dual porosity mechanism for transient groundwater and gas anomalies induced by external forcing abstract the geochemical response of groundwater to external forcing is studied in a tunnel hosted in fractured gneiss near and above an artificial lake having large water level variations dripping waters have been monitored in two zones characterized by highly different flow rates representing different contributions of water from matrix porosity and fractures transient increases of sulfate and magnesium concentrations observed in both zones are not related to meteorology but associated with radon bursts into the tunnel air this indicates that transient enhancement of conductance with discharges of saline water and radon from the matrix porosity to the fractures is a mechanism able to produce both groundwater and gas anomalies in response to hydrogeological or mechanical processes such as increases in pore pressure or changes in crack geometry besides its applications to environmental issues the proposed discharge mechanism may be relevant for the understanding of geochemical precursors of earthquakes as an alternative to aquifer mixing

chlorofluorocarbon apparent ages of groundwaters from west hawaii usa summary the volcanic coastal aquifers of west hawaii supply drinking water to the area s residents and nutrient rich groundwater discharge to the nearby oligotrophic coastal waters despite the societal and ecological importance of the water in these aquifers very little is known about the ages and recharge areas of the groundwater we therefore determined aquifer recharge areas and groundwater residence times by sampling 18 locations for the oxygen and hydrogen isotopic composition of groundwater and chlorofluorocarbon cfc apparent groundwater ages we sampled water supply wells coastal wells and coastal ponds we applied a 18 o altitude gradient and well established lapse rates to find that groundwater recharge predominantly occurs in the area s maximum rainfall zone furthermore the isotopic data suggest that fog drip contributes to aquifer recharge a single water source model yielded recharge years ranging from the mid 1960s to mid 1980s for ten samples 56 of samples alternatively a simple binary mixing model with one water source recharging before1940 and the other after 1940 indicated that 14 samples 78 of samples contained young water that recharged the aquifer between the mid 1970s and mid 1980s we also find that cfcs can be used to distinguish between water originating from different aquifers in the area

evidence for high salinity of early cretaceous sea water from the chesapeake bay crater chemical isotopic and physical evidence indicate that some of the groundwater in the chesapeake bay crater is remnant early cretaceous north atlantic sea water probably 100 145 million years old with an average salinity of about 70 which is twice that of modern sea water geologists and oceanographers generally have to rely on indirect evidence from the analysis of solid materials in deep sediment cores when estimating temperature and salinity levels of the ancient oceans but now a team from the us geological survey has identified a body of underground water that is actually a remnant of a past ocean water a body of early cretaceous north atlantic sea water deep drilling at the site of the chesapeake bay impact crater has yielded groundwater with an isotope and chemical composition signature that together with model analysis suggests that it was trapped in the sediments before the impact occurred around 35 million years ago the water may have lain undisturbed for much longer it has an average salinity of about 70 parts per thousand twice that of modern sea water and is probably 100 145 million years old high salinity groundwater more than 1 000 metres deep in the atlantic coastal plain of the usa has been documented in several locations1 2 most recently within the 35 million year old chesapeake bay impact crater3 4 5 suggestions for the origin of increased salinity in the crater have included evaporite dissolution6 osmosis6 and evaporation from heating7 associated with the bolide impact here we present chemical isotopic and physical evidence that together indicate that groundwater in the chesapeake crater is remnant early cretaceous north atlantic ecna sea water we find that the sea water is probably 100 145 million years old and that it has an average salinity of about 70 per mil which is twice that of modern sea water and consistent with the nearly closed ecna basin8 previous evidence for temperature and salinity levels of ancient oceans have been estimated indirectly from geochemical isotopic and palaeontological analyses of solid materials in deep sediment cores in contrast our study identifies ancient sea water in situ and provides a direct estimate of its age and salinity moreover we suggest that it is likely that remnants of ecna sea water persist in deep sediments at many locations along the atlantic margin

numerical study of airflow in the unsaturated zone induced by sea tides 1 the air pressures in coastal unsaturated zones fluctuate in response to tidal fluctuations two phase air water flow induced by sea tides in a coastal two layered subsurface system is investigated through numerical simulations the system consists of upper and lower layers with permeabilities of ku and kl respectively a water table exists in the lower layer the study demonstrates that airflow in the unsaturated zone is controlled by permeabilities of both layers and the fluctuation of water level the tide induced water level fluctuation may result in significant air pressure fluctuation in the unsaturated zone in an air confined system that is the permeability of the upper layer is about 2 orders of magnitude lower than that of the lower layer in such an air confined system horizontal airflow is dominant in the lower layer and vertical airflow is dominant in the upper layer the simulation results show that the hydraulic head rather than the sea tide is the direct driving force of the air pressure fluctuation above the water table the study on the relation between the air pressure amplitude and the landward distance demonstrates that the air pressure amplitudes increase to a maximum and then decrease with distance the amplitude of air pressure fluctuation decreases progressively with ku in the lower layer in the upper layer however the amplitude tends to increase with ku when ku is very low and decrease with ku when ku is relatively high overall the air flux fluctuations across the atmosphere soil interface attenuate landward gradually and this attenuation becomes faster as the permeability of the upper layer increases

atmospheric pumping a mechanism causing vertical transport of contaminated gases through fractured permeable media as the barometer falls gases are drawn upward out of the permeable earth into the atmosphere conversely a rising barometer pushes air downward in a homogeneous permeable medium these cyclical gas motions are piston like and nearly reversible so they contribute only modestly to the net transport of contaminant gases in a fractured permeable medium however the fractures will generally serve as breathing passages for all of the gas filled porosity greatly increasing the amplitude and nonuniformity of vertical motions the resulting transport process may be orders of magnitude more significant than molecular diffusion according to the theoretical analysis presented here analytical solutions are first derived for the sinusoidal pressure response of a medium containing identical vertical fractures equally spaced by slabs of permeable matrix material these solutions are then used to constrain the relationship between fracture aperture and fracture spacing based on field comparisons between surface and subsurface pressure variations the final phase of the analysis addresses the diffusive and advective transport of an inert trace gas which is carried by an oscillatory flow along a fracture having permeable walls a maximum rate of transport is predicted to occur for an intermediate fracture spacing which is typically a few meters

