twenty years of groundwater evolution in the triassic sandstone aquifer of lorraine impacts on baseline water quality abstract the lorraine triassic sandstone aquifer ltsa which has already been the subject of a chemical and radioisotopic study 1979 is used to investigate the impacts of 20 a of large scale pumping on baseline water quality in parallel new sampling of the aquifer 2001 provides new inorganic geochemical data including trace elements that allow improving the knowledge of baseline conditions and hydrochemical functioning of a major sandstone aquifer the good correlation between 14 c activities temperature and depth along the main flow line indicate regular downgradient trends and possible water stratification unreactive tracers mainly stable isotope ratios 18 o and 2 h as well as c isotopes are used to define a timescale for the aquifer showing two groups of groundwater namely of modern and holocene age and late pleistocene age with a mixing zone baseline quality is then represented by a wide range of concentrations mainly the result of time dependent water rock interaction as already observed elsewhere in triassic sandstone aquifers some trace elements such as li rb cs which are not limited by solubility constraints show linear trends during saturated flow downgradient the chemistry is also specifically characterised by a regular increase in na and cl and locally so 4 as a result of evaporite dissolution related to overlying or basement limits the aquifer is mostly oxidising with a redox boundary marked by u decrease some 40 km from outcrop groundwater abstraction since the 1970s has created a strong lowering 10 150 m of the water table especially from 1970 to 1980 based on nine boreholes previously sampled in 1979 a decreasing evolution in radiocarbon content of the tdic together with significant evolution of 18 o content indicate that old groundwater has moved upgradient the major difference in terms of baseline evolution is observed using cl and na concentration and locally so 4 indicating an increasing influence of water circulation involving overlying or basement formations or of mixing with permian waters from the point of view of aquifer management the perceptible no 3 increase could provide information on the progress of any contamination under the aerobic conditions in addition the few key elements indicators of disequilibrium related to overlying or deep waters should be included in regular monitoring programmes

a 5500 year oxygen isotope record of high arctic environmental change from southern spitsbergen the oxygen isotope composition of chironomid head capsules in a sediment core spanning the past 5500 years from lake svartvatnet in southern spitsbergen was used to reconstruct the oxygen isotope composition of lake water 18olw and local precipitation the 18olw values display shifts from the baseline variability consistent with the timing of recognized historical climatic episodes such as the roman warm period the dark ages cold period and the little ice age the highest values of the record ca 3 above modern 18olw values occur at ca 1900 1800 cal yr bp three negative excursions increasing in intensity toward the present at 3400 3200 1250 1100 and 350 50 cal yr bp are tentatively linked to roughly synchronous episodes of increased glacier activity and general cold spells around the northern north atlantic their manifestation in the svartvatnet 18olw record not only testify to the sensitivity and potential of high arctic lacustrine 18ochir records in tracking terrestrial climate ev

hydrological factors in the interpretation of stable isotopic proxy data present and past a european perspective in the context of this paper stable isotopic proxies are those preserving directly or via known or calculable fractionation factors a record of 18o 16o and or 2h 1h in the water which contributed to their growth suitable proxies include amongst others tree ring cellulose bone phosphate lake sediment minerals and speleothem fluid inclusions a principal aim of studying isotopic proxies is to gain more information about past climates through a knowledge of how rainfall isotope compositions have changed over time however converting back from proxy to rainfall is not necessarily straightforward because however well the isotopic fractionation due to proxy growth or formation is understood a variety of modifying processes may have intervened between this and the actual rainfall events three main reservoirs of environmental water may contribute to the isotopic compositions of terrestrial proxy indicators surface waters soil moisture and groundwater each of these can in principle be isotopically modified compared to rainfall in the locality this review examines these effects and how they may change under different european climate types at the present day it is concluded that while groundwater isotopic compositions typically represent closely the bulk composition of rainfall under a variety of climatic regimes soil and particularly lake waters require detailed study if their isotope systematics are to be adequately understood the review also finds that to a large extent the present is the key to the past in terms of recharge processes during the late pleistocene though glaciation may have had profound isotopic consequences in certain areas while a more general aridity led to the apparent absence of recharge in most areas for much of the late devensian

chemical and isotopic evidence for hydrogeochemical processes occurring in the lincolnshire limestone over 150 groundwater samples from the lincolnshire limestone have been analysed for ph major ions and 13c ratios where possible field eh and iodide concentrations were measured and methane concentrations were determined for 12 samples stable isotope ratios were determined for soil and rock carbonate samples a system of zonation allows the division of hydrogeochemical processes occurring in the aquifer the use of hydrochemical and isotope data in modelling exercises enables the re evaluation and possible enhancement of the understanding of hydrogeochemical processes the carbonate chemistry of outcrop groundwaters is explained by calcite saturation being achieved under open system conditions in the soil zone 13c ratios in the range 15 99 to 10 57 may be generated from a stoichiometric reaction with possible additional partial and or simultaneous exchange with soil co2 or carbonate the isotopic composition of soil carbonate shows the effects of precipitation from soil waters the incongruent dissolution of primary depositional limestone carbonate results in increasing magnesium and strontium concentrations and increasing 13c ratios for the groundwaters with flow down the hydraulic gradient as a result of incongruent dissolution secondary calcite may be precipitated onto fissure surfaces significant nitrate and sulphate reduction in non saline groundwaters is not supported by the results of hydrochemical and isotope modelling exercises however sulphate reduction and methane fermentation may be affecting the isotopic and chemical compositions of saline groundwaters sodium calcium ion exchange leads to limited calcite dissolution deep in the aquifer but the evolution of these groundwaters is confused by the uncertain effects of oxidation of organic carbon and mixing with a saline end member solution

paleoclimatic interpretation of the past 30 ka from isotopic studies of the deep confined aquifer of the north china plain abstract the 18 o and d values in the deep confined aquifer beneath the north china plain which is located at 112 30 e 119 30 e and 34 46 n 40 25 n reflect differences in paleoclimatic conditions between the holocene and the late pleistocene groundwater samples whose 14 c ages are between 12 and 25 ka b p have ranges of 9 4 to 11 7 for 18 o and 76 to 85 for d values these very negative 18 o and d values reflect the cold and arid climate in the last glacial period the temperature estimated in this period is 6 9 c cooler than that of the present the entire ranges of 18 o and d values for samples with 14 c dating from 7 ka b p to present are 7 7 to 10 2 and 63 to 73 respectively the greater 18 o and d enrichments of these samples indicate a period of relatively humid and warm climate in the holocene however the wide ranges of 18 o 9 0 to 11 1 and d 66 to 80 values for samples with 14 c age ranging from 12 to 7 ka b p imply an unstable climatic condition of rapidly increasing temperature which marks the transition from the pleistocene to the holocene

