interpretation of ph and eh trends in a fluvial sand aquifer system ground waters and aquifer materials from a shallow fluvial sand aquifer system 1 km long flow path were sampled and analyzed to determine the hydrogeochemical processes affecting ph and eh measured pt electrode potential the aquifer system is a fine grained sand k 10 3 cm s composed principally of quartz and plagioclase 70 of all grains with minor biotite partially altered to vermicuiite and trace amounts of calcite acid neutralization capacity measurements and x ray diffractograms suggest that acid precipitation recharging the aquifer undergoes a two step neutralization process the first step involves reactions with the surfaces of mineral grains mainly with plagioclase and biotite and the second step involves an irreversible neutralization involving biotite alteration to vermiculite and carbonate mineral dissolution during migration through deep confined parts of the aquifer ground waters attain equilibrium with calcite a thermodynamically based redox model of a closed oxidant system satisfactorily accounts for the sequential reduction of dissolved oxygen ferric oxides and sulfate in the aquifer by the oxidation of dissolved organic carbon and for oxygen only ferrous iron because of the problems of using pt electrodes in ground waters it is recommended that eh measurements be supplemented with dissolved oxygen and sulfide measurements

the shallowater aubrite evidence for origin by planetesimal impacts shallowater is the only known unbrecciated igneous aubrite enstatite achondrite it is a coarse grained orthopyroxenite consisting of in vol poikilitic orthoenstatite crystals 80 up to 4 5 cm in size which contain as inclusions and in the interstices xenoliths of an assemblage of twinned low ca clinoenstatite 1 forsterite 2 9 plagioclase 2 5 metallic fe ni 3 3 troilite 2 9 schreibersite 0 4 weathered opaques 8 and traces of niningerite and oldhamite conclusions 1 shallowater is of igneous origin 2 shallowater could not have formed by internal igneous nor by impact melting processes either on the h or l enstatite chondrite or aubrite parent bodies instead shallowater appears to be a sample of yet a fourth enstatite type asteroid 3 shallowater experienced an extraordinarily complex and unusual three stage cooling history as determined by mineral stability considerations and modelling of micro structural evolution as a function of cooling rate stage 1 very fast cooling from 1 580 c to somewhere above 712 c at a rate of 100 c hour through 1000 c above 1000 c the rate was probably much faster stage 2 very slow cooling annealing from 712 to 680 c at a rate of 7 5 c 106 y stage 3 fast cooling from 680 to 600 c at a rate of 0 5 c day and from 600 to 300 c at a rate of 0 4 c day 4 this complex cooling history suggests an equally unusual origin for shallowater as follows a completely or partly molten asteroid of nearly pure enstatite composition was broken up by low velocity impact with a solid e like object the melt cooled very fast stage 1 due to incorporation of cold 20 projectile debris the xenoliths fragments reassembled into a rubble pile body while t was 712 c and deeply buried materials like the object that is now shallowater cooled very slowly from 712 to 680 c stage 2 the anneal of stage 2 requires burial at a depth of 40 km on a 100 km diameter asteroid excavation from this depth by impact to account for the fast cooling of stage 3 can be accounted for in two scenarios scenario 1 during catastrophic impact the shallowater object could have been by chance near the surface within 10 m of a very large fragment thus accounting for the fast cooling and for surviving for 4 5 109 y scenario 2 the shallowater object may have been excavated by break up and subsequently buried near the surface of a gravitationally reassembled body this would require yet a second break up and reassembly episode 5 the xenoliths represent an enstatite like meteorite type unknown as an individual fall not unexpected for a rock type from an asteroid that appears to have been largely destroyed early in the history of the solar system

mineral stimulation of subsurface microorganisms release of limiting nutrients from silicates abstract microorganisms play an important role in the weathering of silicate minerals in many subsurface environments but an unanswered question is whether the mineral plays an important role in the microbial ecology silicate minerals often contain nutrients necessary for microbial growth but whether the microbial community benefits from their release during weathering is unclear in this study we used field and laboratory approaches to investigate microbial interactions with minerals and glasses containing beneficial nutrients and metals field experiments from a petroleum contaminated aquifer where silicate weathering is substantially accelerated in the contaminated zone revealed that phosphorus p and iron fe bearing silicate glasses were preferentially colonized and weathered while glasses without these elements were typically barren of colonizing microorganisms corroborating previous studies using feldspars in laboratory studies we investigated microbial weathering of silicates and the release of nutrients using a model ligand promoted pathway a metal chelating organic ligand 3 4 dihydroxybenzoic acid 3 4 dhba was used as a source of chelated ferric iron and a carbon source to investigate mineral weathering rate and microbial metabolism in the investigated aquifer we hypothesize that microbes produce organic ligands to chelate metals particularly fe for metabolic processes and also form stable complexes with al and occasionally with si further the concentration of these ligands is apparently sufficient near an attached microorganism to destroy the silicate framework while releasing the nutrient of interest in microcosms containing silicates and glasses with trace phosphate mineral inclusions microbial biomass increased indicating that the microbial community can use silicate bound phosphate inclusions the addition of a native microbial consortium to microcosms containing silicates or glasses with iron oxide inclusions correlated to accelerated weathering and release of si into solution as well as the accelerated degradation of the model substrate 3 4 dhba we propose that silicate bound p and fe inclusions are bioavailable and microorganisms may use organic ligands to dissolve the silicate matrix and access these otherwise limiting nutrients

fate of organic matter during aquifer storage and recovery asr of reclaimed water in a carbonate aquifer abstract understanding the fate of injected organic matter and the consequences of subsequent redox processes is essential to assess the viability of using reclaimed water in aquifer storage and recovery asr a full scale field trial was undertaken at bolivar south australia where two asr cycles injected approximately 3 6 105 m3 of reclaimed water into a carbonate aquifer over a 3 a period organic c within reclaimed water was predominantly in the dissolved fraction ranging from 1 to 2 mmol l 1 10 20 mg l 1 markedly higher than potable supply and stormwater previously reported as source waters for asr between 20 and 24 of the injected dissolved organic c doc was mineralised through reaction with injected o2 and no3 furthermore this was achieved mainly within the first 4 m of aquifer passage despite the presence of residual doc so4 reduction was not induced within the bulk of the injected plume it was only near the asr well during an extended storage phase where deeply reduced methanogenic conditions developed indicating variable redox zones within the injectant plume the quality of water recovered from the asr well indicated that the organic c content of reclaimed water does not restrict its application as a recharge source for asr