forward and back diffusion through argillaceous formations the exchange of solutes between aquifers and lower permeability argillaceous formations is of considerable interest for solute and contaminant fate and transport we present a synthesis of analytical solutions for solute diffusion between aquifers and single aquitard systems validated in well controlled experiments and applied to several datasets from laboratory and field scale problems with diffusion time and length scales ranging from 10 2 108 years and 10 2 102 m one dimensional diffusion models were applied using the method of images to consider the general cases of a finite aquitard bounded by two aquifers at the top and bottom or a semi infinite aquitard bounded by an aquifer the simpler semi infinite equations are appropriate for all domains with dimensionless relative diffusion length zd 0 7 at dimensionless length scales above this threshold application of semi infinite equations to aquitards of finite thickness leads to increasing errors and solutions based on the method of images are required measured resident solute concentration profiles in aquitards and flux averaged solute concentrations in surrounding aquifers were accurately modeled by appropriately accounting for generalized dynamic aquifer aquitard boundary conditions including concentration gradient reversals dimensionless diffusion length scales were used to illustrate the transferability of these relatively simple models to physical systems with dimensions that spanned 10 orders of magnitude the results of this study offer guidance on the application of a simplified analytical approach to environmentally important layered problems with one or two diffusion interfaces

gas transport in a confined unsaturated zone during atmospheric pressure cycles gas transport induced by temporal pressure fluctuations in the atmosphere can be an important mechanism for transport of atmospheric oxygen within the unsaturated zone moreover the presence of oxygen in the unsaturated zone may be a factor controlling oxidation of sulphide minerals and other redox processes a field study was carried out in a glacial aquifer with a 10 12 m thick sandy unsaturated zone to explore gas exchange between the atmosphere and the unsaturated zone the exchange occurs through a geological window in a till layer which covers the sandy unsaturated zone observed pressure distribution and oxygen concentrations within the unsaturated zone were compared to numerical simulations with sutra a finite element and fluid density dependent groundwater flow model the simulations were carried out by modeling the gas pressure distribution within the unsaturated zone based on atmospheric pressure time series the spatial variation in permeability observed from borehole logging was implemented in the model the analysis demonstrated a good match between the field observations and the numerical simulations during an atmospheric pressure cycle atmospheric oxygen migrated more than 10 md 1 horizontally in the capped unsaturated zone the analysis shows that both the amplitude and the length of the period of pressure variations are important for the transport of oxygen and it shows that the combined effects determine the extent of a subsurface zone where atmospheric oxygen can reach

time lapse seismic monitoring some shortcomings in nonuniform processing conceptually repeat or time lapse seismic monitoring is straightforward seismic data sets acquired at different times are calibrated compared and the intersurvey differences analyzed and interpreted in terms of fluid changes or movement

thermal convection of soil air on hillsides although diffusion is usually considered to be the main transport process for volatile constituents in the unsaturated zone of soils and other surficial materials an alternative process of thermally driven convection may be significant especially on hillsides and over irregular bedrock convection in this mode is driven by buoyancy forces arising from differences in soil air density in a temperature gradient for bodies with sloping boundaries the conventional rayleigh criterion is not directly applicable so that flow of air is possible in a wide variety of situations numerical simulations for several simple cases show that air convection is expected within relatively permeable materials such as sandy soils gravel deposits and talus on slopes

determining fault permeability from subsurface barometric pressure measured barometric pressure fluctuations in a borehole drilled 600 m into the unsaturated zone at a site on the eastern slope of yucca mountain nevada are used to compute pneumatic diffusivities and air permeabilities of layered tuffaceous rocks of particular interest is the occurrence of increasing pressure amplitude and decreasing phase lags observed at several deep stations the pressure amplitude increases by 13 and the pressure peak arrives 65 to 72 h earlier as the depth of the unsaturated zone increases from 407 to 436 m this observation is inconsistent with a conventional 1d downward pressure decay model but can be explained by hypothesizing the existence of a lateral pneumatic flow path from a nearby fault a 2d numerical model has been constructed to test this lateral flow hypothesis the modeling results indicate that a leaky fault hypothesis can reconcile the measured barometric data with other geologic mapping and permeability measurements at the site the inferred fault permeability r

three dimensional characterization of a fractured granite and transport properties a three dimensional fracture network in a granite block is reconstructed from a series of experimental serial sections it is visualized and its most important geometrical characteristics are studied namely the orientation of the fractures the connectivity of the fractures the number of cycles per unit volume the distributions of surface areas and of the intersection lengths and the number of finite solid blocks isolated in the solid matrix by the network though the network mostly consists of two families of fractures it is interesting to note that a simple model of randomly oriented monodisperse hexagons often yields a good order of magnitude for the various geometrical properties which have been measured on the real block the flow properties are then studied examples of velocity field are provided as well as histograms of velocities the permeability tensor is determined and is found to be in good agreement with snow s formula finally dispersion is analyzed by means of a random walk method histograms of arrival times are provided and interpreted in terms of dispersion tensor

geometry percolation and transport properties of fracture networks derived from line data summary in most geological instances 2 d or 3 d fracture distributions are not available from field data we show here that when data relative to fractures are collected along a line such as a road or a well estimations can be given to the major geometrical properties of the corresponding fracture networks such as the volumetric density of fractures their percolation character and their macroscopic permeability all these formulae are analytical and can be split into two parts the first one can be derived from the measured data while the second one requires some assumption on the lateral extension of the fractures and on their permeability all these techniques are applied to fractures located in the baget watershed they are also validated on a granite block whose structure is fully known extensions are proposed for networks with variable permeabilities and polydisperse fractures

controls on the long term downward transport of δ h of water in a regionally extensive two layered aquitard system 1 seven high resolution 0 3 0 6 m depth intervals 1 d vertical profiles of the h of pore water were collected across a 300 km2 study area in southern saskatchewan canada to define the vertical controls on solute transport in a 120 m thick two layered aquitard system the 1 d profiles were augmented with an existing h profile collected from a previous study the surficial aquitard in the area consists of quaternary deposits either glacial till or lacustrine deposits 13 to 128 m thick underlain by an upper cretaceous claystone aquitard 80 110 m thick the shape of the individual h profiles and associated 1 d transport modeling suggest diffusion is the regionally dominant vertical transport mechanism across the aquitards the profile shape is controlled by the thickness of the quaternary deposit and the h value at the upper boundary which coincides with the depth of the water table the upper boundary h value varies considerably across the area 149 to 101 perhaps due to differences in local hydrological conditions e g slope aspect infiltration across the landscape modeling of all profiles shows the timing for till deposition and the timing of climate change during the holocene are consistent across the area 30 ka and 7 10 ka before the present respectively corroborating other studies this study provides insights into the hydrogeologic controls on solute transport in an aquitard system and associated geologic and climatic changes for a prairie region over the past 30 ka and improves our understanding of initial and time dependent transport boundary conditions for the study of aquitards

