bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Analysis of Ground Water Recharge Potential on Alluvial Fans Using Limited Data
Authors: Munévar Armin , Mariño Miguel A.
Published: August 2005

A modeling approach is developed to evaluate the potential for artificial recharge on alluvial fans in the Salinas Valley, California, using limited data of soil texture, soil hydraulic properties, and interwell stratigraphy. Promising areas for surface recharge are identified and mapped on a broad‐scale using soil surveys, geologic investigations, permeability tests, and seasonal ground water response to rainfall and runoff. Two‐dimensional representations of the vadose zone at selected sites are then constructed from drillers’logs and soil material types are estimated. Next, hydraulic properties are assigned to each soil material type by comparing them to laboratory‐tested cores of similar soils taken from one site. Finally, water flow through the vadose zone is modeled in two dimensions at seven sites using a transient, finite‐difference, variably saturated flow model. Average infiltration rates range from 0.84 to 1.54 cm/hr and recharge efficiency, the percentage of infiltrated water that reaches the water table, varies from 51% to 79%. Infiltration rates and recharge efficiency are found to be relatively insensitive to recharge basin ponding depth due to the thickness of the vadose zones modeled (31 to 84 m). The impact of artificial recharge on the Salinas Valley ground water basin is investigated by simulating the regional ground water response to surface spreading and streamflow augmentation with a recently calibrated, finite‐element, ground water‐surface water model for the basin. It was determined that a combined approach of surface recharge and streamflow augmentation significantly reduces the state of ground water overdraft and, to a lesser extent, reduces the rate of sea water intrusion.
Role of Macropores in Solute Transport under Ponded Water Condition Produced by Laboratory Simulated Intense Storms
Authors: Iqbal Mohammad Z.
Published: August 2005

Soil macropores are widely studied because they are known to serve as avenues for rapid contaminant transport. Currently, it is understood that a macroporous medium develops regions of mobile and immobile water during flow. Consequently, solutes in the mobile phase bypass a considerable portion of the medium, thus limiting their natural attenuation. It is, however, not adequately documented in the literature what role the macropores play during intense rain events that result in variable ponding depths.

Macropore flow under ponded water conditions was studied on two undisturbed soil columns taken from the loam soils of northeastern Iowa, U.S. The columns were placed on a four‐segment outflow collector system. A slug of water labeled with Br was applied to the columns followed by simulation of 58 mm of rain on column 1 and 53.6 mm on column 2, in one hour, 30 minute, and 15 minute events. During the highest intensity rain event (15 minutes), the total volume of water that exited through the bottom of segments 1,2, 3, and 4 were 21.6%, 34.5%, 28.5%, and 15.4% in column 1, and 1.3%, 15.9%, 72.2%, and 10.5% in column 2, respectively. As the intensity of rain was increased from one hour to the 15 minute event, the total bromide mass recovery increased from 45% (29.2 mg) to 57% (36.9 mg) of the total application (65 mg) for column 1, and from 51 % (33.2 mg) to 59% (38.2 mg) for column 2, respectively. Finally, an examination of dye‐stained high flow regions in column 1 demonstrated that macro‐porosities made approximately 20% of the total cross‐sectional area of the column.

These results suggest that solute transport behavior in macroporous soils can be impacted by ponding depths, and intense rain events can severely restrict contaminant degradation in soils.
Use of Combined Shewhart‐CUSUM Control Charts for Ground Water Monitoring Applications
Authors: Gibbons Robert D.
Published: August 2005

Statistical properties of combined Shewhart‐CUSUM control charts are examined in terms of the site‐wide false positive rate, false negative rate, and average run length (i.e., the average number of sampling events that it takes to detect a significant exceedance). The effects of multiple comparisons (i.e., multiple monitoring wells and constituents), verification resampling, background sample size, and background updating are incorporated into the analysis. The effects of (1) verification resampling plans including no resampling, pass one resample, pass one of two resamples, and pass two of two resamples; (2) background sample sizes (n = 8,12,16,20, and 24); and (3) multiple comparisons (k = 1 to 500 future comparisons) were examined. In addition, various alternative control limit factors (h = SCL= 4.5, 5.0,5.5, and 6.0) were considered, where the control limit is x + hs. Results of simulations revealed that it is possible to balance site‐wide false positive and false negative rates at low levels using combined Shewhart‐CUSUM control charts. The results revealed that it is important to select the appropriate multiplier, verification resampling plan, number of background samples, and number of intervening samples prior to updating background.
Analysis of the Quality of Parameter Estimates from Repeated Pumping and Slug Tests in a Fractured Porous Aquifer System in Wonju, Korea
Authors: Lee Jin‐Yong , Lee Kang‐Kun
Published: August 2005

