geochemical and hydrodynamic controls on arsenic and trace metal cycling in a seasonally stratified us sub tropical reservoir the phase distribution of trace metals and oxyanions including u and as in 2 surface water bodies was investigated within a south texas watershed hosting a high density of surface u mine pits and tailings the objectives of the study were to evaluate the environmental legacy of u mining with particular emphasis on the spatial and temporal variability of water quality in lake corpus christi a downstream reservoir that serves as the major water resource to a population of 350 000 people in the region lyssy pond a livestock pond bordered by u mine tailings was used as a model case study site to evaluate the cycling of u mine derived oxyanions under changing redox conditions although the pond showed seasonal thermal and chemical stratification geochemical cycling of metals was limited to co and pb which was correlated with redox cycling of mn mineral phases and u which suggested reductive precipitation in the pond s hypolimnion uranium levels however were too low to support strong inputs from the tailings into the water column of the pond the strong relationships observed between particulate cr cs v and fe suggest that these metals are associated with a stable particulate phase probably allochthonous alumino silicates enriched in unreactive fe this observation is supported by a parallel relationship in sediments collected across a broad range of sediment depositional processes and histories in the basin arsenic though selectively enriched in the pond s water column was dominated by dissolved species throughout the depth of the profile and showed no sign of geochemical cycling or interaction with fe rich particles arsenic and other oxyanions in the water columns of lake corpus christi and lyssy pond were not affected by the abundant presence of fe rich particles but instead behaved conservatively no evidence was found of anthropogenic impacts of u mines beyond the purely local scale arsenic s presence within the nueces drainage basin is related to interactions between surface and groundwaters with u and as rich geological formations rather than large scale transport of contaminants downstream of the u mine pits and tailings a quantitative mass balance model constructed using monthly hydrological data for the reservoir provides quantitative evidence of seasonal evaporative concentration of as in surface waters demonstrating the predominance of hydrodynamic over geochemical constraints on the cycling of this element

conventional and ion microprobe u pb dating of detrital zircons of the tentudia group serie negra sw spain implications for zircon systematics stratigraphy tectonics and the precambrian cambrian boundary conventional multi grain and ion microprobe dating of detrital zircons from a very low grade metagraywacke of the tentudia group upper part of the serie negra ossa morena zone sw spain reveals an uppermost vendian age for the deposition of the metagraywacke the youngest detrital zircon grain provides a maximum depositional age of about 565 ma thus these data contradict earlier middle to upper riphean ca 1350 850 ma estimates on the age of the tentudia group and favour a precambrian cambrian boundary falling into the range of 540 to 530 ma the presence of about 20 of pan african detrital zircons ranging from about 700 to 550 ma indicates the derivation from gondwana from the upper intercept ages of the fan shaped data field defined by conventionally determined zircon fractions it can be deduced that 2 1 ga old zircons as well as archean zircons existed in the provenance s of the serie negra sediments this mixing of crustal components of different ages is in line with the nd crustal residence age of 1 9 ga the latter value as well as other model ages of the iberian massif indicates unusually high amounts of ancient crust to be present in the strata this is different to other meta sediments of the european hercynides and suggests that the iberian strata of uppermost precambrian age may contain the detritus of more internal older parts of gondwana than other european strata of comparable ages geochemical data on the analysed sample and further metagraywackes of the tentudia group argue for a deposition in an arc environment such a scenario would conform with the syn to post orogenic shallow marine deposition of the studied sediments furthermore an upper time limit for the pre lower cambrian deformational history including two phases of regional deformation is given by the maximum age of deposition implying a very short time interval for deposition and deformation of the tentudia group concerning the u pb systematics of detrital zircon fractions it is probable that numerous previously published conventional multi grain zircon data on meta sedimentary rocks of the european hercynides readily can be explained by the presence of up to 20 of pan african detrital zircons and later phanerozoic lead loss during metamorphic transformation of the sedimentary protoliths moreover this implies that such metasediments originated from post pan african sedimentary precursors

arsenic enrichment in groundwater of west bengal india geochemical evidence for mobilization of as under reducing conditions abstract the mechanism of as release and source s of as has been investigated in a small part of a watershed in the murshidabad district of west bengal analyses include major ion and trace element concentrations as well as o h and s isotope ratios of groundwater surface water and a thermal spring the results indicate that all water samples belong to the ca hco 3 type except for the thermal spring which is of the na hco 3 type shallow and deeper groundwaters have distinct hydrochemical features high as contents were registered only in the deeper groundwater horizon factor analysis and the distribution pattern of major and trace elements indicate that as is present in the aquifer as a scavenged phase by fe iii and to a lesser extent by mn iv phases the release of as into the groundwater occurs gradually in successive stages corresponding to the actual redox state in the aquifer the main stage of as release is related to the bacterial reduction of fe iii to fe ii i e to the simultaneous dissolution of fe oxyhydroxides low redox conditions in highly polluted areas are indicated by low so 4 concentration and high 34 s values during bacterial so 4 reduction residual so 4 in groundwater is depleted in the lighter s isotope 32 s however the cause of the gradual decrease of the redox state in the groundwater is still not well understood

controls on tungsten concentrations in groundwater flow systems the role of adsorption aquifer sediment fe iii oxide oxyhydroxide content and thiotungstate formation abstract groundwater samples were collected along flow paths within the carrizo sand aquifer southeastern texas and the aquia aquifer coastal maryland for analysis of dissolved tungsten w concentrations along with the major solutes ph and measures of in situ redox conditions e g dissolved fe ii fe iii and s ii concentrations in addition sediment samples were collected from both aquifers to evaluate the solid phase speciation of w tungsten concentrations in the carrizo sand aquifer range from 3 64 to 1297 pmol kg 1 mean sd 248 440 pmol kg 1 with the lowest concentrations reported from the recharge area tungsten concentrations progressively increase down gradient along the flow path within carrizo sand aquifer groundwaters reaching the highest levels in sulfidic groundwater roughly 50 60 km from the recharge zone tungsten is strongly correlated with ph and dissolved sulfide i e s ii concentrations in carrizo groundwaters r 0 78 and 0 95 respectively in aquia aquifer groundwaters w concentrations range between 14 3 and 184 4 pmol kg 1 mean sd 63 9 59 pmol kg 1 and exhibit no or at best weak relationships with other geochemical parameters measured along the flow path e g r 0 4 and 0 08 for w vs ph and s ii respectively the data suggest that the increase in w concentrations in carrizo groundwaters reflects in part ph related adsorption desorption which has been shown to be substantial for groundwaters and lake waters with ph 8 owing to the similar chemical properties of w and mo which form thiomolybdates in sulfidic waters the formation of thiotungstate complexes may also be important in the sulfidic waters of the carrizo aquifer the substantially lower w concentrations in aquia aquifer groundwaters reflect the fact that the maximum groundwater ph never exceeds 8 4 mean sd ph 7 97 0 23 dissolved low s ii concentrations remain low mean sd s ii 0 29 0 16 mol kg 1 and that aquia aquifer sediments have substantially higher fe iii oxide oxyhydroxide contents compared to the carrizo sand aquifer our data indicate that ph related adsorption desorption reactions and the fe iii oxide oxyhydroxide content of aquifer sediments are key controls affecting w concentrations in oxic suboxic and anoxic groundwaters and further that the formation of thiotungstate species may also be important in some anoxic i e sulfidic waters