stable isotopes of nonsulphide zn pb ores in britain and ireland fluid characteristics and palaeoclimatic variability stable isotope c o analysis was applied to smithsonites and cerussites from zn pb nonsulphide ores from britain and ireland to determine the nature of the fluids responsible for the precipitation of secondary carbonates and any relationship with palaeoclimatic conditions the carbon isotope compositions of the irish smithsonites show a major contribution of organic carbon whereas those of both zn and pb carbonates in the uk deposits indicate contribution of organic carbon and host rock carbonates 18ovsmow values for cerussite from both areas are about 13 lower than those of smithsonites uk smithsonite 18ovsmow values are more variable than those for cerussites and the irish smithsonites have unusually high values isoscape maps indicate that 18o values for both carbonates are higher in the west and decrease toward the east this trend correlates with a general decrease in the oxygen isotope compositions of rainwater moving eastward and suggests that oxidation of sulphides occurred at temperatures of about 15 20 c under climatic conditions warmer than today supplementary material a comprehensive overview of the investigated sites detailed data for the samples and sem images are available at https doi org 10 6084 m9 figshare c 4579535

isotopic and noble gas study of chalk groundwater in the london basin england abstract the chemical and isotopic composition of groundwater from 52 sites in the london u k area was determined as part of a project aimed at assessing the spatial variation in the age of chalk groundwater and in determining the relationship between fracture and matrix groundwater in this dual porosity system systematic changes in groundwater chemistry take place in the downgradient direction in response to several chemical processes these processes include early concentration by evaporation and congruent dissolution of calcite followed by widespread incongruent dissolution and ion exchange in addition to local oxidation reduction reactions gypsum dissolution and saline intrusion as a result of the above processes chalk groundwater follows an evolutionary path from ca bicarbonate type to na bicarbonate type the age of chalk groundwater was modelled using14c 13c 3h 2h and 180 there is a general increase in the groundwater age in a downgradient direction with the oldest water found in n central areas of the basin groundwater in the unconfined zones and in areas s of the greenwich fault is almost entirely of unevolved modem composition carbon 14 modelling suggests that chalk groundwater in the s basin is generally less than 10000 a old while that in the north is generally between 10000 and 25000 a old the presence of3h in concentrations of up to 7 tu in groundwater which yields ages of several 1000 a however indicates that mechanisms exist for the rapid introduction of recent groundwater to the confined aquifer results of palaeorecharge temperature determinations using 2h 180 and noble gas analytical results suggest that significant devensian recharge did indeed occur in the aquifer a model of the development of the chalk recognizes that it is a classic dual porosity aquifer in which groundwater flow occurs predominantly in the fracture system the upper 50 m of the aquifer was flushed with fresh water during the 2 3 106 a of the quaternary and therefore meteoric water largely replaced the tertiary and cretaceous marine water that previously saturated the system most processes which control the chemistry of the groundwater occur in the matrix where the surface area is exceptionally high although fracture flow dominates the flow regime diffusion from the matrix into the fracture porosity controls the chemistry of chalk groundwater

late pleistocene precipitation δ18o interpolated across the global landmass global water cycles ecosystem assemblages and weathering rates were impacted by the 4 c of global warming that took place over the course of the last glacial termination fossil groundwaters can be useful indicators of late pleistocene precipitation isotope compositions which in turn can help to test hypotheses about the drivers and impacts of glacial interglacial climate changes here a global catalog of 126 fossil groundwater records is used to interpolate late pleistocene precipitation 18o across the global landmass the interpolated data show that extratropical late pleistocene terrestrial precipitation was near uniformly depleted in 18o relative to the late holocene by contrast tropical 18o responses to deglacial warming diverged late pleistocene 18o was higher than modern across india and south china but lower than modern throughout much of northern and southern africa groundwaters that recharged beneath large northern hemisphere ice sheets have different holocene pleistocene 18o relationships than paleowaters that recharged subaerially potentially aiding reconstructions of englacial transport in paleo ice sheets global terrestrial late pleistocene precipitation 18o maps may help to determine 3 d groundwater age distributions constrain pleistocene mammal movements and better understand glacial climate dynamics

limits to recharge of groundwater from tibetan plateau to the gobi desert implications for water management in the mountain front multiple isotopic and hydrogeochemical tracers were utilized to understand the limits to recharge from tibetan plateau to gobi desert the average direct recharge rate according to chloride mass balance is between 0 9 2 5 mm yr 1 based on an annual rainfall of 120 mm yr 1 indicating that this has negligible impact on groundwater the groundwater shows markedly depleted stable isotopic composition compared to modern rainfall the signature of groundwaters around 10 4 parts per thousand to 9 6 parts per thousand delta 18 o in several wells from dajing and south lake playa differ clearly from that of the alluvial fan and modern rainfall and has lower or undetected tritium activity implying that the aquifer in the desert is maintained by palaeowater this groundwater has an estimated 14 c age of similar to 4 kyr with a recharge temperature of 7 3 degrees c at current hydraulic head gradients transit time from the recharge zone wuwei gulang alluvial fan to south lake is approximately 2200 3500 yrs indicating that groundwater flow is relatively slow and that the water resources are non renewable the geochemical information is comparable to the isotopic results of limit recharge sources of groundwater from tibetan plateau to the gobi desert the buildup of dissolved solids through evaporation is a major control on groundwater composition and the dominant anion species change systematically from hco 3 so 4 2 to cl but the dissolved ions from albite calcite dolomite and gypsum also have a significant contribution it is advised to re consider seriously the immigration policy of south lake to meet the groundwater management in the mountain front to gobi desert c 2008 elsevier b v all rights reserved

noble gas cfc and other geochemical evidence for the age and origin of the bath thermal waters uk the city of bath is a world heritage site and its thermal waters the roman baths and new spa development rely on undisturbed flow of the springs 45 c the current investigations provide an improved understanding of the residence times and flow regime as basis for the source protection trace gas indicators including the noble gases helium neon argon krypton and xenon and chlorofluorocarbons cfcs together with a more comprehensive examination of chemical and stable isotope tracers are used to characterise the sources of the thermal water and any modern components it is shown conclusively by the use of 39ar that the bulk of the thermal water has been in circulation within the carboniferous limestone for at least 1000 years other stable isotope and noble gas measurements confirm previous findings and strongly suggest recharge within the holocene time period i e the last 12 kyr measurements of dissolved 85kr and chlorofluorocarbons constrain previous indications from tritium that a small proportion 20 c is incurred there is overwhelming evidence that the water has evolved within the carboniferous limestone formation although the chemistry alone cannot pinpoint the geometry of the recharge area or circulation route for a likely residence time of 1 12 kyr volumetric calculations imply a large storage volume and circulation pathway if typical porosities of the limestone at depth are used indicating that much of the bath bristol basin must be involved in the water storage

