bluuebunny/crossref_metadata_2025 huggingface dataset:
Regional Flow in the Baltic Shield During Holocene Coastal Regression
Authors: Voss Clifford I. , Andersson Johan
Published: August 2005

The occurrence of saline waters in the Baltic Shield in Sweden is consistent with ongoing but incomplete Holocene flushing and depends on the geometry and connectivity of conductive structures at both regional and local scales, and on the surface topography. Numerical simulation of regional variable‐density fluid flow during Holocene land‐rise and coastal regression shows that the existence of any old saline water, whether derived from submarine recharge in regions below Sweden's highest postglacial coastline or geochemical processes in the crystalline rock, is an indication either of slow fluid movements through the bedrock over long times, or of long travel distances through fracture systems before arriving at measurement points. During the land‐rise period, regional flow is not affected by the variable density of fluids in the upper few kilometers of the shield, and the topography of the water table is the only driving force. The spatial distribution of meteoric flushing water and pre‐Holocene waters may be complex, with the possibility of relatively fresh water in fracture zones below salty units even at depths of a few kilometers. The domination of the topographic driving force implies that deep saline water is not necessarily stagnant, and significant flow may be expected to occur in well‐connected horizons even at depth. Local topography variation and fracture zone location combine to create a complex flow field in which local topographic driving forces extend to considerable depth in some areas, whereas regional topographic forces predominate in others. Thus, a pattern may be difficult to discern in measurements of the regional salinity distribution, although it is clear that the coastal region is the major zone of discharge for deeper pre‐Holocene fluids. During the land‐rise period, the regional flow field equilibrates with changing climatic conditions and coastal positions, while the distribution of flushing water and older water lags and will perpetually change between successive glaciations. These characteristics have direct implications for the safety of nuclear water repositories located at depth in Baltic Shield rocks.
SHYDG.FOR—Hydrograph Package for MODFLOW
Authors: Plato Paul R.
Published: August 2005

SHYDG.FOR—Hydrograph Package for MODFLOW, was written for use with the USGS finite‐difference ground‐water flow model (MODFLOW). This program allows the user to specify a list of nodes where model generated heads are saved separately. The program was designed to assist in the calibration of ground‐water flow models by simplifying the process of creating hydrographs of simulated heads to compare with hydrographs of measured water levels. The program consists of two subroutines written in Fortran 77 to be added to MODFLOW and requires minor modification of the MODFLOW main program code.
Stable Isotopes of Oxygen and Nitrogen in Source Identification of Nitrate from Septic Systems
Authors: Aravena R. , Evans M. L. , Cherry J. A.
Published: August 2005

Stable isotopes, 15N and 18O, have been used as tracers to differentiate a contaminant nitrate plume emanating from a single domestic septic system, in a ground‐water system characterized by high and similar nitrate content outside and inside of the contaminant plume. A good delineation of the nitrate plume of septic origin was obtained using 15 N analysis in nitrate. The 15N content ofthe nonplunie nitrate is in agreement with the sources of nitrate: solid cattle manure, synthetic fertilizer (NH4‐NO3), and soil organic nitrogen, at the study site. 18O analysis in nitrate did not provide enough isotopic contrast to permit separation of nitrate derived from the septic system and that in the surrounding ground water, derived from agricultural fertilizer sources. 18O data indicated that nitrification of ammonium is the main process responsible for formation of nitrate at the study site. 18O in ground water clearly delineated the ground‐water plume associated with the septic system and suggest that this tracer should be considered in studies related with contaminant plumes of different origin.
Transient and Steady‐State Solute Transport Through a Large Unsaturated Soil Column
Authors: Porro I. , Wierenga P. J.
Published: August 2005

The use of steady‐state models can sometimes reduce the computational resources and input data required for solution of transient transport problems. A large column experiment was performed to test whether solute transport parameters determined from a steady flow experiment may be used in transient, unsaturated flow and transport model predictions. Tritiated water and bromide were applied at a steady rate to the top of a 0.95 m diameter by 6 m deep soil column containing unsaturated soil. After 10 days, tracers were eliminated from the irrigation water. When the soil moisture content within the column ceased to change, another 10‐day pulse of tritiated water and bromide was applied, followed by water without tracers. Transport model parameters were determined through optimization, using breakthrough curves observed at various depths. The tritiated water and bromide pulses lagged behind the wetting front during infiltration into the relatively dry soil. The bromide pulse moved 17–20% faster than the tritiated water pulse, because of anion exclusion. Breakthrough curves for the transient and steady‐state experiments were similar. Because the solute fronts lagged significantly behind the moisture fronts, steady‐state transport parameters, when used in a fully transient numerical model, fairly described the transport under transient conditions.
Classification of Transmissivity Magnitude and Variation
Authors: Krásný Jiri
Published: August 2005

