bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of Volcanic Tuffs in Ground‐Water Regime of Valle Central, Costa Rica
Authors: Foster Stephen S. D. , Ellis Ann T. , Losilla‐Penon Marcelino , Rodriguez‐Estrada Hugo V. 
Published: March 2006

ABSTRACTLaboratory and field testing programs on the hydraulic properties of volcanic rocks from the Valle Central of Costa Rica in Central America have been undertaken. This area is typical of much of the circum‐Pacific volcanic belt. Most of the tuffaceous deposits are shown to have exceptionally high effective porosity (45‐65%), moderate hydraulic conductivity (0.02‐0.5 m/d) and very broad pore‐size distributions. Rather unexpectedly, they provide the major element of regulating storage in the overall ground‐water regime.
Ground‐Water Contamination and Well Construction in Southeast Nebraska
Authors: Exner Mary E. , Spalding Roy F. 
Published: March 2006

ABSTRACTNitrate‐nitrogen (NO3‐N) concentrations and total (TC) and fecal coliform (FC) densities were determined in ground water from 268 household and stock wells in an 1100 mi2 area of southeast Nebraska. Seventy‐one percent of the samples had NO3‐N concentrations above 10 mg/1 and/or TC densities ≥ 1/100 ml. Most of the NO3‐N contamination is from the dissolution of manure in barnyards and corrals. The average δ15N value was + 11.9%0 for the 115 samples with NO3‐N levels in excess of 8.5 mg/1.Only 10% of the wells met Nebraska's criteria for private well construction. NO3‐N levels exceeded 10 mg/1 in 4% of these wells while 30% contained one or more TC/100 ml. The highest incidence of NO3‐N and coliform contamination occurred in dug or augered wells with open‐jointed casing. The rates were 47% and 80%, respectively.Low levels of atrazine were detected only in the poorly constructed wells. One well contained alachlor.
Brackish Water in Unsaturated Confining Beds at a Texas Lignite Minea
Authors: Dutton Alan R. 
Published: March 2006

ABSTRACTDeposits of low permeability are hydrologic barriers between reclaimed land and juxtaposed aquifers and should limit the impact of mining on ground‐water quality. Clay‐stone and mudstone in argillaceous facies of the Calvert Bluff Formation (lower Eocene, Wilcox Group) function as confining beds in the East Texas Basin. In the subsurface and at the outcrop, water in argillaceous deposits is brackish to saline. Samples of vadose water from the outcrop of confining beds at the Big Brown lignite mine in Freestone County, Texas, have a chloride concentration of up to 3,500 mg/l and total dissolved solids of up to 8,000 mg/l. Ground‐water composition evolved from Eocene sea water by seven‐ to nine‐fold dilution with rain water. Ion exchange, pyrite oxidation, and calcite dissolution further modified water composition. The amount of recharge through the vadose zone where confining layers crop out is probably negligible over an extremely long time. Meteoric flushing in reclaimed land at the surface mine is many times greater than that in unmined mudstone deposits, and the chemical composition of vadose water in reclaimed land is changed by further dilution and water‐rock reactions.
Effect of Agricultural Land Use on Ground‐Water Quality in a Small Pennsylvania Watersheda
Authors: Pionke Harry B. , Urban James B. 
Published: March 2006

ABSTRACTGround‐water quality, determined by 10 samplings of 14 wells within a 7.4 km2 watershed during 1973–1982, was related to land use and geology. The wells represent forest and cropland use associated with three geologic zones. Nitrates, chloride and phosphate concentrations were much higher in ground waters underlying cropland. The mean concentrations ranged from five to seven times those observed in ground water underlying forests. The contamination pattern is consistent with that computed from a nutrient balance, based on known fertilizer and manure use on local croplands. Downgradient from the primary agricultural area, a geologic zone exists through which ground water from agricultural sources must pass to reach the stream. In this zone, the nitrate, chloride, and phosphate concentrations are greatly decreased due to mixing and dilution. The chemical nature of these ground waters reflects more the geochemistry of local geologic deposits than the impact of cropland use.A ground‐water flow system was hypothesized, based on known geologic, hydrologie, and geometric properties. The flow system is supported by the chemical data.
Fault Severed Aquifers Along the Perimeters of Wyoming Artesian Basins
Authors: Huntoon Peter W. 
Published: March 2006