upper neoproterozoic lower cambrian sedimentary successions in the central iberian zone spain sequence stratigraphy petrology and chemostratigraphy implications for other european zones o3 tio2 zr and nb abundances in shales from all the units strongly suggest a gradual compositional change within this sedimentary succession together with the petrological data the chemical results do not reveal any obvious coeval volcanic contribution to the sediments on the basis of the chemical data a comparison is made with other european zones containing detrital sediments composed of reworked crustal components

vertical distribution of as iii and as v in a coastal sandy aquifer factors controlling the concentration and speciation of arsenic in the stuarts point groundwater system northern new south wales australia arsenic species were measured in a bundled piezometer installed in the holocene barrier of the stuarts point coastal sands aquifer northern new south wales australia vertical distribution shows two peaks of elevated as concentration at a depth of 10 11 m concentrations of as tot as v and as iii are in the range of 52 85 38 67 and 14 18 mg l respectively and the ratio of as v as iii is well above 1 at 3 7 2 7 the second peak at a depth of 25 m shows the highest concentrations of as tot as v and as iii with values reaching 337 125 and 212 mg l respectively the as v as iii ratio is below 1 at 0 6 0 7 high as tot and as v concentrations at shallower depths are associated with acidic conditions and very low concentrations of all ions desorption of as from al hydroxides and as enriched feoxyhydroxides are plausible mechanisms releasing as into the groundwater system the elevated concentration of as tot and as iii at 25 m is potentially related to the leaching of the clay surfaces elevated hco3 and alkaline ph conditions at this depth cause desorption of as which is later present as as iii species in the reducing environment the high concentrations of hco3 further reduce the possible extent of as sorption on fe and mn oxyhydroxides the identification of as in a groundwater system associated with the coastal barrier sand dune environment raises serious questions of the suitability of human consumption of untreated groundwater drawn from these aquifer types further investigation both in australia and globally are needed to classified the extent of this hydrogeochemical occurrence near coastal communities that rely on groundwater 2003 elsevier science ltd all rights reserved

conservative behavior of arsenic and other oxyanion forming trace elements in an oxic groundwater flow system summary groundwater samples were collected along a flow path in a shallow fractured tuffaceous aquifer from the oasis valley beatty wash region of southern nevada usa and analyzed for a number of oxyanion forming trace elements including arsenic as antimony sb selenium se molybdenum mo and tungsten w in addition ancillary geochemical parameters including ph major solute compositions dissolved silica dissolved oxygen and iron and manganese concentrations were quantified in the groundwaters arsenic concentrations range from 70 nmol kg up to 316 nmol kg in groundwaters of the oasis valley beatty wash flow system and generally exhibit increasing concentrations with flow down gradient along the flow path antimony w and to a lesser extent mo exhibit similar increasing concentration trends with flow down gradient in the aquifer albeit at lower concentrations levels e g mean sd for sb w and mo are 2 3 0 9 nmol kg 7 4 3 7 nmol kg and 101 19 nmol kg respectively selenium concentration which range between 4 and 11 nmol kg generally decrease in groundwaters with flow down gradients in the oasis valley beatty wash groundwater flow systems inverse modeling of groundwater chemistry evolution from the lower reaches of the oasis valley flow path using phreeqc indicate that the groundwater composition is consistent with mixing of nearly equal proportions of groundwater from upper reaches of oasis valley and beatty wash groundwater along with dissolution of volcanic glass potassium feldspar and gypsum followed by calcite precipitation and formation of secondary zeolites analcime clay minerals ca montmorillonite and cristobalite the geochemical modeling indicates that the concentrations of as and the other oxyanion forming trace elements are controlled by dissolution of volcanic glass water rock interaction with mineralized zones within the aquifer i e sulfide oxidation desorption from aquifer surface sites and mixing of oasis valley and beatty wash groundwaters

factors controlling tungsten concentrations in ground water carson desert nevada an investigation of a childhood leukemia cluster by us centers for disease control and prevention revealed that residents of the carson desert nevada are exposed to high levels of w and this prompted an investigation of w in aquifers used as drinking water sources tungsten concentrations in 100 ground water samples from all aquifers used as drinking water sources in the area ranged from 0 27 to 742 g l ground water in which w concentrations exceed 50 g l principally occurs se of fallon in a geothermal area the principal sources of w in ground water are natural and include erosion of w bearing mineral deposits in the carson river watershed upstream of fallon and possibly upwelling geothermal waters ground water in the fallon area is strongly reducing and reductive dissolution of fe and mn oxyhydroxides may be releasing w however direct evidence that the metal oxides contain w is not available although w and cl concentrations in the carson river a lake and water from many wells appear to be controlled by evaporative concentration evaporation alone cannot explain the elevated w concentrations found in water from some of the wells concentrations of w exceeding 50 g l are exclusively associated with na hco3na hco3 and na cl water types and ph 8 0 in these waters geochemical modeling indicates that w exhibits 10 adsorption tungsten concentrations are strongly and positively correlated with as b f and p indicating either common sources or common processes controlling their concentrations geochemical modeling indicates w concentrations are consistent with ph controlled adsorption of w the geochemical model phreeqc was used to calculate iap values which were compared with published ksp values for primary w minerals fewo4 mnwo4 na2wo4 and mgwo4 were undersaturated and cawo4 and srwo4 were approaching saturation these conclusions are tentative because of uncertainty in the thermodynamic data the similar behavior of as and w observed in this study suggests ground water in areas where elevated as concentrations are present also may contain elevated w concentrations particularly if there is a mineral or geothermal source of w and reducing conditions develop in the aquifer

volcanic glass leaching and the groundwater geochemistry on the semi arid atlantic island of porto santo abstract the groundwater chemistry of the semi arid volcanic island of porto santo part of the madeira archipelago atlantic ocean was investigated generally the groundwater was brackish containing 2 10 mol seawater groundwater with up to 20 mm alkalinity and a na enrichment of up to 30 mm as compared to the na concentration predicted by the seawater na cl ratio was found in the main aquifer also notable are the high concentrations of f up to 0 3 mm b up to 0 55 mm as up to 0 35 m all in excess of who recommendations as well as up to 6 m v geochemical modeling using the phreeqc code was used to explore different scenarios that could explain the genesis of the observed bulk groundwater chemistry first a model for aquifer freshening with the displacement of resident seawater from the aquifer by infiltrating freshwater was tested this scenario leads to the development of nahco3 waters as observed in many coastal aquifers however the measured alkalinity concentration in the groundwater was far higher than the concentration predicted by the freshening model in addition the behavior of modelled ph and pco2 were at variance with their distributions in the field data the second model explored the possible effect of volcanic glass leaching on the groundwater chemistry using insight derived from studies of volcanic glass surface alteration as well as experimental work on water volcanic glass interactions a geochemical model was developed in which the exchange of h for na on the volcanic glass surface is the main mechanism but the exchange of other cations on the volcanic glass surface is also included the uptake of h by the glass surface causes the dissociation of carbonic acid generating bicarbonate this model is consistent with the local geology and the field data it requires however volcanic glass leaching to occur in the unsaturated zone where there is an unlimited supply of co2 the exchange reaction of h for na is confined to the surface layer of volcanic glass as otherwise the process becomes limited by slow solid state diffusion of h into the glass and na out of the glass therefore volcanic ash deposits with their high volcanic glass surface areas and matrix flow are the aquifers where this type of high nahco3 waters can be expected rather than in basalts which predominantly feature fracture flow the trace components f b as and v are believed to originate from hyaloclastites consisting of predominantly 90 of trachy rhyolite volcanic glass although stratigraphically older than the main calcarenite aquifer topographically they are often located at higher altitudes above the phreatic level and located along the main recharge flow path in addition the semi arid climate conditions provide a long groundwater residence time for the reactions as well as limited aquifer flushing