Until now no objective classification of transmissivity has been introduced, in spite of the quantitative nature of transmissivity values and their obvious importance for quantitative appraisals of aquifers or major ground‐water systems. The usual subjective expression of transmissivity, for example as “high” or “low”, prevents the objective comparison of transmissivity values characterizing different areas and hydrogeological environments. A combined classification of magnitude and variation of transmissivity is proposed, with the intention to standardize the expression, comparison, and representation of transmissivity. This classification also enables its compact and unambiguous depiction in tables and maps.
Assessment of Long‐Term Withdrawal Rate for a Coastal Aquifer
Authors: Gupta A. Das , Amaraweera H.B.M.P.
Published: August 2005

The long‐term safe withdrawal rate for a coastal aquifer in Mannar Island of Sri Lanka was assessed through the simulation of interface movement. A range of estimates of natural recharge sequence was first obtained from a water balance study considering the variations of factors affecting the soil moisture balance. The representative recharge sequence was then determined through the simulation of a field observed interface profile along a selected section. Following this, the sustainability of continuous water withdrawal in the future was assessed by limiting the extent of salt‐water upconing. An increase in the withdrawal rate in the future would be possible through proper monitoring of the system response.
Chlorine‐36 in the Snake River Plain Aquifer at the Idaho National Engineering Laboratory: Origin and Implications
Authors: Beasley T. M. , Cecil L. D. , Sharma P. , Kubik P. W. , Fehn U. , Mann L. J. , Gove H. E.
Published: August 2005

Between 1952 and 1984, low‐level radioactive waste was introduced directly into the Snake River Plain aquifer at the Idaho National Engineering Laboratory (INEL), Idaho Falls, Idaho. These wastes were generated, principally, at the nuclear fuel reprocessing facility on the site. Our measurements of 36C1 in monitoring and production well waters, downgradient from disposal wells and seepage ponds, found easily detectable, nonhazardous concentrations of this radionuclide from the point of injection to the INEL southern site boundary. Comparisons are made between 3H and 36Cl concentrations in aquifer water and the advantages of 36C1 as a tracer of subsurface‐water dynamics at the site are discussed.
Vadose Zone Fertilizer‐Derived Nitrate and δ15N Extracts
Authors: Herbei Mitchell J. , Spalding Roy F.
Published: August 2005

Nitrate derived from commercial NH4NO3fertilizer, δ15N =+1.5 %0, applied to fertility plots was extracted from two cores to depths of 46 and 52 ft. In both cores the δ15N of the extracted nitrate‐nitrogen (NO3‐N) showed that it became heavier with depth. Although this isotope fractionation did not cause δ15N values to overlap with those characteristic of animal waste sources (> + 10%0), δ15N values were as high as +8%0at the bottom of one profile. The gradual increase in δ15N with depth in the bottom 20 to 30 ft of the cores is consistent with denitrification at these depths. Clay content was much more variable with depth and was significantly associated with NO3‐N concentrations (r =+0.9) in the core with 30% clay. Correlation of NO3‐N concentrations to clay content was not significant in the other core with 50% clay. In both cores smectite and illite were the dominant clays; chlorite, and aluminum and iron oxyhydroxides were not detected by XRD. Anion exchange capacity measurements confirmed that it was not responsible for the observed variability in NO3‐N concentrations or δ15N values.

Potassium chloride (KC1) extracts yielded significantly higher NO3‐N concentrations (p < 0.005) and lighter δ15N values (p < 0.0001) than distilled deionized water (DDW) extracts. It is postulated that NO3−not extracted by DDW is trapped within the microstructure of the swelling clays. The strongly depleted δ15N of–16.3 %0may be attributed to pH‐mediated aqueous ammonia or nitrate diffusion and/or ammonia volatilization into the smectite microstructure. Results indicated that DDW rather than KC1 extractions of sediments high in smectite (> 40%) provide more realistic estimates of ground‐water loading from nonpoint sources.
Estimation of Dispersion Parameters for Two‐Dimensional Plumes
Authors: Zou S. , Parr A.
Published: August 2005

An analytical method is developed whereby longitudinal and transversal dispersivities can be determined for a two‐dimensional plume generated by slug tracer injection in a uniform ground‐water flow field. One solution procedure requires concentration versus time data from two sampling wells through which the plume passes. A second solution procedure uses a least‐squares method to obtain optimal parameter estimations when only one sampling well is available. Both methods are particularly useful since they do not require a priori knowledge of either the direction or magnitude of the pore velocity. Detailed example calculations illustrate the solution procedures and show that these methods are successful.
Fate of Organochlorine Compounds During Aquifer Storage and Recovery: The Las Vegas Experience
Authors: Mille C. J. , Wilson L. G. , Amy Gary L. , Brothers Kay
Published: August 2005

