Upward Leakage Research Articles

Controls on δ34S and δ18O of dissolved sulfate in aquifers of the Murray Basin, Australia and their use as indicators of flow processes

The usefulness of stable isotopes of dissolved SO4 (δ34S and δ18O) to study recharge processes and to identify areas of significant inter-aquifer mixing was evaluated in a large, semi-arid groundwater basin in south-eastern Australia (the Murray Basin). The distinct isotopic signatures in the oxidizing unconfined Murray Group Aquifer and the deeper reducing Renmark Group confined aquifer may be more sensitive than conventional chemical tracers in establishing aquifer connections. δ34S values in the unconfined Murray Group Aquifer in the south and central part of the study area decrease along the hydraulic gradient from 20.8 to 0.3‰. The concomitant increasing SO4/Cl ratios, as well as relatively low δ18OSO4 values, suggest that vertical input of biogenically derived SO4 via diffuse recharge is the predominant source of dissolved SO4 to the aquifer. Further along the hydraulic gradient towards the discharge area near the River Murray, δ34S values in the unconfined Murray Group Aquifer increase, and SO4/Cl ratios decrease, due to upward leakage of waters from the confined Renmark Group Aquifer which has a distinctly low SO4/Cl and high δ34S (14.9–56.4‰). Relatively positive δ34S and δ18OSO4 values, and low SO4/Cl in the Renmark Group Aquifer is typical of SO4 removal by bacterial reduction. The S isotope fractionation between SO4 and HS− of ∼24‰ estimated for the confined aquifer is similar to the experimentally determined chemical fractionation factor for the reduction process but much lower than the equilibrium fractionation (∼70‰) even though the confined groundwater residence time is >300 Ka years. Mapping the spatial distribution of δ34S and SO4/Cl of the unconfined Murray Group Aquifer provides an indicative tool for identifying the approximate extent of mixing, however the poorly defined end-member isotopic signatures precludes quantitative estimates of mixing fractions.

Relation entre nappes superficielles et aquifère profond dans le bassin de Sfax (Tunisie)

The study of the isotopic composition ( 18 O and 2 H) of groundwater collected in the Sfax basin (Tunisia), helped to understand the behaviour of the different aquifers. It showed that the groundwater in the deep aquifer is old, probably slow moving and recharged under a colder climate than at present. The increasing exploitation of the shallow aquifers probably favoured upward leakage from the deep aquifer. Isotope balance equations allowed us to estimate the contribution of the deep aquifer to the shallow aquifer recharge. L’interprétation des teneurs isotopiques ( 18 O, 2 H) des eaux souterraines du bassin de Sfax, en Tunisie, a permis de comprendre certaines particularités du régime des écoulements dans les différents systèmes aquifères de ce bassin. Cette étude a montré que les eaux de l’aquifère profond, anciennes, vraisemblablement peu circulantes, ont été rechargées sous un climat plus froid que l’actuel. L’exploitation accrue des nappes superficielles a probablement favorisé les phénomènes de drainance verticale ascendante à partir de la nappe profonde. L’utilisation de bilans isotopiques conduit à une estimation de cette participation profonde à l’alimentation des nappes superficielles.

Variabilité climatique durant le Quaternaire dans la nappe du Tarat (Arlit, Niger)

The concentration of major elements and environmental isotopes in the Carboniferous (Guezouman and Tarat), Triassic (Teloua) and Quaternary aquifers allows to describe the ground-water flow and to define the upward leakage. 18O and 2H in water samples from Guezouman and some Tarat aquifers fall on a regressive line with the equation, δ 2H = (8.01 ± 0.50) δ 2 18O + (3.85 ± 3.56), similar to that found for old groundwater in the northern and southern Sahara. The isotopic difference between the Arlit area and the easterly Djado basin groundwater results from the combined effects of continentality and altitude on meteoric waters. The carbon 14 ages, the palaeo-temperatures evaluated from oxygen 18 and nitrate contents in the Tarat aquifer show climatic variations consisting of two humid periods at 10 000 and 30 000 years separated by a warmer period at 25 000. The mean temperatures of the palaeo-recharge, estimated using oxygen 18 data, are 18 °C during the Holocene, 20 °C at 25 000 years and 16 °C at 30 000 years. Water infiltrating during the warming period shows 79 mg·L −1 nitrates. High nitrates could be due to an important meteorological event which entrained and stored organic matter from the surface vegetation and soil by infiltration.

