bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical and Isotopic Constraints on the Origin of Wadi El‐Tarfa Ground Water, Eastern Desert, Egypt
Authors: Sultan M. , Sturchio N.C. , Gheith H. , Hady Y. Abdel , El Anbeawy M.
Published: December 2005

We evaluated the use of the renewable ground water resources of the Eastern Desert to develop sustainable agriculture in Upper Egypt, an alternative that could alleviate some of Egypt's dependence on water from the Nile River. Ground water from shallow aquifers in the Eastern Desert of Egypt, near the intersection of Wadi El‐Tarfa and the Nile River, was analyzed for chemical compositions, stable isotope ratios, and tritium activities. The ground water has a range in total dissolved solids of 300 to 5000 mg/L. Values of δD and δ18O range from ‐10 to +34 %o and ‐2 to +5.2 %o, respectively, and defines a line having a slope of 5.7 that intersects the meteoric water line at about δD = ‐15 %o on a plot of 8D versus δ18O. These findings indicate that the water might have been derived by a combination of evaporation of and salt addition to regional precipitation. Only one sample could have been derived directly by evaporation and transpiration of modern Nile River water. Salinization of the ground water could have occurred through dissolution of marine aerosol dry fallout, carbonate minerals, gypsum, and other trace evaporitic minerals at and near the ground surface. Tritium activities ranged from 0.04 to 12.9 TU (tritium unite), indicating that all but one of the samples were derived at least partly from precipitation that occurred within the last 45 years. These data indicate that Nubian Aquifer paleowater is not a significant component of the shallow aquifers of this portion of the Eastern Desert. The most likely source of this ground water is sporadic flash flood events yielding locally voluminous recharge that accumulates in coarse sediments and fractured rock beneath alluvial channels. The magnitude of this renewable ground water resource and its potential for supporting sustainable agriculture require further investigation.
Partitioning Tracer Tests for Evaluating Remediation Performance
Authors: Cain R. Brent , Johnson Gwynn R. , McCray John E. , Blanford William J. , Brusseau Mark L.
Published: December 2005

Partitioning tracer tests (PTTs) are being used in environmental systems for the detection and estimation of nonaqueous phase liquid (NAPL) saturations in contaminated aquifers. A series of such studies was recently conducted at Hill Air Force Base, Utah, in two hydraulically isolated test cells of an aquifer contaminated by light nonaqueous phase liquids (LNAPL). These experiments were performed before and after two remediation efforts, a complexing sugar flush (CSF) and a recirculating in‐well aeration (IWA) system. The breakthrough curves obtained from monitoring tracer concentrations in the extraction wells indicated the presence of an immiscible phase, and the LNAPL saturation values determined from the pre‐ and post‐PTTs allowed the estimation of remediation efficiencies for both test cells. These remediation efficiencies, a removal of 43% of the LNAPL for the CSF and an increase of 32% for the IWA system, are consistent with data obtained from cores collected from within the experiment zones. The apparent increase in contamination for the IWA cell is likely due to a significant change in the LNAPL distribution caused by the flow system associated with the IWA technology. Several factors influenced the interpretation of the PTT data. Physical heterogeneities at the site caused significant tailing of the tracer concentrations and required the use of a simple extrapolation technique to account for the concentrations below analytical quantification limits. Degradation affected selected nonreactive and reactive tracers, causing the overestimation and underestimation of LNAPL saturations, respectively.
Strontium Isotopes and Major Elements As Tracers of Ground Water Evolution: Example from the Upper Castle Hayne Aquifer of North Carolina
Authors: Woods Terri L. , Fullagar Paul D. , Spruill Richard K. , Sutton Lynn C.
Published: December 2005

The Eocene‐Oligocene Upper Castle Hayne Aquifer (UCH), a well‐indurated limestone with a very high percentage of secondary moldic porosity, is one of the most productive and extensively developed aquifers in the North Carolina Coastal Plain. Ground water from western wells in the UCH is Ca‐ and HCO3‐rich and ground water from easternmost wells is alkali‐ and Cl‐rich. In general, from west to east across the study area, Sr concentrations [Sr] and isotopic ratios of ground water from the UCH and other aquifers evolve toward those of the host aquifer. At the same well site, water from older aquifers usually has a lower 87Sr/86Sr ratio than water from younger aquifers, due to interaction between ground water and sedimentary material in the host aquifers. Comparison of 87Sr/86Sr ratios and [Sr] suggests that most UCH water represents mixing of strontium‐poor recharge water from the Surficial Aquifer with varying amounts of strontium from the aquifer rock. For samples that deviate from the calculated mixing line, strontium ratios can often be used to indicate the source of strontium that did not come from UCH rock. Surface waters are characterized by high 87Sr/86Sr ratios and variable [Sr] that depend on the proportion of intermixed sea water. Water from the overlying Yorktown and Pungo River aquifers can be recognized by higher 87Sr/86Sr ratios than those of the UCH and water from the underlying LCH, Beaufort, and Peedee aquifers can be recognized by lower 87Sr/86Sr ratios and higher [Sr].
Modeling the Effect of Chemical Fertilizers on Ground Water Quality in the Nile Valley Aquifer, Egypt
Authors: Shamrukh Mohamed , Corapcioglu M. Yavuz , Hassona Fayek A.A.
Published: December 2005

