comment on reinterpretation of 36cl data physical processes hydraulic interconnections and age estimates in groundwater systems by e mazor abstract mazor 1992 has reinterpreted several previous 36 cl studies the studies he revised used extensive physical hydrogeological data to aid in interpretation of the 36 cl measurements major ion chemistry and other isotope tracers were considered in order to evaluate the groundwater geochemistry the studies then used simple geochemical models to account for cl behavior in the subsurface the result of these 36 cl dating studies was in reasonable agreement with both numerical models of the aquifer systems and with independent geochemical studies mazor 1992 has reinterpreted these studies based on the assumption that spatial variation in chemical and isotope data should be attributed to unspecified discontinuities in the flow regime the conceptual models of aquifer hydrodynamics resulting from this approach differ radically not only from the previous 36 cl interpretations but also from the findings of virtually all previous hydrogeological and geochemical investigations although mazor s reinterpretations are provocative he does not show how they explain the data of the numerous previous studies better than the conceptual models presented by the authors of those studies nor has he demonstrated that his new models are consistent with the fundamental physical laws governing groundwater flow until this is satisfactorily accomplished i will continue to prefer the original 36 cl interpretations

flow system controls of the chemical evolution of groundwater abstract isotopic and major ion analyses of 130 fresh and brackish groundwater samples reveal a strikingly consistent pattern of variation over 28 000 km 2 of the western canada sedimentary basin hydrodynamic interpretations based on drill stem tests and piezometric data reveal a pattern of broad regional flow from south to north however there is some evidence to suggest that patterns of groundwater flow have been influenced in the past by wisconsin glaciation all the permeable units appear to be recharged by meteoric water in the south where they outcrop or come close to the surface samples of groundwater collected down dip in each of six major sandstone units are progressively enriched in d 18 o na and cl for example the deepest waters of the artesian milk river aquifer are enriched by up to 70 and 15 with respect to the d and 18 o of the modern recharge waters the pattern of chemical evolution is strongly related to the hydraulic characteristics of individual units the isotopic composition is determined by the extent to which hydraulic conductivity has facilitated meteoric water flushing of connate water thus more permeable units and permeable zones within a unit tend to be isotopically lighter because of a more complete and more rapid invasion of meteoric water interestingly the largest conductivity values are found in some of the deepest units 1500 m consequently water in these deeper units have d and 18 o values which approach that of the recharge the major ion chemistry is controlled both by this process and a complex set of rock water interactions in addition to providing information about the chemical evolution of groundwater this study can begin to quantify the complex pattern of flushing in a large sedimentary basin

hydrogeology and hydrochemistry of the milk river aquifer system alberta canada a review abstract the milk river aquifer system consists of 30 60 m of cretaceous sandstone located within the milk river formation southern alberta canada the milk river formation is confined below by 500m of shale of the colorado group and above by up to 120 m of shale the pakowki formation the dominant recharge area for the aquifer is the sweetgrass hills montana where the aquifer crops out from the recharge area the groundwater flows to the north east and west calculated groundwater residence times at the north end of the aquifer about 100 km north of the recharge area range from 250 to 510 ka limited hydrological data from the confining shales suggest that cross formational flow does not occur systematic patterns are observed in major ions na cl hco 3 co 3 and so 4 stable isotopes 18 o and deuterium and field ph on a regional scale several mechanisms have been proposed to explain the geochemical evolution of the groundwaters

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

a tomographic study of the lithosphere beneath the pyrenees from local and teleseismic data a tomographic image of the pyrenean lithosphere from the surface down to 200 km is deduced from the propagation of the seismic waves recorded at the regional pyrenean seismograph network crustal and subcrustal models are derived independently from the inversion of two different data sets p and s velocity models for the crust are obtained from the propagation of local earthquakes the upper crust appears very heterogeneous and exhibits sharp velocity contrasts in the uppermost 7 km an east west trending zone with velocities up to 6 higher than the surrounding material is observed all along the pyrenees this zone coincides in most places with the exposure of the paleozoic rocks of the axial zone low velocities are observed on both sides of this high velocity zone at the surface they coincide with well known sedimentary basins but dip down to about 11 km depth toward the axis of the range in the central and eastern pyrenees two large high velocity bodies stand out in the north pyrenean zone and extend down to the base of the upper crust they coincide with large positive gravity anomalies and are interpreted as lower crust or upper mantle blocks uplifted into the upper crust the lower crust is poorly resolved but appears to be less heterogeneous than the upper crust moreover the lower crustal structure is almost uncorrelated with the upper crustal structure the major feature of the lower crust is a low velocity anomaly which stretches along the north pyrenean fault in the western pyrenees and beneath the axial zone in the central pyrenees its location nearly coincides with the distribution of the seismicity in the upper mantle p models are derived from the travel times of the remote events recorded at the pyrenean stations the most important feature is the presence in the eastern and central pyrenees of a vertical low velocity heterogeneity south of the north pyrenean fault down to 80 100 km this structure exhibits a 2 velocity contrast with respect to the surrounding structures and is interpreted as lower crustal material subducted during the pyrenean convergence this heterogeneity is not observed in the western pyrenees suggesting that the crustal shortening has been completely accommodated by several thrusts in the thinned aquitaine crust

reply to comment on chlorine 36 dating of very old groundwater 3 further results on the great artesian basin australia by t torgersen et al

multi scale approach to invasion percolation of rock fracture networks summary a multi scale scheme for the invasion percolation of rock fracture networks with heterogeneous fracture aperture fields is proposed inside fractures fluid transport is calculated on the finest scale and found to be localized in channels as a consequence of the aperture field the channel network is characterized and reduced to a vectorized artificial channel network acn different realizations of acns are used to systematically calculate efficient apertures for fluid transport inside differently sized fractures as well as fracture intersection and entry properties typical situations in fracture networks are parameterized by fracture inclination flow path length along the fracture and intersection lengths in the entrance and outlet zones of fractures using these scaling relations obtained from the finer scales we simulate the invasion process of immiscible fluids into saturated discrete fracture networks which were studied in previous works

groundwater and microbial processes of alabama coastal plain aquifers 1 we integrate groundwater geochemistry microbiology and numerical modeling techniques to study the origin of elevated salinity and chemical evolution of groundwaters in the coastal plain aquifers of alabama our field data indicate that chemical composition of groundwater evolves by various geochemical and microbial processes as it moves deeper into the subsurface sequential peaks of ca2 mg2 k and na along flow paths indicate that separation of ions may be driven by cation exchange microbial mediated reactions are important for the formation of several discrete hydrochemical zones containing fe2 mn2 sr2 and so42 rich groundwaters elevated fe2 mn2 and sr2 concentrations may be derived from bacterial iron and manganese reduction high sulfate concentrations observed a short distance from the recharge may be partly explained by microbial sulfur oxidation and nitrate reduction denitrification the presence of denitrifying and sulfur oxidizing bacteria in water further supports these reactions major ion compositions and d and 18o values are used to determine the source of salinity and the nature of mixing of different groundwaters three water types were identified these include carbonate groundwater brines associated with evaporites and groundwater of meteoric origin groundwater age differences and flow velocities were calculated using the 36cl cl ratios calculated groundwater flow velocities within the eutaw and tuscaloosa aquifers are about 0 20 m yr and 0 15 m yr respectively we modeled basin scale hydrologic and solute transport processes in a cross section extending from the aquifer outcrops to the gulf coast the modeling result shows that the buried jurassic louann salt can significantly increase groundwater salinity in the overlying coastal plain aquifers by density driven advection and hydrodynamic dispersion the modeling results are consistent with cl br ratios and o h isotope signatures which indicate that salinity of the groundwater could be derived from seawater that has been evaporated beyond halite saturation the predicted groundwater flow pattern reveals the mixing of meteoric water carbonate groundwater from the ordovician knox group and saline brines associated with the louann salt the hydrologic model is consistent with the hydrochemical facies distribution in the alabama coastal plain