Water table fluctuation in soils overlying semi-confined aquifers in response to time-varying replenishment

The water table height in drained agricultural land depends on time-varying replenishment that is due to the vertical downward recharge from irrigation or rainfall, and in some cases to the upward vertical leakage from a semi-confined aquifer. The downward recharge may be assumed to vary exponentially with time, whereas the upward leakage may be expressed as a function of the unknown water table height. Furthermore, the rising of the water level in the field drainage system, that may cause an inverse flow from the drains towards the soil, is introduced through a properly defined boundary condition. A non-homogeneous form of the Boussinesq equation, that is used to describe this particular drainage problem, is solved for three different initial conditions. The same drainage problems were solved numerically by using the finite element method. Comparison between analytical and numerical solutions shows satisfactory agreement. From the analytical solutions we obtain the non-dimensional water table height at the midpoint between the drains, and the non-dimensional discharge of the drains per unit drained area, as functions of non-dimensional time and constants describing the aforementioned drainage conditions. Variation of these functions has also been illustrated graphically in non-dimensional diagrams; these can be used to show the sensitivity to various sets of parameter values and to calculate easily the water table height and the drain discharge in practical problems.

Étude des écoulements souterrains dans le bassin de Bilma-Djado à l'aide des isotopes de l'environnement

Stable ( 2H and 18O)and radioactive isotopes ( 3H and 14C) allow the identification of the pattern of the regional groundwater flow in the Bilma-Djado basin. The general trends of groundwater flow are from the east (Tibesti) to the west (Djado basin), and, to a minor extent, north-south along the Bilma ridge. Another component has been noticed linked to wadis subsurface runoff flowing from Hoggar towards the south-east. The main recharge areas for the aquifers are the Tibesti massif (Holocene recharge) and the eastern border of the Hoggar (present day recharge). The presence of tritium indicates an upward leakage from the Cambro-Ordovician aquifer (2.5 ± 1.0 TU) to the Visean aquifer (1.8 ± 1.0 TU) and the Continental Intercalaire aquifer (2.9 ± 1.0 TU). The main discharges are the direct evaporation of the aquifers and some springs in the border of the Bilma-Djado basin supplied by the Cambrian aquifer. Only in this case, the waters are not affected by the isotopic fractionation effect and lie close to the classical meteoric water line for groundwater recharged during Holocene (5‰).

Geochemistry, origin and recharge mechanisms of groundwaters from the Garoua Sandstone aquifer, northen Cameroon

This paper presents results of the geochemical and isotopic studies on groundwater samples from the Garoua Sandstone Basin, in northern Cameroon. Chemical and environmental isotope data are presented and discussed in terms of the origin of dissolved species and of groundwater. All of the investigated groundwaters are categorized into two chemical types: low mineralized and acidic waters of CaNaHCO 3 type, and relatively high mineralized waters of NaHCO 3 type, with relatively high pH, between 7.40 and 8.22. Interpretation of chemical data, based upon both thermodynamic calculations and stability diagrams, suggests that the chemical evolution of groundwater is primarily controlled by water-rock interactions, involving (1) acidic weathering of aluminosilicates, (2) dissolution of secondary carbonate minerals, and (3) cation exchange of Na + for Ca 2+. However, the original composition of groundwater may have been modified by further secondary processes such as mixing of chemically different water masses, and anthropogenic NO − 3 pollution. Tritium contents in the considered groundwaters are very heterogeneous, suggesting differences in the water turnover time or in the recharge conditions, or both. On the basis of the geographical distribution of 3H contents, a hydrogeological relation between river and the groundwater systems has been proposed for the study site. Interpretation of both 18O and 2H, as well as 3H, suggests that the recharge of the investigated groundwaters may result from three major mechanisms: (1) direct infiltration of local precipitation; (2) lateral inflow of river waters; (3) probably upward leakage of old groundwaters.