ABSTRACTThe mountain uplifts which border the major artesian basins of Wyoming are asymmetric antiforms bounded on one flank by large displacement Laramide thrust faults. These thrusts sever the hydraulic continuity of aquifers, thereby creating separate circulation systems in the hanging wall and foot wall blocks. Fault severing of the Paleozoic aquifers can be identified by (1) potentiometric discontinuities across the faults, (2) water quality contrasts across the faults, and (3) geothermally heated waters in the foot wall blocks.Isolated but active circulation systems develop in the hanging wall blocks in which good permeabilities and good quality water prevail. In contrast the foot walls are generally characterized by poor permeabilities and poor water qualities.Fault severing of the Paleozoic aquifers in the Wyoming foreland province is a significant factor because nearly half of the basin perimeters are fault severed. The result is that exploration for large‐volume, good‐quality supplies must focus on the hanging wall blocks in the fault severed environments.
Economic Aspects in the Investigation of Ground‐Water Contamination Episodes
Authors: Shechter Mordechai 
Published: March 2006

ABSTRACTThe paper examines some economic aspects of ground‐water pollution, focusing on the exploitation of an aquifer as a source of drinking water. Using the contamination episode at Price Landfill, New Jersey, as a case study, it addresses analytical and information issues which characterize ground‐water pollution. Involved here are uncertainties associated with the environmental medium (especially knowledge of solute‐transport processes), and health risk assessment (principally dose‐response relationships). The field application employed two approaches to the modeling of the physical‐chemical processes to derive mortality risk estimates. These estimates in turn form the basis for preliminary assessment of expected damages: reduced longevity, and cost of control and remedial measures. The results are offered as an essential informational input for a benefit‐cost analysis of ground‐water protection and management policies.
Potentiometric Mapping from Incomplete Drill‐Stem Test Data: Palo Duro Basin Area, Texas and New Mexico
Authors: Bair E. Scott , O'Donnell Timothy P. , Picking Larry W. 
Published: March 2006

ABSTRACTDrill‐seem test (DST) data from wildcat wells and wells sponsored by the U.S. Department of Energy were used to construct pressure‐depth diagrams and regional potentiometric surfaces of the Wolf camp and Pennsylvanian aquifers. These deep‐basin aquifers represent the two regionally important downgradient aquifers that underlie the host rock at the proposed high‐level nuclear‐waste repository sites in the Palo Duro Basin area of Texas and New Mexico. More than 5,500 DSTs were screened and classified according to shut‐in pressure and shut‐in time criteria devised to evaluate the quality of the DST data and to delete dubious DST data. After screening, three sets of pressure‐depth diagrams and potentiometric‐surface maps were constructed, corresponding to three levels of data refinement.The initial Wolfcamp and Pennsylvanian regional potentiometric surfaces contained several prominent local mounds and depressions with unrealistic variations in the direction and magnitude of hydraulic gradients. Pressure‐depth data and records and maps of historic oil and gas production showed that many DSTs were performed in depressured oil and/or gas production zones. The low shut‐in pressures recorded during these tests caused abnormally low heads to be calculated and contoured. Formation pressures recorded in these depressured zones represent local temporal pressures in a regional flow system that is probably steady state. Deletion of depressured DSTs produced regional potentiometric surfaces that were more realistic but contained a few large local mounds and depressions caused by local aberrant DST data. Deletion of local aberrant grossly underpressured DSTs not attributable to oil and/or gas production and local aberrant grossly overpressured DSTs, based on comparison of initial shut‐in pressures and heads in the same well and/or in adjacent wells at a similar depth in the same geologic unit, produced potentiometric surfaces that show regional and some local variations in flow directions and hydraulic gradients. Linear regression of the pressure‐depth data showed that most of the refinement in the data was due to culling depressured DSTs. Some additional refinement was due to culling local aberrant grossly underpressured and grossly overpressured DSTs.
Sustained‐Yield Ground‐Water Planning by Goal Programing
Authors: Yazdanian Amin , Peralta Richard C. 
Published: March 2006

