nitrogen isotope hydrochemistry and denitrification within the chalk aquifer system of north norfolk uk abstract although there has been much debate over the potential health risks of nitrate in drinking water there is a real issue of the costs associated with removing nitrate from drinking water supplies in the chalk aquifer system of north east norfolk modern contaminants of a mainly agricultural origin produce high levels of nitrate 15 mg l no3 n in the unconfined valley areas whereas in confined regions the levels of nitrate are low and commonly below detection limits

evidence of cfc degradation in groundwater under pyrite oxidizing conditions summary a detailed local scale monitoring network was used to assess cfc distribution in an unconfined sand aquifer in southwestern ontario where the zone of 1 5 year old groundwater was known with certainty because of prior use of a bromide tracer groundwater 5 years old was confined to an aerobic zone at 5 m depth and had cfc concentrations consistent with modern atmospheric mixing ratios at recharge temperatures of 7 11 c as was observed in the 3 m thick vadose zone at the site at depths below 6 m the groundwater became progressively more reducing however with a denitrifying horizon at 6 7 m depth and a mn and fe reducing zone below 7 m depth in the anaerobic zone 3 h 3 he ratios indicated that groundwater age continued to increase uniformly with depth to a maximum value of 27 years at 13 m depth cfc concentrations however decreased abruptly within the denitrifying zone leading to substantial age overestimation compared to the 3 h 3 he ages noble gas data indicated that the apparent cfc mass loss was not likely the result of gas stripping from possible bubble formation thus cfc degradation was indicated in the anoxic zone the field data are consistent with first order degradation rates of 0 3 yr 1 for cfc 12 0 7 yr 1 for cfc 11 and 1 6 yr 1 for cfc 113 cfc attenuation at this site coincides with a zone where reduced s pyrite is actively oxidized by no 3 and dissolved oxygen do similar behavior has been observed at other sites tesoriero a j liebscher h cox s e 2000 mechanism and rate of denitrification in an agricultural watershed electron and mass balance along groundwater flow path water resour res 36 6 1545 1559 hinsby k hojberg a l engesgaard p jensen k h larsen f plummer l n busenberg e accepted for publication transport and degradation of chlorofluorocarbons cfcs in a pyritic aquifer rabis creek denmark water resour res further demonstrating that the use of cfcs for age dating anaerobic groundwater should be approached with caution particularly if the sediment contains pyrite

chemical heterogeneity in diffusion dominated aquitards 1 high resolution measurements of the three dimensional 3 d variability in pore water electrical conductivity ec were obtained at a clay rich aquitard research site the king site 120 m 70 m area in southern saskatchewan canada using direct push probing technology n 35 boreholes these measurements revealed complex lateral heterogeneity in the subsurface salt distributions which raised questions on the validity of the commonly used approach of transposing chemical data from distributed piezometers onto 1 d depth profiles for interpretation and solute transport modeling two dimensional numerical modeling simulations demonstrated that distributed nonuniform salt inputs have existed at the top of the unoxidized till aquitard for the past 3 5 kyr the source of the nonuniform salt inputs is unclear but may be due to either variations in microtopography 0 5 m or variable penetration depth of surface fractures a suite of generic solutions was developed to estimate the critical depth required to obtain chemical homogeneity in aquitards with nonuniform solute inputs and diffusion as the dominant transport mechanism these solutions are presented for a range of sinusoidal input functions with varying amplitudes magnitudes and wavelengths the solutions indicate ec distributions at the king site should be laterally uniform below a depth of around 20 m bg which is consistent with observed ec values at the site this study shows that aquitards with nonuniform salt inputs at their upper boundary are chemically heterogeneous above some critical depth and thus require careful attention when modeling solute transport processes within them

pore water extraction from the unsaturated and saturated zones a simple inexpensive method for extracting pore water from unsaturated soils which uses a combination of immiscible fluid displacement suction and mechanical compression is described this method uses a squeezing chamber to contain the unsaturated sediments in aluminum core tubing to prevent exposure of the sediments and pore water to atmospheric o2 and subsequent oxidation reactions geochemical artifacts resulting from high compression squeezing are prevented by maintaining the pressure applied during the squeezing at a minimum comparison of squeezed profiles with field measured profiles of ph eh oxidation reduction potential alkalinity and metal speciation indicates good agreement between these parameters using this method depending on the water content of the sediments a range of water volumes several millilitres to excess of 100 ml can be extracted from a single core section 7 6 cm in diameter by 20 cm long pore water was produced immediately from sediments at near saturated condition

