large striated burrows from fluvial deposits of the neogene vinchina formation la rioja argentina a crab origin suggested by neoichnology and sedimentology abstract this study includes three aspects 1 the ichnotaxonomic treatment of large and dominantly vertical burrows ornamented with sharp bioglyphs from the fluvial neogene vinchina and toro negro formations northwest argentina 2 the description and interpretation of the sedimentary facies where these burrows occur and 3 neoichnologic observations on large ornamented burrows from seasonal wetlands of the rio pilcomayo national park argentina as possible modern analogues of the trace fossils and the sedimentary environment a new ichnogenus and ichnospecies capayanichnus vinchinensis is proposed to include the large striated burrows the new ichnotaxon is distinguished by a combination of a predominantly vertical orientation overall l shape when fully developed absence of lining and burrow bifurcation a distinct surface texture and lack of burrow enlargements the hosting sedimentary facies of the vinchina formation can be grouped into fluvial channel and splay floodplain facies associations the rivers of that unit were of two main types single channel rivers with frequent channel avulsion and overbank flow and multichannelised rivers with poorly defined margins at least some of these rivers were ephemeral or with intermittent discharge the climate was probably seasonal and semiarid as suggested by sedimentologic evidence c vinchinensis was dominantly recorded from the top of fluvial channels interpreted as abandoned channels and proximal intermediate and distal splay facies the large ornamented burrows found in an extant comparable example were constructed by freshwater crabs these burrows can be distinguished by the overall architecture the taxonomy and sex of its occupants and the environmental setting where they were found the neoichnologic signatures used in the interpretation of the fossil example include the common oval burrow cross section and the surface texture in particular the surface texture in the modern crab burrows includes abundant comma shaped marks sets of grooves oblique to burrow axis and long segmented grooves the predominantly oval cross section absence of lining and the strongly ornamented burrow surface suggest that c vinchinensis was produced by freshwater crabs the key features of the surface ornament are long sets of three four ridges whose width is in average one third of the burrow major axis other features that also point to a crab origin are a massive filling common burrow ends in a casing mudstone chevron pattern in sets of surface ridges and possible cheliped marks the new ichnotaxon is restricted in the vinchina and toro negro formations to fluvial facies and is absent in shallow lacustrine facies

sedimentation in the lakes and marshes ahwar of the tigris euphrates delta southern mesopotamia the fluvial plains of lower mesopotamia crossed by the tigris and euphrates rivers are occupied by fresh brackish water lakes and extensive reed marshes dominated by phragmites sp and typha sp together locally called ahwar allochthonous sediment is mostly supplied by the tigris and euphrates seasonal floodwaters and by winds which bring aeolian dust from the north west and sand during storms from the western deserts in summer other contributions to the sediment budget are made by in situ biological activity and by biochemical chemical processes within the sediments the sediments are dominantly silts with silt comprising more than 60 of the sediment the remainder of the sediment consists of varying quantities of clay and sand clay is more abundant in the lower parts of most of the analysed cores 30 80 cm in length indicating a change in sediment supply and or sedimentary environment well developed stratification is found only on the river levees and in some clay rich lake and marsh sediments the remainder of the sediments are generally poorly stratified with irregular stratification and considerable bioturbation mineralogically the sediments consist mainly of calcite quartz dolomite and feldspar particularly albite aragonite is present as a result of in situ production by macrofauna the clay fraction 2 n consists of smectite illite smectite illite palygorskite kaolinite and chlorite the total organic carbon toc content is usually 5 except for some peaty surface layers of the freshwater lakes and marshes where toc may rise to 10 20 the sediments have a relatively high calcium carbonate content 20 80 the highest values only being found in mollusc rich horizons the sediments contain high amounts of ca mg and sr and are generally low in al ti k and v values for fe co pb zn and mn are close to the average for mudstones whereas cu and p are relatively low the high ni and cr contents of the sediments are related to high contents in the source material of the major rivers and aeolian deposits multivariate statistical analysis shows that elemental components of surface and source materials correlate well with other sedimentary properties aragonitic molluscs of various species dominate the macrofauna but a microfauna of foraminifers ostracods and diatoms is also present in the sediments

eocene sedimentation and tectonics in the hampshire basin sedimentary evidence in the eocene cuisian lutetian of the hampshire basin indicates important intra eocene movement on the isle of wight and purbeck monoclines and on the ridgeway fault evidence for syn depositional movement includes jurassic and cretaceous chert and flint pebbles in the eocene the distribution of which suggests derivation from both e and w at whitecliff bay two units of cross bedded sand have northward directed palaeocurrents and may have been deposited as localized fans of debris reworked from earlier tertiary sediments on the upwarped side of the monocline three units of laminated muds are intercalated with marine sediments in the eastern part of the basin and suggest periods of low salinity tideless conditions these episodes are attributed to the periodic isolation of the hampshire basin from the fully marine dieppe basin to the se this may have been the result of intermittent movement on a tectonic barrier to the se of selsey the onset of uplift and subsequent exposure of the chalk along the southern margin of the basin proceeded unevenly from early cuisian to late lutetian times movement on the portsdown anticline probably occurred over a similar period the isle of wight and purbeck monoclines are the superficial expressions of faults in the palaeozoic basement and not the result of lateral alpine pressures a minor series of syn depositional folds trend nw se across the basin and may reflect a component of sinistral strike slip on basement faults