Chemical fertilizer use in Egypt has increased significantly since the construction of the Aswan High Dam in 1968. Increased applications of chemical fertilizers in irrigated lands are likely to create nonpoint contamination sources of chemical fertilizer species. This study was conducted to investigate the contamination of ground water by nitrogen and phosphorus chemical fertilizers, as well as the availability of ground water for irrigation and public water supply for the next century. Future concentrations of NO3, and PO3‐ in shallow and deep ground water in the Nile Valley were assessed under realizable rates of fertilizer application. A ground water modeling system (GMS) was used to simulate the three‐dimensional ground water flow and contaminant transport in the Tahta region of the Nile Valley Aquifer, and to predict the future concentrations of chemical fertilizer species. Results of the transport simulation predict the occurrence of ground water contamination at shallow depths (30 m) due to the high rate and method of chemical fertilizer applications. Best management practices should be employed to control and reduce the nitrate leaching and future impact of phosphorus and potassium fertilizer applications. At the same time, new deeper wells should be constructed. In addition, the use of hand pumps, in zones close to croplands (15 m depth) must be avoided due to susceptibility to fertilizer contamination. Ground water from existing deep wells can be used as an alternative water supply. Furthermore, a ground water quality monitoring system should be established for early detection of ground water contamination and to determine progress of the fertilizer contaminant plume. A properly designed system should monitor nitrate and phosphate composition in observation and water supply wells.
Relating Nitrogen Sources and Aquifer Susceptibility to Nitrate in Shallow Ground Waters of the United States
Authors: Nolan Bernard T.
Published: December 2005

Characteristics of nitrogen loading and aquifer susceptibility to contamination were evaluated to determine their influence on contamination of shallow ground water by nitrate. A set of 13 explanatory variables was derived from these characteristics, and variables that have a significant influence were identified using logistic regression (LR). Multivariate LR models based on more than 900 sampled wells predicted the probability of exceeding 4 mg/L of nitrate in ground water. The final LR model consists of the following variables: (1) nitrogen fertilizer loading (p‐value = 0.012); (2) percent cropland‐pasture (p < 0.001); (3) natural log of population density (p < 0.001); (4) percent well‐drained soils (p = 0.002); (5) depth to the seasonally high water table (p = 0.001); and (6) presence or absence of a fracture zone within an aquifer (p = 0.002). Variables 1–3 were compiled within circular, 500 m radius areas surrounding sampled wells, and variables 4–6 were compiled within larger areas representing targeted land use and aquifers of interest. Fitting criteria indicate that the full logistic‐regression model is highly significant (p < 0.001), compared with an intercept‐only model that contains none of the explanatory variables. A goodness‐of‐fit test indicates that the model fits the data well, and observed and predicted probabilities of exceeding 4 mg/L nitrate in ground water are strongly correlated (r2= 0.971). Based on the multivariate LR model, vulnerability of ground water to contamination by nitrate depends not on any single factor but on the combined, simultaneous influence of factors representing nitrogen loading sources and aquifer susceptibility characteristics.
Use of NADP Archive Samples to Determine the Isotope Composition of Precipitation: Characterizing the Meteoric Input Function for Use in Ground Water Studies
Authors: Harvey F. Edwin
Published: December 2005

Stable oxygen and hydrogen isotopes have been used in ground water studies to investigate recharge, mixing, ground water/surface water interaction, advective‐diffusive transport, paleohydrogeologic interactions and to estimate ground water ages. Such studies require that the isotopic composition of precipitation be known, as precipitation is a major input to ground water and surface water systems. As oxygen‐18 and deuterium data for precipitation are lacking across much of the United States, there is need to establish additional local meteoric water lines as isotope input functions across the region, as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation. In the absence of long‐term monitoring stations, one possible solution to this problem is to determine the δ18O and δ2H values of precipitation using archive samples collected at monitoring stations managed by the National Atmospheric Deposition Program (NADP). This study describes and interprets the seasonal δ18O and δ2H composition of archived precipitation samples collected in eastern Nebraska near the town of Mead during the years 1992–1994. Values for δ18O range from ‐23.6 to ‐0.7%o. Values for δ2H range from ‐172 to 0 %o Yearly arithmetic mean δ18O and 82H values for the Mead station are ‐8.1 %c and ‐53 %o, respectively. Weighted yearly means for δ18O and δ2H were ‐7.4 %c and ‐48 %c, respectively. Mead values show a strong isotopic enrichment between winter and summer precipitation, and a strong δ18O‐T correlation (r2= 0.91) for mean monthly values of about 0.5 %o per degree Celsius. The local meteoric water line for the Mead site is δ2H = 7.40 δ18O + 7.32. Deuterium excess values suggest that most of the moisture across the region is derived primarily from a Gulf of Mexico source. The results of this study demonstrate that in the absence of long‐term monitoring stations such as those operated globally by the International Atomic Energy Association, NADP archive samples can be used to determine the isotopic composition of precipitation, to characterize the local meteoric water line and establish the various climatic relationships, and define the meteoric input function for use in ground water studies.
Delineating Ground Water Recharge from Leaking Irrigation Canals Using Water Chemistry and Isotopes
Authors: Harvey F. Edwin , Sibray Steven S.
Published: December 2005