aquifer scale controls on the distribution of nitrate and ammonium in ground water near la pine oregon usa summary geochemical and isotopic tools were applied at aquifer transect and subtransect scales to provide a framework for understanding sources transport and fate of dissolved inorganic n in a sandy aquifer near la pine oregon no3 is a common contaminant in shallow ground water in this area whereas high concentrations of nh4 n up to 39 mg l are present in deep ground water n concentrations n cl ratios tracer based apparent ground water ages n isotope data and hydraulic gradients indicate that septic tank effluent is the primary source of no3 n isotope data n cl and n c relations 3h data and hydraulic considerations point to a natural sedimentary organic matter source for the high concentrations of nh4 and are inconsistent with an origin as septic tank n low recharge rates and flow velocities have largely restricted anthropogenic no3 to isolated plumes within several meters of the water table a variety of geochemical and isotopic data indicate that denitrification also affects no3 gradients in the aquifer ground water in the la pine aquifer evolves from oxic to increasingly reduced conditions suboxic conditions are achieved after about 15 30 y of transport below the water table no3 is denitrified near the oxic suboxic boundary denitrification in the la pine aquifer is characterized well at the aquifer scale with a redox boundary approach that inherently captures spatial variability in the distribution of electron donors

correlation of nitrate profiles with groundwater and sediment characteristics in a shallow sandy aquifer abstract sediment profiles of a shallow sandy aquifer in an agricultural area of denmark can be characterized by a new term called total reduction capacity trc quantifying the total amount of reduced compounds in the aquifer material ferrous iron reduced sulfur compounds solid organic carbon a distinct increase of trc was observed at and below the oxidation reduction front in this study the front was a zone 30 cm wide oxygen nitrate and sulfate were present above the oxidation reduction front but disappeared at the front detailed porewater profiles indicate that denitrification also takes place above the front supposedly in anaerobic microenvironments not evident in the water samples from the small wells the trc profiles showed that some reduction capacity is still present above the oxidation reduction front and is apparently able to support denitrification

denitrification in the recharge area and discharge area of a transient agricultural nitrate plume in a glacial outwash sand aquifer minnesota 1 recharge rates of nitrate no3 to groundwater beneath agricultural land commonly are greater than discharge rates of no3 in nearby streams but local controls of no3 distribution in the subsurface generally are poorly known groundwater dating cfc 3h was combined with chemical ions and gases and stable isotope n s and c analyses to resolve the effects of land use changes flow patterns and water aquifer reactions on the distributions of o2 no3 so4 and other constituents in a two dimensional vertical section leading from upland cultivated fields to a riparian wetland and stream in a glacial outwash sand aquifer near princeton minnesota within this section a plume of oxic no3 rich groundwater was present at shallow depths beneath the fields and part of the wetland but terminated before reaching the stream or the wetland surface groundwater dating and hydraulic measurements indicate travel times in the local flow system of 0 to 40 years with stratified recharge beneath the fields downward diversion of the shallow no3 bearing plume by semiconfining organic rich valley filling sediments under the wetland and upward discharge across the valley and stream bottom the concentrations and 15n values of no3 and n2 indicate that the no3 plume section was bounded in three directions by a curvilinear zone of active denitrification that limited its progress however when recalculated to remove the effects of denitrification the data also indicate changes in both the concentrations and 15n values of no3 that was recharged in the past isotope data and mass balance calculations indicate that fes2 and other ferrous fe phases were the major electron donors for denitrification in at least two settings 1 within the glacial fluvial aquifer sediments beneath the recharge and discharge areas and 2 along the bottom of the valley filling sediments in the discharge area combined results indicate that the shape and progress of the oxic no3 plume termination were controlled by a combination of 1 historical and spatial variations in land use practices 2 contrast in groundwater flow patterns between the agricultural recharge area and riparian wetland discharge area and 3 distribution and abundance of electron donors in both the sand aquifer and valley filling sediments the data are consistent with slow migration of redox zones through the aquifer in response to recharging oxic groundwater during holocene time then an order of magnitude increase in the flux of electron acceptors as a result of agricultural no3 contamination in the late twentieth century to which the redox zone configuration still may be adjusting the importance of denitrification for no3 movement through formerly glaciated terrains should depend on the source areas and depositional environments of the glacial sediments as well as geomorphology and recent stream valley sediment history