groundwater dating with 3h and sf6 in relation to mixing patterns transport modelling and hydrochemistry a comprehensive study of a sandy aquifer of deltaic origin in southern poland included water chemistry isotopes dissolved trace gases and transport modelling tritium sulphur hexafluoride sf6 and freons f 11 f 12 and f 113 showed the presence of modern waters in the recharge areas and shallow confined parts of the aquifer the presence of older holocene waters farther from the recharge areas was indicated by lack of 3h sf6 contents 0 02 fmol l 1 and relatively low 14c values the discharge from the system is by upward seepage in the valley of a major river pre holocene waters of a cooler climate identified on the basis of 18o 2h 14c ne and ar data were found in some distant wells concentrations of n2 ne and ar determined by gas chromatography were used for calculating the noble gas temperatures air excess needed for correction of sf6 and nitrogen content released by denitrification process the time series of 3h content available for some wells supplied quantitative information on age distributions and the total mean ages of flow through the unsaturated and saturated zones the derived 3h age distributions turned out to be very wide with mean values in the range of about 30 to 160 years for each well with determined 3h age the sf6 data showed either a lower age range or the possibility of a lower age as expected due to shorter travel times of sf6 through the unsaturated zone which most probably also resulted in different types of age distributions of these tracers freons appeared to be of little use for individual age determinations a quantitative estimation of two component mixing from sf63h relations is not possible unless the travel time of 3h through the unsaturated zone is comparable to that of sf6 the ratio of integrals of the response function over the age range with tracer and the whole response function yields the ratio of water with tracer to total flow of water that ratio is a tracer dependent function of time transport modelling of sf6 tracer done with mt3d code yielded initially large discrepancies between calculated and measured tracer concentrations some discrepancies remained even after calibration of the transport model with sf6 simulation of tritium contents with a calibrated transport model yielded reasonable agreement with measured contents in some wells and indicated a need for further investigations particularly in the eastern part of the aquifer the existence of distinct hydrochemical zones is consistent with the tracer data young waters with measurable 3h and sf6 contents are aerobic and of hco3ca or hco3so4ca types slightly elevated na and cl contents as well as the highest concentrations of so4 and no3 within this zone are due to anthropogenic influences anaerobic conditions prevail in the far field under the confining cover where pre bomb era holocene waters dominate in that zone dissolved oxygen no3 and u contents are reduced and fe mn and nh4 contents increase in the third zone early holocene and glacial waters occur they are of hco3cana or hco3na types with tds values higher than 1 g l 1 and na content higher than 200 mg l 1 due to either small admixtures of ascending or diffusing older water or freshening of marine sediments a process that is probably occurring till the present time copyright 2005 john wiley sons ltd

preconditioning an ensemble kalman filter for groundwater flow using environmental tracer observations abstract groundwater resources management requires operational regional scale groundwater models accounting for dominant spatial variability of aquifer properties and spatiotemporal variability of groundwater recharge we test the ensemble kalman filter enkf to estimate transient hydraulic heads and groundwater recharge as well as the hydraulic conductivity and specific yield distributions of a virtual phreatic aquifer to speed up computation time we use a coarsened spatial grid in the filter simulations and reconstruct head measurements at observation points by a local model in the vicinity of the piezometer as part of the observation operator we show that the enkf can adequately estimate both the mean and spatial patterns of hydraulic conductivity when assimilating daily values of hydraulic heads from a highly variable initial sample the filter can also estimate temporally variable recharge to a satisfactory level as long as the ensemble size is large enough constraining the parameters on concentrations of groundwater age tracers here tritium and transient hydraulic head observations cannot reasonably be done by the enkf because the concentrations depend on the recharge history over longer times while the head observations have much shorter temporal support we thus use a different method the kalman ensemble generator keg to precondition the initial ensemble of the enkf on the groundwater age tracer data and time averaged hydraulic head values the preconditioned initial ensemble exhibits a smaller spread as well as improved means and spatial patterns the preconditioning improves the enkf particularly for smaller ensemble sizes allowing operational data assimilation with reduced computational effort in a validation scenario of delineating groundwater protection zones the preconditioned filter performs clearly better than the filter using the original initial ensemble

the structural development of the wessex basin the mesozoic and cenozoic structures of southern england form part of a system of disturbances which extends across the channel into northern france they are reviewed in the light of published data from south dorset basin development started with permo triassic rifting and is believed to have continued through the jurassic and early cretaceous with intermittent growth on deep seated listric normal faults probably associated with roll over anticlines this regime had ceased by the aptian and the basin passed through a period of relative stability in the late cretaceous followed by tectonic inversion and in the miocene by northwards compressive movement along the former normal faults this partially restored the earlier separative displacement at depth and probably accentuated pre existing roll over anticlines it was expressed in the surficial upper cretaceous palaeogene sequence as monoclinal flexuring the early rifting and the change from overall n s crustal stretching to compression may reflect plate tectonic events in the north atlantic region

an investigation about natural radioactivity hydrochemistry and metal pollution in groundwater from calabrian selected areas southern italy the increasing interest in radioactivity has brought about the need for an assessment of human exposure to radiation it is therefore necessary to examine naturally occurring radioactivity in the environment especially its occurrence in groundwater the aim of this work was then to study the levels and behavior of the most significant natural radionuclides also in order to improve the knowledge of the hydrochemical processes involved in the selected groundwater systems natural radioactivity in fifteen calabrian groundwaters for human use was investigated through high resolution gamma spectrometry with a negative biased ortec hpge detector and liquid scintillation measurements particular attention was given on those radionuclides 3h 238u 226ra and 228ra which contribute in a significant way to the overall effective dose received by members of the public due to the intake of drinking water originating from groundwater systems the activity concentration of 238u varied from 1 to 51 mbq l as a result of the geology of the investigated area and of the oxidizing conditions that favored u dissolution 226ra presented a broad range of activity concentrations 0 011 0 14 mbq l lower than uranium ones because radium occurs in groundwater under reducing conditions some heavy metals cd pb be hg ag as tl sb se and ni were also investigated through icp ms measurements and compared with the limits set by the italian legislation metals are released into the environment by both natural and anthropogenic sources they leach into underground waters moving along water pathways and eventually depositing in the aquifer

prestack kirchhoff depth migration of shallow seismic data prestack kirchhoff depth migration is applied successfully to shallow seismic data from a waste disposal site near arnstadt in thuringia germany the motivation behind this study was to locate an underground building buried in a waste disposal the processing sequence of the prestack migration is simplified significantly as compared to standard common cmp data processing it includes only two parts 1 velocity depth model estimation and 2 prestack depth migration in contrast to conventional cmp stacking prestack migration does not require a separation of reflections and refractions in the shot data it still provides an appropriate image our data example shows that a superior image can be achieved that would contain not just subtle improvements but a qualitative step forward in resolution and signal to noise ratio

underground renewal time and mixing of the main mineral waters of tunisia a multi tracer study bottled waters are increasingly popular in tunisia most of them come from groundwaters thus raising the question of the long term availability of the mineral groundwater resources water collected from production springs or wells of eleven mineral waters of tunisia among the main commercial brands were analyzed for tritium 3h helium 3 sf6 cfcs and carbon 14 tracer tracer plots indicate that all of the groundwaters of our data set are a mixture of modern rainwater with older groundwater flow waters that are beyond the time scale of the transient tracers 14c data suggest that the age of these old waters which constitute the main water reservoir is of the order of radiocarbon half life or more most of the studied sites have groundwater renewal times in the range 50 150 years for the sites where tracer concentrations are the most diluted by old waters this value logically increase to several centuries