ABSTRACTA method for determining a spatially distributed set of ground‐water withdrawals that maintains a regionally “optimized” potentiometric surface is presented. A goal‐programing approach, in its quadratic form, is used to minimize the sum of squares of differences between the optimized surface and a “target” potentiometric surface. Constraints on withdrawals and recharge, imposed through a two‐dimensional ground‐water flow equation, and bounds on drawdowns assure that the withdrawal strategy developed is realistic and physically feasible. Application is demonstrated using data from the Grand Prairie region of Arkansas.
Hydrogeology of an Atoll Island: A Conceptual Model from Detailed Study of a Micronesian Example
Authors: Ayers Jerry F. , Vacher H. L. 
Published: March 2006

ABSTRACTFindings from a detailed hydrogeologic study of a Micronesian atoll island are combined with published descriptions of the hydrogeology of other atoll islands. The purpose is to propose a conceptual model which describes how the occurrence and flow of ground water in atoll islands are related to the underlying geologic framework. The study island is Deke, a small, uninhabited island on Pingelap Atoll in the Eastern Caroline Islands.Integrated studies on Deke of surface geology and physiography, water levels and their variation, surface geophysics (seismic refraction and resistivity), and subsurface core samples indicate a hydrogeologic system that is more complex than would ordinarily be expected for a small and, at first glance, uncomplicated island. Of utmost importance to the occurrence and flow of ground water is the fact that the island straddles the lagoonward edge of the very firmly indurated reef‐flat plate. This plate is a hard, impermeable substrate beneath the northern portion (ocean side) of the island, occurs at sea level, and is underlain by unconsolidated or loosely cemented sediments. Study results indicate that this reef‐flat plate acts as a confining bed along the ocean side of the lens; elsewhere the lens is unconfined, receives recharge directly, and forms a thicker fresh‐water nucleus.The conceptual model of atoll‐island hydrogeology involves a dual aquifer system: (1) an aquifer of mostly unconsolidated Holocene sediments resting on (2) a once emergent and now very permeable Pleistocene limestone platform. The Holocene aquifer, which is where the island lens occurs, is heterogeneous with respect to its hydraulic properties and is confined in part of the island and unconfined elsewhere, with the location of the two regions depending on where the island sits relative to the pinchout of the reef‐flat plate. In the unconfined region, there is a hydrologically‐important central depression, where low lying sediments are enclosed by ocean‐derived washover fans and a lagoon‐bordering dune. This area is a likely ground‐water sink due to direct evapotranspiration during the dry season. Accordingly, the model includes two flow patterns: a wet‐season pattern radiating outward from the unconfined lagoon‐side of the island, and a dry‐season pattern that includes a superimposed area of centripetal flow at the central depression.
Evaluation of Transient Electromagnetic Soundings for Deep Detection of Conductive Fluids
Authors: Stewart Mark , Gay Michael C. 
Published: March 2006

ABSTRACTTransient electromagnetic sounding methods (TEM) have several advantages over DC resistivity soundings. The principal advantage is that sounding depths several times the receiver‐transmitter spacing can be achieved, resulting in less cumbersome field work and more flexible sounding site selection. The TEM method was tested using a commercially available instrument (Geonics EM‐37) in the Gulf Springs region of west‐central Florida to locate the saltwater interface in the Floridan Aquifer. The Floridan is a thick (200 m), unconfined, karstic, carbonate aquifer within the study area. High annual rainfall and internal drainage create a deep and dynamic interface.Eighty transient soundings were completed in 18 field days. Seventy‐one soundings used a square 80 m × 80 m transmitter loop, and the other nine used a 160 m × 160 m coil. The interface was easily detected from a minimum depth of 60 m to its maximum depth of about 140 meters. Also, a high‐resistivity, low‐porosity zone was detected at depths ranging from 180–250 meters. The TEM data compare well with available chloride concentration data. The TEM interface corresponds to chloride values in excess of 200–400 mg/1. The sounding curves obtained suggest that with presently available instruments the TEM method is not well‐suited for shallow soundings (less than 40–50 meters).
Relations Between Permeability and Electrical Resistivity in Granular Aquifers
Authors: Huntley David 
Published: March 2006