Pumping and slug tests are widely used, relatively simple methods for estimating hydraulic conductivity and storage coefficient. This study tested the reproducibility of pumping and slug tests in estimating aquifer parameters in fractured or fractured porous media. The continuum concept is applied to represent the hydraulic properties by the conventional conductivity and storage coefficient. Repeated tests show discrepancies wider than can be attributed to probable measurement errors or incomplete curve fitting. The sources of discrepancy include turbulent head loss in an observation well, pumping well location, data acquisition period (pumping or recovery), selection of analysis method, test initiation mechanism, applied initial displacement, and selection of data segment for analysis. When we employ a specific test practice or choose a specific analysis method or data segment for the analysis, the resulting parameter estimates show characteristic patterns of distribution with respect to the mean value. This study analyzes the patterns and discusses how to improve the reliability of the parameter estimation.
Application of Flowmeter and Depth‐Dependent Water Quality Data for Improved Production Well Construction
Authors: Gossell M.A. , Nishikawa T. , Hanson R.T. , Izbicki J.A. , Tabidian M.A. , Bertine K.
Published: August 2005

Ground water production wells commonly are designed to maximize well yield and, therefore, may be screened over several water‐bearing zones. These water‐bearing zones usually are identified, and their hydrogeologic characteristics and water quality are inferred, on the basis of indirect data such as geologic and geophysical logs. Production well designs based on these data may result in wells that are drilled deeper than necessary and are screened through zones having low permeability or poor‐quality ground water. In this study, we examined the application of flowmeter logging and depth‐dependent water quality samples for the improved design of production wells in a complex hydrogeologic setting. As a demonstration of these techniques, a flowmeter log and depth‐dependent water quality data were collected from a long‐screened production well within a multilayered coastal aquifer system in the Santa Clara‐Calleguas Basin, Ventura County, California. Results showed that the well yields most of its water from four zones that constitute 58% of the screened interval. The importance of these zones to well yield was not readily discernible from indirect geologic or geophysical data. The flowmeter logs and downhole water quality data also show that small quantities of poor‐quality water could degrade the overall quality of water from the well. The data obtained from one well can be applied to other proposed wells in the same hydrologic basin. The application of flowmeter and depth‐dependent water quality data to well design can reduce installation costs and improve the quantity and quality of water produced from wells in complex multiple‐aquifer systems.
Sensitivity Study on Hydraulic Well Testing Inversion Using Simulated Annealing
Authors: Nakao Shinsuke , Najita Julie , Karasaki Kenzi
Published: August 2005

Cluster variable aperture (CVA) simulated annealing has been used as an inversion technique to construct fluid flow models of fractured formations based on transient pressure data from hydraulic tests. A two‐dimensional fracture network system is represented as a filled regular lattice of fracture elements. The algorithm iteratively changes element apertures for a cluster of fracture elements in order to improve the match to observed pressure transients. Aperture size is chosen randomly from a list of discrete apertures. The cluster size is held constant throughout the iterations. Since hydraulic inversion is inherently nonunique, it is important to use additional information. We investigated the relationship between the scale of heterogeneity and the optimal cluster size and shape to enhance convergence of the inversion and improve the results. In a spatially correlated transmissivity field, a cluster size corresponding to about 20 % to 40 % of the practical range of the spatial correlation is optimal. Inversion results of the Raymond test site data are also presented and based on an optimal cluster size; the practical range of the spatial correlation is estimated to be 5 to 10 m.
Estimating Rainfall Recharge and Soil Water Residence Times in Pukekohe, New Zealand, by Combining Geophysical, Chemical, and Isotopic Methods
Authors: Rosen Michael R. , Bright John , Carran Peter , Stewart Michael K. , Reeves Robert
Published: August 2005

The combined use of geophysical (time domain reflectometry [TDR]), isotopic (δ18 O and δ2H) and chemical (NO 3 ‐N, Cl) techniques indicates that residence times in the unsaturated zone of a fractured basalt aquifer in the Pukekohe region of the North Island, New Zealand, are at least six months. Each technique provides useful information on specific aspects of recharge and residence times, but combined they provide a basis for determining the mechanisms of water movement in the unsaturated zone. TDR soil moisture measurements provide similar rainfall recharge estimates as model calculations over longer time periods (monthly or seasonal) but may be more accurate for shorter time scales (weekly or daily).

The TDR measurements indicate that recharge occurs mainly in the late autumn and winter months. Measurements of nitrate concentrations in the soil profile over this same period, suggest that nitrate is mineralized in the soil during the summer and is flushed past the root zone at the beginning of the recharge period, in early winter. Nitrate concentrations in the soil profile do not increase in concentration later in the recharge period, even after significant recharge events have occurred, because all stored nitrate has already been released. This pattern of nitrate movement indicates that fertilizer applications in spring and early summer will leach less to ground water and applications made in autumn and winter will leach more. Estimations of yearly recharge from mean monthly chloride concentrations (730 mm/yr) are roughly in agreement with the TDR estimates (680 mm/year). However, there is a large range in the chloride estimates (>100%) because monthly chloride concentration measurements in both the rain and soil water vary due to the proximity of the site to the ocean.
Hydraulic Properties and Uncertainty Analysis for an Unconfined Alluvial Aquifer
Authors: Chen Xunhong , Goeke James , Summerside Scott
Published: August 2005

