bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sources of Water to Wells for Transient Cyclic Systems
Authors: Reilly Thomas E. , Pollock David W. 
Published: August 2005

AbstractMany state agencies are currently (1995) developing wellhead protection programs. The thrust of some of these programs is to protect water supplies by determining the areas contributing recharge to water‐supply wells and by specifying regulations to minimize the opportunity for contamination of the recharge water by activities at the land surface. The area contributing recharge to a discharging well is the surface area at the water table through which the water flowing to the well entered the ground‐water system. In the analyses of ground‐water flow systems, steady‐state average conditions are commonly used to simplify the problem and make a solution tractable. However, recharge is usually cyclic in nature, with seasonal cycles and longer term climatic cycles. The effect of these cyclic stresses on the area contributing recharge to wells is quantitatively analyzed for a hypothetical alluvial valley aquifer system that is representative of a large class of ground‐water systems that are extensively developed for water supply. The analysis shows that, in many cases, these cyclic changes in the recharge rates do not significantly affect the location and size of the areas contributing recharge to wells. The ratio of the mean travel time to the length of the cyclic stress period appears to be an indicator of whether the transient effects of the cyclic stress must be explicitly represented in the analysis of contributing areas to wells. For the cases examined, if the ratio of the mean travel time to the period of the cyclic stress was much greater than one, then the transient area contributing recharge to wells was similar to the area calculated using an average steady‐state condition. However, cyclic stresses on systems with ratios less than one do have an effect on the location and size of the areas contributing recharge to wells.
Self‐Potential Method in Hydrogeological Exploration of Volcanic Areas
Authors: Aubert M. , Atangana Q. Yéné 
Published: August 2005

AbstractIn volcanic areas, when two conditions are satisfied, there is a linear correlation between the range of negative self‐potential (SP) anomalies and the thickness of the unsaturated zone measured in borings. The first condition is a high ratio between the resistivity of the unsaturated zone, and the resistivities of the substratum and the water‐saturated zone. The second condition is the homogeneity of the unsaturated zone. From this relation, we develop the concept of a geophysical surface (SPS surface) calculated from SP and topographic data. Under these conditions, the SPS surface is both an equipotential SP surface and the interface between the unsaturated zone and the saturated medium below. Borehole logs for three field sites show that drainage courses and watersheds are located exactly on respectively the valleys and the ridge lines of the SPS surface.
Springs in Spain: Classification According to Their Flows and Lithologies and Their Hydraulic Contributions
Authors: Pérez Eugenio Sanz 
Published: August 2005

AbstractThis paper presents an approach to regional hydrological balance where the number and integrated discharge of springs are used to estimate recharge. This technique is applied to Spain, where approximately two‐thirds of the country has an inventory of spring lithology and discharge (17,000 springs). The data are used to extrapolate results to the entire region and are compared to independent methods of estimating recharge. This is an informative use of commonly available information and it could be applied to other regions with a similar data base.From this sample, a distribution of the spring flow volume contribution in Spain is estimated (a) according to flow spring discharge, (b) as a limit of a lognormal distribution, which in our sample is simplified in a potential formula a(x) = 24,101.x −0.91. In this way it is calculated that the total flow volume of the springs is 14,877 hm3/yr. The study does not take into account seepage (diffuse discharge) draining to seas, rivers, or lakes but only water at the spring source. The most permeable lithological groups considered are the source of 94.2% of the total flow supplied by the springs. Limestone is especially significant, contributing 66.2%. The net recharge of precipitation to ground water varies widely according to lithologies. It reaches to 20.3% in limestones and drops to less than 1% for quartzites, slates, and plutonic rocks.
Multiport Well Design for Sampling of Ground Water at Closely Spaced Vertical Intervals
Authors: Delin Geoffrey N. , Landon Matthew K. 
Published: August 2005

