bluuebunny/crossref_metadata_2025 huggingface dataset:
Patterns and Age Distribution of Ground‐Water Flow to Streams
Authors: Modica Edward , Reilly Thomas E. , Pollock David W.
Published: August 2005

Simulations of ground‐water flow in a generic aquifer system were made to characterize the topology of ground‐water flow in the stream subsystem and to evaluate its relation to deeper ground‐water flow. The flow models are patterned after hydraulic characteristics of aquifers of the Atlantic Coastal Plain and are based on numerical solutions to three‐dimensional, steady‐state, unconfined flow. The models were used to evaluate the effects of aquifer horizontal‐to‐vertical hydraulic conductivity ratios, aquifer thickness, and areal recharge rates on flow in the stream subsystem. A particle tracker was used to determine flow paths in a stream subsystem, to establish the relation between ground‐water seepage to points along a simulated stream and its source area of flow, and to determine ground‐water residence time in stream subsystems. In a geometrically simple aquifer system with accretion, the source area of flow to streams resembles an elongated ellipse that tapers in the down gradient direction. Increased recharge causes an expansion of the stream subsystem. The source area of flow to the stream expands predominantly toward the stream headwaters. Base flow gain is also increased along the reach of the stream. A thin aquifer restricts ground‐water flow and causes the source area of flow to expand near stream headwaters and also shifts the start‐of‐flow to the drainage basin divide. Increased aquifer anisotropy causes a lateral expansion of the source area of flow to streams.

Ground‐water seepage to the stream channel originates both from near‐ and far‐recharge locations. The range in the lengths of flow paths that terminate at a point on a stream increase in the downstream direction. Consequently, the age distribution of ground water that seeps into the stream is skewed progressively older with distance downstream. Base flow ia an integration of ground water with varying age and potentially different water quality, depending on the source within the drainage basin. The quantitative results presented indicate that this integration can have a wide and complex residence time range and source distribution.
Study on the Contamination of Fracture‐Karst Water in Boshan District, China
Authors: Zhu Xue‐Yu , Xu Shao‐Hui , Zhu Jun‐Jie , Zhou Nian‐Qing , Wu Chun‐Yin
Published: August 2005

Boshan is an industrial city in the center of Shandong Province where ground water is the only source for the urban water supply. The major water resource is fracture‐karst water in the middle Ordovician carbonate rocks. Based on the hydrogeological investigation and mapping in this area we studied the geologic and hydrogeologic settings, the major pollution sources and the pathways of contamination, the principal contaminants, and their spatial distribution in ground water. The ground‐water quality has also been estimated by the fuzzy mathematic method. The geostatistical method, such as the kriging method, was taken to simulate spatial distribution of the contaminants. The grey system method was adopted to forecast future contamination. An attempt at the remediation of Cr6+ contamination in fracture‐karst water was also discussed. Finally, some proposals for the protection of the ground‐water environment in Boshan District are offered.
Computer Determination of Aquifer Parameters Using Slope Matching
Authors: Pittenger Robert , Reichard James S.
Published: August 2005

Various numerical methods have been developed to solve aquifer tests and eliminate the subjectivity of traditional graphical type curve methods. The slope‐matching method, which matches the slope of the field data to the slope of the Theis type curve, can be used to numerically solve pump tests for both leaky and non leaky aquifers.

The slope‐matching method was selected for implementation into a C/C++ computer program. The computerized version has the following advantages over the original hand calculator version: (1) it eliminates human error inherent in hand calculations; (2) it has the ability to quickly analyze large data sets and large numbers of data sets; and (3) it can be used on portable computers to analyze test data in the field.

When performed by hand, the slope‐matching method requires the interpolation of values from tables for values of Theis curve slopes and the Bessel function Ko. For the computer implementation, an iterative “guess‐and‐correct” algorithm was developed to eliminate the need to interpolate from tables.

The computer program shows a good correlation with results obtained by hand calculations for both leaky and no leaky aquifers, using the same method. Discrepancies with hand calculations are traced to rounding errors in the estimation of W (u) and elimination of the need to interpolate values from tables.
Modeling Axially Symmetric and Nonsymmetric Flow to a Well with MODFLOW, and Application to Goddard2 Well Test, Boise, Idaho
Authors: Barrash Warren , Dougherty Martin E.
Published: August 2005

Tools for analyzing aquifer test data at the pumping or injection well are limited for aquifer conditions that are not axially symmetric about the pumping well. Accurate simulations of head change at a pumping well can be generated with MODFLOW using a discretization scheme that (1) captures steep gradients adjacent to the cell(s) containing the pumping or injection well and (2) approximates radial flow despite rectangular prism well cell(s). This scheme is based on a very small incremental cell width adjacent to the pumping or injection well cell, and then a logarithmic increase in cell width outward with the expansion factor, α, in the range of 1.2 to 1.5. The validity of this scheme has been demonstrated by comparing model results with analytical solutions and RADMOD (axisymmetric adaptation of MODFLOW) for three radially symmetric confined aquifer scenarios, and with the analytical solution for a nonaxisymmetric confined aquifer scenario. Utility of this scheme is demonstrated with simulation of time‐drawdown behavior at the Goddard2 pumping well in Boise, Idaho where four observation wells did not respond during a pumping test and where 28.8 m of drawdown occurred in the pumping well during the first 2 min of the test. The hydrogeologic setting for the test is interpreted to be a partially penetrating well pumping from a sand‐stringer aquifer that receives leakage from surrounding finer grained sediments, and includes a fault (no‐flow boundary) truncating the aquifer.
Probabilistic Multiphase Flow Modeling Using the Limit‐State Method
Authors: Xiang Yanyong , Mishra Srikanta
Published: August 2005

