helium radon and radiocarbon studies on a regional aquifer system of the north gujarat cambay region india abstract the study reports the age evolution of groundwater as it flows from the recharge area through a regional alluvial aquifer system in north gujarat cambay region in western india radiocarbon 14 c 4 he and 4 he 222 rn dating methods have been employed sediments from a drill core in the cambay basin were also analysed for uranium u and thorium th concentrations and the measured values have been used to estimate the 4 he and 222 rn production rate for groundwater age calculations additionally factors controlling the distribution of 222 rn 4 he and temperature anomalies in groundwater vis a vis their relation to the tectonic framework and lithology of the study area have also been examined the multi isotope study indicated a reasonable correspondence in groundwater age estimates by the three methods employed the groundwater 14 c ages increased progressively in the groundwater flow direction from the foothills of aravalli mountains in the east and reached a value of 35 ka towards the region of lowest elevation linking little rann of kachchh lrk nalsarovar ns gulf of khambhat gk in the western part of the study area in this region groundwater ages obtained for free flowing thermal wells and springs employing 4 he and 4 he 222 rn systematics are in the order of million years such anomalous ages are possibly due to enhanced mobilisation and migration of excess helium from hydrothermal circulation vents along deep seated faults excluding such anomalous cases and considering all uncertainties presently estimated 4 he and 4 he 222 rn groundwater ages are in reasonable agreement with 14 c age estimates in the cambay basin for helium release factor he value of 0 4 0 3 the 4 he method also indicated west southwards progression of groundwater ages up to 100 ka beyond the cambay basin large excess helium concentrations are also seen to be generally associated with anomalous groundwater temperatures 35 c and found to overlie some of the basement faults in the study area particularly along the east and the west flanks of the cambay basin groundwater 222 rn activities in most of the study area are 800 400 dpm l but a thermal spring at tuwa on the east flank of the cambay basin having granitic basement at shallow depth recorded the highest 222 rn activity 63 000 dpm l

argon 39 argon 37 and krypton 85 isotopes in stripa groundwaters abstract 39 ar 37 ar and 85 kr activities in groundwater samples from three boreholes in the stripa granite are compared with 222 rn activities and with data from a granitic groundwater in switzerland in situ production rates in bulk granite and in fracture filling minerals are calculated the measured isotopes in groundwater have been produced by nuclear reactions in the rock matrix it was reported earlier that a large fraction of the in situ produced 222 rn can escape to the water phase due to the unusual microscopic distribution of u which seems to be in close contact with the water phase the same conclusion can be drawn for 85 kr with escape factors between 5 and 25 the 39 ar values in stripa groundwaters are the highest measured so far but consistent with the unusually high neutron flux in stripa as compared to granites with lower u and th contents the 37 ar concentrations appear to be quite high but since it is the first time that this isotope has been identified in groundwater the basis for a comparison with different rock formations is still too small it seems possible that calcite fracture fillings in stripa have a major influence on the concentration of 37 ar in groundwater

review of the modelling of radionuclide transport from u series disequilibria and of its use in assessing the safe disposal of nuclear waste in crystalline rock abstract u series disequilibia from crystalline rocks and u deposits have been used to estimate the timing of hydrogeological events for u and ra mobility and to model the transport rates of u and ra both with some sucess unfortunately activity ratio data alone are not unique to a given process or model and it is shown how inappropriate choice of the model can have quite diverse consequences for interpretation of the data information from other sources is needed to help minimise these non uniqueness problems but as yet the state of methodology is unadequate to assess completely the validity of the models in particular the rate of deposition of u in fractures seems highly dependent upon the availability of trivalent fe and other low temperature minerals whose rates of formation are largely unknown this review reinforces the need to assess closely the suggestion that chemisorption is an effective retardant of fracture borne borne repository source radionuclides

understanding and modelling dissolved gas transport in the bedrock of three fennoscandian sites summary the origin and transport of dissolved gases in the geosphere is of interest for assessment studies of nuclear waste repositories in this paper we analyse available field measurements of helium methane and hydrogen at three fennoscandian sites forsmark and laxemar in sweden and olkiluoto in finland the field data are interpreted using different analytical models all based on the one dimensional diffusion equation the results of the different models provide estimates about the amount of deep gas flux the in situ production and the groundwater residence time of the considered sites the computed helium fluxes which fall within the lower range of crustal degassing fluxes reported by torgersen 2010 are strictly related with the high tightness of the considered fracture media the very high estimates of groundwater residence time indicate that at the considered depths there are only very few flowing fractures while in the rest of the fractured domain groundwater has been almost motionless during a whole glacial cycle

high levels of uranium and radium in groundwaters at canada s underground research laboratory lac du bonnet manitoba canada abstract high concentrations of u and 226 ra and elevated 234 u 238 u activity ratios have been measured in groundwater samples collected from water supply wells and exploratory boreholes in the area surrounding the underground research laboratory url of atomic energy of canada limited in southeastern manitoba all groundwaters come from the lac du bonnet granite batholith or sediments overlying the batholith uranium concentrations attain almost 1 mg l in some shallow low salinity groundwaters whereas 226 ra tends to be high up to 38 bq l in deeper saline waters the u concentrations are some of the highest observed in global groundwaters yet no significant ore body or mineralization is known in the area analyses of unaltered rock samples of the lac du bonnet granite show slight u enrichment over average canadian shield granites 6 5 g g vs 4 g g and altered wall rock in fracture zones is enriched in u by up to an order of magnitude compared to adjacent bedrock low 234 u 238 u activity ratios in this altered rock indicate active and recent leaching of u by groundwater the key control on u concentration appears to be redox potential concentrations of u in rock residence time and groundwater composition are of lesser importance geochemical modelling of the shallower oxidized waters indicates that u speciation consists mainly of anionic carbonate complexes of the uranyl ion this is supported by the remarkable efficiency of an anionic filter developed to remove high levels of u from drinking water in the area in more reducing groundwaters u concentrations are similar to those determined in recent experimental work on uraninite solubility in the ph range 7 8 5 colloidal u is

noble gases in formation fluids from deep sedimentary basins a review abstract atmospheric ne ar kr and xe are observed in fluids occurring in deep basins modifications of their abundance patterns reveal modes of recharge and brine formation phase separations during boiling and association of natural gas with water or oil radiogenic 4 he and 40 ar serve as age indicators of entrapped fluids effective over a significant portion of the geological time scale simultaneous application of 13 c atmospheric noble gases and radiogenic 4 he and 40 ar is recommended to identify a recent bacterial natural gas formation not accompanied by oil and b natural gas formed along with oil in a mature source rock

sources of radiogenic helium in a clay till aquitard and its use to evaluate the timing of geologic events abstract concentrations of dissolved gases he ne ar and n 2 were measured in pore waters collected from a pleistocene 0 80 m depth and cretaceous 80 156 m depth aged clay rich aquitard system using both a conventional copper tube method and in situ diffusion samplers both methods yielded similar results he data revealed a well defined increase in concentration with depth from 1 7 10 8 cm 3 he stp g 1 water near the water table at 2 3 m below ground surface to 6 9 10 6 cm 3 he stp g 1 water at 80 m below ground surface b g the concentration at depth greatly exceeded values for atmospheric solubility at in situ temperatures and could not be attributed to steady state production from decay of u and th within the aquitard system trends in he isotope ratios and concentrations suggest accumulation as a result of both release of residual 4 he from within the pleistocene clay rich till ca 87 and an ascending radiogenic helium flux from underlying cretaceous age sediments ca 13 one dimensional transport modeling of the he data suggests that between 15 ka and 25 ka were required to produce the observed profile this time frame agrees with studies utilizing isotope tracers i e d h and 14 c dic to estimate the timing of deposition for the till at this site our results demonstrate the utility of using helium a nonreactive tracer for delineating hydrogeologic processes in slow permeability geologic strata and also support the contention that thick clay rich surficial aquitards can provide long term containment of contaminants including hazardous wastes