ABSTRACTIncreased demand for quantitative answers to ground‐water problems, particularly associated with the use of numerical models, has increased the need to accurately determine the distribution of hydraulic parameters. Researchers have attempted to find correlations between electrical resistivity and the permeability of fresh‐water aquifers since 1951. Several recent studies report either direct or inverse relations between apparent formation factor and aquifer permeability. The basis for these relations is a direct or inverse relation between porosity and permeability and, as matrix conduction effects are not taken into account, constant fluid conductivity is either implicitly or explicitly assumed.Laboratory experiments conducted on granular materials suggest that matrix conduction (surface conduction) effects are either as important as, or dominant over, porosity‐permeability relations. Our experiments on granular materials show only weak relations between true formation factor and permeability. Relations between apparent formation factor and permeability are good only for constant fluid conductivity. Most importantly, the strongest relationship found was that between permeability and matrix conductivity.These data suggest either that (1) relations between permeability and apparent formation factor must be applied in very restricted geologic environments and only where fluid conductivity remains relatively constant, or (2) more fundamental relations between matrix conductivity and aquifer permeability should be applied.
Ground‐Water Dams for Rural‐Water Supplies in Developing Countries
Authors: Hanson Goran , Nilsson Åke 
Published: March 2006

ABSTRACTThe use of groundp‐water dams to store water in regions with arid or tropical climates is a method that has received considerable attention in the last few years. By storing water behind subsurface dams in natural aquifers or in the sand accumulated in sand storage dams, the disadvantages of conventional surface storage, such as high evaporation rates, pollution, siltation, and health hazards, may be avoided. The techniques are very old, but only recently have there been some attempts to make systematic studies and to develop proper siting, design, and construction methods. This paper presents the experience gained from existing structures all over the world and describes the physical setting in which the techniques may be applied. Design and construction alternatives are shown, and case studies from India and Ethiopia are presented. The construction of ground‐water dams may be a feasible solution to water‐supply problems in many parts of the world if preceded by proper planning and site surveys.
Recovering Fresh Water Stored in Saline Limestone Aquifers
Authors: Merritt Michael L. 
Published: March 2006

ABSTRACTNumerical modeling techniques are used to examine the hydrogeologic, design, and management factors governing the recovery efficiency of subsurface fresh‐water storage. The modeling approach permitted many combinations of conditions to be studied. A sensitivity analysis was used that consisted of varying certain parameters while keeping constant as many other parameters or processes as possible. The results show that a loss of recovery efficiency resulted from: (1) processes causing mixing of injected fresh water with native saline water (hydrodynamic dispersion); (2) processes or conditions causing the irreversible displacement of the injected fresh water with respect to the well (buoyancy stratification and background hydraulic gradients); or (3) processes or procedures causing injection and withdrawal flow patterns to be dissimilar (dissimilar injection and withdrawal schedules in multiple‐well systems). Other results indicated that recovery efficiency improved considerably during the first several successive cycles, provided that each recovery phase ended when the chloride concentration of withdrawn water exceeded established criteria for potability (usually 250 milligrams per liter). Other findings were that fresh water injected into highly permeable or highly saline aquifers would buoy rapidly with a deleterious effect on recovery efficiency.
Aldicarb Studies in Ground Waters from Florida Citrus Groves and Their Relation to Ground—Water Protection
Authors: Dierberg Forrest E. , Given Chris J. 
Published: March 2006