arsenic distributions in porewaters and sediments of puget sound lake washington the washington coast and saanich inlet b c solid phase as mn al and excess 210pb and dissolved total as as 3 as 5 mn 2 fe 2 po 34 nh 4 and h2s profiles in 12 cores from puget sound lake washington the washington coast and saanich inlet b c are presented typically strong correlations between solid phase as and mn concentration maxima in surficial sediments are a result of intense as scavenging in the overlying waters by mn or ferich phases or solid phase as dissolution at depth followed by upward diffusion and co precipitation with mn or fe oxides at or near the sediment water interface atypically anthropogenic inputs cause high sedimentary as concentrations without accompanying high mn levels sedimentary as fluxes are an order of magnitude greater in puget sound and lake washington than off the washington coast and in saanich inlet porewater total as concentration profiles exhibit sub surface maxima with magnitudes 10 60 times greater than in overlying bottom waters porewater maxima in marine environments are proportional to associated solid phase as concentrations these maxima consistently occur within 1 0 cm of the bottom of the 210pb derived surface mixed layer suggesting solid phase as release to porewater in response to a redox gradient across this mixing boundary dissolved as behavior beneath these maxima indicates as removal to solid phases in marine but not lacustrine porewaters porewater as 3as 5 ratios are 1 0 for washington coastal environments and usually between 1 0 4 0 for puget sound and lake washington as 5 is below the detection limit in porewaters of saanich inlet when the overlying bottom water is anoxic but as 3as 5 ratios as low as 2 8 exist in near surface porewater under oxic bottom water conditions

late precambrian thrust and wrench zones in northern brittany france abstract brioverian units of northern brittany armorican massif france were deformed and metamorphosed during a late precambrian tectonic episode the cadomian orogeny kinematic study strain and displacement in the st cast st brieuc area shows that this tectonic episode was characterized by the obduction of a back arc basin over a continental margin around 580 590 ma ago strain pattern analysis reveals a constant interaction between ssw directed imbricated thrust zones and ductile sinistral wrench zones trending n 50 e the arcuate pattern of cadomian structures in this area results from such an interaction thickening as a result of the thrusts induced migmatization and the development of a high temperature belt around 540 ma in the st malo guingamp area

silver and lead in high altitude lake sediments proxies for climate changes and human activities abstract high altitude lake sediments are often used as archives for environmental changes and their chemical and isotopic compositions provide significant constraints on natural and anthropogenic long term changes that have occurred in their catchment area here trace element concentrations and pb isotopes are presented for two sedimentary cores from lake blanc huez in the french alps to trace the impact of climate changes and human activities over the holocene lead and ag contents are very high and clearly dominated by input from a pb ag vein located a few meters from the lakeshore a vein that also buffers the pb isotopes mining of this vein in medieval times is recorded in the corresponding lake sediments with high ag content coupled with high pb u ratio these chemical characteristics can be used to constrain the major holocene climate changes significant advances of glaciers next to the lake produced sediments with ag and pb concentration peaks and high pb u ratios due to accelerated erosion of the pb ag vein similar to the effects of the medieval mining in contrast reduced glacier activity led to the formation of organic rich sediments with high u and as contents and low pb u ratios more generally the observed combination of chemical changes could be used elsewhere to decipher environmental changes over long periods of time

uranium and arsenic dynamics in volcano sedimentary basins an exemplary study in north central mexico abstract uranium and as in deep groundwater of the volcano sedimentary villa de reyes graben around the city of san luis potosi in semi arid north central mexico mean u 7 6 g l 1 max 138 g l 1 mean as 11 4 g l 1 max 25 8 g l 1 partly exhibit concentrations in excess of the who guideline values and thus endanger the quality of the most important drinking water source to unravel the mechanisms for their enrichment in groundwater the potential trace element sources volcanic rocks and basin fill sediments were characterized a total of 131 solid and liquid samples were analyzed for major and trace element composition the as u hydrogeochemical signatures their behavior during rock alteration and evidence from other major and trace element distributions especially rare earth elements strongly argue for dissolution of acid volcanic glass to be the dominating process of u and as release into groundwater this natural baseline quality representing water acid volcanic rock interaction is modified by additional trace element preferentially as mobilization from the sedimentary basin fill representing a secondary source in the course of decarbonatization of playa lake sediments and desorption from fe hydr oxide coated clastic material the common behavior of both elements during magmatic differentiation and growing drift apart in sedimentary environments are important findings of this work comparison with recent findings in a similar environment suggests a common primary trace element source identification but significant differences in the evolution of as and u distribution geological and climatic similarity to numerous volcano sedimentary basins makes the findings useful for water management purposes and transferable to other semi arid regions facing challenges of geogenically impacted drinking water quality

le batholite de de pas nouveau quebec infrastructure composite d arc magmatique proterozoique the de pas batholith in new quebec is a mass of granitoids elongated in a n s direction covering 7000 km2 in the southeastern part of the archean rae province it is located between the paleopro

rb sr evidence for the presence of ordovician gsranites in the deformed basement of the badajoz cordoba belt sw spain a rb sr whole rock investigation of suites of samples from two orthogneiss bodies in the almendralejo area of the oporto portalegre badajoz cordoba belt points to an ordovician age for the granitic magmatism about 470 ma for the almendralejo gneiss peralkaline metagranite and about 425 ma for the ribera del fresno gneiss leucocratic subaluminous metagranite both with high initial87sr 86sr ratios this points to a post ordovician hercynian age for the metamorphism and tectonic deformation that affected the area including the gneisses and rules out the alleged cadomian or even older age

anomalous arsenic concentrations in the ďurkov carbonate geothermal structure eastern slovakia concentrations of as in carbonate reservoirs in slovakia are relatively low with an average value of 0 72 mg l in typical waters of ca mg hco3 type in factor analysis arsenic is in factor 1 with na and cl separated from carbonate aquifer species ca and mg in factor 2 a principal exception is the urkov site in eastern slovakia where as concentration reaches 36 7 mg l median 30 mg l in geothermal waters of the na cl type the 2h and 18o isotopes indicate a primary meteoric origin of the water low 2h and 14c reflect infiltration of surface water during a warmer climatic period in the early holocene meanwhile positive 18o shift about 5 suggests enhanced water rock interactions the conceptual model of as rich water formation includes the following steps a infiltration of meteoric waters and dissolution of evaporates especially halite in the overlying neogene formation b reaction of the highly mineralized water with hg as sb type of mineralization related to the neogene volcanism and c accumulation of as rich geothermal water in triassic carbonates with an additional input of co2 geochemical modeling of the reaction between water and arsenopyrite reproduced measured as concentrations for a typical range of reservoir temperatures analogous to similar geothermal sites around the world concentrations of arsenic in carbonate reservoirs in slovakia are low except for cases where as is enriched by previous water rock interaction related to neogene volcanic activity outside the carbonate reservoirs which then serve exclusively for a secondary accumulation of as rich waters