Two water quality concerns with aquifer storage and recovery (ASR) operations are (1) the fate of organochlorine compounds, such as trihalomethanes (THMs), in the treated recharge source, and (2) the formation of organochlorine compounds from precursor materials following the chlorination of recovered water. The fate of chloroorganic compounds in chlorinated Colorado River water was studied during a 1989 recharge/recovery operation conducted by the Las Vegas Valley Water District (LVVWD). Water samples were obtained from two dual‐purpose wells during the pumping cycle for THMs and other indicators of organochlorine precursors. The percentage recovery of THMs was approximately the same as the percentage recovery of Colorado River water. This suggests that the removal of organochlorine compounds (e.g., by sorption) did not appreciably occur in the aquifer materials at the two well sites. Recovery of source water was incomplete. Accordingly, dissolved organic carbon (DOC), representing precursor material, remained in the aquifer at the end of the pumping cycle. The Las Vegas experience suggests that prolonged recharge and storage of Colorado River water in similar hydrogeologic basins (e.g., the Tucson basin) could result in problems with THM compliance at the well head. This will be a problem if THM standards are reduced during the interval that water is stored.
Sampling Colloids and Colloid‐Associated Contaminants in Ground Water
Authors: Backhus Debera A. , Ryan Joseph N. , Groher Daniel M. , MacFarlane John K. , Gschwend Philip M.
Published: August 2005

It has recently been recognized that mobile colloids may affect the transport of contaminants in ground water. To determine the significance of this process, knowledge of both the total mobile load (dissolved + colloid‐associated) and the dissolved concentration of a ground‐water contaminant must be obtained. Additional information regarding mobile colloid characteristics and concentrations are required to predict accurately the fate and effects of contaminants at sites where significant quantities of colloids are found. To obtain this information, a sampling scheme has been designed and refined to collect mobile colloids while avoiding the inclusion of normally immobile subsurface and well‐derived solids. The effectiveness of this sampling protocol was evaluated at a number of contaminated and pristine sites.

The sampling results indicated that slow, prolonged pumping of ground water is much more effective at obtaining ground‐water samples that represent in situ colloid populations than bailing. Bailed samples from a coal tar‐contaminated site contained 10–100 times greater colloid concentrations and up to 750 times greater polycyclic aromatic hydrocarbon concentrations as were detected in slowly pumped samples. The sampling results also indicated that ground‐water colloid concentrations should be monitored in the field to determine the adequacy of purging if colloid and colloid‐associated contaminants are of interest. To avoid changes in the natural ground‐water colloid population through precipitation or coagulation, in situ ground‐water chemistry conditions must be preserved during sampling and storage. Samples collected for determination of the total mobile load of colloids and low‐solubility contaminants must not be filtered because some mobile colloids are removed by this process. Finally, suggestions that mobile colloids are present in ground water at any particular site should be corroborated with auxiliary data, such as colloid levels in “background” wells, colloid‐size distributions, ground‐water geochemistry, and colloid surface characteristics.
Numerical Simulation of the Wicking Effect in Liner Systems
Authors: Yeh T.‐C. Jim , Guzman Amado , Srivastava Rajesh , Gagnard Philip E.
Published: August 2005

Numerical simulations were carried out to investigate the capillary barrier effect and the wicking ability of multilayer earth liner systems. Two specific cases were studied: a two‐layer liner composed of a fine‐ over a coarse‐textured material, and a three‐layer liner composed of a medium‐textured material in between a fine‐ and a coarse‐textured material. Results of the simulations show that a quadratic relationship exists between the thickness of the fine‐textured material and the arrival time of the wetting front to the interface. At the time the wetting front reaches the interface, the width of the lateral spreading within the fine material is smaller than the thickness of this material. The lateral spreading and thickness are linearly related. The wicking ability of the different materials is more significant under relatively smaller infiltration rates and is controlled by the magnitude of the hydraulic diffusivity. For the two‐layer liner the criteria of minimizing the vertical movement and maximizing the wicking effect within the fine‐textured material conflict. A three‐layer liner satisfies both of these criteria. The results for the three‐layer system show that the medium‐textured material has more superior wicking properties than the fine material does.
Estimation of Aquifer Diffusivity from Analysis of Constant‐Head Pumping Test Data
Authors: Hiller Christian K. , Levy Benjamin S.
Published: August 2005

An approximation of the drawdown function developed by Hantush (1964) for late times was used to estimate the aquifer diffusivity directly from measured data from a constant‐head pumping test. This method of evaluation is especially useful in cases where early time data are absent or are obscured by other phenomena The use of the constant‐head time type curves allows ambiguity in the choice of the time match point because of the shallow slopes of the type curves for later times.

Using the described approximation, constant‐head time type curves specific to the dimensionless distance from the pumping well may be compared with the measured data to find anomalies and bias in the measured data. A case study is presented to compare the results of the analyses with the constant‐head time type curves and with the approximation of the drawdown function. The results show that the approximation is valid after the first 100 minutes of measurement.
Testing an Automated Method to Estimate Ground‐Water Recharge from Streamflow Records
Authors: Rutledge A. T. , Daniel C. C.
Published: August 2005

The computer program, RORA, allows automated analysis of streamflow hydrographs to estimate ground‐water recharge. Output from the program, which is based on the recession‐curve‐displacement method (often referred to as the Rorabaugh method, for whom the program is named), was compared to estimates of recharge obtained from a manual analysis of 156 years of streamflow record from 15 streamflow‐gaging stations in the eastern United States. Statistical tests showed that there was no significant difference between paired estimates of annual recharge by the two methods. Tests of the slopes of best‐fit lines through paired estimates showed that the slopes were not significantly different from unity. Tests of results produced by the four workers who performed the manual method showed that results can differ significantly between workers. Twenty‐two percent of the variation between manual and automated estimates could be attributed to having different workers perform the manual method. The program RORA will produce estimates of recharge equivalent to estimates produced manually, greatly increase the speed of analysis, and reduce the subjectivity inherent in manual analysis.
Comparison of Drilling Reports and Detailed Geophysical Analysis of Ground‐Water Production in Bedrock Wells
Authors: Paillet Frederick , Duncanson Russell
Published: August 2005