fractal geometries of vein systems and the variation of scalingrelationships with mechanism abstract investigation of vein geometries has identified empirical relationships which allow extrapolation of outcrop scale observation to larger scales measurements of vein shapes and aspect ratios in a number of different environments demonstrate that veins follow similar empirical scaling laws to those of faults geometries of veins are easier to characterise accurately than faults because their thickness is related to the variation in displacement from zero at their tips to a maximum at their thickest point vein sizes obey the empirical relationship l kta where l length in mm t thickness in mm 20 1 this suggests that veins amplify initially by inflation and subsequently by elongation

trace analysis for fracture networks of any convex shape 1 statistical properties of traces of fracture networks are related to the fracture volumetric density and to the average fracture surface and perimeter these relations which hold whatever the fracture shapes provided that they are convex can be extended to anisotropic networks these relations can be used to check the statistical consistency of field data and to obtain macroscopic quantities such as the dimensionless density which controls the geometric and transport properties of fractured media a field example of anisotropic subvertical fractures whose sizes obey a power law is analyzed along these lines

repeatability issues of 3 d vsp data increased repeatability is recognized as one major issue for improving the time lapse seismic technology as a reservoir management tool a 3 d vertical seismic profiling vsp data set acquired over a period of two days is used to analyze how repeatable a permanent installed geophone array can be and how repeatability changes with inaccuracies in source positioning it is found that for a frequency range between 3 5 and 50 hz the difference root mean square rms level between two recorded traces belonging to two different shots is about 8 this fact shows that there is a potential for acquiring very accurate time lapse seismic data by using a permanently installed downhole geophone array repeatability variation with increasing shot separation distances is analyzed showing a rapid decrease in repeatability as the accuracy of the positioning of the repeat survey decreases horizontal geophone components show approximately the same degree of repeatability compared to the vertical component but horizontal geophone data is slightly more sensitive to positioning errors the results show that repeated 3 d vsp surveys preferably using permanently installed geophone arrays might be an efficient tool for detailed and precise monitoring of fluid and pressure changes within a hydrocarbon reservoir

stereological analysis of fractures in the roselend tunnel and permeability determination 1 fracture traces and water fluxes have been determined along the 128 m long roselend tunnel french alps fractures can be classified into two families large fractures which intersect the tunnel and small fractures which partially intersect it three different zones in the tunnel are distinguished with mild low and high water fluxes starting from the entrance a stereological analysis of the trace length probability densities of small fractures provides the fracture diameter probability density distribution which is best approximated by a power law large fractures are assumed monodisperse with a 5 m estimated radius the generated fracture networks obtained by combining large and small fractures do percolate while networks consisting of only small fractures do not percolate computed macroscopic permeabilities of the fracture networks are in agreement with the observed water fluxes when the fracture permeability is a power law of its lateral extent with an exponent equal to 3

contaminant transport in layered porous media 2 applications in a companion paper analytical solutions describing the fate of a solute in a layered aquifer system are given in the study presented here these closed form solutions are utilized in solution of several problems of relevance to layered aquifer analysis initially the example problems discussed here are primarily chosen for the purpose of verification of some of these analytical solutions these applications are later extended to other aquifer aquitard configurations to demonstrate the range of problems that may be analyzed using these procedures thus in this sense the problems discussed here cover only a sample of cases which may be studied utilizing the solutions developed earlier in the examples discussed here the importance of advective transport in the vertical direction is emphasized for contaminant transport analysis in a layered system

fracture size estimation using data from multiple boreholes abstract the size of a fracture within a rock mass can be obtained using data sampled from boreholes or exposed surfaces in this study fracture sizes are estimated using data from multiple boreholes the fractures are assumed to be elliptical all having the same aspect ratio but not necessarily occurring parallel to each other formulae for estimating the mean and standard deviation of the characteristic fracture size are developed by considering the number of intersections between the fractures and the boreholes a method is proposed to infer the probability density function of the fracture size from the number of fractures which is obtained by random sampling of fractures in adjacent boreholes the fracture distribution is assumed to follow the form of a fractal exponential or lognormal distribution the performance of the method is validated using monte carlo simulations with different inputs of size distribution fracture density orientation and mean fracture size

geostatistical inverse modeling for the characterization of aquitard heterogeneity using long term multi extensometer data abstract the classical aquitard drainage model compac was used to simulate the deformation of a one dimensional vertically heterogeneous aquitard i e heter compac by coupling heter compac with the quasi linear geostatistical inversion approach the vertical heterogeneities of hydraulic conductivity k v elastic specific storage s ske and inelastic specific storage s skp fields could be characterized with the availability of long term multi extensometer data the methodology was first tested through a group of ten synthetic cases with randomly generated k v s ske and s skp fields results of the synthetic cases revealed that a geostatistical model could characterize the variability of aquitard hydraulic parameter fields and yields improved fits of simulated versus observed zone deformation than a geological model that treats each zone to be homogeneous subsequently the methodology was applied to a research site situated in changzhou city jiangsu province china where long term deformation behaviors of the strata within the aquifer aquitard system have been monitored vertical heterogeneities of k v s ske and s skp fields of the investigated aquitard at the site were characterized using the quasi linear geostatistical approach the correlation length of the three fields that yielded the best quality fit was assessed to be approximately 50 m and the fitting quality was slightly improved in comparison with that produced from calibrating a geological or zonation model through monte carlo analysis of aquitard deformation utilizing the inversed parameters and corresponding uncertainties the investigated aquitard is estimated to have compacted 914 8 42 6 mm before the rise in groundwater levels in adjoining aquifers

interpreting noble gas concentrations as proxies for salinity and temperature in the world s largest soda lake lake van turkey in this work we present noble gas concentration profiles measured in the water column and in the sediment pore water of the earth s largest soda lake lake van eastern anatolia turkey the concentrations of noble gases in particular ar kr and xe in the water body deviate significantly from the expected equilibrium concentrations calculated from the in situ temperature and salinity using existing solubility functions for seawater the specific chemical composition of the water of the soda lake seems to be responsible for the observed deviations our measurements allow the identification and quantification of salinity factors that can be applied to correctly calculate the noble gas equilibrium concentrations for the lake these salinity factors provide a solid and robust empirical basis for the interpretation of noble gas concentration signals measured in the sediment pore water of lake van in terms of palaeosalinity and palaeotemperature