the effects of historic abstraction of groundwater from the london basin aquifers on groundwater quality abstract the basal sands and chalk aquifers in the lee valley and enfield haringey areaas of north london have considerable potential for artificial recharge having been dewatered by groundwater abstraction since the late 1800s trials have been undertaken periodically since the mid 1950s however one of the drawbacks is the potential for developing poor quality groundwater as a result of pyrite oxidation in the basal sands analysis of pumped groundwaters from the basal sands has confirmed the presence of relatively high concentrations of dissolved so4 along with k ca total fe and li porewater chemistry profiles have been obtained from fresh cores through the basal sands and underlying chalk at four sites the site with the highest so4 concentration up to 33 000 mg 1 1 had a porewater ph of 3 45 and has remained dewatered owing to overpumping for more than 70 a water pumped from the chalk showed little evidence of these extreme conditions there was no overall correlation between the bulk pyrite or gypsum content of the sediment and the porewater so4 concentration within the sediment the principal mechanism governing the generation of so4 is the oxidation of pyrite which is present in small amounts the extremely high concentrations of so4 in the porewaters indicate that the extent of oxidation is controlled by the entry of air rather than the input of dissolved oxygen or nitrate in the groundwater or recharge water abstraction from the chalk aquifer over many decades has resulted in the dewatering of the overlying basal sands aquifer allowing air entry and has led to the localized oxidation of pyrite and the accumulation of poor quality porewater in the basal sands the rate of oxidation is probably greatest near to wells and boreholes which allow ready access of air the solutes produced are only available for abstraction after the water table has risen dilution with native chalk groundwater will tend to minimize potential water quality problems future oxidation will be minimized by maintaining a high water table

the saline waters of llandrindod and builth central wales saline or brackish mineral waters have been recorded at several locations in mid wales and the welsh borderlands the main groups are centered on llandrindod wells and builth wells where maximum salinities of 5340 and 16 380 mg l 1 respectively are found the total discharge from these springs is very low combined 2 l s 1 yet their flow remains almost constant residence times of several thousand years are derived using 14 c analysis and 18 o and 2 h results suggest that the waters at llandrindod although not at builth contain a component of late pleistocene water evidence from the br cl ratios and trace elements indicates that the origin of the salinity lies within the lower palaeozoic formations and has not been derived from evaporites the mineral waters have undergone complete reduction of sulphate which has led to high concentrations of ba maximum 53 2 mg l 1 at llangammarch wells the most likely origin of these waters is the deep circulation of meteoric water over a residence time of several thousand years which has risen slowly along minor fracture systems to the points of outlet the interconnected fracture storage of these waters implied from the various lines of evidence must be of the order 30 mm 3

sustainability of thermal energy production at the flooded mine workings of the former caphouse colliery yorkshire united kingdom abstract abandoned flooded coal mine workings are an artefact of fossil fuel exploitation that can be repurposed as a renewable energy resource the warm subsurface waters that fill former workings can be developed to provide efficient and low carbon heat generation using ground source heat pumps in order to determine the long term suitability of flooded mine workings as a sustainable thermal resource we have to understand the hydrological components of the system and how they interact in response to exploitation related disturbance we investigate pump induced mixing dynamics at the former caphouse colliery which has been pumped since 1996 for regional water level management but only recently started to be explored as a thermal resource initial findings from the first 6 months of study show virtually no variation in physiochemical major ion or stable isotope values however placed in context with archived values from 2004 to the present we see a general pattern of mine water quality recovery punctuated by a doubling of cl values 150 mg l to 300 mg l which may suggest recent ingress of deeper sourced saline waters this is supported by o and h isotopic values which are indicative of ancient perhaps late pleistocene confined waters sulphur isotope values 19 7 23 8 are abnormally high as compared to typical values for carboniferous coal measures 0 10 there is no simple explanation so further data collection and investigation are required though we note that these values are similar to lower carboniferous seawater values the relative stability of recent parameters suggests that caphouse waters represent a dependable thermal resource however much about the hydrogeology of the caphouse system is still uncertain so further work is required to check the persistence of recent trends

residence time indicators in groundwater the east midlands triassic sandstone aquifer the east midlands triassic sherwood sandstone aquifer which has been the subject of detailed radiometric age studies is used to investigate both inert and reactive constituents of groundwater as indicators of residence time detailed resampling of the aquifer in 1992 has provided a considerable body of new inorganic geochemistry data though without radiocarbon several inert indicators are defined including the isotopic ratios 18o 2h 36cl noble gas ratios as well as the halogen elements cl br f i and their element ratios these form a group of essentially unreactive tracers primarily reflecting changing rainfall inputs and palaeoclimatic conditions except at outcrop where human impacts are also seen clearly the concentrations of cl mainly from atmospheric sources remain below 25 mg l 1 cl over a distance of some 30 km from outcrop reactive indicators the result of time dependent water rock interactions include 13c mg ca sr ca na cl and show diagnostic trends along the flow lines however the concentrations of certain trace elements li rb cs mn and mo which are not limited by solubility constraints show linear trends along the present day flow gradient this water rock interaction is taking place in groundwaters with low total mineralisation and it can be demonstrated that reactions involving these elements and isotopes are occurring entirely within the aquifer since high salinity groundwaters are found below the sherwood sandstone there is good correlation between some of the elements and 14c activities in the 1977 data set and this has been used to derive a concentration age relationship for the 1992 set of data a chemical timescale for the aquifer is then established using a li and b a combination of five trace elements the age of the fresh groundwater is thus shown to be up to 100 ka bp indicating the likelihood of semi continuous recharge during the devensian glacial period preceding the glacial maximum when no recharge occurred 10 20 ka bp this approach may be of value in extending groundwater dating beyond the radiocarbon timescale as well as interpreting sites where no radiocarbon data are available the scatter from the mean age line indicates those groundwaters which are derived from either rapid or slower than average flow zones within the aquifer as well as age stratification this stratification is borne out by a depth profile of groundwater from a new borehole near to outcrop which is shown by a combination of chemical and isotopic tracers to contain holocene overlying late pleistocene water