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

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

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

groundwater dating by estimation of groundwater flow velocity and dissolved 4he accumulation rate calibrated by 36cl in the great artesian basin australia abstract we tested two methods for dating groundwaters that cannot be reliably measured by 36cl dating alone one based on groundwater flow velocity plus distance along a flow path and the other based on 4he accumulation rates calibrated with 36cl dates we sampled groundwaters along six inferred regional groundwater flow paths in the great artesian basin gab of australia we selected three groundwater paths where the decrease in 36cl was largely controlled by cosmogenic 36cl radioactive decay without a significant increase in chloride concentration the extrapolated groundwater velocities were 0 133 0 018 m y to 0 433 0 140 m y the estimated residence time of 1 06 106 y at the discharge area around lake eyre was comparable to the estimate of 1 2 2 106 y in previous studies on the other hand our estimated 4he accumulation rates for the selected three groundwater flow paths 1 85 0 31 10 11 to 1 51 0 63 10 10 ccstp cm3 y were approximately 2 15 times lower than previously reported rates for the central gab our estimated rate of 1 51 10 10 ccstp cm3 y 1 in the western gab is compatible with previous estimates based on 81kr ages the groundwater residence time estimated from the 4he accumulation rate was approximately 7 105 y near the discharge area at lake eyre finally both estimations were mutually compatible with a 30 error

reply to comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz

radiocarbon and stable isotopes in water and dissolved constituents milk river aquifer alberta canada abstract origin and age of groundwater in the milk river aquifer alberta canada was the focal point of the present study to answer related questions wells in this aquifer were sampled and 2 h and 18 o in water 13 c and 2 h in methane 34 s and 18 o in so 4 13 c and 14 c in dissolved inorganic carbon dic and dissolved organic carbon doc and tritium contents determined stable isotope analyses on ground water permitted the recognition of at least three different zones within the aquifer starting at the recharge zone modern type groundwaters are encountered for the first few kilometers these are followed by groundwater with slightly higher 18 o and 2 h contents i e waters which do not show a glacial signature and were probably recharged under warmer climatic conditions groundwater in the third zone is characterized by higher salinities and a pronounced oxygen isotope shift they show the gradual admixture of far more saline formation waters from the alberta basin sulphate s and sulphate o isotope values indicate a till source for the so 4 however so 4 in wells close to the area where so 4 virtually disappears show isotopic values which suggest that so 4 reduction is occurring although other studies could not find bacterial populations of so 4 reducers methane is present in most wells and based on c and h isotope data has a biogenic origin methane production occurs close to some wells and or it diffuses from the confining shales into the aquifer radiocarbon is measurable only in the first 20 km from the recharge zone however transformation of measured concentrations to water ages is very difficult because of the complexity of the geochemical system comparison with 14 c data on doc was therefore very interesting and this new technique may complement the dic radiocarbon dating two wells near the recharge zone yielded dic doc high molecular weight hmw and doc low molecular weight lmw results the dic dates were much older than doc dates but the differenve in years between the wells for all three types of c were within 1000 a of each other the doc dates led to the conclusion that the initial dic radiocarbon content was as low as 30 modern when the water entered the aquifer the age of the water 20 km from the recharge zone was assessed at 20 000 a resulting in a velocity of 1 m a this result is much higher than estimates by other techniques

isotopic composition 13c 14c 2h and geochemistry of aquatic humic substances from groundwater abstract aquatic humic substances from eight confined and unconfined aquifer aquitard groundwater systems were analyzed for their stable carbon radiocarbon deuterium and elemental contents fractionation of groundwater dissolved organic carbon doc showed that humic substances are an important part of the organic solute load in all groundwaters groundwater humates are distinct from other terrestrial humates and are characterized by low oxygen 36 and high carbon 53 contents elemental data from water table wells suggests this characteristic oxygen depletion is mainly a result of biochemical processes that occur in the vadose zone the stable carbon isotopic composition of groundwater humates range between 31 and 24 pdb with ann average of 26 and reflect their terrestrial origins the deuterium values of groundwater humate vary widely and are mainly a reflection of 2 h h variability in the continental water cycle radiocarbon analyses suggest a predominant soil zone origin for most groundwater humates although some groundwater systems are influenced to varying degrees by buried peat or coal soluble humate 14 c mean residence times of up to several hundred years in the vadose zone before recharging to groundwater are due to the mixing of young and old organic carbon sources rather than advective residence times

strontium isotopic evidence on the chemical evolution of pore waters in the milk river aquifer alberta canada abstract strontium isotope ratios were measured on 13 rock 18 leachate and 28 pore water samples from the milk river aquifer the confining argillaceous formations and the glacial till mantling the recharge area strontium isotope ratios 87sr 86sr of pore waters from the aquifer confining units and the glacial till ranged from 0 7069 to 0 7082 the 87sr 86sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area and this is interpreted to be the result of mixing and water rock interaction within the aquifer the solute composition of the recharging groundwater is modified by the local lithology causing distinct geochemical patterns along different flow paths within the aquifer whole rock 87sr 86sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone the authigenic carbonate cements and rock forming minerals comprising the major lithologic units had little apparent influence on the pore water sr chemistry carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations feldspar separates from the aquifer sandstone have relatively radiogenic sr isotope ratios whereas bentonites from the milk river and colorado shale formations have whole rock and leachate sr isotope ratios that are relatively unradiogenic ratios of most milk river aquifer pore waters are lower than those of any leachates or whole rocks analyzed except the bentonites the 87sr 86sr ratios of exchangeable sr in the bentonites are similar to ratios found in the more evolved pore waters simple rock water interaction models calculated for the whole rock leachate and exchangeable ion pore water pairs indicate that ion exchange with bentonite clays within the milk river and colorado shale formations appears to influence the isotopic evolution of the pore water sr in each of these units

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

radiocarbon in dissolved organic carbon a possible groundwater dating method case studies from western canada this paper explores the feasibility of using 14c in dissolved organic carbon doc as an alternative isotopic ground water dating method two hydrogeologically contrasting groundwater systems were tested the cretaceous age milk river aquifer and low permeability organic rich wisconsinan age prairie tills in southern alberta canada comparisons of radiocarbon data were made between doc fractions dissolved inorganic carbon dic and several dic geochemical age correction models along well defined flow paths the data presented demonstrate that 14c dating of doc fractions can indeed provide an alternative method for determining isotopic groundwater ages under suitable conditions however detailed information may be required regarding 1 the geologic nature of the aquifer and its flow system 2 the isotopically conservative behavior of doc 3 the initial 14c activity of doc in recharge and 4 the effect of bacterial redox processes on the 14c activity of doc in the milk river aquifer doc 14c ages were successfully used to estimate groundwater residence times as well as to further refine input parameter assumptions for the dic method in the prairie tills doc 14c ages were used to establish a maximum age for the pore waters in an environment where the dic method is especially problematic

controls on the distribution of major ions in pore waters of a thick surficial aquitard transport and geochemical processes controlling the chemical and isotopic composition of pore waters in the upper 45 m of a thick surficial clay rich till battleford formation were studied the upper 3 m of the till is oxidized and fractured the remaining 77 m of the till the aquitard is nonfractured and unoxidized concentrations of total dissolved solids so42 na mg2 and k decrease with depth through the unoxidized zone to a depth of about 15 m below ground below which the concentrations remain constant a similar trend was observed for alkalinity however the decrease in concentration occurs over 20 m in contrast to these ions ca2 concentrations increase with depth through the upper 20 m unoxidized zone below which the concentrations remain relatively constant the distribution of dissolved ions shows the presence of two end members elevated solute concentrations in the oxidized zone attributed to geochemical weathering that occurred since the start of the holocene and connate pleistocene age water at depths between 20 and 45 m abiotic and biotic geochemical reaction rates in the aquitard were shown to be extremely slow or not occurring

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

trace element geochemistry of a thick till and clay rich aquitard sequence saskatchewan canada abstract samples collected from a 170 m borehole penetrating till bentonitic clay and sand at the birsay site saskatchewan canada has been studied as a first step for understanding the controls on dissolution and transport of trace elements including rees in porewaters of a clay rich aquitard the ree budgets of the till clay and sand are dominated by apatite and monazite with sporadic zircon and y phosphate apatites contain 0 3 to 1 7 wt ree and monazites 12 to 55 wt all three units are characterized by unusual bulk sample ree patterns with maxima at eu gd convex down patterns from la sm with minima at ce and variably fractionated hree apatites feature maxima at eu gd consequently the complex patterns arise from variable modal proportions of apatite monazite and plagioclase feldspar relative to post archean average shale paas the till is sio2 and cao rich with about half the contents of al2o3 tio2 and fe2o3 these compositional relationship stem from relatively high proportions of quartz and carbonate but low modal abundances of ferromagnesian and ti oxide minerals similarly the till has cs co ni sc v cu pb and zn contents at about half paas the bentonite clay has slightly higher sio2 and cao contents than paas with lower abundances of most other trace elements including ree which plot at 0 7 to 0 9 paas the major and trace element composition is similar to continental arc andesites and the clay is interpreted to have a mixed provenance of arc andesite and eroded underlying sands the composition of the till appears to reflect mixed provenance erosion of the underlying cretaceous clay and sand paleozoic carbonate rocks and the precambrian shield the silicious ardkenneth sand has lower concentrations of ree and most trace elements compared to the clay but the most fractionated ree patterns the clay and till have inherited more subdued ree patterns in part from the underlying sand unit compositional variations between the units are marked by an upturn of nb th u and ree concentrations at the till clay interface 80 2 m and decrease of these elements at the clay sand boundary 156 2 m ce and eu anomalies vary erratically with depth the anomalies appear to reflect the degree of sedimentary sorting which in turn controls the modal abundances of detrital monazite apatite zircon and plagioclase feldspar zr zr hf hf and zr hf ratios are higher in the till than the clay and sand indicating an additional zr hf bearing phase with a distinctively high zr hf ratio the observed small compositional variations in the till and clay are not reflected in variations of geotechnical properties given that the ree budget of the till and clay are dominated by highly insoluble trace minerals it is unlikely that the ree patterns of porewaters will be controlled by bulk sample ree concentrations weathering of the upper 3 m of the till has oxidized fe2 bearing silicates oxides and sulphides and dissolved carbonates relative to the underlying unoxidized till weathering has not disturbed major ree or other trace element compositions