Across the Great Plains irrigation canals are used to transport water to cropland. Many of these canals are unlined, and leakage from them has been the focus of an ongoing legal, economic, and philosophical debate as to whether this lost water should be considered waste or be viewed as a beneficial and reasonable use since it contributes to regional ground water recharge. While historically there has been much speculation about the impact of canal leakage on local ground water, actual data are scarce. This study was launched to investigate the impact of leakage from the Interstate Canal, in the western panhandle of Nebraska, on the hydrology and water quality of the local aquifer using water chemistry and environmental isotopes. Numerous monitoring wells were installed in and around a small wetland area adjacent to the canal, and ground water levels were monitored from June 1992 until January 1995. Using the water level data, the seepage loss from the canal was estimated. In addition, the canal, the monitoring wells, and several nearby stock and irrigation wells were sampled for inorganic and environmental isotope analysis to assess water quality changes, and to determine the extent of recharge resulting from canal leakage. The results of water level monitoring within study wells indicates a rise in local ground water levels occurs seasonally as a result of leakage during periods when the canal is filled. This rise redirects local ground water flow and provides water to nearby wetland ecosystems during the summer months. Chemical and isotopic results were used to delineate canal, surface, and ground water and indicate that leaking canal water recharges both the surface alluvial aquifer and upper portions of the underlying Brule Aquifer. The results of this study indicate that lining the Interstate Canal could lower ground water levels adjacent to the canal, and could adversely impact the local aquifer.
Storage Coefficient Revisited: Is Purely Vertical Strain a Good Assumption?
Authors: Burbey Thomas J.
Published: December 2005

The storage coefficient that Is used ubiquitously today was first defined by the analytical work of Theis and Jacob over a half‐century ago. Inherent within this definition is the restriction of purely vertical compression of the aquifer during a reduction in pressure. The assumption is revisited and quantitatively evaluated by comparing numerical results using both one‐ and three‐dimensional strain models in the presence of three‐dimensional flow. Results indicate that (1) calculated hydraulic head values are nearly identical for both models; (2) the release of water from storage in terms of volume strain is nearly identical for both models and that the location of maximum production moves outward from the well as a function of time; (3) the vertical strain components are markedly different with at least 50% of the total volume of water pumped originating from horizontal strain (and Increasing to as much as 70%); and (4) for the one‐dimensional strain model to yield the necessary quantity of water to the pumped well, the resulting vertical compaction (land subsidence) is as much as four times greater and vertical strain Is as much as 60% greater than the three‐dimensional strain model. Results indicate that small changes in porosity resulting from horizontal strain can yield extremely large quantities of water to the pumping well. This study suggests that the assumption of purely vertical strain used In the definition of the storage coefficient is not valid.
Exploitation of High‐Yields in Hard‐Rock Aquifers: Downscaling Methodology Combining GIS and Multicriteria Analysis to Delineate Field Prospecting Zones
Authors: Lachassagne Patrick , Wyns R. , Bérard Pierre , Bruel Thierry , Chéry Laurence , Coutand Thierry , Desprats Jean‐François , Le Strat Paul
Published: December 2005

Based on research work in the Truyàre River catchment of the Massif Central (Lozàre Department, France), a methodology has been developed for delineating favorable prospecting zones of a few square kilometers within basement areas of several hundred, if not thousand, square kilometers for the purpose of siting high‐yield water wells. The methodology adopts a functional approach to hard‐rock aquifers using a conceptual model of the aquifer structure and of the functioning of the main aquifer compartments: the alterites (weathered and decayed rock), the underlying weathered‐fissured zone, and the fractured bedrock. It involves an economically feasible method of mapping the thickness and spatial distribution of the alterites and the weathered‐fissured zone, on which the long‐term exploitation of the water resource chiefly depends. This method is used for the first time in hydrogeology.

The potential ground water resources were mapped by GIS multicriteria analysis using parameters characterizing the structure and functioning of the aquifer, i.e., lithology and hydrogeological properties of the substratum, nature and thickness of the alterites and weathered‐fissured zone, depth of the water table, slope, fracture networks and present‐day tectonic stresses, and forecasted ground water quality.