AbstractDetailed vertical sampling is useful in aquifers where vertical mixing is limited and steep vertical gradients in chemical concentrations are expected. Samples can be collected at closely spaced vertical intervals from nested wells with short screened intervals. However, this approach may not be appropriate in all situations. An easy‐to‐construct and easy‐to‐install multiport sampling well to collect ground‐water samples from closely spaced vertical intervals was developed and tested. The multiport sampling well was designed to sample ground water from surficial sand‐and‐gravel aquifers. The device consists of multiple stainless‐steel tubes within a polyvinyl chloride (PVC) protective casing. The tubes protrude through the wall of the PVC casing at the desired sampling depths. A peristaltic pump is used to collect ground‐water samples from the sampling ports. The difference in hydraulic head between any two sampling ports can be measured with a vacuum pump and a modified manometer. The usefulness and versatility of this multiport well design was demonstrated at an agricultural research site near Princeton, Minnesota where sampling ports were installed to a maximum depth of about 12 m below land surface. Tracer experiments were conducted using potassium bromide to document the degree to which short‐circuiting occurred between sampling ports. Samples were successfully collected for analysis of major cations and anions, nutrients, selected herbicides, isotopes, dissolved gases, and chlorofluorcarbon concentrations.
Potential for Intrinsic Bioremediation of a DNT‐Contaminated Aquifer
Authors: Bradley P. M. , Chapelle F. H. , Landmeyer J. E. , Schumacher J. G. 
Published: August 2005

AbstractMicroorganisms indigenous to a shallow aquifer, which underlies an explosives‐contaminated site, mineralized 28% of [U‐ring‐14C] 2,4–dinitrotoluene to 14CO2 within 28 days under aerobic conditions. Approximately 20% of added 2,4–dinitrotoluene remained undegraded at the end of the incubation while approximately 22% and 6% were transformed to 4–amino‐2–nitrotoluene and 2–amino‐4–nitrotoluene, respectively. In aquifer microcosms containing 2,6–dinitrotoluene, approximately 67% of the substrate remained undegraded and approximately 14% was transformed to 2–amino‐6–nitrotoluene. The radiolabeled study indicated that about 8% of the 2,6–dinotrotoluene was mineralized to CO2. The demonstrated degradation and subsequent mineralization of dinitrotoluene compounds by aquifer microorganisms are consistent with the decline in dissolved dinitrotoluene concentrations observed along the general ground‐water flowpath at the site. The results indicate that intrinsic bioremediation may be a viable alternative for remediating contaminated ground water at this site.
An Outline of a Guidance Framework for Assessing Hydrogeological Risks at Early Stages
Authors: Rosen Lars , LeGrand Harry E. 
Published: August 2005

AbstractThe prevalent and straightforward routine of impulsively collecting masses of new data for studies relating to ground‐water contamination can be inefficient and costly as it does not provide optimal value from existing hydrogeologic and other information. A preliminary guidance framework is outlined, for early stage monetary risk assessments prior to any new measurements, considering both the probability and the economical consequences of contamination. The framework is aimed at providing a basis for cost‐effective decision‐making regarding ground‐water protection and management actions. It centers on improved conceptual hydrogeological site descriptions based on existing information and professional judgments prior to any new measurements. A key aspect of the framework is to derive maximum possible quantitative understanding of risks from limited prior available qualitative information. The framework has a dual‐site approach, assuming a situation of a contaminant source site and a receptor site. A two‐step procedure leads to the monetary risk assessment with respect to existing compliance levels: (1) conceptual model development, and (2) quantitative model realization, addressing the probability of contaminant release at the contamination source, the hydraulic connection between the source and the receptor, and the contaminant transport conditions. The purpose of the framework is twofold: (1) to provide a risk assessment framework which optimizes use of professional judgment for studies where data are limited, and (2) to give synergistic interpretive values that complement field measurements and that can be used as prior estimates in more detailed studies.
A Semianalytical Model to Predict Recovery of Light, Nonaqueous Phase Liquids from Unconfined Aquifers
Authors: Waddill Dan W. , Parker Jack C. 
Published: August 2005