This paper presents a study on the application of the limit‐state method for probabilistic multiphase flow modeling. The subsurface multiphase flow and heat transport simulator, TOUGH2 (Pruess, 1991), is combined with a computer shell for reliability analysis, CALREL (Liu et al., 1989). As applications of the combined code, the site at Yucca Mountain, Nevada for a potential high‐level radioactive waste repository is modeled under assumed conditions. The probability distributions of various performance functions (liquid saturation, travel time, and flux) are calculated for statistically described infiltration rate and matrix hydrogeologic parameters. Numerical experiments indicates that the limit‐state method compares fairly well with, and thus can be used as an alternative to, the Monte Carlo method for probabilistic multiphase flow simulations.
Closed‐Form Expressions for Water Retention and Conductivity Data
Authors: Leij Feike J. , Russell Walter B. , Lesch Scott M.
Published: August 2005

Closed‐form expressions for quantifying the unsaturated soil hydraulic properties are widely used in computer programs to model subsurface flow and transport in porous media and to investigate indirect methods for estimating these properties. For example, water retention data, which relate soil‐water pressure head (h) and effective water saturation (Se), are frequently used to predict the unsaturated hydraulic conductivity (K). However, the suitability of different functions to describe unsaturated hydraulic data has rarely been investigated comprehensively. We attempted to fit 14 retention and 11 conductivity functions to 903 sets of water retention and hydraulic conductivity data measured on soil and rock samples or horizons reported in the unsaturated hydraulic database UNSODA. Some of the best mean values for r2 and MSE for fitting Se(h) data were obtained with the retention functions reported by van Genuchten (1980), Globus (1987), and Hutson and Cass (1987). A function reported by Gardner (1958) could describe K (h) data quite well whereas functions reported by Brooks and Corey (1964) and van Genuchten (1980), which are respectively based on the conductivity models by Burdine and Mualem, yielded a relatively good description of K(SC) data.
Transmissivity in the Geothermal Euganean Basin: A Geostatistical Analysis
Authors: Fabbri Paolo
Published: August 2005

This paper presents a geostatistical analysis of transmissivity in the Euganean geothermal field (northeast Italy). Few transmissivity values are known while specific capacity values are more common. However, transmissivity is more important than specific capacity in the characterization of aquifers. In this work, therefore, after a simple statistical analysis, an empirical relation with a high determination coefficient (r2= 0.95) is found between the above values. Subsequently, In T structural characteristics of the variable are studied by variogram analysis, identifying a second‐order pseudostationarity and two geometrical anisotropies. The second‐order pseudostationarity and the variogram fit allow a linear kriging procedure to be used to produce a map of transmissivity and kriging standard deviation of the Euganean geothermal field. The fit between geostatistical and hydrogeological analyses shows that a geostatistical approach is useful for both mapping purposes and hydrogeological interpretation.
GIBBTEQ: A MINTEQA2 Thermodynamic Data Error Detection Program
Authors: Onysko Steven J. , McNearny Richard L.
Published: August 2005

The U.S. Environmental Protection Agency geochemical computer code MINTEQA2 contains over 1, 500 aqueous species entries with stoichiometric, thermodynamic, and gram formula weight data. GIBBTEQ is a LOTUS 123 program that scans MINTEQA2 data base entries and directly identifies errors in stoichiometry, species charge, and formula weight. GIBBTEQ indirectly facilitates identification of errors of equilibrium and enthalpy data in MINTEQA2 data base entries by printing those entries in readable format. Anomalies of equilibrium constant, standard free energy and enthalpy of mineral species, and redox potential (for electron‐containing reactions) are amenable to user detection in the program output. MINTEQA2 errors of various types are quantified from GIBBTEQ results. Program availability inquiries can be sent via e‐mail to gibbteq@mines.utah.edu.
Wellbore Skin Effect in Slug‐Test Data Analysis for Low‐Permeability Geologic Materials
Authors: Yang Y. Jeffrey , Gates Todd M.
Published: August 2005

The wellbore skin effect on slug‐test results was analyzed using numerical simulation and field tests for a well at progressive stages of development. The numerical simulation is based on a composite flow model that incorporates a zone of disturbed formation surrounding the wellbore. Field tests were performed on a water‐bearing clayey silt formation at a ground‐water remediation site in Wisconsin. Based on the numerical simulation, the radius of investigation was examined. The results show that the early‐time and late‐time data reflect ground‐water flow in the wellbore skin and undisturbed formation, respectively.