fractal relations for the diameter and trace length of disc shaped fractures analytic relations are developed between the fractal parameters of a random isotropic population of disc shaped fractures and the parameters of the corresponding population of fracture traces expressed in outcrop these relations indicate that a fractal distribution of fracture diameters translates to a fractal distribution of trace lengths and that the parameters for diameter may be uniquely determined from the parameters for trace length probabilistic results demonstrate the accuracy of the analytic relations and identify nonideal behaviors at the limits of the computed trace length data it is expected that these relations will be useful in the three dimensional characterization of fracture systems in rock from in situ trace length data

fracture size and transmissivity correlations implications for transport simulations in sparse three dimensional discrete fracture networks following a truncated power law distribution of fracture size we characterize how different fracture size transmissivity relationships influence flow and transport simulations through sparse three dimensional discrete fracture networks although it is generally accepted that there is a positive correlation between a fracture s size and its transmissivity aperture the functional form of that relationship remains a matter of debate relationships that assume perfect correlation semi correlation and non correlation between the two have been proposed to study the impact that adopting one of these relationships has on transport properties we generate multiple sparse fracture networks composed of circular fractures whose radii follow a truncated power law distribution the distribution of transmissivities are selected so that the mean transmissivity of the fracture networks are the same and the distributions of aperture and transmissivity in models that include a stochastic term are also the same we observe that adopting a correlation between a fracture size and its transmissivity leads to earlier breakthrough times and higher effective permeability when compared to networks where no correlation is used while fracture network geometry plays the principal role in determining where transport occurs within the network the relationship between size and transmissivity controls the flow speed these observations indicate dfn modelers should be aware that breakthrough times and effective permeabilities can be strongly influenced by such a relationship in addition to fracture and network statistics this article is protected by copyright all rights reserved

an analytical solution of two dimensional reactive solute transport in an aquifer aquitard system 1 this article presents an analytical study of two dimensional reactive solute transport in an aquifer aquitard system advection longitudinal and vertical dispersion first order irreversible decay and linear sorption are included for aquifer transport advection vertical diffusion first order irreversible decay and linear sorption are considered for aquitard transport this study solves transport equations in the aquifer and aquitards simultaneously and maintains continuities of concentration and mass flux at the aquifer aquitard interfaces the transport equations are first solved in laplace domain and the solutions are then inverted numerically to yield solutions in the real time domain the zhan solution concentration profiles in the aquifer and the aquitards are obtained and mass transported to the aquitards is also calculated closed form steady state solutions of concentration and mass have been obtained the zhan solution is compared with solutions derived with the averaged volumetric sink source approach the aa solution the aa solution substantially overestimates the concentration and the mass in the upper aquitard when an upward velocity exists in the aquitard the penetrating depths of the solute in the aquitard are similar for the aa solution and the zhan solution

from field data to fracture network modeling an example incorporating spatial structure this paper describes a technique for processing field data for a fracture network model which accounts for the observed spatial variability this has been done by generating a network subregion by subregion where the properties of each subregion are predicted through geostatistics once the geometry of a particular realization is specified flow through the network is studied we develop the method for a two dimensional analysis based on data from fanay augeres a uranium mine in france we plan to extend the analysis to three dimensions and compare the results with in situ test results in particular we have focused on the data collected in a long section of a drift where fractures have been mapped and steady state permeability tests have been performed in 10 boreholes in order to generate fractures in a statistically heterogeneous region we first divided the region into statistically homogeneous subregions in each subregion and for each fracture set we must specify the areal fracture density and the orientation length and aperture distributions we divided the fractures into five sets based on tectonic history and observed that for each set fractures spaced close together tended to have similar orientations this was built into the simulation an estimate of the aperture distribution for each set was made by assuming that the hydraulic apertures of the fractures intersecting a well test zone were proportional to the fracture opening observed in the core data input to the geostatistical analysis for each set consisted of 16 values of mean length and density of fractures in each 5 m by 2 m section of the drift wall the results of the simulation are tables of values for mean length and fracture density for each of the five sets the value of density simulated for each subregion was used directly to determine the number of fractures to be generated of that set in the subregion the value of mean length was used as the mean of the length distribution in the subregion the local coefficient of variation for length was the same in every subregion using the data described above we generated a 100 m by 100 m fracture network in a series of 100 statistically homogeneous subregions the fractured region generated has a total of 65 740 fractures a 70 m by 70 m region was isolated for directional permeability testing results show that the system is barely connected about 0 1 of the fractures essentially control permeability in the language of percolation theory this mesh is close to the critical density for which infinite clusters of fractures are found problems remaining include that 1 the analysis should be extended to three dimensions 2 the geostatistical simulation and network simulation should be combined rather than used as two separate operations and 3 the nature of flow through single fractures at fanay augeres should be investigated

co2 dynamics in the amargosa desert fluxes and isotopic speciation in a deep unsaturated zone 1 natural unsaturated zone gas profiles at the u s geological survey s amargosa desert research site near beatty nevada reveal the presence of two physically and isotopically distinct co2 sources one shallow and one deep the shallow source derives from seasonally variable autotrophic and heterotrophic respiration in the root zone scanning electron micrograph results indicate that at least part of the deep co2 source is associated with calcite precipitation at the 110 m deep water table we use a geochemical gas diffusion model to explore processes of co2 production and behavior in the unsaturated zone the individual isotopic species 12co2 13co2 and 14co2 are treated as separate chemical components that diffuse and react independently steady state model solutions constrained by the measured 13c in co2 and 14c in co2 profiles indicate that the shallow co2 source from root and microbial respiration composes 97 of the annual average total co2 production at this arid site despite the small contribution from deep co2 production amounting to 0 1 mol m 2 yr 1 upward diffusion from depth strongly influences the distribution of co2 and carbon isotopes in the deep unsaturated zone in addition to diffusion from deep co2 production 14c exchange with a sorbed co2 phase is indicated by the modeled 14c profiles confirming previous work the new model of carbon isotopic profiles provides a quantitative approach for evaluating fluxes of carbon under natural conditions in deep unsaturated zones

multisensor streamer recording and its implications for time lapse seismic and repeatability abstract effective time lapse or 4d processing seeks to extract the 4d signature with minimal background noise to help understand reservoir behavior in the production phase and to optimize producer and injector well placement nonrepeatability of source and sensor positions in the presence of overburden heterogeneity limits our ability to repeat seismic data and to deliver 4d signals with low background noise levels to compensate for imperfect receiver repositioning wavefield regularization techniques can enable wavefield matching on a grid common to both data vintages often there is a trade off between reducing the receiver positioning mismatch and crossline interpolation error from wavefield spatial aliasing through the use of towed multisensor marine seismic streamers that record collocated pressure p and acceleration measurements y and z and the application of a matching pursuit interpolation technique a 3d dealiased reconstructed and deghosted pressure wavefield can be obtained on a dens