baseline geochemical conditions in the chalk aquifer berkshire u k a basis for groundwater quality management the chalk aquifer is the most important british aquifer and is also important over much of northern europe aquifer protection requires a sound knowledge of the baseline conditions and how these might vary or have varied with time this detailed geochemical study of a representative area of chalk in berkshire u k includes a consideration of several components 1 the inputs from the atmosphere 2 the interstitial water of the soil and the unsaturated zone 3 the interstitial water in the confined and unconfined sections of the aquifer and 4 the saturated mainly fissure flow along the hydraulic gradient which forms an important water supply of the thames valley region atmospheric inputs form an important source of some elements but the dominant chemical characteristics of the chalk groundwater are acquired during percolation through the soil and the upper unsaturated zone during saturated flow downgradient the chemistry is modified mainly by incongruent reactions of the carbonate matrix and by redox reactions and only to a minor extent by exchange reactions and mixing with residual saline connate water the incongruent reaction of carbonate results in a marked increase in the mg ca ratio and the sr and 13c contents of the groundwater with increased residence time oxygen concentrations are reduced mainly by oxidation of fe2 and the onset of reducing conditions allows dissolved fe2 to increase and rapid denitrification to occur the salinity profile through the confined chalk confirms that residual connate water up to one fifth sea water concentration still remains at depth and this accounts for some salinity increase in the confined groundwater resulting from fissure water pore water diffusional exchange timescales for groundwater movement have been established using tritium radiocarbon and indirectly using inert gas ratios and stable isotope ratios on balance it is concluded that all abstracted water is of holocene age although inert gas temperatures indicate cooler climatic conditions for recharge for some of the confined groundwater the implications for development and aquifer protection are discussed especially the prospect of natural in situ denitrification problems of fe solubility and the recognition of groundwater of different maturities

87sr 86sr in waters from the lincolnshire limestone aquifer england and the potential of natural strontium isotopes as a tracer for a secondary recovery seawater injection process in oilfields the sr isotope composition of formation waters is a sensitive indicator of diagenetic processes in the host sediments mixing processes between different bodies of water and the connectivity of hydrological systems the87sr 86sr ratio of present seawater is constant worldwife while formation waters in hydrocarbon reservoirs have various values depending on the aforementioned effects in most cases different from modern seawater this forms the basis of anatural tracer technique for seawater injection projects involving characterization of the87sr 86sr ratios and sr contents of formation waters in the reservoir before injection commences followed by monitoring of these parameters in the produced water as injection proceeds this method is best suited to reservoirs in which the formation waters have low sr concentrations and87sr 86sr ratios much higher or lower than seawater available data for reservoir formation waters suggest that breakthrough recognition could be expected at 10 seawater in many sandstone reservoirs while the method would be less sensitive in carbonate reservoir or situations where the formation waters had interacted with evaporites as the associated waters tend to have high sr contents in heterogeneous but well mapped reservoirs it may be possible to obtain information about flow paths mechanismsbefore breakthrough combination with other chemical and isotopic tracers creates a very powerful tool the sr method acting as a safeguard should the batch of water containing the conventional tracers be overtaken by subsequently injected seawater the sr method could also be used for injection projects that were begun without the addition of tracers a natural analogue of a water injection process is found in the jurassic lincolnshire limestone aquifer in england where rapidly moving fresh meteoric water mixes progressively with an older saline formation water the87sr 86sr data enable quantitative modelling of this mixing process the infiltrating fresh water becomes progressively modified by dissolution of detrital carbonate and calcite cement in the limestone with depth becoming increasingly dominated by sr derived from the more soluble detrital components the saline formation water contains water molecules of meteoric origin and an87sr 86sr ratio much higher than jurassic seawater or marine carbonate the solute content has been influence by interaction of the water with non carbonate phases

use of 14c modelling to determine vulnerability and pollution of a carbonate aquifer the lincolnshire limestone eastern england abstract the lincolnshire limestone is an important and well studied british aquifer it has been demonstrated by previous workers that the aquifer is affected by agrichemical polution and aquifer protection policy requires in part a knowledge of timescales of groundwater movement this study uses new 14 c data to speculate on such timescales by calculating model ages in non saline groundwaters the main corrections applied to carbon isotope data are for the effects of congruent dissolution and dissolution reprecipitation of soil carbonate and incongruent dissolution of aquifer carbonate although an appropriate small correction is made for ca 2 2na ion exchange no correction is applied for redox processes because they are established as having negligible effects negative model ages calculated for many non saline groundwater support a rapid recharge mechanism to the southern outcrop and suggest that post bomb post 1963 recharge has penetrated deep into the confined aquifer this serves to demonstrate the vulnerability of the southern aquifer to contamination and as a marker of antrhopogenic pollution by so 4 and cl in the confined aquifer however the presence of post bomb c in some no 3 free groundwaters supports the capability of the confined aquifer for in situ denitrification a maximum model age of 5 7 ka is calculated for non saline groundwater the practical problems associated with model ages leads to the recommendation that groundwater 14 c data are best expressed as corrected per cent modern c values in future studies

application of reflectance spectrometry to mineral exploration using portable radiometers the operating parameters of the barringer hand held reflectance radiometer are described laboratory spectra of pure minerals mineral mosaics and lithogeochemical hand specimen and drill core samples alteration halos around two areas of gold mineralization in the abitibi belt ontario are distinguished modified journal abstract

the hydrogeochemistry of methane evidence from english groundwaters the presence of methane ch4 in groundwater is usually only noticed when it rises to high concentrations to date rather little is known about its production or natural baseline conditions evidence from a range of non polluted groundwater environments in england including water supply aquifers aquicludes and thermal waters reveals that ch4 is almost always detectable even in aerobic conditions measurements of potable waters from cretaceous jurassic and triassic carbonate and sandstone aquifers reveal ch4 concentrations of up to 500 g l but a mean value of 10 g l however aquiclude and thermal waters from the carboniferous and triassic typically contain in excess of 1500 g l such high concentrations have so far only been found at redox eh potentials below 0 mv but in general ch4 concentration and eh value are poorly correlated this suggests a lack of thermodynamic equilibrium which is confirmed by comparing pe values calculated from the redox couple c 4 c 4 with those derived from eh genesis of ch4 appears to occur on two timescales a rapid if low rate of production from labile carbon in anaerobic microsites in the soil and a much longer millennium scale of production from more refractory carbon methane is rarely measured in groundwater there is no single ionic determinand which acts universally as a proxy but a combination of high hco3 and low so4 concentrations or the reverse is an indication that high amounts of ch4 may be present