An inverse computational method was used to analyze pumping and recovery tests conducted in an unconfined alluvial aquifer along the Republican River valley in Nebraska. At each test site, a high‐capacity irrigation well was used as a pumping well, and eight observation wells were constructed to measure drawdown during the pumping and recovery tests. The test data were analyzed for four hydraulic parameters: the vertical (K z) and the radial (K r) hydraulic conductivity, the storage coefficient (S), and specific yield (S y). This method provides not only the average values but also estimated standard errors, confidence intervals, and correlation for the aquifer parameters. The standard error and confidence interval indicate the quality of the parameter estimates, and the correlation coefficients are useful in the evaluation of the relationship among the four parameters. High pumping rates seemed to reduce the effects of well borehole storage on drawdown. Because of the significant amount of early‐time data collected, the tests gave high‐quality S values. K r values for most observation locations range from 90 to 120 m/d. It was found that K r and S y had a higher correlation and the ratio of K r/K z varied from approximately 10 to 30.
Seasonal Correlation of Well Contamination and Septic Tank Distance
Authors: Arnade Linda Jeanette
Published: August 2005

Approximately 40,000 residents in Palm Bay, Florida, rely on septic tanks as a means of sewage disposal and on wells as a drinking water source. High levels of precipitation (>63 cm) during the months of July to September and the presence of porous sandy soils result in high water tables and septic tank overflows. The inability of septic tank leachate to percolate through the soil during the wet season results in ground water contamination, thus posing a health risk to those who drink from local wells.

Sixty residential wells in Palm Bay were tested for fecal coliforms, nitrates, and phosphates to determine if season has a significant effect on the correlation between these parameters and the proximity of wells to septic tanks. Ground water samples collected at all distances from septic tanks during the wet season contained twice as many fecal coliforms and higher concentrations of nitrates and phosphates compared with samples collected during the dry season. Results showed a statistically significant correlation between increasing fecal coliform, nitrate, and phosphate concentrations and decreasing distance between wells and septic tanks.
Hydrogeological and Hydrogeochemical Studies for Salt Water Intrusion on the South Coast of Laizhou Bay, China
Authors: Xue Yuqun , Wu Jichun , Ye Shujun , Zhang Yongxiang
Published: August 2005

Sea water intrusion has occurred on the east and southeast coasts of Laizhou Bay, China, since the 1970s (Wu et al. 1993). In 1981, on the adjacent south coast, the intrusion of salt water originating from brine was observed. In this area, the salt water intrusion was caused by the excessive pumping of fresh water in aquifers. Moreover, the simultaneous pumping of fresh water and salt water/brine formed a complicated ground water flow field. The data obtained from observation wells were used to analyze the origin of the salt water and brine, and the genesis of the bicarbonate/sodium water zone. All data suggest that the brine originated from ancient sea water, and that the bicarbonate/sodium water was formed by cation exchange. The variations of chemical compositions along representative flowpaths and the relationships between such variations and salt water intrusion were also discussed.
Uncertainty Quantification for Delineation of Wellhead Protection Areas Using the Gauss‐Hermite Quadrature Approach
Authors: Levy Jonathan , Ludy Eric E.
Published: August 2005

Missing from most wellhead protection area (WHPA) delineation studies is a measure of the uncertainty associated with model predictions. A quantitative representation of that uncertainty can be used by regulators to implement different degrees of protection for areas with different degrees of certainty.

Uncertainty analysis was performed for one‐ and five‐year WHPA delineation for two municipal wells within a buried‐valley glacial‐outwash aquifer in southwestern Ohio. An approximation of the three‐point Gauss‐Hermite quadrature formula was used. This method is an alternative to simple Monte Carlo random sampling, typically requiring fewer model runs. It results in model‐prediction expected values and variances and quantifies parameter main and two‐way interactive effects. This study explored the collective impact of the uncertainties associated with six model parameters. Parameter probability density functions (PDFs) were based on field data and modified using a ground water flow model to ensure that all combinations of parameter values, within their PDFs, yielded an acceptable model calibration.

The one‐year WHPA for the upgradient well had a high degree of associated uncertainty represented by the difference in size between the WHPA low and high 95% confidence interval limits. The large uncertainty was due to the uncertainties associated with model parameter values, especially effective porosity and horizontal hydraulic conductivity. River conductance also had a substantial impact on the WHPA predictions. The WHPAs for the downgradient well and the five‐year WHPA for the upgradient well were limited by upgradient hydrogeologic boundaries; their prediction was, therefore, less sensitive to the uncertainties inherent in the model parameters.
Hydraulic Conductivities of Low Permeability Sediments Inferred from a Triple Pumping Test and Observed Vertical Gradients
Authors: Lebbe Luc , Van Meir Nathalie
Published: August 2005