noble gases dissolved in groundwater in a volcanic aquifer helium isotopes in the kumamoto plain this study investigates a tracing method using dissolved noble gases to survey the groundwater flow in a large groundwater basin the tracing method is based on measuring the concentrations of noble gases and the ratio of helium isotopes in groundwater samples since it is very difficult to detect trace amounts of noble gases and helium with high accuracy in a 15 ml groundwater sample dissolved gases were extracted and purified then a high resolution mass spectrometer was used for measurement and comparison with standard samples we used this method with samples from a confined aquifer formed by the deposition of pyroclastic flow in the kumamoto plain on the west side of mt aso in central kyushu japan the groundwater basin under the plain is divided into four small basins based on the helium concentrations and isotope ratios with two major groundwater flows one flow is buried by the aso pyroclastic flow along the old kase river the other is along the tsuboi river valley these two groundwater flows were identified from the different helium isotope ratios the helium component from the deep mantle is mixed into the groundwater under the kumamoto plain finally data on the concentrations and ratios of3he to4he in groundwater samples were used to determine the location of faults in the volcanic aquifer

shallow structure from a seismic reflection profile across the borah peak idaho fault scarp this is the publisher s version also available electronically from http onlinelibrary wiley com

occurrence of bioglyphs on ocypode crab burrows in a modern sandy beach and its palaeoenvironmental implications abstract the ichnological term bioglyph covers biogenic sculpture on burrow walls bioglyphs in the burrows of ocypodid crabs were studied in a modern unconsolidated sandy substrate looseground on irino coast southwestern japan they are seen exclusively on sides and roof of the burrow and are characteristically seen near the distal end of the burrow moist sandy substrate where sand particles are bound together by surface tension of interstitially suspended water might allow the production of such bioglyphs although bioglyphs are only partially developed in such burrows those interpreted to have formed in semi consolidated substrates firmground are known to be sculptured over the entire burrow surface such difference in the modes of bioglyph occurrence can be used as a criterion to reconstruct the substrate consistency in the rock record

shallow seismic study of a fault scarp near borah peak idaho shallow seismic reflection surveys conducted near borah peak idaho define subsurface structure across a segment of the lost river fault that was reactivated in 1983 four different seismic lines using different sets of recording parameters produced reflections from different depth ranges and at different resolutions the combined interpretation shows the lost river fault zone in the upper 50 m to be 180 m wide and to be composed of high angle faults of various ages the northeast edge of the lost river fault is clearly defined at a depth of approximately 43 2 m the dip of the fault plane in the upper 43 2 m is approximately 55 southwest with an uncertainty of 5 the interpretation presented correlates with surface structure as well as with deeper geophysical data

groundwater transit time distribution and mean from streambed sampling in an agricultural coastal plain watershed north carolina usa we measured groundwater apparent age and seepage rate v in a sandy streambed using point scale sampling and seepage blankets a novel seepage meter we found very similar mtt estimates from streambed point sampling in a 58 m reach 29 years and a 2 5 km reach 31 years the ttd for groundwater discharging to the stream was best fit by a gamma distribution model and was very similar for streambed point sampling in both reaches between adjacent point scale and seepage blanket samples water from the seepage blankets was generally younger largely because blanket samples contained a fraction of young stream water correcting blanket data for the stream water fraction brought estimates for most blanket samples closer to those for adjacent point samples the mtt estimates from corrected blanket data were in good agreement with those from sampling streambed points adjacent to the blankets collectively agreement among age dating tracers general accord between tracer data and piston flow model curves and large groundwater age gradients in the streambed suggested that the piston flow apparent ages were reasonable estimates of the groundwater transit times for most samples overall our results from two field campaigns suggest that groundwater collected in the streambed can provide reasonable estimates of apparent age of groundwater discharge and that mtt can be determined from different age dating tracers and by sampling with different groundwater collection devices coupled streambed point measurements of groundwater age and groundwater seepage rate represent a novel reproducible and effective approach to estimating aquifer ttd and mtt

shallow seismic reflection mapping of the overburden bedrock interface with the engineering seismograph some simple techniques where unconsolidated overburden exceeds 20 m in thickness the reflection method may be efficiently used with a 12 channel engineering seismograph to map topography on the overburden bedrock interface as well as possible structure within the overburden the two techniques we suggest are the simplest forms of reflection profiling which can be applied with a minimum amount of equipment which we suggest is a 12 channel enhancement seismograph a 12 geophone array and a hammer source these techniques require good transmission characteristics of the overburden as well as a sharp velocity discontinuity at the overburden bedrock interface for data processing and display a microcomputer is essential

use of tritium and helium to define groundwater flow conditions in everglades national park the concentrations of tritium 3 h and helium isotopes 3 he and 4 he were used as tracers of groundwater flow in the surficial aquifer system sas beneath everglades national park enp south florida from ages determined by 3 h 3 he dating techniques groundwater within the upper 28 m originated within the last 30 years below 28 m waters originated prior to 30 years before present with evidence of mixing at the interface interannual variation of the 3 h 3 he ages within the upper 28 m was significant throughout the 3 year investigation corresponding with varying hydrologic conditions in the region of taylor slough bridge younger groundwater was consistently detected below older groundwater in the biscayne aquifer suggesting preferential flow to the lower part of the aquifer an increase in he with depth in the sas indicated that radiogenic 4 he produced in the underlying hawthorn group migrates into the sas by diffusion higher 4 he values in brackish groundwaters compared to fresh waters from similar depths suggested a possible enhanced vertical transport of 4 he in the seawater mixing zone groundwater salinity measurements indicated the presence of a wide 6 28 km seawater mixing zone comparison of groundwater levels with surface water levels in this zone indicated the potential for brackish groundwater discharge to the overlying everglades surface water

mapping a bedrock surface under dry alluvium with shallow seismic reflections shallow seismic reflection techniques were used to image the bedrock alluvial interface near a chemical evaporation pond in the texas panhandle allowing optimum placement of water quality monitor wells the seismic data showed bedrock valleys as shallow as 4 m and accurate to within 1 m horizontally and vertically the normal moveout velocity within the near surface alluvium varies from 225 m s to 400 m s all monitor well borings near the evaporation pond penetrated unsaturated alluvial material on most of the data the wavelet reflected from the bedrock alluvium interface has a dominant frequency of around 170 hz low cut filtering at 24 db octave below 220 hz prior to analog to digital conversion enhanced the amplitude of the desired bedrock reflection relative to the amplitude of the unwanted ground roll the final bedrock contour map derived from drilling and seismic reflection data possesses improved resolution and shows a bedrock valley not interpretable from drill data alone