temporal variations in parameters reflecting terminal electron accepting processes in an aquifer contaminated with waste fuel and chlorinated solvents abstract a fundamental issue in aquifer biogeochemistry is the means by which solute transport geochemical processes and microbiological activity combine to produce spatial and temporal variations in redox zonation in this paper we describe the temporal variability of teap conditions in shallow groundwater contaminated with both waste fuel and chlorinated solvents teap parameters including methane dissolved iron and dissolved hydrogen were measured to characterize the contaminant plume over a 3 year period we observed that concentrations of teap parameters changed on different time scales and appear to be related in part to recharge events changes in all teap parameters were observed on short time scales months and over a longer 3 year period the results indicate that 1 interpretations of teap conditions in aquifers contaminated with a variety of organic chemicals such as those with petroleum hydrocarbons and chlorinated solvents must consider additional hydrogen consuming reactions e g dehalogenation 2 interpretations must consider the roles of both in situ at the sampling point biogeochemical and solute transport processes and 3 determinations of microbial communities are often necessary to confirm the interpretations made from geochemical and hydrogeological measurements on these processes

ree geochemistry of oldhamite dominated clasts from the norton county aubrite igneous origin of oldhamite abstract oldhamite dominated lithic clasts represent a new igneous lithology of the aubrite parent body they contain single crystals of oldhamite up to 2 cm in size with inclusions of ferromagnesian alabandite troilite daubreelite caswellsilverite and fe ni metal they are usually in intimate contact with a silicate portion consisting of enstatite forsterite and or plagioclase textural evidence for igneous origin includes apparent primary igneous grain boundaries between oldhamite and forsterite coarse grain size and the presence of round droplet like mn fe mg cr na sulfide inclusions within oldhamite which appear to represent an immiscible sulfide liquid we propose that the oldhamite dominated lithology formed during the melting and fractionation of enstatite chondrite like precursor material and represents a locally cas rich facies during melting two mutually immiscible sulfide liquids a ca sulfide and a mg fe mn cr na sulfide formed in the silicate magma upon cooling the immiscible sulfides crystallized forming large oldhamite crystals containing inclusions of mn fe mg cr na bearing sulfides forsterite enstatite and plagioclase crystallized from the surrounding silicate melt at subsolidus temperatures tiny ferromagnesian alabandite crystals exsolved from oldhamite ree abundances in oldhamite are high about 200 ci but ree patterns are nearly identical within single crystals and from clast to clast indicating equilibrium conditions high ree abundances have been cited as evidence that oldhamite grains in aubrites are nebular relics however we find it difficult to imagine that the rather homogeneous ree patterns of oldhamite in the oldhamite dominated lithology of norton county are not the result of equilibration of the rees with a silicate melt during formation of the igneous aubrites through parent body melting differentiation fractionation and cooling where peak temperatures of around 1450 1500 c must have been reached we conclude that oldhamite in the oldhamite dominated lithology of norton county is of igneous origin and that its ree abundances were established by equilibration with the aubrite silicate melt

self potential signals generated by the corrosion of buried metallic objects with application to contaminant plumes abstractlarge amplitude 100 mv negative electric self potential anomalies are often observed in the vicinity of buried metallic objects and ore bodies or over groundwater plumes associated with organic contaminants to explain the physical and chemical mechanisms that generate such electrical signals a controlled laboratory experiment was carried out involving two metallic cylinders buried with vertical and horizontal orientations and centered through and in the capillary fringe within a sandbox the 2d and 3d self potential sp data were collected at several time steps along with collocated ph and redox potential measurements large dipolar sp and redox potential anomalies developed in association with the progressive corrosion of the vertical pipe although no anomalies were observed in the vicinity of the horizontal pipe this discrepancy was due to the orientation of the pipes with the vertical pipe subjected to a significantly larger eh gradient accounting for the electrical conductivity dis

temporal geophysical signatures from contaminant mass remediation we have previously documented changes in bulk electrical conductivity self potential sp and ground penetrating radar gpr reflections in a field setting caused by biogeochemical transformations of hydrocarbon contaminated media these transformations are associated with hydrocarbon biodegradation the results of surface geophysical surveys acquired in 1996 2003 and 2007 document changes in geophysical signatures associated with removing hydrocarbon mass in the contaminated zone initial investigations in 1996 showed that relative to background the contaminated area was characterized by higher bulk electrical conductivity positive sp anomaly and attenuated gpr reflections repeated surveys in 2003 and 2007 over the contaminated area showed that in 2007 the bulk electrical conductivityhad reverted to near background conditions the positive sp anomaly became more negative and the zone of attenuated gpr reflections showed increased signal strength removal of hydrocarbon mass in the vadose zone o

migration of contaminants in groundwater at a landfill a case study 6 hydrogeochemistry multilevel point samplers located on a longitudinal cross section through the plume of contaminated groundwater in the sand aquifer at the abandoned borden landfill were used to obtain a suite of small volume samples for analysis of major ions and of minor and trace level inorganic constituents calcium is the dominant cation and sulphate and bicarbonate are the dominant anions in the contaminant plume with maximum concentrations of 400 2000 and 1200 mg l 1 respectively beneath the landfill the most highly contaminated water in the aquifer has total dissolved solids of 4000 mg l 1 sulphate and iron are the only inorganic constituents that exceed the recommended limits for drinking water the plume contains above background concentrations of dissolved zinc and manganese no heavy metals or other hazardous inorganic trace elements occur at levels above the maximum limits for drinking water the plume contains levels of total dissolved organic carbon that are above background levels ranging from 30 mg l 1 beneath the landfill to 5 mg l 1 near the front of the plume the landfill which is almost entirely above the water table contains high partial pressures of carbon dioxide and methane the high carbon dioxide levels induce substantial dissolution of calcite which occurs in sand layers in the landfill and in the aquifer immediately below the landfill calcite dissolution is the origin of much of the dissolved inorganic carbon and some of the calcium in the plume most of the sulphate and much of the calcium in the plume appears to be derived from gypsum in construction debris in the landfill groundwater beneath the landfill is saturated with respect to gypsum and slightly supersaturated with respect to calcite some of the dissolved iron in the plume results from the release under reducing conditions of iron from ferric iron coatings on sand grains located in the aquifer beneath the landfill and in the layers in the refuse dissolved iron concentrations appear to be limited by the solubility of siderite dissolved sulphide is present at only very low concentrations and is probably controlled by ferrous sulphide solubility exchange of cations between the aquifer material and the leachate contaminated groundwater is an apparent cause of calcium release and subsequent precipitation of calcite in the plume as much of 80 of the k 20 of the mg2 and 15 of the na in the plume exists on the exchange sites the effects of dispersive and geochemical attenuation were evaluated from the ratios of chloride to other species along a central flow path from the landfill to the front of the plume platinum electrode measurements and electrochemical potentials calculated from equilibrium speciation of analysed constituents varied over a wide range of values and provided poor agreement among methods for the same sample only potentials derived from the iron redox couples and pt electrode measurements exhibited fair agreement for any one sample the rather narrow range of pt electrode potential values along the central flow line through the plume suggest that the electrochemical potentials are buffered apparently as a result of fe oh 3 s ag feco3 s equilibria