evolution of permeability in sand injectite systems abstract sand injectite complexes comprise kilometer scale clastic intrusion networks that act as effective conduits for the migration accumulation and then recovery of hydrocarbons and other fluids an equivalent continuum model is constructed to represent a sand injectite reservoir coupling stress and fluid flow in fractured rock using the continuum simulator toughreact coupled with flac3d to follow deformation and fluid flow a permeability model which uses staged percolation models is proposed to improve permeability estimation of fracture networks by accommodating four different levels of fracture connectivity this permeability model is confirmed against field and laboratory data corresponding to the different connectivities of fracture networks the new constitutive permeability model is incorporated into the coupled hydro mechanical simulator framework and applied to sand injectites with the analysis of permeability evolution mechanisms and mechanical sensitivity the results indicate that when the magnitudes of principal stresses increase in a constant ratio normal closure is the dominant mechanism in reducing fracture aperture and thereby permeability conversely the evolution of stress difference can accentuate aperture and permeability due to an increase in shear dilation for critically or near critically oriented fractures also the evolution of aperture and related permeability of fractured rock are more sensitive at lower stress states than at higher stress states due to the hyperbolic relationship between normal stress and normal closure of the fractures

sequential leachates of multiple grain size fractions from a clay rich till saskatchewan canada implications for controls on the rare earth element geochemistry of porewaters in an aquitard porewater ree concentrations vary by an order of magnitude over 45 vertical m in a thick clay rich till aquitard in southern saskatchewan to address controls on aqueous ree the till was disaggregated into seven size fractions 850 425 850 295 425 180 295 150 180 75 150 and 75 m each fraction was sequentially leached with water l1 1 m naoac ph 5 l2 0 25 m nh2oh hcl l3 1 m nh2oh hcl l4 12 m hcl kclo3 4 m hno3 l5 and the residue digested in na2o2 l6 aqueous leachate of the 75 m size fraction has a near flat ree pattern at 0 1 paas and carries 99 of ree relative to the total from all l1 leached size fractions aqueous leachates of the coarser size fractions have flat patterns 1 to 2 orders of magnitude lower leachate l2 extracts metals held electrostatically on inorganic or organic material the ree also plot at 0 1 paas with a convex up pattern and a maximum at gd leachate l3 of amorphous fe and mn oxyhydroxides carries more ree than l1 l2 or l4 and like l2 has a mildly convex up pattern there are lower ree abundances associated with crystalline fe and mn oxides l4 than with amorphous counterparts and hree are fractionated and depleted leaching of organic matter l5 produces ree patterns comparable to those of l4 the residue l6 has convex down ree patterns at 0 1 to 0 4 paas with prominent positive eu anomalies from plagioclase feldspar excepting the 75 m size fraction natural porewaters have mildly fractionated patterns with lree and mree depletion versus convex up patterns for leachates l1 l2 and l3 lree and mree may readily sorb onto clays or clay coatings in the till and be desorbed during leaching

implications of halide leaching on 36cl studies at yucca mountain nevada 1 chlorine 36 was generated from nuclear tests in the 1950s and 1960s and has been used to identify fast flow paths at yucca mountain the proposed repository for high level nuclear waste fabryka martin et al 1997 1998 bomb pulse 36cl brought into the subsurface by infiltrating rainwater presumably resides along fracture surfaces because of the extremely low rock matrix permeability however leaching a rock sample to extract this salt inevitably extracts pore water chloride cl and rock matrix chloride thereby making it difficult to obtain reproducible measurements or detect the specific bomb pulse signatures complexities introduced by these sources of older chloride include dilution of bomb pulse 36cl cl ratios for samples from strata with a high cl concentration variations in measured ratios as a function of leaching time rock chip size and the differing effects of active leaching from those of passive leaching this work provides both a conceptual model and a mathematical solution for the leaching processes and examines the role of sample leaching in the 36cl studies of yucca mountain rocks an analytical solution is derived for the diffusion of cl and 36cl in composite media rock matrix and water to accommodate variable diffusivity this solution is subsequently used to develop a leaching model that takes into account bomb pulse signal matrix pore water and relatively hard to leach components isolated fluid inclusion and mineral boundary salts the model is then applied to samples from stratigraphic units at yucca mountain to obtain leachate concentrations from different setup methods protocols including duration chip size and gravitational settling of the water rock mixture the model results show that the probability of detecting a 36cl cl bomb pulse signal is severely diminished under longer leaching times and smaller rock fragment sizes and that leaching times of 1 to 10 hours are most likely to be successful in detecting a bomb pulse signal bomb pulse 36cl cl ratios are more likely to be observed if pore water cl concentrations were initially low prior to the introduction of bomb pulse carrying water

sources of chloride and implications for 36cl dating of old groundwater southwestern great artesian basin australia we investigate the relative importance of a number of processes that affect cl and 36cl distribution in the southwestern flow systems of the great artesian basin australia to provide more precise estimates of age and flow and recharge rates in situ production of 36cl secular variations in the rate of production of 36cl and its subsequent fallout as well as rates of diffusion of stable cl from adjacent aquitards mask the interpretation of rates of decay of 36cl cl along hydraulic gradients and can preclude estimating absolute groundwater ages however mean flow velocities calculated from absolute cl concentrations are 0 24 0 03 m yr and are a more reliable parameter than calculated ages because fewer assumptions and approximations are required recharge rates to the main cadna owie formation and algebuckina sandstone aquifer of the great artesian basin estimated from cl mass balance in the unconfined aquifers are 0 16 0 08 mm yr and were probably up to a factor of 3 higher 30 kyr ago as indicated by decreasing cl and 18o concentrations along the head gradient

soil stratigraphy and quaternary caliche in the misis area of the adana basin southern turkey abstract a section at kizildere in the misis adana basin of turkey reveals relations among mature massive caliche calcrete and paleosolic immature caliche and the tertiary clay the handere formation and colluvial deposits it also defines a gradational sequence from unweathered tertiary clay deposits to massive caliches from older to younger the section comprises tertiary clays paleosolic caliche colluvial material massive caliche and lenticular caliche the two massive caliche beds have similar assemblages of carbonate minerals whereas the paleosolic caliche contains more clay minerals and most probably represents an earlier stage of massive caliche formation the variability of types of calcite the quantity and crystallisation state of palygroskite and the presence of kaolinite and degraded smectite all support the view that the massive caliche is the end product of a degradation sequence from the tertiary clay deposit to paleosolic caliche and the lenticular caliche is the well known petrocalcic horizon

differences in groundwater and chloride residence times in saline groundwater the barwon river catchment of southeast australia abstract the residence times of groundwater and chloride and the processes contributing to the development of saline total dissolved solids tds up to 45 379 mg l groundwater within the barwon river catchment of southeast australia were investigated using major ion stable isotope 18 o 2 h and 13 c and radioactive isotope 3 h 14 c 36 cl geochemistry the elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite silicate and calcite minerals groundwater residence times estimated from 14 c vary from modern to 20 ka for groundwater with lower 14 c activities the estimated residence times vary significantly depending on the assumed flow model and the 14 c activity of recharge chloride residence times downgradient of lake murdeduke a saline through flow lake in the centre of the catchment are greater than the corresponding groundwater residence times due to the recycling of cl within the lake precise estimates of chloride residence time could not be determined using 36 cl due to r 36 cl in precipitation being lower than that of groundwater this is most likely due to r 36 cl values in rainfall having been higher in the past than they are at present due to climate variability 18 o 2 h and 13 c values also suggest that the region has experienced increasingly more evaporative conditions with time the results of this study demonstrate that while cl is a useful tracer of hydrological processes it must be applied carefully in arid and semi arid regions of the world in particular recharge rates calculated using chloride mass balance may be underestimated where recycling of cl has occurred

three dimensional unified geological model of the milk river transboundary aquifer alberta canada montana usa the milk river transboundary aquifer canada usa has been so intensively used over the 20th century that concerns have risen about the durability of this resource since the mid 1950s this aquifer actually corresponds to the middle virgelle member of the upper cretaceous milk river formation called eagle formation in montana to assess the conditions needed for a sustainable use of the aquifer a comprehensive and unified portrait of the aquifer is needed across its international boundary the stratigraphic framework and geometry of geological units on both sides of the international border were thus unified in a 50 000 km2 three dimensional 3d geological model the virgelle member is 0 60 m thick and it subcrops near the border and along both sides of the sweetgrass arch it dips away from the subcrop areas in a semi radial pattern the medicine hat gas field hosted by the alderson member alberta which is separated from the other members by a regional unconformity and the tiger ridge gas field n