flow of river water into a karstic limestone aquifer 2 dating the young fraction in groundwater mixtures in the upper floridan aquifer near valdosta georgia abstract tritium helium 3 3h 3he and chlorofluorocarbon cfcs cfc 11 cfc 12 cfc 113 data are used to date the young fraction in groundwater mixtures from a karstic limestone aquifer near valdosta georgia where regional paleowater in the upper floridan aquifer receives recharge from two young sources the flow of withlacoochee river water through sinkholes in the river bed and leakage of infiltration water through post eocene semi confining beds above the upper floridan aquifer in dating the young fraction of mixtures using cfcs it is necessary to reconstruct the cfc concentration that was in the young fraction prior to mixing the 3h 3he age is independent of the extent of dilution with older 3h free and 3hetrit free water the groundwater mixtures are designated as type 1 for mixtures of regional paleowater and regional infiltration water and type 2 for mixtures containing more than approximately 4 of river water the fractions of regional paleowater regional infiltration water and withlacoochee river water in the groundwater mixtures were determined from cl and 18o data for water from the upper floridan aquifer at valdosta georgia the chlorofluorocarbons cfc 11 and cfc 113 are removed by microbial degradation and or sorption processes in most anaerobic type 2 groundwater at valdosta but are present in some aerobic type 1 water cfc 12 persists in both so4 reducing and methanogenic water the very low detection limits for cfcs approximately 0 3 pg kg 1 permitted cfc 11 and cfc 12 dating of the fraction of regional infiltration water in type 1 mixtures and cfc 12 dating of the river water fraction in type 2 mixtures overall approximately 50 of the 85 water samples obtained from the upper floridan aquifer have cfc 12 based ages of the young fraction that are consistent with the 3h concentration of the groundwater because of uncertainties associated with very low 3h and 3he content in dilute mixtures 3h 3he dating is limited to the river water fraction in type 2 mixtures containing more than about 10 river water of the 41 water samples measured for 3h 3he dating dilution of 3h and low 3he concentration limited 3h 3he dating to 16 mixtures in which 3h 3he ages are defined with errors ranging from 2 to 7 5 a 1 after correction for dilution with assumed cfc free regional infiltration water and regional paleowater in the upper floridan aquifer adjusted cfc 12 ages agree with 3h 3he ages within 5 a or less in 7 of the 9 co dated type 2 mixtures tritium data and dating based on both cfc 11 and cfc 12 in type 1 mixtures indicate that travel times of infiltration water through the overlying post eocene semi confining beds exceed 35 a the cfc and 3h 3he dating indicate that the river fraction in most groundwater entered the groundwater reservoir in the past 20 to 30 a few domestic and municipal supply wells sampled intercept water younger than 5 a calculated velocities of river water in the upper floridan aquifer downgradient of the sinkhole area range from 0 4 to 8 2 m d radiocarbon data indicate that ages of the regional paleowater are on the 10 000 a time scale an average lag time of approximately 10 to 25 a is determined for discharge of groundwater from the surficial and intermediate aquifers above the upper floridan aquifer to the withlacoochee river

dissolved gases in groundwater and groundwater dating methods how useful for hydrogeological modeling foreword to the special issue one of the major challenges in hydrogeology is the basic spatial lack of continuous data as this is restricted to available boreholes basic information is provided by the measurements of physical parameters e g porosity and permeability at the well scale information related to a larger part of the aquifer are provided for example by continuous measurement of piezometric levels or spring flow temporal information is extremely powerful in order to characterize aquifer functioning globally groundwater dating has thus been developed in order to provide time constraints in aquifer studies

groundwater residence time downgradient of trench no 22 at the chernobyl pilot site constraints on hydrogeological aquifer functioning following the explosion of reactor 4 at the chernobyl power plant in northern ukraine in 1986 contaminated soil and vegetation were buried in shallow trenches dug directly on site in an aeolian sand deposit these trenches are sources of radionuclide rn pollution the objective of the present study is to provide constraints for the chernobyl flow and rn transport models by characterising groundwater residence time a radiochronometer 3h 3he method t1 2 12 3 a and anthropogenic tracers including cfc and sf6 are investigated along with the water mass natural tracers na cl 18o and 2h the groundwater is stratified as evidenced by na and cl concentrations and stable isotopes 18o 2h in the upper aeolian layer the na cl relationship corresponds to evapotranspiration of precipitation while in the underlying alluvial layer an increase in na and cl with depth suggests both water rock interactions and mixing processes the 3h 3he and cfc apparent groundwater ages increase with depth ranging from recent 1 3 a at a 2 m depth below the groundwater table to much higher apparent ages of 50 60 a at 27 m depth below the groundwater table discrepancies in 3h 3he and cfc apparent ages 20 25 a and 3 10 a respectively were observed during the 2008 campaign at an intermediate depth immediately below the aeolian alluvial sand limit which were attributed to the complex water transfer processes extremely high sf6 concentrations well above equilibrium with the atmosphere and up to 1112 pptv are attributed to significant contamination of the soils following the nuclear reactor explosion in 1986 the sf6 concentration vs the apparent groundwater ages agrees with this interpretation as the high sf6 concentrations are all more recent than 1985 the persistence of the sf6 concentration suggests that sf6 was introduced in the soil atmosphere and slowly integrated in the groundwater moving along the hydraulic gradient the apparent age distribution in the lumped parameter models suggests an exponential or piston flow model in the upper geological section followed by more pronounced mixing processes in the lower section

parameter estimation using groundwater age and head data cape cod massachusetts a practical inversion procedure is used to parametrize an unconfined aquifer on cape cod massachusetts using groundwater age and hydraulic head data the inversion resulted in estimates of the recharge flux homogeneous but anisotropic hydraulic conductivity porosity boundary hydraulic heads and the aquifer thickness the range of estimated values agreed well with independent measurements at the site by themselves hydraulic heads are sensitive to the ratio of recharge flux to hydraulic conductivity the age data are sensitive to the ratio of recharge to porosity together age and head data provide a constraint on both boundary values and material properties however a sensitivity analysis shows that porosity hydraulic conductivity and recharge are all correlated and thus a unique inverse solution requires an independent constraint on one of these parameters simulations also show that groundwater ages at a given point on a streamline are sensitive to the recharge flux at the point where the streamline begins at the water table this implies that a vertical profile of age data will be sensitive to the upstream recharge flux suggesting that spatial patterns in recharge can be estimated using vertical profiles from multilevel monitoring wells because measurements of groundwater age can be made in many shallow aquifers this approach may be applicable to other sites