Both the numerically simulated and the field slug‐test data define a downward concave curve on a semilog plot of time versus the logarithm of dimensionless head. For the Hvorslev (1951) and Bouwer and Rice (1976) methods, the late‐time segment of the simulated data yields estimates of hydraulic conductivity close to the value defined in the flow model. When a wellbore skin exists, the data curve in a plot of the logarithm of time versus the dimensionless head is shifted horizontally along the time axis. This shift leads to an inaccurate determination of hydraulic conductivity based on the Cooper et al. (1967) method. In the plots of time versus dimensionless head derivatives, the data curve geometry depends on the hydraulic properties of the wellbore skin. Consequently, the wellbore skin effect can be identified and eliminated using derivative‐based type curve methods.

For low‐permeability materials, the effect of wellbore skin on estimates of hydraulic conductivity can be minimized through use of the late‐time data. However, proper well installation and development appears to be the most effective and practical solution.
Delineation of Preferred‐Flow Paths by Response to Transient Lagoon Exfiltration
Authors: Donovan Joseph J. , Frysinger Kevin W.
Published: August 2005

Observations of hydraulic head response to lagoon leakage into an extremely heterogeneous aquifer allow qualitative identification of spatial patterns in heterogeneity. In a 150–hour leakage experiment over such an aquifer, the fluid mass balance was estimated using a stage‐fluctuation model while transient response was observed in downgradient wells and springs. Based on timing with respect to pond leakage, water‐level response at different locations within the aquifer may be identified as either within or outside the influence of preferred‐flow paths (PFPs). Flows at springs 150–200 m from the pond increased by 20–60% above baseline flows, showing initial increase within ca. 40 hours. Synoptic water‐level rise patterns observed during the test describe enlargement of a recharge mound from beneath the pond and suggest the spatial pattern of PFPs to > 150 m distant. An analytical model assuming homogeneity (Hantush, 1967), applied to water‐level response for wells > 30 m from the pond, overestimated K by > 1 order of magnitude in comparison to slug‐test estimates. This discrepancy is attributed to the inferred presence of linearly continuous heterogeneities causing preferential flow. Large‐scale hydraulic tests such as this sample the spatial structure for conductive pathways and may be of utility in parameterization of numerical flow models. In contrast, slug‐test results give local parameter estimates, but more limited information on PFP distribution.
Multivariate Statistical Analysis of Environmental Monitoring Data
Authors: Ross D. Lauren
Published: August 2005

EPA requires statistical procedures to determine whether soil or ground water adjacent to or below waste units is contaminated. These statistical procedures are often based on comparisons between two sets of data: one representing background conditions, and one representing site conditions. Since statistical requirements were originally promulgated in the 1980s, EPA has made several improvements and modifications. There are, however, problems which remain. One problem is that the regulations do not require a minimum probability that contaminated sites will be correctly identified. Another problem is that the effect of testing several correlated constituents on the probable outcome of the statistical tests has not been quantified.

Results from computer simulations to determine power functions for realistic monitoring situations are presented here. Power functions for two different statistical procedures: the Student's t‐test, and the multivariate Hotelling's T2test, are compared. The comparisons indicate that the multivariate test is often more powerful when the tests are applied with significance levels to control the probability of falsely identifying clean sites as contaminated. This program could also be used to verify that statistical procedures achieve some minimum power standard at a regulated waste unit.
Diffusive Loss of Non‐Aqueous Phase Organic Solvents from Idealized Fracture Networks in Geologic Media
Authors: Parker Beth L. , McWhorter David B. , Cherry John A.
Published: August 2005

The time for disappearance of stationary, single‐component immiscible‐phase liquid (NAPL) from planar fractures due to dissolution and subsequent diffusion is directly dependent on the ratio of mass storage capacity of dissolved and sorbed contaminant in the matrix to the initial storage capacity for immiscible‐phase liquid in the fractures. This was determined from an analytical solution for three‐dimensional mass transfer into water‐saturated matrix blocks of clay or sedimentary rock represented as rectangular parallelepipeds. A ratio greater than one indicates the number of times the fracture void volume can be completely replenished with the immiscible phase before disappearance ceases. However, each successive fracture replenishment requires longer time for disappearance due to consumption of part of the matrix storage capacity caused by previous fracture loadings. Ultimately, with continued NAPL replenishment in the fractures, this mass redistribution causes the dissolved concentration in the matrix to equal the aqueous solubility, at which point continued disappearance cannot occur. Mass storage capacity ratios for matrix and fracture conditions typical of clays and sedimentary rocks are greater than one for a variety of the common chlorinated solvents. The initial disappearance times for a tri chloro ethylene (TCE) DNAPL in a fractured clay of 10 fracture porosity and 35 percent matrix porosity with parallel, planar fractures, range from 0.01 to 113 days for fracture spacings of 1 cm and 1 m, respectively. Disappearance times for TCE DNAPL are much larger for a generic sandstone with the same fracture porosity and geometry and 10 percent matrix porosity, and range from 0.44 to 4400 days, due to reduced storage capacity in the matrix. These disappearance times, which are short relative to the ages of subsurface contamination at many industrial sites, likely cause many DNAPL source zones, or parts of source zones, to have little or no actual DNAPL phase. However, the matrix retains the equivalent contaminant mass acting as a long term source zone.
Cost‐Effective Monitoring Strategies to Estimate Mean Water Table Depth
Authors: Mew H.E. , Jr M.A. Medina , Heath R.C. , Reckhow K.H. , Jacobs T.L.
Published: August 2005

Cost‐effective monitoring strategies exist for estimating mean depth to the water table and for characterizing fluctuations about that mean. These strategies can also be used to evaluate the utility of sparse water level data sets for making such estimates. This type of information is needed to design or reduce costs of observation well networks, to characterize regional water‐table fluctuations for use in maps or models, and to calibrate ground‐water models using hydraulic head estimates.