distribution of terminal electron accepting processes in an aquifer having multiple contaminant sources abstract concentrations of electron acceptors electron donors and h2 in groundwater were measured to determine the distribution of terminal electron accepting processes teaps in an alluvial aquifer having multiple contaminant sources upgradient contaminant sources included two separate hydrocarbon point sources one of which contained the fuel oxygenate methyl tertbutyl ether mtbe infiltrating river water was a source of dissolved no3 so4 and organic carbon doc to the downgradient part of the aquifer groundwater downgradient from the mtbe source had larger concentrations of electron acceptors dissolved o2 and so4 and smaller concentrations of teap end products dissolved inorganic c fe2 and ch4 than groundwater downgradient from the other hydrocarbon source suggesting that mtbe was not as suitable for supporting teaps as the other hydrocarbons measurements of dissolved h2 indicated that so4 reduction predominated in the aquifer during a period of high water levels in the aquifer and river the predominant teap shifted to fe3 reduction in upgradient areas after water levels receded but remained so4 reducing downgradient near the river this distribution of teaps is the opposite of what is commonly observed in aquifers having a single contaminant point source and probably reflects the input of doc and so4 to the aquifer from the river results of this study indicate that the distribution of teaps in aquifers having multiple contaminant sources depends on the composition and location of the contaminants and on the availability of electron acceptors

the origin of oldhamite in unequilibrated enstatite chondrites abstract we report the results of an ion probe study of rare earth elements rees in six unequilibrated enstatite chondrites oldhamite is confirmed as the major but not the only ree carrier in these meteorites data are also provided for other minerals enstatite niningerite and alabandite that carry detectable amounts of rees although the variety of ree patterns in oldhamite is not as extreme as in hibonite there are seven distinct ree patterns four of which form a continuum that characterize most oldhamite grains from e chondrites two of these patterns f and g were each found in only one weathered grain there is no correlation between ree pattern and oldhamite petrologic setting our trace element data are used to evaluate earlier work and a number of elements zr y sc rees sr se and probably sb and cs including both refractory and volatile species under oxidizing conditions are found enriched in oldhamite a comparison of ree patterns with the results of equilibrium condensation calculations indicates that nebular processes were important in determining the composition of the oldhamite precursors whereas metamorphic processes also affected oldhamite compositions enrichments of chalcophiles are not necessarily due to interaction of oldhamite with nebular gas at low temperatures as previously suggested oldhamite like hibonite was formed from melts whose trace element compositions were determined by high temperature transient events in the solar nebula

normal and reverse zoning in niningerite a novel key parameter to the thermal histories of eh chondrites abstract two zoning trends have been discovered in niningerite grains in the eh chondrites abee kaidun iii south oman st marks yamato 74370 indarch yamato 691 and qingzhen 1 a a normal zoning with decreasing fe content from the core to the rim this is indicative of fe diffusion from niningerite to troilite upon cooling this trend is present in abee kaidun iii south oman st marks and yamato 74370 it may have developed either in the solar nebula or in the eh parent body 2 b a reverse zoning trend with increasing fe content from the core to the rim adjacent to troilite this trend is indicative of fe diffusion from troilite into niningerite as a result of thermal events it is encountered in indarch yamato 691 and qingzhen in qingzhen a reversibly zoned mn rich niningerite is found the composition of which deviates considerably from the average qingzhen compositions 26 0 33 6 mole mns 52 4 57 2 mole mgs and 12 6 21 0 mole fes versus 11 5 16 0 mole mns 67 5 73 6 mole mgs and 13 5 21 5 mole fes this is strongly suggestive of inhomogeneous accretion in that part of the solar nebula where eh chondrites condensed cores of niningerites in indarch contain massive troilite exsolution lamellae this could have formed by 1 1 slow cooling of a fes rich niningerite before accretion in the parent body or by 2 2 a two stage cooling process the results indicate that niningerite is a sensitive detector for reconstruction of the thermal histories of eh chondrites

use of dissolved and vapor phase gases to investigate methanogenic degradation of petroleum hydrocarbon contamination in the subsurface 1 at many sites contaminated with petroleum hydrocarbons methanogenesis is a significant degradation pathway techniques to estimate ch4 production consumption and transport processes are needed to understand the geochemical system provide a complete carbon mass balance and quantify the hydrocarbon degradation rate dissolved and vapor phase gas data collected at a petroleum hydrocarbon contaminated site near bemidji minnesota demonstrate that naturally occurring nonreactive or relatively inert gases such as ar and n2 can be effectively used to better understand and quantify physical and chemical processes related to methanogenic activity in the subsurface in the vadose zone regions of ar and n2 depletion and enrichment are indicative of methanogenic and methanotrophic zones and concentration gradients between the regions suggest that reaction induced advection can be an important gas transport process in the saturated zone dissolved ar and n2 concentrations are used to quantify degassing driven by methanogenesis and also suggest that attenuation of methane along the flow path into the downgradient aquifer is largely controlled by physical processes slight but discernable preferential depletion of n2 over ar in both the saturated and unsaturated zones near the free phase oil suggests reactivity of n2 and is consistent with other evidence indicating that nitrogen fixation by microbial activity is taking place at this site

the kaidun meteorite mineralogy of an unusual cm1 lithology kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises many kaidun clasts have been intensely altered by aqueous fluids as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate and phyllo silicate filled veins in this report we describe an unusual cm lithology containing many mineralogical features not previously reported from any meteorite including pyrrhotite with exclusive needlelike morphologies and thick mantles of phyllosilicate and complex aggregates of phyllosilicate melanite garnet crosscut by pentlandite veins the latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 c which is significantly higher than that attained during secondary processing from other known cm material

lanthanide and actinide chemistry at high c o ratios in the solar nebula abstract chemical equilibrium calculations were performed to study the condensation chemistry of the ree and actinides under the highly reducing conditions which are necessary for the formation of the enstatite chondrites 1 2 our calculations confirm that the ree and actinides condensed into oldhamite cas the major ree and actinide host phase in enstatite chondrites at a carbon oxygen co ratio 1 in an otherwise solar gas five basic types of ree abundance patterns several of which are analogous to ree abundance patterns observed in the ca al rich inclusions cais in carbonaceous chondrites are predicted to occur in meteoritic oldhamites all of the reported ree patterns in oldhamites in enstatite chondrites can be interpreted in terms of our condensation calculations the observed patterns fall into 3 of the 5 predicted categories the reported th and u enrichments and ratios in meteoritic oldhamites are also consistent with predictions of the condensation calculations finally pure ree sulfides are predicted to condense in the 10 6 to 10 9 bar range and may be found in enstatite chondrites if they formed in this pressure range