The methodology involves a coherent process of downscaling that, through applying methods that are increasingly precise but also increasingly costly, enables the selection of sites with diminishing surface areas as the work advances. The resulting documents are used for ground water exploration, although they can also be applied to the broader domain of land‐use management.
Drawdown and Stream Depletion Produced by Pumping in the Vicinity of a Partially Penetrating Stream
Authors: Butler James J. , Zlotnik Vitaly A. , Tsou Ming‐Shu
Published: December 2005

Commonly used analytical approaches for estimation of pumping‐induced drawdown and stream depletion are based on a series of idealistic assumptions about the stream‐aquifer system. A new solution has been developed for estimation of drawdown and stream depletion under conditions that are more representative of those in natural systems (finite width stream of shallow penetration adjoining an aquifer of limited lateral extent). This solution shows that the conventional assumption of a fully penetrating stream will lead to a significant overestimation of stream depletion (> 100%) in many practical applications. The degree of overestimation will depend on the value of the stream leakance parameter and the distance from the pumping well to the stream. Although leakance will increase with stream width, a very wide stream will not necessarily be well represented by a model of a fully penetrating stream. The impact of lateral boundaries depends upon the distance from the pumping well to the stream and the stream leakance parameter. In most cases, aquifer width must be on the order of hundreds of stream widths before the assumption of a laterally infinite aquifer is appropriate for stream‐depletion calculations. An important assumption underlying this solution is that stream‐channel penetration is negligible relative to aquifer thickness. However, an approximate extension to the case of nonnegligible penetration provides reasonable results for the range of relative penetrations found in most natural systems (up to 85%). Since this solution allows consideration of a much wider range of conditions than existing analytical approaches, it could prove to be a valuable new tool for water management design and water rights adjudication purposes.
Explaining the Thinness of the Fresh Water Lens in the Pleistocene Carbonate Aquifer on Andros Island, Bahamas
Authors: Ritzi Robert W. , Bukowski John M. , Carney Cindy K. , Boardman Mark R.
Published: December 2005

Two hypotheses are explored to explain the thinness of the fresh water lens on Andros Island, Bahamas. The lens is an order of magnitude thinner than predicted by the Ghyben‐Herzberg theory. One hypothesis previously posed in the literature is that the base of the lens is governed by the contact between the Lucayan Formation and the pre‐Lucayan limestones. An alternate hypothesis, posed here, is that thinning is caused by the hydraulic influence of low‐permeability paleosols in the Lucayan Formation. These hypotheses were explored, along with the influence of recharge and other factors, using a numerical model for variable‐density flow and salt transport. In the layered system of grainstones/packstones and paleosols within the Lucayan Formation itself, the velocity vectors are nearly horizontal in the grainstones/packstones, and they are nearly vertical in the paleosols. These strata above the pre‐Lucayan, all lower than it in permeability, draw the base of the lens upward to a position well above the contact by significantly reducing pressure within and below the strata relative to hydrostatic pressure. It is the loss of pressure across the paleosols that dramatically thins the fresh water lens, and thus the predominant hydraulic control on lens thickness arises from the existence of paleosols.
Determination of Specific Yield for the Biscayne Aquifer with a Canal‐Drawdown Test
Authors: Bolster Carl H. , Genereux David P. , Saiers James E.
Published: December 2005

Data from a large‐scale canal‐drawdown test were used to estimate the specific yield (s) of the Biscayne Aquifer, an uncon‐fined limestone aquifer in southeast Florida. The drawdown test involved dropping the water level in a canal by about 30 cm and monitoring the response of hydraulic head in the surrounding aquifer. Specific yield was determined by analyzing data from the unsteady portion of the drawdown test using an analytical stream‐aquifer interaction model (Zlotnik and Huang 1999). Specific yield values computed from drawdown at individual piezometers ranged from 0.050 to 0.57, most likely indicating heterogeneity of specific yield within the aquifer (small‐scale variation in hydraulic conductivity may also have contributed to the differences in sy among piezometers). A value of 0.15 (our best estimate) was computed based on all drawdown data from all piezometers.

We incorporated our best estimate of specific yield into a large‐scale two‐dimensional numerical MODFLOW‐based ground water flow model and made predictions of head during a 183–day period at four wells located 337 to 2546 m from the canal. We found good agreement between observed and predicted heads, indicating our estimate of specific yield is representative of the large portion of the Biscayne Aquifer studied here. This work represents a practical and novel approach to the determination of a key hydrogeological parameter (the storage parameter needed for simulation and calculation of transient unconfined ground water flow), at a large spatial scale (a common scale for water resource modeling), for a highly transmissive limestone aquifer (in which execution of a traditional pump test would be impractical and would likely yield ambiguous results). Accurate estimates of specific yield and other hydrogeological parameters are critical for management of water supply, Everglades environmental restoration, flood control, and other issues related to the ground water hydrology of the Biscayne Aquifer.
Numerical Examination of the Factors Controlling DNAPL Migration Through a Single Fracture
Authors: Reynolds D.A. , Kueper B.H.
Published: December 2005