The study is based on a statistical analysis of hourly water levels measured at observation wells by the U. S. Geological Survey (USGS) over a five‐year period. Using Monte Carlo simulation techniques, sampling results for different monitoring strategies were compared with parameters of the underlying distribution of hourly water levels. Monthly, bimonthly, quarterly, and even tri annual water‐level monitoring was found to effectively estimate mean water table depth and standard deviation to within 30 cm. Quarterly and tri annual sampling were found more cost‐effective than monthly observations, and electronic monitoring more effective than manual measurements for sampling made more frequently than monthly. Results have broad application for studies involving surficial aquifers in humid regions of the world where annual rainfall exceeds 50 cm and is reasonably distributed throughout the year. Governmental agencies and universities have a wealth of water table monitoring records, collected either through ambient monitoring or as part of a permit requirement or study. These sparse data sets hold the promise of significantly increasing the hydro geologic knowledge of water table behavior in many regions of the world.
Quantifying Macropore Recharge: Examples from a Semi‐Arid Area
Authors: Wood Warren W. , Rainwater Ken A. , Thompson David B.
Published: August 2005

The purpose of this paper is to illustrate the significantly increased resolution of determining macropore recharge by combining physical, chemical, and isotopic methods of analysis. Techniques for quantifying macropore recharge were developed for both small‐scale (1 to 10 km2) and regional‐scale areas in arid and semi‐arid areas. The Southern High Plains region of Texas and New Mexico was used as a representative field site to test these methods. Macropore recharge in small‐scale areas is considered to be the difference between total recharge through floors of topographically closed basins and interstitial recharge through the same area. On the regional scale, macropore recharge was considered to be the difference between regional average annual recharge and interstitial recharge measured in the unsaturated zone. Stable isotopic composition of ground water and precipitation was used as an independent estimate of macropore recharge on the regional scale. Results of this analysis suggest that in the Southern High Plains recharge flux through macro pores is between 60 and 80 percent of the total 11 mm/y. Between 15 and 35 percent of the recharge occurs by interstitial recharge through the basin floors. Approximately 5 percent of the total recharge occurs as either interstitial or matrix recharge between the basin floors, representing approximately 95 percent of the area. The approach is applicable to other arid and semi‐arid areas that focus rainfall into depressions or valleys.
Development of a Preliminary Ground Water Flow Model for Water Resources Management in the Pingtung Plain, Taiwan
Authors: Ting Cheh‐Shyh , Zhou Yangxiao , Vries J.J.de , Simmers I.
Published: August 2005

Pingtung Plain is formed by Quaternary alluvial fan material from the three main rivers: Kaoping, Tungkang and Linpien. Ground water is the major water supply source on the plain. This is principally extracted from two aquifers. The natural ground water source is derived mainly from direct rainfall percolation and infiltration from the three rivers, with their catchments lying partly outside the plain. Rainfall characteristics are therefore the main factors controlling water resources availability. Pingtung Plain is an important primary production area for southern Taiwan, the comparatively warm climate allowing a long growing season, diversified cropping and the rearing of aquacultural produces. Approximately 75 percent of irrigation and domestic water supplies are derived from ground water. A water balance for the entire plain indicates that ground water resources, under optimized management, are sufficient to meet the existing multi‐purpose uses.

Development of a hydrogeological conceptual model is the first phase of a numerical ground water flow simulation. Preliminary results are encouraging, with the final simulations affording better insight to the hydraulic behavior of the aquifer system. Data input requirements for model operation fall into three categories: hydrological stresses, hydrogeological parameters and boundary conditions.

After the model is built, the normal numerical modeling process requires significant calibration and sensitivity analyses for the hydrogeological parameters and stresses which are the most sensitive, but the least well defined.