dating of syngenetic ice wedges in permafrost with 36cl abstract a new method of permafrost dating with the cosmogenic radionuclide 36 cl is presented in the first application syngenetic ice wedges are dated using the ratio of 36 cl and cl concentrations in ice as the signal 36 cl is produced in the atmosphere by nuclear reactions of cosmic rays on argon stable chlorine enters the atmosphere from the oceans their ratio does not depend on chloride concentration in precipitations and on sublimation of snow in situ production of 36 cl in permafrost ice via cosmic ray induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years 36 cl cl ratios in permafrost samples from cape svyatoy nos laptev sea coast north eastern siberia are measured by accelerator mass spectrometry analysis of the first results and the calculated dates support the feasibility of the 36 cl permafrost dating method

geometrical and fractal analysis of a three dimensional hydrothermal vein network in a fractured granite abstract a three dimensional study of a fracture network has been performed on a 0 66 m 3 block of fine grained granite from la peyratte deux sevres france the block was sawn in nine parallel plates the fractures associated with altered haloes were mapped for each plate using a photographic method the nine fracture sets were subjected to an analysis of the percolated network based on a measurement of the width of altered haloes developed around fractures hydrothermal alteration is created by circulation of a certain amount of fluid flow in the rock we assume that the alteration zone width is proportional to fluid mass flow the width of alteration zones will give a good idea of the path preferentially followed by fluids the relation between fracture length and width of the alteration zone shows that the total fracture network consists in fact of two sorts the largest fractures surface 0 1 m 2 create a loose and poorly interconnected pattern in the block however they have developed wide alteration zones 3 mm and have then had a great role in fluid conduction they represent only 10 of the fractures but are responsible for 47 of alteration in volume approximately 80 of these fractures with wide alteration zones are oriented in the same direction this main network is linked to a more dense highly interconnected system made of shorter fractures with narrower altered zones fractal analysis has also been performed on pictures of the fracture patterns using the linear cantor s dust method fractal dimension values d indicate an anisotropy of fracture distribution on each plane moreover when the planes are compared to one another in succession variations of d values can be noticed indicating an inhomogeneity in the third dimension the study of such a three dimensional fracture set shows that fluids follow preferential paths within a fracture network and helps the understanding of fracture distribution

buried palaeosols of nw sardinia italy as archives of the late quaternary climatic fluctuations abstract a multi disciplinary approach was performed to investigate two compound geosols included between wind blown deposits at the top and interglacial mis 5 beach sediments at the bottom located along the alghero coast north western sardinia italy a sedimentological and morphological study was carried out on the profile in the field and samples collected on the main pedomembers were subjected to several laboratory analyses consisting of physical and chemical determinations on bulk samples mineralogy xrd micromorphology on undisturbed samples thin section sem and edax micro probe analyses dating was performed by means of optically stimulated luminescence osl the studied geosols show the evidence of a complex pedosedimentary evolution around 80 to 70 ka the lower geosol underwent weathering and clay illuviation wet and warm conditions followed by calcification recalcification processes dry contrasted and finally by strong bioturbation around 70 ka the onset of the glacial period mis 4 is marked by the deposition of a sand dune capping the lower geosol these results indicate that the coastal area of the central mediterranean kept the relatively warm conditions typical of the interglacial climate for most of the early wurm and reached cold conditions only at about 70 ka possibly in relation to the rapid cooling of the heinrich event h7 the upper geosol developed on colluvial material including abundant pedorelicts and reddish earth material deposited around 50 ka before being buried by aeolian sand around 43 ka this deposit underwent pedogenesis phases possibly associated to middle wurm interstadial events indicating that in the study area these events were intense enough to influence pedogenesis

distribution of oxygen and hydrogen isotopes in shallow groundwaters from southern india influence of a dual monsoon system oxygen and hydrogen isotopic investigation of groundwater and river water samples from the southern indian peninsula was undertaken to characterise the isotopic nature of the near surface water sources and provide basic framework for future hydrological studies it is assumed that the shallow groundwater retains the isotopic signature of the local precipitation averaged over a few tens of years except in a few cases where the same gets modified by post precipitation evaporation and or recharge contribution from surface water bodies therefore isotopic character of the groundwater can in principle be used to determine the relative influence of the different vapour sources contributing to the local regional precipitation and to characterise the modifications before groundwater recharge in the present context vapour sources for two rainy seasons namely southwest sw and northeast ne monsoon are respectively the indian ocean arabian sea and the asian continental sources together with the bay of bengal this study shows that i the regions dominated by ne monsoon have distinctly depleted isotopic composition compared to those dominated by sw monsoon ii the 18o d regression line slope of 6 in the east coast region is lower than that expected for local precipitation suggesting secondary evaporation iii the orography of the western ghats hill ranges plays a significant role in controlling the isotopic distribution along the west coast region iv the low d excess values in most part of study area indicate secondary evaporation v the high d excess values over the deccan plateau region in the nw part of the study area suggest admixture of recycled moisture with the inflowing oceanic vapour

transport modeling applied to the interpretation of groundwater 36cl age 1 we use reactive transport modeling to consider how diffusion and hydrodynamic dispersion cross formational flow and subsurface production affect the steady state distribution in flow regimes of the radioactive isotope 36cl and the relationship of the isotope distribution to groundwater residence time or age the isotope forms naturally in the atmosphere dissolves in rainwater and then decays in the subsurface with a half life of 301 000 years hence it is important for age dating very old groundwater in a simple flow regime composed of an aquifer confined above and below by aquitards isotopic age may correspond rather well with a groundwater s piston flow age this correspondence is favored where the aquifer is thick cross formational flow is insignificant salinity is low and the diffusion coefficient within the aquitards is small the maximum dateable age however is somewhat smaller than expected from the isotope s half life owing to the effect of dead chloride dating based on isotope abundance the 36cl cl ratio may be less accurate than that based on 36cl concentration cross formational flow can strongly affect the 36cl distribution and abundance preventing the rates and even direction of flow within an aquifer from being interpreted using the piston flow model where salinity is moderate or high the isotope distribution is controlled by subsurface production and dating on the basis of the decay of atmospheric 36cl is not possible in models of simple flow regimes the 36cl method fails to predict groundwater age accurately where groundwater chlorinity exceeds 75 150 mg kg 1 reactive transport models hold considerable promise for improving interpretation of the rates and patterns of groundwater flow from radioisotope distributions

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

comparison of deterministic with stochastic fracture models in water flooding numerical simulations determination of multiphase flow properties considering the variation of fracture patterns i e number of fracture sets their orientation length distribution spacing and in situ aperture remains a key challenge in reservoirs in reservoir engineering one way is by studying outcrop analogs with comparable petrophysical properties and a similar geological history and incorporating these data into model building discretization and numerical simulation the limitation of directly incorporating attributes measured on outcrops is that this method is error prone because of postburial processes mineralized fracture vein attributes are good candidates to use as analogs for open fractures formed under in situ conditions to establish the relationship between fracture length and aperture and help to reveal the conditions at the time of their formation and to quantify fracture induced porosity in rock masses vein attributes determined from scan lines and window samples were combined to condition the stochastic generation of fractures using the discrete fracture network code fracman comparison of water breakthrough time and oil saturation at breakthrough was then determined by applying a constant pressure gradient for each realization to simulate water flooding numerical simulation using the combined finite element finite volume method the different stochastic realizations were compared with discrete fracture and matrix models and we show how the uncertainty in these fracture attributes affects multiphase flow behavior in naturally fractured rocks uncertainty in quantifying these attributes has a profound impact for predicting the oil recovery and water breakthrough time based on limited information from boreholes

percolation model for dilatancy induced permeability of the excavation damaged zone in rock salt a new percolation model is presented that predicts the dilatancy induced permeability increase in the excavation damaged zone edz of rocks salt the micro fracture geometry and network properties of the rock salt samples are determined by visualisation and evaluated by using statistical and stereological methods the permeability at full connectivity is modelled using the cubic law with a semi empirical estimation of the micro fracture aperture this model is coupled with a percolation model to incorporate the connectivity behaviour the percolation threshold is related to the dilatancy boundary which is defined as the starting point for the energy release that causes the grain boundaries to dislocate the shift between the dilatancy boundary and the percolation threshold is further applied to complete the modelling approach the model is calibrated and validated by the stress permeability results of the triaxial measurements the matches vary from satisfactory to excellent