a new groundwater radiocarbon correction approach accounting for palaeoclimate conditions during recharge and hydrochemical evolution the ledo paniselian aquifer belgium abstract the particular objective of the present work is the development of a new radiocarbon correction approach accounting for palaeoclimate conditions at recharge and hydrochemical evolution relevant climate conditions at recharge are atmospheric pco 2 and infiltration temperatures influencing c isotope concentrations in recharge waters the new method is applied to the ledo paniselian aquifer in belgium this is a typical freshening aquifer where recharge takes place through the semi confining cover of the bartonian clay besides cation exchange which is the major influencing process for the evolution of groundwater chemistry particularly in the bartonian clay also mixing with the original porewater solution fossil seawater occurs in the aquifer recharge temperatures were based on noble gas measurements potential infiltration water compositions for a range of possible pco 2 temperature and calcite dissolution system conditions were calculated by means of phreeqc then the sampled groundwaters were modelled starting from these infiltration waters using the computer code netpath and considering a wide range of geochemical processes fitting models were selected on the basis of correspondence of calculated 13 c with measured 13 c the 14 c modelling resulted in residence times ranging from holocene to pleistocene few hundred years to over 40 ka and yielded consistent results within the uncertainty estimation comparison was made with the 13 c and fontes and garnier correction models that do not take climate conditions at recharge into account to date these are considered as the most representative process oriented existing models yet differences in calculated residence times of mostly several thousands of years up to 19 ka are revealed with the newly calculated ages being mostly though not always younger not accounting for climate conditions at recharge pco 2 and temperature is thus producing substantial error on deduced residence times the derived 14 c model ages are correlated with he concentrations measured in the groundwater of the aquifer the obtained residence times show a gap between about 14 and 21 ka indicating possible permafrost conditions which inhibited any groundwater recharge

hydro radio chemical relationships in the giant guarani aquifer brazil abstract this investigation was carried out within the parana sedimentary basin and involved the sampling of 78 pumped tubular wells for evaluating the hydrochemistry and radioactivity due to the nuclides 238 u 234 u 222 rn 226 ra and 228 ra in the brazilian part of guarani aquifer several significant correlations were found involving the geostatic pressure for instance specific flow rate temperature dissolved o 2 free co 2 ph redox potential eh conductivity na hco 3 co 3 2 si calcite cl f so 4 2 and b carbonates precipitation was evidenced by inverse correlation between co 3 2 and ca mg sr and ba whereas na exhibited an opposite trend dissolving rather than precipitating with increasing co 3 2 concentration an inverse correlation between co 3 2 and k was found possibly related to the increasing tendency of k to recombine with the thickness of the clayey layers hco 3 played an important role on na ca mg and sr dissolution the dissolved u content and 234 u 238 u activity ratio data were plotted on a two dimensional diagram that was successfully utilized on identifying an unreported zone of u accumulation though not necessarily of economic size and grade the variability in chemical and radionuclides data indicated an important influence of the underlying paleozoic sediments in the composition of waters from guarani aquifer the available data allowed estimate the groundwater residence time by two u isotopes disequilibrium methods values of 45 61 ka were initially calculated depending on the adopted porosity 15 20 but a longer residence time 640 ka was also estimated which is more compatible with the hydraulic conductivity data in guarani aquifer and groundwater flow velocity occurring at milk river aquifer alberta canada such time range agrees with previously reported 14 c ages exceeding 30 ka bp at the more central parts of the parana sedimentary basin

fracturing induced release of radiogenic 4he and 234u into groundwater during the last deglaciation an alternative source to crustal helium fluxes in periglacial aquifers external 4he sources have been invoked to explain 4he concentrations in groundwater greater than those expected from in situ u and th production in a fractured aquifer of ordovician age located in the st lawrence lowlands quebec canada 4he concentrations of up to 4 48 x 10 5 cm3 stp gh20 1 were measured such concentrations are ca 1000 times higher than would be expected from in situ production a concomitant increase in 4he concentration and 234u 238u activity ratio is shown suggesting a common release process in groundwater for 234u and 4he this process has tentatively been identified as glaciation induced rock fracturing following the laurentide ice sheet retreat the resulting increase in exposed grain surface facilitates 234u release by recoil and that of radiogenic 4he by diffusion using a model of helium diffusion from a spherical grain it is shown that rock fracturing facilitated the release of accumulated 4he at rates ranging from 4 2 x 10 10 cm3stp gh20 1 yr 1 to 1 06 x 10 8 cm3stp gh20 1 yr 1 these release rates are between 1 000 and 30 000 times higher than the local u and th steady state production rate of 3 5 1 4 x 10 13 cm3stp grock 1 yr 1 integration of 4he release rates over time yields a radiogenic 4he concentration of between 3 85 x 10 6 cm3stp gh20 1 and 7 12x 10 5 cm3stp gh20 1 in the range of concentrations measured in the st lawrence lowlands fractured aquifers results support the occurrence of a local radiogenic helium source to explain the excesses measured in groundwater without requiring a significant external he crustal flux

the implications of laboratory222rn flux measurements to the radioactivity in groundwaters the case of a karstic limestone aquifer laboratory time scale experiments were conducted on carboniferous limestone gravels from the mendip hills area england with the purpose of evaluating the release of 222 rn to the water phase the specific surface areas of the samples were 4 14 and 1 69 cm 2 g 1 which provided respectively values of 50 6 and 12 7 pci for the released rn these results allowed the calculation of the emanation coefficient of this rock matrix with respect to the release of rn where completely different values corresponding to 23 and 6 were found suggesting that the extent to which grain boundaries or imperfections in aggregates of micro crystals of calcite intersect the particle surface certainly affects the rn release they also permitted the evaluation of models for the generation of rn in rocks and transfer to water in order to interpret the radioactivity due to this gas in groundwaters from the karstic aquifer of the mendip hills area where the calculated activities in groundwater based on the values of 23 and 6 for the emanation coefficient were about 51 and 15 times higher than actually measured in groundwater therefore the emanation coefficient in nature is considerably smaller than in the lab experiment and another factor k 0 k 1 may be introduced into the equations related to the modelling with the aim of adjusting the theoretical practical results

helium accumulation in groundwater ii a model for the accumulation of the crustal 4he degassing flux abstract a model of 4 he accumulation in a confined aquifer is presented which includes in situ production and a crustal degassing flux of 4 he into the bottom of a confined aquifer the model is consistent with the measurements of 4 he concentration in the great artesian basin australia torgersen and clarke 1985 and also with the measurements of 4 he concentration in the auob sandstone of namibia heaton 1981 the measured value of the crustal degassing flux of 4 he from these two areas is comparable with the 4 he degassing flux calculated from the atmospheric budget of 4 he wasserburg et al 1963 ozima and podosek 1983 a literature review suggests that a crustal degassing 4 he source may account for the 4 he accumulation in many other groundwater systems it is concluded from the literature review the detailed modelling of 4 he accumulation in gab and the auob sandstone and the atmospheric budget that crustal degassing of 4 he may be a common and widespread phenomena