A well‐calibrated simulation model can lead to a reliable and realistic management model. With this in mind, the calibration processes detailed are presented, and these data are introduced as initial values in the calibration process.
How Good Are Estimates of Transmissivity from Slug Tests in Fractured Rock?
Authors: Shapiro Allen M. , Hsieh Paul A.
Published: August 2005

Slug tests in fractured rock usually are interpreted with models that assume homogeneous formation properties, even though hydraulic properties of fractures can vary by many orders of magnitude over the length of boreholes. To investigate the impact of heterogeneity on the interpretation of slug tests in fractured rock, slug tests were conducted over large intervals of boreholes in crystalline rock in central New Hampshire, and interpreted using a homogeneous model. The results of the slug tests were then compared with estimates of transmissivity from fluid‐injection tests conducted over shorter intervals in the same boreholes. The fluid‐injection tests showed transmissivity to vary more than six orders of magnitude over the length of the boreholes; however, the sum of the transmissivities from the fluid‐injection tests were within an order of magnitude of the transmissivity estimated from the slug tests. Although the two estimates of transmissivity were within an order of magnitude of each other, the water level responses during the slug tests did not exactly match the responses predicted by the homogeneous model. To investigate the effect of heterogeneity on water level responses during slug tests, a Laplace‐transform solution was developed for slug tests conducted in boreholes containing multiple fractures with hydraulic properties that vary over the length of the borehole. A comparison of this solution with the homogeneous model shows no difference between the shape of water level responses in a homogeneous formation and a (layered) heterogeneous formation. Furthermore, the transmissivity estimated using a homogeneous model is within an order of magnitude of the prescribed transmissivity in the heterogeneous model. Thus, differences between responses predicted from a homogeneous model and measured water levels during slug tests can be attributed to phenomena such as nonradial flow in the vicinity of the borehole, and not heterogeneous hydraulic properties over the length of the borehole. The experimental results of this investigation show that even when conditions such as nonradial flow are present in the vicinity of the borehole, interpretations of slug tests using a homogeneous model provided order‐of‐magnitude estimates of transmissivity in the crystalline rock terrane under consideration.
How Uncertain Is Our Estimate of a Wellhead Protection Zone?
Authors: Evers Sarah , Lerner David N.
Published: August 2005

Protection zones for wells are defined through the use of pathline tracing in ground water flow models. Traditional approaches to ground water flow modeling focus on obtaining a single best model, occasionally supplemented by the use of sensitivity analyses. In most situations this approach is inappropriate because the ground water flow model is so poorly determined that a variety of different boundary conditions and parameter values would give similar predictions of heads. However, the range of feasible models may well give radically different predictions of the variable for which the model has been built. For example, the area, orientation, or many other descriptive variables of a catchment may be much more sensitive to the parameters used in a ground water flow model than are the values of head commonly used to calibrate the model.

This paper outlines a procedure to determine the range of predictions of catchments which would arise from alternative calibrations of a model. The range of catchments is used to identify zones of certainty and uncertainty, leading to alternative definitions of the protection zone for differing purposes. An example is presented, based on Bestwood Pumping Station, Nottinghamshire, which is located in the Triassic Sandstone Aquifer of the northern East Midlands of the United Kingdom. A trial and error calibration of a ground water flow model is used to determine an acceptable level for automatic calibration in the subsequent step. Only 12 measurements of ground water head were available, and these were used to determine the fit of a variety of model structures. A search routine revealed a range of feasible models and superposition of their catchments delineated the zones of certainty and uncertainty, which had areas of 7.4 and 15.2 km2, respectively.
Ground Water Age and Nitrate Distribution Within a Glacial Aquifer Beneath a Thick Unsaturated Zone
Authors: Johnston C.T. , Cook P.G. , Frape S.K. , Plummer L.N. , Busenberg E. , Blackport RJ.
Published: August 2005

The impact on ground water quality from increasing fertilizer application rates over the past 40 years is evaluated within a glacial aquifer system beneath a thick unsaturated zone. Ground water ages within the aquifer could not be accurately determined from the measured distribution of 3H and as a result, chlorofluorocarbon (CFC) and 3H/3He dating techniques were applied. Beneath a 25 m thick unsaturated zone, ground water ages based on CFC‐11 concentrations were greater than 3H/3He ground water ages by 6 to 10 years, due to the time lag associated with the diffusion of CFCs through the unsaturated zone. Using the corrected CFC‐11 and 3H/3He ground water ages and the estimated travel time of 3H within the unsaturated zone, the approximate position of ground water recharged since the mid‐1960s was determined. Nitrate concentrations within post mid‐1960s recharge were generally elevated and near or above the drinking water limit of 10 mg‐N/L. In comparison, pre mid‐1960s recharge had nitrate concentrations <2.5 mg‐N/L. The elevated NO3− concentrations in post mid‐1960s recharge are attributed mainly to increasing fertilizer application rates between 1970 and the mid‐ to late 1980s. Anaerobic conditions suitable for denitrifkation are present within pre mid‐1960s recharge indicating that removal of DO is a slow process taking tens of years. Over the next 10 to 20 years, nitrate concentrations at municipal well fields that are currently capturing aerobic ground water recharged near the mid‐1960s are expected to increase because of the higher fertilizer application rates beginning in the 1970s and 1980s.
Drawdowns in Coupled Aquifers with Confining Unit Storage and ET Reduction
Authors: Denis Roberto E. , Motz Louis H.
Published: August 2005