nitrate reduction in an unconfined sandy aquifer water chemistry reduction processes and geochemical modeling nitrate distribution and reduction processes were investigated in an unconfined sandy aquifer of quaternary age ground water chemistry was studied in a series of eight multilevel samplers along a flow line deriving water from both arable and forested land results show that plumes of nitrate contaminated groundwater emanate from the agricultural areas and spread through the aquifer the aquifer can be subdivided into an upper 10 to 15 m thick oxic zone that contains o2 and no3 and a lower anoxic zone characterized by fe2 rich waters the redox boundary is very sharp which suggests that reduction processes of o2 and no3 occur at rates that are fast compared to the rate of downward water transport nitrate contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area the persistence of the high content of total dissolved ions in the no3 free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place nitrate is apparently reduced to n2 because both nitrite and ammonia are absent or found at very low concentrations possible electron donors in the reduced zone of the aquifer are organic matter present as reworked brown coal fragments from the underlying miocene and small amounts of pyrite at an average concentration of 3 6 mmol kg electron balances across the redoxcline based on concentrations of o2 no3 so42 and total inorganic carbon tic indicate that pyrite is by far the dominant electron donor even though organic matter is much more abundant groundwater transport and chemical reactions were modeled using the code phreeqm which combines a chemical equilibrium model with a one dimensional mixing cell transport model only the vertical component of the water transport was modeled since in contrast to rates along flow lines the vertical rates are close to constant as required by the one dimensional model average vertical transport rates of water in the saturated zone were obtained by tritium dating the modeling process is a two step procedure first the sediment column is initialized with natural water containing only oxygen as electron acceptor and subsequently agricultural waters containing both oxygen and nitrate are fed into the column the nitrate concentration of agricultural waters entering the saturated zone varies with time and an input function was therefore constructed by linear mixing of natural waters and agricultural waters this input function was fed into the column initialized with natural water and the model run forward in time to the year 1988 where field data are available comparison with field data shows that the variation in groundwater chemistry is well described by the model when reduction of oxygen and reduction of nitrate by pyrite oxidation are the only redox reactions occurring finally predictions are made for the distribution of water chemistry in the year 2003 downward progression of the redoxcline is accelerated by a factor of five due to nitrate pollution of the aquifer but absolute rates remain small of the order of a few centimeters per year the controlling factor for nitrate migration through the aquifer once it has reached the anoxic zone is the concentration and distribution of pyrite in the sediments

attenuation of nitrate in aquitard sediments of southern ontario to examine nitrate persistence detailed geochemical profiling using core squeezed water and piezometer samples was carried out at five sites in southern ontario where groundwater is moving downward in silt rich aquitard sediments at rates of 16 to more than 20 cm year 1 elevated levels of no3 n 5 50 mg 1 1 that occur in the shallow groundwater as a result of agricultural activity were found to be consistently attenuated generally to very low levels 0 05 mg 1 1 n at the redoxcline the horizon marking the boundary between the surficial weathered brown sediments and the underlying unweathered grey sediments tritium dating suggests that groundwater at the redoxcline depths 3 5 m was recharged between 1970 and 1980 thus the n03 depletion appears to result from biodegradation reactions since no major landuse changes have occurred during this period the close association of the nitrate depletion zones with the redoxcline where in particular sediment sulphur contents increase abruptly and where also porewater so42 levels increase suggests that the dominant attenuation reaction is autotrophic denitrification using reduced sulphur compounds present in the unweathered sediment as the electron donor mass balance calculations suggest that the increase in the downward rate of migration of the redoxcline owing to added sulphur consumption from no3 contamination is only about 1 mm year 1 at these sites review of the literature indicates that most silt and clay rich sediments have s contents in the same range or higher than those investigated here thus in most cases where aquifers are overlain by several metres or more of unweathered confining sediments it is likely that a high degree of protection is afforded from surficial no3 contamination

helium diffusivity and fluxes from a sedimentary basin permo carboniferous trough northern switzerland abstract abundances of radiogenic he and ar isotopes observed in ground waters of the permian carboniferous terrigenous sediments pct in northern switzerland exceed those in the overlaying muschelkalk and underlying crystalline basement aquifers eliminating external sources of these species in this case a comparison of the observed abundances with those in situ generated sheds light on mobility of noble gases generated in the pct detailed studies of the parent element and he isotope concentrations in the pct rocks mineral separates pore and ground waters along with the data on logging and porosity allow he isotope production and redistribution in the pct rock water system to be understood and quantified the pct shales generate most of 3he and 4he and both isotopes are almost completely released from the shales into pore space and migrate either into the aquifers with movable waters and further out of the pct or into gas fluid inclusions of the rock forming minerals quartz and plagioclase here we present a he concentration profile based on i helium measured concentrations in ground water samples from 5 aquifers available within the cross section studied ii helium concentrations in 15 pct pore water samples derived from the he partial pressure in gas fluid inclusions recovered by special extraction saturation experiments in order to estimates the rates of he migration through the pct we compare the produced and observed abundances within the frame of 1d diffusion model only two parameters the diffusion coefficient for the whole sequence dall 4 1 10 3 m2 year 1 and the rate of he removal from the crystalline aquifers cr 1 4 10 6 year 1 are required to obtained a good agreement between the observed and calculated he concentrations in pct waters the minimal square deviations are 2 to 3 10 8 mol cm 3 h2o comparable with the accuracy of measurements the following parameters were derived from the modeling the reduction factor dall d0 0 013 the he diffusion fluxes into the overlaying muschelkalk and underlying crystalline aquifers fmu 1 4 10 7 mol m 2 year 1 and fcr 0 24 10 7 mol m 2 year 1 respectively from these values we calculated the mean helium residence times in pct 120 ma and in muschelkalk aquifer 6 ka the relationships between he diffusivities of the pct and the underlying crystalline basement are discussed we further compare our results with other estimates of he mobility in low permeable sediments