radiogenic helium in shallow groundwater within a clay till southwestern ontario 1 profiles of 4he in pore water were measured in clay aquitards in sw ontario the 4he distributions are consistent with groundwater velocities that are 70 of initial 4he for 50 to 60 ka prior to incorporation into the till

the geochemistry of water near a surficial organic rich uranium deposit northeastern washington state u s a abstract the chemistry of three stream three spring and six near surface waters in the vicinity of a holocene organic rich uranium deposit is described with particular emphasis on the chemistry of u results characterize the solution behavior of uranium as u bearing water interacts with relatively undecomposed surficial organic matter of the measured major and trace chemical species only u is consistently highly enriched 17 318 ppb relative to reported values for regional waters or to literature values for waters in largely granitic terrains r mode factor analysis of the chemical data suggests that most u is present in a soluble form but that some u is also associated with fine suspended particulates of clay organic matter or hydrous oxides calculations that apply thermodynamic data to predict u speciation in solution indicate the relative importance of uranyl carbonate and uranyl phosphate complexes analysis of more finely filtered samples 0 05 m vs 0 45 m and direct radiographic observations using fission track detectors suspended in the waters indicate the presence of some uraniferous particulate matter application of existing thermodynamic data for uranous and uranyl bearing minerals indicates that all waters are undersaturated with u minerals as long as ambient eh 0 1 v if coexisting surface and near surface waters are sufficiently oxidizing initial fixation of u in the deposit should be by a mechanism of adsorption alternatively more reducing conditions may prevail in deeper pore waters of the organic rich host sediments perhaps leading to direct precipitation or diagenetic formation of u4 minerals a 234 u 238 u alpha activity ratio of 1 08 0 02 in a spring issuing from a hillslope above the deposit suggests a relatively soluble source of u in contrast higher activity ratios of 234 u 238 u 1 3 in waters in contact with the uraniferous valley fill sediments suggest differences in the nature of interaction between groundwater and the local u rich source rocks

natural radioelement solution by circulating groundwaters in the stripa granite natural radioelement concentrations in groundwaters from the fracture flow regime in the stripa granite were monitored during the period 1977 1986 uranium concentrations from depths of 80 m or less and in minewaters from above the hydraulic sink produced by the deepest mining level 410 m range from 10 to 90 ppb 234u238u activity ratios are characteristic of chemical leaching processes at the shallower depths whilst at about 350 m groundwaters occur which have an additional component of 234u by alpha recoil processes at greater depths u concentrations are indicative of the changed redox conditions and are subject to activity ratio enhancement by the alpha recoil process groundwater residence times may be estimated from the rate of such recoil solution of 234u in zones where chemical leaching of u is not active the 222rn contents of the minewaters are extremely high and can be related to the 222rn flux from fracture surfaces and the fracture width the fracture apertures range from 10 mm for the shallow groundwater zone 222rn contents m for water from the deepest borehole section 222rn content 100 kbq kg 1 the activity ratios 234th238u 210pb222rn and 210po222rn have been used to estimate residence times for th pb and po isotopes solution of ra is controlled by chemical rather than alpha recoil processes the 226ra content of the groundwater increases with salinity and is well correlated with groundwater ca content the 228ra226ra activity ratios in the groundwaters suggest that water rock interaction occurs predominantly with the average granitic matrix rather than with highly uraniferous fracture mineralisation the behaviour of ra th and po isotopes may be used to assess that of homologous fission product and actinide constituents of nuclear wastes in groundwaters

the u isotopes modeling in aquifers from pocos de caldas plateau brazil u modeled groundwater residence times were estimated by changes in 234u 238u activity ratio ar and u content of groundwaters from pocos de caldas city situated at the pocos de caldas alkaline massif brazil the estimated ages are more realistic than others generated by the use of hydraulic conductivity data and available information about the weathering rate of rocks in the plateau the 234u 238u ar and reciprocal of the dissolved u content data also defined a ternary plot that allowed the calculation of the relative volume of three source waters for the mixed water such u isotopes modeling for mixing calculations indicated that the dominant phase 68 in the mixture is thermal

evaluation of pleistocene groundwater flow through fractured tuffs using a u series disequilibrium approach pahute mesa nevada usa abstract groundwater flow through fractured felsic tuffs and lavas at the nevada national security site represents the most likely mechanism for transport of radionuclides away from underground nuclear tests at pahute mesa to help evaluate fracture flow and matrix water exchange we have determined u series isotopic compositions on more than 40 drill core samples from 5 boreholes that represent discrete fracture surfaces breccia zones and interiors of unfractured core the u series approach relies on the disruption of radioactive secular equilibrium between isotopes in the uranium series decay chain due to preferential mobilization of 234 u relative to 238 u and u relative to th samples from discrete fractures were obtained by milling fracture surfaces containing thin secondary mineral coatings of clays silica fe mn oxyhydroxides and zeolite intact core interiors and breccia fragments were sampled in bulk in addition profiles of rock matrix extending 15 to 44 mm away from several fractures that show evidence of recent flow were analyzed to investigate the extent of fracture matrix water exchange samples of rock matrix have 234 u 238 u and 230 th 238 u activity ratios ar closest to radioactive secular equilibrium indicating only small amounts of groundwater penetrated unfractured matrix greater u mobility was observed in welded tuff matrix with elevated porosity and in zeolitized bedded tuff samples of brecciated core were also in secular equilibrium implying a lack of long range hydraulic connectivity in these cases samples of discrete fracture surfaces typically but not always were in radioactive disequilibrium many fractures had isotopic compositions plotting near the 230 th 234 u 1 1 line indicating a steady state balance between u input and removal along with radioactive decay numerical simulations of u series isotope evolution indicate that 0 5 to 1 million years are required to reach steady state compositions once attained disequilibrium 234 u 238 u and 230 th 238 u ar values can be maintained indefinitely as long as hydrological and geochemical processes remain stable therefore many pahute mesa fractures represent stable hydrologic pathways over million year timescales a smaller number of samples have non steady state compositions indicating transient conditions in the last several hundred thousand years in these cases u mobility is dominated by overall gains rather than losses of u

a study of uranium and thorium series isotopes in chalk groundwaters of lincolnshire u k a groundwater investigation is described in which uranium and thorium series radionuclides are applied to the study of the hydrogeologically well documented lincolnshire chalk aquifer system of north lincolnshire england the dominance of eh in controlling the uranium content of groundwaters is discussed and the 230th234u activity ratio used as an indicator of the speciation of uranium in highly reduced waters the 230th234u activity ratio approaches unity suggesting that the uranium in solution is behaving similarly to thorium in the 4 valence state in the oxidised environment the higher uranium content groundwaters exhibit lower 234u238u activity ratios a model of mixing young low 234u238u activity ratio fissure waters with old high 234u238u activity ratio pore waters is discussed but rejected it is considered that preferential dissolution of 234u in the lower rate weathering regimes produces the observed relationship between uranium content and activity ratio a method of in situ rn random release factor determination is suggested however the calculated values for rn are disproportionately high for a fissure flow system this along with evidence of a radium depleted aquifer matrix indicates that radium is being mobilised and transported from the pore water system to the fissure system and subsequently adsorbed by clay minerals lining the chalk fissures