time lapse monitoring of the duri steamflood a pilot and case study this article describes a successful 4 d seismic pilot project in duri field indonesia the site of the world s largest steamflood two baseline and six monitor 3 d seismic surveys were recorded over the same steam injection pattern between 1992 and 1995 seismic analysis thermal simulation and acoustic modeling show the engineering relevance of these data and provide new insights into the seismic response of reservoirs during active steamflooding analyses of the data demonstrate that for the duri steamflood the horizontal and vertical distribution of steam can be tracked over time

overburden complexity and repeatability of seismic data impacts of positioning errors at the oseberg field north sea repeatability of seismic data plays a crucial role in time lapse seismic analysis there are several factors that can decrease the repeatability such as positioning errors varying tide source variations velocity changes in the water layer marine data and undesired effects of various processing steps in this work the complexity of overburden structure as an inherent parameter that can affect the repeatability is studied a multi azimuth three dimensional vertical seismic profiling data set with 10 000 shots is used to study the relationship between overburden structure and repeatability of seismic data in most repeatability studies two data sets are compared but here a single data set has been used because a significant proportion of the 10 000 shots are so close to each other that a repeatability versus positioning error is possible we find that the repeatability decreases by a factor of approximately 2 under an overburden lens furthermore we find that the x and y components have approximately the same sensitivity to positioning errors as the z component for the same events in this three dimensional vertical seismic profiling experiment this indicates that in an area with complex overburden positioning errors between monitor and base seismic surveys are significantly more critical than outside such an area this study is based on a three dimensional three component vertical seismic profiling data set from a north sea reservoir and care should be taken when extrapolating these observations into a general four dimensional framework

detectability and significance of 12 hr barometric tide in radon 222 signal dripwater flow rate air temperature and carbon dioxide concentration in an underground tunnel summary searching for small periodic signals such as the 12 hr s2 barometric tide and monitoring their amplitude as a function of time can provide important clues on the complex processes affecting fluid transport in unsaturated fractured media under multiple influences here first we show that a modified spectrogram analysis msa is more efficient than simple fourier transform to reveal weak periodic signals secondly we show how transient periodic signals can be monitored as a function of time using spectrograms these methods are applied to time series of radon and carbon dioxide concentration dripwater flow rates and air temperature measured during several years in the roselend dead end tunnel located in the french alps near an artificial lake a weak s2 line is evidenced in radon concentration with enhanced amplitude during transient radon bursts similarly the s2 line is observed using msa in dripwater flow rates which sample mainly fracture flow as suggested by a hydrochemical analysis while it is not seen in dripwater flow rates sampling matrix flow in the absence of a strong 24 hr line the presence of a s2 line suggests sensitivity to barometric pressure and thus a significant advective contribution in radon and some dripwater transport no s2 line is observed in the carbon dioxide time series the temporal structure of the s2 component however is not similar in the radon concentration and the dripwater flow rates suggesting in particular that dripwater does not play a significant role in the generation of radon bursts temperature time series exhibit a significant s2 contribution induced by atmospheric pressure spatially organised in the tunnel decreasing vertically upwards a remarkable transient temperature inversion during radon bursts suggests that the additional advective air contributions responsible for the radon bursts occur from the non saturated rocks below the tunnel

fidelity and repeatability of wave fields reconstructed from multicomponent streamer data wave field reconstruction the estimation of a three dimensional 3d wave field representing upgoing downgoing or the combined total pressure at an arbitrary point within a marine streamer array is enabled by simultaneous measurements of the crossline and vertical components of particle acceleration in addition to pressure in a multicomponent marine streamer we examine a repeated sail line of north sea data acquired by a prototype multicomponent towed streamer array for both wave field reconstruction fidelity or accuracy and reconstruction repeatability data from six cables finely sampled in line but spaced at 75 m crossline are reconstructed and placed on a rectangular data grid uniformly spaced at 6 25 m in line and crossline benchmarks are generated using recorded pressure data and compared with wave fields reconstructed from pressure alone and from combinations of pressure crossline acceleration and vertical acceleration we find that reconstruction using pressure and both crossline and vertical acceleration has excellent fidelity recapturing highly aliased diffractions that are lost by interpolation of pressure only data we model wave field reconstruction error as a linear function of distance from the nearest physical sensor and find for this data set with some mismatched shot positions that the reconstructed wave field error sensitivity to sensor mispositioning is one third that of the recorded wave field sensitivity multicomponent reconstruction is also more repeatable outperforming single component reconstruction in which wave field mismatch correlates with geometry mismatch we find that adequate repeatability may mask poor reconstruction fidelity and that aliased reconstructions will repeat if the survey geometry repeats although the multicomponent 3d data have only 500min line aperture limiting the attenuation of non repeating multiples the level of repeatability achieved is extremely encouraging compared to full aperture pressureonly time lapse data sets at an equivalent stage of processing

contaminant transport in layered porous media 1 general solution analysis of transport of contaminants in a layered aquifer system still poses significant challenges although considerable progress has been made in the literature toward the understanding of this problem in this study an analytical approach is chosen as the mode of analysis and a closed form solution is developed for a quasi three dimensional advective diffusion equation defined for a layered aquifer the layered aquifer is idealized as an aquifer aquitard system in which the solution domain is considered to be finite and two dimensional in the aquifer region and infinite and one dimensional in the adjacent aquitards the analytical solution outlined emphasizes the advection of contaminant in the longitudinal direction in the aquifer and also in the transverse vertical direction in the aquiferaquitard system the analytical solution also includes the two dimensional diffusion of the contaminant in the aquifer one dimensional diffusion in the aquitards and first order reaction and retardation terms in both aquifer and aquitards

characterization of leaky faults study of air flow in faulted vadose zones characterization of leaky faults in vadose zones of large thickness is very important for engineering problems such as high level nuclear waste disposal this paper presents analytical solutions for air flow in faulted vadose zones of large or small thicknesses the focus is on those sites where the fault zone is more permeable than its adjacent rock matrix on the basis of the assumptions of a two dimensional air flow in the matrix and a one dimensional air flow in the fault zone analytical solutions are presented for a sinusoidal atmospheric pressure variation a procedure is then provided for extending the application of the solutions to an arbitrary atmospheric pressure variation the solutions can help determine air permeability of leaky faults in the vadose zone