fe and mn levels regulated by agricultural activities in alluvial groundwaters underneath a flooded paddy field abstract iron and mn concentrations in fresh groundwaters of alluvial aquifers are generally high in reducing conditions reflecting low so4 concentrations the mass balance and isotopic approaches of this study demonstrate that reduction of so4 supplied from agricultural activities such as fertilization and irrigation is important in lowering fe and mn levels in alluvial groundwaters underneath a paddy field this study was performed to investigate the processes regulating fe and mn levels in groundwaters of a point bar area which has been intensively used for flood cultivation four multilevel groundwater samplers were installed to examine the relationship between geology and the vertical changes in water chemistry the results show that fe and mn levels are regulated by the presence of no3 at shallow depths and by so4 reduction at the greater depths isotopic and mass balance analyses revealed that no3 and so4 in groundwater are mostly supplied from the paddy field suggesting that the fe and mn rich zone of the study area is confined by the agricultural activities for this reason the geologic conditions controlling the infiltration of agrochemicals are also important for the occurrence of fe mn rich groundwaters in the paddy field area

sulphur cycling in the drinking water catchment area of torgau mockritz germany insights from hydrochemical and stable isotope investigations the hydrochemical composition of groundwater and the isotopic composition of sulphur compounds in sediments 3 4 s of sulphide inorganic sulphate and groundwater 3 4 s 1 8 o of dissolved sulphate have been investigated to reveal the reasons for elevated concentrations of dissolved groundwater sulphate in the drinking water catchment area of torgau mockritz germany the three most important anthropogenic sources of sulphate identified in this study are historic atmospheric sulphate deposition predominantly of anthropogenic origin inorganic fertilization and dissolution of gypsum from waste dumps owing to their overlapping isotopic range no clear differentiation between the individual anthropogenic sources is possible sulphate from the oxidation of sedimentary sulphides however was recognized by its negative sulphur isotope signature 3 4 s 5 the mobilization of sulphate from different soil sulphur species is closely connected with variable isotopic fractionations resulting in a wide isotopic variation range for the sulphate entering the saturated zone generally sulphur and oxygen isotope ratios of the dissolved groundwater sulphate range from 19 to 37 vienna canon diablo troilite and from 2 to 19 vienna standard mean ocean water respectively sulphate from the majority of groundwater samples can be assigned to anthropogenic sources sulphate from sulphide oxidation is especially present in samples from the upper sampling level and the groundwater surface sulphate concentrations above 700 mg l 1 are mostly caused by the oxidation of sulphide sulphate that occurs in low and moderate concentrations dominantly originates from anthropogenic sources 3 4 s distribution patterns were used to locate the sources for the elevated sulphate concentrations in the raw water it was shown that the sulphate is not mobilized in the immediate vicinity of the production wells rather it originates in an area 1 5 km west of the intake the main mobilization mechanism there is the oxidation of reduced sedimentary sulphur species beyond its local significance this study presents a general example how changes in the sulphur cycle indicate major anthropogenically induced alterations of the hydrochemical situation in catchment areas