Solidification fronts and magmatic evolution

Solidification fronts and magmatic evolution

Roberts Rift, Canyonlands, Utah, A Natural Hydraulic Fracture Caused by Comet or Asteroid Impact

AbstractThe impact that created Upheaval crater in Canyonlands National Park, Utah, is invoked here as the source for energy that simultaneously caused Roberts rift. However, no temporal linkage has been proven between the impact and rifting events.Roberts rift lies between 22 and 32 km northeast of the Upheaval impact crater on a subradial trend. The fissure contains clasts that were carried as much as 1,000 m upward from Paleozoic sources into the Mesozoic section.A plausible model for both the rifting and clast movement involves incremental loading of overpressured fluid compartments in the Pennsylvanian Paradox section and attendant hydraulic fracturing of the overlying confining strata during the impact event. The clasts were proppants entrained in upward moving fluids that originated from overpressured aquifers in the Pennsylvanian section or materials eroded from the fissure walls.Alteration halos and mineralization along the fissure reveal that there was upward leakage of reducing fluids from the overpressured zones following opening of the fissure. The fissure infillings became cemented with time, thus reducing fissure permeabilities to negligible.

Asphaltene-rich residues in sandstone reservoirs of Haltenbanken province, mid-Norwegian continental shelf

Thin zones of asphaltene-rich residue are present near the crests of two adjacent oil- and gas-filled structures. In one structure, the Smørbukk Sør Field, multiple thin (5–50 cm) dark coloured zones are observed within the lower 20 m of the 88 m thick Garn Formation. These dark coloured zones tend to occur immediately above stylolitized mica-clay laminations and become gradually lighter upwards, apparently reflecting gradual upward decrease in residue abundance. In the other structure, the Smørbukk Field, the lowermost 1 m of the formation is dark coloured and the sandstone gradually becomes lighter in colour upwards for a distance of about 3 m. Similar, but more diffuse, residues are also present throughout the oil zone in two other fields nearby. Organic geochemical analyses show that the residue-rich (dark coloured) zones differ from the sorrounding lighter coloured sandstone mainly in having a higher content of asphaltenes, whereas the total content of extractable organic matter is often similar. Thus the darker rocks might be regarded more as zones of conspicuous oil staining due to asphaltene deposition, rather than as small tar mats. The residues typically appear to have accumulated under the influence of gravity at points where the downward flow was hindered by a lithological discontinuity. Present day zonation (upward-decreasing gas to oil ratio) in the oil column of the Smørbukk Sør reservoir is consistent with a model of asphaltene precipitation in the lower part of the reservoir in response to upward leakage of gas from an underlying gas condensate reservoir in the Ile Formation. This is also consistent with the available organic geochemical data. In thin section, the asphaltene-rich material is seen to preferentially coat feldspar and clay but not quartz surfaces, thus illustrating why sandstone wettability should be expected to depend on both mineralogy and the asphaltene content of the petroleum involved.

Measurement of soil gas diffusivity in situ

SummaryAssessment of gas diffusivity in situ gives a direct measure of the ability of soils to exchange gas with minimal soil disturbance. A versatile, readily portable probe for measuring the diffusion of a tracer gas through soil in situ is described. The radioactive tracer 85Kr is injected into a cell located at the end of the probe. The change in activity within the cell as the gas diffuses out is measured by a Geiger‐Muller tube in the cell. The probe can be used by insertion either directly into an auger hole (buried‐probe mode) or into a chamber pushed into the soil surface. A method to simulate diffusion numerically using Fick's equation for both methods of insertion is presented. In the tests reported, diffusivity was estimated by expanding or contracting the time axis of the simulation until it matched the observed count rates. A goodness‐of‐fit was attached to each diffusivity estimate. The probe was generally effective, giving diffusivities comparable to those measured in the laboratory on cores taken near the cell (buried‐probe mode) or linked to the surface chamber. Poor fits were found for some diffusivities measured in the buried‐probe mode on coarsely structured soils. These were attributed to non‐uniform distribution of porosity and possible upward leakage of tracer when used at shallow depths in the buried‐probe mode. However, thein situ diffusivities may be more representative than those measured in cores in the laboratory because of the greater sample volume. We show how the probe can be used to detect soil layers that restrict gas diffusivity and differences in aeration status between tillage treatments.