using groundwater geochemistry and environmental isotopes to assess the correction of 14c ages in a silicate dominated aquifer system summary the use of 14c to constrain groundwater residence times requires careful correction of 14c activities a14c and an assessment of the degree of inter aquifer mixing in groundwater of the campaspe valley in the southern murray basin australia 13c values of dissolved inorganic carbon dic range from 18 to 2 using these 13c values to correct 14c ages assuming that dissolution of or exchange with matrix calcite had occurred implies that locally 90 of the dic is derived from carbonates in turn this suggests that low salinity groundwater in the deeper confined calivil renmark formation up to 50 60 km from the basin margins in the campaspe valley has a component of modern recharge which would require that widespread leakage from the overlying shepparton formation had occurred however 87sr 86sr ratios and major ion geochemistry of groundwater imply that negligible inter aquifer mixing has occurred and that calcite dissolution is a very minor process the variable 13c values are most probably due to methanogenesis via reduction of co2 in the groundwater that results in the residual dic being enriched in 13c as methanogenesis by this mechanism has only a minor impact on a14c uncorrected 14c ages are a better estimate of groundwater residence times groundwater in the north of the campaspe valley has a residence time of 9 13 ka which agrees with ages calculated from head gradients and hydraulic conductivities calivil renmark groundwater from the adjacent pyramid hill region in an area where the aquifers contain lower hydraulic conductivity sediments is substantially older up to 20 25 ka the age of groundwater from the shepparton formation increases irregularly with depth with ages of in excess of 25 ka recorded at its base this study illustrates the need to fully understand hydrogeological processes in order to correct 14c ages especially in silicate dominated aquifers where dissolution of carbonates may not be the major process controlling 13c values

isotopic evidence for palaeowaters in the british isles before the 20th century groundwater circulation in the aquifers of the british isles had largely adjusted to the temperate maritime climate and sea levels established over the past 10 ka since the end of the pleistocene however in the last 100 a this natural regime has been disturbed by abstraction of water for public supply and industrial use and palaeowaters from earlier recharge episodes are now becoming a factor to be considered in water balance estimates this paper presents a synthesis of the existing palaeowater distribution in the british isles based on isotopic evidence 18o 2h and and14c as such it has relevance to palaeoclimatic studies in addition to the water resource implications the triassic basins of england and northern ireland contain saline waters beyond the range14c dating 40 ka stable isotopic ratios show enrichment in some basins and depletion in others without an overall pattern that would explain all the observed compositions the results for the wessex basin suggest recharge in pre quaternary times but for the other basins some flushing by pleistocene or holocene meteoric waters is indicated isolated occurrences of apparently long residence waters are found elsewhere throughout the british isles for example from carboniferous and lower palaeozoic strata in such cases environmental isotopes are more useful as constraints on hydrogeological models than as indicators of palaeoconditions major water supply aquifers are restricted almost entirely to england the two sandstone formations triassic sherwood sandstone and cretaceous lower greensand have a greater range of stable isotopic values between phreatic and confined conditions than the two carbonate formations jurassic lincolnshire limestone and cretaceous chalk this indicates that the sandstone aquifers are better archives of information on palaeoconditions than the carbonate aquifers they show that atmospheric circulation patterns over britain have probably remained the same since the late pleistocene however 14c data from all four of the major aquifers emphasise the hiatus in recharge during periglacial conditions which occurred between the late pleistocene and early holocene

oxygen isotope values of precipitation and the thermal climate in europe during the middle to late weichselian ice age abstract the oxygen isotope compositions of 28 mammoth tooth enamel samples from estonia latvia lithuania poland and denmark provide new quantitative records of the middle to late weichselian climate in northern europe the new 18 o data was combined with records of oxygen isotope values from earlier investigations on european mammoth tooth enamel and palaeogroundwaters to study the spatial patterns and temporal variations in the oxygen isotope composition of precipitation and the thermal climate over much of europe the reconstructed geographical distribution of 18 o in precipitation during 52 24 ka reflects the progressive isotopic depletion of air masses moving northeast consistent with a westerly source of moisture for the entire region and a circulation pattern similar to that of the present day regional long term average 18 o w values were 0 6 4 1 lower than at present the largest changes recorded for the currently maritime influenced southern sweden and the baltic region the application of regionally varied t slopes estimated from palaeogroundwater data and modern correlations yield reasonable estimates of glacial surface temperatures in europe and imply 2 9 c lower long term mean annual surface temperatures during the glacial period

paleoclimatic investigations using isotopic signatures of the late pleistocene holocene groundwater of the stratified aquifers in kuwait abstract the study attempts to determine paleo recharge sources for two major aquifer units of kuwait namely kuwait group aquifer kga and dammam formation dfm were collected and analyzed for major ions and isotopes the obtained results of 14c ages indicated that the groundwater samples ranged from 31 9 ky to 3 9 ky in dfm and 23 3 ky to 0 8 ky in kga the variations in 18o signatures with respect to age reflected that there were two major sources of rainwater such as enriched southern indian ocean monsoon and the depleted northwesterly mediterranean vapor source the samples found to show variations during the three marine isotopic stages mis 1 3 heinrich events bolling allerod and dryas time periods in both aquifers a shift in the intertropical convergence zone itcz was witnessed in the groundwater of both aquifers from 7 8 ky to 4 9 ky the variation in the holocene climate is mainly due to the influence of tropospheric easterly jet governed by the swing in itcz as a result of holocene volcanism the mean 18o values of dfm samples 3 81 reflect depletion than kga samples 2 31 and the d excess values were 0 95 and 2 05 respectively thus it could be inferred that the dfm was predominantly recharged during late pleistocene period and it was in a relatively cooler climate than recharge environment of kga the study infers that kga was recharged between 26on and 26 8on latitudes and that of the dfm was noted to be recharged south west of kuwait in two different patches between 25 8on and 26 2on and 26 7on 27 4on latitudes during late pleistocene the kga was concluded to be recharged between 25 5on and 27 5on latitudes south of kuwait during holocene

flow pattern and residence time of groundwater within the south eastern taoudeni sedimentary basin burkina faso mali the knowledge about groundwater flow conditions within the southeastern taoudeni basin aquifer shared by burkina faso and mali is relatively limited with very little information on potentiometric heads recharge processes residence time and water quality a better evaluation of groundwater resources in this area is a strategic point for water resources management in the entire soudano sahelian region which endures since the beginning of the twentieth century a continuous decrease in precipitation amount this paper provides a transboundary synthesis using water 18o 2h and 3h and carbon isotopes 13c and 14c in conjunction with hydrogeological and hydrochemical data the objectives are to improve the conceptual model of groundwater recharge and flow within this sandstone reservoir and to assess the changes in the aquifer due to water abstraction and recent climate changes including an insight into sahelian aquifers palaeorecharge processes the local meteoric water line for the bobo dioulasso station is proposed 2h 8 0 0 5 18o 10 2 2 1 two main tendencies can be derived from groundwater chemistry first a slight evolution from the ca mg hco3 type towards a na k hco3 type that indicates developed interactions between groundwater and clay minerals related to the residence time of groundwater a second tendency towards cl no3 so4 hco3 water types indicates the anthropogenic influence on groundwater related to the poor sanitary conditions observed around wells the carbon 14 activity measured on the tdic varies between 0 3 and 122 pmc so our record contains samples covering a wide period from actual to pleistocene suggesting a continuous recharge of the system through time even if the sahel region has endured many different climate phases which have influenced the infiltration and recharge processes all groundwater samples have stable isotope compositions in the range of the present day regional and global meteoric water line which suggests that the sampled groundwater was not significantly affected by evaporation during recharge evolved waters are depleted relative to unevolved samples by 1 5 2 in 18o and 10 15 in 2h the whole dataset support the hypothesis of a largely unified homogeneous aquifer system with a multilayered structure but it also points out the very low renewability of the resource and a strong anthropogenic contamination of the shallowest horizons