This paper presents a nonsteady coupled aquifer solution in which transient and steady‐state drawdowns due to pumping can be calculated in one or both of two aquifers separated by a semipermeable confining unit in a confined aquifer system. The water pumped is obtained from storage in the aquifers and the confining unit, and a reduction in evapotranspiration (ET) due to a decline in the water table. This solution is different from existing analytical solutions in that it includes both confining unit storage and a drawdown‐dependent ET reduction term. A Laplace space solution obtained for the differential equations subject to the initial and boundary conditions is inverted to the time domain using the Stehfest numerical algorithm. The presence of the ET reduction term in the solution allows the drawdowns to reach a steady‐state condition, and the presence of the confining unit storage term delays the response of the aquifer system to pumping, particularly in the unpumped aquifer. Use of the solution to calculate drawdowns for a representative field case is illustrated, along with verification of the solution using a numerical ground water flow model.
Conducting and Interpreting Slug Tests in Monitoring Wells with Partially Submerged Screens
Authors: Binkhorst Gordon K. , Robbins Gary A.
Published: August 2005

Conducting and interpreting slug tests in wells with screen sections and sand packs that span the water table are severely complicated by sand pack drainage and resaturation. Sand pack drainage greatly reduces the actual head difference between the well and the formation. Resaturation of the drained sand pack must be properly accounted for, or the formation hydraulic conductivity will be underestimated. The magnitude of error is a function of the well geometry, sand pack properties, and the model chosen to interpret the data. A method has been developed to correct for sand pack resaturation by calculating the specific yield of a drained sand pack using the early recharge data of a slug test. Slug tests were conducted in one well in which the water table varied over time, creating both partially and fully submerged screen and sand pack conditions for comparative testing. The mid‐time, log‐linear portion of slug test data was corrected using the calculated specific yield of the drained sand pack to yield essentially the same hydraulic conductivity value as the fully submerged screen results. Not accounting for sand pack resaturation would have yielded a hydrauli c conductivity value that was lower than the submerged screen results by a factor of seven.
Utilization of Intrinsic Boron Isotopes as Co‐Migrating Tracers for Identifying Potential Nitrate Contamination Sources
Authors: Leenhouts James M. , Basset R.L. , III T. Maddock
Published: August 2005

The stable isotopes of the conservative element boron, 11 B and 10 B, have been employed as co‐migrating isotopic tracers to trace potential sources of nitrate observed in ground water pumped from a large capacity 0.167 m 3/s irrigation well in the Avra Valley of southeastern Arizona. The isotopic ratios provided an identifying signature for two nitrogen carrying source waters: municipal waste water and agricultural return flow. Additional chemical parameters were also examined to corroborate the isotopic indications.

Boron isotopes provided a superior delineation of mixing processes in the system compared to the general inorganic chemical parameters. Findings of this investigation indicate that the water pumped by the study well at the beginning of the 1993 irrigation season was composed of a mixture of approximately 25 % municipal waste water and 75 % background ground water. As the irrigation season progressed, an increasing proportion of water was contributed by irrigation return flow from neighboring agricultural fields.
Predicting the Probability Distribution of Yield from Multiple Boreholes in Crystalline Bedrock
Authors: Banks David
Published: August 2005

In many hard rock lithologies, the distribution of borehole yields can often be regarded as being derived from a log‐normally distributed population, characterized by the median yield (m1), and standard deviation of In‐transformed values (σ1. By means of numerical techniques using standard spreadsheet software, the distribution of total yield from two or more boreholes can be calculated, assuming that the yields of the boreholes are statistically independent variables and that there is no significant hydraulic interference between boreholes. The results are not necessarily obvious: (1) the median total yield for a group of y noninterfering boreholes (my) is greater than y.mt. The ratio my/y.m1 increases with increasing y and with increasing σ1; and (2) the standard deviation σy of In‐transformed yield distributions for water systems consisting of y multiple boreholes is less than the standard deviation σ1 of the In‐transformed yield distribution for single boreholes. The standard deviation decreases as the number of boreholes in the group increases.
Simplified Method of “Push‐Pull” Test Data Analysis for Determining In Situ Reaction Rate Coefficients
Authors: Haggerty R. , Schroth M.H. , Istok J.D.
Published: August 2005

The single‐well, “push‐pull” test method is useful for obtaining information on a wide variety of aquifer physical, chemical, and microbiological characteristics. A push‐pull test consists of the pulse‐type injection of a prepared test solution into a single monitoring well followed by the extraction of the test solution/ground water mixture from the same well. The test solution contains a conservative tracer and one or more reactants selected to investigate a particular process. During the extraction phase, the concentrations of tracer, reactants, and possible reaction products are measured to obtain breakthrough curves for all solutes. This paper presents a simplified method of data analysis that can be used to estimate a first‐order reaction rate coefficient from these breakthrough curves. Rate coefficients are obtained by fitting a regression line to a plot of normalized concentrations versus elapsed time, requiring no knowledge of aquifer porosity, dispersivity, or hydraulic conductivity. A semi‐analytical solution to the advective‐dispersion equation is derived and used in a sensitivity analysis to evaluate the ability of the simplified method to estimate reaction rate coefficients in simulated push‐pull tests in a homogeneous, confined aquifer with a fully‐penetrating injection/extraction well and varying porosity, dispersivity, test duration, and reaction rate. A numerical flow and transport code (SUTRA) is used to evaluate the ability of the simplified method to estimate reaction rate coefficients in simulated push‐pull tests in a heterogeneous, unconfined aquifer with a partially penetrating well. In all cases the simplified method provides accurate estimates of reaction rate coefficients; estimation errors ranged from 0.1 to 8.9% with most errors less than 5%. In an example application, the method is used to estimate reaction rate coefficients for a microbiological process (denitrification) using data from field push‐pull tests performed in a petroleum‐contaminated, unconfined alluvial aquifer.
Uses of Chloride/Bromide Ratios in Studies of Potable Water
Authors: Davis Stanley N. , Whittemore Donald O. , Fabryka‐Martin June
Published: August 2005