a borehole methodology for hydrogeochemical investigations in fractured rock research into the development of borehole techniques for hydrogeochemical investigations in fractured rock has resulted in the construction of a geochemical probe controlled and operated with an umbilical cable system this probe has been field tested to a depth of 600 m in a multilevel ported casing at the chalk river nuclear laboratories crnl the probe provides in situ measurements of ph redox potential dissolved oxygen temperature conductivity and pressure while allowing groundwater sample collection both at surface and downhole the multilevel ported casing preserves the subsurface hydrogeochemical zonation and facilitates sampling at various depths in the crnl borehole dilute na hco3 and na cl waters ranging in age from 500 to 12 000 years have been observed in gneissic rock at depths of 85 to 350 m however accurate hydrogeochemical characterization of the low permeability metagabbro present from 400 to 600 m has been frustrated by contamination from casing installation water

sedimentation patterns off the zambezi river over the last 20 000 years marine sediments from continental margins provide high resolution archives of marine and continental climate in particular near large river mouths the zambezi is one of the largest rivers in east africa discharging large amounts of fine grained sediments onto the western margin of the mozambique channel accurate reconstructions of past variations in river discharge can be retrieved from the depositional history of riverine sediments in this study sedimentation patterns along the mozambique margin are inferred from a series of sediment cores spanning the last 20 kyr these cores were retrieved off the zambezi mouth from the shelf and from various depths at the continental slope to provide detailed information on the depositional history of this region high resolution x ray fluorescence and magnetic susceptibility core scanning measurements as well as grain size distributions of the lithogenic sediment fraction and organic matter and carbonate content analyses resolve centennial millennial timescale variations in sediment transport and deposition along the mozambique margin largest changes in lithogenic sediment deposition coincide with the flooding of the mozambique shelf due to deglacial sea level rise and changes in oceanic currents fine grained mainly zambezi sediments were no longer primarily deposited south of the zambezi mouth but increasingly deposited onto the mozambique shelf and transported northwards over the shelf before spilling over to the slope in addition flooding of the shelf initiated remobilization and down slope transport of coarse grained winnowed sediments the heinrich event 1 and younger dryas are clearly indicated as events of increased fine grained sediment deposition along the mozambique margin possibly linked to increased riverine runoff from the zambezi catchment which is in harmony with a southward shift of the intertropical convergence zone itcz and associated african rainfall belts causing wetter conditions this study illustrates that interpreting marine and continental climate proxy records in the vicinity of river deltas in terms of climate change requires proper consideration of sea level and oceanic circulation induced effects on the transport and deposition patterns of fine grained sediments at continental slopes

on the possibility of determining rates of removal of uranium from crystalline igneous rocks using u series disequilibria 1 a u leach model and its applicability to whole rock data the removal of u from granitic rocks is characterised by234u 238u 1 and 230th 234u 1 it is notable from weathered eye dashwa lakes canada granite samples and from the published data that230th 234u ratios seldom exceed a limiting value of about 2 a u leach model is discussed in detail which may account for these observations the model assumes that 230th is practically immobile and that the removal of u can then be measured against the decay rate of the unsupported230th a property of the model is that the isotope ratios reach constant values reflecting a kind of secular equilibrium and this implies that u is seldom removed faster than the decay of230th if the limited230th 234u ratios from the data correspond to secular equilibrium ratios then this allows simple calculation of u leach rates from any given subsurface sample a test for the model using235u 231pa ratios is suggested a comparison of leach rates derivable from u th pb systematics of colorado and wyoming granite samples with the corresponding estimates from the model shows that the latter are high by a factor of 10 50 data from rapidly weathered surface rinds suggests that the presence of labile u restricts the application of the model to subsurface low weathered zones

fracture detection and groundwater flow characterization using he and rn in soil gases manitoba canada abstract surveys of the distribution and migration of he and rn were carried out in the well characterized granitic terrane of the aecl underground research laboratory url manitoba as part of a joint aecl research united kingdom department of the environment and united states department of energy research initiative the investigations were designed to determine whether concentrations of he and rn in soil gases could be used to identify locations of groundwater recharge and discharge from bedrock fractures the results obtained indicate that subsurface transport of he and possibly rn in this setting appears to be controlled largely by the groundwater flow system in the bedrock release of dissolved gases near the ground surface causes soil gas anomalies which reflect discharge from the deeper flow system in the recharge area of the deep groundwater flow system at the url site he abundances are close to the atmospheric level but the discharge area of the deep flow system is characterized by significant he anomalies up to 0 5 ppm above atmosphere levels for rn the recharge area has broadly distributed high concentrations probably caused by local rn production in u rich overburden while the discharge area has only localized concentrations of rn which are not at the same location as the he anomalies the general nature of the groundwater flow regime in both areas is reflected in the presence and distribution of the soil gas anomalies in addition major fractures in bedrock which act as preferential groundwater flow paths have been located from soil gas anomalies even when obscured by overburden of variable thickness and character the distribution of he in soil gas appears to be most representative of groundwater recharge and discharge conditions in the granitic rock while rn may be useful for locating specific channels where more rapid groundwater discharge is occurring from deep fracture zones

radioisotope dynamics the origin and fate of nuclides in groundwater the use of radionuclides as clocks for groundwater dating and as probes to investigate the geometry and spatial extent of the contact area between rocks and water is reviewed subsurface production rates for 222 rn 37 ar 55 kr 39 ar 36 cl 3 he 4 he and 40 ar in various rock types are listed measured rn fluxes from the surface of sandstone grains and from pieces of granite point to scale dependent diffusion coefficients the temporal evolution of subsurface produced 222 rn 37 ar 85 kr and 39 ar activities in groundwaters yields radionuclide escape factors between 0 1 and 9 for the stripa granite sweden and between 1 and 4 for the milk river sandstone canada the combination of 3 h 85 kr 39 ar 14 c 36 cl 4 he in the uk triassic sandstone aquifer allows groundwater dating up to 40 000 a very old groundwaters can be studied using cl 36 cl and 4 he evolution as demonstrated in the milk river aquifer in canada

noble gas residence times of saline waters within crystalline bedrock outokumpu deep drill hole finland abstract noble gas residence times of saline groundwaters from the 2516 m deep outokumpu deep drill hole located within the precambrian crystalline bedrock of the fennoscandian shield in finland are presented the accumulation of radiogenic 4 he 40 ar and nucleogenic 21 ne noble gas isotopes in situ together with the effects of diffusion are considered fluid samples were collected from depths between 180 and 2480 m below surface allowing us to compare the modelled values with the measured concentrations along a vertical depth profile the results show that while the concentrations in the upper part are likely affected by diffusion there is no indication of diffusive loss at or below 500 m depth furthermore no mantle derived gases were found unequivocally previous studies have shown that distinct vertical variation occurs both in geochemistry and microbial community structuring along the drill hole indicating stagnant waters with no significant exchange of fluids between different fracture systems or with surface waters therefore in situ accumulation is the most plausible model for the determination of noble gas residence times the results show that the saline groundwaters in outokumpu are remarkably old with most of the samples indicating residence times between 20 and 50 ma although being first order approximations the ages of the fluids clearly indicate that their formation must predate more recent events such as quaternary glaciations isolation within the crust since the eocene miocene epochs has also direct implications to the deep biosphere found at outokumpu these ecosystems must have been isolated for a long time and thus very likely rely on energy and carbon sources such as h 2 and co 2 from groundwater and adjacent bedrock rather than from the ground surface