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

biogeochemical transformation of fe minerals in a petroleum contaminated aquifer abstract the bemidji aquifer in minnesota usa is a well studied site of subsurface petroleum contamination the site contains an anoxic groundwater plume where soluble petroleum constituents serve as an energy source for a region of methanogenesis near the source and bacterial fe iii reduction further down gradient methanogenesis apparently begins when bioavailable fe iii is exhausted within the sediment past studies indicate that geobacter species and geothrix fermentens like organisms are the primary dissimilatory fe reducing bacteria at this site the fe mineralogy of the pristine aquifer sediments and samples from the methanogenic source and fe iii reducing zones were characterized in this study to identify microbiologic changes to fe valence and mineral distribution and to identify whether new biogenic mineral phases had formed methods applied included x ray diffraction x ray fluorescence xrf and chemical extraction optical transmission and scanning electron microscopy and mossbauer spectroscopy all of the sediments were low in total fe content 1 and exhibited complex fe mineralogy the bulk pristine sediment and its sand silt and clay sized fractions were studied in detail the pristine sediments contained fe ii and fe iii mineral phases ferrous iron represented approximately 50 of fetot the relative fe ii concentration increased in the sand fraction and its primary mineralogic residence was clinochlore with minor concentrations found as a ferroan calcite grain cement in carbonate lithic fragments fe iii existed in silicates epidote clinochlore muscovite and fe iii oxides of detrital and authigenic origin the detrital fe iii oxides included hematite and goethite in the form of mm sized nodular concretions and smaller sized dispersed crystallites and euhedral magnetite grains authigenic fe iii oxides increased in concentration with decreasing particle size through the silt and clay fraction chemical extraction and mossbauer analysis indicated that this was a ferrihydrite like phase quantitative mineralogic and fe ii iii ratio comparisons between the pristine and contaminated sediments were not possible because of textural differences however comparisons between the texturally similar source where bioavailable fe iii had been exhausted and fe iii reducing zone sediments where bioavailable fe iii remained indicated that dispersed detrital crystalline fe iii oxides and a portion of the authigenic poorly crystalline fe iii oxide fraction had been depleted from the source zone sediment by microbiologic activity little or no effect of microbiologic activity was observed on silicate fe iii the presence of residual ferrihydrite in the most bioreduced anoxic plume sediment source implied that a portion of the authigenic fe iii oxides were biologically inaccessible in weathered lithic fragment interiors little evidence was found for the modern biogenesis of authigenic ferrous containing mineral phases perhaps with the exception of thin siderite or ferroan calcite surface precipitates on carbonate lithic fragments within source zone sediments

short term variations in flow velocity of glaciar soler patagonia chile short term variations in ice flow velocity were obtained at intervals of a few hours and a few days in the ablation area of glaciar soler patagonia chile in november 1985 a maximum flow rate was measured at about four times the minimum value a good correlation with a time lag of 7 5 h was found between the ice flow velocity in the lower reaches and the amount of water discharge from the glacier terminus it was concluded therefore that the velocity variations should have resulted from the variations in basal sliding velocity which is strongly controlled by the subglacial water pressure

enstatite aggregates with niningerite heideite and oldhamite from the kaidun carbonaceous chondrite relatives of aubrites and eh chondrites we studied 2 enstatite aggregates en 99 with sizes of 0 5 and 1 5 mm embedded in the carbonaceous matrix of kaidun they contain sulfide inclusions up to 650 m in length which consist mainly of niningerite but contain numerous grains of heideite as well as oldhamite and some secondary phases complex fe ti s hydroxides and ca carbonate both niningerite and heideite are enriched in all trace elements relative to the co existing enstatite except for be and sc the niningerite has the highest ca content about 5 wt of all niningerites analyzed so far in any meteorite and is the phase richest in trace elements the ree pattern is fractionated with the ci normalized abundance of lu being higher by 2 orders of magnitude than that of la and has a strong negative eu anomaly heideite is on average poorer in trace elements except for zr la and li its ree pattern is flat at about 0 5 x ci and it also has a strong negative eu anomaly the enstatite is very poor in trace elements its ce content is about 0 01 that of niningerite but li be ti and sc have between 0 1 and 1 x ci abundances the preferential partitioning of typical lithophile elements into sulfides indicates highly o deficient and s dominated formation conditions for the aggregates the minimum temperature of niningerite formation is estimated to be 850 900 c the texture and the chemical characteristics of the phases in the aggregates suggest formation by aggregation and subsequent sintering before incorporation into the kaidun breccia the trace element data obtained for heideite the first on record show that this mineral in addition to oldhamite and niningerite is also a significant carrier of trace elements in enstatite meteorites

changes in the sorption capacity of coastal plain sediments due to redox alteration of mineral surfaces chemical characteristics of grain coatings in a coastal plain sandy aquifer on the eastern shore of virginia were investigated where sediments have been exposed to distinct groundwater redox conditions dissolved o2 was 5 0 to 10 6 mg l 1 in the regionally extensive aerobic groundwater whereas in a narrow leachate plume it was only 0 001 to 0 9 mg l 1 the amount of dissolved fe in the aerobic groundwater was only 0 005 to 0 01 mg l 1 but it was 12 to 47 mg l 1 in the anaerobic zone the amount of extractable fe was an order of magnitude higher for the aerobic sediments than for the anaerobic sediments indicating that reductive dissolution removed the oxide coatings the capacity for anion sorption on the sediment surfaces as indicated by the sorption of 35so42 was an order of magnitude higher in the aerobic vs anaerobic sediments the presence of anaerobic groundwater did not significantly alter the amount of extractable al oxides on the surface of the sediments and those coatings helped to maintain a high surface area the removal of the fe oxides from the grain surfaces under anaerobic conditions was solely responsible for the significant reduction of so4 sorption observed this loss of capacity for anion sorption could lead to more extensive transport of negatively charged constituents such as some contaminant chemicals or bacteria that may be of concern in groundwater

microbial colonization and weathering of silicates in a petroleum contaminated groundwater abstract the influence of native microorganisms on mineral dissolution and precipitation was examined in a petroleum contaminated aquifer near bemidji minnesota in situ microcosms containing clean silicate fragments were established in the contaminated microbially active groundwater over one year periods the recovered minerals were then examined by sem and esem for microbial colonization patterns and weathering features these experiments reveal distinct patterns of colonization and weathering associated with microbial attachment and growth microcline anorthoclase and oligoclase were widely colonized and the colonized surfaces deeply weathered with secondary clays precipitated on some uncolonized surfaces other feldspars in contrast were uncolonized and unweathered specific mineral removal rate was estimated from etch pit depth while bulk weathering rate was estimated from the rate of change of silica concentration in the groundwater in this system the primary control of silicate dissolution is apparently microbial colonization and metabolic activity