from sedimentary records to sediment budgets multiple approaches to catchment sediment flux this paper reviews the traditional approach to sediment budget studies in geomorphology new approaches and more specifically the potential impact of new methodological advances each component of the budget is discussed including the spatial and volumetric estimations of erosion deposition and storage and the precision and accuracy of flux rate estimation examples are used from recent work in germany the netherlands and the uk and include the pedogenic approach to erosion estimation remote sensing lidar geophysics and sediment based dating techniques for flux rate estimation the precision and accuracy of catchment sediment flux estimates based upon sediment storage is not only dependant upon volumetric accuracy but also on the precision and accuracy of sediment dating in this area there has been a revolution with direct sediment dating techniques tl osl esr freeing budget studies from the constraints and biases of radiocarbon of particular importance is the use of cosmogenic nuclides for dating but which can also be used to derive long term erosion rates but only using a steady state assumption finally a tentative initial application of the sediment budget approach to pleistocene terrace staircase in unglaciated basins is discussed it is argued that only now do we have the techniques available to be able to produce accurate sediment budget estimations at spatial scales greater than that of zero order basins and over time periods greater than that covered by direct observations

aquifer boundaries explored by geoelectrical measurements in the coastal plain of yemen a case of equivalence until 216 vertical electrical schlumberger soundings were made little was known about the subsurface geology at the wadi surdud area in the coastal plain of the yemen arab republic these soundings provide information on the distribution of aquifers aquitards and impermeable rocks and the salinity of the groundwater a first qualitative interpretation of the geoelectrical sounding curves gives a general impression of the hydrogeologic setting and the aquifer boundaries however a more detailed quantitative interpretation shows that no single resistivity model completely satisfies all the hydrogeologic and geologic facts and theories basically two different models are possible in one the thickness of the aquifer is fixed in the other its resistivity is fixed several geologic and hydrogeologic hypotheses may be put forward to support each model varying from relying upon tectonic events and sedimentary depositional environments to influences of agriculture and water abstraction both models are

geochemical study of arsenic release mechanisms in the bengal basin groundwater 1 to investigate arsenic mobility in the bengal basin groundwater we sampled water wells and sediments throughout the region there are strong correlations among high levels of dissolved arsenic and iron ammonia and methane especially in samples from a single site laxmipur no linkage is seen between as and agricultural tracers such as phosphate the association of as and fe occurs because arsenic strongly adsorbs onto feooh particles in river water they flocculate with other fine grained particles at the freshwater saltwater transition zone subsequent bacterially mediated reduction of feooh in the clay releases the adsorbed arsenic weathering of as bearing mica plays a significant role in the as budget the correlated presence of as ch4 and nh4 in water supply wells is the result of diffusion out of organic rich clay into the more permeable zones arsenic is mainly released from recent sediments at 50 m depth deposited in the gbr floodplain as sea level rose throughout the holocene

steady annual and monthly recharge implied by deep unconfined aquifer flow abstract we consider the response of a deep unconfined horizontal aquifer to steady annual and monthly recharge a groundwater divide and a zero head reservoir constrain the aquifer so that sinusoidal monthly and aperiodic annual recharge fluctuations create transient specific discharge near the reservoir and an unsteady water table elevation inland one existing and two new long term data sets from the plymouth carver aquifer in southeastern massachusetts calibrate and confirm hydraulic properties in a set of analytical models geohydrology and simulated groundwater flow 1992 data and a new power law for tritiugenic helium to tritium ratios calibrate the steady recharge that drives the classical parabolic model of steady hydraulics applied hydrogeology 2001 observed water table and gradient fluctuations calibrate the transient recharge models in the latter regard monitoring wells within 1 km of buttermilk bay exhibit appreciable specific discharge and reduced water table fluctuations we apply trans am geophys union 32 1951 238 periodic model to the monthly hydraulics and a recharge convolution integral j hydrol 126 1991 315 to annual flow an infiltration fraction of 0 79 and a consumptive use coefficient of 1 08 10 8 m s c relate recharge to precipitation and daylight weighted temperature across all three time scales errors associated with this recharge relation decrease with increasing time scale

electrical conductivity of brine saturated fractured rock a theoretical analysis shows that electrical conductivity along fractures in a saturated porous rock is a function of many factors fluid and rock conductivities initial fracture aperture and contact area fracture surface geometry asperity height distribution and tip curvature elastic moduli of the rock and confining pressure or normal stress acting across the fracture the conductivity in the fracture plane decreases approximately in proportion to log pressure but the conductivity is influenced by the increased contact area and hence flow path tortuosity along the fracture surface at elevated pressures electrical conductivity in fractures is more affected by flow path tortuosity than is permeability the dependence on pressure was tested using laboratory measurements of conductivity through split cores containing ground saw cut surfaces in a variety of rocks under confining pressures to 200 mpa the conductivity decreased approximately in proportion to log pressure there was little effect of

factors affecting the movement and persistence of nitrate and pesticides in the surficial and upper floridan aquifers in two agricultural areas in the southeastern united states differences in the degree of confinement redox conditions and dissolved organic carbon doc are the main factors that control the persistence of nitrate and pesticides in the upper floridan aquifer ufa and overlying surficial aquifer beneath two agricultural areas in the southeastern us groundwater samples were collected multiple times from 66 wells during 1993 2007 in a study area in southwestern georgia acfb and from 48 wells in 1997 98 and 2007 08 in a study area in south carolina sant as part of the us geological survey national water quality assessment program in the acfb study area where karst features are prevalent elevated nitrate n concentrations in the oxic unconfined ufa median 2 5 mg l were significantly p 0 03 higher than those in the overlying oxic surficial aquifer median 1 5 mg l concentrations of atrazine and deethylatrazine dea the most frequently detected pesticide and degradate were higher in more recent groundwater samples from the acfb study area than in samples collected prior to 2000 conversely in the sant study area nitrate n concentrations in the ufa were mostly 0 06 mg l resulting from anoxic conditions and elevated doc concentrations that favored denitrification although most parts of the partially confined ufa in the sant study area were anoxic or had mixed redox conditions water from 28 of the sampled wells was oxic and had low doc concentrations based on the groundwater age information nitrate concentrations reflect historic fertilizer n usage in both the study areas but with a lag time of about 15 20 years simulated responses to future management scenarios of fertilizer n inputs indicated that elevated nitrate n concentrations would likely persist in oxic parts of the surficial aquifer and ufa for decades even with substantial decreases in fertilizer n inputs over the next 40 years

the study of the interactions between groundwater and sava river water in the ljubljansko polje aquifer system slovenia abstract river basin aquifers are common sites for drinking water wells as bank filtration can be a cost effective pretreatment technology a groundwater vulnerability to pollution depends on a groundwater mean residence time and on a relative contribution of river water versus local precipitation to groundwater environmental isotopes of oxygen and hydrogen 18o and 2h tritium 3h and concentrations of nitrate no3 were used to investigate hydrological pathways mean residence time and interactions between surface water and groundwater in the ljubljansko polje aquifer system in slovenia 18o and 2h values indicate a spatial variability of the influence of individual groundwater sources inside the aquifer local precipitation and the sava river water fractions of river water in groundwater depend on the depth of perforated screens in the pumping wells and their distance from the sava river it was estimated that groundwater at wells klece 11 hrastje 3 and hrastje 8 is mostly composed of recently infiltrated local precipitation while the sava river is the dominant source of groundwater at the well jarski prod 1 groundwater at wells klece 8 klece 12 and jarski prod 3 contains on average between 41 and 48 of the sava river water the 3h and 3h 3he methods indicate short mean residence time of groundwater present at jarski prod 2 7 years and hrastje 7 8 years a small fraction