groundwater geochemistry of the chihuahua city region in the rio conchos basin northern mexico and implications for water resources management the chihuahua city region located in the semiarid arid northern highlands of mexico has experienced intensive groundwater abstraction during the last 40 years to meet water demands in the region a geochemical survey was carried out to investigate the evolution from baseline to modern conditions of a 130 km flow path including the el sauz chihuahua aldama san diego de alcala regions the research approach included the use of major chemical elements chlorofluorocarbons and environmental isotope 18o 2h 13c and 14c tracers stable isotopes indicate that groundwater evolves from the evaporation of local rainfall and surface water groundwater located at the lower end of the flow section is up to 6000 years old and older groundwater in the order of 9000 years bp was found in a deep well located in the upper part of the flow system implying contribution from a neighbour basin the background groundwater chemistry upstream of chihuahua city results from feldspar weathering beyond chihuahua city the chemical conditions are strongly modified owing to disposal of sewage from public and industrial water supplies into the rio chuviscar subsequent allocation of this water to agricultural irrigation areas and direct infiltration under the river bed as a consequence anions like chloride and sulphate are mainly related to surface sources nitrate is controlled in part by sewage from public supply and industry and in part by agricultural practices arsenic and fluoride are related to weathering of rock formations of local mineralized ranges and subsequent enrichment of the basin fill by magmatic processes the results of this study have implications for groundwater management in an arid region that depends entirely on groundwater for domestic industrial and agricultural water consumption copyright 2008 john wiley sons ltd

thermal fractionation of air in polar firn by seasonal temperature gradients 1 air withdrawn from the top 5 15 m of the polar snowpack firn shows anomalous enrichment of heavy gases during summer including inert gases following earlier work we ascribe this to thermal diffusion the tendency of a gas mixture to separate in a temperature gradient with heavier molecules migrating toward colder regions summer warmth creates a temperature gradient in the top few meters of the firn due to the thermal inertia of the underlying firn and causes gas fractionation by thermal diffusion here we explore and quantify this process further in order to 1 correct for bias caused by thermal diffusion in firn air and ice core air isotope records 2 help calibrate a new technique for measuring temperature change in ice core gas records based on thermal diffusion severinghaus et al 1998 and 3 address whether air in polar snow convects during winter and if so whether it creates a rectification of seasonality that could bias the ice core record we sampled air at 2 m depth intervals from the top 15 m of the firn at two antarctic sites siple dome and south pole including a winter sampling at the pole we analyzed 15n 14n 40ar 36ar 40ar 38ar 18o 16o of o2 o2 n2 84kr 36ar and 132xe 36ar the results show the expected pattern of fractionation and match a gas diffusion model based on first principles to within 30 although absolute values of thermal diffusion sensitivities cannot be determined from the data with precision relative values of different gas pairs may at siple dome 40ar 4 is 66 2 as sensitive to thermal diffusion as 15n in agreement with laboratory calibration 18o 2 is 83 3 and 84kr 48 is 33 3 as sensitive as 15n the corresponding figures for summer south pole are 64 2 81 3 and 34 3 accounting for atmospheric change the figure for o2 n2 4 is 90 3 at siple dome winter south pole shows a strong depletion of heavy gases as expected however the data do not fit the model well in the deeper part of the profile and yield a systematic drift with depth in relative thermal diffusion sensitivities except for kr constant at 34 4 suggesting the action of some other process that is not currently understood no evidence for wintertime convection or a rectifier effect is seen

determination of fluid flow properties from the response of water levels in wells to atmospheric loading the water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading the magnitude and character of this response is partly governed by the well radius the lateral hydraulic diffusivity of the aquifer the thickness and vertical pneumatic diffusivity of the unsaturated zone and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer these key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response in many cases the response of a well to atmospheric loading can be broken up into a high intermediate and low frequency response the high frequency response is governed largely by the well radius and lateral diffusivity of the aquifer the intermediate frequency response is governed by the loading efficiency of the aquifer the low frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer cross spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters these estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone the lateral permeability of the aquifer and the composite vertical hydraulic diffusivity of the overlying saturated materials

origin age and movement of pore water in argillaceous quaternary deposits at four sites in southwestern ontario hydrogeologic information in the form of textural properties field and laboratory determined hydraulic conductivity values vertical hydraulic gradients from piezometer nests and major ion and isotopic contents 18o 2h 3h 13c 14c was obtained from four sites located in southwestern ontario on thick deposits of clayey till and glaciolacustrine clay at each site the piezometers were installed from the water table zone situated 1 4 m below the surface to a maximum depth between 20 and 35 m below the surface values of hydraulic conductivity determined in the laboratory by consolidometer and triaxial methods are in the order of 10 8 10 7 cm s and are similar to values calculated from rates of water level rise in piezometers mean values of average vertical groundwater velocity calculated with the measured values of hydraulic conductivity porosity and hydraulic gradient using the darcy equation for a saturated non fractured porous medium range from 0 13 to 0 26 cm yr tritiated pore waters only occur within 3 6 m of ground surface thereby indicating that groundwaters below this depth recharged prior to at least 1952 18o in the pore waters exhibit a distinctive regular shift with depth from water table values of 9 to 10 smow characteristic of present day precipitation to values between 14 and 17 at depths of 20 40 m which are characteristic of much cooler waters corrected 14c ages of the groundwater are greater than 8000 yr b p thereby suggesting that the groundwaters at depth entered these deposits during or after the formation of these deposits approximately 11 000 to 14 000 yr ago 18o 2h and cl concentration profiles were simulated with a one dimensional model for transport by advection and diffusion in a saturated porous medium reasonable agreement between the model and the field profiles was obtained with values of effective diffusion coefficients of 3 0 10 6 cm2 s for 18o 2h and cl and with groundwater velocities between 0 03 to 0 05 cm yr based on these results it is concluded that the pore water in these deposits is a mixture of late pleistocene and modern waters and that the distribution of 18c 2h and cl in these deposits is influenced predominantly by molecular diffusion apparently more so than by hydraulic flow

stereological analysis of fracture network structure in geological formations relationships between three dimensional fracture networks consisting of poly disperse disks and the corresponding two dimensional trace maps are systematically analyzed bulk densities of disks and disk intersections are related to surface densities of traces and trace intersections this results in a new relation for the average length of disk intersections the probability densities of trace lengths and disk intersections are studied for several disk diameter distributions the inverse problem of deriving the disk distribution from the trace distribution is then solved assuming only that the disks have uniformly random locations and orientations these results are applied to a variety of synthetically generated data as well as to several sets of field data analysis of the field data suggests that fracture diameter distributions follow a power law in agreement with previous conclusions based on trace length histograms with exponents varying from 1 3 to 2 1

