality in relation to drinking water standards exceeded expectations. The information obtained from the integrated program allowed estimates to be made about the well's productivity without the expense of conventional coring, flow testing, and completion of the well.
The Impact of Ion Exchange Processes on Subsurface Brine Transport as Observed on Piper Diagrams
Authors: Cates David A. , Knox Robert C. , Sabatini David A.
Published: August 2005

An experimental study was conducted to assess how ion exchange processes, which occur during subsurface transport of oilfield brines, manifest themselves on graphical water quality diagrams. Concentrated brine soil column studies indicated sodium in the brine solution is able to exchange for calcium and magnesium on the soil, thereby retarding transport of sodium relative to the average ground‐water velocity and resulting in the development of a “hardness halo” at the leading edge of the brine plume. In this zone, calcium and magnesium concentrations exceed the values for both the brine and the fresh ground water. The hardness halo manifests itself as a characteristic deviation away from the mixing lines on the Piper diagram. Initially, the hardness halo causes concentrations to plot left of the fresh‐water end member in the cationic triangle. Chloride domination in oilfield brine causes concentrations to plot in the lower right corner of the anionic triangle almost immediately. After the hardness halo passes through the column, the sampling results show a characteristic pattern of movement parallel to the mixing line in the cation triangle or along the (decreasing) hardness axis of the upper diamond of the Piper diagram. The laboratory results were similar to those exhibited by monitoring well samples taken at a field site involving oilfield brine contamination. The results of this study show the Piper diagram to be potentially useful for early detection of brine contamination episodes.
Determining an Optimal Sampling Frequency for Measuring Bulk Temporal Changes in Ground‐Water Quality
Authors: Moline G. R. , Beauchamp J. J. , Wright T.
Published: August 2005

In the Data Quality Objectives (DQO) process, statistical methods are used to determine an optimal sampling and analysis plan. When the DQO decision rule for instituting remedial actions is based on a critical change in water quality, the monitoring program design must ensure that this change can be detected and measured with a specified confidence. Usually the focus is on the change at a single monitoring location and the process is limited to addressing the uncertainty inherent in the analytical methods and the variability at that location. However, new strategies that permit ranking the waste sites and prioritizing remedial activities require the means for assessing overall changes for small regions over time, where both spatial and temporal variability exist and where the uncertainty associated with these variations far exceeds measurement error. Two new methods for assessing these overall changes have been developed and are demonstrated by application to a waste disposal site in Oak Ridge, Tennessee. These methods incorporate historical data where available and allow the user to either test the statistical significance of a linear trend or of an annual change compared to a baseline year for a group of water quality wells.
Enhancing Data Worth of EM Survey in Site Assessment by Cokriging
Authors: Parks Kevin P. , Bentley Laurence R.
Published: August 2005

Ground‐water chemistry data from wells are cokriged with ground conductivity measurements to quantitatively describe ground‐water chemical quality at a site. The cokriged estimates are shown to be superior to both simple rescaling of ground conductivity by a linear regression model and to interpolation of ground‐water chemistry data from wells using ordinary kriging. By extending the use of geophysical measurements in this way, significant cost savings in site assessment can be realized and the geophysics will have more data “worth.”