The migration of five dense nonaqueous phase liquids (DNAPLs) through a single fracture in a clay aquitard was numerically simulated with the use of a compositional simulator. The effects of fracture aperture, fracture dip, matrix porosity, and matrix organic carbon content on the migration of chlorobenzene, 1,2‐dichloroethylene, trichloroethyiene, tetrachloroethylene, and 1,2‐dibromoethane were examined. Boundary conditions were chosen such that DNAPL entry into the system was allowed to vary according to the stresses applied. The aperture is the most important factor of those studied controlling the migration rate of DNAPL through a single fracture embedded in a clay matrix. Loss of mass to the matrix through diffusion does not significantly retard the migration rate of the DNAPL, particularly in larger aperture fractures (e.g., 50 urn). With time, the ratio of diffusive loss to the matrix to DNAPL flux into the fracture approaches an asymptotic value lower than unity. The implication is that matrix diffusion cannot arrest the migration of DNAPL in a single fracture. The complex relationships between density, viscosity, and solubility that, to some extent, govern the migration of DNAPL through these systems prevent accurate predictions without the use of numerical models. The contamination potential of the migrating DNAPL is significantly increased through the transfer of mass to the matrix. The occurrence of opposite concentration gradients within the matrix can cause dissolved phase contamination to exist in the system for more than 1000 years after the DNAPL has been completely removed from the fracture.
Methods to Determine Storativity of Infinite Confined Aquifers from a Recovery Test
Authors: Chenaf Djaouida , Chapuis Robert P.
Published: December 2005

Starting from the equations of Theis and Cooper‐Jacob, two new mathematical methods are proposed for interpreting the residual drawdown data for an infinite confined aquifer. Under Theis' assumptions and using the Cooper‐Jacob approximation, the principal aquifer characteristics of transmissivity, pumping storativity, and recovery storativity are expressed without any correction or additional assumption. An actual case is used for illustration and confirms the validity of proposed equations and methods.
Michigan Basin Regional Ground Water Flow Discharge to Three Great Lakes
Authors: Hoaglund John Robert , Huffman Gary Cecil , Grannemann Norman Guy
Published: December 2005

Ground water discharge to the Great Lakes around the Lower Peninsula of Michigan is primarily from recharge in riparian basins and proximal upland areas that are especially important to the northern half of the Lake Michigan shoreline. A steady‐state finite‐difference model was developed to simulate ground water flow in four regional aquifers in Michigan's Lower Peninsula: the Glaciofluvial, Saginaw, Parma‐Bayport, and Marshall aquifers interlayered with the Till/“red beds,” Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specified‐head boundary, formed from lakes Michigan, Huron, St. Clair, and Erie, with the St. Clair and Detroit River connecting channels.

The model was developed to quantify regional ground water flow in the aquifer systems using independently determined recharge estimates. According to the flow model, local stream stages and discharges account for 95% of the overall model water budget; only 5% enters the lakes directly from the ground water system. Direct ground water discharge to the Great Lakes' shorelines was calculated at 36 m3/sec, accounting for 5% of the overall model water budget. Lowland areas contribute far less ground water discharge to the Great Lakes than upland areas. The model indicates that Saginaw Bay receives only ∼1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only ∼2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas.
Localized Thermal Anomalies in Haloclines of Coastal Yucatan Sinkholes
Authors: Stoessell Ronald K. , Coke James G. , Easley Dale H.
Published: December 2005

A temperature spike is reported in the haloclines of three Yucatan sinkholes along a 1 km NW‐SE transect from 5 to 4 km inland from the Caribbean coast. The temperature spike decreases in magnitude from ∼ 3.5°C to 0.2°C, approaching the coast. The anomaly does not vary diurnally and does not extend down into the underlying sea water. These conditions are inconsistent with explanations such as radiation absorption within the halocline, in situ microbially mediated sulfate reduction within the halocline and the underlying sea water, and sulfide oxidation by photosynthetic purple and green bacteria within the halocline.

One explanation consistent with the shape and halocline location of the temperature spike involves a localized sea water convection cell operating near the coast. Cold sea water from the Caribbean Sea enters the coastal limestone at depths of a few hundred meters and heats up because of the geothermal gradient, buoyantly rising in vertical fractures within the unconfined aquifer. Blocked by the less dense fresh water, the movement stops in the halocline where the warm sea water mixes with brackish water. The convection cycle would be completed by the coastward movement of cooling brackish water. The observed temperature anomalies could possibly be snapshots of this warm layer moving coastward.
Measurement of 3‐D Hydraulic Conductivity in Aquifer Cores at In Situ Effective Stresses
Authors: Wright Martin , Dillon Peter , Pavelic Paul , Peter Paul , Nefiodovas Andrew
Published: December 2005

An innovative and nondestructive method to measure the hydraulic conductivity of drill core samples in horizontal and vertical directions within a triaxial cell has been developed. This has been applied to characterizing anisotropy and heterogeneity of a confined consolidated limestone aquifer. Most of the cores tested were isotropic, but hydraulic conductivity varied considerably and the core samples with lowest values were also the most anisotropic. Hydraulic conductivity decreased with increasing effective stress due to closure of microfractures caused by sampling for all core samples. This demonstrates the importance of replicating in situ effective stresses when measuring hydraulic conductivity of cores of deep aquifers in the laboratory.
Interpretation of Spring Recession Curves
Authors: Amit H. , Lyakhovsky V. , Katz A. , Starinsky A. , Burg A.
Published: December 2005