radioelements radiogenic helium and age relationships for groundwaters from the granites at stripa sweden abstract the solution of radioelements and radiogenic 4he by groundwaters in fractured rocks is dependent upon the radioelement distribution in the rock matrix and the extent of the rock water interface the 234 u 238 u activity ratio and the dissolved u rn and he contents of such groundwaters respond to changes in the flow regime with time although 234 u 238 u activity ratios change with groundwater residence time as a consequence of 234th recoil induced solution of 234u the activity ratio is strongly influenced by the u distribution within fractures by the extent of the rock water interface and by the amount of 238u in solution a model for the quantitative evaluation of these effects is presented groundwaters from depths up to 880 m in the stripa granite have variable dissolved uranium contents and 234 u 238 u activity ratios the uranium geochemistry is primarily determined by variations in flow path rather than by groundwater age dissolved radiogenic 4he in the groundwaters increases with their depth of origin and is dependent upon the u content of the granite and upon its fracture porosity it increases with groundwater residence time but movement of 4he by diffusion and transport processes make the actual groundwater age indeterminate

kinetics of co2 fluid rock reactions in a basalt aquifer soda springs idaho the dissolution of silicate minerals by co2 rich fluids and the subsequent precipitation of co2 as carbonate minerals represent a means of permanently storing anthropogenic co2 waste products in a solid and secure form modelling the progression of these reactions is hindered by our poor understanding of the rates of mineral dissolution precipitation reactions and mineral surface properties in natural systems this study evaluates the chemical evolution of groundwater flowing through a basalt aquifer which forms part of the leaking co2 charged system of the blackfoot volcanic field in south eastern idaho usa reaction progress is modelled using changes in groundwater chemistry by inverse mass balance techniques the co2 promoted fluid mineral reactions include the dissolution of primary plagioclase orthoclase pyroxene and gypsum which is balanced by the precipitation of secondary albite calcite zeolite kaolinite and silica mineral mole transfers and groundwater flow rates estimated from hydraulic head data are used to determine the kinetics of plagioclase and orthoclase feldspar dissolution plagioclase surface area measurements were determined using the evolution of the u series isotope ratios in the groundwater and are compared to published surface area measurements calculated rates of dissolution for plagioclase range from 2 4 10 12 to 4 6 10 16 mol m2 s and orthoclase from 2 0 10 13 to 6 8 10 16 mol m2 s respectively these feldspar reaction rates correlate with the degree of mineral fluid disequilibrium and are similar to the dissolution rates for these mineral measured in other natural co2 charged groundwater systems

the relationship between he and cl as a criterion for the formation of groundwater composition abstract the analysis of the relationship between 1611 parallel determinations of helium and chloride concentrations in the groundwater of crystalline shields and sedimentary basins was performed the comparison showed that groundwaters have helium and chlorides concentrations in the range of 1 8 10 8 to 6 8 mol m3 and of 5 6 10 3 to 6488 mol m3 respectively and relatively stable he rcl ratios equal to 5 5 10 5 in sedimentary basins and 7 5 10 4 in crystalline shields such behavior of helium and chlorides shows that the formation of the groundwater composition is determined primarily by the processes of mixing fresh meteoric and saline sea waters with ancient brines from great depths during sedimentation sea water penetrates the subsurface and mixes with ancient brines on land fresh meteoric waters dilute the mixtures of seawater and ancient brines most of the radiogenic 4he and chlorides comes from the subsurface ancient brine the radiogenic 4he in the host rocks plays a secondary role therefore the concentration of 4he in saline groundwater reflects the size of the impurities of the ancient brine with a very high content of 4he rather than the residence time within the subsurface

the behavior of dissolved uranium in groundwaters of the morro do ferro thorium deposit brazil groundwater samples were collected for several months in boreholes drilled at morro do ferro a thorium and rare earth deposit located on the pocos de caldas plateau minas gerais state brazil an aquifer system has developed in the weathered mantle due to in situ intense alteration the weathered zone includes a thick argillaceous laterite greater than 100 m thick the u content and 324u 238u activity ratio were measured in the groundwater samples and in spoil samples of a borehole drilled in the ore body some possible mechanisms related to the mobilization of uranium are considered such as complexation with humic substances and adsorption by clays

uranium isotopes as tracers of groundwater evolution in the complexe terminal aquifer of southern tunisia abstract the complexe terminal ct multi layer aquifer is formed by neogene paleogene sand deposits upper senonian campanian maastrichtian limestones and turonian carbonates the chemical composition and isotopes of carbon and uranium were investigated in groundwater sampled from the main hydrogeological units of the ct aquifer in southern tunisia we paid special attention to the variability of uranium contents and isotopes ratio 234u 238u to provide a better understanding of the evolution of the groundwater system uranium concentrations range from 1 5 to 19 5 ppb typical of oxic or mildly reducing conditions in groundwaters the lowest concentrations are found southeast of the study area where active recharge is supposed to take place when looking at the isotope composition it appears that all the samples including those from carbonate levels are in radioactive disequilibrium with significant 234u excess a clear cut distinction is observed between turonian and senonian carbonate aquifers on the one hand with 234u 238u activity ratios between 1 1 and 1 8 and the sandy aquifer on the other hand showing higher ratios from 1 8 to 3 2 the distribution of uranium in this complex aquifer system seems to be in agreement with the lithological variability and are ultimately a function of a number of physical and chemical factors including the uranium content of the hosting geological formation water rock interaction and mixing between waters having different isotopic signatures significant relationships also appear when comparing the uranium distribution with the major ions composition it is noticeable that uranium is better correlated with sulfate calcium and magnesium than with other major ions as chloride or bicarbonate the 14c activities and 13c values of dic cover a wide range of values from 1 1 pmc to 30 2 pmc and from 3 6 to 10 7 respectively 14c model ages estimated by the fontes and garnier model are all younger than 22 ka and indicate that the recharge of ct groundwater occurred mainly during the end of the last glacial and throughout the holocene

transverse tectonic structural elements across himalayan mountain front eastern arunachal himalaya india implication of superposed landform development on analysis of neotectonics abstract structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern arunachal sub himalaya mountain front sinuosity smf index values close to one are indicative of the active nature of the mountain front all along the eastern arunachal himalaya which can be directly attributed to the regional uplift along the himalayan frontal thrust hft however the mountain front is significantly sinusoidal around junctions between hft mbt main boundary thrust and active transverse faults the high values of stream length gradient sl and stream steepness ks indices together with field evidence of fault scarps offset of terraces and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults this reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses providing favourable sites for deposition of recent sediments tectonic interactions of these transverse faults with the himalayan longitudinal thrusts mbt hft have segmented the mountain front marked with varying sinuosity the net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements some distinctive examples are in the eastern extremity of ne himalaya across the dibang river valley the nw se trending mountain front is attenuated by the active mishmi thrust that has thrust the mishmi crystalline complex directly over the alluvium of the brahmaputra plains the junction of the folded hft and mishmi thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the dibang river course similarly the transverse faults cut the mountain front along the sesseri siluk siku siang mingo sileng dikari and simen rivers at some such junctions landforms associated with the active right lateral strike slip faults are superposed over the earlier landforms formed by transverse normal faults in addition to linear transverse features we see evidence that the fold thrust belt of the frontal part of the arunachal himalaya has also been affected by the neotectonically active nw se trending major fold known as the siang antiform that again is aligned transverse to the mountain front the folding of the hft and mbt along this antiform has reshaped the landscape developed between its two western and eastern limbs running n s and nw se respectively the transverse faults are parallel to the already reported deep seated transverse seismogenic strike slip fault therefore a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the himalayan region must take into account the role of transverse tectonics