The most extensive data base for fractured bedrock aquifers consists of drilling reports maintained by various state agencies. We investigated the accuracy and reliability of such reports by comparing a representative set of reports for nine wells drilled by conventional air percussion methods in granite with a suite of geophysical logs for the same wells designed to identify the depths of fractures intersecting the well bore which may have produced water during aquifer tests. Production estimates reported by the driller ranged from less than 1 to almost 10 gallons per minute. The moderate drawdowns maintained during subsequent production tests were associated with approximately the same flows as those measured when boreholes were dewatered during air percussion drilling. We believe the estimates of production during drilling and drawdown tests were similar because partial fracture zone dewatering during drilling prevented larger inflows otherwise expected from the steeper drawdowns during drilling. The fractures and fracture zones indicated on the drilling report and the amounts of water produced by these fractures during drilling generally agree with those identified from the geophysical log analysis. Most water production occurred from two fractured and weathered zones which are separated by an interval of unweathered granite. The fractures identified in the drilling reports show various depth discrepancies in comparison to the geophysical logs, which are subject to much better depth control. However, the depths of the fractures associated with water production on the drilling report are comparable to the depths of the fractures shown to be the source of water inflow in the geophysical log analysis. Other differences in the relative contribution of flow from fracture zones may by attributed to the differences between the hydraulic conditions during drilling, which represent large, prolonged drawdowns, and pumping tests, which consisted of smaller drawdowns maintained over shorter periods. We conclude that drilling reports filed by experienced well drillers contain useful information about the depth, thickness, degree of weathering, and production capacity of fracture zones supplying typical domestic water wells. The accuracy of this information could be improved if relatively simple and inexpensive geophysical well logs such as gamma, caliper, and normal resistivity logs were routinely run in conjunction with bedrock drilling projects.
Evidence for Dedolomitization and Mixing in Paleozoic Carbonates Near Oak Ridge, Tennessee
Authors: Saunders James A. , Toran Laura E.
Published: August 2005

Multiport ground‐water sampling systems in five deep core holes near DOE's Y‐12 facility at Oak Ridge, Tennessee provide data on the three‐dimensional distribution of ground‐water types and chemical evolution processes. Interpretation of ground‐water chemistry, coupled with data on the primary and authigenic mineralogy from drill core, indicates the ground water evolves chemically by three main processes: (1) open system dissolution of calcite and dolomite at shallow depths to produce Ca‐Mg‐HCO3 waters; (2) irreversible dissolution of gypsum, which causes dedolomitization and leads to the formation of Ca‐Mg‐SO4 waters at deeper levels; and (3) mixing with deep brines to form saline Na‐Ca‐Cl waters. Evidence for dedolomitization included the precipitation of authigenic calcite in gypsum dissolution cavities, decrease in ground‐water pH, and increases in dissolved Ca, Mg, and SO4. In this study, we document the dedolomitization process along a relatively short (< 2000 ft) flow path in low permeability Paleozoic carbonates. Mixing of the shallower ground water with an Na‐Ca‐Cl brine thought to be present at depth can account for the progressive increase in salinity of ground water with depth and the precipitation of authigenic barite and celestite. The mixing process could be a combination of diffusion from below, diffusion from older matrix water into fractures, or advective mixing.
Characterization of Flow Parameters Controlling Soil Vapor Extraction
Authors: Beckett G. D. , Huntley David
Published: August 2005

Soil parameters controlling vapor flow in the subsurface are necessary to design soil vapor extraction (SVE) cleanup systems. Previous work assumes a confined flow model, with concrete and asphalt surface covers providing the confining layer and preventing air leakage into the zone of vapor transmission. SVE field tests conducted as part of this investigation, however, exhibited responses that are inconsistent with a confined flow model; it appears that the real world leaks. This paper develops a transient soil vapor extraction (SVE) testing method that considers the effects of vertical leakage. Analytic methodologies are developed that allow use of commonly available ground‐water flow type curves to evaluate SVE test data. The key implications of leaky compared to confined flow are (1) smaller values of derived vapor permeability, and (2) decreased radial cleanup efficacy, both with time and distance.
Attenuation and Biodegradation of Chlorophenols in Ground Water at a Former Wood Treating Facility
Authors: Davis Andy , Campbell Jim , Gilbert Craig , Ruby Michael V. , Bennett Meridan , Tobin Susan
Published: August 2005