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

tritium and helium isotopes as hydrologic tracers in a shallow unconfined aquifer measurements of tritium and 3he in groundwater can be used to calculate the age of tritium in groundwater such combined measurements on water samples thus provide a powerful tool towards understanding fluid flow in the near surface saturated zone we report tritium and helium isotope measurements on waters from an unconfined aquifer associated with a low level nuclear waste storage area these values are used to calculate ages of tritium in groundwater from 0 1 to 6 years from the groundwater ages and a three dimensional flow net hydraulic conductivities of 3 3 10 6 to 5 5 10 6 ms 1 for five wells and extreme values from a single well of 18 10 6 and 97 10 6ms 1 are calculated these values agree with hydraulic conductivities obtained from conventional aquifer tests the high conductivity value may indicate an area of preferred fluid flow

the groundwater geochemistry of the bengal basin weathering chemsorption and trace metal flux to the oceans sixty eight groundwater samples from the ganges brahmaputra floodplain in the bengal basin were analyzed to assess the groundwater geochemistry the subsurface hydrology the buffering effects of sediments on trace metal concentrations and their isotopic compositions and the magnitude of the subsurface trace element flux to the bay of bengal and to the global ocean samples obtained from depths of 10 to 350 m were measured for major and trace elements dissolved gas and tritium on the basis of the 3he 3h ages the groundwater at depth 30 150 m appears to be continually replenished indicating that this recharge of groundwater to depth must ultimately be balanced by a significant quantity of submarine discharge into the bay of bengal using the 3he 3h groundwater age depth relationship to calculate a recharge rate of 60 20 cm yr we estimate a subsurface discharge into the bay of bengal of 1 5 0 5 1011 m3 yr or 15 of the surface ganges brahmaputra river gbr flux several trace elements especially sr and ba display elevated concentrations averaging 7 to 9 times the surface gbr water values the submarine groundwater fluxes of sr and ba to the oceans are 8 2 2 108 and 1 5 0 3 108 mol yr or 3 3 and 1 2 respectively of the world total or equal to the surface gbr sr and ba estimated fluxes our groundwater flux for ba agrees with the estimate of moore 1997 3 108 3 109 mol yr on the basis of measured ba and ra excesses in the bay of bengal other trace metals such as u and mo are at low but measurable levels and are not major contributors to the global flux in this river system a comparison of the sr and ba concentrations plus 87sr 86sr ratios in groundwater to the oxalate extractable fractions of a coastal sediment core suggests that weathering of carbonates and minor silicates coupled with cation exchange plus adsorption and desorption reactions controls the trace element concentrations and 87sr 86sr isotopic compositions in both the groundwater and river water our data also imply that other coastal floodplains e g the mekong and the irrawaddy rivers that have high precipitation rates and rapid accumulation of immature sediments are likely to make significant contributions to the global oceanic trace metal budgets and have an impact on the sr isotopic evolution in seawater

tritium helium 3 dating under complex conditions in hydraulically stressed areas of a buried valley aquifer the 3h 3he dating method is applied in a buried valley aquifer near dayton ohio the study area is large not all sampling locations lie along well defined flow paths and existing wells with variable screen lengths and diameters are used reliable use of the method at this site requires addressing several complications 1 the flow system is disturbed because of high pumping rates and induced infiltration 2 tritium contamination is present in several areas of the aquifer and 3 radiogenic helium concentrations are elevated in a significant number of the wells the 3h 3he ages are examined for self consistency by comparing the reconstructed tritium evolution to the annual weighted tritium measured in precipitation deviations result from dispersion tritium contamination and mixing 3h 3he ages are next examined for consistency with chlorofluorocarbon ages the agreement is poor because of degradation of cfcs finally the 3h 3he ages are examined for consistency with the current understanding of local hydrologic processes the ages are generally supported by hydrogeologic data and the results of groundwater flow modeling coupled with particle tracking analyses

some sh wave seismic reflections from depths of less than three metres shallow sh wave reflections are far from routine although their study can provide insights into important properties of near surface materials that cannot be inferred from p wave data alone difficulties in separating sh wave reflections from love waves are generally considered the major obstacle to progress in shallow sh wave seismic reflection this may be the case in surveys undertaken at great depths but it is not necessarily true for reflection data gathered at shallow and ultra shallow depths this paper shows that when sh wave data possess wavelengths greater than the thickness of the superficial layer love waves are not greatly dispersed in this case misinterpretation between parts of reflection hyperbolae and waveguide arrivals is sufficiently limited in a one layer model earth which well approximates typical situations of the near surface underground the most energetic modes the lowermost modes of the dispersed surface waves have a dominant frequency band that falls below the wavelet spectrum of the shallow reflections therefore they can be filtered out in the frequency domain higher modes although their spectral content overlaps that of the reflections exhibit small amplitudes on seismograms and leave strong reflections unaffected we present field examples from three different sites where we were able to obtain ultra shallow reflections 3 m in unconsolidated sediments the high level of resolution vertical resolution up to 15 cm suggests that sh wave reflection imaging has the potential to complement other high resolution techniques such as p wave reflection and ground penetrating radar gpr imaging allowing a better and more complete characterization of the near surface environments