distribution and mobility of geogenic molybdenum and arsenic in a limestone aquifer matrix abstract to investigate the potential of mo and as as possible geogenic contaminants three sediment cores were examined to evaluate their mineralogical association distribution and mobility the cores were described and analyzed for total organic carbon toc ca mg si al p sr as mo fe and s content except in the uppermost segment limestone was the main lithology with the occasional presence of dolomite and clay that change in lithology was also observed in the bulk chemical composition where ca mg and sr concentrations increased with depth while si al and p concentrations decreased with depth minor minerals included pyrite fes 2 powellite camoo 4 and ferrihydrite the minimum maximum median and standard deviations for all analyzed elements including as and mo were comparable for all three cores molybdenum and as however varied significantly with depth and median as and mo values were above their respective crustal averages of approximately 1 1 mg kg and 1 5 mg kg the median values for as were 1 9 mg kg in core dep 1 3 3 mg kg in dep 2 and 1 mg kg in dep 5 the median values for mo were 2 3 mg kg in core dep 1 2 5 mg kg in dep 2 and 2 5 mg kg in dep 5 maximum concentrations for as were 101 9 mg kg 47 5 mg kg and 56 2 mg kg in cores dep 1 dep 2 and dep 5 respectively maximum concentrations for mo were 880 mg kg 123 mg kg and 225 mg kg in cores dep 1 dep 2 and dep 5 respectively electron microprobe analyses of individual minerals revealed variable concentrations of as ranging from approximately 300 to 9000 mg kg in pyrite and up to 17 600 mg kg in powellite camoo 4 the mo concentration in pyrite was consistently below the detection limit of approximately 100 mg kg in powellite the mo concentration was up to 42 wt a subset of 10 samples from different stratigraphic sections and with different as and mo concentrations was further investigated to assess as and mo mobility under changing physicochemical conditions leaching the aquifer matrix with a 1 m naoac solution at a ph of 8 1 removed more than 70 mo in 8 of the 10 samples the maximum value was 97 in contrast to mo as was mobilized to a lesser degree in 8 of the samples less than 30 were removed and the maximum was only 50 molybdenum which seemed to be loosely bound to mineral and organic matter surfaces thus could easily be removed from the aquifer matrix while as on the other hand should be much less mobile because it occurred either tightly adsorbed by hydrous ferric oxide or as an impurity in pyrite thus it is advisable to include mo in the analytical program whenever elevated as concentrations are encountered in groundwater

a review of the source behaviour and distribution of arsenic in natural waters the range of as concentrations found in natural waters is large ranging from less than 0 5 g l 1 to more than 5000 g l 1 typical concentrations in freshwater are less than 10 g l 1 and frequently less than 1 g l 1 rarely much higher concentrations are found particularly in groundwater in such areas more than 10 of wells may be affected defined as those exceeding 50 g l 1 and in the worst cases this figure may exceed 90 well known high as groundwater areas have been found in argentina chile mexico china and hungary and more recently in west bengal india bangladesh and vietnam the scale of the problem in terms of population exposed to high as concentrations is greatest in the bengal basin with more than 40 million people drinking water containing excessive as these large scale natural as groundwater problem areas tend to be found in two types of environment firstly inland or closed basins in arid or semi arid areas and secondly strongly reducing aquifers often derived from alluvium both environments tend to contain geologically young sediments and to be in flat low lying areas where groundwater flow is sluggish historically these are poorly flushed aquifers and any as released from the sediments following burial has been able to accumulate in the groundwater arsenic rich groundwaters are also found in geothermal areas and on a more localised scale in areas of mining activity and where oxidation of sulphide minerals has occurred the as content of the aquifer materials in major problem aquifers does not appear to be exceptionally high being normally in the range 1 20 mg kg 1 there appear to be two distinct triggers that can lead to the release of as on a large scale the first is the development of high ph 8 5 conditions in semi arid or arid environments usually as a result of the combined effects of mineral weathering and high evaporation rates this ph change leads either to the desorption of adsorbed as especially as v species and a range of other anion forming elements v b f mo se and u from mineral oxides especially fe oxides or it prevents them from being adsorbed the second trigger is the development of strongly reducing conditions at near neutral ph values leading to the desorption of as from mineral oxides and to the reductive dissolution of fe and mn oxides also leading to as release iron ii and as iii are relatively abundant in these groundwaters and so4 concentrations are small typically 1 mg l 1 or less large concentrations of phosphate bicarbonate silicate and possibly organic matter can enhance the desorption of as because of competition for adsorption sites a characteristic feature of high groundwater as areas is the large degree of spatial variability in as concentrations in the groundwaters this means that it may be difficult or impossible to predict reliably the likely concentration of as in a particular well from the results of neighbouring wells and means that there is little alternative but to analyse each well arsenic affected aquifers are restricted to certain environments and appear to be the exception rather than the rule in most aquifers the majority of wells are likely to be unaffected even when for example they contain high concentrations of dissolved fe

geogenic as and mo groundwater contamination caused by an abundance of domestic supply wells abstract lacking a connection to a municipal water supply each household in the municipality of lithia approximately 30 km southeast of tampa florida usa is responsible for its own supply of drinking water causing a high density of private domestic supply wells dsw in this area there a multilayered aquifer system exists which can be subdivided into three distinct hydro stratigraphic units which are from the top down the surficial aquifer system sas the intermediate aquifer system ias and the upper floridan aquifer system ufa despite the relatively small area the geochemical and hydrogeological setting in lithia is complex consisting of i extensive cyclical pumping in a municipal well field to the west ii large seasonal changes in hydraulic head ii multiple aquifers with different hydraulic heads and iv a large density of domestic supply wells dsw within the zone of highest as concentrations there are approximately 100 wells in an area of 2 5 km 1 5 km most of these wells have large open screened intervals often open to all three aquifers allowing the downward flow of oxygenated and upward flow of anoxic groundwater a survey of groundwater quality found that as and mo concentrations in the dsw were up to 371 g l and 4740 g l respectively to obtain information about the individual aquifers 5 well clusters with 4 monitoring intervals approximately 50 m 65 m 80 m and 95 m below surface and 8 push core wells approximately 9 m below surface were installed and sampled in those wells as and mo were only elevated in a permeable layer within the ias at a depth of 50 m values were up to 195 g l for as and up to 5050 g l for mo using the tritium helium 3h 3he method the ages of those samples high in as and mo were determined to be 40 30 and 30 years respectively while all other samples had ages older than 50 years this indicated that mixing between young and old groundwater could be responsible for the high as and mo concentrations a good negative correlation for the whole data set was also observed between the concentration 3h and 18o values which together with hydrogeological modeling confirmed that the increased permeability created by the high density of dsw resulted in flow paths that permitted the perpetual mixing of shallow and deep groundwater the release of the as and mo appeared to be a consequence of changes to the physicochemical conditions in the aquifer either via the introduction of oxygen rich fluids into the ias or the mixing of different fluids in the ias or the introduction of oxygen depleted fluids into the ias while the mobilization of geogenic trace metals is often associated with pumping induced hydraulic gradient changes we found that a certain density of multi aquifer wells can be sufficient to alter hydrologic flow paths and induce the mobilization of geogenic trace metals even in the absence of significant pumping in lithia the dsw effectively increased the local scale permeability of the aquifer causing the mixing of oxygen rich surface and deeper anoxic groundwater across a confining unit because the alteration to the hydrologic flow paths was a consequence of changes to the physical structure of the aquifer system rather than due to pumping the alteration is not easily reversible thus significantly complicating site remediation our results provide a cautionary warning of the risks of undue private dsw development in rapidly growing communities