chemical hydrogeology in natural and contaminated environments abstract chemical hydrogeology including organic and inorganic aspects has contributed to an increased understanding of groundwater flow systems geologic processes and stressed environments most of the basic principles of inorganic chemical hydrogeology were first established by investigations of organic free regional scale systems for which simplifying assumptions could be made the problems of groundwater contamination are causing a shift of emphasis to microscale systems that are dominated by organic chemical reactions and that are providing an impetus for the study of naturally occurring and manmade organic material along with the decrease in scale physical and chemical heterogeneity become major controls current investigations and those selected from the literature demonstrate that heterogeneity increases in importance as the study site decreases from regional scale to macroscale to microscale increased understanding of regional scale flow systems is demonstrated by selection of investigations of carbonate and volcanic aquifers to show how application of present day concepts and techniques can identify controlling chemical reactions and determine their rates identify groundwater flow paths and determine flow velocity and determine aquifer characteristics the role of chemical hydrogeology in understanding geologic processes of macroscale systems is exemplified by selection of investigations in coastal aquifers phenomena associated with the mixing zone generated by encroaching sea water include an increase in heterogeneity of permeability diagenesis of minerals and formation of geomorphic features such as caves lagoons and bays ore deposits of manganese and uranium along with a simulation model of ore forming fluids demonstrate the influence of heterogeneity and of organic compounds on geochemical reactions associated with genesis of mineral deposits in microscale environments importance of heterogeneity and consequences of organic reactions in determining the distributions and concentrations cf constituents are provided by several studies including infiltration of sewage effluent and migration of creosote in coastal plain aquifers these studies show that heterogeneity and the dominance of organically controlled reactions greatly increase the complexity of investigations

an experimental and theoretical study of rare earth element partitioning between sulfides fes cas and silicate and applications to enstatite achondrites abstract partition coefficients of the rare earth elements ree between sulfides fes or cas and silicate melt were determined experimentally at 1200 1300 c the ree sulfide silicate partition coefficients d are 1 under the experimental o and s fugacities which demonstrates that the ree are mainly located in the silicate phase rare earth element partition coefficients in the fes silicate system decrease from light to heavy ree while the opposite behavior is found for the cas silicate system where partition coefficients increase from light to heavy ree in both sulfide systems eu is preferentially incorporated into the sulfide phases as also expected from thermodynamic calculations the eu sulfide silicate partition coefficient is about a factor of ten higher than that of neighboring sm and gd in accordance with thermodynamic predictions of ree sulfide silicate partition coefficients the low sulfide silicate partition coefficients indicate that cas oldhamite in enstatite achondrites aubrites cannot have gained its high ree concentrations during igneous differentiation processes the high ree concentrations and the ree patterns in aubritic oldhamite are more plausibly explained by ree condensation into refractory cas the refractory nature of cas prevented major exchange reactions of the oldhamite with other aubritic minerals during the short differentiation and metamorphism period on the aubrite parent body thus oldhamite in aubrites may be relict condensates altered to different degrees during short heating events as originally suggested by lodders and palme 1990

dating degassed groundwater with 3h 3he the production of gases in groundwater under contaminated locations by geochemical and biological processes is not uncommon degassing of these gases from groundwater and repartitioning of noble gases between water and gas phase distorts groundwater dating by 3h 3he we observed noble gas concentrations below atmospheric equilibrium in 20 out of 34 groundwater samples from agriculturally polluted sandy areas in the netherlands from the absence of nitrate in degassed samples we conclude that denitrification causes degassing the 22ne 20ne ratios show that degassing had attained solubility equilibrium and had not caused isotopic fractionation by diffusion to correct for the loss of tritiogenic 3he due to degassing we present a single step equilibrium degassing model we use the total dissolved gas pressure at the monitoring screen to estimate the depth and timing of degassing which is essential to estimate travel times from degassed samples by propagating the uncertainties in the underlying measurements and assumptions through the travel time calculations we found a travel time uncertainty of 3 years a we therefore conclude that 3h 3he dating can produce valuable information on groundwater flow even at sites with strong degassing copyright 2007 by the american geophysical union

geochemistry s vital contribution to solving water resource problems abstract as part of the events celebrating 40 a of iagc it is fitting to trace the modern evolution and development of hydrogeochemistry however fascination with water quality can be traced back more than 2 ka in the post war years hydrogeochemistry was influenced heavily by the advances in other disciplines including physical chemistry metallurgy and oceanography hydrological applications of isotope science also developed rapidly at this time and important advances in analytical chemistry allowed multi element and trace element applications to be made experimental studies on equilibrium processes and reaction kinetics allowed bench scale insight into water rock interaction consolidation of knowledge on processes in groundwaters and the current awareness of hydrogeochemistry by water professionals owe much to the work of robert garrels john hem and co workers in the early 1960s studies of down gradient evolution enabled a field scale understanding of groundwater quality and geochemical processes as a function of residence time dissolution and precipitation processes in carbonate and non carbonate aquifers redox processes cation exchange and salinity origins emerging water resource and water quality issues in the 1960s and 70s permitted the application of hydrogeochemistry to contaminant and related problems and this trend continues the impacts of diffuse pollution from intensive agriculture waste disposal and point source pollution from urban and industrial sources relied on geochemistry to solve questions of origin and attenuation in semi arid regions facing water scarcity geochemical approaches have been vital in the assessment of renewability and characterising palaeowaters the protection and new incoming regulation of water resources will rely increasingly on a sound geochemical basis for management