AbstractContamination of soil and ground water due to spills of light nonaqueous phase liquids (LNAPL or simply oil) is a widespread environmental problem. This paper describes the development and testing of a semianalytical model that may be used to design LNAPL containment and recovery systems at spill sites. The objective of this study was to derive an enhanced semianalytical algorithm for calculating recovery and trapping of free phase oil. The enhancements were derived and evaluated by comparison with an established numerical model that describes transient flow of oil and water. The semianalytical model employs an analytical solution for steady‐state drawdown in an unconfined aquifer due to water pumping. When pumping rates are sufficient to contain the separate phase plume, the model calculates recoverable and residual oil volumes based on the initial free oil distribution. Refinements were implemented to calculate the water‐table drawdown and the maximum unsaturated zone residual saturation (Sog) as functions of soil type. Also the influence of hysteresis on the oil‐water capillary fringe was incorporated into the calculation of oil trapping below a rising oil‐water interface. A method was derived to reduce saturated zone trapping to account for oil recovery that occurs while pumping proceeds. The above enhancements yielded close agreement between the semianalytical model and the transient model predictions of recoverable oil and residual oil in the unsaturated and saturated zones. The models were compared for hypothetical gasoline spills in a sandy and a silt loam soil, using a range of pumping rates and regional water‐table fluctuations. Field data from a pipeline leak were evaluated by the semianalytical model for hypothetical scenarios involving oil recovery from three wells and a falling regional water table. Results suggest that the semianalytical model captures many of the trends of transient oil recovery. Recovery is less accurately predicted when irregular water‐table fluctuations occur.
Saratoga Springs and Early Hydrogeochemistry in the United States
Authors: Davis Stanley N. , Davis Augusta G. 
Published: August 2005

AbstractThe earliest quantitative chemical analysis of ground water from the United States was probably made during 1807. The largest number of early analyses were of water from various mineral springs in and near the towns of Ballston and Saratoga Springs, New York. Although most of the scientific and economic interest at the time centered on the reported health benefits from the water, some of the earliest reports describing the springs contained rudimentary yet scientifically based hydrogeochemical explanations for the dissolved constitutents in the water. One motivation for the early analytical work was the desire to concoct a dry mixture of chemicals that would duplicate the mineral water when mixed with ordinary drinking water. The use of a powder would simplify distribution and bypass dealing with owners of the springs. Early analyses of water from Congress Spring published by different individuals between 1817 and 1856 are similar, and if allowance is made for minor temporal changes in quality, the results would be considered useful even by modern standards.
Borehole Flowmeter Application in Fluvial Sediments: Methodology, Results, and Assessment
Authors: Bomana Gerald K. , Molz Fred J. , Boonec Kelly D. 
Published: August 2005

AbstractIn many situations, inadequate design or performance of ground‐water remediation systems is the result of underestimation of aquifer hydraulic heterogeneity, and in particular, the vertical variation of hydraulic conductivity which plays an important role in contaminant migration. Described herein are applications of the electromagnetic (EM) borehole flowmeter to fluvial sediments in Louisiana and South Carolina. The direction of natural vertical flow in the test aquifers was defined easily, and short pumping tests enabled the calculation of hydraulic conductivity profiles for each test well. The results correlated well with other information obtained independently, including natural gamma logs, driller's logs and a hydraulic conductivity profile based on grain size analysis. Large variations in hydraulic conductivity over short vertical and horizontal distances were documented. Tests in gravel‐packed wells suggested that flowmeters produce misleading data for a variety of reasons in such situations. Among other things, an annulus of high permeability around a well screen allows flow to bypass the meter, and the phenomenon is amplified by high pumping rates. The resulting error is displayed as an erroneous high permeability zone at the top of the well screen. This observation deserves further study. In its present form the EM flowmeter is awkward to handle on a routine basis. However, none of the present design flaws preclude its effective use.
The Theis Solution in Heterogeneous Aquifers
Authors: Serrano Sergio E. 
Published: August 2005