in situ radionuclide transport and preferential groundwater flows at ineel idaho decay series disequilibrium studies uranium and thorium decay series disequilibria in groundwater occur as a result of water rock interactions and they provide site specific natural analog information for assessment of in situ long term migration of radionuclides in the far field of a nuclear waste disposal site in this study a mass balance model was used to relate the decay series radionuclide distributions among solution sorbed and solid phases in an aquifer system to processes of water transport sorption desorption dissolution precipitation radioactive ingrowth decay and recoil isotopes of u 238u 234u th 232th 230th 228th 234th ra 226ra 228ra 224ra and rn 222rn were measured in 23 groundwater samples collected from a basaltic aquifer at the idaho national engineering and environmental laboratory ineel idaho the results show that groundwater activities of th and ra isotopes are 2 4 orders lower than those of their u progenitors which average 1 35 0 40 dpm 238u l with 234u 238u ratios of 1 6 3 0 222rn activities range from 20 to 500 dpm l modeling of the observed disequilibria places the following constraints on the time scale of radionuclide migration and water rock interaction at ineel 1 time for sorption is minutes for ra and th time for desorption is days for ra and years for th and time for precipitation is days for th years for ra and centuries for u 2 retardation factors due to sorption average 106 for 232th 104 for 226ra and 103 for 238u 3 dissolution rates of rocks are 70 to 800 mg l y 4 ages of groundwater range from 10 to 100 years contours of groundwater age as well as spatial patterns of radionuclide disequilibria delineate two north south preferential flow pathways and two stagnated locales relatively high rates of dissolution and precipitation and recoil of 222rn occur near the groundwater recharging sites as well as in the major flow pathways decay of the sorbed parent radionuclides e g 226ra and 228ra on micro fracture surfaces constitutes an important source of their daughter 222rn and 228th activities in groundwater

helium 4 characteristics of groundwaters from central australia comparative chronology with chlorine 36 and carbon 14 dating techniques summary helium isotope and concentration characteristics were determined for a suite of groundwater samples from the amadeus basin in central australia two study areas include a wellfield south of alice springs and the dune plains and mututjulu aquifers near uluru measurements of 36cl cl and 14c on the same sample suite enable us to assess the relative applicability of the three groundwater chronometers over a range of anticipated groundwater residence times ages and to investigate possible causes of discordant ages derived from the different groundwater dating techniques results from the analyses of 39 groundwater samples reveal helium 4 4he concentrations that range from 0 80 to 98 8 10 7 cm3 stp g 1 h2o in the alice springs samples and from 0 47 to 65 6 10 7 cm3 stp g 1 h2o in the uluru samples 4he concentrations yield uncorrected groundwater residence times i e time since recharge of between modern to 2500 ka near alice springs and modern to 1600 ka near uluru assuming an effective porosity of 20 and uranium and thorium contents of 1 7 and 6 1 ppm respectively 36cl cl ratios on the same samples range from 93 to 158 10 15 near alice springs and from 80 to 335 10 15 near uluru representing groundwater residence times near alice springs from modern to 200 ka and from modern to 300 ka near uluru percent modern carbon pmc on the same samples ranged from 64 9 to 12 5 pmc near alice springs and from 93 5 to 30 ka for the amadeus basin groundwater samples the 4he method uncorrected over estimates groundwater residence time compared to 36cl and 14c techniques this implies the presence of an extraneous he component or basal flux of he j0 to reconcile groundwater 4he and 14c residence times it is necessary to adopt j0 values between 0 and 30 10 8 cm3 stp he cm 2 a 1 which supplements in situ produced he within the aquifer adoption of j0 values over this range lowers 4he residence times relative to 36cl and produces closer agreement between the 4he and 14c chronometers the extraneous he component basal flux in amadeus basin samples is dominated by radiogenic crustal 4he without a detectable amount of mantle derived 3he we conclude that the stable tectonic regime albeit with the presence of major faults within the basin inhibits the input of mantle volatiles to the groundwater system so that in this region diffusion is the dominant transport mechanism for he in the crust

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

uranium mobility in the sediment hosted uranium deposit of coutras france abstract recent mobility of u was investigated in the coutras u deposit gironde france located in lutetian sediments near the surface the coutras deposit is a belt of tabular ore bodies separated into two areas by the dronne river the jean vincent area close to the surface and the le fieu area located at a maximum depth of 100 m the immobility of th is supported by whole rock th contents which do not vary significantly with u content the present hydrological regime in the jean vincent area is characterized by oxidizing waters flowing toward the dronne river activity ratios ar of 230th 234u in rocks which range from 0 55 to 12 demonstrate recent u accumulation and leaching the 234u 238u ar range from 0 94 to 1 52 in the rocks and from 0 94 to 1 61 in the waters recent accumulation of u is favored along redox barriers where mo v se and as are also mobilized waters in the le fieu area are nearly stagnant they are reduced and exhibit a different chemical composition than waters in the jean vincent area with higher contents of ca mg na k cl hco3 po4 ra ba mn higher 234u 238u ar 1 33 4 63 and lower u content the le fieu rock samples do not show any isotopic evidence of recent leaching of u but both relative excesses and deficits of 234u are observed preferential mobility of 234u in the reduced le fieu area is interpreted according to the recoil model the results place new constraints on the model of cowart and osmond and should be useful in prospecting for tabular u deposits in reduced environments

radionuclide mobility in thucholitic hydrocarbons in fractured quartzite radioactive hydrocarbons thucholites fill joints and fissures in presvecokarelian quartzites around the town of vastervik southeastern sweden uranium series nuclides including stable end members and carbon isotopes have been measured in surface samples and in drill core material originating down to 60 m below the surface uranium both is adsorbed onto noncrystalline hydrocarbonaceous material and forms different mineral phases the amount of hydrocarbons and uranium rapidly decreases with depth below 60 m the accumulations were too scanty for sampling uranium series nuclides show distinct gradients the surface samples with uranium contents up to 50 wt have been enriched in uranium lead and particularly thorium in geologically recent time probably during the last glaciation along the drill cores thorium has been immobile whereas 226ra and 222rn have migrated uranium has been distinctly migratory at and close to the surface but more or less immobile below 20 m depth almost no foreign rad