atmospheric sulfur deposition 1950 1985 inferred from sulfate in groundwater groundwater sulfate that occurs at concentrations of 6 27 mg l in a shallow water table sand aquifer at a forested site 100 km east of sudbury ontario is used to deduce the trend in atmospheric sulfur deposition between 1950 and 1985 the simple geologic nature of the aquifer made feasible this trend reconstruction the age of groundwater that entered the aquifer during the past 60 years was determined with unusual accuracy 3 years from tritium analyses and flow modeling sulfur isotopes and mass balances indicate that the sulfate in the groundwater zone is of atmospheric origin and is not derived from solid phase material in the sediments evapotranspiration enriches atmospheric sulfate by a factor of about three as it enters the aquifer adsorption of sulfate is not significant groundwater sulfate indicates a decrease of 37 in sulfur deposition at the site between a maximum in the 1960s and lower values observed in the 1980s we attributed most of the decrease bout 80 to lower so2 emissions from the sudbury smelters these emissions are now about one third of the 1960s levels further major decreases in sulfur deposition at this site can be achieved only if emissions from sources distant from sudbury are lowered as well because sudbury now contributes less than 25 of total sulfur deposition

origin and distribution of sulfate in a fractured till in southern alberta canada glacial till in a 22 km sup 2 area of the interior plains region of southern alberta canada consists of an upper brown gypsiferous weathered zone up to 20 m thick and a lower discontinuous grey nonweathered zone up to 25 m thick although the total sulfur content of the two till zones is the same 0 34 the mean total sulfate content of the weathered till 4 0 mg g sup 1 exceeds that the nonweathered till 0 8 mg g sup 1 similarities suggest that all so sub 4 sup 2 in the nonweathered till and 20 of the sulfate in the weathered till was derived from sulfate rich bedrock fragments incorporated in the till during deposition laboratory experiments and delta sup 18 o and delta sup 34 s analyses of total so sub 4 sup 2 and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic s at some time after the till was deposited mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier altithermal period 11 000more to 3000 years b p the following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed the oxidation of reduced s produced so sub 4 sup 2 and h sup the h sup reacted with carbonate minerals under elevated p sub co2 with ca sup 2 loss by exchange for na sup and gypsum precipitation volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity less

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

denitrification in marine shales in northeastern colorado parts of the south platte river alluvial aquifer in northeastern colorado are underlain by the pierre shale a marine deposit of late cretaceous age that is 1000 m thick ground water in the aquifer is contaminated with no3 and the shale contains abundant potential electron donors for denitrification in the forms of organic carbon and sulfide minerals nested piezometers were sampled pore water was squeezed from cores of shale and an injection test was conducted to determine if denitrification in the shale was a sink for alluvial no3 and to measure denitrification rates in the shale measured values of no3 n2 nh4 15n no3 15n n2 and 15n nh4 in the alluvial and shale pore water indicated that denitrification in the shale was a sink for alluvial no3 chemical gradients reaction rate constants and hydraulic head data indicated that denitrification in the shale was limited by the slow rate of no3 transport possibly by diffusion into the shale the apparent in situ first order rate constant for denitrification in the shale based on diffusion calculations was of the order of 0 04 0 4 yr 1 whereas the potential rate constant in the shale based on injection tests was of the order of 60 yr 1 chemical data and mass balance calculations indicate that organic carbon was the primary electron donor for denitrification in the shale during the injection test and ferrous iron was a minor electron donor in the process flux calculations for the conditions encountered at the site indicate that denitrification in the shale could remove only a small fraction of the annual agricultural no3 input to the alluvial aquifer however the relatively large potential first order rate constant for denitrification in the shale indicated that the percentage of no3 uptake by the shale could be considerably larger in areas where no3 advection

characterisation of the input signal to aquifers in the french basque country emphasis on parameters influencing the chemical and isotopic composition of recharge waters summary a hydrochemical and isotopic survey of rainwater and groundwater has been carried out during almost two years on the ursuya mount in the northern basque country southwestern france with the aim of enhancing the understanding of the behaviour of this aquifer and more peculiarly the recharge mode of groundwater the input signal of this aquifer is defined thanks to 112 rainwater samples the computed meteoric water line d 7 3 18 o 5 1 r 0 96 is consistent with that defined in the european iaea wmo network stations the weighted mean deuterium excess about 9 7 is really close to the value obtained for atlantic precipitations and clearly demonstrates an oceanic major origin the computations conducted on the chemical dataset show that the rainwater composition is controlled by four major factors 1 a mixed source of anthropogenic pollution and crustal material 2 a marine source 3 an urban source 4 an acid source further the quantification of neutralizing potentials clearly revealed below cloud processes in which crustal and anthropogenic components are responsible for the neutralization of anions besides the major atlantic origin of the recharge water the chemical and isotopic content of the samples coupled with the corresponding air mass back trajectories revealed four major geographical origins of the components 1 northwestern part of atlantic ocean and 2 southwestern part of atlantic ocean the oceanic influence in airmasses from these origins is highlighted by the stable isotopic content weighted mean close to the atlantic ocean signature and by the chemical concentrations dominated by sea salt elements 3 northern europe with a continental influence shown by a light depletion on isotopic signal besides purely oceanic origin and a higher concentration of crustal and anthropogenic components 4 southeastern area southeastern europe northern africa and mediterranean sea with an isotopic signature consistent with the mediterranean one and a chemical composition clearly influenced by the industrial activities of this region the dataset is confronted with the chemical and isotopic characteristics of groundwater in order to assess the recharge water signature of the aquifer of the ursuya mount the groundwater isotopic signal is close to the defined lmwl showing actual and local recharge nevertheless a slightly difference is observed between the mean value of stable isotopic content in groundwater and in rainwater the slightly depleted values of groundwater besides rainwater can be attributed to a preferential winter autumn recharge an altitudinal gradient about 0 11 18 o 100 m is defined and both water rock interactions and physicochemical processes fingerprint on the groundwater composition are characterised