the structural and sedimentary evolution of the cretaceous north pyrenean basin southern france during the cretaceous the north pyrenees of southern france suffered complex deformation the relatively deep marine north pyrenean basin formed a narrow band of rock adjacent to the north pyrenean fault was metamorphosed iherzolite was emplaced and the bay of biscay opened compression during the late cretaceous and tertiary pyrenean orogeny overprinted and partially masked this earlier history in order to better understand the regional tectonics off the cretaceous northern pyrenees and specifically the early history of the north pyrenean basin we compiled and then palinspastically restored a geologic map of the western north pyrenees lithofacies paleotransport and isopach maps for the early deposits of the basin and a pre albian palinspastic subcrop map show that the basin was an east west elongate fault bounded trough at least 300 km long and from 40 to 60 km wide containing a siliciclastic composite sedimentary package as much as 4 700 m thick detailed structural and stratigraphic studies of the massif d9igountze mendibelza which is located along the southern limit of the north pyrenean basin in the western pyrenees suggest that its cretaceous cover was deposited against an active relatively low angle listric normal fault this fault is on strike with the north pyrenean fault zone a major long lived zone of deformation in the central and eastern north pyrenees

underground production of radionuclides in the milk river aquifer alberta canada abstract most cosmogenic radionuclides that may be used to estimate groundwater ages in excess of 100 ka are also produced underground by in situ nuclear reactions radioactive equilibrium between in situ production and decay would be approached within such long residence times radionuclide production by in situ nuclear reactions within the groundwater and within its host rock has been calculated theoretically and compared with some measured radionuclide contents of the groundwater the fractional transfer of in situ produced 37 ar 39 ar and 222 rn from rock to groundwater necessary to account for the total measured groundwater contents were found to be similar although site specific the implications for radionuclide release mechanisms and for groundwater dating by the use of cosmogenic radionuclides including those which are applicable for very old groundwaters 36 cl 81 kr 129 i are discussed

factors controlling groundwater quality in eastern united arab emirates a chemical and isotopic approach abstract chlorine 36 along with oxygen and hydrogen isotopes and selected major ions were used to investigate the factors controlling groundwater quality in the eastern part of the united arab emirates two main aquifers occupy the study area the eastern gravel plain aquifer that occurs near the coastal area and the inland ophiolite aquifer previous studies suggest that groundwater particularly in the eastern gravel plain aquifer is affected by seawater intrusion and evaporation samples of groundwater from the eastern gravel plain aquifer cl 1000 mg l have r 36 cl values in the range of 13 3 17 4 10 15 while those from the ophiolite aquifer cl 36 cl values in the range of 20 118 10 15 these values indicate the presence of bomb produced 36 cl and are consistent with recent post 1950 recharge of most of the samples d 18 o relationship plots on a typical evaporation line which suggests potential evaporation of the recharging waters prior to infiltration the r 36 cl values of the coastally bound eastern gravel plain aquifer are lower than the ophiolite aquifer which suggests an additional input of chloride to this aquifer moreover in most cases the chloride concentration is not balanced by the concentrations of other cations such as sodium potassium calcium or magnesium seawater intrusion is thus ruled out measurements of bromide concentrations support the contention that organically bound cl is being released into this environment agricultural practices which are extensive in this region are a possible source also sodium and silica concentrations provide evidence for the release of these elements by the weathering of host rocks

chlorine 36 dating of very old groundwater 1 the great artesian basin australia chlorine 36 has many advantages as a dating tool for very old groundwater these advantages include a suitable half life 3 01 x 10 sup 5 years simple geochemistry conservative behavior in groundwater and a general absence of subsurface sources at levels comparable to the atmospheric input recent advances in tandem accelerator mass spectrometry have permitted the analysis of sup 36 cl at low abundance expected following residence in the subsurface for 10 sup 6 years or more in order to test the suitability of sup 36 cl for dating very old groundwater the sup 36 cl cl ratios of 26 groundwater samples from the great artesian basin of australia have been measured groundwater ages calculated from the sup 36 cl data compare favorably with ages computed independently from hydrodynamic simulations

on elevated fluoride and boron concentrations in groundwaters associated with the lake saint martin impact structure manitoba abstract hydrogeological investigations conducted by the geological survey of canada in the lake saint martin region of manitoba have confirmed earlier reports of naturally elevated f and b concentrations in local groundwaters fluoride and b concentrations are highly correlated r 2 0 905 and reach 15 1 mg l and 8 5 mg l respectively virtually all groundwaters with f concentrations greater than the drinking water limit of 1 5 mg l are from wells within the lake saint martin impact structure a 208 ma complex crater 23 km in diameter underlying a large part of the study area the high f groundwaters can be classified into two groups according to their anionic and isotopic compositions group i samples consist of na mixed anion groundwaters with cl greater than 100 mg l and highly depleted 18 o compositions indicative of recharge under much cooler climatic conditions than at present samples belonging to this group exhibit a striking relationship to crater morphology and are found in an arcuate belt within the southern rim of the impact structure group ii high f samples consist of na hco 3 so 4 groundwaters with little cl and less depleted 18 o compositions samples belonging to this group are associated with groundwaters recharged locally on a low ridge within the impact structure this paper traces the probable source of high f groundwaters to phosphatic pellets in shales of the winnipeg formation a regional basal clastic unit which sub crops at shallow depth beneath the crater rim as a result of more than 200 m of structural uplift associated with the impact event this extensive aquifer is known elsewhere in southern manitoba for its naturally softened groundwaters and locally elevated f concentrations group i groundwaters are interpreted as discharge from the winnipeg formation where it abuts against crater fill deposits group ii high f groundwaters are interpreted as modern recharge from within the impact structure displacing group i groundwaters thus elevated f and b concentrations observed in groundwaters of the lake saint martin area represent the geochemical signature of upwelling from a deep regional aquifer the previously unsuspected discharge zone occurs within an isolated sub crop of the aquifer formed as a result of structural uplift caused by the impact event

a transient analysis of slope stability following drawdown after flooding of a highly plastic clay the stability of slopes at bridge abutments across the carrot river in east central saskatchewan was not influenced significantly by drawdown after flooding in the spring of 1995 traditional metho

characterizing the hydrogeology of a complex clay rich aquitard system using detailed vertical profiles of the stable isotopes of water abstract high resolution 1d profiles of the stable isotopes of porewater 2h and 18o obtained by direct porewater equilibration of core samples were used to identify hydrogeologic zones in a thick complex till aquitard system in saskatchewan canada detailed 1d isotope profiles revealed the presence of three distinct hydrogeological zones an upper 5 10 m an intermediate 10 30 m and a lower 30 62 5 m till zone the upper hydrogeological zone was controlled by a sand layer having a high hydraulic conductivity k the lack of vertical variability in the stable isotope data in the intermediate zone suggested groundwater flow and solute transport was controlled by a system of interconnected vertical fractures and lateral sand layers the curved shape of the isotope profile in the lower till zone suggested that solute transport in this zone was controlled mainly by molecular diffusion we show that high resolution vertical stable isotope profiles of porewater obtained from core samples and direct equilibration yield cost effective and invaluable hydrogeologic information on groundwater flow in aquitard systems that cannot be realistically obtained by construction of costly conventional piezometer bundles i e 2h and 18o analyses of water samples and k determinations further the direct equilibration approach overcomes the problem of piezometer leakage in low k aquitards

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

decoupling of solutes and water in regional groundwater systems the murray basin australia documenting the origins residence times and movement of groundwater and the solutes that it contains is critical to understanding hydrogeological systems this study uses cl mass balance to determine the cl accession time i e the time required for cl to accumulate and cl to estimate the residence times of cl in the victorian portion of the murray basin southeast australia much of the murray basin contains saline groundwater with total dissolved solids tds concentrations commonly 14 000 mg l and locally up to 300 000 mg l the total mass of cl stored in the victorian portion of the basin is estimated as between 12 400 and 47 100 mt using present day rainfall totals and cl concentrations in rainfall the cl accession time is 170 to 650 ka aquifer thicknesses and groundwater salinity both increase westwards in this part of the murray basin consequently the cl accession times increase westward from 0 1 0 6 ka to 286 1080 ka by contrast c activities of the majority of the groundwater are 2 pmc and commonly much higher notwithstanding the difficulty in correcting c residence times the widespread occurrence of groundwater with above background c activities implies that groundwater residence times are generally 30 ka which is substantially shorter than the cl accession times rcl the ratio of cl to total cl 10 values of the groundwater are between 20 and 230 and are uncorrelated with cl concentrations while it is difficult to determine precise cl residence times the observation that the rcl values are significantly higher than those that represent secular equilibrium with the aquifer matrix rcl of 5 to 10 indicates that they are up to a few hundred thousand years and similar to the cl accession times the rcl values together with the geology of the aquifers stable isotope ratios and major ion geochemistry precludes halite dissolution incorporation of connate water or the long term diffusion of cl from clays as mechanisms of producing the elevated cl concentrations rather it is most likely that the high cl concentrations result from recycling of solutes in saline lakes and playas or repeated cycles of evapotranspiration in the unsaturated zone