psilonichnus upsilon frey curran and pemberton 1984 burrows and their environmental significance in transgressive albian lower cretaceous sands of glanow stroniczki cracow upland southern poland abstract a considerable upper albian sand lithosome developed on the external margin of the albian epicontinental sea in the polish jura chain miechow synclinorium southern poland is recognized as a shallowing up sequence within the generally transgressive albian sands in particular burrows described as the ichnospecies psilonichnus upsilon frey curran and pemberton 1984 have a particular ecologic and sedimentological significance and constitute the primary focus of this paper in the glanow stroniczki section cracow upland southern poland such burrows seem to be a crucial tool in the interpretation of basin bathymetry indicating a foreshore to backshore beach facies and probably recording a temporary break in sedimentation they were infilled by sand with pebbles or pebble material potentially during hurricane or strong storm action lithification of the burrow infillings and their enveloping concretionary halos should have progressed in a beachrock mode the glanow horst composed of jurassic biohermal limestones was likely an emerged element that neigboured or was surrounded by a beach with active fauna the psilonichnus upsilon burrows in glanow stroniczki closely resemble burrows of the modern ghost crab ocypode in modern settings representatives of ocypode are encountered in extremely shallow marine foreshore intratidal and backshore supratidal to dune environments the ichnological data from glanow stroniczki suggests that fauna behaviorally similar to ocypode may have occupied the beach backshore and to a lesser extent the foreshore zone near the emerged glanow horst

transgression of an estuarine channel and tidal flat complex the lower triassic of barles alpes de haute provence france the lower triassic succession of barles alpes de haute provence france comprises an unconformable quartz arenite sand body of 90m thickness the succession may be informally divided into i lower channellized cross bedded member overlain by ii an upper fining upward member the lower member comprises vertically stacked subtidal channel units separated into five major sand bodies by thin developments of fine grained channel margin and shoal deposits subtidal channel fill deposits are dominated by varying scales of cross bedding these scales vary systematically from the base to the top of the member with large scale planar sets dominating the lowest channel sand body sand body 1 medium scale planar and trough cross bedding characterizing sand bodies 2 4 the largest scale planar sets in the highest sand body sand body 5 this upward change in cross bedding scale is concomitant with a decrease in both the relief of major channel sand body erosion surfaces and the proportion of preserved interchannel shoal deposits the succeeding fining upward member comprises small scale tidal channel units overlain by channel shoal and tidal flat deposits tidal flat sequences are characterized by parallel laminated wave and current rippled sandstones separated by bioturbated fine grained siltstones and mudstones the vertical variation in facies of the lower triassic succession suggests two main periods of deposition the lower member is considered to preserve successively more seaward components of a transgressive estuarine complex the overlying upper member records the seaward progradation of tidal channel shoal and tidal flat environments the unconformity bounded nature of the lower member combined with its systematic variation in facies suggests it may represent an incised valley estuarine fill developed in response to an early triassic relative sea level fall and subsequent rise succeeding tidal channel and tidal flat deposits forming the upper fining upward member reflect a change in sediment supply and or rate of relative sea level rise comparable with a progradational shoreline it is unclear whether this final depositional episode represents a period of highstand progradation or a later lowstand shoreline system developed following a further period of relative sea level fall and rise

groundwater age distributions at a public drinking water supply well field derived from multiple age tracers 85kr 3h 3he and 39ar 1 groundwater age is a key aspect of production well vulnerability public drinking water supply wells typically have long screens and are expected to produce a mixture of groundwater ages the groundwater age distributions of seven production wells of the holten well field netherlands were estimated from tritium helium 3h 3he krypton 85 85kr and argon 39 39ar using a new application of a discrete age distribution model and existing mathematical models by minimizing the uncertainty weighted squared differences of modeled and measured tracer concentrations the observed tracer concentrations fitted well to a 4 bin discrete age distribution model or a dispersion model with a fraction of old groundwater our results show that more than 75 of the water pumped by four shallow production wells has a groundwater age of less than 20 years and these wells are very vulnerable to recent surface contamination more than 50 of the water pumped by three deep production wells is older than 60 years 3h 3he samples from short screened monitoring wells surrounding the well field constrained the age stratification in the aquifer the discrepancy between the age stratification with depth and the groundwater age distribution of the production wells showed that the well field preferentially pumps from the shallow part of the aquifer the discrete groundwater age distribution model appears to be a suitable approach in settings where the shape of the age distribution cannot be assumed to follow a simple mathematical model such as a production well field where wells compete for capture area

ion exchange and trace element surface complexation reactions associated with applied recharge of low tds water in the san joaquin valley california abstract stable isotope data a dissolved gas tracer study groundwater age dating and geochemical modeling were used to identify and characterize the effects of introducing low tds recharge water in a shallow aerobic aquifer affected by a managed aquifer recharge project in california s san joaquin valley the data all consistently point to a substantial degree of mixing of recharge water from surface ponds with ambient groundwater in a number of nearby wells screened at depths above 60 m below ground surface groundwater age data indicate that the wells near the recharge ponds sample recently recharged water as delineated by stable o and c isotope data as well as total dissolved solids in addition to much older groundwater in various mixing proportions where the recharge water signature is present the specific geochemical interactions between the recharge water and the aquifer material appear to include ion exchange reactions comparative enrichment of affected groundwater with na and k at the expense of ca and mg and the desorption of oxyanion forming trace elements as v and mo possibly in response to the elevated ph of the recharge water

seasonal wetland carbonate sequences and dynamic catenas a re appraisal of palustrine limestones abstract palustrine carbonate cyclothems are compared directly to well documented peritidal carbonate cyclothems in the case of the latter the trend of increasing degree of exposure seen vertically through a cyclothem has been interpreted as due to the aggradation of the sediment surface relative to the semi diurnal tidal regime palustrine cyclothems also show similar increases in the degree of exposure and this is interpreted as the effect of sediment aggradation in a seasonal wetland regime the resulting changes in the drainage characteristic revealed in a palustrinc cyclothem reflect a type of seasonally variable catenary relationship referred to here as a dynamic catena this model explains the key features of palustrine cyclothems and suggests the importance of seasonal wetland environments in ancient continental settings

waveform tomography at a groundwater contamination site surface reflection data wehaveappliedacoustic waveformtomographyto452d seismic profiles to image the 3d geometry of a buried paleochannel at a groundwater contamination site at hill air force base in utah the paleochannel which is incised into an alluvium covered clay aquitard acts as a trap for dense nonaqueous phase liquids dnapls that contaminate the shallowest groundwater system in the study area the 2d profiles were extracted from a 3d surface reflection data set first arrival traveltime tomography provided initial velocity models for the waveform tomography we inverted for six frequency components in the band 30 90 hz of the direct and refracted waves to produce 45 2d velocity models the flanks and bottom of a channel with a maximum depth of about 15 m were well modeled in most of the 45 parallel 2d slices whichallowedustoconstructa3dimageofthechannel by combining and interpolating between the 45 image slices the 3d model of the channel will be useful for siting extraction wells within the site remediation program the alluvium that fills the channel showed marked vertical and lateral velocity heterogeneity traveltime tomography and waveform tomography can be complementary approaches used together they can provide high resolution images of complicatedshallowstructures