This communication describes novel methods to measure site‐specific sorption data, and to determine if biodegradation of pentachlorophenol (PCP) in complex technical‐grade formulations occurs at industrial facilities. Ground‐water slurry samples containing between 0.012 and 230 mg/l PCP were collected from a former wood treating site, the liquid and solid fractions separated, and both fractions analyzed for PCP using selective ion monitoring to determine sorption coefficients (Kd(PCP)). Although field sorption coefficients could not be represented by simple Freundlich and Langmuir isotherms, an empirical hyperbolic function (Kd(PCP)) = 0.054 + 0.086/Caq) fit the isotherm (r > 0.99), demonstrating that for PCP > 10 mg/l, no measurable retardation occurred in the aquifer. Biodegradation of PCP in ground water was apparent when PCP concentrations were < 20 mg/1, while at higher concentrations, PCP in the technical‐grade formulation appeared to break down less readily. The results imply that, at the plume periphery, PCP in the subsurface will be attenuated and degrade, while at higher concentrations (i.e., at the source), PCP is mobile, and more recalcitrant to degradation.
A Study of the DRASTIC Methodology with Emphasis on Swedish Conditions
Authors: Rosen Lars
Published: August 2005

A study of the DRASTIC classification methodology, with special emphasis on Swedish conditions, indicated both favorable and unfavorable properties of the system. The study showed that the fairly large number of parameters (seven) and the correlations between these parameters give DRASTIC some advantageous statistical properties. A comparison of the DRASTIC parameters with parameters found to determine the effects on ground‐water quality in surficial aquifers in southwestern Sweden from acid deposition showed a good agreement between these two parameter sets; the study thus indicated that the selection of parameters is relevant for general ground‐water vulnerability assessments in Sweden. The concept of hydrogeologic settings and the possibility to trace results backwards in the system is excellent, but the qualitative weight functions in DRASTIC result in a simplistic index of unclear meaning that is less useful and less distinctive than desired. The system tends to overestimate the vulnerability of porous media aquifers compared to aquifers in fractured media; the rating tables need to be revised so that more weight is given to specific surface and effective porosity, and less to hydraulic conductivity. The applicability of the results would be enhanced and the risk of misuse reduced if the results were more clearly directed toward scientifically defined factors, e.g. sorption capacity, travel time, and dilution.
A Simple and Powerful Method of Parameter Estimation Using Simplex Optimization
Authors: Devlin J. F.
Published: August 2005

The need for objective parameter estimates is common in hydrogeology. The simplex optimization algorithm provides a fast, simple, and versatile method for making such estimates when used to minimize the residuals sum of squares between calculated and observed data points. Examples of the method applied to Pick's Second Law, the advection dispersion equation, and the integrated Monod kinetics equation illustrate its utility. Compiled programs have been developed, and are available on request, for the estimation of diffusion coefficients, contaminant transport parameters (average linear ground‐water velocities, dispersivities, porosities), and biodegradation kinetic constants.
Monitoring Drainage Solution Concentrations and Solute Flux in Unsaturated Soil with a Porous Cup Sampler and Soil Moisture Sensors
Authors: McGuire Patrick E. , Lowery Birl
Published: August 2005

Soil solution samples are often collected and analyzed without consideration for either the drainage period or changes in solution or solute flux. A sampling method to assess the vertical flux of solution and solute in the unsaturated zone was evaluated. Potassium bromide (KBr) solution and distilled water were applied to the surface of a soil. Estimated and measured solution and solute discharge through the soil column were compared. The column consisted of Plainfield sand (mixed, mesic, Typic Udipsamments) packed in a 208‐liter cylinder. Following solution application, discrete samples were collected at one‐ to two‐hour intervals with a ceramic soil solution sampler centrally located in the column. In each test, the Br concentrations of discrete samples were measured, and the Br concentration of a time‐integrated composite sample was calculated. Solution flux was estimated by monitoring vertical soil‐water tension and content gradients with tensiometers and time domain reflectometry probes, respectively, and applying the unsaturated form of Darcy's equation. In three of four tests, differences between measured and estimated solution discharge were 20%. Differences in measured and estimated Br mass discharge ranged from 1 to 37%. Correlation coefficients between estimated and measured Br mass discharge based on discrete and composite sample concentrations were 0.905 (p = 0.095) and 0.70 (p = 0.30), respectively.
An Expert Systems Approach for Assessing the Potential for Pesticide Contamination of Ground Water
Authors: Crowe A. S. , Mutch J. P.
Published: August 2005