AbstractA new solution of the unsteady confined radial flow equation subject to aquifer heterogeneity, as characterized by the statistics of the transmissivity, is presented. Simple applications to the direct and inverse problems useful to field hydro geologists are included. The results use the classical Thies solution as an initial condition and the method of decomposition, which does not require many of the restrictions of the traditional small perturbation methods. Given the mean and variance of the transmissivity, the direct problem aims at the prediction of the mean and the variance of the draw downs. Given the mean and the variance of the draw down, the indirect problem aims at the estimation of the mean and the variance of the transmissivity.
Quantification of Ground‐Water Flow in Fractured Rock, Oak Ridge, Tennessee
Authors: Moore Gerald K. 
Published: August 2005

AbstractThe theory of ground‐water flow in fractured rocks has been used to interpret aquifer tests and stream flow data for the Oak Ridge Reservation of U.S. Department of Energy. This interpretation has resulted in a better understanding of the data needed for ground‐water models. The hydraulic conductivity values calculated from most aquifer tests are meaningless. Slug tests and early data from pumping tests measure the total transmissivity of all fractures within the area of influence; this value can be used to calculate rates of ground‐water flow and transport near the well. Larger transmissivity values are calculated from late aquifer‐test data and from an analysis of stream flow hydrographs because most ground‐water flow occurs in a thin layer at the water table. This layer supplies most ground‐water discharge to streams and apparently is a late‐time water source for pump age from deeper wells.The calibration of distributed flow and transport models will be difficult, if not impossible, because about 90% of the ground‐water flow occurs in only 10% of the area, and the locations of these flow paths are unknown. Also, large changes in transmissivity occur with recharge and discharge cycles that change the saturated thickness of the permeable layer near the water table.
Identifying and Removing Barometric Pressure Effects in Confined and Unconfined Aquifers
Authors: Rasmussen Todd C. , Crawford Leslie A. 
Published: August 2005

AbstractFailing to account for barometric pressure effects in water level measurements can introduce errors by misestimating the total head and by adding noise to water level measurements. For determining the total head in an aquifer, we assert that the air pressure head at the water surface in the well must be added to measured water levels (equivalent to using an absolute pressure transducer) even though the resulting values may have larger temporal and spatial variability than the original water level measurements. At the Savannah River Site in South Carolina, the average barometric pressure variation is 6 to 7 cm, with a range of over 30 cm. Failure to account for barometric pressure variability could result in misestimation of the direction and magnitude of the hydraulic gradient at the site. We also demonstrate procedures for removing barometric effects, such as to reduce noise during an aquifer pumping test, and to identify mechanisms by which barometric pressure affects water levels. Three mechanisms are summarized including: an instantaneous response for confined aquifers; a delayed response due to borehole storage in confined and unconfined aquifers; and a delayed response in unconfined aquifers due to the passage of barometric pressure changes through the unsaturated zone. Using data from the Savannah River Site, barometric efficiencies are estimated using linear regression and a modification of Clark's Method. Delayed responses are estimated using regression deconvolution. The type of barometric effect provides diagnostic information about whether the aquifer is confined or not, the presence of borehole storage or skin effects, and the air diffusivity coefficient within the unsaturated zone. We also show how removal of barometric pressure effects improves the ability to observe otherwise unnoticeable effects.
Hydrogeology and Paleohydrology of Ancient Machu Picchu
Authors: Wright Kenneth R. , Witt Gary D. , Zegarra Alfredo Valencia 
Published: August 2005