Interactions between ground water and wetlands, southern shore of Lake Michigan, USA

Wetlands between, and within, dune-beach complexes along the south shore of Lake Michigan are strongly affected by ground water. The hydrogeology of the glacial drift aquifer system in a 26 km 2 area was investigated to determine the effects of ground water on the hydrology and hydrochemistry of Cowles Bog and its adjacent wetlands. The investigation showed that ground water from intermediate- and regional-scale flow systems discharges to Cowles Bog from confined aquifers that underlie the wetland. These flow systems are recharged in moraines south of the dune-beach complexes. Water from the confined aquifers discharges into the surficial aquifer mainly by upward leakage through a buried till sheet that serves as the confining layer. However, the till sheet is breached below a raised peat mound in Cowles Bog, allowing direct upward discharge from the confinef aquifer into the surficial sand, marl, and peat. The shallow ground and wetland water in the area influenced by this leakage is a calcium magnesium bicarbonate type, with low tritium concentrations consistent with mixing of older ground water and more recent precipitation. Ground water and wetland water from surrounding areas are less mineralized and have higher tritium concentrations characteristic of precipitation in the late 1970s. The results of this study suggest that wetlands in complex hydrogeologic settings may be influenced by multiple ground-water flow systems that are affected by geomorphic features, stratigraphic discontinuities, and changes in sediment types. Discharge and recharge zones may both occur in the same wetland. Multidisciplinary studies incorporating hydrological, hydrochemical, geophysical, and sedimentological data are necessary to identify such complexities in wetland hydrology.

Estimation of spatial recharge distribution using environmental isotopes and hydrochemical data, II. Application to Aravaipa Valley in Southern Arizona, U.S.A.

In Part I ∗ ∗ Adar et al. (this volume). a mathematical model was developed to estimate the spatial distribution of annual recharge rates into an aquifer using environmental isotopes and hydrochemical data. In Part II the model is applied to real data from the Aravaipa Valley in southern Arizona. These data suffer from a paucity of hydrologic information but contain numerous isotopic and hydrochemical analyses. The model is able to extract from the available data both qualitative and quantitative information about recharge into, and flow through the shallow unconfined aquifer in the valley. The model shows that this aquifer is replenished primarily by lateral recharge from the pediments and the tributary Stowe Gulch Basin, as well as by upward leakage from the underlying confined aquifer. Recharge from the Aravaipa Creek is relatively minor. Lateral recharge from the eastern pediments into the unconfined aquifer exceeds that from the western pediments by a factor of two. The western pediments are a major source of recharge for the confined aquifer. These results are tentative because independent means to verify them are currently lacking. We are encouraged, however, that the mass balance errors of water and dissolved constituents do not exceed 4%, and that the flow rate obtained from Darcy's law at one location within the unconfined aquifer in which transmissivity is known, agrees with model prediction. While chemical reactions are ignored in the model, some of the isotopic and chemical species show sufficient spatial variability due to mixing to justify the approach. This is supported by analyses of equilibrium water-mineral interactions conducted by WATEQF.

Ground‐Water Flow in the Coastal Plain Aquifers of South Carolina

ABSTRACTThe characteristics of the Coastal Plain aquifers of South Carolina are being studied as a part of the Regional Aquifer System Analysis program of the United States Geological Survey. Potentiometric maps were constructed for the Middendorf aquifer of Cretaceous age and for the Floridan aquifer system and its sand facies equivalent, Tertiary sand aquifer, prior to development. Also constructed was a potentiometric decline map for the period prior to development to November 1982 for the Middendorf aquifer. These maps are used to describe the ground‐water flow system.The Coastal Plain aquifers are recharged primarily by precipitation in their outcrop areas. Ground water flows from these areas of recharge, through the aquifers, and discharges to upper Coastal Plain rivers, overlying aquifers as upward leakage, and wells.Ground‐water flow in the Floridan aquifer system and the Tertiary sand aquifer prior to development is generally perpendicular to the coast. Predevelopment flow in the Cretaceous aquifers, however, turns northeastward as it approaches the coast, almost paralleling the coast. The change in flow direction is caused by less effective intervening confining units, the aquifers being closer to the land surface, and the rivers at lower altitudes farther upstream in the vicinity of the North Carolina/South Carolina State line.Water‐level declines in the Cretaceous aquifers have occurred throughout much of the eastern part of the Coastal Plain of South Carolina due to pumpage in the Myrtle Beach and Florence areas. Large areally extensive water‐level declines have also occurred in the Floridan aquifer system in South Carolina due to pumpage in the Savannah, Georgia area.