In natural ground water systems, both chlorine and bromine occur primarily as monovalent anions, chloride and bromide. Although dissolution or precipitation of halite, biological activity in the root zone, anion sorption, and exchange can affect chloride/bromide ratios in some settings, movement of the ions in potable ground water is most often conservative. Atmospheric precipitation will generally have mass ratios between 50 and 150; shallow ground water, between 100 and 200; domestic sewage, between 300 and 600; water affected by dissolution of halite, between 1000 and 10,000; and summer runoff from urban streets, between 10 and 100. These, and other distinctive elemental ratios, are useful in the reconstruction of the origin and movement of ground water, as illustrated by case studies investigating sources of salinity in ground water from Alberta, Kansas, and Arizona, and infiltration rates and pathways at Yucca Mountain, Nevada.
Procedures for Uncertainty Analyses Applied to a Landfill Leachate Plume
Authors: Abbaspour K.C. , Schulin R. , van Genuchten M. Th. , Schlappi E.
Published: August 2005

Environmental data often have features that are distinct from data in other branches of science. These features include spatial and/or temporal auto‐correlation, natural heterogeneity, measurement errors, small sample sizes, and simultaneous existence of different types and qualities of data. Realistic environmental modeling requires simulation procedures that account for all of these features. In this study, a model of uncertainty analysis, BUDA, is used to account for the noted features and provide a unified framework for quantification, propagation, and reduction of uncertainty. The BUDA model is used to analyze the development of a chloride plume around an old landfill to the year 2020. This article describes the different components of BUDA as they relate to the landfill application.
Spatial Variability in In Situ Aerobic Respiration and Denitrification Rates in a Petroleum‐Contaminated Aquifer
Authors: Schroth M.H. , Istok J.D. , Conner G.T. , Hyman M.R. , Haggerty R. , O'Reilly K.T.
Published: August 2005

An extensive series of single‐well, push‐pull tests was performed to quantify horizontal and vertical spatial variability in aerobic respiration and denitrification rates in a petroleum‐contaminated aquifer. The results indicated rapid consumption of injected O2 or NO3− in shallow and deep test intervals across a large portion of the site. Computed first‐order rate coefficients for aerobic respiration ranged from 0.15 to 1.69 h−1 in the shallow test interval, and from 0.08 to 0.83 h−1 in the deep test interval. The largest aerobic respiration rates occurred on the upgradient edge of the contaminant plume where concentrations of petroleum hydrocarbons and dissolved O2 were relatively high. Computed first‐order rate coefficients for denitrification ranged from 0.09 to 0.42 h−1 in the shallow test interval, and from 0.11 to 0.28 h−1 in the deep test interval. The largest denitrification rates occurred on the downgradient edge of the plume where hydrocarbon concentrations were relatively high but dissolved oxygen concentrations were small. The rates reported here represent maximal rates of aerobic respiration and denitrification, as supported by high concentrations of electron acceptors in the injected test solutions. Production of dissolved CO2 during aerobic respiration and denitrification tests provided evidence that O2 and NO3− consumption was largely due to microbial activity. Additional evidence for microbial NO3− consumption was provided by reduced rates of NO3−consumption when dissolved O2 was injected with NO3−, and by increased N2O production when C2H2 was injected with NO3−.
Characterization of an Unregulated Landfill Using Surface‐Based Geophysics and Geostatistics
Authors: Woldt Wayne E. , Hagemeister Michael E. , Jones David D.
Published: August 2005

This paper develops a geoelectrical and geostatistical‐based methodology that can be used to screen unregulated landfills for the presence of leachate and obtain an approximation of the vertical/spatial extent of waste. The methodology uses a surface electromagnetic (EM) survey combined with indicator kriging. Indicator kriging allows for the use of EM data that have been collected over highly electrically conductive material such as that occurring within landfills. Indicator kriging maps were generated for several vertical sections cut through a landfill to establish the landfill strata. Similarly, horizontal sections were generated to evaluate the areal extent of waste and leachate in the vadose zone and saturated zones, respectively. The horizontal and vertical maps were combined to estimate the volume of solid waste and liquid within three zones: (1) waste, (2) waste and/or leachate, and (3) potential leachate. The methodology appears hold promise in providing results that can be used as part of a hazard assessment, or to assist in the placement of monitoring wells at sites requiring additional study. A case study is used to demonstrate the methodology at an unregulated landfill in eastern Nebraska.
Review of Phosphate Mobility and Persistence in 10 Septic System Plumes
Authors: Robertson W.D. , Schiff S.L. , Ptacek C.J.
Published: August 2005