aubrites and diogenites trace element clues to their origin we have analyzed by rnaa 25 aubrite and 9 diogenite samples for 13 to 29 siderophile volatile and lithophile trace elements both meteorite classes show a typically igneous siderophile element pattern with ir os re ge more depleted than au ni pd sb but aubrites tend to have about 10 higher abundances 10 3 10 4 cl for the first 4 and 10 2 10 3 cl for the last 4 siderophiles apparently reflecting smaller metal silicate distribution coefficients at lowerf o2 or less complete segregation of metal se is surprisingly abundant in aubrites up to 0 4 cl but te is less so sete 5 cl apparently due to its stronger siderophile character other volatiles ag zn in cd bi t1 show depletions intermediate between lunar dunite and the earth s mantle of 7 aubrites analyzed for ree ce nd eu tb yb lu 6 are depleted in ree 0 08 0 5 cl and 5 show negative eu anomalies the exceptions are bishopville and mt egerton silicate this supports an igneous origin as already noted by boynton and schmitt 1972 no samples of the complementary basaltic and feldspathic rocks have been found thus far but one of our samples of khor temiki dark is a candidate for the basalt it is 5 7 enriched in ree and only slightly less so in rb cs and u though shocked and enriched in siderophiles to 0 05 cl it apparently represents a new meteorite class three diogenites analyzed for ree show very diverse patterns from strongly depleted in light ree for tatahouine ce 0 01 cl to flat for garland 2 5 cl the data confirm the trends found by fukuokaet al 1977 as well as their interpretations factor analysis shows several parallel groupings for aubrites and diogenites siderophiles re ir os pd ge chalcophiles se te volatiles ag in tl and incompatibles u ree and cs or rb but there are some differences for elements such as ni sb cd bi au and zn most of which behave more sensibly in aubrites than in diogenites several element pairs that differ greatly in volatility cs u ge ir correlate closely in aubrites in approximately cl chondrite proportions these correlations and other lines of evidence suggest strongly that aubrites originated by igneous processes in their parent body not by direct nebular condensation the source material may have resembled el chondrites in oxidation state and depletion of refractories metal and volatiles

iron reduction in the sediments of a hydrocarbon contaminated aquifer abstract sediments sampled at a hydrocarbon contaminated glacial outwash sandy aquifer near bemidji minnesota were analyzed for sediment associated fe with several techniques extraction with 0 5 m hcl dissolved poorly crystalline fe oxides and small amounts of fe in crystalline fe oxides and extracted fe from phyllosilicates use of ti citrate edta bicarbonate results in more complete removal of crystalline fe oxides the average hcl extractable fe iii concentration in the sediments closest to the crude oil contamination 16 2 mol g has been reduced by up to 30 from background values 23 8 mol g as a result of fe iii reduction in contaminated anoxic groundwater iron ii concentrations are elevated in sediments within an anoxic plume in the aquifer iron ii values under the oil body 19 2 mol g are as much as 4 times those in the background sediments 4 6 mol g indicating incorporation of reduced fe in the contaminated sediments a 70 increase in total extractable fe at the anoxic oxic transition zone indicates reoxidation and precipitation of fe mobilized from sediment in the anoxic plume scanning electron microscopy detected authigenic ferroan calcite in the anoxic sediments and confirmed abundant fe iii oxyhydroxides at the anoxic oxic boundary the redox biogeochemistry of fe in this system is coupled to contaminant degradation and is important in predicting processes of hydrocarbon degradation

combined 14c and δ13c analysis of petroleum biodegradation in a shallow contaminated aquifer the contamination of soil and groundwater by the accidental release of petroleum hydrocarbons is a common problem that affects drinking water supplies and in situ biodegradation is a promising option for removing contaminants with relatively low costs and minimal health risks total petroleum hydrocarbons tph 13c and 14c isotope ratios in dissolved inorganic carbon dic and other geochemical indicators have been analyzed to demonstrate the effectiveness of in situ biodegradation at a contaminated site the 13c and 14c isotope ratios ranged from 5 4 to 18 4 and from 35 1 to 67 pmc respectively some groundwater samples were contaminated with petroleum hydrocarbons with low 14c and 13c contents indicating the existence of microbial non methanogenic biodegradation whereas low 14c and high 13c contents were associated with the highest tph concentrations confirming that microbial methanogenic biodegradation occurred in these areas differences in the 13c and 14c isotope ratios between monitoring wells in uncontaminated and contaminated areas suggest that the percentage of the dic produced by methanogenic biodegradation decreased from 28 5 32 0 to 5 94 6 67 along the flow direction and became almost zero in downgradient areas and at the edge of the contamination plume

characterisation of organic matter in a shallow reducing arsenic rich aquifer west bengal abstract elevated arsenic in groundwaters extensively exploited for irrigation and drinking water in west bengal and bangladesh is causing serious impacts on human health a key mechanism for the genesis of arsenic as in these waters is microbially mediated reductive transformation of arsenic bearing fe iii hydrated oxides the role of organic c in this process whether from in situ organic matter om i e om from within the sediment or from other sources is widely recognised despite this there is a paucity of data about the characteristics of om in these as rich aquifers extraction and analysis of the polar and apolar fractions from seven different sediments from a known groundwater as hotspot in west bengal revealed om characteristic of the original terrestrial depositional environment however this was overprinted by abundant hydrocarbons with thermally mature e g petroleum distributions these hydrocarbons included abundant high molecular weight n alkanes and unresolved complex mixtures ucms as well as thermally mature distributions of hopanes and steranes additionally at certain depths surface sands 8 and 13 m deeper sands 25 m the om appeared to be biodegraded with the preferential removal of petroleum sourced n alkanes suggesting that indigenous microbes within the aquifer can utilise this carbon source the presence of this previously unreported source of bioavailable organic carbon is of importance as it has the potential to promote microbial activity and subsequent as release in the aquifers

modeling of carbon cycling and biogeochemical changes during injection and recovery of reclaimed water at bolivar south australia 1 managed aquifer recharge is an increasingly popular technique to secure and enhance water supplies among a range of recharging techniques single well aquifer storage and recovery asr is becoming a common option to either augment drinking water supplies or facilitate reuse of reclaimed water for the present study a conceptual biogeochemical model for reclaimed water asr was developed and incorporated into an existing reactive multicomponent transport model the conceptual and numerical model for carbon cycling includes various forms of organic and inorganic carbon and several reactive processes that transfer carbon within and across different phases the major geochemical processes considered in the model were microbially mediated redox reactions driven by the mineralization of organic carbon mineral dissolution precipitation and ion exchange the numerical model was tested and applied for the analysis of observed data collected during an asr field experiment at bolivar south australia the model simulation of this experiment provides a consistent interpretation of the observed hydrochemical changes the results suggest that during the storage phase dynamic changes in bacterial mass have a significant influence on the local geochemistry in the vicinity of the injection extraction well farther away from the injection extraction well breakthrough of cations is shown to be strongly affected by exchange reactions and in the case of calcium by calcite dissolution