chloride and chlorine isotopes 36cl and δ37cl as tracers of solute migration in a thick clay rich aquitard system detailed vertical profiles of dissolved cl and its isotopes 36cl and 37cl provided new information on the origin and systematics of this conservative tracer in pore waters of a thick aquitard system the aquitard system consists of surficial quaternary clay rich till 80 m thick deposited 30 20 kyr b p overlying cretaceous marine clay 76 m thick deposited 71 ma the distribution of cl 37cl and br showed the presence of five distinct end members for cl the top of the unoxidized till a regional aquifer underlying the cretaceous clay two localized geological heterogeneities sand streaks in the till and glacial meltwater emplaced with the till and still present at depths of between 36 and 60 m numerical simulations of the transport of cl from the sand streaks indicated that this geochemical profile has been developing throughout most of the holocene the 36cl measurements showed that the age of the dissolved cl in the upper cretaceous clay is likely between 0 75 and 1 9 myr the 36cl measurements further suggested that the dissolved cl in the till was not directly derived from the underlying cretaceous clay finally it was not possible to quantify the effects of isotopic fractionation of 37cl relative to 35cl because of diffusion in this aquitard system

diffusion as the main process for mass transport in very low water content argillites 2 fluid flow and mass transport modeling 1 on the basis of chloride concentrations of pore water in the tournemire massif part 1 a conceptual model for mass transport in argillites by diffusion is proposed from this conceptual model and current knowledge of the geological history of the massif one dimensional numerical simulations are formulated for chloride transport in tournemire massif over the past 53 ma good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is the main process for mass transport in the massif this model is also tested using deuterium contents of pore water applying variable concentrations to meteoric water circulating in system boundary layers based on the thermal dependency of its isotopic composition these simulations reveal the likely important role of lithologic heterogeneities such as fractures in the horizontal distribution of tracer concentrations

an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada the milk river artesian aquifer underlies 15 000 km2 of southern alberta canada it consists of thin 30 75 m thick sandstone and is confined above by the pakowki shale typically 120 m thick and below by the colorado shale the aquifer subcrops in southern alberta and northern montana groundwater movement is to the north west and east from the outcrop area dominant recharge area cl and i concentrations increase in the direction of flow from less than 0 05 and 0 001 mmol l respectively near the recharge area to more than 140 and 0 15 mmol l at the northern edge of the aquifer similarly waters become more enriched in oxygen 18 and deuterium from less than 21 0 and 167 near the recharge area to values approaching 8 0 and 70 0 in the north isotope values in the recharge area plot on the global meteoric water line and indicate that the recharge waters are isotopically unaltered meteoric waters downgradient from the recharge area the data deviate from the meteoric water line slope of 6 3 instead of 8 0 three mechanisms have been advanced to explain the origin of the chemical and isotopic patterns the introduction of connate formation water through the colorado shale and subsequent mixing with infiltrating meteoric water a finite source of meteoric recharge mixing with more saline water in the aquifer and chemical and isotopic enrichment due to ion filtration hydraulic conductivity and hydraulic head data cl concentrations of drill cuttings and isotopic values from groundwater from the colorado shale provide arguments for reevaluating these ideas an alternative mechanism based on diffusion between saline isotopically enriched water in the colorado shale and fresher isotopically depleted water in the aquifer is tested using an analytical mass transport model although uncertainty exists in the model parameters results showed that the patterns in cl i 18o and 2h in the aquifer can be explained by aquitard diffusion further aquitard diffusion must be considered when using chlorine 36 dating methods in aquifer aquitard systems such as the milk river aquifer

the geochemistry and mixing of leakage in a semi confined aquifer at a municipal well field memphis tennessee usa abstract the memphis aquifer in southwestern tennessee is confined to a semi confined unconsolidated sand aquifer and is the primary municipal water source in the memphis metropolitan area past studies have identified regions in the metropolitan area in which the overlying upper claiborne confining unit lacks significant clay and provides a hydraulic connection between the shallow aquifer and the memphis aquifer in this study major solute chemistry 3h and 3h 3he groundwater dating are used to investigate the extent and chemical effects of leakage through the confining unit to the memphis aquifer in the vicinity of a municipal well field the 3h 3he dates and geochemical modeling of the chemical data are used to constrain mixing fractions and the timing of modern recharge tritium activities of as much as 2 8 tu are observed in shallow production wells but deeper production wells have 3h activities that approach the detection limit trends in water chemistry indicate vertical mixing in the aquifer of shallow na so4 cl rich water and deeper ca mg hco3 rich water water chemistry does not vary consistently with seasonal pumping but 3h activity generally decreases during low use periods stable o and h isotopes show little variation and are not useful groundwater tracers for this study the 3h bearing na so4 cl rich water is interpreted to reflect recharge of modern water through the upper claiborne confining unit the 3h 3he dates from 5 production wells indicate modern recharge that infiltrated 15 20 a ago is present in the shallow production wells geologic data and hydrologic boundary conditions suggest that the most likely source for continued leakage is a nearby stream nonconnah creek geochemical reaction modeling using the netpath computer code suggests that proportions of shallow aquifer water leaking into the memphis aquifer range from 6 to 32 the 3h 3he dating and netpath modeling results correlate well suggesting that these complementary analytical tools provide an effective means to evaluate proportions of modern water leaking into semi confined aquifers these results also indicate a need to carefully consider connections between surface water and semi confined groundwater resources in wellhead protection programs

distribution of the rare earth elements in porewaters from a clay rich aquitard sequence saskatchewan canada a 91 4 m thick porewater profile of the rare earth elements rees is presented from a thick clay rich pleistocene till 0 80 m and cretaceous clay 80 156 m aquitard sequence saskatchewan canada the upper 3 4 m of till is weathered absolute aqueous concentrations of the rees vary by more than one order of magnitude aqueous ree concentrations decrease with depth through the weathered till to a depth of about 15 m below ground below which the concentrations in the unweathered till remain relatively consistent the only porewater sample from the clay 91 4 m has the highest total ree concentration elevated ree concentrations in the oxidized zone attributed to geochemical weathering there is no significant seasonal variation in aqueous ree concentrations within the water columns in the piezometers redox conditions and solution complexation reactions exert predominant controls on the aqueous ree concentrations the majority of ree patterns are coherent characterized by overall negatively fractionated ree with convex down profiles from la to pr or nd and convex up from nd to tb in the porewater sample from the clay the lrees are an exception with a flat normalized profile hree lree fractionations in the porewaters are depth dependent and are mainly controlled by solution complexation with dissolved sulfate phosphate free carbonate ions and doc porewaters in the unweathered till 5 76 2 m are characterized by negative ce anomalies which may reflect in part negative ce anomalies in the host till geochemistry the negative ce anomalies are magnified relative to the host tills during water rock interaction and ree transportation porewaters from the weathered till exhibit strong positive ce anomalies relative to paas the host rocks and their leachates the ce anomalies are predominantly controlled by the redox conditions and solution complexation the large positive ce anomalies in these porewaters are probably caused by the oxidation of ce iii to ce iv that was stabilized in solution through complexation with high contents of inorganic and organic ligands positive eu anomalies relative to paas the host rocks and leachates of the host rocks result from hydrolysis of plagioclase feldspar the limited depth profile for total dissolved rees across the weathered unweathered till boundary is retarded with respect to that previously established for na k mg2 so42 and tds suggesting that chemical reactions control the migration of dissolved rees

temperature as a marker for karstic waters hydrodynamics inferences from 1 year recording at la peyrere cave ariege france abstract we present temperature measurements recorded at a 15 min time step between october 2002 and april 2003 inside the la peyrere cave baget karstic system central pyrenees on six 0 01 c sensitivity sensors distributed on the whole recognized cave down to a depth of 57 m rainy events are associated to a steep signal of a few hundredth to a few tenth of degrees in amplitude starting 1 h to one day after rain and with a sign depending mostly of the outside temperature the temperature signal does not correlate well with the rainfall while the water level does with a maximum water rising rate 2 5 h after rain the spectral density of the temperature signal displays one peak at a period of 3 days which is also present in the rain signal and which is likely to be related to climatic parameters and a broad smooth zone of spectral energy close to a 1 day period by comparing a superficial and a deepest group of sensors we note that the flood signal is more pronounced on the deepest sensor group whatever the outside temperature and that the annual temperature variation is also larger on this sensor group this could indicate that rain water flows in the cave through its base and explain the development in depth of the cave due to the arrival of water with different temperatures and mineralizations at different levels double diffusive convection is likely to be triggered in the cave we suggest that the onset of convection could be associated to the oscillations observed on the temperature signal at the onset of the flood