the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters noble gases inert elements having isotopes produced by the decay of long half life radionuclides offer a powerful approach for tracing fluid circulation and dating groundwaters the u th 4he water ages calculated from the accumulation rate in water of radiogenic 4he produced by decay of u and th contained in the aquifer rocks is frequently higher than the hydrological ages this discrepancy is generally interpreted by two contrasting models i heterogeneities of the aquifers which allow water stagnation and accumulation of large amounts of radiogenic 4he or ii addition of 4he produced in deeper regions of the continental crust in this contribution we propose that the apparent contrast between u th 4he ages and hydrological ages in the paris basin reflects the mixing of different types of water having different residence times we show using the helium isotopic signatures of waters that this mixing occurs between three aquifers the middle jurassic the triassic and the palaeozoic basement which have contrasting helium contents and heterogeneous chemical compositions and permeabilities the difference of radiogenic 4he 4 ratios between the aquifers of triassic and middle jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks this implies residence times for groundwaters circulating in the middle jurassic carbonate aquifer much longer than those obtained from hydrological studies independent fluid age estimates based on the ground palaeotemperatures recorded in the same groundwaters by the atmospherederived noble gases seem to confirm the presence of very old groundwaters in the paris basin the estimation of the residence time of ancient groundwaters is the most challenging problem in basin hydrology e g chapman 1987 typical water residence times of 104 108 years outreach the range of half lives of most of the geochronometers available in hydrology e g 3h 14c and prolonged water rock interactions alter the chemical and isotopic signature of water preventing the identification of the fluid sources on the other hand hydrological modelling faces serious problems of estimating space and time variations of critical parameters such as the permeability due to the petro physical heterogeneities of the aquifers and fluid velocity estimates can be valid only on a local scale e g alexander et al 1987 because noble gases are inert and have isotopes produced by natural decay of long halflife radionuclides these elements have received increasing attention as tracers of groundwater movements in deep aquifers e g marine 1979 andrews et al 1982 1985 bottomley et at 1984 1990 torgersen clarke 1985 zaikowski et al 1987 ballentine et al 1991 stute et al 1992 marty et al 1993 o nions ballentine 1993 groundwaters contain noble gases derived from the atmosphere the crust and the mantle fig 1 studies on water dating are focused mainly on the crustal derived radiogenic noble gas component for obvious reasons although the mantle derived component has the capacity of tracing fluid sources oxburgh et al 1986 and the atmosphere derived component can provide independent estimates on the water residence times pinti et al 1997 in continental environments mantle derived noble gases are generally observed in regions of active volcanism or extensional tectonics ballentine et al 1991 the source is probably sub continental magma intrusion and underplating with successive episodic and tectonically controlled advective transport in the crust torgersen 1993 mantle derived helium can be easily identified from its isotopic signature indeed the mantle is enriched in primordial 3he as indicated by 3he 4he ratios greater than 10 5 whereas the atmospheric ratio is l a x 10 6 and crustalderived radiogenic helium has 3he 4he ratios in the range of 10 8 consequently the geographical distribution of the 3he 4he ratios in sedimentary fluids can be used to identify the fluids pinti d l marty b 1998 the origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters in parnell j ed 1998 dating and duration of fluid flow and fluid rock interaction geological society london special publications 144 53 68 by guest on january 5 2014 http sp lyellcollection org downloaded from

a comparative study of aquifer systems occurring at the parana sedimentary basin brazil u isotopes contribution the radioactivity due to 238u and 234u in three aquifer systems occurring within the parana sedimentary basin south america has been investigated uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the u mobility coefficients between 7 6 10 6 and 1 2 10 3 g cm 3 these values are also compatible with the u preference ratios relative to na k ca mg and sio2 which showed that u is never preferentially mobilized in the liquid phase during the flow occurring in cracks fissures fractures and faults of the igneous basaltic rocks experimental dissolution of diabase grains on a time scale laboratory has demonstrated that the u dissolution appeared to be a two stage process characterized by linear and second order kinetics the u dissolution rate was 8 10 16 mol m 2 s 1 that is within the range of 4 10 16 3 10 14 mol m 2 s 1 estimated for other rock types the 234u 238u activity ratio of dissolved u in solutions was higher than unity a typical result expected during the water rock interactions when preferential 234u leach from the rock surfaces takes place some u isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in sao paulo state a modeling has been also realized considering all u isotopes data obtained in bauru 35 samples serra geral 16 samples and guarani 29 samples aquifers the results indicated that the bauru aquifer waters may result from the admixture of waters from guarani 1 5 and serra geral 98 5 aquifers

contact zones and hydrothermal systems as analogues to repository conditions abstract radioactive waste isolation efforts in the u s a are currently focused on examining basalt tuff salt and crystalline rock as candidate rock types to encompass waste repositories as analogues to near field conditions the distributions of radio and trace elements have been examined across contacts between these rocks and dikes and stocks that have intruded them the intensive study of the stripa quartz monzonite in sweden has also offered the opportunity to observe the distribution of u and its daughters in groundwater and its relationship to u associated with fracture filling and alteration minerals investigations of intrusive contact zones to date have included 1 a tertiary stock into precambrian gneiss 2 a stock into ash flow tuff 3 a rhyodacite dike into columbia river basalt washington and 4 a kimberlite dike into salt with respect to temperature and pressure these contact zones may be considered worst case scenario analogues results indicate that there has been no appreciable migration of radioelements from the more radioactive intrusives into the less radioactive country rocks either in response to the intrusions or in the fracture controlled hydrologic systems that developed following emplacement in many cases the radioelements are locked up in accessory minerals suggesting that artificial analogues to these would make ideal waste forms emphasis should now shift to examination of active hydrothermal systems studying the distribution of key elements in water fractures and alteration minerals under pressure and temperature conditions most similar to those expected in the near field environment of a repository

222rn solution by the circulating fluids in a hot dry rock geothermal reservoir abstract the mechanism of 222 rn release into fracture fluids by direct alpha recoil lattice and grain boundary micro crack diffusion is discussed experimental measurements of 222 rn release into surrounding air and water phases have been made for crystalline rock specimens with well defined surface areas the 222 rn flux from an infinite plane surface and hence the effective diffusion length of 222 rn in the rock matrix has been estimated the 222 rn flux from plane crystalline rock surfaces has been used in conjunction with a simple hydrological model of the reservoir to calculate the 222 rn content of the return fluids of a geothermal doublet circulation system for given production rate and piezometric difference between the injection and production wells the 222 rn content of the return fluid is dependent upon the distribution of flow path lengths and fracture apertures in the reservoir matching of the calculated and experimental 222 rn contents of the return fluids has been used to select appropriate parameters for the reservoir model and hence to estimate the extent of the heat transfer surface the model estimates the fracture width of the flow paths total swept surface area and fracture volume within the reservoir

processes controlling 234u and 238u isotope fractionation and helium in the groundwater of the st lawrence lowlands quebec the potential role of natural rock fracturing abstract the goal of this study is to explain the origin of 234 u 238 u fractionation in groundwater from sedimentary aquifers of the st lawrence lowlands quebec canada and its relationship with 3 he 4 he ratios to gain insight regarding the evolution of groundwater in the region 234 u 238 u activity ratios or 234 u 238 u act were measured in 23 groundwater samples from shallow quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the becancour river watershed the lowest 234 u 238 u act 1 14 0 01 was measured in ca hco 3 type freshwater from the quaternary shallower aquifer where bulk dissolution of the carbonate allows u to migrate into water with little 234 u 238 u isotopic fractionation the 234 u 238 u act increases to 6 07 0 14 in na hco 3 cl type groundwater preferential migration of 234 u into water by recoil is the underlying process responsible for this isotopic fractionation an inverse relationship between 234 u 238 u act and 3 he 4 he ratios has been observed this relationship reflects the mixing of newly recharged water with 234 u 238 u act close to the secular equilibrium and containing atmospheric tritiogenic helium and mildly mineralized older water 14 c ages of 6 6 kyrs with 234 u 238 u act of 6 07 and large amounts of radiogenic 4 he in excess of the steady state amount produced in situ the simultaneous fractionation of 234 u 238 u act and the addition of excess 4 he could be locally controlled by stress induced rock fracturing this process increases the surface area of the aquifer matrix exposed to pore water from which produced 4 he and 234 u can be released by recoil and diffusion this process would also facilitate the release of radiogenic helium at rates greater than those supported by steady state u th production in the rock consequently sources internal to the aquifers could cause the radiogenic 4 he excesses measured in groundwater