petrography mineral chemistry and origin of type i enstatite chondrites abstract optical and cathodoluminescence petrography were coupled with electron microprobe analysis to relate the textures and chemical compositions of minerals in the chondrules and matrix of the indarch kota kota adhi kot and abee type i enstatite chondrites clinoenstatites fall into two distinct chemical groups with characteristic red or blue luminescence red crystals are higher in ti al cr mn and ca and lower in na than blue ones rare forsterites in indarch and kota kota show distinct compositions associated with orange or blue luminescence the chemical ranges are indistinguishable for each color type in chondrules of all textural types and the presence of both color types in a single chondrule or a metal fragment requires mechanical aggregation of both crystals and liquids of both color types porphyritic chondrules are ascribed mainly to aggregation of existing crystals because both types of pyroxene and olivine occur in the same chondrule large crystals of one color type are surrounded by fine grained crystals of another type in some barred and radiating chondrules all types of chondrules are surrounded by fine grained rims rich in sulfide the matrix contains many broken chondrules and individual silicate grains but is rich in sulfide and metal analyses are given of albite minor elements and luminescence color vary between chondrites kamacite schreibersite oldhamite and niningerite although the mineral assemblages do not fit theoretical condensation sequences in detail the red pyroxene and orange olivine might result ultimately from near equilibrium crystallization in which early reduced condensates reacted with a gas while the blue crystals might result from fractional condensation in which early condensates were removed mechanically from a gas subsequent episodes involving mixing melting crystallization condensation fracturing and mechanical aggregation would be needed to produce the complex textures

characteristics of tide water calving at glaciar san rafael chile glacial calving is a poorly understood process this study tests the influence of local environmental variables on the magnitude and frequency distributions of calving behaviour at glaciar san rafael chile near the terminus of the glacier surface speeds average 17 m d 1 in summer and calving is profuse and continual the size location and characteristics of over 7000 calving events were recorded during 32 d in 1991 and 1992 together with meteorological bathymetric and oceanographic data mean daily calving exceeds 400 events per day and the mean calving flux is more than 2 mm 3 d 1 mean annual calving speed and calving flux are about 4500 m a 1 and 2 0 km 3 a 1 respectively this calving speed is higher than that predicted by the established empirical relationship between tide water calving speed and water depth this is surprising given the low salinity of laguna san rafael and that fresh water calving speeds are commonly much lower than those in tide water daily patterns of calving frequency and flux correlate poorly or not at all with meteorological variables but tidal stage may have some control over the timing of large submarine calving events submarine calving produced the largest bergs however the relatively small total flux recorded from the submerged part of the ice cliff may imply unusually rapid melt rates

crude oil in a shallow sand and gravel aquifer ii organic geochemistry abstract crude oil spilled from a pipeline break in a remote area of north central minnesota has contaminated a shallow glacial outwash aquifer part of the oil was sprayed over a large area to the west of the pipeline and part of it accumulated in an oil body that floats at the water table to the east of the point of discharge total dissolved organic carbon tdoc concentrations in shallow groundwater collected in the oil spray area reach 16 mg l this is nearly an order of magnitude higher than the tdoc concentrations of native groundwater 2 3mg l the additional tdoc derives from the partial degradation of petroleum residues deposited at the land surface and transported to the aquifer by vertical recharge in the vicinity of the oil body tdoc concentrations in groundwater are 48 mg l 58 of the tdoc being composed of non volatile organic c the majority of the volatile doc 63 is a mixture of low molecular weight saturated aromatic and alicyclic hydrocarbons derived from the oil downgradient from the oil body along the direction of groundwater flow concentrations of all measured constituents of the tdoc pool decrease concentrations begin to decline most rapidly however in the zone where dissolved o 2 concentrations begin to increase 50m downgradient from the leading edge of the oil within the anoxic zone near the oil body removal rates of isometric monoaromatic hydrocarbons vary widely this indicates that the removal processes are mediated mainly by microbiological activity molecular and spectroscopic characterization of the tdoc and its spatial and temporal variation provide evidence of the importance of biogeochemical processes in attenuating petroleum contaminants in this perturbed subsurface environment

estimating 14c groundwater ages in a methanogenic aquifer this paper addresses the problem of 14c age dating of groundwaters in a confined regional aquifer affected by methanogenesis increasing ch4 concentrations along the groundwater flow system and 13c and 14c isotopic data for dissolved inorganic carbon dissolved organic carbon and ch4 clearly show the effect of methanogenesis on groundwater chemistry inverse reaction path modeling using netpath indicates the predominant geochemical reactions controlling the chemical evolution of groundwater in the aquifer are incongruent dissolution of dolomite ion exchange methanogenesis and oxidation of sedimentary organic matter modeling of groundwater 14c ages using netpath indicates that a significant part of groundwater in the alliston aquifer is less than 13 000 years old however older groundwater in the range of 15 000 23 000 years is also present in the aquifer this paper demonstrates that 14c ages calculated using netpath incorporating the effects of methanogenesis on the carbon pools provide reasonable groundwater ages that were not possible by other isotopic methods

interferometric radar observations of glaciar san rafael chile interferometric radar observations of glaciar san rafael chile were collected in october 1994 by nasa s spaceborne imaging radar c sir c at both l 24 cm and c band frequency 5 6 cm with vertical transmit and receive polarization the c band data did not yield good geophysical products because the temporal coherence of the signal was significantly reduced after 24 h the l band data were however successfully employed to map the surface topography of the icefield with a 10 m uncertainty in height and measure ice velocity with a precision of 4 mm d 1 or 1 4 ma 1 the corresponding error in strain rates is 0 05 a 1 at a 30 m horizontal spacing the one dimensional interferometric velocities were subsequently converted to horizontal displacements by assuming a flow direction and complemented by feature tracking results near the calving front the results provide a comprehensive view of the ice flow dynamics of glaciar san rafael the glacier has a core of rapid flow 4 5 km in width and 3 5 in average slope surrounded by slowermoving ice not by rock ice velocity is 2 6 m d 1 or 0 95 km a 1 near the equilibrium line altitude 1200 m increasing rapidly before the glacier enters the narrower terminal valley to reach 17 5 m d 1 or 6 4 km a 1 at the calving front strain rates are dominated by lateral shearing at the glacier margins 0 4 0 7 a 1 except for the terminal valley section where longitudinal strain rates average close to 1 a 1 this spectacular longitudinal increase in ice velocity in the last few kilometers may be a fundamental feature of tidewater glaciers

recent spatial and temporal variations in debris cover on patagonian glaciers abstract supraglacial debris cover is an important component of glacier mass balance especially in areas characterised by widespread glacier recession mapping of the spatial and temporal changes in debris cover on the surface of the receding outlet glaciers of the temperate north patagonian icefield npi in southern south america between 1987 and 2015 shows that the total amount of debris cover has increased over time from 168 km2 in 1987 to 307 km2 in 2015 the number of debris covered glaciers increased from 24 in 1987 to 31 in 2001 and 32 out of 43 studied glaciers in 2015 the proportion of debris covered area has also increased from 4 1 in 1987 to 7 9 in 2015 with the largest proportional increases occurring east of the ice divide where 15 2 of the glacier ice is now debris covered over this time the total area of the npi decreased from 4133 to 3887 km2 the area occupied by proglacial and ice proximal lakes also increased from 112 to 198 km2 between 1987 and 2015 the terminal environment of many of the outlet glaciers of the npi changed from land terminating to lake calving and these glaciers are now receding into terminal lakes the change in the area of debris covered ice is influenced by the loss of ice at debris covered termini and by an increase in debris cover at higher elevations the glaciers of the npi remain highly dynamic as they recede and are therefore behaving very differently to high elevation glaciers such as those of the himalaya where debris cover leads to glacier stagnation at the termini