the occurrence and geochemistry of arsenic in groundwaters of the newark basin of pennsylvania abstract elevated as concentrations in groundwater in the eastern united states have been recognized predominantly in the accretionary geologic terranes of northern new england a retrospective examination of more than 18 000 existing groundwater samples from the pennsylvania department of environmental protection pa dep drinking water and sampling information system database indicates that elevated groundwater as concentrations occur throughout the northern half of the piedmont province of pennsylvania chemical analyses of 53 samples collected in 2005 from drinking water wells in this area all had detectable as and 23 of these samples contained elevated 133 nmol l or 10 g l concentrations of as elevated concentrations of as in the groundwater samples were most common in the mesozoic sedimentary strata composed of sandstone and red mudstone with interbedded gray shale and gray to black siltstone and shale arsenic was typically not elevated in groundwater of diabase intrusions of the newark basin or in crystalline and calcareous aquifers to the north of the newark basin geochemical parameters such as ph and oxidation reduction potential can indicate mobility mechanisms of as in some regions in this area measured groundwater conditions were predominantly oxidizing eh 50 mv and more than 85 of samples contained arsenate as the dominant as species variations in ph were strongly correlated to the as concentration with highest as concentrations observed at ph values greater than 6 4 the original source of as is most likely the black and gray shales that contain some arsenian pyrite with groundwater concentrations likely to be controlled by adsorption desorption reactions with fe oxides in the red mudstone aquifer materials

factors controlling as and u in shallow ground water southern carson desert nevada abstract unusually high as and u concentrations 100 g l are widespread in shallow ground water beneath the southern carson desert the high concentrations which locally exceed 1000 g l are of concern from a human health standpoint because the shallow ground water is used for domestic supply possible affects on wildlife are also of concern because the ground water flows into shallow lakes and marshes within wildlife refuges arsenic and u concentrations in ground water of the southern carson desert appear to be affected by evaporative concentration redox reactions and adsorption the relation of these elements with cl suggest that most of the high concentrations can be attributed to evaporative concentration of carson river water the primary source of recharge some ground water contains higher as and u concentrations that cannot be explained by evaporative concentration alone oxidation reduction reactions involving metal oxides and sedimentary organic matter appear to contribute as u inorganic c fe and mn to the ground water arsenic in fe oxide was confirmed by chemical extraction and is consistent with laboratory adsorption studies uranium in both sedimentary organic c and fe oxide coatings has been confirmed by fission tracks and petrographic examination arsenic concentrations in the ground water and chemical extracts of aquifer sediments are broadly consistent with adsorption as a control on some dissolved as concentrations an apparent loss of as from some ground water as evaporative concentration proceeds is consistent with adsorption as a control on as however evidence for adsorption should be viewed with caution because the adsorption model used values for the adsorbent that have not been shown to be valid for the aquifer sediments throughout the southern carson desert hydrologic and geochemical conditions in the carson desert are similar to other areas with high as and u concentrations in ground water including the salton sea basin and southern san joaquin valley of california hydrologic and geochemical conditions that produced some sandstone type u ore deposits including those in the non marine closed basin sediments of the morrison formation near grants new mexico suggest that the carson desert may be a modern analog for those systems

radionuclides in ground water of the carson river basin western nevada and eastern california u s a abstract ground water is the main source of domestic and public supply in the carson river basin ground water originates as precipitation primarily in the sierra nevada in the western part of carson and eagle valleys and flows down gradient in the direction of the carson river through dayton and churchill valleys to a terminal sink in the carson desert because radionuclides dissolved in ground water can pose a threat to human health the distribution and sources of several naturally occurring radionuclides that contribute to gross alpha and gross beta activities in the study area were investigated generally alpha and beta activities and u concentration increase from the up gradient to down gradient hydrographic areas of the carson river basin whereas222rn concentration decreases both226ra and228ra concentrations are similar throughout the study area alpha and beta activities and u concentration commonly exceed 100 pci l in the carson desert at the distal end of the flow system radon 222 commonly exceeds 2 000 pci l in the western part of carson and eagle valleys adjacent to the sierra nevada radium 226 and228ra concentrations are alpha emitting radionuclides in the ground water originated from the dissolution of u rich granitic rocks in the sierra nevada by co2 oxygenated water dissolution of primary minerals mainly titanite sphene in the granitic rocks releases u to the water dissolved u is probably removed from the water by adsorption on fe and mn oxide coatings on fracture surfaces and fine grained sediment by adsorption on organic matter and by coprecipitation with fe and mn oxides these coated sediments are transported throughout the basin by fluvial processes thus u is transported as dissolved and adsorbed species a rise in the water table in the carson desert because of irrigation has resulted in the oxidation of u rich organic matter and dissolution of u bearing coatings on sediments producing unusually high u concentration in the ground water alpha activity in the ground water is almost entirely from the decay of u dissolved in the water beta activity in ground water samples is primarily from the decay of40k dissolved in the water and ingrowth of238u progeny in the sample before analysis approximately one half of the measured beta activity may not be present in ground water in the aquifer but instead is produced in the sample after collection and before analysis potassium 40 is primarily from the dissolution of k containing minerals probably k feldspar and biotite radon 222 is primarily from the decay of226ra in the aquifer materials radium in the ground water is thought to be mainly from alpha recoil associated with the decay of th in the aquifer material some ra may be from dissolution or desorption or ra rich coatings on sediments

tectonic setting of cadomian low pressure metamorphism in the central ossa morena zone iberian massif sw spain abstract the upper proterozoic serie negra a monotonous pre and syntectonic slate greywacke series including volcanic episodes crops out widely in the central area of the ossa morena zone sw iberian massif iberian peninsula this unit was affected by complex late precambrian tectonothermal events the cadomian orogeny during which two phases of deformation d1 and d2 are recognized in the 610 585 ma time span the second deformational episode d2 was the most prominent and was related to progressive low pressure high temperature metamorphism lp ht reaching the highest grade in the lower structural levels where thermal evolution led to extensive migmatization and gave rise to the generation of different kinds of anatectic granitoids in this work we present field petrographic and analytical data dealing with the metamorphic evolution of a cadomian lp ht terrane from the central ossa morena zone iberian massif sw spain whose tectonic setting is unclear so far the tectonic setting proposed herein for cadomian d2 lp ht events is discussed in terms of its relationship to plate convergence or to extensional tectonic regimes modelling of the p t t trajectories undergone by a crust moderately overthickened by the thrusting of thinned sialic crust slices reproduces well the observed p t t aths if moderate or low uplift rate and high geothermal gradients are assumed for the uplift history numerical simulations combined with structural and metamorphic evidence support a compressional tectonic setting as responsible for the observed facies series distribution and deformation metamorphism relationships furthermore the regional geodynamic context coeval high pressure metamorphism in neighboring areas of the ossa morena zone and extensive calc alkaline magmatism is consistent with such a tectonic setting a correlation is tentatively proposed here between compressional cadomian deformations in the ossa morena zone upper proterozoic docking of avalonian terranes in ne america and cadomian orogenesis in the northern armorican massif