AbstractThe study of the ancient Inca water supply of Machu Picchu was performed by the authors under an archaeological permit issued by the Peruvian Government in 1994. The study included an evaluation of the hydrogeology of the ancient spring water supply situated on the north slope of the mountain of Machu Picchu and its relationship to the Machu Picchu fault.Based on field measurements, the yield of the primary spring has a seasonal variation of between 25 and 125 liters per minute. This flow adequately provided the domestic water requirements of up to 1000 inhabitants of the mountain top royal retreat of the Inca ruler Pachacuti, occupied primarily between 1450 and 1540 AD. The permanent population between visits of the Inca ruler was about 300. Final abandonment occurred in 1572 AD. The estimated geologic catchment area related to the Machu Picchu fault is roughly 50 percent greater than the topographic basin area. A 749 meter‐long canal delivered the spring flow to the center of the community to serve a total of 16 water supply fountains.A theory that a water shortage caused Machu Picchu to be abandoned proved to be unsubstantiated based on a study of the Quelccaya Ice Cap corings data that demonstrated that the last decade of the occupation was wetter than the previous eight decades. The builders of Machu Picchu developed a community domestic water supply using the spring and a hydraulic infrastructure in an effective and efficient manner. They utilized a gravity flow canal sized to carry the spring flow with a suitable safety factor against overtopping.
Composite Recovery Type Curves in Normalized Time from Theis’ Exact Solution
Authors: Goode Daniel J. 
Published: August 2005

AbstractType curves derived from Theis’ exact nonequilibrium well function solution are proposed for graphical estimation of aquifer hydraulic properties, transmissivity (T), and storage coefficient (S), from water‐level recovery data after cessation of a constant‐rate discharge test. Drawdown (on log scale) is plotted versus the ratio of time since pumping stopped to duration of pumping, a normalized time. Under Theis conditions, individual type curves depend on only the dimensionless pumping duration, which depends in turn on S and radial distance from the pumping well. Type curve matching, in contrast to the Theis procedure for pumping data, is performed by shifting only the drawdown axis; the time axis is fixed because it is a relative or normalized time. The match‐point for the drawdown axis is used to compute T, and S is determined from matching the curve shape, which depends on early dimensionless‐time data. Multiple well data can be plotted and matched simultaneously (a composite plot), with drawdown at different radial distances matching different curves. The ratio of dimensionless pumping durations for any two matched curves is equal to one over the squared ratio of radial distances. Application to two recovery datasets from the literature confirm the utility of these type curves in normalized time for composite estimation of T and S.
Comparison of Models for Delineating Wellhead Protection Areas in Confined to Semiconfined Aquifers in Alluvial Basins
Authors: Forster Craig B. , Lachmar Thomas E. , Oliver Douglas S. 
Published: August 2005

AbstractThe 1986 Safe Drinking Water Act Amendments include provisions for state wellhead protection (WHP) programs that address wellhead protection areas (WHPAs). In many states, WHPAs are delineated based on time‐of‐travel (TOT) criteria. This study compares 250‐day and 15‐year TOT capture zones computed in a confined to semiconfined aquifer system in an alluvial basin using semianalytical and two‐ and three‐dimensional numerical ground‐water flow models, and evaluates the relative importance of several sources of uncertainty, such as aquifer hydraulic conductivity, aquitard leakance, vertical transit time, hydraulic gradients, transient pumping effects, well interference, and three‐dimensional aquifer geometries.A numerical model should be used to delineate 15‐year TOT capture zones for wells in confined to semiconfined aquifers in alluvial basins. A semianalytical program may be acceptable for computing the 250‐day TOT capture zones; however, such codes can be applied only under a very narrow range of conditions.Hydraulic conductivity plays a critical role in controlling the sizes and shapes of capture zones computed in confined to semiconfined aquifers. Small, circular capture zones are computed in low hydraulic conductivity areas. More complex geometries should be expected where hydraulic conductivities are higher and pumping wells are in close proximity to each other. Aquifers with horizontal hydraulic conductivities that are greater than 1,000 times the vertical hydraulic conductivity of the overlying aquitard are effectively fully confined, and larger capture zones would be computed for these aquifers than for semiconfined aquifers where significant leakage is induced by pumping. In addition, relatively large drawdowns are computed in low hydraulic conductivity areas, resulting in short vertical transit times. Vertical transit times are longer where aquifer hydraulic conductivities are higher.