feldspars as a source of nutrients for microorganisms phosphorus and nitrogen are essential macronutrients necessary for the survival of virtually all living organisms in groundwater systems these nutrients can be quite scarce and can represent limiting elements for growth of subsurface microorganisms in this study we examined silicate sources of these elements by characterizing the colonization and weathering of feldspars in situ using field microcosms we found that in carbon rich anoxic groundwaters where p and n are scarce feldspars that contain inclusions of p minerals such as apatite are preferentially colonized over similar feldspars without p a microcline from s dakota which contains 0 24 p 2 o 5 but 1 mu mol g nh 4 super was heavily colonized and deeply weathered a similar microcline from ontario which has no detectable p or nh 4 super was barren of attached organisms and completely unweathered after one year anorthoclase 0 28 p 2 o 5 approximately 1 mu mol g nh 4 super was very heavily colonized and weathered whereas plagioclase specimens 0 01 p 1 mu mmol g nh 4 super were uncolonized and unweathered in addition the observed weathering rates are faster than expected based on laboratory rates we propose that this system is particularly sensitive to the availability of p and the native subsurface microorganisms have developed biochemical strategies to aggressively scavenge p or some other essential nutrient such as fe super 3 from resistant feldspars the result of this interaction is that only minerals containing p will be significantly colonized and these feldspars will be preferentially destroyed as the subsurface microbial community scavenges a limiting nutrient

effect of water washing on c15 hydrocarbon fraction of crude oils from northwest palawan philippines recognition and subsequent correlation of biodegraded and or water washed oils with their unaltered counterparts has been a long recognized problem in petroleum geochemistry because water washing and biodegradation can occur concurrently it is difficult to delineate the individual effects of these two oil altering processes especially on the c15 hydrocarbon fraction both processes can cause an oil to become enriched in sulfur and to have a lower api gravity owing to loss of the more volatile components thus the altered oil may appear to be a high sulfur crude of low maturity altered and unaltered oil fractions extracted from cores of a water washed carbonate reservoir offshore northwest palawan were studied to observe the effect of alteration on correla ion parameters water washing resulted in the following changes 1 depletion of 13c in the c15 branched cyclic alkane fraction whereas virtually no change occurred in isotope composition of the aromatic fraction 2 selective loss of dibenzothiophenes followed by loss of aromatic hydrocarbons and 3 virtually no change in steranes or tricyclic and pentacyclic terpanes with the exception of enhancement of 17 agr h norhopane and decrease of 18 agr h trisnorhopane in situations of severe water washing mild biodegradation also occurred as indicated by the loss of n alkanes and possible selective loss of n alkanes having less than 25 carbon atoms relative to branched alkanes cycloalkanes and aromatic components because cycloalkanes and aromatic hydrocarbons are not generally preferentially utilized by bacteria as long as n alkanes are present the changes observed in these two fractions most likely result from water washing because of the potential for extreme compositional changes in the n alkane and aromatic fractions the most useful correlation parameters between the altered and unaltered oils are sterane and terpane distributions stable carbon isotope ratios are also useful however more studies of oils in which water washing is known to have occurred need to be made to explain the general response or various responses of the isotopic composition of oils to water washing

crude oil in a shallow sand and gravel aquifer iii biogeochemical reactions and mass balance modeling in anoxic groundwater abstract crude oil floating on the water table in a sand and gravel aquifer provides a constant source of hydrocarbons to the groundwater at a site near bemidji minnesota the degradation of hydrocarbons affects the concentrations of oxidized and reduced aqueous species in the anoxic part of the contaminant plume that developed downgradient from the oil body the concentrations of fe2 mn2 and ch4 eh measurements and the 13c ratios of the total inorganic c indicate that the plume became more reducing ver a 5 a period however the size of the contaminant plume remained stable during this time field data coupled with laboratory microcosm experiments indicate that benzene and the alkylbenzenes are degraded in an anoxic environment in anaerobic microcosm experiments conducted under field conditions almost complete degradation 98 was observed for benzene in 125 d and for toluene in 45 d concentrations of aqueous fe2 and mn2 increased in these experiments indicating that the primary reactions were hydrocarbon degradation coupled with fe and mn reduction mass transfer calculations on a 40 m flowpath in the anoxic zone downgradient from the oil body indicated that the primary reactions in the anoxic zone are oxidation of organic compounds precipitation of siderite and a ferroan calcite dissolution of iron oxide and outgassing of ch4 and co2 the major difference in the two models presented is the ratio of co2 and ch4 that outgasses both models indicate quantitatively that large amounts of fe are dissolved and reprecipitated as ferrous iron in the anoxic zone of the contaminant plume

an attempt to understand the behavior of dissolved organic carbon in coastal aquifers of pondicherry region south india groundwaters of the coastal region are significant and serve as a fragile ecosystem in the sedimentary terrain the pondicherry region is characterized by different geological formations of distinct geological epochs cretaceous tertiary and quaternary ninety three samples were collected from specific aquifers with respect to spatial distribution alluvium 31 upper cuddalore 13 lower cuddalore 13 other tertiary 7 cretaceous 24 and mixed multiple completion aquifer 5 the collected samples were analyzed for major ions ca2 mg2 na k hco3 cl po42 so42 f and doc stables isotopes of 18o d and 13c were also analyzed along with heavy metals like al ba fe sr cd and zn the 18o ranges between 6 85 and 2 15 and d ranges between 43 94 and 19 41 the distribution of these environmental isotopes in groundwater of this layered aquifer sequence was also attempted a comparison of the isotopic data with the rainfall local meteoric water line with a equation of d 7 398 18o 5 067 indian meteoric water line and global meteoric water line was performed the 13c values for groundwater ranges from 5 3 to 18 1 the result indicates that the groundwater in the study area is mainly meteoric in origin and few samples show evidence of evaporation the dissolved organic carbon doc is a very important component in biogeochemical cycling of elements characterized by high susceptibility to leaching the range of the doc in the study area is 0 16 mg l factor analysis was applied to classify the groundwater samples and to identify geochemical processes controlling groundwater geochemistry the alluvium aquifers show a complex hydrogeochemistry than the older aquifers the major factor influencing the hydrogeochemistry of the region is rock water interaction and anthropogenic processes hence metal mobility of the groundwater shows the correlation of metal bonding and doc the relation between the doc and heavy metal concentration in the aquifers was also identified