Paleohydrologie isotopique de l'Oued el Akarit (sud tunisie) au Pleistocene superieur et a l'Holocene

Previous data from Gobert and Howe, Coque, and Page on the Upper Quaternary deposits from Wadi el Akarit are expanded through radiocarbon and stable isotope measurements ( 18C and 13C from carbonates, 18O and 34S from sulphates). These new results report on detailed stratigraphic profiles and indicate fluviatile and palustrine environments during the late Pleistocene. Vegetal dams linked to spring activity caused water stagnation. Fine-grained sediments were deposited with appreciable amounts of organic matter which locally developed into some peaty levels. In the upper part of the typical cross-section (located on the left bank about 100-m upstream of the railway bridge), Pleistocene deposits show a palustrine carbonate crust. This formation is attributed to the drainage induced by the major marine regression at glacial maximum. During the Holocene stagnation periods still occurred, interrupted by flood episodes marked by bottom transport and coarse deposits. In the typical cross-section, deposits are well drained and oxidized. However, downstream a stagnation episode takes place with a rich malacofauna dominated by Cerastoderma (“Cardium”). The uneven distribution of rainfall is documented by the alternation of fine and coarse deposits, and it is accentuated by the climatic evolution toward aridity which results in the formation of a gypsum crust after 4000 yr. BP. Later, exceptional floods removed sediments from the wadi channel, cutting the Upper Quaternary deposits for about 13 m along the central course of the wadi. Radiocarbon ages on carbonates are discussed according to various possible origins of total dissolved carbon: atmospheric CO 2, organic activity in the basins and aquifer supply. A simple exchange-mixing model between aquifer bicarbonate and atmospheric CO 2 is used for calculations of initial carbonate activities. Chemical, isotopic and hydraulic steady states are assumed in this treatment. Present-day 14C and 13C contents of aquifer bicarbonate are thus adopted for past values. The model leads to acceptable corrected ages for Pleistocene carbonate samples. Corrected ages are younger than apparent ages by a few thousands of years and become consistent with ages given by organic matter from nearby levels. However, Holocene samples appear overcorrected. Their crystallization appears to be controlled by modern organogenic CO 2 Holocene 14C ages are probably correct. 18O contents of carbonate indicate a continental origin for environmental water. Nodules and carbonate concretions crystallized in bottom sediments through upward leakage of confined aquifers. They show 18O contents compatible with present-day stable isotope compositions of artesian springs. This supports the concept of a good time constancy in stable isotope contents. Shell carbonate values indicate a variable evaporation rate from the same initial waters. 18O and 34S contents of gypsums are also compatible with aqueous sulphates from springs. The data set falls within the range of Permo-Triassic sulphate and suggests deep hydraulic connections within aquifer systems. The entire formation appears to be of continental origin. The occurence of “Cardium”-rich basins can only be attributed to the initial salinity of springs waters (7–9 g 1 −1), sightly increased by evaporation. This signifies that one can not deduce any tectonic uplift from their location with respect to sea level.