a proven method for acquiring highly repeatable towed streamer seismic data seismic reservoir monitoring has become an important tool in the management of many fields monitoring subtle changes in the seismic properties of a reservoir caused by production places strong demands on seismic repeatability a lack of repeatability limits how frequently reservoir changes can be monitored or the applicability of seismic monitoring at all in this paper we show that towing many streamers with narrow separation combined with cross line interpolation of data onto predefined sail lines can give highly repeatable marine seismic data results from two controlled zero time lag monitoring experiments in the north sea demonstrate high sensitivity to changing water level and variations in lateral positions after corrections by deterministic tidal time shifts and spatial interpolation of the irregularly sampled streamer data relative rms difference amplitude levels are as low as 12 for a deep structurally complex field and as low as 6 for a shallow structurally simple field reducing the deg

plume persistence due to aquitard back diffusion following dense nonaqueous phase liquid source removal or isolation 1 at an industrial site on a sand aquifer overlying a clayey silt aquitard in connecticut a zone of trichloroethylene dense nonaqueous phase liquid dnapl at the aquifer bottom was isolated in late 1994 by installation of a steel sheet piling enclosure in response to this dnapl isolation three aquifer monitoring wells located approximately 330 m downgradient exhibited strong tce declines over the next 2 3 years from trichloroethylene tce concentrations between 5000 and 30 000 g l to values leveling off between 200 and 2000 g l tce concentrations from analysis of vertical cores from the aquitard below the plume and also from depth discrete multilevel systems in the aquifer sampled in 2000 were represented in a numerical model this shows that vertical back diffusion from the aquitard combined with horizontal advection and vertical transverse dispersion account for the tce distribution in the aquifer and that the aquifer tce will remain much above the mcl for centuries

natural tracer profiles across argillaceous formations argillaceous formations generally act as aquitards because of their low hydraulic conductivities this property together with the large retention capacity of clays for cationic contaminants has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste in several countries programmes are under way to characterise the detailed transport properties of such formations at depth in this context the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large scale and long term transport behaviour of these formations here tracer profile data obtained by various methods of pore water extraction for nine sites in central europe are compiled data at each site comprise some or all of the conservative tracers anions cl br water isotopes delta 18 o delta 2 h and noble gases mainly he based on a careful evaluation of the palaeo hydrogeological evolution at each site model scenarios are derived for initial and boundary pore water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites using transport parameters derived from laboratory or in situ tests the comprehensive results from this project have been reported in mazurek et al 2009 here the results for three sites are presented in detail but the conclusions are based on model interpretations of the entire data set in essentially all cases the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles transport by advection has a negligible influence on the observed profiles at most sites as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data the advantages and disadvantages of different conservative tracers are also assessed the anion cl is well suited as a natural tracer in aquitards because its concentration varies considerably in environmental waters it can easily be measured although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue the stable water isotopes are also well suited but they are more difficult to measure and their values generally exhibit a smaller relative range of variation chlorine isotopes delta 37 cl and he are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence it is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion leading to relatively sharp changes of boundary conditions can be considered as a pre requisite to obtain well interpretable tracer signatures on the other hand gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation

parameter estimation of an overconsolidated aquitard subjected to periodic hydraulic head variations within adjacent aquifers abstract extensometers provide long term records of deformation over a depth interval of interest an overconsolidated aquitard usually undergoes elastic deformation if the hydraulic head within adjacent aquifers remains higher than the preconsolidation head within the aquitard the vertical hydraulic conductivity k v and elastic skeletal specific storage s ske are two critical parameters that control the deformation behavior of an overconsolidated aquitard and they could be interpreted from valuable extensometer data an analytical solution for the elastic aquitard deformation caused by periodic hydraulic head variations phhv within adjacent aquifers is derived using the separation of variables method based on euler s formula the phase difference in phhv between adjacent aquifers is found to reduce the amplitude of periodic aquitard deformation meanwhile the phase difference is found to cause no influence on the growth pattern of the phase shift which is between the periodic aquitard deformation and phhv versus the period a new parameter estimation method is further proposed to interpret aquitard k v and s ske from periodic aquitard deformation data this new method yields robust k v and s ske estimates of a moderately thick aquitard whose deformation history has been recorded by an extensometer located in shanghai china the field study confirms that the phase difference in phhv between the aquifers adjacent to the overconsolidated aquitard of interest cannot be ignored

fractionation of gases in polar ice during bubble close off new constraints from firn air ne kr and xe observations gas ratios in air withdrawn from polar firn snowpack show systematic enrichments of ne n2 o 2 n2 and ar n2 in the firn ice transition region where bubbles are closing off air from the bubbles in polar ice is correspondingly depleted in these ratios after accounting for gravitational effects gas in the bubbles becomes fractionated during the process of bubble close off and fractionation may continue as ice cores are stored prior to analysis we present results from firn air studies at south pole and siple dome antarctica which add ne kr and xe measurements to the suite of observations ne o2 and ar appear to be preferentially excluded from the shrinking and occluding bubbles and these gases therefore accumulate in the residual firn air creating a progressive enrichment with time and depth in firn air early sealing of gases by thin horizontal impermeable layers into a nondiffusive zone or lock in zone greatly enhances this enrichment a simple model of the bubble close off fractionation and lock in zone enrichment fits the data adequately the model presumes that fractionation is caused by selective permeation of gas through the ice lattice from slightly overpressured bubbles the effect appears to be size dependent because ne o2 and ar have smaller effective molecular diameters than n2 and fractionation increases strongly with decreasing size ne is fractionated 34 2 times more than o2 in south pole firn air and reaches an enrichment of 90 in the deepest sample the large atoms kr and xe do not appear to be fractionated by this process despite the large size difference between the two gases suggesting a threshold atomic diameter of 3 6a above which the probability becomes very small that the gas will escape from the bubble these findings have implications for ice core and firn air studies that use gas ratios to infer paleotemperature chronology and past atmospheric composition

geochemical challenges of diverse regolith covered terrains for mineral exploration in china abstract in recent years mineral exploration has concentrated on concealed deposits in regolith covered terrains in china the regolith covered landscapes mainly include desert windblown sand basins desert peneplains semi arid grassland loess plateaus forestry land alluvial plains and laterite terrains these diverse regolith covered areas represent geochemical challenges for mineral exploration in china this paper provides an overview of recent progress on mechanisms of metal dispersion from the buried ore deposits through the transported cover to the surface and penetrating geochemical methods to detect the anomalies case studies show that in arid and semi arid desert sand covered terrains sampling of fine fraction 120 mesh