ABSTRACTThe disappearance of aldicarb [2–methyl–2(methylthio) propionaldehyde 0‐(methylcarbamoyl) oxime] and its two toxic degradation products, aldicarb sulfoxide and aldicarb sulfone, were measured in laboratory studies using ground waters and subsoils collected from citrus groves in Indian River County, Florida, and incubated under controlled conditions which best represented the in situ environment. The half‐life times for the disappearance of aldicarb and its two oxidized sulfur derivatives in ground‐water‐saturated subsoils ranged from 10–26 days. Based on the degradation rates found in this study, hydrologic parameters obtained for Indian River County subsoils, and amounts of total toxic residue reported entering Florida ground waters, it was estimated that toxic residues in aldicarb‐contaminated ground waters in Indian River County would migrate only short distances (0.3–5.2 m) before conversion of toxic residues to nontoxic residues was complete.
ODE TO THE SAN LUIS DRAIN
Authors: Thomas Harold E. 
Published: March 2006

Abstract. The San Luis Drain (SLD) has enabled us to learn quickly the facts and effects of irrigating only 8,000 acres of seleniferous soils: the dissolving and organic uptake of selenium, its dissemination from ponds, entry into food chains, and accumulation in a wide variety of biota and detritus. If deprived access to SLD, the Westlands Water District (WWD) could direct their toxic wastes down natural slopes by trickling or sumps and drain ditches, but this means toward the Mendota Pool and the Main Canal and Outside Canal which carry water for irrigation and domestic wells; that is more ominous to Merced County than the SLD ever was.The WWD needs detailed testing and mapping of its irrigable lands to discriminate the areas of seleniferous soils from those which are safe for irrigation. In the meantime, in irrigated lands above the Delta‐Mendota Canal, all sumps and drains should be monitored for selenium in toxic concentrations, and irrigation should cease in the areas producing the excessive selenium. Monitors along the Outside and Main Canals (below drainage from known seleniferous areas) might be needed for preservation of good quality, perhaps by dilution with CVP water.
Changes of Ground‐Water Quality Near a Well Undergoing Acid Treatment
Authors: Wojcik Wlodzimierz , Wieczysty Artur 
Published: March 2006

ABSTRACTOne of the rehabilitation methods applied to wells incrusted with iron is acid treatment. In many cases, however, the owners of the wells and contractors are concerned about possible aquifer pollution. The aim of field experiments has been to find out how far hydrochloric acid can migrate within the unconsolidated aquifer during well treatment, and what changes it causes in the quality of ground water.Results indicate that the acid remains near the well where it reacts with clogging deposits. Twenty‐four hours after acidizing, no changes in ground‐water quality were observed in piezometers at greater distances than 5.0 m from the well. After flush pumping, the ground water reverted to its original quality.
Geophysical Mapping of a Buried Basalt/Sedimentary Interface, Eastern Sudan
Authors: Ali Hamid O. 
Published: March 2006

ABSTRACTThe El‐Shawak area in eastern Sudan lies within a large synclinal basin known as the Gedaref Basin, composed principally of elastic sediments of the Nubian Sandstone Formation which are overlain by sheets of basalt and dolerite and underlain by a metamorphic Basement Complex.As a part of a hydrogeological research project in the area, gravity and seismic refraction techniques were combined to locate the extent of the basaltic flow and to determine the thicknesses of the sedimentary formations.The results of these studies show that the topography of the Basement Complex is undulating and characterized by two troughs separated by subsurface ridges. The thicknesses of the Nubian Formation sediments range from 50 m (164 ft) to greater than 250 m (820 ft). Although the thicknesses of the Nubian Formation are favorable for ground‐water occurrence, the yield is very limited because the sediment succession is composed largely of compact mudstone.The application of the gravity method in the El‐Shawak area has shown that a polynomial trend‐surface fit can be used to separate the regional and the residual components to reflect local geological features.