an assessment of the seawater effect by geochemical and isotopic data on the brackish karst groundwater from the karaburun peninsula izmir turkey the study area is located in the center of the karaburun peninsula turkey where several karstic springs discharge near the coast 0 2 m above the sea level the most important discharge points are the ildiri and gerence springs groundwater obtained from ildiri springs and several drill wells provide water to the region during the summer periods the electrical conductivity values are between 1900 and 3900 s cm springs are slightly salty and are not used directly as drinking water salinity was observed in the spring waters under natural flow conditions the salinity values of the drillings and springs were measured in dry and wet seasons spring waters have conductivity values between 3000 and 4000 s cm preliminary surveys reveal that seawater contribution to ildiri springs is 6 5 maximum gerence spring waters discharge to the surface from a region very close to the sea the dominant cation is na and the dominant anion is cl conductivity values were between 7000 and 13 000 s cm gerence spring waters discharge to the sea with seawater contributions ratios between 8 5 and 20 3 depending on the seasonal changes while some spring waters discharge 0 5 1 0 m above sea level the rest of them discharge directly into the sea salinization of gerence spring water is higher than the other springs

outline of upper precambrian and lower paleozoic evolution of the iberian peninsula according to u pb dating of zircons in the northwestern part of the iberian peninsula recent geological studies have defined the following stratigraphic sequence from bottom to top basal orthogneiss of miranda do douro is overlain by a complex of schist and greywacke which have been assigned to the cambrian or late precambrian these are followed by the ollo de sapo gneisses of volcanic sedimentary origin which in turn are overlain by the fossiliferous layers of the lower ordovician the schist and greywacke complex and the lower part of the ollo de sapo formation are transected by granitic dikes viana del bollo orthogneiss all these rocks were folded faulted metamorphosed and intruded by granite plutons during variscan times the emplacement of the miranda do douro and viana del bollo orthogneisses have been respectively dated at 618 9 ma and 465 10 ma by the u pb method on zircons these data yield lower and upper limits for the deposition of the ollo de sapo formation and demonstrate the occurrence of a precambrian basement pan african or cadomian orogeny in the variscan belt in the northwestern part of the iberian peninsula the emplacement of viana del bollo orthogneiss could be genetically related to the main phase of crustal thinning 470 520 ma characteristic of the prevariscan evolution of western europe typology and u pb data of the ollo de sapo zircons indicate the occurrence of inherited old precambrian zircons and yield an age of 325 3 ma for the variscan main thermal event in the area considered four possible evolutionary models for the u pb system of the ollo de sapo zircons are discussed

variscan shear zone deformation of late precambrian basement in sw iberia implications for circum atlantic pre mesozoic tectonics abstract polyphase deformation and metamorphism in the badajoz cordoba shear belt sw spain relate to a poly orogenic evolution involving two major tectonothermal episodes the accretion of mid and lower crust tectonic slices in an orogenic wedge complex during pre variscan times and the development of an intracontinental ductile shear zone during the late palaeozoic structural analysis of zones with different intensities of shear dominated variscan deformation allows a recognition of the poly deformed nature of most units of the belt identification of varying deformation mechanisms and a description of the geometry of early structures the implications for the regional tectonics of this area of the southern iberian massif are discussed in the light of the geodynamic evolution of the ibero armorican arc during the variscan orogeny and the reconstruction of the late precambrian cadomian avalonian panafrican orogen of the circum atlantic region

biogeochemical factors affecting the presence of 210po in groundwater abstract the discovery of natural 210 po enrichment at levels exceeding 500 mbq l in numerous domestic wells in northern nevada usa led to a geochemical investigation of the processes responsible for its mobilization 210 po activities in 63 domestic and public supply wells ranged from below 1 mbq l to 6590 590 mbq l among the highest reported levels in the usa there is little spatial or depth variability in 210 pb activity in study area sediments and mobilization of a few percent of the 210 po in the sediments would account for all of the 210 po in water stable isotope measurements indicate so 4 reduction has occurred in all 210 po contaminated wells sulfide species are not accumulating in the groundwater in much of lahontan valley probably because of s cycling involving microbial so 4 reduction abiotic oxidation of h 2 s to s 0 by mn iv followed by microbial disproportionation of s 0 to h 2 s and so 4 the high ph ca depletion mnco 3 saturation and presence of s 0 in lahontan valley groundwater may be consequences of the anaerobic s cycling consistent with data from naturally enriched wells in florida 210 po activities begin to decrease when aqueous sulfide species begin to accumulate this may be due to formation and precipitation of pos however eh ph diagrams suggest pos would not be stable in study area groundwater an alternative explanation for the study area is that h 2 s accumulation begins when anaerobic s cycling stops because mn oxides are depleted and their reduction is no longer releasing 210 po common features of 210 po enriched groundwater were identified by comparing the radiological and geochemical data from nevada with data from naturally enriched wells in finland and florida and maryland in the usa values of ph ranged from 9 in nevada wells indicating that ph is not critical in determining whether 210 po is present where u is present in the sediments the data suggest 210 po levels may be elevated in aquifers with 1 so 4 reducing waters with low h 2 s concentrations or 2 anoxic or oxic waters with extremely high rn activities particularly if the water is turbid

effects of salinity and an ions on arsenic behavior in sediment of bosten lake northwest china bosten lake the largest inland lake in china has been contaminated with arsenic as due to anthropogenic activities salinity of the lake water has been increasing due to the extremely dry climate and salt drainage from the farmland effects of the increasing salinity on the geochemical behavior of arsenic in sediment are still unclear in this study vertical variation of geochemical fractions of as in sediment and arsenic concentration in porewater along the salinity gradient of bosten lake was studied effects of salinity and ions and anions in porewater on arsenic concentration were also examined arsenic content in the five tessier fractions followed the decreasing order of residual exchangeable fe and mn oxides organic carbonate the ecological risk of arsenic in the sediment was at low or medium levels indicated by the low percentage of exchangeable and carbonate bound fractions contrary to the decreasing electrical conductivity of porewater with depth arsenic concentration in porewater showed an increasing trend with depth arsenic concentration in porewater increased from around zero at the surface layer of sediment to over 600 g l 1 in deeper layers of some sites arsenic concentration inversely correlated with electrical conductivity in porewater arsenic concentration generally decreased with increasing concentrations of so4 2 ca2 mg2 and na but showed no clear relation with concentrations of k and cl this study implies that increase of salinity may decrease the release of arsenic from sediment and its ecological risk

impact of carbo gaseous saline waters registered by soils abstract the impact of carbo gazeous saline spring waters rich in ca fe as and p and chemically stable through time on the chemistry major and trace elements and mineralogy of soils developed from anatexite is presented the soils developed beyond the influence of the spring are typical of a granite pedogenesis on a granitic bedrock with ca loss si al and k conservation the soils influenced by the springs are enriched in ca and fe respectively precipitated as carbonates and oxides in such soils the presence of two ca enrichment peaks may be explained by the occurrence of two distinct precipitation mechanisms for the carbonates 1 related to degassing of the carbo gaseous waters upon emergence at the surface and 2 in the water unsaturated zone related to capillary rise and evaporation processes the precipitation of iron oxides is related to a change in the redox potential of the mineral waters following their emergence at the surface the simultaneous association of as p with fe as evidenced by principal components analysis and in the patterns in concentrations vs depth observed in soils can be explained by adsorption and or coprecipitation of as and p during iron oxide formation while the as and p enrichments and the carbonate formation are independent the extent of the spring influence was studied the soil enrichments in ca and particularly fe sharply decrease with increasing distance from the spring on a metric scale