Knowing vertical conductivities of thick aquitards is important for simulating regional or local ground water flow. These hydraulic parameters are best determined by calibration of these models. Collection of reliable data from heavily pumped ground water reservoirs can be problematic. Another way to infer these hydraulic parameters is the simultaneous interpretation of different parts of a multiple pumping test using an inverse numerical model. Here, the drawdowns observed in the indirectly pumped aquifers allow us to deduce the vertical conductivities of the aquitards with an equivalent accuracy as the horizontal conductivities of the aquifers. When the hydraulic resistances of the aquitards are too large, it becomes impossible to induce observable drawdowns in the indirectly pumped aquifers, and the inverse model loses valuable input data. Observing vertical gradients in and over the aquitards in case of important vertical flow can make up for this loss. These data allow us to estimate the specific discharges through the successive parts of the aquitard and hence their hydraulic resistances. This useful information allows us to consider all these hydraulic resistances in one group of hydraulic parameters during the simultaneous interpretation of the multiple pumping test using an inverse numerical model. As this procedure reduces the number of identified parameter groups, it enhances their reliability. In this paper it is demonstrated how this reliability can be deduced from a number of statistical parameters that can also be used in the collinear diagnosis. The proposed interpretation procedure is demonstrated on a triple pumping test performed in and around the most important aquitard in Flanders, Belgium. The obtained results should first be integrated in a local ground water flow model. By the performance of a number of such integrated hydrogeological studies, the lateral change in the hydraulic properties of this aquitard can be evaluated.
Controlled Laboratory Investigations of Wellbore Concentration Response to Pumping
Authors: Martin‐Hayden James M.
Published: August 2005

The relationship between the ground water sample and the surrounding ground water environment is controlled by wellborn flow and mixing that carry ground water to the sampling device. Controlled laboratory conditions and uniform inflow and inflowing concentration allowed detailed investigations of wellbore concentration responses to pump‐induced flow and mixing independent of external complicating influences. During pumping from the top of the screen, the results agreed with wellbore flow theory except for high‐frequency, high‐amplitude concentration fluctuations and mixing with the blank casing due to slight density contrasts (∼0.005%). Concentration fluctuations indicated partial mixing of ground water with well water and declining concentrations in the blank casing indicated that convection due to the slight density contrast overcame pump‐induced velocities. During pumping from the bottom of the well, opposing forces of buoyancy and pumping produced small‐scale cumulative mixing as the ground water from different portions of the screen approached the pump. Even during low‐flow pumping (i.e., 220 mL/min), 5% of the water was prepurge well water after five well volumes were pumped. In the field the density contrasts that resulted in these mixing processes might be caused by a slight cooling of the wellhead or a slight increase in temperature with depth (>0.2°C/m). If the temperature gradient was more pronounced, the convective mixing of screen water with the potentially altered casing water would be more thorough and sampling without mixing would not be possible. If the temperature gradient is stable or if the water in the blank casing is not significantly altered, casing water mixing will not present a problem.
Recharge Through a Regional Till Aquitard: Three‐Dimensional Flow Model Water Balance Approach
Authors: Gerber Richard E. , Howard Kenneth
Published: August 2005

In southern Ontario, vertical leakage through a regionally extensive till is the primary source of recharge to underlying aquifers used for domestic and municipal water supply. Since leakage is largely controlled by the bulk hydraulic conductivity (K) of the aquitard, accurate estimates of K are necessary to quantify the resource. Considerable controversy exists regarding estimates of K for this aquitard, which vary according to the scale of the test method. For the till matrix, estimates from core samples and slug tests consistently range from 10−11 to 10−10 m/s. Isotopic evidence (3H), on the other hand, indicates that nonmatrix structures such as sand lenses, erosional surfaces, joints, and fractures significantly enhance till permeability. This is confirmed by slug test, pump test, recharge, and water balance studies, which show that K varies over seven orders of magnitude (10−12 to 10−5 m/s).

To provide a regional estimate of bulk K and a reliable estimate of vertical recharge through the Northern Till, a numerical ground water flow model was constructed for the Duffins and Petticoat Creek drainage hasin. The model was calibrated to measurements of hydraulic head and estimates and measurements of base flow throughout the basin. This model demonstrates that the vertical hydraulic conductivity (Kv) for the Northern Till ranges from 5 × 10−10 to 5 × 10−9 m/s, values that are up to 2.5 orders of magnitude greater than matrix K estimates. Regional recharge through the Northern Till is estimated to range from 30 to 35 mm/a.
Travel Time Equations for Dispersive Contaminants
Authors: Wheatcraft Stephen W.
Published: August 2005

Travel time estimates for contaminant fronts or plumes are often obtained using estimates of average pore velocities from Darcy's law calculations. These estimates provide information only about the travel time of the average concentration (or the peak, for contaminant pulses). Equations are developed here for other portions of the breakthrough curve for a nonreactive contaminant, which allow estimates of travel time for concentrations other than the average or the peak. These travel time equations provide a simple method for calculating early arrival times for low concentrations.
Arsenic in Ground Water of the United States: Occurrence and Geochemistry
Authors: Welch Alan H. , Westjohn D.B. , Helsel Dennis R. , Wanty Richard B.
Published: August 2005

Concentrations of naturally occurring arsenic in ground water vary regionally due to a combination of climate and geology. Although slightly less than half of 30,000 arsenic analyses of ground water in the United States were 1 μg/L, about 10% exceeded 10 μg/L. At a broad regional scale, arsenic concentrations exceeding 10 μg/L appear to be more frequently observed in the western United States than in the eastern half. Arsenic concentrations in ground water of the Appalachian Highlands and the Atlantic Plain generally are very low ( 1 μg/L). Concentrations are somewhat greater in the Interior Plains and the Rocky Mountain System. Investigations of ground water in New England, Michigan, Minnesota, South Dakota, Oklahoma, and Wisconsin within the last decade suggest that arsenic concentrations exceeding 10 μg/L are more widespread and common than previously recognized.