aquitard characteristics of clay rich till deposits in east anglia eastern england summary an extensive area of quaternary glacial deposits lowestoft till of elsterian anglian age overlies the regionally important cretaceous chalk aquifer in east anglia in eastern england the glacial deposits act as an aquitard potentially affording protection from surface derived mainly agricultural contaminants however there has been little previous research on the physical and chemical characteristics of the glacial tills and contained pore waters in east anglia to demonstrate this benefit hence this study presents the results from the drilling of two boreholes in northern and southern east anglia at morley and cowlinge respectively and the construction of a high pressure squeezing rig to obtain pore water for major and minor ion stable isotope 18 o 2 h and dissolved organic carbon analysis special features of the mechanical squeezing rig included a high diameter to length ratio of the squeezer dual seepage faces and a unique pore water collection system designed to eliminate the risk of alteration of in situ pore water redox characteristics the hydrochemistry of the pore waters is found to be controlled by i incongruent carbonate dissolution given the high proportion of chalk clasts contained in the till ii cation exchange in the unweathered clay rich till and iii pyrite oxidation associated with the mineralogy of both the chalk and clay material content that comprises the till matrix the clay material is sourced from upper jurassic clays oxford and kimmeridge clay formations found to the west of the region these clays are also considered to be the source of organic material contributing relatively high concentrations of dissolved organic carbon above 2 mg l found in till pore waters below the soil zone concentrations of dissolved inorganic constituents increase with depth with a high total dissolved solids tds content in excess of 1500 mg l measured in the unweathered till below a depth of 5 m below ground level with the highest concentrations maximum of 3738 mg l associated with low permeability clay rich till the stable isotope composition of the pore waters with mean values for 18 o and 2 h of 7 01 and 51 7 at cowlinge and 6 44 and 49 9 at morley respectively are similar to local meteoric water and indicate that groundwater recharge of the tills has occurred during the holocene in the last 10 000 years overall the physical and chemical characteristics of the lowestoft till suggest only limited groundwater recharge of the order of 10 mm a or less in interfluve areas where the till deposits are greater than 15 m thick although higher rates are expected where the till becomes more sand rich for example at valley margins and also northwards in east anglia where the lowestoft till is influenced by the component of anglian ice that advanced from the north containing sand material derived from the floor of the north sea basin

distribution source and evolution of nitrate in a glacial till of southern alberta canada this paper addresses the distribution origin and controls upon nitrate in a 30 km2 area of the interior great plains region of southern alberta canada high concentrations of nitrate 100 mg l 1 no 3 n occurred in several isolated enclaves below the water table in brown weathered till nitrate concentrations of over 300 mg l 1 n were encountered in groundwater samples collected from these enclaves low nitrate concentrations 1 1 mg l 1 no 3 n were also encountered in the weathered till upgradient and downgradient of the nitrate enclaves groundwater samples collected from the underlying grey nonweathered till and bedrock had no 3 n concentrations of 1 1 mg l 1 through the application of geochemical no 3 n and nh 4 n studies environmental isotope studies tritium microbial analyses nitrifiers and laboratory experiments it was shown that the high nitrates found in the weathered till are the result of the oxidation of ammonium present within the tills it is postulated that this oxidation occurred during the holocene epoch when water tables were much lower than present day levels 5 18 m and 2 m below ground respectively through the use of eh measurements the enumeration of denitrifying bacteria and laboratory experiments the potential for denitrification was shown to exist below the present day water table in the weathered till as well as in the nonweathered till and bedrock isotopic data showed that less denitrification may be occurring within the nitrate enclaves than in adjacent downgradient areas