The EXPRES expert system (EX pert system for Pesticide/Regulatory Evaluations and Simulations) has been developed to assist those who are knowledgeable, but not proficient, in the theory of pesticide transport in the subsurface or in the use of pesticide assessment models with a means of assessing the potential for pesticides to contaminate ground water. EXPRES is not intended to replace expert opinion but rather EXPRES is intended to be used as a screening tool by nonexperts who need to evaluate the potential for pesticides to contaminate ground water. EXPRES combines a knowledge‐based system, a graphically based user‐system interface, extensive geographical and pesticide data bases, and three existing pesticide assessment models (LP/LI, PRZM, and LEACHM). Based on the user's available data, objectives of the assessment and time constraints, EXPRES selects the most appropriate model, assists the user in the construction of an input data set, initiates an assessment, and aids in the interpretation of the results of an assessment model. Specific assistance in the construction of the input data set includes providing pertinent data for characterizing a site or a pesticide from its data bases, assisting the user to respond to a prompt from EXPRES, aiding the user in estimating missing values for pesticide or site parameters, and ensuring the zintegrity of the input data set. The inclusion of three models allows EXPRES to select the model which is most applicable for the objectives on the investigation, including: (1) a review of pesticide properties and site characteristics that influence the fate of pesticides in the subsurface, (2) a relative assessment, with respect to other pesticides, of the potential for a pesticide to leach to the water table, (3) a quantitative prediction of the distribution and migration rates of the pesticide with both time and depth, and (4) an evaluation of the processes and factors controlling the fate of the pesticides in the subsurface.
Adsorbed Concentration vs. Lab‐Reported Concentration in Soil
Authors: Mohsen Mohammad F. N.
Published: August 2005

The current practice of how concentration of contaminants in soil is measured allows room for the reported value to be confused with adsorbed concentration. This note clarifies the distinction between lab‐reported concentration and adsorbed concentration in soils. The paper shows that for highly adsorbed substances, the distinction virtually vanishes. However, for poorly adsorbed substances, this distinction can be significant.
Well Discharge Optimization Using Analytic Elements
Authors: Fitts Charles R.
Published: August 2005

Using superpositioned analytic functions (elements), it is possible to directly solve the following well discharge optimization problems in general flow models:

1. Determine the discharge of well A which will produce a certain head or drawdown at location B.

2. Determine the discharge of well A which will produce a specified component of aquifer discharge at location B. These problems often arise while designing contamination remediation systems, designing dewatering systems, or

making ground‐water resource allocation decisions. Such problems are solved by trial and error with nonoptimized models, or solved iteratively with standard optimizing methods. With this analytic formulation, they can be solved directly. This approach can be used to optimize the performance of a single well or to simultaneously optimize the performance of numerous wells. For example, it is possible to solve directly for the combination of discharges at wells A, B, C, D, and E that will produce specified heads at locations F and G while producing specified aquifer discharges at locations H, I, and J. Applications of the method are demonstrated using TWODAN, a program for analytic two‐dimensional flow modeling.
Physical and Mathematical Modeling of Diesel Fuel Liquid and Vapor Movement in Porous Media
Authors: Johnson T. E. , Kreamer D. K.
Published: August 2005

Two‐dimensional physical modeling of diesel fuel leaks was conducted in sand tanks to determine liquid and vapor migration characteristics. Mathematical modeling provided estimation of vapor concentrations at discrete times and distances from the vapor source and was compared to the physical experiment. The mathematical gaseous diffusion model was analogous to the Theis equation for ground‐water flow, accounted for sorptive effects of the media, and was calibrated using measured concentrations from the sand tank. Mathematically different positions of the vapor source were tested to better relate observed liquid flow rates and media configuration to gaseous concentrations. The calculated diffusion parameters were then used to estimate theoretical, three‐dimensional vapor transport from a hypothetical liquid leak of 2.0 1/hr for 30 days. The associated three‐dimensional vapor plume, which would be reasonably detectable by commercially available vadose zone monitors, was estimated to have a diameter of 8 m with a vapor concentration of 50 ppm at the outside edge of the vapor plume. A careful application of the method and values can be used to give a first approximation to the number of vapor monitors required at a field site as well as the optimal locations for the monitors.
Analysis of Slope‐Matching Methods for Aquifer Parameter Determination
Authors: Srivastava Rajesh , Guzman‐Guzman Amado
Published: August 2005

Various methods for numerical determination of aquifer transmissivity and storage coefficients from a single observation well data have recently been proposed. Most of these methods involve reading the slope values from a table or providing an initial estimate for iterative solution. A different formulation of the slope‐matching technique has been suggested in the field of petroleum engineering which obtains the parameter values without using any tables or iterative procedures. In this study we adopt a similar approach and compare the prediction of various techniques. The modification of the approach to include cases with time‐varying parameters is examined. Numerical experiments are performed first on synthetic data to ascertain the relative accuracy of different slope evaluation techniques. It is shown that the slope of the drawdown with respect to the logarithm of time results in the most accurate prediction of aquifer parameters. The inaccuracy involved in application of the slope‐matching methods to cases involving time‐varying parameters is analyzed. The methods are then applied to some field data and the results are compared with published data. AH the methods are found to work reasonably well for the field application.
Assessment of Methods and Conditions to Locate Boundaries: I. One or Two Straight Impervious Boundaries
Authors: Chapuis Robert P.
Published: August 2005