Arsenic release from iron oxide appears to be the most common cause of widespread arsenic concentrations exceeding 10 μg/L in ground water. This can occur in response to different geochemical conditions, including release of arsenic to ground water through reaction of iron oxide with either natural or anthropogenic (i.e., petroleum products) organic carbon. Iron oxide also can release arsenic to alkaline ground water, such as that found in some felsic volcanic rocks and alkaline aquifers of the western United States. Sulfide minerals are both a source and sink for arsenic. Geothermal water and high evaporation rates also are associated with arsenic concentrations 10g/L in ground and surface water, particularly in the west.
Fresh‐Saline Ground Water Interface in the Western Dead Sea Area
Authors: Yechieli Yoseph
Published: August 2005

The interface between fresh and saline ground water was studied in the Dead Sea area, using in situ profiles of electrical conductivity (EC) of water. The slope of the interface was found to be 10 times shallower than normally expected near the ocean because of the greater density contrast (the density of the Dead Sea is 1.23 g/cc). Although the Dead Sea system is extremely dynamic, the Ghyben‐Herzberg approximation was still found to be relevant. The shallow interface is expected to cause Dead Sea water to intrude much farther inland than does sea water adjacent to oceans. This extremely shallow interface needs to be taken into account when exploiting ground water in this area in order to avoid upconing of brines and salinization.

In recent times, the hydrologic system of the Dead Sea area has changed in water levels and salinity. Simulations using SUTRA code were run for a confined subaquifer to examine the effects of such change on the location of the fresh‐saline water interface. Following the changes, the new interface is not parallel to the previous one because the increase in density causes a decrease in the interface's slope.
The Effects of Human Intervention in the Water Regime
Authors: Querner E.P.
Published: August 2005

Water tables in the Netherlands have fallen due to human interventions in the water regime, causing hydrological degradation, particularly over the last 50 years. Factors responsible for this hydrological degradation are increased agricultural crop production, changes in land use, increased drainage, lowering of the drainage base, and increased ground water abstractions. Additionally, variations in the water regime have been caused by differences in meteorological conditions over a number of years. The physically based ground water and surface water model SIMGRO was used to predict the effect of these human interventions. The analysis was carried out in three regions in the Netherlands and various scenarios were defined to represent the man‐induced changes over the last 50 years. Changes in natural recharge of ground water and water tables were used as indicators for the hydrological degradation. The calculations show that the natural recharge increases when water tables are deep. Variations in meteorological conditions over the last 50 years have a pronounced effect on the natural recharge, and the effect is greater than the changes caused by any of the human influences. The lowering of the drainage base causes the greatest change in ground water tables.
A Nondimensional Evaluation of Tracer Sensitivity to Density Effects
Authors: Jalbert Marc , Dane Jacob H. , Abriola Linda M. , Pennell Kurt D.
Published: August 2005

The purpose of this paper is to assess the importance of the density difference between a tracer solution and ground water on the determination of aquifer properties by inversion of tracer signals. To estimate the effect of this density difference, we developed a nondimensional, approximate solution to a Boundary Value Problem (BVP) based on a partial differential equation first presented by Bear and Dagan (1964). The BVP models the displacement of water by another aqueous solution with a different density in a rectangular, vertical cross section of a homogeneous porous medium. A rectangular sandbox analog model was used to verify the validity of the nondimensional solution for the case of a moving interface during the displacement of water by a heavier‐than‐water aqueous solution. A constant flow rate was maintained by applying constant heads at a fully penetrating vertical inflow and outflow chamber. The theory, which can be applied as a prediction tool for laboratory experiments, permits us to explore the implications of using denser‐than‐water tracers for determining aquifer hydraulic conductivity and dispersion coefficient values. According to our assessments, density effects should not be ignored, as small density differences can lead to serious uncertainties in permeability and dispersivity determinations.
Infiltration Measured by the Drip of Stalactites
Authors: Sanz Eugenio , López Juan José
Published: August 2005

The hydrodynamic processes and mechanisms involved in rain infiltration and recharge in local areas of karst terrain can be identified and quantified by using measurements of the seepage of cave stalactites. Detailed measurements of the seepage of stalactites in seven caves located in an area close to the land surface, or the subcutaneous area of the karst, show a diversity of complex factors involved in infiltration: type of precipitation (rain or snow), air temperature, soil type and thickness, etc., which give rise to larger or smaller variations of flow in the espeleothem hydrographs.