Recession curves contain information on storage properties and different types of media such as porous, fractured, cracked lithologies and karst. Recession curve analysis provides a function that quantitatively describes the temporal discharge decay and expresses the drained volume between specific time limits (Hall 1968). This analysis also allows estimating the hydrological significance of the discharge function parameters and the hydrological properties of the aquifer. In this study, we analyze data from perennial springs in the Judean Mountains and from others in the Galilee Mountains, northern Israel. All the springs drain perched carbonate aquifers. Eight of the studied springs discharge from a karst dolomite sequence, whereas one flows out from a fractured, slumped block of chalk. We show that all the recession curves can be well fitted by a function that consists of two exponential terms with exponential coefficients α1 and α2. These coefficients are approximately constant for each spring, reflecting the hydraulic conductivity of different media through which the ground water flows to the spring. The highest coefficient represents the fast flow, probably through cracks, or quickflow, whereas the lower one reflects the slow flow through the porous medium, or baseflow. The comparison of recession curves from different springs and different years leads to the conclusion that the main factors that affect the recession curve exponential coefficients are the aquifer lithology and the geometry of the water conduits therein. In normal years of rainy winter and dry summer, α1 is constant in time. However, when the dry period is longer than usual because of a dry winter, α1 slightly decreases with time.
Comparison of Formation and Fluid‐Column Logs in a Heterogeneous Basalt Aquifer
Authors: Paillet F.L , Williams J.H. , Oki D.S. , Knutson K.D.
Published: December 2005

Deep observation boreholes in the vicinity of active production wells in Honolulu, Hawaii, exhibit the anomalous condition that fluid‐column electrical conductivity logs and apparent profiles of pore‐water electrical conductivity derived from induction conductivity logs are nearly identical if a formation factor of 12.5 is assumed. This condition is documented in three boreholes where fluid‐column logs clearly indicate the presence of strong borehole flow induced by withdrawal from partially penetrating water‐supply wells. This result appears to contradict the basic principles of conductivity‐log interpretation. Flow conditions in one of these boreholes was investigated in detail by obtaining flow profiles under two water production conditions using the electromagnetic flowmeter. The flow‐log interpretation demonstrates that the fluid‐column log resembles the induction log because the amount of inflow to the borehole increases systematically upward through the transition zone between deeper salt water and shallower fresh water. This condition allows the properties of the fluid column to approximate the properties of water entering the borehole as soon as the upflow stream encounters that producing zone. Because this condition occurs in all three boreholes investigated, the similarity of induction and fluid‐column logs is probably not a coincidence, and may relate to aquifer response under the influence of pumping from production wells.
Injection‐Extraction Treatment Well Pairs: An Alternative to Permeable Reactive Barriers
Authors: Cunningham Jeffrey A. , Reinhard Martin
Published: December 2005

Two of the biggest drawbacks of using permeable reactive barriers (PRBs) to treat contaminated ground water are the high capital cost of installation, particularly when the contaminated ground water is deep below ground surface, and the uncertainty of whether or not PRBs remain effective for the long time scales (e.g., decades) needed for many contaminant plumes. The use of an injection‐extraction treatment well pair (IETWP) for capture and treatment of contaminated ground water can circumvent these difficulties, while still providing many of the same advantages offered by PRBs. In this paper, the hydraulics of IETWPs and PRBs are compared, focusing primarily on the width of the captured plume. It is demonstrated that IETWPs act as hydraulic barriers in a manner similar to PRBs, and that IETWPs provide excellent plume capture. A mathematical expression is presented for the plume capture width of an IETWP oriented perpendicular to the ground water flow direction in a homogeneous aquifer. Also discussed are other practical considerations that might determine whether an IETWP is better suited than a PRB for a particular contaminated site; these considerations include operating and maintenance costs, and the conditions under which an IETWP system can be used for in situ remediation.
Effects of Ground Water Exchange on the Hydrology and Ecology of Surface Water
Authors: Hayashi Masaki , Rosenberry Donald O.
Published: December 2005

Ground water exchange affects the ecology of surface water by sustaining stream base flow and moderating water‐level fluctuations of ground water‐fed lakes. It also provides stable‐temperature habitats and supplies nutrients and inorganic ions. Ground water input of nutrients can even determine the trophic status of lakes and the distribution of macrophytes. In streams the mixing of ground water and surface water in shallow channel and bankside sediments creates a unique environment called the hyporheic zone, an important component of the lotic ecosystem. Localized areas of high ground water discharge in streams provide thermal refugia for fish. Ground water also provides moisture to riparian vegetation, which in turn supplies organic matter to streams and enhances bank resistance to erosion. As hydrologists and ecologists interact to understand the impact of ground water on aquatic ecology, a new research field called “ecohydrology” is emerging.
A Comparison of Three‐Dimensional Interpolation Techniques for Plume Characterization
Authors: Jones Norman L , Davis R. Jeffrey , Sabbah Walid
Published: December 2005

Interpolation of contaminant data can present a significant challenge due to sample clustering and sharp gradients in concentration. The research presented in this paper represents a study of commonly used interpolation schemes applied to three‐dimensional plume characterization. Kriging, natural neighbor, and inverse distance weighted interpolation were tested on four actual data sets. The accuracy of each scheme was gauged using the cross‐validation approach. Each scheme was compared to the other schemes and the effect of various interpolation parameters was studied. The kriging approach resulted in the lowest error at three of the four sites. The simpler and quicker inverse distance weighted approach resulted in a lower interpolation error on the other site and performed well overall. The natural neighbor method had the highest average error at all four sites in spite of the fact that it has been shown to perform well with clustered data. Another unexpected result was that the computationally expensive high order nodal functions resulted in reduced accuracy for the inverse distance weighted and natural neighbor approaches.
Applications of a Total Dissolved Gas Pressure Probe in Ground Water Studies
Authors: Manning Andrew H. , Kip Solomon D. , Sheldon Amy L
Published: December 2005