barometric pumping of a fractured porous medium barometric pumping plays a crucial role in the release of trace gases from fractured porous media to the atmosphere and it requires a rigorous and complete modeling in order to go beyond the approximate schemes available in the literature therefore a coupled set of convection and convection diffusion equations for a slightly compressible fluid in unsteady conditions should be solved the numerical methodology is presented and it is applied to conditions close to the ones of the roselend natural laboratory france the precision of the code is assessed and the mechanism of barometric pumping is explained the usual schematization by simple vertical fractures is shown to be only qualitative finally barometric pumping is shown to be efficient in a narrow range of parameter values its efficiency is a decreasing function of the matrix porosity and of the fracture density

repeatability of 3 d ocean bottom cable seismic surveys recent advances allow time lapse 3 d sometimes called 4 d seismic surveys to map gas oil and oil water contacts some have used legacy 3 d data i e data not originally acquired for a 4 d study and found that the varying quality of the different vintages of the data limited the resolution that could be attained how then do we best carry out acquisition and processing for a 4 d seismic program so that the data are repeatable to the extent that differences are attributable to movement of the reservoir fluids and not to the acquisition processing or other factors

use of curved scanlines and boreholes to predict fracture frequencies abstract we advance the method of hudson and priest journal of rock mechanics and mining sciences geomechanics abstracts 20 1983 73 89 to develop a method for a curved scanline to be used to predict the numbers of fractures that would be observed in any direction when sampling along a scanline the probability of intersecting a fracture is influenced by the relative orientations of the fracture and of the scanline at that location this sampling bias can be minimised by the use of the terzaghi correction w cos 1 where is the angle between the scanline and the normal to the fracture these corrected frequencies are used to simulate fracture frequencies for all other orientations by doubly correcting the data modelled fracture frequency is contoured on a graph of simulated scanline plunge against simulated scanline azimuth this method is based upon the assumption that the data collected along the scanline is representative of the fracture population when the terzaghi correction has been applied a graph of cumulative frequency of fractures against distance along a scanline provides a simple method for determining whether the scanline crosses differently fractured areas frequencies are corrected for dip strike and both dip and strike with data from homogeneously fractured areas plotting as straight lines these frequencies can be normalised for ease of comparison

hydrologic issues in arid unsaturated systems and implications for contaminant transport analysis of unsaturated flow and transport in arid regions is important not only in water resource evaluation but in contaminant transport as well partic ularly in siting waste disposal facilities and in remediat ing contaminated sites the water fluxes under consid eration have a magnitude close to the errors inherent in measuring or in calculating these water fluxes which makes it difficult to resolve basic issues such as direction and rate of water movement and controls on unsaturated flow the purpose of this paper is to review these issues on the basis of unsaturated zone studies in arid settings because individual techniques for estimating water fluxes in the unsaturated zone have limitations a variety of physical measurements and environmental tracers should be used to provide multiple independent lines of evidence to quantify flow and transport in arid regions the direction and rate of water flow are affected not only by hydraulic head gradients but also by temperature and air pressure gradients the similarity of water fluxes in a variety of settings in the southwestern united states indicates that vegetative cover may be one of the pri mary controls on the magnitude of water flow in the unsaturated zone however our understanding of the role of plants is limited most unsaturated flow in arid systems is focused beneath topographic depressions and diffuse flow is limited thick unsaturated sections and low water fluxes typical of many arid regions result in preservation of paleoclimatic variations in water flux and suggest that deep vadose zones may be out of equilib rium with current climate whereas water movement along preferred pathways is common in humid sites field studies that demonstrate preferential flow are restricted mostly to fractured rocks and root zones in arid regions results of field studies of preferential flow in humid sites generally restricted to the upper 1 2 m because of shallow water tables cannot be applied readily to thick vadose zones in arid regions

precise determination of ar kr and xe isotopic fractionation due to diffusion and dissolution in fresh water abstract dissolved noble gases are ideal conservative tracers of physical processes in the earth system due to their chemical and biological inertness although bulk concentrations of dissolved ar kr and xe are commonly measured to constrain physical models of atmosphere ocean and terrestrial hydrosphere processes stable isotope ratios of these gases e g 136xe 129xe are seldom used because of low signal to noise ratios here we present the first results from a new method of dissolved gas sampling extraction and analysis that permits measurement of stable ar kr and xe isotope ratios at or below 5 per meg amu 1 precision 1 two orders of magnitude below conventional kr and xe isotopic measurements this gain in precision was achieved by quantitative extraction and subsequent purification of dissolved noble gases from 2 l water samples via helium sparging and viscous dual inlet isotope ratio mass spectrometry we have determined the solubility fractionation factors sol for stable ar kr and xe isotope ratios between 2 and 20 c via laboratory equilibration experiments we have also conducted temperature controlled air water gas exchange experiments to estimate the kinetic fractionation factors kin of these isotope ratios we find that both sol and kin normalized by isotopic mass difference m decrease in magnitude with atomic number but are proportional to m for isotope ratios of the same element with the new ability for high precision isotopic measurements we suggest that dissolved kr and xe isotope ratios in groundwater represent a promising novel geochemical tool with important applications for groundwater modeling water resource management and paleoclimate

the association of gold with calcrete abstract the discovery that au accumulates in calcrete pedogenic carbonate or caliche was made in 1987 by csiro calcrete is a general term describing accumulation of alkaline earth metals in soils of arid and semi arid terrains around the world the principal constituent of calcrete is calcite while au is a noble metal calcrete has been a significant tool in a number of au deposit discoveries so understanding the mechanisms by which these diametrically different components come together is valuable for enhancing future discovery numerous laboratory experiments case histories and exploration models have been published most from australia yet we do not fully understand the mechanisms involved it is timely therefore twenty five years on since the first publication of this phenomenon to review this highly unusual but economically important association critical to any review on au in calcrete is to first consider calcretes themselves the nature of a particular calcrete where it has formed and mode of formation is relevant to how where and why au accumulates within it this review commences with a background nomenclature history classification and some examples of calcrete types found near au deposits how calcretes form their origins and the role of biota is considered their locations in the regolith and landscape as well as exploration models for au in calcrete are discussed a section on the chemistry of au in calcretes details what we know about possible mechanisms of formation and considers what laboratory experiments on microorganisms and abiotic experiments tell us following on is a summary of practical aspects of identifying collecting and analysing samples for exploration purposes selected mineral exploration case histories are described and how they fit into models of exploration and different regolith settings concluding sections include a summary and implications of this accumulated knowledge to discovering au deposits