Hydrogeology of the Syrian steppe and adjoining arid areas

Summary Several major sedimentary basins, in which thick sequences of Palaeogene marls and Neogene-Quaternary sediments have accumulated, can be distinguished in the arid zones which extend from the Great Nefud in Saudi Arabia to the Euphrates river in Syria. Structurally, they represent areas of relative subsidence formed between the Rutbah-Ha'il arch, the Jordan uplift and the Halab uplift. The Syrian steppe and adjoining areas can be subdivided into eastern, western and north-western regional ground-water flow features which follow north-westerly (Palmyrian) and south-south-westerly trends. The eastern regional flow system in the permeable Palaeozoic and Mesozoic strata is related to the development of the broad domal structure of the Rutbah-Ha'il arch. Transmission of flow parallel to a system of north-north-westerly lineaments occurs from the Rutbah area of Iraq to the Wadi-el-Miah area of Syria. Step faulting and the minor anticlinal structures developed in this latter area seem to influence upward leakage from the deeper aquifers into the Cretaceous and Palaeogene chert aquifers. Groundwater transmitted westwards from the Rutbah-Ha'il arch is retarded by the marly facies of the Upper Cretaceous and Palaeogene in the Wadi Sirhan basin. Minor chert aquifers, however, transmit a portion of the flow. Discharge occurs in a zone along the eastern margin of the Wadi Sirhan. The western regional flow system differs from that in the east in that hydraulic interconnection between the upper aquifers with the underlying Mesozoic is negligible. The recharge zone for this system coincides with the higher portion of Jebel-el-Arab. Groundwater transmission in the complex sequence of basaltic sheets of the Syria-Jordan plateau region is controlled by two fracture systems, in addition to the usual lava flow conduits. The north-western regional system is recharged in the Anti-Lebanon and flows south-westwards in fractured limestones and dolomites. Discharge occurs mainly via karstic springs. Upward leakage may occur into the Ghouta gravel aquifer and eventually may be lost by evaporation from Ateibe lake. In the S Palmyrian moutains zone, a flow pattern controlled by linear en-echelon structures transmits groundwater in a north-easterly direction. Discharge from the system takes place at Sabkhet-el-Mouh, south of Palmyra. Hydrogen sulphide water, issuing along the south Palmyrian regional fault system, suggests relatively deep groundwater circulation. Isotopic studies indicate that groundwater age increases along the Palmyrian flow system.

Ground-Water Hydrology Around Salt Domes in the East Texas Basin: A Practical Approach to the Contaminant Transport Problem

Research Article| November 01, 1981 Ground-Water Hydrology Around Salt Domes in the East Texas Basin: A Practical Approach to the Contaminant Transport Problem1 GRAHAM E. FOGG; GRAHAM E. FOGG Bureau of Economic Geology and Department of Geology, The University of Texas, Austin, TX 78712 Search for other works by this author on: GSW Google Scholar CHARLES W. KREITLER CHARLES W. KREITLER Bureau of Economic Geology and Department of Geology, The University of Texas, Austin, TX 78712 Search for other works by this author on: GSW Google Scholar Environmental and Engineering Geoscience (1981) xviii (4): 387–411. https://doi.org/10.2113/gseegeosci.xviii.4.387 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation GRAHAM E. FOGG, CHARLES W. KREITLER; Ground-Water Hydrology Around Salt Domes in the East Texas Basin: A Practical Approach to the Contaminant Transport Problem. Environmental and Engineering Geoscience 1981;; xviii (4): 387–411. doi: https://doi.org/10.2113/gseegeosci.xviii.4.387 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyEnvironmental and Engineering Geoscience Search Advanced Search Abstract Salt domes in the East Texas Basin are being studied as potential sites for deep burial of nuclear wastes. Site selection and risk assessment must address the possible fate of radionuclides should they escape from such a repository. Waste escaping from a dome would, at worst, move into either the Wilcox-Carrizo (Wx-Cz), a thick (~2,000 ft, 600 m), semi-confined, fresh to brackish ground-water system, or the Woodbine Formation, a deeper, saline aquifer. Contaminant transport and destinations would be controlled by: (1) pathways determined by ground-water circulation (i.e., recharge, discharge, and general velocity field), and (2) dilution along pathways, determined by advective dispersion and geochemical attenuation. Because of very large head declines in the Woodbine resulting from hydrocarbon production, potential for upward discharge from the Woodbine to the Wx-Cz appears nonexistent presently. Owing to apparently slow rates of recharge to the Woodbine, its heads may not completely recover for thousands or millions of years after pumping ends. The predominant control on regional ground-water circulation in the Wx-Cz aquifer is topography, which induces downward and upward leakage across the overlying Reklaw aquitard in topographically high and low areas, respectively. Major discharge areas are the Sabine and Trinity Rivers and their tributaries. Fluid pressure versus depth relationships indicate that upward flow components can extend as deep as 1,200 ft (365 m) beneath the Trinity River. Potential impacts of a nuclide escape from Oakwood or Keechi domes into the Wx-Cz would depend in large part on: (1) how deeply recharge occurring over each dome would move contaminants downward, and (2) whether the contaminants would then migrate upward toward discharge areas in the basin due to topographic effects. Orientation of a moderately brackish-water plume extending away from Oakwood dome infers local topographic control on flow but does not appear to. discharge upward. The plume suggests that contaminants escaping from the dome would become significantly diluted within a distance of 5 to 6 mi (9 to 11 km). Details of ground-water circulation around the domes are being analyzed through construction of numerical flow models. Processes of advective dispersion and geochemical attenuation are being investigated by preliminary mapping of aquifer heterogeneities and characterization of aquifer geochemistry by analysis of fluids and core samples. Ground-water chemistry indicates a trend toward greater capacity for attenuation of radionuclides as fluids move from recharge areas into more alkaline, reducing environments in the artesian sections of the Wx-Cz. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.