In some cases, no explanation can be found for the response of stalactites to rainfall, while in others there is a relationship between outer atmospheric parameters and the recharge represented by the stalactite drip. Romperopas Cave (Spain) has both a rapid and a basic flow, with hydrograph recessions similar to those observed in other caves. Water seepage in this cave varies greatly both in space and in time. The infiltration in Altamira Cave (Spain) was calculated and a multiple regression was found between infiltration, rain and outside air temperature. In other cases, the balance of the water on the soil is responsible for the seepage. Thus, a precipitation runoff numerical model that simulated the stalactite hydrographs could be applied to the Baradla and Beké Caves (Hungary). The complex properties of the ground, which are required for other flow numerical models for the unsaturated zone, were not taken into consideration.
Plants As Indicators of Focused Ground Water Discharge to a Northern Minnesota Lake
Authors: Rosenberry Donald O. , Striegl Robert G. , Hudson Dallas C.
Published: August 2005

Determining the discharge of ground water to Shingobee Lake (66 ha), north‐central Minnesota, is complicated by the presence of numerous springs situated adjacent to the lake and in the shallow portion of the lakebed. Springs first had to be located before these areas of more rapid discharge could be quantified. Two methods that rely on the distribution of aquatic plants are useful for locating springs. One method identifies areas of the near‐shore lakebed where floating‐leaf and emergent aquatic vegetation are absent. The second method uses the distribution of marsh marigold (Caltha palustris L.) to locate springs that discharge on land near the shoreline of the lake. Marsh marigold produces large (2 to 4 cm diameter) yellow flowers that provide a ready marker for locating ground water springs. Twice as many springs (38) were identified using this method as were identified using the lack of near‐shore vegetation. A portable weir was used to measure discharge from onshore springs, and seepage meters were used to measure discharge from near‐shore springs. Of the total 56.7 L s−1 that enters the lake from ground water, approximately 30% comes from onshore and near‐shore springs.
Pesticides in Ground Water of the United States, 1992–1996
Authors: Kolpin Dana W. , Barbash Jack E. , Gilliom Robert J.
Published: August 2005

During the first cycle of the National Water Quality Assessment (1992–1996), ground water in 20 of the nation's major hydro‐logic basins was analyzed for 90 pesticide compounds (pesticides and degradates). One or more of the pesticide compounds examined were detected at 48.4% of the 2485 ground water sites sampled. However, approximately 70% of the sites where pesticides were detected, two or more pesticide compounds analyzed were present–documenting the prevalence of pesticide mixtures in ground water. The pesticide concentrations encountered were generally low, with the median total concentration (summation of concentrations for the 90 pesticide compounds) being 0.046 μg/L. Pesticides were commonly detected in shallow ground water beneath both agricultural (60.4%) and urban (48.5%) areas. This is an important finding because, although agricultural activities have long been associated with pesticide contamination, urban areas have only recently been recognized as a potential source of these types of compounds. Pesticides with higher frequencies of detection were generally those with more extensive use, greater environmental persistence, and greater mobility in ground water (lower soil‐water partition coefficients).
Fingering in Unsaturated Zone Flow: A Qualitative Review with Laboratory Experiments on Heterogeneous Systems
Authors: Sililo Oliver T.N. , Tellam John H.
Published: August 2005

Unstable unsaturated zone flow (fingering) is a potentially important process in recharge, pollution, and surface water/ground water body interactions. Extending previous workers' studies on homogeneous systems, sand tank experiments have been carried out on heterogeneous systems. The experiments on initially dry silica sands suggest that (1) stratification will tend to enhance rather than dissipate fingering; (2) in discontinuously layered systems, funneling influences the location of fingers; (3) in multilayered systems, lateral flow on top of fine‐grained layers promotes greater flux (and more fingers) in the down‐dip direction; (4) in systems where a top fine‐grained layer has a variable thickness, finger frequency and, hence, amount of flow will be greatest where the fine‐grained layer is thinnest; (5) surface depressions in an upper fine‐grained layer will concentrate flow, with fingers forming below such areas; and (6) in systems where an upper fine‐grained layer has macropores, the latter will concentrate water flow and fingers will form directly below these zones. The experiments also confirmed that fingers can persist in the same locations from one recharge event to another, and that in initially moist sands, fingers are widened. It is clear that a complex interplay between fingering and funneling processes can occur and that finger behavior is sensitive to heterogeneity.
Anomalous Fresh Water Lens Morphology on a Strip Barrier Island
Authors: Ruppel C. , Schultz G. , Kruse S.
Published: August 2005