large near surface velocity gradients on shallow seismic reflection data extreme velocity gradients occasionally present within near surface materials can inhibit optimal common midpoint cmp stacking of near surface reflection arrivals for example abrupt increases in velocity are observed routinely at the bedrock surface and at the boundary between the vadose and the saturated zone when a rapid increase in near surface velocity is found nmo correction artifacts manifested on cmp gathers as sample reversion sample compression or duplication of reflection wavelets can reduce s n ratio on stacked data or can stack coherently elimination of these nonstretch related artifacts using conventional nmo stretch muting requires near vertically incident reflection arrivals and allowable stretch ratios as small as 5 in some shallow environments radical allowable stretch mutes are not a feasible means to subdue these artifacts if high amplitude coherent noise on near offset traces inhibits identification and digital enhancement of shallow reflections on most shallow seismic refl

shallow seismic reflection profile of the meers fault comanche county oklahoma this is the publisher s version also available electronically from http onlinelibrary wiley com

ghost shrimps decapoda axiidea callianassidae as producers of an upper miocene trace fossil association from sublittoral deposits of lake pannon vienna basin slovakia numerous trace fossils are described from the late miocene sediments of the bzenec formation exposed at the gbely section the vienna basin slovakia during deposition of the sediments the area was part of the large long lived brackish to freshwater lake pannon most of the trace fossils are attributed herein to egbellichnus jordidegiberti igen et ispec nov and are interpreted as burrows produced by decapod crustaceans specifically by a ghost shrimp of the family callianassidae this interpretation is based on two independent lines of evidence environmental requirements of large bioturbators and the burrow morphology itself the new ichnotaxon is distinguished from other related ichnotaxa by a combination of typically inclined roughly at an angle of 45 cylindrical burrows absence of lining and tunnels making loops or bends at approximately right angles the burrow systems at gbely document the survival of ghost shrimp long after the closure of all seaways and the origin of lake pannon as today no ghost shrimp are known from long lived brackish lakes egbellichnus from gbely is the only although indirect record of ghost shrimp from a brackish lake environment reported so far

seismic investigation of near surface geological structure in the paducah kentucky area application to earthquake hazard evaluation abstract seismics method were used to evaluate shallow geological conditions at 33 sites in the vicinity of paducah kentucky a combined set of p and s wave seismic refraction and reflection soundings were used in addition to local borehole information to produce structure maps of 1 a shallow 160 m deep shear wave velocity contrasts across the shallow unconformity were generally 2 to 1 while the contrast at the top of the paleozoic bedrock exceeds 5 to 1 these seismic boundaries have been determined to be very important in modelling and interpreting earthquake ground motion amplification in the paducah area the quality and accuracy of the data and the cost effective nature of the methods suggest that other communities in areas at risk to damage from seismic activity with foundation conditions comparable to paducah might benefit from similar characterization in order 1 to identify seismically hazardous near surface geological conditions and 2 to develop geological models that could be used in computer simulations of site response

seismic reflection investigations of a bedrock surface buried under alluvium seismic reflection techniques were used to characterize a bedrock surface buried under alluvium near a construction site on the campus of baylor university in waco texas one of the objectives of the study was to determine if either compressional or shear seismic profiling could be used to reduce the number of engineering boreholes required to determine the bedrock depth and relief prior to building construction the upper few meters of the alluvium is dry but the lower portion is below the water table making the bedrock surface a difficult target for compressional waves the compressional reflection coefficient at the water table is an order of magnitude greater than that at the bedrock surface and the dry alluvium reduces the signal bandwidth such that the two reflections cannot be distinguished also the multimode rayleigh ground roll traveling along the surface at about half the speed of the compressional wave swamps the reflections by using shear waves to profile the alluvium bedrock interface

hydrological control of as concentrations in bangladesh groundwater 1 the elevated arsenic as content of groundwater from wells across bangladesh and several other south asian countries is estimated to slowly poison at least 100 million people the heterogeneous distribution of dissolved arsenic in the subsurface complicates understanding of its release from the sediment matrix into the groundwater as well as the design of mitigation strategies using the tritium helium 3h 3he groundwater dating technique we show that there is a linear correlation between groundwater age at depths 20 m and dissolved as concentration with an average slope of 19 g l 1 yr 1 monitoring wells only we propose that either the kinetics of as mobilization or the removal of as by groundwater flushing is the mechanism underlying this relationship in either case the spatial variability of as concentrations in the top 20 m of the shallow aquifers can to a large extent be attributed to groundwater age controlled by the hydrogeological heterogeneity in the local groundwater flow system

on modelling hillslope water flow paths and travel times abstract this paper considers a darcian representation of hillslope water flow to derive flow paths and particle travel times under transient conditions of varying degrees of saturation a finite element solution of a porous medium flow equation is used to derive specific discharge fields interpolation within these fields in relation to prevailing water content allows water particles to be tracked within the slope material according to mean pore water velocities and allows the times of such hillslope travel to be determined examples of specific discharge fields particle tracks and slope base arrival times are discussed

intercomparison of tritium and noble gases analyses 3h 3he ages and derived parameters excess air and recharge temperature abstract groundwater age dating with the tritium helium 3 h 3 he method has become a powerful tool for hydrogeologists the uncertainty of the apparent 3 h 3 he age depends on the analytical precision of the 3 h measurement and the uncertainty of the tritiogenic 3 he component the goal of this study as part of the groundwater age dating interlaboratory comparison exercise was to quantify the analytical uncertainty of the 3 h and noble gas measurements and to assess whether they meet the requirements for 3 h 3 he dating and noble gas paleotemperature reconstruction samples for the groundwater dating intercomparison exercise were collected on 1 february 2012 from three previously studied wells in the paris basin france fourteen laboratories participated in the intercomparison for tritium analyses and ten laboratories participated in the noble gas intercomparison not all laboratories analyzed samples from every borehole the reproducibility of the tritium measurements was 13 5 the reproducibility of the 3 he 4 he ratio and 4 he ne ar kr and xe concentrations was 1 4 1 8 1 5 2 2 2 9 and 2 4 respectively the uncertainty of the tritium and noble gas measurements results in a typical 3 h 3 he age precision of better than 2 5 years in this case however the measurement uncertainties for the noble gas concentrations are insufficient to distinguish the appropriate excess air model if the measured helium concentration is not included while the analytical uncertainty introduces an unavoidable source of uncertainty in the 3 h 3 he apparent age estimate other sources of uncertainty are often much greater and less well defined than the analytical uncertainty