hydrochemistry and stable isotopes as tools for understanding the sustainability of minewater geothermal energy production from a standing column heat pump system markham colliery bolsover derbyshire uk abstract the abandoned workings of the former markham colliery are still in the process of flooding they are being exploited via a standing column heat pump arrangement in markham no 3 shaft to produce thermal energy from 2012 water was pumped from 235 m below ground level in the shaft at c 15 c and 2 3 l s through shell and tube heat exchangers coupled to a 20 kw heat pump to supply space heating to commercial offices the thermally spent cool water was returned to the same shaft at c 250 m bgl at around 12 c the mine water contained iron c 6000 mg l chloride and was highly reducing avoiding contact with oxygen was effective in preventing problems with ochre scaling in january 2015 taking advantage of rising water levels the pump was repositioned at 170 m bgl and the reinjection diffuser at 153 m bgl since then both iron concentration and salinity have fallen significantly suggesting stratification in the shaft stable isotope data from sampling in 2015 generally show little variation sulphate 34s exhibits values typical for british coal measures c 5 whilst 18o 2h indicate influence of fresh meteoric waters chloride and sodium concentrations have gradually increased since may 2015 possibly indicating a renewed influence of deeper more saline waters and reflecting the gradual rise of mine water in the shaft further monitoring of mine water chemistry and isotopic composition is required to better assess the sustainability of the markham heat pump scheme and advise on optimal management of this mine water resource

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

chlorine 36 in groundwater as a palaeoclimatic indicator the east midlands triassic sandstone aquifer uk the36cl contents of groundwaters from the east midlands triassic sandstone have been used to deduce rainfall its chloride content and evapotranspiration during the late pleistocene at this time the regional precipitation and evapotranspiration would have been reduced relative to the modern and holocene climate it is estimated that the infiltration was reduced by about 40 mm a 1 the method for evaluation of these palaeoclimatic parameters is dependent upon the major cl source being a marine aerosol fall out this is the general case but groundwater east of the exploited zone of the aquifer contains chloride which is derived from saline formation water with a marinecl br ratio and in equilibrium with the in situ neutron flux the fall out of cosmogenic36cl at the geomagnetic latitude 56 2 n is evaluated as 30 6 atoms m 2s 1 and is significantly greater than that estimated from the theoretical fall out curve of bentley et al 1 the bomb peak of36cl remains entirely within the unconfined zone of the aquifer the assessment of groundwater residence time from the36cl chronometer is shown to be impossible for this aquifer

constraining groundwater flow residence times inter aquifer mixing and aquifer properties using environmental isotopes in the southeast murray basin australia environmental isotopes particularly d 18 o d 2 h and d 13 c values 87 sr 86 sr ratios and a 14 c constrain geochemical processes recharge distribution and rates and inter aquifer mixing in the riverine province of the southern murray basin due to methanogenesis and the variable d 13 c values of matrix calcite d 13 c

the ribe formation in western denmark holocene and pleistocene groundwaters in a coastal miocene sand aquifer the ribe formation is a regionally extensive miocene sand aquifer that is present in western denmark at depths ranging from 100 to 300 m below ground surface groundwater chemistry and isotope data collected from more than 40 wells show that the ribe formation mainly contains high quality ca bicarbonate type groundwater of holocene age 100 10 000 a bp pleistocene age groundwaters identified on the basis of stable isotopes noble gases and corrected 14c values are present below the island of r0m in discharge areas near the coast and in hydraulically isolated inland areas the groundwater age distribution in the ribe formation was successfully simulated with a numerical groundwater flow model and particle tracking only when the 14c content in groundwater was corrected for both geochemical reactions and diffusion the results indicate that geochemical and physical processes significantly influence the 14c content of groundwater and that the correction factors required for the two processes are of the same magnitude flow modelling results indicate that pleistocene groundwaters were emplaced at depth within the ribe fromation under low base level conditions that prevailed throughout the late pleistocene near the coast these waters are essentially isolated from the present flow system and pleistocene freshwater may be present offshore seismic surveys show that conditions offshore are favourable for the presence of pleistocene freshwater within the ribe formation and other aquifers

geochemical constraints on the origin of enigmatic cemented chalks norfolk uk very hard cemented chalk stacks and crusts found locally in the upper part of the cretaceous chalk of north norfolk uk are related to solution features the solution features mainly pipes and caves formed after deposition of the overlying middle pleistocene wroxham crag probably by routing of sub glacial or glacial melt waters derived from late pleistocene glaciers new geochemical particularly stable isotope data shows that cementation of the chalks although related spatially to the solution features was not caused by glacier derived waters the carbon isotope composition of the chalk cements is typically around 9 5 indicative of biologically active soils moreover the oxygen isotope compositions of the cements around 5 are incompatible with water 18 o values much below 9 to 10 which probably precludes isotopically negative glacier derived water as resulting palaeo temperatures are below zero taken together the isotope data suggest chalk cementation occurred under interglacial conditions similar to the present dissolved calcium carbonate for cementation came from dissolution of reworked chalk in overlying mis 12 glacial tills

controls on stable isotope profiles in the chalk aquifer of north east norfolk uk with special reference to dissolved sulphate groundwater samples were collected at a site in n norfolk uk comprising a borehole penetrating upper chalk and piezometers open within the overlyinf glacial deposits and intervening weathered putty chalk the samples were analyzed for 18o water 34s and 18o so4 and 13c hco3 as well as major ions variations in solute concentration and isotopic composition with depth were found to be caused by limited groundwater circulation at the site and incomplete flushing of old groundwater the isotopic data prove the existence of a mineralized palaeowater at depth which has undergone so4 reduction and is being slowly modified by mixing with recent groundwater circulating at a shallow depth in a more transmissive chalk horizon one measured 18o h2o value of 8 25 vsmow represents the lightest value reported for the norfolk chalk aquifer and is evidence for a component of late pleistocene recharge trapped at depth the wide range of observed isotope ratios at the site e g 34s and 18o so4 between 7 8 to 27 8 cdt and 5 2 to 20 0 ovsmow respectively demonstrates the importance of vertical stratification of solutes and the implications this has for interpreting spatial hydrochemical surveys of groundwater