A straight impervious boundary within an ideal confined aquifer may be detected in the semilog drawdown graph of an observation well. This paper gives and assesses two known and one proposed equations that may help to determine the location and orientation of an impervious boundary. Then the two conditions for an adequate detection are established. First, if the distance of the pumping well to the boundary is called “a,” only those observation wells at a distance smaller than a/5 from the pumping well can detect the boundary. Second, data must be collected for approximately two time log cycles after the slope has changed in the drawdown graph. Similar equations, and time or distance conditions, are given for the case of two intersecting straight impervious boundaries. Frequently, the two conditions are not met. In this case, the drawdown graphs give incorrect estimates of aquifer parameters. In most field conditions, a combination of drawdown data, geophysical surveys, and exploratory boreholes is mandatory to locate one or two impervious boundaries. Available methods and a proposed one for recharge boundaries are assessed in a companion paper.
Hydrochemistry of the Mahomet Bedrock Valley Aquifer, East‐Central Illinois: Indicators of Recharge and Ground‐Water Flow
Authors: Panno S. V. , Hackley K. C. , Cartwright K. , Liu C. L.
Published: August 2005

A conceptual model of the ground‐water flow and recharge to the Mahomet Bedrock Valley Aquifer (MVA), east‐central Illinois, was developed using major ion chemistry and isotope geochemistry. The MVA is a “basal” fill in the east‐west trending buried bedrock valley composed of clean, permeable sand and gravel to thicknesses of up to 61 m. It is covered by a thick sequence of glacial till containing thinner bodies of interbedded sand and gravel. Ground water from the MVA was found to be characterized by clearly defined geochemical regions with three distinct ground‐water types. A fourth ground‐water type was found at the confluence of the MVA and the Mackinaw Bedrock Valley Aquifer (MAK) to the west.

Ground water in the Onarga Valley, a northeastern tributary of the MVA, is of two types, a mixed cation‐SO42‐ type and a mixed cation‐HCO3 type. The ground water is enriched in Na+ Ca2+, Mg2+, and SO42‐ which appears to be the result of an upward hydraulic gradient and interaction of deeper ground water with oxidized pyritic coals and shale. We suggest that recharge to the Onarga Valley and overlying aquifers is 100% from bedrock (leakage) and lateral flow from the MVA to the south.

The central MVA (south of the Onarga Valley) is composed of relatively dilute ground water of a mixed cation‐HC03 type, with low total dissolved solids, and very low concentrations of Cl‐ and SO42‐. Stratigraphie relationships of overlying aquifers and ground‐water chemistry of these and the MVA suggest recharge to this region of the MVA (predominantly in Champaign County) is relatively rapid and primarily from the surface.

Midway along the westerly flow path of the MVA (western MVA), ground water is a mixed cation‐HCO3‐ type with relatively high Cl‐, where Cl‐ increases abruptly by one to two orders of magnitude. Data suggest that the increase in Cl‐ is the result of leakage of saline ground water from bedrock into the MVA. Mass‐balance calculations indicate that approximately 9.5% of recharge in this area is from bedrock. Concentrations of Na+, HCO3‐, As, and TDS also increase in the western MVA.

Ground water in the MAK is of a Ca2+‐HCO32‐ type. Mass‐balance calculations, using Cl‐ as a natural, conservative tracer, indicate that approximately 17% of the ground water flowing from the confluence area is derived from the MVA.
One‐Dimensional Moving Finite‐Element Model of Solute Transport
Authors: Gottardi G. , Venutelli M.
Published: August 2005

Solute transport problems with sharp transitions or high advection are difficult to solve with traditional finite‐difference (FD) and finite‐element (FE) techniques. When advection dominates, the solutions obtained by these traditional methods typically suffer numerical smearing or oscillations. In these cases, acceptable numerical solutions of the classical advection‐dispersion equation by FE and FD techniques can be obtained only by using a fine discretization on space and time that allows the stability requirements expressed by the Courant and Peclet numbers to be satisfied. This leads to large computer times. A way for overcoming this problem is to use a moving‐grid method. The dynamically self‐adaptive moving finite‐element (MFE) grid method, used in this work, obtains accurate and efficient solutions of the advection‐dispersion equation in a very wide range of Courant and Peclet numbers. The MFE method accurately simulates, with no oscillations, very steep fronts using space and time step sizes well beyond conventional constraints of the Peclet and Courant numbers. To demonstrate the accuracy and efficiency of the MFE method, some test cases are presented where the MFE, FD, and analytical solutions are compared.
An Investigation of the Relationship Between Actual and Apparent Gasoline Thickness in a Uniform Sand Aquifer
Authors: Ballestero Thomas P. , Fiedler Fritz R. , Kinner Nancy E.
Published: August 2005

A common effort involved in the remediation of contamination by petroleum hydrocarbons in porous media is the monitoring and volume estimation of the immiscible hydrocarbon fluid. The apparent free product thickness indicated by a standard monitoring well is typically much greater than the actual free product thickness in the surrounding soil. This results in significant errors in estimates of drainable fluid (product) volume, which in turn leads to inaccuracies (i.e., over design, improper pump sizing, etc.) with remediation system design.

An equation to predict actual thickness was developed using heterogeneous fluid flow mechanics and hydrostatics. This equation is: tg= t(l – Sg) ‐ ha, where tg= actual formation free product thickness, t = apparent (well bore product) thickness, Sg= specific gravity of petroleum hydrocarbon (gasoline in this research), and ha= distance between the ground‐water table and the free product in the formation.