paleorecharge by the niger river mali deduced from groundwater geochemistry stable isotopes major elements trace elements and noble gases in groundwater from northern mali permit a reconstruction of the paleohydrology of the sahelian and sub saharan regions of west africa major floods of the niger river during the more humid episodes of the holocene probably associated with northward migration of the interior river delta flood zone were responsible for groundwater recharge a marine aerosol input somewhat modified by rock water interaction dominates the groundwater chemistry stable isotope compositions distinguish the saharan zone groundwater from waters recharged in the sahelian zone south of the azaouad ridge carbon 14 dating shows that whereas the latter are modem the saharan zone was recharged in the early to middle holocene noble gas contents suggest that recharge north of azaouad occurred under cooler climatic conditions than presently prevail

uranium geochemistry in groundwater from tertiary sediments abstract dissolved u concentrations and activity ratios ars of the u isotopes in the 238 u decay series were measured in ground and surface waters as part of an investigation to delineate the water quality in a proposed uranium mining area of northwest nebraska in oxidizing groundwaters from 67 wells completed in the tertiary sediments increasing u concentrations in the direction of groundwater flow generally were associated with a maturation of the formation water as evidenced by evolutionary trends in major ion character the increased u levels probably are associated with leaching as shown by the positive correlation between u concentrations and total dissolved solids tds r 0 83 the inverse relationships between tds and u ars r 0 73 and u levels and ars r 0 72 indicate that the decay of excess u 234 is related to maturation of the formation water and to sediment leaching along the flowpath the data are described by a model which incorporates etching decay and recoil and suggests that aquifer residence time can be estimated from the tds level the levels of soluble u in a reducing uraniferous hydrogeologic unit near crawford nebraska are affected by the proximity of the sample collection to ore in groundwater samples having similar chemistries na so 4 cl type similar ehs and collected from a close knit pattern u concentrations ranged from 0 01 to 2 037 g l 1 and ars ranged from 0 75 to 12 6 this high variability in u levels and ars is indicative of uranium ore in small areal studies where low ars almost always are associated with high u concentrations

u series disequilibrium radionuclides in sulphur incrustations from the fumarolic field of vulcano island abstract u series disequilibrium radionuclides 238 u 234 u 210 pb 210 po in sulphur incrustations deposited at la fossa cone vulcano island italy were measured over the period 1990 1995 to collect information about changes in the feeding system of the fumarolic field the 210 po 210 pb and 210 pb pb ratios of the sulphur incrustations allowed the identification of a fumarolic vent which is free from magmatic contribution and remobilized sublimate contamination in spite of the low temperature of the selected fumarole 280 350 c kinetic data show that 210 po is almost fully volatilized due to the relatively high velocity of the gas as a result the 210 po 222 rn activity ratio of the gas can be used to estimate fluid rising times about 100 days 234 u 238 u activity ratios of sulphur incrustations deposited in 1991 1993 showed a shift toward high values typical of nonmagmatic fluids both short lived and long lived u series disequilibrium radionuclides contribute to volcanic forecasting and give information on fluid sources and rising times as well as the residence times of the aquifers involved in the degassing process of the fumarolic field

alabama gulf coast groundwaters 4he and 14c as groundwater dating tools analyses of 4 he and 1 4 c in groundwaters from a miocene quartz aquifer on the alabama gulf coast show the usefulness of 4 he for dating these holocene groundwaters in this aquifer system of low alkalinities and low phs radiocarbon ages can be used without model correction the groundwaters studied ranged from 42 3 to 95 5 modern carbon and yielded uncorrected ages of 375 6790 yr radiogenic 4 he ages ranged from 50 7500 yr

the mechanism of 234u238u activity ratio enhancement in karstic limestone groundwater departamento de petrologia e metalogenia universidade estadual paulista campus de rio claro unesp sao paulo

234u 238u evidence for local recharge and patterns of ground water flow in the vicinity of yucca mountain nevada usa uranium concentrations and 234u 238u ratios in saturated zone and perched ground water were used to investigate hydrologic flow and downgradient dilution and dispersion in the vicinity of yucca mountain a potential high level radioactive waste disposal site the u data were obtained by thermal ionization mass spectrometry on more than 280 samples from the death valley regional flow system large variations in both u concentrations commonly 0 6 10 g l 1 and 234u 238u activity ratios commonly 1 5 6 are present on both local and regional scales however ground water with 234u 238u activity ratios from 7 up to 8 06 is restricted largely to samples from yucca mountain data from ground water in the tertiary volcanic and quaternary alluvial aquifers at and adjacent to yucca mountain plot in 3 distinct fields of reciprocal u concentration versus 234u 238u activity ratio correlated to different geographic areas ground water to the west of yucca mountain has large u concentrations and moderate 234u 238u whereas ground water to the east in the fortymile flow system has similar 234u 238u but distinctly smaller u concentrations ground water beneath the central part of yucca mountain has intermediate u concentrations but distinctive 234u 238u activity ratios of about 7 8 perched water from the lower part of the unsaturated zone at yucca mountain has similarly large values of 234u 238u these u data imply that the tertiary volcanic aquifer beneath the central part of yucca mountain is isolated from north south regional flow the similarity of 234u 238u in both saturated and unsaturated zone ground water at yucca mountain further indicates that saturated zone ground water beneath yucca mountain is dominated by local recharge rather than regional flow the distinctive 234u 238u signatures also provide a natural tracer of downgradient flow elevated 234u 238u in ground water from two water supply wells east of yucca mountain are interpreted as the result of induced flow from 40 a of ground water withdrawal elevated 234u 238u in a borehole south of yucca mountain is interpreted as evidence that natural downgradient flow is more likely to follow southerly paths in the structurally anisotropic tertiary volcanic aquifer where it becomes diluted by regional flow in the fortymile system

use of u isotopes in exploring groundwater flow and inter aquifer leakage in the south western margin of the great artesian basin and arckaringa basin central australia abstract the distribution of uranium isotopes 238u and 234u in groundwaters of the south western margin of the great artesian basin gab australia and underlying arckaringa basin were examined using groundwater samples and a sequential extraction of aquifer sediments rock weathering the geochemical environment and recoil of daughter products control the 238u and 234u isotope distributions giving rise to large spatial variations generally the shallowest aquifer j aquifer contains groundwater with higher 238u activity concentrations and 234u 238u activity ratios close to secular equilibrium however the source input of uranium is spatially variable as intermittent recharge from ephemeral rivers passes through rocks that have already undergone extensive weathering and contain low 238u activity concentrations other locations in the j aquifer that receive little or no recharge contain higher 238u activity concentrations because uranium from localised uranium rich rocks have been leached into solution and the geochemical environment allows the uranium to be kept in solution the geochemical conditions of the deeper aquifers generally result in lower 238u activity concentrations in the groundwater accompanied by higher 234u 238u activity ratios the sequential extraction of aquifer sediments showed that recoil of 234u from the solid mineral phases into the groundwater rather than dissolution of or exchange with the groundwater accessible minerals in the aquifer caused enrichment of groundwater 234u 238u activity ratios in the boorthanna formation decay of 238u in uranium rich coatings on j aquifer sediments caused resistant phase 234u 238u activity ratio enrichment the groundwater 234u 238u activity ratio is dependent on groundwater residence time or flow rate depending on the flow path trajectory thus uranium isotope variations confirmed earlier groundwater flow interpretations based on other tracers however spatial heterogeneity and the lack of clear regional correlations made it difficult to identify recharge and inter aquifer leakage