reactivity of organic matter in aquifer sediments geological and geochemical controls reduction rates in aquifers are commonly carbon limited but little is known about the molecular composition and degradability of sedimentary organic matter som in aquifer sediments the composition source and degradation status of som in aquifer sediments of fluvio glacial pleistocene and shallow marine pliocene origin were determined using flash pyrolysis gas chromatography mass spectrometry incubation experiments 106 d were used to assess the reactivity of som towards molecular oxygen a dominance of lignin derived components and long chain odd over even predominant alkanes indicate that terrestrial higher land plants were the main source of som even in the shallow marine sediments while bacterial lipid derived hopanoids and iso and anteiso c15 and c17 fatty acids indicate a minor contribution of microbial biomass no compositional difference was observed between som present in the fine 63 m and coarse fraction 63 2000 m a significant part of som was not present as low molecular weight compounds but was macromolecularly bound for the fluvio glacial sediments a relatively higher abundance of resistant macro molecular compounds was in agreement with stronger signs of aerobic lignin alkane and hopanoid oxidation the more degraded status of som in the fluvio glacial sediments was consistent with their significantly lower som mineralization 2 6 during incubation as compared with the shallow marine sediments 9 14 the reactivity towards oxygen of som was controlled by the extent of past aerobic oxidation not the age of som but the extent of oxygen exposure during syn and postdepositional conditions seems most important in affecting the degradation status of som in aquifer sediments and thus their ability to reduce oxidants copyright 2004 elsevier ltd

biogeochemistry and natural attenuation of nitrate in groundwater at an explosives test facility an interdisciplinary study was conducted to characterize the distribution and fate of no3 in groundwater at lawrence livermore national laboratory llnl site 300 a high explosives test facility in the semi arid altamont hills of california site 300 groundwater contains no3 concentrations ranging from 200 mg no3 l several lines of evidence strongly suggest that denitrification is naturally attenuating no3 in the confined o2 depleted region of the bedrock aquifer under study tnbs2 a both no3 and dissolved o2 do concentrations in groundwater decrease dramatically as groundwater flows from unconfined to confined aquifer conditions b stable isotope signatures i e 15n and 18o of groundwater no3 indicate a trend of isotopic enrichment that is characteristic of denitrification and c dissolved n2 gas the product of denitrification was highly elevated in no3 depleted groundwater in the confined region of the tnbs2 aquifer long term no3 concentrations were relatively high and constant in recharge area monitoring wells typically 70 100 mg no3 l and relatively low and constant in the downgradient confined region typically 0 1 3 mg no3 l suggesting a balance between rates of no3 loading and removal by denitrification chemolithoautotrophic denitrification with pyrite as the electron donor is plausible in the tnbs2 aquifer based on the low dissolved organic c concentrations 1 5 mg l that could not support heterotrophic denitrification the common occurrence of disseminated pyrite in the aquifer and the trend of increasing so2 4 as groundwater flows from aerobic unconfined to anoxic confined aquifer conditions nitrate sources were investigated by experimentally determining the 15n and 18o signatures of no3 from three potential anthropogenic sources of no3 at site 300 ba no3 2 mock explosive hno3 and photolysis of the explosive rdx hexahydro 1 3 5 trinitro 1 3 5 triazine the isotopic signatures of these potential no3 sources were markedly different than those of no3 in tnbs2 groundwater samples suggesting that other sources must contribute significantly to the no3 loading at site 300 in particular no3 and no2 resulting from rdx photolysis reflected dramatically depleted 15n ca 7 4 and 18o ca 25 7 values

denitrification in a major limestone aquifer abstract the chalk aquifer of eastern central england is seriously affected by nitrates leached from agricultural land and like many similar aquifers its future as a potable resource must depend considerably on the nature and rates of denitrification the regional distribution of nitrate supports a viewpoint based on thermodynamic criteria that denitrification is actively occurring and that the problem will be short lived more detailed considerations based on major ion and environmental isotope data however indicate that denitrification is not significant and that the apparent lowering of nitrate concentration from 10 to 1 no 3 n in the apparent direction of flow is due primarily to mixing between waters of different origins presence of reduced nitrogen species is possible evidence of denitrification in some older waters 4000 yr b p it is concluded that denitrification can not be relied upon to reduce elevated concentrations of nitrate in modern recharge waters