the source and transport of arsenic in a bedrock aquifer new hampshire usa the geographic distribution of elevated groundwater as concentrations in a fractured silicate bedrock aquifer in central new hampshire correlates with the presence of pegmatites which border late devonian granites and intrude metasedimentary rocks as concentrations in the pegmatites averaged 9 6 mg kg which is much higher than the associated granites 0 24 mg kg and metasedimentary rocks 0 8 mg kg as was concentrated in these pegmatites by partial melting of calcareous metapelites and subsequent recrystallization as granites with low as concentrations and pegmatites with high as concentrations arsenic behaves similarly to b which was also concentrated into these late stage fluids arsenopyrite feass with an oxidation reaction rim of scorodite feaso4 2h2o was observed in aquifer materials elevated as concentrations have been observed to occur in other new england locations in pelitic metasediments intruded by anatectic plutons it is proposed that pegmatite formation from partial melting of pelitic metasediments may be an important mechanism for concentrating as in crystalline aquifer materials which can then cause local as enrichment of groundwaters groundwater as concentrations ranged from 26 nmol l to 5300 nmol l with a median value 210 nmol l that is more than 30 times higher than the median for groundwaters from all of new hampshire 6 5 nmol l high chloride concentrations 1 mmol l resulting from road salt contamination of recharge waters suggest that groundwaters are most likely young 670 nmol l or 50 g l have very low fe concentrations 7 samples with low as 7 fe oxyhydroxides form rapidly and have a neutral or negative net surface charge that does not readily adsorb as at ph 7 fe oxyhydroxide formation is slow and depends on dissolved o2 availability however the resultant fe oxyhydroxides have a positive net surface charge and appear to adsorb as readily

benthic foraminifera from the upper collio formation lower permian lombardy southern alps implications for the palaeogeography of the peri tethyan area new palaeontological evidence points to a temporary marine transgression in the early permian into the collio basin a major palaeogeographic feature of the present day southern alps the thick volcaniclastic succession filling the basin collio formation is widely held as deposited in alluvial to lacustrine settings rare calcareous foraminifers were recently found in a single sandstone interval containing phosphate nodules from the uppermost collio formation a temporary seaway necessary for the foraminifera to spread into a continental basin implies that i the collio basin lake was not only an intramontane as commonly viewed but also a coastal lake and ii its altitude did not exceed the amplitude of a first order sea level rise that is about 100 m these constraints along with striking similarities as to tectonic context accumulation rates and geochemical signature suggest that the collio basin was a california type basin resembling in particular the present day salton sea ca usa

chemodynamics of an arsenic hotspot in a west bengal aquifer a field and reactive transport modeling study abstract extremely high as concentrations in drinking water of the ganges delta west bengal and bangladesh has emerged as an issue of great concern in the past decade because of its serious impact on the health of millions of people the distribution pattern of as concentrations in the ganges delta region is patchy and there are numerous as hotspots the present study is perhaps the first attempt in west bengal to characterize such a hotspot by geophysical and geochemical methods and to model the transport of the enrichment plume using a 1d reactive transport model phreeqc the study site is located along the hooghly river 60 km north of kolkota city near the city of chakdaha total as concentrations in the groundwater range from 0 5 to more than 6 mol l 1 the who recommended maximum drinking water concentration is 0 13 mol l 1 i e 10 g l 1 results show groundwater is in chemical equilibrium with siderite and calcite a mineral phase previously shown to be an efficient trap for as iii groundwater redox potential is controlled by the fe oh 3 am fe2 couple the as iii versus as v distribution 42 as iii and 58 as v on average is not at equilibrium with measured eh values no evidence of sulfide solid phases such as as rich pyrite or arsenopyrite was found although amorphous fe dissolution is confirmed to play an important role in the release of as selective dissolution extractions indicate that adsorption of as on carbonates and micas may also be an important component of as cycling in the sediment modelling results demonstrate the role of po 4 3 hco 3 and fe ii in mobilizing the as plume thereby increasing the threat to the 75 000 inhabitants of chakdaha

geodynamic evolution of a cadomian arc region the northern ossa morena zone iberian massif abstract ductile deformation and polyphase metamorphism in the ossa morena zone of the iberian massif are related to two major tectonothermal episodes of cadomian late neoproterozoic to early cambrian and variscan age middle to late paleozoic the available petrological structural and geochronological data suggest that a number of tectono metamorphic and magmatic episodes occurred during the 620 480 ma interval that would comprise a complete cadomian wilson cycle the geodynamic scenario was that of an andean type continental margin an evolutionary model is presented for this orogeny comprising stages of volcanic arc generation crustal thickening back arc extension tectonic inversion and cratonization a correlation with comparable areas from pre mesozoic massifs elsewhere in europe is proposed in particular with the armorican massif of northern france

provenance and fate of arsenic and other solutes in the chaco pampean plain of the andean foreland argentina from perspectives of hydrogeochemical modeling and regional tectonic setting extensive arsenic as enriched groundwater is known to occur in the aquifers of the chaco pampean plain of argentina previous studies speculated that the as mobilization in these groundwaters was a direct result of their elevated ph and oxidative conditions the volcanic glass layers present in the aquifer matrix were hypothesized as one of the possible sources of as to the groundwaters here we examine the groundwater chemistry of the santiago del estero province of chaco pampean plains of argentina and test these hypotheses by using hydrogeochemical modeling within the framework of the regional geologic tectonic setting the study area is located in the active foreland of the andean orogenic belt which forms a continental arc setting and is dotted with several hot springs rhyolitic volcanic glass fragments derived from arc volcanism are abundant within the aeolian fluvial aquifer sediments and are related to the paleo igneous extrusion in the vicinity hydrogeochemical analyses show that the groundwater is in predominantly oxidative condition in addition some of the groundwaters exhibit very high na cl and so42 concentrations it is hypothesized in this study that the groundwater chemistry has largely evolved by dissolution of rhyolitic volcanic glass fragments contained within the aquifer sediments along with mixing with saline surface waters from adjoining salinas which are thought to be partially evaporated remnants of a paleo inland sea flow path modeling stability diagrams and thermodynamic analyses undertaken in this study indicate that the dominant evolutionary processes include ion exchange reactions chemical weathering of silicate and evaporites in monosialitization dominated weathering geochemical modeling predicts that plagioclase feldspar and volcanic glass are the major solids phases that contribute metal cations and dissolved silica to the local groundwaters co influxed oxyanions with similar ionic radii and structure e g mo si v po43 compete with as for mineral surface site leading to as mobilization to the groundwaters without considering the influence of microbial activities further the transition of the ca rich groundwater to na rich groundwater by mixing with water from the salinas and or evaporative concentration might also have led to counter ion effects a type of ion exchange reactions and hence further enrichment of groundwater by as some of the as may also have been contributed from mixing of meteoric water with magmatic sourced water in the geothermal springs