Reconnaissance geophysical studies of the geothermal system in southern Raft River Valley, Idaho

Gravity, aeromagnetic, and telluric current surveys in the southern Raft River have been used to infer the structure and the general lithology underlying the valley. The gravity data indicate the approximate thickness of the Cenozoic rocks and location of the larger normal faults, and the aeromagnetic data indicate the extent of the major Cenozoic volcanic units. The relative ellipse area contour map compiled from the telluric current survey generally conforms to the gravity map except for lower values in the area of the geothermal system. An area of low apparent resistivity values defined by the audiomagnetotelluric (AMT) survey appears to outline the extent of the geothermal reservoir even though the reservoir is deeper than the penetration of the survey. Self‐potential anomalies relate to near surface hydrology. The Raft River Valley is underlain by about 2 km of Cenozoic rock, most of which is Tertiary sediments of the Salt Lake formation. On the west side of the valley the Tertiary rocks appear to be separated from the underlying Precambrian basement by a low angle fault along which the Tertiary rocks have slid off a buried basement dome. Subsequent normal faults displace both the basement surface and the Tertiary beds. The geothermal system occurs where these north‐trending faults intersect a poorly understood northeast‐trending zone that may be a basement shear zone. Apparently deep circulating water at a temperature of about 150°C rises in the area of this intersection and then spreads laterally in porous zones near the base of the Tertiary rocks to form the geothermal reservoir. Upward leakage from the reservoir produces shallower effects that were measured by the AMT survey.

Resonance characteristics of linear lee waves in an atmosphere of three layers

AbstractThe upward leakage of wave energy from a two‐layer troposphere into the stratosphere is examined; the changes produced in the natural complex modes of the system by altering the parameters are found to give rise to some quasi‐resonance phenomena. Under special circumstances there may exist modes which decay extremely rapidly downstream and these provide a qualitative explanation for some features of observed flows.

Resonance characteristics of linear lee waves in an atmosphere of three layers

The upward leakage of wave energy from a two-layer troposphere into the stratosphere is examined; the changes produced in the natural complex modes of the system by altering the parameters are found to give rise to some quasi-resonance phenomena. Under special circumstances there may exist modes which decay extremely rapidly downstream and these provide a qualitative explanation for some features of observed flows.

The Origin of Chemical Variations in Groundwaters from a Small Watershed in Southwestern Ontario

A very striking and unique feature of the groundwater system within the Upper Kettle Creek watershed is the marked concentration decrease of nearly all ionic species in the direction of flow. The conceptual model proposed here attributes this decrease to selective ion filtration by the Port Stanley till. Ionic constituents generated in the shallow groundwater zone by dissolution of the porous medium either pass through the till or accumulate depending upon their relative mobilities. Other important processes that influence the composition of the groundwaters are cation exchange within the Port Stanley till, CO2 gas generation within the soil zones of recharge areas, and the upward leakage of H2S gas from deeper in the Paleozoic section.