The developed theory was compared to data collected from a physical model which simulated field conditions. The theory was used to estimate product thickness in the model, and then these estimates were statistically tested for accuracy. The theoretical slope, (1 – Sg), was not statistically different from the regression slope at test levels of α= 0.05 and α= 0.01, while the theoretical intercept (ha) was statistically different at α– 0.05 and α– 0.01. The discrepancy between the theoretical intercept and the regression intercept was probably due to either an incorrect assumption that ha= hc (hc= average wetting capillary rise), or an incorrect laboratory measurement of hc.

The effects of water‐table fluctuations were also studied. A rising water table caused a decrease in apparent thickness and an increase in actual thickness, and vice versa. No theoretical equation was developed for the effects of water‐table fluctuations, but it was reasoned that hysteresis of the saturation curve and adsorption were the primary factors in the observed trends.

Finally, the developed theoretical equation was compared to the results of previously published predictive methods and experiments. The comparison was made by calculating percent error and using a chi‐square statistic. The developed theory was found to be the best predictor of actual product thickness for both laboratory data sets used.
Estimation of Solute Concentrations Using the Pathline Counting Method
Authors: Johnson Jeffrey A. , Ravi Varadhan , Rumery J. Kevin
Published: August 2005

The paper discusses the use of the “pathline counting” approach to estimate solute concentrations at an extraction well using particle‐tracking flow models. The pathline counting approach is a unique method for predicting solute concentrations due to mixing. The pathline counting method using the semianalytical module RESSQC, contained within the WHPA model, was compared to MT3D, a numerical mass transport code, for a simple hypothetical problem. Results from the comparison indicate that results from the pathline counting approach were in reasonable agreement with the MT3D results. This approach was then applied to a field study, the Park City Bioremediation Project. The migration of a conservative tracer injected into three upgradient cells was simulated to estimate the concentration of solute at two pumping wells. The calculated concentrations compared favorably with measured field concentrations.
Hydrothermal Estimation of Vertical Ground‐Water Flow, Cañutillo, Texas
Authors: Wade Shirley C. , Reiter Marshall
Published: August 2005

The vertical component of specific discharge was estimated across several depth zones in the aquifer system at Cañutillo, Texas. The specific discharge was estimated using temperature and thermal conductivity data from four observation wells bottoming near the base of the aquifer system.

Specific discharge was first calculated (using a steady‐state model) from the slopes of conductive heat flow versus temperature plots. The heat flow plots for all four wells suggested a zone of downward ground‐water flow from ∼ 70 to ∼ 220 feet depth and one or two zones of upward flow from ∼ 800 to ∼ 220 feet depth. Head data from observation wells did support the conclusion of an upper zone of downflow as indicated by the temperature data; however, the head data suggested that ground water should presently be moving downward from ∼ 220 to ∼ 800 feet.

A computer model was developed to determine if the temperatures may be remanent and therefore reflect prepumping ground‐water flow, particularly in the deep flow zone. Computer model estimates were made of during‐pumping downflow in the upper flow zone. For the deep flow zone computer model estimates were made of prepumping upflow. The computer model estimates and steady‐state vertical specific discharge estimates were similar for the upper zone having downward flow. In the deep zone prepumping upflow estimates modeled on the computer were the same order of magnitude as steady‐state heat flow specific discharge estimates. Hence, present temperature data may demonstrate a significant remanent groundwater flow component and therefore might be used to estimate past vertical ground‐water flow.
Nonaqueous Phase Hydrocarbon in a Fine‐Grained Sandstone: 2. Effect of Local Sediment Variability on the Estimation of Hydrocarbon Volumes
Authors: Huntley David , Wallace James W. , Hawk Robert N.
Published: August 2005

The exaggeration of light nonaqueous phase liquids (LNAPL), typically hydrocarbon, by monitoring wells is a well‐known problem that introduces significant errors in the estimation of recoverable hydrocarbon. Farr et al. (1990) and Lenhard and Parker (1990) show that significantly different volumes of hydrocarbon may produce the same thickness of hydrocarbon in a monitoring well, due to differences in the capillary characteristics between soil types. The purpose of our investigation was to evaluate the influence of local sediment variability on estimation of hydrocarbon volumes. Sediment samples from two sites underlain by a relatively homogeneous sandy deposit were collected within a small area. Capillary characteristic curves were determined for 10 samples from one site and 41 samples from the second site using a pressure plate. Grain‐size analysis was performed on all samples for which pressure plate data were available.

The results show significant variability, even for small sites. For example, a hydrocarbon volume of three cm3/cm2 could produce anywhere between 45 and 200 cm of hydrocarbon within an observation well. This suggests that use of an “average” soil sample to characterize hydrocarbon exaggeration, within even a very small site, can lead to substantial errors. It also suggests that maps of apparent hydrocarbon thickness can be extremely misleading, leading hydrologists to place remediation wells in areas of greatly exaggerated thicknesses produced by fine‐grained materials.

Comparison between characteristic curves calculated from grain‐size analysis using the approach of Mishra et al. (1989) to those measured using the pressure plate shows poor correlation that introduces large errors into the estimated hydrocarbon volumes.