the influence of pre devensian glacial deposits on the hydrogeochemistry of the chalk aquifer system of north norfolk uk the distribution of hydrochemical facies in the chalk aquifer system of north norfolk uk is interpreted to reveal the hydraulic and hydrogeochemical processes operating in the area the occurrence of two distinct glacial tills covering the chalk aquifer is shown to dominate aquifer conditions chalk groundwater in the interfluve regions covered by chalky boulder clay is characteristically of the order of 10 000 years old and compares with chalk groundwater of about 1000 2000 years old in areas covered by north sea drift the difference in age reflects the different mechanical compositions of the two glacial tills with the chalky boulder clay containing a higher clay content and lower sand content than the north sea drift hydrochemically chalk groundwater from beneath chalky boulder clay is distinguished from groundwater associated with north sea drift by a hco3 concentration of 300 mgl 1 with higher values occurring beneath chalky boulder clay the reason for the difference is that recharge water entering the carbonatedepleted soils developed on north sea drift attains calcite saturation for low values of soil pco2 in the range 10 2 5 10 2 0 whereas recharge entering carbonate rich soils developed on chalky boulder clay achieves calcite saturation for higher values of soil pco2 in the range 10 2 1 10 2 0 additionally pyrite oxidation and so4 reduction associated with the chalky boulder clay interfluve regions evolve further hco3 and to maintain calcite equilibrium increase the dissolved pco2 of the chalk groundwater in the interfluve regions mg sr and sio2 are able to increase because of the groundwater residence time which favours incongruent dissolution of the rock carbonate and breakdown of clay minerals contained in the glacial deposits and the chalk in contrast modern valley zone chalk groundwaters contain high concentrations of no3 up to 120 mgl 1 so4 up to 130 mgl 1 and cl up to 100 mgl 1 contributed by contamination mainly from an agricultural source the hydrochemical interpretation demonstrates that the varying glacial deposits are important in controlling recharge and groundwater flow within the chalk aquifer the chalk aquifer in the interfluvial areas experiences minor recharge whereas the chalk in the valley zone receives direct modern recharge water at the fluvial margin glacial sands and gravels control the storage and release of water transferred laterally through the glacial tills to the high transmissivity chalk in the valley zone

geochemistry radiocarbon ages and paleorecharge conditions along a transect in the central high plains aquifer southwestern kansas usa abstract water samples from short screen monitoring wells installed along a 90 km transect in southwestern kansas were analyzed for major ions trace elements isotopes h b c n o s sr and dissolved gases he ne n2 ar o2 ch4 to evaluate the geochemistry radiocarbon ages and paleorecharge conditions in the unconfined central high plains aquifer the primary reactions controlling water chemistry were dedolomitization cation exchange feldspar weathering and o2 reduction and denitrification radiocarbon ages adjusted for c mass transfers ranged from 10 ka to reduce the average no3 concentration in recent recharge to the holocene background concentration

modeling channel morphodynamic response to variations in large wood implications for stream rehabilitation in degraded watersheds abstract anthropogenic modification of forests has often decoupled streams from riparian ecosystems and altered natural wood recruitment processes extensive research has shown that large wood significantly impacts channel dynamics especially in small and intermediate sized forested streams where wood pieces are similar in length to channel width and many stream rehabilitation efforts now involve the addition of large wood to streams the primary objective of this research is to investigate the relation between large wood and reach scale channel morphology and hydraulics using a physical model in order to better inform stream rehabilitation programs and future modeling efforts four experiments each comprising numerous five hour runs were conducted using a froude scaled stream table with wood loads scaled to 0 m3 m2 0 011 m3 m2 0 016 m3 m2 and 0 022 m3 m2 the addition of large wood significantly decreased the reach averaged velocity in all experiments and was associated with decreased sediment transport and increased sediment storage in the reach increases in bed and water surface slope compensated for the loss of energy available to transport sediment and enabled the system to reach a new steady state within the equivalent of 6 to 9 years adding wood increased pool frequency as well as the variability in cross sectional depth while causing the reach to undergo a transition from a plane bed to a riffle pool morphology retention of fine sediment increased the availability of fish spawning substrate while increased water stage improved connectivity between the channel and the floodplain the changes in habitat complexity were generally related to the wood load added to the reach but were also dependent on the orientation and arrangement of the pieces these results demonstrate that wood may exert a primary control on channel morphodynamics and the availability of aquatic habitat in intermediate sized streams and suggest that the benefits from stream rehabilitation efforts are highly dependent on project scale the relatively long time needed to realize habitat benefits demonstrates that long term monitoring of rehabilitation projects is necessary

hydrochemical trends palaeorecharge and groundwater ages in the fissured chalk aquifer of the london and berkshire basins uk the hydrochemical radiochemical stable isotope 14c and dissolved noble gas composition of groundwaters has been determined along two profiles across the confined fissured chalk aquifer of the london basin of southern england and for selected sites in the adjacent berkshire basin during downgradient flow in the london basin aquifer the groundwater chemistry is modified by water rock interactions congruent and incongruent reaction of the carbonate lithology resulting in enhanced mg ca and sr ca ratios and 13c contents with increased residence times redox and ion exchange reactions and towards the centre of the basin mixing with a residual saline connate water stored in the chalk matrix there is evidence from anomalous water chemistries for a component of vertical leakage from overlying tertiary beds into the confined aquifer as a result of historical dewatering of the aquifer dissolved noble gas contents indicate the climate was up to 4 5 c cooler than at present during recharge of the waters now found in the centres of both basins stable isotope 2h and 18o depletions correspond to this recharge temperature change for evolved waters having 13c 8 pdb a negative linear correlation is demonstrated between derived recharge temperatures and 13c values which is interpreted as mixing between relatively warm light isotopic fracture borne waters and cooler stored waters of the matrix having a 13c signature more or less equilibrated with the chalk from geochemical 14c 4he age estimates the abstracted water is interpreted as being either of wholly holocene post devensian glacial origin or an admixture of holocene and late pleistocene pre glacial cold stage interstadial recharge devensian pleniglacial stage waters of the last glacial maximum are not represented

identification of connate water in interstitial solution of chalk sediment interstitial solution was recovered from core samples of a borehole through 472 m of the upper cretaceous chalk formation in eastern england the solution has been analysed for major and some minor components and also for oxygen and hydrogen isotopic composition samples of the carbonate rock have also been analysed following acid dissolution the general feature of interstitial solution chemistry is a progressive dilution of dissolved species with decreasing depth from a near marine composition found in the deepest samples which are identified as connate water departures from the expected dilution trend are interpreted as evidence for diagenetic reactions during burial or as a result of freshwater circulation following subaerial uplift sr2 li and f have been enriched in interstitial solution and k has been slightly depleted the profile of chalk chemistry with depth shows no conclusive evidence for changes in the mg and sr content of the bulk carbonate due to freshwater diagenesis the 18o and d of the interstitial water reflect the same mixing as that shown by dissolved species however an apparent depletion of 18o and d in the deepest fluids with respect to the expected marine isotopic composition is tentatively explained as a result of the differences in diffusion rates of aqueous oxygen and hydrogen and of ionic solutes