Measurements of dissolved gases have numerous applications in ground water hydrology, and it is now possible to measure the total dissolved gas pressure in situ using a probe. Dissolved gas pressure is measured by submerging a headspace volume with a gas‐permeable membrane, allowing dissolved gases in the water to equilibrate with gases in the headspace, then measuring the pressure in the headspace with a pressure transducer. Total dissolved gas pressure (TGP) probes have many potential uses in ground water studies employing dissolved gases, including: (1) determining approximate excess air levels, which may provide information about the time and location of recharge; (2) screening wells for air contamination, which can compromise the accuracy of dissolved gas tracer techniques: (3) detecting a trapped gas phase, which can significantly reduce hydraulic conductivity and impede the transport of dissolved solutes and gases; (4) enabling the use of gas‐filled passive diffusion samplers for determining accurate dissolved gas concentrations; and (5) determining relative concentrations of CH4 and CO2 when they are known to be highly abundant. Although TGP probes designed for surface water have been available for several years, TGP probes suitable for ground water applications have only recently become available. Herein we present what are, to our knowledge, the first reported ground water dissolved gas data collected using a TGP probe. We also explain the basic operating principles of these probes and discuss the potential applications listed.
Long‐Term Performance of Permeable Reactive Barriers Using Zero‐Valent Iron: Geochemical and Microbiological Effects
Authors: Wilkin Richard T. , Puls Robert W. , Sewell Guy W.
Published: December 2005

Geochemical and microbiological factors that control long‐term performance of subsurface permeable reactive barriers were evaluated at the Elizabeth City, North Carolina, and the Denver Federal Center, Colorado, sites. These ground water treatment systems use zero‐valent iron filings (Peerless Metal Powders Inc.) to intercept and remediate chlorinated hydrocarbon compounds at the Denver Federal Center (funnel‐and‐gate system) and overlapping plumes of hexavalent chromium and chlorinated hydrocarbons at Elizabeth City (continuous wall system). Zero‐valent iron at both sites is a long‐term sink for carbon, sulfur, calcium, silicon, nitrogen, and magnesium. After about four years of operation, the average rates of inorganic carbon (IC) and sulfur (S) accumulation are 0.09 and 0.02 kg/m2/year, respectively, at Elizabeth City where upgradient waters contain <400 mg/L of total dissolved solids (TDS). At the Denver Federal Center site, upgradient ground water contains 1000 to 1200 mg/L TDS and rates of IC and S accumulation are as high as 2.16 and 0.80 kg/m2/year, respectively. At both sites, consistent patterns of spatially variable mineral precipitation and microbial activity are observed. Mineral precipitates and microbial biomass accumulate the fastest near the upgradient aquifer‐Fe0 interface. Maximum net reductions in porosity due to the accumulation of sulfur and inorganic carbon precipitates range from 0.032 at Elizabeth City to 0.062 at the Denver Federal Center (gate 2) after about four years. Although pore space has been lost due the accumulation of authigenic components, neither site shows evidence of pervasive pore clogging after four years of operation.
Localization of Saturated Karst Aquifer with Magnetic Resonance Sounding and Resistivity Imagery
Authors: Vouillamoz J.M. , Legchenko A. , Albouy Y. , Bakalowicz M. , Baltassat J.M. , Al‐Fares W.
Published: December 2005

To answer one of the main questions of hydrogeologists implementing boreholes or working on pollution questions in a karst environment—i.e., where is the ground water?—numerous tools including geophysics are used. However, the contribution of geophysics differs from one method to the other. The magnetic resonance sounding (MRS) method has the advantage of direct detection of ground water over other geophysical methods. Eight MRSs were implemented over a known karst conduit explored and mapped by speleologists to estimate the MRS ability to localize ground water. Two direct current resistivity imageries (DC‐2D imagery) were also implemented to check their capability to map a known cave.

We found that the MRS is a useful tool to locate ground water in karst as soon as the quantity of water is enough to be detected. The threshold quantity is a function of depth and it was estimated by forward modeling to propose a support graph to hydrogeologists. The measured MRS's signals could be used to calculate transmissivity and permeability estimators. These estimators were used to map and to draw a cross section of the case study site, which underline accurately the known karst conduit location and depth.