delineation of spatial redox zones using discriminant analysis and geochemical modelling in arsenic affected alluvial aquifers this study characterized the redox conditions in arsenic affected groundwater aquifers of the lanyang plain taiwan discriminant analysis was adopted to delineate three redox zones oxidative transitional and reductive zones in different aquifers and yielded 92 3 correctness on groundwater quality data arsenic is mainly distributed in the reductive zone and arsenic distribution in the shallow aquifer is mainly affected by surface activities according to phreeqc modelling results possible mechanisms for arsenic release to groundwater in lanyang plain are explored arsenic released to groundwater in the oxidative zone zone 1 is primarily caused by the oxidations of arsenic bearing pyrite minerals and arsenate is the predominant species while the reductive dissolution of fe oxides are responsible for the high arsenic concentration found in the transitional and reductive zones zones 2 and 3 arsenite is the predominant species the reduction potential of groundwater rises as the depths and zones increase some sulphates may be reduced to form sulphide ions which then react with arsenic to form arseno sulphide deposits such as realgar orpiment and then slightly lower groundwater arsenic concentrations a conceptual diagram which summarized the possible release processes of arsenic in different redox zones along groundwater flow in lanyang plain is postulated arsenic bearing pyrite and arsenopyrite feass are oxidized as they are exposed to the infiltrated oxygenated rainwater releasing soluble arsenate fe ii and so42 into zone 1 the dissolution of arsenic rich fe oxides due to the onset of reducing conditions in zones 2 and 3 is responsible for the mobility of arsenic and likely to be the primary mechanism of arsenic release to groundwater in the lanyang plain copyright 2007 john wiley sons ltd

groundwater nitrate pollution in the recharge zone of a regional quaternary flow system wielkopolska region poland the present study examines the behaviour of nitrate in the recharge zone of a regional quaternary flow system the presence of contaminated groundwater with high nitrate content in the shallow part of the flow system was documented tritium analyses confirmed that these contaminants can migrate downward a high downward gradient exists in the study area extending into the regions of groundwater extraction in the unconfined part of the flow system which is the most vulnerable to pollution a high concentration of nitrate was found to occur at great depth however denitrification processes limit nitrate migration as a result in the deeper parts of the flow system in regions under confined conditions an absence of nitrate was observed and a higher sulphate concentration and total hardness were evident the denitrification was also confirmed by the existence of a high gaseous n2 concentration it was documented that denitrification occurs in both the confined and unconfined parts of the flow system but the potential for denitrification is higher in the confined parts leading to the disappearance of nitrate in deep aquifers autotrophic denitrification supported by sulphide compounds was indicated as the dominant denitrification process

variation of illite muscovite 40 ar 39 ar age spectra during progressive low grade metamorphism an example from the us cordillera 40ar 39ar step heating data were collected from micron to submicron grain sizes of correlative illite and muscovite rich cambrian pelitic rocks from the western united states that range in metamorphic grade from the shallow diagenetic zone zeolite facies to the epizone greenschist facies with increasing metamorphic grade maximum ages from 40ar 39ar release spectra decrease as do total gas ages and retention ages previous studies have explained similar results as arising dominantly or entirely from the dissolution of detrital muscovite and precipitation recrystallization of neo formed illite while recognizing the importance of these processes in evaluating our results we suggest that the inverse correlation between apparent age and metamorphic grade is controlled primarily by thermally activated volume diffusion analogous to the decrease in apparent ages with depth observed for many thermochronometers in borehole experiments our results suggest that complete resetting of the illite muscovite ar thermochronometer occurs between the high anchizone and epizone or at roughly 300 c this empirical result is in agreement with previous calculations based on muscovite diffusion parameters which indicate that muscovite grains with radii of 0 05 2 m should have closure temperatures between 250 and 350 c at high anchizone conditions we observe a reversal in the age grain size relationship the finest grain size produces the oldest apparent age which may mark the stage in prograde subgreenschist facies metamorphism of pelitic rocks at which neo formed illite muscovite crystallites typically surpass the size of detrital muscovite grains it is also approximately the stage at which neo formed illite muscovite crystallites develop sufficient ar retentivity to produce geologically meaningful 40ar 39ar ages results from our sampling transect of cambrian strata establish a framework for interpreting illite muscovite 40ar 39ar age spectra at different stages of low grade metamorphism and also illuminate the transformation of illite to muscovite at frenchman mtn nv where the cambrian bright angel formation is at zeolite facies conditions illite muscovite 40ar 39ar data suggest a detrital muscovite component with an apparent age 967 ma the correlative carrara fm is at anchizone conditions in the panamint and resting spring ranges of eastern california and in these locations illite muscovite 40ar 39ar data suggest an early permian episode of subgreenschist facies metamorphism the same type of data from equivalent strata at epizone conditions greenschist facies in the footwall of the bullfrog fluorspar canyon detachment in southern nevada reveals a period of slow to moderate late cretaceous cooling