uranium series radionuclides in fluids and solids milk river aquifer alberta canada abstract samples from 21 wells completed in the milk river aquifer were sampled and analysed for u isotopes in general u concentrations decrease with distance from the recharge area groundwater samples can be delineated into a small oxic group u content 101t 5 mmol 1 and a more predominant anoxic group u content of 10 7 mmol 1 all groundwater samples were undersaturated with respect to the common u minerals such as uraninite coffinite and rutherfordine the dominant u complexes were uranyl carbonates the234u 238u activity ratios increased from 2 to 11 with distance downflow of the outcrop the highest activity ratio of 11 8 was measured at a well defined redox front whereupon a steady decrease downdip to 4 was observed this decrease was interpreted to be due to the decay of234u excess with age of the groundwater and due to u loss by sorption precipitation processes from solution to solid surfaces two u isotope dating models were used to estimate the age of the groundwater in the milk river aquifer model 1 is a simple model of downdip decay of234u excess in solution under steady state conditions model 2 is a phenomenological model for the evolution of u isotope groundwater composition downdip based on a transport dispersion equation incorporating radioactive decay and assuming that sorption processes are of first order kinetics both models were applied to the u isotope data collected along the same flow path in the aquifer they yielded flowrates of 0 1 0 2 m a and 0 2 0 6 m a respectively the latter range is in good agreement with flowrates of 0 3 m a obtained from hydraulic considerations the lower value derived from model 1 is interpreted in terms of u migration velocity rather than as groundwater flowrate model 2 was also applied to an additional flowpath the calculated flowrate range of 0 1 0 4 m a is in excellent agreement with the hydraulic model flowrate of 0 2 m a the main conclusion of this work is that u isotopes can be used for dating very old groundwaters provided the local hydrogeology and u geochemistry are understood well

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

measurements and interpretations of36cl in groundwater milk river aquifer alberta canada abstract the 36 cl cl ratios of 12 groundwater samples from the milk river aquifer were determined by accelerator mass spectrometry using known cl concentrations 36 cl concentrations were deduced approximately linear relations were observed between the logarithm of the 36 cl concentration the cl concentration and the distance from the recharge area along two flow paths the results are discussed in two approaches 1 in an interpretation of the linear relation between logarithm of the 36 cl concentration and cl concentration excluding and including in situ production of 36 cl 2 in a diffusion model the increase of the cl concentration with the distance from the recharge area is considered to be due to diffusion of cl from the underlying confining colorado shale to the aquifer flow velocities ranging between 0 04 and 0 14 m a and ages of the groundwater between 0 6 and 2 ma are obtained at a distance of 80 km from the recharge area

distribution of arsenic iii arsenic v and total inorganic arsenic in porewaters from a thick till and clay rich aquitard sequence saskatchewan canada abstract inorganic arsenic species were measured in the porewaters collected from eighteen piezometers installed between 3 and 91 4 m below ground in a thick till and clay rich aquitard sequence located in southern saskatchewan to investigate the distribution of and controls on arsenic speciation in the sequence aqueous concentrations of as v as iii and total as are in the range of 0 31 97 0 71 21 and 3 2 98 ppb respectively profiles of as iii and as v concentration distribution with depth broadly track that of total as erratic increases to 15 2 m then more uniform concentrations to 88 m aqueous arsenic is accumulated at the upper redox transition zone 6 14 m the alkaline porewater at 91 4 m contains the highest concentrations of as v and total as which might result from the facilitated desorption of arsenate from the host solid due to decrease of positive surface charge of the oxides in alkaline solution the ratio of as v as iii is greater than unity in the uppermost oxidized porewater 3 m less than unity from 4 6 to 71 6 m and greater than unity in the lowest four porewaters 76 2 to 91 4 m in the 3 m porewater low as iii but high as v as iii is due to the oxidized nature of the near surface weathered till the high as v as iii in the deepest porewater at 91 4 m likely results from the enhanced and heterogeneous oxidation of as iii to as v on clay mineral surfaces in the alkaline solution total as and arsenic speciation may not be controlled by as fe or mn concentrations in the host till or clay dissolved as v and total as positively covary with aqueous chloride whereas dissolved as iii is independent of aqueous chloride aqueous as iii and to a less extent as v and total as are positively correlated with dissolved mn in the till in the clay aqueous as v and total as show strong negative covariation with mn however aqueous as iii as v and total as exhibit almost no correlation with total dissolved fe in the till the as v as iii ratio has strong negative correlation with dissolved mn but positive covaration with dissolved chloride generally good agreement between the redox potentials eh calculated from aqueous as v and as iii concentrations and those measured by a pt electrode throughout most of the unoxidized till suggests the suitability of using as v as iii redox couple as a redox indicator for the studied aquitard system however large negative bias of the calculated eh from the measured eh in the oxidized till upper unoxidized till and the clay is attributed to errors associated with the field measurements of eh

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

directional semivariogram analysis to identify and rank controls on the spatial variability of fracture networks abstract in this study the directional semivariogram is deployed to investigate the spatial variability of map scale fracture network attributes in the paradox basin utah the relative variability ratio r is introduced as the ratio of integrated anisotropic semivariogram models and r is shown to be an effective metric for quantifying the magnitude of spatial variability for any two azimuthal directions r is applied to a gis based data set comprising roughly 1200 fractures in an area which is bounded by a map scale anticline and a km scale normal fault this analysis reveals that proximity to the fault strongly influences the magnitude of spatial variability for both fracture intensity and intersection density within 1 2 km additionally there is significant anisotropy in the spatial variability which is correlated with trends of the anticline and fault the direction of minimum spatial correlation is normal to the fault at proximal distances and gradually rotates and becomes subparallel to the fold axis over the same 1 2 km distance away from the fault we interpret these changes to reflect varying scales of influence of the fault and the fold on fracture network development the fault locally influences the magnitude and variability of fracture network attributes whereas the fold sets the background level and structure of directional variability

application of isotopic methods to dating of very old groundwaters milk river aquifer alberta canada the aim of this joint project was to evaluate the usefulness of available geochemical and isotope techniques for dating very old groundwater this paper represents a synthesis of an iaea sponsored study for which purpose the milk river aquifer groundwaters were sampled from 16 wells during 1985 and subsequent years for the following measurements 2h 3h 13c 18o 14c 39ar 81kr 85kr noble gases including222rn 36cl 129i and u isotopes the milk river aquifer was selected for this study because several preceding investigations had established that this groundwater system contains waters whose ages range from recent to 1ma the present study has established that the milk river aquifer system is very complex both in terms of groundwater origin and in terms of the evolution of its chemical and isotopic contents however this apparent complexity proved to be an interesting challenge with respect to the use of different and complementary approaches to interpretation of the geochemical and isotope data in terms of groundwater residence time thus the groundwater ages based on the hydrodynamic model should be considered as a lower limit of the average groundwater age in the milk river aquifer 0 25ma while those based on the36cl cl data uncorrected for any dilution by dead cl should be considered as an upper limit 2ma the milk river aquifer international project is an excellent illustration of the variety of insight and increased confidence possible in flow system analysis when multiple independent dating methods are combined with detailed hydrogeological studies the conclusion of the present study is that the potential for dating of very old groundwaters by a variety of isotope techniques is very high provided a combination of methods is applied never a simple method by itself

similarities and differences of the spheroidal microstructure in vertisols from turkey and israel abstract vertisols formed on different parent materials from turkey aslanpinari and begdes soil series and israel akko soil series were studied for their microstructure the aslanpinari and begdes soils showed similar spheroidal microstructural development in the abss horizons whereas the spheres of akko differed by being smaller and lacking granostriation micromorphometric analyses of the three soils revealed similar pore characteristics within and between the aggregates of the abss horizons presence of the spheroidal microstructural units and increase of palygorskite and vermiculite in the abss horizon of the bedes soil which is in contrast with increasing smectite in the aslanpinari and akko soils links with an increase in the structural stability index and an increase in the hydraulic conductivity

comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz the milk river aquifer in southern alberta combines apparently simple classical confined aquifer hydrodynamics with somewhat enigmatic groundwater geochemistry of conservative solutes over the past 10 years five major papers have focused on the geochemistry of milk river aquifer groundwater most recently hendry and schwartz 1988 have proposed a different mechanism aquitard diffusion to explain the milk river geochemistry they described and evaluated previously proposed geochemical processes especially ion filtration hendry and schwartz 1988 concluded that ion filtration and the other proposed mechanisms were not supported by the data they then described the aquitard diffusion mechanism and used a simple analytical model to simulate observed aquifer trends in cl sup minus and sup 18 o from the results of this exercise they concluded that diffusion from the aquitards was controlling the solute distributions in the aquifer finally they interpreted previously published sup 36 cl data and new profiles of cl sup minus in the aquitards in terms of the diffusion model upon review the authors do not find the arguments against ion filtration to be as damaging as hendry and schwartz indicate nor do they find the evidence for aquitard diffusion to be as persuasive in this study they will first evaluate hendry andmore schwartz s arguments against ion filtration then they will review the arguments in favor of aquitard diffusion and finally the authors will address the implications for the interpretation of the vertical cl sup minus profiles and the sup 36 cl data less