mineralogy and geochemistry affecting arsenic solubility in sediment profiles from the shallow basin fill aquifer of cache valley basin utah abstract elevated arsenic concentrations have been reported in groundwater samples collected from the semi arid western u s including the cache valley basin utah the volcanic rock in the basin fill aquifers underlying portions of the west is considered the primary source of arsenic but there is debate about the mechanisms that control arsenic solubilization in these semi arid and arid climates sediment cores were collected from a shallow basin fill aquifer in the cache valley basin to systematically determine arsenic mineralogy and solubilization mechanisms in relation to non redox and redox induced soil processes soluble arsenic was present throughout the two studied profiles in varying abundance and oxidation state with the highest concentration of soluble as v and as iii at the depth of the water table sequential chemical extractions of arsenic with oxidation preservation strategies revealed mineral sources and sinks of arsenic vulnerable to altering redox conditions down the profile weathering of primary arsenic bearing minerals resulted in soluble arsenic in the vadose zone once soluble arsenic was leached to the deeper profile arsenic solubility was controlled by carbonate minerals that concentrate at the water table in the zone with alternating oxidizing and reducing conditions iron oxides became the controlling mineral phase the association between arsenic and sulfides limited arsenic solubility at depths under permanent water saturation arsenic solubility was revealed to be controlled by a sequence of processes that prevail under different geochemical regimes down the profile

groundwater chemistry and redox processes depth dependent arsenic release mechanism patchy occurrences of elevated as are often encountered in groundwater from the shallow aquifers 50 m of the bengal delta plain bdp a clear understanding of various biogeochemical processe

natural arsenic contamination of holocene alluvial aquifers by linked tectonic weathering and microbial processes 1 linked tectonic geochemical and biologic processes lead to natural arsenic contamination of groundwater in holocene alluvial aquifers which are the main threat to human health around the world these groundwaters are commonly found a long distance from their ultimate source of arsenic where chemical weathering of as bearing minerals occurs we propose a gbh as model that ties together all of the important tectonic biologic and hydrologic processes that cause natural as release in groundwater in holocene terrestrial deposits processes highlighted by the gbh as model can explain the movement of arsenic from lithosphere to hydrosphere however we propose a factor that has increased dissolved as concentrations in holocene aquifers to levels where human health is threatened mechanical weathering associated with pleistocene glaciation our model invokes erosion of mountain belts aided by glaciers transport of arsenic by surface waters adsorption of as by stream sediments and deposition of stream sediments and organic matter in alluvial deposits subsequently fe iii reducing bacteria present in alluvial aquifers cause the release of sorbed as to groundwater under moderately reducing conditions

direct major and trace element analyses of rock varnish by high resolution laser ablation inductively coupled plasma mass spectrometry la icpms laser ablation inductively coupled plasma mass spectrometry la icpms was used to determine major and trace element concentrations in rock varnish samples from the lahontan range near fallon nv and from a remote wilderness area near the san juan river in southeastern utah the data indicate that rapid la icpms analyses provide ample analytical resolution for semi quantitative compositional determinations of both trace and major elements in the varnish despite the presence of a rock substrate component in most analyses the overall major element contents of rock varnish from the two localities are grossly similar to rock varnish from other locations analyzed by solution icpms electron microprobe and energy dispersive scanning electron microscopy sem differences between microprobe and la icpms analyses may stem from different sampling scales and different degrees of substrate involvement it was possible to detect significant variations in trace element contents in the rock varnish samples the lahontan range is situated within a belt of w mineralization and varnish from that locality contained significantly higher w and mo contents than varnish from localities outside the w belt lead tl bi cd and as contents of varnish coated pebbles from near the san juan river in southeastern utah varied by an order of magnitude as a function of the position of the sampling site on the pebble elevated heavy element contents on the skyward facing varnish surfaces indicate that heavy elements may be preferentially scavenged at the locations most likely to receive direct inputs of atmospherically deposited airborne particulates the source of metal rich airborne particulates in this case is probably any one of several large coal fired power plants in the four corners region proximal to the san juan study area these patterns indicate that rock varnish chemistry is influenced by atmospherically derived fluxes of both dissolved and particulate constituents and that rock varnish can be used as a passive environmental indicator for a wide variety of elements in much the same manner as moss and lichens

the cadomian active margin north armorican massif france a segment of the north atlantic panafrican belt abstract within the european variscan belt the armorican massif northwestern france contains an isolated fragment of the north atlantic panafrican belt the cadomian block mostly unaffected by variscan deformation this block is composed of neoproterozoic rocks ranging in age from 620 to 540 ma brioverian locally overlying a composite basement of icartian 2000 ma or pentevrian 750 ma age the cadomian tectonics the last magmatic manifestations of which are dated at around 540 ma were sealed by a cover of early cambrian rocks in normandy and early ordovician rocks in brittany five units are distinguished in this cadomian block tregor saint brieuc guingamp saint malo and fougeres although the units are bound by major faults the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model the tregor unit represented by the north tregor batholith of crustal affinity and its icartian host rock probably reflects an early cadomian evolution the saint brieuc unit essentially made up of magmatic rocks of juvenile affinity includes two assemblages juxtaposed by the cadomian tectonics 1 a volcanosedimentary succession formed in a typical island arc setting reflecting subduction around 610 ma and 2 a volcanic plutonic complex emplaced around 590 ma in an extensional active continental margin of pentevrian age the guingamp unit predominantly migmatitic includes a tectonic slice of deep origin the extrusion of which accompanied the exhumation of the migmatites it may represent the trace of a possible suture the saint malo unit is composed of brioverian detrital rocks the significance of which is uncertain passive continental margin or accretionary prism it is structured around a late migmatitic dome 540 ma the fougeres unit corresponds to the outer domain of the cadomian orogeny it was only weakly deformed by cadomian tectonics and is intruded by the large mancellian batholith of crustal origin dated at 540 ma together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin marginal basin and volcanic arc before being shortened during the cadomian convergent tectonics

arsenic solubilization and redistribution under anoxic conditions in three aquifer sediments from a basin fill aquifer in northern utah the role of natural organic carbon and carbonate minerals abstract the basin fill aquifers of the western u s contain elevated concentrations of arsenic in the groundwater due to ancient volcanic deposits that host arsenic minerals microcosms were constructed using two oxidized sediments and by contrast a reduced sediment collected from a shallow basin fill aquifer in the cache valley basin northern utah to evaluate the fate of geologic arsenic under anoxic conditions sequential extractions indicated the primary arsenic host mineral was amorphous iron oxides but 13 17 of the total arsenic was associated with carbonate minerals arsenic was solubilized from the sediments when incubated with groundwater in the presence of native organic carbon arsenic solubilization occurred prior to iron reduction rather than the commonly observed co reactivity arsenic v associated with carbonate minerals was the main source of arsenic released to solution and redistributed onto less soluble minerals including fes and siderite as defined by chemical extraction arsenic reduction occurred only in the site oxidized sediments the addition of a carbon and energy source glucose resulted in enhanced arsenic solubilization which was coupled with iron reduction from the site oxidized sediments adding glucose promoted iron reduction that masked the role of carbonate minerals in arsenic solubilization and retention as observed with incubation with groundwater only

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