Electromagnetic surveys of a young, wholly sedimentary, strip barrier island (St. George Island) on Florida's Gulf Coast reveal a Dupuit‐Ghyben‐Herzberg fresh water lens with the thickest part located close to the ocean side of the island at both undeveloped and developed sites. This result is at odds with those obtained on other barrier beaches, where the lens is either approximately symmetric or skewed toward the lagoon side due to higher sea level and greater upper beach storage on the ocean side. The inferred morphology of the fresh water lens on St. George Island can be attributed to variations in hydrogeologic (e.g., hydraulic conductivity, presence of semipermeable confining layer) and/or boundary conditions (e.g., recharge, higher sea level on the lagoon side), but the effects of variations in these factors on the shape of the lens are not separable. We therefore use independent constraints on hydraulic conductivity (from tidal pumping analyses), hydrofacies distribution, and recharge patterns to assess the plausibility that lateral variations in various physical parameters produce the observed lens shape. Dune ridge topography, which may constitute a significant portion of the width of a narrow island, perturbs recharge and shallow ground water flow patterns and may contribute to the development of a thick fresh water lens on an island's ocean side. However, topographic variations alone cannot account for the anomalous form of the island's fresh water lens.
Reducing the Influence of Skin Effects on Hydraulic Conductivity Determinations in Multilevel Samplers Installed with Direct Push Methods
Authors: Henebry Brent J. , Robbins Gary A.
Published: August 2005

Field tests were conducted to investigate skin effects in multilevel ground water samplers installed with direct push methods. Tests consisted of determining hydraulic conductivity values using slug tests in five multilevel samplers before, during, and after development. Development was conducted using a minisurge block tool designed for this study. Post‐development hydraulic conductivity values were found to be 3.2 to 9.6 times greater than predevelopment values. The largest differences were observed in multilevel samplers positioned in low permeable materials that were installed in preprobed holes advanced by hydraulic hammering and pushing as opposed to probes situated in higher permeable materials that were installed in cored holes. The presence and magnitude of the skin effects, as well as the reduction of these effects by rigorous development, were confirmed through comparisons with steady‐state pumping tests conducted in multilevel samplers and previously conducted slug tests in conventional monitoring wells. These results indicate the need for rigorous development prior to hydraulic conductivity testing in ground water samplers installed with direct push methods.
Systematic Makings of Early Stage Hydrogeologic Conceptual Models
Authors: LeGrand Harry E. , Rosen Lars
Published: August 2005

Techniques to obtain optimal value from existing hydrogeological information are neglected in many ground water contamination studies, resulting in great costs to the public. Data collection and routine interpretations should not be good enough for hydrogeologists, who should be inherently adept at keen early perspectives and applying useful generalizations. Techniques are available to obtain and explain expanded knowledge from piecemeal and imprecise information at the early stages of site studies. Scarcity of precise data should not be a deterrent. This needed mindset should precede the prevailing mindset of initial collection of extensive new data, followed by data interpretation and mathematical modeling. The existing mindset is often guided by rigid regulations.

The procedure of interlocking the past with the present to predict the future through the systematic use of generalizations and retrodictive inferences builds a prior conceptual model explanation (PCME). This early PCME is an organized, mental picture or discernment of a hydrogeological setting displaying three‐dimensional hydrogeologic features, the discernment being capable of explaining in narrative form the general fluid mechanics and contaminant behavior within imprecise but reasonable bounds. This characterization is logically followed by possible cause‐and‐effect relations and predictions of extended consequences of natural and human actions. A site PCME has sound support from the cross‐checking of interrelated factors that leads to almost interlocking proofs.
Transient‐State History Matching of a Karst Aquifer Ground Water Flow Model
Authors: Larocque M. , Banton O. , Razack M.
Published: August 2005

Ground water flow modeling in a karst aquifer presents many difficulties. In particular, the hydrodynamic properties and the flow behavior can vary over time. History matching of transient‐state conditions is required to test the accuracy of the model under varying hydrodynamic conditions. The objective of this study was to illustrate how transient‐state conditions can be used to history match a ground water flow model of a large aquifer, the La Rochefoucauld karst (Charente, France). The model used a porous medium equivalent and was based on a steady‐state calibration of hydraulic conductivities. The history match consisted of studying the simulated heads and spring flow rates to test the capacity of the model to reproduce different aspects of the aquifer behavior. The simulated heads and flow rates were analyzed as new data using correlation and spectral analyses to compare the temporal structures of the measured and simulated time series. The analyses provided information on the storage capacity of the aquifer, the input‐output delays, the degree of correlation between input and output, and the length of the impulse response of the aquifer. These data were used to study the impact of the hypotheses underlying the model (hydraulic conductivities, storage coefficient, representation of rivers, use of a porous medium equivalent). The results show that the model adequately simulates the overall behavior of the studied aquifer. The model can be used under variable hydrodynamic conditions to simulate ground water flow on a regional scale. This case study illustrates how a complete history match of a simplified representation of reality can lead to an adequate mathematical tool.
Water Resource Implications of 18O and 2H Distributions in a Basalt Aquifer System
Authors: Larson Kathryn R. , Keller C. Kent , Larson Peter B. , Allen‐King Richelle M.
Published: August 2005