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

isotopic evidence of aquifer recharge during the last ice age in portugal summary the present paper will focus on the research that has been conducted in the palaeowaters in the south of portugal alentejo region three flow directions were identified in sado sedimentary basin aquifer s n sw ne and se nw the last two result from palaeozoic substratum irregularities corresponding to an impermeable tectonic structure horst two aquifers showing different isotopic composition were identified and analysed the eocene and the plio miocene the plio miocene aquifer has an average isotopic composition of 29 6 1 3 in deuterium and 4 65 0 28 in oxygen 18 and the eocene has average values of deuterium of 28 7 2 1 and 4 81 0 11 for oxygen 18 in single cases show that the range of isotopic values overlap for the two aquifers probably as a result of the exploitation in some wells by a mixture of waters from both aquifers the spatial distribution of 3 h and 14 c obtained in the plio miocene waters indicates a flow path from s to n with recent waters near the southern border of the basin and older waters to the n near the sado river the recharge of this aquifer system is diffuse and is dispersed over the entire basin groundwater samples from the two aquifers having similar apparent 14 c ages have distinct isotopic compositions with the eocene aquifer showing an enriched composition relatively to the plio miocene aquifer this suggests that recharge of the eocene waters could have occurred under different climatic conditions

234u 238u activity ratios of dissolved uranium in groundwaters from a jurassic limestone aquifer in england abstract uranium contents and234u 238u activity ratios have been determined for groundwaters from the lincolnshire limestone artesian aquifer in eastern england changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone the western part of the aquifer closest to recharge is dominated by oxidising groundwaters which then enter a reducing zone towards the east where there is an abrupt decrease in eh and the chlorinity of the groundwaters begins to increase uranium contents in the oxidising zone range from 0 7 to 3 4 g kg 1 and234u 238u activity ratio of this dissolved uranium is close to unity the equilibrium value the uranium content decreases abruptly when the grounwaaters enter the reducing zone averaging 0 04 g kg 1 east of the oxidation reduction barrier simultaneously with the decrease in uranium content there is an increase in234u 238u activity ratio and this ratio increases to a maximum within 7 km of the oxidation reduction barrier this increase in activity ratio is attributed to enhanced234u solution due to234th recoil from uraniferous fissure surfaces east of the oxidising zone the activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to234th recoil from the oolith surfaces however the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium 234th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium bearing surfaces in the process of oolith cementation

identification of a holocene aquifer lagoon system using hydrogeochemical data abstract the hydrogeochemical characteristics of the cabo de gata coastal aquifer southeastern spain were studied in an attempt to explain the anomalous salinity of its groundwater this detritic aquifer is characterised by the presence of waters with highly contrasting salinities in some cases the salinity exceeds that of seawater multivariate analysis of water samples indicates two groups of water g1 and g2 group g1 is represented in the upper part of the aquifer where the proportion of seawater varies between 10 and 60 whilst g2 waters taken from the lower part of the aquifer contain 60 70 seawater in addition hydrogeochemical modelling was applied which reveals that the waters have been subject to evaporation between 25 and 35 there was a good agreement between the modelled results and the observed water chemistry this evaporation would have occurred during the holocene in a coastal lagoon environment the resulting brines would have infiltrated into the aquifer and due to their greater density sunk towards the impermeable base the characteristics of this water enabled us to reconstruct the interactions that must have occurred between the coastal aquifer and the lagoon and to identify the environmental conditions that prevailed in the study area during the middle holocene

source of groundwater salinity in coastline aquifers based on environmental isotopes portugal natural vs human interference a review and reinterpretation environmental stable 18o 2h 13c and radioactive 3h and 14c isotopes together with geochemical data were used to identify the origin of salinization in different environments three case studies from sedimentary basins of continental portugal are presented i two at the meso cenozoic portuguese southern border algarve basin and ii one at the lower tagus lower sado basin central portugal with a new data interpretation groundwater salinization occurs in all three cases and may reach values of several grams of total dissolved solids per liter above accepted limits for drinking water the source of this high mineralization could be a seawater intrusion ancient or modern b dissolution from diapiric structures intruding on the aquifer systems c brine dissolution at depth and d evaporation of irrigation water the results obtained have provided an effective label for seawater and freshwater to enable seawater intrusion to be traced as well as the identification of other processes that might be responsible for groundwater salinization such as salt minerals dissolution and ion exchange

characterization of the lowland coastal aquifer of comacchio ferrara italy hydrology hydrochemistry and evolution of the system summary this study delineates the actual hydrogeochemistry and the geological evolution of an unconfined coastal aquifer located in a lowland setting in order to understand the drivers of the groundwater salinization physical aquifer parameterization highlights a vertical hydraulic gradient due to the presence of a heavy drainage system which controls the hydrodynamics of this coastal area forcing groundwater to flow from the bottom toward the top of the aquifer as a consequence relict seawater in stable density stratification preserved within low permeability sediments in the deepest portion of the aquifer has been drawn upward the hydrogeochemical investigations allow identifying the role of seepage and water sediment interactions in the aquifer salinization process and in the modification of groundwater chemistry mixing between freshwater and saltwater occurs however it is neither the only nor the dominant process driving groundwater hydrochemistry in the aquifer several concurring and competing water sediment interactions as nacl solution ion exchange calcite and dolomite dissolution precipitation oxidation of organic matter and sulfate bacterial reduction are triggered by or overlap freshwater saltwater mixing the hyper salinity found in the deepest portion of the aquifer cannot be associated with present seawater intrusion but suggests the presence of salt water of marine origin which was trapped in the inter basin during the holocene transgression the results of this study contribute to a better understanding of groundwater dynamics and salinization processes in this lowland coastal aquifer

book reviewgeothermal energy the potential in the united kingdom r a downing and d a gray editors h m s o norwich 1986 xiii 187 pp stg 20 00 paperback