bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractAn 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

AbstractApproximately 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

AbstractSea 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

AbstractMissing 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

AbstractKnowing 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

AbstractThe 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

AbstractIn 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

AbstractTravel 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

AbstractConcentrations 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

AbstractThe 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

AbstractWater 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

AbstractThe 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

AbstractThe 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

AbstractDetermining 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.