We also found that the DC‐2D imagery could underline the karst structures: It was able to detect the known cave through its associated faults. We prepared a computer simulation to check the depth of such a cave to induce resistivity anomaly which could be measured in similar conditions.
Brackish Karstic Springs Model: Application to Almiros Spring in Crete
Authors: Maramathas Athanasios , Maroulis Zacharias , Marinos‐Kouris Dimitrios
Published: December 2005

A mathematical model is proposed to simulate brackish karstic springs. Rainfall data constitutes model input information while output information is the discharge and the chloride concentration of the water versus time. The model was constructed by considering the mass and mechanical energy balance on the hydrodynamic analog, which includes three reservoirs outflowing in a tube that lies adjacent to the spring. Two reservoirs emulate the karstic system, and the third one emulates the sea. The discharge of the spring is given by the sum of the discharge of the reservoirs, and the chloride concentration by the solution of the mixing problem between the fresh and the salty water, which exists in the tube leading to the spring. The model is applied to the spring of Almiros at Heraklion, Crete, Greece. The agreement between model values and field measurements is very good for depletion periods and satisfactory for recharge periods.
Estimating Deep Recharge Rates Beneath an Interlobate Moraine Using Temperature Logs
Authors: Ferguson Srant , Woodbury Allan D. , Matile Gaywood L.D.
Published: December 2005

The Sandilands area of southeastern Manitoba contains an interlobate moraine that is a major ground water recharge area. Underlying the highly permeable sediments of the moraine are up to 100 m of till and the subcrop of the Winnipeg Formation, which contains a major sandstone aquifer. Ground water flow within the till is examined using high‐resolution temperature profiles and solutions to the differential equation for heat flow in porous media. These analyses indicate that recharge to the sandstone aquifer is occurring at a rate of approximately 2 × 10−8 m/sec beneath the moraine, which is in agreement with recharge rates determined by conventional ground water hydraulics (10−7 to 10−10 m/sec) and another study using multiple environmental tracers (1 × 10−9 to 6 × 10−9 m/sec). The use of temperature to determine ground water flux is not limited by half‐lives as many environmental tracers are, and this allows for cost‐effective estimation of recharge and discharge rates over longer periods.
A Modular Injection System, Multilevel Sampler, and Manifold for Tracer Tests
Authors: Mailloux Brian J. , Fuller Mark E. , Rose George F. , Onstott Tullis C. , DeFlaun Mary F. , Alvarez Enrique , Hemingway Chris , Hallet R. Bruce , Phelps Tommy J. , Griffin Timothy
Published: December 2005

Ground water injection and sampling systems were developed for bacterial transport experiments in both homogenous and heterogeneous unconsolidated, surficial aquifers. Two types of injection systems, a large single tank and a dynamic mixing tank, were designed to deliver more than 800 L of amended ground water to the aquifer over 12 hours, without altering the ground water temperature, pH, Eh, or dissolved gas composition. Two types of multilevel samplers (MLSs) were designed and installed. Permanent MLSs performed well for the homogenous surficial aquifer, but their installation procedure promoted vertical mixing, which could obfuscate experimental data obtained from vertically stratified, heterogeneous aquifers. A novel, removable MLS was designed to fit in 2‐ and 4‐inch wells. Expandable O‐rings between each sampling port hydraulically isolated each port for sample collection when a nut was tightened at the land surface. A low‐cost vacuum manifold system designed to work with both MLS designs used 50 mL centrifuge tubes to efficiently sample 12 MLS ports with one peristaltic pump head. The integrated system was developed and used during four field campaigns over a period of three years. During each campaign, more than 3000 ground water samples were collected in less than one week. This system should prove particularly useful for ground water tracer, injection, and push‐pull experiments that require high‐frequency and/or high‐density sampling.
Variability and Comparison of Hyporheic Water Temperatures and Seepage Fluxes in a Small Atlantic Salmon Stream1
Authors: Alexander Matthew D. , Caissie Daniel
Published: December 2005

Ground water discharge is often a significant factor in the quality of fish spawning and rearing habitat and for highly biologically productive streams. In the present study, water temperatures (stream and hyporheic) and seepage fluxes were used to characterize shallow ground water discharge and recharge within the streambed of Catamaran Brook, a small Atlantic salmon (Salmo salar) stream in central New Brunswick, Canada. Three study sites were instrumented using a total of 10 temperature sensors and 18 seepage meters. Highly variable mean seepage fluxes, ranging from 1.7 × 10−4 to 2.5 cm3 m−2 sec−1, and mean hyporheic water temperatures, ranging from 10.5° to 18.0°C, at depths of 20 to 30 cm in the streambed were dependent on streambed location (left versus right stream bank and site location) and time during the summer sampling season. Temperature data were useful for determining if an area of the streambed was under discharge (positive flux), recharge (negative flux), or parallel flow (no flux) conditions and seepage meters were used to directly measure the quantity of water flux. Hyporheic water temperature measurements and specific conductance measurements of the seepage meter sample water, mean values ranging from 68.8 to 157.9 μS/cm, provided additional data for determining flux sources. Three stream banks were consistently under discharge conditions, while the other three stream banks showed reversal from discharge to recharge conditions over the sampling season. Results indicate that the majority of the water collected in the seepage meters was composed of surface water. The data obtained suggests that even though a positive seepage flux is often interpreted as ground water discharge, this discharging water may be of stream water origin that has recently entered the hyporheic zone. The measurement of seepage flux in conjunction with hyporheic water temperature or other indicators of water origin should be considered when attempting to quantify the magnitude of exchange and the source of hyporheic water.