Phosphate distribution was reviewed in 10 mature, highly monitored septic system ground water plumes in central Canada. It was shown that six plumes (primarily those on calcareous sands) of enriched P concentrations (0.5 to 5 mg/L P) exceeding 10 m in length are present. In each case, phosphate migration velocity is highly retarded (retardation factor, 20 to 100) compared to the ground water velocity, hut migration rates remain sufficiently fast (−1 m/a) to the of concern when considering long‐term operation and the normal setback distance of septic systems from adjacent surface water bodies (∼ 15 m). Much smaller scale phosphate plumes (< 3 m in length) are present at the acidic sites on noncalcareous sands and on silt‐ and clay‐rich sediments.

At all of the sites, ground water concentrations are lower than effluent values by amounts ranging from 23 to 99%, suggesting that P accumulation has occurred in the vadose zone. This was confirmed by sediment analyses at four of the sites which, in each case, showed that zones of Penrichment were present within 1 m of the infiltration pipes (Wood 1993; Zanini et al. 1998). Also, observed phosphate concentrations are generally consistent with values expected based on the solubility constraints of the minerals vivianite in reducing zones (including the septic tank), and strengite and variscite in oxidizing zones, providing further evidence that min‐eral precipitation reactions play a role in limiting P concentrations. Strengite and variscite have the potential to limit P to low con‐centrations (co.1 mg/L) under acidic conditions, but oxidation of sewage efiluent leads to acidic conditions only in noncalcareous terrain or beneath old septic systems where calcium carbonate has been depleted. Overall, phosphate plume migration velocities in ground water appear to be controlled by sorption processes, but the phosphate concentrations that are present in the plumes appear to be strongly controlled by mineral precipitation reactions that occur in close proximity to the infiltration pipes.
Chloride/Bromide and Chloride/Fluoride Ratios of Domestic Sewage Effluents and Associated Contaminated Ground Water
Authors: Vengosh Avner , Pankratov Irena
Published: August 2005

To establish geochemical tools for tracing the origin of ground water contamination, we examined the variations of Cl/Br and Cl/F (weight) ratios in (1) domestic waste water from the Dan Region Sewage Reclamation Project and from reservoirs in the central coast of Israel; (2) associated contaminated ground water; and (3) pristine ground water from the Mediterranean coastal aquifer of Israel. Our data show that supply water, anthropogenic NaCl and fluoridation control the Cl/Br (410 to 873) and Cl/F (468 to 1070) ratios of domestic waste water, and conventional sewage treatment does not affect the anthropogenic inorganic signals. The Cl/Br ratios of ground water contaminated with sewage effluent reflect conservative mixing proportions of sewage and regional ground water components. Sensitivity tests demonstrate that it is possible to detect and distinguish sewage contamination from marine ratios after a sewage contribution of 5 to 15% is mixed with regional ground water. Mixing with Br‐enriched fresh water (e.g., Sea of Galilee; Cl/Br=145), however, would reduce this sensitivity. Since the high Cl/Br signal of sewage effluents is distinguishable from other anthropogenic sources with low Cl/Br ratios (e.g., street runoff, agriculture return flows) and from natural contamination sources (e.g., salt water intrusion; Cl/Br=293), Cl/Br ratios can therefore be a useful inorganic tracer for identification of the origin of contaminated ground water. The Cl/F ratios of sewage‐contaminated ground water (284 to 5186) were higher than those in the original sewage effluent, which suggests retention of fluoride into the aquifer solid phase.
Virus Occurrence and Transport in a School Septic System and Unconfined Aquifer
Authors: DeBorde Dan C. , Woessner William W. , Lauerman Bruce , Ball Patrick N.
Published: August 2005

Federal efforts to establish reliable natural disinfection criteria for ground water supplies require the identification of appropriate indicator viruses to represent pathogenic viruses and an understanding of parameters affecting virus survival and transport in a variety of hydrogeologic settings. A high school septic system and the associated fecal waste‐impacted unconfined sand and gravel aquifer were instrumented to: (1) evaluate if the concentrations of enterovirus and coliphage in this system were sufficient to allow their use as indicator viruses; (2) establish viral transport rates, transport distances, and concentrations in a highly conductive cold water aquifer. Enteroviruses were found in only two of eight assays of the septic tank effluent (0.26 and 4.4 virus/L) and were below detection in eight ground water samples. Male‐specific and somatic coliphage were detectable in both the septic tank effluent (averaging 674,000 and 466,000 coliphage/L, respectively) and in the impacted underlying ground water, decreasing to detection limits beyond 38 m of the drainfield. Virus transport parameters in this aquifer were measured by seeding high numbers of MS2 and ØX174 coliphage into the ground water and documenting their transport over 17.4 m. A portion of the seeded virus traveled at least as fast as the bromide tracer (1 to 2.9 m/d). Proposed natural disinfection criteria would not be met in this aquifer using standard 30.5 m setback distances. In addition, the virus sorption processes and long survival times resulted in presence of viable seed virus for more than nine months.