carbon 14 dating of groundwater in confined aquifers implications of aquitard diffusion the influence of diffusive losses into fine grained aquitards on the 14c age interpretation of groundwater in long thin confined aquifers is examined an analytical model is developed by coupling two one dimensional steady state differential equations one representing advective dispersive transport in the aquifer and the other representing diffusion into the aquitards the results indicate that aquitard diffusion is a mechanism that can cause a significant reduction in 14c concentrations in a confined aquifer groundwater velocities derived from 14c measurements that are unadjusted for diffusion would therefore be underestimated the error that ensues is highly sensitive to the aquifer thickness and the magnitude of the diffusion coefficient in contrast the steady state distribution of 14c is shown to be relatively insensitive to the magnitude of the longitudinal dispersivity value of the aquifer dispersivities representative of the upper range of values that have been reported in the literature produced a negligible difference in steady state 14c concentration compared to results obtained using small dispersivities an equation is presented which permits the adjustment of 14c data to account for diffusion providing that the aquifer aquitard system is not stratigraphically complex and heterogeneous the analysis can be extended to include age dating isotopes that have half lives different from that of 14c the results of this study also apply to age dating in fractured porous media

dissolved gases in the milk river aquifer alberta canada abstract geochemical relations between the noble gases 40 ar 36 ar ratio n 2 and ch 4 contents of groundwaters from the milk river aquifer albert canada have been investigated the ch 4 contents for many of the groundwaters are several times their n 2 contents and cause degassing to occur as the hydrostatic pressure decreases during their ascent in the wells recharge temperatures derived for those groundwaters that were not degassed indicate that the youngest groundwaters were recharged under cooler climatic conditions than prevailed during earlier recharge this conclusion is supported by the stable isotope compositions of the groundwater the 4 he concentration in the groundwater varies with depth according to the theoretical concentration depth profile for accumulated radiogenic 4 he in the aquifer and its adjacent shales the corresponding flux of 4 he to the atmosphere is 4 he production rate excess radiogenic 40 ar is associated with ch 4 and both gases originated within the adjacent shales the ch 4 is biogenic and was produced in an aqueous environment which ranged from marine to freshwater as the connate fluids in these marine shales were replaced the degassing process has been modelled to explain the residual dissolved gas contents of the groundwater and to show that the ch 4 n 2 ratio in situ was 12

characteristics of deep groundwater flow in a basin marginal setting at sellafield northwest england 36cl and halide evidence abstract a number of chemical and physical processes inside and outside a sedimentary basin e g evaporite dissolution and topographic drive respectively affect groundwater flow near the basin s margin contrasting formations at the margin typically basinal sedimentary rocks and basement are host to the interplay between these processes so that groundwater flows and compositions change within a relatively small volume to interpret how groundwater flow and geochemistry have evolved interactions between these processes must be understood such interactions were investigated near the margin of the east irish sea basin in nw england by sampling deep groundwaters to 1500 m below sea level from ordovician volcanic basement rocks and carboniferous to triassic sedimentary cover rocks variable br cl ratios and cl concentrations in deep saline waters and brines indicate mixing patterns variations in 36 cl cl constrain the timing of mixing relatively low br cl ratios ca 1 10 3 by mass characterise brine from the western sedimentary cover and reflect halite dissolution further west saline water with relatively high br cl ratios ca 2 10 3 by mass of uncertain origin occupies the eastern basement these two waters mix across the area however mixing alone cannot explain variable 36 cl cl ratios which partly reflect differing in situ 36 cl production rates in different rock formations most 36 cl cl ratios in groundwater sampled from the eastern metavolcanic basement mean 25 10 15 and western sedimentary cover mean 10 10 15 are at or close to equilibrium with in situ 36 cl production these variations in 36 cl cl across the site possibly took 1 5 ma to be attained implying that deep groundwater flow responded only slowly to the quaternary glaciation of the site interplay between varied processes in basin marginal settings does not necessarily imply flow instability

cross checking groundwater age by 4he and 14c dating in a granite tono area central japan abstract groundwater dating was performed simultaneously by the 4he and 14c methods in granite of the tono area in central japan groundwater was sampled at 30 packed off sections of six 1000 m boreholes 4he concentrations increased and 14c concentrations decreased along a groundwater flow path on a topographic gradient 4he ages were calculated by using the in situ 4he production rate derived from the porosity density and u and th content of the rock neglecting external flux 14c ages were calculated with a noncorrected model in which the initial 14c content was 100 percent of the modern radiocarbon level co 100 pmc a statistical model using the average 14c content of tritium bearing samples co 46 4 pmc and a 13c model based on the isotopic mass balance although the absolute 14c ages calculated by the models were different the relative 14c ages were almost identical the relative 14c ages were considered reliable because dissolved inorganic carbon has no significant geochemical reactions in granite the relation between the 4he ages and the noncorrected 14c ages was 4he age 1 15 14c age 7200 r2 0 81 except in the discharge area the slope of this relation was equivalent to unity which indicates that the 4he accumulation rate is confirmed by the relative 14c ages moreover the accumulated 3he 4he ratio was equivalent to that derived from the 6li n 3h reaction in granite these results show that the accumulated he is of crustal origin produced in situ without external flux except in the discharge area the intercept value of 7200 a implies that the 14c concentrations were diluted due to geochemical reactions tritium bearing samples supported this result simultaneous measurements make it feasible to estimate the accumulation rate of 4he and initial dilution of 14c which cannot be done with a single method cross checking groundwater dating has the potential to provide more reliable groundwater ages the circulation time of the groundwater flow in the tono area may be several tens of thousands of years and the groundwater age calculated from the 4he and 14c ages appears to be consistent with geochemical information such as groundwater types d and 18o

scales and effects of fluid flow in the upper crust two of the most important agents of geological change solar energy and internal heat from the mantle meet and battle for dominance in propelling aqueous and related fluids in the earth s upper crust which prevails and how they interact are subjects of active research recent work has demonstrated that both agents can propel fluids over nearly continental scale distances in a fashion that influences a host of important geological processes and leaves a record in chemical alteration mineral deposits and hydrocarbon resources

using excess 4he to quantify variability in aquitard leakage summary fluid flux through aquitards controls the rate of recharge discharge cross formational fluid flow and contaminant transport in subsurface systems in this paper concentrations of 4 he are used to investigate the spatial distribution of vertical fluid flux through the regionally extensive great artesian basin aquitard system in northern south australia two vertical profiles of 4 he concentration in aquitard pore water augmented with regional sampling of aquifers above and below the aquitard were used to estimate fluid flux at multiple locations over a large spatial area 4 he concentrations in the shallow aquifer above the great artesian basin range from atmospheric equilibrium to 1000 times enriched over atmosphere fluid flux through the aquitard was estimated by fitting observed helium concentrations at each sampling site with a 1 d model of helium transport through the aquitard estimated fluid fluxes through the aquitard vary over three orders of magnitude across the study area in areas of competent aquitard fluid fluxes are less than 0 003 mm yr and mass transport of helium is dominated by molecular diffusion preferential discharge zones are clearly identifiable with fluid fluxes up to 3 mm yr our results show that fluid flux through a regionally extensive aquitard can be highly variable at large spatial scales and that 4 he concentrations in aquifers bounding the aquitard system provide a convenient and sensitive method for investigating aquitard flux at the regional scale

fracture controlled permeability of ultramafic basement aquifers inferences from the koniambo massif new caledonia abstract we study the relationship between fracture distribution and permeability in weathered peridotites exposed to tropical climate using the data from the koniambo massif new caledonia south pacific the vertical distribution of hydraulic conductivity is obtained from packer tests performed on four 200 m deep boreholes a positive correlation is observed between the cumulated width of weathered fractures and the hydraulic conductivity in a given depth interval therefore a two scale model of weathered fractures is developed with small fractures 5 m radius deduced from outcrop data and large fractures 50 m radius from a remote sensing analysis hydraulic conductivity is 10 5 m s in the fractures and 10 8 m s in the matrix permeability fields are computed for the synthetic fractures network models either from flow along the three axes of a periodic cube or from injection through a slit then results are compared to packer tests and show that when both sets of large and small fractures are included the proposed model reproduces reasonably in situ measured data analytical formulae are proposed for computing an approximate permeability from field data the decrease of hydraulic conductivity with depth is also discussed we show that the proposed model for peridotites aquifers is similar to the one currently admitted for granitic rock aquifers it relies on weathering of a pre existing serpentine bearing fractures network which controls permeability in the weathering profile itself but also deeper in the fresh and non weathered rock the proposed conceptual model allows deriving quantitative estimate of hydraulic conductivity from field data which are of primary interest for managing the groundwater resource of peridotite aquifers particularly where mining operations impact groundwater flow