Ongoing decline of water levels in the confined basalt aquifers of the Pullman‐Moscow Basin of Washington and Idaho has prompted study of the timing, amount and distribution of recharge to the system. Previous radiocarbon ages indicate residence times on the order of 103 years and greater and suggest a low rate of recharge to the lower basalt aquifer since the end of Pleistocene time. By contrast, more recent hydrodynamic flow modeling studies invoke a larger Holocene recharge rate through the unconfined loess unit to the upper and lower basalt aquifers, which implies relatively short residence times (102 years). Stable isotopes were used to independently assess contrasting recharge models by comparing 18O/16O and D/H ratios of late‐Holocene shallow ground water and deep ground water. Linear regression of local precipitation ratios yields δD = 6.9 δ18O −18.5. There is no evidence of fractionation of ground water ratios by recharge processes or water‐rock interactions. Deep basalt ground water δ18O values are depleted by 0.4 to 4.9 per mil relative to shallow, recently recharged ground waters and have δ18O values statistically distinct from waters sampled from other stratigraphic units. These findings suggest that the deep waters in the basin were not precipitated under current climate conditions and that aquifer recharge rates to the deep basalt aquifer are substantially lower than have been recently estimated. This in turn suggests that a sustainable ground water exploitation scheme must reduce reliance on the deep ground water resource.
The Coming Paradigm Shift in Forensic Identification Science
Authors: Saks Michael J. , Koehler Jonathan J.
Published: August 2005

Converging legal and scientific forces are pushing the traditional forensic identification sciences toward fundamental change. The assumption of discernible uniqueness that resides at the core of these fields is weakened by evidence of errors in proficiency testing and in actual cases. Changes in the law pertaining to the admissibility of expert evidence in court, together with the emergence of DNA typing as a model for a scientifically defensible approach to questions of shared identity, are driving the older forensic sciences toward a new scientific paradigm.
Extreme Waves Under Hurricane Ivan
Authors: Wang David W. , Mitchell Douglas A. , Teague William J. , Jarosz Ewa , Hulbert Mark S.
Published: August 2005

Hurricane Ivan, a category 4 storm, passed directly over six wave-tide gauges deployed by the Naval Research Laboratory on the outer continental shelf in the northeastern Gulf of Mexico. Waves were observed with significant wave heights reaching 17.9 meters and maximum crest-to-trough individual wave heights of 27.7 meters (91 feet). Analysis suggests that significant wave heights likely surpassed 21 meters (69 feet) and that maximum crest-to-trough individual wave heights exceeded 40 meters (132 feet) near the eyewall.
An Experimental Approach to the Percolation of Sticky Nanotubes
Authors: Vigolo B. , Coulon C. , Maugey M. , Zakri C. , Poulin P.
Published: August 2005

Percolation is a statistical concept that describes the formation of an infinite cluster of connected particles or pathways. Lowering the percolation threshold is a critical issue to achieve light and low-cost conductive composites made of an insulating matrix loaded with conductive particles. This has interest for applications where charge dissipation and electrical conductivity are sought in films, coatings, paints, or composite materials. One route to decreasing the loading required for percolation is to use rod-like particles. Theoretical predictions indicate that this may also be achieved by altering the interaction potential between the particles. Although percolation may not always respond monotonically to interactions, the use of adhesive rods can be expected to be an ideal combination. By using a system made of carbon nanotubes in an aqueous surfactant solution, we find that very small attraction can markedly lower the percolation threshold. The strength of this effect can thereby have direct technological interest and explain the large variability of experimental results in the literature dealing with the electrical behavior of composites loaded with conducting rods.
Triangular and Fibonacci Number Patterns Driven by Stress on Core/Shell Microstructures
Authors: Li Chaorong , Zhang Xiaona , Cao Zexian
Published: August 2005

Fibonacci number patterns and triangular patterns with intrinsic defects occur frequently on nonplanar surfaces in nature, particularly in plants. By controlling the geometry and the stress upon cooling, these patterns can be reproduced on the surface of microstructures about 10 micrometers in diameter. Spherules of the Ag core/SiO

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shell structure, possessing markedly uniform size and shape, self-assembled into the Fibonacci number patterns (5 by 8 and 13 by 21) or the triangular pattern, depending on the geometry of the primary supporting surface. Under proper geometrical constraints, the patterns developed through self-assembly in order to minimize the total strain energy. This demonstrates that highly ordered microstructures can be prepared simultaneously across large areas by stress engineering.
Stem Cell Depletion Through Epidermal Deletion of Rac1
Authors: Benitah Salvador Aznar , Frye Michaela , Glogauer Michael , Watt Fiona M.
Published: August 2005

Mammalian epidermis is maintained by self-renewal of stem cells, but the underlying mechanisms are unknown. Deletion of Rac1, a Rho guanosine triphosphatase, in adult mouse epidermis stimulated stem cells to divide and undergo terminal differentiation, leading to failure to maintain the interfollicular epidermis, hair follicles, and sebaceous glands. Rac1 exerts its effects in the epidermis by negatively regulating c-Myc through p21-activated kinase 2 (PAK2) phosphorylation. We conclude that a pleiotropic regulator of cell adhesion and the cytoskeleton plays a critical role in controlling exit from the stem cell niche and propose that Rac and Myc represent a global stem cell regulatory axis.